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General Composites Discussions Composites Talk
#21

When ordering your gel coats and resins pay attention to the shrinkage and the exotherm.
Some of the products that are available are not true infusion resins; they are really just hand lay with a lot of extra styrene in them. They shrink like crazy! No way to stop print through if you use them.
Heat = print through, some manufacturers have even gone to the expense of creating water cooled molds to eliminate print through!

For Yachts we often skin the mould with two layers of mat before putting in our dry materials for infusion. This helps eliminate print through and acts as a resin rich barrier to prevent osmosis from happening in the future.

#22

It is really, really stupid to dilute polyester resins with styrene to make them infusable.

Base polyesters (unmodified) are really thin, and with the right rheology. (as in: will not thin down much further when energy is applied).
To turn them into hand laminating resins, which are easy to impregnate and will stay in the laminate without draining, the viscosity should be increased dramatically, but the rheology should also change. (viscosity should drop when energy is applied, as in: when laminating).
This is why a 2000 cps polyester resin is easy to laminate with, but a 2000 cps epoxy resin is hard work. Due to rheology.

Thinning down your thixotropic polyester resin (which is expensive to do) to make infusion resin again. Better take the base resin.

#23

Totally agree with you, your chemistry is correct adding styrene is pretty stupid, but resin manufacturers have done it. I was surprised when we ran into this while doing an experimental boat for the navy. The resin they specified was the same resin as they would use for that particular boat when it is hand laid. The resin manufacturer had just added styrene to it to get it down to the cps required. It was a gong show but we could not change anything in the specifications. I guess the point I was really trying to make is that to get a good job you must start with quality materials.

#24

^ Did you guys end up using that resin anyways to make the boat or did you switch to something else? With a thick enough laminate woudl it have mattered? Or was weight a priority as well?

#25

As a supplier, I am usually brought into picture quite late, but I do not hesitate to start discussions with a designer to change the specs on materials, for various reasons.

This includes:
-specifying materials that are extremely expensive or hard to get
-specifying materials that are just slightly off-spec from standard material
-specifying materials not suitable for the production process (hand laminating resin for infusion, for instance)
-specifying non-existent materials (for instance a Lloyds approved uni 700 gr/m2)

Or just plain making a mess of specs, with guessed thicknesses which are way off. I see it all happen…

#26

We had to use it. Military specs. Are like aircraft industry specks, you can’t change anything! It worked, the boat was light and fast everything they wanted……But ugly [FONT=Wingdings]L[/FONT]