Patent GB-693348-A (GB)
Title: Hardness measuring apparatus
IPC: G01N3/44
Filed: 1952-02-01
Abstract: 693,348. Testing hardness of materials. ERNST, A. Feb. 1, 1952, No. 2801/52. Class 106 (ii). Apparatus for measuring the hardness of a material by measuring the difference in penetration of a diamond tip under preload and secondary load comprises a large surface chamber containing a heavy liquid, bounded on its underside by a diaphragm connected to the diamond tip and communicating with a capillary tube. associated with an angularly movable graduated scale, the secondary load being imparted by the hydrostatic head of a liquid in communication with the chamber and with the capillary tube. In the apparatus shown in Fig. 1, a slider 5 is guided on a post 4 fixed by a screw 6 on a slider 3 guided on a post 2 fast on a base 1. A device for the micrometric vertical displacement of a table 7 carried by a cylinder 13 'comprises a sleeve 8 rotatable by handles 9 and prevented from axial displacement by a key 10 fixed to the base 1 by a screw 11 working in a circumferential groove 12 in the sleeve which is internally threaded for co-operation with an external thread on the cylinder 13 which is prevented from rotating by a lug 14 working in a vertical guide 15. A screw 16 provides for vertical displacements of the slider 3 which houses a rod 17 having a flange 18 defining the inoperative position of a diamond 19 mounted at its lower end and a circular plate 20 at its upper end which rests during measuring operations on the lower surface of a diaphragm 21 which functions as the lower end wall of a chamber 21<SP>1</SP> containing a heavy liquid, e.g. mercury, the upper wall being formed by a cover 22 screwed on a cylindrical body 23 fast with the slider 3. The body 23 carries, resiliently assembled at its lower end, a protective cap 24, having a hole at the bottom for the diamond 19. The chamber 21<SP>1</SP> can be filled or emptied through a hole 25 in the cover provided with suitable closing means and a duct 26 communicates through a tap 27 and flexible hose 28 with a ring-shaped capillary tube 31 housed in a groove 30 in the slider 5 beneath a circular graduated scale 32 which is rotatable by a knob 33 and may be read in a pivoted mirror. In an alternative embodiment, Fig. 3, the capillary tube 31 and scale 32 are mounted on the slider 3 and a slider 5a guided on the post 4 carries a vessel 36 containing a heavy liquid at the bottom e.g. mercury and a lighter liquid, which may be coloured at the top, e.g. water and connected at the bottom by a hose 28a to the chamber 21<SP>1</SP> and at the top by a hose 28b with the capillary tube 31. To measure the hardness of a test-piece it is placed on the table 7 which is raised to press the test-piece against the diamond until the mercury in the tube 31 reaches its upper limit, whereupon the scale 32 is rotated to bring an opposite marking into register with the meniscus. The slider 5 or 5a is then raised until it abuts a stop 29 which has been set in predetermined position on the post 4 according to a scale marked thereon in kilograms corresponding to loads on the diamond point due to the head of mercury or mercury and water. This secondary load causes further penetration of the diamond point and when the slider 5 or 5a is returned to its initial position against the slider 3 the meniscus will be displaced from the opposite mark by an amount dependent on the further penetration which in turn depends upon the hardness of the test-piece.