Epoxy-Granite machine bases (was Polymer concrete frame?) - Page 242


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Thread: Epoxy-Granite machine bases (was Polymer concrete frame?)

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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by ckelloug View Post
    The golfer,

    Your block looks pretty nice. I'd suggest vacuum deairing the epoxy before mixing the material up. If possible, a few percent of BYK 525 deairing agent will also help. In about 30 formula tests, I never saw that problem although I always vacuum degassed and tended to use a smaller amount of epoxy and used a pretty thin epoxy.

    Regards,
    Cameron (ckelloug)
    Thanks Cameron. I like the idea of both the vacuum degassing and the use of deairing agent. I will look into finding some of the BYK 525 here in Australia. Building a vacuum degassing chamber might be a good excuse to finally but a venturi valve.

    Quote Originally Posted by svenakela View Post
    Thegolfer, what type of epoxy did you use?
    I used West System epoxy with their 206 slow hardener. I used this type mainly because it was the easiest resin to get my hands on that had technical speciations available. There were a few other "no name" epoxy resins around but I couldn't find any product literature on any of them.

    Quote Originally Posted by ihavenofish View Post
    looks nice. a propane torch will get rid of most of the larger bubbles and foaminess. just run the torch gently over it after the pour.

    to get a properly smooth bubble free surface (one you intend to use mechanically) I think vacuum degassing as mentioned is probably the best way.
    The propane torch idea sounds good also! If it can easily remove the bubbles/foam it might be a winner.



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    I think another reason my first epoxy granite block was so foamy was an extreme overuse of epoxy. My first block was 22.22% resin by weight, a large percentage of which was forced to the top of my mold as I vibrated the wet mixture. I did another test block today with 18.18% resin by weight and it's much better, although nowhere near perfect still. Below is a comparison of my first and second test blocks:



    And a close up of the top of the second test block.



    I am also currently curing a block with only 10% resin by weight, but I can already see that it's too dry. Tomorrow I will try around 12% by weight and see if that helps.

    Thanks for the help so far everyone!



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Thegolfer,

    I find that you really need to get about 29.9 inches of mercury to fully degas epoxy. A venturi won't get to this level but it might be enough to help with your problem. Also, watch out for boilovers in the vacuum chamber as I cant tell you the number of times I applied vacuum too quickly to a beaker of epoxy and found a pool of it running on the follow when the chamber was opened. . .



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Dabit (further up this page) has used EG with 3% by weight epoxy and that only started to be slightly less strong.
    I think for most of his casting he used 8% by weight as the max.

    Sven http://www.cnczone.com/forums/diy-cnc-router-table-machines/320812-aluminium-1250x1250x250-router.html


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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by ckelloug View Post
    Hi Thegolfer,

    I find that you really need to get about 29.9 inches of mercury to fully degas epoxy. A venturi won't get to this level but it might be enough to help with your problem. Also, watch out for boilovers in the vacuum chamber as I cant tell you the number of times I applied vacuum too quickly to a beaker of epoxy and found a pool of it running on the follow when the chamber was opened. . .
    No, a venturi won't get to that level! A full vacuum pump might be a bit out of my price range at the moment though.

    After another couple of casts, I think that my main problem was too much epoxy. I cast a 10% epoxy by weight block last night and it was an unmitigated failure:





    It looks like I've just broken off a chunk asphalt. I have a 15% epoxy by weight block curing now and it looks like it will be 90% good on the degas side of the block. When mixing the 15% it looked fairly friable, whereas the mixtures with more epoxy have been more of a solid gloop.

    Quote Originally Posted by CaptainVee View Post
    Dabit (further up this page) has used EG with 3% by weight epoxy and that only started to be slightly less strong.
    I think for most of his casting he used 8% by weight as the max.
    Wow, 3% by weight is extremely low! Dabit and I must be using very different aggregates. As you can see above, 10% by weight was no where near enough epoxy on my last test block.

    I'm starting to realise that there are a huge number of variables involved in making this stuff!



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    The amount of epoxy needed is highly dependent on the size distribution of the aggregate that you are using. If your aggregate are sized in a suboptimal way, they won't pack together very tightly and a lot more epoxy will be needed to fill the voids. Also, as the number of small particles increases, you end up needing enough epoxy to coat the surface area of all of the particles rather than just to fill the voids in the mixture and that increases the epoxy demand. (you always have to coat all the surface but when you get some very fine fillers, the amount needed to coat the surfaces becomes more dominant) I'd have to do a lot of research through my old posts and data to remember exactly what numbers I thought were reasonable when I was working on EG a lot. I haven't worked on it for a while but I'll probably have a bit more time to think with a change in jobs that just happened. Also, the weight percentage of epoxy will depend on the density of your aggregate.



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Dabit did quite a bit of testing on the strength of various mixes.
    If I recall correctly his conclusion is that when you exceed 8%, cost for the epoxy keeps rising without adding much strength.
    The 3% mix is a lot of hard work in mixing up and requires to be packed in to the mold.

    Indeed it is good to mix sizes but I think that mechanically the last "dry" sample may be very effective.

    But the earlier samples are much nicer to look at

    Sven http://www.cnczone.com/forums/diy-cnc-router-table-machines/320812-aluminium-1250x1250x250-router.html


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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by thegolfer View Post
    I used West System epoxy with their 206 slow hardener. I used this type mainly because it was the easiest resin to get my hands on that had technical speciations available. There were a few other "no name" epoxy resins around but I couldn't find any product literature on any of them.
    Too fast. 206 has a pot life around 20 minutes. My standard hardener is 45 minutes and when we mold bigger shapes we are using a hardener with 120 minutes pot life.
    Buy a can of 209 and try it instead.



