FLUID SEALING TECHNOLOGIES
for DEMANDING APPLICATIONS
YOUR CENTRAL & EASTERN EUROPEAN PARTNER
Materials Chemical Compatibility
Technical Guide to Materials and Chemical Compatibility
ACM (Polyacrylic or Polyacrylate)
These rubbers are usually copolymers of ethyl acrylate and a vinyl ether and are resistant to heat, hydrocarbon oils and in particular, oil additives, especially sulphurised types used for lubrication under extreme pressure conditions. ACM elastomers offer excellent heat resistance; they can typically be used at temperatures of 150°C (up to 175°C for limited periods). They provide high resistance to ozone, weathering and oxidation but are extremely susceptible to hydrolysis, hence their unsuitability for use in aqueous media. Compression set and low temperature flexibility depends on the base polymer and compounding choice. ACM elastomers are used primarily where combined resistance to heat and oil is required, typical uses include O-rings, seals and gaskets mainly for the automotive industry, particularly under-bonnet applications.
AEM (Ethylene Acrylic)
These elastomers are terpolymers of ethylene, methyl acrylate and a cure site monomer. AEM elastomers offer good resistance to heat ageing, weathering, aliphatic hydrocarbons and good low temperature performance. They show poor resistance to strong acids, hydrolyzing agents and some polar fluids. AEM applications are similar to those of ACM elastomers, but AEM has the advantage where low temperature flexibility is concerned. Applications typically include shaft seals, spark plug boots, CV joint bellows and ignition wire jackets.
AU / EU (Polyester and Polyether Urethane)
These elastomers generally show outstanding tensile strength, tear and abrasion resistance, and give excellent protection against oxygen and ozone (except in hot climates, due to greater risk of microbiological attack in AU types, and ultraviolet light in the case of EU types). EU elastomers have a better low temperature flexibility (-35°C typically) and both have excellent resistance to high-energy radiation. Polyurethane rubbers are used where high abrasion resistance and oil / solvent resistance are required together, e.g. hydraulic seals and gaskets, diaphragms, hoses and roller-skate and skateboard wheels. In all applications, consideration should be given to hydrolysis and limited heat resistance.
Chloroprene rubbers are essentially chlorinated polyisoprenes, which exhibit medium resistance to high molecular weight oils. Chloroprene rubbers contain chlorine in the polymer to reduce the reactivity to many oxidising agents, as well as to oil and flame. CR elastomers also have good resistance to ozone cracking, heat ageing and chemical attack. Some of the important applications of CR elastomers include Vee-belts, coated fabrics, cable jackets, tyre-sidewalls, seals and gaskets in contact with refrigerants, mild chemicals and atmospheric ozone.
CSM (Chlorosulphonylpolyethylene or Chlorosulphonatedpolyethylene)
CSM grades contain 24-43% chlorine content to provide excellent ozone and weather resistance, high resistance to many oxidising and corrosive chemicals, good resistance to dry heat to 150°C, low flammability and gas permeability, and also good resistance to hot water (when cured with lead oxide). The low temperature properties are generally limited, depending on the chlorine content of the CSM grade used, and the compression set is not very good. CSM elastomers are generally useful in electrical applications, weather resistant membranes, hoses and acid resistant tank linings.
These halogenated linear aliphatic polyethers show excellent resistance to ozone and weathering and very good resistance to hydrocarbon oils bettered only by polysulphides, fluoroelastomers and high-acrylonitrile nitrile rubbers. They exhibit good mechanical properties but are susceptible to sour gas attack. They are unsuitable for use with ketones and esters, alcohols, phosphate ester hydraulic fluids, sour gas, water and steam, and generally not recommended for rubber to metal bonding (they are corrosive to metals). The main applications for ECO elastomers are centred on the automotive industry, for use as seals, gaskets, diaphragms, cable jackets, belting, plus low temperature Natural Gas diaphragms.
These rubbers are mainly available in two structures – as the copolymer (EPR), or as the terpolymer (EPDM). The properties for both types of rubber are very similar with the polymers exhibiting outstanding resistance to weathering, ozone, water and steam. These rubbers have good chemical resistance and are particularly recommended for use with phosphate ester based hydraulic systems. They are typically used in the production of window and door seals, wire and cable insulations, waterproofing sheets and hoses. They are not suitable for use with mineral oils or petroleum based fluids. These rubbers can either be sulphur or peroxide-cured, in general sulphur-cured grades have superior mechanical properties and inferior high temperature properties and viceversa for peroxide cured grades.
