ISO 48:1994 pdf download – Rubber, vulcanized or thermoplastic – Determination of hardness (hardness between 10 IRHD and 100 IRHD)
Method H: The appropriate method for test pieces of thickness greater than or equal to 4 mm and hardness in the range 85 IRHD to 100 IRHD. Method L: The appropriate method for test pieces of thickness greater than or equal to 6 mm and hardness in the range 10 IRHD to 35 IRHD. NOTE 1 The value of hardness obtained by method N within the ranges 85 IRHD to 95 IRHD and 30 IRHD to 35 IRHD may not agree precisely with that obtained using method H or method L, respectively. The difference is not normally significant for technical purposes. Method M: The microtest for hardness is essntially a scaled-down version of the normal test method N, permitting the testing of thinner and smaller test pieces. It is the appropriate method for test pieces of thickness less than 4 mm and is preferably used for rubbers in the range 35 IRHD to 85 IRHD but may be used for those in the range 30 IRHD to 95 IRHD.
3 Principle
The hardness test consists in measuring the differ- ence between the depths of indentation of a ball into the rubber under a small contact force and a large total force. From this difference, multiplied when us- ing the microtest by the scale factor 6, the hardness in international rubber hardness degrees (IRHD) is obtained by using tables 3 to 5 or on graphs based on these tables or a scale, reading directly in inter- national rubber hardness degrees, calculated from the tables and fitted to the indentation-measuring instru- ment. These tables and curves are derived from the empirical relationship between indentation depth and hardness given in annex A.
4.3 apparent hardness: The hardness, reported to the nearest whole number in international rubber hardness degrees, obtained using the procedures de- scribed in methods N, H, L and M on test pieces of non-standard dimensions, as well as hardness values obtained using methods CN, CH, CL and CM. NOTE 3 Values obtained by methods CN, CH, CL and CM are always given as apparent hardness since tests are commonly made on the complete article where the thick- ness of the rubber will vary, and in many cases the lateral dimensions will not provide the minimum distance between the indentor and the edge necessary to eliminate edge ef- fects. The readings obtained therefore do not in general coincide with readings obtained on standard test pieces as defined in methods N, H, L and M or on a flat parallel-faced slab of the same thickness as the article. Moreover, the readings may depend appreciably on the method of support of the article and whether or not a presser foot is used. It should, therefore, be recognized that results obtained on curved surfaces are arbitrary values applicable only to test pieces or articles of one particular shape and of particular dimensions, and supported in one particular way, and in extreme cases such values may differ from the standard hardness by as much as 10 IRHD. Furthermore, surfaces that have been buffed or otherwise prepared to remove cloth markings, etc., will give slightly different hardness values from those with a smooth, moulded finish.