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IndustryArena Forum > Mechanical Engineering > Epoxy Granite > Epoxy-Granite machine bases (was Polymer concrete frame?)
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  1. #4941
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    Apr 2008
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi guys, i have been following this thread for quite some time now.
    Now i'll actively join as i'm planing to make EG cnc machine.
    I have found local supplier of quartz sand of different granulation.
    All aggregates are 100% washed and flame dried.

    For now i have 4 aggregates

    quartz sand 1,0-3,0mm 2.2€/25kg
    quartz sand 0,9-1,4mm 2.2€/25kg
    quartz sand 0,4-0,9mm 2.2€/25kg
    quartz sand 0,063-1,0mm 2.2€/25kg

    Do i need some with more bigger granules for optimal mix ?
    I have also found locally some flours but they are expensive except limestone, but i dont know if that is good or not.

    Limestone flour 4,63 € /20kg
    Quartz flour 6,83 €/kg
    marble flour 3,78 €/kg

    Which one of flours is best to use, can i make EG without one?

  2. #4942
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Lukahr - I think the epoxy you use is the key vs the mix. I think people are overthinking the solids and not paying attention to the epoxy. I'd use a fine sand with a very thin epoxy (see prior posts) . If you use a std laminating epoxy the relatively high viscosity stops the particles from compacting, in fact the thixotropes used in these resins are designed to stop the resin flowing exactly what you don't want in this application.

    This is why they use a graded approach to the fill. This is an historical hangover from using concrete which is very thick and they start with a large fill size which has large gaps. 1mm sand does not have large gaps (the gap is less then 0.1mm when close packed) . If you use a very thin epoxy (no thickeners) that allows the fill to pack then you just use a single fine sand. It will pack very well. To throw something at you. Granite is difficult to machine on std equipment. Look for some aluminium powder. Granite and aluminium have the same stiffness. If you make an epoxy/aluminium powder mix you can then drill, thread and mill the result on std machinery. It will be as damp as the granite as its the epoxy and the multi interface that is responsible for dampness. It will also be the same density as granite and Al are same density. I've made lots of it in the past for moulds for its heat transferability but it would be excellent in this application. Cheers Peter

    Our range of Aluminum powders and flakes - Australian Metal Powders Supplies - AMPS

    Hi Lukahr - I called AMP and I can buy the aluminium 1mm size for 15 euro per kg. So I expect you can get it there for similar. I think aluminium powder is the go. I can get 5mm pellets for less as well but the powder will pack better. if you use 1mm sand or aluminium then you need less then 150micron to fit the gap. So a two part system in aluminium that I can get is 1000um and 60um this would pack really well. This will cost less then the sand system and you can machine it afterwards...

  3. #4943
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    127

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

    I was planing to use this epoxy EPOX 210. datasheet in attachment.
    But now from looking technical data i see that working time is only 11 minutes with 200g
    This one will become thick - jelly too quick probably.
    Attached Files Attached Files

  4. #4944
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Lukahr - On another thread someone in europe (bolgaria) is using Sika biresin CR83 infusion epoxy. Try for that. Over 1hr gel time very low viscosity, can get 300min gel if you want. Peter
    Attached Files Attached Files

  5. #4945
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    127

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

    Quote Originally Posted by peteeng View Post
    Hi Lukahr - On another thread someone in europe (bolgaria) is using Sika biresin CR83 infusion epoxy. Try for that. Over 1hr gel time very low viscosity, can get 300min gel if you want. Peter
    Ok Sika is also company here in Slovenia, i have checked and they have this resin Biresin_CR83 price is cca. 10€ per kg.

    I'm playing with this excel sheet for aggregate mixture but now i'm wondering should i input largest size of aggregate or smallest if my aggregate is 1-3mm.
    Should i input in grain size 1mm or 3mm ?

    Click image for larger version. 

Name:	EG calculation.jpg 
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  6. #4946
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Lukahr - If you use a small grain size say <1mm then I don't think you need to use a graded approach. Earlier calculations and experience says you are going to achieve a very high packing factor. Just get the most economical aggregate. Are you considering aluminium? The thin epoxy is going to infiltrate very nicely. Peter

    edit - I think 8% is too dry see earlier calculations. I also think that 3mm then 1.4mm is not enough step down. See dwg attached prior. if 3mm grain then next size needs to be 0.45mm or smaller. Cheers Peter

    to check your required resin ratio get a container of known volume place on scale and zero pack in your mixture dry, now you know the volume and weight, then fill with water and weigh. Now you know the resin weight to fill the gaps.

