Al-Zn-Si-Mg Coated Steel Strip Cooling Water pH Control
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Solution Overview
Problem
Al-Zn-Si-Mg alloy coatings on steel strips are highly reactive with quench water, leading to excessive dissolution and the formation of precipitates that cause rapid deterioration of cooling water circuit heat exchangers and undesirable coatings on storage tank surfaces, posing a significant maintenance issue.
Innovation Solution
Controlling the pH of the cooling water to be greater than 5.5 and maintaining a lower temperature, typically below 50°C, to suppress alkalinity and reduce the corrosiveness of the cooling water, thereby minimizing the dissolution of the Al-Zn-Si-Mg alloy coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Al-Zn-Si-Mg alloy coating is applied to steel strip, then cut-edge protection and corrosion resistance are improved, but reactivity with quench water increases causing excessive dissolution and precipitate formation
Solution Approach 1:
The patent applies parameter changes by controlling the pH of cooling water to be greater than 5.5 and maintaining lower temperatures (typically below 50°C) to suppress the alkalinity and reduce corrosiveness of the cooling water, thereby minimizing dissolution of the Al-Zn-Si-Mg alloy coating and reducing reactivity between the coating and quench water
2Reliability
If Al-Zn-Si-Mg alloy coating is applied to steel strip, then corrosion resistance is improved, but heat exchanger deterioration accelerates due to precipitate formation
Solution Approach 1:
The patent controls pH and temperature parameters of the cooling water to prevent excessive dissolution of the coating, thereby preventing precipitate formation that would otherwise accelerate heat exchanger deterioration and extend their service life
3Temperature
If conventional cooling water is used, then cooling function is provided, but rapid deterioration of cooling water circuit heat exchangers occurs due to precipitates
Solution Approach 1:
The patent modifies the chemical parameters (pH > 5.5) and temperature parameters (typically below 50°C) of the cooling water to suppress alkalinity and reduce corrosiveness, preventing precipitate formation and maintaining heat exchanger performance
Solution Approach 2:
The patent uses pH control and temperature control as intermediary mechanisms to mediate between the cooling water and the Al-Zn-Si-Mg alloy coating, reducing their harmful interaction while maintaining the cooling function
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 effectively reduces the formation of precipitates in the quench water, preventing heat exchanger blockage and maintaining the functionality of the cooling water circuit, allowing the heat exchangers to perform optimally.
Implementation Method 1
a water cooling step in which water is sprayed onto the coated strip and the coated strip is cooled by the water
Implementation Method 2
the precipitate problem could be addressed by suppressing the alkalinity of cooling water via pH control of cooling water
Implementation Method 3
to a lesser extent cooling water temperature control (operating at low temperatures) to thereby reduce the corrosiveness of the cooling water towards Al-Zn-Si-Mg alloy coatings
Data Source
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AI summary
A method of forming a coating of an Al-Zn-Si-Mg alloy on a steel strip to form an Al-Zn-Mg-Si coated steel strip is disclosed. The method includes the steps of dipping steel strip into a bath of molten Al-Zn-Si-Mg alloy and forming a coating of the alloy on exposed surfaces of the steel strip and cooling the coated strip with cooling water. The cooling step includes controlling the pH of cooling water to be in a range of p H 5-9. Particular embodiments focus on Al-Zn-Si-Mg alloys that contain the following elements in % by weight: Zn: 30 to 60, Si: 0.3 to 3, Mg: 0.3 to 10, and Balance Al and unavoidable impurities.