Testing fine sand-epoxy mixes.
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- เผยแพร่เมื่อ 3 ก.ค. 2017
- To simplify and reduce the costs of granite-epoxy mixes I decided to use only fine sand as the filler. This video shows how I made samples of various recipes and what effect adding a bit of rebar made to the sample.
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Thank you for sharing all your insights, Jim! Have a great upcoming holiday season and many greetings from Germany. 👋
I use sand mixed with resin to back fill cavities in embossed metal art and it works extraordinarily well. Not much resin is needed to make a rock hard bond and the best part is you have time to mold it in and level it… then it sets in about a three hours. This after months of trying all sorts of things.
The best laid plays of mice and men..... I admire your honesty.
Thanks .. your video gave me an excellent starting point to get a good mix!!
Very informative video, I found it quite helpful, Thanks mate.
Excellent video! I appreciate the experimental approach.
Thanks
For the rebar to be effective, it should not be in the neutral axis in the middle of the sample but should be resisting tension near the top of the sample with the lower strands of epoxy being in compression. If anything it would weaken the sample if placed in the neutral axis where horizontal shear could be greatest. I suspect however that the advantage of the epoxy mixture is in its stiffness and resistance to resonance vibrations. By the time the mixture fails it would be long past acceptable stiffness tolerances. Therefore no need for tensile reinforcement.
As I have explained in other comments, the resin composite is stiffer than the rebar so putting the rebar near the surface would make the sample less stiff. The reason for the rebar is to make the sample stronger not stiffer. If the sample was strong enough without the rebar, the rebar would not be necessary. Without the rebar the sample is very brittle. I dropped one, without rebar, on a hard floor and it snapped.
I have been wondering if a person could use epoxy granite or epoxie concrete to form three 16"×24"×4" slabs and then lap the tops of them together to make surface plates.
Epoxy will stick to some wax covered surfaces as you have discovered. The epoxy contains a solvent, the solvent can dissolve some waxes , for the best results, especially surface finish, then use a release agent and not any old wax.
You need an internal structure, not just a single piece. Like they do in house foundations. It needs to be supported internally in all directions. Even if you brazed some stainless steel tubes together into a 3 dimensional frame, inserted it into your pour and vibrated it.
Like mentioned, you can't just put a middle support inside.
Hope this helps in your structural design.
Also curious how you were gonna drill thru your plates. I was thinking of doing all this same process to strengthen my machine. My thought on making plates would be to draw up screw hole locations in a material, wood or aluminum, insert screws thru the holes in the patterned piece, slide over some sleeves onto the screws, add the internal framing, pour in the aggregate mixture and vibrate it. This would make the job so much faster and more precise on hole locations. :)
Look friend, I keep saying this until I am blue in the face. What you put into your comopsite depends entirely in what properties you want from the final mix. You might want rigidity, strength, flexability. heaviness, lightness, bouyancy, density, compressability, elasticity, weatherability, proof against earthquakes, volcano magma, acid spill, etc etc etc etc etc etc etc etc etc etc etc etc.
You must first specify the properties you require from the composite then figure out how to achieve them.
My little demo was just one tiny example.
Jim, this is wonderful. I have a thought too that may be of interest. I imagine the sand, having an enormous surface area will hold moisture on the surface of each grain and that will weaken the inter-grain adhesion and the end result. I suspect that if you baked the sand, or some other method to remove some moisture, your results might just improve, especially your "drop test".
Although I did not mention it, I did, in fact, bake the sand.
Hi Jim, Interesting video. Do you think some glass or carbon would help to make it more durable. What resin are you using. Cheers Dave.
I do believe it would. Perhaps someone will give it a go. The resin is IN2 INFUSION EPOXY RESIN with AT30 SLOW HARDENER from EasyComposites here in UK.
For rigidity I wonder if you were to use a thin (1-2mm) sheet of aluminium or steel on the top and bottom. Would this form a stress skin? I've done similar with aluminium with plastic core and it was quite surprisingly stiff. Just a thought. Really helpful video though. I'm planning to use this technique to cast a lathe bed, for a home built lathe.
I think that you are correct about adding extra material to the outer surface, but the selection of that material would be critical. To make the whole thing more rigid, the added material should be stiffer or have a higher strain value (compressive and tensile) than the material it will replace. The main reason I mentioned adding rebar in my video was to improve the toughness of the final composite because as you saw it was very brittle. Think about toughened glass - it is harder to break, but put in on supports and jump up and down on it and it flexes like a drumskin. It is no more rigid than ordinary glass. The only way to determine if a particular composite is more rigid is to make it and do proper comparative tests on it as I have done. This is what they do all the time in industry - otherwise airplane wings would come off and landing carriages would collapse.
I've got it in mind to do something like this in the future ... but don't hold you breath on this one.
Thanks for posting this, you are very organized and inspiring. How much did all your epoxy granite supplies cost you?
About 20GBP
Interesting results, thanks for sharing.
The rebar doesn't do much until the casting begins to deform. It helps move away from a brittle failure mode to a ductile failure, hence perhaps the greater deflection. It would have been interesting to see what results you get with pre tensioned rebar.
