GB2297363A

GB2297363A - Ring seal

Info

Publication number: GB2297363A
Application number: GB9601432A
Authority: GB
Inventors: Herbert Hoffelner
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1995-01-24
Filing date: 1996-01-24
Publication date: 1996-07-31
Also published as: ITMI960060A0; IT1281671B1; ITMI960060A1; GB9601432D0; FR2730276A1; DE19502079A1

Description

A SLIDE RING SEAL FOR TURBINE ENGINES 2297363 The invention relates to a

slide ring seal for turbo machines, more particularly gas turbine engines for sealing chambers between a machine stator and a machine shaft relative to one another, the chambers being acted upon by fluid at different pressures.

It is known from EP 0361 245 Bl, in particular for sealing between shafts in turbo machines, to support a sealing ring elastically and centre it against a housing by means of an assembly of prestressed bending springs surrounding the ring. For the primary seal, the sealing ring, which is closed, is arranged on the shaft with a radial gap; the radial gap is of such dimensions that an air bearing is formed when there is a predetermined differential pressure between the two chambers. As a result of axial, disk-like, resilient contact pressure, the sealing ring is provided with secondary sealing with respect to the housing and the two pressure chambers.

With a view to withstanding thermally and mechanically induced expansions in the slide pair (ring, shaft) during operation, the known design requires a comparatively large radial gap for the primary seal and therefore a relatively marked leakage flux. A reduced leakage flux would be conceivable with a smaller radial gap, but in this case there would be an increased risk at least of more frequent and severe contact leading to wear, and, worse, jamming of the slide pair; even brief jamming could render the sealing device completely useless. In view of the relatively large shaft diameters in question (up to and sometimes in excess of 60 mm) and the associated increase in the overall circumferential radial gap volume, the known design would inevitably involve a large leak flow if the danger of premature component wear or seal jamming and destruction is to be prevented.

Furthermore, in the known design the disk-like, axially resilient contact pressure for the secondary sealing means increased structural complexity with the danger of mechanical failure (spring fatigue and breakage).

It has also been proposed to replace the closed sealing ring in the known design by a sealing ring which is continuously segmented over its circumference; as a result of the circumferential connection of the ring segments which are movable relative to one another, the proposed design results in a comparatively complicated construction with increased secondary sealing outlay. For a radially resilient support of the sealing or slide ring a plurality of support springs, i.e. at least two per ring segment, are required. The proposed design could also only be realised with a relatively large radial fitting volume, which is often not available in turbine engines owing to weight and structural regulations.

In addition, eccentricities tend to be produced in the machine shaft in turbo machines as a result of rotor imbalances or extreme load changes. Often these cannot be taken Into account by seals of the above type, or only with an unjustifiably high structural outlay.

It is an object of the invention to provide a slide ring seal which occupies a small fitting volume whilst having a comparatively simple construction, and which allows for optimal, low-leakage sealing between chambers on the shaft at different pressures, even for large shaft diameters and under the thermal and mechanical influences occurring during operation.

According to the invention there is provided a slide ring seal for the shaft of a turbine engine, for sealing between chambers at different pressures, comprising: a housing around the circumference of the shaft, having a recess open to the shaft; a pressure ring radially resiliently supported in the recess around the circumference of the shaft; a slide ring on the shaft circumference and co-operating with the pressure ring; and a sealing ring co-operating with the slide ring on the one hand and the wall of the recess on the other hand, so that a seal is formed between the slide and (preferably) the sealing rings and the shaft and between the sealing ring and the housing.

The combination of the seal and sliding rings or, preferably, at least two seals and two sliding rings, allows for optimal primary and secondary sealing. The primary sealing at the shaft is mainly provided by the slide rings which are divided or slotted over the circumference. The slide rings are constructed and arranged in such a manner that, at a given shaft rotational speed, they set up aerodynamic or hydrodynamic bearing-like support gaps relative to the machine shaft, i.e. small radial support gaps, which are established in use at an order of magnitude which is conventional in air bearings. The adjustment or possibility of regulating the bearing-like, radial support gaps is therefore a function of the local pressure build-up at the shaft and of the radial components of the closing forces transmitted by the resilient mounting of the pressure ring. Preferably this effect is reinforced with the assistance of a sealing fluid pressure admitted via the pressure ring to the slide rings.

