WO2003091609A1

WO2003091609A1 - Brush seals

Info

Publication number: WO2003091609A1
Application number: PCT/GB2003/001799
Authority: WO
Inventors: Ralph Franklyn John Flower
Original assignee: Cross Manufacturing Co 1938 Ltd
Current assignee: Cross Manufacturing Co 1938 Ltd
Priority date: 2002-04-26
Filing date: 2003-04-25
Publication date: 2003-11-06
Anticipated expiration: 2004-10-26
Also published as: AU2003227892A1

Abstract

A brush seal for effecting a seal between one component carrying that seal and a second component relatively movable with respect thereto. The brush seal comprises an elongate bristle pack (16) with a plurality of resiliently deformable bristles supported at one end on a carrier (10) adapted for mounting on the one component. The other ends of the bristles are free for contacting a sealing surface of the second component. The brush seal includes a front plate (14) bearing on the bristles at a region partway along their lengths so as to deform the bristles out of the plane of their undeformed state. This pre-loads the bristles before the seal is put into service. The bristles are preferably configured and deformed in such a way that they adopt a curved profile and contact the sealing surface at substantially 90°. The brush seal may be generally of an annular form and may be used between a housing (20) and a shaft (21) that extends through a bore in the housing.

Description

BRUSH SEALS

This invention relates to a brush seal adapted to effect a seal between a first component and a second component which is relatively movable with respect to the first component. The invention also extends to a method of sealing a first component to a relatively movable second component. It is frequently necessary to effect a fluid-tight seal between two relatively movable components, such as between a rotatable shaft and a housing having a bore through which the shaft extends. Innumerable seal designs have been proposed for this purpose and a machine designer has to select the most appropriate type of seal, having regard to the likely operating conditions to be encountered in service.

For the case of a shaft extending through a bore in a housing and where the shaft rotates at a relatively high speed and in the presence of pressurised hot gases, such as may be encountered in a gas turbine or a jet engine, various designs of brush seal have been developed in an attempt to overcome the unsatisfactory performance of simpler designs of seal, such as a labyrinth seal. In a brush seal, a plurality of fine bristles (often of metal alloys such as stainless steel or bronze wire, or of metallic fibres or synthetic fibres such as of Kevlar), are held in an annular carrier mounted on or to the housing, with the tips of the bristles wiping the surface of the shaft so as to effect a seal thereagainst. Alternatively, the carrier could be mounted on the shaft with the bristle tips wiping against the housing, but this configuration does generally give rise to higher relative speeds between the bristle tips and the component against which they effect a seal.

In a typical brush seal intended for use with a pressure difference thereacross, the bristles are supported against deflection in a direction parallel to the shaft axis for the greater part of the length of the bristles by means of an annular back plate disposed on the low-pressure side of the seal, with the tips of the bristles projecting radially beyond the back plate to wipe against the shaft surface to be sealed. Minor radial excursions of the shaft with respect to the housing are likely to occur during various operating conditions, and more significant radial excursions can be expected for instance as an engine rotor is being run up to operating speed. The clearance between the back plate and the shaft must be sufficient to accommodate the greatest expected excursion, with the bristles flexing as appropriate to maintain a seal despite those excursions. As the end region of the bristles is unsupported where the bristles project beyond the back plate to the shaft, should the pressure differential across the seal increase sufficiently, the bristles can be deflected towards the low pressure region and so lift clear of the shaft. Further, movement may take place between the individual bristles of the seal, consequent upon vibrations which inevitably occur under certain operating conditions and also on account of gas flow patterns. When such bristle movement occurs, again the bristles may be deflected by the pressure on the high pressure side of the seal, so leading to leakage.

It is a principal aim of the present invention to minimise the likelihood of leakage past the seal, during abnormal operating conditions such as when vibrations are occurring, or during an exceptional pressure difference across the seal.

According to one aspect of the present invention, there is provided a brush seal for effecting a seal between one component carrying the brush seal and a second component relatively moveable with respect to the one component, which brush seal comprises an elongate bristle pack having a plurality of resiliently deformable bristles supported at their one ends on a carrier adapted for mounting on the one component and having their other ends free for contacting a sealing surface of the second component, the brush seal including a front plate bearing on the bristles at a region part-way along their lengths to deform the bristles out of a plane containing the bristles in their undeformed state, thereby pre-loading the bristles before the seal is put into service.

