Zhuojin Pipe Fitting Co., LtdKey Considerations for Online Surfacing Repair of Vertical Mill Roller Sleeves
Literature Overview
The paper by Chen Changmin, published in 2018 in New Century Cement Herald (Vol. 24, No. 1, pp. 67-70), addresses the practical challenges encountered during online surfacing repair of vertical mill roller sleeves. Vertical mills are critical grinding equipment in cement production, and their roller sleeves are subjected to severe abrasive and impact wear conditions. The author emphasizes that while online surfacing offers advantages in simplicity and cost savings, the quality, schedule, safety, and cost factors must be rigorously managed throughout the repair process.
Core Technical Points
The fundamental challenge of online surfacing repair lies in performing welding operations on equipment that remains partially or fully within its operational environment. Unlike offline repair conducted in a controlled workshop, online repair faces constraints related to access, residual heat, contamination, and personnel safety. The author identifies four critical control dimensions:
- Pre-job condition verification — Ensuring that the roller sleeve surface is properly prepared, free of residual material, and at an acceptable temperature for welding.
- Process monitoring and skilled personnel deployment — Continuous technical oversight during welding to maintain parameters within specified windows.
- Full-process quality management — From base material assessment through final dimensional verification.
- Safety risk assessment and preventive measures — Particularly relevant when working near operational or partially operational grinding systems.
Process Analysis and Engineering Practice
Surface Preparation Requirements
The roller sleeve surface must be ground to bare metal to a minimum depth of 2-3 mm to eliminate contaminated layers and ensure proper metallurgical bonding. Residual cement particles, lubricants, and moisture must be completely removed. In practice, we have found that inadequate surface preparation is the single largest contributor to surfacing layer spallation in field applications.
Welding Parameters and Heat Input Control
| Parameter | Recommended Range | Rationale |
|---|---|---|
| Heat input | 15-25 kJ/cm | Sufficient fusion without excessive HAZ softening |
| Preheat temperature | 100-150°C | Mitigates hydrogen cracking risk on high-carbon base |
| Interpass temperature | ≤250°C | Controls dilution and microstructure evolution |
| Pass thickness | 3-5 mm | Ensures adequate dilution control |
| Layer overlap | 50-70% | Uniform microstructure and hardness distribution |
Common Defects and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Layer spallation | Inadequate surface preparation; high dilution | Increase grinding depth; use low-dilution consumables |
| Cracking in HAZ | Excessive cooling rate; hydrogen embrittlement | Increase preheat; use low-hydrogen flux/shield |
| Excessive dilution | Excessive heat input; improper torch angle | Reduce amperage; maintain perpendicular torch |
| Porosity | Moisture contamination; poor shielding | Dry consumables; ensure gas flow rate |
Study Insights and Reflections
The paper's emphasis on management and organizational aspects — rather than purely metallurgical considerations — is particularly valuable. In my experience with similar wear-part repair operations, the technical parameters are well-established in literature, but the failure rate is disproportionately driven by procedural lapses: insufficient preheat verification, inadequate operator supervision, and compressed schedules that force shortcuts. The PDCA cycle is inherently applicable here — Plan the repair sequence with proper material selection, Do with strict parameter adherence, Check through hardness profiling and dimensional verification, and Act by updating procedures based on field performance data.
A key insight from this literature is the recognition that online repair quality is not merely a welding metallurgy problem but an integrated engineering management challenge. The author's framework of four control dimensions aligns well with FMEA methodology, where each dimension represents a failure mode category that requires systematic risk assessment and mitigation.
Implications for Engineering Practice
For engineers overseeing vertical mill repair programs, this paper reinforces the necessity of establishing documented procedures that address not only welding parameters but also pre-repair inspections, environmental controls, and post-repair verification protocols. The cost savings associated with online repair compared to offline replacement are real but must be weighed against the risk of premature failure due to inadequate repair quality. A systematic approach incorporating pre-job checklists, real-time parameter logging, and post-repair hardness mapping across the entire surfacing area provides the best balance of economy and reliability.