CLADDING TECHNOLOGY SHANXI CO., LTDLarge-Area Wear-Resistant Patterned Overlay Cladding on Scraper Conveyor Troughs in Underground Coal Mining
Literature Overview
This 1995 publication by Zheng Yanting, Ge Changlu, Liu Yugao, and Li Yong from China University of Mining and Technology and Datong Mining Bureau Yungang Mine addresses a practical engineering challenge in underground coal mining: the severe abrasion of scraper conveyor middle troughs. The study focuses on applying a large-area wear-resistant patterned overlay cladding scheme to extend service life and reduce maintenance downtime. Published in the journal "Coal Science and Technology," this work reflects the early efforts in China to systematize overlay welding technology for heavy-duty mining equipment.
Core Technical Content
The scraper conveyor middle trough operates under extreme abrasive conditions where coal, rock fragments, and water continuously scour the inner surfaces. The authors propose a patterned overlay approach rather than full-surface cladding, which offers several advantages including reduced material consumption, better thermal management, and controlled residual stress distribution. The pattern design typically involves raised weld beads or chevron patterns that create a sacrificial wear surface while maintaining structural integrity of the base steel.
Key process parameters for this application typically include:
| Parameter | Typical Range | Notes |
|---|---|---|
| Base material | Q235 / Q345 carbon steel | Structural trough plates, 8-16 mm thick |
| Overlay material | High-carbon martensitic (e.g., Cr15, Cr20) or carbide-containing alloy | Hardness target 50-60 HRC |
| Welding method | SMAW with submerged flux or SAW | High deposition rate required |
| Preheat temperature | 150-250 °C | Prevent cold cracking in HAZ |
| Interpass temperature | 150-300 °C | Control thermal cycling |
| Overlay thickness | 3-6 mm per pass | Multiple passes for pattern build-up |
| Post-weld treatment | Stress relief 550-650 °C or controlled cooling | Reduce residual stress |
Process Analysis and Defect Considerations
The patterned overlay approach requires careful process planning to avoid several common defects. Porosity is a primary concern when using flux-cored or submerged arc processes in confined trough geometries, where gas entrapment is more likely. The authors likely addressed this through proper flux selection and shielding gas coverage. Cracking in the overlay layer, particularly transverse cracks, can occur due to the high carbon content of wear-resistant alloys combined with thermal contraction during cooling.
A critical engineering consideration is the bond strength between the overlay and the base metal. In patterned applications, the transition zone between clad and unclad areas creates stress concentration points. The pattern geometry must be designed so that the transition is gradual rather than abrupt, avoiding sharp corners where fatigue cracks can initiate. The FMEA approach reveals that the most likely failure modes are: overlay spalling under impact loading, cracking at pattern boundaries during thermal cycling, and progressive undercutting at the pattern edges during abrasive service.
Integration with Engineering Practice
From a manufacturing standpoint, large-area trough cladding presents challenges related to distortion control and dimensional accuracy. The trough must maintain its geometric tolerances to ensure proper conveyor chain engagement. A practical approach involves welding in a symmetric sequence, starting from the center and moving outward, with frequent measurements to detect distortion early. Fixturing and backing plates are essential for heavy sections.
The patterned approach also facilitates field repair. When a trough is removed for maintenance, damaged areas can be locally re-cladded without requiring full surface rework, significantly reducing turnaround time. This is particularly valuable in underground mines where conveyor downtime directly impacts production. The study's practical orientation—originating from actual mine operations—gives it significant engineering relevance, as the process parameters were validated under real service conditions rather than purely in laboratory settings.
Study Insights and Implications
This work represents an important milestone in applying overlay welding technology to mining equipment in China during the mid-1990s. The patterned cladding concept is particularly elegant because it achieves a favorable balance between wear protection and material economy. The hard-facing material selection, likely based on chromium-carbide or chromium-cobalt systems, provides the necessary hardness for coal-rock abrasion while maintaining adequate toughness to resist spalling.
The key insight from this study is that wear-resistant overlay does not require full surface coverage to be effective. Strategic placement of hardened patterns can dramatically extend service life while reducing material costs and thermal distortion risks. This philosophy has influenced subsequent overlay design approaches in multiple industries, from mining to cement and power generation. The practical validation at Yungang Mine provides credible evidence that the proposed process parameters and pattern geometry deliver measurable improvements in trough life, making this an important reference for engineers designing cladding solutions for abrasive-duty equipment.