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Compression Set of Elastomeric Materials & Recognising the Risks

19 Jan 2015 | Posted by Andrew Onions

One of the main challenges presented to a material supplier is to offer the best quality product at the lowest price, and there are a number of ways this can be achieved.

Typically manufacturers will substitute high grade pure polymer and constituents of the mix with lower grade blends and fillers.

The impact that these actions have on the performance of the material are typically recognised through lower tensile strength, elongation and operating temperature. Less obvious is the impact on resistance to media which is generally why a polymer grade is chosen in the first place.
Another, perhaps more critical area that is rarely given consideration and yet is more likely to cause a problem in gasket and sealing applications is compression set.

Compression Set Testing measures the ability of rubber to return to its original thickness after prolonged compressive stresses at a given temperature and deflection.

As a rubber material is compressed over time, it loses its ability to return to its original thickness. This loss of elasticity (memory) will reduce the capability of an elastomeric gasket, seal or cushioning pad to perform over a period of time.
The resulting permanent set that a gasket may take over time may cause a leak where the energy within the material is no longer pushing against a flange face, requiring regular bolt torque checking and tightening which in turn will further compromise the performance of the material.
Excessive use of low grade fillers is the primary reason for increased compression set characteristics with the added negative of a dramatic reduction in media resistance.

Compression Set results for a material are expressed as a percentage maximum figure. The lower the percentage figure, the better the material resists permanent deformation under a given deflection and temperature range. To be clear a low value means that tested rubber has a good capacity to keep its sealing properties and will have a better chance of effecting a seal in a given working environment for a longer period. A less than 20% COMPRESSION SET is an excellent result and gives satisfactory compression results, and therefore a good functional sealing capacity.

Many high grade sheeting materials to a recognised standard will perform in a band of 20 - 25% compression set. Most good quality commercial grade sheeting materials perform in a band of 25 - 35% compression set. Materials with a compression set of 40% and above should be avoided for any sealing application due to the high probability of failure and the inherent risk to both personnel and plant.
We often talk about the total cost of supply - repairing customer relationships where product has failed is generally the most costly both in terms of re-manufacture and replacing product and in rebuilding trust and confidence in your ability to supply - using material with a high compression set in sealing applications is one of those risk areas that can easily be avoided for little extra cost.
For more information on our Rubber Sheeting materials contact your Account Manager or our Sales Office on 01902 307711