CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Weld Overlay Technology in Underground Maintenance of Scraper Conveyors
Literature Overview
The paper by Jia Xiaoping (2020) from Fenxi Mining Group Hexi Coal Mine discusses the application of weld overlay technology in the underground maintenance of scraper conveyors. Scraper conveyors are critical equipment in underground coal mining, used to transport mined coal from the face to the main haulage system. The components of the scraper conveyor that are subject to severe wear include the scraper chain, the trough, the chain sprocket, and the tail wheel. The paper presents a case study of using weld overlay to repair and extend the service life of these components in an underground environment.
Technical Background
Underground scraper conveyors operate in extremely harsh conditions, with continuous exposure to abrasive coal, rock, and water. The wear mechanisms include:
- Abrasive wear from coal and rock particles, which can be highly angular and hard.
- Impact wear from the falling coal and the engagement of the scraper chain with the trough.
- Corrosive wear from water and dissolved minerals, which can accelerate material degradation.
- Fatigue wear from cyclic loading, which can lead to surface cracking and spalling.
The conventional approach to dealing with wear is to replace the worn components with new ones. However, this approach is costly and time-consuming, particularly in an underground environment where access is limited and equipment must be transported through narrow tunnels. Weld overlay technology offers an alternative approach by restoring the worn surface to its original dimensions and providing enhanced wear resistance.
Weld Overlay Materials and Processes
The paper describes the use of several weld overlay materials and processes for the repair of scraper conveyor components:
| Component | Overlay Material | Process | Overlay Thickness |
|---|---|---|---|
| Scraper chain | High-manganese steel (Mn13) | SAW or FCAW | 5-10 mm |
| Trough liner | High-chromium cast iron | SAW | 3-6 mm |
| Chain sprocket teeth | Stellite 6 or Co-based alloy | SAW or PTA | 2-5 mm |
| Tail wheel | High-carbon steel | SAW | 4-8 mm |
| Scraper plate | High-manganese steel | FCAW or GMAW | 5-10 mm |
The selection of the overlay material depends on the specific wear mechanism and the operating conditions. For example, high-manganese steel (Mn13) is suitable for impact abrasion because it work-hardens under impact loading, providing excellent wear resistance in service. High-chromium cast iron is suitable for severe abrasion because of its high hardness and carbide content. Stellite 6 is suitable for high-temperature abrasion and corrosion because of its excellent thermal stability and chemical resistance.
Field Application and Results
The paper presents a detailed case study of the application of weld overlay technology to the scraper conveyor at Hexi Coal Mine. The following table summarizes the results of the field trial:
| Component | Original Service Life | With Weld Overlay | Improvement Factor |
|---|---|---|---|
| Scraper chain | 3-5 months | 12-18 months | 3-4x |
| Trough liner | 2-4 months | 10-15 months | 3-5x |
| Chain sprocket | 6-10 months | 18-24 months | 2-3x |
| Tail wheel | 3-6 months | 12-18 months | 3-4x |
The economic analysis showed that the cost of weld overlay repair was significantly lower than the cost of replacing the entire component. For example, the cost of overlaying a scraper chain was approximately 20% of the cost of purchasing a new chain, and the service life was extended by a factor of 3 to 4. The reduction in downtime due to component replacement was also significant, resulting in increased production and reduced operating costs.
Process Challenges in Underground Environment
The application of weld overlay technology in an underground environment presents several unique challenges:
- Limited space: The welding operation must be performed in a confined space, with limited access for equipment and personnel. This requires the use of portable welding equipment and compact flux and consumable containers.
- Ventilation: The welding operation produces fumes and gases that must be ventilated to ensure a safe working environment. The paper recommends the use of local exhaust ventilation and appropriate personal protective equipment.
- Power supply: Underground power supplies may be limited, requiring the use of battery-powered or diesel-powered welding equipment. The paper describes the use of portable diesel generators to provide the required power for the welding operation.
- Environmental conditions: The underground environment is humid, with high levels of dust and moisture. The welding surfaces must be thoroughly cleaned before welding to prevent porosity and other defects.
- Safety: The welding operation must comply with all applicable safety regulations, including those related to hot work, confined space entry, and explosion prevention. The paper emphasizes the importance of obtaining proper permits and following established safety procedures.
Quality Control and Inspection
The quality of the weld overlay is critical to its performance in service. The paper describes the following quality control measures:
- Visual inspection: The weld overlay is inspected visually for surface defects such as cracks, porosity, and undercut. Any defects are repaired before the component is returned to service.
- Hardness testing: The hardness of the overlay is measured using a portable hardness tester to ensure that it meets the specified requirements. The hardness should be uniform across the overlay and should not show excessive softening at the interface with the base metal.
- Thickness measurement: The thickness of the overlay is measured using an ultrasonic thickness gauge to ensure that it meets the minimum required thickness. The thickness should be uniform across the wear surface.
- Pull-off testing: In some cases, the bond strength of the overlay is verified by performing a pull-off test, where a coupon is attached to the overlay and pulled until failure. The pull-off strength should exceed the specified minimum value.
Study Insights and Reflections
This paper provides a practical example of the application of weld overlay technology in a challenging industrial environment. The underground mining environment is particularly demanding because of the limited space, the harsh operating conditions, and the safety constraints. Despite these challenges, the paper demonstrates that weld overlay technology can be successfully applied to extend the service life of critical equipment, resulting in significant cost savings and reduced downtime.
The study also highlights the importance of material selection in weld overlay applications. The choice of overlay material must be based on a thorough understanding of the wear mechanism and the operating conditions. For example, high-manganese steel is an excellent choice for impact abrasion because of its work-hardening behavior, but it may not be suitable for severe abrasion where high hardness is required. Similarly, Stellite 6 is an excellent choice for high-temperature abrasion but may be overkill for low-temperature applications where lower-cost materials would suffice.