Actually, yes.  Eventually most any polymer will degrade from something.

Every one has an Achilles heel.  Most automotive motor mounts are made from
natural rubber.  The reason really is its glass transtiton temperature.  It
is around -60°C and that makes the mounts very effective in isolating
vibration even at -40 degrees.  The engineers are just very careful with the
temps the mounts see.  Some do have a mount installed in hot regions and
there many engineers will use HNBR.  Its extremely expensive and not likely
to be available in commonly obtained hardware.  If you can get it, EPDM may
not be a bad choice.  Its much more heat stable, has slightly better low
temperature performance but it has no oil resistance.  If you anticipate
leaks of oil on it, it would be a bad choice.

If its possible to determine how hot the mount is getting, that's a good

start for determining how long it will last.  Neoprene's continuous use
temperature is about 80-85°C [176 F to 185 F] meaning it can be expected to
perform acceptably for about 2000 hours at that temperature.  Hotter temps
mean shorter life.  A good rule of thumb is if the Neoprene part will last
2000 hrs at 80°C, then expect 1000 hours at 90°C, 500 hours at 100°C [212 F]
and so forth.  Keep in mind this is just a way to estimate useful life.  You
will reach a temperature where it will have zero hours of life and that
point may not be readily apparent.

Just inspect often until you have confidence it looks OK.  Be looking

for cracks, crazing or chunks falling out (the usual rubber turning to goo
things).  Small radial cracks would be the way I would expect Neoprene to
begin to fail.

Charlie Smith
KIS Cruiser 4021

 Charlie,

I'm a bit slow responding - couldn't find my list of materials.

I'm looking at my Aussie PSRU damper requirements and couldn't help notice
someone actually knew a lot about these compounds.

Charlie you mention HNBR= High temp Nitrile temp range ;
HNBR -35* to+150*C

EPDM  -50*to+130*C ( no oil resistance)

So what can you tell me about;
VIT=Viton
VIT -20* to +200*C

SIL= Silicone
SIL -60 to +200*C

TFV= Teflon Virgin White
TFV -200* to+260*C

TMB= TeflonFilled Grey
TMB-200* to +260* C

I have a contact who can turn these up for me in any shape I need, but I was
wondering if there were any hidden secrets which would limit performance
like the EPDM ( no oil resistance).
George (down under)

Silicone is good to 260C or 500 F
Teflon is good to 450 C or 750 F
Teflon has no bounce.

Paul Lamar
 
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