I was going to ask you a question about the average home casting whether it needed gassing or not but found the answers in comments, you and lucky gen 1001 are the only ones I trust on here for reliable information, thank you for sharing your knowledge it has save me a ton of time and disappointment. Hope you don't mind me asking a question now and then, try not to bother you with common sense stuff . Thank you.
Ray, I will pass your comment on to Luckygen he lives about 100 Km away from me and when he "comes to town" he often visits. I am sure he will be as pleased at your comment as I am. Sharing what I know is what I am on about and I believe that lucky is too. Any questions just ask away....Martin
Bored, waiting on a new video...so watching this video. Great video, again. Your replies to questions here in comments are over the top in details, a literal gold mine of information. Thank you Uncle Martin for sharing your knowledge.
Malcolm, Degassing is a subject that many have a great number of misconceptions about. And in fact many peoples degassing efforts most likely result in more gas rather than less, either because they use the wrong method (washing soda does NOT work), don't do it for long enough or it causes to much splashing at the metal surface. With clean metal melted quickly not too hot and poured without delay for normal hobbyist work I recommend that degassing is hardly necessary. Any gas will be so fine you will need a magnifying glass to see it. If it is much bigger than that it is most likely trapped air through bad pouring and gating methods. However I am trying to get around to doing an update to this video as experience has indicated some improvements are possible and necessary for the lance.... Martin
Great explanation and design process. the reduced number of holes for the lance,for the same flow rate, would increase the velocity of the gas leaving the lance. that might explain why there was a significant difference in the bubbles produced - the gas was flowing out of he holes faster and so broke up more so in the molten aluminum. thanks
Charles, Intuitively what you are suggesting feels correct. However I am at a loss to know if it is so. In fact recent info that I have come across clearly indicates that bubble size is related to just two things;- the size of the orifice that the gas is coming out of, and the liquid into which the gas is flowing. There is no mention of flow rate at all - presumably then higher flow rate just means more bubbles of the same size. In my case with this lance I was concerned that the bubbles coming out of slots so close together might coalesce into larger bubbles simply by mutual contact. Halving the number of holes was an attempt to keep the bubbles further away from their neighbours and so prevent coalescence. Of course it may have all been self defeating as with more bubbles of the same size per hole each bubble would be closer to the bubble before and after from the same hole so coalescence may well still have occurred - life was not meant to be easy!
Thomas, Thank you for your comment. I am glad that you found it both interesting and helpful. Regrettably, as you might gather from my replies to Mark above, degassing is a most difficult area! As always the time is my pleasure.
About 35 years ago I cast a boat of of things in my high school metal shops class. I got rather good at it. Made some complex patterns and the like. We used petrobond sand. Off and on over the years I have cast the odd item in aluminum and a plaster mold for quick and dirty one off items. I'm at the point where I have to get back into casting for small runs of custom items. I have to say I have learned more of the nitty gritty items of casting from your videos than from just about every other video I have watched on TH-cam. Great stuff. I really appreciate your thorough explanations of why you do things the way you do. Do you do any cast iron work?
Kravchenko, Thank you for your comment. Its comments like yours that really make the effort of putting videos on YT worth while. Sadly its a bit difficult to put 60 years of "nitty gritty" learning into a few short videos but I do try to put as much in there as will reasonably fit and I always try to put some more in the next video. Plaster can be a bit problematic for casting metal into unless you do it right in which case it works very well indeed. I would be interested to know of your experiences in doing it. Did you use straight plaster or was it a blend with other materials what preheat treatment did you use to dry the plaster, did you use the rubber pattern technique, have you tried foamed plaster - so many questions!. No, I do not do iron work,tried it once about 50 years ago but managed to get a 2% carbon product because I burnt too much carbon out by doing it wrong. Its very hard on furnaces crucibles and the people doing it so I stuck to bronze and aluminium. Luckygen1001 who lives about 100 Km from me does a lot of iron work. He has been at it for over 30 years and knows it well. He and I have spent a couple of most pleasant afternoons talking foundry and he does seem to know his stuff... Martin
I first did lost foam and lost wax in high school. So that was 35 years ago. The lost wax was done in plaster of Paris as I knew nothing of the correct recipe back then. I grew up way out in the country in Manitoba Canada. Many pieces of crucial information were simply not available back then. But I was to stupid to know what I couldn't do and I fumbled my way through. The first lost wax attempt was a bust. I erroneously thought that wax when heated would shrink. Guess how that worked out! crack! new mold new way of draining the wax! that actually worked out quite well with great retention of the finish including all my imperfections on the wax pattern. Lost foam was tried once. I managed to shut down the high school with that one. (A true pity of course! I think I got more pats on the back for the free afternoon than jibes for my stupidity!) I was not impressed with the surface finish or the general amount of porosity in that casting. I was attempting to do a casting for a headstock of a metal lathe. Degassing is so important to a good casting. A friend of mine and I made casting for water pump housings that were great sieves for cleaning out the water that entered them. In other words they leaked like sieves! We saw first hand how not to make a casting. Then I read in an article that degassing aluminum could be done with chlorine tablet. This I tried, outside on a breezy day. We knew enough about chemistry to recognise that chlorine gas would be produced in copious amounts. It seemed to work. More recent work was for making loudspeaker cast aluminium baskets. This was done with a glass fiber reinforced plaster mix used for porcelain molds. I actually machined these and dried them out in an oven. The two halves either stayed true to the mating surfaces or they would warp slightly and then leak as I poured the nold. Molten aluminium does indeed run out of a mold just like water! Now I'm thinking of setting up a more permanent foundry for similar casting work to what you are doing. Custom casting work and short runs of commercial casting. I think I can do both cast iron ( No experience with. But I do watch luckygen 1001's videos.) I would need dedicated crucibles for that. And most likely means to lift them that are a bit more robust. Sorry to blather on. But you bring back so many memories. And I learn so much from watching these videos. So many things that I say to myself, that's what I was doing wrong! I consider myself better educated each time I watch one of your videos. Thank you!
First, thanks for your videos, they are the most professional I found so far ! In my country argon/degasing tablets are very expensive, is there other techniques to avoid porosity ? like controlling the temperature ? On wikipedia they say "To minimize gas solubility the superheat temperatures can be kept low"
Gaetan, I used to use Hexachlorethane tablets but they are no longer available, then I tried the grey tablets that give off nitrogen gas (are these the ones that you mean?) I did not like them, their action was so violent that they splashed 50 mm of metal out of the crucible and all that splashing up into the air just allows more hydrogen to get in. A local foundry did tests and came to the conclusion that these tablets made gas levels higher not lower! Using washing soda or Epsom salts is a complete waste of time as all they do is bubble water through the metal which will increase gas levels not reduce them. My usual advice to the hobbyist is not to bother degassing and as long as your metal is clean i.e. no oil, grease, paint, corrosion or water and if you melt quickly and do not exceed 760 deg. C (preferably lower) and pour as soon as possible, you should have reasonably gas free castings (well, any gas will be very fine and you probably won't see it) I would recommend not pouring on very humid days and I am also assuming that the castings you are doing are not great thick chunky things that will take for ever to go solid as these are very bad for gas. Good luck with it.... Martin
@@olfoundryman8418 It's probably a bit pointless to respond for me, seeing as your original comments is now 5 years old, but anyway. Both epsom salts (magnesium sulphate, MgSO4) and soda (sodium carbonate, Na2CO3) when store bought will indeed be the hydrated form, meaning that per molecule one or more water molecules will be bound to it. It is however very easy to turn them into the anhydrous i.e. water-free form by heating in an oven at a specified temperature and for a specified time. Those temperatures and times can be found quite easily on the internet. And once all the water has been driven off in the oven all you need to do is store them in a sealed glass jar and they'll remain water-free for use.
Mohammed, Clarity and happiness are what I aim for. If you have any other areas that you would like further clarified just let me know and I will try to answer any questions.
I have thought on this and you are right. The pure aluminum would prefer to be aluminum oxide. As you say it loves water. The water moisture is in the air floating. The pure aluminum attracts to the oxygen in the water and grabs the oxygen from the water to become aluminum oxide. It leaves the hydrogen H2 gas has a small atoms bouncing around against the atoms of aluminum and aluminum oxide Al2 O3 trying to get its electron back. The tiny bubbles of argon bump the tiny hydrogen gas atoms and carry it out. The holes in the lance should be as small as possible and allow the lance to still work. The bubbles at the bottom just as they exit the lance will pick up more H2 being smaller as they rise they will expand due to less pressure and more heat. They will pick up less as they become larger but cross the top layer of the aluminum better. Casting area should be dehumidified as possible. I have a project going but I am building a lance next.
Thomas, Spot on! Another thing about small bubbles is that they rise slower than big ones - you can see this effect in an aquarium with an air stone - this means that the smaller bubbles have more time to collect the hydrogen. Also the bubbles float out any oxide skin films that are bigger than the bubble - the smaller the bubble the more oxide skins you float out. The hydrogen flows from the metal into the argon bubble because there is more hydrogen in the metal than in the bubble its exactly like heat flowing from where there is a lot of it i.e. from where its hotter to where there is less of it i.e. to where its colder. I do know of a foundry that will not pour aluminium on humid days as hydrogen pick up can be quite fast then... Martin
Most of the TH-cam casters I see use washing soda as a degas. I've seen you comment before that using washing soda as a degas isn't the best idea. Why is that? Anyways, another great, informative video.
Mister. It is my intention when (huh - If) my health improves to do a longish video on just this issue, with a great deal of technical info, sources, and experiments included to prove the point. It is my humble opinion that the originator of this process should have their box of matches confiscated for the harm they have done to the hobbyist casting community - whoever they are - I have a pretty good idea! No names no pack drill! Briefly, People seem to think the gas given off when washing soda is plunged into molten aluminium is CO2 - it isn't - but even if it was you can not degas aluminium with CO2 as it and aluminium would react to form C (as smoke) and aluminium oxide (Al2O3) as folded films (bifilms) floating around in the aluminium. There are two common forms of washing soda, one is Na2CO3 the other is Na2CO3.10H2O. This last one is what was traditionally known as washing soda. If you plunge the first one into aluminium you would probably not get many if any bubbles at all. If you plunge the second those 10 molecules of H2O (yes, this version of washing soda is about 64% water) are driven off as steam and this is what we see bubbling out through the aluminium. Now remembering that the hydrogen that we are trying to get rid of from our aluminium got there by the aluminium reacting with water in the form of humidity in the air and in the burnt fuel in the furnace or from wet scrap etc it seems damn silly to me to bubble steam through the aluminium, all it will do is react (in part) with the aluminium to form hydrogen which will immediately dissolve in the aluminium worsening its gas level and aluminium oxide films, these act as weakness within the metal and as nucleation sites for the growth of porosity be it shrinkage or gas. The one saving grace - if we could call it that - here, is that the bubbling is over with quite quickly (maybe 30 seconds from what I have seen on YT) and a lot of the steam seems to escape rather than react as it is moving through the aluminium rather quickly. So while it will INCREASE the Hydrogen gas levels - the exact opposite of what it is supposedly being used to do - it will probably not increase them by all that large an amount - BUT any increase is too much! Its not the best idea - its about the worst!... Martin
@@olfoundryman8418 Although the meaning of such names can differ from one region to another, I'm pretty certain the name washing soda is only used for the hydrated salt of sodium carbonate (Na2CO3·10H2O), but not for the anhydrous salt (Na2CO3). Because the presence of even trace amounts of water can be detrimental to many processes in the lab, it's well known among chemists that certain salts can be used to remove water or at least keep water out. For example many of the solvents commonly used in laboratories (like acetone, ethanol, isopropanol, tetrahydrofuran, toluene etc) have differing amounts of affinity to water (i.e. hygroscopicity), and in order to remove any water they might have already contained they're often pre-dried with drying salts (like sodium carbonate, sodium sulphate, magnesium sulphate, calcium chloride, calcium oxide, etc.). So if you would substitute the anhydrous version for whatever salt you would otherwise have used, that should fix your problem in regards to it producing steam. Seeing as anhydrous salts are not uncommon in chemistry labs, I'm sure you could find some chemical supply houses or wholesalers who will sell it to you, after all they're pretty benign and harmless substances. And if you do somehow end up have difficulty finding such suppliers then eBay would be an option, there are a couple of chemical sellers who ship internationally on eBay. And although not an option for all salts there are several commonly available ones which you can dry yourself till they're completely anhydrous by heating it on a tray in the oven at the correct temperature and for the right amount of time.
Martin on the subject of Argon gas bottle costs, you might wish to look into the deal going at Bunnings where you pay a deposit on the bottle @ $200 and then just pay for the gas each time you return the bottle @ $90 for Argon in a D sized bottle.
Mark, Yes I think that you mentioned this before in a comment to another of my videos. My large rented E cylinder still has heaps of gas inn it so I have not yet had to look into this source.
A most interesting video, Martin. Question; If the hydrogen comes from water vapour reacting with the molten aluminium, then I hypothesize that the source of that water vapour would be the humidity layer at the surface of the aluminium at room temperature. This is somewhat like how low hydrogen welding rods can absorb moisture if left exposed to the atmosphere. The solution for the welding rods is to keep them either in a fresh sealed tin or to keep them in a rod oven to drive off the moisture. Therefore, the solution for reducing the amount of water vapour available to react with the molten aluminium in the crucible would be to pre-heat the aluminium feed stock in a suitable oven or low temperature furnace for a suitable heating time to drive off as much of the surface humidity prior to charging of the crucible. I have noted in numerous casting videos where additional feed stock is to be added to a crucible, that the feed stock is pre- warmed by placing it around the edge of the furnace. This would have the effect of reducing the "loading shock" to the overall temperature of the crucible, but I don't believe that it would be a long enough pre-heat to drive off the majority of the humidity layer or surface absorbed moisture. It appears to me that the best way to reduce this moisture issue is to use an oven or low temperature furnace to pre-heat aluminium feed stock to at least 200 deg. C as this temperature is well above the boiling point of water at 100 deg. C and should drive off the water vapour. What are your thoughts on the matter?
Mark, Basically what you say is correct, but there are many more sources of hydrogen and perhaps the main one is that when we burn a hydrocarbon fuel one of the products of combustion is water vapour. There is in addition the natural humidity in the air which of course varies all the time. In fact some people believe that on very humid days it is difficult to degas properly and to keep the hydrogen level down as the pick up from the reaction of the humidity in the air and the surface of the liquid metal can be quite high (particularly if the surface of the metal is agitated) - this can even be the case with electric melting - the humidity in the air is quite simply that potent a source of hydrogen! Drying ingots, scrap on top of the furnace is indeed common - I do it. It is best remembered that when one puts cold material on top of the furnace moisture in the outgoing furnaces gases will condense on the cold material - it will in fact get absolutely dripping with water initially and one does need to wait until it is well above 100 deg. C before adding it to the liquid metal in the crucible. Scrap that is badly corroded is a problem as the corrosion product is often hydrated and this water can be hard to drive off. Anodised aluminium is a bit problematic too as the anodic film is at least in part Aluminium hydroxide. I do not like to use greasy, dirty, or painted scrap either. I am uncertain as to how hot one really needs to get metal to drive off any occluded surface moisture but I judge that if adding material to liquid metal does not result in bubbles immediately coming to the surface then it was probably dry enough. Incidentally even metal at say 300 deg C (as compared to say 100 deg C is not going to be much less of a loading shock - we have to take the latent heat of fusion into account and I think this is much bigger than the "heat" difference from 100 tor 300 deg C. I do know that some larger foundries preheat their ingot (and possibly scrap) before loading it into the primary melting furnace although and in some disagreement with my loading shock comment above I suspect they do this mainly to increase throughput of said primary melting furnace (in some ways dry hearth melting is a better technique as the charge is thoroughly preheated and the liquid in the furnace is totally protected from loading shock but I have concerns about oxidation with this technique. Other sources of moisture that many people forget about are damp furnace tools and damp fluxes and even bail out ladles. And then of course we have the people who attempt to degas by plunging water of crystallization containing chemicals to the bottom of the melt - the bubbles you see coming from this technique (Many YT videos show this appalling technique) are steam - about the worst thing that you could possibly bubble through your metal. The two most common that come to mind are Washing soda Na2CO3.10H2O and Epsom salts MgSO4.7H2O. It is the 10 and 7 H20 that cause the gas output from these two substances - a most counterproductive technique.
