Steel Sheet Heating via Convex Isotherm Induction
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Solution Overview
Problem
Rapid heating of steel sheets often results in buckling due to thermal expansion constraints, which existing methods struggle to prevent effectively, especially when using conductor rolls or buckling-preventive rolls, leading to facility cost and maintenance issues.
Innovation Solution
The method involves antecedently heating the widthwise central portion of the steel sheet using an induction heating coil with a convex isotherm form toward the upstream side, where the first isotherm is at least 200°C lower than the second, and the heating zone is enlarged to the widthwise edge, preventing the formation of small longitudinal wrinkles and thus buckling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rapid heating is applied to steel sheet, then productivity is improved, but buckling occurs
Solution Approach 1:
The patent applies preliminary action by heating the central portion of the steel sheet before the edge portions. This creates a temperature gradient where the central area expands first, establishing a wrinkle pattern before the edges are heated. This prevents random wrinkle formation and maintains sheet flatness during rapid heating, resolving the contradiction between high heating rate and sheet flatness.
Solution Approach 2:
The patent implements local quality by applying different heating rates to different regions of the steel sheet. The central portion is heated at a higher rate than the edge portions, creating localized thermal expansion control. This differential heating prevents buckling by managing thermal stresses locally, allowing rapid overall heating while maintaining global flatness.
2Manufacturing precision
If conductor roll is used to prevent buckling, then sheet flatness is improved, but facility complexity increases
Solution Approach 1:
The patent replaces the mechanical buckling-preventive roll system with a thermal field control approach. Instead of using mechanical means to constrain the sheet, the invention uses controlled thermal expansion patterns through differential heating. This substitutes a complex mechanical constraint system with a simpler thermal process, reducing facility complexity while maintaining sheet flatness.
Solution Approach 2:
The patent extracts the buckling prevention function from the mechanical constraint system and integrates it into the heating process itself. By making the heating pattern the primary mechanism for wrinkle prevention rather than relying on separate mechanical rolls, the invention simplifies the overall apparatus structure while achieving the same protective function.
3Reliability
If buckling-preventive roll is disposed, then buckling is reduced, but maintenance complexity increases
Solution Approach 1:
The heating apparatus performs self-service by using the heating process itself to prevent buckling. The differential heating pattern automatically manages thermal expansion and prevents wrinkle formation without requiring external mechanical intervention. This self-regulating thermal process eliminates the need for maintenance-prone mechanical rolls, improving reliability while simplifying maintenance.
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 prevents buckling during rapid heating, allowing for stable steel sheet travel and improved product quality by converting small longitudinal wrinkles into a single large wrinkle, reducing defects and facility complexities.
Implementation Method 1
heating a continuously traveling steel sheet by induction heating
Implementation Method 2
direct Joule heating of electrical current into the sheet from electrodes
Implementation Method 3
when the steel sheet is rapidly heated by electrical heating between the conductor rolls as electrodes disposed at upstream and downstream sides thereof, it tends to expand in the width direction of the sheet
Data Source
Figure 1~4
Figure 5(a)~5(c)
Figure 6~8
AI summary
The invention proposes a method for heating a steel sheet wherein the generation of buckling can be prevented regardless of presence or absence of rolls restraining the steel sheet by antecedently heating the widthwise central portion of the steel sheet with a solenoid type induction heating coil having a convex form projected onto the surface of the steel sheet toward an upstream side in rapidly heating the continuously traveling steel sheet, whereby an isotherm of the steel sheet in the heating is a convex form toward the upstream side, so that a large wrinkle is generated on the steel sheet, and also proposes a heating apparatus used in this method.