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    If you really need 10+ percent of epoxy, you should review your aggegate mixture carefully. There seems to be too much space between the grains that can also be filled using a smaller grading.

    In my mixtures, anything above 8% was very wet and slushy, and personally I preferred less epoxy to make the mixture firmer.



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by svenakela View Post
    Too fast. 206 has a pot life around 20 minutes. My standard hardener is 45 minutes and when we mold bigger shapes we are using a hardener with 120 minutes pot life.
    Buy a can of 209 and try it instead.
    Hi Svenakela,

    Yes, I looked at the 209 but decided not to go with it because it's winter here at the moment and the temperature in my garage isn't getting above 12 degrees C. I thought the 209 would take too long to fully cure in these types of temperatures. When I have used all of the 206 I will buy a can of the 209.

    Quote Originally Posted by DaBit View Post
    If you really need 10+ percent of epoxy, you should review your aggegate mixture carefully. There seems to be too much space between the grains that can also be filled using a smaller grading.

    In my mixtures, anything above 8% was very wet and slushy, and personally I preferred less epoxy to make the mixture firmer.
    Hi DaBit,

    You are right, there is a serious flaw in my aggregate ratio. I did another mix with 11.8% epoxy by weight and, although my best block yet, the mix was extremely stiff. My smallest aggregate is ground silica powder. Without the silica the blocks come out like asphalt , with it the mix becomes too stiff. These first blocks were just a bit of fun (and I've learned a lot) but I'm going to have to do some serious research on my aggregate composition if I'm going to get down to your levels of epoxy by weight. I would like to minimise the epoxy in my mix as much as possible because aggregates (even fancy ones) are much less per kilogram to purchase than epoxy! Here's my 11.8% block:



    I'm a third year engineering student, so I have access to a huge amount of online journals through my university library. I've started doing some research on "polymer concrete" and have saved some interesting looking articles to read. There's a fair amount of scholarly knowledge published on polymer concrete, so hopefully I can find some good information. I will share anything that I think is relevant, though I think it's probably all been covered in this thread already!

    One very interesting article that I quickly skimmed was on hybrid polymer concrete structures for machine tools (essentially just filled weldments). Laser cut plates bolted or tack welded into a steel exoskeleton filled with epoxy could make for a very rigid machine!



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Wow can't believe this thread is still going with some of the same ole faces! Walter ever show back up?

    I see people are using vacuum and vibration; good. Only I think 29.9 is a bit deep, the foaming in from boiling the volatiles in the epoxy.
    Did a video on this some thousands of messages ago.

    I experimented with gel coating molds before filling with EG, much easier to de-mold without destroying the mold.

    Cheers!!!



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi jhudler

    What did you use for the Gel coat? was it epoxy base or polyester. What release did you use?

    Regards
    John



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    I paint the surfaces (wood; plywood or MDF) with urethane based automotive primers and paints. This creates a smooth hard surface that can be sanded with extremely fine grit (I stop at 5000).
    Then many coats of wax for release.
    Epoxy only, I never used polyester base anything.

    The reason for the gel coat is simple, you can vibrate using de-airing agent and stop vibrating when the bubbles stop; no worrying about abrading the release agent off the mold. No vacuum needed.
    Another reason is that it just looks sexy when it's done and fixing imperfections in the coat is fairly easy.

    Last edited by jhudler; 08-04-2014 at 04:38 PM.


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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    In general, epoxy, even with reactive dilutants, should not have appreciable volatiles content. A liquid amine hardener is somewhat volatile however a few minutes at 29.x inches won't hurt it a bit. All of the work I've done has been degassed at 29.x and the bubbling quickly stops after a few minutes and results in a gas free sample. My vacuum gauge isn't sensitive enough to measure to tenths but I estimated 29.9 based on the needle position being between 29.5 and 30 being fairly close to 30. A verified 29.9 could be a few tenths high but based on recommendations of degassing equipment mentioned eons ago, I stand by my statement that more than 29 is needed to get the air out. I am fairly certain that bubbling seen in the first few minutes of degassing is air, not volatiles.



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    ckellog;

    Many moons ago you mentioned that Dupont Starblast Ultra could possibly be a source for a pre-graded aggregate mix for epoxy granite. I thought that mixing it with say 3/8" pea gravel rock would make for a good mix.

    If you don't mind, what do you think?

    Cheers!



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Considering cost, it's no necessary, we can make PSD by ourselves, that will be cheap



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by ckelloug View Post
    I am fairly certain that bubbling seen in the first few minutes of degassing is air, not volatiles.
    First you get air and lots of foam until your first slump, which happens fairly quickly. Next you get moisture which will continue to form bubbles for a long time. You will continue to get moisture bubbles from the mold for hours if you don't bake your mold before hand.

    I don't know how much vacuum epoxy can take but I routinely use 29.x (whatever the maximum I get from a 2 stage oil bath vain pump) for several hours with no detrimental effects as far as I can tell. I always heat cure my epoxy so I wouldn't know if excessive vacuum affects room temperature hardening.

    Pete



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    LowAlloy,

    I've emptied my PM box. I don't seem to have modeled the starblast ultra but I liked it because it had a wide variety of sizes and since it is a disposable product, ought to be relatively inexpensive in the US. I never did verify the inexpensive part however.



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Steven.ji;

    It is probably something I know, but just forgot, but the "PSD" abbreviation has slipped my mind. Could you remind me?

    ckelloug;

    Thanks for the reply.



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    Default Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by Low-Alloy View Post
    Steven.ji;

    It is probably something I know, but just forgot, but the "PSD" abbreviation has slipped my mind. Could you remind me?

    ckelloug;

    Thanks for the reply.

    Particle size distribution



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