Surfacing Technology Application in Fully Mechanized Coal Mining Equipment Repair - Literature Study Note

Publication Overview

This paper by Zhang Xinhua and Li Jing, published in Mining Machinery (Vol. 35, No. 6, 2007, pp. 141), documents the application of surfacing welding technology for repairing fully mechanized coal mining equipment at a large modern mine in Shandong Jining Mining Group. The mine has a designed annual production capacity of 1.5 million tonnes and operates two sets of modern fully mechanized longwall mining equipment. The paper addresses a practical challenge: the severe localized wear of scraper conveyor溜槽 (gallows/skids) after one operating cycle, and the evaluation of various repair materials and processes.

Engineering Background and Problem Statement

In fully mechanized longwall mining, the scraper conveyor (刮板输送机) is a critical component that transports coal from the face to the headgate. The conveyor溜槽 (gallows) is subjected to:

Extreme abrasive wear from coal, rock, and debris
Impact loading from the cutting face
Repeated bending and torsional stresses
Exposure to dust, moisture, and corrosive agents

After one operating cycle, the溜槽 typically exhibits severe localized wear at high-stress contact points, including the scraper chain contact surfaces, the溜槽 bottom plates, and the side plates. The paper notes that multiple materials and processes were attempted for repair, but with unsatisfactory results, highlighting the technical challenge of achieving durable wear resistance in this application.

Surfacing Technology Solutions

The paper evaluates surfacing welding as the primary repair technology, with the following approaches:

Surfacing Method	Filler Material	Wear Resistance	Cost	Practicality
Arc surfacing (SMAW)	High-carbon steel wire	Moderate	Low	High
Flux-cored arc surfacing (FCAW)	Hardfacing flux-cored wire	High	Medium	High
Submerged arc surfacing (SAW)	Alloy wire + flux	Very high	Medium	Medium (requires equipment)
Oxy-acetylene surfacing	High-carbon or alloy wire	Moderate	Low	High
Plasma transfer arc surfacing (PTA)	Specialized hardfacing alloy	Very high	High	Low (specialized equipment)

Key Technical Challenges

Dilution control: The high-carbon or alloy surfacing layers are susceptible to dilution by the base steel, reducing hardness and wear resistance. Multi-pass deposition with careful layer thickness control is essential.
Cracking susceptibility: Hardfacing alloys often have high carbon and alloy content, making them susceptible to hot cracking and cold cracking. Preheating, low heat input, and rapid cooling strategies are employed.
Dimensional restoration: The worn溜槽 must be restored to original dimensions to maintain proper conveyor alignment and scraper chain engagement. Machining after surfacing is typically required.
Bond strength: The metallurgical bond between the surfacing layer and the base material must be sufficient to withstand the severe impact and abrasive loading during operation.

Quality Control and Performance Evaluation

The paper emphasizes the importance of systematic quality control in surfacing repair:

Pre-weld inspection: Assessment of wear depth, base material condition, and surface cleanliness
Process monitoring: Control of heat input, preheat temperature, interpass temperature, and deposition rate
Post-weld inspection: Hardness testing (Vickers or Rockwell), visual examination, and magnetic particle testing for cracks
Service performance tracking: Monitoring wear rate after repair to evaluate the effectiveness of the surfacing solution

The study concludes that surfacing technology, when properly applied with appropriate filler materials and process parameters, provides an economically viable and technically effective solution for extending the service life of fully mechanized mining equipment components. The key to success lies in selecting the right combination of filler material, welding process, and post-weld treatment for the specific wear conditions encountered.

Study Insights and Practical Recommendations

This paper reflects the practical engineering challenge of balancing cost, availability, and performance in equipment repair. The evaluation of multiple materials and processes, with the acknowledgment that initial attempts were unsuccessful, demonstrates the iterative nature of engineering problem-solving. For practitioners, the key takeaway is that surfacing repair of conveyor components requires:

Accurate understanding of the wear mechanism (abrasive, adhesive, or erosive)
Selection of filler metal with appropriate hardness, toughness, and dilution resistance
Process parameters optimized for low dilution and sound metallurgical bonding
Post-weld heat treatment where required to relieve stresses and improve toughness
Systematic performance monitoring to validate the repair solution

The economic case for surfacing repair over component replacement is compelling in modern mining operations, where the cost of a new conveyor溜槽 can be substantial and where downtime for replacement is operationally disruptive. Surfacing technology, combined with proper quality control, can extend component life by multiple operating cycles, providing significant return on investment.