Unkown Oring Material Viton or Nitrile - Looking for test

[CR100]

I am looking to determine what material a particaular oring is made of, either viton (FKM) or nitrile.

I tried heating known samples of nitrile and viton along with the unkown oring to 400° in an oven. To see how each oring reacted to the heat, the known sample of nitrile became quite hard while the others did not.

Although this test is by no means 100% positve I am curoious if there is a test I can conduct to identify the material?

 

[JJPellin]

We use a very simple device to test for o-ring material. It is a cylinder with a small weight inside. You raise the weight and drop it onto the o-ring. The amount that it rebounds determines the material. The cylinder is labeled with Viton, EPR and Nitrile. It works very well. I believe we got this one from our mechanical seal supplier. But, they are probably available commercially.

Johnny Pellin

 

[flexibox]

Be careful, when you burn Viton you can get toxic vapours like HF. refer extract. google burn viton.

Decomposition
Hazardous decomposition products: Hydrogen fluoride (HF) and perfluorolefins.
If the finish part is used or tested at temperature above 316°C, the surface of the parts may contain HF or HF condensate, which may cause severe burns, some- times with symptoms delayed for several hours. Wear Neoprene or PVC (if tempera- ture is blow melting point of PVC) gloves when handling parts or equipment after exposure to such high temperatures. if condensate is expected, wash equipment and parts well with limewater (calcium hydroxide solution). Discard gloves after handling degrated these parts.

 

[CR100]

JJPellin, wouldn't the durometer of the material effect the bounce height?

 

[JJPellin]

I don't know. I have never worked with a durometer tester. I just know that our little o-ring tester has alway produced a conclusive result and in cases where we had other confirmation of the material, it was always right.

Johnny Pellin

 

[tom1953]

I think the formulation and the specific rubber would affect the bounce height (resilience) as well as the hardness (durometer). One company used to make rubber balls of the same rubber, and one would bounce very high and the other wouldn't bounce at all because of the differences in plasticizer in the rubber (paraffinic vs. aromatic).

I work with millable urethanes and you can get resilience values from 10% to 60% with different polymers and formulas. So, the tester you're using may work well with one supplier's products, if their resilience values are similar for each rubber type, but I'd be hesitant to use it for testing rubber from other sources.

Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[longeron]

I am pretty certain that DuPont will take a sample and perform some destructive testing to ascertain the composition. Greentweed or Parker would likely also do the same for you.

 

[BenThayer]

we also use what JJPellin describes.

more info at

http://www.allorings.com/orid.htm

 

[tesser]

If your choice is between Viton and Nitrile and you know that it is one of these two (although there are several varieties of Viton), then there is a significant difference in Specific Gravity between the two. I can't remember the numbers now but I think Viton SG is around 2.0 and Nitrile around 1.0. You need to check. It's then a question of finding a liquid or making up a salt solution with an intermediate S.G. - say 1.3 (if my numbers are right). If nitrile it will float - if Viton it will sink.

 

[IFRs]

Expose it to a liquid that is compatible with Viton but attacks Nitrile.

 

[kevindurette]

I reverse engineer hydraulic seal kits all the time. I use the density. Weigh the part, and then divide that by its volume. (You'll need the cross section and ID to get the volume of the torus.) FKM is about twice as dense as NBR. (Off the top of my head, it's about 2.2 and 1.35 for the respective specific gravities, but I have that in a file at work.) Otherwise, one of the techs showed me a neat trick; dropping the edge of a metal ruler produces very different rebound effects between FKM and NBR. In imperial parts following AS 568, FKM is almost always brown in color. I wouldn't heat them; it's time consuming and costly. Any company is going to charge an arm and a leg for any such destructive testing when you compare it to the price of the o-ring.

 

[kevindurette]

By the way, I use the floating trick a lot to identify UHMWPE (which is the only material we typically see that floats in tap water).