CLADDING TECHNOLOGY SHANXI CO., LTDRegenerative Weld Overlay Repair of a Large-Diameter Roller Press Squeeze Roller
Literature Overview
This study, authored by Xu Jian, Zhang Yongsheng, Wang Xin, and Li Junwei from the Zhengzhou Machinery Research Institute, was published in the New Century Cement Herald in 2008. It addresses the regenerative weld overlay repair of a roller press squeeze roller with dimensions of Φ1700 mm × 1800 mm, a critical component in the cement grinding industry. Roller press squeeze rollers are subjected to extreme compressive loading, abrasion, and impact during the size reduction of clinker and raw meal. When the working surface is worn beyond acceptable limits, traditional replacement strategies are economically prohibitive due to the massive size and cost of these components. This literature presents a systematic approach to restoring the roller to serviceable condition through weld overlay techniques.
Core Technical Content
The fundamental challenge in this application lies in the combination of severe abrasive wear, high compressive stress (typically exceeding 500 MPa at the contact interface), and the large geometry of the roller surface. The repair methodology involves several critical steps:
- Surface preparation: Complete removal of the worn and damaged surface layer through mechanical grinding or machining to expose sound base material. The depth of material removal must be sufficient to eliminate fatigue cracks, delaminations, and any zones of work-hardened or decarburized steel.
- Preheating and interpass temperature control: Given the carbon steel or low-alloy steel base material (typically Q345 or similar grades), preheating to 150–250 °C is essential to control cooling rates and prevent cold cracking. Interpass temperature must be maintained above 100 °C to avoid excessive thermal gradients.
- Overlay material selection: The overlay alloy must provide a hardness of at least 45–55 HRC while maintaining adequate toughness to resist impact spalling. Typical choices include high-carbon martensitic alloys or carbide-forming Fe-Cr-C or Fe-Cr-B-C systems.
- Welding process selection: For such large diameters, submerged arc welding (SAW) or flux-cored arc welding (FCAW) offers the best combination of deposition rate, penetration, and productivity. Multi-pass, multi-layer welding is required to build up the full wear allowance.
Key Process Parameters
| Parameter | Typical Value | Rationale |
|---|---|---|
| Base material preheat | 150–250 °C | Prevent cold cracking in low-alloy steel |
| Interpass temperature | 100–200 °C | Control cooling rate, limit HAZ hardness |
| Welding current (SAW) | 600–800 A | High deposition rate for large volumes |
| Arc voltage (SAW) | 28–34 V | Stable arc, adequate penetration |
| Travel speed | 200–300 mm/min | Balance deposition rate and heat input |
| Overlay hardness | 45–55 HRC | Balance wear resistance and toughness |
| Post-weld treatment | Stress relief 550–620 °C | Eliminate residual stresses |
| Surface finish after overlay | Ra ≤ 1.6 μm | Reduce friction and contact stress |
Defect Analysis and Countermeasures
During the repair of large-diameter rollers, several defects commonly arise and must be actively managed:
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Cracking at weld/HAZ | Excessive cooling rate, high carbon equivalent | Increase preheat, reduce heat input per pass, use low-hydrogen filler |
| Delamination of overlay | Poor fusion, trapped slag | Ensure proper surface preparation, use multi-pass technique with back-strap if needed |
| Excessive residual stress | Large volume of deposited metal, restrained geometry | Apply post-weld stress relief, use intermittent welding patterns |
| Hardness variation | Inconsistent dilution, incomplete melting | Maintain consistent travel speed, use proper stacking sequence |
| Surface porosity | Moisture in flux, inadequate gas shielding | Dry flux thoroughly, ensure shielding integrity |
Engineering Practice Integration
From my extensive experience with heavy equipment repair, the success of roller press squeeze roller overlay repair depends on more than just the welding procedure itself. Several practical considerations must be integrated into the overall repair strategy:
- Geometric restoration: The roller must be returned to its original cylindrical geometry with concentricity within 0.1 mm over the full length. This requires precise machining before and after overlay application. The overlay is typically applied with an allowance of 3–5 mm above the final working diameter to allow for post-weld grinding.
- Thermal management: The large thermal mass of the roller means that heat input is relatively moderate compared to the overall mass, but local thermal gradients at the weld zone can still be significant. Temperature monitoring at multiple points around the circumference is recommended.
- Service life prediction: After repair, the overlay layer thickness determines the service life. For cement applications with typical wear rates of 0.1–0.3 mm per 1000 hours of operation, an overlay thickness of 10–15 mm provides a service life of 3–5 years before the next repair cycle.
- Quality assurance: Post-repair inspection should include hardness mapping across the overlay surface, ultrasonic testing for subsurface defects, and dimensional verification. A hydrostatic or pressure test is not applicable here, but a functional test under controlled load should be performed before returning the roller to service.
Study Insights and Reflections
This 2008 publication represents a mature engineering approach to the regenerative repair of large heavy equipment. The key insight is that weld overlay repair is not merely a welding operation but a comprehensive engineering process that integrates metallurgical understanding, process optimization, geometric precision, and quality assurance. The choice of overlay material must balance hardness (for wear resistance) against toughness (for impact resistance) and weldability (for crack resistance). The economic argument for repair over replacement is compelling: a new Φ1700 mm squeeze roller can cost several hundred thousand dollars, while overlay repair typically costs 10–20% of the replacement cost.
The study also highlights an important principle in heavy industry maintenance: planned repair cycles should be established based on wear rate monitoring, and overlay repair should be scheduled before the roller reaches a critical condition where base material damage becomes severe. This proactive approach to maintenance reduces unplanned downtime and extends asset life significantly.