GB2400151A

GB2400151A - Wound metallic wire seal

Info

Publication number: GB2400151A
Application number: GB0307776A
Authority: GB
Inventors: Michael Keith Morrison; Christopher John Hatcher
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2003-04-04
Filing date: 2003-04-04
Publication date: 2004-10-06
Also published as: GB0307776D0

Abstract

A seal comprises a sealing ring 4 in the form of a toroidally wound metallic wire. The sealing ring 4 is secured, by welding, to a support ring 2 and provides a sealing surface afforded by adjacent sections of the respective turns 8 of the wire. A baffle plate 6 is disposed within the sealing ring 4 to restrict air flow across the seal. The baffle plate may be of right angle cross-section to prevent deformation of the windings. The seal is used for maintaining pressure differences at gaps between stationary and rotating parts of a gas turbine engine.

Description

SEALS

This invention relates to seals, and is particularly, although not exclusively, concerned with seals for sealing gaps between rotating components in a gas turbine engine.

It is known to use brush or bristle seals for sealing between rotating components, such as bladed discs and stationary components in gas turbine engines. Such seals are used to support a pressure difference, for example to seal passages for cooling air.

Known bristle seals comprise a mounting ring from which cut wire bristles project generally radially either outwardly or inwardly from the mounting ring. The mounting ring is secured to one of the components defining the gap to be sealed, and the tips of the bristles contact a surface of the other component.

Bristle seals are subject to wear, and consequently over time leakage between the tips of the bristles and the cooperating surface increases. Also, aerodynamic disturbances can cause bristle flutter, lifting them off the cooperating surface and so degrading sealing efficiency. The pressure difference that can be supported by a bristle seal is limited by the tendency of the bristles to deflect.

Bristle seals may be manufactured in a variety of different ways, but one manufacturing process, and associated apparatus, is disclosed in US 4768725. In this process, wires are wound toroidally around an annular former. The windings are subsequently welded to supporting side-plates and then cut to provide freely projecting bristles extending from the side-plates. The former is then removed.

According to the present invention there is provided a seal comprising a sealing ring carried by a support ring, the sealing ring comprising a plurality of wire elements each extending around a circumferential axis of the sealing ring whereby the sealing ring provides a sealing surface which comprises adjacent sections of the respective wire elements, which sections are disposed side by side around the sealing ring. - 2

Thus, in a seal in accordance with the present invention, the sealing surface is made up of wire sections which lie generally parallel to the surface which they engage.

In a preferred embodiment, the wire elements each comprise an individual turn or coil of a continuous helically wound length of wire. The elements, or adjacent coils, abut or lie very close to one another at the sealing surface so that the sealing surface is substantially continuous around the sealing ring. The sealing surface may be either the radially inner or radially outer periphery of the sealing ring although in preferred embodiments the sealing surface is the radially inner periphery of the sealing ring The wire elements may have any desired loop configuration. They may have a circular configuration, but alternatively they may have a configuration such that the section of each element which forms the sealing surface is generally straight oms curved with a radius of curvature greater than the distance between the centre of the element anti to- respective section. For example, the wire elements may be elliptical, with the long axis parallel to the sealing surface, or polygonal, with one side serving as the section whcn forms the sealing surface.

The support ring may be secured to the sealing ring at a position on the sealing ring opposite the sealing surface. In a preferred embodiment, the support ring comprises an outer support ring situated externally of the wire elements. A baffle ring may be disposed inside the wire elements. The baffle ring may extend from the outer ring to a position adjacent to but spaced from the sections of the wire elements which form the sealing surface.

Support means may be provided for resisting lateral deformation of the sealing ring in directions parallel to the central axis of the seal.

The support ring is preferably secured to the wire elements by welding. 3

According to another aspect of the present invention, there is provided a method of manufacturing a seal as defined above, the method comprising the steps (a) winding a wire toroidally around an annular former to form a torodaliy wound sealing ring; (b) securing the sealing ring to a support ring; (c) before or after step (b), removing at least part of the former from the ntenor of the sealing ring.

