[Mechanical Equipment Technology Edition] Daily Question 201803016: Screw Refrigeration Compressors—Overview (2)
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This post was last edited by YORK Industrial Refrigeration on 2018-3-19 at 09:40. This year’s 【Daily Question】is divided into three categories: screw refrigeration compressors, refrigeration systems, and oil circuit systems, aiming to provide a comprehensive understanding of refrigeration technology. (If you encounter something you don’t know or can’t answer, please actively look up information; as you do so, your skills will improve!) ) All participants in the comments on this post will receive 1-3 wealth points; those who give complete answers will get 10-15 points, with the validity period being two days. ============================== Overview of Screw Refrigeration Compressors (2): How do screw refrigeration compressors work? Answer: The machine body, the intake and exhaust end caps (excluding the intake and exhaust ports), and the cover form a sealed volume; its operation is achieved through the periodic changes in the volume of the inter-tooth spaces formed by the rotor tooth surfaces and the inner wall of the cylinder. ============================== High-quality promotions: Mechanical equipment——Videos on the repair and calibration of York compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1806833 Mechanical equipment——Maintenance procedures for York screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1806833 Mechanical equipment——Upgrading of York Quinton control centers https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment——Major repairs of GEA Grasox screw compressors https://bbs.hcbbs.com/thread-1800467-1-1.html Mechanical equipment——Disassembly and maintenance of British HOWDEN screw compressors https://bbs.hcbbs.com/thread-1832529-1-1.html Mechanical equipment——Disassembly and maintenance of Japanese Maekawa MYCOM screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=
It belongs to the volume-type compressors, that is, it compresses gas by means of changes in volume. Screw refrigeration compressors are further divided into single-screw compressors and twin-screw compressors. Among them, a twin-screw compressor operates by the intermeshing and rotation of two screws with spiral flutes located within the compressor housing; together with the interaction between these screws and the inner walls of the housing as well as the inner walls of the suction and discharge ends, this mechanism causes changes in the volume between the screw teeth, thereby enabling the intake, compression, and discharge of gas.
Inhalation process: As the rotor rotates, the volume of the toothed groove gradually increases as it rotates, and it becomes connected to the intake port. Gas coming from the evaporation system enters the toothed groove through this opening, thereby enabling the inhalation of gas. After the rotor rotates to a certain angle, the volume between the teeth passes beyond the suction port position and becomes disconnected from it, thus ending the suction process. Compression process: As the rotor continues to rotate, the gas contained within the toothed grooves enclosed by the housing, the intake end cover, and the exhaust end cover is pushed toward the exhaust end due to the intermeshing of the male and female rotors and the fitting together of their teeth. Meanwhile, the pressure gradually increases, thereby enabling the compression process. Exhaust process: When the rotor rotates to such a position that the toothed groove space is in communication with the exhaust ports on the exhaust end cover, the gas is forced out and exits through these exhaust flanges, thus completing the exhaust process. Since these three processes occur in each tooth groove during the working cycle, when the compressor is running at high speed, the working volumes of several pairs of tooth grooves repeatedly go through suction, compression, and exhaust cycles, thereby ensuring a continuous and steady gas delivery from the compressor.
It consists of a pair of intermeshing male and female rotors with opposite rotation directions; the female rotor is concave while the male rotor is convex. As the rotor rotates at a certain transmission ratio, the volume of the rotor element changes due to the successive penetration of the male and female rotors. The inlet section (meshing line) moves toward the exhaust side, causing the volume of gas trapped in the groove to gradually decrease and the pressure to rise. When the pressure reaches a certain level (or when the rotor rotates to a certain position), the tooth groove (the sealed volume) becomes connected to the exhaust port, and the high-pressure gas is discharged from the compressor and enters the oil separator
Bearings and seals: The male and female screws of a screw-type refrigeration compressor are supported by sliding bearings (main bearings) and radial thrust ball bearings. The main bearings are properly installed and fixed in the suction and exhaust end caps using dowel pins, while two thrust bearings are mounted on each of the male and female screws on the exhaust side to withstand certain axial forces. The shaft seals of screw refrigeration compressors also commonly use friction ring mechanical seals, which are installed on the shaft at the end of the driving rotor adjacent to the coupling; their structure and principle are the same as those of the shaft seals in piston refrigeration compressors. Balancing piston: Due to structural differences, the axial force acting on the male screw, resulting from the pressure difference between the suction and discharge sides, is much greater than the axial force acting on the female screw. Therefore, in addition to a thrust bearing, an hydraulic balance piston is also installed on the male screw to reduce the load exerted by the male screw on the end face of the sliding bearing, thereby lowering the axial force on the thrust bearing. Energy regulation device: It consists of a slide valve, an oil cylinder, an oil piston, a four-way solenoid directional control valve, and oil pipelines. The piston is mounted at the intersection of the two circles at the lower part of the cylinder wall; by changing the position of the slide valve, it is possible to adjust the cooling capacity. When a screw-type refrigeration compressor is in operation, the fundamental volume between the teeth changes periodically, which enables the gas to undergo processes of vapor absorption, compression, and exhaust as it moves along the axis of the rotor.
