GB1262742A - Predictive gauge control method and apparatus with automatic plasticity determination for metal rolling mills - Google Patents

Abstract

1,262,742. Automatic control systems. WESTINGHOUSE ELECTRIC CORP. Jan.31, 1969 [Feb. 2, 1968], No. 5326/69. Heading G3R. A gauge control system for a rolling mill having at least one stand comprises means for adjusting the screwdown by an amount which is predictively determined from the stand spring constant, the plasticity of the material being worked (hot steel strip) which is determined "on line", and the gauge error which in turn is determined from measurements of the roll force and the unloaded roll opening and reference values for these quantities. A prior art system (Spec No 1248978) is discussed in which gauge error and the necessary screwdown correction is determined from measurements of the rolls gap and load force, due allowance being made for mill "spring" and workpiece plasticity, values for which are derived from tables. In the present invention the plasticity is determined "on line", by dividing the load force by the reduction in thickness through the stand. In general, in a multistand mill, the thickness at entry and exit at any stand N is determined from the screwdown position, the force and the spring constant of the stands N-1 and N respectively, but the final thickness is measured by an X-ray gauge 42. In using the values for stand N-1 allowance is made for the transport time between N-1 and N. For the first stand or in a single stand reversing mill entry gauge is measured. Compensation may be provided during acceleration and deceleration by adding a screwdown correcting term equal to a constant times the difference between the instantaneous and the initial speed. Allowance (unspecified) can be made for the elasticity of the workpiece. Alternatively the thickness at exit and entry of any stand may be derived from a find thickness measurement and speed measurements (mass flow technique). In the multistand mill shown, each screwdown position is determined by a digital computer 38 using three terms, (i) a proportional plus integral term from the X-ray gauge 42, the proportionality and integrating constants being different for each stand, (ii) compensating term for acceleration or deceleration, and (iii) the correcting term allowing for mill spring and wcrkpiece plasticity as derived above. A dead band is set for each stand so that small errors affect the last two or three stands only. The calculation is performed at intervals, at a selected rate. The screwdown control is rendered inoperative if a number of conditions are not met, or if the calculated correction is outside limits. Each screwdown is operated by a servo motor 28 with a closed loop control having rate feedback provided by a tachogenerator 29. Tension may be controlled by "loop detectors" L which adjust the speed of each stand and the screwdown correcting signals are fed to these systems to enable them to anticipate the resulting charge of speed.