Stainless Steel Pickling via HCl and Fe3+ Electrolysis
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Solution Overview
Problem
Current pickling processes for stainless steel laminates are inefficient, environmentally impactful, and costly, with high consumption of raw materials and emissions of pollutants like nitrogen oxides and fluorinated compounds, and require prolonged contact times and large-scale facilities.
Innovation Solution
A method involving electrolytic pickling in alternating current using an aqueous solution of hydrochloric acid with Fe3+ ions, followed by chemical pickling and surface passivation, which effectively removes the oxide scale and dechromatized layer while reducing environmental impact and raw material consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional pickling baths using nitric acid and hydrofluoric acid are used, then scale removal is achieved, but large quantities of nitrogen oxides and contaminated waste water are formed, requiring specific emission control and purification measures
Solution Approach 1:
The patent changes the chemical composition parameters of the pickling bath by using hydrochloric acid instead of nitric acid and hydrofluoric acid, and by adding specific additives like ferric chloride and organic inhibitors. This parameter change maintains effective scale removal while eliminating the formation of nitrogen oxides and reducing fluorinated compound emissions, directly resolving the contradiction between manufacturing precision and harmful emissions
Solution Approach 2:
The patent employs a disposable organic inhibitor that forms a protective film during pickling and then degrades, allowing the process to proceed without complex emission control systems. The inhibitor is consumed in the process, replacing the need for expensive and complex gas purification equipment that would be required when using traditional nitric acid-based baths
2Manufacturing precision
If prolonged contact with pickling baths is used to achieve adequate scale removal, then pickling efficiency is improved, but the process becomes slow and requires large sized plants
Solution Approach 1:
The patent applies a preliminary action by adding ferric chloride and organic inhibitors to the pickling bath before the actual pickling process. These additives prepare the chemical environment to enhance pickling efficiency, allowing for shorter contact times while achieving adequate scale removal. The preliminary preparation of the bath composition enables faster processing without sacrificing removal adequacy
Solution Approach 2:
The patent creates a composite pickling solution combining hydrochloric acid with ferric chloride and organic inhibitor additives. This composite formulation synergistically enhances the pickling rate and efficiency, enabling rapid scale removal in shorter contact times. The composite nature of the solution provides both aggressive scale removal capability and controlled reaction kinetics, resolving the contradiction between removal adequacy and process speed
3Manufacturing precision
If high concentrations of mineral acids are used for effective pickling, then scale and dechromatized layer removal is improved, but raw material consumption and environmental impact increase
Solution Approach 1:
The patent implements a self-service mechanism where the organic inhibitor in the pickling bath automatically forms a protective film on the steel surface during the process. This self-forming protection reduces excessive acid consumption and prevents unnecessary acid waste, while the ferric chloride continuously regenerates active pickling species. The system self-regulates to maintain effective surface cleaning without requiring excessive acid dosing, thereby reducing both raw material consumption and environmental impact
Solution Approach 2:
The patent enables easy recovery and recycling of the pickling bath solution. The organic inhibitor degrades into removable byproducts, and the ferric chloride can be regenerated. This allows the majority of the hydrochloric acid and additives to be recovered and reused, significantly reducing raw material consumption and waste generation compared to traditional single-use acid baths, while maintaining high surface cleaning quality
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 achieves high-quality pickling with reduced treatment duration, lower plant requirements, and significant reduction in pollutant emissions and waste, allowing for over 80% removal of scale and dechromatized steel, and enables recycling of hydrochloric acid and metal recovery.
Implementation Method 1
an electrolytic pickling treatment in alternating current in an aqueous electrolytic solution of HCl comprising at least Fe3+
Implementation Method 2
the removal of the scale and of the dechromatized layer, there is also surface oxidation of the laminate
Implementation Method 3
This step is generally carried out by immersing the laminates in acid baths with high oxidizing capability, such as the baths of mixtures of mineral acids
Implementation Method 4
the protective layer of chromium oxide forms on the surface of the laminate
Data Source
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AI summary
The present invention refers to a method for treating in continuous the surface of a laminate made of stainless steel that comprises at least the steps of: (a) subjecting said laminate to an electrolytic pickling treatment in alternating current, in an aqueous electrolytic solution comprising at least HCl and Fe3+ ions; (b) subjecting said electrolytically pickled laminate to a chemical pickling treatment in an aqueous chemical pickling solution comprising at least HCl and Fe3+ ions; (c) subjecting said chemically pickled laminate to a surface finishing and surface passivation treatment.