Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
SAE J2654: Rockwell Hardness Testing for Brake Linings – Quality Control Standard
Purpose of SAE J2654
The SAE J2654 standard defines a nondestructive test method for measuring the Rockwell hardness of brake linings. Hardness measurements serve as a quality control check to ensure consistency in formulation and processing. It is important to note that this method does not measure friction level—hardness is a characteristic of each specific formulation and must be interpreted within its own acceptable range. The standard has been stabilized as of 2015, reflecting its mature and stable technology.
🛠️ Engineering Insight: Hardness is a quality control indicator, not a direct measure of friction performance. Acceptable hardness values and ranges must be established for each formulation and may be affected by processing.
Testing Procedures and Equipment
The test must be conducted under controlled environmental conditions. SAE J2654 recommends that testing be performed at a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5 % to ensure reproducibility.
Sample support is critical: disc pad assemblies can be tested directly on the ground surface if sufficient flat support is available on the backplate. For drum linings, a fixture with the same radius as the lining must be used to prevent movement or flexing during the test.
After replacing or reinstalling the indenter, at least two tests must be performed and discarded to properly seat the indenter; manual seating is insufficient.
| Scale | Symbol | Indenter Diameter | Minor Load | Major Load |
|---|---|---|---|---|
| M | HRM | 6.350 mm (0.2500 in) | 98.07 N (10 kg) | 980.7 N (100 kg) |
| R | HRR | 12.700 mm (0.5000 in) | 98.07 N (10 kg) | 588.4 N (60 kg) |
⚠️ Important: After changing the indenter, always discard the first two test results to ensure accurate measurements.
Engineering Insights and Frequently Asked Questions
Design engineers must recognize that hardness readings are influenced by several factors including temperature, humidity, sample thickness (especially if less than 5 mm), and the specific Rockwell scale used. For sintered metal linings, the standard directs use of Rockwell superficial hardness equipment per ASTM B347.
Frequently Asked Questions
Does hardness correlate with friction level?
No. The standard explicitly states that this method is not a measure of friction level. Hardness is solely a quality control parameter for consistency.
How do temperature and humidity affect hardness readings?
Both can significantly affect the results. That is why controlled conditions (23 ± 2 °C, 50 ± 5 % RH) are recommended, and actual conditions must be recorded in the test report.
Which Rockwell scale is appropriate for different lining materials?
The M scale (6.35 mm ball, 100 kg major load) is commonly used for organic linings. Sintered metal linings often require the Rockwell superficial hardness test (per ASTM B347). The R scale (12.7 mm ball, 60 kg major load) may be used for softer materials.
How should curved drum linings be supported during testing?
A fixture machined to the same radius as the lining must be used to provide proper support and prevent flexing or movement that could invalidate the test.
