Phenolic Molding Problems

[LL631]

I'm working with a supplier to produce a compression molded phenolic resin based friction rotor.
They had some problems with the first trial; the part has splits (mostly at tool mating line) and the flash had a strange sponge/honeycomb structure.

We have no experience in molding so are looking at having to run systematic trials to find some parameters that work, to help narrow our search can anyone identify potential causes for this sort of defect?

Material:
- Novolac Phenolic Resin based (50 - 60%) + Fibre Filler (15 - 25%).

Trial Process:
- Pre-heat; 40s in 900w microwave. (minimum time found to get material to flow).
- Compression mold; 150, 160, 170, 180[sup]o[/sup]C, cure time 180s, pressure ?, rate ?.

 

[Compositepro]

Wow, a 180 second cure! I'm used to minimum 6 hour cure cycle. Phenolic is a condensation cure resin. It releases at least 4% water by weight during cure. Your panel is delaminating due to steam pressure exceeding the resin strength at you cure temperature during cure when you open the mold. Keep the mold closed longer or pre-react the molding compound before cure.

 

[LL631]

Sorry the 180s cure is referring to the time in mold, their usual procedure would then be to post-cure in a graduated oven cycle for 10 hours.

Delamination due to steam pressure looks very plausible, thanks for pointing this out.

I think the material is pre-reacting during pre-heating, they found that less than 30s and the material wouldn't flow, beyond 40s and the material would go hard (presumably reacting too much). Do you think pre-heating at lower energy but for longer will help to give a more complete reaction and time for the water to condensate out? To me the short window between underdone and overdone suggests too much energy is being used.

At lower mold temperature (150[sup]o[/sup]C) it wasn't so bad but the part was flexible when removed, is it a case of more time = more complete reaction or is there a critical temperature that needs to be reached?

Should breathing be considered?

Thanks

 

[SWComposites]

a) you should talk to a chemist at the material supplier.
b) microwave preheating sounds like a very bad idea.