Industries using the Rockwell hardness tester
1. Researching institute
2. National organization
3. University
4. Aeration and space industry
5. Automobile industry
6. Steel industry
There are two types of Rockwell tests: 1. Rockwell: the minor load is 10 kgf, the major load is 60, 100, or 150 kgf. 2. Superficial Rockwell: the minor load is 3 kgf and major loads are 15, 30, or 45 kgf.
In both tests, the indenter may be either a diamond cone or tungston carbide ball, depending upon
the characteristics of the material being tested.
Rockwell Scales
Rockwell hardness values are expressed as a combination of a hardness number and
a scale symbol representing the indenter and the minor and major loads.
The hardness number is expressed by the symbol HR and the scale designation.
The Rockwell hardness test is based on an inverse relationship to the measurement of the additional depth to
which an indenter is forced by a heavy total (major) load beyond the depth resulting from a previously applied preliminary (minor) load.
Initially a minor load is applied, and a zero datum position is established.
The major load is then applied for a specified period and removed, leaving the minor load applied.
The resulting Rockwell number represents the difference in depth from the zero datum position as
a result of the application of the major load. The entire procedure requires as little as a few seconds up to 15 for plastics.
In the Rockwell test, results are quickly and directly obtained without the need for a secondary, dimensional measurement requirement.
The most common indenter type is a diamond cone ground at 120 degrees for testing hardened steels and carbides.
Softer materials are typically tested using tungsten carbide balls ranging in diameters from 1/16 in up to 1/2 in.
The combination of indenter and test force make up the Rockwell scale.
These combinations make up 30 different scales and are expressed as the actual hardness number followed by the letters HR and
then the respective scale. A recorded hardness number of HRC 63 signifies a hardness of 63 on the Rockwell C scale.
Higher values indicate harder materials such as hardened steel or tungsten carbide. These can have HRC values in excess of 70 HRC.
Rockwell test forces can be applied by either closed-loop load cell or traditional deadweight systems.
How to determine which Rockwell Scale to use
Jan 18
Written by: 1/18/2012 3:36 PM
Foremost to any Rockwell test process is identification of the proper hardness scale to
be used on the component to be tested. Rockwell hardness values are expressed as a combination of a hardness number and
a scale symbol representing the indenter and the minor and major loads. The hardness number is signified by the symbol HR and
the scale designation. The combination of indenter and test force make up the Rockwell scale. These various combinations
make up 30 different scales and are expressed as the actual hardness number followed by the letters HR and then the respective scale.
A recorded hardness number of HRC 63 signifies a hardness of 63 on the Rockwell C scale. Higher values indicate harder materials
such as hardened steel or tungsten carbide. The majority of applications are covered by the Rockwell C and B scales for testing steel,
brass, and other metals. However, the increasing use of materials other than steel and brass as well as thin materials necessitates a basic
knowledge of the factors that must be considered in choosing the correct scale to ensure an accurate Rockwell test.
The choice is not only between the regular hardness test and superficial hardness test, with three different major loads for each,
but also between the diamond indenter and the 1/16, 1/8, 1/4 and 1/2 in. diameter carbide ball indenters.
Often an engineering specification is established at the material design phase and the operator can rely on documented scale requirements.
If no specification exists or there is doubt about the suitability of a predetermined scale,
an analysis should be made of the following factors that control scale selection:
Type of material
Specimen thickness
Area / width
Test location
Material homogeneity
Scale limitations
|