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IndustryArena Forum > Mechanical Engineering > Epoxy Granite > Epoxy-Granite machine bases (was Polymer concrete frame?)
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  1. #1541
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    Quote Originally Posted by ckelloug View Post
    .....Vacuum may suck but I personally like it more than spinning drums of epoxy.

    Regards to all,

    --Cameron
    I think you have a valid point here.

    Considering that at 30G 10lbs of E/G weighs 300lbs having a few cubic feet flailing around could be interesting if the balance was off.

    It would however be a way of casting E/G pipes, it is used for concrete pipes up to 5 feet diameter and spincasting of bronze bushing material is routine.
    An open mind is a virtue...so long as all the common sense has not leaked out.

  2. #1542
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    Walter,flies in honey?Is this a result of adding larger aggregate after the fines or has the epoxy started to gel?Dust on the larger aggregate would impead wetting.Roasting the aggregates sounds good enough to eat,but maybe overkill.Global warming of the epoxy mix to lower viscosity is good.Large batches are a different ballgame.A one gallon mix of epoxy will get hot and thin on its own.Prototype small batches require added heat.Large pours will produce their own heat.You are right about zero cps,but difficult to acheive in resins.I am jealous I have no time for E/G experiments.Addictating is'it not :cheers: .I feel bad having a vacuum pump and large paint pot and no time to experiment.Summer is my only busy time,so experimental stuff has to wait untill the fall.Also small batches of epoxy/aggregates is subject to ratio error's
    Larry
    :cheers: My two beers worth.
    L GALILEO THE EPOXY SURFACE PLATE IS FLAT

  3. #1543
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    Here's what i've been thinking about as far as vacuum.



    Take all the crap off the lid and attach a rotary joint on a piece of tubing and maybe leave a vacuum gage.
    If you go to "McMaster-Carr" or "MSC Industrial" and search for rotating joint or rotary joint,you will find many to choose from.
    Not all rotary joints for oil pressure will seal for vacuum.Oil is much easier to seal than air and some hydraulic seals rely on the oil pressure to seal properly.But the good news is,there are some rated for vacuum.
    On the bottom side,attach a ball valve on a piece of pipe to be used as a way to release the epoxy into the pot.
    The inside will need some kind of vane running down the side for mixing...i guess you could epoxy an alluminum vane to the inside
    The two pipes on either end will serve as an axle to turn the pot as well as vacuum, and a way to release the epoxy into the vacuum.
    The rest is just making a simple frame to rest the axles on and be able to turn the pot upright for filling.
    Cleaning it should be a chore:stickpoke

    The one thing i stumped on is the fly in the honey thing....thats a problem.


    RTM must be used by companies that make E/G..I'm assuming thats why they say using granite as an aggregate creates a flow problem.

  4. #1544
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    Mazaholic from Epoxyaholic.
    Get rid of all the crap on the lid?No No.Pictured is an air motor on top driving a slow speed mixer.Perfect for mixing in a vacuum.
    Larry
    Adamant,Cleaning it should be a chore

    The one thing i stumped on is the fly in the honey thing....thats a problem.
    5gal plastic pail fits 10 gal pot and is disposable.
    I hate flys in the honey on my morning toast,perhaps a surfacant or wetting agent sprayed on the flyes would solve the problem.
    L GALILEO THE EPOXY SURFACE PLATE IS FLAT

  5. #1545
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    Wow!
    I didn't even notice...I just grabed the picture off the net for a visual.
    That makes the design even easier.I'm not much on painting,i know what a paint pot is, but not all the varieties.

  6. #1546
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    de Larrard's Paper

    Wow :banana:

    Looks like Larry and Mazaholic are kicking some serious ... on getting deaired mixing accomplished.

    Walter on the other hand has just provided us with a paper that explains how to make mixtures and predict their viscosities, packing densities and strengths.

    Locating the paper below is Walter's success, not mine, he PM'ed it to me instead of posting it and didn't post it when I said it looked awesome. This is a paper by the same guy who wrote the book on concrete properties I just bought and am waiting for.

