Principle of screw compressors

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High-definition animation of the working principle of German GEA screw compressors – it’s amazing! Let’s start with a few animated videos to give you an idea: The history of screw compressors. In 1934, Lysholm, a professor at the Royal Institute of Technology in Sweden, invented the first twin-screw gas compressor. Since the 1960s, oil-injected twin-screw units have been used in refrigeration units. The Swedish company SRM (double-screw) was the first to invent the bilaterally asymmetric screw design, which **improved** the efficiency of screw compressors. In 1960, the Frenchman Zimmern invented a new design for single-screw pumps. The first prototype was developed in 1962. In the early 1970s, the Dutch company GRASSO developed the first single-screw refrigeration compressor. In 1972, Japan began producing single-screw air compressors. In 1982, the production of single-screw refrigeration compressors began. Introduction to the principle of screw compressors: A screw compressor’s cylinder contains a pair of intermeshing spiral male and female rotors, both of which have several recessed teeth; these two rotors rotate in opposite directions. 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 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 serve the purposes of sealing, cooling, and lubrication. 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. Advantages of screw compressors: 1. 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 40,000–80,000 hours. 2. Easy to operate and maintain. 3. Good power balance. It is particularly suitable as a mobile compressor, being small in size, light in weight, and requiring little space. 4. 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. Without any changes to the compressor’s structure, they can be used with various types of working fluids. 5. Multiphase mixed transportation. There is actually a gap between the rotor teeth of a screw compressor, which enables it to withstand liquid impacts and allow it to transport gases containing liquids, dust, or gases that are prone to polymerization. The main disadvantages of screw compressors: 1. High cost. Since the rotor tooth surfaces of screw compressors are spatial surfaces, they must be machined using special cutting tools on expensive dedicated equipment. Additionally, high requirements are also placed on the machining precision of the screw compressor cylinders. 2. It cannot be used in high-pressure environments. Due to limitations such as rotor stiffness and bearing life, screw compressors can only be used in the medium and low pressure ranges, with the discharge pressure generally not exceeding 3 MPa. 3. It cannot be used in miniature applications. Screw compressors rely on clearance sealing to contain gas, and they only exhibit superior performance when their volumetric flow rate is greater than 0.2 m3/min. Tip: Watch it freely over WIFI! http://pubimage.360doc.com/qq3.gif