Patent GB-812450-A (GB)
Title: Improvements in control systems for rotary shears
IPC: B23D36/00
Filed: 1956-09-17
Abstract: 812,450. Shearing. GENERAL ELECTRIC CO. Sept. 17, 1956 [Sept. 21, 1955], No. 28356/56. Class 83 (4). [Also in Groups XXXV and XXXVII] Shearing apparatus 11, 12 is driven by a motor 13 for cutting billet 15 into predetermined lengths, the motor being supplied from a generator 16 having an amplidyne exciter 17. A main field winding 17a of the amplidyne is excited in accordance with the difference between voltages respectively representative of the speed of the shear and of the speed of the billet. The former voltage is derived from the armature of generator 16, whilst the billet-speed voltage is obtained from a tachometer generator 18 driven by the last mill stand 19. The comparison circuit comprises either the entire resistive combination 20, 21 (across which the billet-speed signal voltage is developed) or a tapped portion thereof. When only a tapped portion of the billet-speed voltage is applied to the comparison circuit, the shear speed voltage is reduced and the motor 13 rotates at idling speed as determined by the setting of slider 20a. A device for measuring the lengths to be cut from the billet comprises an impulse counter 32 which may be a capacitor-resistor combination wherein the capacitor charge is increased by each voltage pulse applied to terminals 32a until a predetermined number of pulses have been counted and the output at terminals 32b is sufficient to operate relay 85. An impulse generator 33 comprises a toothed disc 33a driven by the billet and co-operating with permanent magnet 33b having winding 33c. When the leading edge of the billet operates switch 40, a relay 42 is energized so that timing relays 47, 48 are respectively energized and deenergized. The time delay in closure of contact 50 is sufficient to enable the leading edge of the billet to travel for a certain distance before acceleration of the members 11, 12 is initiated for cropping the end of the billet. When contact 50 closes, contactor 52 is energized to actuate brake relay 57, transfer relay 27, and auxiliary relay 64. The whole of the potentiometer 20 is connected in the. comparison circuit, and a brake 70 is removed from shaft 14. Energization of the brake relay actuates relay 72 whereby the voltage comparison circuit is connected to field winding 17a and the armatures of the motor and generator are interconnected. The motor 13 accelerates to its cutting speed and the front end of the billet is cropped. The voltage impulses produced by generator 33 are transmitted to counter 32 when contact 65 of the delayed relay 64 closes. Such delay is adjusted so that the relay operates when the shearing apparatus reaches its normal idling speed in the course of accelerating from zero to cutting speed. This ensures that the first bar cut from the billet is of proper length. During the cutting operation, cam 23 opens contact 25 and closes contact 26 so that the shear decelerates to an idling speed. Operation of relay 85 energizes relay 27 through cam-actuated contact 88 so that the driving motor 13 is accelerated. At the same time, the impulse generator 33 is disconnected from counter 32 and terminals 32a are short-circuited. As a result, the counter is reset and the relay 85 is de-energized to reconnect the impulse generator to the counter. Thus the counter measures consecutive lengths of material and operates periodically to initiate acceleration of the shearing apparatus. During the stopping operation of the apparatus, a field winding 17b of the amplidyne 17 is energized to increase the excitation of generator 16 so that both the cutting and idling speeds of the shears are increased to compensate for the tendency of the billet speed to become greater as the billet emerges from the mill. The amplidyne has an anti-hunting field winding 17c. If the transfer relay should fail to operate properly, the cam 23 actuates switches 25, 26 to ensure that the shearing knives are accelerated to their cutting speed before engaging billet 15. In such an emergency, no attempt is made to out bars of accurate length.