Very interesting material wonder how detailed it could be for making molds, considering it has a termal limit somewhere around 1200-1300C it can easly hold soft metals like aluminium, tin, silver maybe even gold and copper. It could be a stepping stone for many hobbies.
@@kompotreviews5720 Thanks for commenting buddy. I agree with. A homemade crucible, or cupel, made in this simple way, with cheap materials and great accessibility would in fact open up a lot of arts and crafts options. That being said, my crucibles from the video survived temperatures excessive of 1600 C, not F! Talk about a flex haha!
I noticed that your recipe is a 50:50 mix of alumina powder and kaolin powder, but what amounts of grog and charcoal dust? Also, could graphite work as a substitute for the charcoal?
Hey @rpdfangon! Sorry for a late reply, I was traveling. Correct, my kaolin/alumina ratio is 50:50, but I used a very random, by-the-feel amount of grog (fired and crushed pieces of the same ratio) and same with charcoal dust. I am afraid graphite would not work. I mean by mixing graphite with clay you would get excellent high fired crucibles (search historical Hessen crucibles, for instance). But, it would not work like charcoal dust as it would not sublimate or burn out, so no voids would be created in the crucible matrix.
I'm not sure to understand, how do you form your crucible? You pour your silica mixture into a plaster one, wait for it to absorb the moisture, then remove the excess and microwave the whole thing? And then the molds are not fused together and you can separate them? This looks cool, I'd like to try. EDIT: I think I got most of the answer from another comment. The separation of both molds still seems a bit mysterious to me.
Correct until the microwaving! :D The separation of the slip and the mould comes beforehand. I only microwave the plaster mould in order to dry it out sufficiently enough for another slip pouring. The only way I've seen the mould and the slip fusing together is if I poured the slip into a wet mould. It would suck out the moisture, but not all of it, so you end up with basically a very wet clay. It would separate eventually, but it would take weeks!
@@fmdj I stand corrected! I tried microwaving the crucibles after separation from the mould, but they would either explode or crack. So I exerted the drying method as in the video :p
Of course Zakaria. There's is no added binder. The only thing in the slip mixture is kaolin clay powder and aluminum powder. The crushed charcoal is just there to create tiny pores. Hope it helps, Cheers!
@@dogodogo5891 Hi pal, Thanks for the reply. I used charcoal powder/ carbon to form cavities in the matrix of the crucibles. When heated up at high temperature it reacts with oxygen and burns. Basically it sublimates into gas, making these cavities. Aluminium carbide would remain solid at such temperatures and no voids would occur. It would, perhaps, act as a very good temper or agregate for the matrix strength. Hope thst helps!
Hello! How to make alumina slip in this video and please tell me what additive was add that slip ? Upload a video or how to make alumina ceramic in that please tell me details. Thanks for sharing this video.
Hi GoodEnough! Very good tutorial; nice presented. You should go on with your trials and videos. I am directly interested in your ttests, so those are not just plain comments. My questions would be: for what metals are the crucibles intended for? have you noticed a certain life span related to type of metal mold? have you tried a comparison between charcoal and non - charcoal mixtures? I tend to bet on charcoal addition based on your presumptions (and my personal guess) ; but it is confirmed? How large do you consider can this method be expanded? I am targeting it for aluminum - up to 10 kg charge for finished mold up to 3 kg (not sure about output; it is just an estimation). And hoping for a more durable crucible than steel ones. Good luck, you are doing a very good job; both in trials and presentation!
Hi Mihai! My apologies for the late reply! First of all, thank you for commenting and showing interest in my projects. As for the questions, I will try to answer them accordingly. The crucibles I made were intended for the use with ferrous metals, mainly iron alloys, as obtaining crucible steel was a key factor for my dissertation. I saw that the crucibles were really long lasting, when it comes to high hardness, lack of porosity propagation and durability, except when it comes to rapid thermal cycling. I sometimes had no options but to blast the furnaces dull power with them being cold. Slow and steady increase of temperature should be applied, not rapid. Even with a high alumina content, which has great thermal expansion properties, it proved that the biggest enemy is the sudden heating or cooling. I have not tried yet a proper test of various void forming substances, as charcoal was readily available to me, cheap, easily transformed into a powder of fine grain, and non toxic. Also, the lack of its expansion during heating was a desired (albeit accidental) property, as well as complete burnout/sublimation. This method of crucible production could be increased. However, I presume adding central wad or lunge would be necessary, alongside great pressure, to increase density and structurally stability. That's how it's done in the industry. There is a video by British pate on graphite crucible production using moulds and dies. Homemade option, of course is very possible. I bet the elephant in the room would be the ability to melt bigger quantities metal at home. But, 10 kg is nothing that can't be done! I'll make more video's soon :)
@@emel60 Thank you very much for your answer and clarifications! I must agree 10kg looks (and is) like an elephant in the room. To define better -for myself- my needs, I would say I am mostly interested in IC model engines with cast parts net weight up to 0.5kg aluminum. Total aluminum per charge/cast I see as 1.5kg -considering all technological losses- but I consider normal crucible fill to be only 50% clean metal so a 1l crucible would be required (almost 3kg total capacity for aluminum). The majority of casts foreseen will be much less than this maximum. Have you tried any additive for binding aluminum oxide (both when forming and heat tempering)? I have read about 5-7% either water glass or bentonite. I have some pottery grade aluminum oxide but as fine as it is still has a high tendency to set quickly in the slip and also makes me question about cohesion. In trials till now I had rather bad results- as follows; but I'll try to refine techniques, and clear "hot spots": Charcoal powder hardly mixes in the slip; I think its the surface tension matter. I have added about 5% water glass in the mixture because I had good experience previously with it (aluminum oxide refractory coating for furnace and from the remaining formed some small crucibles in silicon patterns). The first trial, with consistency matching yours (high tendency of setting, not related to consistency/water content), dried very quickly in the plaster mold but in less than a minute left no cavity in the middle - solid block - not enough water. Second trial with plaster mold fully dried in microwave oven and a more fluid slip failed to deposit; plaster was not absorbing water almost at all. My guess is water glass from first trial clogged the plaster pores, although i washed mold thoroughly between slip casts. So here I am till now. I'll further test, but maybe scale down until success. Trials were done on a plaster mold made around a 350ml "bio" paper glass. Thanks again for your answer and waiting videos! All the best!