Thanks for the reply Martin. Given what you have written about some of the water coming from hydrocarbon combustion then it becomes obvious as to why many professional foundries use electric induction to heat the large crucible. No combustion and no forced draft to draw in more moisture laden air. It also seems like casting on a humid day needs to be done in a humidity controlled environment, which is something beyond most home foundries. As for the Washing Soda and Epsom Salts, it looks like I will have to investigate the making of an Argon Lance along the lines of the one you have made or look into buying degassing tablets.
Mark, The propensity of aluminium to dissolve hydrogen is perhaps the metals Achilles heel. Degassing is a most difficult area. Big foundries have it well under control with rotary impellor degassing units but this is an option hardly open to the amateur or small foundry. The mechanics of RIDs are nothing special but the impellor is another matter - it has to spin at a few hundred RPM in molten aluminium a substance known for it ability to dissolve almost all other metals (its not supposed to attack Zirconium - but there is not a lot of that around). In addition the impellor has to be mechanical robust and resistant to both oxidation and thermal shock- no easy trick! Quite exotic materials are used - things like silicon nitride - exotic, expensive, and most difficult to machine. Beyond us small operators. And even if one could afford a commercial impellor it would be way to big meant probably for 100 Kg batches as a minimum. If you use a lance you need to maintain a supply of either argon or nitrogen, rental on the bottles is a killer about $250.00 per year for a large bottle. You could investigate own it yourself bottles or the small disposable bottles available at welding shops (note you must use either nitrogen or pure argon NO argon CO2 mixes) Either way its going to cost money - money perhaps better spent on decent crucibles to replace the (Groan) tin cans that many use (this is another sore point of mine but I will not go into it here.) Then lances like mine require constant maintenance - areas of aluminium attack must be checked for and ground out after every use and the boron nitride protective wash must be reapplied before every use. This wash is about $200.00 plus a gallon and that's a small American gallon! But it can be obtained in 1 pint sized containers in the US - last time I came across it at about $80.00 a pint!!! If your lance does not give fine bubbles like mine does then its a waste of time anyway - whatever lance you come up with check the bubble size in a bucket of soapy water. Re degassing tablets - hmm - yes - well. I used to use these - initially they were Hexachlorethane it breaks down to give chlorine which reacts with the aluminium to give Aluminium chloride this is a gas at the temperature concerned and it bubbles up through the melt removing the Hydrogen. ( The suggestion that the chlorine reacts directly with any hydrogen in the melt to give HCl is a complete nonsense)However the fumes coming off the melt are both toxic and very corrosive - everything above shoulder height in my foundry is rusty and the roof above the furnace leaks. In Australia you can no longer buy this substance because of its effect on the Ozone layer. Pity really it did a half decent job of degassing if used properly. I was thus forced to go over to the tablets that dissociate in the melt to produce nitrogen. These are not very good, they breakdown way to quickly (2 to 3 minutes - way too short a time for any meaningful degassing) and they cause extreme turbulence - they splashed 2 inches of metal out of the crucible - I had to sit a steel ring on the top of the crucible to contain this. Such turbulence is likely to INCREASE the hydrogen level as it mixes the metal with the humid furnace atmosphere. In fact a commercial foundry near me conducted trials and were convinced that these nitrogen tablets actually INCREASED their gas levels - the supplier of the tablets of course disagreed! The standard bell plunger used to hold the tablets to the bottom of the melt is a bad design. Its hard to clean and tends to hold the gas back and let it go in large (HUGE) bubbles. I used a spiral, more or less in the shape of a bell plunger, bent up from 3/8 inch steel rod. It was easier to clean and provided I applied a coat of ladle wash before each use it lasted OK and seemed to allow smaller bubbles.My honest advice on degassing to the amateur is Do Not Bother. If you chose your scrap with care, preheat all additions and make sure everything is dry (fluxes etc.) melt quickly, don't over heat (760 deg. C max) and pour with minimum delay your gas levels should be low enough to get away with. This is particularly the case if your castings are relatively thin as solidification will then occur too quickly for much gas to come out of solution (and any that does will be in very fine bubbles - invisible at YT resolutions!) If your castings are on the heavy side and gas becomes a problem then I guess that you will need to rethink. Always remember that gassy metal can be recovered by simply allowing it to solidify very slowly in a wide open topped mould - dried preheated sand might make a suitable mould. This will allow the gas to come out of solution and on remelting most of it will not be redissolved.Humidity controlled environment - that would be a laugh - last foundry I worked in had evaporative cooling blowing on the operators at the casting stations - nice humid air blowing all over the holding pots!! But they did have continuous nitrogen degassing on every holding pot via a silicon carbide "Hocky Stick" - these have a porous bottom leg (the bit you would hit the puck with were it a real hocky stick) the nitrogen came out through this porosity as reasonably fine bubbles. One day maybe I will work up to a video on the subject of degassing if only to dissuade people reaching into their various household cupboards, pulling out some random chemical and in complete ignorance of physics, chemistry, and thermodynamics swearing by all that's holy that it is the go to thing for degassing - I don't mind them destroying their own work but others copy them and their work too is ruined - a bad scene.
David, My understanding of "loading shock" is that when one puts solid aluminium into liquid the relatively cold additions (even if well preheated) will cause a significant drop in the temperature of the liquid metal already in the crucible. - A temperature "shock" if you will. If you add a lot of solid to say a lesser amount of liquid the whole lot can go solid or at least pasty. What actually happens is determined by the relative quantities and specific heat of both solid and liquid aluminium and by its latent heat of fusion. Generally though the temperature recovers quite quickly. However it is best not to add to much solid at once. And never to add once casting has started. Another factor is that such additions can cause the precipitation of surprisingly large particles of intermetallic compounds, these are based on what might be considered unwanted impurity elements in the aluminium - iron manganese chromium etc. these particles are slow to redissolve are very hard and very brittle, they damage tooling and can seriously lower the ductility of any resulting casting should they get cast into it. Often these compounds are found at the bottom of the crucible after a pour - the old timers used to call them "sand" for that's what they resembled. This is more a problem with oft melted scrap, pressure diecast, and older alloys - none of which in my opinion should ever be sand cast. :) The occurrence of these compounds is one of the very good arguments for not melting in steel crucibles.
Hi Martin, first of all thanks for creating such a wonderful and detailed and practical video. Can you explain share detailed video on lance making ? Currently in this video what is the lance specification you used ( Lance inner and outer diameter, having more thickness is helpful for straight length for mechanical strength…
Manoj, First let me admit that the lance was made from “found material” i.e. what I had lying around. I did not do any plans for it - I just made it. The very inner tube is stainless steel, I was told, by the person who gave it to me, that it was “refrigeration tube”. It is 3/8 inch outer diameter and has a 3/64 wall thickness. This tube is thick enough to take a 3/8 NF 24 TPI thread. The outer sacrificial tube is mild steel and is 3/8 ID by ¾ OD. I say “sacrificial” as its job is to protect the inner stainless tube from attack by the molten aluminium. The length of this outer tube is such that with the lance head touching the crucible bottom the tube comes not quite up to the top of the crucible - this way the lid of the lance rests on the top of the crucible. The lance head is made from cast iron which I had purchased as continuously cast bar. The head thickness is about least 5/16 inch - its two pieces - so total thickness is thus about 5/8 inch. The head diameter is preferably at least 3 inch as if less the bubble stream just seems to come together into one central stream as it rises, rather than many streams coming from all around the lance. However, I think the head diameter needs to be 1/3 to ½ the diameter of the inside of the bottom of the crucible. All of the lance that is exposed to the molten aluminium is painted with a wash called Hardcoat BN. This is a boron nitride based wash made by ZYP Coatings in the USA - it is expensive - but it’s the best wash to prevent metal attack. Even so after every days use I inspect the sacrificial outer tube for any areas where the aluminium has begun to attack. I remove these areas with a small carbide burr making sure to get ALL the aluminium removed. The now exposed area of mild steel is oxidized with dull red heat and the whole lance, tubes, head, and all, recoated with the wash. To be honest in using the lance after making that video I found a fault in its design in that the two head plates tended to come apart because the central bolt worked loose. So, I bolted the two plates together with 6 off ¼ inch countersunk bolts. I have been conscious of the need to do an update video but so far bad health is preventing me - one day maybe, I hope!.... Martin PS, is there anything else that you would like to know?
I am wondering that even if the fluidity of the Al is similar to water, that the extra weight of Al would tend to decrease the bubble size until it is very near the surface. What do you think?
Stephen, Two points, first yes, bubbles will grow in size as they ascend as the pressure on them lessens - you can see this in aquariums with air bubblers. There is no reason to think that the same does not occur to bubbles rising through molten metals. Very approximately 100 mm of aluminium gives 1/2 psi so a bubble rising through 100 mm of aluminium would increase in volume by about 3% -not very much so it might be a bit hard to see! second, and as counterintuitive as it may seem the bubble size is determined solely by the hole size the gas is coming out of and the material into which it is coming. There is a graph in John Campbell's book "Complete Casting Handbook" Fig 7.35 page 390 that lists the bubble size for various liquids and a range of hole sizes. For a 0.1mm hole the bubble size is about 1.5 mm for water and (sadly) about 3mm for aluminium As a third point I think that some bubbles coalesce with others on the way up simply by banging into each other and forming the one larger bubble, the larger bubbles then rise much quicker and hit smaller ones above growing even larger, Studying the bubble trail in a tall aquarium is quite instructive... Martin
Insert, Copper is an interesting case. Like aluminium it too will dissolve hydrogen although the solubility of hydrogen in copper does not drop as much as it does in aluminium on solidification so in theory the hydrogen should remail in solid solution where it will likely be quite harmless. However, if you look at some of the videos produced by those ignorant types turning high quality copper wire into low quality ingots just for the sake of making a video and wasting fuel you will often see that the ingots have so much gas in them that they rise like a loaf of bread as they solidify. I show some examples of such ingots in my “Possibilities” video. The gas in these ingots is however not hydrogen - rather it is steam. This results from the copper being oxidized by bad melting practices. The copper oxide thus produced reacts with dissolved hydrogen to produce water as steam. This reaction takes place as the copper is cooling down a little before and during solidification thus causing the gas porosity. It is easiest to prevent this not by degassing to remove the hydrogen but by melting properly so that no oxide is formed. Quite simply - no oxide no water no water no porosity. Argon will remove Hydrogen from copper but practical realities make this difficult for us hobbyists. In the case of brasses and aluminium bronzes the problem does not arise as the zinc/aluminium in these alloys effectively deoxidizes the copper... Martin
Lan, Graphite will certainly not contaminate the molten aluminium. The lance could be made out of graphite but mechanically it is a more difficult material to handle because it is quite brittle. Impellors for rotary degassers (industry best standard for degassing) are commonly made from graphite because it is totally resistant to attack from the molten aluminium. I sometimes use a graphite sheath to protect the steel tube that is the central part of one of my degassing lances. Otherwise I just use a boron nitride wash to protect the steel and cast iron parts of my lance. It is my aim one day (I should live so long) to make a rotary degasser small enough to suit my crucible size as rotary produces smaller argon bubbles and that is a definite aid to good degassing. Also I have recently modified my latest lance (the bigger one shown in this video) and hope to do a short video about these mods in the near future... Martin
Does molten Aluminium attack Stainless Steel in the same way it attacks mild steel? Does Stainless Steel also transfer Iron to the Aluminium if used as a crucible?
Hi, I think your lance design is well developed and you have clearly experimented with the operation of it. I am just wondering though if degassing tablets would be an alternative for someone who only does the occasional casting job. I cannot find a supplier of degassing tablets here in Australia (who will sell in small quantities) and the overseas suppliers won't ship outside their own countries. Just the same, I am interested in your views on how effective the tablets would be.
Mark, I have used degassing tablets. Years ago one could get hexachlorethane degassing tablets and these worked fairly well both at degassing and at floating up oxides within the metal. However these are now considered a no-no as they cause ozone layer depletion. There are degassing tablets available that generate nitrogen gas they are usually grey. I have tried these and to be honest I was not impressed! They bubbled so fiercely that they caused so much turbulence in the crucible of metal that 50 mm of the metal was splashed out all over the inside of my furnace. I had to put a heavy steel ring on top of the crucible to stop this loss. But this sort of turbulence causes more hydrogen to be absorbed from the furnace atmosphere so I was dubious as to if these tablets did any good. A friend and owner of a much bigger foundry did some tests and he became convinced that these tables actually increased the gas level rather than reduced it! I abandoned these tablets in favour of my fine bubble lance and I immediately noticed that I had to use bigger feeders as I no longer had gas to help counteract shrinkage! To be honest my advice to the average occasional metal caster is not to bother with degassing. Just make sure your metal is clean of oil grease paint and is dry, melt as quickly as you reasonably can don't get it too hot, never over 760 deg C. and pour without delay. Assuming that you are not trying to cast very thick parts you should not have too much of a problem with gas. Gas porosity is usually quite fine, around 0.5 mm or less pore diameter, and this is easily smeared over during machining of most aluminium alloys so you wont see it! All my work is heat treated so it machines much better and without smearing and some of it is diamond machined and that will produce such a well finished surface that even very minor porosity is easily seen so I have to degas as well as I can. I think that many occasional casters get way too concerned about gas porosity, unless you get a real bad case (I have seen a few -:)) of gas and assuming that your castings are reasonably thin i.e. the solidify quickly you are unlikely to notice much of a gas problem. If you do then something is wrong so contact me with the details if that is the case. One last thing many people "degas" with washing soda (sodium carbonate) IT DOES NOT WORK in fact it INCREASES the gas level so please don't try it... Martin
Your comments back up some other reading that I was doing yesterday. The consensus was that for small castings, degassing is probably not necessary. I will take on board what you have suggested about not overheating the melt and trying to keep the sections thin. I am guessing that my castings do have quite a bit of porosity but having said that I have never had one fail and the finished castings are either powder coated or don't need a high quality finish anyway. I think Myfordboy started the whole washing soda thing and yes, I too thought it was a good idea since I was seeing lots of bubbles coming to the surface after I stirred the washing soda in to the melt. Thanks for your detailed reply. Mark Presling
Mark, It may well have been myford who started off this whole degas with washing soda rubbish, I am not sure but whoever did start it off has a lot to answer for. The problem is that the hydrogen gets in our molten aluminium from (in the main) its reaction with water in the air. There is of course always water in the air and particularly in furnace gases as water is a product of combustion. The aluminium reacts with the water to form hydrogen which dissolves in the aluminium and aluminium oxide which in the form of thin films floats around in the aluminium causing lines of weakness in the eventual casting. Now washing soda comes in two main forms the first is Na2CO3, it usually is a granular white powder. The second form is Na2CO3.10H2O, this is the traditional "washing soda". It is usually in the form of transparent ice like small crystals. It is the 10H2O that is the problem, this is water of crystallization and it is driven off with moderate heat, this substance is in fact about 63% water by weight. If you plunge the first form into molten aluminium nothing much will happen perhaps a small bubble of two but that's it. The Na2CO3 does NOT break down to produce CO2. Even if it did any CO2 get given off will not degas aluminium as it will react with it to produce C and aluminium oxide. Luckygen1001 proved much of this in one of his videos. However if you plunge the second form into molten aluminium all that water is driven off as steam, lots of it, and this is what you see bubbling out of the aluminium. Remembering how the hydrogen gets into our aluminium it is obvious that the worst thing we could do is to bubble steam through the molten aluminium. This can only INCREASE the hydrogen content so attempting to degas with washing soda is worse that a complete waste of time and sadly so many people have copied the technique simply because someone who has been on YT for a while and knows no better not only insists that the technique works but defends it quite fiercely... Martin
Just wondering after 7yrs if you have ever attempted using tablets and if they work? I have seen a lot of degassing flux tablets on the market that look tempting to try.
