【Mechanical Equipment Technology Edition】Daily Question 201802010: Revisiting High Scores from Festive Periods – Screw Compressors Series (1)

A screw compressor consists of a pair of parallel, intermeshing male and female screws, and it is the most widely used type of rotary compressor. There are single-screw and twin-screw types, and when people refer to screw compressors, they usually mean twin-screw compressors. Screw compressors can be either dry-type or wet-type. The dry-type variant does not involve the injection of any liquid into the working chamber, so the compressed gas remains unpolluted. In the wet-type variant, lubricating oil or other liquids are injected into the working chamber to cool the compressed gas, improve sealing, and lubricate the male and female rotors as well as the bearings, thereby enabling self-driven operation. High-precision filters are then used to remove oil or other liquid impurities from the compressed air, resulting in compressed gas of higher quality. Dry types are generally used in applications where extremely high standards are required for gas quality and the volume of gas handled is not large. Dry screw compressors have a complex structure, are difficult to maintain, generate high noise levels, and are expensive. Wet types are widely used; they have a simple structure, are easy to maintain, and are stable and reliable, making them common in aerodynamic engineering.

Within the compressor casing, a pair of helical rotors that mesh with each other are arranged parallel to one another. A rotor with protruding teeth outside the pitch circle is usually referred to as a male rotor or male screw. A rotor with concave teeth inside the pitch circle is called a female rotor or a recessed rotor. Generally, the male rotor is connected to the prime mover, and it is the male rotor that drives the female rotor to rotate. The last pair of bearings on the rotor provides axial positioning and bears the axial forces in the compressor. The cylindrical roller bearings at both ends of the rotor enable radial positioning of the rotor and bear the radial forces in the compressor. Holes of certain shapes and sizes are provided at both ends of the compressor casing. One is for inhaling air, called the intake port ； The other is for exhaust and intake, called the exhaust port.

1. A screw compressor consists of a pair of parallel, intermeshing male and female screws, and it is the most widely used type of rotary compressor. There are single-screw and twin-screw types; the screw compressors referred to in general terms are twin-screw compressors. Screw compressors can be either dry-type or wet-type. The dry-type variant does not involve the injection of any liquid into the working chamber, so the compressed gas remains uncontaminated. In the wet-type variant, lubricating oil or other liquids are injected into the working chamber to cool the compressed gas, improve sealing, and lubricate the male and female rotors as well as the bearings, thereby enabling self-propulsion. High-precision filters are then used to remove oil or other liquid impurities from the compressed air, resulting in compressed gas of higher quality. Dry types are generally used in applications where extremely high standards are required for gas quality and the volume of gas needed is not large. Dry screw compressors have a complex structure, are difficult to maintain, generate high noise levels, and are expensive ； Wet applications are the most widely used; they have a simple structure, are easy to maintain, and are stable and reliable, making them commonly used in aerodynamic engineering. /2. Introduction to the twin-screw main unit: During operation, the elemental volume between the teeth (i.e., the working volume formed by each pair of teeth) gradually increases as the rotor rotates, and it becomes connected to the air inlet located at the lower left side of the machine. Gas enters this elemental volume through the inlet, thus initiating the air intake process ； Once the rotor rotates to a certain angle, the volume of the space between the teeth exceeds that at the air inlet opening, causing a separation from the air inlet opening and thus ending the air intake process ； Once the rotor reaches a certain angle, the elemental volume between the two adjacent teeth begins to decrease simultaneously, as the protruding teeth of the male screw penetrate into the recessed teeth of the female screw, thereby enabling the compression of the gas. Until the moment when a pair of elementary volumes become connected to the exhaust orifice ； Once the elementary volumes are connected to the exhaust ports, the exhaust process begins, and this process continues until the two teeth are fully engaged, that is, when the two elementary volumes become zero due to the complete engagement of the two rotors. 3. The main components of a screw-type compressor are the rotor, casing, bearings, shaft seals, balance pistons, and energy regulation devices, etc

