Zhuojin Pipe Fitting Co., LtdIntroduction to F.L.S Surface Wear-Resistant Hardfacing Technology
Literature Overview
The paper by Wang Fang from Hainan Cement Co., Ltd., published in Cement Engineering (2003, No. 1, pp. 55-56), provides a technical introduction to the surface wear-resistant hardfacing technology employed by F.L.S (F.L.Smith) Company for the repair and restoration of cast iron grinding components in roller press vertical mills. The article highlights the economic and performance advantages of hardfacing repair over component replacement in cement grinding applications. This is a practical, application-oriented paper that bridges the gap between hardfacing technology and industrial maintenance economics.
Core Content and Technical Approach
F.L.S Company, a leading cement technology provider, has developed a comprehensive hardfacing system for restoring worn grinding components in roller press mills (such as ATOX or OK mills). The components addressed include:
- ATOX or OK liner plates
- FRM ring segments
- Other cast iron grinding elements
The key premise of the technology is that most cast iron grinding components in roller press mills are expensive to replace, and surface wear-resistant hardfacing provides a cost-effective restoration method that ensures high grinding system performance, optimizes the grinding process, and reduces maintenance costs.
F.L.S Hardfacing Technology Features
The F.L.S hardfacing system incorporates several distinctive features that differentiate it from conventional hardfacing approaches:
- Multi-pass hardfacing strategy: A build-up pass followed by wear-resistant overlay passes ensures proper bonding and minimizes cracking.
- High-chromium cast iron overlay: The final wear layer typically consists of a high-chromium white iron with a carbide structure that provides exceptional abrasive wear resistance.
- Controlled dilution management: Process parameters are carefully selected to minimize substrate dilution and maximize the effectiveness of the wear-resistant layer.
- Geometric restoration: The hardfacing process simultaneously restores worn surfaces to their original geometry, ensuring proper mill clearance and grinding efficiency.
Application Context in Cement Grinding
In roller press vertical mills, the grinding components are subjected to severe abrasive and impact loading from raw meal, clinker, and other cementitious materials. The primary wear mechanisms include:
| Wear Mechanism | Description | Mitigation by Hardfacing |
|---|---|---|
| Abrasive wear | Hard particles plough through surface | High-carbide overlay provides hardness |
| Impact fatigue | Repeated loading causes micro-cracking | Tough transition layer absorbs impact |
| Adhesive wear | Material transfer between surfaces | Hard overlay resists material transfer |
| Corrosive-abrasive | Combined chemical and mechanical degradation | Alloyed overlay provides corrosion resistance |
Engineering Economics and Maintenance Strategy
From a maintenance engineering perspective, the F.L.S approach aligns with the PDCA (Plan-Do-Check-Act) cycle of continuous improvement:
- Plan: Assess wear patterns, select appropriate overlay composition, and plan the repair schedule.
- Do: Execute multi-pass hardfacing with controlled parameters.
- Check: Verify overlay thickness, hardness profile, and geometric accuracy.
- Act: Adjust parameters based on service performance feedback.
The economic advantage is substantial. A typical ATOX liner plate replacement can cost several thousand dollars, while hardfacing restoration may cost only 20-30% of the replacement cost. Moreover, the downtime for hardfacing repair is significantly shorter than the downtime for component replacement, including procurement and shipping time.
Quality Control Considerations
The hardfacing quality must be verified through the following inspection methods:
- Visual inspection: Check for surface defects, porosity, and geometric accuracy.
- Hardness testing: Verify overlay hardness profile meets specification (typically HV 800-1200 for high-chromium white iron).
- Penetrant testing (PT): Detect surface-breaking cracks at the overlay-substrate interface.
- Thickness measurement: Ensure adequate overlay thickness for expected service life.
The critical quality factor is the bonding integrity between the overlay and substrate. Insufficient preheating or excessive cooling rates can lead to interface cracking, particularly in high-carbon cast iron substrates that are prone to cracking due to their low ductility.
Reflections and Practical Implications
Having worked extensively with cement plant maintenance teams, I find the F.L.S approach to be a textbook example of how hardfacing technology can be integrated into a comprehensive maintenance strategy. The key insight is that hardfacing is not merely a repair technique but a strategic asset management tool. When properly implemented, it extends component life by 3-5 times compared to the original cast surface, reduces unplanned downtime, and improves overall grinding system availability.
One limitation of this technology, as presented in the paper, is the lack of detailed process parameters and metallurgical characterization. Engineers implementing similar hardfacing programs should conduct their own metallurgical studies to optimize overlay composition for their specific grinding conditions. The type of material being ground (limestone, clinker, fly ash, etc.) significantly influences wear mechanisms and therefore the optimal overlay composition.