  7. #4947
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Lukahr and others - See attached article on concrete aggregate grading I've just found. It states that the idea of an ideal grading has now been abandoned! So have a read and reconsider. Peter

    edit - in summary they have a coarse and a fine. The fine has to be less then 1/10th the size of the coarse. Cheers

  8. #4948
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    I’ll check this and if there is not nessesary to use diferent aggregates ill go with cheaper one that is suitable.

    Im looking into aluminium powders but prices are very high from what i have found.
    I have Found gradings
    Alu 0-0.2mm
    Alu 0.5-1.4mm
    Alu 0.3-0.6mm
    Alu 0.1-0.6mm

    Price is same for all 22€/kg
    Quartz sand is cca 2.5€/25 kg so this is not really comparable regarding price for me


    Sent from my iPhone using Tapatalk

  9. #4949
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    127

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

    Today i have tried mix one random sample.
    I have taken 400g of sand from kids sandbox (inside is sand 0-0.5mm and 0.9-1.2mm) and mixed with 45g of epoxy.
    It was extremely sandy and thick almost like it is not enough epoxy. A have press it into plastic cup without vibrations.

    After EG has hardened i have taken it ouf of jar and tried to break it. I did suceed but it did take some beating.
    But this sample to me it looks to much sandy not enough of connecting epoxy fluid.



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  10. #4950
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Lukahr - How did you decide the resin weight to add? and what resin did you use? Yes it is dry. Are you going to put it back in the sandbox? I've attached a spreadsheet to help. You probably need about 80-90g of resin. You had 10% by weight resin you need about 15-18% depends on sand density and resin density...Peter

  11. #4951
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Lukahr - I built a cad model of hex close pack. The large spheres are 1mm and the small is 0.22mm to snug in. So I expect a <0.2x ratio is ok for coarse/fine. The Keohler article says <0.1x so they do not interact. One thing that can throw out the calculated ratios is the air content in the epoxy. I have degassed a lot of epoxy and there is a large amount of air in it from mixing at the factory. Estimates are from 5% to 10% by volume. The thicker the epoxy the more air in it at delivery. You can warm the epoxy to say 40-50degsC and it will settle out quite well if you don't have a vacuum pump to degas with. Do not heat if mixed!! do not heat the hardener as this has volatiles in it usually. The hardener is usually very thin and degasses naturally. By heating the resin you increase the buoyancy of the air in it and you lower the resin viscosity. This will get out the "transported" air but not the saturated gases only degassing will do that. Say there's 5% transported air then in a 1000ml mix there is 50ml of air this is quite a bit and can throw your volume calc out. So you can account for the air individually in the volume calc or make your resin a bit less dense to account for that.

    back to the hex close pack. We have 4x1mm spheres and 3x0.22mm spheres in the unit (one in the middle and 4x0.5 at the side). So 1mm is 0.524mm3 and the 0.22mm is 0.00586mm3. Coarse is 4x0.524= 2.1mm3 and fine = 3x0.00586=0.0176 so the weight ratio coarse/fine =.018/2.1=0.0086 (say 1%) this is where I feel its not worth the effort. not much space in there... So for a 1kg of sand you need 10g of fines...Its probably all ready in there in the dust!! Peter

  12. #4952
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Quote Originally Posted by peteeng View Post
    Hi Lukahr - How did you decide the resin weight to add? and what resin did you use?
    Everyone seems to use 10% +- of epoxy per weight so i just went with that
    it was just random epoxy that i had lying around, i dont know tehnical details of epoxy.
    Mix was verry dry but probably if hit with good vibrations would start moving.
    Don’t get me wrong sample was hard as rock.
    I needed all my force and multiple hits to concrete ground to break this.


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  13. #4953
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    Sep 2018
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    So i looking for true epoxy in my counry (Russia). Only Sika Biresin CR80 and Biresin LS is available. CR83 and Gurit Prime 27 its not available. May be something else good epoxy?

