Why is material selection so important in rubber engineering?

Why is material selection so important in rubber engineering?

At first glance, if you are not involved in the world of flexible engineering, the question of material selection in rubber might seem odd. After all, rubber is rubber, right? Well, no! In the same way that metals come in different types, each having different mechanical and electrical properties, so does rubber. 

Rubber compounds consist of a variety of raw materials, chemicals, and additives, to create a final product that optimises their characteristics. The production process itself has a significant impact on the properties of the final ‘rubber’ product too. In summary, rubber comes in many different forms, each optimised for specific applications.

Which properties of rubber can be changed?

There are many properties that can be altered during the production of a rubber based product. When deciding which rubber polymer is the best for a given application, it is necessary to consider the requirements in areas such as:

Mechanical properties: Hardness, tensile strength and elasticity, compression etc.

Electrical properties: Conductivity, resistivity etc.

Thermal properties: Resistance to heat, fire, cold. Operating temperature ranges etc.

Environmental properties: Resistance to chemicals, acids, oils, etc.

Weather resistance: Impact of UV radiation, ozone, weathering, etc.

Aesthetics: Colour, texture, etc

Cost: Is there a lower-cost alternative?

Longevity: What is the design life of the product?

Depending on the specific application, some of these characteristics will be of vital importance, whilst others will be negligible. Understanding these priorities is the first stage of material selection. 

What changes the characteristics of rubber?

Having established the required characteristics of a rubber polymer, the next stage is to create it. This is done via the use of different raw rubber materials, additives and processing steps. The starting point is the choice of a natural or synthetic rubber compound. This will decide the basic properties of the final product, such as temperature behaviour, chemical resistance, and elasticity. There are many synthetic rubbers available. Some provide excellent longevity, others focus on their mechanical properties, whilst another may provide exceptional environmental protection. Here are some of the elements and process steps that impact the final rubber polymer:

Rubber compound: Natural or synthetic, selected to provide the base characteristics.

Fillers: Used to change the strength, hardness, electrical conductivity, or abrasive characteristics.

Plasticiser: Affects the hardness, workability, and stretch characteristics.

Cross-linking system: Controls the speed of vulcanisation, and influences dynamic and static properties such as tear resistance.

Processing aid: How the compound will perform during the manufacturing process. Flow, stickiness etc.

Additives: A large number of options which influence electrical conductivity (or resistance), colour, ageing profile, etc.

Common types of rubber

There are many types of rubber that can be used as the starting point of the manufacturing process. Some of the more common types are:

Natural rubber: A polymer that forms in the bark of tropical trees. It is a relatively low-cost material with excellent physical properties, such as resilience, resistance to tears and abrasion, high tensile strength, excellent adhesion, and low temperature characteristics. It offers little protection against UV, ozone, or hydrocarbon solvents and oils, however.

Styrene Butadiene Rubber (SBR): Widely used in the automotive industry, SBR offers excellent resilience, tensile strength, abrasion resistance, ageing, and flexibility at lower temperatures. The greater the styrene content, the harder and less flexible the resultant polymer.

Ethylene Propylene Diene (EPDM): A synthetic rubber extremely suited to withstand the impact of heat, oxidisation, and weather. It also offers good resistance to alkalis, acids, and oxygenated solvents. As with natural rubber, it offers little protection against hydrocarbon solvents, petrol and oils.

Silicone Rubber: Another synthetic rubber, this time offering very low thermal conductivity, with good flexibility at low temperatures. It is however very prone to tearing or abrasive wear, and offers poor resistance to oil, petrol, alkalis, or acids.

Nitrile Rubber (NBR): By contrast, NBR offers excellent resistance to fuel and oils, making it a good choice for automotive seals and gaskets. It works well in a wide temperature range too (-50 C to +150 C). NBR offers less resistance to ozone, sunlight, and natural ageing.

How to select the right rubber for your requirements?

By now, you may be wondering how to select the right rubber polymer and process for your flexible manufacturing needs? The answer is simple however, come and speak to a company with over a century of knowledge and experience in the area! Using your knowledge of the product you wish to develop, we can establish the properties which they will need, and so which rubber polymer best suits your needs. It’s all part of the flexible engineering development process.

About Checkmate Flexible Engineering

We are a specialist engineering company whose core capabilities are the specification, design and building of fabrications from elastomers. We offer a complete service from conception to manufacture.

Our products vary from lightweight to hundreds of kilograms. We have the equipment, materials knowledge, design proficiency and a highly experienced and skilled team able to deliver the standard of service expected by technically demanding customers. Our considerable experience in the design and manufacture of elastomeric products has established a worldwide reputation in the field. 

Clients include the UK MOD, Government Research Establishments, and international shipping companies, as well as NATO forces. We welcome your enquiry and will always discuss projects in confidence. We look forward to hearing from you.