The method of determining the Rockwell hardness includes numerous embodiments of the same principle as the Brinell, but using indenters with several diameters. In the method the following indenters are used: the conical diamond and the balls of hardened steel with diameter of 1/16, 1/8, 1/4 and 1/2 inch. The prints obtained by the Rockwell hardness test are less than Brinell test. It allows you to make tests on rather small area of metal.
Using one of this indentor, it is possible to put different loadings to the majority of the tested materials. The enclosed loadings are much lower than loadings at test according to Brinell and lie in the range from 60 to 150 kgf. One of the tested groups on Rockwell is called «superficial tests». They are intended first of all for the hardness determination of thin metal samples and the wire: the loadings enclosed here are much lower than loadings which are created in other types of tests according to Rockwell.
As well as for tests according to Brinell, the tested surface has to be correctly prepared before test. For exact hardness determination it is necessary to use well-tried technical means. After the sample preparation it is required to choose correctly a scale, proceeding from estimated value of hardness. The «В» and «С» scales are used generally for steel, and the «В» scale is used for softer alloys, and «С» scale is used for solid brands. In cases of doubt in the choice of scale for the unknown alloy, you should use the “A” scale, since it includes a range of hardness, covering the range of the “B” and “C” scales. The hardness indicators for converting from one scale to another the conversion table is drawn up.
After selecting the desired control unit and scale calibration test sample is placed on a table in the testing machine Rockwell. The table can be of various shapes, the choice of which depends on the configuration of the test object. To avoid errors in determining the hardness, the test sample should be sufficient support. The determination of Rockwell hardness measurements based on the high-precision the depth of penetration of the indenter. Therefore, if the test object is not set at the sufficiently solid foundation, the test results may be inaccurate. The range of the depth of the measurement results, constituting 0.00008 inches, can cause a change in the number of Rockwell hardness by 1. The bench model performs depth measurement automatically.
