Rockwell Hardness Number Formula |
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\( HR \;=\; N - \dfrac{ h }{ s }\) (Rockwell Hardness Number) \( N \;=\; HR + \dfrac{ h }{ s }\) \( h \;=\; s \cdot ( N - HR ) \) \( s \;=\; \dfrac{ h }{ N - HR }\) |
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| Symbol | English | Metric |
| \( HR \) = Rockwell Hardness Number | \(dimensionless\) | \(dimensionless\) |
| \( N \) = Constant specific to the Scale | \(dimensionless\) | \(dimensionless\) |
| \( h \) = Depth of Indentation after Major Load | \(in\) | \(mm\) |
| \( s \) = Scale Factor | \(dimensionless\) | \(dimensionless\) |
Rockwell hardness test is a widely used method for determining the hardness of materials, primarily metals and polymers, by measuring their resistance to permanent indentation. Unlike some other hardness tests that measure the size of an indentation optically, the Rockwell test measures the depth of penetration of an indenter. The process involves two stages of loading: first, a preliminary (minor) load is applied to seat the indenter and establish a zero-point for measurement, eliminating the effects of surface roughness. Then, a greater (major) load is applied, causing further penetration. After a specified dwell time, the major load is removed, but the minor load remains applied.
The Rockwell hardness number is then calculated from the difference in the indentation depth between the initial minor load and the final minor load condition (after the major load has been removed and elastic recovery has occurred).
Different Rockwell scales exist, each denoted by a letter (e.g., HRA, HRB, HRC), and they utilize various combinations of indenter types (such as a diamond cone for harder materials or a hardened steel ball for softer ones) and applied loads to suit a wide range of materials and applications. This method is popular due to its speed, simplicity, and direct readout of the hardness value, making it highly suitable for quality control and material evaluation in various industries.
Nusselt Number Interpretation
- Low Rockwell Hardness Number - Indicates softer materials.
- High Rockwell Hardness Number - Indicates harder materials.
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The exact range depends on the scale (e.g., HRC typically ranges from 20 to 70, while HRB ranges from 0 to 100).
