Improvement of Combined Roll Body Surfacing Device

Literature Overview

The 2009 paper by Wang Yijin, published in Mining Machinery, describes the improvement of a combined roll body surfacing device developed at Shanghai Meishan Steel Company's Technical Center. The abstract indicates that large roll bodies are critical components in mining, metallurgy, and cement construction industries, and that surfacing for surface hardening or repair offers significant economic value. The authors note that different types of large roll bodies require different surfacing processes, often involving preheating, interpass insulation, and sometimes interpass or post-weld heat treatment. The paper focuses on the design and improvement of a specialized device that integrates these process steps into a single, efficient system.

This work is particularly relevant given the widespread use of large rolls in industrial processes such as ore dressing, steel rolling, cement grinding, and mineral processing. These rolls are typically large-diameter cylinders (1–3 meters in diameter) with lengths of 2–10 meters, and they are subjected to severe wear, impact, and sometimes corrosive conditions. Surfacing provides a cost-effective means of restoring or enhancing their performance without complete replacement.

Core Technical Content

The combined roll body surfacing device described in the paper integrates several functions into a single system:

Roll rotation and positioning: The device provides precise rotation and axial positioning of the roll body to ensure uniform surfacing coverage around the entire circumference and along the length.
Preheating system: Integrated heating elements (typically electric resistance heaters or induction coils) provide uniform preheating of the roll body to the required temperature before surfacing begins. The preheat temperature depends on the base material and the surfacing consumable, typically ranging from 200–400 °C.
Interpass insulation: Insulating materials or heated enclosures maintain the interpass temperature during multi-pass surfacing, preventing excessive cooling that could cause cracking or poor bonding.
Surfacing torch mounting: The device provides stable mounting and positioning of the surfacing torch (SMAW, SAW, plasma, or oxy-fuel) with precise control of torch angle, stand-off distance, and travel speed.
Post-weld heat treatment: Some configurations include integrated heating and cooling systems for post-weld stress relief or tempering, eliminating the need to transfer the roll to a separate furnace.

The improvement described in the paper likely involved enhancements to one or more of these subsystems to improve efficiency, quality, or versatility. Common improvements include:

Automated torch tracking: Incorporating sensors and feedback control to maintain consistent torch position and travel speed, reducing operator skill requirements and improving overlay uniformity.
Enhanced heating uniformity: Using multiple heating zones with independent temperature control to achieve more uniform preheating and interpass temperature maintenance across the entire roll surface.
Improved insulation: Using advanced insulating materials or active heating to reduce heat loss and maintain interpass temperature more effectively, particularly in outdoor or drafty environments.
Modular design: Designing the device with interchangeable components to accommodate different roll sizes and surfacing processes, improving versatility and reducing changeover time.

Process Analysis and Technical Parameters

The surfacing of large roll bodies presents unique challenges compared to smaller components:

Thermal mass: The large thermal mass of the roll body means that preheating takes significant time and energy, and cooling rates are relatively slow. This can be advantageous for reducing cracking risk but disadvantageous for productivity.
Geometry: The cylindrical geometry requires the surfacing torch to follow a helical path to achieve uniform coverage, which requires precise control of both rotation and axial feed.
Access: Large rolls may have limited access for manual surfacing, particularly at the ends or near the shaft journals. The combined device provides better access and operator comfort.
Quality consistency: Manual surfacing of large rolls is prone to inconsistency, with variations in overlay thickness, hardness, and defect density. Automated or semi-automated devices improve consistency.

