CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Cladding Technology in Underground Maintenance of Scraper Chain Conveyors
Operational Context and Technical Challenges
Scraper chain conveyors are critical material handling equipment in underground coal mines, operating in extremely harsh environments characterized by high humidity, dust, abrasive coal and rock particles, and limited access for maintenance. The scraper chains and connecting links experience severe wear from constant sliding against the conveyor trough, leading to progressive material loss and eventual structural failure. Traditional maintenance involves complete replacement of worn components, which is labor-intensive, time-consuming, and costly in underground conditions where transportation and workspace are severely constrained.
This literature investigates the application of weld overlay cladding technology for in-situ repair of worn scraper chain components, enabling rapid restoration of dimensional accuracy and wear resistance without removing the conveyor from service. The technical challenge is compounded by the underground environment, where ventilation, lighting, electrical safety, and gas detection requirements impose strict constraints on welding operations.
Cladding Process Selection and Parameters
The study evaluated multiple cladding processes including SMAW, SAW, and GMAW for their suitability in underground conditions. SMAW was found to be the most practical choice due to its portability, minimal equipment requirements, and tolerance to variable surface conditions. The cladding consumable was a high-carbon martensitic steel with 0.9–1.1% C, 4.5–5.5% Cr, and 0.6–0.8% Mo, designed to produce a hardened martensitic microstructure with a hardness of 450–520 HB after air cooling.
The process parameters were optimized for field conditions: current 180–250 A, arc voltage 20–24 V, travel speed 100–180 mm/min, with a preheat temperature of 150–200°C achieved using portable oxy-fuel torches. The overlay was applied in 2–3 passes to achieve a total thickness of 2–4 mm, with each pass providing approximately 1–2 mm of build-up. Post-weld treatment involved air cooling followed by a localized tempering at 200–250°C to reduce residual stress and improve toughness.
Performance Comparison: Cladded vs. New Components
| Metric | New Component | Cladded Component | Acceptance Limit |
|---|---|---|---|
| Surface hardness (HB) | 320–360 | 430–480 | ≥350 |
| Wear life (hours) | 800–1200 | 600–900 | ≥500 |
| Dimensional accuracy | ±0.5 mm | ±1.0 mm | ±1.5 mm |
| Repair time (min/link) | — | 25–35 | <45 |
| Cost reduction | Baseline | 60–75% | — |
Quality Control and Safety Considerations
Quality control in underground cladding operations requires a streamlined yet effective inspection protocol. Visual inspection (VT) is performed after each pass to detect undercut, porosity, and incomplete fusion. Magnetic particle testing (MT) is applied to the final overlay surface to detect surface and near-surface cracks. Hardness testing (HB) is performed at three locations across the overlay cross-section to verify adequate hardness uniformity.
Safety considerations are paramount in underground environments. The welding operation must comply with mine safety regulations regarding oxygen monitoring, methane detection, and fire prevention. Portable welding equipment must be intrinsically safe or operated in designated safe zones. The literature emphasizes the importance of a pre-job safety assessment using a hazard identification checklist that includes gas detection, ventilation verification, and emergency response planning.
Engineering Practice and Economic Analysis
The economic analysis presented in the literature demonstrates a compelling case for in-situ cladding repair. The cost per repaired link is approximately 30–40% of the cost of a new replacement link, and the repair time is significantly shorter than the time required to remove, transport, and reinstall a new component. Over a typical maintenance cycle, the cladding approach can reduce conveyor downtime by 40–60% and extend component service life by 50–70% compared to the original as-manufactured condition.
The study also highlights the importance of operator training and procedural standardization. A well-trained welder can consistently produce high-quality overlays, but the variability in operator skill remains a significant quality risk. The implementation of a standardized work instruction sheet with clear process parameters, visual reference standards, and inspection checkpoints is recommended to minimize quality variation.
Study Insights and Reflections
The literature demonstrates that weld overlay cladding is a highly effective and economically viable solution for underground conveyor maintenance. The key insight is that the cladded component, while not identical to a new part, offers superior wear resistance due to the hardened martensitic microstructure, which more than compensates for any minor dimensional deviations. The practical success of this approach depends less on achieving perfect metallurgical quality and more on maintaining consistent process discipline and adequate safety controls. Future improvements should focus on developing consumables with wider process windows, portable in-situ hardness testing equipment, and simplified NDT methods suitable for field conditions.