M Barnwell Services offers an unrivalled range of materials properties suitable for every fluid sealing application and industry. Our Quality and Purchasing teams work hand in hand to source, develop, check and approval a vast range of Materials to meet the increasing demands of today’s engineering applications.
M Barnwell Services are proud to state that we are the UK’s largest independent stockist and distributor of all type of fluid sealing products.
ACM is used mainly by the automotive industry as it is resistant to engine, transmission and ATF oils even at high temperatures. The temperature application range is circa –20°C to +150°C.
Trade name e.g. Vamac® (Du Pont-Dow Elastomers). AEM is like ACM mainly used by the automotive industry. AEM has a higher resistance to low and high temperature than ACM and based on its entire properties can be classified between ACM and FKM. The material is resistant to weathering and ozone and can be used with enriched mineral oils, water and refrigerants. The temperature application range is circa –30°C to +150°C (for a short time +175°C).
Trade name e.g Desmopan® (Bayer). Polyurethanes differ from classic elastomers in that they have much higher mechanical properties, for example, a high resistance to abrasion, wear and extrusion, a high tensile strength and tear resistance. The material is resistant to ageing and ozone and can be used with mineral oils and greases, silicone oils and greases, non-inflammeble fluids HFA and HFB and water up to of 50°C, as well as pure aliphatic hydrocarbons.
Trade name e.g. Neoprene® (Du Pont-Dow Elastomers). Chloroprenes have excellent resistance to ozone, ageing and weathering and also good mechanical properties. They have average resistance to mineral oils, and are suitable for use with many refrigerants. The temperature application range is from –40°C to +100°C.
Trade name e.g. Nordel®‚ (Du Pont-Dow Elastomers). EPDM materials generally have a high resistance to hot water, steam, ageing and chemicals, and are suitable for a wide range of temperature applications. They are divided into sulphur- and peroxide-cured types. Peroxide-cured compounds are suitable for higher temperature ranges and have a much lower compression set.
EPDM has a good resistance to hot water and steam, detergents, caustic potash solutions, sodium hydroxide solutions, silicone oil and greases, many polar solvents, many diluted acids and chemicals. Special qualities are recommended for glycol-based brake fluids. EPDM materials are totally unsuitable for use with all mineral oil products (lubricants, fuels). They can be used between –45°C and +130°C (peroxide-cured –50°C to +150°C).
FEP is a thermoplastic material with similar properties to PTFE. Seamless FEP-encapsulated O-rings have an elastic core in FPM or VMQ. They are used at very high thermal and chemical loads. The extremely high chemical resistance of the cover protects the elastic core material against the chosen medium. Another advantage of the cover is its very low coefficient of friction.
This results in a combination of very high chemical and thermal load bearing ability and the elastic properties of standard commercial elastomers. The core material is chosen to suit the temperature range and medium.
Because of its limited flexibility, great care is required during installation. Warming the material in water or oil to between approx. 80°C and 100°C increases flexibility and supports the installation.
Depending on the core material, the temperature application range is from –55°C to +200°C.
Trade names e.g. Perlast (Idex-PPE), Simriz (FST), Chemraz (Greene Tweed), Kalrez® (DuPont-Dow Elastomers), Parofluor (Parker), Isolast (Trelleborg). The chemical and heat resistance of perfluoro elastomers are similar to those of PTFE. They combine the positive properties of PTFE with the elastic behaviour of FKM. Because this material group is considerably more expensive, perfluoro elastomers are only used if other materials cannot meet the specifications and if safety requirements justify the higher expenditure.
Typical applications for perfluoro elastomers include the chemical, oil, and semiconductor industries, high vacuum technology, and the aerospace industry.
Trade name e.g Viton® (Du Pont-Dow Elastomers). FKM materials are noted for their very high resistance to temperatures and chemicals. Other key benefits are its excellent resistance to ageing and ozone, very low gas permeability (excellent for vacuum application) and the fact that it is self-extinguishing.
The standard FKM material for O-rings has excellent resistance to mineral oils and greases, aliphatic, aromatic and chlorinated hydrocarbons, fuels, non-inflammable hydraulic pressure fluids HFD and many organic solvents and chemicals.
In addition to the standard FKM materials, a number of special compounds with different compositions of polymer chains and varying fluoro contents (65% to 71%) are developed for special applications.
FKM is generally not resistant to hot water, steam, polar solvents, glycolbased brake fluids and low-molecular organic acids.
Trade name e.g. Silastic LS® (Dow Corning). Although fluorosilicone elastomers have the same mechanical properties as silicone, they are far more resistant to oils and fuels. The temperature range of applications is somewhat more restricted than that of silicone. The temperature application range is from –55°C to +175°C.
HG hard fabric materials are produced from various fabric/resin combinations, such as synthetic fibre fabric + phenolic resin, cotton fabric + phenolic resin or polyester fabric + polyester resin. HG materials are selected for application areas in hydraulics with high loads and shear forces. With the selection of the optimal material combinations (fabric/resin) a long product life, high restoring force, low friction (dry-running characteristics exist) and very high contact pressure (load capacity) can be achieved. Standard material displays no moisture expansion in water; or measurable absorption of water.
Trade name e.g. Therban® (Bayer). HNBR is obtained by fully or partially hydrogenating NBR. It leads to considerable improvement in resistance to heat, ozone and ageing, and gives it very good mechanical properties, e.g. good resistance to wear. The media resistance compares to that of NBR. HNBR has a good resistance to some refrigerants. The temperature application range is from -30°C to +150°C.
Trade name e.g. Perbunan® (Bayer). NBR is the most common standard material because of its good mechanical properties and resistance to mineral oil-based lubricants and greases. Good resistance to fuels is usually possible only with special compounds.
