Screw air compressors are positive displacement compressors, which achieve the purpose of gas compression through the gradual reduction of working volume.
The working volume of a screw air compressor is composed of a pair of cogs of rotors placed parallel to each other and engaged with each other and a chassis that accommodates this pair of rotors.When the machine is running, the teeth of the two rotors are inserted into each other’s cogs, and as the rotor rotates, the teeth inserted into the other’s cogs move to the exhaust end, so that the volume enclosed by the other’s teeth gradually shrinks, and the pressure gradually increases until the required pressure is reached. When the pressure is reached, the cogs communicate with the exhaust port to achieve exhaust.
After an alveolar is inserted by the opponent’s teeth engaged with it, two spaces separated by the teeth are formed. The alveolar near the suction end is the suction volume, and the one close to the exhaust end is the volume of compressed gas.With the operation of the compressor, the teeth of the opposing rotor inserted into the cogging move towards the exhaust end, so that the suction volume continues to expand and the volume of the compressed gas continues to shrink, thereby realizing the suction and compression process in each cogging. When the gas pressure of the compressed gas in the cogging reaches the required exhaust pressure, the cogging just communicates with the vent and the exhaust process begins.The changes in the suction volume and compression volume divided into the cogging by the teeth of the opponent’s rotor are repeated, so that the compressor can continuously inhale, compress and exhaust.
Working principle and structure of screw compressor：
1. Suction process: The suction port on the intake side of the screw type must be designed so that the compression chamber can be fully inhaled. The screw type air compressor does not have an intake and exhaust valve group. The intake is only adjusted by the opening and closing of a regulating valve. When the rotor rotates, the tooth groove space of the main and auxiliary rotors is transferred to the air intake end wall opening, the space z* is large, at this time the tooth groove space of the rotor communicates with the free air of the air inlet, because all the air in the tooth groove is discharged during the exhaust, and the tooth groove is in a vacuum state at the end of the exhaust. When it is transferred to the air inlet, the space z* is large. At this time, the tooth groove space of the rotor communicates with the free air of the air inlet, because all the air in the tooth groove is discharged during the exhaust. At the end of the exhaust, the tooth groove is in a vacuum state. When it is transferred to the air inlet, The external air is sucked in and flows axially into the tooth groove of the main and auxiliary rotors.Maintenance of screw air compressor reminds that when the air fills the entire tooth groove, the end face of the air inlet side of the rotor is turned away from the air inlet of the chassis, and the air between the tooth grooves is closed.
2. Sealing and conveying process: At the end of the suction of the main and auxiliary rotors, the tooth groove of the main and auxiliary rotors and the chassis are closed. At this time, the air is closed in the tooth groove and no longer flows out, that is, [sealing process].The two rotors continue to rotate, and their tooth peaks and tooth grooves coincide at the suction end, and the anastomosis surface gradually moves towards the exhaust end.
3. Compression and oil injection process: During the conveying process, the meshing surface gradually moves to the exhaust end, that is, the tooth groove between the meshing surface and the exhaust port gradually decreases, and the gas in the tooth groove is gradually compressed and the pressure increases. This is the [compression process].At the same time as compression, the lubricating oil is also sprayed into the compression chamber and mixed with the chamber gas due to the pressure difference.
4. Exhaust process: When the meshing end face of the screw air compressor maintenance rotor is transferred to communicate with the exhaust of the chassis, (at this time the pressure of the compressed gas is z*high) the compressed gas begins to be discharged until the meshing surface of the tooth peak and the tooth groove is moved to the exhaust end face. At this time, the tooth groove space between the meshing surface of the two rotors and the exhaust port of the chassis is zero, that is, the (exhaust process) is completed. At the same time, the length of the tooth groove between the meshing surface of the rotor and the air inlet of the chassis reaches z*long, and the suction process is in progress.
Screw air compressors are divided into: open type, semi-enclosed type, fully enclosed type
1. Fully enclosed screw compressor: the body adopts a high-quality, low-porosity cast iron structure with small thermal deformation; the body adopts a double-wall structure with an exhaust passage, high strength and good noise reduction effect; the internal and external forces of the body are basically balanced, and there is no risk of open and semi-enclosed high pressure; the shell is a steel structure with high strength, beautiful appearance and light weight.The vertical structure is adopted, and the compressor occupies a small area, which is conducive to the arrangement of multiple heads of the chiller; the lower bearing is immersed in the oil tank, and the bearing is well lubricated; the axial force of the rotor is reduced by 50% compared to the semi-enclosed and open type (the balancing effect of the motor shaft on the exhaust side); there is no risk of horizontal motor cantilever, high reliability; avoid the impact of screw rotor, spool valve, and motor rotor weight on the matching accuracy, and improve reliability; good assembly process.The vertical design of the screw without oil pump enables the compressor to run or stop without oil shortage.The lower bearing is immersed in the oil tank as a whole, and the upper bearing adopts differential pressure for oil supply; the system differential pressure requirements are low. In case of emergency, the bearing lubrication protection function avoids the lack of oil lubrication of the bearing, which is conducive to the opening of the unit during the transition season.Disadvantages: The use of exhaust cooling, the motor is at the exhaust port, which can easily cause the motor coil to burn down; in addition, the failure cannot be ruled out in time.
2. Semi-enclosed screw compressor
Spray-cooled motor, low operating temperature of the motor, long life; open compressor uses air to cool the motor, the operating temperature of the motor is higher, which affects the life of the motor, and the working environment of the computer room is poor; the use of exhaust to cool the motor, the motor operating temperature is very high, the motor life is short.Generally, the external oil is larger in size, but the efficiency is very high; the built-in oil is combined with the compressor, which is small in size, so the effect is relatively poor.The secondary oil separation effect can reach 99.999%, which can ensure good lubrication of the compressor under various operating conditions.However, the plunger semi-enclosed screw compressor is driven by gear to increase the speed, the speed is high (about 12,000 rpm), the wear is large, and the reliability is poor.
Three, open screw compressor
The advantages of open-type units are: 1) The compressor is separated from the motor, so that the compressor has a wider range of applications; 2) The same compressor can be applied to different refrigerants. In addition to halogenated hydrocarbon refrigerants, ammonia can also be used as a refrigerant by changing the material of some parts; 3) According to different refrigerants and operating conditions, motors of different capacities can be used.The main disadvantages of open-type units are: (1) The shaft seal is easy to leak, which is also the object of frequent maintenance by users; (2) The equipped motor rotates at high speed, the air flow noise is large, and the noise of the compressor itself is also large, which affects the environment; (3) It is necessary to configure a separate oil separator, oil cooler and other complex oil system components, the unit is bulky, inconvenient to use and maintain.
Post time: May-05-2023
