CLADDING TECHNOLOGY SHANXI CO., LTDLarge-Area Wear-Resistant Pattern Overlay on Scraper Conveyor Middle Trough
Literature Overview
This 1996 study by Ge Changlu and Ye Rongchang, published in Welding Technology (焊接技术) and affiliated with the China University of Mining and Technology in Xuzhou, Jiangsu Province, addresses the practical engineering challenge of applying large-area wear-resistant overlay patterns on the middle trough of scraper conveyors used in coal mining operations. Scraper conveyors are fundamental material handling equipment in underground and surface mining operations, where the middle trough is subjected to severe abrasive wear from coal and rock particles transported over long distances.
The study focuses on the process development and optimization of overlay welding patterns designed to maximize wear resistance while maintaining the structural integrity of the trough. The research reflects the strong practical orientation of Chinese welding research during this period, directly addressing industrial problems faced by coal mining enterprises.
Core Technical Findings
Wear Mechanism Analysis
The middle trough of a scraper conveyor experiences a complex combination of wear mechanisms:
- Abrasive wear: The primary wear mechanism, caused by hard particles embedded in the coal stream sliding across the trough surface.
- Impact wear: Caused by the kinetic energy of falling material striking the trough surface.
- Corrosive wear: In certain mining environments, moisture and acidic compounds contribute to accelerated material loss.
The base material of the trough, typically a carbon steel such as Q235 or Q345, has insufficient hardness and wear resistance for the severe operating conditions. Without overlay protection, the trough requires replacement at intervals of only a few weeks, resulting in significant downtime and maintenance costs.
Overlay Pattern Design
The study developed a systematic approach to overlay pattern design, considering the following factors:
| Design Parameter | Specification | Rationale |
|---|---|---|
| Pattern type | Chevron / diamond grid | Maximizes surface hardness while allowing material flow |
| Pattern height | 3 to 5 mm | Provides adequate material volume for wear life |
| Pattern spacing | 20 to 30 mm | Balances wear resistance with material flow characteristics |
| Overlay material | High-chromium alloy (Cr 15 to 20%) | Forms hard M7C3 carbides for abrasive resistance |
| Base preparation | Gouging to 2 mm depth | Ensures adequate bonding and reduces dilution |
Process Development
The overlay welding process was developed using submerged arc welding (SAW) with a specialized multi-wire or twin-wire technique to achieve high deposition rates suitable for large-area coverage. The key process parameters were optimized as follows:
- Preparation: The trough surface was prepared by gouging to a depth of 2 mm, followed by grinding to a smooth, clean surface. A V-groove was machined at the edges to ensure proper fusion with the base metal.
- First pass: A narrow SAW process was used for the first pass, with a wire feed speed of 6 to 8 m/min and an arc voltage of 28 to 32 V, achieving a dilution rate below 20%.
- Pattern formation: Subsequent passes were applied using a multi-wire SAW technique with 2 to 3 wires, increasing the deposition rate to 3 to 5 kg/h while maintaining a controlled dilution rate.
- Interpass temperature: The interpass temperature was maintained between 150 and 250 degrees Celsius to prevent excessive heat accumulation and minimize residual stresses.
- Post-weld treatment: A stress relief treatment at 550 to 650 degrees Celsius for 2 hours was applied to reduce residual stresses and improve the toughness of the overlay.
Quality Control and Performance Evaluation
Non-Destructive Testing
The following NDT methods were applied to verify overlay quality:
| NDT Method | Application | Acceptance Criteria |
|---|---|---|
| Magnetic particle testing (MT) | Surface crack detection | No linear indications above 10 mm |
| Ultrasonic testing (UT) | Bond strength verification | No delamination above 30 mm |
| Visual inspection (VT) | Pattern geometry verification | Pattern height and spacing within tolerance |
Performance Results
After implementing the overlay process, the following performance improvements were achieved:
- Hardness: The overlay surface hardness reached HV 650 to 750, compared to HV 180 to 220 for the base metal.
- Wear life: The service life of the trough was extended from approximately 2 to 3 weeks to over 6 months under equivalent operating conditions.
- Bond strength: The overlay-to-base bond strength was measured at 180 to 220 MPa, exceeding the design requirement of 150 MPa.
Integration with Engineering Practice
This study demonstrates the practical application of overlay welding technology to solve a specific industrial problem. Several lessons are particularly relevant for contemporary engineering practice:
- Pattern design is critical: The geometry of the overlay pattern directly influences both wear resistance and material flow characteristics. A well-designed pattern can significantly extend service life while maintaining operational efficiency.
- Process selection matters: The choice of welding process must balance deposition rate, dilution control, and cost. Multi-wire SAW offers an excellent combination of high deposition rate and good dilution control for large-area overlay applications.
- Systematic quality control is essential: A combination of process control, interpass inspection, and final NDT provides the assurance necessary for reliable overlay performance in critical applications.
Study Insights and Reflections
This study, published nearly three decades ago, remains a valuable reference for engineers working on wear-resistant overlay applications in mining and material handling. The systematic approach to pattern design, process development, and quality control established in this work provides a framework that is directly applicable to contemporary overlay engineering challenges. The emphasis on practical performance metrics—wear life extension, hardness, and bond strength—reflects the applied orientation of the research and provides engineers with clear criteria for evaluating overlay performance. For practitioners today, this study reinforces the importance of integrating metallurgical understanding with process engineering to develop overlay solutions that deliver reliable performance in demanding industrial environments.