Effect of methods of demagnetization on the energy required to magnetize steel

Abstract

In this investigation the first series of tests consisted of obtaining zero flux in two varieties of steel from various maximum flux values and by three different methods. B-H curves were obtained after demagnetization by the three methods and from the maximum value of these B-H curves hysteresis loops were taken. One method of demagnetizing was that suggested by the U. S. Bureau of Standards, which consists of current reversals through a magnetizing winding, in which current values are gradually reduced to zero. The second method consisted of applying a negative current of such an amount that the resultant value of flux would be such that when the current was released the flux value would go to zero. The third method was substantially the same as the second except the zero flux was approached from the direction of opposite polarity. The resultant B-H curves proved to be different from each other and to depend upon not only their origin but the previous history of the material as regards methods of demagnetization. The areas between the curves were evaluated. It was found that in cases of two of the three typical B-H curves the B-log H curves gave straight lines for part of the range involved. A second series of tests consisted of taking a set of hysteresis loops and repeating the determinations, using a greater number of steps to find if by taking a greater number of steps there might be a greater indicated energy loss. The results of this group of tests were not sufficiently definite to warrant conclusions.