Todd, Years ago, I used hexachloroethane tablets to try and degas my aluminium. Not having a Reduced pressure test apparatus, I cannot really be sure how well they degassed my metal. I never got any complaints about gas levels though, but then gas is hard to see even in well machined castings as the machining tends to flow metal overt the small gas bubbles and true gas bubbles are indeed small - usually below 0.5 mm. I do feel that the hexachloroethane did a pretty good job of floating oxides etc to the surface. It also did a pretty good job of rotting my tin roof which now leaks. Note that I did not use the traditional bell shaped plunger as these hold the purge gas back until it forms large (read “useless”) bubbles. You can no longer get these tablets as they posed a threat to the ozone layer, well not here in Australia anyway. The tablets that you are referring too are I guess the ones that liberate nitrogen gas when plunged. I was forced to use these when the hexa was phased out and I have to say that I was not impressed. The first problem was that they bubbled so viciously that they threw 50 mm of metal out of my A25 crucible and all over the inside of my furnace. I used to put a high steel ring on the top of the crucible to catch this ejected metal and direct it back into the crucible. This sort of turbulence is very bad as it generates oxide which winds up in the metal as thin films and it exposes metal to the atmosphere and its attendant water (humidity) thus it generates hydrogen in the metal - likely more that it removes??? The second problem was that the tablets only produce nitrogen for a few minutes (2-4) and not long enough to properly remove any hydrogen in the metal - this meant doing it at least twice. Another foundry much bigger than mine did some tests comparing these tablets with argon gas bubbling from a porous Silicon carbide hockey stick type lance. They claimed that their tests showed that not only was the hockey stick better at removing gas but the nitrogen tablets actually made gas levels worse if used once the hockey stick had done its job. I have no reason to doubt their results. This was at least 10 years ago and its why I developed my own argon lance. Somehow, I doubt that the nitrogen tablets have got any better and that it is likely that they just make the foundryman feel good rather than actually do any useful degassing. The manufacturers of said tablets would no doubt disagree 😊. I think that I still have some of these tablets sitting here so if you wish to try them and you live close call in and I will give you some - just need to check that I did not throw them out though. I would doubt that the tablets currently available are any different to the ones I tried. Note that I have done some mods to the lance shown in this video and I really should do an update but health currently prevents…. Martin
Thanks for really useful video. I am very admired by your original lance design. But is it just your home solution, or maybe you took something as a base from industrial prototypes? I ask you because I am aquintenced about main designs of the degassers (graphite rotors or just immersed tubes with holes), however I haven't met somethink like that. So, it's interesting to me, is there similar industial solutions or is it only your original homemade device?
Edward, I am sorry for the delayed reply. I have rather a lot going on and don't always get around to replying as soon as I would like. Your question requires a fairly long answer so forgive me if I put you off until I have the time to answer it properly - soon I hope.... Martin PS, if I forget (I am old 😊) please ask it again to remind me.
Edward, The lance design is my home solution, but it is based on the following; 1, The realization many years ago that for successful degassing the purge bubble size must be as small as possible. This is backed up by the standard industrial practice of using rotary degassers as these chop the bubbles in quite small sizes. 2, The use industrially of porous plug type degassers where the degassing head is made from a porous ceramic - firebrick and silicon carbide are typical,. The pores through which the purge gas emanates are very small and do produce reasonable fine bubbles. Obviously you are aware of these points 1 and 2 3, Based on John Campbells work - the knowledge that the size of bubble generated by blowing gas out of a hole is dependent on the hole size and the liquid into which the gas is being blown. (Bubbles blown in water are about 1/3 the size of bubbles being blown into molten aluminium - for example) The pressure blowing the purge gas through the holes apparently has no effect on the bubble size (rather counter intuitive I feel, but apparently true) Note - very high gas velocities producing very high Reynold’s numbers in the purge gas flow MAY change this - I was yet to explore this avenue. 4, About the smallest hole size I could make was 0.1 mm. According to Campbell (Complete Casting Design Handbook 2015 edition page 390 Fig 7.35) this should give a bubble size of about 3mm in aluminium or about 1mm in water. Indeed, water tests did indicate a size of about 1 mm diameter. I would have liked a smaller bubble size in the molten aluminium but this was about as good as I could do. 5, There is no way that I could drill 0.1 mm holes but I could score a flat disc with 0.1mm deep groves and then clamp another, but unscored, flat disc against it to effectively give me the required 0.1 mm holes. Thus, the lance that I developed. To my knowledge there is nothing like it used industrially. I am not surprised by this as it is too demanding of maintenance. The head (i.e. the two discs) are made from cast iron and they seem to last quite well but do oxidize on the clamped faces and these need periodic re-machining. The vertical hollow shaft through which the gas enters the “head” is a constant source of problems as the rising bubbles seem to disturb the protective coat I use (boron nitride hard coat by ZYP coatings) and the aluminium frequently attacks this shaft. After no more that two uses I have to check the shaft, grind off any attacked areas, oxidize with heat, and then reapply the hard coat. Attack seems to occur about 50% of the time. The head is never attacked. In any case I apply fresh had coat every day before use of the lance, this coat is dried at red heat before use of the lance The inner of this shaft is a stainless steel pipe and if the aluminium gets at it attack is rapid so I use a thick sacrificial sheath of mild steel around it and it is this that I have to remove any attacked areas from. I have tried a graphite sheath but it to had problems - it tended to float and even when I prevented this aluminium seemed to somehow to get up inside the bottom of this sheath and around the inner stainless tube. This was difficult to deal with and I was working on a solution when ill health brought a sad halt to my casting endeavors - so no solution yet! But I do think this is the way to go. One problem I had with the lance design as shown in the video is that for reasons unknown the central bolt holding the two discs together seemed to work loose very easily - the result was that instead of small holes around the discs I had a continuous slit and this produced bubbles that were way too big. I got around this by bolting the two discs together with about 8 small bolts placed fairly close to the outer edge. I hope that this answers your questions - if not do not be afraid to ask further … Martin
It works, so obviously it works. The Chemistry sounds a bit off. Hydrogen 'dissolved' in Aluminium then interacting with Argon ? Do either of those even happen ? Not that i know, but it sounds more like the hydrogen is a bubble in the melt and the inert argon just helps move the hydrogen bubble to the top of the melt by mechanical entrainment. Basically the argon ignores the Al and rises, knocking H bubbles upwards as well.
aga. Not sure there is any chemistry involved its more of a physical process. The hydrogen atom is very small (compared to other atoms) and it fits in between the atoms of most other things. This means it can dissolve in and move through either liquid or solid things all too easily. It causes great trouble in hardened steels with sudden catastrophic brittle failure. Its a pain in copper because it reacts with the often present copper oxide to form steam which fills the copper up with bubbles (of steam). And yet it apparently causes no problems in magnesium alloys. In aluminium it dissolves in the liquid but is much less soluble in the solid so on solidification it tends to precipitate out as small (usually less than 0.5 mm) bubbles. My understanding is that it is in solution as H but comes out as H2. Removal of H by argon (or nitrogen) is I think purely a physical process. Things move from where there is a lot of it to where there is less of it. This is a fundamental law of nature - think of heat, it always flows from where there is a lot of it (i.e. where its hot) to where there is less of it (i.e. where its cold). Thus hydrogen moves from where there is more of it , the aluminium, to where there is almost none of it, the argon bubbles,. There is no "knocking" of hydrogen bubbles for at that stage the hydrogen is not present as bubbles rather it is dissolved in the aluminium, it simply moves into the argon bubbles and there is no reaction between the argon and anything - it is after all an inert gas and thus by definition incapable of reaction. Hydrogen bubbles only form on solidification and by that time it is way to late to try and degas the aluminium. However one thing the argon bubbles do "knock" or rather get under and float up are oxide films. Any film bigger that an argon bubble will be lifted up and floated out of the aluminium - this is one of the reasons for the use of the smallest possible argon bubble size... Martin
In welding, dissolved hydrogen can be a very real problem. We had lots of trouble qualifying in 6061T6 and tried everything we could think of to pass e-xray. Some even resorted to questionable methods when no one was looking. Perfect cleaning and argon coverage just did get us by.
Perry, To be honest I now know of a few errors in this video and I have modified the lance accordingly. I hope to do an update when I am satisfied with these latest mods. However for most "backyard" work and assuming that the castings are not great thick lumps I would recommend not to degas. Instead use clean dry metal, melt quickly, do not get too hot, and cast as soon as hot enough. Many of the so called degasing techniques in use in backyards do not work and some actually add gas!...Martin
Rendi, I use a reasonable quality air hose, it is two layers of some sort of elastomer with fabric in between. I have never had a problem with this hose getting too hot. But I use standard Nito air fittings to couple this hose to the lance and on one occasion this fitting got hot enough to melt the plastic parts inside it. I use a fairly long stainless steel 10mm diameter tube as the main part of the lance and as stainless steel is a relatively poor conductor of heat its not conduction that caused the air fitting to overheat, rather it was the radiant heat from the glowing metal and furnace and the hot gasses coming from the furnace that caused the problem. To avoid a repeat of the fitting failure I added an extra length (about 1/2 a metre) of the stainless steel tube to the lance. I added this extra length via a metal right angle fitting so the hose end of this added tube is well out of the way of all the heat.
Hello Martin, sorry for my bad capacity to English language, but I don't understand the choice of material used for protect the lance. What is your choice ? Many thinks for all Master 👌
Matthew, I paint the lance with a boron nitride paint this paint is called "BN Hardcoat" it is made by ZYP Coatings. They have a web site. It is a water based material and I let it dry then heat the lance to almost red heat before using .... Martin
Mark, The boron nitride coating that I use here is by far the best I have come across but it is expensive - very expensive However you can as you suggest use a coating which has sodium silicate in it as a binder. You could try mixing talc and iron oxide (concrete pigment) with sodium silicate to a very sloppy paste. Start with about equal quantities (by volume) of each. Dilute to watery slurry and apply to a warm lance, dry to red heat slowly at first. Not as good as the BN and will need to be reapplied each time. (I reapply the BN each time anyway) Be sure to remove any areas where the aluminium has begun to attack the underlying lance, take them right out with a carbide burr and oxidise the fresh area at red heat before reapplying the wash. You could also try graphite powder and sodium silicate - there are many possibilities 😊. Good luck... Martin
@@olfoundryman8418 thanks mate.. i just found your channel, it's amazing to see a real pro in action.. i'm a manual machinist that's just starting out in metal casting and your video's are a big help, there's lots of video's about casting on youtube but no one else ive seen gets results anywhere near to what you achieve
Shashi, Sorry but I can't help with a drawing - I never did one - I just made it up as I went along. The only thing I can suggest is that guided by what you can see in the video you do the same... Martin
Mig welder gas is 20% argon 80% co2. Do you think this mix would accomplish anything ? I am planning to try casting for the first time later this summer, so I am doing a little research now. I was thinking urethane foam coated in plaster and buried in loose sand. Any thoughts would be appreciated.
A common question but the answer is NO, well nothing good anyway! Unfortunately aluminium and CO2 react to form aluminium oxide and (presumably) Carbon. The last thing one wants floating around in our aluminium is even more oxide than is already there. The only viable gasses are straight argon ( I use commercial grade) and nitrogen. Bottled nitrogen has higher oxygen and water levels that the commercial argon and the argon gives a drier dross so it is my choice.Be careful of urethane foam with heat it gives of some very nasty gasses including I believe HCN. I know people have used it and presumably lived but I suspect they did it outdoors on a windy day! Plaster coats are a bit troublesome as its difficult to get all the a water out of the plaster - impossible in fact unless you take the plaster up to well above the temp at which the foam would go real funny :) Again I know people use plaster coats but again they don't really do it right the idea is that the gasses from the decomposing foam come out through the coat and into the sand and NOT bubble out through the metal. Looking at most YT videos of it being done one can see that most of the gas does come out through the metal, bad, very bad. Vegoilguy (check out his latest lost foam video) and I are currently working on a simple coat that will allow the gases out through itself, early days yet. but consider not using any coat and using a normal green sand or a CO2 cure silicate sand (your 20 %Ar 80% CO2,( I thought it was the other way around,) should cure a silicate sand off ok) in place of the dry sand ,this was after all the original form of the process of lost foam before coats were developed. The sand should be fairly coarse. Both Foseco and Ask Chemicals have coats commercially available for this process. Sorry to be so negative but the more problems you learn about at this stage the more chance you wild have at success when you actually try it.Good luck and if I can be of any more help just ask, PM if you wish. Rgds, Martin
Sashi, I have never got involved in the degassing of copper. I believe Foseco make some flux type products for this purpose and also that degassing using argon similar to what I do here is practiced. However the lance I use here is not suited to copper, the Boron nitride protective wash is only useable up to about 900 Deg C and above this it breaks down and provides no protection, thus at the temperature of molten copper the lance would be rapidly destroyed... Martin
Shashi, Yes, by all means you can use a ceramic pipe to cover up the steel pipe carrying the argon (or nitrogen). The only thing is that the ceramic will have to be one that is good at taking thermal shock as otherwise it wil shatter when immersed in the molten aluminium. Note that in the video on the smaller lance I used a graphite sleeve. This is quite resistant to attack by the aluminium BUT I found that the aluminium found its way through the joint where the graphite met the top of the lance head and actually worked its way about 30 mm or so up inside the graphite tube around the steel inner. I had coated the inner tube with the boron nitride wash and that saved it. Perhaps an additional short sleeve like I used on the bigger lance head pipe junction may help here. Note that with repeated use I found that the central bolt of the big lance worked loose and the two discs slightly separated giving me an annular gap instead of the desired 16 small holes. To counteract this I had to put 6 countersunk screws through the top disc and thread them into the bottom disc to hold the discs together properly. I day I will do an update to this video to cover this modification.... Martin
Great content, based off this vid I made a Lance of the same design (not quite as pretty as yours :) ), and after testing it in water it looks like it will work great. As far as protecting it, would a boron nitride aerosol spray work, or would it need to be a BN paint?
Iam, I am well pleased than someone thinks enough of it to make one themselves. Be aware that bubble size in water is somewhat smaller than it will be in molten aluminium. A 1 mm to 2mm bubble in water would indicate a 2 to 3 mm bubble size in molten aluminium. The controlling factor in bubble size is the hole size it comes out of, hence my use of about 0.1 mm deep grooves these should give a bubble size of 1 to 2 mm in water. It is important that the two discs making the grooves are held tightly together as if not you get a slot right around the discs where they join and this will give much larger bubbles, approx. 10 mm. Sometimes my discs come a bit loose and I think I need to bolt them together with 6 or so small bolts as well as the central bolt. Perhaps this is worth considering. I have no actual idea of how well this device really does degas aluminium I am just assuming that it does a good job (it should and I note that once I started using it I had to make my feeders a bit bigger this indicates less gas in the metal. However I have made arrangements to borrow a reduced pressure tester so I can actually do a before and after test on my metal for hydrogen gas content and hopefully if time permits also try a few of the other degasing ideas in current use. I hope to do a video on this. So I should find out if I have been wasting my time - I hope not! I use a BN paint "hardcoat " by ZYP coatings, dear as poison! I would think that the aerosol would work too but I have never tried it, did not know it was available. Be aware that the BN is not a cure all. Sometimes the aluminium gets through and gets stuck right into the outer protective sheath that I have on my lance. I check the lance after every use very carefully and any attack is cut out back to clean aluminium free metal with a burr in my Dremel. I then oxidise the cut area with heat and then recoat with the BN. I do recoat before every use attack or not. Also I have had the aluminium work its way inside the outer sheath and up around the inner stainless steel tube , for a distance of some inches in one case and it had started to attach the stainless so check for this too. It got in where the outer sheath rested on the degasing head so I made a fairly tight sleeve (fitted with BN paint inside it) to go over the top of the head and the bottom bit of the sheath, this stopped the problem. Good luck with it.... Martin
Thank you for the detailed reply! I look forward to trying it out, this is strictly a hobby for me so its fun to learn and improve on my limited experience. Your channel is by far the best I've seen on YT on this subject, it is much appreciated for you sharing your knowledge! I'll keep everything you said in mind and try this out as soon as I get the BN. Thanks again
iam, Thank you for your kind words. Passing on the knowledge that I have gained over the years is why I am on YT and sharing it is my pleasure. I wish you luck in your efforts. Please let me know how it all goes... Martin
I hadn't realised that molten Aluminium was such a reactive substance. I was planning on using a steel home made crucible, which from your description sounds like it will only last a small number of pours depending upon the thickness of steel used. Would the same go for any baking trays or steel angle used as ingot moulds?
Mark, you'd be really surprised how long a crucible made of 1/4" steel will last. Mine is the size of a gallon of PAINT! Kiln wash helps, but I don't bother.
