Composition and working principle of centrifugal fan:

Fans are generally divided into two categories: centrifugal and axial flow, and there is also an axial centrifugal fan. The characteristic of a centrifugal fan is that the working medium flows in the axial direction of the fan and out radially. The working principle of centrifugal fan: Centrifugal fan works by utilizing centrifugal force. When the fan impeller is driven to rotate by the motor, the gas inside the impeller is driven to rotate along with it. As a result, the gas obtains energy and is thrown out along the circumference of the impeller under the action of centrifugal force, entering the casing. Due to the increase in flow cross-section and the decrease in flow velocity, some kinetic energy is converted into pressure energy, and then enters the air duct. As the gas inside the impeller flows out, negative pressure is formed at the impeller inlet, and external gas flows in to supplement it. In this way, the fan continuously outputs gas with increased energy. The vibration of a centrifugal fan refers to the bi-directional maximum amplitude of the fan bearings (thrust end and expansion end). According to the technical specifications for power construction and acceptance! Boiler Unit Chapter Dl Knife 5047-95 and Construction and Acceptance Evaluation Standards for Electric Power Construction! According to the regulations of the boiler section, the maximum vibration of the fan bearings shall not exceed 0.10mm.

The hazards of excessive vibration in centrifugal fans:

The impact on the motor: Excessive fan vibration can cause excessive motor current, high temperature rise, and in severe cases, overheating of the motor coil. The impact on bearing anchor bolts: Long term operation of the fan under excessive vibration will loosen the anchor bolts and nuts, causing greater vibration. Raise the temperature of the bearing and burn it out; Bend the fan shaft; It is possible to cause the anchor bolts to be pulled up together. The impact on bearings: Excessive fan vibration can cause an increase in bearing temperature, and rolling bearings are generally not allowed to exceed 80 degrees. At 80. Operating at the above temperatures may result in severe damage to the bearings. The impact on the shaft: Long term operation under excessive vibration can cause the shaft to bend. This can further cause imbalance in the fan rotor, leading to an increase in bearing temperature; Make the motor current too high.

Reasons for excessive vibration of centrifugal fan:

There are three main reasons for excessive vibration of centrifugal fans. The manufacturing quality of the fan; Factors related to installation quality and operation. The main reasons can be summarized as follows: the fan and motor shafts are not concentric; The rotor of the fan is unbalanced; The axial oscillation of the impeller is large; Axis bending; The oil clearance of the bearing ball is too large; Loose foundation bolts of the bearing seat; The motor foundation bolts or platform connection bolts are loose; The gap between the bearing seat and its shim or between shim and shim is too large; The gap between the motor platform and its shim or between shim and shim is too large, and there are non-contact objects between the four legs of the motor and the platform; Friction between rotor and casing; Reverse installation of impeller; Loose connection between impeller and shaft; The direction of adjusting the door opening is incorrect; Insufficient rigidity of the casing causes vibration and rotor resonance; Insufficient basic stiffness; The grouting of the anchor bolt holes is not dense enough, causing the anchor bolts to loosen. The main factors causing excessive vibration in the manufacturing quality of centrifugal fans are: excessive bearing clearance; Axis bending; The outlet angle of the impeller blade is incorrect or deviates beyond the standard; Insufficient rigidity of the casing; Rotor imbalance; The clearance between the impeller and the main shaft is too large. This article does not discuss the manufacturing quality faults of centrifugal fans, but these faults should be checked before fan installation. Discovered during the maintenance process. The main factors causing excessive vibration in the operation of centrifugal fans are: blade dust accumulation or impeller wear leading to rotor imbalance; The wear of the wind turbine casing reduces its stiffness, etc.

Installation procedure for centrifugal fan:

Facility inventory. check Facility maintenance. Basic checks. Draw a line. parallels. Configuration of foundation bolts. Installation of main bearings. Installation of wind turbine casing. Current collector. Installation of regulating door. Installation of motor. One grouting of the facility. Installation of the air door actuator. Installation of cooling water pipes. Secondary grouting of facilities. Secondary alignment of facilities. Installation of wheel protection cover.