According to a second but closely related aspect of this invention, there is provided a method of effecting a seal between the first and second relatively movable components using a brush seal having a bristle pack defined by a plurality of resiliently deformable bristles supported by a carrier and secured to one of the components so that the other free ends of the bristles contact a sealing surface of the other component, in which method the brush seal has a front plate which bears on the bristles at a region part-way along their lengths to deform the bristles out of a plane containing the bristles in their undeformed state, thereby pre-loading the bristles before the seal is put into service.

With the brush seal and method of this invention, the resiliently deformable bristles of the bristle pack are deformed out of their natural, or relaxed, state before the seal is put into service. Thus, any finishing operation of the seal such as machining should be performed with the bristles deformed in this way, such that the free ends of the bristles as deformed will appropriately wipe against the surface to be sealed, when deformed by the front plate. This pre-loading of the bristles reduces their tendency to move for example under conditions of vibration or exceptional gas pressure or flow. Normally, for a seal to be employed for example in a gas turbine where there is likely to be a significant pressure difference across the seal, the front plate should face the high pressure side of the machine and so deform the bristles towards the low pressure side.

By deforming the bristles as described above, the need to furnish a conventional back plate, to support the bristles against movement under gas load, may be reduced or even eliminated. However, despite the pre-loading of the bristles by the front plate, it would be possible for a sufficient pressure difference across the seal to move the bristles towards the low pressure side, so lifting the bristles off the front plate. To minimise the possibility of significant pressure loss and sealing under such conditions, it is preferred for the seal to include a back plate which extends towards the surface to be sealed, spaced from the bristles and on the other side of the bristle pack from the front plate. Such a back plate may be provided with a contact surface for the bristles solely in the region of the bristle pack contacted by the front plate, but on the other side of the bristle pack. Preferably, there is a gap between the contact surface of the back plate and the region of the bristles where the front plate bears thereon, which gap is only slightly greater than the thickness of the bristle pack when relaxed, to give clearance for the bristles to move during normal machine operation and yet to limit bristle movement under exceptional conditions.

In some embodiments of brush seal of this invention, the bristles contact the sealing surface of the second component at a non-perpendicular angle to that surface, considered in the direction normal to the length of the bristle pack. However, with a conventional brush seal, the bristles generally lie in a true radial plane (in the case of a circular seal) and there are certain circumstances where this can be advantageous.

In order to address this, the brush seal of this invention may have the bristles arranged in conjunction with the front plate such that the free ends of the bristles contact the sealing surface of the second component substantially at 90° to that surface, at least in the direction normal to the length of the bristle pack. Thus, for an annular seal which seals to a cylindrical sealing surface, the free ends should contact the sealing surface in a true radial plane, even if the free end of each bristle does not extend radially.

In preferred embodiments of this form of the invention, the elongate bristle pack is supported in the carrier such that the bristles leave the carrier at an acute angle to a plane perpendicular to the sealing surface. The front plate bears on the bristles at a region partway along their lengths and serves to deform the bristles so that their free ends contact the sealing surface of the second component at substantially 90° to that surface.

The bristle pack may be manufactured by conventional techniques as are often employed for brush seals. For example, in the case of metallic bristles, they may be secured between a pair of plates by a welding, brazing or soldering operation, or even by using adhesives, for low-temperature brush seals. Other assembly techniques may be employed, as are well known in the brush seal manufacturing art.

In a preferred design of brush seal of this invention, the carrier supporting the one ends of the bristles is located between a pair of guides permitting sliding movement of the carrier in the general direction of the length of the bristles. Spring means may be provided to urge the carrier towards the surface of the second component to be sealed or in the case of an annular seal, the natural resilience of the bristle pack may be employed for this purpose. The guides may be defined by the internal walls of a chamber within which the carrier is received, the first wall of the chamber defining the front plate of the seal and so being profiled in order to impart the pre-load to the bristles, before the seal is put into service. Similarly, a second wall of the chamber opposed to the first wall thereof may define a back plate for the bristles, as discussed above. Steps may be taken to minimise the friction between the carrier and the guides between which the carrier slides, to facilitate the accommodation of movement between the two components to be sealed, in a direction generally parallel to the length of the bristles.

