CLADDING TECHNOLOGY SHANXI CO., LTDLarge-Area Wear-Resistant Patterned Overlay Welding on Middle Trough of Longwall Mining Conveyor
Literature Overview
The middle trough (scoop conveyor trough) is a critical structural component in longwall mining systems, subjected to severe abrasive wear from coal-rock mixture transport. This study addresses the engineering challenge of applying large-area wear-resistant overlay welding with optimized pattern designs to extend service life. The literature reviews multiple pattern configurations including full coverage, cross-hatch, wave, and segmented strip patterns, evaluating their wear resistance, bonding strength, and cost-effectiveness in field conditions.
Core Technical Content
The fundamental challenge lies in balancing wear resistance with economic feasibility. Full-coverage overlay maximizes protection but significantly increases material consumption and welding time. The study proposes a hybrid pattern approach where high-wear zones receive dense overlay coverage while lower-stress areas use reduced-density patterns. This approach reduces overlay material usage by 35 to 45 percent while maintaining acceptable wear performance.
Pattern Design Principles
The pattern selection follows a systematic approach based on wear zone analysis. The following table summarizes the recommended pattern configurations for different wear severity zones:
| Wear Zone | Pattern Type | Overlay Thickness | Recommended Welding Process | Material Grade |
|---|---|---|---|---|
| High-abrasion (bottom center) | Full cross-hatch | 6-8 mm | SAW multi-pass | Cr-Mo-B cast iron |
| Medium-abrasion (side walls) | Segmented strip | 4-6 mm | SAW single/multi-pass | Cr-Mn-B alloy |
| Low-abrasion (end sections) | Spot/wave pattern | 3-5 mm | FCAW or GMAW | Hardfacing alloy |
| Corner transitions | Overlapping bead | 5-7 mm | SAW with flux shielding | Cr-Mo-B cast iron |
Welding Process Parameters
The selected overlay process must account for the large plate dimensions (typically 2000-4000 mm length, 800-1200 mm width) and the need for uniform dilution control. Submerged arc welding (SAW) was identified as the primary process due to its high deposition rate and excellent slag protection. The following parameters were optimized through trial welding:
| Parameter | Value | Rationale |
|---|---|---|
| Base plate thickness | 12-20 mm Q345B | Standard trough material |
| Preheat temperature | 150-200°C | Prevent cold cracking in base |
| Interpass temperature | 150-250°C | Control thermal cycling |
| SAW current | 450-550 A | High deposition rate |
| SAW voltage | 32-38 V | Stable arc, good wetting |
| Travel speed | 250-350 mm/min | Balance dilution and penetration |
| Wire diameter | 2.0-2.8 mm | Feed stability |
| Flux type | HJ431 or equivalent | Low hydrogen, good slag fluidity |
Dilution Control and Microstructure
Dilution from the base metal is the primary factor affecting overlay hardness. With carbon steel base metal, dilution rates of 25-35 percent are typical for single-pass SAW overlay. The literature reports that multi-pass overlay with a transition layer reduces final dilution to 15-20 percent, achieving overlay hardness of 450-550 HV compared to 300-350 HV for single-pass deposits. The carbide morphology in the overlay is predominantly M7C3 (Cr7C3, Mo6C) type, providing good abrasion resistance against coal-rock mixtures.
Field Performance Data
The study reports comparative field trials over 6-12 month service periods. Full-pattern overlay extended trough life from approximately 3-4 months (unclad) to 14-18 months. The hybrid pattern approach achieved 11-14 months service life with 40 percent reduction in overlay material cost. Post-service examination revealed uniform wear across patterned areas with no spalling or delamination when bonding strength exceeded 250 MPa.
Integration with Engineering Practice
In practice, the large-area application presents several challenges beyond laboratory conditions. First, thermal distortion of the trough plate during multi-pass welding requires careful sequence planning. A symmetric welding sequence from the center outward minimizes angular distortion to less than 2 mm per meter. Second, the pattern transition zones between high-density and low-density areas require careful bead overlap to avoid stress concentration. Third, inspection of large areas for lack of fusion or cracking requires efficient NDT methods; magnetic particle testing (MT) combined with visual examination of bead profile was found to be the most practical approach for field conditions.
Key Questions and Reflections
The most significant insight from this literature is that pattern design optimization is not merely an economic consideration but also a metallurgical one. Overly dense patterns in low-wear zones create unnecessary thermal cycling that can embrittle the base metal near the weld interface. The hybrid approach respects both metallurgical and economic constraints. However, the study does not adequately address the effect of pattern geometry on residual stress distribution, which could influence fatigue life under cyclic loading conditions in mining applications. Future work should incorporate residual stress measurement (X-ray or hole-drilling method) at pattern transition zones to validate fatigue performance predictions.
Summary
This literature provides a practical framework for large-area overlay welding on mining conveyor troughs, emphasizing the synergy between pattern design, process selection, and field performance. The hybrid pattern approach represents a significant advancement over conventional full-coverage methods, offering substantial cost savings without compromising wear resistance. Engineers should note that successful implementation requires rigorous control of preheat, interpass temperature, and dilution management, as well as careful planning of the welding sequence to manage distortion. The study's findings are directly applicable to similar large-component overlay applications in mining, cement, and material handling industries.