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Compression Set Matters

24 Oct 2018 | Posted by Sharon Kendal
Compression Set is defined as the decrease in thickness of a rubber which has been deformed under specific conditions of load, time and temperature. Normally shown as a percentage, it is typically tested to ASTM D395-18 Method B (Compression Set Under Constant Deflection in Air). Generally, a lower percentage of Compression Set indicates a better quality of material.

A good quality Solid Rubber would have a Compression Set below 20%; most Sheet Rubber will have a Compression Set of around 30%, whereas poor quality, under cured or badly mixed Rubber Sheeting will exhibit a Compression set of 45% or more.

Another definition that is commonly used is Material Recovery or even springiness!

So why does Compression Set matter?  

The answer is simply that if your material has a low level of Compression Set it will perform its function as a seal more effectively for longer.  By taking on a Compression Set, the material is no longer effectively resisting compression and ‘pushing back’ against the load.  Once this has happened the internal pressure will have a greater influence and start to create leak paths, requiring the gasket to be further tightened until there is sufficient load to effectively break the mechanical bonds within the material causing catastrophic failure. 
Don’t be fooled if the data sheet for the rubber sheeting material that you are viewing says Compression Set is greater than 50% or, even worse, that it is Not Applicable, as the likelihood of failure in situ has increased dramatically and the effective working life of these high Compression Set materials is considerably shorter than good quality, properly mixed Rubber sheeting.

MacLellan Rubber supply commercial quality and high-quality Rubber Sheeting with full technical data to standard European tests and batch traceability to ensure complete trust and integrity within your supply chain. Read more about us and the sheeting materials we provide.