Mark, Now you get me into a difficult area - one where if I am not careful I will upset people and I do not wish to do that. Steel for ingot moulds is fine I have used such moulds (the same ones) for over 20 years and no problem other than they distort a little more each time that you use them. I would suggest using thick angle or even one side of I beam with the ends welded up at a fair sort of relief angle. Please though can I beg of you NOT to use a steel crucible. Aluminium has a life,sounds odd but it does, starts out nice and fresh from the smelter but with each use and recycle it picks up impurities, the use to which it can be put is determined by how far along the recycle cycle the aluminium has travelled. Perhaps the worst of the impurities is Iron and it CANNOT be removed it just keeps building up. I can assure you that having looked down a microscope at a lot of aluminium alloys a small amount of iron absolutely fills the structure with very, very, very brittle iron compounds These ruin the strength and can lead to catastrophic failure. They also interfere with feeding during solidification and with fluidity during casting. The end of the road is pressure diecasting alloys which have about 1% iron their ultra rapid solidification keeps the worst of the effects of such high iron at bay. One should obviously never use pressure diecasting alloys for sand casting work. After this all you can basically do with it is bury it in a hole in the ground. We should not be destroying our primary raw material.Iron pots will in the end be eaten by the aluminium and the only think that slows it down is the oxide layer on the iron (and any wash applied - but washes are unreliable even the boron nitride one that I use on my transferee ladles and degassing lance) To be honest the Boron nitride wash is dearer than buying good quality clay graphite crucibles. An Iron crucible might last a while and then again it might penetrate at one point on the first use it wil then piddle molten aluminium down you leg or just generally all over the place - it may even ruin the inside of your furnace. I know that decent crucibles are not cheap - I buy them - but all hobbies cost money and the cost of a crucible is well worth it they last for well over 100 melts with aluminium (I have had over 200) and even if a crucible costs you $60.00 its only $.60 per melt - chicken feed! I will have more to say later on this.
A friend asked me why I don't use steel crucibles for aluminium, so I explained to him why I use clay graphite crucibles. He never believed me and months later he said he had two inches of sludge in the bottom of his steel crucible and a lot of his castings were very brittle. Not long after that he got a clay graphite crucible! With 30+ years of casting you tend to make a lot of mistakes to learn from.
Luckygen, Yep, in 30+ years I sure have made a lot of mistakes, but I never made the one of using a steel crucible for aluminium - Perhaps I was fortunate - as very quickly while getting my metallurgy diploma I learned of the problems of iron dissolved in aluminium. The tale of your friend is about what I would expect I will bet that sludge was a collection of plate/needle shaped very brittle crystals - one or more of the several Iron Aluminium Silicon intermetallic compounds known for their extreme embrittleing effect. I hope that your friend dug a hole in his backyard and buried all that brittle metal - nothing much else that you can do with it! As I mentioned in my reply to Mark above I will have more to say on this because its a bit of a hobby horse of mine - I am just trying to find the words to say it without peeing too many people off!
Olfoundryman 100% correct, I couldn't agree more. Unfortunately there is a whole host of morons (I'm not worried about upsetting the stupid TH-camrs eg who use steel crucibles) that make a foundry to melt aluminium but only use it once or twice, they use steel crucibles.....They are dangerous! Why take the risk? If like me you are going to make castings etc, buy some decent crucibles. Salamander crucibles are superb. Excellent for bronzes....I started with aluminium, but it doesn't machine anywhere near as well as beautiful bronze. I have made silicon bronze, aluminium bronze, leaded bronze, and good old fashioned tin bronze. And they all are wonderful alloys. My point is, metal casting is a fantastic hobby, and with the Internet being such a great source of information, anyone with half a brain can do castings and do them to a high standard. Just bear in mind, if you want to be a cheapskate and try the "TH-cam specials" eg "casting a "whatever" For only $1.99". Don't, you will most likely get yourself hurt. Casting metal will not break the bank, but you do need good equipment. Eg, protection is No.1 and it's expensive for good quality items. Face shield, kevlar gloves, leather apron, strong boots. The list goes on, also don't think you are going to get professional results from soda cans, it's not going to happen. The aluminium is of such poor quality. I really should just make a bloody video..........
Gday, great vids, and like a few have already commented, its good to see someone of your experience on this forum showing us amateurs a thing or two. When you're degassing for 7 mins do you still have the furnace on at full or is it off? CheersBob.
Bob, Glad that you liked the videos. Firstly I never run my furnace "full" as it would produce over 500,000 BTUs per hour at that sort of setting! For bronze melting I might use 3/4 of that but for aluminium perhaps half at most. But I know what you are getting at - If I am degassing my 30 kg crucible (an A90) I turn the furnace off when the metal is at about 690 deg C on the way up, I find that during the degassing time the heat in the furnace and in the crucible soaks through to the metal and the metal temp goes up to about 740 deg C despite the furnace being off. (See note below) I like to pour most things around 730 deg C so this just gives nice time to flux the top of the metal and get the ladle hot so I can ladle the metal out and pour each casting (I don't lift the A 90 out of the furnace). If I am melting in the smaller A25 crucible I find that I need to let it get a little hotter before I turn off as the heat soak seems less with this smaller crucible (perhaps because there is more room around it). After degassing and fluxing I lift this crucible out and monitor its temperature while it slowly drops to the 730 Deg C that I want to pour at - this may take a few minutes. Sometimes while waiting for the temp to drop I will cover the top of the crucible and pass argon gas under the cover to prevent any hydrogen pick up from the humidity in the air - this technique is also known to not only prevent Hydrogen pick up but to actually lower hydrogen levels although it may take 15 to 30 minutes to meaningfully lower the Hydrogen levels. This sort of thing is best reserved for alloys know to be bad for gas e.g. piston alloys.All in all I am not that happy with my degassing methods, they are for sure way better than those used by many others but they are not as good as I would like - I am thinking of making a small rotary degasser as these are much better (smaller bubble size) but some aspects of the design are very difficult!Note:- the old adage is that one should degas when metal temperatures are falling i.e. that one should wait until a peak has been reached before starting to degas. I guess I sort of break that rule!Martin.PS. The 7 minutes is perhaps on the short side - ok for 356 (601) alloy but for piston alloys I use 10 minutes.
Thanks for the quick reply Martin, much appreciated, your experience has already put an end to some of my misinformed habits, and please just keep those vids rolling in mate, they are a pleasure to watch and learn from. Cheers Bob
Bob, Do I detect a fellow Aussie? You accent and speed of reply would suggest so. I notice that my last reply has one of those dreaded lines through much of it, I do not know why this happens but happen it does every so often and the line does not appear until after I have hit "reply" so there is nothing I seem to be able to do about it - just try and ignore the line and read through it. I guess I am doing something wrong for it to occur but I don't know what! Most annoying! I hope that the "misinformed habits" that I have put an end too were not the ones that you enjoyed! :) I am always trying to do more videos but it is surprising just how long they seem to take - I do not know how some people do a video every few days - must be all they do!
Yes Martin , Im a Perth boy, and the habits were ones that improved my castings, eg smaller sprues for metal flow, not needing an extension riser on everything I do, all the little things I take note of , as your surface finish is great. Just a hobby for me, also the pattern making side is what I like best though. I think your strike through text on your comments is because of the Dash symbol before the "If" where it started and finished with a : after note. if I put a dash in before the sentence and another after you will get strike though example below. -Cheers Bob-
Bob. Thank you so much for explaining the strike through problem for me. I will now avoid the use of the "dash". Small sprues , yes, the most essential thing to do to get a reasonable casting and so easy to do. A friend (a tame pattern maker) and I poured some pistons a couple of days ago. Piston alloys are, ahem, "difficult" and this was our third try, we have had all sorts of trouble with gas, shrinkage, and air bubbles. It is a large piston , machines to about 4 inch diameter and 6 inch high. It is deliberately heavy (it replaces and iron piston) so the pour weight was 4 kg. we poured it through a slot sprue just 12*4 mm and about 200 high. The metal went through a filter at the sprue base and then via two runners to two side feeders. Fill time was 27 seconds. Most people would reckon that such a small sprue would not work but it did and very well too as we made the best pistons that we have yet managed, proof machining has shown them to be more than useable. In truth we feel the 27 seconds was a little long and are going to increase the sprue to perhaps 15*4.5 to get a fill of more like 20 seconds. Next time we make these pistons I will make a video, people will be amazed at the strangeness of the mould, how it was made, and the smallness of the sprueExactly why some casters seem want to use a huge 25 mm plus diam. sprue that they extend upwards with a tin can full of sand and then cut the worst possible pouring basin, the dreaded funnel in the top of that sand, is beyond me. It is a methodology guaranteed to produce the worst possible casting properties. People have absolutely no idea of just how much metal a 25 mm diam. sprue would carry if you could pour fast enough to keep it full, but at say 200 high a 25 mm diam. sprue will carry 2.5 Kg of aluminium per second! Boy that's a lot of metal, no way any of the castings YTers make need to be poured that fast.Rgds,Martin
Tegrity, As far as I know hydrogen gas absorption while liquid and re-evolution during solidification is not a problem with Zinc based alloys. In addition the high pressures used on the metal would supress any tendency for gas to come out of solution and form bubbles within the casting. Any problems that you are having with bubbles trapped in the casting are most likely air caught up in the extremely turbulent mould fill conditions that exist in the pressure diecasting process... Martin
@@olfoundryman8418 thank you for the info in the zinc alloys,,,we operate a hot bath submerged goose neck injection unit on our machines ,, these goose necks are submerged in the machines holding pot and these machines run a 22 second recycle time ,,so mould face cleanliness is a must as well ,, which honestly I have had better luck correcting mould cavity filling issues by running a lower temp on the molten alloy and running the clamp a bit loose to allow trapped gas in the mould cavities to escape a bit easier but the down side it tends to create a heavier parting line in our patterns and of course the danger of a explosive flashing event ,,which are never any fun I do realize the difference between your process and ours is a night and day difference including the alloy difference but any advise to help run better quality patterns is always much appreciated
@@olfoundryman8418 a few other questions I have is about your melting furnace,, what do you use for fuel on your furnace? Natural gas,Propane,Fuel oil? And your crucibles,,,did you make your own crucible? I have access to foundry clay and some refractory materials that I intend to use for my home/hobby forge I'm working on ,, so I'm considering build as much of my own equipment as I can to save money
Tegrity, My furnace burns diesel fuel. I do not make my crucibles rather I buy them from reputable sources (Vesuvius) - a bit expensive but if well treated they last a long time. There is somewhere on YT a bloke who makes his own clay graphite crucibles, looks to be a damn messy business!.. Martin
Tegrity, Pressure die casting was never my thing! But my observation is that most seem to control fill problems with lots of overflows around the edges of the cavities. I know that with gravity die work venting to remove air is extremely important. Often dies that have been mad in one piece - by say EDM sinking - will not work but if made in segments by more traditional tool making methods they will work as air can get out through the various joins between the segments. Often I will use thin shims (around 0.03 mm thick) between the segments to allow better air flow between them although in pressure die casting these small gaps would likely just fill with flash..Martin
Steven, That is a somewhat dogmatic statement - what is the basis for it? There are differences between Argon and Nitrogen. Firstly, Nitrogen can form small amounts of aluminium nitride - argon will not react with aluminium at all. Secondly, the dross produced with Argon is “drier” than that with nitrogen, by this I mean that the argon dross contains less free aluminium, this may be related to the first difference. However, both argon and nitrogen contain some water, oxygen, and CO/CO2 all of which react with aluminium to produce aluminium oxide, and in the case of the water, dissolved hydrogen (but you get more out than you put in) The argon I use, a commercial compressed grade, contains up to 15 parts per million of water. I would rather it did not but its about the best I can afford to use. Compressed commercial nitrogen is much the same. Where nitrogen is almost certainly better is if it is a liquid supply as this contains less water. This is I believe what Bob Puhakka uses in his foundry. Unfortunately, you cannot keep nitrogen liquid simply by pressure alone, some evaporative leak off must occur. This is not that much of a problem if you are a large foundry using a lot but for small operators it is uneconomic. At my usage rate for example 99% plus of that lovely dry liquid nitrogen would have evaporated off long before I ever got to using it as a degassing agent - hence the best I could do was compressed argon over compressed nitrogen for the drier dross. I did investigate the use of commercially available dries for the argon (silica gel will not cut it.) These will supposedly get the water etc content down to a few parts per billion so may be worth using, again though there are economic considerations. I never got around to trying these. Please note that this video is badly in need of an update as it does contain a few errors and I have since altered the lance head design. I hope with returning health (should I be that lucky) to do the update Thank you for your comment..... Martin
Great work on the improvements of Aluminum Foundry work!! In the past did you ever try coating your lance rod with plaster of Paris? Or ceramics ! Show the complete process of building a lance in a video! Remember we are not machinists
Thomas, The lance was just a little lathe work and to be honesI thought it too boring to bother showing but maybe I could revisit the issue because I have to do an update as I found some mods to the lance were necessary to get it to work as intended. Plaster of Paris Hmm, in a word - no. People seem to use, or rather try and use, it for everything. For any sort of use involving molten metal it needs very careful drying out followed by a an even more careful preheat cycle which amongst other things eliminates residual combined moisture but often if its straight Plaster of Paris results in a lot of cracking. I think it an unsuitable material for this particular use. What I do use is a material called "hardcoat" by ZYP coatings, it is a boron nitride based material and thus rather expensive, but it repels molten metal and fluxes quite strongly (below 900 deg. C only). This is a water based paint on type coating that I use on the degassing lance, bail out ladles, and thermocouple outer sheaths. It works quite well but needs replacing every day of use. I have wondered about more permanent coatings that are applied in sophisticated (and no doubt hideously expensive) ways things like pure alumina, silica, or silicon nitride but I do not know of anyone who has used them. My guess is that they would not work too well or last very long because no one to my knowledge is using them.. Martin
hi i watch as many of your videos as possible and really enjoy your work, im building my own forge this week do you have a video on the temperature probe you use/made thanks
danv8, No, sorry but I do not have a video on the temperature probe. The one I use is commercially purchased. It is what is called an MIMS thermocouple. This is a Mineral Insulated Metal Sheathed thermocouple with an earthed hot junction. I.e. the thermocouple is inside a 6mm heat resistant metal sheath (Inconel or stainless steel) An insulating mineral (commonly magnesium oxide I think) is packed around the thermocouple within the sheath. The thermocouple hot junction is welded to the closed end of the sheath. I protect the sheath with a boron nitride ceramic wash, this works very for aluminium but is not suitable for copper base work as the wash is only good up to 900 deg. C or so. The one I use is a metre long. I have seen such probes on eBay and they are quite cheap also from eBay you can get an instrument to read them, again surprisingly cheaply This item on eBay would be a good start www.ebay.com.au/itm/Digital-K-Type-Thermocouple-Probe-Sensor-Temperature-Controller-Assorted-Probes/282576231648?hash=item41cadb1ce0:rk:60:pf:0&var get the 500 mm probe length. Good luck with your own efforts.... Martin
Frank, Yep, there sure is a way, its called electrolysis and its how they produced the aluminium in the first place! Sad but true, once the aluminium is back to oxide you have to go down the whole electrolysis extraction route again. However most dross contains quite a lot of free metal (sometimes as much as 90%) and this can be recovered with correct fluxing and agitation techniques. (But its a messy business.) It is usual to add a fluoride to the flux used for this purpose. Cryolite (sodium aluminium fluoride) is a common choice but I believe that sodium fluoride will do. The usual mix of sodium and potassium chlorides (lite salt) is not very effective. My furnace is fired with diesel using a commercial burner fed with about 16 Oz air pressure from a large blower and the diesel at about 10 Psi from a sealed tank kept at 10 Psi (NO MORE!) with air pressure... Martin
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I was going to ask you a question about the average home casting whether it needed gassing or not but found the answers in comments, you and lucky gen 1001 are the only ones I trust on here for reliable information, thank you for sharing your knowledge it has save me a ton of time and disappointment. Hope you don't mind me asking a question now and then, try not to bother you with common sense stuff . Thank you.
Ray, I will pass your comment on to Luckygen he lives about 100 Km away from me and when he "comes to town" he often visits. I am sure he will be as pleased at your comment as I am. Sharing what I know is what I am on about and I believe that lucky is too. Any questions just ask away....Martin
Bored, waiting on a new video...so watching this video. Great video, again. Your replies to questions here in comments are over the top in details, a literal gold mine of information. Thank you Uncle Martin for sharing your knowledge.
Rich, My pleasure nephew Richard 😊 More videos on the way but they just seem to take forever to edit… Martin
@@olfoundryman8418 Where are you, hope all is well. Merry Christmas!
Thank you! well explained of aluminium degassing.
Scrap, Thank you for saying so and I hope it was of use to you.... Martin
Thank you for sharing your knowledge!
Austrian, Thank you for your comments - sharing is my pleasure.... Martin
I learn more watching your videos than I could in any other way. Adding this info to my Olfoundryman collection. Thank you. Lincoln, NE USA.
Larry, That you learn something is my pleasure... Martin
I loved the more technical explanation of degassing. Great job.
