GB557585A - Improvements in and relating to electromagnets - Google Patents

Abstract

557,585. Electromagnets. BRITISH THOMSON-HOUSTON CO., Ltd. May 20, 1942, No. 6870. Convention date, May 24, 1941. [Class 35] A plunger type electromagnet comprises a rectangular laminated core structure having an aperture in one side, a pair of polar projections extending outwardly from the core on opposite sides of the aperture, a movable magnetic member extending through the aperture and engaging the projections, a tension member having a central aperture shaped to embrace the polar projections, and means for connecting the tension member to the core structure. In the form shown in section in Fig. 2 and in expanded view in Fig. 3, the rectangular laminated yoke 10 is held between flanged plates 11, 12. The yoke has an internal pole face 16 and two external pole-pieces 18, 19 on either side of an aperture 15, through which projects a T-shaped armature 13. Pole-faces 17, 20, 25 engage yoke faces 16, 18, 19 respectively. The laminations of pole-pieces 18, 19 are reinforced by the tension member in the form of a tie plate 34, which does not link any resultant flux. A shading ring 28 passes into recesses 26, 27. To prevent sticking, the shank of armature 13 is split and a high reluctance shim 65 is inserted, the whole being held together by riveted non-magnetic strips 31, 32. These strips slide in guides 57, 58 and project beyond the yoke to provide a bolt 70 for a pushing load. For a pulling load, the bottom of the armature is divided into two arms 75 each with a riveted bolt-hole 78, 79 engaging facing plates 76, 77. The coil former 45 has an internal split metal sheath 44, and is held firmly by insulated springs 49, 50. An insulating block carries the coil terminals. For D.C. operation, a switch, Fig. 1 (not shown), is provided to reduce the current after operation to the value necessary to hold the armature. This switch is operated by a bar 102 as the armature rises.