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IndustryArena Forum > Mechanical Engineering > Epoxy Granite > Epoxy-Granite machine bases (was Polymer concrete frame?)
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  1. #3561
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    Apr 2007
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    1955
    Cameron - did you get a chance to try washing the agr. with high purity IPA + bake before use yet ? I didn't see it in any of the posts, and I have read most of them I think.

    Maybe with the siloxane bonding agents it does not matter as much, and I guess your fractures are not epoxy - agr bond line failures so far.

  2. #3562
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    Apr 2007
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    Harry,

    I've only done 1 test with aggregate and it was mainly to determine the rheology of the mixture.

    The several packing tests I performed on pure aggregate show that the tiny syntron bin vibrator I am using on my test setup is much too small to have a real effect. As a result, packing densities have been too low for the mixture to have the target modulus. I've got to work on getting a vibrating table now otherwise the effort is for naught. I haven't tried washing the material in IPA or oven or vacuum drying it.

    I have been degassing my epoxy in the vacuum chamber and it hasn't exploded yet thankfully. I do wear an organic vapor respirator when working with the epoxy and hardeners. Most of the constituents of the epoxies and hardeners on my bench have pretty low vapor pressures.

    I've done a number of batches of pure epoxy to evaluate various hardeners and cure cycles and so far, I have to agree with roach that Isophorone Diamine (IPD) gives the best results with Hexion 813. For greatest effect epoxy with IPD should be cured at 85C. Unfortunately, I think IPD too toxic and corrosive to be a good candidate for home use.

    Packing densities for individual aggregates determined with my apparatus using the undersized bin vibrator were:

    #6 Al2O3 68%
    #2 Quartz 70%
    #4 Quartz 69%
    #2/0 Quartz 66%
    IMSIL 1240 55%
    G800 Zeospheres 30%

    Overall density of the aggregate mixture proportioned as in the last posted formula with IMSIL 1240 substituted for G200 Zeeospheres was 74%. The model indicates it should have been more like 84% or 88% depending on assumptions so I believe that the vibration was too low to properly pack the aggregate.

  3. #3563
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    Jun 2005
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    Cameron - thanks for your resume of Maxmod's link.
    My ancient schoolboy French managed some bits, but one thing I think was there was a mention of xylenes as a bonding agent (?)
    Was this what it says, and what think you, if it was ? While they're not particularly pleasant, they would be preferable, certainly more easily obtainable than silanes.

    John
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  4. #3564
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    Apr 2007
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    John,

    I saw the comment on xylenes as a coupling agent but it seemed strange. Some googling indicates its use as an epoxy thinner but I saw no mention of it as a coupling agent anywhere else. It might be worth heading for ye olde library and pulling the paper which I haven't done yet.

  5. #3565
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    Jun 2005
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    On the subject of papers - http://www.waset.org/ijit/v3/v3-3-29.pdf was an interesting read from a different perspective on random packing aggregates. To some extent, it differentiated between the larger particles and the smallest in the way their contribution was made to the strength of the material.
    Generally, I took it to mean that the larger particles were more important in carrying compressive loads, via direct contact, and that the smaller particles were playing a more important role in "locking up" the larger ones, and reducing the epoxy proportions(in our case).
    This would seem to underline the need for maximising the bonding between the larger particles and the epoxy.

    John
    It's like doing jigsaw puzzles in the dark.
    Enjoy today's problems, for tomorrow's may be worse.

  6. #3566
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    Sep 2007
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    Hey guys,

    Been reading this thread for a while and thought I would throw in my 2 cents.

    I have been making cast concrete/ cast polymers / rubbers etc. for some time, so have some experience. I also have tried just about every combination of vacuum/vibrating autoclaving / etc.

    RE: vacuum:

    Vacuum works great with some caveats. You really have to use a larger vacuum chamber to hold the actual mold. Trying to use a mold to serve the purposes of both mold and the vacuum chamber has never worked out for various reasons.

    1.) the mold must seal at the parting lines perfectly. Just the slightest leak will cause air bubbles at that location, not remove them. This is much easier said than done, and getting it right usually requires very heavy-duty/ precise/intelligently designed / expensive molds.

