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IRHD Hardness Tester
Technical Details of IRHD Hardness Tester
The hardness of rubber is one of the most important properties which shall determine the suitability of rubber components for the intended purpose. Improper hardness of any component may defeat the basic purpose for which the component is designed. Thus accurate and reliable determination of the hardness is of extreme importance in rubber field.
Amongst the various methods of the determination of rubber hardness the two most important one are:
Durometer: It uses the principle of indentation of a truncated cone in rubber with varying loads through springs.
Dead Load Hardness Tester: It uses a fixed dead load on the indenter, where as the first method suffers from the disadvantages of permanent set getting developed in the spring and thus affecting the readings, the seconds method being the dead load principle is free from the shortcomings.
The Indian Standard Specifications, British Standard Specifications and the ISO Specifications have also accepted only the dead load hardness tester in their recommendations.
The principle behind determination of hardness by dead load apparatus is based on the measurement of the difference between the depth of indentation of a standard ball into the rubber under a small contact force and a large indenting force. From this difference the hardness in International Rubber Hardness Degree (IRHD) is derived by the use of a suitable table.
Indenter : 2.50 mm hemispherical
Pressure foot : 20mm O.D. x 6 mm I.D.
Force on foot : 8.3 N +1.5
Force on ball : Contact Indenting Total
0.3 N 5.4 N 5.7 N
Related Standards: Methods of Test for Vulcanised Rubber Part II Hardness as per - IS3400 (Part II)-1980.