Sealing rings for a labyrinth seal

This application claims priority to German Patent Application DE102009055914.0 filed Nov. 27, 2009, the entirety of which is incorporated by reference herein.

The invention pertains to sealing rings for a labyrinth seal that are arranged on a rotationally symmetrical component and in frictional contact with a stationary run-in layer, particularly for aircraft gas turbines.

Labyrinth seals are, in principle, contactless shaft seals realized in the form of a smooth gap labyrinth or tumbling collar labyrinth, wherein the sealing effect of these labyrinth seals is based on the elongation of the sealing path due to the arrangement or alternate arrangement of sealing rings (rigid circumferential sealing lips) on the rotating part and/or the stationary housing part. In stationary gas turbines and aircraft engines, the labyrinth seals arranged in the region of the compressors and turbines should prevent a backflow of the air and ensure a minimal pressure loss and therefore a high efficiency of the gas turbine. A corresponding sealing system for gas turbines comprises sealing fins that are arranged on the rotor blade tips—and form sealing rings that lie adjacent to one another on the outer circumference of the rotor—and sealing rings that are arranged adjacent to one another on a shaft or the connecting flanges between the rotor disks and cooperate with the inner circumferential surface of a run-in layer that is rigidly mounted in the gas turbine. During the run-in of the gas turbine, the rotating sealing rings rub against the opposite run-in layer and cut into this layer in order to thusly achieve a minimal gap dimension. However, the distance between the run-in layer and the sealing rings may fluctuate during the operation of the gas turbine due to the thermal expansion of the components and a natural deflection.

Due to the friction between the run-in layer and the sealing rings, the upper part of the sealing rings that engages into the run-in layer is subjected to wear such that the required sealing effect is no longer ensured and the sealing rings need to be rebuilt. This is realized by cutting off approximately two thirds of the sealing ring, subsequently rebuilding the sealing ring of the same material by laser build-up welding and then carrying out a finishing process. This repair procedure is elaborate and does not provide protection from future wear. In order to protect the sealing rings (or blade tips) from wear, it is furthermore known to provide the region of the sealing rings that contacts the run-in layer with a wear protection layer that is galvanically or electrolytically applied onto the sealing rings that are initially fabricated with a machining tolerance and then machined again. However, this method is very time-consuming and cost-intensive. In addition, access to the surfaces subjected to wear and to be coated is limited such that a uniform coating with the wear protection material and a sufficient wear protection are not always ensured during the plasma spraying process.

The invention is based on the objective of realizing sealing rings that are in frictional contact with a run-in layer (friction partner) and intended for a labyrinth seal, in particular, for gas turbines in such a way that a superior wear protection is ensured, wherein the invention also aims to disclose a method for cost-efficiently manufacturing sealing rings that are highly resistant to wear.

The basic idea of the invention is that the part of the sealing rings that comes in frictional contact with a friction partner during operation is in the form of a wear protection ring segment that is built up on a truncated sealing ring and includes a metal matrix with wear protection particles embedded therein. The thusly realized sealing rings are characterized by low wear in the entire contact region with the run-in layer and ensure a high sealing effect over a long period of time.

The inventive sealing rings are manufactured in such a way that only truncated sealing rings are initially formed on a rotationally symmetrical component and a mixture of a metal powder and wear protection particles is supplied to the truncated seals and fused thereon layer-by-layer by a laser beam. The method is much more cost-efficient than other wear protection methods and furthermore provides improved wear protection. It can also be used in the repair of worn-out sealing rings.

In another embodiment of the invention, the proportion of wear protection particles in the wear protection ring segment may be greater toward the edge and/or the tip of the sealing ring than in other regions—that are subjected to less or no wear—in accordance with the load.

The arrangement of the wear protection particles is preferably limited to the edge region of the wear protection ring segment.

In another embodiment of the invention, the metal matrix can be made of the same material as the truncated seal or of another material. The wear protection particles are preferably cubic boron nitride (CBN).

According to the inventive method, the proportion of wear protection particles contained in the flow of metal powder supplied to the laser beam can be controlled such that a particularly high wear protection effect can be achieved in certain regions of the sealing ring.

In another embodiment of the invention, a heat treatment of the entire rotationally symmetrical component or a local heat treatment in the region of the sealing rings is carried out after building up the wear protection ring segments on the truncated sealing rings. It would also be possible to forgo the heat treatment under certain circumstances, for example, when a material that differs from the base material is used for the metal matrix with embedded wear protection particles.

