Patent GB-878491-A (GB)
Title: Method of and apparatus for controlling strip thickness during rolling
IPC: B21B37/16
Filed: 1958-01-20
Abstract: 878,491. Automatic thickness control systems. BRUCKER, H., [trading as REGA, BRUCKER & CO.]. Jan. 20, 1958 [Jan. 18, 1957], No. 1879/58. Class 38 (4). [Also in Group XXII] A method of regulating the thickness of strips or sections to be rolled out in two or more passes is characterized in that from the first pass up to and including the penultimate pass the controlling magnitude determining thickness, such as the roll gap width and/or the longitudinal pull, is, for each pass, initially varied continuously and automatically in the sense of a decreasing thickness until the first of continuously-measured characteristic magnitudes associated with the operation of the rolling mill, for instance rolling force, rolling moment, rotations of the roll gap adjusting spindle or reeling moment, and/or with the quality of the issuing strip, for instance hardness, surface quality, surface structure, ripple or camber, has reached its predetermined critical value, whereafter the said controlling magnitude is so controlled by a regulator controlled by the measured thickness of the strip that the thickness measured when the said critical value is reached is maintained, while during the final pass the thickness of the issuing strip is adjusted to the reference value of the rolling programme by a regulator controlling the said controlling magnitude. The passes can be effected in tandem or multiple rolling mills comprising a number of consecutive roll stands or in a reversing mill in which the direction of strip movement is reversed and the roll gap reduced after each pass. Strip 1 to be rolled enters a roll gap of width s between rolls 3, 4 and issues therefrom with a thickness d which is continuously measured by a gauge 6 which gives a D.C. output voltage corresponding to the strip thickness. The roll gap-the controlling magnitudeis adjusted by a rack-and-pinion 7, 8 driven by a reversible motor 9. D.C. voltage delivered by the gauge 6 and proportional to d is supplied at the beginning of a pass and before a relay 14 is energized through a contact 11 to a zero indicator 22 and is compared thereby with the component voltage applied to the slider of the potentiometer 20 so that the component voltage, to earth, tapped off by the slider is equal to the measurement voltage. The component voltage serves as a reference value for a regulator 26 and is supplied thereto through a lead 24. A zero indicator 27 of the regulator 26 has applied thereto, the full voltage of a D.C. source 19, associated with the potentiometer 20, through a lead 29, and contacts of relays 30, 34. Voltage from lead 29 higher than that from lead 24 so that zero indicator 27 controls the roll-adjusting motor 9, through a reversing contactor 28, to reduce the roll gap s in this first phase before the relay 14 is energized. A number of measuring devices are provided which continuously measure all the relevant characteristic magnitudes and as soon as any one of the characteristic magnitudes reaches a critical value a contact 17 associated with its measuring device closes to energize the relay 14 to close a holding contact 13 and a contact 12 to energize the relay 30 and to switch the contact 11. Current thus ceases to flow to the zero indicator 22 and the motor driving the slider of the potentiometer 20 stops so that the voltage applied to the slider at this instant is maintained and supplied as a reference value through the lead 24 for the rest of the pass. The relay 30 also opens the contact 33 so that current ceases to flow through the zero indicator 27 and the roll-adjusting motor 9 stops. A contact 32 of the relay 30 is also closed and energizes the relay 34 so that a contact 37 thereof is closed so that the measurement voltage of the gauge 6 is supplied through the contact 11, contact 37 through contact 33 of relay 30 and lead 29 to the zero indicator 27 where it is compared with the reference voltage from the lead 24 and controls the motor 9 so that the strip thickness d is kept constant for the rest of the pass at the value measured when the first critical characteristic magnitude was reached and the relay 14 energized. The relays 30, 34 may be time delay relays so that the reduction of the roll gap ceases after a delay after the relay 14 is energized and after a further delay the regulator 26 takes control. Alternatively the delays may be effected by arranging that a second critical value, slightly higher than the first, for each characterizing magnitude when reached terminates the first delay. A change-over contact 36 of the relay 34 operates through a change-over device, not shown, to control the strip speed, the strip crawling when the relay 34 is de-energized and moving at the normal speed when relay 34 is energised and the regulator 26 takes over control. The speed may then continue to increase until the first of magnitudes associated with the rolling mill, for instance centrifugal forces or self-oscillations and/ or with quality of the issuing strip has reached a pre-set critical value or until the temperature of the strip, coolants, lubricants or machine parts has reached a predetermined critical value. When the controlling magnitude is the longitudinal pull applied to the strip the continuously measured characteristics may be the reeling moment or tension applied to the strip cross-section. The controlling magnitude may comprise in combination the roll gap width and longitudinal pull.