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The Many Faces of Buna N (Nitrile) 1

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CaptainC

Aerospace
Oct 29, 2002
2
I have been searching for a specification for Buna N that will insure me that the material does not grow in Jet Fuel.

I've ordered the stuff in about 4 different specs and some batches grow and others do not. The suppliers keep telling me that it is the same material... however, obviously the elastomer industry does not have a handle on their processes.

Is there any specification that I could buy this material to, that will give me consistent material props. ?
 
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acrylonitrile-butadiene rubber (NBR) is a thermoset elastomer principally composed of acrylonitrile and butadiene, with the acrylonitrile content varying from ~ 18% to ~ 50%. The higher the percentage of acrylonitrile in the rubber, the greater the resistance to swelling. Increasing the acrylonitrile content causes a deterioration in compression set, reduces elasticity/cold flexibility, and also reduces the permeability of gases. These factors must be balanced in order to produce the desired properties.

With regards to specification, I suggest the following:

1. Start with applicable aerospace standards like SAE AMS 3212, 3213, 3214, 3215, or 3224. These standards specify fuel-resistant NBR in various durometers.

If you have already done this, and still have excessive variation, then you should

2. Exactly specify the requirements using ASTM D 471 Standard Test Method for Rubber Property-Effect of Liquids. In this standard, you specify the temperature range (85 + 2 C, 100 + 2 C, etc.), the duration (22, 46, 70, 166, 670, 1006, 2998, or 4990 hours), the fluid (standard fuels ranging from 100% isooctane to 100% toluene, or your specific grade), and the acceptance criteria (minimum and maximum change in mass and/or volume-- see sections 9-14).
 
Thank you for the information. I will consult the supplier on the availability of high acrylonitrile NBR. The problem that I am having is that the application necessitates a very cheap material otherwise I would have just used Viton and called it a day.

Would it be a safe assumption that if I were to order the NBR with a higher Shore A that it would contain more acrylonitrile?

The properties are essentially a non issue since the rubber is being used as a seal for shipping purposes. (mostly room temp and disposable)


 
No, a higher Shore A durometer does not mean that it will have more acrylonitrile.
 
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