A Small Brinell Hardness Testing Machine

Abstract

HARDNESS, as recent correspondence in NATURE (vol. cvi., pp. 377, 440, 534, 599, 662, November, 192o–January, 1921) has shown, is a subject of interest to both the engineer and the physicist. Whatever may be the exact physical significance of the term, there can be no doubt that measurements of this property, or group of properties, are of increasing practical importance. In the Brinell method of measuring hardness, as commonly applied, a steel ball of diameter about i cm. is applied to the surface of the test piece under a load of the order of 3000 kg., and the size of the resulting impression is measured. In practice the use of a ball of this size is limited to specimens not much less than one-tenth of an inch in thickness and half an inch in width. In 1913 the necessity arose for the accurate determination of the hardness of the walls of small-arm cartridge-cases at different positions along the length. The thickness of wall, diminishing in some cases to about one-hundredth of an inch near the shoulder, is quite insufficient -for the application of the usual Brinell test. Accordingly, a machine was designed and constructed by Messrs. H. Moore and R. Mather for the Research Department, Woolwich, in which very small balls with correspondingly small loads could be employed. A description of this machine has been given by Mr. Moore in the Proceedings of the Institution of Mechanical Engineers of January, 1921 It was designed to permit of great latitude in the dimensions of the test specimen, of the use of various sizes of ball from 1 mm. diameter upwards, and of loads from 5 to 100 kg. The first machine was in continuous use during the war, and was the subject of a secret patent (Craig, Moore, and Mather's patent), which, however, has now been published. The illustration (Fig. 1) shows a simplified form of the machine constructed by Messrs. Alfred Herbert, Ltd., of Coventry.