Compression Set Testing Under Constant Deflection by ASTM D395 B measuring the capacity of an elastomeric material to get back to its original thickness or shape after compression stress is applied at a certain temperature. This test helps in identifying the best elastomer for industrial use.
Compression Set Testing by ASTM D395 method B is the process of measuring the capacity of an elastomeric material to get back to its original thickness or shape after compression stress is applied at a certain temperature. Elastomers lose the ability to return to their original thickness when compressed for a prolonged period. Results obtained from compression set testing are critical for determining and producing the best elastomeric materials for industrial application. As an example, a compression set is essential for sealing operations.
The test specimen with known thickness is deformed (compressed) up to 25% of its size using a compressing machine for a given time. Spacers are used while compressing for precise measurements, which have their own thickness. A recovery time of 30 minutes is given before the sample is measured again. The value of percentage decrease thus derived indicates the percentage a material sample fails to recover of its original size.
Cylindrical disc specimen sizes categorized into Type 1 & Type 2
In type 1, thickness is 12.5 mm +/- 0.5 mm and diameter is 29.0 mm +/- 0.5 mm
In type 2, thickness is 6.0 mm +/- 0.2 mm and diameter is 13.0 mm +/- 0.2 mm
The compression set is stated as a percentage of the original deflection.
CB = [(To-Ti)/(To-Tn)] x100
CB = Compression Set
To = Original thickness of the sample
Ti= Final thickness of the sampleTn = Thickness of the spacers used