Polyester mold?

General Composites Discussions Composites Talk
#1

I’ve been watching the Fibreglast videos. I like them, but they appear to have been made approximately at the same time I graduated High School (Ragan was President), so I’m wondering if they are up to date with best practices.

Specifically, is it a standard practice to use polyester resin for molds? Keeping in mind that I want to use the Locktite semi-permanent mold release (or similar), and I will be making naked carbon fiber parts that will live their lives in the sun (so high temp UV resistant epoxy).

Thanks!

#2

Yes and no. Polyester tooling gelcoat still performs very well, so that should not be the problem.

However, the shrinkage and heat resistance of plain polyester usually leaves to be desired. Educate yourself on what is available at your favourite supplier. (there are heat resistant polyesters).

By the time Clinton realised that oral enjoyment was also classified as “sexual relations” many suppliers of polyester resins came with “rapid tooling systems” which are filled polyesters or vinylesters, and which produce near shrink free moulds, in a fast way. the trick is that you laminate 4x 1.5oz CSM in one go. The heat generated during cure expands a filler, which counterbalances the shrinkage of the resin. The one I sell in NL has a Tg of 135C (gelcoat) and 85C or 110C of the resin. This is plenty for your purpose. I am sure suppliers near you also carry these systems.

You will most likely want to postcure your products, so make sure your moulds are up to the job.

One other thing: The first 2 products: USE PVA. After that, use semi perm.

And spray your epoxy products with clear. Even UV resistant epoxy will yellow.

#3

Thanks. I don’t have a favorite supplier yet. lol The only local one I have found is Fiberglast, and they are pretty expensive, and I don’t see any infusion supplies there anyway.

So I should make my mold with epoxy then? Is that what you are saying? Or one of the new products you are talking about. I’m not exactly sure what you are saying.

Oh, and I definitely planned to put a layer of automotive clear on my stuff. But thanks for pointing it out to confirm my thoughts.

So, to be clear, use PVA on the finished mold, then semi-perm? The semi-perm I was going to use says to first use their cleaner to “remove any existing wax and PVA from the mold”. Then use their sealer, I think, and then let it cure. So still PVA first? I’m so confused. lol

#4

I think what Herman is saying is to find a low shrinking and high heat resistant polyester resin. I’m thinking of using a vinylester tooling gelcoat for a future hood mold. Or make an epoxy mold.

#5

Either make a good quality rapid tooling system mould, and inquire about Tg first, or make a good quality epoxy mould, but also inquire about the Tg first.

For the epoxy mould: learn to live with less repairability. You will notice repairs. Probably less important as you will be respraying.

For the release: The first 2 products, use PVA, after the first 2 products, use semi perm.

And for your moulds keep in mind that a certain Tg is only achieved after postcuring. Follow the rules of freestanding postcuring strictly. (basicly ramp up very slow, keep for X hours at certain level, ramp down by turning the heater off, and let cool in the oven. (no thermoshock)

Also, keep in mind the heat developed during cure of a tooling system of equal what sort. High peak exotherms can ruin your plug surface, and hence your mould surface.