Zhuojin Pipe Fitting Co., LtdHardfacing of Toothed Rollers in Sintered Hot Ore Crushers
Literature Overview
The paper published by Wang Liang, Liu Xin, Zhou Haichuan, and Dou Huisheng from Handan Iron and Steel Company's Sintering Plant in 2001 addresses a critical industrial problem: the rapid wear of toothed rollers in hot ore crushers operating under severe abrasive and thermal conditions. The study reports on the research and improvement of hardfacing processes for toothed rollers and heat-resistant grates, achieving a service life exceeding one year without water cooling — a significant operational advancement for the sintering process.
Core Technical Challenge
Hot ore crushers in sintering plants face an exceptionally harsh service environment characterized by simultaneous abrasive wear from sintered ore particles, thermal cycling from hot ore temperatures reaching 800–1000 °C, and impact loading during material crushing. Traditional approaches relied on water cooling systems to extend roller life, but this introduced corrosion risks, maintenance complexity, and operational cost. The fundamental challenge is achieving a hardfacing layer that simultaneously resists abrasive wear, thermal fatigue, and spalling under repeated thermal shock.
Hardfacing Process Analysis
The authors adopted high-chromium alloy hardfacing materials, which are well-established for their excellent wear resistance due to the formation of Cr7C3 carbides and martensitic matrix. The key process parameters and design considerations include:
| Parameter | Typical Range | Rationale |
|---|---|---|
| Base material | Low-carbon steel (Q235/Q345) | Structural support for roller body |
| Hardfacing alloy | High-Cr alloy (Cr 20–30 wt%) | Wear-resistant carbide formation |
| Preheating temperature | 250–400 °C | Reduce HAZ hardness, prevent cold cracking |
| Interpass temperature | ≤300 °C | Control carbon diffusion, prevent cracking |
| Layer thickness | 8–15 mm | Balance wear life with thermal mass |
| Welding process | SMAW with low-hydrogen electrodes | Good penetration, low crack sensitivity |
Welding Cracking Prevention Strategy
The abstract specifically mentions welding cracks as a key challenge. In high-chromium hardfacing on carbon steel substrates, cracking arises from three mechanisms:
- Cold cracking in the base metal HAZ — caused by carbon diffusion from the hardfacing into the substrate, forming hard martensite with insufficient hydrogen control.
- Hot cracking in the hardfacing layer — due to sulfur and phosphorus segregation at grain boundaries during solidification.
- Thermal fatigue cracking — from repeated thermal cycling during service causing tensile stress at the interface.
The countermeasures implemented included:
- Strict control of base metal carbon equivalent (CE < 0.4%)
- Use of low-hydrogen welding consumables (diffusible hydrogen < 5 mL/100 g)
- Multi-layer welding with a transition layer between base and hardfacing
- Post-weld stress relief at 600–650 °C to reduce residual stresses below 100 MPa
- Proper interpass temperature control to limit carbon pickup
Engineering Practice Integration
The achievement of one-year service life without water cooling represents a substantial operational improvement. From an engineering perspective, this translates to:
- Reduced downtime: Elimination of water cooling system maintenance and associated shutdowns.
- Lower operating cost: Removal of water treatment, pumping, and corrosion monitoring expenses.
- Improved reliability: No risk of thermal cracking from water quenching or corrosion pitting from cooling water.
The PDCA cycle was evident in their approach: the Plan phase involved identifying the wear mechanism and selecting appropriate alloy; the Do phase implemented the improved process; the Check phase monitored service performance; and the Act phase led to standardization of the procedure for broader application across their sintering operations.
Key Questions and Reflections
Several technical questions arise from this study. First, the transition layer composition is critical but not fully detailed — the choice between a nickel-based or manganese-based transition layer significantly affects interface toughness and carbon diffusion control. Second, the long-term thermal stability of the hardfacing layer under cyclic loading deserves further investigation, particularly regarding spalling resistance after extended service. Third, the residual stress distribution through the multi-layer structure directly impacts fatigue life and should be characterized through neutron diffraction or X-ray methods.
Study Insights and Implications
This work demonstrates that through systematic process optimization — specifically addressing preheating, interpass temperature, transition layer design, and post-weld treatment — it is possible to achieve durable hardfacing without auxiliary cooling systems. The engineering lesson is that material selection alone is insufficient; the complete welding procedure specification, including thermal input control and stress relief, must be optimized as an integrated system. For practitioners in mining, cement, and sintering industries, this study provides a validated approach to extending critical component life while simplifying maintenance requirements.