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IndustryArena Forum > Mechanical Engineering > Epoxy Granite > Epoxy-Granite machine bases (was Polymer concrete frame?)
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  1. #5041
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by Mikeedd View Post
    It is so nice, you are doing theese tests, BadHabbit, I love to see the outcome, as well as the sousvide you will use to cure the final machine :-)
    haha! Nah, if the tests show a significant advantage to postcuring i'll cast in some copperpipes. I can then use these to heat the casting during the postcure and later on use them to make sure the machinebase has a constant temperature... but if postcuring isn't nessesary i'll skip these pipes...

  2. #5042
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Thomas - Are you chasing modulus or strength? or stability? Post cure accelerates the strength development but not modulus. Plus high temp cure can create excessive internal expansion due to various chemical reactions that make large crystals (due to the extra energy available) that sort of force the material apart vs small crystals (look up ettringite) that fill in the available spaces. What temp are to going to simmer at? Peter

  3. #5043
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by peteeng View Post
    Are you chasing modulus or strength? or stability? Post cure accelerates the strength development but not modulus. Plus high temp cure can create excessive internal expansion due to various chemical reactions that make large crystals (due to the extra energy available) that sort of force the material apart vs small crystals (look up ettringite) that fill in the available spaces. What temp are to going to simmer at?
    The manufacturer recommended me 70c for >15 hours for my application. Their explaination was that the higher temperature causes more bonds to be made in the epoxy, thus making it stronger and giving a better binding. My reasoning is that if the bonding of the aggregate changes, so does strength AND modulus. It also raises the glass transistion temperature, but anything around room temperature is good enough for my application. However, i cannot find any information on the effects of postcuring in EG machinebases. It might be because it makes no sense in practice, i don't know. But this is the reason why i want to test the effect for the materials i'm going to use. IF i can avoid postcuring it, i absolutely will. Or at least only do a minimal effort(heating fan in a box with the castings inside for a weekend). But if it proves to have a significant (positive) effect on the modulus i'll incorporate the internal pipes to do a proper postcure and then i might aswell prepare them for controlling the temperature stability of the machine(which i actually don't think will have any real impact on my machine, but whatever, it all fun and games anyways ;-) ).

    /Thomas

  4. #5044
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Sorry Thomas - Your working with epoxy not concrete! Crossed discussions... Yes post cure of epoxy is good. Some epoxies need post cure to get to a "crisp" stage. 70C for 15 hours is typical of boat building epoxies. Higher temp increases the cross linking density. In my years of fibreglass and carbon laminate tests we don't see increases in modulus with post cure vs ambient but do see strength improvement. Will be good to see your results. Plus you are going to get compressive modulus results. If the aggregate is close packed the strain is transmitted by aggregate contact vs thru the resin so you can get a high compressive modulus but a low tensile mod... Your results will be interesting... Peter

    If you cast some of your epoxy say 3mm thick and let it ambient cure for a few days and then break it, it should snap. The resin I use will snap the day after... if its still rubbery then its not a very active hardener and will need post cure.

  5. #5045
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by peteeng View Post
    If you cast some of your epoxy say 3mm thick and let it ambient cure for a few days and then break it, it should snap. The resin I use will snap the day after... if its still rubbery then its not a very active hardener and will need post cure.
    Yeah, the R&G ResinL + GL2 will fully cure at 20c, but it takes a while(by design)... i've tried to demould casts after 48 hours and that is too fast, it's still not "crisp"... the tests i've done with demoulding after 3-5 days works a lot better... the consultant i talked to at R&G also said that they'd recommend start postcuring after around 4 days...

