Gelcoat heat distorton

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#1

A few weeks ago we purchased some orange tooling gel coat from Florida Fiberglass and we’ve been having some problems with it.

We made a mold of some flat parts and that went well. The mold was made with three layers of this orange tooling gelcoat and seven layers 1.5 oz matting. The matting was saturated with Hydrex 100lv resin from Express Composites. The HDT on the resin is 240f or so. The HDT we found out today on the gel coat was 122f. Does that seem very poor for a tooling gel coat? It’s a PE gel coat by the way…

Anyways… Today we left the mold under the heat lamps too long after infusing the part and when we came back the digital thermometer said that the mold was 171f. I knew right away that, that could be very bad. Sure enough, the mold was warped in several places. It’s ok because the parts are literal just flat panels, and we are making more molds as well to increase production. My fear isn’t if the gel coat is good enough to make molds to make simple door sills. My fear is making molds of parts that need t be cured at a higher temperature.

Can anybody suggest any other kinds of tooling gelcoat? Maybe a vinyl ester gelcoat? What about epoxy? If we use an epoxy gel coat will it have to be post cured?

Thanks, John.

#2

if its just flat panels why not use glass?

#3

or plastic or metal? Composite molds are just too much trouble to make if you’re making flat panels. Heating composite panels unevenly is even worse! If you use thick isotropic (read not composite) materials all those problems will go away.

#4

Before buying a product, read the TDS, and you know what you are up to.

Over here I have a tooling gelcoat (VE) which does 133 degrees C. I am sure something similar exists over there as well. I believe Nidacore is running a tooling system RM2000 with the same gelcoat.

Epoxy gelcoat with high TG should be postcured. And you need a high temp epoxy behind it, as polyester will not bond to epoxy gelcoat.

#5

Thanks for the info guys :). The panels we have are flat but have embossed lettering and a 1mm trim around the edge of the mold so thats why we can’t just use a flat sheet of metal or such.

Turns out the problem was that the gel coat we are using has a HTD of 122F if cured at room temperature and 210 if cured at 200F.

We will be trying other gel coats :D.

John