CLADDING TECHNOLOGY SHANXI CO., LTDCladding Repair of Crusher Grate Plates
Literature Overview
This 1991 technical paper by Huang Taiming from the Construction Department of Chongqing Steel describes the application of weld overlay technology for repairing crusher grate plates. Crusher grate plates are critical wear components in impact crushers and hammer crushers used in mineral processing, aggregate production, and steel industry material preparation. These plates are subjected to severe impact loading, abrasive wear from hard rock fragments, and often corrosive environments, making them among the most rapidly consumed components in crushing operations.
Technical Background and Failure Modes
Crusher grate plates serve as the sizing element in crushers, controlling the discharge particle size by allowing only material smaller than the grate opening to pass through. The plates are typically made of medium carbon steel or low-alloy steel and are subjected to a combination of loading conditions that produce complex failure modes:
| Failure Mode | Mechanism | Typical Location |
|---|---|---|
| Abrasive wear | Hard rock fragments sliding/rolling across surface | Upper surface and edges |
| Impact damage | Direct impact from falling rock | Upper surface, near support edges |
| Fatigue cracking | Cyclic impact loading | Corners and edges, near holes |
| Corrosion | Moisture and chemical exposure | Underside and edges |
| Plastic deformation | Excessive impact loading | Edges and corners |
The typical service life of an unrepaired grate plate in a primary crusher can be as short as 2–4 weeks, depending on the material being crushed and the crusher operating parameters.
Cladding Repair Process
Surface Preparation and Assessment
Before applying the overlay, the grate plate must be thoroughly assessed:
- Thickness measurement: Determine the remaining thickness at the thinnest point to ensure adequate material remains for repair
- Crack inspection: Perform magnetic particle testing (MT) or dye penetrant testing (PT) to detect surface and near-surface cracks
- Weld preparation: Machine or grind the worn surface to a clean, flat preparation with appropriate groove geometry
- Contamination removal: Remove all rust, scale, oil, and moisture from the preparation surface
Overlay Process Selection
The choice of welding process depends on the repair requirements and available equipment:
| Process | Suitable For | Deposition Rate | Equipment Complexity |
|---|---|---|---|
| SAW (Submerged Arc) | Large flat areas, thick builds | High (2–5 kg/h) | Moderate |
| FCAW (Flux-Cored Arc) | Medium areas, field repair | Moderate (1–3 kg/h) | Low |
| GMAW (MIG/MAG) | Small areas, finishing | Low (0.5–1.5 kg/h) | Low |
| Oxy-fuel | Small repairs, no electricity | Very low | Very low |
For crusher grate plates, FCAW and GMAW are most commonly used due to their portability and flexibility, while SAW is preferred for major rebuilds in workshop conditions.
Consumable Selection and Deposit Properties
The overlay consumable must balance hardness (for wear resistance) with toughness (to resist impact cracking):
| Consumable Type | Hardness (HV) | Impact Toughness | Application |
|---|---|---|---|
| Fe-Cr-C (high carbon) | 500–800 | Low | Severe abrasion, low impact |
| Fe-Cr-Mo | 400–600 | Moderate | Mixed abrasion and impact |
| Ni-Cr | 350–500 | High | High impact, moderate abrasion |
| Fe-Ni-Cr-Mo | 450–650 | Moderate-high | General purpose |
| Composite (with carbide) | 600–1000 | Low-moderate | Severe abrasion |
For crusher grate applications, a two-layer approach is often optimal: a nickel-based transition layer for weldability and a high-carbon iron or composite hardfacing layer for wear resistance.
Typical Welding Parameters
| Parameter | FCAW | GMAW |
|---|---|---|
| Current | 250–350 A | 180–280 A |
| Voltage | 32–38 V | 22–28 V |
| Travel speed | 200–350 mm/min | 250–400 mm/min |
| Wire diameter | 1.6–2.4 mm | 1.2–1.6 mm |
| Shielding gas (GMAW) | CO₂ or Ar/CO₂ mix | — |
| Interpass temperature | ≤ 250°C | ≤ 300°C |
Quality Control and Inspection
After overlay welding, the following inspections should be performed:
- Visual inspection: Check for cracks, porosity, undercut, and incomplete fusion
- Magnetic particle testing (MT): Detect surface and near-surface cracks in the overlay and heat-affected zone
- Hardness survey: Verify that the overlay hardness meets specification at multiple locations
- Dimensional check: Ensure the plate thickness and flatness are within tolerance for proper grate function
- Bond strength test: If required, perform a bond strength test on a coupon to verify overlay adhesion
Engineering Practice Considerations
The practical implementation of grate plate repair requires attention to several factors:
Cost-Benefit Analysis
The economic justification for repair versus replacement depends on:
- Plate cost: New grate plates can be expensive due to material and manufacturing costs
- Downtime cost: Crusher downtime can cost thousands of dollars per hour in production loss
- Repair cost: Consumable cost, labor, and equipment time for overlay repair
- Extended life: A properly repaired plate can achieve 80–100% of new plate service life
Field Repair Challenges
Field repair of crusher grate plates presents unique challenges:
- Limited access and confined working spaces
- Variable ambient conditions (dust, moisture, temperature)
- Limited equipment availability (generators, compressed gas)
- Need for rapid turnaround to minimize production downtime
- Safety considerations in an active crushing environment
Common Defects and Countermeasures
| Defect | Cause | Countermeasure |
|---|---|---|
| Cracking | High carbon content, low preheat | Increase preheat to 250°C, use low-hydrogen consumable |
| Porosity | Contaminated surface, damp flux | Thorough surface cleaning, flux drying |
| Poor fusion | Inadequate heat input | Increase current, reduce travel speed |
| Excessive dilution | Too fast travel speed | Optimize parameters, use higher current |
| Hardness too low | Excessive dilution | Use higher carbon consumable, reduce dilution |
Summary and Reflections
This paper documents a practical and economically significant application of overlay welding technology in the steel and mineral processing industries. The crusher grate plate repair case demonstrates how overlay welding can extend component life, reduce maintenance costs, and minimize production downtime. The key engineering insight is that successful repair requires a systematic approach encompassing proper assessment, appropriate consumable selection, controlled welding parameters, and thorough quality verification.
For engineers responsible for maintenance planning in crushing operations, the adoption of overlay repair as a planned maintenance strategy—rather than a reactive emergency measure—can significantly improve asset reliability and reduce total maintenance costs. The principles described in this paper remain relevant and applicable to modern crusher grate repair operations, where improved consumables and welding equipment have further enhanced the reliability and economics of overlay repair.