CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Repair of Sintering Trolley Car Body
Literature Overview
This paper, published in Hot Working Technology in 2005 by Cheng Jun and Guo Changqing from Inner Mongolia University of Science and Technology, addresses the practical challenge of repairing worn sintering trolley car bodies through welding overlay. Sintering trolley cars are critical components in iron ore sintering plants, subjected to severe wear from abrasive iron ore and sinter material. The paper presents a systematic approach to overlay repair, including consumable selection, process optimization, and performance evaluation.
Core Technical Content
Sintering trolley car bodies experience combined wear mechanisms including abrasive wear from iron ore particles, impact wear from material charging and discharge, and thermal fatigue from exposure to hot sinter material. The wear rate can reach 5–15 mm per year in severe service conditions, necessitating periodic repair or replacement.
Wear Mechanism Analysis
| Wear Type | Contribution (%) | Characteristic |
|---|---|---|
| Abrasive wear | 50–60 | Primary mechanism from iron ore particles |
| Impact wear | 20–30 | From material charging and discharge |
| Thermal fatigue | 10–15 | From hot sinter material exposure |
| Corrosive wear | 5–10 | From acidic moisture in ore |
Consumable Selection
The authors evaluated several consumable types for the overlay repair:
| Consumable Type | Hardness (HV) | Toughness | Service Life | Cost |
|---|---|---|---|---|
| High-carbon steel wire | 400–500 | Good | 1.0× (baseline) | Low |
| High-chromium cast iron | 800–1000 | Poor | 2.0–3.0× | Medium |
| Medium-manganese steel | 300–400 (as-deposited), 500–600 (in service) | Excellent | 2.5–4.0× | Medium |
| Stellite alloy | 400–500 | Good | 3.0–5.0× | High |
| Carbide-ceramic composite | 1000–1500 | Poor | 4.0–6.0× | Very high |
The optimal selection depends on the specific service conditions and economic considerations. For most sintering trolley applications, medium-manganese steel or high-chromium cast iron provides the best balance of wear resistance, toughness, and cost.
Process Parameters
The recommended welding parameters for overlay repair of sintering trolley car bodies include:
| Parameter | Value | Notes |
|---|---|---|
| Welding Process | FCAW or SAW | High deposition rate required |
| Welding Current | 300–500 A | Depends on wire diameter |
| Travel Speed | 300–600 mm/min | Optimized for deposition rate |
| Preheat | 100–200 °C | Reduces cracking tendency |
| Interpass Temperature | < 300 °C | Controls microstructure |
| Number of Passes | 2–4 | Depends on required thickness |
| Overlay Thickness | 3–8 mm | Based on wear rate and repair interval |
Microstructural Analysis
The microstructure of the overlay layer depends on the consumable type and welding parameters:
Medium-Manganese Steel Overlay
- Matrix: Austenite (70–90%) + Ferrite (10–30%)
- Carbides: MnC, Mn₂₃C₆ (1–5 μm)
- Hardness: 250–350 HV (as-deposited), 400–550 HV (after impact)
- Toughness: Excellent, suitable for impact-abrasion service
High-Chromium Cast Iron Overlay
- Matrix: Martensite + Retained Austenite
- Carbides: M₇C₃ (primary, 20–50 μm) + M₃C (secondary, 1–5 μm)
- Hardness: 700–900 HV
- Toughness: Moderate, may crack under severe impact
Interface Characteristics
The bond interface between the overlay and the base steel substrate exhibits:
- A dilution zone (0.5–2 mm) with gradually changing composition
- A transition zone (0.2–0.5 mm) with mixed microstructure
- A distinct interface with good metallurgical bonding
- No intermetallic formation (compatible iron-based systems)
Defect Analysis and Countermeasures
| Defect Type | Frequency | Root Cause | Countermeasure |
|---|---|---|---|
| Cracking | 15–20% | High carbon equivalent, hydrogen | Preheat, low-hydrogen consumables |
| Porosity | 10–15% | Surface contamination, gas entrapment | Surface cleaning, proper shielding |
| Incomplete fusion | 5–10% | Insufficient heat input, surface rust | Surface preparation, adequate current |
| Excessive dilution | 20–30% | High heat input, thin first pass | Controlled parameters, multi-pass |
| Overlay spalling | 5–10% | Poor bond strength, thermal cycling | Proper preheat, controlled cooling |
Process Optimization Strategy
The authors propose a systematic process optimization approach based on the PDCA cycle:
- Plan: Analyze wear pattern, select consumable, determine overlay thickness
- Do: Execute welding with optimized parameters, maintain process control
- Check: Inspect weld quality, measure hardness and bond strength
- Act: Adjust parameters based on inspection results, document for future repairs
Engineering Practice Integration
The welding overlay repair of sintering trolley car bodies has been implemented in several iron and steel plants in Inner Mongolia, China. A representative case study involves:
| Parameter | Before Repair | After Repair |
|---|---|---|
| Car body thickness | 8 mm (original 16 mm) | 16 mm (restored) |
| Wear rate | 8 mm/year | 3 mm/year |
| Repair interval | 12 months | 36 months |
| Annual repair cost | ¥50,000 | ¥15,000 |
| Production downtime | 48 hours/year | 12 hours/year |
The economic analysis demonstrates that welding overlay repair provides significant cost savings compared to replacement, with a payback period of less than 6 months for the initial investment in welding equipment and consumables.
Key Questions and Reflections
The research raises important questions about the long-term reliability of overlay repairs under cyclic thermal and mechanical loading. While the initial performance is excellent, the long-term behavior under repeated thermal cycling (from hot sinter material to ambient temperature) requires further investigation. Thermal fatigue cracking at the overlay-substrate interface is a potential concern that warrants continued monitoring.
Another significant consideration is the effect of overlay repair on the structural integrity of the trolley car body. The addition of overlay material changes the mass distribution and may affect the dynamic behavior of the trolley during operation. This structural consideration must be incorporated into the repair design to ensure safe operation.
Study Insights and Implications
The most significant contribution of this research is the demonstration that welding overlay repair is a viable and economical alternative to replacement for worn sintering trolley car bodies. The work provides a comprehensive methodology for consumable selection, process optimization, and quality control that can be applied to similar wear repair applications in the iron and steel industry.
For maintenance engineers, the key insight is that overlay repair requires careful planning and execution to achieve optimal results. The selection of consumable, welding process, and process parameters must be tailored to the specific service conditions, and quality control measures must be implemented to ensure reliable performance.
This study provides valuable guidance for the development of overlay repair standards and procedures for mining and mineral processing equipment, contributing to the reduction of maintenance costs and improvement of operational reliability in the iron and steel industry.