Zn-Coated Steel Strip Rolling and Wiping for Surface Defect Control
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Solution Overview
Problem
Existing methods for manufacturing hot dip coated steel sheets face challenges in achieving high surface quality due to defects such as dross, furnace, and coating defects, particularly in applications requiring high finish and formability, and existing solutions compromise corrosion resistance or visibility in the coating process.
Innovation Solution
The method involves cold rolling the steel strip to a specific thickness with a high specific rolling force in the final stand, using work rolls with controlled roughness, and optimizing the gas knife distance and cooling process to reduce defects and waviness, while maintaining a controlled coating thickness and composition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the steel strip is cold rolled with high specific rolling force in the final stand, then the surface quality and formability are improved, but the manufacturing complexity increases
Solution Approach 1:
The patent applies parameter changes by optimizing the specific rolling force in the final stand of the cold rolling process and controlling the roughness of work rolls. These parameter adjustments improve surface quality and formability without requiring fundamental changes to the manufacturing equipment, thus resolving the contradiction between manufacturing precision and device complexity.
2Reliability
If the gas knife distance is optimized to reduce defects, then the coating quality is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by optimizing the gas knife distance before the actual coating process to prevent defect formation. By pre-positioning the gas knife at the optimal distance, the process reduces coating defects without requiring excessive precision during the coating operation itself, thus resolving the contradiction between reliability and manufacturing precision requirements.
3Strength
If the cold rolled strip thickness is controlled within a specific range, then the formability is improved, but the productivity decreases
Solution Approach 1:
The patent applies parameter changes by specifying a controlled thickness range for the cold rolled strip (0.40-1.00 mm). This parameter optimization ensures improved formability while maintaining acceptable productivity levels by identifying the optimal thickness window that balances mechanical properties and production efficiency, thus resolving the contradiction between strength and productivity.
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 significantly reduces defects and waviness, resulting in a high-quality coated steel sheet suitable for visible automotive applications with improved corrosion resistance and formability.
Implementation Method 1
a gas knife having a knife slot from which a wiping gas is projected
Implementation Method 2
optimizing the gas knife distance and cooling process to reduce defects and waviness
Implementation Method 3
cold rolling the steel strip to a specific thickness with a high specific rolling force in the final stand, using work rolls with controlled roughness
Data Source
AI summary
A method manufacturing a steel strip, including the subsequent steps of hot rolling the strip into a hot rolled strip, cold rolling the hot rolled strip and hot dip coating the cold rolled strip with a Zn based coating by leading the strip through a bath including molten zinc and wiping the strip after the coating using a gas knife having a knife slot from which a wiping gas is projected and the steel strip is cold rolled to a final cold rolled thickness of between 0.40 mm and 1.00 mm in a multi-stand cold rolling mill, and the coated steel sheet includes a steel substrate provided with a hot dip metal coating.