What are the key reasons for the unbalance of fan impeller? Impeller unbalance in application can be divided into two types: impeller wear and impeller scaling. These two conditions are related to the ash removal equipment connected to the front of the induced draft fan. The reason for the imbalance of the impeller caused by the dry ash removal equipment is wear, while the reason for the imbalance of the impeller caused by the wet ash removal equipment is scaling. The technicians of Shenman Dynamic Balancing Machine Factory are as follows:
Although the dry test ash removal equipment can remove most of the large particles of smoke and dust, a small amount of large particles and many fine particles of smoke and dust accompany the high temperature and high speed smoke and dust to the induced draft fan, causing continuous erosion of the blades. In the long run, blade wear occurs at the blade inlet and outlet. Because this kind of wear is irregular, resulting in the imbalance of the impeller. In addition, the surface of the impeller is easy to oxidize at high temperature and turn into thick oxide skin. The binding force between the oxide skin and the impeller surface is not uniform. Some oxide skin will fall off automatically under the action of vibration or centrifugal force, which is also one reason for the imbalance of the impeller.
2. Scaling of impeller:
The humidity of flue dust purified by wet ash removal equipment (Venturi water film dust collector) is too high, and the flue dust particles not cleaned are very small, but the viscosity is very high. When they depend on the induced draft fan, they can be sucked on the non-working surface of the blade under the action of the gas vortex, and serious soot scaling will occur at the inlet and outlet of the non-working surface, and gradually thicken. When part of the ash scale falls down under the combined action of centrifugal force and vibration, the balance of the impeller is destroyed, and the entire induced draft fan is subject to vibration.What are the key reasons for the dynamic balance of fan impeller?
1. Ways to solve impeller wear:
For impeller damage caused by dry ash removal, in addition to improving the dust removal function of dust removal equipment, the best way is to improve the wear resistance of the impeller. At the present stage, the more mature way in this regard is thermal spraying technology, that is, the wear-resistant and heat-resistant metal or ceramic materials are changed into high-temperature and high-speed particle flow in a unique way, and sprayed onto the surface of the impeller blade to produce a very strong coat with much higher wear resistance, heat resistance and oxidation resistance than the material of the blade itself. This will not only reduce the damage of the impeller dynamic balance caused by the damage, but also reduce the uneven problems caused by the oxide layer.
When the induced draft fan is used, the impeller which has been solved by thermal spraying shall be the best choice for dry ash removal. For the impeller that has not been solved by overheating spray in application, thermal spray treatment can be considered for the impeller during equipment maintenance. Although this will increase the production or maintenance costs of the impeller, it will increase the service life of the impeller by 1-2 times and increase the maintenance cycle of the induced draft fan. Thus, the operating profit of induced draft fan and all manufacturing systems is reduced, and the comprehensive benefit is very good.
(1) Water spray descaling: It is a common descaling method. The water spray system is installed on the shell of the induced draft fan, and consists of pipes, three nozzles (one at the outlet of the impeller, two at the inlet) and drainage holes. The water source is usually tap water, with a pressure of about 0.3MPa. Such methods are generally reasonable. The defect is that each shutdown takes a long time for descaling, and it needs to be shutdown for many times in a month. It endangers the normal application of the unit.
(2) High-pressure gas descaling: the system adopts the same structure as the sprinkler system, but its pipeline is high-pressure resistant pipeline, special nozzle and high-pressure gas source. This kind of equipment is fast and reasonable for descaling the blades. It can open the high-pressure air source at the interval of the normal shutdown of the induced draft fan, and can successfully descale in only tens of seconds. Because the operation is simple and convenient, it can be carried out many times a day, which not only solves the problem of laborious and costly manual descaling, but also sharply reduces the production cost of all units. The question is whether the customer has a prepared high-pressure air source (the pressure is between 0.8 and 1.5 MPa, and can use compressed air or nitrogen), otherwise, special high-pressure compressor equipment must be used.
(3) Air flow continuous purging and descaling: structurally speaking, the continuous purging equipment does not use external air source. It uses the exhaust pressure of the induced draft fan itself to lead a small amount of smoke and dust (1%~2% of the rated wind speed) from the inside of the induced draft fan to the special nozzle, which is set at the inlet of the impeller, and shoots the smoke and dust cough into the non-working surface of the blade at a high speed. This type of purging is continuous, and it is started with the opening of the induced draft fan, Not only will the soot just stuck on the blade be scraped away, but also the soot deposition and thickening can be avoided, and there is no need to shut down the machine for descaling. The equipment has simple structure, small modification to the induced draft fan, and excellent anti-scaling effect. It is a new technology with great development.
Whether the impeller is treated by thermal spraying or the impeller is descaled in various ways, its function is not easy to be used once and for all. After the induced draft fan is applied for a long time, the vibration will still exceed the allowable upper limit. At this time, the imbalance problem of the impeller can only be solved according to the dynamic balance correction. In the past, the dynamic balance correction of the impeller was generally carried out on the dynamic balance machine, which is very inconvenient for the induced draft fan in application, especially for the large fan. Therefore, the on-site dynamic balancing technology has gained more and more attention in recent years. Its key advantages compared with the past way are
(1) Avoid tedious disassembly work, save disassembly and transportation costs, and reduce maintenance time;
(2) The original installation precision is stored, and the balance precision of all induced draft fan systems is improved. The test standards are summarized as follows.
Test equipment: field dynamic balance instrument
Test steps:
(1) Stick reflective strips on the fan shaft, and measure the original vibration values: direct frequency amplitude Vrmso, power frequency amplitude Vo, phase angle φ o；
(2) Measured vibration value after adding test weight: pass frequency amplitude Vrmsl, power frequency amplitude V1, phase angle φ 1. Automatically calculate the dynamic balance solution results (counterweight value and angle of adding counterweight);
(3) After adding counterweight, measure the remaining vibration values: pass frequency amplitude Vrms2, power frequency amplitude V2, phase angle φ 2. If it can meet the vibration inspection and acceptance specifications.
Test duration: for skilled field test engineers, it only takes 1-2 hours to complete the above work. On-site dynamic balancing technology is a mature and easy to use maintenance technology, which can easily, conveniently and economically solve the imbalance problem.
