CLADDING TECHNOLOGY SHANXI CO., LTDOnline Overlay Repair Device for Grinding Disc and Grinding Roller
Literature Overview
This 2012 publication by Wang Minsheng, Cheng Zhiguo, Liu Jianwei, Zhao Chunyan, Wu Zaimin, and Li Xiaoping, from the Harbin Welding Research Institute of the Mechanical Science Institute and Yushan Wanyangqing Cement Co., Ltd., describes the development and application of a novel online overlay repair device for grinding discs and grinding rollers in cement grinding mills. The work addresses a significant practical challenge in the cement industry: the need for rapid, in-situ repair of worn grinding components without complete equipment shutdown.
Core Technical Content
Cement grinding mills operate under extreme conditions of abrasive wear, with grinding discs and rollers subjected to continuous contact with hard cement clinker particles at high loads. Traditional repair methods require complete removal of worn components, transportation to a workshop for overlay welding, and reinstallation—a process that can result in production downtime of several days or even weeks. The online repair device described in this study enables overlay welding directly on the installed equipment, dramatically reducing repair time and associated production losses.
Device Configuration and Operating Principles
The online overlay repair device integrates several key subsystems:
| Subsystem | Function | Key Specifications |
|---|---|---|
| Positioning system | Aligns welding torch with worn surface | 3-axis adjustment, ±0.5 mm accuracy |
| Welding power source | Provides arc energy for overlay | 400–800 A, 25–35 V (SAW or FCAW) |
| Wire feed mechanism | Delivers consumable wire | 5–15 m/min, adjustable |
| Flux supply system | Provides protective flux for SAW | Automatic replenishment, hopper capacity 20 kg |
| Cooling system | Manages thermal input to base metal | Water-cooled torch, flow rate 8–12 L/min |
| Monitoring system | Tracks welding parameters in real time | Current, voltage, travel speed, interpass temperature |
| Safety enclosure | Protects operator from arc radiation | UV/IR shielding, fume extraction |
Welding Process Selection for Online Repair
The choice of welding process for online overlay repair of grinding components involves careful consideration of several factors:
- Submerged Arc Welding (SAW): Preferred for thick overlay layers (3–8 mm) due to high deposition rate (2.5–4.0 kg/h) and good penetration. The flux provides excellent protection against atmospheric contamination in the enclosed mill environment. Typical parameters: 500–700 A, 28–32 V, 8–12 m/min travel speed.
- Flux-Cored Arc Welding (FCAW): Suitable for thinner repairs (1–3 mm) and for situations where flux handling is impractical. Deposition rate of 1.5–3.0 kg/h with good adaptability to irregular surface geometries.
- Gas Metal Arc Welding (GMAW): Used for finishing passes and for repairs in positions where flux cannot be effectively applied. Lower deposition rate (1.0–2.0 kg/h) but excellent bead appearance and minimal spatter.
Overlay Material Selection
For cement grinding applications, the overlay material must balance hardness, toughness, and resistance to abrasive wear by cement clinker (which contains hard quartz, feldspar, and calcite particles). The study recommends the following overlay material specifications:
| Material Type | Typical Composition | Hardness (HV) | Application |
|---|---|---|---|
| High-carbon martensitic | 1.2–1.5% C, 0.5% Mn | 550–650 | General grinding disc repair |
| High-chromium cast iron | 12–20% Cr, 1.0–1.5% C | 600–800 | Severe abrasion areas |
| Cr-Mo-B alloy | 3% Cr, 0.8% Mo, 0.2% B | 700–850 | High-wear zones |
| Hardfacing composite | WC-Co or CrC-NiCr | 900–1200 | Critical wear points |
Engineering Implementation and Quality Control
The study documents several practical challenges encountered during online repair implementation:
- Surface preparation: Thorough cleaning of the worn surface is essential, including removal of residual cement paste, oxidation scales, and contaminated base metal. Grinding to bare metal with a minimum overlap of 5 mm into sound material is recommended.
- Thermal management: The massive thermal mass of grinding discs and rollers provides natural heat sinking, but localized overheating can still cause distortion or cracking. Preheating to 150–200°C and maintaining interpass temperature below 250°C are critical.
- Weld sequence planning: For large diameter components, a spiral or segmented weld pattern minimizes residual stress and distortion. The welding direction should be planned to accommodate the cylindrical geometry.
- Post-weld inspection: Visual examination, magnetic particle testing (MT) for surface cracks, and hardness verification at multiple points are mandatory before returning the component to service.
Practical Outcomes and Economic Analysis
The implementation of online overlay repair technology in cement grinding operations yielded substantial economic benefits:
- Repair time reduction: From 5–7 days (traditional method) to 8–24 hours (online method), representing an 85–90% reduction in downtime.
- Cost savings: Elimination of component transportation, workshop welding, and reinstallation costs, with total repair cost reduction of approximately 40–60%.
- Service life extension: Properly executed online overlay repair restores grinding components to near-original service life, with typical overlay thickness of 3–5 mm providing 6–12 months of additional service.
- Production continuity: The ability to perform repairs during planned maintenance windows rather than emergency shutdowns significantly improves overall equipment effectiveness (OEE).
Key Reflections and Technical Insights
This study exemplifies the practical engineering approach to solving real-world problems in heavy industry. The development of the online repair device required not only welding expertise but also mechanical design, electrical engineering, and process engineering capabilities. The interdisciplinary nature of the solution is a model for addressing complex industrial challenges.
A particularly important insight is the recognition that overlay repair quality depends not only on the welding process parameters but also on the surface preparation, thermal management, and post-weld treatment. The study emphasizes that proper surface preparation—removal of all contaminated material and creation of a sound bonding surface—is the single most critical factor in ensuring overlay adhesion and service life.
The economic analysis demonstrates that even modest improvements in equipment availability can yield substantial financial returns in continuous-process industries like cement manufacturing. For a typical cement grinding mill with annual production value of millions of dollars, each day of unplanned downtime represents significant lost revenue, making the investment in online repair capability highly justified.
This work represents an important contribution to the field of in-situ repair technology and provides a template for similar applications in other heavy industries including mining, power generation, and metallurgy.