Hot-Rolled Steel Strip Cooling Layout to Prevent Surface Phase Change
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Solution Overview
Problem
Existing methods for producing hot-rolled steel strips with controlled-rolling face inefficiencies due to high cooling rates causing temperature differences that can lead to phase transformation of the surface layer, resulting in reduced mechanical properties and prolonged waiting times before finish rolling.
Innovation Solution
A production equipment line featuring a reversible rough rolling mill with a slow cooling apparatus upstream and a rapid cooling apparatus downstream, allowing for controlled cooling to maintain the surface temperature above the phase transformation temperature, thereby reducing waiting times and improving rolling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If high cooling rate is applied to cool the sheet bar before controlled-rolling, then the waiting time is reduced, but the surface layer temperature drops below phase transformation temperature causing phase transformation and reduced mechanical properties
Solution Approach 1:
The cooling process is divided into two distinct stages: a first cooling stage using a slow cooling apparatus to reduce temperature while preventing phase transformation, and a second cooling stage using a rapid cooling apparatus to quickly lower temperature before controlled-rolling. This segmentation allows optimization of each stage's cooling rate for different objectives.
Solution Approach 2:
The slow cooling apparatus performs preliminary cooling action before the rapid cooling apparatus operates. This preliminary action reduces the sheet bar temperature to an intermediate level while maintaining surface temperature above phase transformation point, preparing the material for the subsequent rapid cooling phase without causing harmful phase transformation.
2Reliability
If slow cooling is applied to prevent phase transformation, then mechanical properties are maintained, but the waiting time before controlled-rolling is prolonged
Solution Approach 1:
The cooling process is divided into two distinct stages: a first cooling stage using a slow cooling apparatus to reduce temperature while preventing phase transformation, and a second cooling stage using a rapid cooling apparatus to quickly lower temperature before controlled-rolling. This segmentation allows optimization of each stage's cooling rate for different objectives.
Solution Approach 2:
The two cooling apparatuses operate in sequence without interruption to the production flow. The slow cooling apparatus operates continuously during the first stage, followed immediately by the rapid cooling apparatus in the second stage, ensuring continuous temperature reduction while maintaining material integrity throughout the process.
3Device complexity
If air cooling is used to cool the sheet bar, then equipment complexity is reduced, but temperature control precision is insufficient leading to phase transformation
Solution Approach 1:
The slow cooling apparatus acts as an intermediary cooling device between the rough rolling mill and the rapid cooling apparatus. It provides controlled cooling with moderate cooling rate, serving as a bridge that prepares the sheet bar for rapid cooling while preventing temperature from dropping too quickly and causing phase transformation.
Solution Approach 2:
The system changes the cooling rate parameter through different apparatuses: the slow cooling apparatus operates at a lower cooling rate to prevent phase transformation, while the rapid cooling apparatus operates at a higher cooling rate to quickly cool the material before controlled-rolling. This parameter change allows optimization of temperature control at different process stages.
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 effectively decreases the time required for controlled-rolling to commence while preventing surface layer phase transformation, enabling efficient production of hot-rolled steel strips with enhanced mechanical properties.
Implementation Method 1
one of a slow cooling apparatus for slowly cooling the material to be rolled and a rapid cooling apparatus for rapidly cooling the material to be rolled after the slow cooling
Implementation Method 2
one of a slow cooling apparatus for slowly cooling the material to be rolled and a rapid cooling apparatus for rapidly cooling the material to be rolled after the slow cooling
Data Source
AI summary
A production equipment line for a hot-rolled steel strip comprises a rough rolling mill comprising rough rolling mills for hot rolling a material, which is heated to a predetermined temperature to a finish rolling start sheet thickness and a finish rolling mill comprising finish rolling mills for controlled-rolling the material to a final sheet thickness. At least one of the rough rolling mills is a reversible rolling mill. The production equipment line is provided on an upstream side of the reversible rolling mill with one of a slow cooling apparatus for slowly cooling at a water volume density of less than 1000 L/min·m2 and a rapid cooling apparatus for rapidly cooling after the slow-cooling at a water volume density of not less than 1000 L/min·m2 and the other of the slow cooling apparatus and rapid cooling apparatus on a downstream side of the reversible rolling mill.