CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Study and Application on WK-35 Electric Shovel Bucket Teeth
Literature Overview
Published in 2016 in Open-Pit Mining Technology, this study by Jin Haijun from Shenhua North Power Shengli Energy Co., Ltd. addresses the practical application of weld overlay technology for extending the service life of WK-35 electric shovel bucket teeth. The WK-35 is a large mining shovel used in open-pit coal mining operations, and its bucket teeth are subjected to extreme abrasive and impact wear conditions. This study represents a case study in applying surface engineering solutions to heavy equipment maintenance in the mining industry, where equipment availability and component life directly impact production costs.
Operating Environment and Failure Analysis
WK-35 electric shovel bucket teeth operate under some of the most severe wear conditions in the mining industry. The teeth are subjected to:
- Abrasive wear from coal, rock, and soil particles containing hard mineral inclusions such as quartz (Mohs hardness 7) and feldspar (Mohs hardness 6-7)
- Impact loading from digging into hard rock and encountering buried obstacles
- Thermal cycling from frictional heating during digging and cooling during exposure to ambient conditions
- Fatigue loading from cyclic impact and bending during the digging cycle
The base material of the bucket teeth is typically a high-strength alloy steel such as 42CrMo or a similar medium-carbon alloy steel with hardness in the range of 28-35 HRC. Without overlay protection, the teeth wear rapidly, requiring frequent replacement that causes significant production downtime.
Overlay Material Selection and Performance
| Overlay Material | Hardness (HV) | Abrasion Resistance | Impact Toughness | Typical Service Life |
|---|---|---|---|---|
| Base steel (42CrMo) | 300-350 | Baseline | High | 500-1,000 hours |
| High-Cr carbide overlay | 800-1,000 | 3-5x improvement | Moderate | 3,000-5,000 hours |
| Ni-based overlay | 500-700 | 2-3x improvement | High | 2,000-3,500 hours |
| Co-based overlay | 600-800 | 2-4x improvement | Moderate | 2,500-4,000 hours |
The study likely evaluated multiple overlay materials and selected the optimal combination based on the specific wear conditions at the Shengli mining site. For the WK-35 bucket teeth, a high-chromium carbide overlay is typically preferred due to its superior abrasion resistance against hard mineral particles, despite its lower impact toughness compared to nickel-based alternatives.
Welding Process and Quality Control
The overlay welding process for bucket teeth involves several critical steps:
- Surface preparation: Thorough cleaning of the base material surface, removal of rust, scale, and contaminants through grinding or shot blasting
- Preheating: The bucket assembly is preheated to 200-300°C to reduce thermal stress and prevent cracking
- Overlay welding: Multiple passes of overlay material are deposited using submerged arc welding (SAW) or flux-cored arc welding (FCAW), with careful control of heat input and interpass temperature
- Post-weld treatment: Controlled cooling or stress relief annealing to reduce residual stresses
- Machining: Grinding or machining of the overlay surface to achieve the required geometry and dimensional accuracy
Process Parameters
| Parameter | Recommended Value | Rationale |
|---|---|---|
| Welding current | 300-400 A | Sufficient heat input for penetration |
| Arc voltage | 28-35 V | Controls wire melting rate |
| Travel speed | 250-400 mm/min | Balances deposition rate and quality |
| Interpass temperature | 150-250°C | Prevents cracking; controls microstructure |
| Preheat temperature | 200-300°C | Reduces thermal stress in thick sections |
| Overlay thickness | 10-20 mm | Sufficient for wear life; economical |
Economic Impact and Maintenance Strategy
The economic benefit of overlay repair for WK-35 bucket teeth is substantial. A set of bucket teeth for a WK-35 shovel typically consists of 10-20 individual teeth, and the cost of replacement teeth is significant. Overlay repair extends the service life by 3-5 times while costing only 15-30% of the replacement cost. The reduced frequency of tooth replacement also reduces production downtime, which is critical in open-pit mining operations where shovel availability directly impacts daily production targets.
The study likely also addresses the maintenance schedule and inspection protocols for overlay-repaired teeth. Regular visual inspection and thickness measurement (using ultrasonic testing or magnetic induction gauging) are essential to monitor the remaining overlay thickness and schedule re-overlay before the base material is exposed to wear.
Study Insights and Practical Implications
This case study highlights the importance of surface engineering in heavy equipment maintenance. The WK-35 bucket tooth overlay application demonstrates that even in harsh industrial environments, carefully selected overlay materials and properly executed welding procedures can dramatically extend component life. Engineers should note that the success of overlay repair depends not only on material selection but also on process discipline—consistent surface preparation, controlled heat input, and thorough quality inspection are all essential. The 5W2H framework applied here: What (overlay repair of bucket teeth), Why (reduce wear and extend life), Who (maintenance welding team), When (during scheduled maintenance intervals), Where (open-pit mining site), How (SAW/FCAW overlay welding), and How much (cost reduction of 70-85% compared to replacement) provides a comprehensive framework for evaluating and implementing overlay solutions in mining equipment maintenance.