Patent GB-663362-A (GB)
Title: Improved method of, and means for, obtaining constant tension and uniform speed of metal strip in metal rolling machines
Inventor: LEIGH JOHN AUSTIN
IPC: B21B35/00
Filed: 1946-08-09
Abstract: 663,362. Fluid-pressure servomotor control systems. VICKERS-ARMSTRONGS, Ltd. Aug. 13, 1947 [Aug. 9, 1946 ; March 19, 1947], Nos. 23730/46 and 7623/47. Class 135. In a hydraulically-driven, reversible rolling-mill in which metal strip is passed alternately in opposite directions through rolls 117, Fig. 1, means is provided for maintaining constant the speed and tension of the strip between the rolls and drums 110, 110<SP>1</SP> on which the strip is coiled. An electric motor 100 drives a variable-stroke hydraulic pump 101 supplying a fixed-stroke hydraulic motor 102 which drives the rolls 117, and an electric motor 118 drives variable-stroke hydraulic pumps 103, 103<SP>1</SP> serving variable-stroke motors, e.g., swashplate motors, 109, 109<SP>1</SP> driving the coiling drums 110, 110<SP>1</SP>. The stroke of the pumps 101, 103, 103<SP>1</SP> is adjustable by a common handwheel 108. Control units 110a, 110b, incorporating servomotors controlled by the pressure in the supply pipes 114, 114<SP>1</SP> of the motors 109, 109<SP>1</SP>, transmitted through pipes 112, 112<SP>1</SP>, are connected through linkage to levers 111, 111<SP>1</SP> for adjusting the displacement of the motors. As the drum on which the strip is being coiled increases in diameter the speed and tension of the strip tend to increase, throwing a greater load on the corresponding hydraulic motor 109 or 109<SP>1</SP> and thereby causing a rise in the hydraulic supply pressure to the motor. The reaction of the control unit 110a or 110b is to increase the displacement of the motor so that its speed is reduced and its torque increased. The linkage connecting each control unit to its motor comprises a slotted link 120 with a block 123 slidable therein and connected to a rod 124 of the servomotor, the link 120 being movable by a handle 119 so that a given movement of the servomotor may either increase or decrease the displacement of the motor. This is necessary since the motor of the drum from which the strip is being uncoiled functions as a pump to provide a tension in the strip between the uncoiling drum and the rolls, and as the diameter of the drum decreases the consequent increase in pressure in the pipe 114 or 114' is required to cause a reduction, rather than an increase, in the displacement of the motor to maintain a constant tension in the strip. The control point of the units 110a, 110b is varied by handwheels 113, 113<SP>1</SP>. Each control unit includes a piston 36, Fig. 2, subjected to the pressure in the pipe 112 or 112<SP>1</SP> and loaded by a spring 35, adjustable by a shaft 60 operated by the handwheel 113 or 113<SP>1</SP>, worm gearing 59 and a screw 58 engaging one end of a housing 43, the other end of which forms a spring abutment. The setting of the spring is indicated by a pointer 46 connected by a cam or lever and link to the housing 43. Connected to the piston 36 by a link 33 is a lever 31, pivoted at 32, this lever being pivotally connected to a further lever 16, pivoted at 16', which is itself pivoted to another lever 14 pivotally connected at 14a to a rod 13a of a dashpot device centred by an adjustable leafspring 12. Connected at 14<SP>1</SP> to the lever 14 is a control valve 4 of the servomotor, this valve being supplied with liquid at a constant pressure by a gear pump 41 driven by an electric motor 42. This motor also drives, through bevel gearing, an eccentric 48 which imparts to a link 49 and a lever 50, pivoted at 51, an oscillating motion which is transmitted through a member 32<SP>1</SP> to the lever 31, to eliminate static friction. The pivot of the lever 31 is movable along the lever by an adjuster 52, so that the displacement of the control valve 4 for a given movement of the piston 36 may be varied. The pivot 16<SP>1</SP> of the lever 16 is carried by a rod connected to a diaphragm 18 which modifies the displacement of the control valve 4 according to the rate of change of pressure in the pipe 112<SP>1</SP>. A piston valve 28, connected at 16a to the levers 16, 31 normally half uncovers a port 19<SP>1</SP> and a piston valve 25 connected to a movable body 21, normally half uncovers an exhaust port 27, so that the pressure in a conduit 26, and therefore the pressure acting on the diaphragm 18, is half the pressure in a pipe 40<SP>1</SP> connected to the pump 41. When the piston 36 is displaced, e.g. by an increase in pressure in the pipe 112<SP>1</SP>, the pivot point 16a moves in the direction of the arrow A, the levers 16, 14 pivot about the points 16<SP>1</SP>, 14a respectively and the control valve 4 is moved to the right. The movement in the direction of the arrow A of the piston valve 28 decreases the area of the port 19' whereby the pressure on the diaphragm 18 is reduced enabling the latter to move the pivot point 16' to the right and increase the deflection of the control valve 4, the lever 16 pivoting about the point 16a and the lever 14 about the point 14a. The movement of the piston valve 28, however, also moves a further piston valve 53 which uncovers a port 55 in the body 21 permitting pressure liquid to flow from the pipe 40<SP>1</SP> to an end 56 of the body 21 whereby the latter is moved in the same direction and by the same amount as the valve 28 but at a rate determined by a dashpot 22 whose piston is connected to the valve 25. At the completion of the movement of the body 21, the exhaust port 27 is obturated to the same extent as the port 19<SP>1</SP> and the diaphragm 18 is again exposed to half the pressure of the pump 41. The rate of movement of the dashpot 22 is adjustable by a valve 57. The piston rod 8 of the servomotor is connected at one end to the lever 111 or 1111 and at its other end operates in a bore 9 containing a plunger 11 of the dashpot device to which the rod 13a is connected. An adjustable vent 10, by which liquid may pass into or out of the bore, is provided. When the servomotor piston 6 is deflected the plunger 11 is displaced in the same direction to move the control valve 4 towards its central position, thus tending to stabilize the apparatus and prevent the servomotor from overshooting. The plunger 11 is returned to its initial position under the influence of its spring 12 as liquid is displaced into or out of the bore 9. In a modification, the means for increasing the movement of the control valve 4 according to the rate of change of pressure in the pipe 112<SP>1</SP> comprises a plunger connected to the point 16a and operating in a cylinder having an adjustable leak and a connection to a further cylinder containing a spring- loaded plunger connected to the point 16<SP>1</SP>. Specification 663,366 is referred to.