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    Default 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.

    Attached Thumbnails Attached Thumbnails Epoxy-Granite machine bases (was Polymer concrete frame?)-al2o3-jpg  
    Last edited by peteeng; 10-30-2019 at 02:32 AM.


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    Default 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

    Attached Thumbnails Attached Thumbnails Epoxy-Granite machine bases (was Polymer concrete frame?)-zytel-43-jpg  
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    Default 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 Epoxy-Granite machine bases (was Polymer concrete frame?)-alumina-jpg   Epoxy-Granite machine bases (was Polymer concrete frame?)-alumina-2-jpg  


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    Default 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

    Attached Thumbnails Attached Thumbnails Epoxy-Granite machine bases (was Polymer concrete frame?)-tetrium-milled-jpg  


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

    Quote Originally Posted by peteeng View Post
    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
    You are having fun with this, a few years ago there was a Zone member that was casting small Z axes blocks which had an a aluminum filler which worked very well, and was strong, I don't think he used very much if any fiber as his parts machined very well

    Mactec54


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

    Hi Mactec and others - I have made moulds for things using epoxy/aluminium (Aluminum) powder in the past mainly for heat transfer characteristics. It machines very well as aluminium machines well. My aim with Tetrium is to maximise its stiffness and be machinable. If the part is not to be post machined then using the Al2O3 (Alumina) is the go as it has the potential to be very stiff and easy to make. Epoxy granite using SiO2 will get to ~35GPa and using aluminium powder will get to ~20GPa. My current aim is to be equal to monolithic aluminium in stiffness.

    Tetrium uses two very high stiffness fibres (vs a particle) and one of these pulls out of the epoxy vs cuts as far as I can see under magnification. This roughens the surface. Does not affect its performance, a wipe with epoxy or paint it will fix that. The fibres parallel to the cut do cut. The next block aim is to maximise density, then the next, next block will be made to test its modulus. I have discussed testing its dampness at a Uni lab and initially they wanted $33000AUD and 60 test samples. I talked them down to a one test sample and $600.... So I'd like to know its damping factor. I'm sure "as it is" it will make very good damp parts. I want to get into the mill design asap and I need to settle on a std formula and know its stiffness to do this.

    Unfortunately I have not been able to get my resin of choice. It's a Reichhold tooling resin and it used to come into australia then they mixed Aluminium Trihydride powder with it here. I used to get pails of it without filler. They now bring it in premixed and are unwilling to bring it in unmixed. So I have to use an epoxy which is a bit thicker then the Polylite resin. I may have a look at acrylics and have been looking for a suitable phenolic for years.

    For your interest - Many things can be infused or embedded in epoxy including plastination of body parts see https://fasciaresearchsociety.org/plastination Cheers Peter



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

    Obivan - These guys get good epoxy in Russia. Peter ??????? - positive couple



    https://ecovanna.ru/



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

    Hi All - That Russian casting epoxy looks fantastic. Very thin and clear, no bubbles and can cast up to 100mm thick!. Which means with a filler probably no limit to part thickness. Perfect for epoxy alumina or EG. I'll send them a note and see if I can get it sent to Oz. I'm setting up a 200x200x40mm billet of Tetrium. The aim with this billet is to maximise the fibre density. So since I know the volume I shall calculate the weight of fibres required to achieve 50% volume fraction. Then I shall try to squeeze that amount into the mould. Usually with carbon fibres and glass fibres or sand this is easy. But the high stiffness fibre I have is slightly curly so does not pack well. Once I figure the max pack I shall freeze the formula and then do the mechanical testing. Then I can start designing the Mill. Keep Making - Peter



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

    Hi Alll - I made a block of Tetrium yesterday 200x200x40mm thick. Turned out not as dense as I want but for now I think it's as best I can do in my garage. Also didn't get the vacuum down as far as I liked. When I tested the system I got down to 200Pa but the job only got to 1200Pa. I'll have to make make better fixtures and get a press to consolidate the dry stack better. But it's good enough for parts. This block is being sent to a friend who will make motor mounts out of it as a test. So short list is; make a metal flat mould/table with vacuum clamp and make the block for modulus testing. This block weighs 3.4kg and has a density of 2200kg/m3...By the way the fibres are black so close to what Mr Ford said, "You can have any colour you like as long as its black"...Cheers Peter

    Attached Thumbnails Attached Thumbnails Epoxy-Granite machine bases (was Polymer concrete frame?)-tetrium-block-2-1-jpg   Epoxy-Granite machine bases (was Polymer concrete frame?)-tetrium-block-2-3-jpg  