The brush seal may be used to effect a seal between planar or curved surfaces, but mostly the brush seal will be of annular form, to effect a seal between a housing defining a bore through which a shaft extends, with the brush seal being secured on or to the housing and with the free ends of the bristles wiping against a cylindrical surface of the shaft. For such a case, the bristles may extend generally radially (ignoring the deformation of the bristles in the axial direction, by the front plate) or may be arranged to lie at an acute angle with respect to the true radial direction, when it is anticipated that a shaft always will rotate in the same sense, with respect to its housing. By way of example only, several specific embodiments of this invention will now be described in detail, reference being made to the accompanying drawings in which:-

Figure 1 is a diagrammatic section through a first embodiment of brush seal of this invention; Figure 2 is an end view on part of the seal of Figure 1 , as fitted to a housing for sealing to a shaft;

Figures 3 and 4 show second and third embodiments of brush seal of this invention, similar to that of Figure 1 ;

Figure 5 is a diagrammatic section through a fourth embodiment of brush seal;

Figures 6, 7, 8 and 9 show four further embodiments of brush seal; Figure 10 is a diagrammatic section similar to that of Figure 1 but showing a modified form of brush seal; and

Figure 11 is a similar section but of a further modified form of brush seal. Referring initially to Figures 1 and 2, there is shown a first embodiment of brush seal of this invention as comprising a carrier 10 of generally L-shaped section and including a base region 11 and a back plate 12. The carrier 10 is of annular shape, and so the outer surface 13 of the base region 11 is of cylindrical form. The carrier 10 includes a front plate 14 having an increased thickness part 15 which is juxtaposed to the base region 11 of the carrier, a bristle pack 16 being supported between the base region 11 and the increased thickness part 15 of the front plate 14. The base region 11 , bristle pack 16 and increased thickness part 15 of the front plate are all metallic and are secured together by means of a circumferential weld bead 17, extending around the periphery of the annular seal. The bristles themselves may be of stainless steel wire, a bronze wire or other suitable materials such as synthetic fibres which may carry metallic threads, having regard to the intended use of the seal. As shown in Figure 2, the bristles may typically extend at 45° to the true radial direction or at some other angle, again having regard to the intended use of the seal. The front plate 14 has a radially inner part 18 which is bent back towards the back plate 12, so deforming the bristles of the bristle pack 16 to take up a curved form, as shown in Figure 1. The radially inner edge of the back plate 12 is profiled so as to lie essentially parallel to the deformed bristles of the bristle pack, but with a small clearance L between the bristles and that radially inner edge.

In use, the brush seal of Figure 1 is suitably held to a housing 20 having a bore through which a shaft 21 extends. For example, the housing may be counter-bored around the shaft bore, the counter-bore diameter corresponding to that of the outer surface 13 of the carrier 10, such that the seal may be received in the counter-bore, coaxial with the shaft. The bristles of the pack 16 should have a finished length such that the free ends 22 of the bristles wipe against the cylindrical surface of the shaft 21, to effect a seal thereagainst. Though the length of each bristle may extend essentially radially (ignoring the bend imparted by the front plate 14), for many applications it is preferred for the bristles to extend at an angle to the true radial direction, as shown in Figure 1. In this way, the bristles may have a better sealing effect against the shaft, as the shaft rotates.

In view of the bending of the bristles imparted by the front plate, the bristle pack takes up a generally conical form, with each bristle subjected to a pre-load by the front plate. This restricts relative movement between the bristles of the bristle pack and so minimises the amount of movement that may otherwise take place during use of the brush seal, due to machine vibration and gas flow patterns.

Under some conditions of service, sufficient gas pressure may be encountered on the high pressure side of the seal (the front plate side of the seal) further to deflect the bristles toward the back plate. However, such deflection of the bristles is restricted by the radially inner part of the back plate and the maximum permitted movement of the bristles in this way is limited to the clearance L, defined above.

Referring now to Figure 3, there is shown a second embodiment of seal of this invention. In this embodiment, and also for the following embodiments, like reference numbers are used to indicate like parts and those parts will not be described again. In the embodiment of Figure 3, both the front plate 24 and the back plate 25 are configured more closely to follow the curvature of the bristles, imparted by the configuration of the front plate 24. This reduces the volume within the seal element adjacent the bristle pack, but in other respects the embodiment of Figure 3 operates in much the same manner as does the seal of Figures 1 and 2.

