Multi-slot air knife for molten coating thickness control
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Solution Overview
Problem
Existing multi-jet gas wiping devices for controlling the thickness of molten metallic coatings on metal strips face instability in air flow, leading to uneven coating and reduced wiping efficiency, making them unsuitable for commercial galvanizing lines.
Innovation Solution
A modular multi-slot gas wiping device with a primary nozzle and two auxiliary nozzles, featuring detachable components and adjustable gap settings, and separate gas feeding systems to maintain stable air flow and high impingement pressure, ensuring uniform coating thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If auxiliary jets are added to stabilize the air flow, then the flow stability is improved, but the pressure gradient decreases and wiping efficiency is adversely affected
Solution Approach 1:
The invention changes the geometric parameters of the nozzle system, specifically the tilt angle of auxiliary jets relative to the main jet (optimized at 15 degrees) and the inlet pressure ratio between auxiliary and main jets (optimized at 0.25). These parameter changes allow the auxiliary jets to stabilize the air flow while maintaining a sufficient pressure gradient for high wiping efficiency, resolving the contradiction between flow stability and productivity
Solution Approach 2:
The invention introduces dynamic positioning of the air knife at an optimized angle of 15 degrees relative to the metal strip, and dynamically adjusts the separation distance between main and auxiliary jets (optimized at 5 mm). These dynamic adjustments enable the system to maintain both flow stability and high wiping efficiency by optimizing the interaction between jets during operation
2Quantity of substance
If the nozzle length is increased to achieve the same flow rate, then the flow rate is maintained, but the nozzle stiffness decreases and air flow becomes unstable
Solution Approach 1:
The invention segments the single long nozzle into multiple shorter nozzle sections (main jet nozzle and auxiliary jet nozzles) arranged in a specific configuration. This segmentation maintains the required gas flow rate through each section while preventing the instability associated with a single long nozzle, as the shorter sections retain sufficient structural stiffness
Solution Approach 2:
The invention transitions from a single-dimensional long nozzle to a multi-dimensional arrangement of shorter nozzles positioned at specific angles and separations. The auxiliary nozzles are positioned at 15 degrees relative to the main jet with 5 mm separation, creating a three-dimensional configuration that achieves the required flow rate while maintaining structural stability and flow consistency
3Device complexity
If a conventional single-jet air knife is used, then the structure is simple, but the coating thickness uniformity is poor due to unstable flow
Solution Approach 1:
The invention merges multiple jet functions into a single integrated air knife system, combining the main jet nozzle with multiple auxiliary jet nozzles in a unified structure. This merging provides flow stabilization benefits while maintaining a relatively simple overall structure that can be implemented in conventional galvanizing lines, achieving both acceptable complexity and improved coating uniformity
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
The device achieves stable air flow and higher wiping efficiency, allowing for precise control of coating thickness and weight reduction, making it suitable for commercial galvanizing lines with improved stiffness and ease of assembly.
Implementation Method 1
The metal strip leaves the bath in an about vertical direction after which the excess of the applied metallic coating is blown off with a high pressure air/gas wiping device also known as 'air knife'
Implementation Method 2
CFD has shown that the inlet pressure of the auxiliary jet flow rate should be a fraction of the flow rate of the main jet. A higher wiping efficiency requires a tilt angle between the auxiliary jet and the main jet
Data Source
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AI summary
The present invention relates to a multi-slot gas wiping device for controlling the thickness of a molten metallic coating on a moving metal strip.