Rockwell Hardness Testers

After holding the preload for the specified dwell time, an additional load known as the major load is then applied. At this point, the total force has been reached and the major load is also held for a specific dwell time. After the major load is released, the depth measurements are taken from the reference point to the final depth of the penetrator after having undergone the major load. This distance between these depth reference points are then measured and converted into the Rockwell Hardness Value.

The Rockwell hardness tester has many different scales depending on the application of the tester on different materials. HR is used to express the hardness scale and the hardness value. There are a total of 30 Rockwell hardness scales which are specific for different applications. Rockwell regular and Rockwell superficial are two divisions on the Rockwell scales which each have 15 individual scales. Superficial Rockwell scales use a preliminary load of 3kgf and have a major load of either 15kgf, 30kgf or 45kgf. Superficial scales are used for materials that are as thin as 0.15mm (or 0.006 inches). Regular Rockwell scales use a preload of 10kgf and a major load of 50kgf, 100kgf or 150kgf. The use of the scales strictly depends on the hardness, thickness, indentation positioning and scale limitations of the materials being tested. It is important that the material is at least 10 times as thick as the depth of the Rockwell indentation. Diamond indenters are commonly used for harder materials such as case hardened steels. Ball indenters are more commonly used for softer and thinner materials such as copper alloys and sheet metals.

The most popular scales for Rockwell Regular hardness testing are HRC and HRB which use a diamond and ball penetrator respectively. The most common uses for the HRC scale include steel, hard cast irons, case hardened steel and other materials harder than 100 HRB. The most common uses for the HRB scale include copper alloys, soft steels, aluminum alloys and softer irons. Superficial scales are used where the standard Rockwell scales are incapable of testing due to the properties of the material. Materials that are too thin or small for the Rockwell regular scales can benefit from Superficial Rockwell testing.