|
Junior
|
|
|
Group: Forum Members
Posts: 73,
Visits: 473
|
B: the coupling coat seems to be a chemical bond between the surface vinylester resin and the tooling polyester resin. So using the coupling coat without using the whole system might not make that much sense.
If this is the case I would need the coupling coat then?
|
|
|
|
|
Dravis
|
|
|
Group: Forum Members
Posts: 592,
Visits: 1.9K
|
Yes, i think you will need the coupling coat if you use the unimould gelcoat..
Unimould and Epoxy moulds also make a high temperature in-mould postcure of the parts possible.. That part has been critical in some of my projects.
"Sapere Aude"... Dare to KNOW!
The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...
103% of all people do not understand statistics...
Do not adjust our mind, theres a fault in reality :-)
|
|
|
|
|
Hanaldo
|
|
|
Group: Forum Members
Posts: 2.5K,
Visits: 28K
|
oekmont (21/04/2017)
Are you going to use the mold to produce carbon parts? The i would highly recommend to make a test sample. Because epoxy sometimes releases quite poorly from polyester molds. Even with most release agents excluding pva.
Have you guys really measured the difference between doing the main reinforcement in one shot, or doing it layer by layer? Because if the sounds to me like a good way to get an even "warpier" laminate. In polyester resins, most shrinkage happens during the solid state (reference: prof. Schürmann from the university of darmstadt). So after your first layer you've got a slightly warped laminate, caused by the shrinkage of the resin. After that you apply the next layer. This cures until the resin becomes solid, without warping the pice further, because the resin will flow in a way wich compensates the shrinkage. But after that the resin of your second layer will shrink even more, now unable to flow any more, bending your mold in the same direction as the first layer did. Ever new layer will warp your mold even further. Compared to that, applying all layers at once will result in the same linear shrinkage, but will not warp the part that much. Never tried layer by layer, but in theory it doesn't sound like an good idea to me. At least with regular polyester.This is largely accurate, however with GP resin you need to control the exotherm. Filled tooling resins like the Unimould tooling resin are formulated to require a certain minimum thickness so that they can exotherm and 'bake' themselves at 60 degrees to achieve their full properties. Regular GP resins aren't designed like that, and so the thicker you build them the more heat they generate and the more uncontrolled the rate of shrinkage. By allowing it to cure layer by layer, you allow the heat to dissipate and so don't get that uncontrollable shrinkage. Yes, you will still get shrinkage in the solid state - this is the advantage of tooling resins vs GP resins.
|
|
|
|
|
Junior
|
|
|
Group: Forum Members
Posts: 73,
Visits: 473
|
So what would you guys recommend as a cheaper 'hobby' alternative?
|
|
|
|
|
Hanaldo
|
|
|
Group: Forum Members
Posts: 2.5K,
Visits: 28K
|
GP resin is fine mate, it is the cheaper alternative. Hell, even some big companies still build tools with polyester laminating resin. It just isn't quite as good, but you get what you pay for. You will still be able to produce a very useable mould.
|
|
|
|
|
Junior
|
|
|
Group: Forum Members
Posts: 73,
Visits: 473
|
GP resin is fine mate, it is the cheaper alternative What about the gelcoat/coupling coat?
|
|
|
|
|
Hanaldo
|
|
|
Group: Forum Members
Posts: 2.5K,
Visits: 28K
|
Junior (21/04/2017)
GP resin is fine mate, it is the cheaper alternative What about the gelcoat/coupling coat? GP resin will bond ok to vinyl ester gelcoat, so you can use that. The reason the coupling coat is there is that mineral filled resins tend to trap voids behind the gelcoat, so you can't use the Unimould tooling resin directly behind the gelcoat. The coupling coat is also a vinyl ester laminating resin so it will shrink less and print less. You can also use a regular vinyl ester laminating resin rather than a coupling coat. Coupling coats are considered a 'premium' laminating resin, so they are better but a bit more expensive. A regular vinyl ester would be better than a regular polyester if you can stretch the budget.
|
|
|
|
|
oekmont
|
|
|
Group: Forum Members
Posts: 550,
Visits: 27K
|
I would say it depends:
If you are making a large part (the absolute shrinks depends on the mold size) with critical tolerance in straightness or critical joints to other parts (like a car hood) you might need the extra tooling resin to get a good result. Depends on your demands on an even clearance between the body panels.
Smaller, or less demanding parts will turn out fine.
The time saving aspect of the tooling resin might be very small in comparison to the overall amount of work you've got to do for a large mold. Regular polyester resin reacts quite fast. Multiple layers per day should be possible
|
|
|
|
|
Junior
|
|
|
Group: Forum Members
Posts: 73,
Visits: 473
|
The moulds will be used to make two halves of a kayak that will be joined together with composite tape.
|
|
|
|
|
oekmont
|
|
|
Group: Forum Members
Posts: 550,
Visits: 27K
|
As you can correct the inaccuracies during the final bonding process this might work well with regular resin. As long as you are building grp hulls, you might just use regular Gelcoat for your molds as well. When doing crp you should use a polyester based gel coat like the stuff from easycomposites to avoid the epoxy/polyester problem. And you should try grp first to check if everything fits nicely
|
|
|
|