Hot-Rolled Steel Strip Cooling Control via Dynamic Water Density
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Solution Overview
Problem
Existing methods for cooling hot-rolled steel strips during the hot-rolling process face challenges in maintaining uniformity and precision of cooling, especially when transportation speeds change, leading to deviations in coiling temperature due to variations in cooling length and water flow density.
Innovation Solution
A method involving a first cooling phase under film boiling conditions, followed by a second cooling phase with a water amount density of at least 2 m^3/min/m^2, where the cooling conditions are controlled to maintain a target temperature range and minimize changes in cooling length and water density, ensuring that at least 80% of the cooling occurs under nucleate boiling conditions, and optionally including a third cooling phase with reduced water density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the length of cooling is changed in accordance with transportation speed by controlling valve opening and closing, then the cooling amount can be adjusted, but the temperature of the steel strip after rapid cooling changes significantly making it extremely difficult to control the coiling temperature within the target range
Solution Approach 1:
The invention dynamically adjusts the water amount density of cooling water in accordance with transportation speed changes, rather than changing cooling length. The control unit modifies the intensity of cooling (water density) to compensate for speed variations, maintaining stable coiling temperature. This dynamic adjustment prevents the temperature deviations that occur when cooling length is changed.
Solution Approach 2:
The invention changes the parameter of water amount density (from 1.5-2.5 m³/min/m² baseline) in response to transportation speed changes. When speed increases, water density increases; when speed decreases, water density decreases. This parameter change approach maintains consistent cooling effectiveness despite speed variations, solving the temperature control precision problem.
2Productivity
If rapid cooling is performed with high water amount density to maintain workability and strength, then cooling efficiency improves, but temperature uniformity deteriorates due to transition boiling state
Solution Approach 1:
The invention carefully controls water amount density within the specific range of 1.5-2.5 m³/min/m² to maintain nucleate boiling state. By adjusting this parameter in response to speed changes while staying within the optimal range, the system achieves both high cooling efficiency and temperature uniformity, avoiding transition boiling.
Solution Approach 2:
The control unit continuously monitors transportation speed and adjusts water amount density accordingly to maintain stable nucleate boiling conditions. This feedback mechanism ensures that cooling remains in the stable nucleate boiling regime, preventing transition boiling and maintaining temperature uniformity while achieving rapid cooling.
3Stability of the object's composition
If the number of drainage units is increased to prevent cooling water from entering air-cooled areas, then cooling uniformity improves, but installation complexity and cost increase due to high capability requirements
Solution Approach 1:
The invention prevents cooling water from entering air-cooled areas by controlling the water supply in advance, rather than relying on complex drainage facilities to remove excess water. The control unit adjusts water density and supply timing to ensure water does not overflow into adjacent air-cooled zones, eliminating the need for high-capability drainage systems.
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 suppresses temperature deviations and ensures precise control of coiling temperatures, maintaining uniformity and stability across varying transportation speeds by maintaining consistent cooling conditions in the second cooling phase.
Implementation Method 1
the steel strip is cooled, for example, by using water as a cooling medium
Implementation Method 2
there is known a method of cooling, which avoids the cooling in a state of transition boiling, which is a primary factor of nonuniformity in cooling, as much as possible, and employs cooling in a state of nucleate boiling
Data Source
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AI summary
The present invention provides a method for cooling a hot-rolled steel strip after a finishing rolling in which a transportation speed varies, the method including: setting a transportation-speed changing schedule on the basis of a temperature of a steel strip before the finishing rolling and a condition of the finishing rolling; performing a first cooling in which the hot-rolled steel strip is cooled under a film boiling state in a first cooling section; performing a second cooling in which the hot-rolled steel strip is cooled with a water amount density of not less than 2 m2/min/m2 in a second cooling section; and coiling the hot-rolled steel strip, in which a cooling condition is controlled in the first cooling so as to satisfy 0.8 ≤ (T2a' - T2a)/ΔTx ≤ 1.2.