Screw air compressors and piston air compressors can be said to be the two models with high market share in the current air compressor market. Piston air compressors were mostly used before. In recent years, with the characteristics of screw air compressors, they have gradually replaced piston air compressors and become the mainstream of the air compressor market. So, what is the difference between piston air compressors and screw air compressors?
Structure and working principle
1. Piston type oil-free air compressor.
The piston type oil-free air compressor consists of a compressor host, cooling system, regulating system, lubrication system, safety valve, motor, and control equipment. The compressor and motor are fastened to the base with bolts, and the base is fixed with anchor bolts. During operation, the motor directly drives the crankshaft through the coupling, driving the connecting rod, crosshead, and piston rod, causing the piston to reciprocate within the compressor cylinder, completing processes such as suction, compression, and discharge. This machine is a double acting compressor, where the piston moves up and down with air intake, compression, and discharge.
2. Screw air compressor.
The screw air compressor consists of a screw head, a motor, an oil and gas separation tank, a cooling system, an air conditioning system, a lubrication system, a safety valve, and a control system. The whole machine is installed in a box, self-contained, and placed directly on a flat cement floor without the need for anchor bolts. The screw head is a dual axis volumetric rotary compression head. During operation, the motor directly carries the main rotor through a coupling (or belt). Due to the mutual meshing of the rotors, the main rotor directly drives the auxiliary rotor to rotate together. The coolant is directly sprayed into the rotor engagement part through the nozzle at the lower part of the compressor housing, mixed with air, and carries away the heat generated by compression, achieving the cooling effect. Simultaneously forming a liquid film to prevent direct metal to metal contact between the rotors and the gap between the enclosed rotor and housing. The sprayed coolant can also reduce the noise generated by high-speed compression.
The main components of a screw air compressor are the screw head and the oil and gas separation tank. The screw head sucks in air through a suction filter and an intake control valve, while injecting oil into the air compression chamber to cool and seal the head, lubricate the screw and bearings, and generate compressed air in the compression chamber. The compressed oil and gas mixture is discharged into the oil and gas separation tank. Due to the effects of mechanical centrifugal force and gravity, the vast majority of oil is separated from the mixture of oil and gas. The air passes through the oil and gas separator core made of borosilicate glass fiber, and almost all the oil mist is separated. The oil separated from the oil and gas separator core returns to the screw head through the return pipe. There is an oil filter installed on the return pipe. After being filtered by the oil filter, the clean oil flows back to the screw head. After oil separation, compressed air leaves the oil cylinder through the minimum pressure control valve and enters the aftercooler. The aftercooler cools the compressed air and discharges it into the air storage tank for use by various gas consuming units. The condensed water is concentrated in the gas storage tank and drained through an automatic drain or manual drain. When oil is separated, compressed air exits the oil cylinder through the minimum pressure control valve and enters the aftercooler. The aftercooler cools the compressed air cooler into the air storage tank.
characteristic
1. Piston type oil-free air compressor.
The piston rings in the oil-free air compressor cylinder and the packing in the packing device both use polytetrafluoroethylene with self-lubricating properties as the sealing element. Therefore, the cylinder and packing device do not require the injection of lubricating oil for lubrication. Under normal circumstances, the compressed gas is basically pure and free of oil stains, and there is no need to add an oil removal device. The disadvantages of this machine are high motor power, unstable exhaust pressure, high exhaust temperature, loud noise, heavy maintenance workload, and high maintenance costs.
2. Screw air compressor.
The precise coordination between the anode and cathode rotors of the screw air compressor reduces gas reflux leakage and improves efficiency; Only the rotors mesh with each other, without the reciprocating motion of the cylinder, reducing vibration and noise sources. The unique lubrication method has the following advantages: continuously injecting coolant into the compression chamber and bearings simplifies the complex mechanical structure; Injecting coolant can form a liquid film between the rotors, and the secondary rotor can be directly driven by the main rotor without the need for high-precision synchronous gears; Injecting coolant can increase air tightness, reduce the noise generated by high-frequency compression, and absorb a large amount of compression heat. Therefore, screw air compressors have the advantages of low vibration, no anchor bolt fixation, low motor power, low noise, high efficiency, stable exhaust pressure, and no vulnerable parts.
Main faults
1. Piston type oil-free air compressor.
The piston ring and packing device do not require oil lubrication. Under normal circumstances, compressed gas is essentially pure and free of oil. However, due to the frequent incomplete oil scraping and poor sealing of the oil scraper ring, the oil often runs to the packing device and even the piston ring, causing the compressed gas to contain oil. In addition, the exhaust temperature is high, sometimes up to 200 ℃; The cooler is blocked and the cooling effect is poor; The piston ring is prone to wear due to oil contamination; Valve leakage; Wear of cylinder liner, etc.
2. Screw air compressor.
Screw air compressors have few malfunctions, and as long as the oil and gas separator, air and oil filters are regularly maintained, their normal operation can be ensured. The maintenance of two 10m3 screw machines is due to sewage pipeline blockage and control panel malfunction. In the past two years, the host system has been running normally.
