Principle and advantages of screw compressors

Thread Content

Principle and Advantages of Screw Compressors I. Introduction to the Principle of Screw Compressors A screw compressor features a pair of intermeshing spiral male and female rotors inside its cylinder; both rotors have several recessed 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 length and diameter of the rotor determine the compressor’s exhaust volume (flow rate) and exhaust pressure; the longer the rotor, the higher the pressure ； The larger the rotor diameter, the greater the flow rate. The spiral rotor groove is 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. Each rotor of the screw machine is supported by anti-friction bearings, which are fixed by end caps located near the end of the shaft. The intake side is supported by roller bearings, while the exhaust side is supported by opposing tapered roller bearings. Usually, it is the bearings on the exhaust side that position the rotor; these are thrust bearings that resist axial forces, bear radial loads, and provide the necessary minimum clearance for axial movement. The working cycle can be divided into three processes: intake, compression, and exhaust. As the rotor rotates, each pair of intermeshing teeth sequentially completes the same working cycle. II. Advantages of screw compressors: 1) Screw compressors, like piston compressors, both belong to the category of positive-displacement compressors. In terms of performance, screw air compressors have the following advantages. 2) High reliability. Screw compressors have few components and no vulnerable parts, which ensures reliable operation and a long service life; the interval between major overhauls can reach 40,000 to 80,000 hours. 3) Easy to operate and maintain. Screw compressors have a high degree of automation; operators do not require extensive professional training, and they can operate unattended. 4) Good dynamic balance. Screw compressors have no unbalanced inertial forces, allowing them to operate at high speeds smoothly and even without a foundation. They are particularly suitable as mobile compressors, offering small size, light weight, and low space requirements. 5) Strong adaptability. Screw compressors feature forced gas delivery; their volumetric flow rate is hardly affected by the discharge pressure, allowing them to maintain high efficiency over a wide range of conditions. Without any changes to the compressor’s structure, they can be used in various operating scenarios. Knowledge link: Excerpt from \"Screw Compressors\" by Xing Ziwen. In the 1930s, Swedish engineer Alf Lysholm, while researching gas turbines, sought a type of compressor that could perform rotational motion, with a speed much higher than that of piston compressors, so that it could be driven directly by the gas turbine without experiencing surge. To achieve the above goals, he invented the screw compressor. 　　Theoretically, screw compressors possess the desired characteristics, but since they require a very large volume of exhaust gas to meet the requirements of gas turbine operation, they have not been used in this field. Nevertheless, Alf Lysholm and his company SRM in Sweden continued to conduct in-depth research on the application of screw compressors in other fields. 　　In 1937, Alf Lysholm developed two types of experimental screw compressor prototypes at SRM Company, achieving satisfactory test results. 　　In 1946, the British company James Howden, based in Scotland, was the first to obtain a license from the Swedish company SRM to manufacture screw compressors. 　　Subsequently, various companies in Europe, the United States, and Japan also obtained such licenses from the Swedish company SRM to engage in the production and sales of screw compressors. The first type of screw compressor to be developed was the oil-free screw compressor. 　　In 1957, oil-injected screw air compressors were introduced to the market. 　　In 1961, the oil-injected screw refrigeration compressor and the screw process compressor were also developed successfully. 　　Through subsequent ongoing fundamental research and product development tests, and by continuously improving the rotor design as well as developing specialized equipment for rotor manufacturing, the superior performance of screw compressors has been continually enhanced.