@@mihaimastacaneanu8505oh wow! I admire the project! I would say fingers crossed, but it takes everything else than luck- persistence, patience, sweat and blood! If successful, will you machine the parts by yourself or have them done professionally? I feared you might want to melt 10kg of cast iron or steel, one more difficult than the other. Aluminum, on the other hand, is much more manageable to work with, not just for the more forgiving casting process, easier alloying, but for the simplicity and lower cost of melting- low melting temperature for the win! A few kilograms to melt should not be such a problem, and making crucibles to hold 3 kg as well. Regardless, I would definitely make the crucibles thicker. Either a thicker slip or dye cast, it doesn't matter, but I would not trust my thin ones to hold a few kilograms and survive the transport, tongs, hits, heats. First one in this video is quite thick (7-8 mm), and by the time I made the last one for the experiment I managed to make them super thin (1.5mm). I really would not trust a kg of molten metal to something so thin, let alone three! I didn't notice that the charcoal dust had mixing issues. In this video I shook the slip vigorously and I got a rather homogeneous mixture. Perhaps I forced the charcoal to soak up water and made it sink. You can clearly see it in the color change before /after shaking. Ok, after leaving some jars im peace , it did separate by sedimentation. Even the cross-section of the fired crucibles didn't exhibit uneven porosity. Personally, I avoided sodium silicate for the lower melting temperature. I needed +1600 C for the experiment and it would reduce the structural stability of the vessels. At least I thought so. But, for melting aluminum, I am sure it would be quite adequate. It is possible that you clogged the pores of the mould. I did, by not completely removing the previous failed slip (from the very bottom) . It didn't soak the water there or it tore apart my good slip by sticking during extraction haha! Oh wow! I wish my slip dried so fast! I have issues with patience so it sounds like a charm that it dried so quickly... But yeah, I confirm that it is tricky to get a feel for the proper water ratio. It changes with each mixture and type of clay. I wanted to try bentonite clay in the slip, due to the availability (cheapest kitty litter, available on any store), but I opted for kaolin clay for the historical accuracy and much higher melting temperature. I aimed for the full nine yards! Once again, I intended to melt cast iron and steel. For melting aluminum, I suppose, it would be even better. I remember it is very plastic so working with it would be much easier than pure alumina or even my alumina-kaolin mix. That's why I chose the slip method- I wasn't capable of hand-working this clay mixture. It was short, not plastic. But wouldn't bentonite increase drying time? I'd like to see your projects man, they sound very demanding. Thanks for the comment. It feels nice to be appreciated and useful :p
@@emel60 I have a small lathe and a small mill and my intention is to start with very small models, making them myself, then go higher and maybe multi-cylinder. Many plans available use aluminum cast parts and in certain aspects, I prefer it compared to metal removal from solid (of course, it is a matter of technology to fit the shape but milling and mainly CNC milling requires a lot of money for expensive devices - not to speak of milling tools which is not one to fit all; I mean for proper job you need a bunch of expensive bits). Concerning your presentation(s), I like that it is technically focused and keeps the right balance to be useful (hard to find in many tutorials). Thanks for further info about your way to obtain crucibles (and for advice about safety), in a new hobby you tend to ignore or minimize risks, because you're pursuing results. I also consider slip method a good way to go; as I found a cheap enough source alumina powder - if I can achieve good enough crucibles. I'm new in this domain so I would not have to show much. But I have spotted some people who seem to do things the right way and I'm following them :P. Their results are rather to be watched instead my beginner achievements. I already have names in my mind and although some are dealing with aluminum casting, good practices and brilliant idea could be expanded. Patience I have a lot, but not always when comes about new things, which is not exactly a good thing :D. I follow either gas/ electric/ microwave paths just to find one that fits. Ready made solutions are hard to find here where I live (Romania) because of lack of an effective market. Iron/ cast iron I consider already a tough target - for me. Both in technical requirements for equipment, power level and consistency of results. Otherwise cast iron is used in model engines for cylinder liners and piston rings (so it is in sight), but requires very good mechanical properties, homogeneity ... In addition I take in consideration steel heat treatments/ forging in my oven(s); but never iron/ steel casting because of the level-up required. Well, never say never, but would be many rivers to cross ... Cheers!
