Rubber Engineering Guide
Rubber Industry Precision Tolerances

The dimensional tolerances given below provide a guideline of what can be considered "precision" in a rubber product. Although tighter tolerances are frequently available, there are many factors that must be considered. Please contact Molding Solutions with any specific questions.

Dimension Size Fixed
Dimension
Closure
Dimension
Above 0.00" to 0.40" ±0.006'' ±0.008''
Above 0.40" to 0.63" ±0.008'' ±0.010''
Above 0.63" to 1.00" ±0.010'' ±0.013''
Above 1.00" to 1.60" ±0.013'' ±0.016''
Above 1.60" to 2.50" ±0.016'' ±0.020''
Above 2.50" to 4.00" ±0.020'' ±0.025''
Above 4.00" to 6.30" ±0.025'' ±0.032''
Above 6.30" Multiply By ±0.004''/ln. ±0.005''/ln.
Reprinted with permission from RMA Rubber Handbook for Molded Products

For more information about industry standards for rubber products, contact:
The Rubber Manufacturers Association
1400 K Street, N.W.
Washington, D.C. 20005





Rubber Compounds

Choosing a rubber compound: The information below allows the identification of the compound types that have the required characteristics for a specific application. Keep in mind that these results are achieved under laboratory test conditions and that results may vary in a specific application. Always test a specific compound in each application to assure that it will perform as required. Molding Solutions cannot be held responsible for improper use of this information.

RUBBER SELECTION TABLE
CHARACTERISTIC BEST GOOD MARGINAL POOR VARIES
Abrasion Resistance AU/EU, BR NBR, SBR, CR, CSM , CM, NR, IR, FKM, EPDM IIR, ACM, ECO VMQ, FVMQ ~
Acid Resistance EPDM, CR, FVMQ, CSM, CM FKM, IIR, NR, IR, NBR, ECO SBR, VMQ, AU/EU, BR ACM ~
Alkaline Resistance EPDM, FVMQ, CM IIR, CSM, NR, IR , NBR, CR FKM, SBR, ECO, BR ACM, VMQ AU/EU
Compression Set NR, IR NBR, FKM, SBR, VMQ , CM, ECO, BR FVMQ CR, IIR, ACM, AU/EU , CSM EPDM
Fuel Resistance, Aliphatic Hydrocarbon FKM, FVMQ, ACM NBR, ECO, AU/EU CSM, CM CR, VMQ, EPDM, SBR , IIR, NR, IR, BR ~
Resistance to Gas Permeability ECO FKM, CSM, CM, AU/EU, IIR, BR EPDM, CR, NR, IR FVMQ, SBR, VMQ, ACM ~
Heat Resistance, Aging @ 212°F FKM, VMQ, FVMQ, ACM EPDM, CR, IIR, CSM, ECO, NBR, SBR, CM NR, IR, AU/EU, BR ~ ~
LP Gas & Fuel Oil Resistance NBR, FKM, FVMQ, ECO CM, CR, ACM, CSM AU/EU VMQ, EPDM, SBR, IR , NR, BR ~
Ozone Resistance FKM, IIR, VMQ, FVMQ, CSM, CM, AU/EU EPDM, CR, ACM, ECO NBR SBR, NR, IR, BR ~
Resilience, Rebound FVMQ, NR, IR VMQ, FKM, SBR, BR , NBR, ECO EPDM, CR, ACM, CSM IIR, CM, AU/EU ~
Steam Resistance EPDM IIR NBR, SBR, CR, VMQ, ECO, NR, IR, BR FKM, CSM, FVMQ, ACM, CM, AU/EU ~
Tear Resistance AU/EU NBR, CR, NR, IR , BR, SBR, ECO, IIR FKM, EPDM, CSM, CM VMQ, ACM FVMQ
Vibration Dampening IIR CR, ACM, NR, IR, FVMQ, CM, ECO NBR, FKM, EPDM, SBR , VMQ, CSM, AU/EU, BR ~ ~
Water Resistance FKM, EPDM, VMQ, FVMQ, NR, IR, BR NBR, SBR, IIR, CM , CSM, ECO CR AU/EU, ACM ~
Weather Resistance FKM, EPDM, IIR, VMQ, FVMQ, ACM, CSM, CM, AU/EU ECO NBR, SBR, CR BR, NR, IR ~


Characteristics of Rubber Compounds

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




CHLORINATED POLYETHYLENE (CM) An elastomer made from a high density polyethylene, with limited resistance to petroleum oils, and good resistance to oxidation. Chlorination is canbe varied. Resistance to petroleum oils improves with increased chlorine content. Seldom used alone, can be blended to improve flame and impact resistance.
Specific gravity 1.16 to 1.32
Tensile strength 4,000
Elongation, max 5x
Hardness, Shore A 40-90
Brittle point (F) -40




CHLOROPRENE / NEOPRENE (CR) Among the earliest of the synthetic rubbers, can be compounded for service at temperatures of --65 to +300F, 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




CHLORINATED SULFONATE POLYETHYLENE (CSM) The ethylene monomer with some hydrogen replaced by chlorine and sulphur groups is the main constituent of this elastomer.
Specific gravity 1.18
Tensile strength (psi) 3,000
Elongation, max 6x
Hardness, Shore A 50-90
Brittle point (F) -70




EPICHLOROHYDRIN (CO, ECO) A recent addition to the oil resistant polymers; aliphatic polyether with cholorofunctional side chains. Both CO and ECO have excellent resistance to hydrocarbon oils, fuels and ozone. The corrosive nature of epychlorohydrinis a sometimes limiting factor in some applications.
Specific gravity 36 to 1.27
Tensile strength 2,500
Elongation, max 4x
Hardness, Shore A 40-90
Brittle point (F) 10 to -50




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




FLUOROCARBON (FKM) Due to its wide spectrum chemical compatibility and temperature range and low compression set, this is the most significant elastomer development in recent times. Of major importance in the seal industry.
Specific gravity 1.85
Tensile strength 2,500
Elongation, max 3x
Hardness, Shore A 60-95
Brittle point (F) -40




FLUOROSILICONE (FVMQ) Provide chemical properties similar to those of fluorinated organic elastomers: excellent resistance to hydrocarbon fuels, petroleum oils and silicone fluids.
Specific gravity 0.98
Tensile strength 1,200
Elongation, max 4x
Hardness, Shore A 60-80
Brittle point (F) -85




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 1.00
Tensile strength 4,000
Elongation, max 4x
Hardness, Shore A 40-90
Brittle point (F) -40




POLYACRYLATE (ACM) This material has outstanding resistance to petroleum fuel and oil, and possesses complete resistance to oxidation, ozone and sunlight, and an ability to resist flex cracking. It has good resistance to hot air.
Specific gravity 1.09
Tensile strength 2,500
Elongation, max 4x
Hardness, Shore A 40-85
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 4,000
Elongation, max 7x
Hardness, Shore A 30-90
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




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




URETHANE (AU /EU) Exhibit outstanding mechanical and physical properties in comparison with other elastomers, especially in its resistance to oils, hydrocarbon fuels, oxygen, ozone and weathering. Its toughness and abrasion resistance is particularly suitable for seals in systems of high pressures, shock loads and abrasive contamination.
Specific gravity 1.05 to 1.30
Tensile strength 10,000
Elongation, max 7x
Hardness, Shore A 40-100
Brittle point (F) -60 to -90




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