GB/T 5766-2023Test method of Rockwell hardness for friction materials (English PDF)

3.1 Rockwell hardness

The specified steel ball indenter is used to apply the initial test force and the main test force successively to the surface of the friction material product under the specified conditions, then the main test force is removed and the initial test force is retained. Use the indentation depth residual increment e of the steel ball indenter under the two test forces to calculate the value according to formula (1). where.

130 -- The theoretical maximum value of Rockwell hardness; during the test and shall not be damaged after the test. The diameter of the indenter depends on the Rockwell hardness tester in use. The indenter is equipped with a scale or other suitable device to measure the indentation depth caused by the indenter. The minimum graduation value of the indentation depth is 0.001 mm.

5.2 Dryer

There is a desiccant inside.

5.3 Specimen holder

The specimen holder shall meet the requirements of sample size and shape and be able to fit closely to the specimen.

7.1 Preparation before the test

7.1.1 According to the hardness of the friction material, select the appropriate scale according to Table 1, and the Rockwell hardness value shall be within the range of 50~115.The R scale is applicable to soft friction materials, and the P scale is applicable to hard friction materials. If the hardness values of a friction material tested by two scales are both within the limit, the scale with the smaller hardness value should be selected. The same scale shall be used for friction materials of the same texture. In addition to this method, the R scale can also be measured by the Rockwell-alpha hardness method and the test shall comply with the provisions of Appendix A.

7.1.2 Place the hardness tester on a horizontal platform with the main axis of the indenter perpendicular to the surface of the specimen. The steel ball shall be able to slide freely in the indenter shaft sleeve hole and must be clean and free of defects.

7.1.3 The specimen holder shall fit tightly against the hardness tester test bench. The supporting surface of the specimen holder and the hardness tester test bench shall be clean (see Figure 1 for the specimen holder).

7.3.2 Electric Rockwell hardness tester

7.3.2.1 Select a suitable scale according to the provisions of 7.1.1, and select a suitable specimen holder and test bench according to the provisions of 5.3 and 7.1.3.

7.3.2.2 Place the specimen in contact with the steel ball indenter without impact and apply the initial test force.

7.3.2.3 Turn on the power switch, conduct the test, and record the Rockwell hardness value to one decimal place.

7.3.2.4 Change the measuring point and repeat the steps in 7.3.2.2 and 7.3.2.3.

7.4 Result expression and calculation

7.4.1 Rockwell hardness is expressed by the measured hardness value suffixed with the Rockwell hardness symbol (HR) and the letter of the scale used.

EXAMPLE: 80 HRM means the Rockwell hardness value measured using the M scale is 80.

7.4.2 The value directly read by the digital hardness tester is the hardness value. For the dial hardness tester, subtract the number of times the long pointer passes through the zero point of the B dial (B0) after the main test force is applied from the number of times the long pointer passes through the zero point of the B dial (B0) after the main test force is removed, and read the value according to the following method.

-- If the difference is 0, and the scale reading plus 100 is the Rockwell hardness

A.1 Operation steps

A.1.1 Use an indenter with a diameter of 12.7 mm and a main load of 588.4 N.

A.1.2 Measure the elastic constant of the machine as follows. Place a soft copper block (at least 6 mm thick) on the platform and apply a small load. Reset the depth indicator to zero and apply the main load. Maintain the main load until the depth indicator stabilizes. Note down the reading, remove the main load, and reset the depth indicator to zero. Repeat the above steps until the depth indicator reading is constant after each application of the main load. This means that the indenter is no longer pressing further into the copper block. The constant depth reading is the displacement of the depth indicator due to the elasticity of the instrument. Record the constant depth reading and record it as a value (ds) in units of 0.002 mm.

A.1.3 Replace the copper block with the specimen and place it on the platform. Check whether the surface of the specimen and the surface of the indenter are free of dust, dirt, grease and scale, and check whether the surface of the specimen is perpendicular to the direction of the applied load. After the minor load is applied, the depth indicator shall be reset to zero within 10 seconds and the main load shall be applied immediately. After applying the main load for 15 seconds, observe and record the indentation depth and record it as a value in units of 0.002 mm (dh is the indentation depth at 15 seconds).

NOTE: If the machine is calibrated directly using Rockwell hardness values, it is convenient to proceed as follows. After the main load is applied, record the number of times the pointer passes through the zero point on the red scale. Subtract this number from the number of times the pointer passes through the zero point after the main load is removed. If the difference is 0, record the hardness value as the reading plus 100.If the difference is 1, record the scale reading without change; if the difference is 2, record the scale reading minus 100.

A.2 Result presentation

Rockwell-alpha hardness is calculated according to formula (A.1). where. Ra -- Rockwell-alpha hardness value; […]