Later comments. Just a guess: binders like bentonite in very small quantities might not affect strength at high temp. The matrix is actually formed by alumina and when bentonite starts melting, potentially alumina already starts sintering. And a question: how would you consider adding a quantity of silicon carbide to the slip - ups and downs (parameters would be grain size and percentage). Target would be a microwave susceptor "alloy" crucible alumina/ silicon carbide. Do you think that it will be susceptible to cracking? I will anyway make a proto to see how it will work. Have you tried silicon carbide in place of alumina with the same slip method or you consider alumina cheap and fit enough to stay on it?
can you expand on the details of the slip? did you grind the grog? It looks quite coarse. Is the purpose of the carbon powder simply to create porosity in the ceramic?
Hey nitrous dude! The slip was made using about 50-50 kaolin and alumina powders, random amount of fired grog made from the same fabric (some crucibles had cracks, some were ugly, some were accidentally dropped in anger), finely crushed charcoal, also of random amount and a bit of water. The grog was a bit coarse, but I did not see any big performance difference in fine or coarse, except interior wall surface finish. The purpose of the charcoal powder was to creat cavities after it burned off (solid turning into a gas). They greatly improved the structural stability of the crucibles; they become more tough because cracks can't propagate as they normally would. The round-ish cavities act as a crack stopper/buffer. This was evident in mechanical properties after firing the crucibles. They were really hard to break, even with a hammer- considering how thin they were. But, more importantly, the cavities massively helped during rapid, high temperature heating, as the thermal conducting was reduced due these air pockets in the fabric. Consequently the thermal stresses were reduced. I also think that the powder accelerated drying, as the charcoal is really hydroscopic, taking water from the slip into itself (porous structure).
@@emel60 those details are great! If you're interested, you might try using fine aluminum particles (not powder - but fine granules) in your mix. if you make the system alkaline, the aluminum will release hydrogen gas, essentially 'expanding' the fabric, as you are calling the dry slip mixture. This is one of the methods used to make aerocrete expanded cements. Have you tried using sodium silicate solution (water glass) as a binder - not to use in a slip-based system, but for extruded/pressed castings?
@@en2oh @nitrous dude interesting! At first I wanted to do something similar, like Mathew did in this video; the end result is the same: plenty of voids :) th-cam.com/video/v8oEzVFaJ0A/w-d-xo.html The way I'm making these vessels, the only obstacle I can see by using ground aluminum is that it may cause havoc in the microwave ahahahha (not saying I won't try :p)! As for glass water, I wanted to make some cores for some future casting, and using them for some future molds. I'm unsure what would be the maximum withstanding temperature of such fabric. It can withstand the temperature of 1100 C on its own, quite low by refractory standards, but as an addition, it might be increased. I will try to do some research on this topic. Cool thinking, though!
@@emel60 Thank-you so much for the reference! I greatly appreciate it. My friend told me that he saw your video and that you gave me a shout out, so I just had to watch your video. Thanks again. Subbed as well.
Dry press the powder into a finished product? You'll need to make sure you have proper pressure, rather than worry about the mixture. On the market there are plenty of >99% alumina laboratory ware, and I believe they are sintered by using compression. Ultimately, the mixture depends on the intended use of the ware. Cheers!!
Salam Alaykum Abdul, I mde this alumina grog myself. Before I made good crucibles, I had plenty of broken attempts and random patterns which I fired as a test. Then I crushed it into a coarse powder and used this powder as grog to reinforce all other crucibles. Hope i helped!
Hello my friend. I found a patent on google that spoke about a mixture of "10-30% thermoplastic plastic or an resin organic binder with pure aluminum oxide powder at a temperature of 150-200 DEG C." I also found work by a different youtuber using sodium silica to bind a carbide crucible. The patent does mention PVA as a binder, but for a different slip method. Do you know of or have you succesfully used any binders to make pure alumina crucibles. Thank you!?
Hey Pigeon with cool wings! I have not used such PVA or other polymer binders but I have used two different types of clay. For the first type, as in the video above, I used kaolin, which is mostly silica and alumina in itself. For the second one I used finely crushed boron trioxide glass and wetted alumina. It was a pain in the ass to dry, and crubmly af, but it did seem promising for the temperature resistance! Problem is that adding anything to the crucible mix will remove the pureness of alumina. I can only think of extremely high pressure applied to crucible shaped dies filled with alumina powder. I think that would be the only 'pure' solution.
@@emel60 a few days ago i watched a quick animated video of a sintering machine. One of the modules involved "dewaxing" the crucible before high heat firing by melting out the binder. I am now wondering if a simple wax, or rabbit skin glue would work. Maybe even rice starch!? idk. I'll let you know.
@@MetallicWingPigeon that... Is brilliantly simple and I feel stupid now. I've done plenty of lost wax casting, yet it never occurred to me ahaha! Please do a update when you try it! Cheers
Cool process im curious though what is your intention with the finished crucibles? Doesnt look like you could do much more than a bit of jewlery casting... or are you perfecting the process before scaling up for 1 tonne SG iron charges? :)
I successfully used these wee crucibles for making my own crucible steel buttons, after which I broke them apart to reveal the minute amount of shiny stuff (they were lidded). However, the original crucible pattern I shamelessly copied was a porcelain laboratory crucible I stole from my moms work place, even more shamelessly. They were used to heat various crap and even melt gold! So, repeated use of the wee buggers was intended- I just didn't try and/or care about not breaking one after use! Ash glaze and interior slag made them too ugly. Jewelry casting would prove to be a piece of cake! As for one tonne of liquid SG iron charge... big things have small beginnings! Although, I'm still recovering from the emotional trauma and burned feet :s
Hey Said, bud! Since they are very thin, they dry over several hours, depending on the ambient temperature. Afterwards I place them in the pot for about half an hour on low heat. It makes sure they are 'bone dry' and ready for firing. I guess I could have skipped the first drying process and directly put them in the pot, but I didn't want to risk getting cracks from uneven heating, or deforming them when placing into the pot when they are 'leather hard', i.e. soft. I'm sure a proper oven would preform much better and safer than a pot :p
Hey Dustin, For the grog I recycled previous broken or firing test crucibles of the same mix. Literaly just fired waste crushed into coarse-ish powder. Hope that helps!
