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Analysis of working principle of screw air compressor system

Time: 2020-12-21 10:03:27

Main engine/motor system:

The single screw air compressor is also called worm air compressor. The meshing pair of the single screw air compressor is composed of a 6-head screw and 2 11-tooth star wheels. The worm meshes with two star wheel at the same time even though the worm force is balanced, the displacement is doubled. We usually say screw compressor generally refers to double screw compressor.
Screw-type (i.e., twin-screw) compressors have a pair of rotors with spiral teeth meshing with opposite rotation. The rotor with convex tooth surface is called the positive rotor, and the rotor with concave tooth surface is called the negative rotor. With the rotation of the rotor in the body, the working volume due to tooth invasion or detach and constantly change, thus periodically changing the volume between each pair of rotor teeth, to achieve the purpose of suction, compression and exhaust.
The main machine is the core component of screw machine, any brand of screw machine its main machine structure and working mechanism are similar

A.Breathe in process

The rotor rotates, a toothed continuously from Yin Yang rotor rotor of a tooth, tooth between volume expanding gradually, and suction orifice connected, gas by suction orifice into volume between teeth, until the volume reaches the maximum value between teeth, and suction orifice disconnect, joint action by tooth and the shells closed volume between teeth, suction process is over. It is worth noting that the volume between the teeth of the Yang rotor and the Yin rotor is not connected with each other

B.The compression process

The rotor continues to rotate. Before the volume between the teeth of the Yin and Yang rotors is connected, the gas in the volume between the teeth of the Yang rotor is compressed first by the intrusion of the teeth of the Yin rotor. After a certain Angle, the volume between Yin and Yang rotor teeth is connected to form a v-shaped tooth volume pair (elementary volume). With the mutual extrusion of the two rotor teeth, the elementary volume is gradually pushed forward and the volume is gradually reduced to realize the compression process of gas. The compression process is completed until the element volume is connected with the exhaust orifice.

C.Exhaust process

As the rotor is rotating, the volume of the basic element shrinks, and the compressed gas is sent to the exhaust pipe, the process continues until the volume is the smallest.
With the continuous rotation of the rotor, the above suction, compression, exhaust process cycle, the volume of each element successively work, constitute the working cycle of screw refrigeration compressor.
From the analysis of the above process, it can be seen that the two rotors turn to the side catering to each other, that is, the side where the convex teeth and the concave teeth cater to each other, and the gas pressure shrinks and forms a higher pressure, which is called the high pressure area. On the contrary, the screw turned to the side opposite each other, that is, convex teeth and concave teeth each other off the side, the volume between the teeth in the expansion of the lower pressure, known as the low pressure area. The two areas are separated by the contact line of the housing and the rotor, and the axial plane of the two rotors can be roughly considered as the interface between the high and low pressure areas. In addition, the spiral channel formed by the meshing lines between the Yin and Yang rotors causes the gas in the volume of the base element to move spirally from the suction end to the exhaust end while being compressed.
Screw compressor as a rotary compressor, in the structure has the characteristics of centrifugal compressor, the working principle is also belongs to the category of positive displacement compressor.


·The machining precision of spiral rotor space surface is high
·The meshing line between the rotors cannot achieve good interstage sealing and is limited by the stiffness of the rotor. At present, the screw compressor cannot reach higher end pressure
·The medium periodically passes through the suction and exhaust orifice at high speed, through the leakage of cracks and other reasons, so that the compressor noise is large, it is necessary to take noise-cancelling measures to reduce noise

Because of the above characteristics, screw compressor is generally used in the following working conditions

·Traffic is not very high ·Need long period to run smoothly ·Low exhaust pressure

Because of the above characteristics, screw compressor is generally used in the following working conditions

·Traffic is not very high ·Need long period to run smoothly ·Low exhaust pressure


It is composed of air frame, suction end seat and exhaust end seat, which is the main component of compressor. The body is the central part connecting each part, it provides the correct assembly position for each part, guarantees the Yin and Yang rotor meshing in the cylinder, carries on the work reliably. The shape of the end face is ∞, which is suitable for the outer cylinder of the two meshing rotors, so that the rotor is accurately loaded into the body. The inner wall of the body is provided with a radial suction orifice that meets the requirements of rotor rotation Angle to ensure that the rotor can realize the suction process smoothly during rotation.
The suction and exhaust end seat is the sealing connector located at the front and rear ends of the engine body. It not only makes the end face seal of the engine body, but also provides the bearing assembly position of Yin and Yang rotor and supporting rotor.

The rotor

The main components of variable-volume compression are composed of Yin and Yang rotors. Rotor profile is machined with high precision special machine tools, special cutting tools, is one of the key parts of the compressor. The rotor profile is usually a unilateral asymmetrical cycloid -- an arc profile. Yin and Yang rotor in the structure of the following two ways.
The positive rotor is connected with the motor as the active rotor to transfer torque and drive the negative rotor (driven rotor) to rotate through the meshing relationship. The Yin and Yang rotors transmit the torque by engaging with the driving gear driven by the motor through their driven gears.


Bearing is to support the Yin and Yang rotor, and ensure the rotor high-speed rotation parts. The motor end generally adopts roller bearing for supporting. Secondly, when the rotor rotates and compresses the gas, axial thrust will be generated. In order to overcome this axial force, the other end of the rotor adopts oblique column bearing, which not only overcomes the axial force of the rotor rotation, but also bears radial force.  
Most screw compressors are lubricated by oil injection. Through the mixing of lubricating oil and cutting into the compressor, with the flow of the medium for lubrication and sealing the machine.
The advantages are as follows
·Lower the exhaust temperature.
·Reduce working medium leakage and improve sealing effect
·Enhance the lubrication of parts, improve the service life of parts
·It has absorption and damping effect on sound waves and can reduce noise
·Remove mechanical impurities and reduce wear and tear
However, due to the large amount of oil injection, it is necessary to add lubricating oil system and oil and gas separator at the compressor outlet, which will increase the volume and complexity of the unit. At the same time, this method cannot be used for non-polluting media. Therefore, there are also parts of the screw compressor machine is oil-free lubrication.
The use of oil-free compressor has higher requirements on the engagement clearance, the stiffness and mass of the rotor and the machining quality of the whole unit

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