GB2291939A

GB2291939A - Brush seal for a turbo-engine

Info

Publication number: GB2291939A
Application number: GB9515468A
Authority: GB
Inventors: Walter Liebald; Lothar Reisinger; Thomas Miller; Klemens Werner
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1994-07-30
Filing date: 1995-07-28
Publication date: 1996-02-07
Anticipated expiration: 2015-07-28
Also published as: GB9515468D0; ITMI951467A0; FR2723163A1; IT1275498B; ITMI951467A1; GB2291939B; DE4427265C1; FR2723163B1

Abstract

The brush seal is intended to seal off spaces at different pressures. The bristles (B) are held by a clamping tube (2) on a core (1) extending over the periphery, project from a longitudinal slot (6) in the clamping tube (2) and extend by way of an axial peripheral gap (U) in a sealed manner towards the rotor (7). The longitudinal slot (6) is formed by portions (C, D) of the clamping tube (2) bent over in a curve towards the bristles (B). Furthermore, the bristles (B) are arranged between parallel faces of the axial peripheral gap (U) over the greater part of their longitudinal extension. In addition, the bristles (B) in the axial peripheral gap (U) extend in a sealed manner along one gap face and form an axial gap (A) opposite the other gap face. A wall portion (3) facing the space (R1) of higher pressure has axially traversable slots (8) through which the axial gap (A) is acted upon with high-pressure fluid (F). <IMAGE>

Description

Brush Seal for a Turbo-Engine The present invention relates to a brush seal for a turbo-engine between spaces under different pressures in which bristles are held on a core by a clamping tube extending over the periphery, wherein the bristles project from a longitudinal slot in the clamping tube and extend by way of an axial peripheral gap in a sealed manner towards a rotor.

A brush seal of this type is known from DE-OS 39 07 614. In this case the clamping tube is secured in an annular space adapted to the external circular shape of the clamping tube, the bristles being arranged opposite slightly rounded corners (shown only diagrammatically) of the tube slot. Starting from the longitudinal slot in the clamping tube, the bristles are first passed directly through a short portion of an axial peripheral gap. In accordance with the merely diagrammatic illustration in this case, the front wall portion - starting from the short axial portion of the peripheral gap - forms an abrupt enlargement of the gap in front of the bristles; only the rear wall portion terminates radially on the inside in a region close to the rotor and forms an abutment face for the bristles.

The bristles are therefore forced in axially by the said short portion of the peripheral gap; they then expand from that point in the manner of a bundle with an increasing radial extension towards the rotor.

It has been found in practice that partial edge compression occurs on the bristles along the slightly rounded corners, with extremely small radii, on the longitudinal slot of the clamping tube, and this can result in premature wear of the bristles; such wear occurs in particular in conjunction with the desired use of very fine or extremely thin bristles or fibres. The origin of this edge compression lies in the insufficiently scrupulous observation of component dimensions and in the nature of securing and joining up the brushes (core) during production.

A further disadvantage of the known brush seal is that comparatively high differential pressures cannot readily be controlled in a sealed manner. At high differential pressures the bristles are caused to vibrate predominantly axially. These vibrations are caused inter alia by uncontrolled secondary high-pressure fluid flows. These high-pressure fluid flows flow into the bristles on the radially inner side (primary seal).

The said bristle vibrations result in wear of the respective wall portions, in particular radially on the inside and along the gap faces, and consequently in an increased susceptibility to wear of the bristles themselves, and this in turn drastically shortens the life of the brushes.

On the other hand, it must be taken into consideration that the bristles of a brush seal are subjected not only to peripheral but also to axial deflexions with respect to eccentricities of the shaft caused by operational conditions. In this respect it is difficult on the one hand to avoid the above-mentioned vibrations and on the other hand to provide the brush with a certain "snug fitting" which is necessary to compensate for resilient deformation of the bristles.

It has already been proposed in the case of a brush seal to provide individual bores in the radially outer peripheral region of the wall portion facing a high-pressure side, in order to aerate a front peripheral recess between the wall portion and the bristles. This proposed step, however, has been found to be insufficient to overcome the problem of vibration indicated earlier.

An object of the invention is to provide a brush seal, of the type defined in the introduction and as known from DE-OS 39 07 614, in which the bristles are constructed and arranged in a wear-resistant manner, in particular with respect to overcoming large pressure differences, and in which optimum sealing is provided.

