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IndustryArena Forum > Mechanical Engineering > Epoxy Granite > Mold release + EG + vibration => problems?
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  1. #1
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    Mold release + EG + vibration => problems?

    Hi,

    I've been doing some testing with mold releases. And i'm not too happy about the results i'm getting, so i'm wondering if any of you guys care to share what you do?

    I'm using laminated plywood as material for my form(example: https://www.bord.com.au/app/uploads/2019/06/Formply.jpg). I've tried applying multiple coats of proper release wax and also i've tried applying PVA on top of the wax. But when the EG "grinds" against the the mould surface during vibration i think the stones in the EG causes defects in the release-film and the epoxy starts to stick the mold...not a lot, but i fear that my rather complex 2000kg casting will cause me huge problems if i don't address this problem early on...

    What do you guys do to prevents problem during pouring and vibrating?

    /Thomas

  2. #2
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    Re: Mold release + EG + vibration => problems?

    Depending on what's available to you locally, I suggest using particle board with a melamine laminated surface. Think kitchen countertop material.

    The laminate is non-porous and is less likely than wood fibers to become scratched or dented and thus disrupt the mold release layer.

    If the partcle board laminate isn't thick enough to withstand the casting pressure, back it up with plywood.

    Or just buy the laminate material and laminate it to plywood or particle board at the thickness/strength you require.

  3. #3

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    Re: Mold release + EG + vibration => problems?

    What spumco said is a much better bet in general, but when I need to release molded parts off a slightly textured or porous surface (like a 3d print), I've had good results with the Partall Hi-Temp paste wax. On a smooth surface it's a typical wax that you buff off completely, but it also seems to work pretty well when you need to build up a thicker layer for less optimal conditions. Seems to dry harder than other waxes. For what it's worth. But getting a good release off that much surface area of plywood sounds like a chore, for sure

  4. #4
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    Re: Mold release + EG + vibration => problems?

    Hi BH - What wax were you using? and did you apply multiple coats? The usual test for a good wax coat is to use masking tape. If it sticks the wax is not thick enough. Formply is quite porous and will take many layers of wax to seal and coat it. But 2 coats of PVA release (not PVA glue!) Should be fine that's exactly what they do for concrete. If you want a polished finish you have to build up the wax and buff to a good film thickness. The PVA won't give you a polished finish but will give you an easy release. The other approach is to use a surface tissue and give the mould a coat of epoxy with the tissue this will protect the surface and give it a gloss finish on a well waxed surface! You can colour this coat as well if you wish... If you use 200gm plain weave and black resin it will look like carbon fibre!! Peter

    White melamine is airtight, I've found formply not as good under vacuum so I expect its more porous then melamine....

  5. #5
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    Re: Mold release + EG + vibration => problems?

    Hi,
    in the marine industry there is a high build polyester resin type paint that you can spray(preferably), or brush on, and it dries quite hard and can be rubbed smooth (with wet and dry) and polished
    to a high degree. Its used to make fibreglass molds and is presents a perfect surface for release wax and/or PVA.

    I used to buy a litre at a time from a place that made fibreglass body panels and flairs for cars, it cost 20 bucks or a box of beer. Great stuff.

    Craig

  6. #6
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    Re: Mold release + EG + vibration => problems?

    Quote Originally Posted by spumco View Post
    Depending on what's available to you locally, I suggest using particle board with a melamine laminated surface. Think kitchen countertop material.

    The laminate is non-porous and is less likely than wood fibers to become scratched or dented and thus disrupt the mold release layer.

    If the particle board laminate isn't thick enough to withstand the casting pressure, back it up with plywood.

    Or just buy the laminate material and laminate it to plywood or particle board at the thickness/strength you require.
    I've never used melamine faced chipboard for substantial epoxy castings but I have used it quite a lot for flanges when splitting moulds for composite parts with no problems whatsoever,including autoclave cured moulds.I can see no problems with casting as long as the structure is suitably rugged and well supported.Given the size of the project it would be worth a trial casting at least as deep as the intended part to prove the process.With large parts and lots of mixes is it feasible to de-gas before casting?Pretty much any normal wax should give a clean release.

  7. #7
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    Re: Mold release + EG + vibration => problems?

    Hi Routalot - Degassing lots of resin is a problem. My vacuum chamber will take a 10 litre bucket. You can only degas the top of the epoxy. The hydrostatic pressure stops it from degassing properly. You have to have a mixer in the chamber to circulate the resin. I use a paint mixer through an electrical gland and silicon oil works well.

