Rolling Line Pass Change Control for Shorter Transition Strips
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Solution Overview
Problem
The existing method of 'wedge-on-wedge rolling' for changing the final rolling dimension in a rolling line leads to mass flow problems and results in a long transition time and significant scrap material due to the need for artificially limited adjusting cylinder traverse speed, which restricts production throughput and increases waste.
Innovation Solution
The method involves a two-phase approach where the first phase maintains the last rolling mill stand's roll gap unchanged, allowing intermediate dimensions to be achieved through sequential pass changes, and the second phase dynamically adjusts the last rolling mill stand to the new final dimension, enabling a shorter transition time and reduced scrap material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the adjusting cylinder traverse speed is increased to reduce transition time and increase productivity, then the exit speed and acceleration of the rolling material increase, but the acceleration capacity of the work rolls of the subsequent rolling mill stand becomes insufficient, leading to mass flow problems and material upset
Solution Approach 1:
The rolling line is divided into multiple rolling mill stands with sequential pass changes. The first rolling mill stand performs the initial pass change to create a wedge, while subsequent stands perform follow-up pass changes. This segmentation allows each stand to handle a portion of the dimension change, distributing the acceleration demand and preventing mass flow disruptions.
Solution Approach 2:
The first rolling mill stand performs a preliminary pass change to create a wedge in the rolling material before the material enters subsequent stands. This preliminary action prepares the material for the dimension change, allowing subsequent stands to complete the transition with controlled acceleration rates that match their work roll acceleration capacity.
2Reliability
If the adjusting cylinder traverse speed is limited to prevent mass flow problems, then mass flow stability is maintained, but the transition time increases and production throughput decreases
Solution Approach 1:
The total dimension change is segmented across multiple rolling mill stands, each performing a portion of the pass change. This allows the adjusting cylinder traverse speed to be optimized for each stand's capabilities, maintaining mass flow stability while collectively achieving the dimension change more rapidly than a single stand could.
Solution Approach 2:
Multiple rolling mill stands are combined to perform the dimension change operation. The first stand creates the initial wedge, and subsequent stands add additional wedges to complete the transition. This merging of multiple stands' capabilities achieves the dimension change faster than any single stand could, increasing production throughput without sacrificing mass flow stability.
3Ease of manufacture
If all rolling mill stands approach their pass changes simultaneously according to load redistribution, then wear distribution is optimized, but mass flow problems occur due to coordinated dimension changes
Solution Approach 1:
The pass change timing is made dynamic rather than simultaneous. The first rolling mill stand performs its pass change first to create a wedge, and subsequent stands perform their pass changes sequentially after the material has progressed through the line. This dynamic timing sequence prevents coordinated dimension changes that would disrupt mass flow, while still achieving optimized wear distribution through the load redistribution calculation.
Solution Approach 2:
The load redistribution calculation is performed preliminarily to determine the optimal timing sequence for each stand's pass change. This preliminary planning ensures that stands perform pass changes in a sequence that maintains mass flow stability, with subsequent stands waiting for the material to progress before performing their dimension changes.
Data Source
AI summary
A method for operating a rolling line with rolling mill stands arranged one behind the other in the rolling direction, for the rolling of rolling material from a previous final rolling dimension to a changed new final rolling dimension is disclosed. According to the method, the rolling is carried out in two temporal phases I and II. In the first temporal phase, the rolling is carried out with a first load redistribution with known wedge-on-wedge rolling. In the first load redistribution the last rolling mill stand maintains its previously set gap unchanged. To shorten a transition time and wedge length during a transition, the rolling mill stands drive pass changes in accordance with a second load redistribution. The second load redistribution, differently than in the first temporal phase I, dynamically drives the last rolling mill stand to the new final rolling dimension.