Types of Rubber Compounds and the Properties of Lining Rubber
We supply a large amount of information regarding rubber and their durable lining properties to assist you and to help make an informed decision regarding your lining and lagging projects.
The following will show you the details in the difference and similarities between these soft and hard rubbers as well as their physical properties and durability potential. If this information is not enough All State Conveyors will be happy to speak to you to assist you with your choice for your project.
The duro types of lining rubbers produced from various rubbers are divided into two categories: Soft and Hard.
Soft rubber linings normally have a hardness range of 40º to 80º IRHD and are intended specifically for conditions which are corrosive or abrasive.
Hard rubber lining and ebonites have a hardness range of 25º to 80º on the Shore D scale.
Because there are so many variables which govern the detailed properties of vulcanised rubbers (cured rubber), it is not possible when describing individual types of rubber to be precise about the actual chemical resistance and the temperature range over which they may be used. Therefore, details of the different rubbers are intended for guidance only and opinion should be sought from the lining contractor for more precise.
ASC stocked Rubber Lining is generally designed for vulcanisation at elevated temperatures but we also stock some rubber lining that contains accelerated systems which are capable of promoting vulcanisation at ambient temperatures. We also have certain rubber lining which can be applied in the form of pre-vulcanised (cured) sheets or laminates for your convenience.
Soft Rubber Linings
*Temperature range for lining and sheet rubbers can vary due to the compound design. It is critical to check with your supplier or the manufacturer.
Natural (NA) or Synthetic Polyisoprene (IR) Rubber
Lining rubber compounds are resistant to the majority of inorganic chemicals with the exception of strong oxidising agents. Polyisoprene has a good consistency and low impurities but resistance to organic chemicals is limited due to the composition being unsuitable for use with hydrocarbons, halogenated hydrocarbons, sunlight and ozone, mineral oils, many vegetable oils and esters. When suitably compounded, polyisoprene can be utilised with a temperature range of -30ºC to +100ºC*.
Styrene-Butadiene Rubber (SBR)
Co-polymers or styrene-butadiene has properties broadly similar to those of the polyisoprene rubbers, when compounded for the same duties. They have good wear resistance and are very stable when protected by the right compound composition.
Polychloroprene Rubber (CR)
Polychloroprenes (the polymer) or Neoprene as it is commonly known, gives lining compounds a greater resistance to heat, ozone, sunlight, chemicals, flammability, mineral oils, greases, diluted acids and alkalis compared to polyisoprene rubbers. This rubber has the perfect balance between fatigue resistance and mechanical properties and bonds well to substrates. The rubber should not be used with halogenated hydrocarbons or aromatic hydrocarbons.
Selected polymer grades can be used continuously within the temperature range -20ºC to +100ºC* depending on the polymer crystallinity and compound design.
Butyl Rubber (BR)
Butyl rubber is the industrial name for the co-polymers of isobutylene with a small percentage of isoprene. This rubber has good flexibility and impermeability properties. Chlorinated or brominated butyl rubbery, that is generally easier to process, is also available. A thorough understanding of your conveyor system plays an important role in defining the specific grade of Butyl to be used for certain applications.
Lining compounds based in butyl rubbers have very good resistance to heat and chemicals, that inclide some oxidising chemicals, and have low permeability to gases. This rubber should not be used in the presence of free halogens, petroleum oils, hydrocarbons and halogenated hydrocarbons.
When suitably compounded, butyl lining rubbers have lower water absorption then most other rubbers and can be used within the temperature range -30ºC to +170ºC*.
Ethylene Propylene Rubbers (EPR or EPDM)
Ethylene propylene rubbers are available as a co-polymer (EPR) or the ter-polymer (EPDM). EPDM is commonly requested and a popular choice. Lining compounds based in these polymers have the most water resistance, a very good resistance to extreme variant temperatures, acids, alkalis, salts, ozone and many organic chemicals but are not resistant to oils hydrocarbons and chlorinated solvents. The polymers may be compounded for use within the temperature range of -30ºC to +110ºC* and EDPM also has good electrical resistance.
