Precautions for measuring the thickness of the coating by the hardness tester

The surface roughness, curvature and thickness of the sample will have an impact on the measurement error. Because the surface roughness has a great influence on the measured indentation size, in general, the rougher the surface, the measured hardness value will be lower. If the thickness of the sample is small enough, the hardness value measured by the hardness tester will be low. At this time, the measured value needs to be corrected.

The degree of precision of the measuring device affecting the hardness tester and the operational measurement of the hardness tester are correct enough, and the measurement result will have a great error. Therefore, it must be qualified by the metrological department, not exceeding the verification period and not damaged by itself. The Brinell hardness tester performs Brinell hardness measurement. The Brinell hardness tester must be sent to the metrological verification department for periodic verification operations, and the pressure head should be pressed slowly and smoothly into the sample surface.

The influence of the indentation diameter measurement is derived according to the formula, and the relative error of the hardness value can be obtained as the relative error of the indentation measurement. According to the calculation formula of Brinell hardness, the measurement error of indentation has a great influence on the error of hardness value, so the error of indentation measurement is the main source of error. If the measurement value of indentation diameter is too large, the calculated hardness value will be biased. Small, on the contrary, the hardness value will be higher than the ratio. In order to reduce the error, it is necessary to ensure the accuracy of the Microscope for measuring the indentation diameter, and secondly, when conditions permit, a larger load force and a larger steel ball should be used for the measurement. The larger the diameter of the mark, the smaller the relative error is. The influence of the ball indenter on the Brinell hardness increases the diameter of the ball indenter, and the hardness value decreases, and vice versa. If the steel ball used is small, when the load is applied. The steel ball itself will also undergo elastic and plastic deformation, which has a great influence on the error of low hardness value, so it must be measured under the standard indenter diameter.

Effect of test load force If the test load force increases, the measured hardness will decrease. Conversely, the hardness value will increase the Brinell hardness as the load force changes. The compliance of the Brinell hardness test depends on the accuracy of the weight, the accuracy of the applied load device and the correctness of the applied load force. The practice shows that the relative error of the hardness value is related to the relative error of the load. Therefore, in order to improve the measurement accuracy of the hardness value, it is necessary to reduce the load error, for example, the operator operates according to the basic principle of Brinell hardness, and periodically checks and calibrates the Brinell hardness tester under the standard conditions of the Brinell hardness test.

The temperature change of the sample affects the measurement personnel to measure the ambient temperature before measuring the hardness value of the sample. If the ambient temperature deviates from the standard ITI value, the measured hardness value must be temperature corrected to reduce the error. The change of temperature will cause the change of the structure of the material, and the test of Brinell hardness is greatly affected by the structure of the material. Therefore, when the temperature of the sample increases, the Brinell hardness value will decrease. Otherwise, the Brinell hardness value will be Therefore, the temperature of the sample must be consistent with the temperature of the laboratory. In the actual test work, it is possible to control the ambient temperature and the sample temperature within the required standard test temperature conditions. The standard provisions in the "Metal Brinell Hardness Test Method" are used to measure the Brinell hardness of the surface of the material.