Field Weld Overlay Repair of CLF140-65 Roller Mill Roller Surface

Literature Overview

This paper by Xu Minghua, Wang Xin, Li Junwei, and Huang Zhiquan (2007, published in New Century Cement Bulletin) documents a practical field repair case involving the weld overlay restoration of a CLF140-65 roller mill roller surface at Suzhou Dongwu Cement Co., Ltd., with technical support from the Zhengzhou Machinery Research Institute. The study is significant for its focus on field repair of heavy-duty cement mill components, where downtime costs are extremely high and traditional replacement of the entire roller is economically prohibitive. The paper provides detailed process parameters, material selection rationale, and post-repair performance data that are directly applicable to similar repair scenarios in the cement and mineral processing industries.

Core Technical Points

The CLF140-65 roller mill is a vertical roller mill used for grinding cement clinker. The roller surface is subjected to severe abrasive wear, impact loading, and thermal cycling, leading to material loss of 10 to 30 mm over the service life of the roller. The repair strategy involves removing the worn surface layer by grinding, followed by multi-pass weld overlay using a wear-resistant alloy to restore the roller to its original diameter and surface hardness.

The key technical parameters documented in the study are summarized below:

The study emphasizes several critical aspects of field repair welding:

• Surface preparation: Complete removal of the worn and cracked surface layer by grinding to expose sound base material. Any residual cracks or inclusions in the base material must be identified and addressed before overlay welding begins.
• Preheating: Preheating to 200-250°C is essential to reduce thermal stresses in the thick cast steel roller and to prevent hydrogen-induced cracking in the heat-affected zone.
• Interpass temperature control: Maintaining interpass temperature below 200°C prevents excessive grain growth in the base material HAZ and limits residual stress accumulation.
• Post-weld heat treatment: Normalization at 850°C relieves residual stresses, refines the grain structure in the HAZ, and ensures the mechanical properties of the base material are restored.

Process and Standards Analysis

The field repair process follows a PDCA (Plan-Do-Check-Act) cycle that is well-suited to the constraints of on-site work:

1. Plan: Assess the extent of wear and damage, select overlay material and process, qualify the welding procedure, prepare surface, plan logistics for on-site equipment.
2. Do: Execute surface preparation, preheating, multi-pass overlay welding, and post-weld heat treatment according to the qualified procedure.
3. Check: Perform visual inspection, magnetic particle testing (MT) of the overlay surface, ultrasonic testing (UT) of the overlay/base interface, hardness testing, and dimensional verification.
4. Act: Address any defects found during inspection, adjust process parameters for subsequent passes, and document lessons learned for future repairs.

The study notes that the repair was performed in accordance with the general principles of NB/T 47014 (welding procedure qualification) and JB/T 4730 (NDT methods), adapted for field conditions where full laboratory testing is not available.

Engineering Practice Integration

The practical lessons from this repair case are directly transferable to similar field repair scenarios:

• Equipment portability: The use of submerged arc welding with a portable welding head and flux-cored wire provides the combination of high deposition rate and good weld quality needed for large-area overlay repair. The deposition rate of SAW (approximately 200-300 g/min) is significantly higher than manual arc welding, reducing repair time and downtime costs.
• Heat input management: The high thermal mass of the roller mill roller (typically 20-50 tons) provides natural cooling, but the large cross-section also means that thermal stresses can be significant. The preheating and interpass temperature control are critical to managing these stresses.
• Surface quality: The final surface finish of the overlay layer is critical for the rolling contact performance of the mill. The study specifies a surface roughness of Ra 6.3 or better, achieved through post-weld grinding.
• Repair economics: The cost of field repair (approximately 15-20% of the cost of a new roller) and the time savings (repair in 3-5 days vs. 8-12 weeks for a new roller) make this approach highly attractive for production-critical equipment.

Key Questions and Reflections

A key question addressed in this study is the long-term durability of field-repaired rollers compared to new rollers. The authors report that the repaired roller achieved a service life of approximately 80-90% of a new roller before the next repair cycle was required. This performance level is considered acceptable given the economic advantages of repair over replacement.

The study also raises the issue of residual stress management in thick-section field repairs. While post-weld normalization effectively relieves residual stresses, the large thermal gradients during welding of a thick roller can create stresses that are difficult to fully relieve. The authors recommend that future repairs incorporate stress-relief annealing at a lower temperature (600-650°C) for an extended duration (4-6 hours) to further reduce residual stresses, particularly in the HAZ region.

Study Insights and Implications

This paper exemplifies the practical application of weld overlay technology in a heavy industrial setting where economic and logistical constraints demand innovative solutions. The detailed documentation of process parameters, inspection methods, and performance results provides a valuable reference for engineers planning similar field repairs. The study reinforces the principle that weld overlay is not limited to corrosion protection but is equally applicable to wear restoration and surface hardening of large heavy-duty components. For cement plant operators and repair contractors, this case study demonstrates that well-planned field overlay repair is a viable and cost-effective alternative to component replacement.