GB881738A - Improvements in electromagnetic presses - Google Patents

Abstract

881,738. Electromagnets. ELEMAG-ANSTALT A.G. March 27, 1958 [March 29, 1957], No. 9855/58. Class 35. [Also in Group XXII] An electromagnetic press comprises a winding 4 carried in a stationary structure 1 and acting upon at least one linearly moving armature 5 connected to the press punch 9, the winding being energized by a grid-controlled multivalve rectifier 38, 39, and speed-responsive electro-mechanical control means being provided mechanically connected both to the armature and the stationary structure and electrically connected to the grids of at least some of the valves for generating a bias voltage for these grids depending on the speed of the armature and acting to reduce this speed and hence slow down the punch towards the end of its working stroke. The press may have two armatures 5 connected to a common punch and acting in unison. The speed-responsive control means may be an inductance coil 23 connected to the stationary structure at 22, and a permanent magnet 24 connected to the armature at 25 so that movement of the armature causes the magnet 24 to move within the coil 23 and thus generate a voltage proportional to armature speed. This voltage is impressed upon the grids of the full-wave three-phase valve rectifier 38, 39 to reduce the excitation current passed by these valves and thus slow down the punch. The Specification states that an arrangement utilizing a pair of charged plates to generate the controlling voltage could be used instead. The lower limit of the working stroke of the punch is determined by adjustment of the fixed contact 29 relative to the moving contact 26 carried by the armature; closure of these contacts resulting in the discharge of a capacitor 64 through a transformer primary 62 which induces a voltage in the transformer secondaries 71-73 to block operation of the valves. The upper limit of the stroke is adjusted by a screwed bush 12, the armature being retracted by the spring 16, although other means of retraction e.g. electromagnetic, hydraulic or pneumatic may be used.