big bubble in epdm extrusion

[Solrubber]

Hello,

We are extruding epdm rubber sponge and we have had this trouble for long time. Periodicaly, the extrusion will make big bubble (not the regular cellular bubble sponge) along the smalest part of our design. This appears after the curing. We have augmented the shape of the uncured strip to help prevent lack of rubber in the tuber. Any idea of what could be the cause of this problem? We use 1.6 phr of dessicant.

When whe use the rubber quickly after mixing it does those bubble and, when the Ts2 is to long,even after a 24h relaxing it does thos bubbles. But if the ts2 is just a bit shorter we have problem of shape (not big enough).

Any suggestion would be appreciate

Thank you

Solange

 

[Elastomatt]

Solange,

Is there anything inside the bubble? I had a similar problem and on cutting open the bubble/blister something resembling a large brown grain of sand was sat in the hole.

My lab informed me it was the desiccant we used that was either poorly dispersed or ineffective.

Elastomatt.

 

[mhallin]

Hi,

I would agree with Elastomatt, it sounds like a moist problem. I think you could increse the amount of dessicant(calcium oxide) to at least 3-4 Phr without a problem. Also make sure the dessicant has been keept in a closed container prior to mixing, if it is exposed to moist the dessicant gets spent and you will loose it's function in the rubber material.
It could also be a good idea to check that your vacuum zone of the extruder is working properly and is not blocked.

Good Luck!