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Metal Casting Technologies : March 2005
which can be used in any orientation. In this example, loads are applied mechanically by winding the geared crank. The apparatus shown in figures 5 and 6 is a portable impact Pin Brinell machine. The Pin Brinell uses a calibrated shear pin to control the load applied by impacting with a hammer. After impacting, the width of the impression is measured and converted to an equivalent Brinell number. TEST PROCEDURE It is important to select the correct indenting force and ball diameter for the part to be tested; the section size and location of the test specimen site should be considered. As a guide, for ferrous alloy greater than 15mm thickness, a 3000 kg force applied to a 10mm ball is recommended. For sections less than 15mm, a 750 kg force applied to a 5mm ball is preferred. With sections of less than 5mm, a 120 kg force applied to a 2 mm ball can be used. The test site should be at least one ball diameter away from edges of the test piece. The test piece should be cool to the touch and the surface to be indented flat, smooth and free from scale and foreign matter. The surface should be ground deep enough to get down to a uniform structure of the casting. The bearing surface of the test piece and that of the anvil should be flat, clean and free from foreign matter so as to avoid the test piece from moving when loaded. The test piece should be supported so that the test surface is normal to the axis of the indenter. With some larger test pieces, it may be necessary to proved additional support to accommodate overhanging sections. The machine should be operated according to the manufacturers instructions. Before commencing a series of tests, the accuracy of the machine should be checked using a standard test block of known and similar hardness to the test piece. A test block is shown in figure 7. With the test piece correctly prepared and supported, apply the force and maintain full force for a duration of not less than 10 seconds or longer than 15 seconds. Care should be taken to ensure the application and removal of the force is done without shock or vibration. Wherever possible, three readings should be taken on each test piece. The diameter of the impression is measured using a portable microscope with a graduated scale. The test site is usually illuminated with artificial light so as to provide contrast betwwen the indentation and test piece. See figure 8. 4. Portable C-Clamp mechanical model 5. Pin Brinell kit 6. Operation of Pin Brinell apparatus 4 5 6