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A matter of substance

Industrial seal materials and properties

Rubber is one of the most common materials for seals but perhaps not always the most suitable. This article gives a run-down of alternative materials and their applications in various industries.

The right seal material is one of the most important considerations when selecting a seal that addresses your specific challenges. Used in numerous industries, seals must withstand varied temperatures, pressures, and fluids. Rubber is often used for seals, offering flexibility and durability at a range of temperatures. However, there are a vast number of material options available that are better suited to certain applications.

Maintaining reliability under extreme temperatures

Thermal resistance is absolutely crucial to prevent a seal from breaking down or melting under extreme temperatures. There is even the chance of certain polymers emitting dangerous fumes if exposed to temperatures that are too high. In applications that run at extremely high temperatures, a seal made from hydrogenated nitrile rubber (HNBR) can work well. A seal made from silicone elastomer is well suited to colder temperatures. Polyurethanes and polytetrafluoroethylene (PTFE) are a suitable option for applications with a large temperature range, as they will function well in both extreme cold and heat.

A lightweight option for heavy-duty equipment

In a bid to decrease resource consumption and improve efficiency, plastics are increasingly replacing metal components in machinery and parts such as in shafts. Seals made from a light and compact polyurethane or glass-fiber reinforced plastic provide a lightweight, cost-effective but robust option for heavy-duty equipment. They can also be easily produced according to customer-specific designs.

Additional industry requirements

In industries such as food and beverage or medicine, strict regulations apply to the types of seal material and lubricant that may be used in applications. In order to ensure compliance, the appropriate seal must be chosen that is made of an approved material and functions well with suitable lubricants. Similarly, in the maritime industry where environmentally acceptable lubricants (EALs) are required in protected areas such as US waters, a seal must be compatible with certain lubricants.Water repellence and low absorption rate are other beneficial properties in industries where water is present. In certain applications, a seal will need to demonstrate high chemical resistance, for example against brake fluid in automotive equipment. Seal materials with good chemical resistance are PTFE and fluorocarbon rubber compounds.

Seals for where space is limited

Compact axial seal designs work well in confined spaces such as gearboxes and are often made of a rubber compound such as nitrile rubber (NBR) or a fluoroelastomer (FKM). Seals made of these materials can reduce contact force while maintaining effective contaminant exclusion and high energy efficiency. They can be fitted in areas where space is limited while still offering high abrasion resistance, good chemical resistance, and reduced wear and noise.

Traditional materials still standing the test of time

While huge advancements have been made in sealing technology, there is still a market for leather seals. A traditional material, leather is pliable, tough, and continues to function under high pressures at extremely cold temperatures.

Felt is another more traditional material that still demonstrates good sealing properties for certain applications. Felt can be woven either from wool or synthetic materials and is often used alongside roller bearings. Seals made of felt have a slightly lower temperature limit but often have higher abrasion resistance. A main advantage of felt seals is that they can be pre-saturated in lubricant for a high level of filtration, high retention of oil, and low friction.

The CR Seals handbook

Seals are a crucial part in a vast number of applications in many industries. To find out more on the materials and information discussed in this article, take a look at the CR Seals handbook from SKF, available here.