    /Thomas

  6. #5046
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by badhabit View Post
    Hi,

    I just got a package in the mail, the forms for casting standard 100*200 testing-samples:


    I'm going to cast 5 different samples and send it to a national test institute. This will at least give me the compressionstrength and e-modulus for the Silimix282 + R&G resinL/GL2...i'll make one sample without the postcuring and a sample with postcuring. I want to see what difference(if any) it makes to the e-modulus(my guess is none...or close to). I'll also send a sample with larger aggregate mixed in with the Silimix282. Since the largest size is 4mm in the 282, i'll try to add some ~15mm aggregate. This is to determin how it effects e-modulus and if it would be more cost effective in a larger cast, saving on both the Silimix and a little of epoxy...

    /Thomas
    Hi Thomas

    Did you these results?

    Thanks
    Sus

  7. #5047
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by suspension View Post
    Hi Thomas

    Did you these results?

    Thanks
    Sus
    Yes and no:-) I didn't get the institute to do the testing. Mostly because the ones i talked to usually "just" test concrete and their main focus is compressive testing, which isn't very usefull for my/our purpose. I ended up being assured by the videos of Stefs machine performing very well, so i ditched the "official testing" and went on with my casting...

    However, i'm not done using EG and i have other projects in mind. But the next time around, i'm going to try to solve some of the issues i have had in my project: Mainly proper simulation models and proper degassing during casting. I've been thinking about doing the flex-testing(just as you) for quite some time, but haven gotten around to do it yet. But this is defently something i'll need to do before any new projects with it. I no longer think i need "official help" from a 3rd party to validate the stiffness of the EG, so i'll just to the testing myself. Peter(and you now :-) ) has posted quite a lot on this forum about this, and i like the idea of testing a known material first, like aluminium, to validate the process before testing own samples.

    I've also been thinking about solving the degassing part by curing the casting under pressure. This is a whole other beast to tackle, but nonetheless something that defently will affect the stiffness and strength of the final casting. From my casting this is how a "cross-section" looks like:
    Attachment 468324
    I've tried degassing the mix, but it was not possible with my mix, the gas simply could not get out, even under "full" vacuum. The next step would be to try to add an additive to the mix that allows better degassing, but this might also affect the shrinkage of the casting and might not be desireable. So to minimize the airpockets i would like to try to cure it under e.g. 10bar of pressure to effectively shrink the "bubbles" to 1/10 of their normal size. This doesn't remove the air, but my hope was that it would minimize the effect of the trapped air. However, this does come with its own set of problems(and dangers!) but it might be a way...

    /Thomas

  8. #5048
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by badhabit View Post
    Yes and no:-) I didn't get the institute to do the testing. Mostly because the ones i talked to usually "just" test concrete and their main focus is compressive testing, which isn't very usefull for my/our purpose. I ended up being assured by the videos of Stefs machine performing very well, so i ditched the "official testing" and went on with my casting...

    However, i'm not done using EG and i have other projects in mind. But the next time around, i'm going to try to solve some of the issues i have had in my project: Mainly proper simulation models and proper degassing during casting. I've been thinking about doing the flex-testing(just as you) for quite some time, but haven gotten around to do it yet. But this is defently something i'll need to do before any new projects with it. I no longer think i need "official help" from a 3rd party to validate the stiffness of the EG, so i'll just to the testing myself. Peter(and you now :-) ) has posted quite a lot on this forum about this, and i like the idea of testing a known material first, like aluminium, to validate the process before testing own samples.

    I've also been thinking about solving the degassing part by curing the casting under pressure. This is a whole other beast to tackle, but nonetheless something that defently will affect the stiffness and strength of the final casting. From my casting this is how a "cross-section" looks like:

    I've tried degassing the mix, but it was not possible with my mix, the gas simply could not get out, even under "full" vacuum. The next step would be to try to add an additive to the mix that allows better degassing, but this might also affect the shrinkage of the casting and might not be desireable. So to minimize the airpockets i would like to try to cure it under e.g. 10bar of pressure to effectively shrink the "bubbles" to 1/10 of their normal size. This doesn't remove the air, but my hope was that it would minimize the effect of the trapped air. However, this does come with its own set of problems(and dangers!) but it might be a way...