The toroidal winding, and the apparatus for carrying out the toroidal winding, may be as described in US 4768725, the disclosure of which is incorporated herein by reference.

In step (c), the entire former may be removed, and may be replaced by a baffle ring inserted within the windings of the sealing ring. Alternatively, the former may be assembled from a baffle ring and a removable former component, so that the removable component is removed in step (c), leaving the baffle ring in place.

In order to enable removal of the former, or the removable former component, the former or the component may be radially split so that it can be extracted by passing between adjacent windings of the sealing ring.

Alternatively, the former, or the removable former component, may be made from a material which becomes fluent under predetermined conditions. For example, the material of the former or the removable component may have a relatively low melting point, so that it can be removed by heating the sealing ring and the former to a temperature above the melting point, so enabling the former or the removable component to flow away between the windings of the sealing ring. Alternatively, the material of the former or the removable component may be soluble in a suitable solvent. - 4

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a sectional view through a seal; Figure 2 is a view of the seal taken in the direction of the arrow 11 in Figure 1; Figure 3 is a sectioned fragmentary view of the seal; Figure 4 is a fragmentary view of part of the seal; Figures 5 to 7 correspond to Figure 1 but show alternative embodiments of the seal; Figure 8 shows a part of a seal having inclined windings; and Figures 9 and 10 correspond to Figure 1 but show alternative embodiments.

The seals shown in the drawings are primarily intended for use in high temperature environments, such as gas turbine engines. In the embodiments shown in the drawings, the seals are secured to a stationary component of a gas turbine engine, and sealingly engage a cylindrical outer surface of a rotating component. However, it will be appreciated that seals in accordance with the present invention may be used in other configurations, and in environments other than gas turbine engines.

The seals shown in Figures 1 to 4 comprise an external support ring 2, a toroidal winding of metallic wire 4, and an internal baffle ring 6.

The sealing ring 4, as can be appreciated from Figure 3, comprises a torodal winding which provides a plurality of elements, each comprising a single turn 8 of the wound sealing ring 4. In the embodiment of Figures 1 to 4, these elements 8 are approximately circular, centred on the circumferential axis 10 of the sealing ring 4. - 5

As shown in Figure 1, the baffle ring 6 extends across a diameter of the radial cross- section of the sealing ring from a position adjacent the support ring 2. The baffle ring 6 stops short of the wire elements 8 at the end opposite the support ring 2, leaving a clearance c.

The support ring 2 is welded to the sealing ring 4 and the baffle ring 6 to secure the components of the seal together. In use, the support ring 2 is mounted on a stationary component of a gas turbine engine, and the sealing ring 4 engages a cylindrical surface 14 of a rotating component 12 having a diameter D. The surface 14 may be treated to provide hard wearing characteristics.

The radius R of the turns 8 of the sealing element 4 is selected so that, when Installed, the turns 8 are resiliently compressed between the support ring 2 and the surface 12.

This ensures that, during rotation, the resilience of the sealing element will compensate for any non-circularity or eccentricity of the surface 14, so enabling the individual turns 8 to remain in contact with the surface 14.

It will be appreciated that the sections of the turns 8 in contact with the surface 14 will be closely packed, and preferably in contact with one another, to provide a substantially continuous sealing surface in contact with the surface 14. As a result of this, adjacent turns 8 will be spaced from one another at the outer diameter of the sealing element 4, adjacent the support ring 2. However, the baffle ring 6 will restrict flow across the seal, leaving open only the clearance c. Consequently, the seal provides a labyrinth effect restricting leakage of gas from one side of the seal to the other. If necessary, leakage can be restricted still further by forming the sealing ring 4 as several layers of windings, rather than the single layer shown in Figures 1 to 4.

The wire used to form the sealing ring 4 may have any suitable crosssection. If circular cross-section wire is used, the result will be that, when the sealing ring 4 is new, small leakage paths will exist at the surface 14 owing to the gaps between adjacent wires at their points of contact with the surface 14. However, as the sealing - 6 ring 4 beds in, the sections of wire engaging the surface 14 will become flattened as a result of wear, as shown in Figure 4. This will reduce the spaces between adjacent wires at surface 14, possibly closing them entirely, so that the effectiveness of the seal improves as wear takes place. It will be appreciated that the contact surface of each turn 8 will achieve its maximum extent when the wire has worn to half of its original thickness.

