Stock material or miscellaneous articles – All metal or with adjacent metals – Mass of only fibers
Patent
1993-05-17
1994-07-05
Zimmerman, John
Stock material or miscellaneous articles
All metal or with adjacent metals
Mass of only fibers
428608, 4151745, 277 53, 427216, B32B 502, F01D 1102, B22F 326
Patent
active
053266471
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 continuation of PCT/EP 92/01812 filed Aug. 8,
1992, pending.
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to an abradable layer for labyrinth seals of a turbo-engine, particularly a gas turbine, made of a layered composite material with a core and a shell and embedments, and to a process for the manufacturing of this abradable layer.
Abradable layers for turbo-engines are known from the European patent Document EP-OS 0 166 940. The abradable layers disclosed there have the purpose of keeping the radial gap between the rotor blades and the housing as small as possible. When such abradable layers for labyrinth seals having, for example, labyrinth peaks, are used on the rotor shaft and the abradable layer on the housing, the danger of self-ignition of the abradable layer exists. This danger exists because, at the inlet, the labyrinth peaks are in a much more intensive frictional contact with the abradable layer than the individual blade tips of a rotor with the housing abradable layer.
For this reason, the abradable layers are not, as disclosed in the European Patent Document EP-OS 0 166 940 made of a core material of graphite or ceramics, but of a metal felt or metal fabric which better carries off heat, without any sheathings or embedments.
Despite this difference, engine failures occur as a result of the self-ignition of abradable layers made of metal felt or metal fabric on labyrinth seals. In this case, there is a local overheating of the metal felt or metal fabric as a result of an intensive frictional contact with the labyrinth peaks. As a result, there are exothermal reactions between condensed hot atmospheric oxygen (0.4 to 1 MPa at 280.degree. to 600.degree. C.) and the large specific oxidizable metal surface of the metal felt or metal fabric. In this case, the combustion rate is higher than the carrying-off of heat so that the seal construction is destroyed in an explosive manner. In this case, there may also be a partial welding-together of the abradable layer material with the rotor.
It is an object of the present invention to provide an abradable layer of the above-mentioned type with improved starting and grind-in characteristics in the case of which an exothermal reaction is checked, and the thermal conduction characteristics are improved.
According to the present invention, this object is achieved in that the core is made of a felted or three-dimensionally crosslinked fiber body of iron, nickel or cobalt base alloys. The shell is made of one or several precious-metal alloys. Each metal core is surrounded by the shell material. The embedments consist of oxidation-resistant sliding materials from the group of oxides, carbides or nitrides with a hexagonal crystal lattice layer structure.
This solution has the advantage that the core made of an iron, nickel or cobalt alloy furnishes the required stability in order to form an abradable layer that corresponds to the shape. The precious metal shell has a higher resistance to oxidation than the dimensionally stable core material and limits and prevents the propagation of an exothermal reaction through the oxidation-resistant barrier layer. The fiber body starts to glow locally and also partially starts to melt so that the seal is ground in, but an explosion-type propagation of the combustion is prevented. At the same time, the precious metal shell increases the carrying-off of heat because precious metals, as a result of their higher electron mobility, exhibit a higher heat conduction than non-precious metals.
In the case of conventional abradable layers for blade devices, embedments have the task of grinding in the metallic blade tips and therefore consist of corundum or other hard grinding particles. In the case of labyrinth seals, such grinding particles would wear away the metallic peaks of the labyrinth seals and would increase the leakage rate. The embedments according to the invention, consisting of sliding materials from the group of oxides, carbides or nitrides with a hexagonal crystal lattice l
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Merz Herbert
Weiler Wolfgang
MTU Motoren -Und Turbinen-Union
Zimmerman John
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