What is  Rockwell Hardness test and how to perform in the lab?


Rockwell test is developed by the Wilson instrument co U.S.A in 1920. This test is an indentation test used for smaller specimens and harder materials.  The test is subject of IS: 1586.In this test indenter is forced into the surface of a  test piece in  two  operations, measuring the permanent  increase  in depth  of  an  indentation from the depth increased from the depth reached under a datum load  due to an additional load.  Measurement of indentation is made after removing the additional load. Indenter  used is the cone having an angle of 120 degrees made of black diamond.


LAB WORK -

Title  Rockwell Hardness test 

 Objective

 To determine the hardness the Hardness of the given  Specimen using Rockwell hardness test. Materials and equipments required Rockwell hardness testing machine. Black diamond cone indenter,  Hard steel specimen. Theory Rockwell test is developed by the Wilson instrument co U.S.A in 1920. This test is an indentation test used for smaller specimens and harder materials.  The test is subject of IS: 1586.In this test indenter is forced into the surface of a  test piece in  two  operations, measuring the permanent  increase  in depth  of  an  indentation from the depth increased from the depth reached under a datum load  due to an additional load.  Measurement of indentation is made after removing the additional load. Indenter  used is the cone having an angle of 120 degrees made of black diamond. 

Precautions 

1.  Thickness of  the specimen  should not be  less than  8 times the depth of  indentation to avoid the deformation to be extended to the opposite surface of a  specimen. 

 2.  Indentation should  not be  made  nearer to the edge of  a  specimen to avoid  unnecessary concentration of stresses. In such case distance from the edge to  the center  of  indentation  should  be greater than  2.5 times diameter of  indentation. 

 3.  Rapid rate of applying load should be avoided. Load applied on the ball may rise  a little because of its sudden action. Also rapidly applied load will restrict plastic flow of a material, which produces effect on size of indentation. 

Procedure 

1.  Examine hardness testing machine (fig.1). 

 2.  Place the specimen on platform of a machine. Using the elevating screw raise  the platform and bring the specimen just in contact with the ball. apply an initial load until the small pointer shows red mark.

  3.  Release  the operating  valve to  apply additional load.  Immediately after the  additional load applied, bring back operating valve to its position. 

 4.  Read  the  position  of  the  pointer  on  the C  scale,  which gives the hardness number..




5.  Repeat the procedure five times on the specimen selecting different points for indentation


Observation 

1.  Take  average  of five  values of indentation of  each specimen. Obtain the  hardness number from the dial of a machine.

 2.  Compare Brinell and Rockwell hardness tests obtained


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