CLADDING TECHNOLOGY SHANXI CO., LTDExperimental Study on Magnetic Control of Strip Cladding Current
Overview of the Topic
Strip cladding, also known as submerged arc strip cladding, is a widely used process for producing bimetallic clad plates in the pressure vessel and heat exchanger industries. The process involves feeding a metal strip and a backing strip through a submerged arc welding pool, creating a metallurgical bond between the two materials. The stability and control of the welding current directly affect the quality of the bond line and the uniformity of the clad layer. This literature presents an experimental investigation into magnetic control techniques for optimizing strip cladding current characteristics.
Core Technical Content
The fundamental challenge in strip cladding is maintaining a stable arc and uniform current distribution across the strip width. Variations in current density lead to uneven melting, resulting in bond defects such as lack of fusion, inclusions, and intermetallic compound formation. The literature proposes a magnetic control approach that uses external magnetic fields to influence the arc plasma and current distribution within the welding pool.
The following table summarizes the experimental parameters investigated in the study:
| Parameter | Range Tested | Optimal Value | Effect on Quality |
|---|---|---|---|
| Welding current (A) | 600–1200 | 850–950 | Controls melt depth and bond strength |
| Arc voltage (V) | 25–35 | 28–32 | Affects arc stability and penetration |
| Travel speed (m/h) | 15–40 | 25–30 | Influences dilution and cooling rate |
| Magnetic field strength (mT) | 0–50 | 15–25 | Controls current distribution uniformity |
| Strip thickness (mm) | 1.0–3.0 | 1.5–2.0 | Balances bond strength and productivity |
| Backing strip composition | Mild steel | Low-carbon steel | Provides thermal mass and support |
Magnetic Control Mechanism
The study explains that applying a transverse magnetic field to the welding arc induces electromagnetic forces on the molten metal in the welding pool. These forces, described by the Lorentz force equation F = J × B, redirect the current flow and modify the temperature distribution within the pool. The key findings include:
- A transverse magnetic field of 15–25 mT effectively suppresses arc wandering and improves current distribution uniformity across the strip width.
- The magnetic field reduces the lateral temperature gradient in the welding pool, leading to a more uniform fusion line and reduced risk of lack of fusion defects.
- The optimal magnetic field strength depends on the welding current; higher currents require proportionally stronger magnetic fields to maintain control.
Experimental Results and Defect Analysis
The experimental results demonstrate significant improvements in clad plate quality when magnetic control is applied. The following table compares the quality metrics with and without magnetic control:
| Quality Metric | Without Magnetic Control | With Magnetic Control (20 mT) | Improvement |
|---|---|---|---|
| Bond strength (MPa) | 280–320 | 340–380 | 15–20% |
| Bond line uniformity (±mm) | ±0.5 | ±0.2 | 60% |
| Lack of fusion defects (%) | 3–5% | <0.5% | 85–90% |
| Intermetallic compound thickness (μm) | 8–12 | 4–7 | 35–40% |
| Surface flatness (mm/m) | 0.8–1.5 | 0.3–0.6 | 50–60% |
The microstructural analysis reveals that magnetic control reduces the formation of brittle intermetallic compounds at the bond line. In stainless steel/carbon steel clad plates, the intermetallic phase (Fe-Cr intermetallics) thickness is reduced from approximately 10 μm to 5 μm, which significantly improves the ductility and toughness of the bond line. This is attributed to the more uniform temperature distribution that slows down the diffusion-driven intermetallic formation kinetics.
Engineering Practice Implications
The study highlights several practical considerations for implementing magnetic control in strip cladding production:
- Magnet configuration: Permanent magnets or electromagnets can be used, with electromagnets offering adjustable field strength. The magnets should be positioned perpendicular to the welding direction and at a distance of 20–50 mm from the arc.
- Process integration: The magnetic control system must be synchronized with the strip feeding and torch travel mechanisms to maintain consistent field application throughout the welding pass.
- Cost-benefit analysis: While magnetic control systems add equipment cost, the reduction in defects and rework leads to significant savings in production costs and improved yield rates.
- Material compatibility: The magnetic control approach is applicable to various material combinations including stainless steel/carbon steel, nickel alloy/carbon steel, and titanium/carbon steel clad plates.
Study Insights and Implications
This literature presents an innovative approach to improving strip cladding quality through electromagnetic field manipulation. The key insight is that the welding pool is not merely a thermal phenomenon but also an electromagnetically active system that can be deliberately controlled. Engineers should recognize that traditional process optimization approaches focusing solely on electrical parameters and travel speed may leave significant quality improvements untapped. The magnetic control technique represents a paradigm shift toward multi-physics process control, where thermal, electromagnetic, and fluid dynamic aspects are simultaneously optimized. Future research should explore the combination of magnetic control with other advanced techniques such as pulsed current welding and ultrasonic vibration to achieve even higher quality clad plates for critical pressure vessel applications.