Not yet, bud. I'm planning to melt several different alloys in the crucibles. Firstly aluminum, for some slingshots (I know, I know, I should grow up!). My bet is that the crucibles will withstand the low(er) heat of these alloys, as they survived liquefied steel and cast iron, both heavily corrosive to the vessels, and extremely hot. I'll make an update fpr sure!
Hi @trollforge! I'm writing here to updated you that I've finally managed to work some more on my projects and I've successfully melted bronze for some artistic knife fittings. Worked like a charm. Although, the design of the crucible is not overly friendly for manipulation while charged with molten metal. They survived, as did I!
Hi Said! The ratio of about 50:50 is what I used for mixing alumina and kaolin powders. I added random amounts of grog and charcoal powder, but less than the first two. As for water, I added enough so thst the slurry/slip is neither to runny ir too thick. Hope that helps!
@@sidalisaid12 according to the alumina-silica phase diagram, the 50-50 ratio mixture vessels can theoretically withstand +1800 degrees Celsius. I reached +1600 C, and they withheld it perfectly.
According to the alumina-silica phase diagram, these crucibles would theoretically withstand temperatures exceeding 1800 C (I made it as simple as possible, as proper tertiary phase diagram can't be used- I have no clue what the lady sold me/ what my kaolin clay powder consists of, so I used average kaolin composition). More precisely, the alumina to kaolin volume ratio of 50:50 consists of about 70% alumina to 30% silica for the crucible. Looking at the same phase diagram, the temperature at which this crucible ceramic would degrade is, give or take, 1890 C. My laser thermometer peaked just over 1600 C during the furnace run, and I believe it was even higher- alumina has a property of high IR reflectivity, and the thermometer has different readings for different materials due to emissivity, which I could not care less about. Thank you for the comment!
Wait. You made that mixture by mixing Al2O3 and only C? And added water put on gypsum crucible that soak and dries it and then you put it in microwave oven? That easy? What happend with carbon? It must make many pores in it? Can you use normal oven without microwaves?
Hello bud! Close enough- I mixed up the alumina and kaolin powders (various amounts every time, with no obvious changes of properties), with water and then I added charcoal dust and mixed again- until I had no lumps. I pour the slip (slurry) into the gypsum mould and yes, it soaks up the water from the slurry, leaving a leatherhard "shell/form". I remove this shell and then I dry the wet gypsum mould in the microwave, several seconds on medium or low and repeat until dry. If you overdo it, they will crack. Do not put shells in the microwave as they will always explode! You only dry the gypsum mould, not the alumina shells! That's it, that easy! :) You can use a regular oven instead, yes, but this is a faster option...and I believe the microwave uses less power, thus money. The charcoal dust will not burn when dried in the oven (too low temperature). The charcoal dust acts as a void/cavity former once the alumina crucibles are fired up and the dust sublimates at high temperatures, leaving many, many voids/cavities. These holes strengthen the ceramic matrix and also prevent thermal shock cracks BUT slows down heat conduction. Keep exploring and cheers!
@@synth1002 no problem, bud! Well, I had to use kaolin just as a binder and to make pure alumina more...plastic and workable. Besides, the alumina content in kaolin is also high, the rest being some silica. I am sure you can figure out how to work with pure alumina. Perhaps using isopropyl instead of water I'll try once I'm on my vacation!
It's in my plan to trx it out! As a very refracted material, it might be a good idea to try it out. Highly hygroscpic, top! That would, perhaps, eliminate the need for a binder. As for working with steel or cast iron, I know that any micro trace of magnesium results in spherodizing the cementite, making a tough material. Thanks for the comment,
Very interesting material wonder how detailed it could be for making molds, considering it has a termal limit somewhere around 1200-1300C it can easly hold soft metals like aluminium, tin, silver maybe even gold and copper. It could be a stepping stone for many hobbies.
@@kompotreviews5720 Thanks for commenting buddy.
I agree with. A homemade crucible, or cupel, made in this simple way, with cheap materials and great accessibility would in fact open up a lot of arts and crafts options.
That being said, my crucibles from the video survived temperatures excessive of 1600 C, not F! Talk about a flex haha!
I noticed that your recipe is a 50:50 mix of alumina powder and kaolin powder, but what amounts of grog and charcoal dust? Also, could graphite work as a substitute for the charcoal?
Hey @rpdfangon! Sorry for a late reply, I was traveling.
Correct, my kaolin/alumina ratio is 50:50, but I used a very random, by-the-feel amount of grog (fired and crushed pieces of the same ratio) and same with charcoal dust.
