Mechanical characteristics

Elastomers which we use are mainly the result from a compromise of all mechanicals characteristics. 

Some characteristics could be improved but it would be to the detriment of other characteristics of this mix.

The only way to know if the choice (form, quality, material) proposed or chosen is the good, is to realize a test on the application herself.

• Elongation at break 
• Density
• Compression set
• Hardness 
• TR10

The compression set (ASTM D395) of a material is the permanent deformation remaining when a force (that was applied to it) is removed. The term is normally applied to soft materials such as elastomers. There are two ways this is normally measured; compression set A and compression set B. 

Compression set A 

This has the formal name compression set under constant force in air. In compression set A a force of 1.8 kN is applied to the specimen for a set time at a set temperature. Compression set A is defined as the percentage of original specimen thickness after the specimen has been left in normal conditions for 30 minutes.

CA, the compression set A is given by CA = [(to - ti) / to] * 100, where to is the original specimen thickness and ti is the specimen thickness after testing.

Compression set B 

This has the formal name compression set under constant deflection in air. The specimen is compressed to 25% of its original heiht for a set time and at a set temperature. Compression set B is (like Compression set A) defined as the percentage of original specimen thickness after it has been left in normal conditions for 30 minutes.

CB, the compression set B is given by CB = [(to - ti) / (to - tn)] * 100, where to is the original specimen thickness, ti is the specimen thickness after testing and tn is the spacer thickness or the specimen thickness during the test 

Results indicated on Material Data Sheets are get in Laboratory on test tube in particularly conditions.

Values can vary on a same material following test conditions. 

This retractation process at the temperature is currently the reliablest test for sealing performance at low temperature. 

TR10 test assess directly when a material stop to be elastic and start to behave a plastic. Consequently, this test predicts the comportment of the seal at low temperature. 

Laboratory test serve to help at the material choice but don't have considerate like a technical specification. Tests in real utilization stay essential.