Zhuojin Pipe Fitting Co., LtdOverlay Welding Technology for EBZ125 Roadheader Turntables
Literature Overview
This paper by Liu Weibin and colleagues, published in Mining Machinery (2009, Vol. 37, Issue 22), describes the overlay welding technology applied to the left and right drive turntables of the EBZ125 roadheader. The EBZ125 is a specialized equipment for tunnel excavation in coal and semi-coal-rock roadways, manufactured by Shaanxi Construction Machinery Co., Ltd. The drive turntables are critical components that transmit rotary motion to convey collected material through the transport mechanism, and they are subjected to cutting action by external non-metallic abrasives.
Core Technical Analysis
The EBZ125 roadheader operates in extremely demanding conditions where the drive turntables experience continuous contact with abrasive rock and coal particles. The non-metallic abrasives—primarily silica-bearing rock fragments—induce severe abrasive wear on the turntable surfaces, directly determining the service life of the roadheader. The overlay welding approach provides a surface hardening strategy that extends component life without requiring complete replacement of the turntable assembly.
| Parameter | Specification |
|---|---|
| Equipment | EBZ125 Roadheader |
| Critical Components | Left and Right Drive Turntables |
| Application | Coal and semi-coal-rock roadway excavation |
| Wear Mechanism | Non-metallic abrasive cutting |
| Key Performance Requirement | Abrasion resistance of turntable surface |
| Repair/Enhancement Method | Overlay welding |
| Manufacturer | Shaanxi Construction Machinery Co., Ltd. |
Process Design and Metallurgical Considerations
The overlay welding process for the roadheader turntables requires careful process design to address several competing requirements. The base material of the turntable is typically a medium-carbon or low-alloy steel designed for structural strength and toughness. The overlay layer must provide high hardness and abrasion resistance while maintaining sufficient adhesion to the base metal to prevent spalling or delamination under impact loading.
Key process parameters include:
- Electrode or wire selection: High-carbon chromium or carbide-containing consumables are typically used to achieve the required surface hardness (targeting HV 600-900 range).
- Welding current and voltage: Must be optimized to achieve adequate penetration for metallurgical bonding while minimizing dilution of the overlay layer.
- Interpass temperature control: Prevents excessive softening of previously deposited layers and controls residual stress accumulation.
- Layer thickness: Must be sufficient to provide wear life while maintaining structural integrity of the turntable.
- Post-weld heat treatment: May be required to relieve residual stresses and improve toughness of the overlay layer.
Engineering Practice and Quality Control
The quality of the overlay welding repair is critical to the long-term reliability of the roadheader. Common defects that must be prevented include:
| Defect Type | Cause | Countermeasure |
|---|---|---|
| Cracking | Excessive carbon equivalent, high restraint, rapid cooling | Preheat, low hydrogen consumables, controlled cooling |
| Spalling | Poor metallurgical bond, excessive dilution | Optimize welding parameters, ensure clean base surface |
| Porosity | Contamination, inadequate shielding | Surface preparation, gas shielding |
| Incomplete fusion | Low current, poor technique | Increase current, improve travel speed control |
| Excessive dilution | High current, deep penetration | Reduce current, use higher deposition rate consumables |
The post-weld inspection should include visual examination for surface defects, magnetic particle testing for subsurface cracks, and hardness profiling across the overlay thickness to verify the hardness gradient and dilution level.
Key Reflections
This case study illustrates the practical application of overlay welding in extending the service life of heavy mining equipment components. The EBZ125 roadheader operates in underground environments where equipment availability directly impacts production output, making preventive maintenance and component life extension strategies economically essential.
The choice of overlay welding over alternative surface enhancement methods (such as thermal spraying, laser cladding, or surface hardening) reflects the practical constraints of underground mining operations: portability of equipment, availability of skilled welders, and the need for field-applicable repair techniques. Overlay welding using SMAW or FCAW processes can be performed with relatively simple equipment and does not require the sophisticated setups needed for laser or plasma-based methods.
However, the study also highlights the limitations of this approach: overlay welding produces relatively thick layers (typically 1-3 mm per pass) with significant dilution from the base metal, which reduces the effective hardness of the final overlay. Modern alternatives such as laser cladding or cold spray can produce thinner, more dilution-free layers with superior performance, but at significantly higher equipment and operational costs.