I am afraid graphite would not work. I mean by mixing graphite with clay you would get excellent high fired crucibles (search historical Hessen crucibles, for instance). But, it would not work like charcoal dust as it would not sublimate or burn out, so no voids would be created in the crucible matrix.
Always add the powder to the water because of the surface tension and it won't be lumpy.
Interesting! I use that technique for my cocoa, and yet I overlooked it for this purpose! Thanks!
Nice one bud! Exactly what I need!
What do you need it for? :)
I'm not sure to understand, how do you form your crucible? You pour your silica mixture into a plaster one, wait for it to absorb the moisture, then remove the excess and microwave the whole thing? And then the molds are not fused together and you can separate them?
This looks cool, I'd like to try.
EDIT: I think I got most of the answer from another comment. The separation of both molds still seems a bit mysterious to me.
Correct until the microwaving! :D
The separation of the slip and the mould comes beforehand. I only microwave the plaster mould in order to dry it out sufficiently enough for another slip pouring.
The only way I've seen the mould and the slip fusing together is if I poured the slip into a wet mould. It would suck out the moisture, but not all of it, so you end up with basically a very wet clay. It would separate eventually, but it would take weeks!
@@emel60 thx!
@@fmdj I stand corrected! I tried microwaving the crucibles after separation from the mould, but they would either explode or crack. So I exerted the drying method as in the video :p
Would you like please share us,
What kind of binder that you use
Of course Zakaria. There's is no added binder. The only thing in the slip mixture is kaolin clay powder and aluminum powder. The crushed charcoal is just there to create tiny pores.
Hope it helps,
Cheers!
ThankYou for the answer Sir
@@zakariajaya7570 I'm glad to help! Try it yourself :)
you said used some carbon as ingredients, did you think grayish color can be aluminum carbide?
@@dogodogo5891 Hi pal,
Thanks for the reply.
I used charcoal powder/ carbon to form cavities in the matrix of the crucibles. When heated up at high temperature it reacts with oxygen and burns. Basically it sublimates into gas, making these cavities.
Aluminium carbide would remain solid at such temperatures and no voids would occur. It would, perhaps, act as a very good temper or agregate for the matrix strength.
Hope thst helps!
Hello! How to make alumina slip in this video and please tell me what additive was add that slip ?
Upload a video or how to make alumina ceramic in that please tell me details.
Thanks for sharing this video.
Hey buddy! I'm unsure whether you watched the video or read some of the comments. If you did, and still have questions - let me know
Hi GoodEnough! Very good tutorial; nice presented. You should go on with your trials and videos. I am directly interested in your ttests, so those are not just plain comments. My questions would be: for what metals are the crucibles intended for? have you noticed a certain life span related to type of metal mold? have you tried a comparison between charcoal and non - charcoal mixtures? I tend to bet on charcoal addition based on your presumptions (and my personal guess) ; but it is confirmed? How large do you consider can this method be expanded? I am targeting it for aluminum - up to 10 kg charge for finished mold up to 3 kg (not sure about output; it is just an estimation). And hoping for a more durable crucible than steel ones.
Good luck, you are doing a very good job; both in trials and presentation!
Hi Mihai!
My apologies for the late reply!
First of all, thank you for commenting and showing interest in my projects.
As for the questions, I will try to answer them accordingly.
The crucibles I made were intended for the use with ferrous metals, mainly iron alloys, as obtaining crucible steel was a key factor for my dissertation.
I saw that the crucibles were really long lasting, when it comes to high hardness, lack of porosity propagation and durability, except when it comes to rapid thermal cycling. I sometimes had no options but to blast the furnaces dull power with them being cold. Slow and steady increase of temperature should be applied, not rapid. Even with a high alumina content, which has great thermal expansion properties, it proved that the biggest enemy is the sudden heating or cooling.
I have not tried yet a proper test of various void forming substances, as charcoal was readily available to me, cheap, easily transformed into a powder of fine grain, and non toxic. Also, the lack of its expansion during heating was a desired (albeit accidental) property, as well as complete burnout/sublimation.
This method of crucible production could be increased. However, I presume adding central wad or lunge would be necessary, alongside great pressure, to increase density and structurally stability. That's how it's done in the industry. There is a video by British pate on graphite crucible production using moulds and dies. Homemade option, of course is very possible. I bet the elephant in the room would be the ability to melt bigger quantities metal at home. But, 10 kg is nothing that can't be done!
I'll make more video's soon :)
@@emel60 Thank you very much for your answer and clarifications!
I must agree 10kg looks (and is) like an elephant in the room.
To define better -for myself- my needs, I would say I am mostly interested in IC model engines with cast parts net weight up to 0.5kg aluminum. Total aluminum per charge/cast I see as 1.5kg -considering all technological losses- but I consider normal crucible fill to be only 50% clean metal so a 1l crucible would be required (almost 3kg total capacity for aluminum). The majority of casts foreseen will be much less than this maximum.
Have you tried any additive for binding aluminum oxide (both when forming and heat tempering)? I have read about 5-7% either water glass or bentonite. I have some pottery grade aluminum oxide but as fine as it is still has a high tendency to set quickly in the slip and also makes me question about cohesion.
In trials till now I had rather bad results- as follows; but I'll try to refine techniques, and clear "hot spots":
Charcoal powder hardly mixes in the slip; I think its the surface tension matter.