    2. The pressure on the exterior can distort the actual mold, especially in the middle of long flat spans.

    3. The removal of air bubbles can be less than homogenous.

    In addition, with epoxies especially, it is very easy to remove the very volatiles that are required for proper curing. It's best to pull on it with medium vacuum, release, vacuum again, release, etc. etc. etc.

    Vibration:

    Vibration is definitely more important than vaccum degassing for consolidation /compaction. I use a 4' x8' steel table with a Vibco SCR1000 vibrator attached to the underside, with the entire top sitting on Goodyear air shocks.
    It has variable frequency and amplitude. You really will never know the right settings until you try it, as the size, weight, and configuration of the mold makes each one unique.

    The best technique is to bolt the mold inside the vacuum chamber, bolt the vacuum chamber on the vibrating table, and go to town. If you really want the ultimate, follow this up with autoclaving or just use the vacuum chamber as a pressure chamber, reducing the remaining air bubbles in size.

    I've made concrete using this technique that was on the order of 10,000-15,000 + psi using only silica sand as the aggregate.

    Hope this helps,

    Burt

  7. #3567
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    Apr 2007
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    Burt,

    This is exactly the kind of information I hoped somebody would post. Most of what I and others have learned has been by trial and error and mistakes.

    I agree with you that vacuum molds are very difficult though they are not impossible. I have a test mold for 8x8x 5/8 sample plates that I fabricated from A2 tool steel. It is made out of 1/2 inch thick plates and a 1 inch thick spacer ring cut from a single piece of 1 inch plate. It has two large glue joined o-ring seals. There's $200 worth of material, $125 worth of precision grinding I had to sub out, and around 100 hours of my time machining o-ring grooves, holes for allen head cap screws to compress the o-rings etc. I am fairly certain it would cost thousands of dollars if I had it fabricated commercially. I still use this mold in my vacuum chamber as it prevents me from inadvertently sucking epoxy into my vacuum pump.

    I understand point 2 of your note about warping of a vacuum mold but we had only anecdotal evidence before your post about the boiling off of critical mixture components. Jack Hudler had issues with the Reichhold 37-606 hardener boiling off on him back in <A href=http://www.cnczone.com/forums/showpost.php?p=363937&postcount=2373>post 2373</A>.

    I think your post also clarifies the level of vibration needed to make E/G work and it is unfortunately far more substantial than the starters of this thread envisioned.

    Thank you kindly for your comments. You are the first one here to share specific experience with vibration and vacuum in this context.

    Regards all,
    Cameron

  8. #3568
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    Feb 2009
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    16
    Quote Originally Posted by Nami View Post
    Vibration is definitely more important than vaccum degassing for consolidation /compaction.
    Burt
    Burt,
    You think for less than a 100# EG setup, a hammer drill set to hammer only pounding on the table the mold is attached to would hit hard enough to do the job? I'm thinking of a mold holding the EG, bolted/clamped to a table hanging from rope or sitting on springs. Ground the hammer drill body, and use a modified hammer bit that bolts to the table to transmit energy to the free moving EG/mold/table mass.

    If we're after high controlled acceleration as opposed to frequency & displacement, this has high potential to couple lots of energy to the EG in short blows.

    Thom

  9. #3569
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    Sep 2007
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    10
    Solar,

    Way back when I first started, probably about 13 years ago, we tried similar things as the hammer drill, palm sanders, etc, etc. on our first small scale experiments.

    They really can't impart the amount of energy that is required. Remember that any force applied in that way is going to have an equal and opposite force in the other direction. Whether the mass is suspended by strings, springs, etc. the mass of the hammer drill (even with you holding on to it for dear life), is so much less than the mold/mixture/table, that most of the energy is going to be witnessed going the wrong way. Picture the stereotypical construction worker using a jackhammer. Sure it gets the job done, but how much more work would get done if half of the energy wasn't being wasted knocking the guys fillings loose?

    The beauty of vibrators that are bolted to the table is that they build on harmonics to keep the energy flowing. I don't know if can describe this succinctly enough, but if you've ever read Tesla's biography and his work with vibrators and harmonics, he realized that a relatively small vibrator could bring down quite a large structure. If you've ever seen the footage of the Tacoma bridge collapsing, it was the same phenomena, it was just the wind that supplied the energy, and when the natural frequency was reached, boom.

