CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Repair of Crusher Grate Plates Technical Study Note
Literature Overview
This 1991 study by Huang Taiming from the Construction Department of Chongqing Iron and Steel Company addresses the weld overlay repair of grate plates used in industrial crushers. Crusher grate plates are consumable components that determine the final product size in crushing operations and are subjected to severe impact loading, abrasion, and wear. The frequency of grate plate replacement represents a significant operational cost in mineral processing and aggregate production facilities. This study provides practical guidance on extending the service life of grate plates through overlay welding, contributing to the body of knowledge on economic repair practices in heavy industry.
Application Background and Technical Requirements
Crusher grate plates serve as the sizing element in jaw crushers, cone crushers, and impact crushers. They are typically arranged in a parallel or converging pattern to define the discharge opening. The grate plates experience:
- Impact loading from falling ore fragments at velocities of 5–15 m/s
- Abrasive wear from the sliding contact with ore particles containing hard mineral phases (quartz, corundum)
- Fatigue loading from cyclic stress during continuous crusher operation
- Corrosive environment when processing wet or chemically aggressive ores
The base material for grate plates is typically low-carbon steel (Q235 or Q345) or low-alloy steel, which provides adequate toughness and weldability but insufficient surface hardness to resist the abrasive and impact wear conditions. The original surface hardness of the base plate is typically 150–200 HB, which is far below the minimum requirement of 400–600 HB for acceptable wear resistance in crusher applications.
Overlay Process Selection and Parameters
The study evaluates several overlay welding processes for grate plate repair:
| Process | Hardness Achieved (HB) | Dilution (%) | Cost per m² | Service Life Improvement |
|---|---|---|---|---|
| SMAW with hardfacing electrode | 400–550 | 15–25 | Low | 2–3× |
| SAW with hardfacing wire | 450–600 | 10–18 | Medium | 3–4× |
| FCAW with cored wire | 450–650 | 8–15 | Medium | 3–5× |
| PTA powder cladding | 500–700 | 5–10 | High | 4–6× |
For the economic constraints of a steel construction department, the study recommends a combination of SMAW and FCAW processes as the optimal balance between cost and performance.
Recommended Process Parameters for FCAW Overlay
| Parameter | Specification |
|---|---|
| Wire type | FCAW cored wire with Cr-C-Mo or Cr-C-Ni-Cr₃C₂ composition |
| Wire diameter | 1.2 mm |
| Shielding gas | CO₂ (100%) or Ar + CO₂ (80/20) |
| Current | 180–250 A |
| Voltage | 22–28 V |
| Travel speed | 200–400 mm/min |
| Preheat | 100–150 °C |
| Interpass temperature | <200 °C |
| Overlay thickness | 3–6 mm |
| Number of passes | 2–3 layers |
Defect Analysis and Quality Control
The primary defects encountered in grate plate overlay repair include:
| Defect | Cause | Detection Method | Acceptance Criteria |
|---|---|---|---|
| Surface cracks | High carbon content; restricted cooling | Visual + MT | No longitudinal cracks >1 mm |
| Crater cracks | Inadequate end cap; rapid cooling | Visual + PT | No cracks at weld termination |
| Excessive porosity | Wet flux; contaminated surface | RT or UT | No porosity >2 mm in clusters |
| Undercut | Excessive travel speed; improper angle | Visual | Max 0.5 mm deep |
| Insufficient penetration | Low heat input; excessive speed | Macrograph | Full fusion to base metal |
| Hardness non-uniformity | Inconsistent heat input | Hardness survey | Within ±50 HB of target |
Engineering Practice Integration
The study emphasizes several practical considerations that are critical for successful grate plate overlay in a plant maintenance environment:
- Surface preparation: The worn surface must be ground to remove all cracked, decarburized, and contaminated material. A minimum of 2 mm of sound base metal must be exposed before overlaying begins.
- Weld sequence planning: For large grate plates, the welding sequence should follow a symmetric pattern from the center outward to minimize distortion. The plate should be clamped or backed to prevent warping.
- Hardness verification: After overlay completion, a grid of hardness test points should be established to verify uniformity. The target hardness range of 450–600 HB should be achieved across the entire overlay surface.
- Post-weld treatment: For high-carbon overlay materials, a controlled cooling rate is essential. Wrapping the repaired plate with insulating blankets or placing it in a warm furnace (150–200 °C) for 2 hours prevents quench cracking.
- Service monitoring: After returning the repaired grate plate to service, the wear rate should be monitored at regular intervals to establish a predictive maintenance schedule.
Study Insights and Implications
This study exemplifies the pragmatic engineering approach that characterizes plant-level maintenance operations. The focus on cost-effective solutions using readily available welding consumables and equipment reflects the economic realities of industrial maintenance. The systematic evaluation of different overlay processes, combined with practical quality control criteria, provides a decision-making framework that can be applied to similar wear component repair applications. The study also highlights the importance of hardness uniformity as a quality indicator — a non-uniform hardness distribution indicates inconsistent process control and may lead to premature localized failure. For modern practitioners, the fundamental principles described here remain relevant, though the available consumable options and process capabilities have expanded significantly since 1991.