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In our JÄGER Wiki we have summarized some basic terms of rubber and plastics processing. In addition to a selection of different materials, you will also find a short description of recognised manufacturing and testing methods.
Acrylate rubbers (ACM) have a high resistance to mineral oils and elevated temperatures up to 160°C. Even sulfur-based additives of modern lubricants are no problem for ACM grades. Copolymers of acrylate and ethylene (AEM) are used to improve elasticity and resistance to water, acids and alkalis. The high resistance to hot air and hot oil makes ACM particularly interesting for the automotive and engine sector. ACM is primarily processed into hoses, seals and membranes. AEM grades are also processed for cooling water hoses, air intake hoses, cable sheathing and in special formulations as flame-retardant products without halogen content. The mechanical properties of ACM and AEM are rather moderate.
Acrylonitrile Butadiene Rubber (NBR)
The demand for an oil, grease and fuel resistant rubber led to the development of acrylonitrile butadiene rubber, colloquially known as nitrile rubber (NBR), in the 1930s. Due to the proportion of acrylonitrile units along the polymer chain, NBR has good to excellent resistance to mineral oils, fuels and solvents. At the same time, reinforced NBR vulcanizates show good mechanical properties.
Products made of NBR are always interesting when good resistance to oils, greases and fuels is required. This can be in the food sector, but also in technical areas or the automotive industry. The products range from hoses, O-rings, balls and flat seals to complex molded parts.
Butadiene Rubber (BR)
Butadiene rubber was developed in the 1920s through the polymerization of butadiene. As a so-called all-purpose rubber, BR is still one of the most frequently used rubber types in terms of volume. BR is characterized in particular by excellent elasticity, especially at very low temperatures. This results in excellent abrasion resistance and low dynamic heating. The aging and oil resistance of BR is comparatively poor.
Butadiene rubber is mainly used in the tire industry as a blending component. The addition to natural rubber or styrene-butadiene rubber makes it possible to significantly improve the abrasion and rolling resistance of a tread compound. In technical rubber goods BR is used to improve the elasticity of other rubbers in conveyor belts, shoe soles, roller covers or bearing elements. Pure BR compounds are generally not used due to their difficult processability.
The addition of a small proportion of isoprene in the production of polybutylene led to the development of butyl rubber in the mid-20th century. The particularly low gas permeability combined with very good resistance to polar chemicals, especially at elevated temperatures, distinguishes IIR from many other rubbers. IIR also exhibits extremely low elasticity over a very wide temperature range, which is equivalent to a high damping effect. The resistance to ozone and oxygen as well as (UV) light is particularly good with IIR.
A large part of the IIR rubber production is used in tire construction. As a so-called innerliner, the particularly low gas permeability is used to produce a tubeless tire. IIR is also used for bicycle tubes. The high damping capacity allows the use as a buffer spring or damper. IIR is also used to manufacture heat-resistant products such as bellows or boiler seals and for seals in contact with polar solvents. A further field of application is the production of chewing gum masses.
Chloroprene Rubber (CR)
In the course of the developments in the field of synthetic rubbers at the beginning of the 20th century, it was possible to produce chloroprene rubber (CR), a rubber similar to the general-purpose rubbers SBR and BR, which however showed a significant improvement in its aging properties. This special property, coupled with good mechanical behavior, but also significantly better resistance to acids, alkalis and polar chemicals, made chloroprene rubber the most important special-purpose rubber for many years. CR is also resistant to oils and greases and, to a limited extent, fuels.
CR-based compounds are used in many technical rubber products. The good aging properties and increased media resistance at a physical value level comparable to that of general-purpose rubbers make CR products interesting for stressed parts in outdoor applications and in contact with many different media. This includes bellows, cable sheathing, hoses, stop buffers and conveyor belts. CR is also used in the production of sports articles and clothing in contact with seawater. Here often as a foamed version. In dissolved form CR is a main component of many adhesives.
Compression molding process (CM)
Compression molding (CM) describes a discontinuous process for the production of rubber moldings. In this process, the raw compound is placed directly or in the form of a preformed blank in a preheated cavity or a cavity of the mold. By pressing the tool halves under high pressure the mixture is brought into the desired shape and vulcanized. The vulcanized molded part is then removed hot. Compared to transfer and injection molding, the heating time is longer, as the heat transfer is only effected via the wall of the cavity. Due to the simple design, the mold costs are very low in comparison. Compression molding is particularly suitable for large-volume parts or small quantities.
The term elastomers covers wide-meshed cross-linked polymers which are characterised by high elasticity and thus good recovery after mechanical stress. Elastomers, colloquially known as rubber, are produced from rubbers by cross-linking reactions with sulphur (vulcanisation), peroxides or similar chemicals.
