CLADDING TECHNOLOGY SHANXI CO., LTDOn-Line Cladding Repair of Graded Crushing Teeth - Study Notes
Literature Overview and Background
This study investigates the feasibility and methodology of on-line overlay welding repair for graded crushing teeth used in mineral processing crushers. Crushing teeth — also known as jaw plates, cone crusher mantles, and roll crusher teeth — are critical wear components that undergo severe abrasive and impact loading during ore processing operations. The term "graded" refers to the progressive wear profile that develops across the tooth surface, creating varying thickness requirements for repair.
The innovation highlighted in this literature is the transition from traditional replacement-based maintenance to in-situ overlay repair, which reduces downtime, minimizes material waste, and extends component service life. This approach is particularly relevant for large-scale mining operations where crusher teeth weigh several tons and replacement logistics are costly and time-consuming.
Technical Approach and Process Design
Wear Mechanism Analysis
Crushing teeth experience a complex combination of wear mechanisms:
| Wear Type | Mechanism | Typical Location |
|---|---|---|
| Abrasive wear | Hard ore particles plowing surface | Central crushing zone |
| Impact wear | Repeated compressive loading | Leading edges |
| Fatigue wear | Cyclic stress causing surface spalling | High-stress concentration areas |
| Adhesive wear | Metal-to-metal contact transfer | Less common in mineral processing |
The graded wear pattern means that the required overlay thickness varies significantly across the tooth surface — from 0 mm at the unworn edges to 30–50 mm in the deepest wear zones. This non-uniformity presents a unique challenge for repair welding.
Overlay Material Selection
The selection of overlay material depends on the ore being processed:
| Ore Type | Abrasiveness | Recommended Overlay | Hardness (HBW) |
|---|---|---|---|
| Limestone | Low | High-carbon martensite (Cr12) | 500–600 |
| Iron ore | Medium | Medium-Cr alloy (Cr26) | 550–650 |
| Bauxite | Medium-high | High-Cr carbide (Cr26-Cr30) | 550–650 |
| Quartzite | High | High-Cr alloy + carbide | 600–700 |
| Granite | Very high | Ceramic-reinforced or Stellite | 600–700 |
Welding Process Selection
For on-line repair, the following processes are considered:
- Flux-cored arc welding (FCAW): High deposition rate (5–8 kg/h), suitable for building up large volumes of material; requires flux handling in field conditions.
- Submerged arc welding (SAW): Excellent for thick deposits (up to 50 mm in multiple passes); requires flux collection systems for on-line application.
- Gas metal arc welding (GMAW): Most flexible for on-line use; moderate deposition rate (3–5 kg/h); good visual monitoring capability.
- Hot-wire TIG (HWT): Excellent for precise surface contouring; lower deposition rate but superior surface finish.
The study recommends a hybrid approach: FCAW or SAW for bulk material buildup, followed by GMAW or HWT for surface finishing and contour restoration.
Process Parameters and Quality Control
Typical Repair Welding Parameters (FCAW)
| Parameter | Value | Notes |
|---|---|---|
| Current | 450–650 A | Depends on wire diameter |
| Voltage | 32–40 V | Arc stability critical |
| Travel speed | 200–400 mm/min | Slower for thicker passes |
| Wire feed speed | 8–15 m/min | Correlated with current |
| Wire diameter | 1.6–2.4 mm | Thicker for higher deposition |
| Shielding gas | CO₂ or Ar/CO₂ mix | For FCAW with external shielding |
| Preheat | 100–200 °C | Reduces residual stress and cracking |
| Interpass temp | ≤300 °C | For martensitic overlay alloys |
Defect Prevention Strategy
| Defect | Cause | Prevention |
|---|---|---|
| Cracking | High carbon martensite formation | Preheat, low carbon filler, post-weld stress relief |
| Porosity | Surface contamination, flux moisture | Clean surface, dry flux storage |
| Poor fusion | Insufficient heat input | Increase current, reduce travel speed |
| Excessive dilution | Base metal mixing | Use compatible filler, control penetration |
| Distortion | Uneven heat input | Symmetrical welding sequence, clamping |
On-Line Repair Procedure
The on-line repair methodology described in the study follows a structured approach:
- Assessment: Measure wear profile using laser scanning or coordinate measuring machine to establish the graded wear map.
- Surface preparation: Grind away loose material, scale, and severely contaminated zones; establish a sound base for welding.
- Fixture and clamping: Secure the tooth assembly to prevent movement during welding; provide thermal mass to minimize distortion.
- Bulk buildup welding: Apply material in layers following the graded wear map, starting from the deepest wear zones and building outward.
- Surface finishing: Apply final passes to restore the original geometric profile within tolerance (typically ±2 mm).
- Post-weld treatment: Stress relief at 550–650 °C for 2–4 hours, or controlled cooling to reduce residual stress.
- Inspection: MT for surface defects, UT for volumetric defects in critical areas, hardness mapping across the overlay.
Engineering Case Study
The study presents a case involving the repair of cone crusher mantle teeth for a copper mine processing plant. The original teeth had a service life of approximately 8 weeks before requiring complete replacement. After implementing the on-line repair methodology:
- First repair extended life by 6 weeks (total service: 14 weeks)
- Second repair extended life by 5 weeks (total service: 19 weeks)
- Third repair extended life by 4 weeks (total service: 23 weeks)
The cumulative service life improvement of nearly 3x the original represents a significant economic benefit. The overlay material used was a high-chromium alloy (Cr26) with a hardness of 600 HBW, applied in 4–5 passes with a total overlay thickness of 35 mm at the deepest wear zone.
Key Technical Challenges and Solutions
The study identifies several critical challenges specific to on-line repair:
Challenge 1: Heat-affected zone degradation. Repeated welding on previously repaired areas can cause cumulative HAZ softening. The solution is to limit repairs to a maximum of 3 cycles and to perform stress relief between repair cycles.
Challenge 2: Geometric accuracy. Restoring the precise tooth profile is essential for proper crusher operation. The study recommends using CNC-guided welding or robotic welding for the finishing passes to achieve ±1.5 mm dimensional accuracy.
Challenge 3: Residual stress accumulation. Multiple welding passes introduce significant residual stresses that can lead to premature failure. Post-weld stress relief is mandatory after each repair cycle, and the residual stress should be verified to be below 150 MPa in the overlay layer.
Challenge 4: Field conditions. On-line repair occurs in dusty, vibration-prone environments. The study emphasizes the need for dedicated welding enclosures, compressed air for flux removal, and portable equipment capable of withstanding harsh conditions.
Study Insights and Recommendations
This literature makes a compelling case for transitioning from replacement to repair for large crusher components. The economic analysis shows that on-line repair reduces total cost of ownership by 40–60% compared to replacement, while also reducing environmental impact through material conservation. The technical approach is sound, with appropriate material selection, process parameters, and quality control measures.
However, the study could benefit from more detailed discussion of the metallurgical evolution during multiple repair cycles. Specifically, the interaction between the base metal, first repair overlay, and subsequent repair overlays creates a complex multi-layer microstructure that may not be adequately characterized. Future work should include metallographic examination of multi-cycle repair zones to establish clear limits on repair frequency.
The practical implication for maintenance engineers is clear: establish a systematic repair program with defined criteria for when repair is appropriate versus when replacement is necessary. A maximum of 3 repair cycles, combined with mandatory stress relief and inspection between cycles, provides a balanced approach to extending component life while maintaining structural integrity. This literature represents a valuable contribution to the field of maintenance welding and should inform the development of repair procedures for similar heavy-duty wear components across mining and mineral processing industries.