GB2213540A

GB2213540A - Shaft seal

Info

Publication number: GB2213540A
Application number: GB8828438A
Authority: GB
Inventors: Guenter Pietsch
Original assignee: Blohm and Voss GmbH
Current assignee: Blohm and Voss GmbH
Priority date: 1987-12-11
Filing date: 1988-12-06
Publication date: 1989-08-16
Anticipated expiration: 2008-12-06
Also published as: DE3742080A1; GB2213540B; DE3742080C2; AU609910B2; CN1035711A; NL8803034A; AU2657688A; KR890010436A; GB8828438D0; JPH0814321B2; SE8804472D0; KR0121287B1; SE8804472L; SE470140B; JPH01193466A; NL193289B; NL193289C; CN1015817B

Description

Z- U Shaft seal for the sealing of a licruid medium The invention relates

to a shaft seal for the sealing of a liquid medium against a gaseous medium, in particular the atmosphere, the seal having the features set forth in the preamble of claim 1.

In shaft seals of this kind (German Auslegeschrift 1 525 882 and German Auslegeschrift 1 101 074) the liquid medium comprises lubricating oil which has a relatively high degree of viscosity. Moreover, the liquid medium has a pressure which is not higher or not notably higher than the gaseous medium, so that approximately the same pressure conditions prevail on this side and on the far side of the sealing strip; Accordingly it is important with these known seals to avoid the lubricating oil passing through the gap between the sealing strip and the shaft into the space of the gaseous medium, since this would lead to lubricating oil losses.

For this reason the angle of the conical projection with the shaft is selected to be 45 degrees and larger so that the formation of a lubricant wedge which could reduce the contact pressure of the sealing strip on the shaft is largely avoided.

This measure has however shown itself to be unfavourable when conditions prevail at which the liquid medium is of low viscosity, for example consist of water, and the pressure of the water is larger than the pressure of the gaseous medium, such as is the case with shaft seals for the propeller shafts of ships. Under these conditions the lubrication of the sealing strip by the water which is a poor lubricant would namely not suffice in order to ensure a sufficient lifetime of the sealing lip.

The invention is thus based on the problem of achieving adequatelubrication of the sealing strip under the named conditions and thus of increasing the required lifetime.

This object is satisfied, in accordance with the invention, in that the angle of the conical projection amounts to at most 12 degrees, with the angle being kept smaller the lower the degree of viscosity of the liquid is.

In accordance with the invention there is thus a leakage of water through the gap between the sealing strip and the shaft which is consciously induced by the very acute cone angle, by which is ensured that the lubrication is sufficient despite the poor lubricating characteristics of the water. The entry of the leakage water into the gas conveying space is not disadvantageous here because the leakage water can readily be removed by relatively simple known conveying means.

The low cone angle of at most 12 degrees acts thereby in the sense of the conveyance that is required because a pressure wedge forms between the shaft and the cone which hydrodynamically "floats up" the sealing lip, i. e. widens it, and thus induces the intended leakage to the gas conveying space.

Lip ring seals have admittedly already become known (German Auslegeschrift 1 248 399) in which a very accute cone angle of 4 degrees to 8 degrees is used, however this is not a cone which is effective in operation, but rather a cone present on the sealing lip prior to installation which in Z a the operating state is removed by the elastic deformation against the shaft, and which only has an effect with relation to the contact pressure. In accordance with an embodiment of the subject of the invention provision is made that hydrodynamically acting conveying grooves are provided at the surface of the conical projection which are so shaped that they convey the liquid medium from the higher pressure medium to the lower pressure medium. In this way the intended medium flow to the gaseous medium is assisted and amplified, which is desired under certain conditions. Furthermore provision is made that the conveying grooves are shaped in the manner of a thread with a pitch directed towards the sealing strip (related to the direction of rotation of the shaft); and that the conveyor grooves surround the periphery of the projection with at least one thread turn. In this way one is able to match the conveying intensity of the conveying grooves in a simple manner to the prevailing local requirements by correspondingly varying the thread pitch.

The subject of the invention is schematically illustrated in the drawing. There is shown, in each case in cross-section Fig. 1 a sealing lip in accordance with the invention without conveying grooves, Fig. 2 a sealing lip in accordance with the invention with conveying grooves, Fig. 3 a sealing arrangement with two sealing lips arranged axially behind one another.

The sealing lip shown in Fig. 1 has a clamping part 1, a web 2 and a lip part 3. The lip part 3 contacts the shaft 7 with a sealing strip 4, i.e. the actual sealing lip, which in the present embodiment forms a rounded edge. A conical ring projection 5 extends from the sealing strip 4 in the direction towards the medium W to be sealed and forms a very acute angle alpha with the shaft 7. The conical ring projection 5 is of smooth shape at its surface facing the shaft 7._ At its side facing the gaseous medium G the lip part 3 is likewise of conical shape. This cone which is substantially shorter in the axial direction than the cone which faces the liquid medium has no importance for the inventive function of the lip part.

The sealing lip shown in Fig. 2 consists of the same components as the sealing lip of Fig.1 with the sole distinction that the conical ring projection 5 is provided at its conical surface 5 facing the shaft 7 with conveying grooves 6 in the manner of a multi-start thread.

It can be seen from Fig. 3 that the sealing lips of the invention can not only be used as individual seals but can also be used in sealing arrangements of customary construction with two or more sealing lips arranged spaced apart behind one another. In the illustrated sealing arrangement the sealing lip adjacent the medium W to be sealed is designated with 1, 4, 5 and the sealing lip adjacent the gaseous medium is designated with 11, 41, 5 z P. a t e n t

Claims

C 1 a i m s

Shaft seal f or the sealing of a liquid medium against a gaseous medium, in particular the atmosphere, comprising an annular sealing lip of elastomeric material which has a sealing strip surrounding and contacting the shaft, wherein a conical ring projection extends from the sealing strip towards the liquid medium to be sealed and forms an angle with the shaft in the operating state, characterized in that, in the presence of a low viscosity liquid as a liquid medium and at pressure conditions at which the liquid medium has a higher pressure than the gaseous medium, the angle amounts to at most 12 degrees, with the angle being kept smaller the lower the degree of viscosity of the liquid is.
2.

Shaft seal in accordance with claim 1, characterized in that hydrodynamically acting conveying grooves are provided at the surface of the conical ring projection, with the conveying grooves being so shaped that they convey the liquid medium from the higher pressure medium to the lower pressure medium.
3. Shaft seal in accordance with claim 2, characterized in that the conveying grooves are formed in the manner of a thread with a pitch directed towards the sealing strip; and in that the conveying grooves surround the periphery of the ring projection with at least one. thread turn.

Published 1989 at The Patent Office, State House, 66171 High Holborn, London WClR 4Tp. Further copies maYbe obtained from ThePatent Office. Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD. Printed by Multiplex techniques Itd, St Mary Cray, Kent, Con- 1187