Features of Screw Air Compressor Lubrication System

Screw-type air compressors have two design forms, single rotor and double rotor, as well as two structures that lubricating oil and compressed air contact and do not contact.

The twin-rotor screw air compressor has two structural forms. In the oil-containing overflow lubrication type, lubricating oil is injected into the cylinder to absorb the heat generated when air or gas is compressed, and the lubricating oil can also play a sealing role between the rotors. Because the cylinder is lubricated by the oil of the rotor, this machine does not have a synchronous gear. They need an external circulation system to control the oil temperature, and an oil removal system is needed to remove the oil mixed in the discharged compressed air or gas. In this type of air compressor, in addition to gears and bearings that require oil lubrication, the lubricating oil must also lubricate the contact surface of the rotor. When gas leakage must be minimized, lubrication seals are used.

In a dry screw air compressor, no oil is supplied to the air cavity, and the compressor oil does not contact the compressed air, only the bearings, synchronous gears and transmission mechanism are lubricated. Because the rotors are not lubricated, synchronous gears are needed to keep the rotors in contact with each other. These compressors are used to provide oil-free air and gas. However, because there is no oil-liquid seal between the rotors, in order to minimize the amount of gas leakage, the operating speed must be relatively high, usually water cooling of the cylinder and oil cooling of the rotor bearings are required. Since the parts that need to be lubricated for dry screw air compressors are mainly gears and bearings, the journal bearings can be ordinary radial sliding bearings or rolling bearings, while thrust bearings can be tilting pad bearings or angular contact rolling bearings, and gears are precision cut Straight or helical gears.

Single screw air compressor is a conical screw with teeth rotating between wheels. The gear teeth sweep through the threaded cavity of the screw, allowing the air to be compressed through the upwardly decreasing space. The toothed star wheel is mainly used to bear the stress acting on the wheel and to contact the side surface of the screw cavity. Lubricating oil is injected into the casing to play the role of lubrication, cooling and sealing, and its structure and function are basically the same as that of a twin-screw air compressor.

When selecting lubricating oil for oil-containing screw air compressors, the working conditions are relatively strict. Because the lubricating oil is repeatedly heated and cooled in the compressor cylinder at a high circulation speed, the contact area with oxidation is greatly increased. , The heating intensity is high, and it is constantly catalyzed by copper, iron and other metals in the cooler, and the oil is easy to be oxidized and deteriorated. The mixed condensate will emulsify the lubricating oil, and the absorbed particulate impurities, suspended dust and corrosive gases will accelerate the aging of the oil. Then, the good oxidation stability, proper viscosity, and anti-emulsification of the oil are to ensure effective cooling, sealing, corrosion protection and lubrication. At the same time, in order to make the compressor oil separate and recover well from the compressed air, it must Choose oils that are not volatile. In addition, when the lubricating oil enters the oil separator, the oil foam generated will cause the oil separation element to be soaked seriously, which will increase the resistance, cause the compressor internal overload, and increase the oil consumption. Therefore, the compressor oil should also have a good Resistance to foam.