CLADDING TECHNOLOGY SHANXI CO., LTDCladding Technology Application in Underground Maintenance of Scraper Conveyors
Literature Overview
This 2020 publication by Jia Xiaoping from Fenxi Mining Group Hexi Coal Mine explores the application of cladding technology for the in-situ maintenance of scraper conveyors operating underground in coal mines. Underground scraper conveyors are critical material handling equipment in coal mining operations, transporting extracted coal from the face to the main haulage system. The scraper chains and troughs (the main body of the conveyor) are subjected to severe abrasive wear from coal, rock fragments, and moisture. Traditional maintenance approaches involve replacing worn components or applying surface treatments such as painting or epoxy coatings. Cladding offers a more durable and long-lasting solution, but its application in the challenging underground environment presents unique challenges.
Operating Environment and Wear Mechanisms
Underground scraper conveyors operate under the following conditions:
| Condition | Description | Impact on Wear |
|---|---|---|
| Abrasive particles | Coal, rock, grit in transported material | Abrasive wear on trough surfaces |
| Moisture | High humidity, water ingress | Corrosion, reduced coating adhesion |
| Chemical agents | Sulfur compounds, acidic drainage | Corrosive attack on steel surfaces |
| Mechanical impact | Falling coal chunks, rock fragments | Impact wear, spalling |
| Temperature | Ambient mine temperature (15–30 °C) | Moderate thermal stress |
| Space constraints | Limited access, confined working areas | Difficulty in equipment setup |
The primary wear mechanism is abrasive wear, where hard particles embedded in the transported material scrape against the trough surface. Secondary mechanisms include adhesive wear from chain contact and impact wear from falling material.
Cladding Process Adaptation for Underground Use
The underground environment imposes significant constraints on cladding process selection. The following table compares conventional processes with their adaptability to underground conditions:
| Process | Underground Suitability | Key Constraint |
|---|---|---|
| GMAW (MIG) | Moderate | Requires shielding gas cylinder; fume extraction needed |
| FCAW (Flux-Cored) | High | Self-shielded, no gas cylinder needed; mobile |
| GTAW (TIG) | Low | Requires precise control; difficult in confined space |
| SAW (Submerged Arc) | Low | Requires flux supply; limited position flexibility |
| Manual arc (SMAW) | High | Most portable; low equipment requirement |
| Laser cladding | Very low | Requires laser system; not practical underground |
| PTA | Low | Requires powder system; limited mobility |
For underground scraper conveyor maintenance, FCAW and manual arc welding (SMAW) are the most practical options due to their portability, self-shielding capability, and tolerance of imperfect surface conditions. The cladding material is typically a high-carbon, high-chromium cast iron (e.g., Cr13 or Cr26) or a nickel-based alloy for superior wear resistance.
Field Implementation Challenges
The practical application of cladding technology underground faces several challenges:
- Surface preparation: Worn trough surfaces are often contaminated with coal dust, moisture, and previous coatings. Thorough cleaning is essential for adequate bond strength but is difficult in confined spaces.
- Heat input control: The trough is typically thin-walled (6–12 mm), and excessive heat input can cause distortion or burn-through. Low-current, multi-pass techniques are necessary.
- Residual stress management: Cladding on thin-walled troughs introduces residual stress that can lead to cracking or distortion. Stress relief may not be practical underground, so process parameters must be optimized to minimize residual stress.
- Ventilation and safety: Welding fumes and sparks pose safety hazards in underground environments with potentially explosive atmospheres. Hot work permits, fire watches, and adequate ventilation are mandatory.
- Downtime minimization: Production loss during maintenance is costly. Cladding operations must be planned to minimize the time the conveyor is out of service.
Quality Control in Underground Conditions
| Inspection Method | Application | Practicality Underground |
|---|---|---|
| Visual inspection (VT) | Surface quality, porosity, cracks | Always available |
| Magnetic particle testing (MT) | Surface and near-surface cracks | Portable equipment available |
| Penetrant testing (PT) | Surface cracks, porosity | Portable, but requires cleaning |
| Hardness testing | Clad layer hardness verification | Portable hardness testers available |
| Ultrasonic testing (UT) | Interface integrity, thickness | Limited by geometry and access |
| Destructive testing | Bond strength, microstructure | Not practical in situ |
Key Questions and Reflections
A fundamental question in underground cladding applications is the long-term durability of the cladding layer under continuous abrasive wear. Unlike stationary equipment, scraper conveyor troughs are in constant motion, and the cladding layer is subjected to continuous abrasive action. Field data on cladding service life in underground conveyors is limited, and engineers should develop monitoring programs to track wear rate and plan maintenance intervals accordingly.
Another reflection concerns the training and qualification of welders for underground cladding work. The confined working conditions, limited access, and safety constraints require specialized training. Welder performance qualification procedures should be adapted to reflect the actual working conditions, including position, access limitations, and surface preparation challenges.
Summary
The application of cladding technology for underground scraper conveyor maintenance offers a promising approach to extending component life and reducing replacement frequency. However, the unique challenges of the underground environment—confined space, safety constraints, surface preparation difficulties, and limited equipment access—require careful process selection and thorough planning. FCAW and SMAW processes with high-chromium or nickel-based cladding materials represent the most practical solutions. Engineers should focus on optimizing process parameters for thin-walled troughs, ensuring adequate surface preparation, and implementing practical quality control measures. With proper planning and execution, cladding can significantly improve the reliability and cost-effectiveness of underground material handling systems.