Electrical Industry and Research

Abstract

SEVERAL notable developments have taken place in the research laboratories of the Metropolitan Vickers Electrical Co., Ltd., during the past year. The investigations on the ‘creep’ or deformation of metals under stress at high temperatures have led to definite results which are of importance in mechanical engineering. It has been proved that even at the lower stresses and temperatures of turbine practice steels cannot be regarded as permanently elastic materials. They are subject to gradual stretch or other permanent distortion. A quick method of testing steels has been developed in the laboratories, and thoy can now be placed in order of merit after a duration test of only a few days.‘Creep’ tests as ordinarily applied may last for months. A particular sample was subjected to test for twelve months and was found to creep at the rate of one part in a hundred million per hour. For the next two months, however, after the year was completed, it only increased at a tenth of this rate. The limit of sensitivity of the apparatus has now been reached, but it is not yet possible to say definitely that creep has ceased. If we consider a turbine cylinder 100 inches in diameter and subject to a rate of increase of one part in a hundred million per hour over a period of ten years, its diameter would have increased by nearly one-tenth of an inch, and this increase would seriously limit the life of the turbine. Other useful mechanical researches are being made in the laboratory as to the effect of surface hardening on the fatigue resistance of gear-wheel teeth. The results obtained are of great use in designing the best driving gears for electric trams and locomotives.