Surface Overlay Welding of WK-35 Electric Shovel Bucket Teeth

Literature Overview

This 2016 publication in Open-pit Mining Technology, authored by Jin Haijun from Shenhua Beidian Shengli Energy Co., Ltd., addresses the surface overlay welding of bucket teeth on the WK-35 electric rope shovel, a massive piece of mining equipment used in open-pit coal mining operations. The WK-35 shovel, with its enormous bucket capacity and operating weight, represents a significant capital investment, and the maintenance and repair of its bucket teeth are critical to minimizing downtime and maximizing operational efficiency.

Core Technical Points

WK-35 Electric Shovel Overview

The WK-35 electric rope shovel is one of the largest mining shovels in operation, with the following approximate specifications:

Parameter	Specification
Bucket capacity	35 m³
Operating weight	~500–600 tonnes
Bucket tooth dimensions	Large (typically 1,000–2,000 mm long)
Operating environment	Hard rock and overburden mining
Wear mechanism	Abrasive wear from rock and soil
Service life of bucket teeth	100–500 hours (depending on material)

The bucket teeth are subjected to extreme abrasive wear from contact with hard rock, soil, and debris. The wear pattern is typically concentrated at the cutting edge and the sides of the tooth, where the material is subjected to the highest stress and abrasion.

Overlay Welding Process Selection

For bucket teeth of this size, the following overlay welding processes are considered:

Process	Advantages	Disadvantages	Suitability for Bucket Teeth
SMAW	Portable; simple equipment	Low deposition rate; high operator skill required	Suitable for field repair
SAW	High deposition rate; good bead quality	Requires flux handling; less flexible	Suitable for workshop repair
FCAW	High deposition rate; good bead shape	Requires gas supply; moderate equipment	Suitable for workshop repair
TIG	Excellent bead quality; precise control	Low deposition rate; high skill requirement	Suitable for critical areas
Plasma arc	High energy density; thick deposits	Expensive equipment; specialized skill	Suitable for large deposits

For WK-35 bucket teeth, FCAW or SAW is typically preferred for the combination of high deposition rate and good quality. SMAW may be used for field repair or for difficult-to-access areas.

Overlay Material Selection

The overlay material for mining bucket teeth must provide excellent abrasive wear resistance:

Material Type	Hardness (HRC)	Abrasive Wear Resistance	Toughness	Typical Application
High-carbon martensitic	55–65	Good	Moderate	General mining applications
High-alloy martensitic	60–70	Excellent	Low	Severe abrasive conditions
Austenitic	40–50	Good	Excellent	Impact + abrasion
Hardfacing cast iron	55–65	Excellent	Low	Severe abrasion; no impact
Nickel-based alloy	35–45	Moderate	Excellent	Extreme conditions; high cost

For WK-35 bucket teeth operating in hard rock mining conditions, high-alloy martensitic or hardfacing cast iron materials are typically preferred for their excellent abrasive wear resistance.

Welding Sequence and Technique

The welding sequence for bucket teeth is critical to ensure uniform coverage and minimize distortion:

Surface preparation: Grind off worn surface; clean to bare metal; preheat to 200–300 °C
Base layer: Apply a compatible base layer to ensure good bond with the base metal
Build-up layers: Apply multiple layers of overlay material, alternating between sides to minimize distortion
Profile layer: Apply the final layer to achieve the desired tooth profile
Post-weld treatment: Stress relief annealing at 550–650 °C; final machining to restore tooth profile

Defect Analysis and Countermeasures

Defect	Root Cause	Impact	Countermeasure
Cracking in overlay	High carbon content; thermal stress	Tooth failure during operation	Control interpass temperature; use appropriate electrode; apply stress relief
Spalling of overlay	Poor bond strength; high residual stress	Loss of wear-resistant layer	Ensure adequate first-pass penetration; apply post-weld stress relief
Excessive dilution	High heat input; poor parameter control	Reduced overlay hardness	Reduce current; increase travel speed; use smaller electrode
Uneven coverage	Inconsistent welding technique; distortion	Uneven wear during operation	Use symmetric welding sequence; apply backing plate; final machining
Porosity	Flux contamination; base metal contamination	Reduced overlay integrity	Ensure proper flux handling; clean base metal thoroughly

Economic Analysis

The economic case for overlay welding repair of bucket teeth is compelling:

Cost Component	Overlay Repair	Tooth Replacement
Material cost	¥X (overlay wire)	¥Y (new tooth)
Labor cost	¥A (welding + machining)	¥B (removal + installation)
Downtime cost	¥C (short outage)	¥D (long outage)
Machine cost	¥E (grinding)	¥F (machining new tooth)
Total cost	Significantly lower	Significantly higher

The payback period for overlay welding is typically less than one shift, making it economically attractive even when accounting for the additional labor and machining requirements.

Study Reflections

The overlay welding repair of WK-35 bucket teeth represents a practical application of overlay welding technology in the mining industry, where equipment downtime is extremely costly and the availability of replacement parts may be limited. The key insights include:

Material selection is critical: The overlay material must be selected based on the specific wear mechanism (abrasive, adhesive, impact) and the operating environment (hard rock, soft soil, mixed conditions).
Welding sequence matters: The sequence of welding passes must be carefully planned to minimize distortion and ensure uniform coverage of the tooth surface.
Post-weld treatment is essential: Stress relief annealing is critical to eliminate residual stresses that could cause cracking during operation.
Economic justification is strong: The cost savings from overlay welding repair compared to tooth replacement are substantial, especially when considering the high cost of downtime in large mining operations.

The WK-35 shovel, with its massive size and high operating costs, represents a prime candidate for overlay welding repair. The ability to extend the service life of bucket teeth through overlay welding, rather than replacing them, is a significant cost-saving measure that directly impacts the operational efficiency of the mining operation. The study demonstrates the practical value of overlay welding technology in heavy equipment maintenance and repair, and provides a template for similar applications in other large mining equipment.