WO1988001351A1

WO1988001351A1 - Rotary screw compressor

Info

Publication number: WO1988001351A1
Application number: PCT/SE1987/000363
Authority: WO
Inventors: Arnold Englund
Original assignee: Svenska Rotor Maskiner Ab
Priority date: 1986-08-20
Filing date: 1987-08-19
Publication date: 1988-02-25
Also published as: SE8603528L; KR880701835A; SE8603528D0; JPH02500676A; SE455117B

Abstract

Rotary screw compressor comprising a male rotor (2) and a female rotor (3) having intermeshing, helically extending grooves. The rotors are at their ends provided with shaft journals for journalling the rotors. In order to eliminate the need for shaft sealings around the shaft journals (4, 5) at the high pressure end, the rotors are so shaped that a sealing effect is established between the rotor end surfaces (8, 9) and the high pressure end wall (10). This has been achieved by making the rotor grooves shallow and the shaft journals (4, 5) slender.

Description

ROTARY SCREW COMPRESSOR

The present invention relates to a rotary screw compressor comprising a male rotor and a female rotor having intermeshing, helically extending grooves. The rotors of a compressor of this kind are provided with shaft journals for journalling the rotors.

Compressors of the specified kind are well-known. Representative examples thereof are disclosed in the Swedish published patent applications 374 946 and 418 889.

In such compressors there is a clearance between the end surfaces of the rotors and the end wall at the high pressure end, as mechanical contact between said surfaces should be avoided. The clearance constitutes a leakage path for the compressed working fluid, flowing from a compression chamber exposed to the end wall radially inwards to the shaft journal and along the same towards the bearing. A rotor in a compressor of this kind usually has its helical grooves extending so deep in the rotor so that the radial distance between the shaft journal and the bottom of a groove will be small, resulting in that the leakage path constituted by the clearance will be very short. The compressed working fluid therefore can reach the shaft journal without appreciable obstacle. In order to prevent the compressed working fluid from leaking therefrom to the bearing chamber, normally a shaft sealing is provided between the bearing and the rotor body.

The object of the present invention is to simplify a compressor of the specified kind by eliminating the need for shaft sealings at the high pressure end of the compressor. According to the invention this has been achieved in that the compressor has the features specified in claim 1.

Advantageous embodiments of the invention are specified in the dependent claims. The invention will be explained more in detail through the following exemplification thereof, illustrated in the accompanying drawings of which

Figure 1 is a longitudinal section through the high pressure end of the compressor, and Figure 2 is a section taken along the lines 2-2 of figure 1, omitting details not essential to the invention.

In figure 1 the discharge end of the compressor is shown. The compressor comprises a male rotor 2 having five grooves and a female rotor 3 having six grooves. Each of the rotors is at the high pressure end provided with a shaft journal 4, 5 journalled in needle bearings 6, 7. Between the end surfaces 8, 9 of the rotors and the end wall a clearance d is formed.

As introductionally has been described, the clearance d constitutes a leakage path for compressed working fluid, which therethrough reaches the shaft journals 4, 5 and further on the bearings.

As can be seen in figure 2, the rotors are made with relatively shallow grooves and relatively slender shaft journals. Thereby is achieved that the distance 1_m and 1_f, respectively, between the bottom of a groove and the related shaft journal will be long. By a shallow groove, a groove depth of about 1/6 to 1/5 of the rotor diameter is ment, and by a slender shaft journal, a diameter thereof of about 1/4 of the rotor diameter is ment. The length of the leakage path will then correspond to about 15 to 20 % of the related rotor diameter. The length between the bottom of a groove and the shaft journal is sufficient to establish a closed clearance sealing effect through the clearance between the rotor end surfaces and the end wall, which considerably reduces the leakage. A satisfactional sealing is attained therethrough, which eliminates the need for a special shaft sealing for each of the shaft journals.

In the embodiment shown, the lobe combination 5+6 is chosen, as rotors with many lobes are favourable for achieving a small groove depth. Therefore also lobe combinations of 5+7 and more are particularly suitable for a compressor according to the invention.

The sealing is more efficient the narrower the clearance d between the rotor end surfaces 8, 9 and the end wall 10 is. In order to attain as narrow clearance as possible the shaft journals 4, 5 are journalled immediately adjacent the end wall 10. Thereby the increasing risk for inclination of the rotor end surfaces caused by the slender shaft journal is counter-acted and the clearance can be kept narrow. As bearings 6, 7 needle-bearings are used so that the radial dimensions thereof are minimized. In this way the holes in the end wall for the shaft journals can be made small, which contributes to attain a long sealing clearance 1_m, 1_f, respectively.

Claims

1. Rotary screw compressor comprising a male rotor (2) and a female rotor (3) having intermeshing, helically extending grooves, said rotors at their ends being provided with shaft journals for journalling the rotors, characterized in that the grooves of the male rotor (2) and the grooves of the female rotor (3) are so shallow and their related shaft journals (4, 5) at the high pressure end so slender that the radial distance between the bottom of a groove and the related shaft journal (4, 5) is long enough to establish a closed clearance sealing effect between the end surfaces (8, 9) of the rotors (2, 3) and the end wall (10) at the high pressure end.

2. Rotary screw compressor according to claim 1, characterized in that said radial distance is greater than 1/6 of the related rotor diameter.

3. Rotary screw compressor according to claim 1 or 2 , characterized in that the shaft journals (4, 5) at the high pressure end are journalled immediately adjacent the end wall.

4. Rotary screw compressor according to any of claims 1 to

3, characterized in that the shaft journals (4, 5) at the high pressure end are journalled in bearings of small radial dimensions, preferably needle bearings.

5. Rotary screw compressor according to any of claims 1 to

4, characterized in that the shaft journals (4, 5) at the high pressure end have no shaft sealings.