|
ChrisR
|
|
|
Group: Forum Members
Posts: 363,
Visits: 3K
|
1) shrinkage is variable, use as a guide but the test is normally done without reinforcement, this reduces shrinkage hugely. 2) don't know, I don't use it 3) don't know, I never use fillers 4) if using epoxy then woven roving/woven fabric (or powder bound CSM as normal CSM doesn't work with epoxy) 5) resin dependant, I'd be looking to pot a core in to stiffen and reduce cost, if using PE then 3/4 layers tops 6) don't know, I don't do it 7) loads of joining techniques to choose from, skill dependent. easiest will be butt jointed with reinforcement backing on the B-side to join together, if you get better at it then a scarf joint will be 1000% better
|
|
|
|
|
Shinobiwan
|
|
|
Group: Forum Members
Posts: 14,
Visits: 97
|
I've been looking into this more thoroughly and I believe I can do way with the two parts joined together and instead simply go for a thicker layup on a single mould to achieve a similar result. Surface finish inside the part is irrelevant aside from cosmetic considerations and that's all I'd really be gaining from going the two part route. I do have some more questions though. - What's the shrinkage like on polyester and epoxy. Looks to me like polyester can be around 6-9%. I need to be under 1% for things to fit. Any way to improve this on polyester since epoxy is much more expensive.
- Can I use Unimold Tooling Resin for layup of parts since its cheaper than epoxy and no shrinkage unlike normal polyester resins.
- How much ATH filler is it possible to add to epoxy laminating resin in order to reduce costs?
- Which matting to use? Alternate Woven Roving and 450g CSM? Loudspeaker cabinets need stiffness and damping. Mass helps.
- What's the maximum safe thickness to laminate in one sitting? I've heard around 12mm
- Can I brush in polyester pattern coat primer in mould prior to lay up?
- Construction is a clamshell. What's the best way to glue to halves together with gelcoat at the interface.
Thanks for any advice.
|
|
|
|
|
Shinobiwan
|
|
|
Group: Forum Members
Posts: 14,
Visits: 97
|
Dimensions are approx 800mm x 550mm x 185mm. Really important question: What's the shrinkage like on Polyester, Vinylester and Epoxy laminating resins? With holes and critical parts fitting together during assembly the shrinkage really needs to be less than 1%.
|
|
|
|
|
ChrisR
|
|
|
Group: Forum Members
Posts: 363,
Visits: 3K
|
I think you need to post the dimensions of the thing including hole size etc (or pm of you don't want to make that public) if you want any specific advice.
|
|
|
|
|
Shinobiwan
|
|
|
Group: Forum Members
Posts: 14,
Visits: 97
|
ChrisR (29/12/2016)
50mm!! you're not building a submarine hull!!Overkill? OK well how best to add mass and thickness?
|
|
|
|
|
ChrisR
|
|
|
Group: Forum Members
Posts: 363,
Visits: 3K
|
50mm!! you're not building a submarine hull!!
|
|
|
|
|
Shinobiwan
|
|
|
Group: Forum Members
Posts: 14,
Visits: 97
|
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.
|
|
|
|
|
ChrisR
|
|
|
Group: Forum Members
Posts: 363,
Visits: 3K
|
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.
|
|
|
|
|
Shinobiwan
|
|
|
Group: Forum Members
Posts: 14,
Visits: 97
|
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.
|
|
|
|
|
Shinobiwan
|
|
|
Group: Forum Members
Posts: 14,
Visits: 97
|
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.
|
|
|
|