inert gas purge or vacuum for thick section peroxide cured elastomers

[gumby69]

I know bumping is commonly used and with FKM incorporation of a desiccant is helpful, but how practical is it to purge a large transfer or compression mold for a peroxide cured elastomers like HNBR or EPDM and is it effective?
Thanks
gumby69

 

[GrahamBennett]

Use CaO in peroxide cured HNBR and EPDM too. It is possible to use a vacuum hood for transfer and compression moulding.

 

[btrueblood]

We have a part some 36" in diameter that is transfer molded using peroxide-cured epdm. We have considered a vacuum system, and may have to do so in the future. The biggest concern is how to port sufficient vacuum flow area, it will be a bit of a design challenge in the existing mold. Our vendor has other, smaller parts with vacuum systems for perfluoro-elastomers; the vacuum porting was designed into the molds from the start.