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Teflon finish blistering on coolant water valve

I am an Account Engineer for an automotive HVAC supplier. We use a metal coolant/water valve. The valve has a stem cylinder inside made of a copper alloy(brass)finished with Teflon. The coolant used is a"50-50" polyethylene glycol.

We are coming across valves where the Teflon finish is blistering and exfoliating causing the valve to fail operation.

What would cause the Teflon finish to lose it's bond?

Could it be in the "finish" process?

What chemicals or substances can cause Teflon to deteriorate?

Any insight would be greatly appreciated!

Greg Gagnon
- Warren, Michigan
2000

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2000

To coat a Brass part with Teflon® has the problem of the curing temperature of the coating. To polymerize the PTFE you must to cure the coated part at 375¾C. this temperature causes a problem of copper oxidation that makes the adhesion fails. I suggest you tree possible solutions:

a) Change the substrate from brass to aluminum

b) precoat the part with stainless steel and after that to coat with Teflon®.

c) try a low temperature Teflon® coating.

Jordi Pujol
- Barcelona, Spain

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2000

Greg,

I sure like Jordi Pujol's idea of perhaps using a lower temperature 'Teflon' coating.

Firstly, however, why not go to the Horse's Mouth and hit on DUPONT for some answers? Dammit, they should know!

Teflon is their trade name. But I thought, probably erroneously,that the true, pure Teflon per se had to be sintered at high pressure to make it into pipe, bar, etc. However, there are lower temperature 'fluorocarbons' which cost less, are even weldable and are, and (but I don't know this) maybe much, MUCH more suitable for coating.Materials such as HALAR ectfe, TEFZEL and even Dupont's own FEPTEFLON.

It seems that your problem is one of he bond. There are precious few chemicals which attack PURE Teflon which may have around a 100 °F edge over the lesser teflon-like fluorocarbons which also have a scintillating performance.

Lastly, go to your 'local' pots and pan mfgr. Ask them what type of so-called "Teflon" they use to coat their pans. (I wouldn't mind even knowing this out of pure curiosity!)

Cheers !

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).