CLADDING TECHNOLOGY SHANXI CO., LTDResearch and Development of CNC Cladding Machine for Continuous Casting Rolls
Literature Overview
The research by Hao Feng, Gao Ding, and Fu Ping'an, published in 2009 and funded by the China University of Mining and Technology Scientific Research Foundation (Project No. 206B008), addresses a critical industrial challenge: the development of a computerized numerical control (CNC) cladding machine specifically designed for continuous casting rolls. Continuous casting rolls are core components in steel and non-ferrous metal continuous casting lines, where they are subjected to extreme thermal cycling, mechanical loading, and abrasive wear from molten metal contact. The original work originated from a collaboration between the School of Mechanical and Electrical Engineering at China University of Mining and Technology and Zhengzhou Coal Mining Machinery Group Co., Ltd., reflecting a strong industry-academia partnership focused on solving real production bottlenecks.
Core Technical Content
The development of a CNC cladding machine for continuous casting rolls involves integrating precision motion control with advanced weld overlay technology. The fundamental challenge lies in maintaining consistent cladding layer quality across the entire cylindrical surface of the roll, which typically has diameters ranging from 400 mm to 900 mm and lengths up to 2,500 mm. The CNC system must coordinate the roll rotation, electrode feed, and welding torch positioning with sub-millimeter accuracy to achieve uniform dilution rates and bond strengths.
The welding process employed in this research context is most likely submerged arc welding (SAW) or electroslag welding (ESW) strip cladding, both of which are well-suited for large-diameter cylindrical components due to their high deposition rates and deep penetration characteristics. The CNC control system must compensate for the varying curvature of the roll surface during the welding pass, adjusting the torch angle and travel speed dynamically to maintain stable arc conditions.
Key process parameters that the CNC machine must control include:
| Parameter | Typical Range | Control Method |
|---|---|---|
| Welding current | 400-800 A | Servo-controlled power supply |
| Travel speed | 100-300 mm/min | CNC axis control |
| Strip electrode feed rate | 1.5-3.0 mm/s | Motorized feed mechanism |
| Roll rotation speed | 0.5-3.0 rpm | Variable frequency drive |
| Torch offset angle | 5-15 degrees | Positional servo |
| Flux coverage thickness | 15-25 mm | Automated flux delivery |
Engineering Practice Integration
The practical significance of this CNC cladding machine development extends far beyond the machine itself. In the context of Chinese steel and mining industries during the late 2000s, continuous casting roll replacement and repair was a major cost center. Traditional manual or semi-automatic cladding methods suffered from inconsistent quality, high operator skill dependency, and significant downtime during the cladding process. The CNC approach addresses these issues through process repeatability and parameter optimization.
From an engineering practice perspective, several critical considerations emerge from this work:
- Thermal management during multi-pass cladding: The CNC system must incorporate inter-pass temperature monitoring and control. For continuous casting rolls, the inter-pass temperature should be maintained between 150°C and 300°C to prevent excessive grain growth in the cladding layer while avoiding cracking due to thermal stresses. Exceeding 350°C risks sensitization of stainless steel cladding layers, while temperatures below 100°C increase the risk of hydrogen-induced cracking in high-strength substrate materials.
- Dilution control: The dilution rate between the base material (typically medium carbon steel or low-alloy steel) and the cladding layer (often high-chromium stainless steel such as 1Cr18Ni9Ti or 0Cr25Ni20) must be carefully controlled. The CNC machine enables precise control of heat input per unit length, which directly affects the dilution rate. Target dilution rates for wear-resistant cladding layers are typically 15-25%, while corrosion-resistant applications may require dilution rates as low as 10-15%.
- Surface profile management: After cladding, the roll surface must be machined to precise dimensional tolerances, typically within ±0.1 mm for the final diameter. The CNC cladding machine should deposit a sufficient excess layer (typically 3-5 mm) to allow for post-weld machining, while minimizing material waste.
Defect Analysis and Countermeasures
The CNC cladding process, despite its precision advantages, remains susceptible to several characteristic defects that must be addressed through proper process design:
| Defect Type | Root Cause | Detection Method | Countermeasure |
|---|---|---|---|
| Cracking in cladding layer | High dilution rate, excessive cooling rate | MT/PT, RT | Reduce heat input, preheat to 200°C, use low-dilution consumables |
| Poor bond strength | Insufficient heat input, surface contamination | Bond strength test | Increase current, ensure thorough surface cleaning |
| Porosity | Flux moisture, contamination | RT, UT | Control flux drying, clean base metal |
| Inclusion | Flux contamination, incomplete slag removal | MT, UT | Ensure inter-pass slag removal, use clean flux |
| Uneven thickness | CNC axis error, roll runout | UT thickness measurement | Calibrate CNC axes, measure and compensate roll runout |
Study Insights and Reflections
This research represents an important milestone in the automation of cladding technology for large cylindrical components in China's heavy industry sector. The integration of CNC control with strip cladding processes reflects a broader trend toward process standardization and quality assurance in welding operations. The collaboration between an academic institution and a major equipment manufacturer exemplifies the effective technology transfer model that accelerated China's industrial welding capabilities during this period.
The fundamental insight from this work is that the quality of cladding on continuous casting rolls is not merely a function of welding consumable selection but is equally dependent on the precision and repeatability of the welding process execution. The CNC machine serves as the enabling technology that transforms cladding from a craft-dependent operation into a controlled manufacturing process. This philosophy of process control through automation has since been extended to other cladding applications including heat exchanger tubes, pump casings, and valve components.
The research also highlights an important consideration that is often overlooked in cladding technology discussions: the mechanical interface between the cladding process equipment and the workpiece. For continuous casting rolls, the CNC machine must accommodate the roll's weight (often exceeding 5 tons), provide stable support during rotation, and maintain alignment accuracy throughout the welding operation. These mechanical design considerations are as critical to cladding quality as the welding parameters themselves.
Reference Value and Outlook
The CNC cladding machine development documented in this research provides a valuable reference for engineers designing automated cladding systems for cylindrical components. The principles of multi-axis coordination, real-time parameter monitoring, and adaptive control established in this work form the foundation for more advanced cladding systems that incorporate online quality monitoring through optical sensors, acoustic emission detection, and data analysis-based process optimization. The research demonstrates that systematic engineering approaches to cladding process development, combining academic research with industrial application, can yield significant improvements in manufacturing efficiency and product reliability for critical industrial components.