    <A href="http://fire.nist.gov/bfrlpubs/build98/PDF/b98023.pdf"> link to pdf of de Larrard's paper from NIST</A>

    It's got some incredibly interesting equations in it that predict the viscosity and strength and the packing density according to the particle sizes for regular concrete but in general form such that they ought to work for E/G if we plug in the right numbers. There is a bunch of data on the properties of dry mixtures correlated with the equations. The data show that the models will work just fine for our purposes. Anybody who wants to read de Larrard's book but doesn't want to spend the money should read this paper!!!! I'm not done reading it yet but as an aside, it shows that the yield strength of the regular concretes is best with silica fume!!!!!!

    I've absolutely got to go to bed now but maybe some of our friends in more convenient time zones will see this and say more. :tired:

    --Cameron

  7. #1547
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    Wow Larry, that changes everything. My only complain is about viscosity- I did away with heating and was left with lava like substance- at 20% epoxy. I think everyone knows that 20% epoxy is way to high and bad for your wallet. If I can't work it at 20%, how am I going to get it down to 15%?

    I totally overlooked the self heating feature. And I do remember leaving 1/2 quart of epoxy in the pot and seeing that thing smoking.. I should test some large batches.

    Now about the fly in the honey effect. Like I said, it has to do with viscosity. Lets take sand for example, and you are wetting it with water. Rising and lowering water content will change the...water content ((chair)) but the sand will be easily workable (throughout the water content ).

    Ok, a better visual example. Put the sand in the glass and add water. All the way to 50% or more. Press compaction or vibrocompaction will make the sand settle down and form thick solid brick. Not the case with high viscosity matrix- the sand will be suspended like fly in the honey and everything will just jell-o around. Hope you get the picture...
    Water viscosity is 1, antifreeze is 20 and my epoxy is 600. It's still very low viscosity epoxy, nonetheless.

    I was always using heat so getting to 15% was not a problem. Heat lowers viscosity.
    Not this time. I was pouring column of my tiny benchtop drill and didn't heat anything. I mixed epoxy/hardener and added 20% of Zeeospheres. They provide great flow and seem to help de-bubble epoxy. Then added 40- 50% of large 5-15mm quartz. Then 10-15% of very fine silica (40micron with aver particle size 2.9micron). It did thicken the mix but not much. So I grabbed the 0.5-1.0mm sand. I was adding sand and mixing at the same time. The mix was workable, somewhat workable and then it stopped.

    Point is that this mix wasn't dry- I've done under 10% mixes and I know dry mixes. This was very wet mix, I say 20% or more and I couldn't move the stick. I should probably mention that the mix had almost zero flow..

    btw,
    RTM E/G casting is done with water like resins introduced from the bottom of a mold- no air bubbles.


    Thanks for posting it Cameron. I was going to post it but.. I lost it.
    _

  8. #1548
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    Quote Originally Posted by ckelloug View Post
    Greybeard,

    I'd think about using water instead of weights in you Mk2 jig. Everybody can measure water but weight takes a scale. You need to go all of the way to failure to find flexural strength while you only need a regular set of weights vs. displacements to find flexural modulus. I'm a bit vague form the diagram about how the needle suspension of the mirror and the adjustments work.
    Good point. Perhaps the Mark 3 will have a plastic measuring jug on the beam.

    The beam has a flat end(might be a piece of glass glued on) and the needle is held horizontally against it by the flat leaf spring. At one end of the needle, a small mirror is glued to the needle. As the beam is deflected downwards, the needle rolls and turns the mirror.
    It's a device I've used for small deflection measurements before, and works a treat.
    The zeroing screw allows you to fine tune the angle of the mirror.
    Once you have placed the sample in position, drop the beam on to it.
    The leaf spring is then eased away from the beam, and the needle/mirror placed in position. It's roughly positioned by hand, then the reflected laser spot can be "zeroed" with the screw.


