Zhuojin Pipe Fitting Co., LtdApplication of Hard Overlay Wear-Resistant Lining Plates in Electric Shovel Buckets
Literature Overview
The paper by Wang Hui, Tang Linlin, Wang Meng, and Yu Bing from Shandong Borun Industrial Technology Co., Ltd., published in Open-Pit Mining Technology (2011, Vol. 26, No. 3, p. 49), presents a case study on the application of hard overlay wear-resistant lining plates on the interior of electric shovel buckets used in open-pit mining operations. The authors analyze the operating conditions of electric shovel buckets, evaluate the wear resistance of hard overlay materials, and demonstrate that composite overlay lining plates can significantly extend bucket service life while reducing maintenance difficulty and costs. This is a classic example of applying advanced welding technology to solve a real-world industrial wear problem.
Operating Conditions and Wear Mechanisms
Electric shovel buckets in open-pit mining are subjected to extreme wear conditions characterized by:
- Abrasive wear from contact with hard rock and soil materials, often containing silica, quartz, and other hard minerals.
- Impact loading from the collision of bucket teeth and bucket walls with rock during digging and loading operations.
- Cyclic thermal stress in certain applications where material temperature variations occur.
- Corrosive environments in wet mining conditions where moisture accelerates material degradation.
The dominant wear mechanism in most open-pit mining applications is abrasive wear, where hard mineral particles plow across the bucket surface, causing material removal. The wear rate is governed by the Archard equation, which relates wear volume to applied load, sliding distance, and the hardness of the counterface materials. This makes surface hardness the primary design parameter for wear-resistant overlay materials.
Wear Mechanism Classification
| Wear Type | Mechanism | Dominant Material Property | Typical Service Life Without Overlay |
|---|---|---|---|
| Abrasive (two-body) | Hard particles plow surface | Surface hardness, toughness | 3–6 months |
| Abrasive (three-body) | Loose particles between surfaces | Hardness, ductility | 2–4 months |
| Impact wear | High-energy impact from rock | Toughness, hardness | 4–8 months |
| Corrosive wear | Chemical + mechanical action | Corrosion resistance | 2–3 months |
| Adhesive wear | Material transfer between surfaces | Hardness, surface finish | Variable |
Hard Overlay Lining Plate Technology
The paper describes the use of hard overlay welding to deposit wear-resistant lining plates on the bucket interior. The key technical aspects include:
- Overlay material selection. Hard overlay materials typically contain high concentrations of alloying elements such as chromium, molybdenum, tungsten, and vanadium, which form hard carbides (e.g., Cr7C3, WC, VC) that provide abrasion resistance. The overlay microstructure is generally a high-hardness martensitic matrix with dispersed carbide particles.
- Overlay process. The lining plates are typically produced using submerged arc welding (SAW) or flux-cored arc welding (FCAW) for high deposition rates and low dilution with the base metal. Multiple passes may be required to achieve the desired overlay thickness, typically 6–12 mm for bucket applications.
- Bonding strength. The overlay-to-base metal bond strength is critical for preventing delamination under impact and cyclic loading. The authors emphasize the importance of proper base metal preparation, including shot blasting to remove rust, scale, and contaminants, and ensuring adequate preheating to prevent cold cracking.
Typical Hard Overlay Material Properties
| Material Type | Hardness (HRC) | Dilution Rate | Key Carbides | Typical Application |
|---|---|---|---|---|
| High-carbon martensite | 50–58 | 5–10% | Fe3C | General wear surfaces |
| Chromium carbide | 58–65 | 3–8% | Cr7C3 | Abrasive mining wear |
| Tungsten carbide | 60–68 | 3–8% | WC, Fe3C | Severe abrasive wear |
| Vanadium carbide | 55–62 | 5–10% | VC, Fe3C | Impact-abrasive wear |
| Ceramic-reinforced | 65–75 | 2–5% | SiC, B4C | Extreme wear conditions |
Performance Results and Economic Analysis
The paper reports that the application of hard overlay lining plates resulted in:
- A 3–5 fold increase in bucket service life compared to unlined buckets.
- A 40–60% reduction in maintenance frequency, as the lining plates can be replaced independently of the bucket shell.
- A significant reduction in welding repairs during maintenance, as the lining plates can be removed and replaced rather than requiring in-situ welding of the entire bucket surface.
- Improved overall equipment availability due to reduced downtime for bucket replacement.
The economic analysis, while not quantified in detail in the paper, suggests that the initial investment in overlay lining plates is recovered within 1–2 maintenance cycles, after which the extended service life provides substantial cost savings.
Study Insights and Implications
This paper demonstrates the practical value of hard overlay welding technology in extending the service life of mining equipment. However, several considerations should be noted for engineers evaluating similar applications:
- Toughness-hardness trade-off. Hard overlay materials with very high hardness (HRC > 60) tend to be brittle and susceptible to spalling under impact loading. The selection of overlay material must balance abrasion resistance with impact toughness, particularly for applications involving large rock fragments.
- Residual stress management. Multi-pass overlay welding introduces significant residual stresses that can lead to cracking or delamination. Stress-relief heat treatment may be necessary for thick overlay deposits, but this must be balanced against the potential for softening of the overlay microstructure.
- Base metal compatibility. The base metal of the bucket shell (typically low-carbon or low-alloy steel such as A514 or equivalent) must be compatible with the overlay material to prevent cracking at the interface. Preheating temperatures of 100–200°C are typically recommended.
- Geometric constraints. The curvature of the bucket interior can complicate the overlay welding process, particularly at the transition between the bucket wall and the bucket bottom. Proper welding position management and electrode selection are critical.
The paper's recommendation to apply overlay lining plates rather than overlay the entire bucket surface is a practical approach that simplifies maintenance and reduces cost. This modular approach allows worn lining plates to be removed and replaced without affecting the structural integrity of the bucket shell.
In summary, this paper provides a clear demonstration of how hard overlay welding technology can be applied to solve severe wear problems in mining equipment. The combination of appropriate material selection, proper welding process control, and modular design of the lining plates offers a cost-effective solution for extending equipment life and reducing maintenance costs in open-pit mining operations.