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The Factors Affect The Accuracy Of Hardness Test And The Treatment Methods

1. The surface of the sample 

when using the Rockwell hardness tester to test the hardness of workpiece, it is required that the tested its surface should be smooth, non—scale, non—decarburized layer and free from dust and dirt. If the tested workpiece surface is rough, the test value will be much lower and the data dispersion will be larger. 

For the forgings and castings in the tested rough workpiece surface, we can use a polisher to make it smooth and then go to test it again. 

2.The thickness of tested workpiece 

The tested workpiece should be thick enough or else the hardening deformed area of the bottom indentation of the sample will spread to the interface, which is with the anvil, causing the deformation of bearing surface of tested workpiece. It will make the testing result be inaccurate. 

3. Sample with curved surface 

If the tested workpiece is curved, the hardness value got from the test will have some deviation compared with plane workpiece. Thus, the testing result should be added or subtracted by a correction value. When testing on the convex cylinder, it should add a correction value. In contrast, when testing on the concave cylinder, it should subtract a correction value. 

4.The placement of curved surface 

When we choose an anvil and put away the tested workpiece, we should be careful to make the testing surface upright with the indented axis. Moreover, we should prevent the tested workpiece from shifting、having local elastic deformation and the wrong direction during after burning process. 

5. Hardness block gets invalid 

The hardness could only be allowed to use its positive surface and can not provide infinite tests possibly. When it is full, it should be replaced by new hardness block. If the hardness block becomes rust, the test will be not accurate, which needs to substitute with a new one. Every hardness block produced by Shenyang Tianxing is marked with effective date and please to use the hardness block.

6. After burning is not right 

During the test, we should be in a slow and even after burning process and make stress value indicator coincides with counterpart the tick line accurately. If it doesn’t get to or surpass the tick line, that will influence the testing accuracy because of the incorrect test force. 

Different test conditions have different surveyor robs, so we should pick up the test force accordingly. If we are wrong in it, we will make the measurement become invalid. 

7. Reading is not completely dependable 

During the operation process of Rockwell and Rockwell superficial hardness test, the operator should remain unchanged as much as possible. They should also adjust the position of reading to be identical to the position of adjusting the drum; otherwise, there will be errors when it comes to reading. 

8.Head damaged 

Abrasion, punch and the test of particularly hard material will cause the indenter to be damaged probably. When the instrument has been used for a long time or the accuracy of test has been declined, we should use eight ~ten times magnifier to check the indenter. When crack、 scar and defect happens to the indenter of the diamond, it means the deformation of ball indenter. We should replace it with a new one.