Media Resistance
Immersion Tests
Significance and Test Method
In technical applications, elastomer components usually come into contact with various media. Especially in fluid technology, a wide variety of chemical fluids are involved and seals and dampers are sometimes directly exposed to the media. Substances applied indirectly, such as lubricants, also have an influence on the components.
Rubber materials react to the substances in different ways. It is not uncommon to see an increase in volume due to swelling or a shrinkage as a result of the extraction of compound ingredients.
In the worst case, the interlacing of the elastomer is strongly altered by chemical attack. As a result, the materials soften or harden, lose their elasticity or become brittle, form cracks or break even under light tensile or bending stress.
Additional thermal stress on the materials usually intensifies the effects. These irreversible damages often lead to a loss of function and failure of the component.
Significance of immersion tests for Application Technology
Immersion tests help to ensure the functionality of rubber parts, for instance seals, hoses or dampers, when exposed to media, operating fluids and auxiliary materials. They provide information on the compatibility of the elastomers with the tested media and their chemical resistance. Immersion tests are often indispensable when selecting materials for new applications.
The immersion test
Many standards and test specifications describe testing methods for testing the chemical resistance and determining the behaviour of elastomers in contact with liquids. These include DIN ISO 1817, ISO 1817, VDA 675 301, VDA 675 302, VDA 675 303, VDA 675 304 and VDA 675 305.
Immersion tests always follow the same basic principle, regardless of the standard. First, certain material characteristics are determined in the original state, such as hardness and density, compression set or tensile strength, and the volume of the test specimen is recorded.
Then the test specimens are completely immersed in the defined medium and left there for a given time at a predefined temperature. The exact immersion conditions are specified in the individual regulations. For tests with highly volatile media above boiling temperature, we have a large number of autoclaves available for this purpose.
After completion of the immersion, the test specimens undergo the same measurements as prior to the media tests.
Based on the changes in material properties and volume compared to the original parts, it is possible to make statements about chemical or physical reactions of the elastomer in contact with the media:
- Influence by swelling or extraction (increase or decrease in volume)
- Change in hardness ( brittleness or softening)
- Change in the compound’s chemical structure as a result of chemical attack
We carry out immersion tests in oils, fuels, coolants, refrigerants, superheated steam and many other media. Simply contact us.
Downloads
Detailed information on chemical and physical changes of elastomers in contact with media, on possible failure modes and technical background knowledge can be found in our technical reports:
Chemical attack and swelling - degredation of the network structure by a contact medium
In the technical report, Bernhard Richter and Ulrich Blobner explain the causes and effects of chemical attacks and swelling, show the typical damages and give tips on how to avoid media-related failures.
