Rockwell hardness
The Rockwell method is a method of determination of material hardness based on penetration of a firm tip into the material and measurement of the depth of penetration.
There are 11 scales of hardness determination by Rockwell's method (A, B, C, D, E, F, G, H, K, N, T) based on the combination "indenter (tip) – loading". Two types of indenters are most widely used: a ball from tungsten carbide with the diameter 1.5875 mm or the same ball from tempered steel and a conic diamond tip with the tip angle 120°. Possible loadings are 60, 100 and 150 kgf. The hardness value is defined as a relative difference in the depth of indenter penetration at application of the basic and initial (10 kgf) loadings.
The most widely used Rockwell hardness scales are the following:
| Scale | Indenter | Loading, kgf |
|---|---|---|
| A | Diamond cone with tip angle 120° | 60 |
| B | Ball with the diameter 1/16 inches (1.5875 mm) from tungsten carbide (or the tempered steel) | 100 |
| C | Diamond cone with tip angle 120° | 150 |
Carrying out of a test:
– the scale suitable for a tested material is chosen (A, B or C);
– the corresponding indenter and loading are set up;
– before starting the test the correctness of fitting the tip and the table is checked;
– the reference block is set onto the anvil;
– the initial loading in 10 kgf is applied, the scale is zeroed out;
– the basic loading is applied after which it is to be waited for application of the maximum effort;
– the loading is removed;
– the value of hardness is read out according to the corresponding scale;
– the operations procedure when checking the hardness of a tested sample is the same as for the reference block.