In order to achieve as broad an application area as possible for the Rockwell process, several Rockwell methods have been developed for both the Rockwell and the Super Rockwell processes.
The individual Rockwell methods are distinguished from each other by:
- Type of indenter (material, shape and size or ball diameter);
- Magnitude of total test force (total force or main load);
- Scale division (basis h0 for the residual indentation depth (h) to be measured is 100 or 130 units (depending on the scale: 1 unit E = 0.002 mm or 0.001 mm)); see also table in illustration "Rockwell hardness test".
The five resulting Rockwell methods use five different indenters (diamond cone with 120o curvature or a hard metal ball made from tungsten carbide with diameters of: 1/16",1/8",1/4",1/2") and six different total test forces (15, 30, 45, 60, 100, 150 kgf).
This results in 30 different - standardised according to ISO 6508 and ASTM E18 – Rockwell scales (e.g. A, B, C, 30N, 15T) and test methods (e.g. HRA, HRBW, HRC, HR30N, HR15TW), each covering different hardness ranges and consequently the widest variety of materials and application areas (see table below and poster "Hardness testing of metallic materials").
Rockwell is often used as a "quick test" in production or in the laboratory, as well as for other processes, such as the Jominy test.
The most common Rockwell method in practice is HRC. In principle, ball indenters are used for the hardness testing of softer materials and diamond indenters for testing harder materials. The diamond would destroy softer materials or pierce through them.
Rockwell methods and applications
The following table shows the Rockwell methods standardised according to ISO 6508 and their applications. The preload for all methods is 10 kgf.