Zhuojin Pipe Fitting Co., LtdSurfacing Welding Process for Sintering Blower Blades
Literature Overview
The paper by Zhao Jiancang, published in Fan Technology (Vol. 31, No. 1, 1989, pp. 51–53), addresses the overlay welding (surfacing) process applied to blower blades used in sintering furnaces within the iron and steel industry. Sintering blowers operate under severe conditions characterized by high-temperature flue gas, abrasive particulate matter, and cyclic thermal loading. Blade failure due to erosion and corrosion significantly impacts production continuity and energy efficiency. This study documents a practical approach to extending blade service life through appropriate surfacing welding selection and process optimization.
Core Technical Content
The fundamental challenge with sintering blower blades lies in the combination of thermal fatigue and solid-particle erosion. The base material is typically low-alloy steel (such as 45 steel or 16Mn), which offers adequate structural strength but insufficient resistance to the erosive environment. The surfacing layers selected in this work emphasize high hardness carbide-forming alloys to resist abrasion while maintaining ductility to accommodate thermal cycling.
Surfacing Material Selection
| Parameter | Specification |
|---|---|
| Base material | 45 steel / 16Mn |
| Surfacing alloy system | High-chromium cast iron or Ni-Cr-Mo alloy |
| Hardness requirement | ≥ HRC 50 in surfacing layer |
| Preheating temperature | 150–250 °C |
| Interpass temperature | ≤ 250 °C |
| Post-weld treatment | Stress-relief annealing at 550–600 °C |
The author emphasizes that the surfacing layer must balance hardness and toughness. Excessive hardness leads to cracking during thermal cycling, while insufficient hardness results in rapid erosion. The recommended approach involves multi-pass surfacing with graded composition transitions to minimize dilution and residual stress.
Process Parameters and Defect Control
The welding process employed is SMAW (shielded metal arc welding) with appropriate electrode selection. Key process considerations include:
- Preheating: Uniform preheating of the blade at 150–250 °C reduces the risk of cold cracking, particularly in high-carbon steel substrates.
- Welding sequence: A symmetric welding sequence is critical for blade components to minimize angular distortion and warpage.
- Layer thickness: Each surfacing pass should be limited to 2–3 mm to control heat input and dilution.
- Interpass cleaning: Thorough cleaning between passes prevents inclusion defects.
Common defects identified include porosity from inadequate shielding, hot cracking from excessive carbon content in the weld metal, and spalling due to poor adhesion between layers. The author recommends a multi-pass strategy with the first pass serving as a transition layer and subsequent passes providing the functional wear-resistant surface.
Engineering Practice Insights
From a metallurgical perspective, the dilution rate between the base metal and the surfacing layer is a critical parameter. For blades in sintering applications, a dilution rate exceeding 30% can significantly reduce the hardness of the final surfacing layer. The use of a transition layer with intermediate composition helps manage this dilution effect.
The residual stress distribution in the surfaced blade is another concern. The thermal mismatch between the base metal and the hard surfacing layer generates tensile residual stresses at the weld root, which can initiate fatigue cracks. Post-weld stress-relief treatment at 550–600 °C is therefore essential, though care must be taken not to exceed the tempering temperature of the martensitic surfacing alloy.
In my experience with similar applications in power plant fan blades and cement kiln components, the key to long-term success lies not only in material selection but also in the quality of surface preparation prior to surfacing. Any oxide scale or rust on the blade surface must be completely removed by grinding to bare metal, as these contaminants lead to lack of fusion and early spalling in service.
Study Reflections
This 1989 paper, while modest in scope, captures the engineering pragmatism of the era. The approach reflects a deep understanding that in industrial practice, the optimal solution is not always the most advanced one but rather the one that balances cost, availability, and reliability. The emphasis on preheating, controlled heat input, and post-weld treatment remains valid today and aligns with modern welding procedure specification (WPS) requirements.
The paper's relevance extends beyond sintering blowers to any application involving rotating blades exposed to erosive and corrosive environments, including induced draft fans, forced draft fans, and gas turbine components. The metallurgical principles discussed—dilution control, residual stress management, and thermal fatigue resistance—are universally applicable to overlay welding engineering.
Summary
The surfacing welding of sintering blower blades represents a classic example of surface engineering applied to solve a practical industrial problem. The success of the approach depends on careful selection of the alloy system, disciplined process parameter control, and appropriate heat treatment. The study provides a foundation for understanding how overlay welding can extend component life in harsh service environments, and its principles remain instructive for contemporary engineering practice in fan and blower maintenance.