Zhuojin Pipe Fitting Co., LtdHard Surfacing Wear-Resistant Plates for Coal Preparation Plant Chutes
Literature Overview
This paper by Wang Meng, Liu Shuliang, and Tang Linlin from Shandong Borun Industrial Technology Co., Ltd., published in Coal Processing and Comprehensive Utilization (2010, No. 6, pp. 32-33), reports on the application of hard surfacing wear-resistant plates manufactured using flux-cored wire open-arc surfacing (FCAW) technology as lining material for coal and gangue transport chutes in the Wangtaipu Coal Preparation Plant. The study demonstrates the microstructural characteristics, wear resistance, and economic benefits of the surfacing approach in a demanding abrasive environment.
Application Background and Wear Mechanism
Coal preparation plant chutes are subjected to severe abrasive wear from the continuous impact and sliding of coal particles, gangue, and moisture-laden material. The wear mechanism is predominantly abrasive, with two-body abrasion from hard mineral particles (quartz, feldspar) embedded in the coal mass and three-body abrasion from loose particles moving between the chute surface and the material stream.
The service conditions include:
| Parameter | Typical Value |
|---|---|
| Material hardness (Mohs) | 5-7 (quartz particles) |
| Impact velocity | 3-8 m/s |
| Material temperature | 20-60 °C |
| Abrasive particle size | 0.5-25 mm |
| Service life requirement | >12 months |
Conventional carbon steel chutes typically fail within 3-6 months due to abrasive wear, requiring frequent replacement and causing significant downtime. The hard surfacing approach aims to extend service life by providing a wear-resistant surface layer on a ductile base plate.
Surfacing Process and Microstructural Analysis
The hard surfacing wear-resistant plates were manufactured using flux-cored wire open-arc surfacing (FCAW) on carbon steel base plates. The surfacing alloy was a high-carbon, high-chromium composition designed to produce a martensitic microstructure with dispersed hard carbides.
Microstructural Characteristics
The deposited layer microstructure consists of:
- Martensitic matrix: Formed by rapid solidification and self-quenching from the high carbon equivalent of the surfacing alloy. The martensite provides the base hardness of the deposit.
- Dispersed carbides: Primary carbides (Cr7C3, Cr23C6, and Fe3C) nucleate during solidification and provide the primary wear resistance mechanism. The carbide morphology—whether rod-like, worm-like, or cubic—affects the wear resistance characteristics.
- Uniform distribution: The paper reports a uniform microstructure with no significant defects, indicating good process control during surfacing.
Wear Resistance Performance
The wear resistance of the surfaced plates was evaluated through comparative testing against the original carbon steel chute material. The hard surfacing alloy typically achieves surface hardness of 55-65 HRC, compared to 15-25 HRC for the base carbon steel. This hardness improvement translates to a significant increase in abrasive wear resistance, as the wear rate of surfacing alloys is inversely proportional to the square of the hardness for abrasive wear conditions.
The microstructural uniformity is particularly important for chute lining applications, as non-uniform microstructures can create localized soft spots that initiate preferential wear and lead to premature failure. The FCAW process with flux-cored wire provides consistent arc characteristics and metal transfer, contributing to the uniform microstructure reported in this study.
Economic and Operational Benefits
The application of hard surfacing wear-resistant plates in the Wangtaipu Coal Preparation Plant demonstrated measurable economic benefits:
| Metric | Original Carbon Steel Chute | Surfaced Wear-Resistant Plate | Improvement |
|---|---|---|---|
| Service life | 3-6 months | 12-18 months | 2-3x extension |
| Replacement frequency | 2-4 times/year | 1 time/year | 50-75% reduction |
| Downtime for replacement | 8-16 hours/year | 4-8 hours/year | 50% reduction |
| Total cost per year | High (material + labor + downtime) | Lower (despite higher initial cost) | Significant savings |
The extended service life reduces not only material costs but also the indirect costs associated with production downtime, maintenance labor, and logistics for spare parts. For coal preparation plants operating at high capacity, even a modest extension of chute lining life can result in substantial annual savings.
Engineering Considerations for Chute Lining Application
Several practical considerations must be addressed when applying hard surfacing wear-resistant plates as chute lining:
- Thermal expansion mismatch: The surfacing layer and base plate have different thermal expansion coefficients, which can cause delamination under thermal cycling. The surfacing process must produce a metallurgical bond with adequate ductility in the transition zone.
- Impact resistance: While hardness improves wear resistance, excessive brittleness in the surfacing layer can lead to spalling under impact loading. The martensitic microstructure must be tempered to an appropriate hardness level that balances wear resistance with impact toughness.
- Mounting and installation: Surfaced plates must be securely attached to the chute structure using welding, bolting, or mechanical fastening. The attachment method must accommodate differential thermal expansion and vibration loading.
- Surface preparation: Before surfacing, the base plate surface must be cleaned and prepared to ensure proper wetting and adhesion. Surface oxidation, rust, and contamination must be removed by grinding or shot blasting.
The paper provides a clear demonstration that hard surfacing technology can be effectively applied to extend the service life of wear-critical components in coal processing applications. The combination of appropriate alloy selection, controlled surfacing process, and proper installation practice results in a cost-effective solution that significantly improves the operational reliability of coal preparation plant chutes. Engineers considering similar applications should pay particular attention to the balance between hardness and toughness in the surfacing alloy, as the optimal composition depends on the specific wear conditions and impact loading in the application.