It belongs to the volume-type compressors, which compress gas by changing its volume. Screw refrigeration compressors are further divided into single-screw compressors and twin-screw compressors. Among them, a twin-screw compressor operates by the intermeshing and rotation of two screws with spiral flutes located within the compressor housing; together with the interaction between these screws and the inner walls of the housing as well as the inner walls of the suction and discharge ends, this mechanism causes changes in the volume between the screw teeth, thereby enabling the intake, compression, and discharge of gas.
Working principle of screw refrigeration compressors: Bearings and seal rings: The male and female screws of a screw refrigeration compressor are supported by sliding bearings (main bearings) and radial thrust ball bearings. The main bearings are properly installed and fixed in the suction and exhaust end caps using dowel pins, while two thrust bearings are mounted on each of the male and female screws on the exhaust side to withstand certain axial forces. The shaft seals of screw refrigeration compressors also commonly use friction ring mechanical seals, which are installed on the shaft at the end of the driving rotor adjacent to the coupling; their structure and principle are the same as those of the shaft seals in piston refrigeration compressors. Balancing piston: Due to structural differences, the axial force acting on the male screw, resulting from the pressure difference between the suction and discharge sides, is much greater than the axial force acting on the female screw. Therefore, in addition to a thrust bearing, an hydraulic balance piston is also installed on the male screw to reduce the load exerted by the male screw on the end face of the sliding bearing, thereby lowering the axial force on the thrust bearing. Energy regulation device: It consists of a slide valve, an oil cylinder, an oil piston, a four-way solenoid directional control valve, and oil pipelines. The piston is mounted at the intersection of the two circles at the lower part of the cylinder wall; by changing the position of the slide valve, it is possible to adjust the cooling capacity. When a screw-type refrigeration compressor is in operation, the fundamental volume between the teeth changes periodically, which enables the gas to undergo processes of vapor absorption, compression, and exhaust as it moves along the axis of the rotor.
The cylinder contains a pair of intermeshing spiral male and female rotors, both of which have several concave teeth, and they rotate in opposite directions to each other. The gap between the rotors and between the casing and the rotors is only 5–10 microns. The main rotor (also known as the male rotor or convex rotor) is driven by an engine or electric motor (with electric motors being the most common). The other rotor (also known as the female rotor or concave rotor) is driven either by an oil film created by oil injection from the main rotor, or by synchronous gears at the ends of the main rotor and the female rotor. So there is no metal contact in the drive (theoretically). The spiral rotor groove becomes filled with gas as it passes through the air intake. As the rotor rotates, its grooves are enclosed by the casing walls, forming compression chambers. Once these grooves are sealed, lubricating oil is injected into the compression chambers to provide sealing. Cooling and lubrication functions. As the rotor rotates to compress the lubricant + gas (referred to as the oil-gas mixture), the volume of the compression chamber decreases, compressing the oil-gas mixture toward the exhaust port. As the compression chamber passes through the exhaust port, the oil-gas mixture is discharged from the compressor, completing one cycle of suction – compression – exhaust.
Working principle of screw refrigeration compressors: The compressor consists of a pair of intermeshing rotors, one female and one male, with opposite rotation directions; the female rotor is concave while the male rotor is convex. As the rotor rotates at a certain speed ratio, the volume of the rotor’s elemental chamber changes due to the successive penetration of the male and female rotors; the area where they intersect moves toward the exhaust end. As a result, the volume of gas trapped within the grooves gradually decreases, and the pressure rises. When the pressure reaches a certain value (or when the rotor rotates to a specific position), the grooves (which represent the enclosed volumes) become connected to the exhaust port, allowing the high-pressure gas to be discharged from the compressor and enter the oil separator.
The refrigerant at low temperature and pressure is drawn in through the compressor inlet, along with refrigeration oil. As the pair of synchronous screws mesh, they compress the gaseous refrigerant; the resulting high-temperature, high-pressure refrigerant containing oil is then discharged. In the oil separator, the refrigeration oil and the refrigerant are separated from each other. The high-temperature, high-pressure refrigerant goes on to a subsequent condensation unit where it is cooled down, while the refrigeration oil passes through two stages of filters before being injected back into the screw compressor. Process load regulation is achieved using a slide valve.
A twin-screw (compressor) consists of a pair of intermeshing male and female rotors with opposite rotation directions; the female rotor is concave while the male rotor is convex. As the rotor rotates at a certain transmission ratio, the volume of the rotor element changes due to the successive penetration of the male and female rotors. The inlet section (meshing line) moves toward the exhaust side, causing the volume of gas trapped in the groove to gradually decrease and the pressure to rise. When the pressure reaches a certain level (or when the rotor rotates to a certain position), the tooth groove (the enclosed volume) becomes connected to the exhaust port, and the high-pressure gas is discharged from the compressor and enters the oil separator.