GB880689A - Improvements in or relating to extrusion plant for cable manufacture - Google Patents

Abstract

880,689. Automatic control systems. KRAFT, J., KRAFT, A., and KRAFT, J., [trading as KRAFT MASCHINENFABRIK, J. A.]. Nov. 18, 1957 [Nov. 17, 1956; July 26, 1957], No. 35922/57. Class 38 (4). [Also in Group IX] In a control system for extrusion plant for cable manufacture Ward-Leonard speed control is applied to each component driving motor, the generators of such sets having their excitations regulated directly or indirectly through magnetic amplifiers. The conductor is paid-out from reel Ab, fed through tension measuring rollers Tw1 and into the extrusion machine Sp where a plastic sheath is formed. The diameter of the sheathed cable is monitored at Dg, the cable being drawn from the machine Sp by drawing rollers Az ; it passes then over further tension rollers Tw4 and on to the take-up reel Aw. The motors M1-M4 are supplied by generators G1-G4 which, except for G4, are excited through magnetic amplifiers Mv1 Mv2, Mv3. The required processing speed is set on controller So and the device Dv distributes the appropriate signals to the magnetic amplifiers for maintaining the proportional relative speeds of motors M1-M3. The armature voltage of M3 is used to excite G4 so that the reeling motor speed varies with that of the drawing rollers. These two motors are excited in series from a D.C. source and M 1 and M2 are likewise excited from the same source. Speed control of motor M1 in dependence on the conductor tension is achieved by a signal from rollers Tw1 varying one resistance of a regulator Kr1 in G1 field circuit. The other variable resistance is for manual speed control. Similarly speed control of the take-up reel is achieved by a signal from rollers Tw4 operating regulator Kr4. The provision of a separate voltage source HS enables the reel to take-up cable slack prior to commencing the extrusion process. Constant speed in the extrusion machine is obtained by controlling amplifier Mv2 in dependence upon the output of tacho-generator Td2, thus compensating for load variations, and in dependence upon G2 armature voltage to compensate for supply variations. Amplifier Mv3 is likewise controlled by tacho-generator Td3 output and G3 armature voltage, but a supplementary control is provided by thickness gauge Dm fed by scanner Dg (which may be photo-electric) to maintain a constant cable diameter. The paying-out reel stand is constructed with provision for two reels, which can be driven simultaneously, and means for joining the ends of an expiring and a new reel whilst maintaining the feed. Similarly the take-up reel stand has provision for two reels and means for transferring the running cable from a full reel to an empty one, including a cutter for severing the cable. Each of the four reel supports pivots to facilitate reel removal. Mention is made of the possibility of varying the overall plant speed as a function of the temperature of the extrusion material so enabling the plant to start from cold.