Zhuojin Pipe Fitting Co., LtdOverlay Welding Technology for EBZ125 Roadheader Turntable Components
Literature Overview
This 2009 paper published in Mining Machinery (Vol. 37, Issue 22, pp. 60-61) by Liu Weibin, Zhang Yawen, and Lei Zhenhua from Shaanxi Construction Machinery Co., Ltd. Heavy Equipment Research Institute describes the overlay welding technology applied to the left and right turntables of the EBZ125 roadheader. The EBZ125 is a dedicated coal roadheader designed for coal and semi-coal-rock tunnel excavation. The drive mechanism turntables are critical components that transfer the collected material through the conveying system, experiencing severe abrasive cutting action from non-metallic abrasives in the mined material.
Functional Analysis and Wear Mechanism
The turntables in the EBZ125 roadheader serve as the interface between the cutting head and the conveyor system. During excavation, the cut material (coal, rock fragments, and associated fines) flows over the turntable surfaces, creating a high-energy abrasive environment. The wear mechanism is predominantly micro-cutting and micro-ploughing by hard mineral particles (quartz, feldspar) embedded in the material stream.
The severity of wear is exacerbated by:
- Impact loading from falling material fragments
- Variable material composition (soft coal to hard rock)
- Continuous operation with minimal maintenance intervals
- Difficulty of accessing the component for inspection during operation
Overlay Welding Process Selection
| Process Parameter | Specification | Justification |
|---|---|---|
| Welding method | SAW (submerged arc welding) or GMAW | High deposition rate, consistent quality |
| Consumable type | High-carbon martensitic or high-chromium alloy | Hardness > 50 HRC, good toughness |
| Number of layers | 3-5 layers | Build sufficient thickness for machining allowance |
| Base metal | Medium carbon structural steel (Q345 or similar) | Structural strength requirement |
| Preheat | 150-250°C | Reduce cracking tendency |
| Final hardness | 45-55 HRC | Balance wear resistance and toughness |
| Surface finish | Ra 6.3 μm (as-welded) | Adequate for material flow |
Technical Challenges and Solutions
The primary technical challenges in overlay welding roadheader turntables include:
- Dilution control: The first weld layer experiences the highest dilution from the base metal, which can reduce hardness by 10-20%. Solution: Apply a transition layer with a consumable of intermediate composition, followed by the final hardfacing layers.
- Residual stress management: The large surface area of turntables creates significant welding distortion. Solution: Use back-step welding sequence, controlled heat input, and post-weld stress relief at 550-600°C.
- Crack resistance: The high-carbon martensitic overlay is inherently crack-sensitive. Solution: Maintain interpass temperature above 200°C, use low-hydrogen consumables, and ensure adequate preheat.
- Impact toughness: Purely hard overlays may be too brittle for impact loading. Solution: Select a duplex or composite overlay with a tough binder phase and hard carbide particles.
Engineering Practice Recommendations
For roadheader manufacturers and maintenance operations, the following practices are recommended:
- Implement a scheduled overlay welding maintenance program based on operating hours (typically every 500-800 hours depending on material hardness).
- Develop in-house welding procedure specifications (WPS) qualified through destructive testing of coupon welds.
- Train welding operators specifically on overlay welding techniques, as the skill requirements differ from structural welding.
- Monitor turntable thickness through ultrasonic thickness gauging to predict remaining service life.
- Consider robotic overlay welding for high-volume production to ensure consistency and reduce operator fatigue-related defects.
Study Insights
This case demonstrates that overlay welding is a cost-effective and technically viable solution for extending the service life of critical roadheader components. The selection of appropriate overlay material, process parameters, and welding sequence is essential for achieving the desired balance between wear resistance and structural integrity. Engineers should approach overlay welding as a system engineering challenge rather than a simple surface treatment, considering the entire degradation mechanism and service conditions when developing the overlay welding specification.