RUBBER SELECTION GUIDE

Transcription

1 RUBBER SELECTION GUIDE The information below is intended to give a broad overview of the properties of a number of different rubbers. This is intended to aid in the selection of rubbers for particular service conditions. A guide of this sort is only intended as a first step in selection mainly to eliminate materials which are obviously unsuitable. Beyond this, factors such as component size can have a major influence on properties such as oxidation resistance and oil resistance. Also, the properties of a vulcanized rubber can be significantly influenced by details of the compounding. Practical materials will have, in addition to the base polymer, fillers, antidegradants, crosslinking agents, accelerators etc. All of these can have an influence on the physical and chemical stability of the finished material. In critical applications it is therefore advisable to give considerable thought, or take advice, on the formulation of the compound. As the potential for 'tailoring' compound to specific applications is essentially limitless, it is often advisable to carry out preliminary qualification tests to ensure that the compound chosen will perform as intended. Trade names are given to assist in recognition, but the list is necessarily only partial, and is given in alphabetical order. Trade names are generally registered and/or copyright and are indicated by an asterisk after the name see below. Abbreviations used are those based on latest ISO recommendations. The temperature ranges quoted are only a rough guide, because the temperature range possible will depend upon the particular application, and may depend on detailed differences between alternative versions of the same rubber. In some cases greater extremes of temperature can be tolerated than indicated below. The information given in this document is given in good faith, but Delta Rubber Limited can accept no responsibility for the information. Normal screening procedures should be operated before any material is selected for service.

2 ACRYLIC RUBBER ACRYLIC RUBBER Alkyl acrylate copolymer ACM Hytemp The outstanding property of this material is its resistance to hot oil and to oxidation. It is suitable for continuous use at temperatures up to 150C, and intermittent exposure up to about 180C. This is provided it is not exposed to water or moisture to which it has poor resistance. It is generally not suitable for use much below 10C and has poor resistance to acids and bases. It has only modest dynamic properties and rather poor compression set. Widely used in automotive transmissions and hoses. BUTADIENE RUBBER BUTADIENE RUBBER Polybutadiene BR This material has a very low glass transition temperature in the region 75C to 100C. This results in very low hysterisis and good flexibility at ambient temperatures and these properties are maintained to temperatures well below zero. It has high abrasion resistance in severe conditions. Mainly used in tyres in blends with natural rubber and SBR. BUTYL RUBBER BUTYL RUBBER Isobutyleneisoprene copolymer IIR This rubber has very high impermeability to gases and is hence used for the inner tubes of pneumatic tyres, and in vacuum and high pressure applications. It has an unusually broad loss peak so that, despite having a glass transition temperature as low as 65C, it displays high damping at ambient temperatures It has good ozone, weathering, heat, and chemical resistance. Not suitable for use in contact with mineral oils.

3 CHLOROBUTYL CHLOROBUTYL CIIR Similar in properties to butyl rubber EèvF, but with improved oòone and environmental resistance and greater stability at high temperatures. Improved compatibility with other rubber types in blends. CHLORINATED POLYETHYLENE CHLORINATED POLYETHYLENE CPE Good chemical resistance to hydrocarbon fluids and elevated temperatures. Used for hose linings. moor mechanical strength. jechanical properties may deteriorate above 100C. CHLOROSULPHONATED POLYETHYLENE CHLOROSULPHONATED POLYETHYLENE CSM Hypalon This is a material with Neoprene polychloroprene 'plus' qualities. It is suitable for continuous use up to about 130C and intermittent use up to some 30C above this. It has excellent resistance to oxygen, ozone and most chemicals, including water, but has poor fuel resistance. It has low gas permeability. It has poor compression set resistance which limits its usefulness in dynamic sealing applications.

4 EPICHLORHYDRIN EPICHLORHYDRIN CO High resistance to ageing, oxidation, ozone, and hot oil. Good resistance to hydrocarbon solvents, moderate low temperature flexibility. Poor abrasion resistance and electrical properties. ETHYLENE ACRYLIC ETHYLENE ACRYLIC AEM Vamac This has better low temperature performance (to 40C) and dynamic properties than acrylic (qv), but at the expense of fluid resistance. It has good compression set resistance, but poor resistance to aromatic hydrocarbons, strong acids and bases. ETHYLENE PROPYLENE RUBBER ETHYLENE PROPYLENE RUBBER Ethylene propylene copolymer, or a terpolymer with a diene EPM, EPDM Durtal, Nordel, Vistalon Probably the most water resistant rubber available, and this resistance is maintained to high temperatures (up to 180C in steam for peroxide cures). The highest temperature resistance is achieved by using peroxide cured grades. Has excellent resistance to atmospheric ageing, oxygen and ozone up to about 150C. It has good resistance to most waterbased chemicals and to vegetablebased hydraulic oils. However, it has very poor resistance to mineral oils and diester based lubricants.