The co-operation of the various rings may simply be by way of wedge (i.e. in view of the rotational symmetry conical) surfaces, by which the pressure ring urges the slide ring radially inwards and axially outwards to urge the sealing ring in turn against the wall of the housing to form the secondary seal. in the preferred type with two pairs of slide and sealing rings the pressure ring urges the slide rings outwards in opposite directions.

The sealing rings are always, i.e. both when the machine is inoperative and in all operating states, arranged with radial gaps relative to the shaft of dimensions such that shaft contact is practically ruled out over the entire operating range. Furthermore the sealing rings can be arranged to effect an optimal secondary sealing of the recess on the housing relative to the two pressure chambers. At the same time they act as friction dampers with their axially external end surfaces relative to radial counter surfaces on the housing.

The slide rings are preferably prestressed in the centripetal direction, so that they rest against and enclose the machine shaft when the machine is inoperative.

By appropriately selecting the spring force and the bearing surface inclination, it is possible to adjust the centripetal force components acting upon the slide rings and the axial force components acting upon the sealing rings. The slide rings are essentially prevented from rotating by the frictional forces generated at the matching conical bearing surfaces. Slight movements in the circumferential direction are, however, possible.

Even extreme radial rotor and shaft deflections can be overcome and are transmitted via the slide rings and the pressure ring to spring means, e.g. a spring plate, and thereby optimally damped.

The slide ring seal can be used for both directions of rotation. It can be used as a fluid or gas seal and with its comparatively simple construction can also be easily assembled or dismantled. Optimal sealing quality can be obtained in particular in respect of large shaft diameters. Accordingly, it is possible to manage high sliding velocities by the airbearing effect at high rotational speeds.

A sealing fluid can also be supplied, either radially externally via the housing or from radially inwardly via the machine shaft. The slide ring seal is then particularly suitable for sealing pressure chambers (bearing chambers) containing oil or oil mist relative to atmospheric pressure chambers or pressure chambers acted upon by compressor air or an exhaust gas. For the sealing tasks named by way of example, the slide ring seal can also be constructed as a pure differential pressure seal.

Two embodiments of the invention will now be explained in further detail with the aid of the accompanying drawings, in which:

Fig. 1 is a central longitudinal section through a slide ring seal representing a first embodiment of the invention with a sealing fluid supply via the housing, Fig. 2 is a partial sectional view along the line II-II in Fig. 1, Fig. 3 is a view similar to Fig. 1 of a second embodiment, in this case showing a sealing fluid supply via the machine shaft, and Fig. 4 is a view along the line of section W-W in Fig. 3.

Figs. 1 and 2 and Figs. 3 and 4 respectively illustrate slide ring seals for turbo machines, more particularly gas turbine engines, for optimally sealing chambers Rl, R2 between a machine stator, represented by the housing 10, and a machine shaft 8 relative to one another. The chambers Rl,R2 are acted upon by fluid at different pressures.

In Fig. 1 a machine shaft section is shown having a housing shown broken away on the outside on the side facing the stator and a shaft section shown broken away on the circumference. The housing 10 on the machine stator includes a recess I open towards the machine shaft 8 for receiving a pressure ring 2, which is radially resiliently supported in the recess around the circumference, and slide and sealing rings 4, 5; 6, 7. There are two slide ring/sealing ring pairs, roughly mirror-symmetrically about a central radial plane, the sealing rings being located axially outwardly of their respective slide rings. The slide and sealing rings 4, 5; 6, 7 form a primary seal against the shaft circumference, the seal being supplied with sealing fluid F as will be explained later. At the locations b between the sealing rings and the shaft, this primary seal comprises radial circumferential gaps between the sealing rings 6, 7 and the shaft; these radial circumferential gaps are dimensioned in such a manner that there is no shaft contact at any time. At the locations c between the slide rings 4, 5 and the shaft there is initially contact with the shaft but radial support gaps, which are supplied with sealing fluid F, are created relatively quickly after the machine has been started. The slide rings 4, 5 are supported axially on one side against the pressure ring 2 and on the other side against the sealing rings 6, 7, in each case via matching conical bearing surfaces. The bearing surface inclination is indicated by the angles a and 8 for the axially inner and outer faces of the rings respectively. The two slide rings 4, 5 are thus similarly shaped in respect of their bearing surfaces tapering in the shape of a wedge or cone in the direction of the base of the recess 1.

