Elastomer:

Trade Name:

Abbreviation:

Chemical Name:

Temp. Range:

Hardness:

Compression Set:

Elongation @ Break:

Tensile Strength:

100% Modulus:

N

Nitrile

NBR / Buna-N

acrylonitrile

butadiene

-30°C — 150°C

70 shore A

13%

329%

15.7 MPa

4.3 MPa

V

Viton

FKM

fluorocarbon

elastomer

-20°C — 200°C

77 shore A

18%

211%

15.2 MPa

6.6 MPa

EP

EPDM

EPDM

ethylene propylene

diene monomer

-55°C — 150°C

68 shore A

15%

210%

11.5 MPa

3.1 MPa

PTFE

Teflon

PTFE

polytetrafluoro-

ethylene

-200°C — 260°C

55 shore D

-

350%

25.0 MPa

-

K

Kalrez®

FFKM

perfluoro-

elastomer

-30°C — 260°C

75 shore A

18%

170%

16.5 MPa

7.0 MPa

A

Aflas®

TFE / P

tetrafluoroethylene-

and propylene

-30°C — 204°C

77 shore A

42%

211%

14.5 MPa

-

Custom Moulding:

Abrasion Resist:

Tear Resist:

Price:

Light Hydrocarbons:

Oils:

Acids:

Bases:

Hot Water:

Ozone:

Chemical Resist:

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NITRILE

Nitrile (also called Buna-N) is a copolymer of acrylonitrile and butadiene. By varying the percentage of each from 18% to 50%, this compound exhibits a wide range of chemical resistance and physical properties. There are tradeoffs though. For example, increasing the acrylonitrile fraction improves hydrocarbon compatibility but reduces low temperature performance.

Nitrile is the most commonly used elastomer for o-rings across all industries. Nitrile has excellent resistance to most petroleum products such as hydraulic fluids, fats, animal and vegetable oils, flame retardant liquids, grease, water and air. On physical properties, it offers good compression set performance as well as good tear and abrasion resistance.

Nitrile is not recommended for applications where it is exposed to ozone, sunlight or external weather conditions. It should also not be used in ketones, esters (including hydraulic oils); and chlorinated hydrocarbons.

VITON

Viton (also called FKM) is a fluorocarbon elastomer which is a copolymer of vinylidene and hexafluoropropylene. Fluoroelastomers are highly fluorinated compounds. Since the carbon-fluorine bond is so tenacious, higher fluorine content relates to better chemical compatibility. Fluorine content can range from 64% to 70%. In addition to the fluorine content, other factors such as curing process have a large effect on the physical properties, operating temperature, and chemical resistance of the compound.

FKMs is generally considered the best selection for hydrocarbon services especially at higher temperatures. FKMs are also used widely in lubricants, halogenated hydrocarbons, silicone-based fluids, water, and acids. They have good compression set characteristics and are resistant to ozone and sunlight degradation. FKMs are not recommended for ketones, amines, and low molecular weight ethers, esters, hot water, or steam. They are also not generally recommended for temperatures below -26°C.

EPDM

EPDM is a terpolymer of ethylene, propylene and diene. It is usually either sulphur or peroxide cured, with peroxide curing more expensive but resistant to more applications including heat, water, steam, alcohols, ketones, engine coolants, alkali, mild organic and inorganic acids and bases, oxygenated solvents, ozone and UV sunlight. EPDM compounds are not recommended for gasoline, petroleum oil and grease, and hydrocarbon environments.

PTFE

PTFE or polytetrafluoroethylene is commonly known by its brand name Teflon. It is a hydrophobic material with low coefficient of friction against most materials, making it difficult for most materials to bond or stick to PTFE. It is also chemically inert to almost any process sealed with mechanical seals. Although PTFE is an exceptional material, it has some special considerations when used as a secondary seal or gasket. PTFE is a hard plastic material with almost no resiliency, requiring the secondary seal be designed with this limitation in mind. It can also be damaged easily by scratching. For this reason, PTFE is commonly used in two forms for use in mechanical seals.

Non-filled PTFE (also called virgin PTFE) is most often used where mechanical properties are not the most important requirement. This material is used in extremely aggressive service where elastomeric compounds are not suitable. It is also used in services such as batch processes where the changing chemical or process conditions make selection of a single elastomer grade impossible.

Filled PTFE (also called encapsulated PTFE) are o-rings designed with an inner elastomer core, commonly Viton or EPDM, with an outside coating of PTFE. This combines the best of both materials; the chemical resistance of PTFE with the resilient properties of elastomers. A common brand name of excapsulated PTFEs is Teflex®.

