Filtration System for Coated Steel Strip Cooling
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Solution Overview
Problem
Galvanized steel strips coated with magnesium and zinc often exhibit dark spots due to the presence of Mg2Zn11 on their surface, which form during the cooling process after exiting the hot-dip coating bath, leading to surface defects known as 'freckles' or 'bright spots', particularly on thicker products.
Innovation Solution
A cooling method involving the suction and filtration of gas to capture at least 50% of particles larger than 2.5 µm, followed by blowing the filtered gas at velocities between 1 to 80 m/s onto the coated steel strip, utilizing a cooling device with a filtration system and distribution chambers to minimize particle impact and reduce Mg2Zn11 nucleation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If gas is blown onto the coated steel strip during cooling, then cooling efficiency is improved, but dark spots form due to particle contamination
Solution Approach 1:
The gas is filtered before being blown onto the coated steel strip to remove particles that would cause dark spots. The filtration system captures particles with a diameter of at least 2.5 μm, preventing their deposition on the strip surface during the cooling process.
Solution Approach 2:
A filtration system is introduced as an intermediary between the gas source and the coated steel strip. This filtration system (9) captures particles from the gas stream, allowing only clean gas to contact the strip surface, thereby preventing dark spot formation while maintaining cooling efficiency.
2Manufacturing precision
If cooling rate is increased to prevent dark spots, then surface quality is improved, but energy consumption increases
Solution Approach 1:
Instead of using rapid cooling to prevent dark spots (which would increase energy consumption), the invention converts the harmful effect of gas particles into a beneficial solution by filtering them out. The same gas flow that could cause contamination is now used for cooling, with particles removed by the filtration system, achieving surface quality improvement without excessive energy use.
3Object-affected harmful factors
If filtration system captures particles, then dark spot formation is reduced, but device complexity increases
Solution Approach 1:
The harmful particles are extracted from the gas stream using a filtration system. The system captures particles with a diameter of at least 2.5 μm, removing them from the gas flow before it contacts the coated steel strip, thereby reducing dark spot formation.
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
Significantly reduces the presence of dark spots on the steel strip surface by removing larger particles that contribute to Mg2Zn11 formation, particularly effective for thicker strips, as demonstrated by experimental results showing a decrease in dark spot density.
Implementation Method 1
filtering said sucked gas by means of a filtering system (9) capturing at least 50% of the particles having a size of at least 2.5 μm
Implementation Method 2
blowing, at a velocity from 1 to 80 m.s-1, said sucked and filtered gas onto said coated steel strip (S)
Data Source
AI summary
A cooling method of a travelling coated steel strip, exiting a hot-dip coating bath, including the steps of A) sucking a gas into a cooling device, B) filtering the sucked gas by a filtering system capturing at least 50% of the particles having a size of at least 2.5 µm, C) blowing, at a velocity comprised from 1 to 80 m.s-1, the sucked and filtered gas onto the coated steel strip.