Factors affecting Measurement Accuracy of Webster Durometer

The Webster hardness tester is a small, portable and easy-to-operate hardness testing tool, which is widely used in hardness testing of materials such as aluminum profiles. However, some improper operations may affect the accuracy of the measurement results.

The following are several key factors affecting the measurement accuracy of the Webster hardness tester and suggestions for correct operation:

1. Requirements for the distance between adjacent indentations

During the test, the distance between two adjacent indentations should be no less than 6mm to avoid the influence of the previous indentation on the accuracy of the next measurement. This is because indentations that are too close may cause local deformation or stress concentration of the material, thereby affecting the accuracy of the measurement results.

2. The influence of oxide film on hardness

Although the oxide film on the surface of the aluminum profile is thin, it will also affect the hardness measurement results. Especially when the oxide film is thick, its hardness is usually higher than that of the base material, which will cause the measurement value to be higher. For an oxide film with a thickness of 10μm, the hardness measurement value may be 0.5~1HW higher. Therefore, before measurement, the oxide film on the surface should be removed as much as possible or its influence on the measurement result should be considered.

3. Treatment of profile coating

The coating on the surface of aluminum profile (such as paint, coating, etc.) will seriously affect the measurement accuracy. These coatings are usually soft and have a large difference in hardness from the base material, so they need to be removed with sandpaper or solvent before measurement. After removing the coating, make sure that the surface of the sample is clean and free of residue to avoid affecting the measurement results.

4. Suggestions for Standard Operation

Accuracy Check: The accuracy of the instrument should be checked frequently during use, and the full scale point (20HW) and the calibration point should be checked for inaccuracy. If inaccuracy is found, it should be corrected in time to ensure the accuracy of the measurement results.

Verticality and Contact: During the measurement process, it should be ensured that the surface of the specimen is perpendicular to the indenter and that the bottom of the specimen is in good contact with the anvil line. This helps to reduce measurement errors and improve the accuracy of the measurement results.

Force Application: Sufficient grip force should be applied at one time to ensure that the indenter can be fully pressed into the surface of the specimen. Slow force application may result in low measured values because the material will generate a certain resistance during the gradual deformation process.

Avoid twisting: During the test, the specimen should be prevented from twisting or shaking. This may cause inaccurate measurement values and damage the indenter. Therefore, the specimen should be fixed and stable during measurement.

Read the maximum value: When testing softer specimens, the pointer may slowly drop after reaching a certain position. At this time, try to read the maximum value indicated by the pointer as the measurement result, because this is the hardness value shown by the material under maximum pressure.

Following the above recommendations and performing standardized operations will help improve the measurement accuracy and reliability of the Webster hardness tester.