Among all kinds of fan products, centrifugal fans are often used as boiler induced draft fans, site ventilators, etc., and are commonly used ventilation equipment, mainly using the centrifugal force generated by the impeller when it rotates. Air is exhausted.
1)Schematic diagram of centrifugal fan structure
In the schematic diagram of the cross-sectional structure of the centrifugal fan:
1—V belt pulley; 2, 3—bearing seat; 4—spindle; 5—shaft disc; 6—rear disc; 7—volute; 8—vane; 9—front disc; 10—air inlet; 11—outlet Air outlet; 12—base.
2)the introduction of the components of the centrifugal fan
The impeller is a centrifugal fan The main component of the impeller is composed of blades, front and rear disks that connect and fix the blades, and a hub. The blade type of centrifugal fan can be divided into three types: backward type, radial type and forward type according to the relationship between its outlet direction and the rotation direction of the impeller:
(1) The bending direction of the backward blade is exactly the same as the natural motion trajectory of the gas, so the collision between the gas and the blade is less, the energy loss and noise are small, and the efficiency is high.
(2) The bending direction of the forward blade is opposite to the motion trajectory of the gas, and the gas is forcibly changed direction, so its noise and energy loss are large and the efficiency is low.
(3) The characteristics of radial blades are between the backward type and the forward type.
2. Current collector
The collector is installed in front of the impeller, which enables the airflow to fill the inlet section of the impeller evenly, and the resistance loss when the airflow passes through it is very small. The main types are:
(1) Cylindrical shape: A vortex area will be formed at the inlet of the impeller, and the effect will be worse when the air is taken in directly from the atmosphere.
(2) Conical shape: It is better than the cylindrical shape, but it is too short and the effect is not good.
(3) Arc: better than the first two.
(4) Conical arc shape: This type of collector is basically used in high-efficiency fans.
The cooperation between the collector and the impeller should be in the form of a sleeve gap. In order to ensure the performance of the centrifugal fan, it should be ensured that the gap between the collector and the impeller with the mouth meets the drawing standards. For some fans with high gas temperature and large machine size, in order to ensure that when the fan is running at high temperature, the air inlet ring and the impeller do not rub after the thermal expansion of the casing, and the gap between the air inlet ring and the impeller inlet is not completely uniform. Generally, the top is large and the bottom is small, and the left and right are uniform. Adjust the gap between the air inlet ring and the impeller inlet to ensure that the gap value meets the requirements of the drawing.
The performance and efficiency of the centrifugal fan are mainly determined by the impeller, but the shape and size of the volute and the shape of the suction port will also affect it. The function of the volute is to collect the gas thrown from the impeller, so that it flows to the exhaust port, and in the process of this flow, part of the dynamic pressure energy obtained by the gas from the impeller is converted into static pressure energy to form a certain wind pressure. .
4. Snail tongue
There is a tongue-like structure at the outlet of the volute of the centrifugal fan, which is generally called the volute tongue. The volute prevents the gas from circulating in the casing. The composition of the snail tongue includes:
(1) Sharp tongue; used for high-efficiency fans, the noise of the fans is generally relatively large.
(2) Deep tongue; mostly used for low-speed fans.
(3) Short tongue; mostly used for high-speed fans.
(4) Flat tongue; used for low-efficiency fans, with low fan noise.
The gap between the top of the volute tongue and the outer diameter of the impeller has a great influence on the noise. The smaller the gap, the greater the noise; the larger the gap, the less noise. Generally take s=(0.05~0.10)D2. The arc at the top of the volute tongue has no obvious impact on the aerodynamic performance of the fan, but has a greater impact on the noise. If the arc radius is small, the noise will increase, generally take r=(0.03~0.06) D2.
5. Bearing box
The bearing box of the centrifugal fan is mainly where the transmission parts are located. It is composed of the main shaft, the bearing and the pulley. At the same time, it is also supported by the bearing seat. Some centrifugal fans use couplings to connect the transmission.
6. Adjust the damper
The air door of the centrifugal fan is the main component for controlling the flow. During installation, attention should be paid to whether the rotation direction of the blades of the adjustment door is correct, and the direction of the intake air should be consistent with the rotation direction of the impeller. The common adjustment door is the petal-type blade type adjustment door, and the adjustment range is from 0° (fully open) to 90° (fully closed). Adjust the handle position of the door so that it is on the right side when viewed from the direction of the air inlet. For a right-hand rotary fan, push the handle from bottom to top to fully close to fully open. For left-rotating fans, the handle is pulled from top to bottom from fully closed to fully open.