CLADDING TECHNOLOGY SHANXI CO., LTDModification of Strip Cladding Automatic Equipment
Literature Overview and Engineering Context
Strip cladding, also known as strip metalizing or electroslag weld overlay, is a well-established process for producing clad plates with uniform, defect-free overlay layers. The process involves passing an electric current through a strip of cladding metal (the consumable) and a backing strip, with an electric arc maintained between the strip and the base metal. The molten pool is covered by a granular flux, which protects the weld from atmospheric contamination and provides thermal insulation. This study focuses on the modification and retrofitting of an existing strip cladding automatic welding machine to improve productivity, reduce defects, and expand the range of applicable materials.
Core Technical Analysis
Original Equipment Configuration and Limitations
The original strip cladding machine, while functional for standard carbon steel and stainless steel cladding applications, exhibited several limitations that restricted its applicability in modern manufacturing environments:
- Limited travel speed range (maximum 2.0 m/min), constraining throughput for large-format plates
- Manual flux feeding mechanism with inconsistent flux coverage, leading to localized oxidation and slag inclusions
- Fixed electrode holder geometry, preventing optimization for different strip thicknesses and cladding configurations
- Absence of real-time monitoring of arc parameters, making process control reactive rather than proactive
- Manual torch positioning with limited repeatability, resulting in inconsistent weld bead profiles
Key Modification Areas
The retrofitting program addressed five major subsystems of the strip cladding machine:
- Travel drive system: Upgraded from a single-motor mechanical drive to a dual-motor servo drive system with independent speed control for each axis. This enabled variable travel speeds from 0.5 to 4.0 m/min with programmable acceleration and deceleration profiles.
- Flux feeding system: Replaced the gravity-fed hopper with a pneumatic conveyor system equipped with a flow meter and feedback control loop. This ensured consistent flux coverage across the entire welding length.
- Torch assembly: Redesigned the torch holder to accommodate adjustable electrode angles (15° to 45° from vertical) and incorporated a water-cooled copper nozzle for extended service life.
- Process monitoring: Integrated a real-time data acquisition system to monitor and record arc voltage, arc current, travel speed, and flux flow rate, with automatic alarm and shutdown capabilities for out-of-tolerance conditions.
- Workpiece support: Added a vacuum table system for precise positioning and clamping of large-format plates, reducing distortion and improving weld consistency.
Performance Comparison
The following table compares the performance of the original and modified equipment:
| Parameter | Original Equipment | Modified Equipment | Improvement |
|---|---|---|---|
| Max travel speed | 2.0 m/min | 4.0 m/min | 100% |
| Flux coverage uniformity | ±15% | ±3% | 80% reduction in variation |
| Arc voltage stability | ±2.0 V | ±0.5 V | 75% improvement |
| Weld bead width consistency | ±8 mm | ±2 mm | 75% improvement |
| Defect rate (per 100 m) | 12 defects | 2 defects | 83% reduction |
| Daily productivity (m²) | 8 m² | 18 m² | 125% increase |
Process Optimization and Welding Parameters
Parameter Selection for Different Cladding Configurations
The modified equipment enabled systematic optimization of welding parameters for various strip cladding configurations. The following table presents the recommended parameter ranges:
| Application | Strip Thickness (mm) | Current (A) | Voltage (V) | Speed (m/min) | Flux Rate (kg/m) |
|---|---|---|---|---|---|
| SS304/CS (1 pass) | 1.0 | 800-1000 | 18-22 | 1.5-2.5 | 0.8-1.2 |
| SS316L/CS (2 passes) | 0.8 | 700-900 | 16-20 | 1.0-2.0 | 0.6-1.0 |
| Inconel 625/CS (1 pass) | 1.2 | 900-1100 | 20-24 | 1.0-1.8 | 1.0-1.5 |
| Duplex 2205/CS (2 passes) | 1.0 | 850-1050 | 19-23 | 1.2-2.0 | 0.9-1.3 |
Defect Analysis and Root Cause Investigation
Using a systematic approach based on the 5W2H method, the following defect patterns were identified and addressed:
- What: Slag inclusions were the most common defect in the original equipment, occurring at a rate of 8 per 100 m
- Where: Predominantly at the start and end of each weld pass, where flux coverage was inconsistent
- Why: The gravity-fed flux system could not maintain adequate coverage at varying travel speeds
- When: During the first 50 mm and last 50 mm of each pass
- How: Replaced with pneumatic flux feeding and added lead-in/lead-out tabs with pre-wetted flux
- Who: Operator training was enhanced with visual aids showing proper flux application
- Which: The pneumatic flux system proved to be the single most impactful modification
Engineering Practice Integration
Implementation Challenges and Lessons Learned
The retrofitting project encountered several challenges that are instructive for similar equipment modification programs:
- Integration of legacy systems with modern controls: The original machine used relay-based control logic, which required complete replacement with a PLC-based system. The integration of the new servo drives with the existing mechanical structure required custom mounting brackets and alignment.
- Operator training and acceptance: Operators initially resisted the modified equipment due to unfamiliarity with the new interface. A comprehensive training program, including hands-on sessions and visual reference guides, was essential for successful adoption.
- Consumable compatibility: The modified equipment required specific strip and flux combinations that were not always readily available. Developing a qualified consumable list through welding procedure qualification (per NB/T 47014 or ASME IX) was a prerequisite for production use.
Quality Assurance Protocol
The modified equipment is supported by a comprehensive quality assurance protocol that includes:
- Pre-weld inspection of base metal surface condition and strip material certification
- In-process monitoring of arc parameters with automatic logging
- Post-weld visual inspection for surface defects and slag removal verification
- Periodic metallographic examination (every 100 m of production) for microstructural assessment
- Bond strength testing (peel test or shear test per ASTM G144) at defined intervals
- NDT (MT or UT) for critical applications requiring defect-free cladding
Study Insights and Conclusions
The modification of strip cladding automatic equipment demonstrates that significant improvements in productivity, quality, and flexibility can be achieved through targeted retrofits rather than complete equipment replacement. The key success factors were the systematic identification of process bottlenecks, the selection of cost-effective modern components, and the establishment of a robust quality assurance framework. For manufacturing facilities operating legacy strip cladding equipment, this study provides a practical roadmap for modernization that can yield substantial returns on investment through reduced defect rates, increased throughput, and expanded material applicability. The experience also underscores the importance of operator training and consumable qualification in realizing the full benefits of equipment upgrades.