FEP/PFA (Fluoroethylene Propylene-Perfluoroalkoxy)
These chemically modified fluorocarbon copolymers (fluoropolymers) appear more like plastic than rubber, they are extremely resilient and show excellent chemical resistance. Mechanical properties are very good even at high temperatures. Non-stick characteristics are excellent and abrasion resistance can be classified as moderate. The effective continuous temperature range is from -100°C to +200/250°C for FEP/PFA respectively. Typical applications include door seals and sealing systems in diaphragm pumps, cryogenic plants, sealed filter units, corrosive fluid plants, relief and emergency valves and pneumatics. Fluoropolymers are often used to encapsulate other elastomers to produce composite seals.
FEPM or TFE/P (Tetrafluoroethylene/Propylene)
A copolymer of tetrafluoroethylene and propylene, FEPM is solely produced by the Asahi Glass Company, and sold under the name Aflas®. FEPM vulcanisates exhibit similar thermal stability to FKM elastomers, but better electrical resistance and a different chemical resistance profile. FEPM compounds have the ability to resist a wide range of chemical combinations such as sour gas and oil, acids and strong alkalis, ozone and weather, steam and water, all hydraulic and brake fluids, alcohols, amine corrosion inhibitors, water-based drilling and completion fluids, high pH completion fluids and high energy radiation. However, they are not compatible with aromatic hydrocarbons, chlorinated hydrocarbons (e.g. M.E.K. and acetone), organic acetates and organic refrigerants. FEPM elastomers are suitable for long-term service in air up to 225°C and for short periods up to 250°C, but are limited in low temperature applications. They are finding wide applications mainly in oil-field operations and chemical processing as O-rings, seals and gaskets, cable insulating and jacketing and hose liners.
FFKMs exhibit outstanding high temperature properties and are the most chemically resistant elastomer available; effectively a rubber form of PTFE. They are superior to FKM elastomers, showing continuous dry-heat resistance to 260°C, with extended performance to 330°C for high temperature grades. They are extremely inert chemically and show excellent resistance to the majority of chemicals that attack other elastomers. Other notable properties include excellent resistance to oil-well sour gases, high temperature steam, low out-gassing under vacuum and good long-term high temperature compression set resistance. Typical applications are sealing systems for oil refineries, pharmaceutical plant, aerospace, chemical plant and the semiconductor industry. See Page 11 for details of Perlast®, the FFKM Perfluoroelastomer material from PPE.
FKM/FPM (Fluoroelastomer or Fluorocarbon)
This class of rubber is available as a copolymer, terpolymer or tetrapolymer; the type determines the fluorine content and thus, chemical resistance. FKM materials are either bisphenolcured or peroxide-cured for better resistance to wet environments. General properties include excellent resistance to heat, aliphatic and aromatic hydrocarbons, chlorinated solvents and petroleum fluids. Fluoroelastomers have a clear superiority in O-ring sealing force retention over most other oil-heat resistant rubbers with the exception of perfluoroelastomers such as Perlast® (see page 11). FKM/FPMs do show poor resistance to ethers, ketones, esters, amines and hydraulic fluids based on phosphate esters. Special compounds are required to provide suitable resistance to hot water, steam and wet chlorine. Typical applications are for valve-stem seals, crankshaft seals, diesel engine cylinder O-ring seals, pinion seals, glow plug seals, ducting expansion joints and seals for the aerospace industry.
FVMQ elastomers are modified silicone rubbers, which have many of the properties associated with silicone rubber but show great improvements in oil and fuel resistance. Typical properties include excellent resistance to ozone, oxygen, weathering and non-adhesive characteristics. They have a very wide service temperature range and low chemical reactivity. They do however have low tensile strength, poor tear and abrasion resistance and high gas permeability. Typical uses include sealing systems requiring wide temperature exposure and resistance to aerospace fuels and oils.
