CLADDING TECHNOLOGY SHANXI CO., LTDRoller Press Roller Surface Weld Overlay Repair Technology
Literature Overview
This 2007 publication in the journal Mining Machinery, authored by Shi Liyan, Zhang Yachun, and Zhang Xinsheng, addresses the practical engineering challenge of roller press roller surface repair through weld overlay technology. The research draws from field experience at Tangshan Keyuan Environmental Protection Technology Equipment Co., Ltd., CCCC First Navigation Bureau First Company Xingang Project Department, and Tangshan Jidong Cement Co., Ltd. Equipment Management Department. The study is particularly valuable because it bridges the gap between academic research and shop-floor reality, documenting the specific challenges, process parameters, and quality control measures encountered during actual roller repair operations.
Technical Context and Problem Definition
Roller presses are critical equipment in cement grinding, mineral processing, and coal preparation circuits. The rollers, typically made of medium-carbon steel or low-alloy steel with a hardfaced surface, operate under extreme conditions: high contact pressure (up to 100 MPa), severe abrasion from feed material, and cyclic thermal loading. Over time, the working surface of the rollers wears unevenly, developing grooves, dents, and localized material loss that degrades grinding efficiency and increases energy consumption. When the remaining surface thickness falls below the allowable limit, the rollers must be either re-profiled by machining (which reduces the roller diameter and eventually renders it unusable) or rebuilt by weld overlay.
Weld Overlay Process Selection
The selection of the weld overlay process for roller repair depends on several factors: the geometry of the roller surface (curved, large diameter), the required overlay thickness (typically 20-60 mm total), the alloy system of the overlay material, and the production schedule constraints. The most commonly employed processes for roller repair include:
| Process | Typical Application | Overlay Thickness per Pass | Deposition Rate (kg/h) | Heat Input Control |
|---|---|---|---|---|
| Submerged Arc Welding (SAW) | Large surface areas, multi-pass buildup | 5-8 mm | 15-25 | Excellent (flux coverage) |
| Electroslag Welding (ESW) | Very thick deposits (>50 mm) | 10-15 mm | 20-30 | Very good (controlled slag pool) |
| GMAW with Flux Cored Wire | Complex geometries, field repair | 3-5 mm | 8-15 | Good (adjustable) |
| Oxy-Fuel Welding | Small repairs, in-situ patching | 1-3 mm | 2-5 | Poor (difficult to control) |
For roller press applications, submerged arc welding is the predominant choice due to its high deposition rate, excellent penetration, and the ability to deposit thick layers with good mechanical properties. The flux-cored wire or solid wire used must be compatible with the base metal and designed to produce a hard, wear-resistant microstructure.
Overlay Material Selection
The overlay material for roller press rollers is typically a high-carbon, high-chromium martensitic steel or an austenitic stainless steel, depending on the specific service conditions. For cement grinding applications, a high-carbon martensitic alloy (such as a 12Cr1MoV-based or 5CrMo-based composition) is commonly specified, with a hardness target of 50-58 HRC after proper heat treatment. For applications involving more aggressive or corrosive feed materials, an austenitic stainless steel overlay (such as a 310 or 309-based composition) may be selected, with a hardness of 25-35 HRC but superior corrosion resistance.
The key material design considerations include: carbon content (0.8-1.4% for martensitic types), chromium content (8-14% for enhanced hardenability and wear resistance), molybdenum addition (0.5-1.5% for secondary hardening and temper stability), and the balance between hardness and toughness to prevent spalling under impact loading.
Process Parameters and Quality Control
The welding process parameters must be carefully optimized to achieve the desired overlay properties while minimizing defects. The following parameter ranges represent typical values for SAW overlay on roller surfaces:
- Arc voltage: 28-35 V
- Arc current: 500-700 A
- Travel speed: 80-120 mm/min
- Wire feed speed: 15-22 m/min
- Flux type: Rutile or basic flux, particle size 0.9-2.5 mm
- Interpass temperature: 150-250°C (controlled to prevent excessive HAZ softening)
- Preheat temperature: 100-200°C (depending on base metal carbon equivalent)
The quality control plan for roller overlay repair typically includes: visual inspection of all welds for surface defects, magnetic particle testing (MT) of the overlay surface and HAZ for cracks, ultrasonic testing (UT) for internal porosity and lack of fusion, hardness testing at multiple locations to verify uniformity, and dimensional inspection to confirm the roller profile meets the specified tolerance (typically ±0.5 mm for diameter and ±0.3 mm for out-of-round).
Common Defects and Countermeasures
The most frequently encountered defects in roller overlay repair include:
| Defect Type | Root Cause | Detection Method | Countermeasure |
|---|---|---|---|
| Cracks in overlay layer | Excessive carbon equivalent, inadequate preheat | MT, PT | Increase preheat, reduce travel speed, use low-hydrogen filler |
| Porosity | Flux moisture, inadequate flux coverage | UT, RT | Dry flux storage, ensure full flux coverage |
| Incomplete fusion | Excessive travel speed, low arc current | UT | Reduce travel speed, increase current |
| Excessive dilution | Too thick first pass, excessive penetration | Hardness test, XRD | Use thinner first pass, adjust wire stick-out |
| Hardness non-uniformity | Variable heat input, inconsistent interpass temperature | Hardness mapping | Strict process parameter control, automated welding |
Engineering Practice and Lessons Learned
The field experience documented in this study highlights several practical considerations that are often overlooked in laboratory research. First, the geometry of the roller surface presents unique challenges for welding access and torch positioning. The curvature of the roller surface, combined with the need to maintain a consistent wire-to-plate angle, requires specialized welding fixtures or robotic welding systems with multi-axis capability. Manual welding on curved surfaces is prone to inconsistent penetration and uneven bead width, which directly affects the final surface profile.
Second, the thermal management of the roller during multi-pass overlay is critical. The large thermal mass of the roller means that heat accumulates gradually during continuous welding, leading to elevated interpass temperatures that can soften the base metal and reduce the hardness of previously deposited layers. Effective thermal management strategies include: welding in a spiral pattern to distribute heat evenly, using water cooling jackets to remove excess heat, and allowing adequate cooling time between passes.
Third, the surface finishing operation after overlay is equally important as the welding itself. The as-welded surface of a roller overlay typically has a roughness (Ra) of 25-50 μm, which is far too rough for efficient grinding operation. The surface must be ground or machined to achieve a Ra of 3.2-6.3 μm, which requires careful control of the grinding process to avoid introducing residual stresses or thermal damage to the overlay layer.
Study Insights and Implications
This research underscores the importance of process integration in weld overlay repair applications. The success of roller overlay repair depends not only on the selection of the appropriate overlay material but also on the optimization of every step in the fabrication sequence, from base metal preparation through welding, heat treatment, surface finishing, and final inspection. The study demonstrates that a systematic approach to process development, combined with rigorous quality control, can achieve reliable repair results that restore the roller to its original performance characteristics.
The economic implications are significant: successful overlay repair can extend the service life of a roller by 2-3 times compared to the original manufacturing, while reducing the cost by 40-60% compared to purchasing a new roller. However, this economic benefit is contingent upon the quality of the repair, which in turn depends on the competence of the welding personnel, the availability of proper equipment, and the implementation of a comprehensive quality assurance program.
This literature provides valuable practical guidance for engineers involved in roller repair operations. The documented process parameters, defect analysis, and quality control procedures serve as a useful reference for developing site-specific welding procedures and for training welding personnel. The study also highlights the need for continued research into advanced overlay materials and processes that can further improve the wear life and reliability of roller press equipment.