Comments on the results obtained in the comparison of the HRC scales maintained at ETCA, IMGC and MPA NRW

In the framework of the Bureau Communautaire de References (BCR), for the maintenance of the European HRC Scale, a new comparison of the HRC scales maintained at Etablissment Technique Central de l'Armemant (ETCA), France, Istituto di Metrologia "G. Colonnetti" (IMGC), Italy and Materialprufungsamt Northrein-Westfalen (MPA-NRW) has been heald in MArch 1994, following previous European comparison held in 1980, 1985 and 1989. This last comparison has benn planned taking into account also the new version of the ISO and EN Standards on the calibration of hardness standardising blocks for HRC scale, that is ISO 674 and EN 10109-3, whereas the previous ones used a specific procedure with a dwell time of 30 s. The main problem is the very significant change of the procedure describing the calibration of HRC standardising blocks. For this reason it has been decided to perform a comparison on the blocks of the series MPA-1, used for the 1989 comparison, with the previous procedure, to get information on the stability of the scales maintained at ETCA, IMGC and MPA-NRW. A new series of blocks, selected by IMGC, has been used to perform a comparison adopting the new procedure. The blocks of the series MPA-2, used in 1989 to compare the three Hardness standard machines with a common indenter, have been used for the same scope with the common indenter Cappelluzzo & Ienna CI 48536, adopting the new procedure. In this way it was possible to evaluate the stability of the hardness standard machines compared, the differences of the machines themselves and the effect of changes produced by the new EN10109 standard.