GB2286434A

GB2286434A - Gap seal between two moving components

Info

Publication number: GB2286434A
Application number: GB9502173A
Authority: GB
Inventors: Axel Rosmann
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1994-02-05
Filing date: 1995-02-03
Publication date: 1995-08-16
Anticipated expiration: 2015-02-03
Also published as: DE4403605C2; GB9502173D0; FR2715983B1; GB2286434B; DE4403605A1; FR2715983A1

Description

2286434 GAP SEAL BETWEEN TWO MOVING COMPONENTS The invention concerns a

gap seal between two components capable of relative motion, in particular for sealing two chambers of differing pressure by means ofgap seal elements which are fixed to the first of the two components and, in the idle state, rest against the second component under prestress.

A gap seal is here taken to mean a seal in which the two chambers are not fully cut off from each other by a solid seal. Examples are brush seals with gap seal elements consisting of brushes in the form of metal wires or fibres, for example of carbon or glass. The tips of the wires or fibres, which are fixed to one of the mobile components, slide on the other component.

The sealing effect between two spaces depends on there remaining a residual gap which is composed of the spaces between the individual brushes and the space between the set of brush tips and the second component. Known in the art is the practice of pressing the brush tips on to the second component under spring pressure by elastic bending of the brushes. The abrasion of the brush tips is thus of critical importance for the sealing effect and for the service life of the gap seal. As soon as the elastic adjustment of the seal tips given by elastic bending of the brushes is used up through abrasion on the second component there is a progressive loss of the sealing effect of the brush seal and it ceases to have operational use.

The object of the invention is specify a gap seal of this type and to increase the service life of this gap seal and to assure a sealing effect of uniformly high quality throughout the service life of the seal.

This object is achieved, according to the invention, in that the gap seal elements are flexurally elastic and have fluid-dynamic skimming faces on their tips, the flexural strength, i.e. the elastic constant, of a gap seal element and the size of its skimming face being matched to the physical characteristics of the gap fluid so as to produce, in operation, a gliding action of the skimming face.

An advantage of this gap seal is that the gap;seal elements rest on the surface of the second component only in the idle state; upon attainment of the operation-induced relative speed between the two mobile components the tips of the gap seal elements glide on the film of gap fluid and do not contact the second component. In the operating state, the gap seal according to the invention advantageously forms a contactless seal which is at the same time capable of coping with changes in the gap width due to differential thermal expansion between the two components or other influences such as a varying suspension gap between a carrying component and the travelling component in high-speed suspension railways or balance errors of rotating components in machines, particularly high-speed drives.

In a preferred development of the invention, the gap seal elements are fixed to the first component perpendicularly or nearly so, the gap seal elements being bent, folded or angled in the direction of motion in the region of their free ends to form a following angle relative to the direction of motion. This has the advantage that, with a relatively simple method of fixing the gap seal elements, namely across the gap, the following angle produces an enlarged lift face at the tip of the gap seal elements, so that the gap seal elements can glide on the film of gap fluid even at a low relative speed between the moving components.

In another preferred development of the invention, which can be combined with the previous, the gap seal elements are fixed to the first component at a trailing angle relative to the direction of motion. This i, i enables the gap seal elements to be packed more closely so that the space between them in the direction of motion is minimized, thereby reducing leakages which flow through these intermediate spaces from the low- pressure chamber into the chamber with higher pressure.

The transverse dimension of a gap seal element, relative to the direction of motion, is preferably several times its dimension in the direction of motion so as to achieve, advantageously, a large fluid-dynamic skimming surface on the tips with, at the same time, a low flexural resistance of the gap seal element, which encourages an early gliding action of the skimming faces.

The gap seal elements are preferably lamellae, one end of each lamella being fixed to the first component with its width transverse to the direction of motion. The lamellae are of such a length and thickness that they fill out the cross-section of the gap and can advantageously be relatively tightly packed.