    Quote Originally Posted by ckelloug View Post
    As for the bubble in a vacuum question, like many of your questions it sounds simple but it isn't. These are the questions we learn from as I have from all of your other questions......

    I would assume that to first order, you could model the vacuum contribution initially as 14.7psi of pressure equating to a force on a circle the same diameter of the bubble creating an upward force opposed by the weight of the bubble and the weight of the epoxy above it.
    Yes, this was all I was looking for, because I did the calculation just like that.
    Have I made a mistake here ?
    I was considering the case before the air was removed, and took the air pressure to be exerting a force downwards on the bubble proportionate to its diameter.

    EDIT
    I now realize that as this figure is far greater than the buoyancy figure, all bubbles should sink. (chair) ...Help :drowning:


    When I multiplied the buoyancy of the bubble (ie the volume of the bubble times the density of the epoxy) by the 60G gravity the spinning gave me, it didn't amount to anything like the air pressure component opposing it.
    Yes of course it helps, but I was expecting the spinning to produce a force an order of magnitude greater than the air pressure.


    Quote Originally Posted by ckelloug View Post
    All I can say is that I think I'd rather have something under vacuum even with the morass I see above than 5kg of epoxy granite spinning at 600 rpms. The latter should make some nice molded in place architectural molding however.
    --Cameron
    OK, so now, trying to turn(sorry) a problem into an opportunity, I go back to another idea of spin casting the mix inside plastic pipes, and taking a space frame approach to the machine structure.

    Pack the wettish mix into plastic pipe and spin it around its long axis till pre-cured. This, when pushed out of the pipe (could be round or square I suppose), will produce a beam that has air/excess epoxy along the central, neutral axis. I'm not sure how a mixed aggregate will behave, if there will be any exchange of particle distribution, but I think it will give a skin effect of highest density on the outside. Useful ?
    It wouldn't take too much ingenuity to fix inserts in place either.

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

  9. #1549
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    John and Geof,

    You might be onto something with the spincasting. When Geof said it, I harkened back to a Discovery channel program on spin casting concrete pipes the size of my office. Too big. Rather than trying to spin the mold, a spincasting head spinning at umpteen bajillion RPM's would work well since for a gantry, since it needs to be hollow anyway since the central portion carries no load and from my calculations adds so much weight as to needlessly increase deflection.

    In highschool a long time ago when I got to do some work in a college biology lab we used an ultracentrifuge which spun (for argument since my memory isn't that good) we'll say 50 ml samples at 30,000 rpm when we needed to settle something awful. Since the opposing forces to the deairing are most acute in deep beakers of epoxy, spin casting will likely work well as the layer deposited per amount of time is pretty thin.

    As long as the voids in the resultant part are smaller than the griffith size for the design load and the epoxy is fully whetting the particles, the voids don't matter as long as they don't coalesce around the aggregate particles and make what I've been calling type 2 voids that disconnects th aggregate from the epoxy and leave it rattling around in the bubble to be a bit metaphorical.

    One would likely have to use a very thixotropic mixture with some bizarre additives and do the piece in several spins so that it could at least gel at some thickness before the next spin and layer, otherwise, it will likely drip or run off of the mould. (A thixotrope is the correct name for a substance whose viscosity decrease under shear).

    I like this for a production method because epoxy droplets flying at high speed have enough energy when they hit the mould to cause them to flow fully before they set up and won't move.

  10. #1550
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    Quote Originally Posted by walter View Post
    I was always using heat so getting to 15% was not a problem. Heat lowers viscosity.
    Not this time. I was pouring column of my tiny benchtop drill and didn't heat anything. I mixed epoxy/hardener and added 20% of Zeeospheres. They provide great flow and seem to help de-bubble epoxy. Then added 40- 50% of large 5-15mm quartz. Then 10-15% of very fine silica (40micron with aver particle size 2.9micron). It did thicken the mix but not much. So I grabbed the 0.5-1.0mm sand. I was adding sand and mixing at the same time. The mix was workable, somewhat workable and then it stopped.

