CLADDING TECHNOLOGY SHANXI CO., LTDQuality Control of Wear-Resistant Parts Cladding in Cement Equipment
Literature Overview
This 2014 publication in the New Century Cement Guide by Zhang Liguo and Zhong Libin from Sinoma International Engineering Co., Ltd. Tianjin Branch addresses the practical challenges of maintaining cladding quality on wear-resistant components in cement production equipment. Cement plants are notorious for their abrasive and corrosive operating environment, where equipment components such as kiln linings, mill liners, fan blades, and conveyor parts experience severe wear. The study provides a comprehensive quality control framework specifically tailored to the cement industry, drawing on extensive field experience from Sinoma's engineering operations.
Core Technical Content
Cement equipment components face a unique combination of wear mechanisms:
- Abrasive wear from cement clinker and raw meal particles (primarily quartz, feldspar, and calcite)
- Impact wear from falling materials in mills and kilns
- Corrosive wear from SO2, CO2, and acid compounds at elevated temperatures
- Thermal fatigue from cyclic heating and cooling
The overlay materials used in cement equipment include:
| Application | Overlay Material | Hardness (HRC) | Service Life Improvement |
|---|---|---|---|
| Mill liners (grinding balls) | High-chromium cast iron (Cr20) | 55-62 | 3-5x |
| Fan blades and hoods | Stellite 6 / Co-Cr alloy | 40-45 | 4-6x |
| Kiln shell wear plates | H13 hot work steel | 45-50 | 2-3x |
| Conveyor wear plates | Mn13 high-manganese steel | 20-25 (work-hardened to 45-50) | 2-4x |
| Silo and hopper linings | Hardfacing alloy (Fe-Cr-C) | 50-60 | 3-5x |
| Crusher hammers and jaws | Ni-Hard II | 55-65 | 4-7x |
Quality Control Framework
The study proposes a systematic quality control approach based on the PDCA (Plan-Do-Check-Act) cycle:
Planning Phase
- Material selection based on wear mechanism analysis: Identify the dominant wear mechanism for each component and select the overlay material accordingly. For abrasive wear, high-carbon, high-chromium materials are preferred; for impact-abrasive wear, high-manganese austenitic materials are more appropriate.
- Process selection: Match the welding process to the component geometry and production volume. GMAW is preferred for large, flat surfaces; SAW is suitable for thick overlays; and manual arc welding is used for complex geometries and repair work.
- Specification development: Define acceptance criteria for hardness, bond strength, surface finish, and defect tolerance.
Execution Phase
- Surface preparation: Remove rust, scale, and old coating to a clean, sound surface. Surface roughness should be Ra 12.5-25 μm to ensure good metallurgical bonding.
- Welding process control: Monitor current, voltage, travel speed, and electrode/feed wire temperature throughout the welding operation. Deviations from specified parameters must be recorded and investigated.
- Layer-by-layer inspection: After each layer, inspect for cracks, porosity, and incomplete fusion. Any defects must be repaired before proceeding to the next layer.
Checking Phase
- Hardness testing: Measure hardness at multiple locations across the overlay surface. The hardness profile should be uniform within ±5 HRC of the target value.
- Bond strength testing: Perform tensile bond strength tests per ASTM A263 or equivalent. Acceptance criterion is typically ≥ 400 MPa.
- Non-destructive testing: Apply magnetic particle inspection (MT) for surface cracks and dye penetrant inspection (PT) for surface-breaking defects. Ultrasonic testing (UT) may be used for subsurface defect detection on thick overlays.
Action Phase
- Documentation and traceability: Record all process parameters, test results, and any corrective actions taken. This documentation is essential for continuous improvement and for identifying failure modes when components are removed from service.
- Field performance tracking: Monitor the service life of cladded components and correlate with the quality of the overlay work. This feedback loop is critical for refining material selection and process parameters.
Common Defects and Root Cause Analysis
| Defect | Frequency | Root Cause | Corrective Action |
|---|---|---|---|
| Overlay spalling | High | Poor surface preparation, excessive dilution | Improve grinding quality, use buffer layer |
| Cracking at bond line | Medium | High residual stress, brittle HAZ | Increase preheat, apply post-weld stress relief |
| Incomplete fusion | Medium | Low current, excessive travel speed | Adjust process parameters, verify electrode condition |
| Porosity | Medium | Moisture in consumables, contaminated surface | Dry electrodes/flux, clean surface thoroughly |
| Excessive undercut | Low | Poor technique, improper electrode angle | Retrain welder, adjust electrode angle to 70-80° |
| Hardness variation | Medium | Inconsistent process parameters, dilution variation | Implement real-time parameter monitoring |
Engineering Practice Insights
The cement industry presents unique challenges for cladding quality control due to the scale of operations and the continuous nature of production. Equipment downtime for re-cladding is extremely costly, with each day of downtime potentially costing tens of thousands of dollars in lost production. Therefore, the quality of the initial cladding work has a direct and significant impact on the overall economics of cement plant operations.
A key insight from this work is that the most effective quality control is achieved through a combination of process standardization and operator training. Automated welding systems (GMAW with mechanized heads) provide superior consistency compared to manual welding, but require significant capital investment. For smaller components and repair work, manual welding is more practical, but requires rigorous qualification of welders and continuous monitoring of their performance.
The study also emphasizes the importance of surface preparation as the most critical factor in overlay quality. Even with the best welding consumables and process parameters, poor surface preparation will result in inadequate bonding and premature failure. The recommendation to grind to a minimum of Sa 2.5 surface cleanliness (per ISO 8501-1) is a practical guideline that should be followed in all cement equipment cladding operations.