Gunner wrote:
Im now needing to occasionally replace o-rings in machine tools and
whatnot and need to purchase a selection of them to keep in the truck.

Most applications will be for air, in an oily environment, though a
few will be for hydraulic fluids. Is there some material best suited
for general use?

And will they degrade in a short period of time, in the back of my
service truck in hot weather?

What material should I be using?

I will likely purchase from ebay one of those 400 piece selections
for $10 or so, unless someone has better suggestions.

Grants recent thread on O/A o rings brought this to mind.

Thanks in advance

Gunner

These seem most common:

For background information, see O-Rings.

O-Rings are available in five different materials from Scientific
Instrument Services. Each type has its advantages and disadvantages as
listed in the O Ring Comparison Chart. Of the various types of O-Rings
available from SIS, Buna-N is the most sidely used type of O ring in
the seal ring. It is also the least expensive type of O-Ring seal. It
does however have severe temperature and chemical resistance
limitations.

NITRILE OR BUNA N (NBR) Typical Trade Names:

Chemigum Goodyear Tire & Rubber Co.
Paracril Uniroyal
Hyvcar Goodrich Chemical Co.
Krynac Polysar, Ltd.
Ny Syn Copolymer Rubber & Chem. Corp.
Buna N or Nitrile, is a copolymer of butadiene and acrylonitrile.
Acrylonitrile content is varied in commercial products from 18% to 48%.
As the nitrile content increases, resistance to petroleum base oils and
hydrocarbon fuels increases, but low temperature flexibility decreases.
Due to its excellent resistance to petroleum products, and its ability
to be compounded for service over a temperature range of -65 to + 275
degrees F (- 54 to +135 degrees C), Nitrile is the most widely used
etastomer in the seal industry today. Most military rubber
specifications for fuel and oil resistant MS and AN 0-rings require
nitrile base compounds. It should be mentioned, however, that to obtain
good resistance to low temperature with nitrile compounding, it is
almost always necessary to sacrifice some high temperature fuel and oil
resistance. Nitrile compounds are superior to most elastomers with
regard to compression set or cold flow, tear and abrasion resistance.
Inherently, they do possess good resistance to ozone, sunlight or
weather but this can be substantially improved through compounding.
However, since ozone and weather resistance are not always built in,
seals from nitrile bases should not be stored near electric motors or
other equipment which may generate ozone, or in direct sunlight.

Nitrile Is Recommended for:

General purpose sealing.
Petroleum oils and fluids.
Cold Water.
Silicone greases and oils
Di-ester base lubricants (MIL-L-7808).
Ethylene glycol base fluids (Hydrolubes)
Nitrile is not recommended for:

Halogenated hydrocarbons (carbon tetrachloride, trichloroethylene)
Nitro hydrocarbons (nitrobenzene, aniline)
Phosphate ester hydraulic fluids (Skydrol, Fyrquel, Pydraul).
Ketones (MEK, acetone)
Strong Acids Ozone
Automotive brake fluid.


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O-Rings are available in sizes (sizes 0, 1, 2 and 3) which correspond
to the diameter of the cross section of the O-Ring. Within these groups
the O-Rings are classified according to their inside diameter. To see a
complete selection of the various sizes and types of O-Rings available
from Scientific Instrument Services, just click on the hyperlink on the
size list above. If the size you require is not listed, it may still be
available. Contact us with your requirements.

Although I've not done business with these folks before.

dennis
in nca