Principle of rockwell & superficaial rockwell
To measure Rockwell or Rockwell Superficial hardness, first apply a preload force and then the test force to a specimen and return to the preload force using a diamond indenter (tip cone angle: 120º, tip radius: 0.2 mm) or a sphere indenter (steel or carbide ball). This hardness value is obtained from the hardness formula expressed by the difference in indentation depth h (µm) between the preload and test forces. Rockwell uses a preload force of 10 kgf, and Rockwell Superficial 3 kgf. A specific symbol provided in combination with a type of indenter, test force, and hardness formula is known as a scale. International standards define various scales of related hardness.