GB2397353A

GB2397353A - A sealing arangement for a labyrinth seal for a shaft

Info

Publication number: GB2397353A
Application number: GB0301181A
Authority: GB
Inventors: Richard Nicolson
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2003-01-18
Filing date: 2003-01-18
Publication date: 2004-07-21
Also published as: GB0301181D0

Abstract

A sealing is formed from a number of sealing elements (1, 21, 31, 41, 51) held in association in order to create a barrier as part of a labyrinthine seal for a shaft (47, 57). Each sealing element (1, 21, 331, 41, 51) is independently secured to the shaft (47, 57) to allow for seating of the sealing element (1, 21, 31, 41, 51) whilst consistently presenting the barrier. Typically, each sealing element (1, 21, 31, 41, 51) is secured to the shaft (47, 57) through a dove-tail relationship of a bulbous end (2, 22, 32, 42, 52) of the element (1,21, 31,41, 51) within a slot (46, 56) of the shaft (47, 57). Thus, rotation of the shaft (47, 57) creates centrifugal forces which in turn generate a sealing force (S, SS) creating the association between adjacent sealing elements (1, 21, 31, 41, 51) to form a barrier and also location of the seal element (1, 21, 31, 41, 51) on the shaft (47, 57). Typically, association is through fin edge (6, 7) abutment between adjacent seal elements (1) or overlap between fin segments (26, 27, 37, 47) of adjacent seal elements.

Description

- 1 2397353 A Seal Arrangement The present invention relates to seal

arrangements and more particularly to labyrinth seals typically used In large turbine engines.

Large turbine engines operate by through combustion to generate rotation of a shaft. Along the main shaft of a large turbine, seals are provided to limit unwanted air leakage from one zone to another. These seals are typically of a labyrinth type whereby close proximity between opposed parts of the seal create a marked resistance to flow across that seal. These opposed seal parts are often upstanding elements adjacent one another. On a main shaft, it has been known to provide a J-shaped seal strip with an upstanding part of the strip presented in order to create the labyrinth seal while a curved bottom part is held in place within a slot created in the shaft. T ypically, such location is provided by a socalled caulking wire which extends about the shaft causing force fitting of the J-shaped seal member into the slot of the shaft. It will be appreciated that such J-shaped seal strips are susceptible to becoming loose and even falling out of location about the shaft. A modification is therefore to provide an overhanging slot for location of the J-shaped seal strip but nevertheless that overhang has been found to open due to thermal cycling of the shaft. In the above circumstances, displacement or fall out of J-shaped seal elements or fins will significantly alter the efficiency of the gas turbine. Furthermore, if or when the J- shaped seal strip fails, the whole seal strip must be replaced or adjusted greatly increasing the complexity and cost of replacement.

In accordance with the present invention there is provided a seal arrangement for a shaft wherein a seal Is secured in use to a shaft to present a barrier as part of a labyrinth seal, the arrangement characterized in that the barrier is formed by a plurality of seal elements held in close association to form the barrier, such close association allowing independent seating of each seal element whilst consistently presenting the barrier to form the labyrinth seal.

Preferably, each seal element is secured to the shaft through a flange or - 2 screwthread or dovetail or firtree association of a mounting base of the sealing element. Advantageously, each seal element includes a bulbous base, which defines shoulders extending in opposite directions in order to engage in use with respective seal surfaces of a slot in a shaft. That bulbous base acts as a mounting base for the sealing element.

Typically, each seal element includes a fin upstanding from the slot.

Preferably, the oversized shoulders of the seal element are in a substantially dovetail relationship with the slot formed in the shaft.

Preferably, the inter-association between respective seal elements is by edge to edge abutment between adjacent fins. Alternatively, interassociation between respective seal elements is through fin overlap between adjacent seal elements.

Possibly, such overlap is through laterally extending flat portions or segments of the fins in adjacent seal elements. Such laterally extending portions may be configured with alternate off-set between adjacent fins at either side of each seal element.

