Rotational hysteresis loss in electrical sheet steels

The paper describes how rotational hysteresis loss in small disc samples of sheet steel may be measured in a simple manner a new method, the loss being determined directly without the inclusion of eddy-current losses. The difficulty in the way making measurements on a single disc, due to the magnetic anisotropy of the material, is indicated. The magnetic anisotropy in commercial electrical sheet materials is then briefly discussed, and it is shown how by use of a sample made up of three similar discs the experimental difficulty may be overcome. The observed results on four electrical sheet materials are then given. The loss, plotted against flux density, is seen to fall rapidly towards zero near saturation, as has been found for various ferromagnetics by other investigators, but a sharp increase in loss, hitherto unreported, is shown to occur, for all four materials, at a point near the ¿knee¿ of the magnetization curve. A qualitative explanation of this phenomenon and of the general form of the loss curve is given on the basis of the ¿domain¿ theory of ferromagnetism.