An axially outwardly directed force on the sealing rings 6, 7 via the respective slide rings provides the secondary sealing of the recess 1 of the housing 10 relative to the two chambers Rl and R2. In this respect, the sealing rings 6, 7 are guided on their axially outer surfaces in a radially displaceable fashion on radial counter surfaces e, f of the recess 1 in a sealing and friction-damping manner.

To allow for expansion and contraction the pressure ring 2 and the two slide rings 4, 5 are divided in each case at least at one circumferential location X;Y (Figs. 2 and 4). The divisions can be constructed as axially parallel slots which are offset relative to one another over the circumference. The sealing rings do not need to be divided since they have sufficient clearance from the shaft.

By way of the relative mutual bearing surface inclinations a; 8 relative to the pressure ring 2 on the one hand and the respective sealing ring 6 or 7 on the other hand the slide rings 4, 5 are biased in the centripetal direction so that they rest with their inner surfaces against the circumference of the machine shaft 8 when the machine is inoperative.

It can also be seen from Figs. 1 and 3 that the slide rings 4, 5 are arranged spaced apart axially, an annular chamber 9 being formed between the slide rings 4, 5, the pressure ring 2 and the shaft 8, which chamber is acted upon by the supplied sealing fluid F, and is in communication via the pressure ring 2 with the recess 1 for the secondary sealing.

The pressure ring 2 comprises on the one hand two axially outer generally cylindrical circumferential sections, which on the side remote from the base of the recess 1 extend at a radial distance from the corresponding sealing and slide ring 6,4; 7,5, and on the other hand a central projection 17 (Figs.1 and 3), which extends round the circumference and tapers symmetrically in a wedge or conical shape in the direction of the shaft circumference to form the bearing surfaces on both sides for the slide rings.

The pressure ring 2 is radially resiliently supported against the base of the rotationally symmetrical recess 1 of the housing 10 by means of a spring plate 3, which is continuously uniformly corrugated over the circumference, as can be seen in Fig.2. A radial clearance between the pressure ring 2 and the base of the recess 1, which can vary during operation, is indicated by a in Figs. 1 and 3. As shown in Figs. 1 and 3 the spring plate 3 is held in a circumferential rebate in the pressure ring 2 facing the base of the recess 1. In this manner, the spring plate 3 is protected against undue axial displacement.

In the slide ring seal illustrated in Figs. 1 and 2 the sealing fluid F is supplied to the recess 1 via at least one radially outer bore 11 located in the sealing housing 10 and, via the pressure ring 2, to the annular chamber 9.

The spring plate 3 has at least one aperture 13 for the passage of the sealing fluid F supplied via the radially outer bore 11; the aperture 13 communicates with circumferential grooves 14, 15 in the housing 10 and the pressure plate 2 respectively, facing the spring plate 3. The first circumferential groove 14 formed in the base of the recess I is connected to the external bore 11; the second circumferential groove 15 formed in the base of the rebate in the pressure ring 2 is connected via at least one radial aperture 16 in the pressure ring 2 to the annular chamber 9.

A part of the sealing fluid flows via the outer circumferential groove 14 and the circumferential intermediate chambers produced between the spring plate 3 and the recess base as a result of the spring -g- corrugation, into annular chambers which are formed within the recess 1 between each sealing and slide ring 6, 4; 7, 5 and the corresponding cylindrical sections of the pressure ring 2. The sealing fluid supply and the spring thus subject the slide rings 4, 5 via the pressure ring 2 to radial components of the closing forces.

Instead of the aperture 13, or in addition, the spring plate 3 can be divided at a circumferential location Z (Fig.2) by an axial slot, which is connected for the flow of fluid to the two circumferential grooves 14,15.

In the slide ring seal illustrated in Figs. 3 and 4 the sealing fluid F is supplied from the hollow cylindrical machine shaft 8, whose internal chamber 81 is connected for the flow of fluid to the annular chamber 9 via one or more apertures 12 in the shaft casing. The pressure ring 2 has a circumferential groove 15, similar to that in the embodiment of Fig.l. 20 A further advantageous feature of the slide ring seal in respect of assembly and maintenance is that the housing 10 with its recess 1 is formed by two axially releasable housing components 18, 19, which can be secured to one another axially and radially. The securing can be effected by means of screw connections uniformly distributed over the circumference. The slide ring seals illustrated in Figs. 1 to 4 operate according to the pressure conditions: Pl in chamber Rl>P2 in chamber R2, with P3 (sealing fluid) in the annular chamber 9 being > Pl and > P2.

