Oil-free screw compressor and design method therefor

Patent metadata

Field	Value
Publication number	US-2017284392-A1
Application number	US-201515513841-A
Country	US
Kind code	A1
Filing date	Sep 24, 2015
Priority date	Sep 29, 2014
Publication date	Oct 5, 2017
Grant date	—

Abstract

The oil-free screw compressor includes: a casing having a rotor chamber; a bearing supporting rotary shafts of screw rotors; a shaft seal device with an oil seal portion and an air seal portion; a ventilation gap positioned between the oil seal portion and the air seal portion; and an atmosphere open passage communicating an atmosphere side of the casing with the ventilation gap communicate. A most narrowed portion, an air seal portion, and oil seal portions are set such that the followings is established:
( La/Sa 2.5 )/( Lh/Sh 2.5 )>| P 2|/Δ Pb
La: effective shaft seal length Sh: effective open cross-sectional area (most narrowed portion of atmosphere open passage) Lh: effective narrowed length (most narrowed portion of atmosphere open passage) Sa: shaft seal cross-sectional area |P2|: negative pressure in rotor chamber during unloading operation ΔPb: minimum differential pressure in the oil seal portion during the unloading operation

First claim

1 . An oil-free screw compressor comprising:
a pair of female and male screw rotors which meshes with each other in a non-contact manner; a casing having a rotor chamber in which the screw rotors are housed; a bearing which supports rotary shafts of the screw rotors; a shaft seal device which includes an oil seal portion disposed on a bearing side and an air seal portion disposed on a rotor chamber side and shaft-seals the rotary shaft; a ventilation gap which is positioned between the oil seal portion and the air seal portion and is formed between an outer peripheral surface of the rotary shaft and an inner peripheral surface of the shaft seal device; and an atmosphere open passage which makes an atmosphere side of the casing and the ventilation gap communicate with each other, wherein assuming an effective open cross-sectional area as Sh and an effective narrowed length as Lh in a most narrowed portion where the atmosphere open passage is most narrowed, and assuming a shaft seal cross-sectional area in a direction orthogonal to a rotary shaft as Sa and an effective shaft seal length as La in a fine gap in the air seal portion, assuming an absolute value of a negative pressure in the rotor chamber during an unloading operation as |P2|, and assuming a minimum differential pressure in the oil seal portion during the unloading operation as ΔPb, the most narrowed portion, the air seal portion and the oil seal portion are set such that a following relationship is established.
( La/Sa 2.5 )/( Lh/Sh 2.5 )>| P 2|/Δ Pb

2 . The oil-free screw compressor according to claim 1 , wherein
the atmosphere open passage has an atmosphere open hole formed in the casing, and at least one communication hole formed in the shaft seal device, and an annular space which surrounds the shaft seal device in a circumferential direction is formed by both of or either one of an inner peripheral side of the casing and an outer peripheral side of the shaft seal device, and the atmosphere open hole and at least one of the communication holes communicate with each other through the annular space, and the most narrowed portion is smaller one between an open cross-sectional area of the atmosphere open hole and a total open cross-sectional area of the at least one communication hole.

3 . The oil-free screw compressor according to claim 1 , wherein the oil seal portion is a visco-seal.

4 . A method of designing an oil-free screw compressor comprising:
a pair of female and male screw rotors which meshes with each other in a non-contact manner; a casing having a rotor chamber in which the screw rotors are housed; a bearing which supports rotary shafts of the screw rotors; a shaft seal device which includes an oil seal portion disposed on a bearing side and an air seal portion disposed on a rotor chamber side and shaft-seals the rotary shaft; a ventilation gap which is positioned between the oil seal portion and the air seal portion and is formed between an outer peripheral surface of the rotary shaft and an inner peripheral surface of the shaft seal device; and an atmosphere open passage which makes an atmosphere side of the casing and the ventilation gap communicate with each other, wherein assuming an effective open cross-sectional area as Sh and an effective narrowed length as Lh in a most narrowed portion where the atmosphere open passage is most narrowed, and assuming a shaft seal cross-sectional area in a direction orthogonal to a rotary shaft as Sa and an effective shaft seal length as La in a fine gap in the air seal portion, assuming an absolute value of a negative pressure in the rotor chamber during an unloading operation as |P2|, and assuming a minimum differential pressure in the oil seal portion during the unloading operation as ΔPb, the most narrowed portion, the air seal portion and the oil seal portion are set such that a following relationship is established.
( La/Sa 2.5 )/( Lh/Sh 2.5 )>| P 2|/Δ Pb

5 . The method of designing an oil-free screw compressor according to claim 4 , wherein
the atmosphere open passage has an atmosphere open hole formed in the casing, and at least one communication hole formed in the shaft seal device, and an annular space which surrounds the shaft seal device in a circumferential direction is formed by both of or either one of an inner peripheral side of the casing and an outer peripheral side of the shaft seal device, and the atmosphere open hole and at least one of the communication holes communicate with each other through the annular space, and the most narrowed portion is smaller one between an open cross-sectional area of the atmosphere open hole and a total open cross-sectional area of the at least one communication hole.

6 . The method of designing an oil-free screw compressor according to claim 4 , wherein the oil seal portion is a visco-seal.

7 . The oil-free screw compressor according to claim 2 , wherein the oil seal portion is a visco-seal.

8 . The method of designing an oil-free screw compressor according to claim 5 , wherein the oil seal portion is a visco-seal.

Assignees

• Kobe Steel Ltd

Inventors

• Yano Yoshio
• Miyatake Toshiyuki

Classifications

• F04C18/16 Primary

  with helical teeth, e.g. chevron-shaped, screw type {(for non-parallel axes of movement F04C18/48)} · CPC title

• F04C27/00 Primary

  Sealing arrangements in rotary-piston pumps specially adapted for elastic fluids · CPC title

• F04C29/00

  Component parts, details or accessories of pumps or pumping installations, not provided for in groups F04C18/00 - F04C28/00 · CPC title

• F04C27/009

  Shaft sealings specially adapted for pumps · CPC title

• F04C27/005

  Axial sealings for working fluid · CPC title