The casing is an important part of the centrifugal fan. The main channel of the gas passing through the centrifugal fan is the casing of the fan. Once deformation, improper installation, and poor sealing occur, it will directly affect the wind pressure, flow and other parameters in the fan. , the result is that the operation effect of the fan cannot meet the production or ventilation requirements.
1. Requirements for the casing of the centrifugal fan
1. The shape of the casing of the centrifugal fan should ensure that the inhaled medium can enter the impeller evenly, and be effectively guided to the outlet when discharged from the impeller, without pulsation or large eddy current, and the pressure loss should be reduced.
2. The casing of the centrifugal fan should have sufficient rigidity to make the deformation and vibration of the casing smaller.
3. The inlet should be made into a convergent shape (the inlet of the casing can also form an air inlet independently), and its axis should be basically the same as the axis of the impeller; the flange surface of the air inlet should be flat and perpendicular to the axis.
4. The outlet flange surface should be flat and conform to the given direction.
5. For the casing of a large centrifugal fan, the lower part should have a foot supporting the total weight of the fan, and the basic installation holes of each fan should not be less than 4.
6. The side plate and worm plate of the casing are allowed to be spliced under the condition of ensuring the strength, and the flatness of the side plate should meet the relevant regulations.
7. There must be no gas leakage at the connection of the fan casing.
8. For the centrifugal fan with direct drive, the casing should be firmly connected with the motor or the base, so that the center of the casing should be consistent with the axis of the motor, and should have sufficient strength to withstand the dynamic load generated by the operation; for other transmission methods For the fan, the center of the casing should be consistent with the axis of the bearing.
9. The pipeline connected to the inlet and outlet of the casing should have independent supports, and no external force should be applied to the casing.
2. Installation process of centrifugal fan casing
1. Inspection and repair: Before installation, check whether all parts of the centrifugal fan are complete, and check whether the main parts such as the casing, impeller, main shaft, and transmission box are deformed and damaged due to transportation. Otherwise it should be repaired.
2. Removal of sundries: Check whether there are tools and sundries that have been dropped or left inside the fan casing, otherwise they should be removed. The fan casing needs to clean the impeller gland first, and there should be no oil stains, burrs and rust.
3. Adjust the impeller gland bolts: Before lifting, loosen the impeller gland bolts by about 10mm, remove all the wooden pads protecting the bearing, and then tighten the impeller gland bolts, and strictly follow the Tighten the bolts with the specified torque, and lock the double lug stopper. At the same time, the bolts that fix the main bearing seat and the rear guide vane seat should also be checked, and the assembled temperature measuring components should be checked to confirm that they are in good condition, so as to avoid rework.
4. Hoisting the casing: Install the casing and the rear guide vane assembly base plate of the centrifugal fan on the casing foundation, hang the anchor bolts, and assemble the casing and the rear guide vane with a crane Lift it on the base plate, check the vertical condition of the casing, and the casing cannot be deflected.
5. Install the bracket plate: The bracket plate of the centrifugal fan should be in close contact with the base plate, and the bracket plate and the base plate should be connected and fixed with bolts. Tighten with a torque wrench.
6. Adjustment deviation: Taking the center of the bearing group as the benchmark, adjust the elevation deviation of the center of the main bearing box by adjusting the pad iron group until it meets the requirements of the drawing: the deviation of the shaft levelness should meet the requirements of the drawing, and the vertical and horizontal The center deviation should meet the drawing requirements.
7. Install the air hood: Install the conical cold air hood on the relevant flange of the front cold air hood, connect and fix it with bolts, and add aluminum silicate sealing rope to the flange joint surface.
3. Packing and sealing method of centrifugal fan casing
There are many sealing methods for centrifugal fans, but without any disassembly of the centrifugal fan, there is a simple packing sealing method. Each set of packing seals consists of a section of packing, two pressing parts, and two or four semicircular workpieces. The specific method is as follows:
1. Sleeve the two workpieces marked with the word “shell” on the shaft, and weld the groove toward the bearing box to form a ring; then put the two semi-circular workpieces without the word “shell” on the transmission shaft, and The groove is welded into a ring toward the casing. This allows the drive shaft to pass through the two rings with the grooves facing each other.
2. Weld the ring marked with the word “shell” on the casing, pay attention that the inner circle of the ring should be equal to the clearance of the transmission shaft. Then, the hexagonal heads of the bolts of the two pressing pieces are respectively welded on the casing so that one end of the pressing pieces can be pressed on the ring.
3. Cut a piece of packing and wrap it in the groove of the ring, and tighten the nut of the pressing piece to make one end press the ring. At this time, a simple packing seal can be installed successfully.
This packing and sealing installation method of centrifugal fan only needs to machine the workpiece in the early stage, and the installation workload is very small in the later stage. It is very suitable for centrifugal fans for induced drafts that do not require sealing. It does not require a lot of time and is simple and convenient.
