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Technical Glossary Compression Set

[Compression Set]

Compression set is the permanent set due to heated compression of a rubber material. A small value indicates that material has a strong ability to recover when compressed for a long period of time. This can be evaluated by tests based on JIS K 6262 standards. A cylinder-shaped test piece is subjected to compressive strain corresponding to 25% of the thickness; after the test piece is kept for a fixed time at high temperatures, it is removed and the thickness is measured after 30 minutes. The compression set rate Cs (%) is indicated by the following equation:

t0: Prior thickness of a test piece (mm)
t1: Spacer thickness (mm)
t2: Thickness (mm) of a test piece 30 min. after removing it from compression equipment

Generally, higher compressibility and test temperatures will mean a greater compression set.At our firm, a given material is compressed at an atmospheric temperature of 100 and compression is released after retention for 70 hours; compression set is then calculated after 30 minutes at normal temperatures.

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