In the third embodiment of seal, shown in Figure 4, a seal element is assembled from the bristle pack 16 between a pair of simple annular rings 27 and 28, a weld bead holding the assembly together, as discussed above. An annular groove 29 is formed in an end face of housing 20, one ring 27 of the seal being received in that groove and the other ring 28 being received in a corresponding groove formed in an annular front plate 30. That front plate is bolted to the housing by a plurality of bolts 31 on a common pitch circle, so securely holding the seal in position. The front plate 30 is profiled in a generally similar manner to that described with reference to the first and second embodiments, and the housing itself is profiled at 32, to define a back plate providing the required clearance L between the radially inner edge of the back plate and the bristles of the bristle pack.

The brush seal element made up from the bristle pack and rings 27,28 of the third embodiment may be located within a guide assembly which is itself secured to a housing, rather than directly to the housing as shown in Figure 4. Figures 5, 6 and 7 show three such possibilities.

In the embodiment of Figure 5, there is shown a chamber defined by a simple L-shaped component 34 having a base region 35 and defining a back plate 36. A front plate 37 is welded to the base region 35, and serves to deform the bristles of the bristle pack 38 back towards the back plate, but with a clearance L left between the bristle pack and the radially inner edge 39 of the back plate 36. The brush seal element is free to slide within the chamber between the back plate and the front plate, over a limited range of movement. This allows the seal element to follow shaft excursions such as may occur during the running up to speed of the rotor of a gas turbine or similar engine, even though the chamber remains stationary, bolted or otherwise secured to the housing.

In the embodiment of Figure 6, a more rigid design of chamber is provided, the front plate 41 being of similar strength to that of the back plate 36. Here, the front plate 41 is secured to the base region 35 of the L-shaped carrier by an edge of the base region being turned over, to grip the front plate. As shown, notches 42 are formed through ring 27, to allow equalisation of pressure, above and below the rings 27 and 28.

The embodiment of Figure 7 is generally similar to that of Figure 5, except that the front plate 37 is held in position by a double-coil retaining ring 43, fitted into an annular groove 44 formed in the base region of the carrier.

Figures 8 and 9 show two further possibilities, these broadly corresponding to the arrangement shown in Figure 6. Here, the rings 27 and 28 have appropriately been profiled, in order to reduce friction between those rings and (in Figures 8 and 9) the back plate, but possibly also the front plate (in Figure 9). In other respects, the embodiments of Figures 8 and 9 are similar to those of the previous embodiments. In Figure 10, there is shown a carrier 50 including a back plate 51 and a front plate 52 which together with the back plate defines a cavity 53 within which is mounted a bristle pack. The bristles 55 of the bristle pack are held between mounting bars 56,57 and the assembly is integrated into a unit by means of a weld bead 58 or some other appropriate jointing technique, depending upon the materials from which the bristles are made. For example, the bristles and bars may be brazed or soldered together, or, depending upon the intended application, an adhesive may be employed.

As can be seen in Figure 10, the mounting bars 56,57 are configured such that when their outer surfaces are parallel to or perpendicular to the sealing surface 59, the bristles leave the bars at an acute angle to the sealing surface. The bristles are deformed to take up a curved profile by the front plate 52, bearing on the bristles close to their free ends 60. The arrangement of the bars 56,57 and the front plate 52 is such that a sufficient curve is imparted to the bristles, in order to have the free ends 60 of the bristles contacting the sealing surface 59 substantially at 90°, pre-loading the bristles as described in said application. Thus, the free ends of the bristles lie essentially in a true radial plane, though the free ends of the bristles could be inclined to a true perpendicular to the sealing surface at the point of contact, as shown in Figure 2 of said application. As with the embodiments described in said application, a small clearance may exist between the bristles and the back plate, to restrict the maximum movement of the bristles towards the back plate, when the seal is in service and subjected to a high pressure on the front plate side of the seal.

The arrangement of Figure 10 may be used to effect a seal on a planar sealing surface, or that sealing surface could be the outer cylindrical surface of a shaft. Particularly in the latter case, the bars 56,57 may float to a small extent within the cavity 53, in order to obtain a good sealing function against the surface.

