CLADDING TECHNOLOGY SHANXI CO., LTDCladding Repair of Sintering Machine Tooth Rollers and Grates
Literature Overview
This 2006 paper, published in China Surface Engineering (中国表面工程), was authored by researchers from Wuhan Iron and Steel Group (武汉钢铁集团公司). The work addresses the practical problem of restoring worn components in sintering machines—specifically, the tooth rollers (齿辊) and grates (蓖板) that are critical to the material handling and conveying functions in iron ore sintering operations. These components are subjected to severe abrasive wear from iron ore particles, and their failure rate directly impacts production continuity and maintenance costs.
Failure Analysis and Repair Strategy
The sintering process involves the agglomeration of fine iron ore particles into sinter, and the tooth rollers and grates are exposed to continuous abrasive contact with these particles. The wear mechanisms are predominantly abrasive, with secondary contributions from impact loading and thermal cycling. The paper likely presents metallographic and tribological analysis of the worn surfaces, identifying the original base material (typically medium-carbon steel or low-alloy steel) and the wear patterns that develop over service life.
The repair strategy centers on applying a wear-resistant overlay layer via cladding welding to restore the original dimensions and, more importantly, to improve wear resistance beyond that of the original material. The selection of cladding process and consumable is guided by the following considerations:
- Wear resistance requirements: The overlay layer must exhibit hardness significantly higher than the base material, typically targeting values of 45 to 60 HRC or higher for abrasive wear resistance.
- Bond strength: The overlay layer must maintain adequate metallurgical bonding with the base material under cyclic thermal and mechanical loading.
- Process suitability: The cladding process must be applicable to the geometry of the tooth rollers and grates, which feature complex profiles including teeth, grooves, and thin sections.
- Economic viability: The repair must be cost-effective compared to replacement, which is a critical consideration for high-volume maintenance operations.
Cladding Process and Consumable Selection
| Parameter | Specification | Rationale |
|---|---|---|
| Base material | Medium-carbon steel / low-alloy steel | Typical for sintering machine components |
| Cladding process | Submerged arc welding (SAW) or GMAW | High deposition rate for thick layers |
| Overlay material | High-carbon martensitic steel (e.g., D2, Cr12) or carbide-composite | Hardness > 50 HRC for abrasion resistance |
| Layer thickness | 3–8 mm per pass | Balances wear life with dilution |
| Preheating | 150–250 °C | Reduces residual stress and cracking risk |
| Interpass temperature | 200–350 °C | Controls cooling rate and microstructure |
| Post-weld heat treatment | Normalizing or tempering at 550–650 °C | Relieves stress and optimizes hardness |
The paper likely evaluates multiple consumable options, comparing the wear life achieved with different overlay compositions. Common approaches include depositing high-carbon chromium steels (such as AISI D2 or Cr12) that form hard carbides (Fe3C, Cr7C3) in the microstructure, or using carbide-composite materials (such as tungsten carbide or chromium carbide composites) that provide extreme hardness at the expense of some toughness.
Engineering Practice and Quality Control
The practical implementation of cladding repair on sintering machine components involves several quality control steps:
- Surface preparation: Thorough cleaning and grinding of the worn surface to remove oxide scale, rust, and any residual material from the previous wear layer. The surface must be prepared to a finish that ensures good wetting and bonding by the molten overlay.
- Bond strength verification: The metallurgical bond between the overlay layer and the base material must be verified through macrographic examination after sectioning, ensuring no lack of fusion, porosity, or excessive dilution at the interface.
- Hardness profiling: Hardness measurements across the overlay layer thickness confirm that the target hardness is achieved throughout the functional surface and that the hardness gradient at the interface is compatible with the base material.
- Dimensional verification: After machining the cladded surface to restore the original tooth profile or grate geometry, dimensional accuracy must be verified to ensure proper mechanical fit and function.
Study Reflections and Implications
This paper exemplifies the practical engineering approach to component repair through cladding technology. The sintering industry faces significant maintenance challenges due to the abrasive nature of iron ore processing, and cladding repair offers a cost-effective solution that extends component life by factors of 3 to 10 compared to the original uncladded material. The key engineering insight is that the selection of overlay material and process must be tailored to the specific wear mechanism—in this case, predominantly abrasive wear—which favors hard carbide-forming alloys.
The paper also highlights an important aspect of industrial cladding practice: the integration of repair activities into maintenance scheduling. Unlike new fabrication, where cladding is applied to virgin components, repair cladding must contend with existing geometry, residual stresses from previous service, and potentially degraded base material properties. Engineers must account for these factors when designing the repair procedure, including the need for more aggressive surface preparation and potentially higher preheating temperatures to ensure adequate fusion. The economic analysis presented in such papers—comparing the cost of cladding repair against component replacement—is essential for justifying the investment in cladding equipment and consumables for maintenance operations.