Patent GB-668750-A (GB)
Title: Apparatus for testing the hardness of materials
IPC: G01N3/42
Filed: 1949-11-28
Abstract: 668,750. Testing hardness of materials. GRODZINSKI, P., STERN, W., BEARD, F. A., and INDUSTRIAL DISTRIBUTORS (SALES), Ltd. Nov. 28, 1949, No. 30421/49. Class 106 (ii). Apparatus for testing the hardness of materials by indentation comprises an indenter and an optical system for measuring the size of indentation in which the axis of the optical system is adjustable in a plane through the centre line of the indenter so as to intersect it on the surface of the test piece and in which the indenter and optical system are mounted for straight line movements in the direction of their longitudinal axes towards and away from the test piece surface. A specimen holder 8, finely adjustable by micrometer screws 9, 10, is supported by a holder 3 adjustable in a socket 4 in a base 2 and the indenter mechanism is carried by a block 14 guided in vertical ways 13 in a support 12 which can be lowered on a pillar 11 by a hand wheel 15 on a spindle 16 through rack 'and pinion. Part of the weight of the block 14 and indenter mechanism is balanced by a counterweight sliding in the hollow pillar 11 supplemented by a weight 20 adjustable on a lever 19 clamped to spindle 16 when the indenter is in raised, inoperative position. The indenter holder is guided in brackets 22, 23 between sets of rollers comprising six miniature ball bearings 24, Fig. 5, arranged on eccentric shafts 24<SP>1</SP> for finely adjusting the clearance between the bearings and holder, the shafts then being locked by set screws. Weight blocks, preferably between 200 and 1500 grms. are loaded on a platform 25 on top of the indenter holder and a diamond indenter 26 is exchangeably mounted. The indenter may be a standard diamond pyramid indentor or a double-cone indenter. The weight of the indenter 26 and holder 21 is balanced by a lever 27 supported on a bracket 28 attached to the support 12 and provided with a sliding weight 29 and threaded ring 30 for course and fine adjustment, the inner end of lever 27 being in rolling contact with the underside of platform 25. The optical system comprises an illuminator 44 with iris diaphragm and microscope 45 adjustably arranged at an angle to the direction of indenter movement so that their inclined axes may be caused to intersect on the test piece surface. The microscope 45 is brought into operative position and withdrawn by a hand wheel 46 operating a rack and pinion device and its holder is mounted on a vertical turntable for angular adjustment on the support 12 by a worm gear 48 and can be locked by screws 49. For fine adjustment provision may be made for horizontal displacement. In operation the indenter and optical system are centred, the test load is placed on platform 25, the microscope is moved out of the path of the indenter which is then racked down by hand wheel 15 until the weight of the assembly is transferred by cross-piece 31 on to plungers 33 of a hydraulic pressure device arranged between brackets 22, 23. A bracket 42, Fig. 6, on the indenter assembly engages an adjustable stop 42<SP>1</SP> on a piston 38 operating in a pump cylinder 37 to build up pressure below the plungers 33, which operate in cylinders with return springs 36, which pressure is released through a valve 39 opened by pin and lever device 40, 41 at a constant speed determined by a control valve with spindle 39<SP>1</SP> adjusted by a setting knob. When the indenter begins to penetrate the specimen electric contact between the cross-piece 31 and the plunger 33 is broken and a lamp 43 is extinguished. Specification 651,800 is referred to.