CLADDING TECHNOLOGY SHANXI CO., LTDHigh-Speed Strip Cladding Process and Equipment Development
Literature Overview
The study by Li Chunxu, Wang Xijing, Wei Jikun, and Li Heqi from Gansu University of Technology, published in the Welding Journal in 1991, represents an early yet pioneering investigation into high-speed strip cladding processes and associated equipment. This work emerged during a period when Chinese industrial sectors — particularly in pressure vessel fabrication, heat exchanger manufacturing, and wear-resistant component production — were increasingly demanding advanced cladding technologies capable of depositing uniform, defect-free overlay layers at production-relevant speeds. The authors addressed the fundamental challenge of reconciling deposition rate with metallurgical quality, a trade-off that has remained central to cladding engineering for decades.
Core Technical Content and Process Analysis
The research focuses on the development of a high-speed strip cladding system that integrates wire feeding mechanisms, arc control circuits, and traverse systems to achieve continuous overlay deposition at elevated travel speeds. The key innovation lies in the design of a dedicated wire-feeding and gun positioning apparatus that maintains consistent arc parameters despite the increased deposition rate. The process operates on principles analogous to submerged arc welding (SAW) and electroslag welding (ESW) overlay techniques but introduces modifications to accommodate higher productivity requirements.
The following table summarizes the typical process parameters and equipment features discussed in the study:
| Parameter | Typical Range | Engineering Significance |
|---|---|---|
| Travel speed | 300–800 mm/min | Determines deposition rate and dilution |
| Wire feed speed | 15–45 m/min | Controls metal deposition volume |
| Arc voltage | 22–32 V | Affects arc stability and penetration |
| Welding current | 400–700 A | Governs heat input and dilution |
| Strip width | 12–25 mm | Matches substrate geometry |
| Flux type | Rutile or basic | Influences slag fluidity and protection |
The authors emphasize that maintaining arc stability at high speeds requires precise synchronization between wire feeding and gun traverse. Any deviation in feed rate results in arc length variation, which in turn causes porosity, undercuts, or incomplete fusion at the bond line. The equipment design incorporates a mechanical linkage system that ensures the wire tip remains at a fixed distance from the substrate regardless of traverse speed fluctuations.
Metallurgical Considerations
A critical aspect of the study is the analysis of dilution behavior in high-speed strip cladding. At elevated deposition rates, the heat input per unit length decreases, which theoretically reduces dilution of the substrate into the overlay layer. However, the authors observed that excessively high speeds lead to incomplete melting of the preceding weld pass, resulting in poor interpass bonding and increased susceptibility to interfacial cracking. The optimal speed window was identified as the range where the trailing edge of the weld pool maintains sufficient temperature to remelt the previous pass by 30–50%, ensuring metallurgical continuity without excessive dilution.
The microstructure of the deposited overlay was examined through metallographic analysis. At moderate speeds, the overlay exhibits a fine-grained columnar structure with good toughness. At the upper end of the speed range, equiaxed grains begin to appear in the upper portions of the deposit, indicating rapid solidification. This microstructural evolution has direct implications for mechanical properties, particularly hardness uniformity and resistance to thermal fatigue.
Engineering Practice and Quality Control
From a quality assurance perspective, the study highlights several critical inspection points for high-speed strip cladding operations:
- Visual inspection (VT): Checks for surface uniformity, undercut, and spatter accumulation along the strip edges.
- Magnetic particle testing (MT): Essential for detecting transverse cracks at the bond line, particularly in nickel-based alloy overlays where HAZ cracking is prevalent.
- Ultrasonic testing (UT): Used to verify bond integrity and detect lack of fusion between successive passes.
- Hardness profiling: Hardness traverses from the substrate through the bond line to the overlay surface confirm dilution levels and microstructural transitions.
The authors also discuss the importance of preheating and interpass temperature control. For stainless steel overlays on carbon steel substrates, a preheat temperature of 150–200°C is recommended to reduce residual stresses and minimize the risk of hot cracking. Interpass temperatures should not exceed 250°C for austenitic stainless steel overlays to avoid sensitization in the heat-affected zone.
Study Insights and Reflections
Reflecting on this 1991 work in the context of modern cladding practice, I find it remarkable how accurately the authors identified the fundamental trade-offs that still govern process optimization today. The synchronization of wire feed and traverse remains the single most critical control parameter in any high-speed strip cladding operation, whether the process is now executed by automated wire-feed systems or robotic SAW overlay machines. The equipment design philosophy — mechanical reliability over electronic complexity — was pragmatic for the era but also proved durable; many modern automated cladding systems still employ similar mechanical linkage concepts for gun positioning.
One area where the study could be extended is the quantitative modeling of dilution as a function of process parameters. The authors provided empirical correlations but did not develop a predictive thermal model. Today, finite element thermal analysis (FEA) can be applied to predict dilution profiles with high accuracy, enabling process windows to be defined before physical trials. Nevertheless, the empirical data presented remain valuable as benchmark values for validating computational models.
The study also raises the question of how high-speed strip cladding compares with more modern techniques such as plasma transferred arc (PTA) cladding and laser cladding in terms of productivity and quality. While PTA and laser cladding offer superior dilution control and finer microstructures, they operate at significantly lower deposition rates. For large-area, thick-overlay applications such as pressure vessel heads and heat exchanger tubesheets, high-speed strip cladding may still be the most cost-effective solution, particularly when the overlay thickness exceeds 5 mm.
This literature serves as an important historical reference for engineers seeking to understand the evolution of cladding technology in China. It demonstrates that the fundamental principles of arc stability, dilution control, and bond line integrity are timeless, even as equipment and monitoring technologies continue to advance.