Zhuojin Pipe Fitting Co., LtdDevelopment of Wear-Resistant Overlay Electrodes for Centrifugal Fans
Literature Overview
The article "Development of Wear-Resistant Overlay Electrodes for Fans" by Liu Pengshan, published in "Fan Technology" in 1991 (Volume 33, Issue 4, pages 30-32), addresses the development of specialized welding electrodes for overlay welding on centrifugal induced draft fans used in industrial applications. Classified under TG422.1 (electrodes), this work is significant because it bridges the gap between welding consumable development and the specific wear demands of fan components such as impellers, inlet cones, and diffusers. The author describes the design philosophy, composition optimization, and performance testing of wear-resistant overlay electrodes tailored for fan service conditions.
Core Technical Content and Materials Design
Centrifugal induced draft fans operate in environments where the gas stream carries abrasive particles such as dust, ash, and particulate matter. The fan components—particularly the impeller blades and the inlet cone—are subjected to erosive wear that progressively reduces their efficiency and can lead to catastrophic failure if not addressed. The author's approach to developing wear-resistant overlay electrodes involves a systematic optimization of the electrode coating composition to achieve a deposited metal with the desired balance of hardness, toughness, and erosion resistance.
The design philosophy centers on the concept of composite microstructure: the overlay deposit should contain hard, wear-resistant phases (such as chromium carbides, carbides of molybdenum, or borides) dispersed in a tougher metallic matrix. This composite structure provides wear resistance through the hard phases while maintaining structural integrity through the ductile matrix. The author discusses that the particle size, shape, and distribution of the hard phases are critical factors influencing wear performance.
| Electrode Design Parameter | Typical Specification | Effect on Performance |
|---|---|---|
| Carbon content in deposit | 2.0-3.5 wt% | Higher carbon increases carbide volume fraction |
| Chromium content | 20-30 wt% | Forms Cr7C3 and Cr23C6 carbides |
| Molybdenum content | 2-5 wt% | Enhances hardenability and high-temperature strength |
| Electrode coating type | Cellulose or basic | Affects arc stability and spatter |
| Recommended current range | 100-200 A | Depends on electrode diameter |
| Target deposit hardness | 55-65 HRC | Balance of wear resistance and toughness |
The author emphasizes that the electrode coating composition must be carefully designed not only for the deposited metal composition but also for arc stability, slag fluidity, and spatter control. A poorly designed coating can lead to excessive spatter, poor arc characteristics, and inconsistent deposit composition, all of which compromise the wear performance of the overlay.
Process Considerations and Application
The welding process for fan component overlay is typically SMAW using the developed electrodes. The process parameters must be optimized to minimize dilution and ensure complete fusion with the base metal. For fan impellers, which are often made of cast iron or low-alloy steel, the base metal composition significantly affects the dilution rate and, consequently, the final deposit properties. The author recommends a two-pass overlay approach: the first pass uses a transition electrode to ensure good bonding and reduce dilution, while the second pass uses the high-alloy wear-resistant electrode to achieve the target hardness.
Preheating is an important consideration for fan components, particularly for cast iron impellers. A preheat temperature of 200-300°C is recommended to reduce the risk of cracking in the cast iron base metal. The interpass temperature should be maintained below 200°C to prevent softening of the previous pass. Post-weld cooling should be controlled to avoid rapid quenching, which can lead to excessive martensite formation and cracking in the deposit.
The author also discusses the importance of surface preparation before overlay welding. The base metal surface must be clean and free of oxide, scale, and contamination. For fan impellers, the impeller blades are typically ground to remove surface oxide and to create a slightly roughened surface that promotes mechanical interlocking between the base metal and the overlay deposit.
Performance Testing and Results
The wear performance of the developed electrodes was evaluated through standardized testing methods, including pin-on-disc abrasion testing and field trials on actual fan components. The author reports that the optimized electrode compositions achieved a 3-5 times improvement in service life compared to the original unhardened fan components. The wear rate was reduced significantly, particularly in conditions involving moderate to severe abrasive loading.
The mechanical properties of the deposited metal were characterized through hardness testing, tensile testing, and metallographic examination. The metallographic analysis revealed a composite microstructure consisting of primary carbide particles embedded in a martensitic matrix, confirming the design intent of the electrode composition. The hardness distribution across the deposit was found to be relatively uniform, with a slight gradient near the fusion line due to dilution.
Engineering Practice and Reliability
In industrial fan maintenance, the overlay welding of wear-resistant electrodes is a standard practice for extending the service life of fan components. The key to successful application lies in the selection of the appropriate electrode for the specific service conditions. For fans handling dry, abrasive materials such as cement or fly ash, high-carbon, high-chromium electrodes are recommended. For fans handling wet or corrosive materials, austenitic or nickel-based electrodes may be more appropriate.
From a reliability engineering perspective, the overlay welding of fan components should be incorporated into a planned maintenance program. The overlay thickness should be sufficient to last for the planned maintenance interval, and the overlay should be inspected periodically for wear progression. When the overlay thickness falls below a critical minimum, the component should be removed for re-overlay welding before failure occurs.
Study Insights and Reflections
This article by Liu Pengshan represents an early but sophisticated approach to welding consumable development for a specific industrial application. The systematic approach to electrode composition design, incorporating both metallurgical principles and practical welding considerations, exemplifies the kind of engineering rigor that I believe is essential for producing reliable welding consumables. The emphasis on composite microstructure design—hard phases in a tough matrix—has been validated by decades of subsequent research and remains the gold standard for wear-resistant overlay materials. For engineers working in power generation, cement, and mining industries where centrifugal fans are ubiquitous, this work provides a valuable foundation for understanding the metallurgical and process considerations that underpin successful fan component protection. The practical focus on electrode design, rather than abstract metallurgical theory, makes this work particularly accessible and actionable for field engineers and maintenance personnel.