Its properties are mainly determined by the acrylonitrile content (ACN between 18% and 50%). A low ACN content ensures good flexibility at low temperatures, but offers limited resistance to oils and fuels; as the ACN content increases, flexibility at low temperatures decreases and resistance to oils and fuels improves. The standard NBR material offers an average ACN content to suit a wide range of applications with balanced properties. It has good mechanical technological values such as high abrasion resistance, as well as good resistance to mineral oil-based lubricants and greases, hydraulic oils H, H-L, H-LP, non-inflammable hydraulic fluids HFA, HFB, HFC, aliphatic hydrocarbons, silicone oil and greases and water to approx. +80°C.
NBR is generally not resistant to aromatic and chlorinated hydrocarbons, fuels with a high aromatic content, polar solvents, glycol-based brake fluids, and non-inflammable hydraulic fluids HFD. It has a low resistance to ozone, weather and ageing, but in most applications, e.g. when the material is wetted with oil, this has no negative effect.
Cotton or synthetic fibre fabric can be used as the basis for rubber fabric materials. The standard material for hydraulic seals is cotton fabric. In addition to the standard material, a whole range of other fabric types and almost all elastomers for impregnation are available. For the production of hydraulic seals, the fabric is impregnated with an NBR elastomer solvent. Subsequently, appropriate dimensions are cut out of the impregnated cloth and rolled for further processing and then vulcanised in a vulcanisation press, under the influence of temperature and time, to produce hydraulic seals. Hydraulic seals are either produced totally of rubber fabric material or segments of the elastomer part are reinforced with fabric, e.g. the running surface or the side facing away from the pressure, to achieve better protection from gap extrusion. The so called multi component seal can be produced by vulcanising pure elastomer onto the seal.
The advantages of impregnated rubber fabric hydraulic seals are varied. They have high wear resistance, very good friction and sliding characteristics (due to the lubricant stored in the fabric lubricant pockets), good low temperature resistance and high pressure load and extrusion resistance. In addition rubber fabric hydraulic seals are inherently very dimensionally stable and have a low moisture expansion tendency in hydraulic media. Due to their robust design and material combinations they are particularly well suited for rough application conditions, such as in mobile hydraulics or other heavy duty applications.
Natural rubber is still obtained from the latex of certain plants. Vulcanised natural rubber has good low temperature and mechanical properties and a high elasticity. NR vulcanised materials are resistant to water, glycols, alcohols, glycol-based brake fluids, silicone oils and greases and diluted acids and bases. The temperature application range is from approx. –50°C to +80°C.
PTFE is a fluorinated plastic. PTFE has numerous positive characteristics, which have become indispensable in seal technology. It distinguishes itself by its almost universal chemical resistance, its wide operational temperature range of -100°C to +250°C, an extremely low friction value which results in very good sliding characteristics, no stick-slip effect, particular rigidity and almost unlimited ozone, weathering and ageing resistance. PTFE is impervious to almost all known hydraulic media, lubricants, chemicals and solvents.
Only elementary fluorine and alkaline metals attack it at high temperatures and pressures. Pure PTFE contains no extractable substances which could wander and negatively affect adjacent materials. It is, therefore, physiologically harmless and particularly suitable for food and beverage applications, pharmaceuticals and medical application areas. PTFE is non-flammable and so does not constitute an additional hazard in case of fire.
PTFE is not or only slightly elastic. For this reason, PTFE seal elements are activated by elastic energising elements in the form of o-rings or stainless steel springs. Pure PTFE is not totally without disadvantages as it has a tendency to cold flow or crawl under pressure load. These weaknesses are counteracted by the use of seal compounds mixed with fillers. Compounds filled with bronze for example, give PTFE the ability to adapt to most application conditions.
Trade name e.g. Buna Hüls® (Hüls). SBR is used in glycol-based brake fluids, water, alcohols, glycols, silicone oils and greases. The temperature application range is from –50°C to +100°C.
Trade name e.g. Aflas® (3M). TFE/P is a relatively new addition to the group of fluoroelastomers and is noted for its excellent thermal (0°C to +200°C) and chemical resistance. It is particularly suitable for use in hot water, steam, acids, alkaline solutions, ammonia, amines, alloyed engine and transmission oils, brake fluids (based on glycol, mineral oil and silicone oil), crude oil, sour gas.
TPU materials belong to the group of thermoplastic elastomers TPEs. The strength of the TPUs lies in the good combination of physical and chemical characteristics as well as ease of processing to provide economical technical solutions. TPUs are produced on thermoplastic injection moulding machines and have been established in the seal technology sector and in particular, hydraulic applications, for many years.
TPU materials stand out from the classic elastomers due to their distinctly higher mechanical strength. Other outstanding material characteristics are high abrasion, wear and extrusion resistance, high pressure load capacity, as well as a high tear and elongation at break resistance. TPU materials display good flexibility (also in the higher hardness areas) at temperatures between -40°C and +100°C and very good ageing and ozone resistance.
TPU materials are suitable for application in mineral oils and greases, hydraulic oils H, HL, HLP, silicone oils and greases, highly non-flammable hydraulic fluids HFA and HFB and water up to 50° as well as pure aliphatic hydrocarbons.
Trade name e.g. Silopren® (Bayer). Silicone rubbers are noted for its wide thermal range and excellent resistance to ozone, weathering and ageing. Compared with other elastomers, silicone’s mechanical properties are on the low side. Generally, silicone materials are physiologically harmless; they are also used by the food and medical industries.
The standard silicone material can be applied at temperatures from –55°C to +200°C and is resistant to water (up to 100°C), alphatic engine and transmission oils, animal and plant oils and fats.
Silicone is generally not resistant to fuels, aromatic mineral oils, steam (short term up to 120°C possible), silicone oils and greases, acids and alkalis.