Methods to reduce centrifugal fan vibration during installation:

Inspection and maintenance of facilities. The inspection of facilities mainly involves checking the manufacturing quality of the manufacturer and whether there is any damage or deformation during transportation. The main inspection items include checking the curvature of the shaft, which should not exceed 0.1mm. Due to limited conditions, only a theodolite can be used for rough inspection on site. Most manufacturers are able to conduct precise testing. Check if the blade outlet angle of the impeller matches the manufacturer's preset drawing. Use a vernier caliper to check if the fit clearance between the spindle and impeller meets the preset drawing. Check whether the thickness of the wind turbine casing and the reinforcement bars comply with the preset drawings. Check that the regulating door should be flexible, not stuck, and able to fully open and close. Check the ellipticity of the current collector to ensure it meets the requirements.

Domestic fans generally require maintenance. The main maintenance items include bearing maintenance and impeller maintenance. Assembly of wheels. Clean the bearings and bearing housing with kerosene or gasoline. Measure the thrust clearance of the bearing using the lead wire method. Expansion gap. Adjust the oil clearance of the ball and the end clearance of the bearing, and adjust the above clearances. The thrust clearance is generally between 0 and 0.40, and the expansion clearance is determined by calculation to allow the shaft to expand freely. Measure the oil clearance of the ball, which is related to the type of bearing. Generally, four points are measured, and the average value is taken to compare with the manufacturer's technical data. If the oil clearance of the ball is too large, the bearing should be replaced. The end clearance of the bearing can allow the outer ring of the bearing to expand freely and the sealing between the upper and lower covers of the bearing housing is good, without oil leakage, generally around 0.1mm.

Before assembly, the fit clearance between the shaft and the hole should comply with the manufacturer's technical specifications. When assembling the impeller, it should be noted that the direction of the inlet and outlet air should be consistent with the rotation direction of the rotor. Check the shaking of the impeller (with the bearing seat aligned and the rotor installed), and measure its axial direction with a dial gauge. The radial oscillation should not exceed Zmm. Conduct a static balance test on the rotor to see if it is balanced. If there is an imbalance, it should be reported to the manufacturer for handling. Welding addition method can be used for processing. parallels. Configuration of foundation bolts.

The installation of the fan adopts the inclined pad iron installation method. The size of the pad iron and the number of pad iron groups are related to the pressure on the foundation. Concrete grade. The specifications of the anchor bolts are related. During the installation process, the size of the pad iron is generally 160-200x80-100, and the thickness of the thin edge of the inclined pad iron is not less than 4mm, with a slope of 1:10-1:20. The configuration of the shim shall be carried out in accordance with the specifications. The concrete surface where the pad iron is required to be placed must be polished flat, and the pad iron and foundation must be checked for color printing. The contact area between shims should not be less than 75%, and a 0.1mm feeler gauge should not be able to fit between shims. Each set of shims should not exceed 4 pairs. Each side of the anchor bolt is equipped with a set of shims, which are arranged in parallel or in a T-shaped pattern. Anchor bolts are generally provided by manufacturers and their verticality should be checked. Installation of main bearings.

For large centrifugal fans such as induced draft fans with supporting bearings on both sides of the impeller, bearing bases should be installed first. Install the bearing base based on the marked centerline and elevation requirements, taking into account the expansion value. After installation, perform grouting once (using ordinary cement with a grade not lower than the foundation concrete grade). After the grouting reaches its strength, the installation of the bearing seat can be carried out. Before installing the bearing seat or rotor, first place the lower air casing in place and temporarily fix the current collector on the shaft with lead wire. After hoisting the rotor, connect the bearing base and the bearing seat with bolts, thus installing the bearing seat on the bearing base. For single suction fans, their bearings and rotor shafts are supplied. The impeller is combined into one unit. When installing, the lower air cover should also be placed in place first, and then according to the centerline of the foundation. Elevation. Install the main bearing for the levelness of the shaft. After the installation of the main bearing is completed, another grouting can be carried out first, or wait for the wind turbine casing. After the motor installation is completed, re measure the installation dimensions and perform grouting together.

