ISO 48-4:2018 pdf download – Rubber, vulcanized or thermoplastic — Determination of hardness — Part 4: Indentation hardness by durometer method (Shore hardness).
4 Principle An indentor of specified dimensions is pressed into a test piece under a specified load and the depth of indentation measured. This indentation is converted to a hardness value by means of a specified relation. 5 Choice of durometer When using durometers, the scale should be chosen as follows: — for values less than 20 with a type D durometer: type A; — for values less than 20 with a type A durometer: type AO; — for values over 90 with a type A durometer: type D; — for thin test pieces (less than 6 mm thick): type AM. 6 Apparatus 6.1 Durometer types A, D and AO These durometers consist of the components specified in 6.1.1 to 6.1.5. 6.1.1 Pressure foot The pressure foot for types A and D shall have a diameter of 18 mm ± 0,5 mm and a central hole of diameter 3 mm ± 0,1 mm. For type AO, the pressure foot shall have a minimum area of 500 mm 2 with a central hole of diameter 5,4 mm ± 0,2 mm. The tolerances on the dimension of the central hole and the requirement for the size of the pressure foot only apply to instruments used on a stand. 6.1.2 Indentor The indentor shall be formed from a hardened-steel rod of diameter 1,25 mm ± 0,15 mm to the shape and dimensions shown in Figure 1 for type A durometers and Figure 2 for type D durometers. Type AO durometers shall have a round indentor with a radius of 2,5 mm ± 0,02 mm in accordance with Figure 3. 6.1.3 Indicating device This is a device for allowing the extent of protrusion of the point of the indentor beyond the face of the pressure foot to be read. It shall be calibrated directly in terms of units ranging from 0 for the maximum protrusion of 2,50 mm ± 0,02 mm to 100 for zero protrusion obtained by placing the pressure foot and indentor in firm contact with a suitable flat, hard surface (e.g. glass).