Application of Surfacing Welding Technology in Underground Repair of Scraper Conveyor Systems

Literature Overview and Industrial Context

The paper by Jia Xiaoping, published in Inner Mongolia Petrochemical Industry in 2020, examines the practical application of surfacing welding technology for the in-situ repair of scraper conveyor components in underground coal mine environments. Scraper conveyors are critical material handling equipment in underground mining operations, subjected to severe abrasive wear from continuous contact with coal, rock fragments, and other mining debris. The paper focuses on the repair of high-wear components such as head frames, filter troughs, and scraper chain attachments, demonstrating that surfacing welding can significantly reduce maintenance time and costs while improving operational efficiency.

Wear Mechanisms and Component Analysis

Underground scraper conveyors experience a complex combination of wear mechanisms that vary by component location and function. Understanding these mechanisms is essential for selecting appropriate surfacing welding alloys and process parameters.

The head frame, which serves as the structural support and guide for the scraper chain at the discharge end, is particularly susceptible to wear due to the concentrated impact and abrasion from the coal discharge stream. The filter trough, which separates coal from water in wet mining operations, experiences continuous sliding contact with wet coal slurry, leading to uniform but persistent surface degradation.

Surfacing Welding Process Selection and Execution

The selection of surfacing welding process and consumables is dictated by the underground environment constraints, including limited power availability, confined working spaces, and the presence of potentially explosive gases.

Process Selection Criteria

Shielded metal arc welding (SMAW) is the preferred process for underground applications due to its equipment portability, independence from external gas supplies, and adaptability to various welding positions. For critical components requiring higher quality and thinner overlay deposits, gas tungsten arc welding (GTAW) with self-contained gas cylinders can be employed where ventilation conditions permit. Submerged arc welding (SAW) is generally not practical for in-situ repair due to equipment size and the requirement for flux recovery.

Filler Metal Selection

The filler metals selected for scraper conveyor repair are predominantly hardfacing alloys of the cobalt-based (Stellite type) and high-chromium cast iron categories. Cobalt-based alloys offer excellent hot hardness and wear resistance in dry and wet conditions, with hardness values of 40-50 HRC after welding. High-chromium cast iron alloys provide superior abrasive wear resistance in wet conditions due to the formation of a self-forming oxide film, achieving hardness of 55-65 HRC. The selection between these two categories depends on the specific service conditions of each component.

Surface Preparation and Welding Procedure

Proper surface preparation is critical for ensuring adequate metallurgical bonding between the overlay and the base metal. The worn surface is ground to a depth of 3-5 mm below the original surface profile to remove damaged material and provide a clean, sound substrate. Preheating is applied to 150-250 degrees Celsius depending on the base metal carbon equivalent and thickness. The surfacing is applied in multiple passes with controlled overlap to ensure uniform coverage and minimize dilution. Post-weld cooling is controlled to prevent cracking in the hardfacing layer.

Performance Results and Economic Analysis

The application of surfacing welding technology for scraper conveyor repair has demonstrated substantial economic benefits. The repair cycle time is reduced by approximately 60 percent compared to component replacement, as in-situ repair eliminates the need for disassembly, transportation, and reinstallation. The service life of repaired components is extended by a factor of three to five times compared to the original unworn condition, due to the superior wear resistance of the hardfacing alloys.

The economic analysis reveals that the investment in surfacing welding equipment and training is recovered within the first two to three repair cycles, after which the operation achieves net savings. The reduction in maintenance downtime also contributes to increased production output, which often represents a more significant economic benefit than the direct material savings.

Study Reflections and Engineering Considerations

This paper provides a practical demonstration of how established welding technologies can be effectively deployed in challenging field environments to solve real engineering problems. The key success factors identified in the study include thorough understanding of the wear mechanisms, appropriate selection of hardfacing alloys matched to service conditions, and disciplined execution of welding procedures under field conditions.

From a metallurgical perspective, the dilution control during surfacing is a critical quality parameter. In field conditions, achieving consistent dilution levels is more challenging than in a controlled workshop environment. The use of multi-pass surfacing with increasing hardness levels—starting with a softer, more ductile transition pass and finishing with a harder, more wear-resistant top pass—can mitigate dilution-related issues and improve the overall quality of the overlay. The technology discussed in this paper is directly relevant to pipeline and pipe fitting repair operations, where similar in-situ surfacing techniques are employed to restore worn or corroded surfaces on pipeline elbows, tees, and reducers in service.