CLADDING TECHNOLOGY SHANXI CO., LTDF.L.S Company Surface Wear-Resistant Weld Overlay Technology Introduction
Literature Overview
This 2003 technical review by Wang Fang from Hainan Cement Co., Ltd. introduces the surface wear-resistant weld overlay technology developed by F.L.S (F.L.Smith) company, a leading global engineering and equipment supplier for the cement industry. The article provides a comprehensive overview of F.L.S's approach to applying wear-resistant overlay coatings to cement mill components, including mill liners, grinding rollers, and classifier blades. The technology is particularly relevant for engineers in the cement and mining industries who face severe abrasion challenges.
Core Technical Points
F.L.S's wear-resistant weld overlay technology encompasses several key aspects:
- Overlay alloy selection: F.L.S uses a range of proprietary overlay alloys tailored to specific wear conditions in cement mills. The alloys include:
| Alloy Type | Composition (wt%) | Hardness (HV) | Wear Resistance | Application |
|---|---|---|---|---|
| High-Cr cast iron | 28-32% Cr, 3-4% C | 500-600 | Excellent | Mill liners |
| High-Cr steel | 20-25% Cr, 0.5-1.0% C | 450-550 | Good | Grinding rollers |
| Austenitic Mn steel | 12-14% Mn, 1.0-1.5% C | 300-400 (work-hardened) | Good | Classifier blades |
| Ni-Cr alloy | 15-20% Ni, 10-15% Cr | 400-500 | Excellent | High-temperature zones |
- Welding process selection: F.L.S employs various welding processes depending on the component geometry and wear conditions:
- Submerged arc welding (SAW) for thick overlay layers on mill liners.
- Electroslag welding (ESW) for very thick overlays (>10 mm).
- Gas metal arc welding (GMAW) for moderate thickness overlays on rollers.
- Plasma transferred arc (PTA) welding for precision overlays on small components.
- Overlay design: The overlay thickness is optimized based on the expected wear rate and service life. Typical overlay thicknesses range from 3-10 mm for mill liners and 2-5 mm for rollers.
- Post-weld treatment: Some overlay alloys require post-weld heat treatment to achieve optimal hardness and toughness. For example, high-Cr cast iron overlays may require annealing to relieve residual stresses and prevent cracking.
Process Parameters and Quality Control
F.L.S's welding procedures include the following key parameters:
| Process | Heat Input (kJ/mm) | Interpass Temp (°C) | Preheat (°C) | PWHT (°C) |
|---|---|---|---|---|
| SAW | 2.0-4.0 | 200-300 | 150-250 | 600-700 |
| ESW | 5.0-10.0 | 250-350 | 200-300 | 650-750 |
| GMAW | 0.5-1.5 | 150-250 | 100-200 | 550-650 |
| PTA | 0.3-0.8 | 100-200 | 50-150 | 500-600 |
Quality control measures include:
- Visual inspection (VT) of all overlay welds for surface defects.
- Magnetic particle testing (MT) for surface and near-surface cracks.
- Ultrasonic testing (UT) for internal defects and bond strength verification.
- Hardness testing (HV) to verify that the overlay hardness meets specifications.
- Wear testing on coupon samples to validate wear resistance.
Common Defects and Countermeasures
| Defect | Cause | Countermeasure |
|---|---|---|
| Cracking | High residual stress; poor weldability | Preheat; controlled interpass temp; PWHT |
| Poor bond | Insufficient penetration; contamination | Clean base metal; increase heat input |
| Excessive dilution | High heat input; thin base metal | Reduce heat input; use GTAW for first pass |
| Hardness variation | Inconsistent welding parameters | Monitor and control parameters; qualified welders |
| Spatter | Excessive arc voltage; poor shielding | Adjust parameters; improve shielding gas flow |
Engineering Practice Implications
For cement mill operators, the adoption of F.L.S's wear-resistant weld overlay technology offers several benefits:
- Extended component life: Properly designed and applied overlay coatings can extend the service life of mill liners and rollers by 2-5 times compared to uncoated components.
- Reduced downtime: Longer service life means fewer shutdowns for component replacement, reducing production losses.
- Energy efficiency: Harder overlay surfaces can improve grinding efficiency, reducing specific energy consumption.
- Cost savings: Despite the initial cost of overlay welding, the extended service life and reduced downtime result in significant cost savings over the component lifecycle.
The article also emphasizes the importance of proper maintenance and inspection of overlay-coated components. Regular inspection using UT and MT can detect cracks and bond failures before they lead to catastrophic failure.
Key Questions and Reflections
A critical question is the long-term reliability of overlay coatings under cyclic loading and thermal cycling. Cement mill components experience repeated mechanical loading and thermal variations, which can lead to fatigue cracking and spalling of the overlay. The article does not extensively address these long-term degradation mechanisms, which are critical for predicting service life.
Another reflection is the importance of welder qualification and training. The quality of the overlay weld is highly dependent on the skill of the welder and the consistency of the welding parameters. F.L.S's approach likely includes rigorous welder qualification procedures, but the article does not provide details on this aspect.
Study Insights and Outlook
This literature provides a practical overview of F.L.S's wear-resistant weld overlay technology for cement mill components. The key insight is that proper alloy selection, process optimization, and quality control are essential for achieving reliable, long-lasting overlay coatings. Engineers in the cement industry should adopt these principles when specifying and implementing weld overlay solutions for their mill components. Future developments in this field may include advanced overlay alloys with improved wear resistance, automated welding systems for consistent quality, and predictive maintenance systems based on wear monitoring. The integration of these technologies will further enhance the reliability and cost-effectiveness of cement mill operations.