GB306232A - Electro-magnetic testing of steel wire ropes and other articles of magnetisable material - Google Patents

Abstract

306,232. Wall, T. F. Dec. 20, 1927. Magnetic tests. - Steel wire ropes, rails, or other articles of magnetizable material are tested for flaws by means of a. magnetic system comprising a laminated iron core having a coil, preferably excited by alternating current, the magnetic circuit through the coil and the laminated core being completed through a portion of the article under test, a search coil being arranged to embrace a portion of the flux through this path. The laminated core L, Fig. 2, provided with a magnetizing winding E, has two limbs L', L<2> with clearance holes through which passes the steel rope &c. R to be tested. These limbs are formed with slots B<1>, B<2> extending below the hole and leaving narrow projections A<1>, A<2> on which are wound search coils S', S<2> connected in series so that their electromotive forces oppose one another in a circuit containing a voltmeter or an amplifier supplying an indicating or recording voltmeter or a string galvanometer. Normally the electromotive forces of the coils S<1>, S<2> balance one another but this balance is disturbed on passage of a flow, causing a resultant electromotive force, which is indicated on the voltmeter. Alternatively a single search coil 8. Fig. 4, may embrace both projections A<1>, A<2>, an electromotive force being generated by a difference in the fluxes in these projections. In another arrangement, the slot B<2> and coil S<2> are omitted, an opposing electromotive force equal to that normally generated by the coil S<1> being supplied by, for example, a transformer connected across the coil E. Fig. 4 shows a construction which can be applied to a rope in situ. The limb L', L<2> are divided through the centre of the holes through which the rope R passes, the outer portions being secured by non-magnetic clamping plates C after the rope is in position. The rope is guided by pulleys P. Instead of the search coil or coils being located in slots B<1>, B<2>, they may be arranged to lie either on the surface of the hole through which the rope passes, or embedded in a groove in this surface. One coil may be arranged in each half of the hole, the two coils being connected in series. The apparatus may then be applied to a rope in situ. According to the first Provisional Specification the magnetic circuit may be excited by direct current and a ballistic galvanometer connected to the search coil. A valve may be connected in the search coil circuit to eliminate the reverse throw. The balancing electromotive force may be provided by a second system provided with a length of rope similar to that under test. When using alternating-current excitation, the current coil of a wattmeter may be connected in series with the magnetizing coil and the pressure coil in series with the search coil.