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ASTM D395 Compression Set Fixture Method B - Unuo Instruments

What is ASTM D395 Compression Set Fixture?

1. What is ASTM D395 Compression Set Fixture?

ASTM D395 Compression Set Fixture, sometimes also called compression set test fixtures, is to test rubber products to retain its elastic properties after a certain period of compressive stresses. According to ASTM D395, mainly there are 2 methods for the compression set fixtureMethod A compression set under constant force in air and Method B compression set under constant deflection in air.

Unuo Instruments manufactures & supplies ASTM D395 compression set fixture for both methods.

2. Why compression set test is needed?

Compression set is one of the most important proprties of rubber, particularly to the rubber used in machinery mountings, vibration dampers, ans seals. The compression set test helps the people to know if the tested rubber can meet their requirements or not before bulk production and to make improvements accordingly. Tested by compression set test equipment in given temperature and humidity condition for a certain period, the test imitates the real use occasion, speed up the process, and save cost.

3. What is the principle of ASTM D395 compression set fixture?

1) Compression set test fixture Method B:

Place the standard specimens between the flat steel plates and use a suitable spacer(to maintain the constant deflection). For ASTM D395, normally spacer thickness 9.5mm & 4.5mm are adopted. Tight the bolt and make sure the steel plate would contact the sample evenly. Then place the compression set test fixture in with sample in the specified environment for a certain period of time according to the test needs.

ASTM D395 Compression set fixture Method B - Unuo Instruments

2) Compression set test fixture Method A:

Place the standard sample in parallel between the pressure plates, and rotate the bolt to apply the specified pressure. After placed in a specific environment for a certain period of time, the pressure is removed. And measure the final thickness after cooling period.

compression set apparatus


Due to different test methods, the results of the two tests cannot be compared. Please select the corresponding test method according to the test needs. Method B is not suitable for vulcanized rubber with a hardness greater than 90IRHD.
The rubber compression set relates to the elasticity and recovery ability of rubber. Generally, soft foam materials (rubber, sponge products) need to be tested for the compression set. The better the material’s rebound ability under the same conditions, the stronger the resistance to deformation


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