CLADDING TECHNOLOGY SHANXI CO., LTDHardfacing Repair of Electric Shovel Drive Wheels and Bucket Teeth
Literature Overview and Background
The electric shovel (bucket-wheel excavator) is a critical piece of mining equipment operating under extreme abrasive and impact conditions. The drive wheel and bucket teeth are subjected to continuous material abrasion, cyclic loading, and environmental corrosion. This literature presents a systematic hardfacing repair process for these components, covering consumable selection, preheating parameters, welding procedure, and post-weld inspection. The study draws upon field experience from open-pit mining operations and laboratory validation, making it a valuable reference for engineers working in heavy-equipment maintenance.
Core Technical Content
The hardfacing process described employs multi-layer welding with specific electrode or wire selections to achieve the required hardness and wear resistance. The drive wheel typically receives a multi-pass build-up weld followed by a hardfacing overlay, while bucket teeth are restored to original geometry with a combination of fill weld and hardfacing layers.
| Component | Base Material | Hardfacing Consumable | Target Hardness (HRC) | Layers |
|---|---|---|---|---|
| Drive Wheel | Low-carbon steel (Q235) | Ni-Cr-Mo cast iron electrode (E5015-Ni-Cr-Mo) | 45–55 | 2–3 |
| Bucket Teeth | Medium-carbon steel (45 steel) | Co-based or Cr-based hardfacing wire | 50–60 | 3–4 |
The preheating temperature is maintained at 250–350 °C for the base metal to reduce residual stress and minimize the risk of cold cracking. Interpass temperature is controlled not to exceed 400 °C. The welding current for the build-up pass is typically 280–340 A with an arc voltage of 28–32 V, while the hardfacing pass uses a slightly reduced current of 240–300 A to ensure proper dilution control.
Process Parameters and Defect Analysis
A common challenge in hardfacing repair is controlling dilution between the base metal and the overlay layer. Excessive dilution leads to reduced hardness and premature wear failure. The literature emphasizes the importance of maintaining a dilution ratio below 30% for Co-based hardfacing and below 40% for Ni-Cr-Mo cast iron hardfacing. Common defects observed include hot cracking in the hardfacing layer, porosity from moisture contamination, and incomplete fusion at the base-metal/overlay interface.
Using the FMEA framework, the following risk assessment is proposed:
| Failure Mode | Severity | Occurrence | Detection | RPN | Countermeasure |
|---|---|---|---|---|---|
| Hot cracking in overlay | 9 | 5 | 4 | 180 | Reduce carbon content; increase preheat |
| Porosity | 7 | 6 | 3 | 126 | Dry electrodes; clean surface |
| Incomplete fusion | 8 | 4 | 5 | 160 | Increase current; proper bevel preparation |
| Cracking at weld toe | 7 | 5 | 4 | 140 | Post-weld stress relief at 550–600 °C |
Engineering Practice Insights
In field practice, the repair cycle for bucket teeth is typically 2000–3500 operating hours depending on the abrasiveness of the material being excavated. A key insight from this literature is the recommendation to use a graded transition layer between the base metal and the final hardfacing layer when the hardness differential exceeds 20 HRC. This graded approach significantly reduces the risk of interfacial cracking during service. Additionally, the use of a 45° bevel preparation on the drive wheel contact surface ensures adequate penetration and mechanical interlock of the overlay with the base metal.
Post-weld magnetic particle inspection (MT) is mandatory for the base-metal welds, while visual inspection and hardness mapping are required for the hardfacing layers. The literature also highlights the importance of maintaining proper layer thickness — typically 3–5 mm per pass for hardfacing — to avoid excessive heat input that could compromise the base metal microstructure.
Study Insights and Implications
This literature provides a practical, field-validated approach to hardfacing repair that can be directly applied to similar heavy-equipment maintenance scenarios. The emphasis on dilution control and graded layering is particularly noteworthy and aligns with modern best practices in weld overlay engineering. For engineers working on mining equipment repair, the key takeaway is that consumable selection must be matched to the specific wear mechanism — abrasion, impact, or a combination thereof — and that process discipline in preheating and interpass temperature control is non-negotiable for achieving reliable service life.