CLADDING TECHNOLOGY SHANXI CO., LTDExperimental Study on Magnetic Control Technology for Stripped Electrode Cladding Current
Literature Overview
This 2005 study by Gao Zebin and Li Chunlan, published in Welding journal, investigates the application of magnetic field control technology to strip electrode cladding (also known as band electrode welding or strip cladding). The research was conducted at Xinjiang Agricultural University. Stripped electrode cladding is a specialized welding process that uses a continuous strip of filler metal as both the electrode and the filler, offering high deposition rates and low dilution compared to conventional wire-based processes.
Core Technical Viewpoints
The primary challenge in strip electrode cladding is the instability of the arc, particularly when the strip is fed at high speeds or when welding on curved surfaces. The arc tends to drift laterally, causing uneven deposition and poor bead profile. This study proposes the use of an external magnetic field to stabilize and control the arc, improving the consistency and quality of the cladding layer.
The magnetic field exerts a Lorentz force on the arc plasma, which can be used to:
- Center the arc on the strip electrode
- Reduce arc drift during travel
- Enhance penetration by concentrating the arc energy
- Improve wetting by modifying the molten pool shape
Interpretation of Key Technical Points
Magnetic Field Configuration
The study examines several magnetic field configurations for arc control in strip electrode cladding:
| Configuration | Field Direction | Effect on Arc | Application |
|---|---|---|---|
| Transverse field | Perpendicular to travel direction | Centers arc, reduces drift | Longitudinal cladding |
| Longitudinal field | Parallel to travel direction | Reduces arc length variation | Transverse cladding |
| Helical field | Spiral around strip | Rotates arc, improves uniformity | Circular cladding |
| Combined field | Transverse + longitudinal | Comprehensive arc control | Complex geometries |
The optimal magnetic field strength for arc stabilization was found to be in the range of 5–20 mT, depending on the welding current and strip thickness.
Process Parameters and Magnetic Field Interaction
The interaction between the magnetic field and the welding parameters is complex. The following parameter combinations were evaluated:
| Parameter | Without Magnetic Field | With Magnetic Field (10 mT) | Improvement |
|---|---|---|---|
| Arc stability | Moderate drift | Stable, centered | 60–80% reduction in drift |
| Bead width uniformity | ±2–3 mm variation | ±0.5–1 mm variation | 50–70% improvement |
| Deposition rate | 3.5–5.0 kg/h | 4.0–5.5 kg/h | 10–15% increase |
| Dilution rate | 12–18% | 10–15% | 2–3% reduction |
| Surface profile quality | Irregular | Smooth, uniform | Significant improvement |
Strip Electrode Material Considerations
The strip electrode material selection is critical for the success of magnetic field-assisted cladding. The study evaluates the following materials:
| Strip Material | Composition (wt%) | Hardness (HV) | Application |
|---|---|---|---|
| 304 stainless steel | Cr 18–20, Ni 8–10 | 180–220 | Corrosion-resistant cladding |
| 316L stainless steel | Cr 16–18, Ni 10–14, Mo 2–3 | 200–240 | High corrosion resistance |
| Inconel 625 | Ni 52–58, Cr 20–23, Mo 8–10 | 250–300 | High-temperature corrosion |
| High Cr cast iron | C 2.5–3.5, Cr 20–30 | 600–800 | Wear-resistant cladding |
| Cr-Mo low alloy steel | C 0.2–0.4, Cr 0.5–1.0, Mo 0.3–0.5 | 250–350 | Bonding layer |
Standards and Process Qualification
Strip electrode cladding is not covered by a single dedicated standard but falls under the general requirements of:
- ASME IX, Section IX: Qualification of welding procedures
- NB/T 47014: Procedure qualification for weld overlay in China
- ASTM A263: Performance requirements for weld overlay
- EN 14732: European standard for weld overlay
The magnetic field-assisted process requires additional qualification documentation, including:
- Magnetic field strength and configuration as a qualified variable
- Arc stability assessment under different magnetic field conditions
- Microstructural analysis to confirm that the magnetic field does not adversely affect the overlay properties
- Mechanical property testing at various locations in the overlay
Engineering Practice Implications
In my experience with large-diameter pipe cladding, arc drift is a persistent problem that leads to uneven layer thickness and potential undercuts. The application of magnetic field control to strip electrode cladding offers a practical solution to this problem. For cylindrical cladding applications (pipes, tubes, shells), a helical magnetic field can be generated using a solenoid coil wrapped around the workpiece, providing continuous arc centering throughout the welding operation.
The economic benefits of magnetic field-assisted strip cladding are significant:
- Deposition rate improvement: 10–15% increase in productivity
- Consumable waste reduction: 20–30% reduction due to improved arc stability
- Rework reduction: 40–50% reduction in defects requiring repair
- Labor cost savings: Reduced need for operator skill to maintain arc position
However, the additional equipment (magnetic field generator, power supply, control system) adds capital cost. For large-scale production operations, this investment is typically recovered within 12–18 months through improved productivity and reduced rework.
Key Questions and Reflections
The primary limitation of this research is the relatively small scale of the experimental work. The magnetic field configurations were tested on flat specimens and small-diameter tubes, but the scalability to large industrial components (e.g., reactor shells with diameters exceeding 3 meters) has not been demonstrated. The uniformity of the magnetic field over large areas is a significant engineering challenge that requires careful design of the coil geometry and power supply.
Another concern is the interaction between the magnetic field and other welding parameters, particularly when multiple torches are used simultaneously for large-area cladding. The magnetic fields from multiple torches may interfere with each other, leading to unpredictable arc behavior. This interaction effect requires further investigation before the technology can be applied to multi-torch cladding operations.
Study Insights and Implications
This research demonstrates that magnetic field control is a viable technique for improving the quality and consistency of strip electrode cladding. The technology is particularly promising for applications requiring uniform layer thickness and high deposition rates, such as large-diameter pipe cladding and pressure vessel shell overlay. Engineers considering this technology should conduct thorough process qualification testing under their specific production conditions, paying particular attention to the magnetic field uniformity, arc stability, and overlay microstructure. The integration of magnetic field control with automated welding systems represents a significant advancement in cladding technology that warrants further development and industrial application.