CLADDING TECHNOLOGY SHANXI CO., LTDRegenerative Weld Overlay Repair of Large-Diameter Roll Press Extrusion Rolls
Literature Overview
This 2008 study by Xu Jian, Zhang Yongsheng, Wang Xin, and Li Junwei from the Zhengzhou Machinery Research Institute addresses the regenerative weld overlay repair of a large-diameter roll press extrusion roll with dimensions of Φ1700 × 1800 mm, used at Jiangxi East Asia cement production facilities. The research documents a comprehensive repair methodology for restoring worn or damaged large-scale industrial rolls through weld overlay cladding, providing practical guidance for the rehabilitation of heavy-duty cement industry equipment.
Background and Technical Challenge
Roll press extrusion rolls in cement production are subjected to severe abrasive wear, impact loading, and corrosive chemical attack from cement slurry. The large diameter (1700 mm) and substantial length (1800 mm) of the roll present significant challenges for weld overlay repair, including:
- Large thermal mass requiring significant heat input for base metal preparation
- Difficulty maintaining uniform weld bead quality over the entire cylindrical surface
- Thermal distortion and residual stress management in thick-section components
- Selection of appropriate overlay material compatible with the base steel
The study addresses these challenges through a systematic approach combining base metal preparation, multi-pass weld overlay, and post-weld treatment.
Repair Process and Technical Parameters
Base Metal Preparation
| Operation | Specification | Purpose |
|---|---|---|
| Grinding | Remove 3-5 mm of damaged surface | Eliminate worn and cracked material |
| Surface cleaning | Flapless grit blasting to SA2.5 | Remove scale, rust, and contaminants |
| Preheating | 200-250°C | Reduce thermal stress, prevent hydrogen cracking |
| Surface marking | Divide roll into 8-12 repair sectors | Organize welding sequence and thermal management |
The base metal preparation is critical for ensuring adequate fusion between the overlay layer and the existing roll surface. Insufficient removal of damaged material results in poor bond strength and early overlay failure, while excessive grinding reduces the remaining roll diameter and may compromise structural integrity.
Weld Overlay Process
The repair employs submerged arc welding (SAW) overlay with a multi-pass approach:
| Parameter | Value | Rationale |
|---|---|---|
| Welding process | Submerged arc welding (SAW) | High deposition rate, deep penetration, low spatter |
| Electrode | Flux-cored wire with stainless steel or hardfacing alloy | Provide wear and corrosion resistance |
| Current | 450-600 A | Ensure adequate penetration and fusion |
| Voltage | 32-38 V | Balance arc stability and bead profile |
| Travel speed | 150-250 mm/min | Control bead width and height |
| Number of passes | 4-6 passes | Build overlay to required thickness |
| Interpass temperature | Below 250°C | Prevent excessive softening of base metal |
| Overlay thickness | 8-12 mm total | Restore original roll diameter plus wear allowance |
The multi-pass SAW overlay technique allows for gradual buildup of the overlay layer while managing thermal input and residual stress. Each pass is deposited with a slight overlap (approximately 20-30% of bead width) to ensure complete coverage and minimize lack of fusion between adjacent beads.
Welding Sequence and Thermal Management
For a roll of this size, the welding sequence is critical to minimize distortion and residual stress. The study recommends a symmetrical, alternating sequence where opposite sectors of the roll are welded in succession. This approach balances thermal input around the circumference and prevents eccentric growth of the roll.
The use of temporary cooling devices such as water-cooled copper backing plates or directed water jets helps control the cooling rate and reduces the risk of hardening and cracking in the heat-affected zone (HAZ) of the base metal.
Material Selection and Performance
The selection of the overlay material is guided by the service conditions of the roll press extrusion roll:
| Material Type | Composition | Application |
|---|---|---|
| High-chromium cast iron | 12-14% Cr, 2-3% C | Abrasive wear resistance |
| Stainless steel | 18-20% Cr, 2-3% Ni | Corrosion resistance |
| Hardfacing alloy | Cr-Co-W or Cr-Mo-B | Combined wear and impact resistance |
| Martensitic stainless steel | 12-13% Cr, 0.3-0.5% C | High hardness after heat treatment |
The study evaluates the performance of several overlay materials under simulated cement production conditions. The results indicate that high-chromium cast iron and martensitic stainless steel overlays provide the best combination of wear resistance and cost-effectiveness for this application. The hardness of the overlay layer typically ranges from 55-62 HRC for martensitic stainless steel and 50-58 HRC for high-chromium cast iron.
Performance Testing
The repaired roll underwent comprehensive testing before returning to service:
- Hardness testing: Vickers and Rockwell hardness profiles across the overlay thickness to verify uniform hardness distribution
- Bond strength testing: Shear test specimens machined from the overlay/base metal interface to confirm adequate bond strength (typically exceeding 300 MPa)
- Non-destructive testing: Magnetic particle inspection (MT) and ultrasonic testing (UT) of the overlay surface and subsurface to detect cracks and lack of fusion
- Dimensional inspection: Profile measurement to verify roundness and diameter accuracy after machining
Engineering Practice Insights
The repair of large-diameter rolls through weld overlay cladding requires careful attention to several practical aspects:
- Equipment capability: The welding equipment must be capable of handling the large thermal mass of the roll and maintaining consistent arc characteristics over extended welding operations. Robotic SAW systems are preferred for consistency, but manual SAW with skilled operators is feasible.
- Thermal management: The large cross-section of the roll absorbs significant heat, which can slow the cooling rate and promote softening of the HAZ. Active cooling strategies may be necessary to maintain the desired hardness in the overlay layer.
- Quality control: Given the criticality of roll press operations in cement production, rigorous quality control at each stage of the repair is essential. In-process inspection of weld beads, interpass temperature monitoring, and post-weld NDT are standard practices.
- Cost-benefit analysis: The regenerative repair approach typically costs 30-50% of the price of a new roll, with a service life restoration of 70-90% of the original. This makes weld overlay repair an economically attractive option for large-diameter rolls.
Study Insights and Implications
This literature provides a practical and detailed account of weld overlay repair for large industrial rolls, emphasizing the importance of systematic process planning and quality control. The documented repair methodology can be adapted for other large-diameter cylindrical components in cement, mining, and heavy industry applications.
The study highlights the versatility of weld overlay technology as a maintenance and rehabilitation tool. Rather than replacing entire worn components, targeted weld overlay repair extends service life while minimizing downtime and costs. This approach aligns with modern sustainability goals by reducing material waste and energy consumption associated with manufacturing new components.
For engineers involved in maintenance planning and asset management, this literature underscores the value of weld overlay as a proven technology for component rehabilitation. The key success factors—proper base metal preparation, appropriate material selection, controlled thermal management, and rigorous quality control—are transferable to other industrial repair applications.