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The \"oil-free\" nature of air compressors means that the gas does not come into contact with oil during compression. However, components such as the bearings and synchronous gears of the compressor still require lubrication; effective shaft seals are used to isolate these lubricated components from the compression chamber. Ensure that lubricant does not enter the compression chamber. Oil-free air compressors are classified based on whether the compressed air contains oil; corresponding to them are oil-based air compressors or micro-oil air compressors. Oil-free air compressors are classified based on different compression methods or the structure of the main unit. Some of the common types of oil-free air compressors include: 1. Dry oil-free screw air compressors; 2. Water-lubricated oil-free screw air compressors; 3. Oil-free piston air compressors; 4. Oil-free scroll air compressors; 5. Oil-free rotary vane air compressors; 6. Centrifugal air compressors. Below, we will focus on the most popular types currently available, namely dry oil-free screw air compressors and water-lubricated oil-free air compressors. Introduction to dry oil-free screw air compressors: These are essentially twin-screw compressors in which there is no lubrication within the compression chamber; lubricant is only present in the gearbox, making them essentially dry in nature. There is a gap between the rotors, which do not touch each other; they have a synchronous gear structure, and torque as well as positioning are transmitted between the rotors via synchronous gears. Both the male and female rotors at the intake and exhaust ends are equipped with shaft seal structures to separate the process gas from the lubricating oil. The surface of the rotor has a special coating; due to the lack of contact, the compression pressure is not very high at first. To increase the pressure, two-stage compression is used. The best compression effect is achieved through isothermal compression; however, this is not feasible in practice. Therefore, after the first stage of compression, there is an intercooler and a water trap (to reduce temperature and remove water), and there is also a rear cooler after the second stage of compression. The pressure after the first stage of compression is approximately square root of 2; this pressure then enters the second stage of compression. The pressure produced by the second stage meets the system’s requirements, so its compression ratio is higher, the operating conditions are more severe, and its lifespan is shorter compared to that of the first stage. Due to the high rotation speed and the high temperature inside the head, the head housing is made using the one-time lost foam technique to help reduce the temperature. The head housing and the rotor are completely separate. The housing is generally cooled by oil. Introduction to water-lubricated oil-free systems: Water-lubricated oil-free air compressors are typically single-screw air compressors. Their characteristic is that water is used as the lubricant medium, and a water-based substance is employed for sealing; thus, there is no oil at all, and compressed air that is pure and oil-free is produced. Since water is sprayed into the compression chamber, the temperature remains around 40-50 degrees, enabling constant-temperature compression and thus a higher volumetric efficiency; this results in a 15% improvement in efficiency compared to dry, oil-free screw air compressors. It’s cheap. Its disadvantage is a high failure rate (such as wear-prone components of the star wheel body). Why are water-lubricated oil-free machines generally single-screw rather than twin-screw? The reason is that when the single-screw pump is in operation, there is a speed difference between the screw and the star-shaped vanes, resulting in one-way compression; air can be compressed easily, and thus the rotational speed is low. Double-screw compressors achieve compression in the same direction; they require high rotational speeds. Moreover, the lubricating effect of water is not as good as that of oil, and compressed air tends to flow back. In oil-free piston air compressors, the motor drives the crankshaft via a belt, which in turn causes the connecting rods and pistons to move back and forth, thereby enabling the processes of intake, compression, exhaust, and expansion. Oil-free scroll air compressors work by having the moving scroll rotate around the center of the fixed scroll’s base circle; the two scrolls mesh with each other to enable the processes of suction, compression, and exhaust. Oil-free air compressors are widely used in various fields that require high-quality air, such as the pharmaceutical, food, and precision electronics industries. However, oil-free compressed air can be obtained not only through oil-free machines but also via appropriate, stable oil removal equipment.