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The durometer hardness method is widely used in the plastic and rubber industries. The durometer method applies a predetermined test force to a spherical- or conical-shaped indenter. The indenter is applied to the test specimen at the test force for a predefined time period. The resulting indentation is converted into a hardness value by means of a dial gauge. Test loads range from 822 gf (A scale) to 4550 gf (D scale). Non-standard “micro” scales are also available. These micro scales permit testing on thin or very narrow specimens.
The International Rubber Hardness Degrees (IRHD) test method originated in Europe. It provides a very repeatable result on rubber parts of various shapes and sizes. It is especially important in determining the hardness of rubber )-rings. The IRHD method employs a preliminary test load that is applied to the specimen via an indenter. The test is zeroed at this indentation position, then the total test force is applied. The distance between the two applied forces is measured and coverted to an IRHD hardness value. Preliminary test forces are 8.46 gf for micro scales and 295.7 gf for regular scales. Total test forces are 15.7 gf for micro and 597 gf for regular scales.
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