Alternatively, such overlapping portions may have a stepped displacement to allow overlap between adjacent fins of each seal element. Such stepped displacement in the overlapping portions may be at one side or both sides of the fins of each seal element.

Advantageously, each seal element includes a shroud plate directly above the slot.

Possibly, a sealing force is provided in use by rotation of the shaft to generate a centrifugal force urging the oversized shoulders into engagement with the sealing surfaces of the slot.

Normally, the shoulders and the sealing surfaces are in an angular relationship such that greater centrifugal force will increased the sealing force provided. - 3

Also in accordance with the present invention is a turbine engine incorporating a seal arrangement as described above.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which; Figure 1 is a perspective view of three sealing elements in accordance with a first embodiment of the present invention; Figure 2 is a perspective view of sealing elements in accordance with a second embodiment of the present invention; Figure 3 is a perspective view of sealing elements in accordance with a third embodiment of the present invention; Figure 4 is a cross-section of a seal arrangement in accordance with the present invention; Figure 5 is a perspective view of sealing elements in accordance with a fourth embodiment of the present invention; and, Figure 6 is a cross-section of a sealing arrangement incorporating sealing elements in accordance with the fourth embodiment of the invention depicted in Figure 5.

The present invention provides a sealing arrangement which comprises a number of individual sealing elements which are collectively arranged about a shaft in order to present a barrier as part of a labyrinth seal. Each seal element can be secured to the shaft in an appropriate way and substantially independent of other sealing elements to allow individual installation or removal along with - 4 adjustment. Each sealing element is therefore individually seated about the shaft such that in combination with other sealing elements a ring of such elements is provided to create a barrier. The sealing element can be secured through a screwthread or flange or firtree type securing mechanism typically used to mount onto rotors but the preferred method of securing the sealing elements to the shaft is through a dovetail approach. In such circumstances, a mounting end of each sealing element is located within a substantially reciprocal By shaped slot within the shaft. The mounting end which has a bulbous shape therefore dovetails into a similarly shaped slot to achieve appropriate presentation of parts of the sealing element to form the sealing barrier as part of a labyrinth seal for the shaft. The present invention is described principally with respect to such a dovetail securing mechanism but it will be appreciated that other securing mechanisms can be used.

Figures 1 to 3 respect rely illustrate three embodiments of sealing elements in accordance with the preser invention. As indicated above. a common feature between all three embodiments is a bulbous or oversized mounting or base portion which includes oversized shoulders. In use, these oversized shoulders will engage with sealing surfaces of a slot formed in a shaft. Typically, that shaft will rotate to generate centrifugal forces which force the oversized shoulder portions into stronger sealing engagement with the sealing surfaces of the slot at higher shaft rotation speeds.

Figure 1 illustrates in a perspective view a number of sealing elements 1 in accordance with a first embodiment of the present invention. Thus, the sealing elements 1 include a bulbous base 2 incorporating respective oversized shoulders 3,4 extending in opposed direction either side of an upstanding fin element 5. In use, the elements 1 will be arranged to form a ring within a slot of a shaft (not shown).

Respective opposed edge surfaces 6,7 of the fins 5 are held in an abutting association in order to create an upstanding seal collar barrier which in association with other structures (not shown) will form a labyrinth seal.

The seal elements 1 will be sized as required in accordance with a sealing - 5 function created within the labyrinth seal as described and in accordance with known theory. It is not critical that the abutting edge surfaces 6,7 of the fins 5 create a perfect seal but rathe in combination with other elements establish a labyrinthine path for any flow across the seal. Nevertheless, in accordance with the present invention, the seal elements 1 are substantially independently located within the slot and therefore can adjust lateral). and radially as well as pivot about the abutting edge surfaces 6,7 within the seal. Thus, the seal elements 1 can adjust their seating within the slot dependent upon prevailing circumstances including loading. Clearly, within a turbine engine the shaft upon much the seal elements 1 will be located will be thermally cycled and therefore this adjustability between the elements 1, 2 will ensure that an appropriate seal is maintained through that thermal cycling whilst the bulbous base 2 through the oversized shoulders 3,4 ensure that there is appropriate presentation of the fin in an upright configuration and that if an opening in the slot is eroded then a seal is still maintained ah a substantially central location of the fin. However, as indicated above, alternative means of securing the elements to form the seal barrier may be used.

