Oil-free screw compressor

Abstract

Provided is an oil-free screw compressor that minimizes the pressure loss at an annular space for connecting an open air hole and a communication hole and that prevents lubricating oil from flowing in during unloading operation. The oil-free screw compressor is provided with: a casing (12) that has a rotor chamber (150); a bearing (22) that supports the rotating shaft (21) of a screw rotor; a shaft sealing device (20) comprising an oil seal section (31) and an air seal section (60); an open air hole (24a) that is formed in the shaft sealing device; at least one communication hole (31a) that is formed in the rotating shaft; and an annular space (25) that connects the open air hole with at least one communication hole. The annular space is provided with an inner circumferential annular space (24g) that is formed on the inner circumferential side of the casing. The oil-free screw compressor is configured so that the expression shown is satisfied when the opening cross-sectional area of the inner circumferential annular space is denoted by S1, the total opening cross-sectional area of the communication holes is denoted by S2, the opening cross-sectional area of an i-th communication hole among the communication holes is denoted by S2i, and the number of communication holes is denoted by n (n is a natural number of 1 or more).

Description

technical field [0001] The invention relates to an oil-free screw compressor. Background technique [0002] In an oil-free screw compressor, air is compressed by a pair of male and female screw rotors that can rotate without oil supply and in a non-contact manner. In oil-free screw compressors, compressed air generated in the rotor chamber may leak while being transmitted along the rotating shaft, or lubricating oil supplied to gears driving the rotating shaft and bearings supporting the rotating shaft may flow into the rotor chamber. In order to prevent this, a shaft seal is provided between the rotor chamber and the bearing. The shaft seal device includes an air seal portion that seals compressed air from the rotor chamber, and an oil seal portion that seals lubricating oil from the bearing. [0003] During the unloading operation, when the rotor chamber has a negative pressure, lubricating oil supplied to the bearing and the like may pass through the oil seal and flow i...

AI Technical Summary

Problems solved by technology

Therefore, in Patent Document 2, a large pressure loss occurs not at the plurality of communicating holes but at the annular space.

[0010] In this way, in both Patent Document 1 and Patent Document 2, there is a possibility that a large pressure loss occurs at the annular space connecting the atmospheric opening hole and the communication hole, so that the prevention of lubricating oil from flowing into the air cannot be fully exerted during the unloading operation. Effect of rotor chamber inflow

However, neither Patent Document 1 nor Patent Document 2 takes this point into special consideration.

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