The invention provides a brush seal as claimed in Claim 1.

The axially traversable slots make it possible for the bristles to be acted upon - as a pack sealed in the axial and peripheral directions - by the high-pressure fluid by way of the respective small axial gap on the high-pressure side over a large area in the peripheral and radial directions, the high-pressure fluid flowing at the radially inner end of the small axial gap with the remaining portion of high-pressure fluid into the primary seal and then from there into a space of lower pressure.

According to the invention the width of the small axial gap may be estimated essentially as being 1/10 of the maximum width of the pack of brushes.

As a substantial proportion or the substantial proportion of high-pressure fluid can be supplied to the seal by way of the respective arrangement and design of the axially traversable slots through a first space and from there by way of the small axial gap, the bristle vibrations which occur can be prevented. Comparatively large radii of curvature are preferably present at the longitudinal slot in the clamping tube opposite the bristles (Claim 2), so that the edge compression of the relatively thin bristles as noted above can be prevented.

With respect to comparatively high temperatures and rotational speeds, the use of bristles produced from silicon carbide is advantageous (Claim 3). These bristles have excellent resistance to temperature and wear. The bristles may be produced as silicon-carbide fibres with diameters of up to 0. 14 mm or slightly over. In addition, with a pack of bristles which is sealed in the axial and peripheral directions, a reliable hold is provided on the housing formed by two wall portions (Claim 4).

Concerning the optimum compensation of the axial thrust which arises and/or the shaft eccentricities which arise from imbalances of the rotor, the embodiments according to Claims 5 and 6 are advantageous.

Claims 7 to 10 relate to advantageous embodiments and alternatives with respect to the arrangement and design of the axially traversable slots. Arranged uniformly distributed over the periphery (Claim 7), it is particularly advantageous (Claim 8) for the slots to be arranged in the peripheral direction, for example as elongate holes, i. e. with respect to the greatest peripheral longitudinal extension thereof, transversely or in an overlapping or divergent oblique position with respect to the relative setting angles of the bristles.

Alternatively, the axially traversable slots may be arranged as straight elongate holes uniformly over the periphery tangentially (with respect to the external or internal diameter of the respective wall portion) (Claim 15).

An alternative to the invention which is reliable in operation and easy to assemble is set out in Claim 11.

Extreme differences in pressure between the spaces to be sealed can advantageously be overcome by double seals according to one or more of Claims 12 to 14.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which Fig. 1 is a median longitudinal section through the brush seal associated with a rotor or a turbo-engine shaft, Fig. 2 is a front view of part of the brush seal as seen in the direction X in Fig. 1, illustrating a first embodiment of a slot, Fig. 3 is a front view similar to Fig. 2 with a second embodiment of a slot, Fig. 4 is an axial section of a double seal with seals according to Fig. 1 and in a stepped arrangement, and Fig. 5 is an axial section of a double seal with seals arranged in line with seals according to Figs.

1, 2 and 3.

Fig. 1 shows a brush seal for a turbo-engine, which is in the form of a rotor-stator seal, namely for sealing between spaces R1, R2 subjected to different pressure. In this case the bristles B are held by a clamping tube 2 on a core 1 extending over the periphery of the stator. The clamping tube 2 is clamped between two wall portions 3, 4 of a seal casing in an annular space 5. The annular space 5 passes into an axial peripheral gap U between the two wall portions 3, 4, the bristles B projecting out of a longitudinal slot 6 in the clamping tube 2. The bristles B extend over the axial peripheral gap U with their radially inner ends in a sealing manner against the rotor 7. The bristles B are able to compensate for eccentricities of the rotor or the shaft or imbalances of the rotor, namely by resilient deformation.The bristles are therefore able to compensate for even extreme changes in the radial gap without difficulty. In addition, the bristles B form a pack of brushes sealed in the axial and peripheral directions, the bristles B being arranged over the greater part of their longitudinal extension between the parallel faces of the axial peripheral gap U.

As may be seen further from Fig. 1, the pack of brushes in the axial peripheral gap U should extend in a sealed manner on the respective, in this case right-hand, face of the gap. The pack of brushes should form an axial gap A with respect to the other face of the gap.

