Abstract: To solve the severe wear problem of exhaust fan impellers in our plant, based on extensive research, our plant boldly adopted a ceramic-metal composite process, successfully applying wear-resistant engineering ceramics to the wear prevention of fan impellers. This increased the service life of the fan impellers by more than five times, providing an effective and reliable method for wear resistance and safe production of fan impellers in our plant. Keywords: Ceramic, Adhesive, Wear, Fan Taking our plant as an example, because the boiler uses a water film dust collector and the coal used has a high ash content, and the water film dust collector has low efficiency, the ash content in the flue gas is relatively high. Furthermore, when the ash content of the coal fluctuates significantly, the dust removal efficiency of the water film dust collector is unstable, leading to accelerated wear on the induced draft fan blades. This is especially true for the airfoil blades; wear and tear causing ash ingress leads to dynamic imbalance, fan vibration, and forced shutdown, resulting in reduced unit output and significantly impacting the economic and social efficiency of the power plant. For many years, although many surface strengthening methods have been used, including surface welding of wear-resistant materials, thermal spraying, spray welding, surface coating with various polymer coatings, surface quenching, or chemical heat treatment, the results have not been ideal. In 2003, based on extensive research, our plant boldly adopted the ceramic-metal composite manufacturing technology of Beijing Titanium Shield Technology Co., Ltd., applying wear-resistant engineering ceramics to the fan impeller for wear resistance and protection, and achieved initial success. Subsequently, after further process improvements, the technology was applied to the impellers of four Y4-73NO.22F fans in our plant. The longest service life has exceeded three years, more than tripling the previous lifespan. This has provided a reliable guarantee for the safe and efficient operation of our plant's units, resulting in good economic benefits. II. Impeller Operating Conditions Our plant's boiler dust collector is a Venturi water film dust collector, designed for coal with an ash content of 22.81%. Since the unit went into operation in 1991, it has consistently burned coal with low ash content (12%), and the dust removal effect has been good, with no apparent wear issues with the induced draft fan. After 1996, due to constraints in the coal market, our plant began burning inferior coal with a higher ash content, reaching 48%. Subsequently, the dust collector became less efficient and overloaded. The problem of accelerated wear on the induced draft fan gradually became prominent. Our plant's induced draft fan model is Y4-73N022F, with an output of 283,300 cubic meters per hour and backward-curved airfoil blades. In 1998, the induced draft fan began to vibrate frequently, and the blades at the "fish head" area suffered from wear, resulting in severe dust leakage and significantly hindering the safe and economical operation of our plant. Maintenance personnel repaired the blades and balanced them on average once a week, creating a relatively passive production situation. Therefore, the plant leadership was determined to reverse this situation and take all possible measures to solve the problem. There were two approaches to solving this problem: one was to completely solve the low dust removal efficiency problem, and the other was to enhance the wear resistance of the induced draft fan impeller. The former was unlikely because the coal type could not be changed, and replacing the water film dust collector with an electrostatic precipitator would require tens of millions of yuan, which was impractical. Therefore, efforts could only be made on the second method. III. Wear Analysis and Countermeasures for Induced Draft Fan Blades The induced draft fan impeller mainly discharges boiler combustion exhaust gas into the atmosphere through flues, chimneys, and other systems. In current overhauled units, due to the use of electrostatic precipitators, the dust removal efficiency can reach over 99.9%, and the hard particles contained in the flue gas are very low. Therefore, the wear on the induced draft fan impeller is particularly slight, and in some power plants, it can last for several overhaul cycles. However, for boilers using water film dust collectors, the low dust removal efficiency means that burning high-ash coal will lead to severe impeller wear, especially for airfoil impellers. If wear at the blade inlet leads to ash ingress, the impeller will lose its dynamic-static balance, generating strong vibrations and severely impacting the safe operation of the fan. Taking our factory's fan impeller as an example, wear mainly occurs at the impeller inlet, with triangular wear areas forming near the back plate at both the blade inlet and outlet ends. The steel plates in these areas are frequently worn through or have deep grooves, with particularly severe wear at the weld seams. To address the severe impeller wear problem in our