Rockwell Hardness Test

The Rockwell hardness test method consists of indenting the test material with a diamond cone or hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load FO usually I 0 kgf. When equilibrium has been reached, an indicating device, which follows the movements of the indenter and so responds to changes in depth of penetration of the indenter is set to a datum position. While the preliminary minor load is still applied an additional major load is applied with resulting increase in penetration . When equilibrium has again been reach, the additional major load is removed but the preliminary minor load is still maintained. Removal of the additional major load allows a partial recovery, so reducing the depth of penetration. The permanent increase in depth of penetration, resulting from the application and removal of the additional major load is used to calculate the Rockwell hardness number.

H R = E - e

FO = preliminary minor load in kgf

F1 = additional major load in kgf

F = total load in kgf

e = permanent increase in depth of penetration due to major load Fl measured in units of 0.002 mm

E = a constant depending on form of indenter: I 00 units for diamond indenter, 130 units for steel

ball indenter

HR = Rockwell hardness number

D = diameter of steel ball

MAGNETIC PARTICLE EXAMINATION (M.P.I.)

MAGNETIC PARTICLE EXAMINATION (M.P.I.) INTRODUCTION This method is used for detecting cracks and other discontinuities open to surface or sub surface in ferromagnetic materials. Fine magnetic particles are applied to the surface of a part which has been suitably magnetized. The particles are attracted to regions of magnetic non-uniformity associated with defects and discontinuities, thus producing indication which are observed visually. PRINCIPLE When a piece of metal is placed in a magnetic field and the lines of magnetic flux get intersected by a discontinuity such as a crack or slag inclusion in a casting, magnetic poles are induced on either side of the discontinuity. The discontinuity causes an abrupt change in the path of magnetic flux flowing through the casting normal to the discontinuity, resulting a local flux leakage field and interfering with the magnetic lines of force. This local flux disturbance can be detected by its affect upon magnetic particles that collect o...

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Mechanical Engineering

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