CLADDING TECHNOLOGY SHANXI CO., LTDOnline Wear-Resistant Cladding Process Application on Roller Presses
Literature Overview
The reference by Pan Yuanchan (2010), published in New Century Cement Herald and associated with Baoshan Kunsteel Jiahua Cement Building Materials Co., Ltd., addresses an innovative approach to roller press roll maintenance: online (in-situ) cladding repair that eliminates the need for complete roll removal from the press frame. This represents a significant advancement over conventional repair methods that require complete disassembly, transportation to a workshop, and reinstallation—processes that can consume weeks of production downtime. The paper documents the technical development, implementation, and results of online cladding operations performed directly on installed roller press equipment.
Core Technical Innovation
The fundamental challenge of online cladding is the geometric constraint: the roll is mounted within the press frame, with limited access for welding equipment and personnel. Traditional repair methods require complete disassembly, which for large roller presses (roll diameter > 600 mm) can require 5–10 days of downtime. The online approach reduces this to 2–4 days by performing welding operations in the installed position, using specialized equipment and techniques adapted to the constrained geometry.
Equipment and Setup Requirements
| Equipment | Specification | Purpose |
|---|---|---|
| Portable welding positioner | 0–360° rotation; 0–5° tilt | Roll positioning for access |
| Manual welding station | SMAW with low-hydrogen electrodes | Transition and working layers |
| SAW head (portable) | 4G2 or 8G2 type | High-deposition-rate passes |
| Induction heater | 30–50 kW; contact type | Preheating and interpass heating |
| Gas shielding system | Mixed gas (80% Ar + 20% CO₂) | GMAW overlay if applicable |
| Portable stress relief unit | Induction or flame type | Post-weld stress relief |
| Measuring instruments | Dial indicator, micrometer, hardness tester | Quality verification |
Process Adaptation for Online Conditions
The online cladding process requires several adaptations from conventional workshop procedures:
- Roll support and positioning: The roll must be supported on temporary bearings or V-blocks that allow controlled rotation. The welding positioner provides consistent positioning for mechanized processes.
- Access management: Welding access is limited to the exposed circumference; the roll must be rotated to bring each section into the working position. A systematic rotational sequence ensures complete coverage.
- Heat input control: With limited cooling time between passes (due to the roll being in a confined space), interpass temperature control is critical. The use of portable thermocouples with real-time monitoring is essential.
- Shielding gas management: In confined spaces, gas flow must be carefully managed to prevent gas accumulation and ensure adequate shielding at the weld pool.
Material and Process Parameters for Online Application
| Parameter | Online Value | Workshop Value | Rationale |
|---|---|---|---|
| Preheat temperature | 300 °C | 250 °C | Higher due to constrained cooling |
| Heat input | 10–15 kJ/cm | 15–20 kJ/cm | Lower to reduce distortion |
| Pass thickness | 2–4 mm | 3–5 mm | Thinner passes for better control |
| Interpass temperature | ≤ 200 °C | ≤ 250 °C | Stricter control in confined space |
| Welding sequence | 6-segment spiral | Continuous spiral | Adapted to access pattern |
| Stress relief | Induction, 550 °C × 1.5 h | Furnace, 580 °C × 2 h | Equipment limitation |
Performance Results and Comparison
The paper presents comparative data between online and offline (workshop) repair methods:
| Performance Metric | Online Repair | Workshop Repair | Assessment |
|---|---|---|---|
| Downtime (days) | 2–4 | 7–14 | Significant improvement |
| Overlay hardness (HV) | 620–680 | 630–700 | Comparable |
| Bond strength (MPa) | 230–260 | 240–280 | Acceptable |
| Service life (months) | 8–12 | 10–14 | Slightly shorter |
| Cost per repair (index) | 1.0 | 1.8–2.5 | Significant savings |
| Surface quality (roughness) | Ra 6.3–12.5 μm | Ra 3.2–6.3 μm | Requires final grinding |
The slightly shorter service life of online repairs is attributed to marginally higher residual stresses and slightly lower hardness uniformity, but the overall cost-benefit analysis strongly favors the online approach for most applications.
Quality Control in Online Conditions
Quality control in online conditions presents unique challenges:
- UT inspection: Limited access for UT probes on the installed roll; alternative methods such as phased array UT with custom probes may be required.
- Hardness testing: Multiple points must be tested across the overlay; results should be mapped to identify any soft zones.
- Visual inspection: Full circumference inspection is mandatory; defects must be identified and repaired before the roll is returned to service.
- Dimensional verification: Runout and diameter measurements must be taken at multiple axial positions; tolerance is typically ± 0.05 mm for diameter and ± 0.03 mm for runout.
Key Reflections
The innovation documented in this reference represents a pragmatic engineering solution to a real production constraint. The willingness to accept slightly reduced performance (shorter service life, marginally lower hardness) in exchange for dramatically reduced downtime and cost is a mature engineering judgment. The paper demonstrates that online cladding is not a compromise that sacrifices quality but rather an optimized approach that balances multiple competing objectives. For cement plants operating with high production targets and limited maintenance windows, this approach is particularly valuable. The key to success is rigorous process control—particularly preheating, interpass temperature management, and post-weld stress relief—which must be maintained even under time pressure.