Rockwell Principle

For a better understanding, the different steps of the Rockwell method are illustrated and numbered in the figure below, showing the dial indicator, that records the displacements of the penetrator.

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1. First, a preliminary test force Fo is applied (preload), determining a light penetration; after that, the dial indicator must be reset to zero.

2. Gradually and avoiding any impact, an additional test force (F1) is applied to reach the required test load (F). With this force applied, the penetrator penetrates according to the hardness of the material self.
One must wait until penetration is completed. The dial indicator shows the penetrator’s displacement.

 

3. The additional force F1 can be removed, returning to the preload; in this way, the indenter remains in the indentation, but all elastic strains given by the load application will be eliminated. The dial indicator will show the difference of penetration between preload and test load. Indenters, preloads, test loads and unit of measurement are standardized in two groups: standard Rockwell and Superficial Rockwell.