The difference between oil screw compressor and oil-free screw compressor

The difference between oil-free screw compressor and oil screw compressor

1. Definition and distinction:

The rotors of the oil-free screw compressor are not directly in contact, there is a certain gap between them. The gear drives the Yin rotor to rotate, and the synchronous gear ensures the rotor gap while transmitting the power. The so-called "oil-free" means that the gas does not contact with the oil completely during the compression process, but the compressor bearings, synchronous gears and other parts still need to be lubricated with lubricating oil, but between these lubrication parts and the compression chamber, using an effective shaft seal isolation

In the oil injection screw compressor, a large amount of lubricating oil is injected into the compressed gas medium for lubrication, sealing, cooling, and noise reduction. Oil injection screw compressor is not equipped with synchronous gear, and the outer rotor directly drives the inner rotor to rotate. In addition to reducing the exhaust temperature, the lubricating oil also provides lubrication for bearings, mechanical seals, sliding valves and other friction pairs.

2. Structural differentiation:

A) There is a gap between the rotor of the oil-free screw compressor, no contact between the rotor, with a synchronous gear structure. The rotor relies on the synchronous gear to transmit torque and positioning. The oil injection screw presses the machine without synchronous gear structure, and the Yin and Yang rotor is directly engaged.

B) The oil-free screw compressor has a shaft seal structure on the male and female rotor at the inlet and exhaust end to isolate the medium gas from the bearing lubricating oil. The oil injection screw compressor has a shaft seal structure only at the shaft extension end connected to the driver to prevent the lubricating oil leakage and the medium gas from making contact with the lubricating oil.

3. Differentiation of application scope

Because the rotor of the oil-free screw compressor does not contact with each other, the medium gas and the lubricating oil are separated by the shaft, will not directly contact, so the oil-free screw compressor is widely used in the exhaust gas recovery, coke oven gas recovery, CBM pressurization, pressure change adsorption and other medium gas contains dust and liquid, the gas composition changes greatly. Oil-free screw compressor can meet the requirements of medium and long-term continuous operation of industrial production, and generally the continuous and uninterrupted operation time reaches one hour. However, the volume efficiency of the oil-free screw compressor is lower than that of the oil-injection screw compressor, and the single-stage pressure ratio generally does not exceed 10

The rotor of the oil injection screw compressor is directly engaged for transmission, with high volume efficiency, and a single-stage pressure ratio of more than 10. However, due to the direct contact between the lubricating oil and the process medium, the medium gas is required to be relatively clean, and a large number of impurities and moisture cannot be mixed, otherwise the lubrication and lubricating effect of the lubricating oil will be affected. Moreover, when selecting the lubricating oil, it is required to select a special synthetic oil that does not react with the medium gas. Therefore, the oil injection screw is generally used in a single medium gas condition, such as air compressor, refrigeration compressor, etc.