Chromium Coating Stripes Elimination via Electrolyte Control
Solution Overview
Problem
Electroplated chromium coatings on uncoated steel strips often exhibit a stripy appearance at lower line speeds, which is visually undesirable despite having no adverse effects on performance, and existing methods to address this issue have been ineffective.
Innovation Solution
A method for electrolytically depositing a chromium metal-chromium oxide coating on steel strips using an electrolyte solution with a trivalent chromium compound, free of chloride ions and boric acid, with a specific pH range of 1.5 to 3.0, a complexing agent to Cr 3+ molar ratio of 1:1 to 2.5:1, and a chromium concentration of up to 250 mM, and a plating temperature between 30 and 70 °C, utilizing an anode with a catalytic coating of iridium oxide to reduce Cr 3+ ion oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If electroplating is performed at lower line speeds, then the chromium coating can be deposited, but the coated product exhibits a stripy appearance that is visually undesirable
Solution Approach 1:
The patent applies parameter changes by removing chloride ions and boric acid buffering agents from the electrolyte solution, adjusting the pH to a specific range (1.5-3.0), and optimizing the complexing agent to Cr3+ molar ratio. These parameter modifications eliminate the stripy appearance while enabling effective plating even at lower line speeds, thus resolving the contradiction between surface appearance quality and productivity.
2Productivity
If conventional electrolyte solutions containing chloride ions and boric acid are used, then the plating process can proceed, but the coated product shows stripy appearance
Solution Approach 1:
The patent applies the extraction principle by removing harmful components (chloride ions and boric acid buffering agents) from the electrolyte solution. This elimination of specific substances prevents the formation of stripy appearance on the coated product while maintaining efficient plating process operation, thereby resolving the contradiction between productivity and surface appearance quality.
3Reliability
If anode oxidation of Cr3+ ions occurs, then the electrolyte composition changes, but this leads to increased dragout losses and reduced current efficiency
Solution Approach 1:
The patent applies the 'blessing in disguise' principle by using an anode material (iridium oxide or mixed metal oxide coating) that prevents the harmful oxidation of Cr3+ ions. This conversion of a potentially harmful process (anode oxidation) into a beneficial one (maintaining electrolyte stability) reduces dragout losses and improves current efficiency while maintaining reliable electrolyte composition.
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 results in a shiny, stripy-free surface and improves the surface appearance, increasing current efficiency and reducing dragout losses, while allowing for effective application of organic coatings with enhanced adherence.
Implementation Method 1
an anode comprising a catalytic coating of iridium oxide or a mixed metal oxide for reducing or eliminating the oxidation of Cr 3+
Implementation Method 2
electrolytically depositing the chromium metal - chromium oxide coating on blackplate
Implementation Method 3
as disclosed in WO2014202316-A1, it occurs occasionally that at lower line speeds, the resulting coated product has a stripy appearance
Data Source
Figure 1~2
Figure 3~4
AI summary
This invention relates to a method for electroplating uncoated blackplate with a plating layer and an improvement thereof. The invention also relates to a method wherein the coated blackplate is further coated on one or both sides by a film lamination step or a direct extrusion step, and to the use of said coated blackplate in a process to produce containers for packaging purposes.