Zhuojin Pipe Fitting Co., LtdImprovement of Combined Roll Surfacing Device
Literature Overview
The paper by Wang Yijun, published in Mining Machinery (Vol. 37, No. 2, 2009, pp. 88-89), describes the improvement of a combined roll surfacing device developed at Shanghai Meishan Steel Company's Technical Center. The paper addresses the practical challenges of surfacing large rolls used in mining, metallurgy, and cement industries, where the need for surface hardening or repair is frequent and the economic value of extending roll service life is substantial.
Technical Background
Large rolls are critical components in:
- Mining: Crushers, screens, and conveyors
- Metallurgy: Hot rolling mills, cold rolling mills, and finishing mills
- Cement and building materials: Crushers, mills, and kiln preheaters
These rolls typically have diameters ranging from 500 mm to 3000 mm and lengths from 1000 mm to 6000 mm. They operate under severe conditions involving high loads, abrasive contact, and often elevated temperatures. Without surface protection, roll surface wear can be significant, leading to reduced product quality, increased energy consumption, and frequent downtime for roll replacement or regrinding.
The Original Device and Its Limitations
The original combined roll surfacing device was designed to perform multiple surfacing operations on a single roll in one setup. However, it had several limitations:
| Limitation | Impact |
|---|---|
| Limited roll size range | Could not accommodate the largest rolls used in modern mills |
| Manual operation | High operator skill requirement, inconsistent quality |
| Limited process flexibility | Could not easily switch between different surfacing alloys |
| Inadequate preheat capability | Difficulty maintaining required preheat temperature for large rolls |
| No interpass temperature control | Risk of cracking in high-carbon surfacing layers |
| Manual post-weld heat treatment | Inconsistent stress relief, risk of distortion |
Device Improvements
Structural Improvements
The improved device incorporates several key enhancements:
- Expanded roll size range: The device can now accommodate rolls with diameters from 300 mm to 3500 mm and lengths up to 8000 mm, covering virtually all industrial roll applications.
- Robust support structure: Reinforced support bearings and cradle design prevent roll sagging and vibration during surfacing, ensuring consistent bead quality.
- Modular design: The device can be configured for different surfacing methods (SMAW, SAW, FCAW) by swapping torch assemblies and power sources.
Process Integration
The improved device integrates multiple process steps into a single operation:
- Preheating: Electric resistance heating bands wrapped around the roll provide uniform preheating to the required temperature (typically 200-400°C depending on the base material and surfacing alloy).
- Surfacing: Automated or semi-automated surfacing with constant parameter control ensures consistent bead quality.
- Interpass temperature monitoring: Thermocouples embedded in the roll or attached to the surface provide real-time temperature feedback, allowing automatic adjustment of travel speed or arc current to maintain interpass temperature within the specified range.
- Post-weld heat treatment: The device includes a furnace or heating system for stress relief heat treatment, eliminating the need to move the roll to a separate facility.
Control System
The improved device features a microprocessor-based control system that:
- Monitors and records all process parameters (current, voltage, travel speed, temperature)
- Provides automatic parameter adjustment based on temperature feedback
- Generates process reports for quality documentation
- Alerts the operator to parameter deviations that could lead to defects
Process Parameters for Different Roll Types
| Roll Type | Base Material | Surfacing Alloy | Preheat | Interpass Temp | Post-Weld HT |
|---|---|---|---|---|---|
| Crusher roll | Q345 | High-Cr martensitic | 250-350°C | 250-350°C | 550-600°C × 2h |
| Mill roll | 50Mn | Medium-Cr austenitic | 150-250°C | 150-250°C | 650-700°C × 2h |
| Conveyor roll | 20 steel | Low-Cr martensitic | 100-200°C | 100-200°C | 500-550°C × 2h |
| Kiln roll | 45 steel | Ni-based alloy | 200-300°C | 200-300°C | 700-750°C × 2h |
Economic Analysis
The improved device provides significant economic benefits:
- Reduced setup time: Integrated process reduces total processing time by 40-50%
- Improved quality consistency: Automated control reduces defect rate from 5-10% to below 1%
- Extended roll life: Properly executed surfacing with integrated heat treatment extends roll life by 3-5×
- Reduced labor cost: Semi-automated operation reduces skilled labor requirement
- Faster turnaround: Integrated heat treatment eliminates transport time to separate facilities
For a typical steel mill, the annual savings from extended roll life and reduced downtime can exceed several million yuan, providing a rapid return on investment for the improved device.
Study Reflections
This paper exemplifies the practical approach to engineering improvement: identifying specific limitations of an existing system and developing targeted solutions that address those limitations. The improved roll surfacing device is not a revolutionary innovation but rather a systematic enhancement of an existing technology that addresses real-world operational challenges.
The integration of preheating, surfacing, and post-weld heat treatment into a single device is particularly significant. In many industrial settings, these processes are performed in separate facilities, requiring multiple handling operations that introduce risks of damage, contamination, and thermal shock. By integrating these processes, the improved device ensures that the roll is maintained at the correct temperature throughout the entire process, reducing the risk of cracking and distortion.
The emphasis on process documentation and quality control is also noteworthy. In modern manufacturing environments, traceability and quality documentation are essential for meeting customer requirements and regulatory standards. The control system's ability to record and report process parameters provides the documentation needed for quality assurance.
For engineers working on surface engineering of large components, this paper highlights several important principles:
- Process integration: Combining related processes into a single system reduces handling risks and improves quality consistency.
- Temperature control: Maintaining proper preheat and interpass temperatures is critical for preventing defects in hardfacing applications.
- Automation: Even partial automation significantly improves quality and reduces labor requirements.
- Documentation: Process parameter recording enables quality traceability and continuous improvement.
The paper also demonstrates that significant improvements can be achieved through incremental development rather than radical redesign. The improved device builds on the success of the original device, adding features that address specific operational challenges without compromising the proven aspects of the original design.