Rockwell Test:
This is similar to the Brinell test. Both of these tests have similarities when it comes to the degree of indentation caused by the indenter under a static load. Rockwell test is conducted with the choice of three varying loads and indenters. In the case of Brinell test, the indenters and loads are smaller in nature thus indentation of the load is made smaller and shallower.
Rockwell scales vary based on the indenter and applied load. The scale employed is a function of the applied load and the indenter used. During its operation, a load worth 10kg is applied to facilitate an indentation that sets the indenter and holds it in the proper position. No Rockwell hardness value consists of a number alone. This is because while performing a hardness test, the result depends on the indenter and the load employed to the test. This makes the dial machine have two sets of figures – one red and the other black. They differ by 30 hardness numbers. Furthermore, the dial consist of both the B and C scales.
The B-scale is used in testing materials of medium hardness while the C-scale is used in testing material that is greater than B100. For good practice, it’s always good to choose a scale with the smallest ball since sensitivity is lost as the indenter size increases. Rockwell scales are divided into 100 divisions, and each division is equal to 0.002 mm in the indentation. The higher the number on the scale, the harder the material.
Rockwell Superficial Hardness Test:
This test is designed to test surface hardness where shallow indentations are desired. It operates like a regular Rockwell hardness tester though it employs both minor and major loads and has a more sensitive depth measuring system. It uses the N and T scales. The W, X and Y scales are used for very soft material. The tests it performs correspond to the 15T, 30T, 45T, 15N and 45N levels, depending on the indenter and load used for the test.
The Rockwell test is very accurate and precise. Also, it is a rapid test to run, and readings are taken direct from the machine without calculations. It is more objective and covers a wide variety of material hardness. On the contrary, it closely resembles the Brinell test and is relatively expensive. Lastly, it is not suitable for field service and has a destructive look.
Vicker’s Hardness Test:
It uses a small diamond square-pyramid indenter. The tip is of 136 degrees and loads between 5 and 120kg in 5-kg increments. It has a specimen holder, a screw and a foot lever for resetting. Primarily, it used in research applications. It is very accurate in measuring indentations and is a very rapid method. On the contrary, it is a very destructive test and is much slower than Brinell and Rockwell test. The cost of the equipment is higher though it’s widely accepted.