However, the slide ring seal can also be operated without the radially outer (Figs. 1 and 2) or inner (Figs. 3 and 4) sealing fluid supply. It can be operated by the differential pressure between the pressure in the chamber Rl upstream and the pressure in the chamber R2 downstream of the seal in accordance with the equation Pl>P2, a pressure P3 existing within the annular chamber 9 which is lower than the pressure PI existing in the upstream chamber Rl and greater than the pressure P2 in the downstream chamber R2; the sealing fluid for the primary and secondary sealing is made available from the chamber Rl having the greater pressure Pl. However, the slide ring seal can also be operated with the reverse pressure arrangement, namely P2 in R2 > Pl in Rl, wherein P3 in the annular chamber 9 is < P2 and > Pl.

For use on or in the vicinity of a turbine, i.e. in areas of high temperature loading and heat radiation, the slide rings 4, 5 and/or the sealing rings 6, 7 can be manufactured from a temperature- resistant and wear-resistant ceramic material.

Furthermore, the surface of the machine shaft 8, more particularly in the regions of the slide rings 4, 5 arranged on the shaft, can be provided with a wear resistant and temperature-resistant ceramic coating.

The above-mentioned rings or coatings can be made of a ceramic material, which is selected from the oxides, carbides and nitrides. The materials can be, for example, zirconium oxide, silicon oxide or silicon nitride.

As a further development of the invention, the surface of the machine shaft 8, more particularly in the regions of the slide rings 4, 5 arranged on the shaft, can be provided with a metallic wear- and temperature-resistant coating. Suitable materials are, for example, chromium or other alloys, based e.g. on Ni or Co. For uses at lower temperatures, e.g. on or in the vicinity of compressors for gas turbine engines, the sealing and slide rings 5, 7; 4, 6 can be manufactured from a glass and/or carbon fibre- reinforced plastics material, an annular core being reinforced in each case by fibres extending circumferentially and being stabilised in respect of wear resistance by crossover fibre layers on all or sections of the outer surfaces.