The seal of Figures 1 to 4 is capable of supporting a significant pressure difference The stiffness of the seal, and consequently its ability to resist distortion as a result of pressure differences, can be increased by increasing the stiffness of the wire from which the sealing ring 4 is made either by appropriate selection of the material of the wire or by increasing its cross-section. However, these measures will also increase the stiffness of the sealing ring 4 in the radial direction, so increasing the contact force acting on the surface 14. Figures 5 and 6 show auxiliary measures for resisting pressure differences acting on the seal.

In Figure 5, the baffle ring 6 has a lateral projection 16 terminating at a support surface to which engages, or lies close to, the inside of the elements 8 on the side exposed to the higher pressure.

In the embodiment of Figure 6, the baffle ring 6 is similar to that of Figure 1, but the support ring 2 has a lateral extension 18 which terminates at a support surface which engages the outside of the sealing ring 4 on the side exposed to the lower pressure.

Figure 7 shows two seals disposed in series, with the result that each seal is exposed to only half of the total pressure drop occurring along the gap to be sealed. It will be appreciated that more than two seals could be disposed in series if required.

The turns 8 of the sealing ring 4 may be disposed radially with respect to the axis of rotation of the rotor 12, so that they lie generally perpendicular to the surface 14.

However, as shown in Figure 8, the turns 8 may lie in a plane which is inclined to the radial direction, as represented in Figure 8 by a lay angle O. As shown, the turns 8 are inclined away from the radial direction in the direction of rotation of the rotor 12 This increases the radial compliance of the turns 8, with respect to the axis of rotation of the rotor 12, since the turns can deflect away from the surface 14 not only by distortion of the loop shape of the turns, but also by bending. This enables a relatively stiff wire to be used for the sealing ring 4, in order to withstand the pressure differential across the seal, while avoiding excessive contact forces between the turns 8 and the surface 14.

Figure 9 shows a modified seal in which the sealing ring 4 has an elliptical loop configuration. In the embodiment of Figure 10, the sealing ring 4 has a generally polygonal configuration, in this case in the form of a triangle, with one side of the polygon engaging the surface 14. Variations in the loop profile, as shown in Figures 9 and 10, can serve to provide a desired radial compliance or resistance to pressure differentials. In addition, the profiles illustrated in Figures 9 and 10 serve to increase the axial extent of the contact region between the sealing ring 4 and the surface 14, particularly after bedding in of the sealing ring 4 has occurred.

Seals as described above may be manufactured in any suitable way. In one technique, the wire from which the sealing ring 4 is formed may be wound continuously onto a straight former of the desired cross-section (ie in order to achieve the desired loop profile for the turns 8). When the winding has the desired length, corresponding to the circumference of the eventual sealing ring 4, it is removed from the former and transferred to the baffle ring 6 which may have a single radial split to enable the ring to receive the winding. This split can be welded once the winding is installed, and the baffle ring 6 and sealing ring 4 can then be fitted within the support ring 2 and continuously welded on each side.

Alternatively, the winding can be formed in its eventual toroidal form by winding directly onto the baffle ring 6 using appropriate equipment, such as the machine disclosed In US Patent 4768725. In order to achieve the desired loop profile for the turns 8 of the sealing ring 4, a removable former component is moulded onto the baffle ring 6 to support the wire as it Is wound. The removable former component may, for example, be made from a material which can be removed by the application of heat, for example 8 by melting, or by the use of a solvent. Thus, the sealing ring 4, on the former comprising both the baffle ring 6 and the removable former component, is secured to the support ring 2 by welding, following which the removable former component is removed. - 9 -

Claims

1 A seal comprising a sealing ring carried by a support ring, the sealing ring comprising a plurality of wire elements each extending around a circumferential axis of the sealing ring, whereby the sealing ring provides a sealing surface which comprises adjacent sections of the respective wire elements, which sections are disposed side by side around the sealing ring.