One exemplary embodiment of the invention is described below with reference to the drawings, in which

FIG. 1 shows a partial view of the turbine of an aircraft engine with labyrinth seals arranged in this region;

FIG. 2 shows a graphical representation of the process sequence for realizing sealing rings;

FIG. 3 shows a schematic sectional representation of a sealing ring with a graduated distribution of wear protection particles over the height thereof, and

FIG. 4 shows a schematic sectional representation of a sealing ring, in which the incorporation of wear protection particles is limited to the edge region of the sealing ring.

In the partial view of the turbine of an aircraft engine illustrated in FIG. 1 , the arrows indicate the flow direction of the turbine cooling air. The turbine disks are identified by the reference symbol 1 and the turbine blades are identified by the reference symbol 2 . Guide vanes 3 are respectively assigned to the turbine blades 2 . The turbine disks 1 are connected to a turbine shaft 4 and connected to one another by connecting flanges 5 . A first labyrinth seal 6 and a second labyrinth seal 7 are arranged in the region between the turbine disks 1 and ensure the lowest pressure loss possible between the two turbines stages. The labyrinth seals 6 , 7 comprise adjacently arranged sealing rings 8 (sealing lips) that are integrally formed on the respective connecting flange 5 and tapered toward the free end, wherein these sealing rings rotate together with the turbine disks 1 . The first labyrinth seal 6 comprises a stationary run-in layer 12 that is fixed on a stator 11 connected to the engine housing 10 by a holding element 9 and has a honeycomb structure in this case, but may also be realized in the form of another suitable friction partner such as, for example, felt metal that allows the tips of the sealing rings 8 to penetrate into the run-in layer 12 . The sealing gap of the labyrinth seal 6 can be maintained very small in this fashion.

The wear of the sealing rings 8 to be expected due to the frictional contact between the sealing rings 8 and the run-in layer 12 is counteracted in that wear protection particles 13 —for example of a cubic boron nitride—are incorporated into the upper part of the sealing rings 8 that are subjected to the frictional contact with the run-in layer 12 . According to FIG. 3 , the proportion of wear protection particles 13 incorporated into a metal matrix 16 in the upper part of the sealing rings 8 may continuously increase toward the tip of the sealing rings 8 . In addition, the incorporation of wear protection particles 13 may be limited to the edge region in the upper part of the sealing rings 8 as shown in FIG. 4 . In this case, the proportion of wear protection particles 13 may furthermore increase from the bottom toward the top in the edge region.

The above-described sealing rings 8 are manufactured in such a way that, during the fabrication of a rotationally symmetrical component provided with sealing rings 8 such as, for example, a turbine disk 1 for an aircraft engine, only truncated sealing rings 14 are initially realized on the component, in this case the connecting flange 5 between two turbine disks 1 . A wear protection ring segment 15 having wear protection particles 13 embedded in a metal matrix 16 is subsequently built up on the truncated sealing rings 14 by laser build-up welding. According to FIG. 2 , the wear protection ring segment 15 is built up on the respective truncated sealing ring 14 with the aid of a metal powder/wear protection particle mixture 18 that is supplied to a laser beam 17 by a powder nozzle 19 . The metal powder forming the base material is fused on by the laser beam 17 and forms the metal matrix 16 , in which the wear protection particles 13 are embedded. During the layer-by-layer application of the fused-on metal powder, the proportion of wear protection particles 13 in the metal powder/wear protection particle mixture 18 can be controlled in such a way that it continuously increases in each successive layer ( FIG. 3 ) or the wear protection particles 13 are only situated in the edge region of the wear protection ring segment 15 produced on the truncated sealing ring 14 . After the build-up of the wear protection ring segment 15 is completed, a heat treatment (stress relief annealing) of the entire component or only a local heat treatment is carried out, wherein it would also be possible, if applicable, to forgo this heat treatment under optimized process parameters. It is also possible that the metal powder used for producing the wear protection ring segment 15 is not made of the truncated sealing ring material, but of another material.

1 Turbine disk

2 Turbine blade

3 Guide vanes

4 Turbine shaft

5 Connecting flange

6 First labyrinth seal

7 Second labyrinth seal

8 Sealing rings

9 Holding element

10 Engine housing

11 Stator

12 Run-in layer (friction partner)

13 Wear protection particles

14 Truncated sealing ring

15 Wear protection ring segment

16 Metal matrix

17 Laser beam

18 Metal powder/wear protection particle mixture

19 Powder nozzle