Zhuojin Pipe Fitting Co., LtdOverlay Repair of Squeeze Rollers in Cement Raw Material Final Grinding Systems
Literature Overview
This paper by Zhang Yongsheng, Ni Junjie, Yang Wei, and Zhang Haiyan (2012) from the Zhengzhou Machinery Research Institute addresses a highly specific industrial problem: the overlay repair of squeeze rollers in the raw material final grinding system of cement plants. Unlike clinker grinding systems where roller press failures have limited production impact, the raw material grinding roller press is a critical bottleneck. If the roller press fails, the kiln feed is interrupted, threatening continuous kiln operation. The authors highlight that the repair cycle of the squeeze rollers must align with planned kiln shutdown maintenance windows, a requirement that is difficult to achieve in practice.
Core Technical Content
Operating Conditions of Raw Material Squeeze Rollers
The raw material squeeze roller operates under conditions that are more severe than clinker grinding in several respects. The raw meal contains harder and more abrasive minerals such as bauxite, silica sand, and limestone fragments. The moisture content in raw meal is typically higher than in clinker, leading to adhesion and paste buildup on the roller surface. The roller surface is subjected to:
| Parameter | Typical Range |
|---|---|
| Roller diameter | 600-1200 mm |
| Roller width | 600-1200 mm |
| Operating pressure | 8-15 MPa |
| Raw meal temperature | 80-150°C |
| Surface speed | 2.0-4.5 m/s |
| Abrasive content (SiO2) | 15-35% |
| Moisture content | 1-3% |
Overlay Material Selection
The choice of overlay material for cement raw material squeeze rollers must balance hardness, toughness, and resistance to adhesive wear from moist raw meal. Common overlay systems include:
| Overlay System | Hardness (HRC) | Wear Resistance | Toughness | Suitability |
|---|---|---|---|---|
| High-carbon steel (H11) | 50-55 | Medium | Good | General duty |
| High-chromium cast iron (Cr15) | 55-60 | High | Low | Dry abrasive |
| Nickel-aluminum bronze | 40-45 | Medium | Excellent | Adhesive wear |
| Hardfacing with CrC3 | 60-65 | Very high | Poor | Severe abrasion |
| Multi-layer composite | 50-60 | High | Moderate | Balanced |
The authors note that a single overlay material rarely satisfies all requirements simultaneously. A multi-layer approach with a tough base layer and a hard surface layer is often necessary. The dilution from the roller substrate (typically 45CrNiMo or similar) into the first overlay layer must be carefully managed to ensure the final surface layer achieves the target hardness.
Scheduling Challenges
The critical insight of this paper is the scheduling mismatch between roller repair cycles and kiln maintenance windows. Kiln shutdowns are typically planned at intervals of 6 to 12 months, lasting 2 to 4 weeks. Roller wear rates depend on feed composition, moisture, and operating pressure, making it difficult to predict exactly when the rollers will reach end-of-life. If the rollers fail outside a planned shutdown, the kiln must be stopped, incurring enormous production losses. Conversely, if repair is scheduled too early, the rollers are replaced before their full service life is exhausted, resulting in unnecessary material and labor costs.
Engineering Practice Recommendations
Based on the analysis in this paper and broader industry experience, I would recommend the following approach to managing squeeze roller overlay repair in raw material grinding systems:
- Condition monitoring: Install surface roughness gauges and thickness gauges on the roller surface to track wear rate in real time. The wear rate should be calculated on a daily basis and extrapolated to predict remaining life.
- Flexible repair design: Design the overlay system with a modular approach, where a sacrificial surface layer of 3 to 5 mm can be ground off and renewed without disturbing the underlying structural layers. This allows partial repairs during short maintenance windows.
- Pre-fabricated overlay segments: For large rollers, consider overlaying pre-fabricated segments that can be rapidly installed during a kiln shutdown, rather than welding the entire roller surface in situ.
- Feed composition management: Work with the kiln operations team to optimize raw meal composition for roller life. Reducing the proportion of highly abrasive minerals in the feed, even slightly, can significantly extend roller life.
Study Insights and Reflections
This paper raises an important point that goes beyond pure welding technology: the integration of component repair with plant-wide production scheduling. In cement industry practice, the raw material grinding system is the upstream feeder for the kiln, and any disruption cascades through the entire production line. The welder or repair engineer must understand not only the metallurgy of the overlay but also the economics of kiln downtime. This paper serves as a reminder that technical solutions must be embedded within the operational context of the plant. The ideal repair cycle is one that aligns with planned maintenance, but achieving this requires a combination of accurate wear prediction, flexible repair technology, and disciplined operational planning.