Figure 2 illustrates a number of seal elements 21 in accordance with a second embodiment of the present invention. Thus, the seal elements 21 again have a bulbous base 22 with oversized shoulder portions 23,24 extending in opposite directions we a fin element 25 upstanding. As previously, the bulbous portion 22 is located with1 a slot formed in a shaft (not shown) in order to create a sealing arrangement in accordance with the present invention. The oversized shoulder portions 23,4 are held in a sealing engagement with sealing surfaces of that slot in use. In the second embodiment of the invention depicted in Figure 2 the upstanding fins 25 include overlapping segments 26,27 at each end. In such circumstances, although the bulbous base portion 22 of each element 21 may be in abutting engagement with its adjacent seal element 21 the end segments 26,27 are staggered or inter-leaved as depicted in Figure 2 such that the fins 25 of each seal element 21 create a sea barrier for use within a labyrinthine seal as described previously. Clearly, the degree of overlap between the overlapping end segments 26,27 is a design choice and dependent upon seal hi 6 efficiency as well as weight implications. It is not imperative that the associated elements 21 and segments 26,27 provide a perfect barrier but only an adequate barrier as part of a labyrinth seal. The elements 21 and segments 26,27 may be in forced association due to the means by which the element is secured to the shaft or rotationally induced centrifugal forces.

Figure 3 is a perspective view of a number of seal elements 31 in accordance with a third embodiment of the present invention. The seal elements 31 include a bulbous base 32 which extends in opposite directions in order to present oversized shoulders 33,34 either side of an upstanding fin 35. As previously, with the first and second embodiments respectively depicted in Figures 1 and 2, the seal elements 31 are associated together in use to form a ring such that the bulbous portion 32 is located within a slot formed in a shaft in order to present the upstanding fins 35 as a barrier which forms part of a labyrinthine seal. However, alternative means of securing the elements 31 to the shaft may be used.

In accordance with the third embodiment, the upstanding Ens 35 incorporate step displaced overlapping segments 36 such that there is at least partial overlap between those segments 36 and part of a neighbouring fin 35. It will be appreciated that step displaced overlapping segments may be provided at either end of the fin 35 such that as shown in broken line a further overlapping segment 37 could be provided for a better barrier formed by juxtaposed fins 35.

In the first, second and third embodiments of the present invention described above, it will be appreciated that the barrier created by the upstanding fins 5,25,35 either directly or through overlapping segments 26,27 creates a barrier seal arrangement for use within a labyrinthine seal arrangement.

Figure 4 is a cross-sectional illustration of a seal arrangement in accordance with the present invention. Figure 4 is substantially generic with respect to the embodiments depicted in figures 1 to 3. Thus, a seal element 41 includes a - 7 bulbous base 42 which provides oversized shoulders 43,44 with a fin 45 extending upwardly from the base 42. The seal element 41 is located within a channel or slot 46 within a shaft 47. Typically, this shaft 47 may be the main shaft of a turbine engine. As that shaft 47 rotates a centrifugal force is created in order to provide a sealing force between the shoulders 43,44 and seal surfaces 48,49 of the slot 46. The upstanding fin 45 is located in an opening of the slot 46.

