CLADDING TECHNOLOGY SHANXI CO., LTDField Cladding Repair of Metal-Matrix Ceramic Grinding Discs
Literature Overview and Industrial Application Context
The study by Ni Junjie and Yang Wei of the Zhengzhou Institute of Mechanical Research, published in the New Century Cement Guide in 2013, addresses the field repair of metal-matrix ceramic grinding discs using arc cladding technology. Metal-matrix composite (MMC) grinding discs are widely used in the cement industry for grinding clinker and raw materials in ball mills and vertical mills. These discs are typically fabricated from a metal matrix reinforced with ceramic particles or fibers, providing a combination of toughness and wear resistance. However, the grinding discs are subjected to severe abrasive wear during operation, and when the disc surface is worn beyond the acceptable limit, the entire disc must traditionally be replaced at significant cost and downtime. The field cladding repair methodology presented in this study offers a practical solution for restoring worn grinding discs to service condition.
Technical Methodology and Process Parameters
The field repair process involves the application of a wear-resistant alloy overlay onto the worn surface of the grinding disc using arc welding techniques. The following table summarizes the key process parameters and materials used:
| Process Parameter | Specification |
|---|---|
| Welding process | Submerged arc welding (SAW) or flux-cored arc welding (FCAW) |
| Filler metal | High-chromium cast iron (e.g., 35CrMo) or carbide-containing alloy (e.g., Cr3C2 or WC particles) |
| Wire diameter | 2.0–3.2 mm |
| Welding current | 400–600 A |
| Arc voltage | 28–36 V |
| Travel speed | 150–350 mm/min |
| Cladding thickness | 3–8 mm per repair cycle |
| Number of passes | 1–3 passes depending on wear depth |
| Preheat temperature | 150–200 °C |
| Interpass temperature | ≤300 °C |
The selection of filler metal is critical to the success of the repair. High-chromium cast iron alloys provide good wear resistance through the formation of hard chromium carbides, while carbide-containing alloys offer superior abrasion resistance through the dispersion of hard carbide particles (Cr3C2 or WC) in a tougher matrix. The choice between these two types of filler metal depends on the specific wear conditions in the grinding mill—high-chromium alloys are preferred for moderate abrasive wear, while carbide-containing alloys are used for severe abrasive wear conditions.
Field Repair Procedure and Quality Control
The field repair procedure follows a systematic approach to ensure reliable repair quality:
- Assessment and preparation: The worn surface is assessed to determine the depth of wear and the extent of damage. The surface is ground to remove all worn material and any contaminated zones, exposing sound base metal. The surface roughness is controlled to Ra ≤ 12.5 μm to ensure good weld adhesion.
- Preheating: The grinding disc is preheated to 150–200 °C using a gas flame or electric heating element. Preheating reduces the thermal gradient at the weld zone, minimizing the risk of cracking in the base metal and the weld metal.
- Cladding welding: The cladding is applied in one or more passes, with the first pass providing full penetration into the base metal and subsequent passes building up the required thickness. The welding sequence is planned to minimize distortion, with alternating weld directions and a spiral or circumferential welding pattern.
- Post-weld treatment: The cladding surface is ground or machined to the required dimensional accuracy and surface finish. For carbide-containing overlays, the surface may be peened to enhance fatigue resistance.
- Quality verification: The repair is verified through visual inspection, magnetic particle testing (MT) for surface cracks, hardness testing of the cladding layer, and dimensional inspection. The hardness of the cladding layer should be ≥500 HV for high-chromium alloys and ≥700 HV for carbide-containing alloys.
Engineering Practice and Performance Evaluation
The field cladding repair methodology was applied to multiple grinding discs in cement production facilities. The performance evaluation included monitoring of the discs during subsequent operation to assess wear resistance and service life:
- Wear resistance: The cladded grinding discs exhibited wear rates of 0.3–0.8 mm per 1000 hours of operation, compared to 1.5–3.0 mm per 1000 hours for the original metal-matrix composite discs. This represents a wear resistance improvement of 3–5 times.
- Service life: The cladded discs achieved service lives of 800–1500 hours, compared to 300–600 hours for the original discs, representing a significant extension of service life.
- Cost-effectiveness: The field repair cost was approximately 20–35% of the cost of replacing the disc with a new unit, providing substantial economic savings.
- Production impact: The repair could be performed during scheduled maintenance periods, minimizing production downtime compared to the extended lead time required for disc replacement.
A notable finding from the field trials was that the cladding layer exhibited good adhesion to the metal-matrix composite base material, with no instances of delamination or spalling observed during the service life of the repaired discs. This is attributed to the careful control of welding parameters and the use of compatible filler metals that minimize dilution and cracking at the interface.
Key Reflections and Study Insights
This research demonstrates the practical applicability of arc cladding technology for the field repair of worn components in heavy industry. The methodology is particularly valuable for large, expensive components such as grinding discs, where replacement is costly and time-consuming. The key to successful field repair lies in the careful selection of filler metal, the optimization of welding parameters, and the implementation of rigorous quality control procedures. The research also highlights the importance of post-repair performance monitoring to validate the effectiveness of the repair methodology and to provide data for continuous improvement. From a broader perspective, this work contributes to the development of a sustainable repair culture in heavy industry, where the extension of component life through surface engineering is preferred over premature replacement. The methodology can be adapted for the repair of other worn components in the cement, mining, and power generation industries, providing a versatile tool for asset management and maintenance engineering.