CLADDING TECHNOLOGY SHANXI CO., LTDApplication of RMD-01 Overlay Electrode on Single-Roll Crusher - Literature Study Note
Literature Overview
This 2003 study by engineers from Tongling Iron and Steel Company's Sintering Plant documents the practical application of RMD-01 overlay welding electrode for repairing and hardening the working surface of a single-roll crusher used in iron ore processing. Single-roll crushers are critical components in sintering and pelletizing operations, where they crush raw iron ore to a specified particle size distribution. The crusher roll experiences severe abrasive wear from iron ore particles, and periodic overlay welding is essential to restore dimensions and extend service life.
Application Background and Service Conditions
Single-roll crushers in sintering plants operate under the following conditions:
- Material processed: Iron ore, limestone, and mixed raw materials
- Particle size of feed: 200–500 mm
- Target discharge size: 0–40 mm
- Roll diameter: 1200–2000 mm
- Roll width: 800–1500 mm
- Operating speed: 15–30 rpm
- Wear rate: 2–5 mm per month depending on ore hardness
- Service life between repairs: 3–6 months
The RMD-01 electrode is a nickel-based or high-alloy overlay electrode specifically designed for severe abrasive wear applications. The "RMD" designation indicates a specialized hardfacing electrode formulation.
RMD-01 Electrode Characteristics
| Property | Specification |
|---|---|
| Electrode type | SMAW hardfacing electrode |
| Diameter | 4.0 or 5.0 mm |
| Composition type | High-chromium or Ni-based alloy |
| Overlay hardness (as-welded) | 45–55 HRC (480–580 HV) |
| Coating type | Basic or rutile |
| Welding position | All positions (PA, PB, PC, PD, PE, PF) |
| Preheat requirement | 150–250 °C |
| Post-weld treatment | Not required (can be used in as-welded condition) |
| Typical dilution rate | 15–25% |
Welding Procedure Design
Pre-Weld Preparation
- Machining: Grind or mill away damaged overlay material to sound base metal
- Surface preparation: Clean base metal surface to bare metal, remove rust, scale, and oil
- Edge preparation: Bevel the edges of the wear zone to ensure proper fusion
- Preheating: Apply induction heating or gas heating to achieve 150–250 °C uniformly across the weld area
Overlay Welding Procedure
| Layer | Process | Purpose | Parameters |
|---|---|---|---|
| Transition layer | GMAW or SAW | Reduce dilution, improve bond | Low heat input, 1–2 passes |
| Build-up layers | SAW | Restore dimensions | 600–800 A, 30–35 V |
| Surface layer | SMAW (RMD-01) | Provide wear resistance | 120–180 A, 22–28 V |
Post-Weld Treatment
- Stress relief: Optional low-temperature stress relief at 400–500 °C for 1–2 hours
- Grinding: Grind overlay surface to specified profile and finish (Ra ≤ 12.5 μm)
- Hardness verification: Spot-check overlay hardness to confirm ≥ 45 HRC
Performance Evaluation and Results
| Performance Indicator | Before Overlay | After Overlay | Improvement |
|---|---|---|---|
| Roll surface hardness | 20–25 HRC (base metal) | 45–52 HRC (overlay) | 2× increase |
| Roll wear rate | 3–4 mm/month | 1–1.5 mm/month | 60% reduction |
| Service life | 3 months | 8–10 months | 2.5–3× extension |
| Cost per month of operation | 100% (baseline) | 35–45% | 55–65% savings |
| Number of shutdowns per year | 4–5 | 1–2 | Significant reduction |
Defect Analysis During Application
| Defect | Frequency | Cause | Resolution |
|---|---|---|---|
| Cracking | Low | Insufficient preheat | Increase preheat to 250 °C |
| Poor fusion | Occasional | Contaminated base metal | Improve surface cleaning |
| Excessive dilution | Moderate | High heat input on first pass | Use transition layer with lower current |
| Porosity | Rare | Wet flux or contaminated wire | Store electrodes properly |
| Undercut | Moderate | Travel speed too high | Reduce speed by 10–20% |
Engineering Practice Lessons
This application demonstrates several important principles in overlay welding for mining and processing equipment:
- The transition layer concept is critical: When overlaying high-alloy hardfacing material on low-carbon steel, a transition layer of intermediate composition significantly reduces cracking susceptibility and improves bond quality.
- Economic justification is compelling: The overlay repair program reduced annual shutdown frequency from 4–5 times to 1–2 times, with substantial savings in both material cost and lost production.
- Procedural discipline matters: Consistent preheating, proper electrode storage, and systematic hardness verification are essential for reliable results.
- The as-welded condition is acceptable: For single-roll crusher applications, the RMD-01 overlay can be used without post-weld heat treatment, simplifying the repair process and reducing downtime.
The study serves as a practical case study demonstrating how systematic overlay welding programs can dramatically improve the economics of heavy-duty processing equipment maintenance.