In manufacturing plants and facilities, rubber hoses are used in a variety of applications. In some cases, the type of rubber that the hose is made of is not suitable to the application it is being used for, resulting in potential safety risks for workers and equipment. The purpose of this article is to help the reader to determine the appropriate rubber compound for the application that is required.
By Vincent Kiathadi, Sales Engineer at Wah Joo Seng International Trading Pte Ltd.
There are plenty of rubber types on the market. The most commonly used are Natural Rubber (NR), Styrene-Butadiene Rubber (SBR), Nitrile Rubber (NBR), Ethylene Propylene Diene Monomers Rubber (EPDM) and Neoprene/Chloroprene Rubber (CR). For this article, we will base our discussion solely on these five types. Each of them has unique traits that make them suitable to a specific application.
Many factors must be considered when choosing the right material to use, including environmental factors—such as extreme temperatures, exposure to oils, fluids and chemicals—combined with physical requirements such as strength, flexibility and impact resistance. Where possible, speak to an expert to help you choose the right one.
- Natural Rubber (NR)
Natural rubber (NR) exhibits high tensile strength, abrasion resistance, resilience, tear strength and low hysteresis, giving it the most robust physical properties of any of the types compared here. It is ideal for bulk or dry material transfer.
Natural rubber is a polymer of isoprene (2-methyl-1,3-butadiene) with a molecular weight of 100,000 to 1,000,000. Unlike synthetic rubber, it is bio-degradable and ecologically friendly, as its material is obtained from cultivated rubber trees (hevea brasiliensis) in the form of latex (isoprene).
Polyisoprene, which is chemically similar to NR, has lower strength properties than the natural form but better low-temperature properties. Both rubbers are susceptible to degradation by weathering characteristics, and both show poor resistance to mineral and petroleum-based oils and fuels, making them unsuitable for oil/fuel transfer, which might cause the hose to swell and become weakened.
NR has the lowest operating temperature range, typically from -50°C to 70°C, hence it is only applicable for a moderate application.
- Styrene-Butadiene Rubber (SBR)
Styrene-Butadiene Rubber (SBR) is a copolymer of styrene and butadiene and is a cheaper alternative to NR. SBR compounds have similar physical properties to those of natural rubber, though they are not as robust. SBR is suitable for use as a utility hose to transfer air and water.
SBR is not oil resistant hence is not applicable for fuel transfer hose. Like natural rubber, it will swell and become weakened by oil and hydrocarbon.
- Ethylene Propylene Diene Monomers (EPDM)
Ethylene Propylene Diene Monomer (EPDM) is the product of Ethylene and Polypropylene polymerization. EPDM elastomers have a fair tensile strength and excellent resistance to weathering, ozone and chemicals. They also exhibit excellent electrical insulation properties.
Due to its weather, heat and ozone resistance, EPDM is the perfect hose cover, especially for outdoor environments. High-temperature tolerance— between 150°C (302°F) and 204°C (400°F) in water or steam)—makes EPDM an excellent steam hose, and it is also a great choice for conveying low and high pH fluid.
However, EPDM is not oil resistant—thus unsuitable for fuel transfer hose—and can also be very costly.
- Nitrile Rubber (NBR)
Nitrile rubber (NBR) is the general term for acrylonitrile butadiene copolymer. The acrylonitrile content of nitrile sealing compounds varies considerably—from 18% to 50%—which influences the physical characteristics of the finished material.
Of all the types examined here, Nitrile Rubber (NBR) has the best oil resistance, making it the ideal choice for a fuel transfer hose. The higher the acrylonitrile content, the better the resistance to oil and fuel. However, this may come at a cost; elasticity and compression resistance are adversely affected, and because of these effects, a compound with medium acrylonitrile content is often selected.
NBR has decent mechanical properties when compared with other elastomers, and high wear resistance. However, NBR is not ozone or weather resistant and therefore not ideal as a hose cover.
- Neoprene (CR)
Neoprene (CR) is typically used as hose cover because of its flame-retardant property. It also exhibits decent ozone, aging and chemical resistance. It has good mechanical properties over a wide temperature range, typically as high as 121°C (250°F) and as low as -40°C (-40°F). Neoprene demonstrates good oil resistance and was originally intended to be an oil resistant replacement for natural rubber.
Neoprene is made from the polymerization of Chloroprene monomer, which was the first synthetic rubber developed commercially.
The table below summarizes the advantages and disadvantages of different rubber hoses.
Vincent Kiathadi is the Sales Engineer at Wah Joo Seng International Trading Pte Ltd. He can be reached at vincent.k@wahjooseng.com.
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