Doug, Glad that you liked it
Answered my questions about degassing Al.. thanks again, information even I can understand...
Malcolm, Degassing is a subject that many have a great number of misconceptions about. And in fact many peoples degassing efforts most likely result in more gas rather than less, either because they use the wrong method (washing soda does NOT work), don't do it for long enough or it causes to much splashing at the metal surface. With clean metal melted quickly not too hot and poured without delay for normal hobbyist work I recommend that degassing is hardly necessary. Any gas will be so fine you will need a magnifying glass to see it. If it is much bigger than that it is most likely trapped air through bad pouring and gating methods.
However I am trying to get around to doing an update to this video as experience has indicated some improvements are possible and necessary for the lance.... Martin
Great explanation and design process.
the reduced number of holes for the lance,for the same flow rate, would increase the velocity of the gas leaving the lance.
that might explain why there was a significant difference in the bubbles produced - the gas was flowing out of he holes faster and so broke up more so in the molten aluminum.
thanks
Charles, Intuitively what you are suggesting feels correct. However I am at a loss to know if it is so. In fact recent info that I have come across clearly indicates that bubble size is related to just two things;- the size of the orifice that the gas is coming out of, and the liquid into which the gas is flowing. There is no mention of flow rate at all - presumably then higher flow rate just means more bubbles of the same size. In my case with this lance I was concerned that the bubbles coming out of slots so close together might coalesce into larger bubbles simply by mutual contact. Halving the number of holes was an attempt to keep the bubbles further away from their neighbours and so prevent coalescence. Of course it may have all been self defeating as with more bubbles of the same size per hole each bubble would be closer to the bubble before and after from the same hole so coalescence may well still have occurred - life was not meant to be easy!
Very interesting and useful information. Thanks again for your time.
Thomas, Thank you for your comment. I am glad that you found it both interesting and helpful. Regrettably, as you might gather from my replies to Mark above, degassing is a most difficult area! As always the time is my pleasure.
About 35 years ago I cast a boat of of things in my high school metal shops class. I got rather good at it. Made some complex patterns and the like. We used petrobond sand. Off and on over the years I have cast the odd item in aluminum and a plaster mold for quick and dirty one off items. I'm at the point where I have to get back into casting for small runs of custom items. I have to say I have learned more of the nitty gritty items of casting from your videos than from just about every other video I have watched on TH-cam. Great stuff. I really appreciate your thorough explanations of why you do things the way you do. Do you do any cast iron work?
Kravchenko, Thank you for your comment. Its comments like yours that really make the effort of putting videos on YT worth while. Sadly its a bit difficult to put 60 years of "nitty gritty" learning into a few short videos but I do try to put as much in there as will reasonably fit and I always try to put some more in the next video.
Plaster can be a bit problematic for casting metal into unless you do it right in which case it works very well indeed. I would be interested to know of your experiences in doing it. Did you use straight plaster or was it a blend with other materials what preheat treatment did you use to dry the plaster, did you use the rubber pattern technique, have you tried foamed plaster - so many questions!.
No, I do not do iron work,tried it once about 50 years ago but managed to get a 2% carbon product because I burnt too much carbon out by doing it wrong. Its very hard on furnaces crucibles and the people doing it so I stuck to bronze and aluminium. Luckygen1001 who lives about 100 Km from me does a lot of iron work. He has been at it for over 30 years and knows it well. He and I have spent a couple of most pleasant afternoons talking foundry and he does seem to know his stuff... Martin
I first did lost foam and lost wax in high school. So that was 35 years ago. The lost wax was done in plaster of Paris as I knew nothing of the correct recipe back then. I grew up way out in the country in Manitoba Canada. Many pieces of crucial information were simply not available back then. But I was to stupid to know what I couldn't do and I fumbled my way through. The first lost wax attempt was a bust. I erroneously thought that wax when heated would shrink. Guess how that worked out! crack! new mold new way of draining the wax! that actually worked out quite well with great retention of the finish including all my imperfections on the wax pattern. Lost foam was tried once. I managed to shut down the high school with that one. (A true pity of course! I think I got more pats on the back for the free afternoon than jibes for my stupidity!) I was not impressed with the surface finish or the general amount of porosity in that casting. I was attempting to do a casting for a headstock of a metal lathe. Degassing is so important to a good casting. A friend of mine and I made casting for water pump housings that were great sieves for cleaning out the water that entered them. In other words they leaked like sieves! We saw first hand how not to make a casting. Then I read in an article that degassing aluminum could be done with chlorine tablet. This I tried, outside on a breezy day. We knew enough about chemistry to recognise that chlorine gas would be produced in copious amounts. It seemed to work. More recent work was for making loudspeaker cast aluminium baskets. This was done with a glass fiber reinforced plaster mix used for porcelain molds. I actually machined these and dried them out in an oven. The two halves either stayed true to the mating surfaces or they would warp slightly and then leak as I poured the nold. Molten aluminium does indeed run out of a mold just like water! Now I'm thinking of setting up a more permanent foundry for similar casting work to what you are doing. Custom casting work and short runs of commercial casting. I think I can do both cast iron ( No experience with. But I do watch luckygen 1001's videos.) I would need dedicated crucibles for that. And most likely means to lift them that are a bit more robust. Sorry to blather on. But you bring back so many memories. And I learn so much from watching these videos. So many things that I say to myself, that's what I was doing wrong! I consider myself better educated each time I watch one of your videos. Thank you!
@@KravchenkoAudioPerth nice to hear i was not alone bumbling around with casting 30 + years ago in Canada.
Wonderfull and thanks for sharing with us
Rabih, As always sharing is my pleasure... martin
First, thanks for your videos, they are the most professional I found so far ! In my country argon/degasing tablets are very expensive, is there other techniques to avoid porosity ? like controlling the temperature ? On wikipedia they say "To minimize gas solubility the superheat temperatures can be kept low"
Gaetan, I used to use Hexachlorethane tablets but they are no longer available, then I tried the grey tablets that give off nitrogen gas (are these the ones that you mean?) I did not like them, their action was so violent that they splashed 50 mm of metal out of the crucible and all that splashing up into the air just allows more hydrogen to get in. A local foundry did tests and came to the conclusion that these tablets made gas levels higher not lower! Using washing soda or Epsom salts is a complete waste of time as all they do is bubble water through the metal which will increase gas levels not reduce them. My usual advice to the hobbyist is not to bother degassing and as long as your metal is clean i.e. no oil, grease, paint, corrosion or water and if you melt quickly and do not exceed 760 deg. C (preferably lower) and pour as soon as possible, you should have reasonably gas free castings (well, any gas will be very fine and you probably won't see it) I would recommend not pouring on very humid days and I am also assuming that the castings you are doing are not great thick chunky things that will take for ever to go solid as these are very bad for gas. Good luck with it.... Martin
Thank you so much !
@@olfoundryman8418 It's probably a bit pointless to respond for me, seeing as your original comments is now 5 years old, but anyway. Both epsom salts (magnesium sulphate, MgSO4) and soda (sodium carbonate, Na2CO3) when store bought will indeed be the hydrated form, meaning that per molecule one or more water molecules will be bound to it. It is however very easy to turn them into the anhydrous i.e. water-free form by heating in an oven at a specified temperature and for a specified time. Those temperatures and times can be found quite easily on the internet. And once all the water has been driven off in the oven all you need to do is store them in a sealed glass jar and they'll remain water-free for use.
Thanks for the clarification
I am very happy with this important Notes
Mohammed, Clarity and happiness are what I aim for. If you have any other areas that you would like further clarified just let me know and I will try to answer any questions.
I have thought on this and you are right.
The pure aluminum would prefer to be aluminum oxide. As you say it loves water. The water moisture is in the air floating. The pure aluminum attracts to the oxygen in the water and grabs the oxygen from the water to become aluminum oxide. It leaves the hydrogen H2 gas has a small atoms bouncing around against the atoms of aluminum and aluminum oxide Al2 O3 trying to get its electron back. The tiny bubbles of argon bump the tiny hydrogen gas atoms and carry it out. The holes in the lance should be as small as possible and allow the lance to still work. The bubbles at the bottom just as they exit the lance will pick up more H2 being smaller as they rise they will expand due to less pressure and more heat. They will pick up less as they become larger but cross the top layer of the aluminum better.
Casting area should be dehumidified as possible. I have a project going but I am building a lance next.
Thomas, Spot on! Another thing about small bubbles is that they rise slower than big ones - you can see this effect in an aquarium with an air stone - this means that the smaller bubbles have more time to collect the hydrogen. Also the bubbles float out any oxide skin films that are bigger than the bubble - the smaller the bubble the more oxide skins you float out. The hydrogen flows from the metal into the argon bubble because there is more hydrogen in the metal than in the bubble its exactly like heat flowing from where there is a lot of it i.e. from where its hotter to where there is less of it i.e. to where its colder. I do know of a foundry that will not pour aluminium on humid days as hydrogen pick up can be quite fast then... Martin
Most of the TH-cam casters I see use washing soda as a degas. I've seen you comment before that using washing soda as a degas isn't the best idea. Why is that? Anyways, another great, informative video.
Mister. It is my intention when (huh - If) my health improves to do a longish video on just this issue, with a great deal of technical info, sources, and experiments included to prove the point. It is my humble opinion that the originator of this process should have their box of matches confiscated for the harm they have done to the hobbyist casting community - whoever they are - I have a pretty good idea! No names no pack drill!
Briefly, People seem to think the gas given off when washing soda is plunged into molten aluminium is CO2 - it isn't - but even if it was you can not degas aluminium with CO2 as it and aluminium would react to form C (as smoke) and aluminium oxide (Al2O3) as folded films (bifilms) floating around in the aluminium.
There are two common forms of washing soda, one is Na2CO3 the other is Na2CO3.10H2O. This last one is what was traditionally known as washing soda. If you plunge the first one into aluminium you would probably not get many if any bubbles at all. If you plunge the second those 10 molecules of H2O (yes, this version of washing soda is about 64% water) are driven off as steam and this is what we see bubbling out through the aluminium. Now remembering that the hydrogen that we are trying to get rid of from our aluminium got there by the aluminium reacting with water in the form of humidity in the air and in the burnt fuel in the furnace or from wet scrap etc it seems damn silly to me to bubble steam through the aluminium, all it will do is react (in part) with the aluminium to form hydrogen which will immediately dissolve in the aluminium worsening its gas level and aluminium oxide films, these act as weakness within the metal and as nucleation sites for the growth of porosity be it shrinkage or gas. The one saving grace - if we could call it that - here, is that the bubbling is over with quite quickly (maybe 30 seconds from what I have seen on YT) and a lot of the steam seems to escape rather than react as it is moving through the aluminium rather quickly. So while it will INCREASE the Hydrogen gas levels - the exact opposite of what it is supposedly being used to do - it will probably not increase them by all that large an amount - BUT any increase is too much!
Its not the best idea - its about the worst!... Martin
@@olfoundryman8418 Thank you very much! You are a wealth of information!
@@olfoundryman8418 Although the meaning of such names can differ from one region to another, I'm pretty certain the name washing soda is only used for the hydrated salt of sodium carbonate (Na2CO3·10H2O), but not for the anhydrous salt (Na2CO3). Because the presence of even trace amounts of water can be detrimental to many processes in the lab, it's well known among chemists that certain salts can be used to remove water or at least keep water out. For example many of the solvents commonly used in laboratories (like acetone, ethanol, isopropanol, tetrahydrofuran, toluene etc) have differing amounts of affinity to water (i.e. hygroscopicity), and in order to remove any water they might have already contained they're often pre-dried with drying salts (like sodium carbonate, sodium sulphate, magnesium sulphate, calcium chloride, calcium oxide, etc.).
So if you would substitute the anhydrous version for whatever salt you would otherwise have used, that should fix your problem in regards to it producing steam. Seeing as anhydrous salts are not uncommon in chemistry labs, I'm sure you could find some chemical supply houses or wholesalers who will sell it to you, after all they're pretty benign and harmless substances. And if you do somehow end up have difficulty finding such suppliers then eBay would be an option, there are a couple of chemical sellers who ship internationally on eBay. And although not an option for all salts there are several commonly available ones which you can dry yourself till they're completely anhydrous by heating it on a tray in the oven at the correct temperature and for the right amount of time.
Martin on the subject of Argon gas bottle costs, you might wish to look into the deal going at Bunnings where you pay a deposit on the bottle @ $200 and then just pay for the gas each time you return the bottle @ $90 for Argon in a D sized bottle.
Mark, Yes I think that you mentioned this before in a comment to another of my videos. My large rented E cylinder still has heaps of gas inn it so I have not yet had to look into this source.
A most interesting video, Martin.
Question; If the hydrogen comes from water vapour reacting with the molten aluminium, then I hypothesize that the source of that water vapour would be the humidity layer at the surface of the aluminium at room temperature.
This is somewhat like how low hydrogen welding rods can absorb moisture if left exposed to the atmosphere. The solution for the welding rods is to keep them either in a fresh sealed tin or to keep them in a rod oven to drive off the moisture.
Therefore, the solution for reducing the amount of water vapour available to react with the molten aluminium in the crucible would be to pre-heat the aluminium feed stock in a suitable oven or low temperature furnace for a suitable heating time to drive off as much of the surface humidity prior to charging of the crucible.
I have noted in numerous casting videos where additional feed stock is to be added to a crucible, that the feed stock is pre- warmed by placing it around the edge of the furnace. This would have the effect of reducing the "loading shock" to the overall temperature of the crucible, but I don't believe that it would be a long enough pre-heat to drive off the majority of the humidity layer or surface absorbed moisture.
It appears to me that the best way to reduce this moisture issue is to use an oven or low temperature furnace to pre-heat aluminium feed stock to at least 200 deg. C as this temperature is well above the boiling point of water at 100 deg. C and should drive off the water vapour.
What are your thoughts on the matter?
Mark, Basically what you say is correct, but there are many more sources of hydrogen and perhaps the main one is that when we burn a hydrocarbon fuel one of the products of combustion is water vapour. There is in addition the natural humidity in the air which of course varies all the time. In fact some people believe that on very humid days it is difficult to degas properly and to keep the hydrogen level down as the pick up from the reaction of the humidity in the air and the surface of the liquid metal can be quite high (particularly if the surface of the metal is agitated) - this can even be the case with electric melting - the humidity in the air is quite simply that potent a source of hydrogen! Drying ingots, scrap on top of the furnace is indeed common - I do it. It is best remembered that when one puts cold material on top of the furnace moisture in the outgoing furnaces gases will condense on the cold material - it will in fact get absolutely dripping with water initially and one does need to wait until it is well above 100 deg. C before adding it to the liquid metal in the crucible. Scrap that is badly corroded is a problem as the corrosion product is often hydrated and this water can be hard to drive off. Anodised aluminium is a bit problematic too as the anodic film is at least in part Aluminium hydroxide. I do not like to use greasy, dirty, or painted scrap either. I am uncertain as to how hot one really needs to get metal to drive off any occluded surface moisture but I judge that if adding material to liquid metal does not result in bubbles immediately coming to the surface then it was probably dry enough. Incidentally even metal at say 300 deg C (as compared to say 100 deg C is not going to be much less of a loading shock - we have to take the latent heat of fusion into account and I think this is much bigger than the "heat" difference from 100 tor 300 deg C.
I do know that some larger foundries preheat their ingot (and possibly scrap) before loading it into the primary melting furnace although and in some disagreement with my loading shock comment above I suspect they do this mainly to increase throughput of said primary melting furnace (in some ways dry hearth melting is a better technique as the charge is thoroughly preheated and the liquid in the furnace is totally protected from loading shock but I have concerns about oxidation with this technique. Other sources of moisture that many people forget about are damp furnace tools and damp fluxes and even bail out ladles. And then of course we have the people who attempt to degas by plunging water of crystallization containing chemicals to the bottom of the melt - the bubbles you see coming from this technique (Many YT videos show this appalling technique) are steam - about the worst thing that you could possibly bubble through your metal. The two most common that come to mind are Washing soda Na2CO3.10H2O and Epsom salts MgSO4.7H2O. It is the 10 and 7 H20 that cause the gas output from these two substances - a most counterproductive technique.
Thanks for the reply Martin.
Given what you have written about some of the water coming from hydrocarbon combustion then it becomes obvious as to why many professional foundries use electric induction to heat the large crucible. No combustion and no forced draft to draw in more moisture laden air.
It also seems like casting on a humid day needs to be done in a humidity controlled environment, which is something beyond most home foundries.
