GB939584A - Improvements in or relating to permanent magnet chucks and holding devices - Google Patents

Abstract

939,584. Holding devices. JAMES NEILL & CO. (SHEFFIELD) Ltd. Jan. 19, 1962 [Jan. 21, 1961], No. 2518/61. Class 35. A magnetic holding device has a grid 7 consisting of spaced bars of high permeability material which slides between the holding surface assembly and the magnet assembly and switches the holder " on " or " off." The holding surface comprises an assembly of alternate plates of high permeability material 1 and non- magnetic material 2 and the magnet assembly has magnet plates 9 separated by permeable spacers 8. The magnets which are made of high coercivity material e.g. barium ferrite, are magnetized across their thickness in opposite directions and are supported on non-magnetic inserts 15 in base 6. In the " on " position shown the bars of the shunt grid 7 are positioned to magnetically connect each spacer 8 with its corresponding plate 1 in the holding face to retain a workpiece 17 as shown. In the " off " position, Fig. 4 (not shown), the grid is moved to the right so that each bar spans adjacent spacers 8 and short circuits the flux to release the workpiece. The grid bars must be wider than a magnet plate but narrower than the combined width of a magnet plate and spacer and the necessary movement may be less than half the width of a magnet plate. In a modification, one magnet assembly is in contact with the holding surface and separated by the movable shunt grid from another similar magnet assembly which is spaced from the first by the width of a magnet plate, Figs. 7, 8 (not shown). In all examples narrow workpieces 16 are effectively held by the reinforcement of the main flux by a second flux which passes through the base 6, and better release obtained by using the maximum possible width of the shunt bar together with narrow non-magnetic inserts in the holding surface.