Thick Section Rubber Molding

[sluggo]

Greetings Rubber head Guru's

We are accomplished molders but have never ventured into the thick section molding. I currently have a contract to mold a 6"diameter by 8.5" cylinder (top and bottom edges have a 2" radius fillet). I'm searching for info on cure times, more or less shrinkage due to the thick section, how to overcome Backrind or other molding defects.

Thanks and God Bless
Sluggo

 

[tom1953]

Sluggo,
A couple of questions:
What type of compound are you molding, polymer-wise and cure system-wise (sulfur or peroxide?), and what are the compound's curing characteristics? Do you have curemeter data? Does the compound revert upon over-curing (like natural rubber)?

I'm not a molding expert, but I'm pretty sure that the answers to these questions will help others give you some guidance.


Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[edine]

Large thick sections often require lower temperature and slower cures. Lower temperature give you a longer time before reversion occurs. You need really good packing, but the rubber can't be moving out the overflows once it has started to crosslink. Make sure you are getting enough cure in the middle. Cut when cool to look for bubbles or use an embedded thermocouple to monitor actual temperatures. Shrinkage can be different, but I've never found a better way than to just measure it and cut steel.