    _
    Teacher, Teacher,

    I think I know the answer to that one. As the particle size gets below 30 um according to my understanding of the Gamski/Gupta model, the amount of epoxy needed to wet this goes to incredible amounts. The last best theory I had said that 30um was the minimum size of aggregate before this effect would either wreck the material strength or require too much epoxy to be a good thing. So you're telling me that the 3um stuff not only ruins the epoxy fraction like I thought but it also completely trashes the mixture Rheology.

    According to my best aggregate theories from a while back, the correct solution to this problem is to skip that fine silica flour with the 3um average size altogether. You can get any packing density you need with random larger particles. Cap the whole thing off with silyated silica fume (which is much smaller) to dispersion harden the matrix and this is closer to what you want.

    Thanks for the writeup. This has been interesting and helpful.

    --Cameron

  11. #1551
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    Walter,I guess you know you still need some heat with the small batches.On your last mix which was wet and stopped,is it possible the aggregates locked on to each other as in vibratory compactation?
    I have been searching forever for thinner epoxy withought much luck.Have found epoxy as low as 100cps but extremely fast.Thinking back,Reichold was to contact Cameron.I guess it did not happen.If they do contact Cameron,perhaps he would ask of 100cps epoxy or lower viscosity.
    Back to the stopped mix.Is it possible a high percentage of larger aggregate gets to heavy to stir manually?
    I think it is a little early to experiment with larger batches.
    Larry
    L GALILEO THE EPOXY SURFACE PLATE IS FLAT

  12. #1552
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    .

  14. #1554
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    Fumed silica,Silicon dioxide:Trade names Cab-O-Sil,Aerosil etc.have rheological properties such as thixotropy which in small amounts can thicken epoxy to jello consistency or mega CPS.Cameron pointed out 2 posts ago some particle sizes require too much epoxy to wet out.Fumed silicas are in this category.
    Larry
    L GALILEO THE EPOXY SURFACE PLATE IS FLAT

  15. #1555
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    Paint pot,vacuum pot guidelines.Air motor on top good.this is a slow speed mixer.
    A mix will foam 3X the volume under vacuum.A 10 gallon pot will hold a 5 gallon pail,1.5 gallon mix should be safe not to boil over.Tank liners are available and not to costly to be disposible.wE DO NOT WANT TO CLEAN THE TANK EVERYTIME.A 10 gallon pot is not going to evacuate a huge mix,bear in mind.
    I don't have an air motor on my 10 gallon Binks but have the stirring rod and propeller,I just crank it by hand.Tanks with no agitator,agetating,but could be rotated like a concrete mixer while under vacuum.
    Are tanks popular?The tank pictured by Mazaholic is or was on E-bay.Last time I checked 23bids at 350US.
    More good lookin E-bay tanks....#290101690233 or 290101690279.
    Things to consider:A 10 gal pot is heavy,check the shipping charges.
    New tank?Won a lottery fine otherwise 1 to 2 grand.
    TANKS A LOT
    Larry
    L GALILEO THE EPOXY SURFACE PLATE IS FLAT

  16. #1556
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    Hi all,

    I just put in a sample request at 3M for some Novec 4430 and 4432 fluoro surfactants. These surfactants should cure problems that are related to the ratio of the surface energy of the aggregates to the surface energy of the epoxy. I've decided to "come clean" and get some of RancherBill's hi tech soap

    I also invited the 3M folks to participate here on the thread. I may have a bit of an edge in actually getting samples as I put my official title and work address on the request. I did tell them what we were doing and that it wasn't an official company project so I hope it either balances out or they decide to help us for good PR. Cabot was sure gracious with the samples and advice.

    Larry,

    I wanna make sure that we have the same definition of thixotrope. I am using the definion that a thixotrope is an additive that causes the mixture to get thinner under applied shear and then thicken when it is not moving. An example would be paint that flows off the brush but then doesn't run down the wall once there is no shear from the relative movement of the brush and the wall. Most of your posts have been short on the topic so I can't tell from context if you mean thixotrope or just generically thickener as both meanings would be possible.

