ISO 48 Rubber, Vulcanized or Thermoplastic - Standard Test for Determination of Hardness

Material Testing

ISO 48 Rubber, Vulcanized or Thermoplastic - Standard Test for Determination of Hardness

ISO 48 specifies four methods for determining the hardness of vulcanized or thermoplastic rubbers on flat surfaces (standard hardness methods) and four methods for determining the apparent hardness of curved surfaces (apparent hardness methods). Hardness is expressed in international rubber hardness grades (IRHD). The methods cover the hardness range of 10 IRHD to 100 IRHD.

ISO 48 Rubber, Vulcanized or Thermoplastic - Standard Test for Determination of Hardness

These methods differ mainly in the diameter of the scoring ball and the magnitude of the scoring force; they are chosen to suit the particular application.

This International Standard specifies the following four methods for determining standard hardness:

  • Method N (normal test) is suitable for rubbers with a hardness in the 35 IRHD to 85 IRHD range, but can also be used for hardness in the 30 IRHD to 95 IRHD range.
  • Method H (high hardness test) is suitable for rubbers with hardness in the range of 85 IRHD to 100 IRHD.
  • Method L (low hardness test) is suitable for rubbers with a hardness in the range of 10 IRHD to 35 IRHD.
  • Method M (microtest) is essentially a reduced version of the normal test method N, allowing thinner and smaller test pieces to be tested. It is suitable for rubbers with hardness in the 35 IRHD to 85 IRHD range, but can also be used for hardness in the 30 IRHD to 95 IRHD range.

In the range of 85 IRHD to 95 IRHD and 30 IRHD to 35 IRHD, the hardness value obtained by the N method may not exactly match that obtained using the H method or the L method, respectively. The difference is normally not significant for technical purposes. Due to various surface effects in rubber and the possibility of slight surface roughness (for example, produced by polishing), microtesting may not always yield results that are in agreement with those obtained by normal experimentation.

This International Standard also specifies four methods for determining the apparent hardness of curved surfaces, CN, CH, CL and CM. These methods are modifications of the N, H, L, and M methods, respectively, and are used when the rubber surface being tested is curved.

In this case, there are two possibilities:

  • The test piece or product being tested is large enough for the hardness instrument to rest on; or
  • The test piece or product under test is small enough for both the test piece and the instrument to rest on a common support.

Apparent hardness can also be measured on non-standard flat test pieces using the N, H, L, and M methods.

EUROLAB assists manufacturers with ISO 48 test compliance. Our test experts, with their professional working mission and principles, provide you, our manufacturers and suppliers, the best service and controlled testing process in our laboratories. Thanks to these services, businesses receive more effective, high-performance and quality testing services and provide safe, fast and uninterrupted service to their customers.

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