Rockwel Hardness Testing Machine

7/30/2019 Rockwel Hardness Testing Machine

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Description of Equipment

Rockwell hardness test:

Hardness may be defined as the resistance of the material to penetration/indentation.The Rockwell hardness test is based on the measurement of the depth of penetrationof the indenter into the specimen. The salient features of a typical Rockwell HardnessTesting Machine are shown in Fig. 7.

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Major load is supplied by a dead weight loading lever (L) having a ratio of 25 to 1.Rockwell number is read from the dial gauge (D), connected to the plunger system inthe head of the tester by means of the Index Lever (M) having 5: 1 ratio.

The dial gauge is a 1 mm gauge, i.e. one revolution of the pointer equals 1 mm travel

of the dial rack. There are 100 divisions to a revolution and as the lever ratio is 5:1,each division on the dial represents a depth of 0.002 mm. When minor load is appliedthere is a fixed zero or set point. Two scales are provided on the dial gauge. The outer circle is in black, and all readings with diamond indenter are taken on this. The inner circle is in red, and all readings with ball indenters are taken from this. The set point isalways same regardless of the scale. Fig. 8 shows steel ball and diamond coneindenter.

The general principals of the Rockwell hardness test are illustrated in Fig. 9 (ballindenter) and Fig. 10 (diamond indenter) and the accompanying Tables 1 and 2 (inappendix I).

Experimental Procedure

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You will be provided four medium carbon steel specimens having composition of 0.45 % carbon with different cooling rates (furnace cooled, air cooled, fan cooled andwater quenched).

1. Observe the microstructures under the optical microscope, as high magnification

as possible.2. Sketch neatly the different phases and structures of each specimen.3. Determine the hardness of each sample using Rockwell Hardness Tester

(procedure and precautions are given in appendix II).4. Convert all the harness values to Vickers' hardness (HV) through the conversion

table given in appendix III.5. Analyse the results and establish the relationships amongst cooling rate,

microstructure and hardness of specimens.

References1. R. A. Higgins, "The Properties of Engineering Materials".2. M. F. Ashby & D. R. H. Jones, "An Introduction to Microstructures, Processing

and Design".3. S. H. Avner, "Introduction to Physical Metallurgy".4. C .O. Smith, "The Science of Engineering Material

Appendix I

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Table 1 Symbols and Designation Associated with Fig. 9. ___________________________________________________________________________________

Number Symbol Designation ___________________________________________________________________________________

1 --- Diameter of ball = 1/16 in. (1.588 mm)3 P 0 Preliminary test force = 10 kgf 4 P1 Additional force = 90 kgf 5 P Total test force = P 0 + P 1 = 10 + 90 = 100 kgf 6 --- Depth of penetration under test force before

application of additional load7 --- Increase in depth of penetration under additional

load8 e Permanent increase in depth of penetration under

preliminary test force after removal of additionalforce, the increase being expressed in units of 0.002 mm.

9 xx HRB Rockwell B hardness = 100-e ___________________________________________________________________________________

Table 2 Symbols and Designation Associated with Fig. 10. ___________________________________________________________________________________

Number Symbol Designation ___________________________________________________________________________________

1 --- Angle at the top of the diamond indenter (120)2 --- Radius of curvature at the tip of the cone (0.200

mm)3 P 0 Preliminary test force = 10 kgf 4 P1 Additional force = 90 or 140 kgf 5 P Total test force = P 0 + P 1 = 10 + 140 = 150 kgf 6 --- Depth of penetration under test force before

application of additional load7 --- Increase in depth of penetration under additional

load8 e Permanent increase in depth of penetration under

preliminary test force after removal of additionalforce, the increase being expressed in units of 0.002 mm.

9 xx HRC Rockwell C hardness = 100-e ___________________________________________________________________________________

Appendix II

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Measurement of Harness

1. Place the specimen on the plane anvil.2. Raise the anvil by rotating the capstan slowly until the tip of the indenter touches the specimen.3. Further elevate the anvil gently until the small pointer in the dial gauge points to the red dot i.e. set

position.

4. Turn the outer ring of the indicator gauge until the large pointer reads 0 on the appropriate scale.5. Push the crank handle to apply the major load.6. The load is to be maintained for about 10 seconds before pushing crank handle in the reverse

direction to remove the major load.7. Read the hardness number while the minor load is still being applied.8. Turn the capstan in the reverse direction to lower the anvil and remove the specimen.9. The next test is carried out now as before.

Precautions1. Ensure that both surfaces of the specimens are flat and positioned securely on the anvil.2. Rotate the capstan gently during elevation of the anvil. Otherwise due to abrupt strike of the

indenter tip with the sample, the indenter may be destroyed.

Appendix III

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Rockwel Hardness Testing Machine