Zhuojin Pipe Fitting Co., LtdSurfacing Repair Technology for Roller Press Roller Surface
Literature Overview
This paper by Shi Lianyan, Zhang Yachun, and Zhang Xinsheng, published in Mining Machinery (2007, Vol. 35, Issue 1, pp. 35-36), examines the surfacing repair technology applied to the working surface of roller press rollers. The authors, representing Tangshan Keyuan Environmental Protection Technology Equipment Co., Ltd., CCCC First Harbor Engineering Company, and Tangshan Jidong Cement Co., Ltd., discuss the working principles of roller presses, the mechanisms of roller surface degradation, and the application of surfacing welding for roller restoration.
Roller Press Working Principles and Wear Mechanisms
A roller press is a size reduction machine used in cement, mining, and chemical industries to crush and grind materials through compression. The two counter-rotating rollers compress the feed material between their surfaces, and the resulting high contact stresses cause progressive surface degradation.
| Operating Parameter | Typical Range |
|---|---|
| Roller diameter | 800-2500 mm |
| Roller width | 500-1500 mm |
| Maximum compression force | 50-300 MN |
| Contact stress | 1500-3000 MPa |
| Roller surface hardness (new) | 55-62 HRC |
| Feed material hardness | 3-7 Mohs |
| Operating temperature | Ambient to 150°C |
| Service life (before repair) | 6-18 months |
The primary wear mechanisms on roller surfaces include:
- Abrasive wear: Hard particles in the feed material plow and remove material from the roller surface.
- Adhesive wear: Cold welding at asperity contacts followed by material transfer.
- Fatigue spalling: Subsurface crack initiation and propagation under cyclic contact stress, leading to surface flaking.
- Corrosive wear: Chemical attack by moisture or acidic components in the feed material.
Surfacing Repair Technology
Consumable Selection
The selection of surfacing consumable depends on the material being processed and the desired surface properties:
| Application | Recommended Surfacing Alloy | Hardness | Key Properties |
|---|---|---|---|
| Cement grinding | High-Cr martensitic (Cr 12-15%) | 58-62 HRC | High abrasion resistance |
| Iron ore processing | Hardfacing carbide composite | 60-65 HRC | Extreme abrasion resistance |
| Limestone grinding | Medium-Cr austenitic (Cr 8-10%) | 45-50 HRC | Impact toughness + abrasion |
| Coal handling | Ni-Cr-Mo austenitic | 40-45 HRC | Corrosion + abrasion resistance |
Process Parameters
| Parameter | Specification |
|---|---|
| Welding process | SAW or FCAW preferred; SMAW for field repair |
| Welding current | 300-500 A (SAW); 180-280 A (FCAW) |
| Travel speed | 250-400 mm/min |
| Wire diameter | 1.6-2.4 mm |
| Preheat temperature | 100-200°C |
| Layer thickness | 3-8 mm total |
| Number of passes | 2-4 depending on depth of wear |
Surface Preparation
The worn roller surface must be prepared before surfacing:
- Machining: Remove the damaged surface layer to expose sound base material. The machining depth should exceed the maximum depth of fatigue spalling (typically 1-3 mm).
- Cleaning: Remove all oil, grease, and contamination. Solvent cleaning followed by grinding is recommended.
- Roughening: Light grinding of the prepared surface to improve mechanical keying between the base material and the surfacing layer.
Practical Considerations and Operational Notes
The authors emphasize several critical operational considerations for surfacing-repaired rollers:
- Thermal management: Roller bodies are large mass components with high thermal inertia. Uneven heating during surfacing can cause significant distortion. The welding sequence should follow a symmetric pattern to distribute heat evenly around the roller circumference.
- Post-weld stress relief: Stress relief at 550-600°C for 2-4 hours is recommended to reduce residual stresses that could contribute to early fatigue failure.
- Surface finish: The final surfacing surface should be machined or ground to achieve a surface roughness of Ra 6.3-12.5 μm. Too smooth a surface reduces material retention during compression; too rough a surface increases rolling resistance and energy consumption.
- In-service monitoring: The repaired roller should be monitored for early signs of wear, including changes in compression force, product size distribution, and audible noise from the roller press.
Key Reflections and Study Insights
This paper provides a practical framework for roller press maintenance that is directly applicable to engineers in cement, mining, and aggregate processing industries. The discussion of wear mechanisms is particularly valuable because it connects the fundamental tribology to the practical selection of surfacing materials and process parameters. The paper's emphasis on surface preparation quality is well-founded—in field repair applications, inadequate surface preparation is the single most common cause of premature surfacing failure. The integration of this repair technology into a preventive maintenance program, with scheduled roller inspection and planned surfacing before critical wear limits are reached, represents the optimal approach to lifecycle cost management. Engineers should also consider that the economic viability of surfacing repair depends on the frequency of roller changes; for high-throughput operations, the cumulative savings from repeated surfacing repairs can be substantial compared to periodic roller replacement.