GB1267581A - Rolling mill control system - Google Patents

Abstract

1,267,581. Rolling. ALCAN RESEARCH & DEVELOPMENT Ltd. 13 March, 1969 [14 March, 1968], No. 13408/69. Heading B3M. [Also in Division G3] Bending jacks between upper and lower work roll chocks of a four-high rolling mill stand are automatically controlled by signals corresponding to changes of bending force and rolling load to maintain those signals in a constant, adjustable, ratio. In Fig. 1, material 35 is rolled between work rolls 16, 18 associated with backup rolls 12, 14 in a rolling mill stand to which load is applied at each end by motor-driven screws 22. Hydraulic jacks 28 between the work rolls and further jacks 30, 31 between the work and back-up rolls tend to bend the work rolls in opposite senses and transducers 81, 80 produce electrical signals -corresponding to the fluid pressures applied to the jacks which may each consist of a number of jacks in parallel. The difference between these signals, corresponding to the bending force, produced between terminals 86, 87, is compared with a signal, at output terminals 71, 72 of a potentiometer 70, corresponding to an adjustable proportion of the rolling load as measured by load cells 60 between the lower back-up roll 14 and the frame of the stand. Any difference is effective through a moving coil 52 to operate a valve 51 and adjust, in opposite senses, the fluid pressures applied to the two sets of jacks to maintain a desired proportionality, corresponding to the setting of potentiometer 70, between the resultant bending force and the rolling load. Potentiometer 70 is adjusted to suit different widths of strip and may be calibrated in widths. Flatness of the strip is observed during slow threading of the mill and a potentiometer 77 manually adjusted to apply a bias at terminals 73, 74 sufficient to ensure a zero signal to the moving coil when the strip is flat. Hydraulic prestressing jacks (not shown) are provided between the back-up rolls and a transducer responsive to the pressure applied to these jacks subtracts a signal from the load cell signal to represent true rolling load. A signal dependent on the force of the jacks between the work and back-up rolls is also subtracted from the load cell signal. Modifications of the bending force control using A.C. and D.C. signals and alternative manual control to facilitate threading, roll changing and bring- ing the mill to rest are described. Metal strip to be rolled is supplied to the roll stand from a reel (not shown) having mechanical resistance to rotation to provide back tension and the rolled strip is wound up on a motor-driven reel (not shown). Signals from a gauge (not shown) responsive to rolled strip thickness automatically control screw-down to maintain a desired thickness. The rolled strip also passes over a roll which produces electrical signals corresponding to the pressure applied by the strip at a number of points across its width. Lack of equality of these signals represents lack of flatness and suitably weighted signals taken from portions near each edge are combined to control the bending jacks and compared to control the bending jacks and slow screwdown at the appropriate end to effect correction. At the end of a pass a torque detector associated with the supply reel detects that tension is lost at the end of the strip and applies bias to the bending force control system so that the working rolls are bent towards each other at their ends to oppose sideways movement of the strip tail as it passes. After a slight delay, the response of the bending force control system is slowed to avoid a sudden control effect when the strip leaves the stand. Signals corresponding to one pass may be stored capacitively until the next pass.