EPDM gasket stretching 1

[Tocani]

Hi, i'm currently working on an incident regarding some engine radiator EPDM gaskets about 722 overall length and 3mm section
There is a small batch of 32 pieces which supposedly left manufacturing plant within length specification but when arrived to to assembly plat (radiator assembly) they were measured on a go nogo gage and resulted to be about 3mm longer than upper specification
im launching the next actions
- Packaging tests with lower and higher material density per box
- Thermally validate autoclave operation

what wold the causes be to get the gaskets stretched?
Can you share some information regardig how curing affect gasket length?

I Really appreciate your comments

 

[Metten]

If stretched during transport: high pressure and/or stretching could cause permanent set if the set is not good or the parts were not adequately vulcanized. Were they stored for a long time?

curing in a mold gives the size of the mold (but keep the natural shrinkage of the material in mind). Large force could permanently deform the article, the effect is greater with less elasticity (crosslink density)

 

[Tocani]

Yes failed gaskets were stored somewhere between 1 to 4 months
Some of the stored boxes where slightly collapsed and the carton dividing layers (7 layers per box) where also collapsed
where do you think i can find information about curing times and epdm vulcanization?

best regards

 

[Metten]

Only the supplier can give information of the normal curing of the used formulation and should be able to give info on the results of the lot in question.
Might be interesting to know if the gaskets are post cured or not.

 

[Tocani]

Just visited supplier and yes gaskets are post cured for 10 min at 130°C on the autoclave (peroxi)
They told me that the magnitude of influence for the curing to accomplish is the steam pressure
which does not make much sense to me

anyway they just don't want to admit that there was a problem with their line but as they could not prove calibration of the measuring instruments on the autoclave we agreed on running a compression set for every batch cured and the pieces had to be taken from different areas inside the autoclave.

Thank you very much for your support!

 

[Metten]

10 minutes postcure does not make sense to me. 2-3 hours at 120 to 150°C sounds normal (up to 24 hours even).

Steam pressure is directly linked to the temperature. If they are 100% certain of the temperature, they know the pressure. I they are not sure about the pressure, that would mean they can't prove the temperature reached.