    Commercial degassers for large quantities use a thin film approach where the resin is run over a plate in vacuum so there is effectively no depth. Another approach is to drop the resin through the vacuum in a thin stream. I have found for large quantities the best thing to do is to heat the epoxide (no added hardener!!! to about 40deg, it degasses very quick at that temp. This means you can degas a few buckets and set them aside covered. Let them cool and then add hardener when needed. Mix very gently by hand with a paint mixing stick not a power drill. Add a small amount of pigment to the mix so you know its mixed only takes a couple of minutes of easy stirring. I've used a microwave for heating epoxide. Do it on lowest setting its easy to cook the epoxide with uwaves... epoxy is a polar molecule which is exactly what uwaves like to get excited...

    Hardener is very thin and will be degassed anyway. They say the epoxide has up to 5% by volume air in it from the manufacturing stirring... Don't degas hardener you will boil off active constituents very quick and run the risk of it becoming inactive!! Then theres the issue of the aggregate its nearly impossible to mix aggregate in and not introduce air. I think you have to live with the porosity plus most recipes I've seen are too dry so porosity is a given... Unless you dry stack the mould and pour resin in until filled with a very very thin resin...Peter

  8. #8
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    Re: Mold release + EG + vibration => problems?

    Quote Originally Posted by peteeng View Post
    Hi Routalot - Degassing lots of resin is a problem. My vacuum chamber will take a 10 litre bucket. You can only degas the top of the epoxy. The hydrostatic pressure stops it from degassing properly. You have to have a mixer in the chamber to circulate the resin. I use a paint mixer through an electrical gland and silicon oil works well.

    Commercial degassers for large quantities use a thin film approach where the resin is run over a plate in vacuum so there is effectively no depth. Another approach is to drop the resin through the vacuum in a thin stream. I have found for large quantities the best thing to do is to heat the epoxide (no added hardener!!! to about 40deg, it degasses very quick at that temp. This means you can degas a few buckets and set them aside covered. Let them cool and then add hardener when needed. Mix very gently by hand with a paint mixing stick not a power drill. Add a small amount of pigment to the mix so you know its mixed only takes a couple of minutes of easy stirring. I've used a microwave for heating epoxide. Do it on lowest setting its easy to cook the epoxide with uwaves... epoxy is a polar molecule which is exactly what uwaves like to get excited...

    Hardener is very thin and will be degassed anyway. They say the epoxide has up to 5% by volume air in it from the manufacturing stirring... Don't degas hardener you will boil off active constituents very quick and run the risk of it becoming inactive!! Then theres the issue of the aggregate its nearly impossible to mix aggregate in and not introduce air. I think you have to live with the porosity plus most recipes I've seen are too dry so porosity is a given... Unless you dry stack the mould and pour resin in until filled with a very very thin resin...Peter

    Thanks for that,I've only cast epoxy in batches of 2Kg or so and the degassing was done after mixing.No problems with those mixes.I can understand why a mix with aggregate would be problematic.Given the cost of epoxy I must admit to wondering if there is an opportunity for somebody to supply hobby size iron castings for home finishing and assembly.Most urban centres would have a machine shop with the capacity to skim a few surfaces flat and I would hope a keen hobbyist could drill a few holes....

  9. #9
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    Re: Mold release + EG + vibration => problems?

    Hi Routalot and others - I think hobbyists will move towards UHPC or CSA Grout. A just add water solution is better than sourcing all the components doing all the trials then ending up with a material that is not specified. Buy CSA grout - fully specified half the cost of EG unless you get the aggregate for free and its 30-35GPa out of the bag and its designed to de-air (concrete people talk about de-airing not de-gassing) . If you use sand, gravel and epoxy its tough to get past 35GPa modulus. Badhabit have you thought about concrete? Peter

    https://durcrete.de/

  10. #10
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    Re: Mold release + EG + vibration => problems?

    Hi all,

    Thanks for all the replies.

    I did some more testing a couple of days ago. And i think i'll be able to release the casting from the mold with a couple of polished wax coats and a couple of PVA layers after all... i just did a couple of test-casts and they do release nice and "mirror like finish", but just stick more than i expected....It seemed like they just needs more force than i expected... I've designed the molds so i'll always will be able to pry the mold material of at some way or the other...

    In my testing of resin-to-solids ratio i found that i'm able to vibrate 10% by weight works fine and 12% will defently be easy "vibrateable".... so i'll start of with 12% and move to 10% after the first couple of batches if everything can be vibrated nicely into the first(and most detailed) part of the mold...

    I've looked a lot into the whole UHPC vs. EG debate and had to make a decision at some point and chose EG. There is pro's and con's with both approaches and some of them are IMO quite hard to quantity(e.g. recyclability or prior experience with the material). I've already ordered 2000kg of Silimix 282 and ordering around 200L of epoxy in a couple of days. The first portion of steel for inserts has already arrived and i've started preparing them for casting(drilling and tapping anchors). I'm properly going to finishing them of in the sandblaster before casting...

