Patent Application
20090047132
This invention relates generally to turbine engines, and more specifically to blades used in axial compression systems.
In a gas turbine engine, air is pressurized in a compression module during operation. The air channeled through the compression module is mixed with fuel in a combustor and ignited, generating hot combustion gases which flow through turbine stages that extract energy therefrom for powering the fan and compressor rotors and generating engine thrust to propel an aircraft in flight or to power a load, such as an electrical generator.
The compression system includes a rotor assembly comprising a plurality of rotor blades extending radially outward from a disk. More specifically, each rotor blade has a dovetail which engages with the disk, a platform forming a part of the flow path, and an airfoil extending radially from the platform to a tip. The platform may be made integral to the blade or, alternatively, made separately.
In some designs, the rotor blade, especially those in a fan rotor and the front stages of a multistage compression system, have a pair of circumferentially extending shrouds on the airfoil, one projecting from the pressure surface and one projecting from the suction surface. The shrouds are located at a radial location between the blade dovetail and the blade tip. In some other designs, the shrouds may be located at the tip of the blade airfoil. During normal operation of the compression system, the blades twist and the shrouds on adjacent blades contact with each other, forming a shroud ring that provides support to the blades. During engine operation, the shroud ring resists vibration and twisting of the blades. The term “midspan shroud” is used herein to refer to all supports on fan and compression system blades that contact with each other during operation, and includes all supports located anywhere on the span of the blade, including supports at the tip of the blade. The “midspan shrouds”, as used herein, may be located anywhere along the blade span, not just at the midpoint of the span.
During certain abnormal events, such as a bird impact, other foreign object impact, or stalls during engine operation, the normal contact between the shrouds of adjacent blades is disturbed. The contact forces become high and misaligned due to the impacts and the shrouds become disengaged fully or partially. This is called “shingling” of the blades. Shingling causes significant wear and tear damage on the midspan shrouds. When the speed of the compressor rotor drops, the shingled blades may rebound, causing further wear and tear on the shrouds.
Conventional blades sometimes have wear pads brazed on the contact faces on the midspan shrouds. Wear pads 51, 52, such as shown in
It is desirable to have a durable blade with wear pads that resist impact and tear type of damage, and further resist such damage when the compression system blades rebound from shingling. It is desirable to have manufacturing methods to apply the wear pads and brazing in such a way that the blades are durable. It is desirable to have repair methods to apply the durable wear pads to blades that have been used in service.
The above-mentioned needs may be met by exemplary embodiments with at least one recess on the midspan shroud and a wear pad attached into the recess of the midspan shroud.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding part of the specification. The invention, however, may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
In operation, air flows through fan assembly blades 24 and compressed air is supplied to high pressure compressor 14. The air discharged from fan assembly 122 is channeled to compressor 14 wherein the airflow is further compressed and channeled to combustor 16. Products of combustion from combustor 16 are utilized to drive turbines 18 and 20, and turbine 20 drives fan assembly 122 via shaft 31. Engine 10 is operable at a range of operating conditions between design operating conditions and off-design operating conditions.
Moreover, during shingling events, such as due to bird impact or other unusual loading events, the contact forces between the adjacent midspan shrouds and their orientations are changed such that the midspan shrouds become disengaged, resulting in shingling. This is schematically shown in
A preferred embodiment of the invention is shown in
In the preferred embodiment, the softer AuCuNi foil reduces braze interface separations. As explained previously, the side pull and tear damage of the midspan shroud 25, 26 wear pad 51, 52 are very significant when shingled midspan shrouds rebound. It has been seen that such a failure of the wear pad is a cohesive failure (within the wear pad) rather than adhesive (in the interface). To prevent cohesive failure of the wear pad 251, 252 due to tear during a shingling event, in the preferred embodiment shown in
A durable blade 224 is made by forming a recess 257, 258 on the midspan shroud 225, 226 face 261, 262 using conventional means such as machining.
The recessed wear pad 251, 252 can be used to repair blades that have been used in service in order to improve their durability. For blades that have been used in service, the repair process involves several steps comprising: removal of any existing wear pad by a suitable method such as a chemical or mechanical method, machining the midspan shroud, cleaning and inspection, building up the midspan shroud by welding if necessary, blending any weld build up by machining, heat treating, forming a recess 257, 258 on the face 261, 262 of the shroud 225, 226 such as shown in
In the preferred embodiments of the durable blade, its manufacturing method and the repair method, AuCuNi foil 255, 256 of thickness 1-3 mils is placed into a previously formed recessed groove 257, 258 of a Ti-6Al-4V blade midspan shroud 225, 226. The WC—Co wear pad 251, 252 is placed on top of the braze foil 255, 256. The blade 224 is placed into a vacuum chamber for induction brazing. The midspan shroud 225, 226 is placed into the induction coil. AC current passes through the coil and generates a magnetic field in the midspan shroud which generates eddy currents in the shroud which rapidly increases the temperature to brazing range. Brazing temperature is 1750-1900 F. Duration for the braze is about 1-3 minutes. Vacuum used is about 10̂−5 torr.
In alternative embodiments of the present invention, other wear pad materials and braze foils may be used in recesses formed in the midspan shroud contact faces using the teachings herein. It is possible to use the wear pads 251, 252 on only certain selected regions of the blade contact surfaces 261, 262. It is also possible to apply the teachings herein to other locations on the blades which may experience shingling, such as for example, blade platforms and tip shrouds.
While there have been described herein what are considered to be preferred and exemplary embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein, and it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention.
