Heat treating o-rings to raise durometer

[Dougt115]

I have a high pressure system with an o-ring and backup o-ring that is jamming. The suspect is the pressure extruding the backup o-ring into the gap between the rod and cylinder.

The backup o-ring is rated at 90A. I was wondering if I could heat treat the O-rings and permanently increase the hardness. If so any ideas as to the heating profile?

 

[dgallup]

I have never heard of such a thing. 90A Shure is already pretty hard for an o-ring. Generally, back up rings are not o-rings. Take a look at Parker Parbak backup rings:

http://www.darcoid.com/images/uploads/pdfs/Parbak-Back-Up-Sizes.pdf

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[Dougt115]

I did look at Parker. even contacted them. They said heating the parts will degrade the material and is therefore not advised.

 

[EdStainless]

Yes, you could heat the rubber and it would become harder, but it would loose almost all elasticity.
This is what happens in high temp service.
Use a proper backing ring, and maybe you need a different elastomer for your service.
Just because a ring is Viton does not make it the same as other Viton. The fillers and additives are critical.

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Plymouth Tube

 

[ornerynorsk]

Can you quantify what "high pressure" is? If you're extruding O-rings AND backup washers, you may have other issues besides the seals themselves. My first guesses would be fluid incompatibility and excessive clearance or damage. You also could be exceeding the design pressure limit of those types of seals. I've used u cups with great success at higher pressure applications, but you need to nail down all of your other possibilities.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[Dougt115]

The estimated pressure is >4000psi and >140°F. Rod is 0.2195 inches and the bore is .22. The shoulder for the backup o-ring was .210 so I have changed it to .218.

 

[ornerynorsk]

O-rings are also available in 90 hardness, in addition to the backup washer. Viton, as Edstainless mentioned, is going to handle heat much better then Buna-N or even HNBR, but will be less abrasion resistant. Kalrez is rated up to 600 F if memory serves, and comes in 75A hardness, slightly harder than a standard Buna-N. How's the bore finish? Have you determined if there is any bulging or tolerance issues along the length of the bore? What fluid is being used? What is your current o-ring material?

If you currently have an o-ring and 1 backup washer, your gland might be properly sized for a u-cup, you'd have to check the book. Parker claims O-rings can be effective up to 5000 psi, but for all practical purposes, I've found that to be a bit optimistic, particularly in high heat applications. >140 is fairly hot for a hydraulic system.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.