Induction fan impeller?

I. Main causes of imbalance in impellers The reasons for imbalance in impellers during use can be briefly divided into two categories: wear of the impeller and scaling on the impeller. These two situations are related to the dust removal devices connected in front of the exhaust fans. In the case of dry dust removal systems, wear is the main cause of impeller imbalance, while in wet dust removal systems, scaling is the primary factor contributing to impeller imbalance. The details are as follows. 1. Impeller wear 　　 Although dry dust removal systems can remove most of the large-particle dust from flue gas, a small amount of large particles along with many tiny dust particles pass through the exhaust fan along with the hot, fast-flowing gas, subjecting the blades to continuous erosion. Over time, blade-like wear forms at the outlet of the blade. Since this wear is irregular, it causes imbalance in the impeller. Furthermore, the impeller surface oxidizes easily at high temperatures, forming a thick layer of oxide scale. The adhesion of these oxide scales to the surface of the impeller is not uniform; some of these oxide scales fall off automatically due to vibration or centrifugal force, which is also one of the reasons for impeller imbalance. 2. Scaling of the impeller The flue gas purified by the wet dust removal device (Venturi water film dust collector) has a high humidity; although the unremoved dust particles are very small, they have high viscosity. As they pass through the exhaust fan, they are attracted to the non-working surfaces of the blades due to gas vortices; this results in significant dust accumulation, especially at the inlet and outlet of these non-working surfaces, with the accumulation gradually increasing in thickness. When some of the ash and scale fall off due to the combined effect of centrifugal force and vibration, the balance of the impeller is disrupted, causing vibration throughout the exhaust fan. II. Strategies to address impeller imbalance 1. Methods to address impeller wear 　　 For impeller wear caused by dry dust removal, in addition to improving the dust removal efficiency of the dust collector, the most effective approach is to enhance the impeller’s resistance to wear. At present, the more mature method in this area is thermal spraying technology, which uses special methods to convert wear-resistant and high-temperature resistant materials such as metals or ceramics into a stream of particles at high temperature and high speed, which are then sprayed onto the surface of the impeller blades to form a super-strong coating that possesses much higher wear resistance, heat resistance, and oxidation resistance than the material of the impeller itself. This not only reduces the damage to the impeller’s dynamic balance caused by wear, but also alleviates the imbalance issues resulting from the formation of an oxide layer. When selecting an exhaust fan, for dry dust removal, impellers that have undergone thermal spraying treatment should be given priority. For impellers that have not been heat-sprayed during use, heat-spraying the impellers can be considered during equipment maintenance. Although this increases the manufacturing or maintenance costs of the impeller, it doubles to twice its original lifespan, thereby extending the major overhaul cycle of the induced draft fan. This reduces the operating costs of the induced draft fan and the entire production system, resulting in excellent overall benefits. 2. Methods for removing scale from impellers 　　 (1)**Descaling: This is a commonly used method for removing scale.** The system is installed on the casing of the exhaust fan and consists of pipes, 3 nozzles (1 located at the impeller outlet and 2 at the inlet), and a drain hole. The water source is usually tap water, with a pressure of about 0.3 MPa. This method is usually effective. The downside is that the time required for descaling each time the machine stops operating is long, and it needs to be stopped several times a month for descaling. It affects the normal operation of the unit. 　　 (2) High-pressure gas descaling: This system adopts a structure similar to that of the **system, but its pipes are high-pressure resistant, along with specialized nozzles and a high-pressure gas source. This device is fast and effective at removing scale from the blades; it can activate a high-pressure air source during the downtime of the exhaust fan, and scale removal can be completed in just a few dozen seconds. Due to its simple and convenient operation, it can be performed many times a day; it not only eliminates the problems associated with manual descaling, such as labor intensity and time consumption, but also significantly reduces the production costs of the entire unit. The question is whether the user has an available high-pressure gas source (with a pressure between 0.8 and 1.5 MPa; compressed air or nitrogen can be used), otherwise, a dedicated high-pressure compressor unit is required. 　　 (3) Continuous airflow scouring for descaling: Structurally, a continuous scouring device does not require an external air source; it utilizes the exhaust pressure of the exhaust fan itself to direct a small amount of flue gas (1%–2% of the rated air volume) from inside the fan to specialized nozzles located at the inlet of the impeller. These nozzles eject the flue gas at high speed onto the non-working surfaces of the blades. This scouring is continuous, starting as soon as the exhaust fan begins to operate. It not only removes dust that has just adhered to the blades but also prevents dust accumulation from increasing, eliminating the need to stop the machine for descaling. This device has a simple structure, requires minimal modifications to the induced draft fan, and offers excellent anti-scaling performance; it is a new technology with great potential for development. 3. Correction of the impeller’s dynamic balance 　Whether it is an impeller that has been treated with thermal spraying or one that has had its scale removed using various methods, the effects achieved are not permanent. Even after long-term use, the exhaust fan may still experience vibrations that exceed the allowable upper limit. At this point, the imbalance problem of the impeller can only be resolved through dynamic balancing correction. Previously, the dynamic balancing of impellers was usually carried out on a dynamic balancer, which is very inconvenient for fans in use, especially large-scale fans. Therefore, on-site dynamic balancing technology has received increasing attention in recent years. Its main advantages over previous methods are (1) it eliminates the need for tedious disassembly and assembly, saving costs associated with these processes as well as transportation costs, and reducing repair time ； (2) It preserves the original installation accuracy and improves the balance accuracy of the entire induced draft fan system. Its testing method is briefly described as follows. Testing equipment: On-site dynamic balancers, models: LC-810, LC-820, LC-830. Testing steps: (1) Attach reflective strips to the fan shaft, and measure the initial vibration values: fundamental frequency amplitude Vrmso, power frequency amplitude Vo, and phase angle φo ； (2) Measured vibration values after adding counterweights: power frequency amplitude Vrmsl, line frequency amplitude V1, phase angle φ1; the dynamic balance solution (counterweight value and angle of application) is automatically calculated ； (3) After adding weights, measure the remaining vibration values: power-frequency amplitude Vrms2, line-frequency amplitude V2, and phase angle φ2; as long as these values meet the vibration acceptance criteria, it is acceptable. Testing time: For experienced field testers, completing the above tasks takes only 20–40 hours. On-site dynamic balancing technology is a mature and practical maintenance technique that can simply, quickly, and cost-effectively resolve imbalance issues. (This article is from “Sanjiu Chemical Network WWW.39HG.COM”)

For the dynamic balancing of fan impellers, there are specialized balancing machines used for this purpose, as well as on-site balancing equipment that allows balancing to be carried out right at the location. It seems that using fiberglass for the impellers in exhaust fans isn’t a good idea, as the temperature in such fans usually exceeds 80 degrees, and fiberglass doesn’t seem to be able to withstand such temperatures. You might consider using stainless steel impellers, which would be a better option