KALREZ®

Perfluoroelastomers (also called FFKM) are a terpolymer of flourinated, saturated monomers. Kalrez® is the common brand name as originally manufactured by DuPont. It represents the state-of-the-art in elastomers for high temperatures and aggressive chemical applications, resisting over 1,800 different chemicals including concentrated nitric acid, sodium hydroxide and ethylene diamine while offering the high temperature stability of PTFE.

There are literally dozens of FFKM compounds currently on the market. While there are many grades with a wide range of chemical resistances, many others were developed to address specific applications while sacrificing compatibility in other areas. Greater care should be taken in selecting FFKM compounds than any other class of elastomers. This is because these compounds are generally used in applications that seal the mot aggressive chemicals or operate at very high temperatures. In these cases, the consequences of failure can be unacceptable. The other reason is that the properties and compatibility of these materials can vary widely from one compound to another.

AFLAS®

Aflas® (also called TFE / P) is a copolymer of tetrafluoroethylene and propylene with a fluorine content of approximately 54%. This material is unique due to its resistance to petroleum products, steam, phosphate-esters and a wide spectrum of automotive fluids and additives. It is resistant to motor oils of all types, engine coolants with high level of rust inhibitors, extreme pressure gear lubricants, transmission and power steering fluids, brake fluids, mineral oil and silicone oil. TFE / P is also ideal for heat transfer media, amines, acids and bases, as well as hot water and steam up to 170°C

GRAPHITE

Flexible graphite (also called Grafoil®) is an excellent material for secondary seals. In many ways, it is ideal. It has near universal chemical compatibility. It is stable at the highest temperatures that will be seen in any centrifugal pump. It is soft and conforms to mating surfaces to provide an excellent seal.

It does, though have one major disadvantage. Flexible graphite has essentially no resiliency. Once the material is deformed, it will not spring back into its original shape. While this is useful for forming the gaskets, it does not allow the gasket to be installed like most other secondary seals. Flexible graphite gaskets must be either held in place by mechanical means or by hydraulic loading. In some cases like sleeve gaskets, the flexible graphite is mechanically clamped into place. The gasket will be deformed to provide an effective seal but the gasket will be physically held in place by the clamping components.

HNBR

Hydrogenated Nitrile (also called HNBR) has been developed to meet higher temperatures than standard Nitrile (NBR) while retaining resistance to petroleum based oils. Obtained by hydrogenating the nitrile copolymer, HNBR fills the gap left between NBR, EPDM and FKM elastomers where high temperature conditions require high tensile strength while maintaining excellent resistance to motor oils, sour gas, amine / oil mixture, oxidized fuels and lubricating oils

SILICONE

Silicones (also called VMQ) are a group of elastomeric materials made from silicone, oxygen, hydrogen and carbon. Extreme temperature range and low temperature flexibility are characteristics of silicone compounds. As a group, silicones have poor tensile strength, tear resistance and abrasion resistance. Special compounds have been developed with exceptional heat and compression set resistance. Silicones possess excellent resistance to extreme temperatures from -50°C — 232°C.

Silicone compounds are very clean and are used in many food and medial applications because they do not impart odour or taste. Silicone compounds are not recommended for dynamic O-ring sealing applications due to relatively low tear strength and high coefficient of friction. Silicone is resistant to hot air, ozone, UV radiation, engine and transmission oils, animal and vegetable fats and oils and brake fluids. VMQ also has low resistance to mineral oils.

FLUORO-

SILICONE

Fluorosilicone (also called FVMQ) combined the good high and low temperature properties of silicone with limited fuel and oil resistance. Fluorosilicones provide a much wide operational temperature range than Fluorocarbon rubbers. Primary uses of fluorosilicone o-rings are in fuel system at temperatures up to 177°C and in applications where the dry-heat resistance of silicone o-rings are required.

NEOPRENE

Neoprene (also called CR) are homopolymers of chloroprene (chlorobutadiene) and were among the earliest synthetic rubbers used to produce seals. CR has good aging characteristics in ozone and weather environments, along with abrasion and flex cracking resistance. CR is desired in many sealing applications for refrigerants like Freon and ammonia, as well as silicone oils, water, ozone, vegetable oils, alcohols and low-pressure oxygen. CR is not effective in aromatic and oxygenated solvent environments and has a very low resistance to mineral oils.