Strip flatness acts as a core quality indicator in cold rolling production. Smooth and flat strip steel meets the processing and application requirements of downstream industries. In contrast, wave and warping defects reduce product qualification rates and increase production losses. Mainstream six-high cold rolling mills adopt two sets of bending devices for shape adjustment. However, traditional control methods have obvious limitations and struggle with high-order complex shape defects. An innovative combined bending force control strategy effectively solves these technical problems and achieves stable improvement in actual production.
1. Basic Relationship Between Bending Force and Strip Shape
Six-high cold rolling mills are equipped with independent work roll and intermediate roll bending mechanisms. The bending force of the two sets of rollers serves as the core method to reshape roll gaps and correct strip flatness. Nevertheless, the two bending systems have completely different regulatory characteristics.
Rollers produce elastic deformation under rolling pressure during operation. This changes the roll gap profile and causes various strip shape defects. Bending force actively creates controllable roller deflection. It offsets rolling deformation and restores the strip to a flat state.
1.1 Work Roll Bending Force Characteristics
Work roll bending force strongly affects the edge area of steel strips. It efficiently eliminates common defects such as bilateral waves and central protrusion. It acts as the main method for basic shape correction. Under the same load, its adjustment efficiency for symmetric secondary shape defects is 2 to 3 times higher than intermediate roll bending force.
1.2 Intermediate Roll Bending Force Characteristics
Intermediate roll bending force realizes uniform full-width adjustment with gentle variation trends. It targets local waves at the strip center and quarter-width positions, including typical quarter waves and compound edge-center waves. These complex high-order defects cannot be completely eliminated by conventional bending control.
In actual production, strip shape defects are divided into two categories. Secondary defects such as central waves and bilateral waves are mature and easy to control. In comparison, quaternary defects represented by quarter waves and local compound waves feature scattered distribution and complex causes. They remain difficult problems restricting high-precision cold rolling production.
2. Limitations of Traditional Bending Force Control Modes
Most six-high cold rolling mills carry dual bending devices, but traditional control logic fails to realize collaborative advantages. Traditional equipment adopts a relay adjustment mode. The system preferentially uses work roll bending force. It activates intermediate roll bending only after the work roll bending reaches its adjustment limit.
This mode regards the two bending systems as substitute tools. It only focuses on secondary shape correction and ignores the unique advantages of intermediate roll bending in solving high-order defects. For stubborn quarter waves and quaternary shape problems, traditional methods mainly rely on slow segmented cooling adjustment. This solution features low speed, poor precision and repeated defects, which seriously restrict production efficiency and surface quality.
Some equipment distinguishes the two bending characteristics but simplifies calculation logic. It weakens the influence of work roll bending on the strip central area. Calculation errors and adjustment deviations still exist, making complex shape defects difficult to eliminate fundamentally.
3. Optimized Combined Bending Force Control Strategy
To solve the shortcomings of traditional relay control, the new six-high cold rolling mill bending force control strategy maximizes the differentiated characteristics of dual bending systems. It realizes coordinated adjustment through scientific proportion matching and adapts to automatic and manual production scenarios.
3.1 Simulation Analysis of Bending Regulation Rules
Professional simulation models are built to verify bending force variation laws. The system simulates adjustment effects under different strip widths and intermediate roll shifting distances. It summarizes accurate matching rules for combined bending control.
Simulation results prove distinct collaborative mechanisms. Synchronous proportional adjustment of dual bending forces efficiently eliminates secondary defects such as central waves and bilateral waves. Reverse proportional adjustment suppresses quaternary quarter waves without affecting basic flatness. This core principle supports high-precision correction of complex shape defects.
3.2 Dual Application Modes for Full Production Scenarios
The strategy designs two executable modes to adapt to automatic production lines and on-site operation.
Online Closed-Loop Automatic Control: The system collects real-time flatness data and automatically separates secondary and quaternary defect proportions. It calculates optimal work roll and intermediate roll bending values based on preset matching rules. This automatic adjustment features fast response and high precision for continuous large-scale production.
Manual Parameter Adjustment: Technical teams pre-set fixed proportion coefficients for different strip specifications and mill states. Operators adjust dual bending forces according to actual wave types. Synchronous adjustment solves conventional central and edge waves, while reverse adjustment eliminates quarter waves. This method has low operation thresholds and supports rapid on-site defect correction.
Strip width and intermediate roll shifting distance are two key influencing factors. Dynamic calculation models update bending proportion parameters in real time during specification switching to maintain stable control accuracy.
4. Field Application and Verification Results
The optimized six-high cold rolling mill bending force control strategy has been verified in actual production. The original relay control mode caused frequent quarter wave defects and large flatness deviation. After applying the new strategy, the independent relay program is disabled while roller cooling functions remain normal.
On-site adjustment with matched bending proportions rapidly removes quarter wave defects. The overall flatness deviation decreases significantly, and strip surface stability improves obviously. This strategy shows strong universality. Most mainstream six-high rolling mills can adopt this solution simply by fine-tuning proportion coefficients.
Based on field data, manufacturers further optimize mill configurations to strengthen intermediate roll bending performance. This improvement greatly enhances the overall effect of combined bending force control.
5. Conclusion
Shape control is the core difficulty of cold rolling technology. Bending force control possesses huge optimization potential for high-precision production. The improved six-high cold rolling mill bending force control strategy abandons the traditional passive relay adjustment mode. It realizes complementary collaboration between work roll and intermediate roll bending systems.
This solution effectively solves long-standing high-order shape defects. It provides both high-precision automatic control models and simple manual operation methods. Without large-scale equipment transformation, the strategy reduces production defects, improves product quality and lowers operating costs. It has great promotion value for ordinary strips and high-end precision steel plates, laying a solid foundation for high-quality cold rolling production.
