CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Repair Process Research for Crusher Hammer Heads
Literature Overview
This technical note examines the weld overlay repair process for crusher hammer heads, which are critical wear components in impact crushers used in mining, quarrying, and aggregate processing industries. Hammer heads are subjected to severe impact and abrasive wear as they strike and break rocks, and their service life directly affects crusher productivity and operating costs. Weld overlay repair provides a cost-effective method to restore worn hammer heads to serviceable condition. This study covers the technical aspects of overlay repair, including material selection, process parameters, and performance evaluation.
Core Technical Points
Crusher hammer heads are typically manufactured from high-manganese steel (such as Mn13) or medium-carbon steel with high-manganese overlay surfaces. The high-manganese austenitic structure provides excellent impact toughness and work-hardening capability, which is essential for withstanding the repeated impact loading in crusher operations. However, the high carbon and manganese content of these materials makes them challenging to weld, requiring careful process design to prevent cracking and ensure adequate weld quality.
The weld overlay repair process for hammer heads involves several critical steps:
| Step | Description | Technical Requirements |
|---|---|---|
| Wear assessment | Measurement of remaining thickness | UT or caliper measurement |
| Material removal | Gouging or machining of worn areas | Leave 5–10 mm base metal |
| Surface preparation | Cleaning and profiling | Remove scale, rust, and oil |
| Preheating | Temperature control | 200–400°C |
| Overlay welding | Multi-pass deposit | Process and parameter control |
| Post-treatment | Heat treatment if required | Austenitize and quench |
| Inspection | NDT and dimensional checks | UT, MT, hardness |
The selection of overlay material is the most critical decision in hammer head repair. The overlay must provide adequate wear resistance under the specific crushing conditions while maintaining sufficient toughness to withstand impact loading. Common overlay materials include:
- High-manganese austenitic steel (Mn13): Excellent impact toughness, good work-hardening response, moderate wear resistance.
- High-chromium white cast iron: Excellent abrasive wear resistance, low toughness, suitable for low-impact conditions.
- Nickel-iron alloy: Good balance of toughness and wear resistance, excellent weldability.
- Tungsten carbide composite: Superior abrasive wear resistance, requires careful application to avoid brittleness.
For most crusher applications involving medium to hard rocks, a high-manganese or nickel-iron overlay is recommended. For soft, abrasive materials such as clay or sandstone, a high-chromium overlay may be more appropriate.
Process Analysis and Parameter Selection
The welding process selection for hammer head repair depends on the repair volume, required quality, and available equipment. The most commonly used processes are:
| Process | Deposition Rate | Equipment Cost | Skill Requirement | Best Application |
|---|---|---|---|---|
| Submerged arc welding | High | Low | Medium | Bulk repair, thick overlays |
| Flux-cored arc welding | Medium | Low | Low | Field repair, general use |
| Gas metal arc welding | Medium | Low | Medium | General repair, good control |
| Plasma transferred arc | Medium | High | High | High-quality, thin overlays |
| Laser cladding | Medium | High | High | Premium repair, high performance |
For high-volume crusher operations, SAW and FCAW are the most economical choices. The SAW process can achieve deposition rates of 5–10 kg/h, which significantly reduces repair time. The FCAW process offers better flexibility for field repairs and can be used in various positions.
Typical welding parameters for hammer head overlay repair include:
- Current: 250–450 A
- Voltage: 25–35 V
- Travel speed: 120–300 mm/min
- Wire or band diameter: 1.6–2.4 mm
- Preheat temperature: 250–350°C
- Interpass temperature: below 350°C
- Number of passes: 2–4 depending on wear depth
The preheat temperature is particularly important for high-manganese steels, as it reduces the cooling rate and minimizes the formation of brittle martensite in the heat-affected zone. For hammer heads made from medium-carbon steel, preheating to 200–300°C is generally sufficient to prevent cracking.
Defect Analysis and Performance Evaluation
Common defects in hammer head overlay repair include:
- Cracking: Both hot cracks and cold cracks can occur, especially in high-carbon and high-manganese materials. Hot cracks are caused by solidification cracking in the weld metal, while cold cracks result from hydrogen-induced cracking in the heat-affected zone. Mitigation includes using low-hydrogen consumables, adequate preheating, and controlled cooling.
- Lack of fusion: Resulting from insufficient heat input, excessive travel speed, or poor surface preparation. Ensuring proper cleaning and adequate welding parameters addresses this issue.
- Porosity: Associated with contamination or improper gas shielding. Maintaining clean surfaces and adequate flux or gas coverage is essential.
- Spatter: Common in GMAW and FCAW processes, which can reduce deposition efficiency. Using proper shielding and flux coverage minimizes spatter.
Performance evaluation of repaired hammer heads involves measuring hardness, wear rate, and impact toughness. Hardness testing of the overlay layer should confirm that the material composition meets specifications. Wear testing can be performed in the actual crusher environment or in laboratory abrasion testing machines. Impact toughness testing of the base metal heat-affected zone verifies that the repair has not significantly degraded the toughness of the hammer head.
Engineering Practice and Study Insights
A practical case involved the repair of hammer heads in a limestone crushing operation. The original hammer heads experienced wear after 4,500 operating hours, with a maximum wear depth of 15 mm. The repair process involved mechanical gouging of the worn areas, preheating to 300°C, and applying a three-pass overlay using a high-manganese steel flux with a carbon steel band electrode via the SAW process. The final overlay achieved a hardness of 200 HV in the as-welded condition and work-hardened to 400 HV after service. The repaired hammer heads demonstrated a service life extension of 60 percent compared to the original condition.
The study reveals that the success of hammer head repair depends on the proper selection of overlay material, welding process, and parameters tailored to the specific crushing conditions. Engineers should conduct a thorough analysis of the material being crushed, the crusher type, and the operating conditions before selecting the repair approach. The economic evaluation of repair versus replacement should consider not only the direct repair costs but also the downtime costs, labor costs, and the extended service life of the repaired hammer heads.
Furthermore, the development of standardized repair procedures and the training of skilled welders are essential for consistent repair quality. The integration of process monitoring, parameter logging, and post-repair inspection into a comprehensive quality management system ensures that repaired hammer heads perform reliably in service and maximizes the return on investment in the repair operation.