Generally. the bulbous base 42 is smaller than the slot or channel 46 to facilitate lateral slide assembly of the seal elements 41 into the slot 46 upon fabrication. The angular configuration between the shoulders 43, 44 and the seal surfaces 48,49 is such that there is a seating effect due to the sealing force created by centrifugal rotation which positions the upstanding fin 45 substantially as required. The relatively large contact surface between the shoulders 43,44 on the surfaces 48,49 diminish the prospect of abrasion or at least extend the operational life of the slot 46 and seal element 41. Rapid abrasion or other distortion of the slot or seal element can lead to displacement of the desired position of the outstanding fin 45 as part of a labyrinthine seal and eventually fallout of the seal element 41 from the slot 46. Similarly, by providing shoulders 43,44 which extend in opposite directions the present seal arrangement has a similar location effect irrespective of which side of the barrier created by the fins 45 is subject to load pressure in a ring combination as described previously with respect to Figures 1,2 and 3.

Generally, the bulbous base 42 is of a similar shape to the inner cavity 40 of the slot 46. Thus, the slopes or angular inclination between the shoulders 43,44 on the sealing surfaces 48,49 are such that there is a tendency towards flat face-to-face abutment between those shoulders 43,44 and the surfaces 48,49. This tendency to flat abutment provides a predictability with regard to positioning of the fin 45. Generally.

such positioning will be central within the opening of the slot 46.

As indicated above, generally the sealing force provided in the direction of - 8 arrowhead S is created by rotation of the shaft 47 but alternatively it will be understood that the bulbous base 42 could be a snug fit within the cavity 40 or that cavity 40 could be hydraulically pressurised in order to create the sealing pressure between the shoulders 43,44 and the sealing surfaces 48,49. However, care should be taken with respect to the desirable position adjustability of individual seal elements 41 within the slot 46 in accordance with the present invention. The present seal arrangement comprises a plurality of seal elements in abutment or close association through overlapping sections as described previously in order to create the barrier. The individual sealing elements 41 can be marginally displaced within the overall ring created by the seal elements in order to relieve localised stress and so prolong sealing arrangement life.

These overlapping sections between adjacent seal elements 41 as depicted in cross-section in Figure 4 are shown as broken line 39. Thus, by combination of a number of sealing elements a desired upstanding barrier is created in a sealing arrangement which forms part of a labyrinthine seal for the shaft 47. In the embodiments shown, these seal elements 41 are held in a sealing engagement with surfaces 48,49 of a slot within the shaft 47. This sealing engagement may be supplemented centrifugal force. In operation the sealing elements 41 are retained in abutment by a sealing force S but are also adjustable for position where required to relieve stress in the seal barrier created by the fins 45 about the shaft 47. In such circumstances, the individual seal elements 41 have a bias or tendency towards the desired presentation of the upstanding fin 45 due to the angular relationship between the shoulders 43,44 and the surfaces 48, 49. Such contact is over a wide area and there is greater frictional resistance to movement which In turn can cause abrasion but also due to the relatively large area of contact the effects of such abrasion over unit time will be greatly diminished and presentation of the fin 45 in the desired orientation continued for a longer period of operation.

Figures 5 and 6 illustrate a fifth embodiment of the present invention which is a further refinement for greater overall sealing effect. Thus, a number of sealing elements 51 are closely associated with each other in order to create through - 9 - upstanding fin parts 55 a barrier for use within a labyrinthine seal. The seal elements 51 comprise a bulbous base 52 which presents shoulders 53,54 to sealing surfaces 58,59 of an aperture 56 in a shaft 57. Typically, the shaft 57 is the main shaft of a turbine engine and the barrier created by fins 55 is part of a labyrinthine seal within that turbine engine. Alternative means of securing the elements to the shaft could be used, including screwthread attachment, flange assembly and firtree root mounts in reciprocal cavities in the shaft.

