Electrolytic Hot-Strip Pickling with Cathodic-Anodic Scale Removal
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Solution Overview
Problem
Existing methods for electrolytically pickling hot strips often result in incomplete scale removal, jagged surfaces, and increased grain boundary oxidation, particularly in high-strength steels, due to the limitations of direct current pickling and prolonged processing times.
Innovation Solution
A method involving sequential electrolytic pickling in a first acidic bath with cathodic polarization to mechanically flake off scale, followed by a second acidic bath with anodic polarization to remove surface defects, thereby achieving a technically pure surface by accelerating scale removal and reducing diffusible hydrogen.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If prolonged pickling time is used to remove surface defects, then scale removal is improved, but grain boundary oxidation increases
Solution Approach 1:
The pickling process is divided into multiple sequential baths with different functions: initial pickling bath for scale removal, followed by one or more finishing pickling baths for defect removal. This segmentation allows each bath to be optimized for its specific purpose, preventing grain boundary oxidation while achieving complete scale removal and surface defect elimination.
2Device complexity
If direct current pickling is used, then the process is simpler, but scale removal is incomplete and processing time increases
Solution Approach 1:
The invention employs alternating current (AC) pickling instead of direct current (DC) pickling. The periodic reversal of current direction in AC pickling prevents polarization buildup and maintains high pickling efficiency throughout the process, enabling complete scale removal in shorter time compared to DC pickling, while the process remains relatively simple to implement.
3Productivity
If cathodic polarization is used for scale removal, then scale flaking is accelerated, but hydrogen absorption increases
Solution Approach 1:
The pickling process is segmented into distinct functional stages: an initial cathodic or amphoteric pickling bath for accelerated scale removal, followed by one or more anodic finishing baths that remove surface defects without significant hydrogen absorption. This segmentation allows the benefits of cathodic polarization to be utilized temporarily without the detrimental long-term hydrogen absorption effects.
Solution Approach 2:
The invention converts the harmful effect of hydrogen absorption during cathodic pickling into a beneficial process by immediately following it with anodic pickling. The anodic stage removes excess hydrogen and surface defects, effectively converting the previously harmful hydrogen absorption into a controlled intermediate step that accelerates overall scale removal while preventing net hydrogen damage.
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 significantly reduces surface defects, improves forming properties, and enhances fatigue strength by ensuring complete scale removal and minimizing hydrogen absorption, leading to improved surface roughness and reduced risk of liquid metal embrittlement.
Implementation Method 1
In this first pickling process, hydrogen is selectively generated at the surface to be pickled through cathodic polarization (cathodic pickling), thus promoting a primarily 'mechanical' flaking off of the scale.
Implementation Method 2
This is followed by electrolytic pickling in a second pickling bath containing an acidic medium with anodic polarization (anodic pickling). This process removes surface defects, particularly damaged grain layers and inconsistencies.
Data Source
Figure 1~3
Figure 4
AI summary
Method for electrolytic pickling of a hot strip, wherein the hot strip is first pickled in a first pickling bath containing an acidic medium with cathodic polarization and subsequently in a second pickling bath containing an acidic medium with anodic polarization.