Hot-Rolling Flatness Control Across Passes to Stabilize Strip Profile
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Solution Overview
Problem
In hot-rolling metal strip processes, fluctuations in central flatness lead to instability and poor product quality, particularly when rolling thin or high-strength strips, due to increasing rolling pressure and work roll wear, causing edge sharpening and uneven center flatness across the finishing train.
Innovation Solution
A method is developed to determine manipulated variables for active profile and flatness actuators, specifying pass-specific interval ranges for target central flatness within predetermined limits, using a technological model to calculate precise profile and flatness values for each pass, ensuring the central flatness remains within optimal bounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rolling pressure is increased to improve manufacturing efficiency, then productivity increases, but central flatness uniformity deteriorates
Solution Approach 1:
The finishing train is divided into multiple passes (first pass, second pass, third pass, etc.), with each pass having specific target central flatness values and interval ranges. This segmentation allows progressive control of flatness throughout the rolling process, maintaining precision even as productivity increases through multiple passes.
Solution Approach 2:
Target central flatness values and interval ranges are predetermined for each pass before the rolling operation begins. The technological model calculates these target values in advance based on the specific pass number and rolling conditions, enabling proactive control rather than reactive adjustment.
2Loss of substance
If work roll wear is allowed to increase to reduce manufacturing cost, then loss of substance decreases, but manufacturing precision deteriorates
Solution Approach 1:
The control system dynamically adjusts target central flatness values based on the pass number and rolling conditions. As rolling progresses and work roll wear occurs, the system adapts by modifying target values for subsequent passes, maintaining manufacturing precision throughout the work roll's service life without requiring premature replacement.
Solution Approach 2:
The system uses a technological model that incorporates feedback from actual rolling conditions to calculate appropriate target central flatness values for each pass. This feedback mechanism allows the system to compensate for work roll wear and other changing conditions, maintaining precision while extending work roll life.
3Manufacturing precision
If the number of finishing stands is increased to improve manufacturing precision, then profile control improves, but device complexity increases
Solution Approach 1:
Each finishing stand in the train is equipped with active profile and flatness actuators that can perform multiple functions. These actuators can control both profile and central flatness, allowing a single stand to accomplish what would otherwise require multiple specialized stands, thereby reducing overall device complexity while maintaining precision.
4Strength
If rolling pressure is increased to process high-strength strips, then strength of processed material improves, but manufacturing precision deteriorates
Solution Approach 1:
The system changes the control parameters (target central flatness values and interval ranges) based on the pass number and the specific material being processed. For high-strength strips requiring higher rolling pressures, the system adjusts the target central flatness parameters accordingly, allowing aggressive processing while maintaining precision through adaptive control.
Data Source
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AI summary
The invention relates to a method for ascertaining control variables for active profile and flatness control elements for at least one rolling stand for hot-rolling a metal strip using a plurality of i=1...I successive passes and for ascertaining profile and average flatness values for the hot-rolled metal strip. In the prior art, it is basically known that said control variables and values should be calculated using a technological model. For this purpose, target flatness values and target profile values for the metal strip are specified after the last pass and process-related flatness thresholds are specified after the individual passes for the technological model. The aim of the invention is to develop such a known method such that the occurrence of fluctuations in the average flatness of the metal strip after the individual passes and the resulting disadvantages for the rolling stability and the product quality are prevented. This is achieved by the method according to the invention in that respective pass-specific interval ranges are likewise additionally specified for the target average flatness of the metal strip after a specified pass k, where i=1... <k<...I, and for the target average flatness after the following passes, and the successive calculation of the control variables and profile values is then carried out while also taking into consideration said additional specifications.