The wall portion 3 facing the space R1 of higher pressure P1 additionally comprises axially traversable slots 8 by which the axial gap A is acted upon by a high-pressure fluid. As shown by arrows F, a relatively high proportion of high-pressure fluid therefore flows into the axial gap A, or over the front of the pack of brushes, in the direction towards the primary seal on the rotor. Between the end of the wall portion 3 situated radially on the inside and the surface of the rotor 7, a remaining proportion of high-pressure fluid flows into the primary seal in the direction of the arrows F'.The primary seal at the rotor 7 is therefore supplied by portions of high-pressure fluid as shown by the directions of the arrows F and F. A common portion of high-pressure fluid flows from the primary seal as shown by the arrow F' into the space R2 in which the pressure (P2) is considerably lower than in the space R1.

For greater resistance to temperature and wear, the bristles B should be produced from silicon carbide or silicon-carbide fibres. In addition, in the case of the seal arrangement as shown in Fig. 1, it is essential that the clamping tube 2 should have the longitudinal slot 6 thereof formed with portions C, D bent over to form an arc of a circle opposite the bristles B. The bent-over portions C, D result in the formation of relatively large circular rounded portions, thereby avoiding the risk of undesirable surface compression on the bristles.

As is further evident from Fig. 1, the surrounding portions C, D have flaps L, by which the clamping tube 2 is clamped at the greatest diameter thereof in the axial direction inside the annular space 5 between the two wall portions 3, 4.

In addition, it is evident from Fig. 1 that the bristles B of the pack of brushes together with the axial peripheral gap U are set axially obliquely with respect to the circular outline of the core 1 of cylindrical cross-section opposite the rotor surface.

It is further evident from Fig. 2 that the bristles B of the pack of brushes are set continuously uniformly obliquely in the peripheral direction, starting from a common peripheral line at the core 1, opposite the adjacent outer periphery of the rotor 7 (Fig. 1). The above-mentioned oblique setting of the bristles B is characterized for example in Fig. 2 by the angle a, in which case the said angle a should be understood as being the angle of inclination of the individual bristles, in this case for example relative to a longitudinal median plane M.

It is further evident from Figs. 2 and 3 that the axially traversable slots 8 and 8' are constructed in the manner of elongate holes and that they are arranged longitudinally on the periphery in a relative overlapping position (Fig. 2) or a divergent oblique position (Fig. 3) with respect to the respective setting angle of the bristles B. As shown in Fig. 2, therefore, the axially traversable slots 8 are symmetrically curved longitudinally in the peripheral direction and, in addition, are arranged offset with respect to one another uniformly over the periphery on two different radii of curvature RA, RA'. As shown in Fig. 3, the axially traversable slots 8' are straight in the manner of elongate holes and are arranged tangentially relative to the inner circular peripheral face of the wall portion 3 in respectively uniform oblique positions.

Furthermore, it is evident from Fig. 1 that the wall portion containing the slots 8, in this case the front wall portion 3, forms portions of the annular space 5 and is connected to the other wall portion 4 as a seal support with axial clamping of the clamping tube 2 by welding (numeral S). Instead of the said welding S it is also possible for a suitable; easily releasable screw fastening of the wall portion 3 to be provided on the respective part of the wall portion 4.

Fig. 4 illustrates a double seal in a respective individual design according to Fig. 1, in which the reference numerals 1, 2' etc. act as a basis with respect to the second sealing part following the first.

In Fig. 4 the two seals are thus arranged axially and radially offset with respect to each other, and the respective primary seals are formed on portions of a rotor R which are stepped relative to each other.

Instead of the rotor R, a seal support (rotating) stepped accordingly could also for example be provided.

With respect to the said steps of the rotor R, the seals rest with the radially inner portions of the sealing parts 4, 4' thereof against correspondingly stepped portions of the housing in the axial and peripheral directions in a rotationally fixed manner. The two respective radially outer portions of the wall portions 4, 4' are held axially at a distance on the housing G by an intermediate ring A. The two respective radially outer portions of the sealing parts 4, 4' are positioned and secured axially on the housing by a clamping ring K. In addition, in the arrangement as shown in Fig. 4, the respective front or upstream wall portions 3 have the axial slots in the configuration according to Fig. 2 or Fig. 3.In the seal arrangement as shown in Fig. 4, in particular extreme differences in pressure (P1 > P2) relative to the spaces R1 and R2 respectively acted upon accordingly by the fluid can be overcome in an ideally sealed manner. A pressure P3, which is < P1 in space R1 and > P2 in space R2, is therefore present in the locally stepped pressure chamber R2' bounded by the bristles B and B'. The same or an at least comparable respective pressure ratio can act as a basis in the respective spaces in the double seal as shown in Fig. 5 with respect to the spaces R1 or R2' or R2 respectively. In Fig. 5 an in-line double seal in a respective design according to Figs. 1, 2 and 3 is involved, in which in a modification from Fig. 4 a correlation extending in a straight line is present between the respective seating faces of the seals on the housing G and counter faces of the rotor R or a corresponding machine shaft.

