Hardness inspection of coating

1 Inspection equipment

When testing the macroscopic hardness of the coating and selecting the Hardness Tester used, the softness and hardness of the coating material and the thickness of the coating should be considered, so as to avoid the reaction with the hardness of the substrate in the measurement results and cause errors. It is generally recommended to use the standard Rockwell hardness test machine and superficial Rockwell hardness testing machine.

2. Specimen Preparation

For the sample for measuring the hardness of the coating, the surface and its blue side should be flat and the two planes should be parallel to each other, and the coating surface should be smooth and clean. At least five pressure points shall be measured for each sample. The distance between two measuring points or the distance between any measuring point and the edge of the sample shall not be less than 3mm. The thickness of the sample should ensure that there is no obvious deformation on the back of the sample after the test. For cylindrical samples, the measuring surface should be ground so that it is parallel to the drill seat of the Hardness Tester.

3. Inspection method

Each revolution of the dial pointer of the standard Rockwell Hardness Tester (testing machine) indicates that the indenter has an indentation depth of 0.203mm. In order to accurately measure the coating thickness, the minimum coating thickness should be more than 1o times the indentation depth. Therefore, when testing the hardness of the coating with each scale of the standard Rockwell Hardness Tester, the thickness of the coating should be greater than 2mm. (Related Instruments: Thickness Gauge)

When testing, the hardest wear-resistant coating is declared to use C scale and A scale, and the surface Rockwell hardness is measured by 15N, 3oN, 45N scale; for slightly soft coatings, B scale or A scale can be used, and the surface Rockwell hardness is measured by 15T , 30T, 45T scale measurement. The principle of use depends on the thickness of the coating. Thin coatings are tested by superficial Rockwell hardness; for softer coatings, use a superficial Rockwell Hardness Tester with a main load of 15 kg, using steel balls with a diameter of 1.588mm (1/16″), R15T Scale; diameter 3.175mm (1/8″) steel ball, R15W scale; diameter 12.7001Tlm (1/2″) steel ball, R15Y scale.

When the steel ball is installed or replaced, the reading of the hardness for the first time will not be included in order to prevent the reading from being inaccurate due to improper installation of the steel ball. The test points should be evenly distributed on the centerline of the coating surface and avoid defects. The number of measurement points should not be less than 5, and finally take the average as the hardness value of the coating.