Metal working – Method of mechanical manufacture – Impeller making
Reexamination Certificate
1999-07-02
2001-03-20
Cuda Rosenbaum, I (Department: 3726)
Metal working
Method of mechanical manufacture
Impeller making
C029S889100
Reexamination Certificate
active
06202302
ABSTRACT:
DESCRIPTION
1. Technical Field
This invention relates to a method for forming a modular section of a rotary machine and more particularly to a method that avoids the need to disassemble and reassemble portions of the stator assembly after a machining operation.
2. Background of the Invention
An axial flow rotary machine, such as a gas turbine engine for an aircraft, has a compression section, a combustion section, and a turbine section. An annular flow path for working medium gases extends axially through the sections of the engine.
The engine adds fuel to the working medium gases and burns the fuel in the combustion section to form hot, pressurized gases. The hot, working medium gases are expanded through the turbine section to extract energy as work from the gases. The energy is transferred to the compression section to raise the pressure of the incoming gases.
The turbine section includes a rotor for receiving this work from the hot working medium gases. The rotor extends axially through the engine. The rotor includes a rotor assembly in the compression section and a rotor assembly in the turbine section. The rotor assemblies includes arrays of rotor blades which extend outwardly across the working medium flow path through which the gases are directed. Rotor blades in the turbine section receive energy from the hot, working medium gases and drive the rotor assembly at high speeds about an axis of rotation. Rotor blades in the compression section transfer energy to the working medium gases to compress the gases as the airfoils are driven about the axis of rotation by the rotor assembly.
The engine includes a stator disposed about the rotor. The stator includes a stator assembly having an outer case. The outer case extends circumferentially about the flow path to bound the working medium flow path. The stator assembly includes seal elements, such as a circumferentially extending seal member which is disposed radially about the rotor assembly. The seal member is formed of arcuate segments which permit the seal member to change diameter in response to operative conditions of the engine. The seal member cooperates with knife edge elements on the rotor assembly to form a seal that blocks the leakage of working medium gases from the flowpath. The seal member is ground to a precise contour such that the seal member can be disposed in close proximity to the rotor assembly.
The stator assembly also has arrays of stator vanes which extend radially inwardly across the working medium flow path. The stator vanes are commonly called vane clusters and have one or more airfoils or stator vanes. The stator vanes are disposed between the arrays of rotor blades in both the compression section and turbine section. The stator vanes guide the working medium gases as the gases are flowed along the flow path. Each has an airfoil which is designed to receive, interact with and discharge the working medium gases as the gases are flowed through the engine.
The airfoils in the turbine section are bathed in hot working medium gases under operative conditions. Certain airfoils in the turbine section, such as stator vanes in the high pressure turbine, are cooled by flowing cooling air through the airfoil to avoid unacceptably high temperatures in the walls of the airfoil. Each stator vane has one or more large openings near the outer case for receiving the cooling air. The stator vane has many small cooling air holes which extend from the interior to the exterior of the airfoil. The cooling air holes discharge cooling air and cool the airfoil by convection and by providing film cooling to regions of the airfoil such as the leading edge or the trailing edge.
The cooling holes which provide this film cooling and convection cooling are very small and are precisely located to avoid over temperaturing critical regions of the stator vane under operative conditions. The holes may be as small as 14 to 20 mils (0.014 to 0.020 inches) in diameter and are easily plugged by any small particles which might inadvertently enter the stator vanes during fabrication and assembly. Plugging the holes will block the flow of cooling air and will cause premature failure of the turbine vane. This results in a loss of engine efficiency and expense in replacing the turbine vane. These particles are removed from the stator vanes prior to final build-up of the case and stator vane assembly. Final build-up of the case and the stator vane assembly might occur by disposing the assembly directly in the engine or in a modular unit of the engine. The modular unit of the engine is later assembled into the remainder of the engine.
Machining operations of various components in the engine during assembly and final build up of the engine create the type of particles which are able to enter the turbine vane. These particles are small enough to plug the cooling air holes if carried into the cooling air holes under operative condition.
An example of one machining process creating small particles is the final grinding of the contour of the seal element mentioned above for the turbine section. This precision machine operation, commonly referred to as a grinding operation, takes place with the vane clusters installed in the case that supports the clusters. The seal is then ground to the final contour required for the seal member. Thereafter, the vane clusters are disassembled from the engine case. The vane clusters are individually cleaned. After cleaning, the vane clusters are inspected for handling damage and are reassembled to the turbine case. During reassembly, feather seal members are disposed in feather seal slots between adjacent segments if required by the design. These feather seals prevent leakage of gases from the flow path through the gap between adjacent segments.
There may be difficulty in inserting the feather seal at final assembly in the appropriate slots because of tolerance variations between the location of the slots and because the surface of the seal element must be reassembled to form a smooth contour. Adjacent segments are preferably kept together during assembly and disassembly to keep the orientation in which they were ground so that surfaces will evenly match upon reinstallation in the turbine case. Again, because of tolerance variations, it is important that adjacent segments remain together during cleaning and reassembly to insure that the as-ground contour of the seal is minimally disturbed by reassembly. Occasionally, the seal segments must be re-ground to replace an individual seal segment that was replaced because of damage during handling. This requires reassembly of the vane clusters and seal segments into the case and regrinding of the entire seal member.
Although the process of disassembly and cleaning may add many hours of labor and increase processing time by several days, the end result is an acceptable assembled case and stator vane assembly. For example, the case and vane assembly will have an acceptable relationship between the surface of adjacent seal segments. Cleaning will have removed any particles of seal material that were generated during the grinding operation and that were carried into the interior of the stator vane by the machining fluid or which entered after seal particles were thrown into the air by the grinding process.
The above art notwithstanding, engineers working under the direction of Applicant's assignee have sought to reduce the processing time for forming the final contour of the seal member without affecting the final result of matched seal segments and the clean interior on the turbine vanes so that the case and vane assembly may then be assembled into a modular unit or directly installed in the engine.
SUMMARY OF INVENTION
This invention is in part predicated on the recognition that masking portions of the case and stator vane assembly during the grinding operation of the seal member may block the movement of seal particles into the interior of some and even all of the stator vanes during the grinding operation and avoid the necessity of disassembling the stator vanes from
Cuda Rosenbaum I
Fleischhauer Gene D.
United Technologies Corporation
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