The various elastomers or the underlying rubbers are classified into general-purpose rubbers, special-purpose rubbers and high-performance rubbers.
All-purpose rubbers are used especially in tire construction or for increased mechanical requirements.
Special-purpose rubbers also have special chemical or thermal resistances.
High-performance rubbers are those that are adapted to extreme chemical or environmental influences.
Epichlorohydrin (ECO) has similar properties to NBR, but convinces with its significantly better heat resistance and resistance to mineral oils. Long vulcanization times and tempering are required as part of the manufacturing process.
The properties of ECO are low gas permeability, excellent ozone and weathering resistance, good compression set and good heat resistance (up to 120°C).
EPDM rubbers stand for a class of polymers that are copolymers made up of the units ethylene, propylene and a diene component necessary for sulfur crosslinking. Since the development of EPDM in the 1950s, EPDM has become widespread in industry as a versatile material and is now one of the most frequently used elastomers for technical consumer goods in industry and trade.
The good resistance of EPDM to weathering of various kinds makes EPDM particularly popular for outdoor applications and as an inexpensive yet long-term resistant material in various sealing applications. Be it as a profile for sealing in the automotive sector or as an O-ring in drinking water applications for sealing taps and pipe connections. Peroxide cross-linked EPDM compounds can also be used at temperatures up to 150 °C. The resistance to greases and oils, however, is poor with EPDM.
Extrusion is a continuous process for the production of endless profiles. In a screw unit, the raw mixture is plasticized and preheated. Any pins that may be present ensure final homogenisation. The preheated mixture is then continuously pressed through the opening of a nozzle, also known as a mouthpiece, and then vulcanized. Various techniques such as infrared radiation or hot air are used for vulcanization.
The elastomer fluorosilicone rubber (FVMQ) is one of the types of silicone rubber. In addition to very high resistance to heat and cold, the properties of FVMQ include excellent resistance to ageing, weathering and ozone as well as good resistance to chemicals.
In order to meet the high demands of the chemical industry, but also the aerospace industry, the development of fluororubbers (FKM/FPM) took place in the middle of the 20th century. Fluororubbers are a class of rubbers which are characterized by their excellent resistance to most chemicals, oils, greases and fuels, but also by their very good resistance to high temperatures up to above 200 °C. At the same time, fluororubbers have good resistance to ageing and weathering.
Fluororubbers are used wherever high chemical resistance and/or high temperature resistance is required. This includes many seals and hoses in the automotive sector, but FKM is also frequently used in technical equipment.
Hydrogenated Nitrile Rubber (HNBR)
The high proportion of unsaturated double bonds in nitrile rubbers ensures relatively low temperature resistance and poor aging behavior. To compensate for this, hydrogenated nitrile rubber (HNBR) was established on the market in the 1980s. Hydrogenation with hydrogen reduces the proportion of double bonds to a minimum. This results in an improved aging behavior and at the same time a significantly increased temperature resistance. The resistance to mineral oil is maintained.
Products made of HNBR are used where an NBR reaches its limits. Here, the significantly improved high temperature range is particularly noteworthy. Similar to NBR, HNBR becomes interesting whenever good resistance to oils, greases and fuels is required. Especially in the engine compartment of modern motor vehicles HNBR is used in high temperature resistant seals and hoses.
Injection molding process (IM)
Injection molding (IM) describes a discontinuous process for the production of rubber moldings. In this process, the raw compound is first fed into a screw unit and plasticized, possibly homogenized and preheated by active heating elements and mechanically by the shear forces acting on it. A piston then presses the mixture via a distribution system into the cavities or cavities of the mold. Here, vulcanization takes place in a similar way to the TM or CM process, whereby preheating the compound significantly reduces the heating times. Injection molding is suitable for high quantities or high tolerance requirements. The tool costs are significantly higher compared to the CM process.
Als Kautschuk bezeichnet man die unvernetzten, polymeren Ausgangsstoffe zur Herstellung von Elastomeren beziehungsweise Gummi. Dabei wird zwischen Naturkautschuk, der aus dem Saft (Latex) des Kautschukbaums gewonnen wird, und den auf petrochemischem Wege hergestellten Synthesekautschuken unterschieden. Kautschuke sind plastische Rohstoffe, die erst durch die weitmaschige Vernetzung mit Schwefel oder Peroxiden ihre technisch nutzbaren elastischen Eigenschaften erhalten.
Natural Rubber (NR)
Natural rubber is obtained from the sap or latex of the rubber tree (Hevea Brasiliensis). For this purpose, the trees are scratched in the bark and the sap is collected. Natural or chemical coagulation is used to separate the rubber from the aqueous components, which are then purified and dried and preserved by various processes. Natural rubbers are available as smoked skins, but also as air-dried sheeting. The chemical name for natural rubber is cis-1,4-polyisoprene. Natural rubber is characterized by very good elasticity and high mechanical strength.