In a further preferred development of the invention, several rows of gap seal elements are arranged in series transversely to the direction of motion. This advantageously increases the sealing effect. In addition, the successively arranged gap seal elements can be offset in the direction of motion so that the intermediate space between two gap seal elements in a first row is covered by a gap seal element in the next row, and so on. This further reduces the leakage flow through the intermediate spaces.

Additional resistance to the leakage flow can be achieved, advantageously, if the gap seal elements are profiled transversely relative to the direction of motion along their length which extends across the gap. Advantageously, this profiling can comprise projections or teeth along one or both edges. This measure offers a further improvement if preferably several sets of gap seal elements are arranged in series as described above, since they can then be interlocked transversely relative to the direction of motion. The interlocking teeth or projections of the profiled gap seal elements disposed in series transversely relative to the direction of motion advantageously increase the resistance to the leakage flow and increase the sealing effect of the gap seal.

The gap seal elements are preferably made from sheets or foils. This has the advantage that lamellar gap seal elements and gap seal element edge profiles can be mass-produced cost-effectively. Where high operating temperatures are to be anticipated these sheets and foils are primarily of metal. However, in a further preferred development of the invention, gap seal elements of a plastics material, preferably nylon or Teflon, are used. Nylon is used because of its toughness and low cost and Teflon because of its high temperature stability. Moreover, these plastics materials can replace the metal brushes commonly used in brush seals due to the fact that in operation the gap seal solution according to the invention means that the frictional heat generated is substantially less than is the case with conventional brush seals.

If the gap seal elements are composed of reinforced plastics materials, preferably from the polyester, epoxy, PEEK, polyimide, bismalimide or phenol resin group, these being preferably reinforced with carbon, glass or aramide fibres, the flexural resistance of the gap seal elements can be advantageously matched from a wide range of products to the characteristics of the film of gap fluid while the size of the fluid-dynamic skimming face remains the same.

A tightly-packed bundle of elastic lamellar gap seal elements made from foils or sheets can exhibit an internal friction on contact surfaces between two successive gap seal elements. If the gap seal elements are composed of coated sheets or foils this friction can be reduced and frictional corrosion impeded. To this end, the gap seal elements are preferably coated with a film of SiC, TiN, Teflon or dry-film lubricant or they are made from foils or sheets coated with these materials.

In the case of industrial-scale applications, the gap seals are not firstly produced as individual elements which are then fixed to the first component, preferably at an angle; instead a continuous band made of foil is compressed in the manner of a zig-zag or concertina and fixed to the first component. It can be fixed into a prepared groove in the first component by soldering, welding or pressing. The side of the concertina-type band which will face the second component is then removed, for instance by grinding, so that the folded band is cut on one side into single flexible lamellae. This can be followed by a pressing and forming stage in which the bundle of lamellae is bent into a following or trailing angle and, as a final stage, the fluid-dynamic skimming face is ground to a final dimension simultaneously on all the gap seal elements.

If the continuous band is coated before being compressed in the manner of a concertina, the above production sequence produces a gap seal with a bundle of lamellae which are coated on the intermediate faces. Gap seals having lamellar gap seal elements with profiled edges can be produced by profiling the edges of the continuous band.

If several continuous bands which are compressed in the manner of a concertina are fixed to the first component transversely relative to the direction of motion this produces a gap seal with several lamellae disposed in series which can also be offset relative to each other and/or interlocked.

For a better understanding of the invention, embodiments of it will now be described in greater detail with reference to the accompanying figures, in which:

Fig. 1 shows a cross-section of a gap seal between two components; Fig. 2 shows a section E of the gap seal of Fig.

Fig. 3 shows a longitudinal section through the same gap seal; Fig. 4 shows several gap seal elements arranged in series transversely relative to the direction of motion; Fig. 5 shows a longitudinal section through the arrangement according to Fig. 4, along the line CC; Fig. 6 shows an enlarged section B of Fig. 4; Figs. 7 to 9 show different fixing arrangements and following angles and gap seal element bends; and Figs. 10 to 13 show different profiles and arrangements of the edges of the gap seal elements.

