Hard Overlay Wear-Resistant Plate Properties and Application in Coal Washing Plant Chutes

Literature Overview

The paper by Wang Meng, Liu Shuliang, and Tang Linlin (2010), published in "Coal Processing and Comprehensive Utilization" (No. 6, pp. 32-33), presents the development and application of hard overlay wear-resistant plates fabricated by flux-cored wire open-arc overlay welding technology. The study focuses on the microstructural characteristics, wear resistance properties, and practical application of these plates as lining material in the middle coal and gangue transport chutes of the Wangtaipu coal washing plant. The classification codes TD94 (coal washing) and TG455 (welding processes) reflect the interdisciplinary nature of the work, combining mining engineering with advanced welding technology. The practical outcome of this research is a significant extension of chute service life, demonstrating the economic viability of hard overlay welding for wear protection in coal handling systems.

Fabrication Technology and Process Parameters

The hard overlay wear-resistant plates are produced by depositing multiple layers of hardfacing alloy onto a steel substrate using flux-cored wire open-arc (GMAW-F) overlay welding. The open-arc configuration, combined with the self-shielded flux-cored wire design, provides the process flexibility required for manufacturing large-area wear-resistant plates in a workshop environment.

Fabrication Process Parameters

The multi-pass overlay approach is critical for achieving both the required overlay thickness and uniform hardness distribution. Each successive pass dilutes the previous layer with base metal, so the final passes must be designed to restore the target hardness. The overlapping bead pattern ensures complete surface coverage without gaps that would allow abrasive material to contact the base substrate.

Microstructural Characteristics and Wear Mechanisms

The overlay layer microstructure produced by the hardfacing alloy typically consists of a tempered martensite or bainite matrix with dispersed hard carbide particles. The carbide phase, often consisting of M7C3 or M23C6 type carbides depending on the specific alloy composition, provides the primary wear resistance mechanism. The matrix phase provides toughness and crack resistance, preventing spalling of the hard carbide particles under impact loading.

Microstructural Components and Functions

The wear mechanism in coal washing plant chute applications is primarily abrasive, where coal particles and gangue fragments are carried by water flow and impact the chute lining surface at high velocity. The hard carbide particles in the overlay layer resist micro-cutting and ploughing by the abrasive particles, while the tougher matrix phase absorbs impact energy and prevents crack propagation. The uniform microstructure and absence of defects reported in the study indicate good process control during plate fabrication.

Application Performance and Economic Analysis

The hard overlay wear-resistant plates were applied as lining material in the middle coal and gangue transport chutes of the Wangtaipu coal washing plant. The practical results demonstrated significant extension of chute service life compared to conventional unlined or painted steel chutes. The wear-resistant lining effectively protected the chute structure from abrasive erosion, reducing maintenance frequency and unplanned shutdowns.

Application Performance Comparison

The economic analysis favors the hard overlay lined chute for continuous coal washing operations, where the initial investment in overlay welding is recovered through reduced maintenance costs and improved plant availability within the first year of operation. The smooth surface finish of the overlay layer also improves material flow characteristics, reducing bridging and plugging problems that can occur with rough, corroded conventional steel surfaces.

Quality Control and Inspection

The study reports that the fabricated hard overlay wear-resistant plates exhibited uniform microstructure without defects such as porosity, cracks, or slag inclusions. This quality level was achieved through careful process control, including:

• Pre-weld cleaning of substrate surfaces to remove oil, rust, and scale
• Consistent welding parameters maintained throughout the overlay process
• Interpass slag removal and surface inspection between passes
• Post-weld hardness testing at multiple locations to verify uniformity
• Visual and magnetic particle inspection for surface and near-surface defects

The absence of defects in the overlay layer is particularly important for wear-resistant applications, as even small surface defects can initiate cracks that propagate under cyclic loading and lead to spalling of the overlay material.

Study Insights and Conclusions

This study demonstrates the successful application of hard overlay welding technology for wear protection in coal washing plant equipment. The combination of flux-cored wire open-arc overlay welding with carefully selected hardfacing alloy consumables produces wear-resistant plates with uniform microstructure, high hardness, and excellent abrasion resistance. The practical application in the Wangtaipu coal washing plant validates the technology and demonstrates significant economic benefits through extended service life and reduced maintenance costs. For coal processing and handling operations, the adoption of hard overlay wear-resistant linings represents a mature, cost-effective solution to the persistent challenge of abrasive wear in material handling equipment. The key to successful implementation lies in consistent process control during plate fabrication and proper installation to ensure the overlay layer remains intact during service.