    A quick analogy would be pushing a kid on a swing. If you time it right, once the kid is swinging it takes little energy to keep him going. But if you don't pay attention and don't syncronize your push, everything comes to a screeching halt. I think that with a hammering action from a handheld drill this is probably going to occur quite often, because you can't really time it right. They do make linear vibrators that work, but again, they are bolted to the table or mold itself.

    This isn't to say that you want to reach the natural frequency of your mold/mixture. Many times when you do there occurs a rather interesting phenomena called a standing wave, and this can cause strange effects, including separation of the aggregates. This is why variable speed is really advantageous.

    In summary, If you want to save money for the initial experiments, I would think that you would definitely be better served to find a used vibrator (boy, that just doesn't sound right) on ebay, or even make one. Really all they are is an electric motor with an eccentric weight on the end. Of course, the real ones are built to take the abuse day after day. Mine was $1000.00 new, but it's still going strong.

    I would think that if you kept the experimental mold size small, a decent small motor with an off-balance flywheel would get you started. Just keep clear and don't expect it to last forever! Combine it with variable speed and you maybe surprised at how well vibration works.

    As an example, with regular concrete, the less water you use, the stronger the mix. The problem is placing the concrete gets more difficult as the amount of water goes down. This is where vibration rules. I like to amaze people by mixing some up that's so dry and rich that I can make a snowball out of it, place it on the table, hit the switch, and watch it melt into a fluid.

    Here is a link to the vibrator I have. Look under SCR vibrators in the catalog, it's the SCR1000. That's right, 1000lbs. of force.

    http://www.vibco.com/productcats/productcats.htm

    Here's one for ya on ebay...

    http://cgi.ebay.com/NEW-Martin-Motom...QQcmdZViewItem

    Just kidding.

    Actually, here's a pretty good deal...

    http://cgi.ebay.com/Martin-CD-Series...QQcmdZViewItem

    or this one...

    http://cgi.ebay.com/Renold-Ajax-Elec...QQcmdZViewItem

    O.K. last one...

    http://cgi.ebay.com/Vibrator-VIBCO-S...QQcmdZViewItem

    Now find a small bell jar, bolt the vibrator to the bottom of the base, and go to town.

    I also really recommend air bags for the suspension system. Must less resistance than springs, and much quieter.

    Good luck guys,

    Burt

  10. #3570
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    Nov 2007
    Posts
    7
    <<<An important thing I noted in this document (but I went very quickly through it) is that the vibration of the material was capital, and that the acceleration more than frequency was the most important parameter. It states that vibrating over 2G of acceleration gives much better results than a long vibrating at less that 2G, even by tweaking the frequency....as far as I see, he has not used vacuum at all...Magic vibration?>>>


    It's true...and the big PC makers (Accures, Cleveland Polymer, and now closed ITW Polymer Castings) only use vibration (no vacuum) to remove air pockets from their castings. The main problem with vibrating too long (>30 mins.) is that the aggregates start settling, leaving a resin rich pour surface that shrinks more than the bottom surface. Not a good thing when trying to cast to tight tolerances

  11. #3571
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    Apr 2006
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    225
    Hi everyone,

    First post here on this thread. Im gonna build a new CNC mill soon ( my 3rd one, first I used steel, second alum ) and I'm considering using Epoxy concrete for it, I read that sticky post already and I got some doubts about some stuff...

    There is a company here that manufactures a bunch of kinds of Epoxys for everything and they make plastic granites as well, Im wondering on what's best to use with the polymer to make as strong and vibration damping as possible.

    Well I dunno if it works like regular granite machine basis that the more quatz you have on your granite the best, thats why they use black granite... If its that way i should just use black granite powder on the mix ( If i make the mix myself ), or I can ask the guys from this company what product they have that use more quartz on its composition.

    Can you mix a bunch of things? like I dunno 20 different elements? Or its better to sitck with just one or two of the hardest thing you can find and the epoxy?

  12. #3572
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    Apr 2007
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    777
    Hi Brenck,

    Thanks for posting. Although it's been a long time in coming, I'm rapidly coming to the conclusion that settling the aggregate with sufficient vibration is the single largest problem eclipsing both the need for good epoxy and the proper aggregate grading.

    From the research papers posted here like this paper from <A href=http://fire.nist.gov/bfrlpubs/build99/PDF/b99032.pdf> NIST</A>, natural granite as opposed to quartz has slightly different properties but either should be fine.