Inside the compressor housing, a pair of intermeshing spiral rotors are arranged parallel to each other; the rotor with protruding teeth on its pitch circle (as seen in a cross-section) is usually referred to as the male rotor or male screw； A rotor with concave teeth inside the pitch circle (as seen in a cross-section) is called a female rotor or female screw. Generally, the male rotor serves as the driving rotor, and it is the male rotor that causes the female rotor to rotate. The ball bearings on the rotor enable axial positioning of the rotor and withstand the axial forces in the compressor. The tapered roller thrust bearings at both ends of the rotor enable radial positioning of the rotor, and they bear the radial and axial forces in the compressor. Holes of certain shapes and sizes are provided at both ends of the compressor unit; one of them, used for drawing in air, is called the suction port ； The other one for exhaust and intake is called an exhaust port.

The screw compressor referred to in general terms is actually a twin-screw compressor, whose basic structure is shown in the attached diagram. Inside the compressor housing, a pair of intermeshing spiral rotors are arranged parallel to each other; the rotor with protruding teeth on its pitch circle (as seen in a cross-section) is usually referred to as the male rotor or male screw ； A rotor with concave teeth inside the pitch circle (as seen in a cross-section) is called a female rotor or female screw. Generally, the male rotor serves as the driving rotor, and it is the male rotor that causes the female rotor to rotate. The ball bearings on the rotor enable axial positioning of the rotor and withstand the axial forces in the compressor. The tapered roller thrust bearings at both ends of the rotor enable radial positioning of the rotor, and they bear the radial and axial forces in the compressor. Holes of certain shapes and sizes are provided at both ends of the compressor unit; one of them, used for drawing in air, is called the suction port ； The other one for exhaust and intake is called an exhaust port.

A oil-injected screw air compressor unit consists mainly of two parts: the main unit and the auxiliary units. The main unit includes the screw air compressor itself and the main motor, while the auxiliary units comprise the air intake and exhaust systems, the oil injection and oil-gas separation systems, the cooling system, the control system, and the electrical system.

A rotor with protruding teeth (as viewed in cross-section) is called a male rotor or male screw； A rotor with concave teeth inside the pitch circle (as seen in a cross-section) is called a female rotor or female screw. Generally, the male rotor serves as the driving rotor, and it is the male rotor that causes the female rotor to rotate. The ball bearings on the rotor enable axial positioning of the rotor and withstand the axial forces in the compressor. The tapered roller thrust bearings at both ends of the rotor enable radial positioning of the rotor, and they bear the radial and axial forces in the compressor. Holes of certain shapes and sizes are provided at both ends of the compressor unit; one of them, used for drawing in air, is called the suction port ； The other one for exhaust and intake is called an exhaust port.

Inside the compressor housing, a pair of intermeshing spiral rotors are arranged parallel to each other; the rotor with protruding teeth on its pitch circle (as seen in a cross-section) is usually referred to as the male rotor or male screw； A rotor with concave teeth inside the pitch circle (as seen in a cross-section) is called a female rotor or female screw. Generally, the male rotor serves as the driving rotor, and it is the male rotor that causes the female rotor to rotate. The bearings on the rotor enable axial positioning of the rotor and withstand the axial forces in the compressor. The tapered roller thrust bearings at both ends of the rotor enable radial positioning of the rotor, and they bear the radial and axial forces in the compressor. Holes of certain shapes and sizes are provided at both ends of the compressor unit; one of them, used for drawing in air, is called the suction port ； The other one for exhaust and intake is called an exhaust port.

A screw compressor consists of a pair of parallel, intermeshing male and female screws； A rotor with protruding teeth outside the pitch circle is usually referred to as a male rotor or male screw. A rotor with concave teeth inside the pitch circle is called a female rotor or a recessed rotor. Generally, the male rotor is connected to the prime mover, and it is the male rotor that drives the female rotor to rotate. The last pair of bearings on the rotor provides axial positioning and bears the axial forces in the compressor. The cylindrical roller bearings at both ends of the rotor enable radial positioning of the rotor and bear the radial forces in the compressor. Holes of certain shapes and sizes are provided at both ends of the compressor casing. One is for inhaling air, called the intake port ； The other is for exhaust and intake, called the exhaust port.