This document specifies four methods for the determination of the hardness of vulcanized or
thermoplastic rubbers on flat surfaces (standard-hardness methods) and four methods for the
determination of the apparent hardness of curved surfaces (apparent-hardness methods). The hardness
is expressed in international rubber hardness degrees (IRHD). The methods cover the hardness range
from 10 IRHD to 100 IRHD.
These methods differ primarily in the diameter of the indenting ball and the magnitude of the indenting
force, these being chosen to suit the particular application. The range of applicability of each method is
indicated in Figure 1.
This document does not specify a method for the determination of hardness by a pocket hardness
meter, which is described in ISO 48-5.
This document specifies the following four methods for the determination of standard hardness.
— Method N (normal test) is appropriate for rubbers with a hardness in the range 35 IRHD to 85 IRHD,
but can also be used for hardnesses in the range 30 IRHD to 95 IRHD.
— Method H (high-hardness test) is appropriate for rubbers with a hardness in the range 85 IRHD
to 100 IRHD.
— Method L (low-hardness test) is appropriate for rubbers with a hardness in the range
10 IRHD to 35 IRHD.
— Method M (microtest) is essentially a scaled-down version of the normal test method N, permitting
the testing of thinner and smaller test pieces. It is appropriate for rubbers with a hardness in the
range 35 IRHD to 85 IRHD, but can also be used for hardnesses in the range 30 IRHD to 95 IRHD.
NOTE 1 The value of the hardness obtained by method N within the ranges 85 IRHD to 95 IRHD and 30 IRHD to
35 IRHD might not agree precisely with that obtained using method H or method L, respectively. The difference
is not normally significant for technical purposes.
NOTE 2 Because of various surface effects in the rubber and the possibility of slight surface roughness
(produced, for example, by buffing), the microtest might not always give results agreeing with those obtained by
the normal test.