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Nitrile, Buna N (NBR, XNBR) |
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NBR,
Buna N, and Nitrile all refer to the same elastomer, composed of a
butadiene and acrylonitrile copolymer. For simplicity we will refer to
this elastomer as Nitrile.
Nitrile is
the most commonly used elastomer in the seal industry because of its
relatively low cost, and good mechanical properties such as tear,
abrasion, and compression set resistance. It also offers excellent
resistance to a wide variety of petroleum based products such as
lubricants and greases.
The fluid
swell resistance properties of NBR compounds are determined by the
acrylonitrile (ACN) content of the base polymer. ACN content can very
between 18%, for applications where good flexibility at low
temperatures is needed, to as high as 50%, where superior resistance to
fuels is required.
Typical limiting
properties of Nitrile are its poor ozone and weather resistance and its
moderate service temperature range of -54°C (-65°F) to 124°C (255°F).
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Advantages |
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- Good balance of desirable properties.
- Excellent oil and fuel resistance.
- Good water resistance.
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Disadvantages |
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- Poor weather resistance.
- Moderate heat resistance.
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Ethylene-Propylene Rubber (EP, EPM,EPR, EPDM) |
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Ethylene-propylene compounds are frequently used in applications
requiring excellent resistance in phosphate ester fluids at higher
temperatures. In addition, EPR also exhibits excellent resistance to
hot water and steam, alcohols, automotive glycol-based brake fluids,
ketones, detergent and silicone oils. The typical temperature service
range is from -54°C (-65°F) to 149°C (300°F). EPR compounds may be
sulfur-cured or peroxide-cured with the latter offering better long
term compression set resistance
EPR is not suitable for use with mineral oil products such as petroleum based lubricant oils, and fuels. |
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Advantages |
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- Excellent weather resistance
- Good low temperature flexibility
- Excellent fluid and chemical resistance
- Good heat resistance
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Disadvantages |
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- Poor mineral oil products resistance
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Polychloroprene (CR, Neoprene®) |
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Commonly
called Neoprene®, these elastomers are unusual in that there overall
physical characteristics classifies it as a general-purpose material.
It offers excellent resistance to ozone and weather environments, and
also has good abrasion and flex cracking resistance. Additionally, CR
exhibits moderate oil resistance while working in service temperatures
of -54°C (–65°F) to 121°C (250°F). It is also used extensively for
sealing refrigeration fluids.
Polychloroprene compounds are not compatible with chlorinated hydrocarbons, polar solvents, or aromatic
hydrocarbons. |
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Advantages: |
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- Excellent ozone resistance
- moderate oil resistance
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Disadvantage: |
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- not compatible with chlorinated hydrocarbons/polar solvents/aromatic hydrocarbons
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Silicone (VMQ, PMQ, PVMQ) |
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Compared
with other elastomers, silicone has relatively low tensile strength, as
well as poor tear and wear resistance. It is, however, clean
physiologically and therefore commonly used for food and drug
applications. Since silicone does not require the traditional "Carbon
Black" for strengthening purposes, it is compoundable in a variety of
colors. Silicone exhibits good oil resistance and the widest
temperature range of all the elastomers, from 232°C (450°F) down to
-59°C (-75°F). Silicone is good to use with oxygen, dry heat, vegetable
oils, and alcohol.
Silicone should not be used with Hydrocarbon fuels, acids, alkalis, and superheated water steam over 121°C (250°F).
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Advantages: |
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- Excellent at temperature extremes
- Excellent compression set resistance
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Disadvantage: |
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