Basic O-Ring Elastomer Types
EIGHT BASIC O-RING ELASTOMERS
The following are brief descriptions of eight of the most comnnonly used O-ring
elas-tomers. There are of course, many other specialized polymers, and Parker has prepared
formulations on most of them. The ones listed herein however, account for well over 95% of
all O-ring production.
Due to its excellent resistance to petroleum products, and its ability to be compounded
for service over a temperature range of -65° to +275°F (-54" to +135"C),
nitrile is the most widely used elasfomer in the seal industry today. Most military rubber
specifications for fuel and oil resistant MS and AN O-rings require nitrile based
compounds. It should be mentioned, however, that to obtain good resistance to low
temperature in a nitrile material, it is almost always necessary to sacrifice some high
temperature fuel and oil resistance. Nitrile compounds are superior to most elas-tomers
with regard to compression set, cold flow, tear and abrasion resistance. Inherently,
nitrile based compounds do not possess good resistance to ozone, sunlight or weather.
However this specific weakness has been substantially improved through Parker compounding
Nitrile is recommended for:
General purpose sealing.
Petroleum oils and fluids.
Silicone greases and oils.
Di-ester based lubricants (MIL-L-7808).
Ethylene glycol based fluids (Hydrolubes).
Neoprenes can be compounded for service at temperatures from -65° to +250°F (-54° to
+121°C). Most elastomers are either resistant to deterioration from exposure to petroleum
lubricants or oxygen. Neoprene is unusual in having limited resistance to both. This
characteristic, combined with a broad temperature range and moderate cost accounts for its
use in many sealing applications.
Neoprene is recommended for:
Refrigerants (Freons, ammonia).
High aniline point petroleum oils.
Mild acid resistance.
Silicate ester lubricants.
Ethylene propylene has won broad acceptance in the sealing world because of its excellent
resistance to Skydrol and other phosphate ester type hydraulic fluids. Ethylene propylene
has a temperature range from -65° to +300°F (-54° to +150°C) for most applications.
Ethylene propylene is recommended for:
Phosphate ester based hydraulic fluids. (Skydrol, Fyrquel, Pydraul)
Steam (to +400°F) (+204°C).
Silicone oils and greases.
Ketones (MEK, acetone).
Automotive brake fluids.
Fluorocarbon elastomers were first introduced in the mid-1950s. Since that time, they have
grown to major importance in the seal industry. Due to their wide spectrum chemical
compatibility and broad temperature range, fluorocarbon elastomers represent one of the
most significant elastomer developments in recent history. The working temperature range
of fluorocar-bon is considered to be from -20° to +400°F (-29° to +204"C) but some
lormulations have been known to seal at temperatures up to +600°F (316°C) for short
periods of time. Likewise, some fluorocarbons have been known to seal at -65°F (-54°C)
in some static low temperature applications. Recent developments in material formulation
have further improved the characteristics of this very useful seal material. Fluorocarbon
materials should be considered for use in aircraft, automotive and other devices requiring
maximum resistance to deterioration by environment and fluids.
Fluorocarbon is recommended for:
Di-ester based lubricants (MIL-L-7808, MIL-L-6085)
Silicate ester based lubricants
Silicone fluids and greases.
Halogenated hydrocarbons (carbon totrachlorido, trichloroethylene).
Selected phosphate ester fluids.
Prior to the introduction of ethylene propylene, butyl was the only elastomer which was
satisfactory for Skydrol 500 service over a temperature range from -65° to +225°F
(-54" to +107°C). In addition, butyl exhibits excellent resistance to gas permeation
which makes it particularly useful for vacuum applications.
Butyl is recommended for:
Phosphate ester type hydraulic fluids (Skydrol, Fyrquel, Pydraul).
Ketones (MEK. acetone).
Silicone fluids and greases.
This material has outstanding resistance to petroleum based fuels and oils. In addition,
polyacrylte has good resistance to oxidation, ozone, and sunlight combined with an
excellent ability to resist flex cracking. Compounds of polyacrylate have been developed
which are suitable for continuous service in hot oil over a temperature range from 0° to
+300°F (-18° to +150°C). Resistance to hot air is slightly superior to nitrile
polymers, but tear strength, compression set and water resistance are inferior to many
other polymers. There are several polyacrylate types available commercially, but all are
essentially polymerization products of acrylic acid esters. The greatest use of
polyacrylate elastomers is by the automotive industry in automatic transmission and power
steering devices using Type A transmission fluids.
Polyacrylate is recommended for:
Automatic transmission fluids
Power steering fluids.
The silicones are a group of elastomeric materials made from silicone, oxygen, hydrogen
and carbon. As a group, the silicones have rather poor tensile strength, tear and abrasion
resistance. Special Parker silicone compounds have been developed which exhibit
exceptional heat and compression set resistance. High strength materials have also been
developed but their strength does not compare to conventional elastomers. Silicones have
excellent resistance to temperature extremes. Flexibility below -175°F (-114°C) has been
demonstrated and Parker has developed silicone compounds which will resist temperatures up
to +700°F (+371°C) for short periods. The maximum temperature for which silicones are
recommended for continuous service in dry air is +450°F (+232°C). The ability of
silicone to retain its original physical properties at these high temperatures is superior
to most other elastomer materials.
Silicone compounds are not normally recommended for dynamic sealing
applications due to silicone's rather low abrasion resistance.
Silicones are recommended for:
High-aniline point oils.
Fluorosilicone elastomers combine the good high and low temperature properties of silicone
with basic fuel and oil resistance. The primary uses of fluorosilicone materials are in
fuel systems at temperatures up to +350°F (-i-177°C) and in applications where the
dry-heat resistance of silicone is required but the material may be exposed to petroleum
oils and/or hydrocarbon fuels. The high temperature limit for fluorosilicone is limited
because temperatures approaching +350°F may degrade certain fluids producing acids which
attack the fluorosilicone elastomer. High strength fluorosilicone materials are available
and certain of these exhibit much improved resistance to compression set.
Fluorosilicone is recommended for:
Petroleum oils and fuels.
CHROMASSURE... Color Assurance O-Rings
Error resulting from a mix-up in basic polymer is potentially the greatest quality problem
a seal user can experience. Basic polymer differences can result in a seal swelling to
lock up a unit, shrinking away from the gland wails thereby providing a leak path or
complete degradation as a result of fluid and/or temperature incompatibility. With the
cost of product liability claims on the rise, a seal user can't afford to take unnecessary
chances. Parker Seal CHROMASSURE materials offer you high-performance, color coded O-rings
comparable to their black rubbur counterparts. CHROMASSURE provides vivid color
identification by basic material-polymer. All popular polymer groups are represented as
With CHROMASSURE O-rings and seals, positive color identification is an
integral part of the material from the initial blending of the compound's ingredients. The
color is due to use of throughout the O-ring, it cannot be worn off.
Advantages of CHROMASSURE
- Assist in eliminating assembly errors incorrect
- Upgrade product quality and reliability.
- Minimize warranty and liability problems
- Protect and insure your aftermarket