compression set

The compression set (DVR ) is a measure of how elastomers behave during prolonged, constant pressure deformation and subsequent relaxation.

Compression set in elastomers

According to DIN 53 517 and DIN ISO 815 or ASTM D 395 ( compression set DVR, engl. ) Is the compression set measured at constant deformation. This is the deformation component of the test material dar. Many test methods for elastomers, such as tensile strength characterize the quality and condition of the material. The DVR, however, is an important factor that must be considered before use of a material for a particular purpose. Especially for the use of seals and shims made ​​of elastomers is the permanent deformation, the compression set (DVR ) is an important parameter.

Test methods

To determine this size, a cylindrical test specimens to eg 25 % compressed and stored for a certain time at a certain temperature so. The temperature and the medium ( usually air, but also oils and other utility liquids ) for the compression test depends on the test material, its intended use, and the experimental setup from (for example, 24 hours at 70 ° C for an EPDM profile Building ). 30 minutes after the discharge amount is measured at room temperature again and determines therefrom the permanent deformation. A abweichenendes method (Daimler -Benz) requires that the specimens to cool 2 hours in a stretched state, then they are relaxed and measured after 30 minutes.

A DVR of 0% means that the body has its original thickness fully achieved again says ( in reality impossible), a DVR of 100 % means that the body was completely deformed during the test and no provision shows.

The calculation is done using the following formula: DVR (%) = (L0 - L2 ) / ( L0 - L1) x 100 %

Where:

  • DVR = compression set in%
  • L0 = height of the specimen before the test
  • L1 = height of the specimen during the test ( spacer)
  • L2 = height of the specimen after the test

Practical significance

For example, a gasket is compressed during the assembly to a predetermined thickness, and exerts a pressure on the flange of. Over time, this pressure decreases, as the rubber is deformed plastically. Is this plastic part - so the DVR - too large, the pressing force and thus the sealing effect can be so strong that leaks occur (these can be heated completely but also in sections occur ), especially if it is to be interpreted " just ". The DVR in gaskets should not exceed a value of about 40% in the continuous operating temperature.

Tension ( ZVR )

For O- rings or similar circular parts is analogous to the tension set ( ZVR ) provides: The diameter of the parts is determined with a cone plug gauge, these are then measured back to a metal cylinder with a defined diameter tensioned and after stressing again.

The calculation is done using the following formula: ZVR (% ) = ( H0 - H2 ) / ( H0 - H1) x 100 %

Where:

  • ZVR = Tension in%
  • H0 = inner diameter of the ring, before the test
  • H1 = diameter of the test mandrel during the stress
  • H2 = inner diameter of the ring after the test
Gasket#Flange gasket
247740
de