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On the Magnetic Properties of Sheet Steels: A Study of the Effects of Previous Magnetisation on the Permeability and Magnetic Materials in the Form of Thin Sheets.

Fleming, J. C. (1925) On the Magnetic Properties of Sheet Steels: A Study of the Effects of Previous Magnetisation on the Permeability and Magnetic Materials in the Form of Thin Sheets. Doctoral thesis, University of Surrey (United Kingdom)..

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Abstract

The experimental work described in this paper was carried out on sheet specimens of Stalloy and Mumetal, together with a few tests on Lohys. The main object was to determine the effect of magnetic polarisation due to previous magnetisation on the magnetisation curves and magnetic losses. The specimens were tested with D.C. by means of ballistic galvanometer, and with 50 cycle A.C. supply, by means of A.C. potentiometer and synchronous rectifier voltmeter. The maximum reduction in permeability,at a given flux density, which was recorded in the D.C. tests amounted to about 45% with Stalloy and Lohys compared with 31% with Mumetal. The A.C. figures were about the same for Stalloy and somewhat lower for Mumetal. The D.C. hysteresis loss increased by a maximum amount of 36% for Stalloy compared with 4% for Mumetal. The A.C. losses, including eddy currents, showed smaller increases, which became hardly measurable in the case of Mumetal. These extreme figures are obtained at very low flux densities, and following polarisation at very high magnetising force. No appreciable effect results from polarisation unless the normal working flux density is low and the polarising magnetising force Is at least 5 times normal. The effect of polarisation on the shape and location of the bysteresis loops was investigated. The degree of stability of the changes was investigated and was found to be surprisingly high with Stalloy. The polarisation in Mumetal could toe reduced somewhat by vibration, A.C. magnetisation etc., but only to the extent of leas than 50% . It has been, shown that very serious polarisation can be produced in Mumetal by mechanical shock when the magnetising current is flowing. Comparison of D.C. and A.C. magnetisation curves drew attention to the discrepancy between these, a subject which has received the attention of many investigators recently. The curves are discussed and certain suggestions are made In an appendix, the theory of the ballistic galvanometer is considered, with particular reference to the use of the instrument for iron testing when shunted to give critical damping.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors :
NameEmailORCID
Fleming, J. C.
Date : 1925
Contributors :
ContributionNameEmailORCID
http://www.loc.gov/loc.terms/relators/THS
Additional Information : Thesis (M.Sc.)--University of Surrey (United Kingdom), 1925.
Depositing User : EPrints Services
Date Deposited : 22 Jun 2018 15:16
Last Modified : 06 Nov 2018 16:54
URI: http://epubs.surrey.ac.uk/id/eprint/848461

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