Zhuojin Pipe Fitting Co., LtdWear-Resistant Surfacing Electrode Process Testing and Application in Centrifugal Induced Draft Fans
Literature Overview
Liu Dongju of Shenyang Blower Co., Ltd. published a practical engineering paper in Fan Technology (Vol. 42, No. 6, 2000, pp. 27-29) presenting a wear-resistant surfacing welding process for components of centrifugal induced draft fans. Induced draft fans in power plants and industrial processes handle hot flue gas containing abrasive fly ash and particulate matter, subjecting fan blades and other components to severe erosive wear. The paper proposes a feasible wear-resistant surfacing process scheme and describes the testing methodology used to validate the process.
Service Environment and Wear Mechanisms
Centrifugal induced draft fans operate under conditions that create a unique combination of wear mechanisms. The fan blades are exposed to high-temperature flue gas, typically in the range of 150 to 350 degrees Celsius, containing abrasive particles of fly ash, silica, and other mineral matter. The wear mechanism is primarily erosive, with abrasive particles impacting the blade surface at high velocity and removing material through micro-cutting and micro-ploughing actions. The high-temperature environment also contributes to thermal fatigue cracking and oxidation, which can accelerate wear by weakening the surface and creating initiation sites for material removal.
The selection of wear-resistant surfacing material must address these multiple wear mechanisms simultaneously. The overlay alloy must provide sufficient hardness to resist abrasive wear, adequate toughness to prevent brittle fracture under impact loading, and oxidation resistance to maintain surface integrity at operating temperatures. The metallurgical bond between the overlay and the base metal must also be strong enough to withstand the cyclic thermal and mechanical loading experienced during fan operation.
Surfacing Process Parameters
| Parameter | Typical Range | Rationale |
|---|---|---|
| Electrode type | Wear-resistant surfacing electrode with hardfacing alloy core | Provides required hardness and wear resistance |
| Electrode diameter | 3.2 mm to 4.0 mm | Balances deposition rate with penetration control |
| Welding current | 100 to 200 amperes depending on electrode diameter | Controls melting rate and bead geometry |
| Travel speed | 150 to 300 mm/min | Balances deposition rate with dilution control |
| Interpass temperature | Below 200 degrees Celsius | Prevents grain coarsening and excessive softening |
| Number of passes | 2 to 4 passes depending on required thickness | Builds up adequate overlay thickness |
| Bead overlap | 30 to 50 percent | Ensures uniform coverage and eliminates gaps |
Process Testing Methodology
The testing methodology described in the paper follows a systematic approach to validate the surfacing process before production application. The testing sequence begins with single-pass weld tests to establish baseline welding parameters, followed by multi-pass weld tests to evaluate the process for building up the required overlay thickness. Each test coupon is subjected to comprehensive examination including visual inspection, hardness profiling across the overlay thickness, metallographic examination of the overlay structure and interface, and wear testing to quantify the wear resistance of the overlay.
The wear testing methodology is particularly important for validating the practical performance of the surfacing process. The author describes the use of laboratory wear tests that simulate the operating conditions of the induced draft fan, including the abrasive particle size distribution, impact velocity, and temperature range. The wear test results are compared with the wear performance of uncoated base metal and with previously used surfacing solutions to demonstrate the improvement achieved by the new process.
Application Performance and Lessons Learned
The practical application of the wear-resistant surfacing process to induced draft fan components provides valuable engineering data on the durability and performance of the overlay in actual service. The paper reports on the service life of surfaced fan blades compared to uncoated blades, demonstrating the improvement in wear resistance achieved through the surfacing process. The analysis of failed surfaced components, where applicable, provides insight into the failure mechanisms and helps refine the process for future applications.
A key practical consideration is the repairability of surfaced fan components. When a fan blade is removed for maintenance or replacement, the remaining surfacing layer must be removed and new surfacing applied. The process must therefore be designed to allow for repeated surfacing operations without compromising the base metal integrity. This requires careful control of total heat input over multiple surfacing cycles and verification of the base metal condition before each surfacing operation.
Study Reflection and Practical Recommendations
This paper represents a practical engineering approach to solving a specific wear problem in the fan manufacturing industry. The systematic testing methodology, from single-pass qualification through multi-pass evaluation to full-scale wear testing, provides a framework that can be applied to other wear-resistant surfacing applications. For engineers developing surfacing solutions for abrasive wear environments, the key lessons include the importance of matching the overlay material to the specific wear mechanism, the necessity of comprehensive wear testing before production application, and the value of field performance data for process refinement. The induced draft fan application highlights the need for surfacing processes that can be applied to large, complex geometries with consistent quality, which requires careful planning of welding sequences and access arrangements.