GB1343607A - Apparatus for testing the hardness of materials - Google Patents

Abstract

1343607 Hardness testing: measuring thickness AMERICAN CHAIN & CABLE CO Inc 5 March 1971 6180/71 Headings G1M, G1N and G1S A device for testing hardness by the double indentation technique comprises a fixed indenter 3, an anvil 13 for supporting a test specimen, a bellows 15 for applying a minor and a major force successively to the anvil to indent the specimen, and an electromagnetic transducer 59 for determining the difference in depth of the indentations produced by the major and minor forces. The anvil 13 is supported on an air bearing 16-18 for vertical movement, and the bellows contains a block 45 to reduce its dead space. An automatic control system for applying preset pressures to the bellows to produce the minor and major forces, Fig. 3, comprises two regulators 51 and 52, time switch mechanisms 55 and 56 which control valves 52, 54, 57 and 58, and a flow control valve 56'. In use, the minor force is applied to the anvil by the pressure from regulator 51 being applied to the bellows at a controlled rate through control valve 56', valve 52 being initially open and valves 54, 57 and 58 closed. When the pressure in the bellows reaches that of regulator 51, valve 52 closes and storing comparator 64 is actuated by switch mechanism 55 to store the output of transducer 59 which corresponds to the indentation under the minor load. -Switch mechanism 56 then opens valve 54 to apply the pressure of regulator 53 to the anvil to produce the major indentation force. Valve 54 is then closed and switch mechanism 55 opens valves 52 and 58 so that the pressure in the bellows falls to that set by regulator 51 and the minor force is thus again applied to the anvil. At this point, switch 55 again actuates the storing comparator which stores the output of transducer 59 corresponding to the indentation produced by the major load as measured under the minor load. The difference in the two stored readings i.e. the indentations produced by the minor and major loads respectively as measured under the minor load, is read out at 65 to indicate the hardness. Switch mechanism 56 then opens valve 57 to reduce the pressure in the bellows to zero. The value read out at 65 may be compared automatically with a predetermined value and specimens may be located automatically on the anvil. The output of transducer 59 may also be used to indicate specimen thickness.