Fluid reaction surfaces (i.e. – impellers) – Multiple axially spaced working members
Reexamination Certificate
1999-04-13
2001-06-26
Lopez, F. Daniel (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Multiple axially spaced working members
C416S20100A, C416S24100B, C416S20400A, C416S24400R
Reexamination Certificate
active
06250883
ABSTRACT:
TECHNICAL FIELD
The present invention relates to gas turbine engines and in particular to ceramic turbine wheels for use in such engines.
BACKGROUND OF THE INVENTION
It has long been recognized that the efficiency and performance of gas turbine engines could be improved by increasing the temperature of the gas through the engine's turbine section. Historically, these temperatures have been limited by the materials used, usually high temperature steel or nickel alloys, to form the first stage turbine wheel. The first stage being downstream of the engine's combustor experiences some of the highest gas and metal temperatures in the engine. To permit higher gas temperatures it has been proposed to form the first stage turbine wheel from a ceramic material such as silicon nitride (Si
3
N
4
) or silicon carbide (SiC). In particular, it is has been proposed to use a ceramic blisk wheel, which is a wheel where the blades and disk are one piece. However, the attachment of a ceramic blisk to surrounding metal components in an engine is complicated by their different thermal expansion properties. Metals expand and contract as temperature changes while ceramics in comparison expand and contract very little. Thus, the attachment mechanism used to mount the ceramic blisk in an engine must meet a number of criteria. First, it must provide the proper radial positioning, also referred to as piloting, of the blisk to control any unbalance which may result in unacceptable engine vibration. Second, it must be able to transfer torque from the blisk to the engine shaft without generating unacceptable contact stresses on the blisk. Lastly, it must maintain the integrity of the engine components in the event that the blisk fails. Unlike metals, when ceramic fails it often powderizes. For a ceramic blisk in a stack of components which are secured by a tieshaft, loss of the blisk will leave an axial gap. Due to axial forces acting on the components, these components will move axially to fill this gap, which can result in a failure of the entire engine.
Accordingly, a need exists for a mounting assembly for holding a ceramic blisk in a gas turbine engine that provides the proper radial positioning, allows torque transfer without undue contact stress, and maintains the integrity of the rotating components in the event of a failure of the blisk.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a ceramic blisk assembly that properly positions the blisk in the radial direction.
Another object of the present invention is to provide a ceramic blisk assembly that allows for torque transfer without generating unacceptable contact stresses on the blisk.
Yet another object of the present invention is to provide a ceramic blisk assembly that maintains the integrity of the rotating components in the event that the blisk fails.
The present invention accomplishes these objects by providing a ceramic blisk assembly that comprises a ceramic blisk having a forward and aft axial facing surface. To allow for torque transfer from the blisk, a forward and aft attachment ring contact the forward and aft axial facing surfaces respectively. These rings are mounted to other rotating components in the engine and are made of metal. A metal shim or precious metal coating may be disposed between the contacting surfaces to further reduce any stresses at the point of contact. To provide radial piloting, metal pilot rings are disposed underneath the regions where the attachment rings and blisk make contact. Lastly, the aft attachment ring has an axially extending base portion that is slightly spaced apart from a stop that extends inwardly from the forward attachment ring. This arrangement prevents the other components in the engine from shifting in the event that the blisk fails.
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“Brevet D'Invention. Rotor en matieres ceramiques, en particular pour turbines a gaz,” Ministere de la Production Industrielle, Republique Francaise, Apr. 1944.
Meacham Walter Lee
Robinson Daniel Joe
Allied-Signal Inc.
Lopez F. Daniel
Woo Richard
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