Moisture-Controlled Stripping Gas for Defect-Free ZnAlMg Coating
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Solution Overview
Problem
Existing methods for applying ZnAlMg or ZnAl layers on flat steel products often result in surface defects such as marbling and toothpick defects, and are not robust against varying environmental conditions, while consuming excessive energy and resources.
Innovation Solution
A device and method that control the moisture content of the stripping gas by maintaining a specific dew point or moisture volume fraction, ensuring the gas is unsaturated, to prevent condensation and surface defects, using a combination of dry gas and water vapor to achieve a homogeneous coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dry stripping gas is used to blow off the zinc layer, then the coating thickness can be controlled, but surface defects such as marbling and toothpick defects occur
Solution Approach 1:
The invention changes the parameter of the stripping gas from completely dry to having a controlled moisture content. By adjusting the moisture content to a specific range (dew point between -30°C and +10°C), the gas prevents surface defects while maintaining coating thickness control capability.
Solution Approach 2:
The stripping gas is created as a composite mixture of dry gas and water vapor. This composite gas combines the coating control benefits of dry gas with the surface quality benefits of humidified gas, achieving both thin coating and defect-free surface.
2Object-affected harmful factors
If the surrounding air humidity is high, then surface defects are reduced, but energy consumption increases due to the need for humidity control
Solution Approach 1:
The invention implements a feedback control system that continuously monitors the moisture content of the stripping gas and adjusts the humidification level accordingly. This ensures optimal surface quality while minimizing energy consumption by avoiding over-humidification.
Solution Approach 2:
Instead of using completely dry gas or saturating the gas with moisture, the invention applies partial humidification to achieve the optimal dew point range. This partial action is sufficient to prevent surface defects without the excessive energy consumption of full saturation.
3Object-affected harmful factors
If water vapor is added to the stripping gas, then surface quality improves, but condensation may occur
Solution Approach 1:
The invention carefully controls the temperature and moisture content parameters of the stripping gas to maintain a dew point between -30°C and +10°C. This parameter control allows water vapor addition for surface quality improvement while preventing condensation by keeping the gas temperature above its dew point.
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 method ensures a durable, robust, and energy-efficient application of ZnAlMg or ZnAl layers with consistent surface quality, independent of environmental conditions, avoiding marbling and toothpick defects.
Implementation Method 1
a water vapor device (50) configured to provide gaseous water vapor
Implementation Method 2
means for determining gas humidity arranged in or at the stripping nozzle device (14) to determine the moisture content of the stripping gas
Data Source
AI summary
A device and method for applying ZnAlMg layers or ZnAl layers to the front and rear side of a flat steel product, includes moving the flat steel product from an input side to an exit side of a zinc alloy melt bath, providing a dry gas stream, providing a water vapor gas, combining the dry gas stream and the water vapor gas to obtain a stripping gas as a mixture, determining the gas humidity of the stripping gas, discharging the stripping gas through at least one gas nozzle which serves to blow off the front side and through at least one gas nozzle which serves to blow off the back side in order to blow off the front side and rear side of the flat steel product with the stripping gas.