    /Thomas

  11. #11
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    Re: Mold release + EG + vibration => problems?

    Hi Thomas - Wax and PVA do not provide a slip- release. Wax has to be thick enough so it shears on release. Some wax stays on the mould some stays with the part. Thats how the release works. The bigger the part the harder it is to release a waxed mould. It has to be "peeled" out vs "sheared" out. To get a slip release a liquid wax or silicon has to be used. Similarly with PVA. This provides quite a grip to the surface and has to be peeled off. PVA is water soluble and if you provide a water inlet in the bottom of the mould you can use your house water to "water release" the part. Partly pressure partly the PVA dissolving. PVA is used in the marine industry as it is impermeable to gasses. A new mould that is styrene based that is not completely cured can be stuck up due to the styrene in the part permeating through the wax dissolving the wax and binding the part to the mould. In your case both can't happen. You are using ply or melamine and epoxy. If you have adequate wax on the mould then the PVA is not needed and the release will be easier. talk to a composite materials supplier and they will have waxs with various slips. Get the slipperiest wax and put lots on. Being a very thick part it has no flex so can't be peeled from the mould like thin fibreglass part are. There are paste wax and liquid wax combos that maybe more suitable for this type of job. The paste is applied, typically a new mould will require 6 or more coats of wax in my experience. Then you can use a liquid (paraffin or silicon) on top of that to make it a really slippery surface. Composite parts do not like this as they will prerelease but cast parts often use a silicon wiped on release as a cast part can't prelease.... If its a one off mould then wax up really well, can't have too much in this case and make the mould so it can be disassembled.. Good luck... Peter

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    Re: Mold release + EG + vibration => problems?

    Hi Peter,

    Thanks for the input!

    I've designed the mold to be taken apart from the outside and "bottom up" using "tabs" to interlock some parts of the mold and then a ton of screws to keep everything i place. So the plan is to flip the casting after pouring, unscrew the gazillion screws, undo all the bolts holding the anchors in place and then hopefully be able to take each piece of the mold of the casting. Each mold part is designed so i have some sort of "leverage" to get them of... I will know if it worked in about a month or so :-) I'm about halfway with the cnc cutting the mold parts on my gantry router. It takes 8 full sheets of 15mm laminated plywood and one sheet of 9mm, so quite a lot of milling...

    /Thomas

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    Re: Mold release + EG + vibration => problems?

    Hi BH - Your well on the way just keep us informed we like to know what happened to these projects! Most people don't realise that a paste wax system is designed to provide grip to the part. If the part does not stick to the mould then it can't conform to the mould and stay conformed as the part cures.... I've been involved with a few large aluminium moulds for cast PU parts and we used liquid silicon. Those things slid out as if on banana skins... Peter

    https://www.compositesworld.com/arti...release-update

    Peter

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    Re: Mold release + EG + vibration => problems?

    Quote Originally Posted by peteeng View Post
    Most people don't realise that a paste wax system is designed to provide grip to the part. If the part does not stick to the mould then it can't conform to the mould and stay conformed as the part cures.... I've been involved with a few large aluminium moulds for cast PU parts and we used liquid silicon. Those things slid out as if on banana skins...
    I haven't seen any mention of two kinds of wax...? I've been testing with this one: https://shop1.r-g.de/en/art/165160 , can you recommend any other wax for me?

    I'm not too keen on silicone-based stuff. The few times i've used it, it got EVERYWHERE....all tools, the floors, doorhandles, buttons....everywhere.... and i thought at the time i was carefull with it....i guess not :-) But it could be because i used an aerosol-based product, and not just a liquid i could paint on.... but then again, i'd need to get it off the casting afterwards.....

    /Thomas

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    Re: Mold release + EG + vibration => problems?

    Hi BH - I haven't used Partall but its a common brand and spec for low temp cure. It will be fine for the job just make sure it has enough on use the masking tape test and let every coat cure proper before the next coat.... follow the directions and it will be fine. Silicone is great but can transfer if sprayed or knocked over! Don't ask...
    I'm not sure PVA helps in your case as you are disassembling the mould and styrene transfer is not in the mix... But PVA is sort of an insurance policy if your uncertain of the process or use it in places you think maybe a bit tight to remove.... Keep us in the loop... Peter

    I like liquid waxes less elbow grease gets on the mould.... apply with rag not sprayed... plus this is good for coating nuts and bolts and various bits that you may not want to get stuck to the mould or part. Use in well ventilated place, generally uses naptha as solvent and its a bit heavy duty on the human system..

