Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Laminated – embedded member or encased material
Reexamination Certificate
1999-11-15
2001-09-11
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Laminated, embedded member or encased material
C416S233000, C416S24100B, C415S200000
Reexamination Certificate
active
06287080
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a gas turbine blade composed of two or more components made from different materials, and more particularly to a formulation used in the construction of a lightweight jet engine fan blade.
2. Discussion of the Prior Art
Gas turbines include, but are not limited to, gas turbine power generation equipment and gas turbine aircraft engines. A gas turbine includes a core engine having a high pressure compressor to compress the air flow entering the core engine, a combustor in which a mixture of fuel and the compressed air is burned to generate a propulsive gas flow, and a high pressure turbine which is rotated by the propulsive gas flow and which is connected by a larger diameter shaft to drive the high pressure compressor. A typical front fan gas turbine aircraft engine adds a low pressure turbine (located aft of the high pressure turbine) which is connected by a smaller diameter coaxial shaft to drive a front fan (located forward of the high pressure compressor) and to drive an optional low pressure compressor (located between the front fan and the high pressure compressor). The low pressure compressor sometimes is called a booster compressor or simply a booster.
The fan and the high and low pressure compressors and turbines have airfoils each including an airfoil portion attached to a shank portion. Rotor blades are those airfoils which are attached to a rotating gas turbine rotor disc. Stator vanes are stationary airfoils which are attached to a non-rotating gas turbine stator casing. Typically, there are alternating circumferential rows of radially-outwardly extending rotor blades and radially-inwardly extending stator vanes. When present, a first and/or last row of stator vanes (also called inlet and outlet guide vanes) may have their radially-inward ends also attached to a non-rotating gas turbine stator casing. Counterrotating “stator” vanes are also known.
Conventional airfoil designs used in the compressor section at the engine typically have airfoil portions that are made entirely of metal, such as titanium, or are made entirely of a composite. A “composite” is defined to be a material having any (metal or non-metal) fiber filament embedded in any (metal or non-metal) matrix binder, but the term “composite” does not include a metal fiber embedded in a metal matrix. The term “metal” includes alloys such as titanium Alloy 6-2-4-2. An example of a composite is a material having graphite filaments embedded in an epoxy resin.
The all-metal blades, including costly wide-chord hollow blades, are heavier in weight which results in lower fuel performance and require sturdier blade attachments, while the lighter all-composite blades are more susceptible to damage from bird ingestion events. Known hybrid blades include a composite blade having an airfoil shape which is covered by a surface cladding (with only the blade tip and the leading and trailing edge portions of the surface cladding comprising a metal) for erosion and foreign object impacts. The fan blades typically are the largest (and therefore the heaviest) blades in a gas turbine aircraft engine, and the front fan blades are usually the first to be impacted by foreign objects such as birds. What is needed is a lighter-weight gas turbine blade, and especially an aircraft-engine gas turbine fan blade, which is both lighter in weight and better resistant to damage from ingestion of foreign objects and blade out events.
SUMMARY OF THE INVENTION
The present invention is a formulation which can be cured onto a metal aircraft engine fan blade, thereby making the blade lighter, without sacrificing any of the structural integrity of the blade, that is, its resistance to foreign object impacts and the like.
The formulation comprises a polyurethane elastomer composition, formed by adding an anti-oxidant to a curative, melting the resultant composition, and mixing the composition. The curative with anti-oxidant is then mixed with a prepolymer, thereby forming a polyurethane composition, and cast into a preheated mold. The mold holding the polyurethane is placed into an oven at a predetermined temperature for a predetermined period of time, and thereafter, the polyurethane is demolded and placed into an oven at a predetermined temperature for a predetermined period of time sufficient to cure the polyurethane elastomeric composition.
Each mold is formed by a cavity within the metallic fan blade in the form of a pocket and a removable caul sheet. Each fan blade may have a plurality of pockets. The caul sheet is a composite that is affixed to the fan blade so that each of the pockets is temporarily enclosed. The caul sheet includes at least one injection port to provide a flow path for the uncured elastomer into the pockets, which have assumed the shape of a mold with the attachment of the composite caul sheet. The details of the injection system are the subject of co-pending application identified as Attorney Docket 13DV-12944 assigned to the Assignee of the present invention, incorporated herein by reference. After the polyurethane elastomeric composition is injected through at least one injector port into the mold, the elastomer is cured.
In one alternate embodiment, an anti-oxidant and/or a hindered amine light stabilizer and/or an ultraviolet absorber are optionally added to the curative. These chemical formulations assist in preventing deterioration of the blade as a result of exposure to radiation from the sun and exposure to the atmosphere as desired, thereby, when included, extending the life of the elastomer and the blade. Thus, the combination of additives can provide high temperature optimization and environmental protection.
An advantage of the present invention is that the polyurethane elastomer can be cured directly to the blade. Because the pockets form part of the mold, the polyurethane elastomer mates with essentially 100% of the available interface surface area of the blade. Because of the excellent adhesive characteristics of the elastomer to the metal, the maximization of the surface area contact between the elastomer and the metal provides for a strongly bonded insert.
Another advantage of the present invention is that since the polyurethane elastomeric insert is cured in place, there is no misfit between the pocket and the blade so that the blade having the cured elastomeric insert is aerodynamic, with little or no trimming required to remove excess material. This permits unimpeded flow of air entering the compressor while allowing the blade to operate at temperatures up to 310° F.(155° C.).
Another advantage of the present invention is that the blade having the cured elastomeric inserts is significantly lighter than a corresponding blade comprised solely of a metallic alloy, yet provides aerodynamic stability of such a blade. This weight advantage provides a corresponding improvement in fuel efficiency of the engine without adverse effects on performance.
Still another advantage of the present invention is the cost savings associated with replacing expensive metallic alloys such as titanium alloys with inexpensive polyurethane elastomers.
Finally, the present invention provides an advantage over a system in which elastomers are cured and then assembled into the pockets with an adhesive, since the time consuming and labor intensive step of adhesive bonding is eliminated and the potential for unbonded interfaces between the elastomer and the blade pocket is greatly reduced. The current system is self-adhesive and problems with fit-up are eliminated.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
REFERENCES:
patent: 5295789 (1994-03-01), Daguet
patent: 5634771 (1997-06-01), Howard et al.
patent: 5655883 (1997-08-01), Schilling
patent: 5720597 (1998-02-01), Wang et al.
patent: 5791879 (1998-08-01), Fitz
Begovich, Jr. Joseph T.
Chao Herbert S.
Evans Charles R.
Lin Wendy W.
Ward Douglas D.
General Electric Company
Hess Andrew C.
Look Edward K.
McAleenan James M
Narciso David L.
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