PTFE Seal Temperature

[cnuk]

I have a PTFE (graphite filled) seal that I am testing running on a 2" shaft @ 500 RPM, 500 Psi. Test fluid is water at 50°C. It is grease lubricated. We are measuring temperature near the seal of 150°C which seems ridiculously high to me. Are you surprised by the temperature? I would never have guessed that a PTFE seal could generate that much temperature on its own. At this temperature you can't expect PTFE to perform a sealing application for long.

Any comments?

 

[patprimmer]

PTFE has good properties at 150 deg C.

I would not expect so high a temperature. To reduce temperature I would back of the preload at the gland nut a little, until I had a very slight leak, like a drip every minute or so.

If the seal is to tight, it will generate heat and the shaft will expand, causing more heat and more consequential expansion etc etc until it dissappears up it's own rear end in a puff of smoke.

Regards

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[cnuk]

Thanks for the reply. We don't have control over the preload with our design. As far as properties go, we ran the material on our DMTA and the modulus drops by a factor of 4 between 100C and 150C, both far lower than room temp obviously. We see what I would call creep at current operating temperature. Not encouraging since the target life is quite long.

 

[patprimmer]

PTFE creeps a lot even at room temperature.

You give no details at all about your design, so I am taking SWAGs (Scientific Wild A** Guess)at it.

Any good design with PTFE will have some back up solid mechanical device to restrain or compensate for creep if the load is moderate or higher and is continuous.

All PTFE/graphite powder gland seal ropes I have seen are retained by an adjustable gland nut. This is for a very good reason.

Some have aramid fibre or carbon fibre reinforcement incorporated into the rope to reduce creep.

I cannot imagine a PTFE lip type moulded seal generating anything like that temperature, especially close to water at 50 deg C. To do this it would need to be so tight it would tear itself to bits in a matter of seconds.

Lip type seals are usually reinforced by a spring to preload the lip to the shaft.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.