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Polymer Seal

Polymer Seal

(OP)
Hello All,

We have a UHMW seal that is currently failing when subjected to testing. When exposed to -40F the seal is not reliable. The seal works fine at higher temperatures (200F). I ran TMA on the new versus used seal and found the CTE to be about 30 points lower on the used seal. I am attributing this to material degradation from the thermal cycling, however would like some input if this would be the main cause. Additionally, open to recommendations on other materials to use. We are looking at carbon filled teflon also and saw worse sealing. The seal is part of a pump. We have checked dimensions and surface finish on mating parts. Thanks for your time!

RE: Polymer Seal

From what you describe it could be thermal ageing but that can be prevented using the right antioxidant (i.e. stabilizer). Use a higher molecular weight one that will stay in the plastic instead of leaching out and use enough to be sure of stability i.e. 0.2 weight%. Best of all would be a combination of hindered amine i.e. Chimassorb 944

https://www.basf.com/group/corporate/en/literature...

and Irganox 1330

http://www.specialchem4polymers.com/tds/irganox-13...

Chris DeArmitt PhD
President - Phantom Plastics LLC

Consulting, ideas and training on plastic materials
www.phantomplastics.com

RE: Polymer Seal

UHMW what? PE? What is the fluid being pumped? What kind of seal? Is this a static seal, like an O-ring, a lip seal, or the secondary seal on a mechanical shaft seal?

Rick Fischer
Principal Engineer
Argonne National Laboratory

RE: Polymer Seal

(OP)
Yes, UHMWPE. Fluid exposure is DOT 4 brake fluid. It is a secondary seal on a mechanical shaft. We are also looking at changing the design to include a mechanical seal such that we are not replying on material properties only.

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