What is rubber 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.
How do you measure compression on a rubber set?
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.
What is compression set value?
Compression set is the difference between the original thickness of the specimen and the thickness after test, expressed as a percentage of the original thickness. In determining compression set by Method B, the specimen is compressed to 75% of its original thickness.
What is good compression set?
Good compression set properties are mostly to do with good rubber choice and fully chemically cross linked and post cured products. The compression set test is a common test in our laboratory. A standard test specimen is measured then compressed in a jig to a certain percentage of its original thickness.
What is compression set resistance?
Compression set (c-set) resistance is the measurement of how well a material can revert back to its natural shape after being compressed by a load. A material that returns close to its original thickness is said to have ideal compression set resistance.
Why does compression set happen?
Compression Set Cause: Physical and chemical changes can occur to an elastomer at elevated temperatures that result in set. Cross-link density can increase, this results in the O-ring losing its elasticity and ability to return back to the original shape, this is a permanent chemical change.
What is a low compression set?
The more indented, the higher the compression set. The less indented, the lower the compression set. An object’s compression set can be measured and is expressed as a percentage of the permanent deformation caused by whatever force was exerted on it.
How much does rubber compression?
Rubber gaskets are compressed or squeezed by a percentage of their original size. A gasket that compresses too much or too little will not form a proper seal. The ideal compression percentage is 40, the maximum is 50, and the minimum is between 10 to 15.
What is low compression set rubber?
If a gasket material has a low compression set, it is suitable for products that see constant use. This is because materials with a low compression set will return to their original shape and density after being compressed, which gives them a long lifespan.
How do you compress rubber?
Steps
- Run hot water over the rubber. At first, try using tap water.
- Place the rubber in boiling water if hot tap water fails to shrink the rubber. The high heat will force the rubber to shrink if you allow it to boil for 5 to 10 minutes.
- Bend the rubber into shape.
What happens when you compress rubber?
Rubber is in fact quite compressible. Apply pressure in all three dimensions and rubber will shrink in volume.
What does high compression set mean?
If a material has a high compression set, it does not return to its original shape or density after being compressed, leaving the material with a permanent indentation. That means they will not wholly regain their original shape and end up remaining deformed.
How is a compression set used for rubber?
ASTM D395 Standard Test Methods for Rubber Property—Compression Set is the test method used and it calls for the material to be 25% deformed (compressed) for a given period. After a 30-min recovery time, the sample is measured. The value derived is the percentage a material sample fails to recover of its original height.
What is the purpose of compression set testing?
Compression set testing measures the ability of rubber to return to its original thickness after prolonged compressive stresses at a given temperature and deflection.
How is the compression set of elastomers determined?
The degree to which the elastomer has permanently deformed is a function of the type of elastomer, temperature, time, and chemical interactions. Several test methods exist for quantifying the compression set of elastomers.
What does one hundred percent compression set mean?
One hundred percent compression set means that the test specimen remained in the deformed position and did not recover at all when removed from the fixture. ASTM D-395 Method B / Option 2 / Type 2 calls for three specimens, each to be 0.24 inches in thickness and 0.51 inches in diameter.