This VDA recommendation is based on DIN ISO 48-2 with the following deviations.
- This test method can be applied to all elastomeric parts.
- Preparation of the test pieces and kind of embedding procedure are given.
The procedure, how to determine hardness on embedded samples is specified.
This test method can provide data for
- qualification tests on different elastomers which are in question for a specific application (quality determination),
- comparison tests on different delivery batches of a specific elastomer compound (quality assurance).
The time between vulcanization and testing of elastomers shall be at least16 h and not longer than 6 months when investigating to this procedure.
Before testing, test pieces must be stored in unstressed condition for 8 h min. at (23 + 5) °C.
The object of this test method is the accurate determination of the micro hardness of elastomers, between 35 to 98 IRHD (International Rubber Hardness Degree). It permits accurate and reproducible hardness determinations to be made on test pieces of small dimensions, e.g. lip seals, o-rings or other formed parts.
Hardness value determined on parts can deviate to the hardness of the compound, caused by imbedding, different sample size, and eventually curved surface. The value is part and preparation related and is named “apparent hardness”.
This procedure applies, when test pieces shall be measured which need to have special preparation due to small dimensions and/or shape. It shall be considered that eventually present inhomogeneity, surface hardening, unevenness or roughness (e.g. caused by grinding) can have an influence on the measured micro hardness values.
The special features of this test procedure are
- the test piece pretreatment (see section. 3.4 and 3.5)
- the fixing of the test pieces during measurement by the means of a cylindrical pressure body.