GB2418965A

GB2418965A - A brush seal for sealing between a rotating shaft and a housing

Info

Publication number: GB2418965A
Application number: GB0422126A
Authority: GB
Inventors: Robert Hirst
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2004-10-06
Filing date: 2004-10-06
Publication date: 2006-04-12
Also published as: GB0422126D0

Abstract

A brush seal for sealing between a rotating shaft and a housing comprises an annular head portion 2 that is co-axial with the rotating shaft and is mounted to the housing 4 in such a way that it has a radial clearance 6 which allows the brush seal to move radially. A plurality of tightly packed bristles 14 are orientated at an angle r with respect to the plane that is normal to the longitudinal axis of the shaft.

Description

24 1 8965

TITLE

Brush seals

DESCRIPTION

Technical Field

The present invention relates to brush seals for dynamic shaft sealing, and in particular to brush seals that reduce or eliminate damage to the bristles or the rotating shaft caused when the shaft undergoes movement or vibration in the radial direction.

Background Art

Brush seals are a common way of providing a seal between a rotating shaft and a housing. They are often found in gas or steam turbine engines where they seal between the low-pressure and high-pressure regions of the engine. An example of a segmented brush seal is described in United States Patent 5,176,389to Noone et al. A plurality of tightly packed bristles 30 are sandwiched between an annular backing plate 20 and an annular side plate 25 as shown in Figure 3. The bristles extend radially inwardly at a constant skew angle (normally 45 degrees).

In a typical installation, the backing and side plates 20 and 25 are rigidly secured to a housing coaxial with a rotating shaft of the gas or steam turbine engine stub that the tips of the bristles 30 wipe against the surface of the shaft to create an effective seal.

When viewed in radial cross section, the bristles 30 will be positioned perpendicular to the surface of the rotating shaft. Although the bristles can flex slightly to accommodate a limited amount of movement between the rotating shaft and the housing, repeated or large movement or vibration in the radial direction over a long period of time will eventually cause severe damage to the bristles and the shaft, and the brush seal will have to be replaced. - 2

Summary of the Invention

The present invention provides a brush seal for sealing between a rotating shaft and a housing, the brush seal comprising an annular head portion coaxial with the shaft and mounted to the housing, and a plurality of bristles orientated at an angle with respect to the plane that is normal to the longitudinal axis of the shaft.

Because the bristles are not positioned perpendicular to the surface of the rotating shaft, they can flex or deflect freely to accommodate any movement or vibration of the rotating shaft in the radial direction. This reduces the damage to the bristles and the shaft, and improves the useful lifetime ofthe brush seal.

The brush seal can be used to seal between the high-pressure and lowpressure regions of a gas or steam turbine engine, for example. In this case the tips of the bristles are preferably inclined towards the highpressure region so that the positive and uniformly distributed pressure difference across the brush seal will prevent the bristles from over deflecting, and return the bristles to their original position after the rotating shaft has moved away.

Tile annular head portion is preferably slidably mounted to the housing so that it can move in the radia! direction. This allows the.u'ar head portion to accorlllllodate larger movements or vibrations of the rotating shaft in the radial direction that might otherwise cause the bristles to over deflect. The radial movement of the annular head portion must be limited to avoid permanent misalignment of the brush seal with respect to the rotating shaft. Radial movements in the order of a millimetre at most are therefore considered to be appropriate for most practical purposes.

At least one bypass seal can be provided between the housing and the annular head portion. Tl1e bypass seal prevents air from flowing around the outside of the annular head portion and bypassing the brush seal. (he bypass seal can be a spring seal and is preferably received in an annular channel provided in the wall of the housing. More particularly, the annular head portion is preferably mounted in a groove formed in the radially inner surface of the housing. The annular charnel for the bypass seal is then formed in a sidewall of this groove. A second bypass seal of the same or different type can also be provided in an annular channel formed in an opposite sidewall of the groove.

For ease of installation, the brush seal is preferably formed in a plurality of segments.

The annular head portion will therefore be segmented into several pieces and each segment will include a plurality of bristles. The annular head portion segments can then be slid into the groove funned in the radially inner surface of the housing one at a time. The end ['aces of each segment of brush seal are preferably oblique with respect to the radial direction. By this is meant that the faces arc generally planar and the annular head portion, if viewed axially, is generally shaped like a parallelogram.

he end faces can also be straight with respect to the radial direction. However, snaking the end faces oblique enables the adjacent segments to slide over each other and allow for differential expansion.

One of the abutting end faces of a pair of adjacent brush seal segments preferably includes a slot for receiving an interface seal. The interlace seal will normally be in sliding contact with the end face of the adjacent brush seal segment to reduce leakage.

The interface seal can be a spring seal and of "double E" construction, for example.