2 A seal as claimed in claim 1, in which the wire elements comprise respective turns of a continuous helically wound length of wire.

3 A seal as claimed In claim 1 or 2, in which the wire elements abut one another at the sections which afford the sealing surface.

4 A seal as claimed in any one of claims 1 to 3, in which the sealing surface is situated at the radially inner periphery of the sealing ring.

A seal as claimed in any one of the preceding claims, in which the wire elements have a circular loop profile.

6 A seal as claimed in any one of claims 1 to 4, in which the wire elements have an elliptical loop profile, the long axis of the elliptical loop profile being parallel to the sealing surface.

7 A seal as claimed in any one of claims 1 to 4, in which the section of each wire element which affords the sealing surface is straight.

8 A seal as claimed in claim 7, in which each wire element has a polygonal loop profile of which one side constitutes the straight section. -

9 A seal as claimed in any one of the preceding claims, in which the support ring Is secured to the sealing ring at a position opposite the sealing surface.

A seal as claimed in claim 9, in which the support ring comprises an outer support ring situated externally of the wire elements.

11 A seal as claimed in any one of the preceding claims, in which a baffle ring Is disposed inside the wire elements.

12 A seal as claimed in claim 11, in which the baffle ring extends diametrically across the interior of the sealing ring and terminates at a position spaced from the sections of the wire elements affording the sealing surface.

13 A seal as claimed in claim 11 or 12, in which the baffle ring comprises a support surface disposed within the sealing ring for abutment with internal surfaces of the wire elements to limit displacement of the wire elements in a direction parallel to the central axis of the seal.

14 A seal as claimed in any one of the preceding claims, in which the support ring is provided with a support surface disposed externally of the sealing ring for abutment with the wire elements to limit displacement of the wire elements In a direction parallel to the central axis of the seal.

A seal as claimed in any one of the preceding claims, in which the wire elements lie in respective planes which are inclined to a radial plane passing through the respective wire elements.

16 A seal as claimed in any one of the preceding claims, in which the support ring Is secured to the sealing ring by welding. - 11

17 A seal substantially as described herein with reference to, and as shown in, Figures 1 to 4 or Figures 1 to 4 as modified by any one of Figures 5 to 10 of the accompanying drawings.

18 A sealing arrangement extending across a gap between two relatively rotatable components, the sealing arrangement comprising a seal in accordance with any one of the preceding claims, the support ring being secured to one of the components and the sealing surface of the sealing ring engaging a surface of the other component.

19 A gas turbine engine including a sealing arrangement in accordance with claim 18.

A method of manufacturing a seal in accordance with any one of claims 1 to 17, the method comprising the steps; (a) winding a wire toroidally around an annular former to form a toroidally (b) securing the sealing ring to a support ring, (c) before or after step (b), removing at least part of the former from the interior of the sealing ring.

21 A method as claimed in claim 20, in which, in step (c) the entire former Is removed from the interior of the sealing ring following which a baffle ring is introduced into the sealing ring.

22 A method as claimed in claim 21, in which the former comprises a baffle ring and a removable former component and in which, in step (c), the removable former component is removed from the interior of the sealing ring. - 12

23 A method as claimed in claim 20 or 21, in which the former, or the removable former component, is radially split and in which, in step (c), the former or removable former component is withdrawn from the interior of the sealing ring between adjacent wire elements of the sealing ring.

24 A method as claimed in claim 20 or 21, in which the former or the removable former component is removed from the interior of the sealing ring by means of a solvent or by the application of heat.

A method of manufacturing a seal in accordance with any one of claims 1 to 17, the method comprising the steps: (a) winding a wire helically around a straight former, (b) withdrawing the former from the helically wound wire, (c) forming the helically wound wire into a sealing ring, (d) securing the sealing ring to a support ring.

26 A method of manufacturing a seal in accordance with any one of claims 1 to 17, the method being substantially as described herein.