Hot-Rolled Steel Cooling via Top-Bottom Heat Transfer Ratio Control
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Solution Overview
Problem
Hot-rolled steel sheets with a wave shape in the rolling direction are not uniformly cooled due to local contact with transportation rolls and aprons, leading to uneven heat dissipation and temperature variations across the sheet.
Innovation Solution
The method involves controlling the top and bottom heat transfer coefficient ratio of the hot-rolled steel sheet to a specific value, determined by experimental correlation data, to minimize temperature standard deviation and ensure uniform cooling. This is achieved by adjusting the amount of heat dissipated from the top and bottom surfaces during the cooling process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the hot-rolled steel sheet is cooled using conventional laminar cooling with uniform water supply, then the cooling process is simple, but the temperature distribution becomes non-uniform due to wave shape contact with transportation rolls
Solution Approach 1:
The patent applies local quality by differentiating the cooling approach for different regions of the steel sheet. Specifically, it distinguishes between contact portions (where the sheet touches transportation rolls) and non-contact portions, applying different heat transfer coefficient ratios to each region to achieve uniform overall cooling despite the wave shape variations
2Productivity
If the cooling water supply is increased to cool the steel sheet faster, then the productivity improves, but the temperature uniformity deteriorates due to enhanced contact cooling at wave portions
Solution Approach 1:
The patent controls the top and bottom heat transfer coefficient ratio specifically at contact portions to compensate for the enhanced cooling effect. By adjusting the cooling intensity distribution locally at contact versus non-contact portions, it maintains temperature uniformity while achieving high cooling speeds through the run-out table
Solution Approach 2:
The patent changes the heat transfer coefficient ratio parameter as a function of position along the run-out table. It establishes that the heat transfer coefficient ratio should be controlled within specific ranges (0.5-2.0 at contact portions, 0.3-1.5 at non-contact portions) to achieve both fast and uniform cooling
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively achieves uniform cooling of hot-rolled steel sheets by maintaining the temperature standard deviation within a minimal range, thereby reducing variations in yield stress and tensile strength, and ensuring consistent material quality.
Implementation Method 1
the top surface and the bottom surface of the hot-rolled steel sheet H are not uniformly cooled. That is, there was a problem in that, due to cooling deviation caused by the wave shape of the hot-rolled steel sheet H, it became impossible to uniformly cool the steel sheet in the rolling direction.
Implementation Method 2
the portions that locally come into contact with the transportation rolls 220 or the aprons become more easily cooled than other portions due to heat dissipation by contact.
Data Source
Figure 1
Figure 2
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AI summary
The method for cooling a hot-rolled steel sheet of the invention includes a target ratio-setting process in which a top and bottom heat transfer coefficient ratio X1, at which a temperature standard deviation Y becomes a minimum value Ymin, is set as a target ratio Xt based on correlation data between a top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet and the temperature standard deviation Y of the hot-rolled steel sheet; and a cooling control process in which at least one of an amount of heat dissipated from a top surface by cooling and an amount of heat dissipated from a bottom surface by cooling of the hot-rolled steel sheet in the cooling section is controlled so that the top and bottom heat transfer coefficient ratio X of the hot-rolled steel sheet in the cooling section matches the target ratio Xt.