As for the Washing Soda and Epsom Salts, it looks like I will have to investigate the making of an Argon Lance along the lines of the one you have made or look into buying degassing tablets.
Mark, The propensity of aluminium to dissolve hydrogen is perhaps the metals Achilles heel. Degassing is a most difficult area. Big foundries have it well under control with rotary impellor degassing units but this is an option hardly open to the amateur or small foundry. The mechanics of RIDs are nothing special but the impellor is another matter - it has to spin at a few hundred RPM in molten aluminium a substance known for it ability to dissolve almost all other metals (its not supposed to attack Zirconium - but there is not a lot of that around). In addition the impellor has to be mechanical robust and resistant to both oxidation and thermal shock- no easy trick! Quite exotic materials are used - things like silicon nitride - exotic, expensive, and most difficult to machine. Beyond us small operators. And even if one could afford a commercial impellor it would be way to big meant probably for 100 Kg batches as a minimum. If you use a lance you need to maintain a supply of either argon or nitrogen, rental on the bottles is a killer about $250.00 per year for a large bottle. You could investigate own it yourself bottles or the small disposable bottles available at welding shops (note you must use either nitrogen or pure argon NO argon CO2 mixes) Either way its going to cost money - money perhaps better spent on decent crucibles to replace the (Groan) tin cans that many use (this is another sore point of mine but I will not go into it here.) Then lances like mine require constant maintenance - areas of aluminium attack must be checked for and ground out after every use and the boron nitride protective wash must be reapplied before every use. This wash is about $200.00 plus a gallon and that's a small American gallon! But it can be obtained in 1 pint sized containers in the US - last time I came across it at about $80.00 a pint!!! If your lance does not give fine bubbles like mine does then its a waste of time anyway - whatever lance you come up with check the bubble size in a bucket of soapy water. Re degassing tablets - hmm - yes - well. I used to use these - initially they were Hexachlorethane it breaks down to give chlorine which reacts with the aluminium to give Aluminium chloride this is a gas at the temperature concerned and it bubbles up through the melt removing the Hydrogen. ( The suggestion that the chlorine reacts directly with any hydrogen in the melt to give HCl is a complete nonsense)However the fumes coming off the melt are both toxic and very corrosive - everything above shoulder height in my foundry is rusty and the roof above the furnace leaks. In Australia you can no longer buy this substance because of its effect on the Ozone layer. Pity really it did a half decent job of degassing if used properly. I was thus forced to go over to the tablets that dissociate in the melt to produce nitrogen. These are not very good, they breakdown way to quickly (2 to 3 minutes - way too short a time for any meaningful degassing) and they cause extreme turbulence - they splashed 2 inches of metal out of the crucible - I had to sit a steel ring on the top of the crucible to contain this. Such turbulence is likely to INCREASE the hydrogen level as it mixes the metal with the humid furnace atmosphere. In fact a commercial foundry near me conducted trials and were convinced that these nitrogen tablets actually INCREASED their gas levels - the supplier of the tablets of course disagreed! The standard bell plunger used to hold the tablets to the bottom of the melt is a bad design. Its hard to clean and tends to hold the gas back and let it go in large (HUGE) bubbles. I used a spiral, more or less in the shape of a bell plunger, bent up from 3/8 inch steel rod. It was easier to clean and provided I applied a coat of ladle wash before each use it lasted OK and seemed to allow smaller bubbles.My honest advice on degassing to the amateur is Do Not Bother. If you chose your scrap with care, preheat all additions and make sure everything is dry (fluxes etc.) melt quickly, don't over heat (760 deg. C max) and pour with minimum delay your gas levels should be low enough to get away with. This is particularly the case if your castings are relatively thin as solidification will then occur too quickly for much gas to come out of solution (and any that does will be in very fine bubbles - invisible at YT resolutions!) If your castings are on the heavy side and gas becomes a problem then I guess that you will need to rethink. Always remember that gassy metal can be recovered by simply allowing it to solidify very slowly in a wide open topped mould - dried preheated sand might make a suitable mould. This will allow the gas to come out of solution and on remelting most of it will not be redissolved.Humidity controlled environment - that would be a laugh - last foundry I worked in had evaporative cooling blowing on the operators at the casting stations - nice humid air blowing all over the holding pots!! But they did have continuous nitrogen degassing on every holding pot via a silicon carbide "Hocky Stick" - these have a porous bottom leg (the bit you would hit the puck with were it a real hocky stick) the nitrogen came out through this porosity as reasonably fine bubbles. One day maybe I will work up to a video on the subject of degassing if only to dissuade people reaching into their various household cupboards, pulling out some random chemical and in complete ignorance of physics, chemistry, and thermodynamics swearing by all that's holy that it is the go to thing for degassing - I don't mind them destroying their own work but others copy them and their work too is ruined - a bad scene.
Can you explain loading shock? Regards, David
David, My understanding of "loading shock" is that when one puts solid aluminium into liquid the relatively cold additions (even if well preheated) will cause a significant drop in the temperature of the liquid metal already in the crucible. - A temperature "shock" if you will. If you add a lot of solid to say a lesser amount of liquid the whole lot can go solid or at least pasty. What actually happens is determined by the relative quantities and specific heat of both solid and liquid aluminium and by its latent heat of fusion. Generally though the temperature recovers quite quickly. However it is best not to add to much solid at once. And never to add once casting has started. Another factor is that such additions can cause the precipitation of surprisingly large particles of intermetallic compounds, these are based on what might be considered unwanted impurity elements in the aluminium - iron manganese chromium etc. these particles are slow to redissolve are very hard and very brittle, they damage tooling and can seriously lower the ductility of any resulting casting should they get cast into it. Often these compounds are found at the bottom of the crucible after a pour - the old timers used to call them "sand" for that's what they resembled. This is more a problem with oft melted scrap, pressure diecast, and older alloys - none of which in my opinion should ever be sand cast. :) The occurrence of these compounds is one of the very good arguments for not melting in steel crucibles.
Hi Martin, first of all thanks for creating such a wonderful and detailed and practical video. Can you explain share detailed video on lance making ? Currently in this video what is the lance specification you used ( Lance inner and outer diameter, having more thickness is helpful for straight length for mechanical strength…
Manoj,
First let me admit that the lance was made from “found material” i.e. what I had lying around. I did not do any plans for it - I just made it. The very inner tube is stainless steel, I was told, by the person who gave it to me, that it was “refrigeration tube”. It is 3/8 inch outer diameter and has a 3/64 wall thickness. This tube is thick enough to take a 3/8 NF 24 TPI thread. The outer sacrificial tube is mild steel and is 3/8 ID by ¾ OD. I say “sacrificial” as its job is to protect the inner stainless tube from attack by the molten aluminium. The length of this outer tube is such that with the lance head touching the crucible bottom the tube comes not quite up to the top of the crucible - this way the lid of the lance rests on the top of the crucible. The lance head is made from cast iron which I had purchased as continuously cast bar. The head thickness is about least 5/16 inch - its two pieces - so total thickness is thus about 5/8 inch. The head diameter is preferably at least 3 inch as if less the bubble stream just seems to come together into one central stream as it rises, rather than many streams coming from all around the lance. However, I think the head diameter needs to be 1/3 to ½ the diameter of the inside of the bottom of the crucible. All of the lance that is exposed to the molten aluminium is painted with a wash called Hardcoat BN. This is a boron nitride based wash made by ZYP Coatings in the USA - it is expensive - but it’s the best wash to prevent metal attack. Even so after every days use I inspect the sacrificial outer tube for any areas where the aluminium has begun to attack. I remove these areas with a small carbide burr making sure to get ALL the aluminium removed. The now exposed area of mild steel is oxidized with dull red heat and the whole lance, tubes, head, and all, recoated with the wash.
To be honest in using the lance after making that video I found a fault in its design in that the two head plates tended to come apart because the central bolt worked loose. So, I bolted the two plates together with 6 off ¼ inch countersunk bolts. I have been conscious of the need to do an update video but so far bad health is preventing me - one day maybe, I hope!.... Martin
PS, is there anything else that you would like to know?
I am wondering that even if the fluidity of the Al is similar to water, that the extra weight of Al would tend to decrease the bubble size until it is very near the surface. What do you think?
Stephen, Two points, first yes, bubbles will grow in size as they ascend as the pressure on them lessens - you can see this in aquariums with air bubblers. There is no reason to think that the same does not occur to bubbles rising through molten metals. Very approximately 100 mm of aluminium gives 1/2 psi so a bubble rising through 100 mm of aluminium would increase in volume by about 3% -not very much so it might be a bit hard to see!
second, and as counterintuitive as it may seem the bubble size is determined solely by the hole size the gas is coming out of and the material into which it is coming. There is a graph in John Campbell's book "Complete Casting Handbook" Fig 7.35 page 390 that lists the bubble size for various liquids and a range of hole sizes. For a 0.1mm hole the bubble size is about 1.5 mm for water and (sadly) about 3mm for aluminium
As a third point I think that some bubbles coalesce with others on the way up simply by banging into each other and forming the one larger bubble, the larger bubbles then rise much quicker and hit smaller ones above growing even larger, Studying the bubble trail in a tall aquarium is quite instructive... Martin
Very interesting...
Does molten copper need degassing? If so, would argon work for that too? How about any of the brasses?
Insert, Copper is an interesting case. Like aluminium it too will dissolve hydrogen although the solubility of hydrogen in copper does not drop as much as it does in aluminium on solidification so in theory the hydrogen should remail in solid solution where it will likely be quite harmless. However, if you look at some of the videos produced by those ignorant types turning high quality copper wire into low quality ingots just for the sake of making a video and wasting fuel you will often see that the ingots have so much gas in them that they rise like a loaf of bread as they solidify. I show some examples of such ingots in my “Possibilities” video. The gas in these ingots is however not hydrogen - rather it is steam. This results from the copper being oxidized by bad melting practices. The copper oxide thus produced reacts with dissolved hydrogen to produce water as steam. This reaction takes place as the copper is cooling down a little before and during solidification thus causing the gas porosity. It is easiest to prevent this not by degassing to remove the hydrogen but by melting properly so that no oxide is formed. Quite simply - no oxide no water no water no porosity. Argon will remove Hydrogen from copper but practical realities make this difficult for us hobbyists. In the case of brasses and aluminium bronzes the problem does not arise as the zinc/aluminium in these alloys effectively deoxidizes the copper... Martin
Can this argon lance and diffuser plate be made of graphite, or will it contaminate the molten aluminium in the cubicle?
Lan, Graphite will certainly not contaminate the molten aluminium. The lance could be made out of graphite but mechanically it is a more difficult material to handle because it is quite brittle. Impellors for rotary degassers (industry best standard for degassing) are commonly made from graphite because it is totally resistant to attack from the molten aluminium. I sometimes use a graphite sheath to protect the steel tube that is the central part of one of my degassing lances. Otherwise I just use a boron nitride wash to protect the steel and cast iron parts of my lance. It is my aim one day (I should live so long) to make a rotary degasser small enough to suit my crucible size as rotary produces smaller argon bubbles and that is a definite aid to good degassing. Also I have recently modified my latest lance (the bigger one shown in this video) and hope to do a short video about these mods in the near future... Martin
Does molten Aluminium attack Stainless Steel in the same way it attacks mild steel?
Does Stainless Steel also transfer Iron to the Aluminium if used as a crucible?
Hi, I think your lance design is well developed and you have clearly experimented with the operation of it. I am just wondering though if degassing tablets would be an alternative for someone who only does the occasional casting job. I cannot find a supplier of degassing tablets here in Australia (who will sell in small quantities) and the overseas suppliers won't ship outside their own countries. Just the same, I am interested in your views on how effective the tablets would be.
Mark, I have used degassing tablets. Years ago one could get hexachlorethane degassing tablets and these worked fairly well both at degassing and at floating up oxides within the metal. However these are now considered a no-no as they cause ozone layer depletion. There are degassing tablets available that generate nitrogen gas they are usually grey. I have tried these and to be honest I was not impressed! They bubbled so fiercely that they caused so much turbulence in the crucible of metal that 50 mm of the metal was splashed out all over the inside of my furnace. I had to put a heavy steel ring on top of the crucible to stop this loss. But this sort of turbulence causes more hydrogen to be absorbed from the furnace atmosphere so I was dubious as to if these tablets did any good. A friend and owner of a much bigger foundry did some tests and he became convinced that these tables actually increased the gas level rather than reduced it! I abandoned these tablets in favour of my fine bubble lance and I immediately noticed that I had to use bigger feeders as I no longer had gas to help counteract shrinkage! To be honest my advice to the average occasional metal caster is not to bother with degassing. Just make sure your metal is clean of oil grease paint and is dry, melt as quickly as you reasonably can don't get it too hot, never over 760 deg C. and pour without delay. Assuming that you are not trying to cast very thick parts you should not have too much of a problem with gas. Gas porosity is usually quite fine, around 0.5 mm or less pore diameter, and this is easily smeared over during machining of most aluminium alloys so you wont see it! All my work is heat treated so it machines much better and without smearing and some of it is diamond machined and that will produce such a well finished surface that even very minor porosity is easily seen so I have to degas as well as I can. I think that many occasional casters get way too concerned about gas porosity, unless you get a real bad case (I have seen a few -:)) of gas and assuming that your castings are reasonably thin i.e. the solidify quickly you are unlikely to notice much of a gas problem. If you do then something is wrong so contact me with the details if that is the case. One last thing many people "degas" with washing soda (sodium carbonate) IT DOES NOT WORK in fact it INCREASES the gas level so please don't try it... Martin
Your comments back up some other reading that I was doing yesterday. The consensus was that for small castings, degassing is probably not necessary. I will take on board what you have suggested about not overheating the melt and trying to keep the sections thin. I am guessing that my castings do have quite a bit of porosity but having said that I have never had one fail and the finished castings are either powder coated or don't need a high quality finish anyway. I think Myfordboy started the whole washing soda thing and yes, I too thought it was a good idea since I was seeing lots of bubbles coming to the surface after I stirred the washing soda in to the melt.
Thanks for your detailed reply.
Mark Presling
Mark, It may well have been myford who started off this whole degas with washing soda rubbish, I am not sure but whoever did start it off has a lot to answer for.
The problem is that the hydrogen gets in our molten aluminium from (in the main) its reaction with water in the air. There is of course always water in the air and particularly in furnace gases as water is a product of combustion. The aluminium reacts with the water to form hydrogen which dissolves in the aluminium and aluminium oxide which in the form of thin films floats around in the aluminium causing lines of weakness in the eventual casting.
Now washing soda comes in two main forms the first is Na2CO3, it usually is a granular white powder. The second form is Na2CO3.10H2O, this is the traditional "washing soda". It is usually in the form of transparent ice like small crystals. It is the 10H2O that is the problem, this is water of crystallization and it is driven off with moderate heat, this substance is in fact about 63% water by weight. If you plunge the first form into molten aluminium nothing much will happen perhaps a small bubble of two but that's it. The Na2CO3 does NOT break down to produce CO2. Even if it did any CO2 get given off will not degas aluminium as it will react with it to produce C and aluminium oxide. Luckygen1001 proved much of this in one of his videos. However if you plunge the second form into molten aluminium all that water is driven off as steam, lots of it, and this is what you see bubbling out of the aluminium. Remembering how the hydrogen gets into our aluminium it is obvious that the worst thing we could do is to bubble steam through the molten aluminium. This can only INCREASE the hydrogen content so attempting to degas with washing soda is worse that a complete waste of time and sadly so many people have copied the technique simply because someone who has been on YT for a while and knows no better not only insists that the technique works but defends it quite fiercely... Martin
Just wondering after 7yrs if you have ever attempted using tablets and if they work? I have seen a lot of degassing flux tablets on the market that look tempting to try.