The typical surfacing parameters for large roll bodies include:

Parameter	Typical Value	Notes
Preheat temperature	200–400 °C	Depends on base material and consumable
Interpass temperature	150–350 °C	Maintained throughout multi-pass deposition
Surfacing process	SAW, plasma, or SMAW	SAW preferred for high deposition rate
Overlay thickness	5–15 mm	Depends on application and wear rate
Post-weld treatment	Stress relief at 550–650 °C	Optional, depending on requirements
Surfacing speed	100–400 mm/min	Depends on process and consumable

Engineering Practice and Economic Analysis

The economic benefits of using a combined roll body surfacing device are substantial:

Reduced labor cost: Automated or semi-automated surfacing reduces the number of operators required and decreases the time spent on each roll.
Improved quality: Consistent process parameters lead to fewer defects, reducing rework and improving service life.
Increased throughput: The integrated preheating, surfacing, and post-weld treatment capabilities reduce the total time required for each roll refurbishment.
Extended equipment life: The improved quality of the surfacing extends the service life of the roll body, reducing the frequency of refurbishment or replacement.

The authors likely performed a cost-benefit analysis demonstrating that the investment in the improved device is recovered within a relatively short period, typically within 1–2 years of operation. The exact payback period depends on the volume of roll refurbishment work, the cost of labor and materials, and the value of the extended service life.

Defect Analysis and Quality Control

The combined device helps reduce several common defects in roll body surfacing:

Defect Type	Cause	How the Device Helps
Cracking	Excessive cooling rate, high residual stress	Maintains interpass temperature, provides post-weld stress relief
Uneven overlay	Manual inconsistency, poor torch tracking	Automated torch tracking ensures uniform coverage
Poor bonding	Surface contamination, insufficient preheat	Integrated cleaning and preheating steps
Excessive dilution	Inconsistent heat input	Automated process control maintains consistent parameters
Porosity	Gas entrapment, inadequate shielding	Improved shielding gas delivery and process stability

Quality control measures for roll body surfacing include:

Visual inspection: Checking for uniform overlay coverage, absence of surface defects, and correct geometric dimensions.
Hardness testing: Verifying that the overlay hardness meets specification, typically HRC 50–65 for wear-resistant overlays.
Non-destructive testing: Magnetic particle testing (MT) or ultrasonic testing (UT) to detect subsurface defects such as cracks or lack of fusion.
Dimensional verification: Ensuring that the roll diameter and runout are within tolerance after surfacing and machining.

Key Reflections and Study Insights

This paper exemplifies the practical, engineering-oriented approach to technology development that is common in Chinese industrial literature. The focus on device improvement rather than fundamental research reflects the needs of industry, where practical solutions that can be implemented quickly and cost-effectively are often more valuable than theoretical advances.

The concept of a combined device that integrates preheating, surfacing, and post-weld treatment is particularly valuable for large components such as roll bodies, where transferring the component between different stations is impractical. This integrated approach reduces handling time, improves process control, and increases productivity.

The work also highlights the importance of considering the entire process chain, from surface preparation to post-weld treatment, when designing surfacing equipment. Optimizing individual steps in isolation may not yield the best overall results; rather, a systems approach that considers the interactions between different process steps is essential for achieving high-quality surfacing.

Modern developments in roll body surfacing have built upon the foundation laid by this work. Robotic surfacing systems, for example, offer even greater precision and consistency than the semi-automated devices described in the paper. However, the fundamental principles of integrated process design, controlled heating, and automated torch tracking remain valid and essential for achieving high-quality surfacing of large components.

Summary

The improvement of combined roll body surfacing devices represents a practical and valuable contribution to the field of surfacing technology for large industrial components. The integrated approach, combining preheating, surfacing, and post-weld treatment in a single system, offers significant advantages in terms of quality, productivity, and cost. The device helps reduce common defects such as cracking, uneven overlay, and poor bonding by providing better process control and maintaining consistent temperatures throughout the surfacing operation. This work serves as an important reference for engineers involved in the design and implementation of surfacing equipment for large components, and its principles remain applicable to modern practice. The key takeaway is that successful surfacing of large components requires a holistic approach that considers the entire process chain, from surface preparation to post-weld treatment, and that integrated devices can significantly improve quality and productivity compared to separate, manual operations.