Electromagnetic testing for mechanical flaws in steel wire ropes

This paper contains an account of an electromagnetic method of testing for mechanical flaws in wire ropes such as colliery winding ropes, the method comprising the use of a ¿search band of flux ¿ in combination with a search-coil system. In the introduction are detailed the advantages of the use of alternating as compared with direct current for the excitation of the magnet system. Section 1 describes the results of an experimental investigation of the penetration of magnetic flux in ¿locked coil¿ wire ropes, for a supply frequency of 50 and 20 cycles per second respectively. In Section 2 the effect of mechanical strain on magnetic permeability is considered, with special reference to a.c. excitation. In Section 3 the change in reluctance of the air space due to eccentricity of the rope in the magnet system is examined. Section 4 contains an account of the construction of the rope-testing magnet system, and the method of utilizing the search band of flux is explained. Section 5 contains the results of tests on a length of wire rope which was specially constructed for the purpose by Messrs. Latch and Batchelor, and in which a series of hidden flaws were incorporated. A complete rope-testing equipment constructed in accordance with the principles explained in this paper has been installed in one of the Carlton Main Co.´s collieries in south Yorkshire.