The arrangement of Figure 11 is similar in principle to that of Figure 9, but differs in that a carrier 62 is defined by a back plate 63 and a front plate 64 which plates together serve to clamp the bristles, with a weld bead 65 (or some similar jointing technique) unifying the assembly. The bristles leave the clamping region of the carrier at an acute angle to the sealing surface 59 but the front plate 64 is profiled suitably so that the free ends 66 of the bristles again contact the sealing surface substantially at 90°. Though the brush seal embodiments described above are of annular form and are intended to be used to effect a seal between a housing and a shaft extending through a bore in that housing, the brush seal could be of linear form, to effect a seal between two relatively moveable components, each having substantially planar surfaces. Further, the brush seal could be configured to have some special shape, to suit other relatively moveable components, perhaps having arcuate surfaces.

Claims

1. A brush seal for effecting a seal between one component carrying the brush seal and a second component relatively moveable with respect to the one component, which brush seal comprises an elongate bristle pack having a plurality of resiliently deformable bristles supported at their one ends on a carrier adapted for mounting on the one component and having their other ends free for contacting a sealing surface of the second component, the brush seal including a front plate bearing on the bristles at a region part-way along their lengths to deform the bristles out of a plane containing the bristles in their undeformed state, thereby pre-loading the bristles before the seal is put into service.

2. A brush seal as claimed in claim 1 , wherein the bristles of the bristle pack are normally linear but are deflected to assume a curved profile by the front plate bearing on the bristles.

3. A brush seal as claimed in claim 1 or claim 2, wherein a clearance is provided between the bristles and the front plate, over that part of the length of the bristles between the carrier ends thereof and the region where the front plate bears on the bristles.

4. A brush seal as claimed in any of the preceding claims, wherein there is provided a back plate for the bristles, on the side of the bristle pack opposed to the front plate.

5. A brush seal as claimed in claim 4, wherein the back plate is provided with a contact surface for the bristles solely in the region of the bristle pack contacted by the front plate, but on the other side of the bristle pack.

6. A brush seal as claimed in claim 5, wherein there is a gap between the part of the front plate bearing on the bristles and the contact surface of the back plate which gap is slightly greater than the thickness of the bristle pack, thereby to give clearance for the bristles to move.

7. A brush seal as claimed in any of claims 1 to 6, wherein the configuration of the carrier for the one ends of the bristles and of the front plate bearing on the bristles at a region partway along their lengths is such to deform the bristles so the free ends thereof contact the sealing surface of the second component at substantially 90° to that sealing surface.

8. A brush seal as claimed in claim 7, wherein the one ends of the bristles are supported in a mount which mount is disposed within the carrier and is free to perform small excursions with respect thereto.

9. A brush seal as claimed in any of claims 1 to 7, wherein the carrier comprises two adjacent plates between which the one ends of the bristles are secured.

10. A brush seal as claimed in claim 9, wherein the bristles are secured to the two plates of the carrier by one of welding, brazing or soldering.

11. A brush seal as claimed in any of claims 1 to 7, wherein the carrier supporting the one ends of the bristles is located between a pair of guides permitting floating movement of the carrier in the general direction of the length of the bristles.

12. A brush seal as claimed in claim 11 , wherein the guides are defined by internal walls of a chamber within which the carrier is received, a first wall of the chamber also defining the front plate of the seal.

13. A brush seal as claimed in claim 12, wherein a second wall of the chamber opposed to the first wall thereof defines a back plate for the bristles.

14. A brush seal as claimed in any of claims 10 to 13, wherein the contacting areas of the carrier and the guides are profiled to minimise the contact friction therebetween.

15. A brush seal as claimed in any of the preceding claims, wherein the seal is of generally annular form, for effecting a seal between a housing and a shaft extending through a bore in the housing, the brush seal being adapted for mounting on the housing so that the free ends of the bristles may wipe over a cylindrical surface of the shaft, the bristles being deformed by the front plate to take up a conical form.

16. A brush seal as claimed in claim 15, wherein the bristles extend from their one ends to their other ends at an acute angle with respect to the true radial direction of the annular brush seal.

17. A method of effecting a seal between the first and second relatively movable components using a brush seal having a bristle pack defined by a plurality of resiliently deformable bristles supported by a carrier and secured to one of the components so that the other free ends of the bristles contact a sealing surface of the other component, in which method the brush seal has a front plate which bears on the bristles at a region part-way along their lengths to deform the bristles out of a plane containing the bristles in their undeformed state, thereby pre-loading the bristles before the seal is put into service.

18. A method as claimed in claim 17, wherein the free ends of the bristles contact the sealing surface of the second component at substantially 90° to that sealing surface.