I agree it would be interesting, but rather difficult to implement I think.
@@JimTaylor42 naw. threaded rod. couple of locknuts n washers down the length so theyre set in the poxy. poke em out the sides of the mold and use them to hold it all together as well. torque them up... mold will need bracing to take tension.
countersunk insert on the inside of mold gives recess to cut bar off and seal up flush... but it aint concrete so you arent worried about cancer i guess...
Good work.. Thank you.
@ bardzo ciekawy test i wnioski. te informacje przydadzą mi się w moim projekcie, dziękuję.
jack.
Greetings. Very interesting topic as I'm designing/planning my next DIY cnc machine. Few stupid questions if I may? Is that "kiln sand" sand that is used in metal foundry casting? What do you think about if tried with glass beads (sand blasting alternatives) with rebar? Also is the epoxy and hardener same as used with fiber glass? Not a native English speaker, hence the question.
Yes, the sand was kiln sand but I think that foundry sand is something different - green sand is one of its names. Sand blasting beads could be a neat idea since it is likely to have an angular surface and the resin can key onto it. Rebar would make the eventual structure stronger and less brittle. Again, yes the resin and hardener are what is normally used for making boats, mending cars etc.
Awesome seeing really well made datum like this! I was curious if you've tested just pure resin?
No, I haven't done that. I don't think that pure resin will be much different in mechanical properties, from the sand/resin composite. The main reason for adding sand or other filler to the resin is to bulk out the resin and make the final thing cheaper. The addition of rebar or other material is to make the final part less brittle.
seen another videos. pure epoxy is the worst of all. best one i have seen seems to be a fine mix of powder (silica sanad extremely thin , etc) and iron (really fine)
Jim,
The bench was moving when you put slight pressure on it when writing. I think the bench is flexing making the readings similar. Using a rigid bench might give more accurate results.
Even if the bench flexes a bit, the reading will still be accurate as it is measuring the forces at either end of the spring balance. The force at the top end of the balance and the force on the test sample are the same; otherwise the resultant force would cause something to fly off - which would be a simple demonstration of Newton's 3rd law. This is exactly what happens when the sample fails.
Can you post a Bill of Materials for your epoxy mixes?
The stress in bending is an angular line from the top to the bottom surface. For a rectangle the lowest stress, zero is in the center. So rebar placed near the center will have a low stress. You could ave uses rubber and the numbers would have been almost the same. Tension the stress is uniform so the rebar would help. check the rules for rebar in concrete structures to find the optimum fraction of the thickness of a rectangle. So the two rebars would be located the same distance of top and bottom.
The intention of the rebar is to make the composite part stronger and less brittle (unlike the one I dropped which snapped) but not less rigid. Rebar is not necessarily more rigid (lower strain value) than the epoxy composite so putting it near to the surface may make the part less rigid. Like putting elastic bands near the surface. The purpose of the exercise is to make a part that is strong, very rigid, 'dead' and not brittle. In fact the test sample with the rebar measured slightly less rigid than one without rebar and with the same epoxy recipe. But under the test conditions it did not fail.
As I have said, you design the compososite according to your needs. If you need it to be stronger than the filler, then use an addition that is stronger than the filler. Wherease if you want it to be more rigid than the filler use a more rigid material in the composite. If you want the composite to be much heavier and resonance resisting then use a 'dead' material. As you say, the added material should be placed within the composite where the stresses are most concentrated if you want it stronger. There is very little benefit in putting a less rigid material that the filler close to the surface if you want a more rigid composite. Consult materials properties tables to find an appropriate material to add. As an example; cast iron is 70 times more rigid than aluminium and its alloys.
Have you considered a metal-epoxy composite? I've had decent luck using fine steel wires taken from steel mesh. Chopped up into 1/2-1.5" strands. Works decently. Burn and wash the mesh if galvanized so as to get the zinc off. Don't breathe in the fumes.
Yes I have added metal rods to the mix. And I would imagine that lots of fine wires would also certainly improve the strength of the composite.
Use candlewax on the backboard and drip it onto the screws (and wipe down with knife blade) before you add epoxy.
Then you can just stuff the screwdriver in the screws and the wax will move later. No more clogged screws.
Great idea - thanks.
Good
But my Question is that these two pieces can sharp the any knief????
i want to make resin based sharpining stone can you tell me method or formula
What is your mixture of resin and sand? Or is it a bought product? Thank you for the video!
It's just a standard slow cure liquid epoxy resin with enough sand to allow it to flow and leave no liquid resin on the surface.You can add more sand to make a stiffer mix.
have you tried using aluminum or steel shavings in your mix?
No i haven't - I'm really just trying what I have got on hand. I've got a box of st.steel wire rods and I am thinking of putting some of them in the next part I make. Al or St shavings - sounds expensive.
