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Shinobiwan
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Hi everyone. First off thanks to everyone on here. I've read a lot of interesting threads and have learnt a lot. I've got a project going on right now where I need to cast multiples of a large piece. The volume of the pattern is 37ltrs which is around 41kg of resin with no filler. I've worked out the split lines on the mould and I think these will work well given the shape. All surfaces have a draft of 6 degree's and any parallel sides are on the split lines. If anyone can take a quick look over the attached image and just make sure I haven't made any glaring errors. My question is how to cast such a large piece. I'll be using ATH filler in a quantity of 1:1 ie. 1 part ATH to 1 part mixed resin. - Will this allow to mix a few batches of resin and pour this in to the mould before the whole thing sets?
- What's the maximum safe amount of resin/ATH amount to mix in one container? Any idea on pot life?
- What's the best choice of resin? EC sell xencast P6 which I plan if suitable.
- Can I do an in-mould coating of pattern coat primer to provide a surface that will accept paint straight out of the mould?
Thanks for any help.
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Fasta
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I did a few large castings a while ago that was about 8kg resin. I used a specific casting polyurethane resin from Axon and it all went well.
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Shinobiwan
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Nice work there! You have me a little worried since you classify 8kg as large. The one's I'm looking to do are 41kg of resin assuming a density of 1.1g/cm3.
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Fasta
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For me any resin with more than 1kg is large as you likely have to consider resin exotherm due to the volume and heat. I sourced this polyurethane as it was specifically for mass casting.
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Hanaldo
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I would be extremely amazed if there is any thermoset resin system out there that can do a 40kg pour in one shot, even with filler... That is some mass. I'd wager you will need to do it in multiple pours.
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ChrisR
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- Will this allow to mix a few batches of resin and pour this in to the mould before the whole thing sets? With anything, test first but you are more likely to have colour differences and casting errors/fractures
- What's the maximum safe amount of resin/ATH amount to mix in one container? Any idea on pot life? - Resin dependent, but the manufacturer should be able to give you an idea. I've seen less than 1" in the bottom catch fire with a quick curing PE, I mix a maximum of 1.0kg in one hit typically with a long pot life epoxy, and 0.75kg of PE
- What's the best choice of resin? EC sell xencast P6 which I plan if suitable.
- Can I do an in-mould coating of pattern coat primer to provide a surface that will accept paint straight out of the mould?
why are you casting such a large part? Surely wet lay would be a better option, you're talking boat quantities of resin there. You'll use less expensive resin with a CSM or woven roving and you'll reduce the exotherm. Layup both sides then mould the two together in the last pass off a resin rich layer?
Any quantity of PU resin is susceptible to foaming too, it would be a shame to waste £400 of resin!!!! That would be a very expensive "teaching moment"
Looking at the datasheet, 6min pot life is nothing, you'll barely get 1/2 kilo mixed, rested/degassed and poured in that time!
If you're intent on casting such a large volume in one shot, you can get (very expensive) mixing tube machines - not sure what they are actually called but have seen them - you basically have 2-3 containers mounted on it and the machine pumps the resin/hardener/filler down to a mixing head, minimal exposure to humidity/water, essentially unlimited batch as it mixed at the nozzle.
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Shinobiwan
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Hanaldo (28/12/2016)
I would be extremely amazed if there is any thermoset resin system out there that can do a 40kg pour in one shot, even with filler... That is some mass. I'd wager you will need to do it in multiple pours. Is it OK to do multiple pours? Would the part be weakened? If I can get away with allowing the resin to set between pours then that'll make my life much easier. I was under the impression it needed to be done in one shot ie. multiple pours done before the whole casting sets.
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Shinobiwan
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ChrisR (28/12/2016)why are you casting such a large part?
Thanks for the reply. The part is half a speakers cabinet. I have some 16 of that very same mould to reproduce. The cabinets need to have a high mass and stiffness to offer the best sound. The more inert the better.
Surely wet lay would be a better option, you're talking boat quantities of resin there. You'll use less expensive resin with a CSM or woven roving and you'll reduce the exotherm. Layup both sides then mould the two together in the last pass off a resin rich layer?
The problem with wet lay is that I'd have a hard time trimming in order to bring the two mould halves together to bond them to each other. Would it be OK to remove the cured parts from the mould halves, trim them a few mm short then place them back in the mould ready to put it together and do a final pour of PU resin to bond them?
Any quantity of PU resin is susceptible to foaming too, it would be a shame to waste £400 of resin!!!! That would be a very expensive "teaching moment"
Ouch yes I agree!
Looking at the datasheet, 6min pot life is nothing, you'll barely get 1/2 kilo mixed, rested/degassed and poured in that time!
Exactly my concern. Can multiple pours with setting between be done without weakening the part. I suppose it depends on the resin used and if it adhere's well to cured resin. Btw I don't intent to degass, some small voids aren't a problem and this isn't an intricate part with fine surface detail. The finished castings will be sprayed.
If you're intent on casting such a large volume in one shot, you can get (very expensive) mixing tube machines - not sure what they are actually called but have seen them - you basically have 2-3 containers mounted on it and the machine pumps the resin/hardener/filler down to a mixing head, minimal exposure to humidity/water, essentially unlimited batch as it mixed at the nozzle.
Sadly I think unless I find a more elegant solution to just pouring a ton of resin into a large mould then this is something I'm going to have to consider. I've already got a couple of such machines bookmarked and will start making enquires on price and suitability in the new year. If we're talking a couple of thousand then I can swallow that but I fear they're more, much more.
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ChrisR
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If it's a speaker cab then forget non reinforced unless you can vac form. personally, I'd be looking at a woven roving/CSM mix with PE resin, with maybe a CF 1st layer where visible, it'll look much nicer, especially as you can get some really nice decorative finishes. or at least that for the first pull just to see how things go. You'd probably only use £50 of resin and similar in glass. The reinforcement will help with damping and strengthening the cab, plus it will make finishing easier as the edges won't be brittle. Once you've got 1 done, maybe look at an epoxy with a long pot life. I use a huntsman resin with a pot life of 2 hours (look up 5052), it's not cheap but for me it's worth it as I can take all the time I need  Also, doing a wet lay you can vac bag it after layup to consolidate a bit more, adding a peelply to the inner face will help with bonding and/or a smoother finish on the b-side.
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Shinobiwan
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Thanks again Chris I take it pouring such a large mould using resin and a lot of filler won't produce the strength required? The more I think about the more I think your offering a better way to do things. I have a couple of questions. How thick can the lay up be? I mean can I build up a thickness of 50mm or so where needed ie. driver flanges/mounting points. Whats the machinability like? I'll be throwing these back on the CNC after moulding to do the driver recesses and holes. Would it be a better idea to machine these details into the moulds and not do this secondary operation after the fact? I'll revise the mould and post back with an image to see if its suitable.
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