I have added about 5% water glass in the mixture because I had good experience previously with it (aluminum oxide refractory coating for furnace and from the remaining formed some small crucibles in silicon patterns).
The first trial, with consistency matching yours (high tendency of setting, not related to consistency/water content), dried very quickly in the plaster mold but in less than a minute left no cavity in the middle - solid block - not enough water.
Second trial with plaster mold fully dried in microwave oven and a more fluid slip failed to deposit; plaster was not absorbing water almost at all. My guess is water glass from first trial clogged the plaster pores, although i washed mold thoroughly between slip casts.
So here I am till now. I'll further test, but maybe scale down until success. Trials were done on a plaster mold made around a 350ml "bio" paper glass.
Thanks again for your answer and waiting videos! All the best!
@@mihaimastacaneanu8505oh wow! I admire the project! I would say fingers crossed, but it takes everything else than luck- persistence, patience, sweat and blood! If successful, will you machine the parts by yourself or have them done professionally?
I feared you might want to melt 10kg of cast iron or steel, one more difficult than the other. Aluminum, on the other hand, is much more manageable to work with, not just for the more forgiving casting process, easier alloying, but for the simplicity and lower cost of melting- low melting temperature for the win!
A few kilograms to melt should not be such a problem, and making crucibles to hold 3 kg as well.
Regardless, I would definitely make the crucibles thicker. Either a thicker slip or dye cast, it doesn't matter, but I would not trust my thin ones to hold a few kilograms and survive the transport, tongs, hits, heats. First one in this video is quite thick (7-8 mm), and by the time I made the last one for the experiment I managed to make them super thin (1.5mm). I really would not trust a kg of molten metal to something so thin, let alone three!
I didn't notice that the charcoal dust had mixing issues. In this video I shook the slip vigorously and I got a rather homogeneous mixture. Perhaps I forced the charcoal to soak up water and made it sink. You can clearly see it in the color change before /after shaking. Ok, after leaving some jars im peace , it did separate by sedimentation. Even the cross-section of the fired crucibles didn't exhibit uneven porosity.
Personally, I avoided sodium silicate for the lower melting temperature. I needed +1600 C for the experiment and it would reduce the structural stability of the vessels. At least I thought so. But, for melting aluminum, I am sure it would be quite adequate.
It is possible that you clogged the pores of the mould. I did, by not completely removing the previous failed slip (from the very bottom) . It didn't soak the water there or it tore apart my good slip by sticking during extraction haha!
Oh wow! I wish my slip dried so fast! I have issues with patience so it sounds like a charm that it dried so quickly... But yeah, I confirm that it is tricky to get a feel for the proper water ratio. It changes with each mixture and type of clay.
I wanted to try bentonite clay in the slip, due to the availability (cheapest kitty litter, available on any store), but I opted for kaolin clay for the historical accuracy and much higher melting temperature. I aimed for the full nine yards! Once again, I intended to melt cast iron and steel. For melting aluminum, I suppose, it would be even better. I remember it is very plastic so working with it would be much easier than pure alumina or even my alumina-kaolin mix. That's why I chose the slip method- I wasn't capable of hand-working this clay mixture. It was short, not plastic. But wouldn't bentonite increase drying time?
I'd like to see your projects man, they sound very demanding.
Thanks for the comment. It feels nice to be appreciated and useful :p
@@emel60 I have a small lathe and a small mill and my intention is to start with very small models, making them myself, then go higher and maybe multi-cylinder. Many plans available use aluminum cast parts and in certain aspects, I prefer it compared to metal removal from solid (of course, it is a matter of technology to fit the shape but milling and mainly CNC milling requires a lot of money for expensive devices - not to speak of milling tools which is not one to fit all; I mean for proper job you need a bunch of expensive bits).
Concerning your presentation(s), I like that it is technically focused and keeps the right balance to be useful (hard to find in many tutorials).
Thanks for further info about your way to obtain crucibles (and for advice about safety), in a new hobby you tend to ignore or minimize risks, because you're pursuing results. I also consider slip method a good way to go; as I found a cheap enough source alumina powder - if I can achieve good enough crucibles.
I'm new in this domain so I would not have to show much. But I have spotted some people who seem to do things the right way and I'm following them :P. Their results are rather to be watched instead my beginner achievements. I already have names in my mind and although some are dealing with aluminum casting, good practices and brilliant idea could be expanded.
Patience I have a lot, but not always when comes about new things, which is not exactly a good thing :D.
I follow either gas/ electric/ microwave paths just to find one that fits. Ready made solutions are hard to find here where I live (Romania) because of lack of an effective market.
Iron/ cast iron I consider already a tough target - for me. Both in technical requirements for equipment, power level and consistency of results. Otherwise cast iron is used in model engines for cylinder liners and piston rings (so it is in sight), but requires very good mechanical properties, homogeneity ...
In addition I take in consideration steel heat treatments/ forging in my oven(s); but never iron/ steel casting because of the level-up required.
Well, never say never, but would be many rivers to cross ...
Cheers!
Later comments. Just a guess: binders like bentonite in very small quantities might not affect strength at high temp. The matrix is actually formed by alumina and when bentonite starts melting, potentially alumina already starts sintering.
And a question: how would you consider adding a quantity of silicon carbide to the slip - ups and downs (parameters would be grain size and percentage). Target would be a microwave susceptor "alloy" crucible alumina/ silicon carbide. Do you think that it will be susceptible to cracking? I will anyway make a proto to see how it will work.