    /Thomas
    Hi Thomas

    I also ditched the 3rd party testing due to exact same reason - All of the institutions I talked to were mainly focused on civil engineering and not in this sort of application. I re-did the flexural modulus testing with the sample and got very similar results (30) for my grout.

    These days I am doing the shrinkage tests for the grout - which seem to be more challenging though. But based on the tests so far, the grout mixture seem to shrink even through its been more than 30 days old now. This made me look in to materials again. Each option seem to have its own problems and uncertainties. With EG, the biggest issue seem to be low flexural modulus - I have seen a thread in this forum where a professionally created EG mix only gave 12! However I doubt there are other issues with EG such as cracking/shrinking and inability to handle dynamic/impact loads? Did you do any research in this area?

    There seem to be even less information about UHPC/Grout case. Alex who built a CNC with durcrete mentions that there was considerable shrinkage. Not sure if this shrinkage is limited to fist days only. Also, there seem to be only two companies operating in this area, durcrete and rampf group. Rampf's epuself is super expensive. They dont seem to sell the other material they produce. I wish if Alex can give us some info on the shrinkage/accuracy of his CNC which I think is few years old now. Also do you know if Sef's machine give consistent accuracy with in say 10um tolerance?



    Thanks
    Sus

  9. #5049
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by suspension View Post
    [...] I re-did the flexural modulus testing with the sample and got very similar results (30) for my grout.

    These days I am doing the shrinkage tests for the grout - which seem to be more challenging though. But based on the tests so far, the grout mixture seem to shrink even through its been more than 30 days old now. This made me look in to materials again. Each option seem to have its own problems and uncertainties. With EG, the biggest issue seem to be low flexural modulus - I have seen a thread in this forum where a professionally created EG mix only gave 12! However I doubt there are other issues with EG such as cracking/shrinking and inability to handle dynamic/impact loads? Did you do any research in this area?

    There seem to be even less information about UHPC/Grout case. Alex who built a CNC with durcrete mentions that there was considerable shrinkage. Not sure if this shrinkage is limited to fist days only. Also, there seem to be only two companies operating in this area, durcrete and rampf group. Rampf's epuself is super expensive. They dont seem to sell the other material they produce. I wish if Alex can give us some info on the shrinkage/accuracy of his CNC which I think is few years old now. Also do you know if Sef's machine give consistent accuracy with in say 10um tolerance?
    I haven't done much research into EG vs. UHPC, it mostly seems like a "religious war" and in my opinion there is not a clear "winner". The biggest downside to UHPC (as far as i've research!) is that it behaves like a concrete(duh!) so it keeps "moving" for a very long time. EG does not, but it then have other properties that are undesireable(toxic before hardening, non-newtonic makes degassing problematic, it is a plastic makes process "dirty" and recycling hard etc) and EG is very(purely) dependent on the aggregate to get a good result(=high modulus)..

    A modulus of 12 seems wrong, epoxy in itself is something like 3-4ish. So 12 seems low...i would expect at least double for a "professional solution".... i really need to do the test on my(and Stefs) mix using Silimix282... What was the coupon-size you cast for the test you made? Were your samples "perfect smooth square" or did you have an "open side" on your mold giving an rough side? I was thinking about casting a 800x20x20 coupon and stuffing it from the end making all sides smooth, but i'm worried about the air affecting the result "unfair" due to the narrow cross-section...and making the crosssection bigger increases the forces required to make deflection very quickly....

    I haven't seen any information from Stef regarding accuracy tests for his machine, but his surfacefinish looks spot on(in aluminium though)....so that is mainly what i based my comment about Stefs machines performance on....