@@JimTaylor42 Aluminum or steel shavings would be cheap since there a constant
issue to deal with at any machine shop. However they would do far less for
ending up with a good vibration absorbing material which is what you'd want and
what that epoxy sand mixture helps provide. Cast iron is still used in the building of machine tools because of it's natural dampening property's. Like concrete it's not the best under high tension loads so that rebar is added to concrete. The cast iron
shapes are manipulated to increase the strength where needed. I highly doubt metal
shavings even cast iron one's would increase the strength by much if at all. If adding metal shavings did more or even equaled what re-bar does then it would certainly be used while building with concrete simply because of the cost cutting over the more
traditional re-bar. So just like casting a machine tool part then designing the part with a cross section that increases strength in the directions needed is a priority. A steel I
beam is designed to be stiff in both directions, a piece of flat bar is far stronger
through it's vertical direction as just one example.
Very Nice!..Have you done some concrete test?
No. Concrete is a chemical process using water. It will not work with epoxy. Did you know that concrete will set under water?
@@JimTaylor42 .. In brazil the concrete is very common and I would like to make some test mixing with micronized plastic and check your mechanics resistance .in this case I dont will mixing with epoxy.
Add vibration before it sets with an orbital sander
It woorking good ?
As discussed by others in previous comments: Adding chopped or even continuous fiber would be interesting.
Yes indeed it would. It would make the resulting composite much lighter which would be the reverse of what I wanted for my particular application. For my cnc machine I needed a dense dead weight that would kill any resonances.
Jim Taylor I was talking about a small fraction to add toughness and strength. If you used natural fibers (flax) damping should be best per weight. A small fraction can make huge differences.
Thanks for the clarification.
Wouldn't your displacement be down to sand and resin ration as your not using so much resin
Hi can you do it with cement to test compression test in laboratory
No can do.
Why would you want to do compression test. Tensile is the way here.
The rebar is in the centroid of the sample so it will have no effect. Place the rebar along the top and bottom edge and it would make a huge difference. This is basic engineering.
Please see my reply to Field Pictures below.
I'm thinking of adding a little fiberglass too...
Fiberglass matting might improve the strength whilst powder would probably only act as an extra filler.
Very interesting... maybe if resin combined with portland cement and sand the final result will be good
I really would like to see the results of that.
I was thinking yer right. mortar, cement powder, or rock dust should work as easily.
AIRCRETE also, can be mixed by weights also has large variations in strength\weight ratios.
The point is different size of aggregate to fill the mixture, at least 3 sizes
Add 3.5% metamucil, or pure psyllium husk, to get a more regular consistency!
I have no idea how this would affect the physical properties of the result.
could I use dolomite powder same ratio?
Of course you can - it would simply confer different properties on the final composite which you would need to test.
You should use normal plastic tape if you want to remove it later or put grease on the items that should not stick.
I think that the table top bend affects the results, just a notice.
Believe me it does not. What is indicated on the dial gauge is the actual load on the test piece.
Can u share resin name ?
👌
Has anyone mixed epoxy with concrete to form machine bases?
Concrete contains cement which needs water to make it work.
Also add fibre.
Instead of rebars, steel wire mesh layers would give you lighter samples.
Depends on how much steel wire mesh you put in to get the same strength.
@@jamestaylor7025 Of course, indeed. But having (hypothetically) the same weight of wire mesh as rebar would give the metal a much larger contact area between the metal and epoxy. The rebars total cross section will give you their tensile strength, and if that tensile strength is larger than the force it takes to separate the epoxy from the metal, the effective strength of the rebar will be "lost", so to speak.
@@pierrec1590 That is why, usually, rebar is as rough as hell and twisted to an helical shape. There are many other factors to consider. You may want the strength to be in the lateral direction or longitudinal direction or both etc etc. Consider fiberglass or carbon fiber strands - on their own they are not very rigid but put them into a composite and it becomes stronger and lighter than steel.
Methinks a bit of wax won't hurt the finish... Should release easily... floor wax... any paste was actually....
says the armchair engineer.
p.s. ... Ilike your granite epoxy ideas... best of the batch I've watched...
weld bolts or nuts into that rebar... Or weld an arch into a pair forming two ends of a concrete bench type set...perhaps??
I had plans for using AIRCRETE until I found this idea.
Worth a try.
Rebar should be tensioned to get benefits from it.
If you are making reinforced concrete lintles I would agree. Otherwise, I am not so sure. It all depends on the application and the properties you want from the composite.
Rebar doesnt make a structure stiffer until it fails unless its prestressed. Also i think you need the aggregate to be of mixed sizes bigger aggregates make a stronger composite
OK so this video was posted 5 years ago so its a bit old and no idea why it popped up on my 'recommended' but it just so happens I have been investigating something that may be of use called 'forged carbon fibre': th-cam.com/video/25PmqM24HEk/w-d-xo.html -This would provide some serious strength if combined with CF rods or sheets within your castings, CF extremely stiff stuff. With orientated CF Tow fibres this stuff can be twice as strong as aluminium at half the weight...
Rebar should not have a smoothe surface.
tin foil
use some real rebar ie 3/4 thick
This is worse than what hes currently using... Which is already not good at all for this system.
Source : i work in a composites R&D lab