Have you tried silicon carbide in place of alumina with the same slip method or you consider alumina cheap and fit enough to stay on it?
Is it just powdered alumina, charcoal and water?
Hi Adriano,
Yes, the mixture is what you wrote plus kaolin powder. It makes working with alumina easier, more plastic.
can you expand on the details of the slip? did you grind the grog? It looks quite coarse. Is the purpose of the carbon powder simply to create porosity in the ceramic?
Hey nitrous dude!
The slip was made using about 50-50 kaolin and alumina powders, random amount of fired grog made from the same fabric (some crucibles had cracks, some were ugly, some were accidentally dropped in anger), finely crushed charcoal, also of random amount and a bit of water.
The grog was a bit coarse, but I did not see any big performance difference in fine or coarse, except interior wall surface finish.
The purpose of the charcoal powder was to creat cavities after it burned off (solid turning into a gas). They greatly improved the structural stability of the crucibles; they become more tough because cracks can't propagate as they normally would. The round-ish cavities act as a crack stopper/buffer. This was evident in mechanical properties after firing the crucibles. They were really hard to break, even with a hammer- considering how thin they were.
But, more importantly, the cavities massively helped during rapid, high temperature heating, as the thermal conducting was reduced due these air pockets in the fabric. Consequently the thermal stresses were reduced.
I also think that the powder accelerated drying, as the charcoal is really hydroscopic, taking water from the slip into itself (porous structure).
@@emel60 those details are great! If you're interested, you might try using fine aluminum particles (not powder - but fine granules) in your mix. if you make the system alkaline, the aluminum will release hydrogen gas, essentially 'expanding' the fabric, as you are calling the dry slip mixture. This is one of the methods used to make aerocrete expanded cements.
Have you tried using sodium silicate solution (water glass) as a binder - not to use in a slip-based system, but for extruded/pressed castings?
@@en2oh @nitrous dude interesting! At first I wanted to do something similar, like Mathew did in this video; the end result is the same: plenty of voids :)
th-cam.com/video/v8oEzVFaJ0A/w-d-xo.html
The way I'm making these vessels, the only obstacle I can see by using ground aluminum is that it may cause havoc in the microwave ahahahha (not saying I won't try :p)!
As for glass water, I wanted to make some cores for some future casting, and using them for some future molds. I'm unsure what would be the maximum withstanding temperature of such fabric. It can withstand the temperature of 1100 C on its own, quite low by refractory standards, but as an addition, it might be increased. I will try to do some research on this topic.
Cool thinking, though!
@@emel60 Thank-you so much for the reference! I greatly appreciate it. My friend told me that he saw your video and that you gave me a shout out, so I just had to watch your video. Thanks again. Subbed as well.
nice work men, can carbon dust come from wood charcoal?
hello my friend. Great job! I want to dry press. What should I use as a mixture?
Dry press the powder into a finished product?
You'll need to make sure you have proper pressure, rather than worry about the mixture. On the market there are plenty of >99% alumina laboratory ware, and I believe they are sintered by using compression.
Ultimately, the mixture depends on the intended use of the ware.
Cheers!!
Where do you get this alumina grog from?
Salam Alaykum Abdul,
I mde this alumina grog myself. Before I made good crucibles, I had plenty of broken attempts and random patterns which I fired as a test. Then I crushed it into a coarse powder and used this powder as grog to reinforce all other crucibles.
Hope i helped!
Hello my friend. I found a patent on google that spoke about a mixture of "10-30% thermoplastic plastic or an resin organic binder with pure aluminum oxide powder at a temperature of 150-200 DEG C." I also found work by a different youtuber using sodium silica to bind a carbide crucible. The patent does mention PVA as a binder, but for a different slip method. Do you know of or have you succesfully used any binders to make pure alumina crucibles. Thank you!?
Hey Pigeon with cool wings!
I have not used such PVA or other polymer binders but I have used two different types of clay.
For the first type, as in the video above, I used kaolin, which is mostly silica and alumina in itself.
For the second one I used finely crushed boron trioxide glass and wetted alumina. It was a pain in the ass to dry, and crubmly af, but it did seem promising for the temperature resistance!
Problem is that adding anything to the crucible mix will remove the pureness of alumina. I can only think of extremely high pressure applied to crucible shaped dies filled with alumina powder. I think that would be the only 'pure' solution.
@@emel60 a few days ago i watched a quick animated video of a sintering machine. One of the modules involved "dewaxing" the crucible before high heat firing by melting out the binder. I am now wondering if a simple wax, or rabbit skin glue would work. Maybe even rice starch!? idk. I'll let you know.
@@MetallicWingPigeon that... Is brilliantly simple and I feel stupid now. I've done plenty of lost wax casting, yet it never occurred to me ahaha! Please do a update when you try it!
Cheers
Cool process im curious though what is your intention with the finished crucibles? Doesnt look like you could do much more than a bit of jewlery casting... or are you perfecting the process before scaling up for 1 tonne SG iron charges? :)
I successfully used these wee crucibles for making my own crucible steel buttons, after which I broke them apart to reveal the minute amount of shiny stuff (they were lidded).
However, the original crucible pattern I shamelessly copied was a porcelain laboratory crucible I stole from my moms work place, even more shamelessly. They were used to heat various crap and even melt gold! So, repeated use of the wee buggers was intended- I just didn't try and/or care about not breaking one after use! Ash glaze and interior slag made them too ugly.
