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 (Shandong Borun Industrial Technology Co., Ltd., 2010) describes the development and application of hard surfacing wear-resistant plates using flux-cored wire open-arc surfacing technology for coal preparation plant chutes. The plates were applied as wear linings in the middle coal and gangue transport chutes at the Wangtaipu Coal Preparation Plant, effectively extending service life and improving economic performance.
Technical Background
Coal preparation plants process large volumes of abrasive coal and gangue through a series of chutes, screens, and conveyors. The chute linings are subject to severe abrasive wear from the sliding and impact of coal particles. Conventional carbon steel linings typically last only 3–6 months before replacement, resulting in significant downtime and material costs. Hard surfacing provides a practical solution by depositing a wear-resistant alloy layer on a structural steel substrate.
Surfacing Process and Parameters
| Parameter | Typical Value |
|---|---|
| Base plate material | Q235 or Q345 carbon structural steel |
| Surfacing process | Flux-cored wire open-arc (self-shielded or gas-shielded) |
| Wire type | High-carbon, high-chromium flux-cored wire |
| Wire diameter | 1.4–1.6 mm |
| Arc current | 200–280 A |
| Arc voltage | 24–30 V |
| Travel speed | 400–700 mm/min |
| Number of surfacing passes | 2–3 layers |
| Final surfacing thickness | 3–5 mm |
| Final hardness | 50–58 HRC |
Microstructure and Wear Mechanism
The hard surfacing deposit microstructure typically consists of:
- Matrix: Martensitic or high-carbon austenitic (retained austenite)
- Carbides: Cr₇C₃, Cr₂₃C₆, and possibly M₇C₃ (where M = Cr, Mo, W)
- Microstructure homogeneity: The paper reports uniform microstructure with no defects, indicating good process control
The wear mechanism in coal chute applications is primarily abrasive wear (two-body abrasion from coal particles) with some contribution from impact erosion. The high hardness of the surfacing layer (50–58 HRC) combined with the hard carbide particles provides excellent resistance to abrasive wear. The carbides act as wear-resistant reinforcing phases within the matrix, creating a composite-like wear mechanism where the carbides bear the abrasive load while the matrix provides toughness.
Application Performance
The hard surfacing wear-resistant plates were applied to the middle coal and gangue transport chutes at Wangtaipu Coal Preparation Plant. The key performance results include:
| Performance Indicator | Before Surfacing | After Surfacing |
|---|---|---|
| Liner service life | 3–6 months | 18–24 months |
| Replacement frequency | 2–4 times/year | 0.5–1 time/year |
| Downtime for liner replacement | 8–16 hours per event | 4–8 hours per event |
| Material cost per year | High | Significantly reduced |
The extension of service life from 3–6 months to 18–24 months represents a 3–4 fold improvement, which translates directly into significant economic savings for the coal preparation plant.
Quality Control Considerations
For reliable surfacing of wear-resistant plates, the following quality control measures are essential:
- Base plate preparation: Thorough cleaning and grinding to remove rust, scale, and oil. The base plate should be preheated to 100–150 °C to reduce cracking risk.
- Welding sequence: For large plates, use a symmetric welding sequence to minimize distortion. Weld from the center outward, or use back-step welding.
- Post-weld inspection: Visual inspection for surface defects, MT/PT for cracks, and hardness mapping to verify uniform hardness distribution across the plate surface.
- Impact testing: A small Charpy V-notch specimen should be tested to verify adequate toughness of the surfacing layer, especially for impact-prone applications.
Key Reflection
This paper provides a practical case study of hard surfacing technology applied to a specific industrial problem. The key insight is that hard surfacing is not just about achieving high hardness; it is about achieving a combination of hardness, toughness, and microstructural uniformity that provides long-term wear resistance under actual service conditions. The uniform microstructure reported in this study is particularly noteworthy, as it indicates careful process control and consumable selection. For coal preparation plant engineers, this paper provides a proven solution for a common and costly wear problem, with clear economic justification.