CLADDING TECHNOLOGY SHANXI CO., LTDOn-Site Weld Overlay Repair of CLF140-65 Roller Press Roller Surface
Literature Overview
The CLF140-65 roller press is a critical piece of equipment in cement and mineral processing industries, used for grinding and size reduction of raw materials. The roller surface undergoes severe wear from abrasive materials, and periodic repair by weld overlay is essential to maintain production capacity. This study note examines the technical challenges and solutions encountered during on-site weld overlay repair of the roller surface, including material selection, process optimization, and quality assurance.
Equipment and Wear Analysis
The CLF140-65 roller press operates under extreme conditions:
| Parameter | Value |
|---|---|
| Roller diameter | 1400 mm |
| Roller width | 650 mm |
| Operating pressure | 80–120 MPa |
| Throughput | 60–80 t/h |
| Feed material | Limestone, clay, coal |
| Abrasiveness index | 15–25 (Mohs equivalent) |
| Typical wear life | 8,000–15,000 hours |
The wear mechanism is predominantly abrasive wear from hard mineral particles, with secondary contributions from adhesive wear and impact fatigue. The roller surface typically shows uniform wear in the central region with accelerated wear at the edges due to material flow patterns.
Material Selection for Overlay Repair
The selection of overlay material is critical for achieving acceptable wear resistance and bonding strength:
| Material | Hardness (HV) | Wear Resistance | Bond Strength | Cost |
|---|---|---|---|---|
| High-carbon steel (Cr12MoV) | 600–700 | Excellent | Good | Moderate |
| High-manganese steel (Mn13) | 200–300 | Very good (work-hardening) | Good | Low |
| Carbide composite (WC-Co) | 1200–1500 | Excellent | Moderate | High |
| Stellite 6 (Co-Cr-W) | 400–500 | Very good | Good | High |
| Martensitic stainless steel | 500–600 | Good | Good | Moderate |
For the CLF140-65 roller press application, high-carbon high-chromium steel (such as Cr12MoV or equivalent) is typically selected for its excellent abrasive wear resistance and reasonable cost. The overlay hardness of 600–700 HV provides a wear life improvement of 3–5 times compared to the base roller material (typically 200–250 HV).
On-Site Welding Process Design
Process Parameters
| Parameter | Value | Rationale |
|---|---|---|
| Welding method | GTAW + GMAW combination | GTAW for first pass (low dilution), GMAW for subsequent passes |
| Shielding gas | Argon (GTAW), Ar+CO2 80:20 (GMAW) | Adequate protection for high-carbon steel |
| Heat input (GTAW) | 0.8–1.2 kJ/mm | Low heat input to minimize dilution and residual stress |
| Heat input (GMAW) | 1.5–2.5 kJ/mm | Moderate heat input for productivity |
| Interpass temperature | ≤150°C | Prevents excessive softening and reduces residual stress |
| Preheat temperature | 100–150°C | Reduces cooling rate, prevents cracking |
| Post-weld treatment | Stress relief at 550–600°C for 2 hours | Reduces residual stress to prevent delayed cracking |
Welding Sequence Design
The welding sequence for a roller surface repair must account for the cylindrical geometry and the need to minimize distortion:
- Surface preparation: Grind the worn surface to remove all damaged material, exposing sound base metal. The surface should be prepared to a smooth finish with no cracks, porosity, or contamination.
- First pass (GTAW): Apply a thin transition layer (1–2 mm) using GTAW with low heat input. This pass establishes good bonding and provides a suitable surface for subsequent passes.
- Subsequent passes (GMAW): Apply the bulk of the overlay material using GMAW with appropriate wire feed speed and travel speed. Multiple passes should be applied in a pattern that distributes heat evenly across the roller surface.
- Final pass: Apply a final finishing pass with slightly lower heat input to ensure uniform surface hardness and minimal surface defects.
- Post-weld stress relief: Apply heat treatment to reduce residual stresses to acceptable levels.
Quality Control and Inspection
| Inspection Method | Purpose | Acceptance Criteria |
|---|---|---|
| Visual inspection (VT) | Surface defects, undercut, lack of fusion | No cracks, undercuts < 0.5 mm, uniform surface |
| Magnetic particle testing (MT) | Surface and near-surface cracks | No indications exceeding acceptance criteria |
| Ultrasonic testing (UT) | Internal defects, bond quality | No defects exceeding 10% of acceptance area |
| Hardness testing | Overlay hardness verification | 600–700 HV minimum |
| Bond strength testing | Overlay-base bond quality | Minimum 200 MPa shear strength |
| Dimensional inspection | Profile accuracy | Within ±0.5 mm of specified profile |
Engineering Challenges and Solutions
Challenge 1: On-Site Welding Environment
On-site repair presents unique challenges compared to shop fabrication:
- Limited access: The roller is typically in-situ or partially disassembled, limiting access for welding equipment and positioning.
- Environmental contamination: Dust, moisture, and oil contamination can affect weld quality.
- Temperature control: Maintaining interpass temperature and preheat temperature is difficult in an open environment.
- Equipment constraints: Portable welding equipment may have limited capability compared to shop equipment.
Solution: Use portable equipment with adequate capability, establish clean working areas, use temperature monitoring devices, and implement rigorous cleaning procedures between passes.
Challenge 2: Residual Stress Management
The high residual stresses generated during welding can cause delayed cracking, particularly in high-carbon overlay materials. The challenge is compounded by the inability to perform full heat treatment in some on-site situations.
Solution: Implement strict interpass temperature control (≤150°C), use low-heat-input processes, and perform localized stress relief treatment where full heat treatment is not feasible.
Challenge 3: Surface Profile Accuracy
The roller surface profile must be maintained within tight tolerances to ensure proper operation of the roller press. Welding distortion can cause profile deviation that affects grinding performance.
Solution: Apply welding in a pattern that distributes heat symmetrically, use backing plates to control distortion, and plan for post-weld grinding to restore the specified profile.
Study Insights and Practical Recommendations
The on-site repair of roller press surfaces is a practical application of weld overlay technology that requires careful balancing of multiple competing requirements. The key insights from this study are:
- Material selection must be application-specific: High-carbon high-chromium steels provide excellent wear resistance for abrasive applications but require careful process control to prevent cracking. The selection should be based on a thorough understanding of the wear mechanism and operating conditions.
- Process control is paramount: The success of on-site repair depends heavily on strict adherence to welding parameters, particularly interpass temperature and heat input. Even minor deviations can lead to significant quality issues.
- Quality assurance must be integrated: Non-destructive testing should be performed at multiple stages of the repair process, not just at completion. Early detection of defects allows corrective action before they become critical.
- Documentation is essential: Complete records of materials, parameters, inspection results, and heat treatment should be maintained for each repair, enabling traceability and continuous improvement.
The economic benefit of weld overlay repair is substantial, typically extending roller life by 3–5 times compared to replacement, with a cost savings of 60–80% compared to new roller procurement. However, this benefit is only realized when the repair is performed to specification with proper quality control.