    I guess I'll have to call Reichhold again in answer to your question about low viscosity epoxy. Looking through the datasheets however as do some Reichhold formulations, further Alkyl Glycidyl Ether can be added to the epoxy we have and it might approach 100cps. Datasheet attached for reference.

    I'm planning on looking into surfactants first as I think surface energy is more of a problem specifically than viscosity although lower viscosity usually lowers surface energy. The epoxy chemistry isn't as good with too much 37-058 so I'd like to believe that surfactants and bonding agents well let us continue on with the epoxy we have.

    At any rate, in terms of the overall mix design, I believe that it makes sense to leave out the aggregate between 1um and up to about 60um because of Gupta's idea that aggregate particles must be wet by a 30um epoxy layer. Walter's test showing the horrid rheology of such a mixture pretty much cinches it for me that 1-60um aggregate is bad.

    I do have decent evidence from papers and books that some amount of silica fume or carbon black will provide a mix that dries with a much higher modulus than a mix that contains no sub micrometer fraction. This is borne out in PC concrete in that de Larrard paper Walter found recently. It may be worth reducing the small aggregate further leave more "bad rheology budget" for the effect of the submicron particles which help optimize the overall modulus of the material due to dispersion hardening. It's also worth noting that silyated silica fume claims to have relatively small rheological effects according to the cabot data sheet.

    My first planned experiment is to examine the effect of carefully weighed portions of carbon black added to carefully weighed portions of epoxy. If 3M comes through with some novec then I'll see if the rheology is the same with the carbon black and the surfactant as without the surfactant. I really want to see how the Reichhold aggregate design does with and without the novec.

    --Cameron
    <I>Bring me a new E/G material and epoxy will invent a new material property to avoid sticking to it.</I>
    Attached Files Attached Files

  17. #1557
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    Tanks Larry

    I'm going to hit up some of the flea markets in my area.
    I see those things sometimes when i'm looking for other stuff for ideas.Funny thing,now that i'm looking for one,i probably won't find one.

  18. #1558
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    Cameron.
    That would be great if we could get some input from the professional epoxy gurus.
    Nice work!

  19. #1559
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    Cam I have been short{5'/7"} on the posts as to me it is a non issue.Walter already has problems with mixes being too thick.Fumed silicates will add to the problem.You are 100 and 2 % right.Quote"
    I wanna make sure that we have the same definition of thixotrope. I am using the definion that a thixotrope is an additive that causes the mixture to get thinner under applied shear and then thicken when it is not moving. An example would be paint that flows off the brush but then doesn't run down the wall once there is no shear from the relative movement of the brush and the wall. Most of your posts have been short on the topic so I can't tell from context if you mean thixotrope or just generically thickener as both meanings would be possible.
    Copy
    "Fumed silica has a chain-like particle morphology. In liquids, the chains bond together via weak hydrogen bonds forming a three dimensional network, trapping liquid and effectively increasing the viscosity. The effect of the fumed silica can be negated by the application of a shear force (e.g. mixing, brushing, spraying etc), allowing the liquid to flow, level out and permit the escape of entrapped air. However, when the force is removed, the liquid will ‘thicken up’ again. This property is called thixotropy."
    I use thixotropic paints,True they thin under shear or mixing but the stir marks remain on the surface after mixing,These mixes are not pourable as of jello like consisanty.I spray these mixes to acheive textured coatings on professional loudspeaker cabinets.I have no Poissins formula or NIST papers only practical experience on using the materials,backyard formulating.Where is Andrew,He seems to understand my backyard technology.
    Larry
    L GALILEO THE EPOXY SURFACE PLATE IS FLAT

  20. #1560
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    Maz, good idea.I went to my compressor supplyer for oil and there was the 10 gallon pot for 100bucks.Apparently high pressure pumps are in Vogue and paint pots are old technology.Cheap!!Good hunting.
    Larry
    L GALILEO THE EPOXY SURFACE PLATE IS FLAT

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