Fig. 1 shows a cross-section of a gap seal between two components 1, 2, which are capable of relative motion, for effecting a seal between two chambers of differing pressure, not illustrated. The gap seal possesses a large number of individual gap seal elements 3 which are fixed in a row along the direction of motion to the first 1 of the two components 1, 2 and extend more or less radially inwards, towards the second component 2. By this means, the cross- sectional area of the gap 4 is reduced to the spaces between the gap seal elements 3 themselves and between the tips of the gap seal elements 3 and the second component 2. The gap seal elements 3 are flexurally elastic lamellae which bear on the second component 2 in the idle state.

At high relative speed between the two components 1 and 2 their tips glide on a cushion of gap fluid.

Fig. 2 shows a section E of the gap seal cross section from Fig. 1, showing the emergent gliding cushion of gap fluid having the thickness S. In order to achieve assured gliding of the tips 5 of the gap seal elements 3 upon attainment of the operational relative speeds between the components 1 and 2, the tips 5 possess fluid- dynamic skimming faces 6 substantially parallel to the surface of the second component, the size of the skimming face 6 and the stiffness of a gap seal element 3 being matched to the physical characteristics of the gap fluid, such as its viscosity and density. In this example, the direction of the motion between the two components is indicated by the arrow F with, in this example, the second component 2 rotating and the component 1 stationary.

Such gap seals are used advantageously in turbine engines, the rotating component 2 representing or being connected to one of the engine shafts, with the component 1 connected to the housing. Alternatively, the component 2 can be a rail and the component 1 belong to a linear-motion suspension railway.

Fig. 2 therefore demonstrates that the invention is also applicable to linear-motion components, for example for sealing the suspension gap between the carrying structure and the suspended vehicle in a suspended railway operating at high speeds.

Fig. 3 shows a longitudinal section through the gap seal, viewed on A in Fig. 1. The gap seal element 3 has been soldered, welded, cemented or pressed into a groove 7 of the component 1, its tip 5 gliding on the gap fluid so as to form a minimal space between the tips 5 and the component 2, thereby reducing the abrasion of the gap seal element 3 and increasing its service life.

Fig. 4 shows how several sets of gap seal elements 3 can be arranged in series in the plane of the gap transversely relative to the direction of motion, arrow F, of the cbmponent 2. This arrangement reduces the leakage flow between the two chambers to be sealed particularly if, as shown by Fig. 6 in an enlarged section B from Fig. 4, the gap seal elements 3 are offset relative to each other along the direction of movement, since then the leakage flow which passes through the gap seal in the arrow direction D must overcome a substantially increased flow resistance.

Fig. 5 shows a longitudinal section through the arrangement according to Fig. 4, along the line CC. Within the component 1, the gap seal elements 3 are fixed into three grooves 7 and in operation, with the component 2 moving at high speed relative to the component 1, form a film or cushion of gap fluid having the thickness S, so that a contactless seal is produced.

Figs. 7 to 9 show different fixing arrangements and following angles P and bends of the gap seal elements 3. The fixing angle a, which defines the deviation of the orientation of the gap seal elements 3 in the component 1 from a fixed position perpendicular to the gap 4, decreases from Fig. 7, in which there is the greatest deviation, to Fig. 9 in which the deviation is practically zero. The following angle i.e. the angle between the trailing end of the element 3 and the second component 2, depends on both the fixing angle a and a predefined bend 8 which, as shown by Figs. 7 to 9, can have different forms. Thus, in Fig. 7, the gap seal element 3 is mostly straight but is bent or folded at a point towards the tip. In Fig. 8 the gap seal element is essentially curved uniformly 3 along its full length and in Fig. 9 it has two bend points 9 and 10.

