Rockwell Hardness ASTM D785, ISO 2039
The Rockwell Hardness test is a hardness measurement based on the net increase in depth of impression as a load is applied. Hardness numbers have no units and are commonly given in the R, L, M, E and K scales. Higher numbers indicate harder materials.
A standard specimen is placed on the surface of the Rockwell Hardness tester. A minor load is applied and the gauge is set to zero. The major load is applied by tripping a lever. After 15 seconds the major load is removed. The specimen is allowed to recover for 15 seconds and then the hardness is read off the dial with the minor load still applied.
A standard specimen of 6.4mm (0.25 in) thickness is either molded or cut from a sheet.
The hardness is read directly from the dial with either the R, L, M, E or K scales. The higher the number in each scale, the harder the material. R and M scales are commonly used with plastics.
**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. Standards can be obtained from appropriate standard authorities.