GB/T 5766-2023 in English

GB/T 5766—2023 Interpretation of the Rockwell Hardness Test Method Standard for Friction Materials

1. Background and Significance of the Standard

The GB/T 5766 series of standards has undergone several revisions since its first release in 1986 and has now become an important technical specification for the friction material industry. This revision (GB/T 5766—2023) mainly optimizes the test environment, instrument requirements and hardness test methods, further improving the scientificity and practicality of the standard.

2. Main Contents of the Standard

3. Analysis of key technical changes

a) Test environment requirements

The new standard stipulates stricter temperature and humidity control ranges: (23±5)°C and (50±10)% to ensure the stability of the test results.

b) Instrument parameter requirements

New technical indicators for Rockwell hardness testers, including key parameters such as support platform rigidity, indenter accuracy, and steel ball surface roughness, have been added. In particular, the minimum graduation value of the indenter's indentation depth has been increased to 0.001mm, which significantly improves the measurement accuracy.

c) R scale and Rockwell-alpha hardness method

The new standard introduces the use of the R scale and allows the use of the Rockwell-alpha (Ra) hardness test method. This method is particularly suitable for soft friction materials. By optimizing the combination of the indenter diameter and the test force, the scope of application has been significantly expanded.

4. Operation steps and precautions

Sample preparation stage

• The sample needs to be placed in the dryer for more than 24 hours to ensure that the state is stable.
• The number of measurement points should be determined according to the sample area, generally 4-10, and evenly distributed.

Key points in the measurement process

When using a manual or electric Rockwell hardness tester, pay attention to the following: the order of applying the initial test force and the main test force, the accurate reading of the indentation depth, and the requirement for the spacing between the measurement points (not less than 4d).

5. Implementation suggestions

a) Choose a suitable scale

According to the hardness of the friction material, the R scale should be used first. For products of the same material, the scale consistency should be maintained.

b) Calibration and maintenance

It is recommended to calibrate the Rockwell hardness tester regularly using a standard block and ensure that the indenter steel ball has no scratches or deformation.

c) Data recording and analysis

The test results should be presented in the form of mean ± standard deviation. Refer to formula (2) to calculate the standard deviation to ensure the reliability of the data. $$ S={\sqrt{\frac{\sum(X_{i}-{\overline{{X}}})^{2}}{n-1}}} $$