  14. #4954
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Obvian - The CR80 is fine. Low viscosity and a selection of hardeners. There are lower ones but 400mP.s is not bad. CR80 has less viscosity then LS as well. Peter

  15. #4955
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    The producer Biresin CR80 sika does not reveal the secret about included or not difunctional reactive dilluent. Only i know about it : bisphenol-A-(epichlorhydrin) and epoxy resin (number average molecular weight <= 700)
    1,4-bis(2,3-epoxypropoxy)butane
    So what reason so low viscosity of CR80 ( about 900 ) or Prime 27 or others.
    Dow and Hexion resin minimum viscosity is 3000-4000 without dilluent.

  16. #4956
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hello Obvian - Being an infusion resin means that the epoxy is very unlikely to have diluents or solvents as these would flash off in the process. Thin epoxies are not secret. Epoxies are a very large chemical group and you can get ones that are thin and some are thick. Traditional epoxies for laminating use medium weight base epoxies because they are more common and cheaper. Plus for laminating they add thixotropes so the resin does not run downhill on vertical surfaces very fast. Prepregs use heavy weight epoxies because they have to be hot processed and at room temp they need to be sticky and thick. So just like oils and greases epoxies are formulated at different molecular weights which result in different viscosities for different purposes. If you have technical questions ask Sika, in my experience they are very helpful in the technical area. Peter

  17. #4957
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi Lukahr and others.... On the point of addition rate of epoxy. Using the spreadsheet you can see that a flat addition rate of 10% by weight can be way too dry depending on the density of the sand you use. The density of sand can range from 2600 thru to 3800kg/m3. The addition rate is actually a volume calculation not a weight calculation. So either do the dry stack and water test to determine your required epoxy ratio, or if you know the density of the sand then you can estimate it with the spreadsheet. Looking at this sand blasting media spec you can see the sand density is 3940kg/m3 yet the bulk density is 1970kg/m3 so it comes in the bag at a volume fraction of 1970/3940= 50%. So by tamping this will get better say 60% then you can use the spreadsheet to figure out the epoxy addition if you know the epoxy density. Then you can verify that with the water addition test.... cheers Peter

    using rule of mixtures the al2O3 has a e=200GPa plus so 200*.5*.5= 50GPa this is far above any published stiffness for EG that I can find. The best is in the high 30GPa's. So I think the AL2O3 is a great way to go. If you get to 0.6 packing then its 60Gpa which is close to aluminium at 69GPa very good

    200GPa modulus of sand
    0.5 = sand volume fraction
    0.5 = efficiency of round particles in a matrix to transfer strain within the matrix.

    normal silica sand is only 69GPa stiffness so the Al2O3 is well ahead of it in this department. In fact it is the same stiffness of steel.

  18. #4958
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi All - On the point of rule of mixtures (ROM). I looked at a 43% glass zytel plastic published figures. The resin has a density of 1140kg/m3 and glass is 2550kg/m3. So I plugged these into the spreadsheet and here's the result. If I use an efficiency of 0.5 then it predicts the stiffness to be 14Gpa and the dry modulus of Z43 is ....... drumroll 14GPa so I'm happy ROM works here. The wet stiffness is 11Gpa but I expect we will be in dry environments. So this makes a strong case for the AL2O3 sand even at 50% packing its still much much stiffer than any other FG out there. Cheers Peter

  19. #4959
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi All - Looking at Alumina grit the modulus of it is 200-400GPa or 300GPa average. It seems the grain is anisotropic so its stiffer in one direction then the other. But seems its average is 300GPa not 200GPa <WOW!!> so I expect the Epoxy-Alumina to be a minimum of 300*0.5*0.5= 75GPa which is stiffer than aluminium. Cheers Peter
    Attached Thumbnails Attached Thumbnails alumina 2.JPG  

  20. #4960
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    Re: Epoxy-Granite machine bases (was Polymer concrete frame?)

    Hi All - Here's a new test piece of Tetrium, facing threads and engraving. Because of the fibre reinforcement it didn't engrave wonderfully. Next I'm making a large chunk 300x300x40. Then some part moulds and parts... Peter

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