    My conclusion from the 2 years of research here is that there are three basic criteria you need to produce a material with the properties of a commercial material e.g. modulus 4,000,000psi or 28 GPa like Zanite or Accures.

    First, you want an epoxy that sets up hard and has a modulus ideally better than 375,000 psi or 2.6GPa. Secondly, you need the right aggregate grading for your available aggregate which should have as wide a range of sizes as possible. We've been studying mixes than go from micron sized particles to about 4mm. Finally, you need to compact the material with vibration using an acceleration greater than or equal to 2g and do so for long enough to obtain an aggregate percentage of better than 85%.

    In addition to the basic criteria, easier processing and better properties can be had with the addition of deairing agents like BYK A-525 and coupling agents like silanes (Dow Z6040/Z6020) or titantes (Kenrich KR and LICA series or duPont Tyzor). These Deairing agents and coupling agents will help to minimize voids and microvoids in the mixture.

    Without going to some of the extremes we've been criticized for in the past, you are likely to come up with a material that has a modulus of about 2,000,000 psi or about 14 GPa. This is both demonstrated by the models and measured on the samples I have tested from several regulars here.

    The lower modulus material is probably suitable for a thick cast base ideally supported by something like steel underneath. I wouldn't rely on unreinforced sections that are less than 4 inches square. Even a 4 inch square section used as a beam is likely to deflect by thousandths of an inch at the center under its own weight if it runs more than a foot or so supported only at the ends. This sort of deflection may be fine in lower precision applications but I think it limits the applicability of E/G parts made without large scale vibration systems to settle the aggregates.

    I'd ask your supplier if they have a formula for mineral casting epoxy and also for an aggregate of the right size distribution premixed since as Thomas Zietz's group discovered, it is easier to buy material than to make it.

    You can certainly mix all sorts and sizes of aggregate as we have done to get a mix that will compact to the desired density. Having hard high modulus materials like quartz is certainly good, especially for the largest aggregate in your mixture. As near as I can tell, slightly softer materials for the smaller particles don't matter much.

    The general consensus of numerous papers is that Epoxy Granite is about 10 times as good at damping as cast iron in many frequency ranges. Nobody on this group has posted any of their own measurements although that french paper a few posts back from MaxMod has some measurements taken with the resources of a large university. The composition doesn't seem to matter much even up to 86% density.

    Feel free to ask any other questions you or others might have!

    Regards all,
    Cameron

  13. #3573
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    Apr 2006
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    225
    Thanks Cameron,

    I mean my prupose is not to make the best granite epoxy ever made, but if im going to make it I should at least do it right.

    I have access to a vabrating table in my college I might use that if I make my own.

    When I look at the pictures of machine structures made out of E/P it looks like they use small grain of mineral adittives. But you say people have tried even with 4mm grain size...

    I wonder if its better to use thin powder mineral or a large grain.

    But have you guys got to a % of ideal mix? Like % Epoxy and % of minnerals? Because if there is I might just ask the company what product they have that matches this mix and ask what minnerals they have on each one so i can choose the one its hardest.

    Have people consider on mixing stuff like glass fiber with it? Or even carbon fiber if someone what to spend more money on that, not like a sheet of carbon fiber, but like random fibers on the mix, pasically like ABS or other plasctic they have micro glass fibers on it...

    I immagine if someone tryed to use bamboo fiber mixed all together, its a strong natural fiber

  14. #3574
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    Apr 2007
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    Brenck,

    The mineral size distribution required is dependent on what you have available and the amount of vibration available to compact it.

    The last formulation I posted from the model is the following:

    0.18744 Agsco #6 Brown Aluminum Oxide
    0.38420 Agsco #4 Quartz
    0.12950 Agsco #2 Quartz
    0.11514 Agsco #2/0 Quartz
    0.11352 3M G800 Zeeospheres
    0.07020 3M G200 Zeeospheres

    G200 Zeeospheres 2.5 gm/cc
    G800 Zeeospheres 2.2 gm/cc
    Quartz 2.65 gm/cc
    Brown Aluminum Oxide 3.97 gm/cc

    These are volume percentages of solid given so to actually make the mixture, you have to weight the components. If you assume that you are trying to make 100ml solid volume of the mixture then there is 18.7% of the aluminum oxide component which is 18.7ml * 3.95g/ml and so forth. These sizes won't be completely applicable to you because they are related to the size distributions within each aggregate type provided by U.S. supplier AGSCO. Also note #6 Al2O3 is graded as an abrasive and that is a single size range while the quartz is graded differently and ranges very widely in size for each grade. If you're not trying for either optimal or of commercial quality, A friendly civil engineering major could probably work out a reasonable mixture for you using Fuller's formula for concrete mixing. I'd also encourage you to ask your supplier for the mix they use for synthetic granite.

