Hot-dip Galvanizing Steel Dross Removal via Three-Tub Circulation
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Solution Overview
Problem
Conventional dross removal methods in galvanized steel sheet manufacturing are inefficient and incomplete, with dross with small sizes flowing back into the coating bath, leading to low removal efficiency and quality defects in the steel sheets.
Innovation Solution
A method involving a circulation system of three tubs - a coating tub, a separating tub, and an adjusting tub - where the coating bath is circulated to precipitate top-dross in the separating tub by lowering its temperature and dissolve residual dross in the adjusting tub by controlling the iron unsaturation, effectively removing dross before it forms harmful sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional dross removal methods are used, then dross removal is performed, but dross with small sizes flows back into the coating bath, resulting in low removal efficiency and quality defects
Solution Approach 1:
The coating bath system is divided into three separate tubs (coating tub, separating tub, adjusting tub) that function independently but are connected through circulation. Each tub performs a specific function: the coating tub for coating application, the separating tub for dross removal through temperature control, and the adjusting tub for composition adjustment. This segmentation allows optimized dross removal without compromising coating quality.
Solution Approach 2:
The invention utilizes temperature and composition parameter changes to control dross formation and removal. By lowering the temperature in the separating tub, dross is precipitated and removed. The adjusting tub then modifies the composition (particularly iron content) and temperature to prevent dross formation when the bath returns to the coating tub. These parameter changes enable effective dross removal while maintaining coating quality.
2Productivity
If sheet threading speed is increased to improve productivity, then coating rate increases, but bottom-dross rises in the coating bath and adheres to steel sheets, causing quality degradation
Solution Approach 1:
The invention performs preliminary dross removal in the separating tub before the coating bath returns to the coating tub. By removing dross in advance through temperature-controlled precipitation and flotation, the coating bath is cleaned beforehand, preventing dross adhesion even at high sheet threading speeds. This preliminary action enables high productivity without quality compromise.
Solution Approach 2:
The separating tub and adjusting tub act as intermediary components between the coating tub and the external environment. These intermediary tubs provide a buffer zone where dross is removed and bath composition is adjusted, mediating between high-speed coating operations and quality requirements. The circulation system through these intermediaries enables continuous dross removal at high 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 method almost completely renders dross harmless by separating and removing it efficiently, preventing surface defects and improving the quality of galvanized steel sheets while allowing for increased coating rates and productivity.
Implementation Method 1
Fe is supersaturated by decreasing the bath temperature of the circulation bath, so that it is possible to precipitate Fe of the coating bath as the top-dross and to separate by the flotation
Implementation Method 2
precipitate Fe of the coating bath as the top-dross
Implementation Method 3
separate by the flotation
Implementation Method 4
Fe of the coating bath is unsaturated by increasing the bath temperature, so that it is possible to dissolve and remove the top-dross with small sizes which is not able to be separated and removed in the separating tub
Implementation Method 5
dissolve and remove the top-dross
Implementation Method 6
the coating bath is circulated in order of the coating tub, the separating tub, and the adjusting tub
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A manufacturing equipment for galvanized steel sheet includes coating tub to coat steel sheet dipped in coating bath wherein the bath including molten zinc and Al is stored at bath temperature T1, separating tub to separate by a flotation top-dross by precipitating the top-dross in the bath wherein the bath transferred from the coating tub is stored at bath temperature T2 lower than T1, adjusting tub to dissolve dross wherein the bath transferred from the separating tub is stored at bath temperature T3 higher than T2 and Fe of the bath is unsaturated, and circulator to circulate the bath in order of the coating tub, the separating tub, and the adjusting tub.