GB304212A - - Google Patents

Abstract

304,212. Associated Electrical Industries, Ltd., (formerly Metropolitan- Vickers Electrical Co., Ltd.), (Assignees of Dean, D. W.). Jan. 16, 1928, [Convention date]. Shearing.-A rotary shearing-machine, Figs. 2, 3, particularly for cutting strips of steel for making pipes &c. is driven by an electric motor which may be controlled by a hand switch or may be governed by an electric control system which automatically regulates the speed of the cutters to correspond with the speed of the work and which leaves the cutters in a definite angular position so that strips may be cut into uniform lengths. The shear-motor 5, Fig. 4, is driven by a motor-generator-set comprising a synchronous motor 1, a generator 6 for supplying power to the shear-motor and an exciter 3 for supplying current to the control circuits. The work is delivered to the machine along a roller table 61, Fig.. 5, and past pinch-rolls 62 which are driven by a motor 8, the shaft of this motor being coupled to pilotgenerator 9, Fig. 4, which, in conjunction with a second pilot-generator 7 driven directly by the shear-motor, controls the speed of the shear-motor, this control being effected by a relay 22 having an armature 13 which, when energized by current in the coil 14 due to a difference of speed between the pilot-generators 7, 9 short circuits a resistance 19 in the field circuit 21 of the shear-motor. The mains A, B for the control circuits are first coupled by a switch 42 in order that the circuits may be self-holding through a no-volt relay 47a after which the switch may be moved to positions corresponding to hand-control or automatic control. When under automatic control, the work closes a' starting switch 53, Fig. 5, thereby completing the circuit through the field winding 26 of the generator 6 by means of a relay 29 and also closing the armature circuit of the shear-motor 5 by relay 56. A second circuit controlled by the relay 29 energizes a coil to release a resiliently applied brake 36 on the shear-motor shaft. Cutting continues till the trailing end of the work passes over a stopping switch 54, when, provided the cutters are in the required angular position, the field circuit for the generator 6 is broken and the brake 36 is applied. The contact 56 is also broken but the circuit through the armatures of the generator 6 and the shear-motor is maintained by a contact 60 so that dynamic braking is applied to the motor until failure of voltage across the motor armature allows the contact 60 to open. If at the time the switch 54 is opened, the cutters are incorrectly positioned, a drum-switch 55 on the cutter shaft maintains the motor circuit until the cutters have rotated into the required angular position. The speeds of the pinch-rolls 62 and of the cutters are adapted to correspond to different linear speeds of work, by variable resistances 27, 28 controlling the field 26 of the main generator 6 and by variable resistances 32, 25 controlling respectively the fields 31 of the pilot-generator 7 and the field 24 of the pinch-roll motor. A single pair of rheostats 41, 39 may be provided to control these four resistances. The pinch-roll motor has a drooping speed-load characteristic and is normally driven at a speed slightly in excess of that of the entering work.