Screw compressor for high input power

Abstract

The invention relates to oil-flooded screw compressors having a male rotor and female rotor each featuring preferably a ratio of male-to-female rotor lobes of 4:6, 5:6 or 5:7. In order to decrease the bearing load at higher working pressures, the profile sections of the rotors are shortened, and an intermediate plate is appropriately arranged in the free space formed.

Description

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In the following, the invention is described in an example of embodiment. The accompanying drawing shows in:

FIG. 1 a screw compressor of known design.

FIG. 2 a screw compressor according to the invention.

FIG. 3 the working cavity volume as a function of the male rotor position for a screw compressor according to the invention.

FIG. 4 an sample of an intermediate plate according the invention.

In the screw compressor according to the invention, the same components as in the case of the known compressor are used to a large extend. The compressor is driven via a coupling not shown at the drive-shaft end 5, which is a fixed part of the male rotor 2. The interlobe spaces of the five-lobe male rotor 2 the profile section of which has a wrap angle of 180° and of the six-lobe female rotor 3 the profile section of which has a wrap angle of 150°, form working cavities, to which adjoins according to the invention on the suction side in the rotor-housing section 13 the intermediate plate 7, which can comprise two parts for the male- and female-rotor side and incorporates parts of suction channel 4 with inlet port 6. The ratio L/A between the length of the profile section of the rotors L and distance between the rotor axes A lies approx. between 0,7 to 1,3.

Due to rotation of the rotors, the volume of a working cavity considered increases (suction process 15), then remains constant for a range of the angle of rotation (transfer phase 16), and decreases (compression process 17 and discharge process 18). Due to the shape of the inlet port, the latter gets disconnected from the working cavity considered as a result of rotor rotation, after the transfer phase 16 has begun.

The compressor can be fitted with an economizer port 8 on the wall of the housing enclosing the rotors between the suction- and discharge side of the compressor, preferably arranged in the area of the transfer phase 16 of the working cavity after the disconnection of the working cavity from the suction port.

Both rotors 2 and 3 are supported by radial bearings 1 on the suction side and by radial bearings 9 and axial bearings 10 on the discharge side. For compensation of the axial thrust, a contactless sealing rotating balance piston 11 is arranged on male rotor 2. Balance piston 11 is supplied with pressurized oil and axially counteracts the gas force exerting on male rotor 2.

The intermediate plate is fixed at the suction housing adjacent to the working chamber on the suction side. The intermediate plate consists of a similar material as the material of the housings, cast grey iron or steel, or aluminium or another rigid material suitable for refrigerants and oil.

The intermediate plate 7 contains parts of the suction channel 6. It continues the suction channel 6 in axial direction from the suction housing to the grooves of the rotor profile of male and female rotor. Another feature of the intermediate plate is characterized by location of parts of oil return channels 20 for oil drainage from bearings or shaft seal or combinations of this to grooves of rotor profile of male and female rotor. The intermediate plate 7 seals the grooves of rotor profile of male and female rotor at the end face 21 of the rotor pair without direct contact.

Claims

1. Oil-flooded screw compressor for high input power featuring two rotors, a male rotor 2 having essentially convex lobe flanks featuring four, five or six lobes, and a female rotor 3 having essentially concave lobe flanks featuring six or seven lobes, with the male rotor having a drive-shaft end 5, and both rotors are enclosed in housing sections: a suction-housing section 12 having at least parts of a suction channel 4 for passing of the working fluid into the interlobe spaces of the rotor pair, a rotor-housing section 13 at least partially enclosing the profile section of the rotors 2 and 3, and a discharge-housing section 14 having at least an outlet port for passing the gas out of the interlobe spaces of the rotor pair due to rotation of the rotors 2 and 3, and a discharge channel,whereinthe ratio L/A between the length L of the profile section of the rotors and distance A between the rotor axes, which determines the bearing load, is decreased by shortening the profile sections of both rotors, and adjacent to the suction side of the profile section of the rotors an intermediate plate 7 is fixed in the rotor-housing section 13 containing parts of the suction channel 4 with inlet port 6, sealing the end face of the profile section of the rotors contactless, and filling appropriately the space formed by shortening of the profile sections of the rotors.

2. Screw compressor according to claim 1 wherein the male rotor 2 of the compressor according to the invention has a wrap angle in the range of approx. 140° to 250°.

3. Screw compressor according to claim 1 wherein the length L of the profile sections of the rotors of the compressor according to the invention has a ratio to the distance A between the rotor axes of 0,7 to 1,3.

4. Screw compressor according to claim 1 wherein the intermediate plate 7 is arranged within the rotor-housing section 13.

5. Screw compressor according to claim 1 wherein the economizer port 8, has a connection to the working cavity within the transfer phase 16.