ROCKWELL HARDNESS TEST

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Rockwell Hardness Test

The Rockwell Hardness test is a hardness measurement based on the net increase in depth of impression as a load is applied. Hardness numbers have no units and are commonly given in different scales. The higher the number in each of the scales means the harder the material.

The Rockwell hardness test does not serve well as a predictor of properties such as strength or resistance to scratches, abrasion, or wear, and should not be used alone for product design specifications.

The Rockwell hardness test is used to measure the hardness of metal measures resistance to penetration, the depth of the impression is measured rather than the diametric area..

Rockwell Typical Scale Properties

Types of indenters used

Conical diamond with a round tip for harder metals to ball indenter’s ranges with a diameter ranging from 1/16” to 1/2” for softer materials. 

In both tests, the indenter may be either a diamond cone or steel ball, depending upon the characteristics of the material being tested

If no specification exists or there is doubt about the suitability of the specified scale, an analysis should be made of the following factors that control scale selection:

Type of material Specimen thickness Test location Scale limitations

Types of the Rockwell Test

There are two types of Rockwell tests:

Rockwell: the minor load is 10 kgf, the major load is 60, 100, or 150 kgf.

Super Rockwell: the minor load is 3 kgf and major loads are 15, 30, or 45 kgf.

Principe of the Rockwell Test

The indenter moves down into position on the part surface A minor load is applied and a zero reference position is

established The major load is applied for a specified time period (dwell

time) beyond zero The major load is released leaving the minor load applied The resulting Rockwell number represents the difference

in depth from the zero reference position as a result of the application of the major load

Test Procedure

Performing a Rockwell test consists of

Putting gently the specimen in contact with the indenter Applying a minor load Automatically or manually zero the penetration measuring

instrument or dial gage Applying gradually the major load Removing gently the total load while leaving in place the

preliminary one (so that the elastic deformation following the removal of final load is recovered)

Measuring the depth of penetration using the Instrument

Considerations for Test 

Require clean and well positioned indenter and anvil The test sample should be clean, dry, smooth and oxide-free surface The surface should be flat and perpendicular to the indenter Low reading of hardness value might be expected in cylindrical surfaces Specimen thickness should be 10 times higher than the depth of the indenter The spacing between the indentations should be 3 to 5 times of the indentation

diameter Loading speed should be standardized No specimen preparation required Hardness value directly readable, no optical evaluation required Quick & cost-effective process Non-destructive testing Not always the most accurate hardness testing method The test location must be completely free of all contamination (e.g. scale, foreign bodies

or oil) The indenter has unknown effects on the test results With increasing hardness, it becomes increasingly difficult to distinguish between

materials