Silicone Rubber Product Recommendation Request 3

[bcavender]

I am looking for a two part, pourable, semi flexible, silicone rubber material (or better technology) that can handle a large number of thermal cycles from ambient to appx 230 degrees F without surface spalling, cracks, etc.

Cured molded part maximum bending would be less than 5% in any dimension. Operating enviro is ph neutral with no UV or electrical stresses.

Application is to assist internal shape holding for a plastic part during secondary operations on the plastic’s surface.Tough and reasonably economic is paramount.

All comments and suggestions welcome!

Best regards,
B

 

[btrueblood]

Silicone rubber sounds like what you want, there are dozens of suppliers (search on google or amazon). Most of them can go to 400 F without damage (we have some silicone baking pans for cupcakes that get used a lot, and other than some discoloration, they are holding up well after years of roughly weekly use). Not sure how much stress, or how firm you want the stuff to be, most pourable silicones are pretty soft, i.e. less than 40 Shore A durometer, though the McMaster catalog lists a silicone casting compound that has cured hardness of 65 durometer. Silicones also typically release well from surfaces.

 

[3DDave]

I suggest using a conical plug into the silicone part so that you can more easily encourage the silicone part to come out by pulling the plug first.

 

[bcavender]

Btrue/Dave,

That is an excellent help! I will experiment with Shore A 20 and 30 to see which best fits the flex needed.

This durometer scale turned out to be a good guideline:

Link

I'm interested to learn about these materials' coefficient of thermal expansion to get a feel for the size change expected over the temp range ... the 3D design is next. Def will be putting in draft angles.

Thanks!
B

 

[Compositepro]

Silicone rubber becomes quickly degraded by contact with most thermoset resins during cure. FEP release film can be used to protect the silicone from direct contact. Silicone trapezoid extrusions wrapped in FEP film are used fill hat stiffeners for composite aircraft parts. Due to the high CTE of silicone, the forms can be easily pulled out after cure, and reused many times.

Silicone rubber is also very useful in the trapped rubber molding process, where the expansion of the rubber is used to generate pressure on the composite in a metal mold during heat cure.