Zhuojin Pipe Fitting Co., LtdTungsten Carbide Overlay Welding on Hammer Crusher Hammers
Literature Overview
This technical report by Li Shuping, Tang Qingchun, Huang Shuhao, and Liu Yetong (2009) documents a practical quality control (QC) group project at Liuzhou Nonferrous Smelting Co., Ltd. The company operates hammer crushers processing 40,000 tonnes per annum of lead-zinc ore. The original hammer material was 45 steel with an average service life of only 25 days, creating significant material waste and production disruptions. The solution involved developing a tungsten carbide (WC) overlay welding process to extend hammer life.
Problem Analysis and Solution Approach
The root cause of the short hammer life is straightforward: 45 steel (0.42-0.50% C, quenched and tempered) has insufficient hardness and wear resistance for abrasive ore crushing applications. The ore being processed—lead-zinc minerals—contains hard abrasive particles that rapidly wear down the hammer striking surfaces. A systematic approach to solving this problem follows the classic engineering methodology:
| Parameter | Original Condition | Target Condition |
|---|---|---|
| Hammer material | 45 steel | 45 steel + WC overlay |
| Surface hardness | ~250 HB | >800 HV (WC layer) |
| Average service life | 25 days | Target: 3-5× improvement |
| Annual ore throughput | 4×10⁴ t/a | Unchanged |
Overlay Welding Process Design
The overlay welding of tungsten carbide requires careful consideration of several metallurgical challenges:
- Thermal cracking susceptibility: WC particles have very low thermal expansion compatibility with steel, and the high melting point of WC (2870°C) creates steep thermal gradients during solidification.
- Porosity formation: The decomposition of WC at welding temperatures can release carbon, leading to gas porosity in the weld metal.
- Bond strength: The overlay must maintain adhesion to the 45 steel base under repeated impact loading from ore crushing.
- Dilution control: Excessive dilution from the base metal reduces the hardness and wear resistance benefits of the WC overlay.
The practical process parameters typically employed for WC overlay on steel include:
| Process Parameter | Typical Range |
|---|---|
| Shielding gas | Argon or Argon-Helium mixture |
| Current type | Direct current electrode negative (DCEP) |
| Current density | 30-60 A/mm² |
| Interpass temperature | <150°C |
| Preheating | 100-200°C (to reduce thermal stress) |
| Layer thickness | 2-3 mm per pass |
| Number of layers | 2-4 passes |
Engineering Practice and FMEA Considerations
From a failure modes and effects analysis (FMEA) perspective, the critical failure modes for this application include:
- Overlay spalling: Loss of WC layer due to insufficient bond strength or excessive impact energy during ore crushing. Mitigation involves ensuring proper preheat, controlling interpass temperature, and possibly using a transition layer (such as a nickel-based or cobalt-based alloy) between the 45 steel and the WC overlay.
- Cracking at fusion boundary: Caused by high residual stresses from thermal mismatch between WC-rich overlay and ductile steel substrate. Countermeasures include post-weld stress relief annealing and using multiple thin layers rather than a single thick deposit.
- Uneven wear: If the overlay thickness is insufficient or the geometry is poorly designed, the overlay may wear through before the hammer itself fails. Design considerations include maintaining a minimum overlay thickness of 3 mm and ensuring uniform coverage on the striking surfaces.
Study Insights and Implications
This case study exemplifies the practical application of overlay welding technology in mineral processing industries. The economic benefit is substantial: extending hammer life from 25 days to potentially 100-150 days reduces replacement frequency by 4-6 times, directly impacting maintenance costs and production continuity. The approach demonstrates that even relatively simple metallurgical modifications—adding a hardfacing overlay—can yield dramatic improvements in component life.
For engineers in similar applications (cement industry, mining, power generation), this case provides a template for evaluating overlay welding as a solution to premature wear. The key success factors are proper process development (including consumable selection, parameter optimization, and quality control), operator training, and systematic monitoring of overlay thickness during maintenance intervals. The study underscores that overlay welding is not merely a laboratory exercise but a proven industrial solution when properly implemented with attention to metallurgical compatibility and process control.