Todd,
Years ago, I used hexachloroethane tablets to try and degas my aluminium. Not having a Reduced pressure test apparatus, I cannot really be sure how well they degassed my metal. I never got any complaints about gas levels though, but then gas is hard to see even in well machined castings as the machining tends to flow metal overt the small gas bubbles and true gas bubbles are indeed small - usually below 0.5 mm. I do feel that the hexachloroethane did a pretty good job of floating oxides etc to the surface. It also did a pretty good job of rotting my tin roof which now leaks. Note that I did not use the traditional bell shaped plunger as these hold the purge gas back until it forms large (read “useless”) bubbles. You can no longer get these tablets as they posed a threat to the ozone layer, well not here in Australia anyway. The tablets that you are referring too are I guess the ones that liberate nitrogen gas when plunged. I was forced to use these when the hexa was phased out and I have to say that I was not impressed. The first problem was that they bubbled so viciously that they threw 50 mm of metal out of my A25 crucible and all over the inside of my furnace. I used to put a high steel ring on the top of the crucible to catch this ejected metal and direct it back into the crucible. This sort of turbulence is very bad as it generates oxide which winds up in the metal as thin films and it exposes metal to the atmosphere and its attendant water (humidity) thus it generates hydrogen in the metal - likely more that it removes??? The second problem was that the tablets only produce nitrogen for a few minutes (2-4) and not long enough to properly remove any hydrogen in the metal - this meant doing it at least twice. Another foundry much bigger than mine did some tests comparing these tablets with argon gas bubbling from a porous Silicon carbide hockey stick type lance. They claimed that their tests showed that not only was the hockey stick better at removing gas but the nitrogen tablets actually made gas levels worse if used once the hockey stick had done its job. I have no reason to doubt their results. This was at least 10 years ago and its why I developed my own argon lance. Somehow, I doubt that the nitrogen tablets have got any better and that it is likely that they just make the foundryman feel good rather than actually do any useful degassing. The manufacturers of said tablets would no doubt disagree 😊. I think that I still have some of these tablets sitting here so if you wish to try them and you live close call in and I will give you some - just need to check that I did not throw them out though. I would doubt that the tablets currently available are any different to the ones I tried. Note that I have done some mods to the lance shown in this video and I really should do an update but health currently prevents….
Martin
Thanks for really useful video. I am very admired by your original lance design. But is it just your home solution, or maybe you took something as a base from industrial prototypes? I ask you because I am aquintenced about main designs of the degassers (graphite rotors or just immersed tubes with holes), however I haven't met somethink like that. So, it's interesting to me, is there similar industial solutions or is it only your original homemade device?
Edward, I am sorry for the delayed reply. I have rather a lot going on and don't always get around to replying as soon as I would like. Your question requires a fairly long answer so forgive me if I put you off until I have the time to answer it properly - soon I hope.... Martin
PS, if I forget (I am old 😊) please ask it again to remind me.
Edward, The lance design is my home solution, but it is based on the following;
1, The realization many years ago that for successful degassing the purge bubble size must be as small as possible. This is backed up by the standard industrial practice of using rotary degassers as these chop the bubbles in quite small sizes.
2, The use industrially of porous plug type degassers where the degassing head is made from a porous ceramic - firebrick and silicon carbide are typical,. The pores through which the purge gas emanates are very small and do produce reasonable fine bubbles.
Obviously you are aware of these points 1 and 2
3, Based on John Campbells work - the knowledge that the size of bubble generated by blowing gas out of a hole is dependent on the hole size and the liquid into which the gas is being blown. (Bubbles blown in water are about 1/3 the size of bubbles being blown into molten aluminium - for example) The pressure blowing the purge gas through the holes apparently has no effect on the bubble size (rather counter intuitive I feel, but apparently true) Note - very high gas velocities producing very high Reynold’s numbers in the purge gas flow MAY change this - I was yet to explore this avenue.
4, About the smallest hole size I could make was 0.1 mm. According to Campbell (Complete Casting Design Handbook 2015 edition page 390 Fig 7.35) this should give a bubble size of about 3mm in aluminium or about 1mm in water. Indeed, water tests did indicate a size of about 1 mm diameter. I would have liked a smaller bubble size in the molten aluminium but this was about as good as I could do.
5, There is no way that I could drill 0.1 mm holes but I could score a flat disc with 0.1mm deep groves and then clamp another, but unscored, flat disc against it to effectively give me the required 0.1 mm holes.
Thus, the lance that I developed.
To my knowledge there is nothing like it used industrially. I am not surprised by this as it is too demanding of maintenance. The head (i.e. the two discs) are made from cast iron and they seem to last quite well but do oxidize on the clamped faces and these need periodic re-machining. The vertical hollow shaft through which the gas enters the “head” is a constant source of problems as the rising bubbles seem to disturb the protective coat I use (boron nitride hard coat by ZYP coatings) and the aluminium frequently attacks this shaft. After no more that two uses I have to check the shaft, grind off any attacked areas, oxidize with heat, and then reapply the hard coat. Attack seems to occur about 50% of the time. The head is never attacked. In any case I apply fresh had coat every day before use of the lance, this coat is dried at red heat before use of the lance
The inner of this shaft is a stainless steel pipe and if the aluminium gets at it attack is rapid so I use a thick sacrificial sheath of mild steel around it and it is this that I have to remove any attacked areas from. I have tried a graphite sheath but it to had problems - it tended to float and even when I prevented this aluminium seemed to somehow to get up inside the bottom of this sheath and around the inner stainless tube. This was difficult to deal with and I was working on a solution when ill health brought a sad halt to my casting endeavors - so no solution yet! But I do think this is the way to go.
One problem I had with the lance design as shown in the video is that for reasons unknown the central bolt holding the two discs together seemed to work loose very easily - the result was that instead of small holes around the discs I had a continuous slit and this produced bubbles that were way too big. I got around this by bolting the two discs together with about 8 small bolts placed fairly close to the outer edge.
I hope that this answers your questions - if not do not be afraid to ask further
… Martin
It works, so obviously it works.
The Chemistry sounds a bit off. Hydrogen 'dissolved' in Aluminium then interacting with Argon ?
Do either of those even happen ?
Not that i know, but it sounds more like the hydrogen is a bubble in the melt and the inert argon just helps move the hydrogen bubble to the top of the melt by mechanical entrainment.
Basically the argon ignores the Al and rises, knocking H bubbles upwards as well.
aga. Not sure there is any chemistry involved its more of a physical process. The hydrogen atom is very small (compared to other atoms) and it fits in between the atoms of most other things. This means it can dissolve in and move through either liquid or solid things all too easily. It causes great trouble in hardened steels with sudden catastrophic brittle failure. Its a pain in copper because it reacts with the often present copper oxide to form steam which fills the copper up with bubbles (of steam). And yet it apparently causes no problems in magnesium alloys. In aluminium it dissolves in the liquid but is much less soluble in the solid so on solidification it tends to precipitate out as small (usually less than 0.5 mm) bubbles. My understanding is that it is in solution as H but comes out as H2. Removal of H by argon (or nitrogen) is I think purely a physical process. Things move from where there is a lot of it to where there is less of it. This is a fundamental law of nature - think of heat, it always flows from where there is a lot of it (i.e. where its hot) to where there is less of it (i.e. where its cold). Thus hydrogen moves from where there is more of it , the aluminium, to where there is almost none of it, the argon bubbles,. There is no "knocking" of hydrogen bubbles for at that stage the hydrogen is not present as bubbles rather it is dissolved in the aluminium, it simply moves into the argon bubbles and there is no reaction between the argon and anything - it is after all an inert gas and thus by definition incapable of reaction. Hydrogen bubbles only form on solidification and by that time it is way to late to try and degas the aluminium. However one thing the argon bubbles do "knock" or rather get under and float up are oxide films. Any film bigger that an argon bubble will be lifted up and floated out of the aluminium - this is one of the reasons for the use of the smallest possible argon bubble size... Martin
In welding, dissolved hydrogen can be a very real problem. We had lots of trouble qualifying in 6061T6 and tried everything we could think of to pass e-xray. Some even resorted to questionable methods when no one was looking. Perfect cleaning and argon coverage just did get us by.
Fascinating stuff. Thanks
Perry, To be honest I now know of a few errors in this video and I have modified the lance accordingly. I hope to do an update when I am satisfied with these latest mods. However for most "backyard" work and assuming that the castings are not great thick lumps I would recommend not to degas. Instead use clean dry metal, melt quickly, do not get too hot, and cast as soon as hot enough. Many of the so called degasing techniques in use in backyards do not work and some actually add gas!...Martin
what hose melting temperature you use?
because i afraid the conduction will attack my hose i use high temperature melting hose.
Rendi, I use a reasonable quality air hose, it is two layers of some sort of elastomer with fabric in between. I have never had a problem with this hose getting too hot. But I use standard Nito air fittings to couple this hose to the lance and on one occasion this fitting got hot enough to melt the plastic parts inside it. I use a fairly long stainless steel 10mm diameter tube as the main part of the lance and as stainless steel is a relatively poor conductor of heat its not conduction that caused the air fitting to overheat, rather it was the radiant heat from the glowing metal and furnace and the hot gasses coming from the furnace that caused the problem. To avoid a repeat of the fitting failure I added an extra length (about 1/2 a metre) of the stainless steel tube to the lance. I added this extra length via a metal right angle fitting so the hose end of this added tube is well out of the way of all the heat.
Hello Martin, sorry for my bad capacity to English language, but I don't understand the choice of material used for protect the lance. What is your choice ? Many thinks for all Master 👌
Matthew, I paint the lance with a boron nitride paint this paint is called "BN Hardcoat" it is made by ZYP Coatings. They have a web site. It is a water based material and I let it dry then heat the lance to almost red heat before using .... Martin
is there anything else that would work as a coating? I'm thinking maybe sodium silicate or maybe ceramic exhaust manifold paint might work
Mark, The boron nitride coating that I use here is by far the best I have come across but it is expensive - very expensive However you can as you suggest use a coating which has sodium silicate in it as a binder. You could try mixing talc and iron oxide (concrete pigment) with sodium silicate to a very sloppy paste. Start with about equal quantities (by volume) of each. Dilute to watery slurry and apply to a warm lance, dry to red heat slowly at first. Not as good as the BN and will need to be reapplied each time. (I reapply the BN each time anyway) Be sure to remove any areas where the aluminium has begun to attack the underlying lance, take them right out with a carbide burr and oxidise the fresh area at red heat before reapplying the wash. You could also try graphite powder and sodium silicate - there are many possibilities 😊. Good luck... Martin
@@olfoundryman8418 thanks mate.. i just found your channel, it's amazing to see a real pro in action.. i'm a manual machinist that's just starting out in metal casting and your video's are a big help, there's lots of video's about casting on youtube but no one else ive seen gets results anywhere near to what you achieve
What dia should we take.
Shashi, Based on the limited number of sizes that I have tried I think that 100 mm would be a good starting point... Martin
@@olfoundryman8418 Thanks for your reply. Can you share the drawing with me.
Shashi, Sorry but I can't help with a drawing - I never did one - I just made it up as I went along. The only thing I can suggest is that guided by what you can see in the video you do the same... Martin
Mig welder gas is 20% argon 80% co2. Do you think this mix would accomplish anything ? I am planning to try casting for the first time later this summer, so I am doing a little research now. I was thinking urethane foam coated in plaster and buried in loose sand. Any thoughts would be appreciated.
A common question but the answer is NO, well nothing good anyway! Unfortunately aluminium and CO2 react to form aluminium oxide and (presumably) Carbon. The last thing one wants floating around in our aluminium is even more oxide than is already there. The only viable gasses are straight argon ( I use commercial grade) and nitrogen. Bottled nitrogen has higher oxygen and water levels that the commercial argon and the argon gives a drier dross so it is my choice.Be careful of urethane foam with heat it gives of some very nasty gasses including I believe HCN. I know people have used it and presumably lived but I suspect they did it outdoors on a windy day! Plaster coats are a bit troublesome as its difficult to get all the a water out of the plaster - impossible in fact unless you take the plaster up to well above the temp at which the foam would go real funny :) Again I know people use plaster coats but again they don't really do it right the idea is that the gasses from the decomposing foam come out through the coat and into the sand and NOT bubble out through the metal. Looking at most YT videos of it being done one can see that most of the gas does come out through the metal, bad, very bad. Vegoilguy (check out his latest lost foam video) and I are currently working on a simple coat that will allow the gases out through itself, early days yet. but consider not using any coat and using a normal green sand or a CO2 cure silicate sand (your 20 %Ar 80% CO2,( I thought it was the other way around,) should cure a silicate sand off ok) in place of the dry sand ,this was after all the original form of the process of lost foam before coats were developed. The sand should be fairly coarse. Both Foseco and Ask Chemicals have coats commercially available for this process. Sorry to be so negative but the more problems you learn about at this stage the more chance you wild have at success when you actually try it.Good luck and if I can be of any more help just ask, PM if you wish. Rgds, Martin
Thanks for your detailed reply. I think this will help eliminate a few rabbit holes.
Ken
For 99% of the stuff you do at home you don't need to degas. It's good foundry practice that's more important.
How much time it will take for degassing 150 kg of copper.
Sashi, I have never got involved in the degassing of copper. I believe Foseco make some flux type products for this purpose and also that degassing using argon similar to what I do here is practiced. However the lance I use here is not suited to copper, the Boron nitride protective wash is only useable up to about 900 Deg C and above this it breaks down and provides no protection, thus at the temperature of molten copper the lance would be rapidly destroyed... Martin
Can I use ceramic pipe. Steel pipe shall be covered with ceramic pipe.
Shashi, Yes, by all means you can use a ceramic pipe to cover up the steel pipe carrying the argon (or nitrogen). The only thing is that the ceramic will have to be one that is good at taking thermal shock as otherwise it wil shatter when immersed in the molten aluminium. Note that in the video on the smaller lance I used a graphite sleeve. This is quite resistant to attack by the aluminium BUT I found that the aluminium found its way through the joint where the graphite met the top of the lance head and actually worked its way about 30 mm or so up inside the graphite tube around the steel inner. I had coated the inner tube with the boron nitride wash and that saved it. Perhaps an additional short sleeve like I used on the bigger lance head pipe junction may help here. Note that with repeated use I found that the central bolt of the big lance worked loose and the two discs slightly separated giving me an annular gap instead of the desired 16 small holes. To counteract this I had to put 6 countersunk screws through the top disc and thread them into the bottom disc to hold the discs together properly. I day I will do an update to this video to cover this modification.... Martin
Great content, based off this vid I made a Lance of the same design (not quite as pretty as yours :) ), and after testing it in water it looks like it will work great. As far as protecting it, would a boron nitride aerosol spray work, or would it need to be a BN paint?
Iam, I am well pleased than someone thinks enough of it to make one themselves. Be aware that bubble size in water is somewhat smaller than it will be in molten aluminium. A 1 mm to 2mm bubble in water would indicate a 2 to 3 mm bubble size in molten aluminium. The controlling factor in bubble size is the hole size it comes out of, hence my use of about 0.1 mm deep grooves these should give a bubble size of 1 to 2 mm in water. It is important that the two discs making the grooves are held tightly together as if not you get a slot right around the discs where they join and this will give much larger bubbles, approx. 10 mm. Sometimes my discs come a bit loose and I think I need to bolt them together with 6 or so small bolts as well as the central bolt. Perhaps this is worth considering. I have no actual idea of how well this device really does degas aluminium I am just assuming that it does a good job (it should and I note that once I started using it I had to make my feeders a bit bigger this indicates less gas in the metal. However I have made arrangements to borrow a reduced pressure tester so I can actually do a before and after test on my metal for hydrogen gas content and hopefully if time permits also try a few of the other degasing ideas in current use. I hope to do a video on this. So I should find out if I have been wasting my time - I hope not! I use a BN paint "hardcoat " by ZYP coatings, dear as poison! I would think that the aerosol would work too but I have never tried it, did not know it was available.
Be aware that the BN is not a cure all. Sometimes the aluminium gets through and gets stuck right into the outer protective sheath that I have on my lance. I check the lance after every use very carefully and any attack is cut out back to clean aluminium free metal with a burr in my Dremel. I then oxidise the cut area with heat and then recoat with the BN. I do recoat before every use attack or not. Also I have had the aluminium work its way inside the outer sheath and up around the inner stainless steel tube , for a distance of some inches in one case and it had started to attach the stainless so check for this too. It got in where the outer sheath rested on the degasing head so I made a fairly tight sleeve (fitted with BN paint inside it) to go over the top of the head and the bottom bit of the sheath, this stopped the problem. Good luck with it.... Martin
Thank you for the detailed reply! I look forward to trying it out, this is strictly a hobby for me so its fun to learn and improve on my limited experience. Your channel is by far the best I've seen on YT on this subject, it is much appreciated for you sharing your knowledge! I'll keep everything you said in mind and try this out as soon as I get the BN. Thanks again
iam, Thank you for your kind words. Passing on the knowledge that I have gained over the years is why I am on YT and sharing it is my pleasure. I wish you luck in your efforts. Please let me know how it all goes... Martin
I hadn't realised that molten Aluminium was such a reactive substance. I was planning on using a steel home made crucible, which from your description sounds like it will only last a small number of pours depending upon the thickness of steel used.