The installation of the main bearing requires a deviation of 1~from the longitudinal and transverse centerlines; The diagonal deviation of the main bearing cluster soil is Zmm; Elevation deviation is 1mm; The deviation of the spindle levelness is 0.2m, and the installation of the Mo wind housing. After the rotor installation is completed, the installation of the wind turbine casing can be carried out. The flanges of the wind casing are sealed with asbestos rope. Tighten the flange bolts. The principle of aligning the wind shell is based on the centerline, but more importantly, the clearance between the sub openings must meet the requirements. The centerline can be appropriately offset while ensuring the clearance between the ports. Current collector. Installation of regulating door. After assembling the wind shell, connect the current collector to the regulating door with bolts and connect the regulating door and current collector to the wind shell with bolts. Seal the flange with asbestos rope. This is the wind shell. Current collector. After assembling the regulating door as a whole, it can be adjusted according to the axial direction of the impeller and collector. Radial clearance (sub mouth clearance) is used for overall alignment of the wind turbine casing. During installation, pay attention to adjusting the air inlet direction of the door to be consistent with the rotation direction of the rotor. Installation of motor. The installation of the main bearing and the regular motor is based on the axial clearance of the coupling and the radial direction of the coupling. Axial clearance deviation is used for alignment. When aligning, first adjust the clearance between the wheels to within the range, and then install two sets of magnetic dial gauges on the coupling. One set is used to measure the radial deviation of the wheels, and the other set is used to measure the axial deviation of the wheels. When the axial deviation cannot be measured with a magnetic dial gauge, use a feeler gauge to measure the clearance around the wheels to determine the axial deviation of the two wheels. Find the axial direction of the wheel during one alignment. The radial deviation shall not exceed 0.10mm. After the motor is installed, grouting can be carried out once (grouting of the anchor bolt holes). One grouting. Before grouting, clean the anchor bolt holes without any debris. Accumulation of dust. Oil stains and accumulated water.

The grade of the grouted concrete shall not be lower than that of the foundation concrete, and the grouting shall be dense without any air holes. The next step of construction can only be carried out after the grouting reaches the required strength. The general time for a grouting to reach strength is 5-7 days. Secondary grouting of facilities. Ordinary cement is used for secondary grouting around the platform. The theoretical grouting height is 50mm. Its grade shall not be lower than the original foundation concrete grade. Pay attention to spot welding the pad iron before secondary grouting. Secondary alignment of facilities. After the secondary grouting reaches the strength, secondary alignment is carried out by adjusting the position of the motor, adding or removing gaskets, so that the clearance between the fan and the motor meets the preset regulations, radially. The axial deviation is within the range of 0.10mm. Finally, tighten the anchor bolts to the torque value. Install the wheel protection cover and add lubricating oil (grease) for partial trial operation.

Precautions for reducing the vibration of centrifugal fans:

Carefully inspect the manufacturing quality of the manufacturer's facilities and whether there is any damage or deformation during transportation. Especially the curvature of the shaft; The clearance between the impeller and the shaft; Bearing ball oil clearance; The shaking of the impeller, the balance of the rotor, etc. According to the manufacturer's technical data and power construction and acceptance technical specifications! Inspect the fan, especially the thrust clearance of the bearings. Expansion gap; The clearance at the end of the bearing should comply with regulations. According to the manufacturer's technical data and power construction and acceptance technical specifications! Install the fan. The longitudinal and transverse centers of its bearings. Elevation; The levelness of the spindle; Installation of shims; Tightening of foundation bolts; The clearance and axial direction between the motor and fan wheels; Radial deviation should comply with regulations. The trial operation of the fan should be carried out according to the operating procedures. Before trial operation, the outlet plug door and the population control door should be closed. After the motor reaches its rated speed, open the outlet plug door. Open the population control door and operate with a load of 5-10% for 1 hour. During the 1-hour trial operation of the fan, everything must be normal before gradually opening the regulating valve to continue the load test operation (the load should be increased to the rated load within 1 hour, and the current should not exceed the rated current). Inspect the fan according to the operating procedures; Daily maintenance; Minor repair; overhaul Especially for fans that transport flue gas and air powder mixtures, their impellers. Leaves. The wind turbine casing is prone to wear and dust accumulation. Make the rotor unbalanced; The stiffness of the wind shell decreases; Axis bending. These are all reasons that can easily increase the vibration of the fan, and special attention should be paid.