AU609910B2 - Shaft seal for sealing off a liquid medium - Google Patents

Description

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__09 9 I 'j rF Ref: 79608 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class *1

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Complete Specification Lodged: Accepted: Published: Priority: Related Art: This document contains the amendments made under Section 49 and is correct for printing.

Name and Address of Applicant: Address for Service: Blohm Voss AG Hermann-Blohm-Strasse 3 2000 Hamburg 11 FEDERAL REPUBLIC OF GERMANY Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Shaft Seal for Sealing Off a Liquid Medium The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/4 -2- TECHNICAL FIELD The invention relates to a shaft seal for sealing off a liquid medium I against a gas medium.

BACKGROUND OF THE INVENTION In shaft seals of the :ype described in German Applications 1525882 and 1101074, the liquid medium is a lubricating oil having high viscosity.

Further, the pressure of the liquid medium is not higher, or only insignificantly higher, than that of the gas medium so that about the same pressure is present on both sides of the packing strip. Therefore, the important point in the known seals is to avoid that lubricating oil passes through the gap between the packing strip and the shaft into the space of the gas medium as this would imply losses of lubricating oil.

For this reason, the angle which the cone-like protrusion includes with the shaft is 450 or more so that one essentially avoids the development of a lubricating-oil wedge, which could reduce the pressure urging the packing strip toward the shaft.

However, this measure is not advantageous under conditions under S which the liquid medium is of low viscosity, when it is water, and S when the pressure of the water is greater than the pressure of the gas medium as in the case of shaft seals of propeller shafts of ships.

I t Under these conditions, lubrication of the packing strip by the C, poorly lubricating agent water would not suffice for ensuring a sufficient c" service life of the packing strip.

i It is the object of the present invention to overcome or substantially ameliorate the above disadvantages.

There is disclosed herein a shaft seal for sealing off a liquid medium from a gas medium, said shaft seal comprising: L •an annular sealing lip of an elastometric material, in the form of a Speripheral packing strip; ,3Q a cone-like annular protrusion extending from said annular sealing I: t lip in direction of said liquid medium, said protrusion forming in an operational state an angle of not more than 12 degrees with said shaft, the i value of said angle being dependent on the viscosity of said liquid medium, S such that the angle is smaller when the viscosity is lower.

R 62 P'-ro /1462R .ntu of Dec frn-y c Fritz BrUning Christian Hilbich TO: THE COMMISSIONER OF PATENTS

AUSTRALIA

SBR/TGK/225F 3- In the preferred embodiment the very acute cone angle induces a I desired leakage of water through the gap between the packing strip and the shaft, whereby it is guaranteed that the lubrication is adequate despite the poor lubricating properties of the water.

Typically, entry of leaking water into the gas-filled space is not a disadvantage because the leaking water can be easily removed by relatively simple known transporting means.

Advantageously, in the preferred embodiment the small cone angle of at most 12° favours the desired transport because a pressure wedge develops between the shaft and the cone so that the packing strip is hydrodynamically "floated," expanded and, hence, the intended leakage to the gas-filled space is induced.

Annular lip seals with a very acute cone angle of 4 8 degrees are known (German Application 1248399 Published for Opposition), but this is not an operational cone but a cone which is present at the sealing lip before its mounting, which is removed in the operational state by elastic deformation at the shaft, and which is effective only in regard to the pressure force.

It is preferred that on the surface of the cone-like protrusion there Sare provided hydrodynamically effective grooves which are configured so that they convey the liquid medium from the medium of the higher pressure to the medium with the lower pressure.

It*' In this way the intended flow of the medium to the gas medium is supported and enhanced, which is desired under certain conditions.

It is further preferred that the conveying grooves are configured as a thread with a pitch directed toward the packing strip, and the conveying grooves surround the circumference of the protrusion with at least one I( thread groove.

In this way one can easily adapt the intensity of conveying through the grooves to the respective local requirements by varying the pitch of the thread.

S' CC C C SRAtt A 0-rr 4 A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Fig. 1 is a cross section of a sealing lip, according to the invention, without grooves; Fig. 2 is a cross section of a sealing lip, according to the invention, with conveying grooves; Fig. 3 is a cross section of a sealing assembly with two sealing lips arranged axially one behind the other.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The sealing lip shown in Fig. 1 comprises a clamping portion 1, a web member 2, and a lip portion 3. Lip portion 3 abuts shaft 7 with a packing strip 4 which forms a rounded edge in the embodiment under consideration.

A cone-like annular protrusion 5, which forms with shaft 7 a very acute angle alpha, extends from packing strip 4 toward the medium W to be sealed off. The cone-like annular protrusion 5 is smooth on the surface facing shaft 7. On the side of the gas medium G, the lip portion 3 is likewise conical. This cone, which in the axial direction is substantially shorter than the cone facing the liquid medium, is without relevance for the functioning of the lip member according to the invention.

The sealing lip illustrated in Fig. 2 is composed of the same components as Lhe sealing lip of Fig. 1, except for the cone-like annular protrusion 5 provided with conveying grooves 6 in the form of multiple threads on the cone surface 5 facing shaft 7.

1 It follows from Fig. 3 that the sealing lips according to the preferred form of this invention can be used not only as single seals but also in conventional sealing assemblies with two or more spaced sealing lips arranged one behind .the other. In the sealing assembly illustrated, *1 the sealing lip close to the medium W to be sealed off is denoted by 1, 4, 5, and the sealing lip adjacent to the gas medium is denoted by *trct t 7 W 62R r O^

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Claims (3)

1. 2. The shaft seal of claim 1, wherein hydrodynamically effective conveying grooveq are provided on a surface of said cone-like annular protrusion.
2. 3. The shaft seal of claim 2, wherein said conveying grooves are provided in a form of a thread with a pitch, said pitch extending in direction of said sealing lip, said thread circumscribing a periphery of said annular protrusion at least 360 degrees.
3. 4. The shaft seal of any one of claims 1 to 3 in combination with the shaft. A shaft seal substantially as hereinbefore described with reference to the accompanying drawings. 8« DATED this THIRTY-FIRST day of JANUARY 1991 Blohm Voss AG Patent Attorneys for the Applicant SPRUSON FERGUSON c C II RLF/1462R