According to the invention, as not additionally shown, however - in the case of the double seal according to Fig. 4 or 5 - only the wall portion 3 of a seal facing the space R1 with the highest fluid pressure (P1) can have the axial slots 8 or 8'.

The relatively small axial gap A noted in conjunction with Fig. 1, can be estimated as having a width which is 1/10 of the maximum bristle width at the peripheral gap U.

Claims

Claims:

1. A brush seal for a turbo-engine between spaces at different pressures in which the bristles are held on a core by a clamping tube extending over the periphery, wherein the bristles project from a longitudinal slot in the clamping tube and extend by way of an axial peripheral gap in a sealed manner towards a rotor, characterized in that - the longitudinal slot is formed by portions of the clamping tube bent over in a curve towards the bristles, - over the greater part of their longitudinal extension the bristles are arranged between parallel faces of the axial peripheral gap, - the bristles in the axial peripheral gap extend in a sealed manner along one gap face and form an axial gap with the opposite gap face, - a wall portion facing the space of higher pressure has axially traversable slots through which the bristles are acted upon, in use, with a high-pressure fluid by way of the axial gap, - the slots and the bristles overlap in positions angled with respect to one another over the periphery.

2. A brush seal according to Claim 1, wherein the bristles are produced from silicon carbide.

4. A brush seal according to Claim 2, wherein the bent-over portions of the clamping tube extend into end flaps clamping the clamping tube between two wall portions inside the annular space on the greatest diameter of the tube in the axial direction.

5. A brush seal according to any one of Claims 1 to 4, wherein the bristles of the brush seal together with the axial peripheral gap are set axially obliquely with respect to the circular outline of the core of cylindrical cross-section opposite the rotor surface.

6. A brush seal according to any one of Claims 1 to 5, wherein the bristles of the pack of brushes, each starting from a common peripheral line on the core, are set continuously uniformly obliquely towards a periphery of the rotor in the peripheral direction.

7. A brush seal according to any one of Claims 1 to 6, wherein the slots are distributed equally distant over the periphery.

8. A brush seal according to Claim 7, wherein the slots are arranged longitudinally on the periphery in an overlapping or divergent oblique position relative to the setting angle of the bristles.

9. A brush seal according to Claim 7 or 8, wherein the slots are curved in the manner of elongate holes along the periphery.

10. A brush seal according to Claim 7 or 8, wherein the slots are symmetrically curved longitudinally in the peripheral direction and are arranged offset with respect to one another uniformly over the periphery on at least two different radii of curvature.

11. A brush seal according to any one of Claims 1 to 10, wherein the wall portion containing the slots forms portions of the annular space and, with axial clamping of the clamping tube, is connected in a releasable manner or by welding to the remaining wall portion to form a stationary seal casing.

12. A brush seal according to any one of Claims 1 to 11 and constructed as a double seal with two respective separate wall portions, two clamping tubes, two seal casings with respective annular spaces and associated peripheral gaps for guiding the respective packs of brushes, wherein the respective wall portions and the packs of the bristles are arranged at a distance axially and relative to the rotor and enclose a pressure space sealed off from the spaces with an extremely high pressure difference.

13. A brush seal according to Claim 12, wherein the seal casings are offset axially and radially with respect to each other with associated wall portions, annular spaces, peripheral gaps and bristles for sealing with a stepped rotor or rotating seal support.

14. A brush seal according to Claim 12 or 13, wherein at least the wall portion of a seal facing the space with the highest fluid pressure is provided with the axial slots.

15. A brush seal according to Claim 7, wherein the slots are formed by straight elongate holes which in length are arranged in the respective wall portion tangentially or at peripheral distances continuously and uniformly on a larger radius on the outside than on the inside.

16. A brush seal substantially as herein described with reference to any one of the embodiments shown in the accompanying drawings.