2024-10-30 13:55:44

Detailed explanation of the difference between scroll and screw air compressors

Scroll air compressors and screw air compressors are both positive displacement rotary compressors. Scroll air compressors use the meshing of rotors and stators to form multiple compression chambers. As the rotors translate and rotate, the volume of each compression chamber changes continuously, achieving the suction and compression of gas; while screw air compressors compress air by relying on the volume change of the tooth grooves of the yin and yang rotors that mesh parallel to each other in the casing.


Working principle of scroll air compressor


The main components of the scroll compressor are two involute scroll scrolls of the same shape but with an angular phase position of 180° relative to each other. One is a fixed scroll, and the other is driven by an eccentric shaft, and its axis revolves around the axis of the fixed scroll. During work, the two scrolls form sealing lines at multiple locations, and with appropriate sealing at the end faces of the two scrolls, several crescent-shaped air cavities are formed. The sealing line at the common tangent point between the two scrolls is constantly shifted along the vortex curve as the scroll revolves around the revolution, so that the shape and size of these crescent-shaped air cavities are constantly changing. The suction port of the compressor is opened on the upper part of the fixed scroll shell. When the eccentric shaft rotates clockwise, the gas enters the suction cavity from the suction port and is successively ingested into the outer crescent-shaped air cavities that are connected to the suction cavity. As these outer crescent-shaped air cavities are closed and no longer connected to the suction cavity, their closed volumes are gradually transferred to the center of the fixed scroll and continue to shrink. The gas is continuously compressed and the pressure increases.


Working principle of screw air compressor


The screw air compressor cylinder is equipped with a pair of intermeshing spiral male and female rotors, which rotate in opposite directions. The gap between the rotors and between the casing and the rotor is only 5 to 10 wires. The main rotor is driven by an engine or an electric motor, and the female rotor is driven by the oil film formed by the main rotor through oil injection, or by the synchronous gears at the main rotor end and the concave rotor end. The spiral rotor groove is filled with gas when passing through the suction port. When the rotor rotates, the rotor groove is closed by the casing wall to form a compression chamber. When the rotor groove is closed, lubricating oil is sprayed into the compression chamber to seal, cool and lubricate. When the rotor rotates to compress the lubricant + oil-gas mixture, the volume of the compression chamber decreases, and the oil-gas mixture is compressed to the exhaust port; when the compression chamber passes through the exhaust port, the oil-gas mixture is discharged from the compressor, completing a suction-compression-exhaust process. Each rotor of the screw machine is supported by a friction-reducing bearing, and the bearing is fixed by the end cover near the end of the shaft. The intake end is supported by a roller bearing, and the exhaust end is supported by a pair of conical rollers. The bearing at the exhaust end usually positions the rotor, that is, the thrust bearing, resists axial thrust, bears radial loads, and provides the necessary minimum axial running clearance. The working cycle can be divided into three processes: suction, compression and exhaust. As the rotor rotates, each pair of meshing teeth completes the same working cycle one after another.


Advantages of vortex air compressor


1. There is no reciprocating mechanism, so the structure is simple, the volume is small, the weight is light, the parts are few (especially the wearing parts are few), and the reliability is high;


2. The torque change is small, the balance is high, the vibration is small, the operation is stable, so the operation is simple and easy to realize automation;


3. It has a high efficiency within the refrigeration capacity range it adapts to;


4. Low noise


Advantages of screw air compressor


1. Screw compressors are the same as piston compressors, both of which are positive displacement compressors. In terms of the use effect, screw air compressors have the following advantages.


2. High reliability. The screw compressor has few parts and no wearing parts, so it operates reliably, has a long life, and the overhaul interval can reach 40,000-80,000 hours.


3. Easy operation and maintenance. The screw compressor has a high degree of automation, and the operator does not need to undergo long-term professional training, and can achieve unattended operation.


4. Good power balance. Screw compressors have no unbalanced inertial force, the machine can work smoothly at high speed, and can achieve foundationless operation. It is particularly suitable for mobile compressors with small size, light weight, and small footprint.


5. Strong adaptability. Screw compressors have the characteristics of forced gas transmission, and the volume flow is almost unaffected by the exhaust pressure. They can maintain high efficiency in a wide range and are suitable for a variety of working conditions without any changes to the compressor structure.


Disadvantages of vortex air compressors


1. The surfaces of its moving parts are mostly curved, and the processing and inspection of these curved surfaces are relatively complicated. Some require special equipment, so the manufacturing cost is relatively high.


2. The moving parts or between the moving parts and the fixed parts often maintain a certain movement gap to achieve sealing. The gas passing through the gap is bound to cause leakage, which limits the rotary compressor from achieving a large compression ratio. Therefore, it is mostly used under air conditioning conditions.


Disadvantages of screw air compressors


1. The rotor tooth surface is a spatial curved surface, which needs to be processed on expensive equipment using special tools. The machining accuracy of the body parts is also required to be high, and high-precision equipment must be used:


2. Since the inter-tooth volume is periodically connected to the suction and exhaust ports, the compressor noise is relatively high;


3. Due to the limitations of rotor stiffness and bearing life, the compressor can only rely on gap sealing, so the screw compressor can only be used in medium and low pressure ranges, and cannot be used in high pressure occasions;


4. Due to the large amount of oil injection and the complex oil treatment system, there are many auxiliary equipment for the unit;


5. The screw compressor relies on gap sealing and does not have superior performance in a small volume range.


Application of vortex air compressors


The vortex compressor is mainly used in offices, hospitals, laboratories and other places with high requirements for noise and vibration. It should be said that the vortex compressor is a type of air compressor with the lowest noise and vibration. There is no such thing as energy saving. If you want to use a vortex compressor, I recommend you to use a Hitachi brand machine. The product is not cheap, but the quality is really good.


Application of screw air compressors


Screw air compressors are widely used in many industrial fields such as machinery, metallurgy, electronic power, medicine, packaging, chemicals, food, mining, textiles, transportation, etc., becoming the mainstream product of compressed air compressors.