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Factors Effect the Accuracy of Hardness Testing and Solutions

1. Surface of Specimen

In hardness testing, the surface of specimen is required to be smooth, scale free, no decarburized  layer or present. The roughness of specimen will lower the test result and make the data dispersion higher.

2. Thickness of Specimen

The specimen should have enough thickness, otherwise, the harden deformation part on the bottom of specimen will extend to the contact surface with anvil, leading to the deformation of supporting surface and the inaccuracy of test result.

3. Specimen with Curved Surface

If the specimen has curved surface, the hardness value will have certain deviation compared with the  flat ones. Therefore, the test result should add or minus a modification value. While test convex cylinder surface, add a modification value, and while test hollow cylinder surface, minus a modification value.

4. Place of Specimen

While choosing anvil and placing specimen, please notice that keep the test surface verticle to  indenter axis, preventing specimen displacement, part deformation and wrong direction of loading test  force.

5. Invalid of Hardness Block

Only the observe side of test block is allowed to use in hardness testing. However, it can't be used for unlimited times. When the test block is full of indentations, users should change a new one. If the test block rusts, the test result will be inaccurate, and users should also change a new one. The date of production will be marked on every test block of Shenyang Tianxing. Please use it within the valid date.

6. Inaccurate Force Loading

While testing hardness value, people should load test force slowly and evenly, making indicater hand coincide with relevant scale line. Being not reached or past will effect the test accuracy. 

Different test force is applied according to different test condition and different scale. If a wrong test force is applied, the test will be invalid.

7. Inaccurate Reading

In Rockwell and superficial Rockwell hardness testing process, the visual angle of operater should remain unchanged. The visual angle of reading scale should be the same with adjusting barrel dial, otherwise, reading error will occur.

8. Damage of Indenter

Abrasion, impact, or testing extrame hard material may all damage the indenter. Testers which are used for too long time or test accuracy declines should be checked with 8-10x magnifier on indenter.  When crack, blackspot, or flaw appears on the diamond cone indenter, or ball indenter deforms, the indenter should be replaced by a new one.