Hot-Rolled Steel Strip Cooling Sequence for Controlled-Rolling Start
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Solution Overview
Problem
Existing methods for producing hot-rolled steel strips with controlled-rolling face inefficiencies due to long waiting times before the start of controlled-rolling, which decreases rolling efficiency and risks surface layer temperature falling below the phase transformation temperature during cooling.
Innovation Solution
A production equipment line and method incorporating a reversible rough rolling mill, slow cooling, and rapid cooling apparatuses, where slow cooling is performed at a water volume density of less than 1000 L/min·m² and rapid cooling at a density of not less than 1000 L/min·m², arranged next to each other, to maintain the surface temperature above the phase transformation temperature during cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If air cooling is used to cool the sheet bar before finish rolling, then the central temperature can be reduced to the controlled-rolling start temperature, but the waiting time increases to 200-300 seconds which decreases rolling efficiency
Solution Approach 1:
The invention applies water cooling (hydraulic principle) instead of air cooling to rapidly reduce the sheet bar temperature to the controlled-rolling start temperature. By spraying water on the sheet bar surface, the cooling time is dramatically reduced from 200-300 seconds to a much shorter duration, thereby eliminating the idle waiting time and improving rolling efficiency without compromising the central temperature control.
Solution Approach 2:
The invention performs preliminary water cooling of the sheet bar immediately after rough rolling, before the sheet bar enters the finish rolling mill group. This preliminary action reduces the temperature in advance, so that when the sheet bar reaches the finish rolling mill, the controlled-rolling can start immediately at the target temperature, eliminating the need for long waiting periods and improving overall productivity.
2Loss of time
If water cooling is used to cool the sheet bar, then the cooling time is reduced, but the surface layer temperature may fall below the phase transformation temperature which causes phase transformation and affects mechanical properties
Solution Approach 1:
The invention applies different cooling intensities to different regions of the sheet bar. Water cooling is applied to the surface layers to achieve rapid cooling, while the core temperature is controlled through the thermal mass and slower heat conduction. This local differentiation allows the surface to cool quickly without causing the core temperature to drop below the phase transformation temperature, preventing unwanted phase transformation in the critical core region.
Solution Approach 2:
The invention changes the cooling parameters by using water cooling instead of air cooling, which provides much higher heat transfer coefficients. This parameter change enables rapid cooling of the sheet bar surface while maintaining better control over the temperature distribution, reducing cooling time from minutes to seconds while preventing surface temperature from dropping below the phase transformation temperature.
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 reduces the time required for controlled-rolling to start while preventing surface layer temperature drops, thereby enhancing the efficiency of hot-rolled steel strip production.
Implementation Method 1
slow cooling is performed by a slow cooling apparatus at a water volume density of less than 1000 L/min·m²
Implementation Method 2
rapid cooling is performed by a rapid cooling apparatus at a water volume density of not less than 1000 L/min·m²
Data Source
AI summary
A production equipment line for a hot-rolled steel strip comprises a rough rolling mill group comprised of plural rough rolling mills for hot rolling a material which is heated up to a predetermined temperature to a finish rolling start sheet thickness and a finish rolling mill group comprised of plural finish rolling mills for controlled-rolling the material to a final sheet thickness, wherein at least one of the plural rough rolling mills is a reversible rolling mill. The production equipment line for a hot-rolled steel strip is provided with a slow cooling apparatus for slowly cooling the material at a water volume density of less than 1000 L/min·m2 and a rapid cooling apparatus which is arranged next to the slow cooling apparatus and rapidly cools the material after the slow-cooling at a water volume density of not less than 1000 L/min·m2.