Which Elastomers Offer the Best Mechanical Strength?
With rubber products often being utilised in challenging environments, there’s a significant requirement in many situations for an end product which offers a substantial mechanical strength.
In order for this to be delivered, it is important that the correct base materials are selected; those which offer the most favourable mechanical properties.
When identifying the most suitable rubber for use based upon it’s mechanical strength, it is important to consider a number of different properties, these being:
- Tensile Strength
- Flex Cracking Resistance
- Tear Resistance
- Abrasion Resistance
Further to the selection of the correct base material for a particular application, the ability to ‘compound’ this with ingredients which are able to fine tune certain characteristics and properties is commonly the most appropriate way to engineer the most suitable compound.
A good level of polymer in the overall blend is needed first and foremost which can then be reinforced with high grade additives. Poor mechanical performance is often a very good indicator of a low grade or commercial rubber. Furthermore, the correct cure cycle and, in some cases, a post cure, can fully optimise physical characteristics.
Looking at the above in a little more depth:
Elastomers are available in a range of hardnesses, ranging from 20 Shore A to 90 Shore A for thermoset rubbers up to Shore D scale for thermoplastic elastomers, however the most common range is generally seen as between 50 Shore A and 80 Shore A. Hardness can also be measured in IRHD (International Rubber Hardness Degrees) which are broadly equivalent to Shore A. i.e. 50 shore A equals 50 IRHD. The actual hardness selected will depend upon the application and other considerations.
Tensile strength is the maximum tensile stress reached in stretching a test piece of a given elastomer. In short, it is the maximum force a material can withstand without fracturing when stretched. Tensile strength is an indication of how strong a compound is and is an important consideration specifically for applications where a large ‘pull’ force is present.
The extensibility of an elastomer is the property from which its name derives; elasticity. That is, the ability if rubber to stretch and return to its original shape, an ability which sets it apart from virtually all other materials.
Flex Cracking Resistance
In situations where an elastomer is subject to bending, a property requiring particular attention is the flex cracking resistance. When a material is repeatedly bent or flexed, over time this can lead to flex cracking, especially in extreme temperature environments. The flex cracking resistance of an elastomer defines ability to withstand the formation of such cracks.
In basic terms, the tear resistance of a material relates to how well it can withstand the effects of tearing, however more specifically and in relation to elastomers, this defines the resistance against the growth of cuts under tension. Base materials with a low tear resistance generally have a poor resistance to abrasion and when damaged will quickly fail, hence the importance of consideration being given to the property.
The abrasion resistance of a material defines the ability to resist such wear by sliding or scuffing. When sliding, localised friction forces will impose high energy levels on an elastomer and abrasion and wear take place when these forces can no longer be withstood.
Using a selection of 12 different elastomers as the base for the majority of compounds for the manufacture of both rubber sheeting, reinforced rubber sheeting and rubber coated textiles, we work closely with every single one of our clients to ensure that the final elastomer meets the correct specifications. The below looks at these 12 base materials based upon their mechanical strength properties:
Please note: Whilst most main rubbers are outlined below, our capabilities and experience allow us to manufacture a much wider range of blends and formulations. The inherent characteristics of a polymer can be improved through the inclusion of additives, including the mechanical properties.
|Hypalon||Good / Excellent|
|Neoprene||Good / Excellent|
|Butyl||Fair / Good|
|EPDM||Fair / Good|
|Vamac||Fair / Good|
For the best mechanical strength, the option from the above is clearly Natural Rubber. Tensile strength, elongation and abrasion resistance properties are regarded as excellent across a sufficiently wide hardness range, and in most instances, offers the highest resilience of all elastomers. However, operating temperature is low and limitations can render it unsuitable in many environments.
Taking this into consideration can introduce other options including hypalon, neoprene and nitrile for consideration. A broad consideration matrix must be applied to include mechanical, chemical and environmental factors and, of course, cost as well.
As discussed, the mechanical properties of rubber can be optimised in a number of different ways, however certain applications require mechanical limits significantly beyond what rubber alone can offer. In such instances, the optimal solution here is to reinforce the rubber article with another material. Typically for rubber sheeting and mouldings, textiles are used. In particular, tear and tensile performance improves significantly, most commonly at the expense of elasticity due to the fact that the textile will not stretch. As the textile is often inserted in the middle of the rubber the sheet, hardness and abrasion resistance are able to be engineered in the same way as a 100% rubber article.
Should you be looking for more in-depth, backed up information and data surrounding the mechanical strength of any number of our main elastomers, we welcome you to give our technicians a call on 01524 585200 where we will be only more than happy offer guidance and assistance.