BUTADIENE RUBBER (BR) An elastomer with properties somewhat similar to natural rubber. Although its properties are not quite that of Natural Rubber, in some cases its low temperature characteristics are better.
Specific gravity.................................0.91
Compression set..................................B
Elongation, max............ ..................6x
Hardness, Shore A............................ 40-80
Brittle point (F).................................-100
BUTYL RUBBER (IIR) A petroleum product made of co-polymerizingisobutylene and isoprene (for desired degree necessary to vulcanization). Has excellent resistance to gas permeation, making it useful for vacuum applications.
Specific gravity....................................0.92
Tensile strength...................................3,000
Elongation, max...................................3x
Hardness, Shore A................................40-80
Brittle point (F).....................................-80
CHLOROPRENE / NEOPRENE (CR) Among the earliest of the synthetic rubbers, can be compounded for service at temperatures of --65° to +300°F, and most are either resistant to deterioration from exposure to petroleum lubricants, or to oxygen. (Neoprene is a Trademark of DuPont)
Specific gravity.......................................1.24
Tensile strength.......................................4,000
Elongation, max.......................................6x
Hardness.................................................30-90
Brittle Point..............................................-80
ETHYLENE PROPYLENE COPOLYMER (EPM/EPDM) Elastomers prepared from ethylene and propylene monomers , at times with a small amount of a third monomer (Etlylene Propylene Terpolymer). Excellent resistance to phosphate ester type hydraulic fluids.
Specific gravity..........................................86
Tensile Strength.........................................3,000
Elongation, max.........................................6x
Hardness, Shore A.....................................30-90
Brittle Point (F)..........................................-90
NATURAL RUBBER (NR) Found in the juices of many plants (shrubs, vines and trees), the principal of which is the HeveaBrasiliensis, native to Brazil. Especially vulnerable to petroleum oils, natural rubber has been all but completely replaced by synthetics for seal use.
Specific gravity..............................................0.92
Tensile strength..............................................4,000
Elongation, max..............................................7x
Hardness, Shore A...........................................30-90
Brittle point (F).................................................-80
NITRILE BUTADIENE (NBR) A copolymer of butediene and acrylonitrile, due to its excellent resistance to petroleum products and wide temperature range, the most widely used elastomer in the seal industry. Somewhat vulnerable to ozone, sunlight or weather.
Specific gravity.............................................1.0
Tensile strength..........................................4,000
Elongation, max..............................................4x
Hardness, Shore A......................................40-90
Brittle point (F)...............................................-40
POLYISOPRENE (IR) A synthetic elastomer with characteristics equal to, or similar to, those of Natural Rubber.
Specific gravity.....................................0.91
Tensile strength...................................4000
Elongation, max.......................................7x
Hardness, Shore A...............................30-90
Brittle point (F)........................................-80
STYRENE BUTADIENE (SBR) Best known as Buna S , this, along with natural rubber, account for 90% of the total world rubber consumption. Its chemical composition is of styrene and butadiene rubber, and it is not recommended for exposure to ozone, petroleum oils or sunlight.
Specific gravity......................................0.94
Tensile strength....................................3,500
Elongation, max....................................6x
Hardness, Shore a..................................40-90
Brittle point (F).....................................-80
SILICONE (SI / VMQ / PVMQ) The silicones are a group of materials made from silicone, oxygen, hydrogen and carbon which have poor tensile strength, and resistance to tear and abrasion, but exceptional heat and compression set resistance. High strength silicones have also been developed, but do not normally compare to natural rubber.
Specific gravity.....................................0.98
Tensile strength...................................1,200
Elongation, max.......................................7x
Hardness, Shore A...............................30-85
Brittle point (F).............................-90 to -180
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