Insert the tapered end of the standard test bar after cleaning into the space provided between the ball and the plunger and slide it further beyond the tapered position. The test bat will thus be firmly gripped between the ball and the plunger pressed by a spring. The specimen to be tested be properly ground or filed and polished at the surface where it is to be tested to ensure accurate readings, With standard test bar inserted place the tester vertically on the specimen such that the ball touches the polished surface. Give a blow on the top of the plunger, with a hammer.
The blow should not be very hard and should as vertical as possible. The blow will cause two indentations, one on the standard test bar and the other on the specimen. The diameters of these two indentations should be measured accurately with magnifier having, lease count of 0.1 mm provided with the machine. If the indentations so obtained are slightly elliptical, average diameter should be found out. The distance between the centers of any two indentations on standard test bar should be less than 15mm. If the bar is fully utilized it has to be replaced. The limiting indentation diameter on the standard test bar is 4.2mm.
Diameter of ball indentation -
1) On the test bar 1.8 mm.
2) On the specimen (steel in natural condition) 1.7 mm.
Tensile strength founds from Tables 50.8 tone/sq. inch after multiplying with 1.575 to convert in to kg/sq. mm comes to 80 Kg./sq.mm.
Brinell Hardness Number found from tables 225 BHN.
Multiplying factor inscribed on standard test bar: 1.14. Therefore, the tensile strength of specimen is 80 x 1.14 = 91.20 Kg/sq. mm in and the Brinell hardness = 225 x 1.14 = 256.5 BHN. When after some use, the protruding end of the plunger gets deformed by blows, it may be reconditioned and rounded off again or simply replaces.
Poldi type Impact Hardness Tester is not designed to replace the tensile strength testing machine or standard hardness tester. The accuracy of this hardness tester may very sometimes to the extent+/- 10% as against the more accurate table type standard Hardness testers. However, the Poldi Impact Hardness Tester has the advantage of easy handling and greater flexibility.