Technical

    Hardness

    Hardness typically specifies a material’s resistance to penetration. The most commonly used hardness measuring scales in the field of elastomers is Shore Hardness. There are two reference scales: Shore A and Shore D.

    Resistance to Penetration

    Hardness typically specifies a material’s resistance to penetration. The most commonly used hardness measuring scales in the field of elastomers is Shore Hardness. There are two reference scales: Shore A and Shore D.

    To measure the hardness degree, both scales use a Durometer, but have different indenters: the indenter for Shore A features a truncated cone point, while the one for Shore D has a point at a 30° angle.

    Shore A is used for hardness values between 40 and 95 Shore; for higher values Shore D is used.

    In both cases, the measurements conform to standards DIN 53505 and ASTM D2240. See below for the reference scales’ overlapping pattern, as well as the position of the main polymers.

    In the field of seals, hardness is a very important parameter, as it affects both dynamic friction and stiction (stick and slip).

    If pressure and surface finish are equal, a lower hardness reduces stiction, while a higher hardness reduces dynamic friction. Hardness, in turn, is influenced by temperature – the higher the temperature, the lower the hardness. In general, elastomers with a lower hardness, (i.e. softer), are better suited for rougher surfaces, but are more prone to extrusion.

    International Rubber Hardness Degrees (IRHD) is another, less commonly used, hardness measuring scale.

    Hardness Scale

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