Would the same go for any baking trays or steel angle used as ingot moulds?
Mark, you'd be really surprised how long a crucible made of 1/4" steel will last. Mine is the size of a gallon of PAINT! Kiln wash helps, but I don't bother.
Mark, Now you get me into a difficult area - one where if I am not careful I will upset people and I do not wish to do that. Steel for ingot moulds is fine I have used such moulds (the same ones) for over 20 years and no problem other than they distort a little more each time that you use them. I would suggest using thick angle or even one side of I beam with the ends welded up at a fair sort of relief angle. Please though can I beg of you NOT to use a steel crucible. Aluminium has a life,sounds odd but it does, starts out nice and fresh from the smelter but with each use and recycle it picks up impurities, the use to which it can be put is determined by how far along the recycle cycle the aluminium has travelled. Perhaps the worst of the impurities is Iron and it CANNOT be removed it just keeps building up. I can assure you that having looked down a microscope at a lot of aluminium alloys a small amount of iron absolutely fills the structure with very, very, very brittle iron compounds These ruin the strength and can lead to catastrophic failure. They also interfere with feeding during solidification and with fluidity during casting. The end of the road is pressure diecasting alloys which have about 1% iron their ultra rapid solidification keeps the worst of the effects of such high iron at bay. One should obviously never use pressure diecasting alloys for sand casting work. After this all you can basically do with it is bury it in a hole in the ground. We should not be destroying our primary raw material.Iron pots will in the end be eaten by the aluminium and the only think that slows it down is the oxide layer on the iron (and any wash applied - but washes are unreliable even the boron nitride one that I use on my transferee ladles and degassing lance) To be honest the Boron nitride wash is dearer than buying good quality clay graphite crucibles. An Iron crucible might last a while and then again it might penetrate at one point on the first use it wil then piddle molten aluminium down you leg or just generally all over the place - it may even ruin the inside of your furnace. I know that decent crucibles are not cheap - I buy them - but all hobbies cost money and the cost of a crucible is well worth it they last for well over 100 melts with aluminium (I have had over 200) and even if a crucible costs you $60.00 its only $.60 per melt - chicken feed! I will have more to say later on this.
A friend asked me why I don't use steel crucibles for aluminium, so I explained to him why I use clay graphite crucibles. He never believed me and months later he said he had two inches of sludge in the bottom of his steel crucible and a lot of his castings were very brittle. Not long after that he got a clay graphite crucible! With 30+ years of casting you tend to make a lot of mistakes to learn from.
Luckygen, Yep, in 30+ years I sure have made a lot of mistakes, but I never made the one of using a steel crucible for aluminium - Perhaps I was fortunate - as very quickly while getting my metallurgy diploma I learned of the problems of iron dissolved in aluminium. The tale of your friend is about what I would expect I will bet that sludge was a collection of plate/needle shaped very brittle crystals - one or more of the several Iron Aluminium Silicon intermetallic compounds known for their extreme embrittleing effect. I hope that your friend dug a hole in his backyard and buried all that brittle metal - nothing much else that you can do with it! As I mentioned in my reply to Mark above I will have more to say on this because its a bit of a hobby horse of mine - I am just trying to find the words to say it without peeing too many people off!
Olfoundryman 100% correct, I couldn't agree more. Unfortunately there is a whole host of morons (I'm not worried about upsetting the stupid TH-camrs eg who use steel crucibles) that make a foundry to melt aluminium but only use it once or twice, they use steel crucibles.....They are dangerous! Why take the risk? If like me you are going to make castings etc, buy some decent crucibles. Salamander crucibles are superb. Excellent for bronzes....I started with aluminium, but it doesn't machine anywhere near as well as beautiful bronze. I have made silicon bronze, aluminium bronze, leaded bronze, and good old fashioned tin bronze. And they all are wonderful alloys. My point is, metal casting is a fantastic hobby, and with the Internet being such a great source of information, anyone with half a brain can do castings and do them to a high standard. Just bear in mind, if you want to be a cheapskate and try the "TH-cam specials" eg "casting a "whatever" For only $1.99". Don't, you will most likely get yourself hurt. Casting metal will not break the bank, but you do need good equipment. Eg, protection is No.1 and it's expensive for good quality items. Face shield, kevlar gloves, leather apron, strong boots.
The list goes on, also don't think you are going to get professional results from soda cans, it's not going to happen. The aluminium is of such poor quality. I really should just make a bloody video..........
Gday, great vids, and like a few have already commented, its good to see someone of your experience on this forum showing us amateurs a thing or two. When you're degassing for 7 mins do you still have the furnace on at full or is it off? CheersBob.
Bob, Glad that you liked the videos. Firstly I never run my furnace "full" as it would produce over 500,000 BTUs per hour at that sort of setting! For bronze melting I might use 3/4 of that but for aluminium perhaps half at most. But I know what you are getting at - If I am degassing my 30 kg crucible (an A90) I turn the furnace off when the metal is at about 690 deg C on the way up, I find that during the degassing time the heat in the furnace and in the crucible soaks through to the metal and the metal temp goes up to about 740 deg C despite the furnace being off. (See note below) I like to pour most things around 730 deg C so this just gives nice time to flux the top of the metal and get the ladle hot so I can ladle the metal out and pour each casting (I don't lift the A 90 out of the furnace). If I am melting in the smaller A25 crucible I find that I need to let it get a little hotter before I turn off as the heat soak seems less with this smaller crucible (perhaps because there is more room around it). After degassing and fluxing I lift this crucible out and monitor its temperature while it slowly drops to the 730 Deg C that I want to pour at - this may take a few minutes. Sometimes while waiting for the temp to drop I will cover the top of the crucible and pass argon gas under the cover to prevent any hydrogen pick up from the humidity in the air - this technique is also known to not only prevent Hydrogen pick up but to actually lower hydrogen levels although it may take 15 to 30 minutes to meaningfully lower the Hydrogen levels. This sort of thing is best reserved for alloys know to be bad for gas e.g. piston alloys.All in all I am not that happy with my degassing methods, they are for sure way better than those used by many others but they are not as good as I would like - I am thinking of making a small rotary degasser as these are much better (smaller bubble size) but some aspects of the design are very difficult!Note:- the old adage is that one should degas when metal temperatures are falling i.e. that one should wait until a peak has been reached before starting to degas. I guess I sort of break that rule!Martin.PS. The 7 minutes is perhaps on the short side - ok for 356 (601) alloy but for piston alloys I use 10 minutes.
Thanks for the quick reply Martin, much appreciated, your experience has already put an end to some of my misinformed habits, and please just keep those vids rolling in mate, they are a pleasure to watch and learn from. Cheers Bob
Bob, Do I detect a fellow Aussie? You accent and speed of reply would suggest so. I notice that my last reply has one of those dreaded lines through much of it, I do not know why this happens but happen it does every so often and the line does not appear until after I have hit "reply" so there is nothing I seem to be able to do about it - just try and ignore the line and read through it. I guess I am doing something wrong for it to occur but I don't know what! Most annoying! I hope that the "misinformed habits" that I have put an end too were not the ones that you enjoyed! :) I am always trying to do more videos but it is surprising just how long they seem to take - I do not know how some people do a video every few days - must be all they do!
Yes Martin , Im a Perth boy, and the habits were ones that improved my castings, eg smaller sprues for metal flow, not needing an extension riser on everything I do, all the little things I take note of , as your surface finish is great. Just a hobby for me, also the pattern making side is what I like best though. I think your strike through text on your comments is because of the Dash symbol before the "If" where it started and finished with a : after note. if I put a dash in before the sentence and another after you will get strike though example below. -Cheers Bob-
Bob. Thank you so much for explaining the strike through problem for me. I will now avoid the use of the "dash". Small sprues , yes, the most essential thing to do to get a reasonable casting and so easy to do. A friend (a tame pattern maker) and I poured some pistons a couple of days ago. Piston alloys are, ahem, "difficult" and this was our third try, we have had all sorts of trouble with gas, shrinkage, and air bubbles. It is a large piston , machines to about 4 inch diameter and 6 inch high. It is deliberately heavy (it replaces and iron piston) so the pour weight was 4 kg. we poured it through a slot sprue just 12*4 mm and about 200 high. The metal went through a filter at the sprue base and then via two runners to two side feeders. Fill time was 27 seconds. Most people would reckon that such a small sprue would not work but it did and very well too as we made the best pistons that we have yet managed, proof machining has shown them to be more than useable. In truth we feel the 27 seconds was a little long and are going to increase the sprue to perhaps 15*4.5 to get a fill of more like 20 seconds. Next time we make these pistons I will make a video, people will be amazed at the strangeness of the mould, how it was made, and the smallness of the sprueExactly why some casters seem want to use a huge 25 mm plus diam. sprue that they extend upwards with a tin can full of sand and then cut the worst possible pouring basin, the dreaded funnel in the top of that sand, is beyond me. It is a methodology guaranteed to produce the worst possible casting properties. People have absolutely no idea of just how much metal a 25 mm diam. sprue would carry if you could pour fast enough to keep it full, but at say 200 high a 25 mm diam. sprue will carry 2.5 Kg of aluminium per second! Boy that's a lot of metal, no way any of the castings YTers make need to be poured that fast.Rgds,Martin
I wonder if this process would benefit in Zinc die casting operations this is very interesting😊 I run a 35 ton zinc die casting press from Dietech
Tegrity, As far as I know hydrogen gas absorption while liquid and re-evolution during solidification is not a problem with Zinc based alloys. In addition the high pressures used on the metal would supress any tendency for gas to come out of solution and form bubbles within the casting. Any problems that you are having with bubbles trapped in the casting are most likely air caught up in the extremely turbulent mould fill conditions that exist in the pressure diecasting process... Martin
@@olfoundryman8418 thank you for the info in the zinc alloys,,,we operate a hot bath submerged goose neck injection unit on our machines ,, these goose necks are submerged in the machines holding pot and these machines run a 22 second recycle time ,,so mould face cleanliness is a must as well ,, which honestly I have had better luck correcting mould cavity filling issues by running a lower temp on the molten alloy and running the clamp a bit loose to allow trapped gas in the mould cavities to escape a bit easier but the down side it tends to create a heavier parting line in our patterns and of course the danger of a explosive flashing event ,,which are never any fun I do realize the difference between your process and ours is a night and day difference including the alloy difference but any advise to help run better quality patterns is always much appreciated
@@olfoundryman8418 a few other questions I have is about your melting furnace,, what do you use for fuel on your furnace? Natural gas,Propane,Fuel oil? And your crucibles,,,did you make your own crucible? I have access to foundry clay and some refractory materials that I intend to use for my home/hobby forge I'm working on ,, so I'm considering build as much of my own equipment as I can to save money
Tegrity, My furnace burns diesel fuel. I do not make my crucibles rather I buy them from reputable sources (Vesuvius) - a bit expensive but if well treated they last a long time. There is somewhere on YT a bloke who makes his own clay graphite crucibles, looks to be a damn messy business!.. Martin
Tegrity, Pressure die casting was never my thing! But my observation is that most seem to control fill problems with lots of overflows around the edges of the cavities. I know that with gravity die work venting to remove air is extremely important. Often dies that have been mad in one piece - by say EDM sinking - will not work but if made in segments by more traditional tool making methods they will work as air can get out through the various joins between the segments. Often I will use thin shims (around 0.03 mm thick) between the segments to allow better air flow between them although in pressure die casting these small gaps would likely just fill with flash..Martin
awsome!
Dry nitrogen is a better choice of gas for degassing.
Steven, That is a somewhat dogmatic statement - what is the basis for it?
There are differences between Argon and Nitrogen. Firstly, Nitrogen can form small amounts of aluminium nitride - argon will not react with aluminium at all. Secondly, the dross produced with Argon is “drier” than that with nitrogen, by this I mean that the argon dross contains less free aluminium, this may be related to the first difference.
However, both argon and nitrogen contain some water, oxygen, and CO/CO2 all of which react with aluminium to produce aluminium oxide, and in the case of the water, dissolved hydrogen (but you get more out than you put in) The argon I use, a commercial compressed grade, contains up to 15 parts per million of water. I would rather it did not but its about the best I can afford to use. Compressed commercial nitrogen is much the same. Where nitrogen is almost certainly better is if it is a liquid supply as this contains less water. This is I believe what Bob Puhakka uses in his foundry. Unfortunately, you cannot keep nitrogen liquid simply by pressure alone, some evaporative leak off must occur. This is not that much of a problem if you are a large foundry using a lot but for small operators it is uneconomic. At my usage rate for example 99% plus of that lovely dry liquid nitrogen would have evaporated off long before I ever got to using it as a degassing agent - hence the best I could do was compressed argon over compressed nitrogen for the drier dross. I did investigate the use of commercially available dries for the argon (silica gel will not cut it.) These will supposedly get the water etc content down to a few parts per billion so may be worth using, again though there are economic considerations. I never got around to trying these.
Please note that this video is badly in need of an update as it does contain a few errors and I have since altered the lance head design. I hope with returning health (should I be that lucky) to do the update
Thank you for your comment..... Martin
Great work on the improvements of Aluminum Foundry work!!
In the past did you ever try coating your lance rod with plaster of Paris?
Or ceramics !
Show the complete process of building a lance in a video! Remember we are not machinists
Thomas, The lance was just a little lathe work and to be honesI thought it too boring to bother showing but maybe I could revisit the issue because I have to do an update as I found some mods to the lance were necessary to get it to work as intended. Plaster of Paris Hmm, in a word - no. People seem to use, or rather try and use, it for everything. For any sort of use involving molten metal it needs very careful drying out followed by a an even more careful preheat cycle which amongst other things eliminates residual combined moisture but often if its straight Plaster of Paris results in a lot of cracking. I think it an unsuitable material for this particular use. What I do use is a material called "hardcoat" by ZYP coatings, it is a boron nitride based material and thus rather expensive, but it repels molten metal and fluxes quite strongly (below 900 deg. C only). This is a water based paint on type coating that I use on the degassing lance, bail out ladles, and thermocouple outer sheaths. It works quite well but needs replacing every day of use. I have wondered about more permanent coatings that are applied in sophisticated (and no doubt hideously expensive) ways things like pure alumina, silica, or silicon nitride but I do not know of anyone who has used them. My guess is that they would not work too well or last very long because no one to my knowledge is using them.. Martin
I agree with Mr me … Martin please upload complete video of building a lance ….
hi i watch as many of your videos as possible and really enjoy your work, im building my own forge this week
do you have a video on the temperature probe you use/made
thanks
danv8, No, sorry but I do not have a video on the temperature probe. The one I use is commercially purchased. It is what is called an MIMS thermocouple. This is a Mineral Insulated Metal Sheathed thermocouple with an earthed hot junction. I.e. the thermocouple is inside a 6mm heat resistant metal sheath (Inconel or stainless steel) An insulating mineral (commonly magnesium oxide I think) is packed around the thermocouple within the sheath. The thermocouple hot junction is welded to the closed end of the sheath. I protect the sheath with a boron nitride ceramic wash, this works very for aluminium but is not suitable for copper base work as the wash is only good up to 900 deg. C or so. The one I use is a metre long. I have seen such probes on eBay and they are quite cheap also from eBay you can get an instrument to read them, again surprisingly cheaply
This item on eBay would be a good start www.ebay.com.au/itm/Digital-K-Type-Thermocouple-Probe-Sensor-Temperature-Controller-Assorted-Probes/282576231648?hash=item41cadb1ce0:rk:60:pf:0&var get the 500 mm probe length.
Good luck with your own efforts.... Martin
Awesome video Martin! Is there any way to convert the dross (aluminum oxide?) back to a useable form? How is your furnace powered?
Frank, Yep, there sure is a way, its called electrolysis and its how they produced the aluminium in the first place! Sad but true, once the aluminium is back to oxide you have to go down the whole electrolysis extraction route again.
However most dross contains quite a lot of free metal (sometimes as much as 90%) and this can be recovered with correct fluxing and agitation techniques. (But its a messy business.) It is usual to add a fluoride to the flux used for this purpose. Cryolite (sodium aluminium fluoride) is a common choice but I believe that sodium fluoride will do. The usual mix of sodium and potassium chlorides (lite salt) is not very effective.
My furnace is fired with diesel using a commercial burner fed with about 16 Oz air pressure from a large blower and the diesel at about 10 Psi from a sealed tank kept at 10 Psi (NO MORE!) with air pressure... Martin
hello Nr West