The interface sea! car. be riveted or spot welded to the brush seal segi^l.e-clt at its radially outer end.

Drawings Figure I is a radial cross sectional view of a brush seal according to the present invention; Figure 2 is an axial view showing two adjacent segments of the brush seal of l;igure 1; Figure 3 is a radial view showing an end face of a segment of the brush seal of Figure 1; and Figure 4 is a top view showing in detail the shape of the slot and seal in the end face of the segment of leisure 3. - 4

With reference to Figures 1 to 4, a brush seal includes an annular head portion 2 of T shaped radial cross section that is mounted to the outer casing or housing 4 of a gas turbine engine. The annular head portion 2 is slidably received in an annular groove 6 formed in the radially inner surface of the housing 4. The groove 6 has a T0-shaped radial cross section and includes a pair of shoulders 6a. A small gap of about I mm is provided between the radially outer suriacc 2a of the annular head portion 2 and the circumferential surface 6b of the groove so that the annular head portion can undergo a limited amount of movement in the radial direction between the surface 6b and the shoulders 6a. The sidewalls 6c of the groove include annular channels 10 in which bypass seals 12 are located. Each bypass seal 12 is a spring seal as shown in detail in Figure 1. The bypass seals 12 prevent air from flowing through the groove 6 around the outside of the annular head portion 2.

A plurality of tightly packed bristles 14 are mounted to the annular head part 2 so that their tips 14a brush against the surface of a rotating shaft (not shown). Instead of being perpendicular to the longitudinal axis of the rotating shaft, the bristles 14 are mounted at an angle so that they can easily flex or deflect to accommodate small movements and vibrations of the rotating shaft in the radial direction. The plane P that is normal to the longitudinal axis of the rotating shaft (and also to the longitudinal axis of the annular head par! 2, which is coaxial with the rotating shale) is reprcscntcd in Figure] by the dashed line. The bristles 14 are therefore inclined to the plane P at an angle 0, which is about 20 or 30 degrees. The annular head part 2 is rigidly fixed into tile parent body.

The tips 14 of the bristles are inclined towards the high-pressure side of the gas turbine engine. A positive and uniform pressure difference therefore exists across the brush seal as shown by the anow labelled "+ve AP" in Figure 1. This pressure difference serves to keep the bristles 14 from over deflecting. It also returns the bristles 14 to their original position after the rotating shaft has moved away. Larger movements of the rotating shaft are accommodated by tile radial movement of the annular head portion 2 within the annular groove 6. - s -

The brush seal is formed as several segments as shown in Figure 2. (Although the brush seal segments in Figure 2 have been drawn as being straight, it will be readily appreciated that they are in fact curved in the circumferential direction.) The end faces 16 of each segment are cut at an angle to allow them to slide over each other.

The interface between each adjacent pair of segments has a seal cut into it. This is shown most clearly in Figures 3 and 4. An interface seal 18 is engaged in one end face of each brush seal segment. The interface seal 18 sits in a groove 20 in the end face of the brush seal segment and can be secured to the segment by a rivet or a spot weld (not shown). The interface seal 18 is made of spring steel and is of the "double 12" construction shown in Figure 4. The interface seal will simply slide against the end face of the adjacent brush seal segment to discourage leakage. It will be readily appreciated that the gap between the adjacent brush seal segments will be kept to an absolute minimum and sized to allow for differential expansions only.

Claims

l. A brush seal for sealing between a rotating shaft and a housing, the brush seal comprising an annular head portion coaxial with the shaft and mounted to the housing, and a plurality of bristles orientated at an angle with respect to the plane that is normal to the longitudinal axis of the shalt.
2. A brush seal according to claim l, wherein the annular head portion is slidably mounted to the housing so that it can move in the radial direction.
3. A brush seal according to claim l or claim 2, further including at least one seal between the annular head portion and the housing.
4. A brush seal according to claim 3, wherein the at least one seal is a spring seal received in a channel provided in the housing.
5. A brush seal according to any preceding claim, formed in a plurality of segments.
6. A brush seal according to claim 5, wherein the abutting faces of each of the plurality of segments Ore oblique with respect to the radial direction.
7. A brush seal according to claim 5 or claim 6, wherein one of an abutting faces of a pair of adjacent segments includes a slot for receiving an interface seal.
8. A brush seal according to claim 7, wherein the interface seal is in sliding contact with the other of the abutting faces of the pair of adjacent segments.
9. A brush seal according to claim 7 or claim 8, wherein the interface seal is a spring seal.
] O. A brush seal according to any of claims 7 to 9, wherein the interface seal is r iveted to the segment at its radially outer end.
11. A brush seal according to any of claims 7 to 9, wherein the interface seal is spot welded to the segment at its radially outer end.

5] 2. A brush seal substantially as herein described and with reference to the drawings.