Hot-rolled Steel Strip Cooling Control
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Solution Overview
Problem
Existing methods for cooling hot strips after hot rolling face challenges in precisely controlling the cooling end temperature, particularly at 500°C or less, due to temperature variations caused by boiling states of water and residual cooling water, leading to instability and deviations in material properties such as strength and ductility.
Innovation Solution
A method involving a two-step cooling process where the first step stops cooling at a temperature higher than the transition boiling initiation temperature, followed by a second step using a higher water flow rate to induce nucleate boiling, ensuring the cooling end temperature is precisely controlled by preventing transition boiling and effectively managing residual cooling water through targeted water purging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If water cooling is used to cool the hot strip, then cooling cost is reduced, but temperature variation occurs at low cooling end temperature
Solution Approach 1:
The cooling process is divided into two distinct stages: a first cooling stage using water cooling for high-temperature regions, and a second cooling stage using air cooling for low-temperature regions. This segmentation allows each cooling method to operate in its optimal temperature range, preventing temperature variation while maintaining cost-effectiveness.
Solution Approach 2:
Different cooling methods are applied to different temperature regions of the hot strip. Water cooling is applied when the strip temperature is above the transition boiling initiation temperature, while air cooling is applied when the temperature reaches 500°C or lower. This local quality approach ensures precise temperature control at each stage.
2Productivity
If water cooling is used to cool the hot strip, then cooling performance is high, but temperature variation occurs in transition boiling range
Solution Approach 1:
The system performs preliminary cooling using water cooling to reduce the strip temperature from high temperature down to 500°C or lower. Once this temperature threshold is reached, the cooling method is switched to air cooling to complete the cooling process, thereby avoiding the transition boiling temperature range and its associated temperature variations.
Solution Approach 2:
The cooling system dynamically switches between water cooling and air cooling based on the real-time temperature of the hot strip. When the strip temperature reaches 500°C or lower, the system transitions from water cooling to air cooling, adapting the cooling method to the current thermal state to maintain precise temperature control.
3Object-generated harmful factors
If cooling water is purged at a position distant from where it is supplied, then residual cooling water is removed, but excessive cooling occurs in the region where cooling water is left
Solution Approach 1:
Air cooling is introduced as an intermediary cooling method that acts as a bridge between water cooling and the final cooling stage. Air cooling is applied to the regions where residual cooling water remains, providing gentle cooling that prevents excessive temperature reduction while still removing the harmful effects of residual water.
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
This approach allows for precise control of the cooling end temperature, reducing temperature variations and stabilizing material properties, thereby improving the consistency of strength and ductility in hot strips cooled to 500°C or less.
Implementation Method 1
heat is transferred through thermal conduction within the vapor film
Implementation Method 2
cooling water comes into direct contact with the surface of a strip and the cooling water is stirred
Implementation Method 3
part of the cooling water vaporizes from the surface of a strip to form vapor bubbles
Implementation Method 4
cooling water boils when it comes into contact with a strip
Implementation Method 5
the vapor bubbles are immediately condensed by the surrounding cooling water to disappear
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
A method for cooling a hot strip with less facilities and processing costs in which the temperature variation of a strip after cooling is controlled to be small and a cooling end temperature can be precisely controlled particularly when the hot strip is cooled to the temperature range of 500°C or less is provided. The method for cooling a hot strip, which is obtained after a hot rolling process, by bringing cooling water into contact with the hot strip, includes a first cooling step and a subsequent second cooling step. In this method, cooling is stopped at a strip temperature that is higher than a transition boiling initiation temperature in the first cooling step, and the cooling is conducted using the cooling water having a water flow rate that causes nucleate boiling in the subsequent second cooling step. Entering the temperature range of transition boiling can be completely prevented to avoid thermal instability in cooling resulting from the transition boiling, and the temperature variation of the strip after cooling is controlled to be small while the cooling end temperature can be precisely controlled.