factory, we have conducted extensive research over the years, carrying out in-depth studies and discussions on methods for extending the service life of wind turbine impellers both domestically and internationally. These methods can be summarized as follows: Surface overlay welding: Using wear-resistant welding rods or wear-resistant powder blocks to overlay wear-resistant alloys on the worn areas of the wind turbine blades; Surface coating: Coating or bonding high-polymer wear-resistant materials to the worn areas of the blade surface; Thermal spraying (welding): Using plasma spraying or oxyacetylene flame, spraying ceramics or tungsten carbide onto the worn surface of the blades, or spraying and welding nickel-based + tungsten carbide alloys; Surface bonding or welding of ceramics: Composite wear-resistant engineering ceramics onto the surface of the wind turbine blades using high-strength, high-temperature resistant adhesives or special welding processes. In 2002, our factory's production technicians conducted on-site investigations at various power plants and relevant research institutions. They concluded that thermal spraying for wear resistance was limited by the spraying materials and processes, resulting in less effective wear resistance. Furthermore, the large amount of heat input could potentially cause impeller deformation, and this technology was currently used sparingly. Surface welding was widely used and was our company's primary maintenance method, but variations in the quality and process of the welding electrodes resulted in less than ideal wear resistance performance and effects. Surface ceramic inlay, with its increased thickness, added to the impeller's weight, potentially causing overload operation of the induced draft fan. After investigating the Mudanjiang Thermal Power Plant, Hohhot Thermal Power Plant, and Harbin Thermal Power Plant, which used ceramic bonding, we concluded that Beijing Titanium Shield Technology Co., Ltd.'s ceramic bonding technology was relatively successful. The Mudanjiang Thermal Power Plant's impeller wear-resistant treatment, implemented in June 1999, has been running for over 40,000 hours without any problems. During regular inspections, occasional small pieces of ceramic have been found to have fallen off; these can be easily repaired on-site. The ceramic pieces are only 2 mm thick, having minimal impact on the impeller's weight, and can be installed on-site. Simple maintenance and considerable benefits. Therefore, our factory decided to adopt ceramic bonding technology to treat the impeller of the induced draft fan for wear resistance. IV. Feasibility Analysis of Ceramic Sheets Bonded to Fan Impellers The wear-resistant effect of ceramic bonding to fan impellers depends on two conditions. First, the ceramic must have excellent wear resistance, at least three times higher than WC sprayed or welded materials. Second, a reliable bond between the ceramic and the metal is required; that is, the adhesive used must have high bonding strength, good toughness, and be temperature and corrosion resistant, with an aging life of at least ten years and a strength decrease of no more than 10%. Furthermore, ceramic wear resistance is advantageous for water film dust removal induced draft systems as it does not accumulate dust. 4.1 Performance of Wear-Resistant Ceramics The ceramics used as wear-resistant materials mainly include alumina, silicon carbide, silicon nitride, and zirconium oxide. For the operating conditions of fan impellers, cold-pressed sintered alumina ceramic is used for wear resistance. Its main characteristics are low price, low density, and excellent wear resistance. Actual measurements show that the cold-pressed sintered alumina ceramic blocks have a hardness of HRA88, a specific gravity of 3.7, and wear resistance approximately 5 times that of high-chromium cast iron and 100 times that of ordinary carbon steel. When used in fans, the ceramic sheets are only 1.5mm thick, and the weight per square meter (10,000 sheets) is only 5.5 kg. U-shaped ceramic blocks can be used at the fan blade inlet, with a frontal dimension reaching 6mm. Compared to general thermal spraying and welding materials, with a maximum thickness of only 1-3mm, the wear resistance of ceramics fully meets the expected targets. 4.2 Adhesive Performance Verification: While the pulverizer operates at 90℃, the induced draft fan operates at a higher temperature, between 140-160℃. However, the pulverizer impeller rotates at more than twice the speed of the induced draft fan, and operates under the influence of high-speed scouring airflow carrying hard particles. Therefore, the adhesive must possess certain high-temperature resistance, as well as certain shear strength and anti-aging properties. The coefficient of thermal expansion of ceramics is only half that of metals, therefore the adhesive also needs to have good toughness. The main properties of the adhesive formulated accordingly are as follows: tensile strength (metal-metal) at different temperatures is 50 MPa (room temperature), 36 MPa (100℃), and 20 MPa (150℃); shear strength is 28 MPa (room temperature), 20 MPa (100℃), and 10 MPa (150℃). The adhesive's toughness is between that of ceramics and metals, and it does not shrink after curing. Calculations show that at 90℃, when a Ф2020 diameter dust extraction fan impeller rotates at 1440 rpm, the centripetal force on a 10×10×1.5 mm ceramic piece at the outermost edge of the impeller is 0.446 kgf, while the shear force provided by the adhesive at this temperature is 360 kgf (100℃). The adhesive force is nearly 450 times the centripetal force on the ceramic piece. This demonstrates that the adhesive has an extremely high bonding safety factor. V. Analysis of Test Results Based on the above feasibility analysis and referring to the application experience of other factories, our factory carried out anti-wear treatment on the impeller of one of the induced draft fans during the major overhaul in May 2003 by bonding ceramic tiles. Wear-resistant ceramic tiles and specially shaped ceramic wear-resistant parts were laminated at the fish-head part of the blades, the windward side of the blades, and the connection part of the rear plate. The blade surface used ceramic tiles with dimensions of 10×10×1.5mm, and U-shaped ceramic tiles were used at the inlet, with a thickness of 6mm on the windward side. The construction process strictly followed the on-site construction procedures, including surface sandblasting, activation coupling agent treatment of metal and ceramic surfaces, and corresponding heat curing treatment. After bonding, it was put into use directly without dynamic balancing. During this period, the boiler burned coal with an ash content of over 45%. After one year of operation, the ceramic wear was very slight, and the condition was good. During the major overhaul inspection in 2005, it was found that except for a small number of ceramic tiles falling off, the rest were basically intact. Analysis of the ceramic tile wear at different locations revealed that the average wear on the ceramic tile along the airflow direction was less than 0.1 mm. The wear was more severe closer to the outer circumference of the impeller, i.e., the outlet end of the blades, with an average wear of 0.2 mm, significantly more severe than the wear on both sides of the central hub. This is because the airflow velocity is higher closer to the outer circumference of the impeller, resulting in more severe wear. Compared to the airflow direction, the ceramic tile wear was most severe in the direction perpendicular to the airflow (at the inlet's "fish head" area), reaching up to 0.3-0.5 mm. This actually conforms to the ceramic erosion mechanism, i.e., the larger the airflow angle, the more severe the wear. Furthermore, the vortex formed at the joints caused the most severe wear on the metal substrate along the joints, even wearing through the metal liner, resulting in some ceramic tiles being completely suspended and causing some ceramic tiles to fall off at the windward joints. During the unit's overhaul in 2004, another induced draft fan also adopted this technology. The difference was that this time, Titanium Shield Company directly cooperated with the impeller manufacturer, performing the ceramic tile bonding installation directly at the factory. It can be said that the process is very comprehensive, with the overall construction technology and appearance quality being superior to on-site construction. This is because the impeller manufacturer can coordinate its production process according to the ceramic tile application process requirements of Titanium Shield Company. Routine inspections of this fan since its operation have not revealed any ceramic tile detachment, achieving good results. Sixth, Economic Benefit Analysis: Before adopting this technology, our factory's induced draft fan impellers typically began to show wear and dust ingress at the blade head area after 6 months of operation, requiring frequent welding repairs. Because welding damaged the overall strength and plasticity of the base material, cracks frequently appeared during operation, necessitating further welding repairs, creating a vicious cycle. Generally, a new impeller could no longer be repaired after about a year and had to be replaced. Replacing one impeller costs 40,000 yuan, totaling 160,000 yuan for 4 fans. However, after adopting the ceramic tile application process, it is expected to operate fully for about 4 years, saving 480,000 yuan. This significantly reduces maintenance workload and ensures full unit output, resulting in considerable economic and social benefits. VII. Conclusion Our factory has successively applied ceramic anti-wear technology to a total of 4 impellers. After three years of actual operation, the results show that as long as the process is strictly followed during construction, regular inspections are conducted during use, and maintenance is carried out strictly according to the maintenance procedures, applying ceramic anti-wear coating to the impeller surface is a reliable and effective wear-resistant and anti-wear measure. It not only extends service life and has significant economic benefits, but also improves equipment reliability and has important social significance.