Performance characteristics of centrifugal fan

Development prospect of centrifugal fan

With the advancement of China's industrialization process, the industrial industry is vigorously carrying out energy conservation and consumption reduction, industrial upgrading, integration and reorganization, and industrial infrastructure needs a lot of updating. As an important supporting equipment of industry, centrifugal fans will be more used in the fields of electric power, cement, petrochemical industry, coal, mining and environmental protection. Under the new economic development situation, the centrifugal fan industry will continue to maintain rapid growth in the future. It is estimated that by 2022, the market scale of centrifugal fan industry will reach 96billion yuan.

Performance characteristics of centrifugal fan

Centrifugal fan is essentially a variable flow constant pressure device. When the speed is constant, the pressure flow theoretical curve of centrifugal fan should be a straight line Due to internal losses, the actual characteristic curve is curved. The pressure produced in the centrifugal fan is greatly affected by the change of inlet air temperature or density. For a given intake air volume, the pressure produced at the highest intake air temperature (the lowest air density) is the lowest For a given pressure and flow characteristic curve, there is a power and flow characteristic curve When the blower operates at a constant speed, for a given flow, the required power increases with the decrease of inlet air temperature.

Maintenance of centrifugal fan failure

The wear of the transmission part of centrifugal fan is a common equipment problem, including the wear of the bearing position of suction fan, bearing chamber, blower shaft bearing position, etc. In view of the above faults of centrifugal fan, the traditional maintenance methods include surfacing, thermal spraying, electric brush crossing, etc., but they all have certain disadvantages: the thermal stress caused by repair welding high temperature cannot be completely eliminated, which is easy to cause material damage, resulting in bending or fracture of components; However, due to the limitation of coating thickness, brush plating is easy to peel off, and the above two methods are to repair metal with metal, which cannot change the "hard to hard" coordination relationship, and under the comprehensive action of various forces, it will still cause the re wear of the rubber coated roller. In view of the above problems, contemporary western countries mostly adopt the repair method of polymer composite materials, and the American fuchy blue technology system is widely used. It has super strong adhesion, excellent compressive strength and other comprehensive properties, and can be disassembled and machined free. There is no effect of repair welding thermal stress, and the repair thickness is not limited. At the same time, the metal material of the product does not have the concession, which can absorb the impact vibration of the equipment and avoid the possibility of re wear. In the domestic application of centrifugal fan fault repair, it also gradually replaces the traditional method.

Precautions for centrifugal fan

Shutdown procedure of centrifugal fan

1. Emergency shutdown: during the trial operation of the unit, in case of one of the following situations, the emergency shutdown shall be carried out immediately. The operation of emergency shutdown is to press the stop button of the main motor, and then deal with the aftermath after shutdown.

a. The centrifugal fan suddenly vibrates strongly and has exceeded the trip value.

b. There is scraping or abnormal friction sound inside the body.

c. Smoke appears at any bearing or seal, or the temperature of a bearing rises sharply to the alarm value.

d. When the oil pressure is lower than the alarm value and cannot return to normal.

e. The liquid level in the oil tank is low, and there is suction phenomenon.

f. The shaft displacement value shows obvious continuous growth and reaches the alarm value.

2. Normal shutdown: the normal shutdown of the unit shall be operated according to the following procedures.

a. Gradually open the vent valve (or outlet bypass valve) and gradually close the exhaust valve.

b. Gradually close the inlet throttle valve to 20 ~ 25 °.

c. Press the stop button and pay attention to whether there is any abnormality during the shutdown process.

d. The oil supply can be stopped 5 ~ 10min after the unit stops, or when the bearing temperature drops below 45 ℃. For units with floating ring seals, the sealing oil pump must continue to supply oil until the temperature of the machine body is lower than 80 ℃.

After the unit stops, the rotor should be turned 180 ° regularly within 2 ~ 4 hours.

Installation matters of centrifugal fan

1. The installation of the whole centrifugal fan unit should be directly placed on the foundation and leveled with pairs of inclined sizing blocks.

2. For the centrifugal fan assembled on site, the cutting surface on the base should be properly protected from corrosion or operation. When the base is placed on the foundation, it should be leveled with pairs of inclined sizing blocks.

3. The bearing seat shall be closely connected with the base, and the longitudinal non levelness shall not exceed 0.2/1000. Measure on the main shaft with a level gauge, and the horizontal non levelness bottom shall not exceed 0.3/1000. Measure on the horizontal split of the bearing seat with a level gauge.

4. Before grinding and scraping the bearing bush, the axis line of the rotor and the axis line of the housing should be corrected first, and at the same time, the gap between the impeller and the air inlet and the gap between the main shaft and the shaft hole of the rear side plate of the housing should be adjusted to make it comply with the provisions of the technical documents of the equipment.

5. When assembling the main shaft and bearing bush, the inspection shall be carried out according to the provisions of the technical documents of the equipment. An interference of 0.03 ~ 0.04 mm should be maintained between the bearing cover and the bearing bush (measure the outer diameter of the bearing bush and the inner diameter of the bearing seat).

6. When assembling the fan casing, the position of the casing should be aligned based on the rotor axis line, and the axial and radial clearance between the impeller air inlet and the casing air inlet should be high-speed to the range specified in the equipment technical documents. At the same time, check whether the anchor bolts are fastened. If the clearance value is not specified in the technical documents of the equipment, the general axial clearance should be 1/100 of the outer diameter of the impeller, and the radial clearance should be evenly distributed, and its value should be 1.5/1000 ~ 3/1000 of the outer diameter of the impeller (the smaller the outer diameter takes the larger value). When adjusting, try to reduce the clearance value to improve the efficiency of the fan.

7. When aligning the fan, the different axial degrees of the fan shaft and the motor shaft: the radial positioning displacement should not exceed 0.05 mm, and the inclination should not exceed 0.2/1000.

8. For the centrifugal fan equipped with rolling bearings, the different degrees of bearing holes on the two bearing frames can be subject to flexible rotation after the rotor is installed.