. The strength of materials; a text-book for engineers and architects. ells Hardness Testing Machine.—In this machinea hardened steel ball is pressed with a predetermined forceagainst the plate whose hardness is required. The diameterof the resulting curved depression is then found and from thisthe hardness number is obtained in the manner describedbelow. Fig. 189 shows the Brinell machine made by Messrs. J. «fe Co., Ltd. The specimen is placed upon the top• of the stand, which is then adjusted by the hand-wheel tobring the specimen into contact with the hardened steel ball(10 mm. di
. The strength of materials; a text-book for engineers and architects. ells Hardness Testing Machine.—In this machinea hardened steel ball is pressed with a predetermined forceagainst the plate whose hardness is required. The diameterof the resulting curved depression is then found and from thisthe hardness number is obtained in the manner describedbelow. Fig. 189 shows the Brinell machine made by Messrs. J. «fe Co., Ltd. The specimen is placed upon the top• of the stand, which is then adjusted by the hand-wheel tobring the specimen into contact with the hardened steel ball(10 mm. diameter) which projects from the conical end of theplunger of the machine. The upper portion of the machinecomprises a small fluid-operated testing-machine, oil being theworking fluid. By means of a small projecting pump-handlethe pressure of the fluid is increased until the cross-piece floats, the pressure being indicated on the dial. Weightsare provided with the machine, which make the floating occurat a force of 500 to 3000 kg. (increasing 500 kg. at a time).. ~1 Fig. 189.—Brinell Hardness Testing Machine. [To face page 402. THE TESTING OF MATERIALS 403 The pressure depends only on the weight applied and notupon the accuracy of the gauge. If P is the load, D the diameter of the ball and d that of theimpression, the quantity H = D _ V D2 - d^ D is called the Brinell Hardness Number. The following tablegives values. BRINELLS HARDNESS NUMBERS (for load 3000 kg.)Diameter of Steel Ball =10 mm. Diameter Diameter Diameter Diameter of Hard- of Hard- of Hard- of Hard- Ball Im- ness Ball Im- j ness Ball Im- ness Ball Im- ness pression Number pression Number pression Number pression Number mm. mm. mm. mm. 2-0 946 3-25 351 4-50 179 5-75 105 2-05 898 3-30 340 4-55 174 5-80 103 2-10 857 3-35 332 4-60 170 5-85 101 215 817 3-40 321 4-65 166 5-90 99 2-20 782 3-45 311 4-70 163 5-95 97 2-25 744 3-50 302 4-75 159 6-0 95 2-30 713 3-55 293 4-80 156 6-05 94 2-35 683 3-60 286 4-85 153 6-10 92
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