Patent Application
20100259013
This application claims priority to German Patent Application DE102009016803.6 filed Apr. 9, 2009, the entirety of which is incorporated by reference herein.
This invention relates to an abradable labyrinth seal for a fluid-flow machine for sealing a sealing gap between a stationary carrier provided with an abradable lining of porous material formed by hollow bodies and a rotary component provided with sealing fins oriented towards the abradable lining, in particular for hot gas sealing in the area of the turbine of a gas-turbine engine.
On machines with flowing fluids, it is often necessary to seal gaps between moving and static components against the flowing medium. The quality of the seals used for this purpose considerably influences the efficiency of these machines. For sealing the gap, as is generally known, labyrinth seals are used which include several, circumferential sealing strips or sealing fins arranged at a certain distance to each other and extending transversely to the flow direction. In order to minimize the radial gap between the rotary and the stationary component to improve the efficiency and performance of fluid-flow machines, it is possible to let the tips of the sealing strips rub against an abradable lining. However, the abradable seals shall not only prevent the respective stage of the fluid-flow machine from being flown over, but also thermally insulate the casing structure, for example the hot-gas conveying wall sections of a turbine stage, or control the heat flux into the wall sections in such a manner that the thermal expansion of the stationary components or the casing expansion, respectively, corresponds to the thermal expansion of the rotary components, i.e. the rotor disks and blades, thereby ensuring a minimum gap dimension in dependence of the operating conditions or the hot-gas temperatures, respectively.
As is generally known, honeycomb structures filled with a thermal insulating material are used as rub-in or abradable lining, respectively, which, while having good rubbing or wear characteristics, do not satisfy the respective requirements on the thermal insulation of the stationary component with regard to obtaining a constantly small gap width. Furthermore, smearing may occur in the rubbing area between the sealing fins and the honeycomb structure which may result in overheating and, finally, cracking of the sealing fins.
Specification EP 1013890 B1 describes an abradable labyrinth seal whose abradable lining completely consists of a foamed, metallic, corrosion-resistant high-temperature alloy, i.e. a metal foam with closed-pore structure in which thin walls enclose between them a plurality of cavities. Alternatively, it has also been proposed to produce such a structure from pre-made metallic hollow spheres. The foam structure used as abradable lining has high heat-insulating effect. However, due to the irregularity of the foam structure, material accumulations with resultant strong heating as well as chipping of the brittle metal foam structure may occur here as well. Furthermore, this abradable structure does not allow the thermal insulation to be adequately influenceable in accordance with the varying temperature conditions in the fluid-flow machine, for example the different hot-gas temperatures in the areas of the high-pressure turbine and the low-pressure turbine of a gas-turbine engine.
In a broad aspect, the present invention provides an abradable labyrinth seal with thermal insulation adapted to the respective operational situation and reliable sealing effect as well as a long service life.
On the basis of an abradable labyrinth seal for a fluid-flow machine for sealing a sealing gap between a stationary carrier provided with an abradable lining of porous material formed by hollow bodies and a rotary component provided with sealing fins oriented towards the abradable lining, the present invention, in its essence, provides that hollow bodies conforming in shape and size are exactly linearly arranged side by side and one above the other in x, y and z direction and are interfacially connected and form an ordered, open or closed-pore cellular structure, with the hollow bodies being arranged and orientated such that the tips of the sealing fins approximately centrally meet the hollow bodies. Since the hollow bodies are arranged such that the tips of the sealing fins essentially centrally contact the hollow bodies, material accumulations resulting in excessive heating and consequential cracking of the sealing fins will not occur. Thus, a reliable sealing effect, safe operation and long service life of the fluid-flow machine are ensured. Depending on the required thermal insulation relative to the carrier component, the degree of open-porosity is variable and may also be zero where maximum heat insulation is required.
The abradable lining is produced by sintering green spheres including a core coated with sinterable metal powder under temperature and pressure, with the core material outgassing in the process and the remaining hollow spheres being interfacially joined and formed to produce a longitudinal elongation in flow direction. Thus, it is more easily possible that the sealing strips essentially centrally meet the hollow bodies and not the material accumulations of the hollow-body structure. However, the hollow bodies can also be designed as radially or tangentially elongating elements.
The shape of the hollow bodies and the amount of interfacial contact therebetween as well as the amount and proportion of open pores is controlled by the amount and type of the pressure applied on the linearly arranged green-sphere sinter material.
In a further development of the present invention, layers of relatively small hollow bodies located in the existing interspaces can be arranged between the individual hollow-body layers to provide for the reduction of open porosity or the formation of a closed-pore abradable lining.
The present invention is more fully described in light of the accompanying drawing showing a preferred embodiment. In the drawing,
In
The abradable lining 10 is a defined, ordered cellular structure of hollow bodies 11 made of high-temperature resistant, sintered material and essentially conforming in shape and size and connected to each other by sintering under pressure and being exactly linearly arranged to each other in x, y and z direction, forming here three hollow-body layers 13 lying exactly one above the other. An essential feature of the abradable labyrinth seal is that the hollow bodies 11 of the abradable lining 10 are positioned such in relation to the sealing fins 8 that the tips of the latter are essentially centrally orientated to the hollow bodies 11 of the abradable lining 10. Thus, accumulation of material during rubbing of the abradable lining 10 and, in consequence thereof, severe heating or even cracking of the sealing fins 8 is precluded.
The ordered cellular structure for the abradable lining 10 is produced by sintering of styrofoam spheres coated with a sinterable metal powder. In a preferred method, the green spheres, yet unsintered and coated with the sintering material to the required wall thickness, are, for the production of the hollow sphere structure (abradable lining 10), placed in a mold and sintered therein by application of pressure and temperature and simultaneously joined to each other by sintering. According to the pressure force and pressure direction applied, the hollow spheres produced during sintering are flattened at the mating faces with the mold wall or the adjacent hollow spheres and, as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 016 803.6 | Apr 2009 | DE | national |
