Rubber and Silicone (cross-post)

[Steinbru@VNET.IBM.COM]

Useful references.

--REFERENCE--------------------------------------------------------------------
Date:    Fri, 23 Oct 1998 17:11:51 -0400
From:    "Steeves, Mike" <MiSteeves@nbpower.com>
Subject: Re: another bad sound

As this is digested, I hit another subject....

>You do realize that silicone destroys rubber don't you?

Well, it isn't quite that simple.  We talk about "rubber" as if we know
what it is.  In reality, natural rubber is very hard to find.  I suspect
that you won't find any on our cars.

There is a range of substitutes used on cars.  Perhaps the most common
is "Nitrile Rubber", or "Buna-N".  It is lousy stuff, disintegrates on
its own after a few years,  but:  It is impervious to most hydrocarbons,
and it is cheap.

Another choice is EPDM, EPR, Ethelyne Proplyene or some such name.  It
lasts for an incredibly long time, but isn't very resistant to
hydrocarbons (gas, oil, etc).

Viton or Fluorocarbon is great stuff.  Lasts forever, impervious to
hydrocarbons, good high and low temperature performance, and more
expensive than Nitrile.  I suspect the average life of a car would be
greatly extended if most Nitrile was replaced by Viton.

Silicone rubber is very soft and pliable, lasts well, withstands high
temperatures (max 232 C), but isn't compatible with many fluids.

I just pulled up a document here which contains a "Fluid compatibility
table".  For silicon oils or greases, it is listed as "satisfactory"
(the highest it gets) for all materials except silicone and
fluorosilicone.

Just for interest's sake:  I see looking through this document that
"Butadiene is primarily a tire polymer".  Also "Butyl Rubber has
excellent resistance to gas permeation ... which accounts for its wide
use in the manufacture of inner tubes and the inside layer of tubeless
tires."

This comes from "The Parker O-Ring Handbook", but it applies to far more
than just O-rings.

Conclusion:  Silicone lube is compatible with commonly used elastomers
on cars.

Michael