5 FLUOROELASTOMERS FLUOROELASTOMERS FKM DaiEl, Fluorel, Technoflon, Viton This is a family of rubbers designed for very high temperature operation. They can operate continuously somewhat in excess of 200C depending on the grade, and intermittently to temperatures as high as 300C. They have outstanding resistance to chemical attack by oxidation, by acids and by fuels. They have good oil resistance. However, at the high operating temperatures they are weak, so that any design must provide adequate support against applied forces. They have limited resistance to steam, hot water, methanol, and other highly polar fluids. They are attacked by amines, strong alkalis and many Freons. There are standard and special grades the latter can be designed to have special properties such as improved lowtemperature resistance. HYDROGENATED NITRILE RUBBER HYDROGENATED NITRILE RUBBER HNBR Therban, Tornac, Zetpol The properties of hydrogenated nitrile rubber depend on the acrylonitrile (ACN) content, and on the degree of hydrogenation. They can be tailored to particular applications, but have the general advantage over standard nitrile rubber of having higher temperature resistance and higher strength. They have good high temperature oil and chemical resistance and are resistant to amines. They are suitable for use in methanol and methanol/ hydrocarbon mixtures if the correct ACN level is selected. They have good resistance to hot water and steam. They can have excellent mechanical properties including strength, elongation, and tear. Also, abrasion resistance, compression set, and extrusion resistance. For the best properties peroxide curing is used, unless low hysteresis is required. They are reported to be satisfactory up to temperatures around 180C in oil. Fully saturated grades have excellent ozone resistance. They have poor resistance to some oxygenated solvents and aromatic hydrocarbons.

6 ISOPRENE RUBBER ISOPRENE RUBBER Synthetic cispolyisoprene IR Natsyn This is the same polymer as natural rubber but made synthetically. Essentially similar in properties to natural rubber (qv) it may be somewhat weaker because it is not 100% the cis isomer. NATURAL RUBBER NATURAL RUBBER cispolyisoprene NR The outstanding strength of natural rubber has maintained its position as the preferred material in many engineering applications. It has a long fatigue life and high strength even without reinforcing fillers. Other than for thin sections it can be used to approximately 100C, and sometimes above. It can maintain flexibility down to 60C if compounded for the purpose. It has good creep and stress relaxation resistance and is low cost. Its chief disadvantage is its poor oil resistance and its lack of resistance to oxygen and ozone, although these latter disadvantages can be ameliorated by chemical protection. NITRILE RUBBER NITRILE RUBBER acrylonitrilebutadiene copolymer NBR Breon, Chemigum, Europrene, Hycar, Krynac, Nipol At temperatures up to 100C, or with special compounding up to 120C, nitrile rubber provides an economic material having a high resistance to aliphatic hydrocarbon oils and fuels. Different grades are available the higher the acrylonitrile (ACN) content, the higher the oil resistance but the poorer is the low temperature flexibility. It has high resilience and high wear resistance but only moderate strength. It has limited weathering resistance, and poor aromatic oil resistance. It can generally be used down to about 30C, but special grades can operate at lower temperatures.

7 PERFLUORO ELASTOMERS PERFLUORO ELASTOMERS FFKM Chemraz, Kalrez, Perfluor, Simriz, Zalak These are materials having even greater heat and chemical resistance than the fluoroelastomers. They can be used in extreme conditions up to temperatures around 300C or even higher with special compounding. Their disadvantages are difficult processing, very high cost, poor physical properties at high temperature, and their high glass transition temperatures which limit their use at low temperatures. Most materials cannot be used below zero Celsius, and even at normal ambient temperatures their creep properties are likely to be poor. POLYCHLOROPRENE POLYCHLOROPRENE CR This rubber has a generally good balance of mechanical properties and fatigue resistance second only to natural rubber, but with superior chemical, oil, and heat resistance. It is widely used in general engineering applications. It is less resistant than natural rubber to low temperature stiffening but can be compounded to give improved low temperature resistance. It has good ozone resistance. It is suitable for use with mineral oils and greases and dilute acids and alkalis, but is unsuitable in contact with fuels. It has generally poorer set and creep than natural rubber. POLYSULPHIDE RUBBER POLYSULPHIDE RUBBER TR Thiokol Very good resistance to oils, fuels, solvents, oxygen, and ozone. Impermeable to gases. Poor mechanical properties and poor heat resistance.

8 POLYURETHANE RUBBER POLYURETHANE RUBBER AU (polyester) EU (polyether) Adiprene, Estane, Genthane These materials have high tear strength and good wear resistance. Their upper temperature limit is typically 80C. They have excellent resistance to weathering and oxidation. They resist hydrocarbon fuels and mineral oils but some grades hydrolyse in hot water. They are one of the best rubbers for abrasion resistance and are therefore used in reciprocating seals. Some grades are castable. SILICONE (and FLUOROSILICONE) RUBBER SILICONE )& FLUOROSILICONE RUBBER MQ (methyl groups on chain) VMQ (methyl and vinyl groups) PMQ (methyl and phenyl groups) FMQ (methyl and fluorine groups) Silastic The outstanding property of these materials is their very wide temperature range. Typically the range is 60C to 200C and above, with PMQ down to 90C. They do not have very good physical properties, but the properties they do have are retained to high temperatures. FMQ has better oil and water resistance than the others. They are used in room temperature vulcanizing (RTV) sealants for joints. Beware corrosion if acetic acid is present as a curing agent.

9 STYRENE BUTADIENE RUBBER STYRENE BUTADIENE RUBBER SBR This is the highest volume general purpose synthetic rubber. It is very weak unless reinforcing fillers are incorporated. With suitable fillers it is a strong rubber although not approaching natural rubber or polychloroprene. Otherwise it has similar chemical and physical properties to natural rubber, with generally better abrasion resistance but poorer fatigue resistance. TETRAFLUOROETHYLENE/PROPYLENE TETRAFLUOROETHYLENE/PROPYLENE FEPM Aflas This is a high temperature polymer capable of operating in the range 20C to 200C (to 260C in steam). It has good overall chemical resistance including amines, methanol, steam and hot water. Its hydrocarbon resistance approaches that of FKM copolymer. It has, however, poor compression set and a high minimum working temperature. Hypalon, Nordel, Viton, Kalrez and Neoprene polychlorprene are all registered trademarks of DuPont Dow Elastomers