Patent GB-301762-A (GB)
Title: Improvements in or relating to the hardness testing or hardness testing and hardening of metals
IPC: G01N3/42
Filed: 1927-08-29
Abstract: 301,762. Herbert, E.. G. Aug. 29, 1927. Testing hardness of materials.-Articles or surfaces to be hardened, or tested for hardness, are bombarded with balls moving with a predetermined velocity. The process may also be used for hardening, or testing, the balls. The process may be used for gears, bearings, and internal surfaces such as bores of cylinders or guns, and parts of the surfaces not to be acted on may be covered. Two methods of testing may be employed. According to one method the velocity of the balls is such as to be only just insufficient to indent surfaces possessing that degree of hardness which has been selected as adequate, any softer surfaces or parts thereof being indented. In another method and for obtaining an absolute measure of hardness, the velocity of the balls is such that all parts of the work are indented. The velocity of the balls being known or ascertainable, the hardness can be ascertained by measuring the diameter of the indentations. In using the process for the workhardening of metal surfaces the work is placed in a jet or shower of steel balls whose velocity is only just sufficient to indent very slightly surfaces of correct hardness, so as to produce a thin work hardened or super-hardened layer which resists any further indentation. The velocity of the balls is then increased, so that the layer is increased in hardness and depth of hardening. The velocity of the balls is then again increased and the process repeated until any further increase would not produce any increase of hardness but only a roughening or indenting of the surface, the maximum hardness having been attained, this being measurable by the pendulum work-hardening test as described in Specification 207,876. The apparatus used mav be adapted to make the process up to the hardening limit a continuous one. In one construction of apparatus the balls fall by gravity on the surface to be tested or hardened. The balls are contained in a hopper f, Fig. 1, slidably mounted on a tube d with apertures e through which the balls enter the tube when the hopper is raised to this level. The hopper is supported by a chain f<1> over pulleys and counterweighted by the weight f<3>. The surface to be tested or hardened is mounted in a chamber a on a platform b, Fig. 4, which is adjustable by means of movable rods b<1> and the part of the surface on which the balls are falling is indicated by the movement of a pointer b<5> over a chart on the top of the casing a. The, platform is preferably set obliquely so that the balls rebound at an angle and fall into a. shoot c. The height from which balls fall is adjusted by a height regulator g, Fig. 5, suspended within the tube d by a cord h, Fig. 1, over pulleys h<1>, and with a height indicator h<2> at the other end. The regulator comprises a star shaped baffle g<1>, Fig. 6, preferably of rubber, and a distributor diaphragm g<2>, Fig. 7. In a modified form of apparatus the balls are continuously fed to the top of the tube d by a chain and bucket elevator. The fall tubei d is of flat section, and the height regulator comprises a funnel extending the full width of the tube which allows the balls to flow out as a sheet of single thickness. Also the platform is automatically reciprocated across the line of the descending sheet of balls. In another construction the balls are raised by a centrifugal projector, and in a further construction, Fig. 13, the balls are deflected from the rotary projector o by two series of deflectors q, q' of resilient material so that the useful momentum of the balls is determined by the velocity of the rotor. Alternatively the work might be arranged in a direct stream of the balls from the rotor, the deflectors q, q<1> may be curved so as to focus the balls on to any part of the surface, and may be oscillated or adjustable to vary the direction of the jet.