What is Rockwell Hardness Testing?
The Rockwell Hardness Test is generally a non-destructive test performed on samples when it is necessary to determine how hard a material is. Hugh M. Rockwell (1890–1957) and Stanley P. Rockwell (1886–1940) from Connecticut co-invented the first tester and a patent was granted in 1919. The Rockwell Hardness test is generally considered easier to perform compared to other methods such as Vickers or Brinell.
Hardness is defined as a material’s resistance to permanent indentation. Current Rockwell Hardness test methods are specified in ASTM E-18 and anyone wishing to perform a Rockwell Hardness test should become familiar with this test standard.
Rockwell Hardness Test Procedure
The Rockwell hardness test consists of indenting the test material with a diamond cone or hardened steel ball indenter. Each time a test is performed two loads are applied to the sample being tested. First, the indenter is forced into the test material under a preliminary minor load and this depth is recorded. With the minor load still applied an additional load is introduced known as the major load which increases the depth of penetration on the sample. The Major load is then removed, and the force on the sample is returned to the minor load. The increase in the depth of penetration that results from applying and removing the major load is used to calculate the Rockwell hardness value.
Rockwell Hardness Scales
There are several different Rockwell Scales each denoted by a single letter. Each scale requires different loads or indenters, so careful consideration should be given to which scale you are working with when evaluating results.
Scale
Abbreviation
A
HRA
B
HRB
C
HRC
D
HRD
E
HRE
F
HRF
G
HRG
H
HRH
K
HRK
Superficial Scales
The Rockwell Hardness test also uses superficial scales. These use lower loads and shallower indentions when a sample may be too brittle or thin for a standard Rockwell Hardness Test.
Superficial Rockwell hardness tester: 15N, 30N, 45N, 15T, 30T, 45T, 15W, 30W, 45W, 15X, 30X, 45X, 15Y, 30Y, 45Y
Polymer/Plastic Scales
There are also Rockwell Hardness Scales used for polymers and plastics. Those are scales R, L, M, E and K. Like other scales different sized indenters are used depending on the scale.
United's TRU-BLUE II Rockwell Hardness Tester is available in a variety of configurations depending on your requirements. The TB II Meets all NIST, ISO, CE, ASTM requirements and is capable of performing a variety of Rockwell Hardness tests including 15 Regular scales: A, B, C, D, E, F, G, H, K, L, M, N, P, S, V, and 15 Superficial scales: 15N, 30N, 45N, 15T, 30T, 45T, 15W, 30W, 45W, 15X, 30X, 45X. 15Y, 30Y, 45Y
