INDIRECT VERIFICATION OF ELASTOMER HARDNESS TESTERS USING HARDNESS REFERENCE BLOCKS
A. Štibler, K. Herrmann
Abstract:
Hardness measurement methods for rubber and plastics are described in the standards ISO 7619-1, ISO 7619- 2, ISO 868 and ISO 48. Rising requirements for the accuracy of this hardness measurement have led to the result that the users of rubber hardness testers and also metrology experts who deal with their calibration need a calibration method to check the overall function of the testers acknowledged by a standard. Therefore extensive experiments were conducted in a cooperation between the Physikalisch - Technische Bundesanstalt (PTB) in Braunschweig (Germany) and the ZAG Ljubljana (Slovenia). The results have been used as a basis for the elaboration of the relevant international standard ISO 18898 which was published in 2006. In this standard direct verification methods are laid down. An indirect verification method using rubber hardness reference blocks, which is also applicable for the verification of hardness testers, is presented in this paper. At present hardness reference blocks are available only for some of the hardness scales which are used for rubber materials. Suchwise, Shore A, IRHD N and IRHD M reference blocks are available in the market. During the verification process the hardness tester is calibrated by using rubber hardness reference blocks. The evaluation of the repeatability and the error of the hardness testers including the uncertainty of measurement of the calibration results is given in this paper.