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

    Quote Originally Posted by peteeng View Post
    Hi Alll - I made a block of Tetrium yesterday 200x200x40mm thick. Turned out not as dense as I want but for now I think it's as best I can do in my garage. Also didn't get the vacuum down as far as I liked. When I tested the system I got down to 200Pa but the job only got to 1200Pa. I'll have to make make better fixtures and get a press to consolidate the dry stack better. But it's good enough for parts. This block is being sent to a friend who will make motor mounts out of it as a test. So short list is; make a metal flat mould/table with vacuum clamp and make the block for modulus testing. This block weighs 3.4kg and has a density of 2200kg/m3...By the way the fibres are black so close to what Mr Ford said, "You can have any colour you like as long as its black"...Cheers Peter
    What was in your complete mixture and is it cost effective I'm interested in doing some parts like this as well, I have some very good 2 stage vacuum pumps and can make any kind of molds

    Mactec54


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

    Hi Martec - As I want to commercialise this product I can't say exactly yet but it's mainly a metal fibre. There are a couple of metal fibre makers in europe and I'm sure in the USA as well. If you are to make parts for yourself then look up "infusion" processes for composites. Parts for yourself would be better to use carbon fibre or glass fibre. For instance if you used a quadraxial stack of glass you will get better properties then epoxy granite and glass is easy to infuse. CF is tricky to infuse in thick sections. You can make glass blocks and post machine or make one off simple moulds from MDF or ideally aluminum for production parts. If you use a quadaxial stack of CF then you are at 65GPa which is close to aluminium. F1 teams call this black aluminium. My aim is a product that can be made in large billets and sold like metal that routers can machine easily. Slightly different objective then making parts for yourself. Sounds simple make a mould, put it under vacuum and suck some resin in but as usually easier said then done. But it all can be figured out. Regards Peter

    If I where to make parts for myself I'd do them as glass fibre stack then post machine or make a mould and infuse. Much easier. Yes Tetrium is economical compared to billet aluminium a long as I can get the volume to get the fibre at the right price. The usual commercialisation hurdle. Need volume to make it work but at start up how do you do that? Its tempting to use very low pressures but if you go really low you will pull out constituents of the resin hardener and it may not go off! So an ideal pressure is around 500-600Pa this minimises the air volume in the part, and burns off the water in the constituents. You will need a resin trap and if you do make one that has a glass or acrylic port so you can see whats going on inside. This way you can put a hardener in there under process pressure and see if its outgassing. If not all good. If its giving off vapours then increase to find out at what pressure it does not outgas, that's your bottom process pressure for that hardener.

    Last edited by peteeng; 11-10-2019 at 03:21 AM.


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

    Hi All- To summarise my research and practicum so far on EG:

    One off parts or small run with finish machining on routers and mills
    This means ceramics are out. So use aluminium powder, metal fibes, glass fibres or carbon fibres as all of these are readily available. If you can use vacuum infusion processes then you will achieve very low porosity and if you use the vacuum for consolidation pressure you will achieve high reinforcement volume ratios. Convert your weights to volumes as just going by weights is an unreliable process as the resins and reinforcements vary in density so weight ratios can be very different for different materials. Traditional epoxy granite can be bettered in terms of stiffness by using glass fibre and carbon fibre and they machine well on routers or mills.

    The epoxy needs to be a very thin type typically used for infusion or deep clear castings. It will be a 100% solids epoxy no solvents and it will be suitable for thick sections ie its hardener will be a slow hardener not an active hardener. This is for ceramic reinforcements as well. Suitable epoxies have been discussed in prior posts. Epoxy is used because its shrinkage is very small and it produces parts with very little internal stress ie the part will not change shape over time. Other types of resins will cause the part to change shape due to their large shrinkage values.

    Multi parts requiring a mould or parts that do not require post machining
    If you commit to a mould and you do not intend to post machine the part this is the reinforcement I would choose:
    1) Alumina Al2O3 grit 300GPa about 50%-60% packing factor ~1mm particles. Typically this is a grit blasting media available in brown or white grit. Will produce a material near stiffness of aluminium. Can be drilled with a masonry drill for instance to instal inserts.
    2) Sand or Sio2 70Gpa about 50%-60% packing factor ~1mm particles will produce a material same as traditional epoxy granite or better

    The optimal grading theory using 3 or 4 or 5 sizes of particles has been thrown out. This is a hangover from concrete that uses large rocks that have large gaps. You may get small pockets of good interspersion but generally its all compromised by viscosity and improper settling.

    Use a single small diameter grit and you will get a better pack and a better result. Use a very thin epoxy. Traditional hand layup epoxies are too thick to penetrate, too thick to flow, too thick to degas, too thick to mix & did I say too thick?just too thick! for many reasons...

    Using moulds
    Moulds require a space to be packed and this is the most difficult issue in producing moulded shapes. Therefore the particle approach is best as they pack easily and with a bit of tamping will pack even better. Long fibre or fabric cloth can be difficult or impossible to pack into certain shapes. Therefore again particles are good. Moulding using alumina for instance means you could mould in fastener threads, or thread inserts or blank bits of metal for post machining. Moulds would be net shape and you can premake the slurry and pour in or pack it dry and use vacuum to fill the part.

    Anything else I should add? Please ask. Peter



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