Figs 10 to 13 show different profiles 11, 12 and arrangements of the edges 13, 14 of the gap seal elements 3. The profiling can be applied to one side, as in Figs. 10 to 12, or to both sides as in Fig. 13. The profiling can consist of, for example, teeth 11 or rectangular projections 12.

In Figs 10 and 11, the gap seal elements 3 each have a smooth edge 15 and a profiled edge 16 possessing saw-teeth 11. If the gap seal elements 3 are arranged in series, the edges 13 and 14 can be disposed in alternating sequence, as shown by Fig. 10, or they can be interlocked, as shown by Fig. 11. Analogous arrangements can also be achieved with the projections 12, as shown by Figs. 12 and 13. By means of the profiling and different arrangements it is possible to optimize the resistance to the leakage flow between the two spaces of differing pressure in widely differing applications.

Claims

CLAIMS:

1. Gap seal between two components capable of relative motion for sealing two chambers of differing pressure, including a set of gap seal elements to be fixed to the first component and, in the idle state, to bear on the second component under prestress, characterized in that the gap seal elements (3) are elastic and possess fluid-dynamic skimming faces (6) on their tips, the flexural resistance of a gap seal element (3) and the size of its skimming face (6) being such that, in operation, the skimming faces (6) lift from and glide over the second component.

2. Gap seal according to Claim 1, in which the gap seal elements (3) are bent, curved or angled in the vicinity of their ends near the second component to form a following angle relative to the direction of motion.

3. Gap seal according to Claim 1 or 2, in which the gap seal elements (3) are fixed to the first component (1) at a following angle relative to the direction of motion.

4. Gap seal according to any preceding claim in which the width of a gap seal element (3) across the direction of motion is a multiple of its length in the direction of motion.

5. Gap seal according to any preceding claim in which the gap seal elements (3) are lamellae, each being fixed at one end to the first component (i) with its width transverse to the direction of motion.

6. Gap seal according to any preceding claim in which several sets of gap seal elements (3) are arranged in series across the direction of motion.

7. Gap seal according to Claim 6, in which the sets of gap seal elements (3) are mutually offset in the direction of motion.

a

8. Gap seal according to any preceding claim in which the gap seal elements (3) are profiled along their length which extends across the gap, preferably with projections (12) or teeth (11).

9. Gap seal according to Claim 8 when dependent on Claim 6 or 7, the profiling is adapted to interlock adjacent sets of gap seal elements (3).

10. Gap seal according to any preceding claim in which the gap seal elements (3) are made from sheets or foils.

11. Gap seal according to any preceding claim in which the gap seal elements (3) are made from plastics materials, preferably nylon or Teflon.

12. Gap seal according to any of Claims 1 to 10, in which the gap seal elements (3) are composed of reinforced plastics materials, preferably from the polyester, epoxy, PEEK, polyimide, bismalimide or phenol resin group, the reinforcement being preferably carbon, glass or aramide fibres.

13. Gap seal according to any preceding Claim in which the gap seal elements (3) are composed of coated sheets or foils, the coating preferably being a film of SiC, TiN or dry-film lubricant.

14. A gap seal substantially as described with reference to any of the embodiments shown in the accompanying drawings.

15. A method of operating a gap seal as claimed in any preceding claim, in which the relative motion of the two components gives rise to a gliding action of the skimming face (6) of each seal element on the second component.

16. A shaft seal incorporating a gap seal according to any of claims 1 to 14.

17. A method of making a gap seal between two components, including the following steps: a foil is taken from a continuous band and folded and compressed 1 in zig-zag fashion; one edge of the compressed zig-zag band is then fixed in the first component; the other edge of the zig-zag band is then removed so that the folded band is cut on that side into single flexible lamellae forming gap seal elements; and finally fluiddynamic skimming faces are formed on the ends of all the gap seal elements.

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