GB650407A - Improvements in apparatus for measuring the hardness of materials - Google Patents

Abstract

650,407. Testing hardness of plastic materials. WALLACE & CO., Ltd., H. W., and MORE, A. R. June 22, 1948, No. 16730. [Class 106 (ii)] Apparatus for measuring the hardness of a plastic material by measuring the difference in the penetration of a plunger indenting the material under two set loads successively using either the upper or lower surfaces in contact with the specimen as datum surface comprises a cast base 1 carrying a glass plate 3 to support a specimen, and a column 4 upon which slides the upper portion 7 of a carriage under the control of a rack 12 and pinion 11 manipulated by a hand wheel 10, the lower portion 18 of the carriage sliding on the upper portion under the control of rack 25 and pinion 24 manipulated by a hand wheel 26, keys 14, 19 preventing angular displacement and a set screw 21 limiting downward movement of the portion 18. An indentor 30 is fixed to a plunger 29 which is coupled preferably magnetically with gauge mechanism 37 for indicating its displacement and the weight of the plunger, which forms the minor load, is initially borne by a weight 28, which forms the additional load and is initially borne by an arm 27 of the lower portion 18 of the carriage. The gauge is carried by a neck 33 of a casing 31 having a bush 42, the bush 42 sliding loosely in a hole in the arm 27 and the neck 33 in a hole in an arm 8 of the upper portion 7 of the carriage, which arm 8 supports the weight of these parts initially. To make a test measuring the indentation from the upper surface of the specimen, a shoe 44 is attached to the bush 42 and surrounds the indentor 30, the specimen is placed on the plate 3 and the wheel 10 turned to lower the carriage, the shoe 44 makes contact with the specimen, the weight of the parts supported by the arm 8 is transferred to the specimen, as the weight 28 is lowered with the carriage, the plunger is left floating in the specimen under the minor load, the indicator needle settles and the dial is set to indicate 100 so that, when the carriage is lowered still further to transfer the weight 28 to a shoulder 43 on the plunger which then sinks into the specimen until it floats under the major load, the hardness of the specimen may be read from the gauge. To make a test measuring the indentation with reference to the supporting surface, the shoe 44 is removed and the position of the lower portion 18 of the carriage is adjusted so that it comes up against a stop 16 on a hand wheel 13 which is now turned downward. The wheel 10 is then turned to lower the carriage until the indentor 30 rests on the specimen and thereafter until the needle indicates 100. The wheel 26 is then turned to lower the lower portion 18 of the carriage until the needle comes to rest indicating the hardness. To overcome any frictional resistance the apparatus is preferably gently vibrated by means of an electric buzzer 55.