Nitrile Rubbers (NBR and XNBR)
butadiene co-polymer (Nitrile Rubber NBR) and its variant, carboxylated nitrile rubber (XNBR), have excellent resistance to swelling from mineral oils and fuels. Polymers of high acrylonitrile to butadiene ratios have the best resistance and also have lower gas permeability. Higher butadiene ratios have better low temperature properties. The higher the arcrylonitirite content the higher the resistance to oil but it affects the low temperature flexibility. The polymers should not be used with phenols, ketones, strong carboxylated acids, aromatic hydrocarbons and nitrogen derivatives.
Carboxylated nitrile rubber is normally used for its outstanding abrasion resistance especially in combination with butadiene rubbers. Depending on compounding techniques, nitrile rubber lining has similar physical properties to polyisoprene rubbers and is suitable for use within the temperature range of -20ºC to +110ºC*.
Polybutadiene Rubber (BR)
Polybutadiene rubber is normally used in combination with polyisoprene or carboxylated nitrile rubber to produce linings with superior abrasion resistance compared to the individual rubbers and to improve the lower temperature properties of nitrile rubber.
Chlorosulphonated Polyethylene Rubber (CSM)
Chlorosulphonated polyethylene rubber is a synthetic polymer with excellent resistance to heat, ozone and oxidising chemicals. It can be compounded for excellent resistance to atmospheric conditions i.e. oxygen, ozone and water. The lining has also great resistance to chemicals such as sodium hypochlorite as a bleaching agent and sulphuric acid. It has good resistance to many oils, lubricants and aliphatic hydrocarbons but is not suitable to use with esters, ketones, chlorinated solvents and aromatic hydrocarbons.
Chlorosulphonated polyethylene may be used for linings operating continuously within the temperature range -5ºC to +105ºC*.
Hard Rubber and Ebonite Linings
Hard rubber linings are usually produced by incorporating higher levels of sulphur in the formulations, compared to those used in soft rubber linings. As the level of sulphur used is increased, the percentage of the residual unsaturation in the polymer decreases thus producing a harder lining. The process is known as hot vulcanisation.
What is Hot Vulcanisation?
Lining Rubber Hot vulcanisation can be produced by several methods.
Vulcanisation with an autoclave produces saturated hot steam or radiant thermal heat under pressure to bond the lining rubber to the substrate within a heated jacket and sealed chamber. Vulcanisation can also be produced with hot air or water at ambient pressure. The method employed depends upon the design and size of the equipment. The duration of vulcanisation will also depend upon the method used and the composition of the lining material.
When highly unsaturated rubbers are used with sulphur levels between 25 and 50 parts by weight per 100 parts by weight of rubber then hard vulcanisates, commonly called ebonites, are formed which are thermoplastic materials. These ebonites can be produced from natural or synthetic polyisoprenes, styrene-butadiene, acrylonitrile-butadiene and polybutadiene rubbers and blends of those rubbers.
Some hard rubbers are produced with relatively low sulphur levels by the incorporation of various resins. When it is necessary to create flexible or impact-resistant ebonites then polymers with a limited liability to harden when vulcanised are added to formulations.
Hard rubbers and ebonites generally have a higher resistance to chemicals than soft rubbers based on the same polymer types. This resistance again generally increases with the decrease in the un-saturation of the vulcanised polymer. Resistance to chlorine gas and most aliphatic carboxylic acids is particularly improved.
Due to the increase in saturation when high levels of sulphur are used, ebonites usually have low elongation at a break of 2% to 10%. Hence, they are brittle compared to soft rubber lining materials at ambient temperatures. This brittleness can be reduced by using flexibilising additives.
Ebonites are normally used within the temperature range 0ºC to 100ºC. For lower operating temperatures, ebonites are modified with flexibilisers or non-ebonite hard rubbers are often used.
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