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Performance characteristics of five commonly used elastomers

Performance characteristics of five commonly used elastomers
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With over forty years’ experience of producing elastomer components for a wide and varied range of industriess and customers right across the world, we’d like to think we know a thing or two about Elastomers.

In layman’s terms, elastomer is another word for rubber, but what makes elastomers special is their ability to ‘bounce back’. Specifically, some elastomers can be stretched by up to 700 times their original length - but due to their chemical make-up, they have the capacity to return to their original shape with little or no permanent damage or deformation.

This is achieved through the chaotic structural make-up of elastomers that contain polymer chains which wind and tangle in a jumbled mess when viewed under a microscope. However, when the elastomer is stretched, the polymer chains are forced into the same direction in which the rubber is being pulled. As elastomer strives to revert back to its original state, the polymer chains return to their position once tension has been released.

A portmanteau of Elastic and Polymer, Elastomer’s versatility make it the perfect material for seals, adhesives and moulded flexible parts, and in our latest blog, we look at five specific varieties in closer detail, comparing their typical properties, and some of their common uses.

EPR/EPDM: Ethylene-Propylene

Mainly available in two structures, either as a copolymer (EPR), or as a terpolymer (EPDM), Ethylene-Propylene is commonly used in the production of seals and gaskets in the food industry, window door seals, wire and cable insulations, waterproofing sheets, and hoses.

Advantages
⦁ Outstanding resistance to weathering, ozone, water and steam
⦁ Good chemical resistance
⦁ Sulphur-cured grades have superior mechanical properties
⦁ Peroxide-cured grades have superior high temperature properties

Disadvantages
⦁ Sulphur-cured grades have inferior high temperature properties
⦁ Peroxide-cured grades have inferior mechanical properties
⦁ Not suitable for use with mineral oils, or petroleum based fluids

NBR: Nitrile or Acrylonitrile Butadine

Nitrile rubber can be classified into three types based on the acrylonitrile (ACN) content (low, medium and high). The higher the ACN content, the higher the resistance to aromatic hydrocarbons.

The unique balance of oil, chemical, heat and cold resistance allows it to work well in a wide variety of automotive and industrial applications, making it the ideal material for gaskets and seals, hoses and cable jacketing.

Advantages
⦁ 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
⦁ Low compression set

Disadvantages
⦁ High acrylonitrile (ACN) content can make flexibility poor

HNBR: Hydrogenated Nitrile

A saturated version of NBR elastomers, HNBR components show superior heat resistance, as well as good resistance to many oil additives, hydrogen sulphide, high-energy radiation and amines present in crude oil.

Typical deployments are in extreme environments such as oil-fields and under-bonnet automotive applications.

Advantages
⦁ Excellent wear resistance
⦁ High tensile strength and high hot-tear resistance
⦁ Low compression set

Disadvantages
⦁ Can be attacked by ozone, ketones, esters and aldehydes

VMQ/PVMQ: Silicone

A group of elastomers, made from silicon, oxygen, hydrogen and carbon, silicones are renowned for their retention of flexibility and low compression set characteristics, within one of the widest working temperature ranges for elastomers.

Platinum-cured silicones offer enhanced levels of purity and low extractables making them ideal for pharmaceutical, biomedical and food & drink applications.

Advantages
⦁ Suitable for high and low temperature applications
⦁ Excellent resistance to ozone and weathering
⦁ Good resistance to compression set at high temperatures
⦁ Low level of combustible components; even when exposed to flame
⦁ Excellent compression set and high physiological inertness (tasteless, odourless and completely non-toxic)
⦁ Resistant to bacteria, fungi, a wide range of media including high energy radiation

Disadvantages
⦁ Poor tensile strength
⦁ Low tear and abrasion resistance
⦁ High gas permeability

FKM/FPM: Fluoroelastomer or Fluorocarbon

FKMs are available as a copolymer, terpolymer or tetrapolymer, depending on the level of chemical resistance required, and are either bisphenol-cured, or peroxide-cured to provide better resistance to wet environments.

Typically, FKM components will be used in applications with 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

Advantages
⦁ Excellent resistance to heat, aliphatic and aromatic hydrocarbons
⦁ Excellent resistance to chlorinated solvents and petroleum fluids
⦁ Clear superiority in O-ring sealing force retention

Disadvantages
⦁ Poor resistance to ethers, ketones, esters, amines
⦁ Poor resistance to hydraulic fluids based on phosphate esters

As experts in the field, Novotema offer a range of specialist services related to the design, moulding, testing and supply of elastomer components, so whatever your engineering dilemma may be, our team of fully qualified and experienced engineers are always on hand to provide innovative solutions to ensure your business challenges are met with an appropriate technical solution.

For more information about elastomers, and their suitability for your needs, chat with our experts online today, or drop us a line here.

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