What is a screw air compressor?
A screw compressor is a rotary displacement compressor, in which a pair of spiral rotors that mesh with each other are arranged in parallel within the compressor body. Rotors with convex teeth in the pitch circle are usually referred to as male rotors; A rotor with concave teeth within the pitch circle is called a female rotor. Generally, the male rotor is connected to the prime mover and drives the female rotor to rotate. The ball bearings of the rotor enable the rotor to achieve axial positioning and withstand the axial force of the compressor. Similarly, the cylindrical roller bearings at both ends of the rotor enable the rotor to achieve radial positioning and withstand the radial force of the compressor. At both ends of the compressor body, holes of certain shapes and sizes are respectively opened. One is for suction, called the suction port. The other is for exhaust, called the exhaust outlet.
Definition and classification of screw compressors
According to the operating mode: there are two types of oil free compressors and oil injection compressors;
2. According to the type and purpose of compressed gas: air compressors, refrigeration compressors, and process compressors
3. According to structural form: divided into mobile and fixed, open and closed, etc.
4. According to cooling methods: air cooling and water cooling
5. According to the starting method: reactance start, direct start, Y - △ start, soft start, variable frequency start
6. According to lubrication methods: micro oil compressor, water spray oil-free compressor, dry oil-free compressor.
Working principle of screw compressor
The intake port on the intake side of the screw compressor must be designed so that the compression chamber can fully absorb air. However, the screw compressor does not have intake and exhaust valve groups, and the intake is only regulated by the opening and closing of a regulating valve. When the rotor rotates, the tooth groove space of the main and auxiliary rotors is the largest when it turns to the inlet end wall opening. At this time, the tooth groove space of the rotor is connected to the free air at the intake port, because the air in the tooth groove is completely discharged during exhaust, When the exhaust is completed, the tooth groove is in a vacuum state. When it is turned to the air inlet, external air is sucked in and flows axially into the tooth groove of the main and auxiliary rotors. When the air fills the entire tooth groove, the end face of the intake side of the rotor rotates away from the air inlet of the casing, and the air between the tooth grooves is closed. The above is the intake process.
At the end of suction, the main and auxiliary rotor teeth are sealed with the casing, and the air is sealed in the teeth groove and no longer flows out, which is the sealing process. The two rotors continue to rotate, and their tooth peaks and grooves coincide at the suction end. The mating surface gradually moves towards the exhaust end, which is the conveying process.
During the transportation process, the meshing surface gradually moves towards the exhaust end, meaning that the gap between the meshing surface and the exhaust port gradually decreases, and the gas in the gap is gradually compressed, resulting in an increase in pressure. This is known as the compression process. At the same time of compression, lubricating oil is also sprayed into the compression chamber and mixed with air due to the pressure difference.
When the meshing end face of the rotor is turned to be connected to the exhaust of the casing, the compressed gas (with the highest compressed gas pressure at this time) begins to be discharged until the meshing surface of the tooth peak and tooth groove moves to the exhaust end face. At this time, the space between the meshing surfaces of the two rotors and the exhaust port of the casing is zero, which completes the exhaust process. At the same time, the length of the tooth groove between the meshing surface of the rotor and the exhaust port of the casing reaches the longest, and the suction process is also ongoing.