Claims

CLAIMS 1. A slide ring seal for the shaft of a turbine engine, for sealing

between chambers (R1, R2) at different pressures, comprising: 5 a housing (10) around the circumference of the shaft (8), having a recess (1) open to the shaft (8); a pressure ring (2) radially resiliently supported in the recess around the circumference of the shaft, a slide ring (4,5) on the shaft circumference and co-operating with the pressure ring (2); a sealing ring (6,7) co-operating with the slide ring on the one hand and the wall of the recess (1) on the other hand, so that a seal is formed between the slide ring and the shaft and between the sealing ring (6,7) and the housing (10).
2. A slide ring seal according to claim 1, in which the radial resilience of the pressure ring (2) is arranged to exert a combined axial and radially inward force on the slide ring (4,5), which in turn exerts an axial force on the sealing ring.
A slide ring seal according to claim 1 or 2 and having two pairs of slide and sealing rings, arranged more or less mirror-symmetrically about the plane of the pressure ring.
4. A slide ring seal according to claim 3, in which the slide rings (4, 5) are supported via matching conical bearing surfaces against the pressure ring (2) on one side and against the sealing rings (6, 7) on the other side so as to press the sealing rings (6, 7) axially against the walls of the recess (1).
5. A slide ring seal according to any preceding claim in which the pressure ring (2) and the slide rings (4, 5) are each divided at at least one circumferential location (X; Y).
6. A slide ring seal according to any preceding claim, in which the bearing surface inclination (a;B) relative to the pressure ring (2) on the one hand and the respective sealing ring (6; 7) on the other hand prestresses the slide rings (4, 5) in the centripetal direction In such a manner that they rest with their inner surfaces against the circumference of the machine shaft (8) when the machine is inoperative.
7. A slide ring seal according to any preceding claim, in which the sealing rings (6,7) are closed over their circumference and form a permanent contact-free radial gap (b) for the primary seal with the shaft.
8. A slide ring seal according to claim 3, in which the slide rings (4, 5) are arranged axially spaced apart, an annular chamber (9) being formed between the slide rings (4, 5), the pressure ring (2) and the shaft (8) which annular chamber is acted upon by sealing fluid, and is connected through the pressure ring (2) to the recess (1) for the secondary seal.
9. A slide ring seal according to claim 8, in which the sealing fluid is supplied via at least one radially external bore (11) formed in the sealing housing (10) leading to the recess (1), and, via the pressure ring (2), to the annular chamber (9).
10. A slide ring seal according to claim 8, in which the sealing fluid is supplied from the cylindrical machine shaft (8), which is hollow and whose internal chamber (81) is connected to the annular chamber (9) for the flow of fluid via one or more apertures (12) in the shaft casing.
11. A slide ring seal according to any preceding claimin which the pressure ring (2) is radially resiliently supported at the base of the rotationally symmetrical recess (1) by means of a spring plate (3) extending round the recess in a corrugated fashion.
12. A slide ring seal according to claim 11, in which the spring plate (3) is held in a circumferential rebate in the pressure ring (2) which is open relative to the base of the recess (1).
13. A slide ring seal according to claims 9 and 11, in which the spring plate (3) has at least one aperture (13) for the passage of the sealing fluid, which aperture communicates with circumferential grooves (14, 15) in the housing and pressure ring respectively, which are open on both sides facing the spring plate (3), one groove being connected at the base of the recess (1) to the radially external bore (11) and the other at the base of the rebate of the pressure ring (2) via at least one radial aperture (16) in the pressure ring (2) to the annular chamber (9).
14. A slide ring seal according to claims 10 and 11, in which the pressure ring (2) at the base of the rebate for the spring plate (3) has a circumferential groove (15), which is open to the spring plate (3) and is connected via at least one radial aperture (16) in the pressure ring (2) to the annular chamber (9).
15. A slide ring seal according to claim 13 or 14, in which the circumferential groove (15) in the pressure ring is connected via circumferential intermediate chambers, formed between the spring plate (3) and the pressure ring (2) as a result of the spring corrugation, to further annular chambers, which are formed within the recess (1) between the sealing and slide rings (6, 4; 7, 5) and corresponding sections of the pressure ring (2).
16. A slide ring seal according to any of claims 11 to 15, in which the spring plate (3) is divided at at least one circumferential location (Z).
17. A slide ring seal according to any preceding claim, in which the pressure ring (2) comprises outer circumferential sections, which on the side remote from the base of the recess (1) extend at a radial distance from the respective sealing and slide rings (6,4; 7,5), and a central projection (17), which extends round the circumference and tapers symmetrically in the manner of a cone in the direction of the shaft circumference to form the bearing surface on both sides.
18. A slide ring seal according to any preceding claim in which the recess (1) is formed by two axially releasable housing components (18,19), which can be secured to one another axially and radially in concentric fashion.
19. A slide ring seal according to any claim in which the slide rings (4, 5) and/or the sealing rings (6, 7) are manufactured from a temperatureand wearresistant ceramic material.
20. A slide ring seal according to any preceding claim in which the surface of the machine shaft (8), at least in the regions of the slide rings (4, 5), is provided with a wear- and temperature-resistant ceramic coating.
21. A slide ring seal according to claim 19 or 20, in which the ceramic material is an oxide, carbide or nitride or a mixture of these.
22. A slide ring seal according to any of claims 1 to 18, in which the surface of the machine shaft (8), at least in the regions of the slide rings (4, 5) arranged on it, is provided with a metallic wear- and/or temperature-resistant coating.
23. A slide ring seal according to any of claims 1 to 18, 20 and 22, in which the sealing and slide rings (6, 7; 4, 5) are manufactured from a glassand/or carbon-fibre-reinforced plastics material, each consisting of an annular core reinforced by fibres extending in the circumferential direction and being stabilised in respect of wear-resistance by means of crossover fibre layers covering at least part of the outer surfaces.
24. A slide ring seal substantially as described herein with reference to any embodiments shown in the accompanying drawings.
25. A turbine engine including a seal as claimed in any preceding claim.
26. A method of operating a turbine engine as claimed in claim 25, in which the differential pressure between the chamber (R1) upstream and the chamber (R2) downstream of the seal, a pressure (P3) existing within the annular chamber (9), which is formed between sections of the shaft, the slide rings (4, 5) and the pressure ring (2), which pressure is lower than the pressure (P1) existing in a chamber (R1) upstream of the seal and greater than a pressure (P2) existing in the other chamber (R2) downstream of the seal, the sealing fluid for the primary and secondary sealing being made available from the chamber (R1) having the highest pressure (P1).