Viton seals: What are the differences in colour? 1

[mechcad8]

Can anybody help?
Are there any differences between black, brown or green viton flat seals. I have an application (Steam @ 140°C pressure 2.3bar - also vacuum at 100mbar) where I have validated the use of a 70 shore hardness Viton seals on some Solenoid valves. The seals were black in colour. Our production have been using black for the last year. My company have just had a delivery of brown seals which the supplier are claiming are still Viton at 70 shore hardness - but they feel phyisically softer to touch. (We do not have a hardness tester.)
Can anybody confirm what the different colour indicates?
I do not want to approve this unless their is a clear explaination for the difference in colour.
Thank you in advance.

 

[ejc]

If the vendor claims that the material is still Viton and has a hardness of 70 durometer, the rubber probably is and does.
Color is either a result of an additive, enabling identification of compounds; or a result of a required element of the mixture. The main example is the color black, which results from the addition of carbon into the mixture. The carbon black increases the chemical resistance of the rubber. For this reason the main difference in the different colors of the “same” rubber is the chemical compatibility. Note that this compatibilty change may be minimal for certain applications.
If you have an extreme application, verifying that the brown Viton will work in the application is not a bad idea. For this reason, color (especially if the compatibility of black rubber is required) should be a part of your purchase specification.

 

[berti]

Hi all,

"VITON(C)" and "70 Shore A" is not enough information to characterize a sealing material.

Viton or more general Fluorocarbon rubber (FKM or FPM)includes different materials.

They can have different fluorine content (between 66 and 71 % fluorine) and hence very different swelling behaviour in solvents as e.g fuels, aromatics, methanol ...

Next point is crosslinking system. There are at least 3 different, old aminic - which is no longer used for seals probably-, bisphenolic and peroxidic, which makes differences concerning dynamic behaviour and resistance against hot water and steam.

Further there can be some differences in type and amount of fillers, e.g. lead oxide is used for best hot water/steam resistance or lots of Barium sulfate for cheaper compound.

To make a long story short: Insist in your "old" material if you know it works or discuss a specification including at least FKM type and density and swelling/resistance data in one or more substance important for your application.

HTH Berti

 

[BCAREY]

Green is the color of choice in Europe for color coding viton, whereas brown is the color in the US. Black is the normal color to be used and in fact offers the optimum performance. The color coding is used when the equipment manufacturer is concerned that the user may elect to change seals on their own and replace a black seal with NBR or EPR resulting in a liability issue.
Viton is not available in just one grade. There are several grades available which accentuate one or two properties, at the sacrifice of other properties.
As you increase the fluorine content you improve chemical compatibility, but sacrifice properties such as compression set.
You should describe your application to your seal supplier and have your options explained to you