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Investigation of Compression Set of Rubber Compounds

Compression deformation can be defined as a permanent deformation that occurs below the yield point of the material. It is similar to creep, cold flow, or stress relaxation.
Why is it important to compress the permanent deformation properties?
The rubber compound is tense and permanently deformed. This permanent deformation is of particular concern when elastomers are used to create seals. Reducing the sealing force creates the possibility of leakage over time.
As an example, the cross section of a typical seal is shown below.
Figure 1 represents a new O-ring placed in a cross section of a slot. The O-ring is round in cross section. Figure 2 shows the installation of a cap that compresses the O-ring. Figure 3 shows the cross-section of an O-ring after prolonged use. The cross-section of the O-ring has been permanently deformed to take it out of its compressed shape. The degree to which the elastomer has been permanently deformed is a function of the type of elastomer, temperature, time, and chemical interaction.
Figure 1: Virgin O-ring placed in the groove
Virgin O-ring placed in the groove
Figure 2: Cap installed, compressed O-ring
O-ring news
Figure 3: Cover removed, O-ring has taken a set
O-ring cover removed
Figure 4: Comparison of originals and use cross sections
Comparison of compression
Test compression set
The test method for determining the compression set of an elastomer is present. Two common test methods are ASTM D-395 and ASTM D-1414. Both test methods use the same inspection device but different samples.
The following constant deflection test device is shown in the figure. The test process is as follows:
1.) Rubber samples are measured to determine their height.
2.) 75% of the height of the sample is installed at intervals.
3.) Fasten the plate down to ensure that the fixture plate is in full contact with the spacer.
4.) The fixture containing the compressed sample is placed in a temperature chamber at a certain temperature for use at a specified time.
Samples of 5.) were removed from the fixture and their height was measured after 30 minutes. The result is calculated and expressed as a percentage. A zero compression set means that the sample is fully restored to its original height. A one hundred percent compression set is defined as the specimen remaining in the deformed position and not recovering when removed from the fixture.
specimen
ASTM D-395 Method B/Size 2/Type 2 requires three samples, each 0.24 inch thick by 0.51 inch diameter. This specification allows the use of plied specimens, which means that samples can be tested and cut from standard 0.080 inch thick test panels.
ASTM D-395
ASTM D-395 Method B/Option 1/Type 1 requires two specimens, each of which is 0.49 inches thick by 1.14 inches in diameter.
ASTM D-395 Method B
ASTM D1414 Method B requires a cross section of an O-ring or O-ring for testing.
ASTM D 1414
Rubber compounds are tested based on the temperature range of the polymer.
Shown below is a typical test temperature of a polymer as listed in ASTM D2000. This is very important when considering the temperature of the compression deformation test data to consider.
Customers sometimes see a high compression as being in the l50'C test, such as a material, when the application may only be set at room temperature. If the compression set is done at a lower temperature, the result is usually much better than at high temperatures. This may mislead consumers into thinking that the compound will not work, and that the compound actually exceeds their requirements.

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