The main area of application for natural rubber is in the field of tire construction. The low heat build-up under dynamic load and the high tear resistance due to the formation of self-reinforcing crystallites (strain crystallization), which occurs at high elongation, are the basis for use in tire tread compounds, especially for truck tires. Due to their high elasticity, other areas of application for natural rubber are in the field of (vibration) dampers and as bearings and clutches for moving parts in the automotive and mechanical engineering industries.
Due to its high tensile strength, natural rubber is used in the agricultural sector, especially for belts and tapes, but also in a variety of moulded parts and roller coatings. Natural rubber is also used in rubber-metal spring elements and buffers.
Polycarbonate (PC) is classified in the group of thermoplastics. It is especially known for its water-clear, glass-like appearance.
The material shows its strengths in insulation against electric current and has high strength, impact resistance and hardness. Due to its transparent “color” and special strength, the material is also used as an alternative to glass (e.g. burglar-resistant glazing, safety helmets and visors).
The word ‘polymer’ comes from the Greek and is composed of the terms ‘polý’ and ‘méros’ and means ‘many parts’. Polymers are made up of many individual, mostly regularly arranged repeating units. These repeating units are called monomers.
The chemical properties such as resistance to media and ageing, but also temperature resistance are determined by the monomers, while the mechanical properties and processing behavior are determined by the chain length and the arrangement of the chains in relation to each other.
Polymerization is the chemical reaction of individual molecules, so-called monomers, to form a long unit of repeating units to form a polymer. A distinction is made here between homopolymers, which are made up of one type of monomer, and copolymers made up of different monomers. The polymers obtained can be varied by selecting the process conditions such as temperature, type of catalyst or solvent used. In this way, the physical properties such as the processability etc. of the polymer can be significantly influenced. Solvent resistance, temperature resistance etc. are influenced by the choice of monomers.
Rubber is the term used to describe the uncrosslinked, polymeric starting materials used to manufacture elastomers or rubber. A distinction is made between natural rubber, which is obtained from the sap (latex) of the rubber tree, and synthetic rubber produced by petrochemical means. Rubbers are plastic raw materials that only acquire their technically useful elastic properties through wide-mesh cross-linking with sulfur or peroxides.
Silicone Rubber (VMQ)
Unlike other rubbers or elastomers, silicone rubbers are not based on organic carbon chains, but on inorganic silicon-oxygen compounds, also known as siloxanes. Silicone rubbers have excellent elastic properties over an extremely wide temperature range of approx. -60 to +200 °C. At the same time, they are resistant to aging and weathering and exhibit moderate to good resistance to oils and solvents.
Silicones are also physiologically harmless and inherently flame retardant. Silicones are used in particular in seals and hoses in high-temperature and low-temperature applications, but silicones are also widely used in the medical sector or for thermal and electrical insulation of electronic components.
Styrene Butadiene Rubber (SBR)
Styrene butadiene rubber (SBR) was developed at the beginning of the 20th century with the aim of providing a cheap alternative to the expensive natural rubber and reducing dependence on imports from Brazil and East Asia. At the same time, the partly scarce availability of natural rubber, especially for countries like Germany, was to be compensated.
With the development of modern synthesis processes, SBR has become the most commonly produced synthetic rubber and, in particular due to its excellent wet grip properties, it is impossible to imagine car tires without it. However, SBR also plays an important role in highly stressed technical goods, such as conveyor belts in mining, because of its special mechanical strength.
Synthetic rubbers describe artificially man-made rubbers. They are usually based on organic monomers on a petroleum basis.
Synthetic rubbers differ from one another in the structure of the polymer chains (microstructure), which leads to a large variety of types.
Transfer molding (TM) describes a discontinuous process for the production of rubber moldings. Analogous to classical compression molding, the raw compound is brought into the corresponding mold in a cavity in the mold, a so-called cavity. For this purpose, the raw mix is placed in a storage pot, which is connected to the cavity via fine channels. When the tool is moved together, a punch presses the mixture through the channels into the cavity. The mixture is preheated so that the heating time can be reduced compared to the CM process. Transfer molding is suitable for medium to high volumes. The tooling costs are significantly higher compared to the CM process.
The term vulcanization refers to the chemical-physical transformation of the plastic rubber mass into the rubber-elastic state. For this purpose, the polymer chains are generally cross-linked in a wide-mesh manner using chemical cross-linking agents. Fixed points connect the polymer chains and thus ensure the formation of the rubber-specific restoring forces. Vulcanization usually requires high temperatures, time and pressure.