This copolymerised structure of isobutene and isoprene has an effective long-term temperature range of -50° to +120°C. The key properties for this rubber are very low gas permeability and water absorption with very good resistance to ozone, weathering and oxygen. All grades have very low elastic resilience and are suitable for use with many fluids except for mineral and petroleum based chemicals. Typical applications are tyre inner tubes, vacuum seals and membranes, pharmaceutical enclosures and shock absorbers.
Synthetic version of natural rubber; its strengths and uses are similar, but its relative purity means that IR materials tend to 16 crystallise less at low temperatures. Consequently, it has better performance at lower temperatures but, at normal temperatures, its performance is inferior to natural rubber.
NBR (Nitrile or Acrylonitrile Butadine)
The properties of this copolymer are governed by the ratios of the two monomers acrylonitrile and butadiene. Nitrile rubber can be classified as three types based on the acrylonitrile (ACN) content (low, medium and high). The higher the ACN content, the higher will be the resistance to aromatic hydrocarbons. The lower the ACN content, the better will be the low temperature flexibility. The most commonly specified, and the best overall balance for most applications is, therefore, 'medium nitrile'. High Nitrile: Medium Nitrile: Low Nitrile: >45% ACN content 30 – 45% ACN content < 30% ACN content General characteristics of NBRs include excellent resistance to aliphatic hydrocarbon oils, fuels and greases, very low gas permeability, improved heat ageing and ozone resistance, improved tensile and abrasion strength, hardness, density and low compression set. Typical applications are as gaskets and seals, hoses and cable jacketing in hydraulic/pneumatic systems and oil/hydrocarbon based environments.
HNBR (Hydrogenated Nitrile)
HNBR elastomers are a saturated version of NBR, showing superior heat resistance. General properties include excellent wear resistance, high tensile strength, high hot-tear resistance, low compression set and very good ozone and weathering resistance. They also exhibit good resistance to many oil additives, hydrogen sulphide, high-energy radiation and amines present in crude oil. HNBRs fill the gap between NBRs and FKMs in many areas of application where resistance to heat and aggressive media are required simultaneously, and may therefore provide a lower cost alternative to FKM elastomers. Typical applications are in extreme environments such as oil-fields and under-bonnet automotive.
NR (Natural rubber )
Natural rubber (tapped from the cultivated rubber tree) exhibits high tensile strength, abrasion resistance, resilience, tear strength and low hysteresis. These rubbers exhibit the best long range elasticity. The chemically similar IR (polyisoprene) has lower strength properties than the natural form but better low-temperature performance. Both rubbers are susceptible to degradation by weathering, and both show poor resistance to mineral and petroleum-based oils and fuels. Main applications apart from tyres are for vibration mounts, springs and bearings.
Polytetrafluoroethylene is not an elastomer but an extremely inert thermoplastic, unaffected by virtually all known solvents. It also exhibits this inert characteristic over a wide range of temperatures. Its hardness and lack of elasticity prevents its general use as an elastomeric sealing ring, but it is often used as a back-up ring. Typical applications are backing rings, bearings and non-stick requirements, or for use in composite seals when combined with elastomers.
This copolymer of styrene and butadiene is used in general applications where exposure to mineral oils is not required. Originally developed to replace natural rubber, it performs better at high temperatures, although tensile strength, resilience and abrasion resistance are inferior at lower temperatures. SBRs have inferior weathering and chemical resistance to most other elastomers. Typical applications are sealing requirements for hydraulic braking systems.
These elastomers, which include the phenyl substituted silicones are noted for their high and low temperature applications (phenyl silicones offer exceptionally low temperature flexibility). They have excellent resistance to ozone and weathering and good resistance to compression set at high temperatures. They do, however, have poor tensile strength, low tear and abrasion resistance and high gas permeability. Silicones have a low level of combustible components; even when exposed to flame, the elastomer is reduced to a nonconducting silica ash. Silicones also exhibit excellent compression set and high physiological inertness (tasteless, odourless and completely non-toxic). Silicones are also resistant to bacteria, fungi, a wide range of media including high energy radiation and excellent release properties (except to glass). Platinum-cured silicones offer enhanced levels of purity and low extractables making them ideal for pharmaceutical, biomedical and food & drink applications.