Introduction of ASTM D395 Compression Set Fixture

1. What is ASTM D395 Compression Set Fixture?

ASTM D395 Compression Set Fixture, sometimes also called compression testing machine, is to test rubber products to retain its elastic properties after a certain period of compressive stresses. Compression Set Testing measures the ability of rubber to return to its original thickness after prolonged compressive stresses at a given temperature and deflection. The lower the percentage figure, the better the material resists permanent deformation under a given deflection and temperature range.According to ASTM D395, mainly there are 2 methods for the compression set fixture – Method A compression set under constant force in air and Method B compression set under constant deflection in air.


GESTER Instruments manufacturer & supplier ASTM D395 compression set fixture for both methods.


2.How do you measure a compression 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.


3. 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.


4. What causes compression set?

Many factors can contribute to compression set failure of an O-ring seal, including: Excessive temperature developed causing the O-ring to harden and lose its elastic properties. 


5.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 tensile compression tester in with sample in the specified environment for a certain period of time according to the test needs.


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.


Conclusion:

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.


GESTER INTERNATIONAL CO.,LIMITED is a national high-tech enterprise engaged in R&D and production of high precision physical properties testing equipment with 20+ years experience, expertly specialized in providing integrated laboratory testing solutions for children's products, textile, footwear and furniture. It has passed ISO 9001 certificate, "AAA Enterprise in Quality, Service and Credit" and was audited as SGS audited supplier.


GESTER is a textile testing equipment manufacturers which integrates research & devolepment, prodution and sales in one. So far, GESTER owns two production factories and four sales teams for textile tester, footwear tester, Mask Tester and Protective Clothing Tester, Lab Incubator, Biological Safety Cabinet, Lab Oven etc. We have applied for dozens of patents from the State Intellectual Property Office.


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