stand elastomer pict.

The following is a brief description of the basic elastomer families.

Nitrile or Buna
Ethylene-Propylene
Polychloroprene
Silicone

 

 

 

 

Nitrile, Buna N (NBR, XNBR)

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 -54C (-65F) to 124C (255F).

 

Advantages

  • Good balance of desirable properties.
  • Excellent oil and fuel resistance.
  • Good water resistance.

Disadvantages

  • Poor weather resistance.
  • Moderate heat resistance.

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Ethylene-Propylene Rubber (EP, EPM,EPR, EPDM)

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 -54C (-65F) to 149C (300F). 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.

Advantages

  • Excellent weather resistance
  • Good low temperature flexibility
  • Excellent fluid and chemical resistance
  • Good heat resistance

Disadvantages

  • Poor mineral oil products resistance

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Polychloroprene (CR, Neoprene)

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 -54C (–65F) to 121C (250F). It is also used extensively for sealing refrigeration fluids.

Polychloroprene compounds are not compatible with chlorinated hydrocarbons, polar solvents, or aromatic hydrocarbons.

Advantages:

  • Excellent ozone resistance
  • moderate oil resistance

Disadvantage:

  • not compatible with chlorinated hydrocarbons/polar solvents/aromatic hydrocarbons

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Silicone (VMQ, PMQ, PVMQ)

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 232C (450F) down to -59C (-75F). 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 121C (250F).

 

Advantages:

  • Excellent at temperature extremes
  • Excellent compression set resistance

Disadvantage:

  • Poor physical strength

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