As indicated previously, during normal operation the bulbous base 52 of the sealing element 51 is forced by centrifugal forces due to rotation of the shaft 57 to create a sealing force between the shoulders 53,54 and the surfaces 58,59. In such circumstances, egress of combustion gas or other elements into the slot 56 is prevented. However, in some circumstances, prevention of egress of contaminants or other materials into the slot 56 may not be possible whilst the shaft 57 is not rotating, or is not rotating with sufficient rapidity to create the necessary sealing force in the direction SS. In such circumstances, as illustrated in the fifth embodiment depicted in Figures 5 and 6, a shroud seal 60 is provided either side of the fin 55. Thus, the shroud seal 60 sits above an opening in the slot 56 so that as depicted in Figure 6 a bottom surface of the shroud seal 60 is slightly above an upper surface of the shaft 57 about the opening of the slot 56. In this configuration (Figure 6) a sealing force between the shoulders 53,54 and the surfaces 58,59 is provided by the centrifugal effect of rotating the shaft 57. However, when there is no rotation of the shaft 57, or insufficient rotation to create the necessary centrifugal force, the shroud seal 60 rests upon the upper surface of the shaft 57 about the opening of the slot 56 in order to provide a seal which prevents egress of contaminants etc. into the slot 56. Generally, the weight of the bulbous base 52 is utilised in order to create the sealing effect of the shroud seal 60.

As can be seen in Figure 5 where inter-leaving or overlapping fins 55 are utilised a shroud seal 60 on one side of the fin 55 extends for the full length of that fin 55 but on the other side a shroud seal 60a is provided which acts between the overlapping - 10 sections of the fins 55 either side of a middle seal element 51. The overlapping portion is depicted in Figure 6 by broken line 61.

As an alternative to using a bulbous base the sealing elements in accordance with the present invention could be secured to the shaft 57 through any conventional means such as flanges, bolts, firtree or other techniques. It is the close abutment or overlap between adjacent fins in order to provide a barrier and so sealing function as part of a labyrinth seal which defines the core of the present invention.

Centrifugal force in addition to creating a sealing force between a sealing element and a mounting slot can also be utilised to cause the fins of adjacent sealing elements to lean against each other to provide stiffening and dampening as required.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon. - 11

Claims

Claims 1. A seal arrangement for a shaft wherein a seal is secured in use

to a shaft to present a barrier as part of a labyrinth seal, the arrangement characterized in that the barrier is formed by a plurality of seal elements held in close association to form the barrier, such close association allowing independent seating of each seal element whilst consistently presenting the barrier to form the labyrinth seal.
2. An arrangement as claimed in claim 1 wherein each seal element is secured to the shaft through a flange or screwthread or dovetail or firtree association of a mounting base of the sealing element.
3. An arrangement as claimed in claim 1 wherein each seal element includes a bulbous base which defines shoulders extending in opposite directions in order to engage in use with respective seal surfaces of a slot in a shaft.
4. An arrangement as claimed in any of claims 1,2 or 3 wherein each seal element includes a fin upstanding to define the barrier.
5. An arrangement as claimed in any preceding cla m wherein said association between adjacent seal elements is by abutment.
6. An arrangement as claimed in any of claims 1 to 4.vherein association between adjacent seal elements is through overlap segments extending laterally from each seal element to overlap with adjacent seal elements in the arrangement.
7. An arrangement as claimed in claim 6 wherein the overlap segments are step displaced with respect to adjacent seal elements.
8. An arrangement as claimed in any preceding claim wherein each seal element - 12 includes a shroud seal associated with the seal element in order to provide sealing about the means by which the sealing element is secured to a shaft.
9. An arrangement as claimed in any preceding claim wherein a sealing force is provided in use by rotation of the shaft to generate a centrifugal force urging the sealing element into association with the shaft.
10. An arrangement as claimed in claim 9 when dependent upon claim 3 wherein the shoulders and sealing surfaces are urged into compressive engagement by the sealing force created by centrifugal forces caused upon rotation of the shaft.
11. An arrangement as claimed in claim 10 wherein the shoulders and the sealing surfaces are in an angular relation such that greater centrifugal force increases the sealing force in order to achieve appropriate presentation of the barrier.
12. A sealing arrangement substantially as hereinbefore described with reference to the accompanying drawings.
13. A turbine engine incorporating a sealing arrangement as claimed in any preceding claim.
14. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.