Jewelry casting would prove to be a piece of cake!
As for one tonne of liquid SG iron charge... big things have small beginnings! Although, I'm still recovering from the emotional trauma and burned feet :s
What is the time between making them and drying them with fire and burning them well?
Hey Said, bud!
Since they are very thin, they dry over several hours, depending on the ambient temperature. Afterwards I place them in the pot for about half an hour on low heat. It makes sure they are 'bone dry' and ready for firing.
I guess I could have skipped the first drying process and directly put them in the pot, but I didn't want to risk getting cracks from uneven heating, or deforming them when placing into the pot when they are 'leather hard', i.e. soft.
I'm sure a proper oven would preform much better and safer than a pot :p
What mix of grog did u mix with the alumina?
Hey Dustin,
For the grog I recycled previous broken or firing test crucibles of the same mix. Literaly just fired waste crushed into coarse-ish powder.
Hope that helps!
I searched so much to find an alumina processing video.
İs it made of pure alumina powder?
Yes, friend, it is. Some kaolin is mixed just because I needed some plasticity of the matrix. Otherwise a pure mixture works with slip casting.
Have you had any luck with melting Aluminium, Copper, or Brass, in these?
Not yet, bud. I'm planning to melt several different alloys in the crucibles. Firstly aluminum, for some slingshots (I know, I know, I should grow up!). My bet is that the crucibles will withstand the low(er) heat of these alloys, as they survived liquefied steel and cast iron, both heavily corrosive to the vessels, and extremely hot. I'll make an update fpr sure!
@@emel60 Awesome, that is why I subscribed!
@@trollforge many thanks bud!
Hi @trollforge! I'm writing here to updated you that I've finally managed to work some more on my projects and I've successfully melted bronze for some artistic knife fittings. Worked like a charm. Although, the design of the crucible is not overly friendly for manipulation while charged with molten metal. They survived, as did I!
@@emel60 Awesome!
good job . Can you give us the amount of material(Charcoal, aluminum. Water)plz
Hi Said!
The ratio of about 50:50 is what I used for mixing alumina and kaolin powders. I added random amounts of grog and charcoal powder, but less than the first two.
As for water, I added enough so thst the slurry/slip is neither to runny ir too thick.
Hope that helps!
@@emel60 thanks 👍
@@emel60 What is the highest degree he can handle?
@@sidalisaid12 according to the alumina-silica phase
diagram, the 50-50 ratio mixture vessels can theoretically withstand +1800 degrees Celsius. I reached +1600 C, and they withheld it perfectly.
what sort of tempersture could this handle?
According to the alumina-silica phase diagram, these crucibles would theoretically withstand temperatures exceeding 1800 C (I made it as simple as possible, as proper tertiary phase diagram can't be used- I have no clue what the lady sold me/ what my kaolin clay powder consists of, so I used average kaolin composition).
More precisely, the alumina to kaolin volume ratio of 50:50 consists of about 70% alumina to 30% silica for the crucible. Looking at the same phase diagram, the temperature at which this crucible ceramic would degrade is, give or take, 1890 C.
My laser thermometer peaked just over 1600 C during the furnace run, and I believe it was even higher- alumina has a property of high IR reflectivity, and the thermometer has different readings for different materials due to emissivity, which I could not care less about.
Thank you for the comment!
Wait. You made that mixture by mixing Al2O3 and only C? And added water put on gypsum crucible that soak and dries it and then you put it in microwave oven?
That easy? What happend with carbon? It must make many pores in it? Can you use normal oven without microwaves?
Hello bud!
Close enough- I mixed up the alumina and kaolin powders (various amounts every time, with no obvious changes of properties), with water and then I added charcoal dust and mixed again- until I had no lumps. I pour the slip (slurry) into the gypsum mould and yes, it soaks up the water from the slurry, leaving a leatherhard "shell/form". I remove this shell and then I dry the wet gypsum mould in the microwave, several seconds on medium or low and repeat until dry. If you overdo it, they will crack.
Do not put shells in the microwave as they will always explode! You only dry the gypsum mould, not the alumina shells! That's it, that easy! :)
You can use a regular oven instead, yes, but this is a faster option...and I believe the microwave uses less power, thus money.
The charcoal dust will not burn when dried in the oven (too low temperature). The charcoal dust acts as a void/cavity former once the alumina crucibles are fired up and the dust sublimates at high temperatures, leaving many, many voids/cavities. These holes strengthen the ceramic matrix and also prevent thermal shock cracks BUT slows down heat conduction.
Keep exploring and cheers!
@@emel60 Thanx for the answers, it would be interesting making kaolin powder from scratch, if it's even possible :D
@@synth1002 no problem, bud!
Well, I had to use kaolin just as a binder and to make pure alumina more...plastic and workable. Besides, the alumina content in kaolin is also high, the rest being some silica.
I am sure you can figure out how to work with pure alumina. Perhaps using isopropyl instead of water
I'll try once I'm on my vacation!
Anyone try this with MgO?
It's in my plan to trx it out! As a very refracted material, it might be a good idea to try it out. Highly hygroscpic, top! That would, perhaps, eliminate the need for a binder.
As for working with steel or cast iron, I know that any micro trace of magnesium results in spherodizing the cementite, making a tough material.
Thanks for the comment,