    /Thomas

  10. #5050
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by badhabit View Post
    I haven't done much research into EG vs. UHPC, it mostly seems like a "religious war" and in my opinion there is not a clear "winner". The biggest downside to UHPC (as far as i've research!) is that it behaves like a concrete(duh!) so it keeps "moving" for a very long time. EG does not, but it then have other properties that are undesireable(toxic before hardening, non-newtonic makes degassing problematic, it is a plastic makes process "dirty" and recycling hard etc) and EG is very(purely) dependent on the aggregate to get a good result(=high modulus)..

    A modulus of 12 seems wrong, epoxy in itself is something like 3-4ish. So 12 seems low...i would expect at least double for a "professional solution".... i really need to do the test on my(and Stefs) mix using Silimix282... What was the coupon-size you cast for the test you made? Were your samples "perfect smooth square" or did you have an "open side" on your mold giving an rough side? I was thinking about casting a 800x20x20 coupon and stuffing it from the end making all sides smooth, but i'm worried about the air affecting the result "unfair" due to the narrow cross-section...and making the crosssection bigger increases the forces required to make deflection very quickly....

    I haven't seen any information from Stef regarding accuracy tests for his machine, but his surfacefinish looks spot on(in aluminium though)....so that is mainly what i based my comment about Stefs machines performance on....

    /Thomas
    I just glanced through this paper - which surveys many previous research on this subject (Only epoxy based I think). And it shows a table of various previous researches. For me it looks like many of the researches report EM below 20 for EG. This seem to be agree with Pete's observation of 17 GPA.
    Since the aggregates I used had max size of around 15mm, Pete suggested I have a minimum cross section of at least 40mm and length of 800. So my specimen was 50x50x1000mm. Its was a full solid block/beam. It was not that difficult to deflect. I applied forces starting from 4Kg up to 17Kg and measured the deflections which ranged from 3um to 16um.

  11. #5051
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Why worry so much about air? That small amount of air should reduce modulus by only a small amount.

    You get a much bigger stiffness increase by increasing section size by a little bit. 10% increase in section size results in a much greater increase in stiffness than a 10% increase in material modulus does.

    Sent from my SM-S921B using Tapatalk
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  12. #5052
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Thomas - Try for a thinner epoxy. 10bar requires a considerable structure to be strong enough. Typical autoclave pressures are <6bar which makes the bubbles go into solid solution. ie no bubbles. I would not be too concerned about the porosity. But degassing large volumes of epoxy is not trivial. The hardeners are usually very thin and do not require degassing, The resin can be degassed by heating to 40-50degs (even 60C we warm honey to 60C alot) and it degasses by itself nearly. Then allow it to cool and mix carefully. Do not use a high speed mixer, a simple paint paddle is best. Add some pigment to the mix so you can tell you have mixed it and then pour carefully.

    Degassing can only occur at the resin surface. The hydrostatic pressure prevents bubbles from forming in the depths of the resin. You need to add a wire mesh or sponge or something to act as a bubble generator to the bucket. Or if you heat the resin simply stir it with a paint stirrer to bring new resin to the surface. I tried drop stream degassing, thin plate flow degassing, sparging and other odd ways but they work for small quantities. Heating was the best, most sensible way. The chemist at the supplier can help with the max temp for the resin but since it gets to 90degs C in exotherm I think it can be heated quite hot by itself. At 40-60C its so thin and the internal air is warm so makes bubbles very easily... You will only be able to remove what's called transport air, that's the air introduced in making the stuff and the air that gets introduced as it splashes around in factory and in trucks. The saturated gases are very difficult to remove in large lots. But again, I wouldn't worry about small amounts of porosity, other bigger issues to deal with. But the Grail is out there! I think you need to look at vacuum casting that would help a lot with where your heading. Don't need super strong moulds, will degas to a degree by itself and the logistics of dry filling a mould then introducing resin under say 50-75% vacuum is much better then mixing aggregate and pouring aggregate mix etc..

    But I feel engineering grouts have a much better chance of achieving high modulus and buying grout and adding water is much easier than the epoxy route. Peter

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