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#632052 - 11/07/04 01:32 AM How to tell between Nitrile/Buna-N and Viton?
metroplex Offline


Registered: 09/12/02
Posts: 1904
Loc: SE MI
How do I tell the difference between these type of O-rings?

I read that Nitrile is only good up to 250F while Viton can handle 400F.

I thought of a simple test:

Sandwich a o-ring test subject in two metal washers and clamp it on a vice.

I turned on my MAPP torch and went to work on the washers... turning them red hot and letting it cool down.

After about 2 of these "tests", the test o-ring popped loose without cracking, melting, or otherwise deteriorating.. but it wouldn't pop back up to its normal thickness and some of the external material clung to the metal washer.

I'm not sure (I dont have an IR thermometer) but when the metal is red hot, it would most likely be above 250F ... right?

Or is there a simpler test? I know they sell a testing device but I wanted a simple way of doing this without costing me a whole lot of money.

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#632053 - 11/07/04 01:40 AM Re: How to tell between Nitrile/Buna-N and Viton?
moribundman Offline


Registered: 06/02/03
Posts: 23591
quote:
I'm not sure (I dont have an IR thermometer) but when the metal is red hot, it would most likely be above 250F ... right?
[LOL!] YES!

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#632054 - 11/07/04 01:49 AM Re: How to tell between Nitrile/Buna-N and Viton?
kenw Offline


Registered: 10/10/04
Posts: 1979
Loc: Houston
it's also above 400F.

can't you just BUY o-rings that are labelled as Viton?

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#632055 - 11/07/04 02:22 AM Re: How to tell between Nitrile/Buna-N and Viton?
moribundman Offline


Registered: 06/02/03
Posts: 23591
I just remembered that burning Viton is a really bad idea due to the formation of highly carcinogenic hydrogen fluoride. Burned Viton should not even be handled with bare hands.

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#632056 - 11/07/04 02:33 AM Re: How to tell between Nitrile/Buna-N and Viton?
HunterG69 Offline


Registered: 08/04/04
Posts: 50
Loc: Calgary
Burning Viton is bad, produces hydro fluoric acid.

You can tell an O-Ring is Viton because it costs 5 times as much!! [Smile] There is no difference between Nitrile and Buna-N.

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#632057 - 11/07/04 02:34 AM Re: How to tell between Nitrile/Buna-N and Viton?
metroplex Offline


Registered: 09/12/02
Posts: 1904
Loc: SE MI
how about burnt Nitrile/Buna-N?

Just out of curiosity... would burnt Viton smell like burnt rubber (like doing a burnout in your car)?

Both "test" O-rings smelled like burnt rubber when I decided to just take the MAPP torch flame directly onto the rings.

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#632058 - 11/07/04 02:57 AM Re: How to tell between Nitrile/Buna-N and Viton?
moribundman Offline


Registered: 06/02/03
Posts: 23591
I really don't know how it smells and I'll keep my sniffer away from burned synthetics if possible. I remember reading the warning regarding Viton when I was looking into getting high quality Viton valve stem seals as replacement for the OEM seals, which tend to harden and shrink over the years.

Could it be that burned Viton smells similar to burned teflon? It think the materials are somewhat similar.

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#632059 - 11/07/04 03:02 AM Re: How to tell between Nitrile/Buna-N and Viton?
metroplex Offline


Registered: 09/12/02
Posts: 1904
Loc: SE MI
I know that teflon also produces HF gas, but the MSDS for Viton does not indicate it is carcinogenic if thermally decomposed.

I bought the cheap plumbing aisle o-rings to test, so I'm pretty sure they're not Viton. I just wanted to see how they'd fare when the metal surrounding it is heated red-hot.

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#632060 - 11/07/04 04:15 AM Re: How to tell between Nitrile/Buna-N and Viton?
MolaKule Offline


Registered: 06/05/02
Posts: 14637
Loc: Midwest
According to my sources:

1. Nitrile Elastomers (NBR) are good to 230 F, while an advanced nitrile polymer (HNBR) is good to 275 F, but cost 15X that of NBR.

2. Viton or FKM elastomers are good to 302 F.

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#632061 - 11/07/04 04:18 AM Re: How to tell between Nitrile/Buna-N and Viton?
metroplex Offline


Registered: 09/12/02
Posts: 1904
Loc: SE MI
Thanks for the info!

How about polyurethane o-rings?

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#632062 - 11/07/04 04:26 AM Re: How to tell between Nitrile/Buna-N and Viton?
labman Offline


Registered: 03/14/03
Posts: 8711
Loc: Nothern USA
Identifying unknown rubbers and plastics without expensive equipment is tough. Even finding out what something you buy is really made out of can be tough sometimes. The traditional burned rubber smell is various sulfur compounds, mercaptans etc. Higher grade rubbers may use other curing agents. A burning hair or singed chicken smell means it contained nitrogen, Nylon, Nitrile, and maybe that is the N in Buna-N. Occasionally sniffing small quantities of even the burning Viton isn't going to hurt anybody.

The shop manual for my 92 Grand Am had some simple tests for plastics in the body section. Check any you have access to.

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#632063 - 11/09/04 08:14 AM Re: How to tell between Nitrile/Buna-N and Viton?
Blue99 Offline


Registered: 09/27/03
Posts: 2233
Loc: Wisconsin
Fluid incompatibility might be a practical test for identifying viton vs. buna-N O-rings.

Viton is rated excellent in the Fuel Oil C or Toluene test. Buna-N has a poor rating. Soaking the unknown sample & comparing to a known buna-N O-ring soaked in the same test fluid would be a practical test.

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