    I didn't have enough vibration to compact my last test to meet the conditions of the model so it didn't get the 89% minerals 11% epoxy I had in mind. So I still don't know for certain that the model is acting properly although I suspect it is. At the compaction level I got, I only got 76% minerals, 24% epoxy by volume.

    You do have to realize that the epoxy needed is a function of how close together you can get the aggregate to pack. It would in fact be possible to mix two batches of this stuff with the same components and different vibration levels, to cure it, and to have one fall apart like cornbread crumbs and the other be much stronger than concrete. I consider >89% minerals and <11% epoxy to be the target but that means the size percentages and vibration schedules have to be adjusted to get that to happen.

    All of the reinforcements that you have mentioned are good reinforcements for some composites applications. Fiber reinforcements, especially short fibers are more effective at increasing tensile strength and less effective at compressive strength. Fibers have been suggested before but their exact effect isn't something we have quantified as nobody here has tested it that I know of. Short fibers could be an asset at low aggregate contents but they will surely reduce the packing density and thus the modulus at higher densities.

    In conclusion, dry mix aggregate and try to get yourself a mixture that is a dense as possible after vibrating it. Figure out the free space in the mixture by using mass to find the volume of solids via the density of the material as outlined above. Divide this by the amount of space the material occupies in the measuring vessel after vibration and that is the actual packing density Phi. Phi is also the minimum amount of epoxy needed to fill all the voids.

    Best of Luck,

    Cameron

  15. #3575
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    Apr 2006
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    Thanks for the explanations.

    I dunno why but something makes me think that if you add to much minnerals the minnerals will sink to the bottom and the epoxy will float... And considering it will vibrate it makes me think that migh be even worse... Its like Poliester resin you vibrate so the bubles come up en then dissapear...

    Does epoxy have problem with bubbles?

  16. #3576
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    Apr 2007
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    Brenck,

    Like epoxy resin, polyester resin also will get bubbles. Vibration will get a lot of bubbles out. It's true that some epoxy will float to the top if a vibrated mixture is epoxy rich.

    To put it in perspective, a minimally vibrated part with haphazard aggregate mixture like those I have tested has about the same stiffness as softwood used in construction.

    Regards,

    Cameron

  17. #3577
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    Dec 2006
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    90

    Tested/Locked-Down Set of Plans

    Is anyone aware of a tested, locked-down and well detailed set of plans and instructions available to build a mill and/or lathe and/or combo machine. Preferably somewhat larger and more rigid than Sherline and Taig and CNC ready.

    Because of my knowledge and skills limitations they would need to be in layman's terms, include "recipe" components and procedures and not require much investment in specialized equipment

    I'd be more than happy to pay a fair price for these.

    So, am I dreaming in techni-colour?

    Thanks kindly,
    Gerry

  18. #3578
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    Feb 2009
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    Gerry, If you want a machine, I recommend buying something with the bugs worked out already. There is the maxnc, syilamerica, etc. When you add up the price of parts and time involved you may be better off. Building one from scratch is usually best if you need to fit a specific role or are trying to build a better mouse trap. It's like making your own brake caliper. You could cut a solid block of steel, or run to autozone. But if you want a titainium brake caliper...

  19. #3579
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    Mar 2005
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    Quote Originally Posted by romihs View Post
    I came across a very interesting CNC mill design built on an EQ table.
    http://www.meisterkuehler.de/forum/w...aschine-3.html
    Just an occasional reader, but it doesn't look like his pour turned out very well? He used a lot of large aggregate, which is very non-uniformly distributed (mostly sunk to the bottom):


  20. #3580
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    Jun 2005
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    I think he's being overly critical. That looks fine to me! Nice clean core, good distribution.
    Looks like he poured an EG Top layer.


    -------------

    Wait a second! That's Concrete not EG. Nice setup though!

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