Roll Stand Tension Control During Stepped Strip Rolling
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Solution Overview
Problem
Existing methods for controlling outfeed-side strip tension in roll stands during stepped rolling of metal strip are inadequate for handling rapid changes in roll gap size and resulting thickness differences, leading to instability and suboptimal tension control due to high inertia of upcoilers and uncontrollable position of dancer rolls.
Innovation Solution
The method involves controlling the outfeed-side strip tension using an upcoiler as an actuator to a predetermined target tension, while simultaneously positioning the roller unit of the outfeed-side strip accumulator to individually predetermined target positions to compensate for rapid thickness changes, leveraging the lower mass inertia of the roller unit for quick reaction to dynamic changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the upcoiler is used as an actuator to control outfeed-side strip tension, then the strip tension can be controlled to a predetermined target tension, but the high inertia of the upcoiler prevents rapid compensation for quick changes in thickness
Solution Approach 1:
The control system is segmented into two independent actuators: the upcoiler for average tension control and the roller unit for dynamic compensation. This segmentation allows each component to operate in its optimal performance range without being constrained by the limitations of the other.
Solution Approach 2:
The roller unit is introduced as a dynamic compensation mechanism that can rapidly adjust to thickness changes. Its lower inertia enables it to respond quickly to dynamic variations, complementing the upcoiler's stable but slow response characteristics.
2Reliability
If the roller unit is force-controlled to maintain desired strip tension, then the tension control function is provided, but the position of the roller unit becomes undetermined leading to instabilities
Solution Approach 1:
The control methods for the upcoiler and roller unit are merged into a unified control strategy. The upcoiler handles average tension while the roller unit handles dynamic compensation, and both control loops work together to achieve stable and accurate tension control without position indeterminacy.
Solution Approach 2:
The control system incorporates feedback mechanisms that monitor both tension and position parameters. By using feedback from thickness measurements and position sensors, the system can adjust the roller unit's position and force to maintain stability while achieving the desired tension control.
3Productivity
If the roll gap is changed rapidly to introduce thickness differences in stepped rolling, then the productivity is improved, but the existing control system cannot compensate for these rapid changes maintaining constant strip tension
Solution Approach 1:
The control system performs preliminary action by detecting roll gap changes and anticipating the resulting thickness variations before they fully manifest. This allows the roller unit to be pre-positioned or pre-adjusted to compensate for upcoming thickness changes, maintaining tension constancy even during rapid roll gap transitions.
Solution Approach 2:
The system dynamically changes control parameters based on the rolling conditions. When rapid roll gap changes are detected, the control strategy shifts to prioritize the roller unit's dynamic compensation capability, adjusting its position and force parameters to maintain constant strip tension despite the changing thickness profile.
Data Source
AI summary
A method for operating a roll stand for the stepped rolling of metal strip is described. The metal strip is initially fed into a roll stand on the infeed side, where it is step-rolled. This creates a leading and a trailing section of the metal strip, each with different thicknesses. After the roll stand, the step-rolled metal strip initially passes through an outfeed-side strip accumulator before it is wound into a coil by an upcoiler. The outfeed-side reel is controlled to a constant strip tension. To keep the outfeed-side strip tension sufficiently constant even in the case of rapid changes in the size of the roll gap and the resulting rapid changes in thickness in the rolled metal strip the control of the strip tension with the aid of the upcoiler is supplemented by a position control for a roller unit in the outfeed-side strip accumulator.