    Another suggestion is to use mylar tape. Packing tape is commonly used for one off moulds where surface finish is not important. A packaging company may have a wide sticky tape that you can apply to the surface. Then a quick wipe with wax and your done... for instance in the photo attached there is no wax involved. The timber has been wrapped with clear packing tape and the melamine has a plastic film on it... this is an epoxy infusion of steel and other fibres.. Mould is dry stacked then use vacuum to pull epoxy resin through the part. You could do this as well but keep going the way you know... That mould has been used 3 times no wax... chunk of Tetrium out of mould cleaned up in router, very little porosity due to vacuum process...
    Attached Thumbnails Attached Thumbnails liquid wax.jpg  

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    Re: Mold release + EG + vibration => problems?

    Quote Originally Posted by peteeng View Post
    Another suggestion is to use mylar tape. Packing tape is commonly used for one off moulds where surface finish is not important. A packaging company may have a wide sticky tape that you can apply to the surface. Then a quick wipe with wax and your done... for instance in the photo attached there is no wax involved. The timber has been wrapped with clear packing tape and the melamine has a plastic film on it... this is an epoxy infusion of steel and other fibres.. Mould is dry stacked then use vacuum to pull epoxy resin through the part. You could do this as well but keep going the way you know... That mould has been used 3 times no wax... chunk of Tetrium out of mould cleaned up in router, very little porosity due to vacuum process...
    I've done quite a lot of regular infusion projects and i used this sort of tape: https://www.easycomposites.co.uk/flash-release-tape it does not require any wax or anything. Epoxy just don't stick to it. It is actually quite nice tape...

    I also considered the "wrap the form"-approach, but it has quite a lot of recesses etc...it is going to be a nightmare to wrap....IF i can find "tape"/wrap wide enough.... "stacking" the tape side-by-side is to tedious for me and will most likely cause stripes in the surface...then i like to odds with the wax better...

    /Thomas

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    Re: Mold release + EG + vibration => problems?

    I have done a few molds using mdf with only wax.
    These released very well but I have only done smaller parts, that are not cast but molded in to place using drier mixes.

    But I think that the aggregate moving wax around on the surface may be a good point and I think it might be less of a problem with mdf as that will get slightly impregnated with the wax.

    Another thing I think might be overlooked is the stiffness of the mold material. The stiffer it is, the more difficult it will release because it is harder to peel.
    Here mdf may also have an advantage is it is permeable to air.
    Sven
    http://www.puresven.com/?q=building-cnc-router

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    Re: Mold release + EG + vibration => problems?

    Quote Originally Posted by badhabit View Post
    Hi Peter,

    Thanks for the input!

    I've designed the mold to be taken apart from the outside and "bottom up" using "tabs" to interlock some parts of the mold and then a ton of screws to keep everything i place. So the plan is to flip the casting after pouring, unscrew the gazillion screws, undo all the bolts holding the anchors in place and then hopefully be able to take each piece of the mold of the casting. Each mold part is designed so i have some sort of "leverage" to get them of... I will know if it worked in about a month or so :-) I'm about halfway with the cnc cutting the mold parts on my gantry router. It takes 8 full sheets of 15mm laminated plywood and one sheet of 9mm, so quite a lot of milling...

    /Thomas
    If you are using plywood then you can urethane coat to seal it this works very well ( Clear urethane ) light sand and add some more coats then you can wax it, this works really well for plywood and no sticking at all

    So I lightly sand the ply then add first coat of urethane let dry another light sand coat again up to 3 coats this seals the plywood then you can wax, I have used this without waxing for simple parts and they release without sticking

    Coating your plywood is important as the epoxy will soak into the surface this would take a lot of waxing to get it sealed without first coating the plywood with urethane or some similar coating
    Mactec54

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    Re: Mold release + EG + vibration => problems?

    Quote Originally Posted by mactec54 View Post
    If you are using plywood then you can urethane coat to seal it this works very well ( Clear urethane ) light sand and add some more coats then you can wax it, this works really well for plywood and no sticking at all

    So I lightly sand the ply then add first coat of urethane let dry another light sand coat again up to 3 coats this seals the plywood then you can wax, I have used this without waxing for simple parts and they release without sticking

    Coating your plywood is important as the epoxy will soak into the surface this would take a lot of waxing to get it sealed without first coating the plywood with urethane or some similar coating
    I'm using plywood meant for concrete forms. They looks like this:
    Attachment 458744

    The surface is already almost mirror-like...so i don't think it would help much as i think it is more an issue that the granite is scratching the release-film...

    /Thomas

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