Brown and black marking after post-cure 1

[bbyanar]

Hello All,

https://files.engineering.com/getfi...89c0-4258-bfe4-bc6eb90d53e1&file=IMG_8498.jpg

https://files.engineering.com/getfi...7c0c-411f-a541-20a0a3fee293&file=IMG_8497.jpg

We are having the issues you see in the images, basically this happens right after post-cure ends. We post cure around 200 C and 4 hours. This happens in occasion, sometimes more than others. It doesnt seem to be in a single spot. The markings are not only on the surface but also seem to be "melted" into the silicone.

Any suggestions ?

Thanks

 

[Compositepro]

Probably contamination in the silicone that discolored during post cure.

 

[bbyanar]

Hey, thank you for the response. I just realised that the markings are not only in the surface but also inside the silicone as well. So I assume its not contamination with the oven.

Here are the pictures that shows the markings from top side and side view.

https://files.engineering.com/getfi...f8bd-48eb-8a2f-7725bf560d54&file=IMG_8499.jpg

https://files.engineering.com/getfi...9851-4066-978b-da520ef2d694&file=IMG_8500.jpg

thank you again

 

[bbyanar]

What can the contamination be ? Since this happen both in precolored peroxide ready silicone and also in our own mixed products. I am also suprised that this discoloration doesnt happen during the compression molding process but only in post cure.

 

[Compositepro]

Probably debris from somewhere in the shop. That is for you to determine.

 

[GrahamBennett]

We always had problems of discolouration when curing white silicone parts. We solved it by working only under clean room conditions (not easy when the rest of the mixing/curing area is full of carbon black mixes!

http://www.over50sforum.com