Development of CNC Surfacing Machine for Continuous Casting Rolls

Literature Overview

The paper by Hao Feng, Gao Ding, and Fu Ping'an, published in Welding Technology (2009, Vol. 38, Issue 10, pp. 29-32), describes the design and development of a novel CNC surfacing machine specifically tailored for continuous casting rolls. The machine was developed by China University of Mining and Technology and Zhengzhou Coal Mine Machinery Group Co., Ltd., supported by the China University of Mining and Technology Research Fund (206B008). The machine features a high degree of automation and stable surfacing quality, incorporating a SINUMERIK 801 CNC system and a dual-microcomputer digital control system for the submerged arc welding process.

Core Technical Points

Machine Design and Architecture

The CNC surfacing machine was designed to address the specific requirements of continuous casting roll surfacing, which demands high geometric accuracy, uniform overlay thickness, and consistent weld quality over long cylindrical surfaces. The machine architecture integrates a conventional machine tool mechanical platform with advanced CNC control and digital welding control systems. The SINUMERIK 801 CNC system provides precise control of the machine motion, including the rotation of the roll, the axial feed of the torch, and the vertical positioning of the torch head. The dual-microcomputer digital control system for the submerged arc welding process independently manages the welding parameters including current, voltage, wire feed speed, and travel speed, ensuring that the welding process is optimized regardless of the machine motion profile.

The separation of motion control and welding process control into independent systems represents a sound engineering architecture. The CNC system focuses on geometric accuracy and repeatability, while the welding control system focuses on process stability and weld quality. This modular approach allows each subsystem to be optimized independently and facilitates troubleshooting and maintenance.

Surfacing Quality Requirements for Continuous Casting Rolls

Continuous casting rolls are subjected to extreme operating conditions including high thermal loads from molten steel, mechanical contact pressure from the solidifying shell, and corrosive attack from molten slag. The surfacing layer must provide a combination of thermal fatigue resistance, wear resistance, and corrosion resistance. The submerged arc welding process was selected because it offers high deposition rates suitable for building up thick overlay layers, good weld quality with low porosity, and the ability to achieve deep penetration for strong metallurgical bonding with the roll base material.

The CNC control ensures that the torch follows a precise helical path over the roll surface, maintaining constant overlap between adjacent passes and uniform deposition thickness. The dual-microcomputer welding control system provides real-time feedback control of welding parameters, compensating for variations in roll surface condition and environmental factors that could affect weld quality.

Process Integration and Quality Assurance

The surfacing process for continuous casting rolls involves several critical quality control checkpoints. The roll surface must be thoroughly prepared by machining or grinding to remove surface defects and provide a sound base for surfacing. The preheating temperature should be controlled to prevent cracking in the base material, which is typically a low-alloy steel. The surfacing layer thickness must be uniform across the entire roll surface to ensure consistent performance during service. Post-weld inspection should include dimensional measurement, hardness mapping, and non-destructive testing to verify weld quality.

The CNC system enables the collection and recording of process data for each surfacing operation, facilitating traceability and quality documentation. This data can be used for process optimization and to establish baseline performance data for future operations.

Integration with Engineering Practice

The development of dedicated CNC surfacing machines represents a significant advancement in the industrial application of surface engineering technology. The transition from manual or semi-automatic surfacing to fully automated CNC-controlled surfacing addresses several critical challenges: operator variability, process consistency, and productivity. In the context of continuous casting rolls, where the cost of roll replacement and the associated production downtime are substantial, the investment in automated surfacing equipment is economically justified by the improved quality consistency and extended service life of the refurbished rolls.

The SINUMERIK 801 CNC system is a well-established industrial platform with proven reliability in machine tool applications. Its integration into a surfacing machine demonstrates the versatility of CNC technology and its applicability to welding and surfacing operations. The dual-microcomputer welding control system reflects the engineering principle that welding process control requires specialized algorithms and real-time response capabilities that are distinct from general-purpose motion control.

Study Insights and Implications

This study exemplifies the integration of mechanical engineering, control systems engineering, and welding metallurgy in the development of specialized industrial equipment. The key insight is that surfacing quality is determined not only by the welding process parameters but also by the precision and consistency of the machine motion that positions the torch relative to the workpiece. The CNC system ensures geometric precision, while the digital welding control ensures process stability, and together they produce surfacing layers of consistent quality that meet the demanding requirements of continuous casting roll service. The modular system architecture adopted in this design is a best practice that facilitates future upgrades and maintenance, and the approach can be extended to other cylindrical component surfacing applications in the steel industry.