Apparatus For Aligning And Arc-removing Turbine Nozzle Vanes

Abstract

The present disclosure relates to a method and means for precisely aligning a particularly shaped element having a hollow cross-sectional area, in this case an arcuately contoured hollow turbine nozzle vane, with a pair of correspondingly shaped electrodes to permit the vane's precise arc removal without damaging the structure on which the vanes are mounted.

Description

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Gas turbine nozzle assemblies circumferentially or laterally deformed including a few damaged vanes, have been discarded simply for want of adequate removal devices. Attempts at hand removal of the damaged vanes inevitably results in the destruction of the nozzle assembly due to their weight reducing construction and high burning currents used in electrode or arc removal destroys the vane's supporting structure by improper placement of the electrodes. Many gas turbine or similar assemblies have been discarded for want of an adequate aligning and removing device.

The present invention is directed to providing an apparatus for positioning a shaped vane or nozzle assembly and ensuring the precise arc removal by providing a vertically displaceable carriage carrying a cross-shaped bracket securing the assembly. The nozzle assembly having at least one defective vane is positioned to align these vanes with a correspondingly shaped electrode means mounted on a bed. Operatively disposed with respect to the electrode means, an aligning means including a guide member, a follower member and a holding member precisely aligns the vane to permit the precise removal upon electrical contact thereof without incurring damage to the supporting structure of the nozzle assembly.

A fundamental object of the invention is to provide an apparatus for positioning and ensuring the precise arc removal of a discretely shaped vane.

Another object is to ensure such precise arc removal without damaging the vane's supporting structure.

An additional object of the invention is to provide a means for modifying existing electrolytic-discharge metal-removing machines to greatly increase the adaptability of such machines for precise arc removal work.

Yet another object is to provide an apparatus for enabling the removal of hollow gas turbine nozzle vanes with minimum or no damage to the vanes' supporting structure.

An additional object is to ensure operator safety by eliminating less stable platforms hitherto used in high current arc removal operations.

These and other objects of the invention will become more apparent and more readily understood with the included drawings and ensuing description.

FIG. 1 is a perspective view of the invention supporting a portion of the turbine nozzle assembly;

FIG. 2 is a side view of the invention with the nozzle assembly in cross section;

FIG. 3a is a front view of the principal components of the aligning means;

FIG. 3b is an end view, shown partially in section, of the aligning means;

FIG. 3c depicts the spring biased finger in detail;

FIG. 4 is a partial perspective view of the invention operatively engaging the turbine assembly with the first electrode removing the connection between a turbine nozzle vane and the inner annular rim;

FIG. 5 is a partial perspective view showing the second electrode removing the connection between the turbine nozzle vane and the outer annular rim.

PREFERRED EMBODIMENT OF THE INVENTION

Referring now to the drawings, FIG. 1 shows the main portions of an electric discharge metal removing machine including a carriage 10 and a bed 11. The carriage is carried on a support, not shown, in mechanically cooperating ways for imparting vertical reciprocal motion.

Gas turbine nozzle assemblies are included in every gas turbine engine for properly directing the passage of gases onto moveable turbine blades carried within the engine. Noting the drawings, such a turbine nozzle assembly 9, only a portion of which being shown in FIGS. 1, 4, and 5 for simplicity, is generally constructed of an inner annular rim 9a and an outer annular rim 9b between which a plurality of turbine nozzle vanes 9c are secured. Because of weight limitations, the assembly must be constructed of lightweight materials and, because of the temperatures involved, sophisticated alloys must be used. An example nozzle assembly is constructed of a 50 percent cobalt metal alloy with the hollow nozzle vanes having a substantially arcuate cross-sectional area. Upon the damaging or deterioration of one or more vanes, removal by arc burning has been difficult due to the nature of the metal and the relatively lightweight construction. Failure to provide precise alignment between a burning electrode and a damaged vane results in the destruction of either the inner or the outer annular rim, in which case, the assembly is discarded.

A cross or X-shaped bracket mechanism 13 is journaled onto an outwardly extending shaft 12 secured to the carriage and includes four radially extending arms 15. Each of the arms carries a thumb screw clamp 16 that permits the free rotation on the shaft when its respective clamp block 16a is not screwed into frictional engagement with a disc element 14. The disc element, affixed to the carriage, and the selectively engaging clamp block provide solid anchoring of a bracket-mounted nozzle assembly at a desired degree of angular rotation. A commercially available toggle latch 17 is bolted onto the outward end of each arm and is each adapted to force its piston 17a against a flattened portion of the inner annular rim 9a when the rim has been positioned with one of its holes engaging an adjacent mounting pin 17b (note FIG. 1 shows the upper two toggle latches with their pistons and mounting pins engaging a portion of the inner annular rim while the bottom toggle latches are open or disengaged).

A pair of guiding bars 18 are pivotally disposed on the carriage, each on a pin 18a, and, through a separate guiding screw 19, impart a lateral displacement to a turbine nozzle assembly mounted on the X-shaped bracket mechanism in the manner set out above. Such displacement not only corrects possible axial deformation of the nozzle assembly as the assembly operatively opposes the burning electrodes 32 and 33, but also serves to more securely anchor the assembly.

Fixedly connected on bed 11, a base plate 30 supports a U-shaped electrode mounting block 31 carrying a pair of substantially opposed electrodes 32 and 33. Each electrode, preferably made of carbon or a similar refractory material, is shaped to substantially correspond to the cross-sectional configuration and area of the turbine nozzle vanes sought to be removed. The electrodes are insulated from the mounting block and are electrically connected to a conductor 34 extending to a remotely located high-current source. Here it should be pointed out that a similar electrical conductor 35 connected to the carriage is coupled to the opposite polarity of the same source to provide a closed electrical circuit between the electrodes, nozzle assembly, and the carriage when the burning or arc removal operation is occurring.

Extreme heat present in gas turbine engines and mechanical stress and strains often cause a lateral or circumferential shift of the inner annular rim 9a with respect to the outer annular rim 9b with the result that a precise vane-electrode alignment is extremely difficult. While the above disclosed means for securing the nozzle assembly onto the carriage does, in part, straighten a deformed nozzle assembly, there usually still exists a partial deformation and a consequent destruction of the assembly because of vane-electrode malalignment.

A means for correcting such malalignment is included as an essential part of the instant invention and consists of an insulating strip member 36 electrically insulating a longitudinal guide member 37 slideably supporting a block shaped follower member 38. Mechanically cooperating dadoed surfaces on the guide member and the follower member permit a selective longitudinal displacement of the follower member in accordance with different sized turbine nozzle assemblies. A roller pin 39 is provided for resting on the outer annular rim as best shown in FIG. 4 and a spring-biased finger member 40 having a portion 40a is carried on the follower member.

The members 36, 37, and 38 of the aligning means are orientated and mounted with respect to the electrodes 32 and 33 so that when portion 40a of the finger member abuts the trailing edge of damaged vane disposed on a bracket mounted nozzle assembly, the electrodes and the damaged vane are in precise alignment. However, it has been found that when an inner annular rim has been shifted with respect to an outer annular rim, alignment of both ends of a damaged vane to both electrodes could not be made. A keeper groove 41 was provided across follower member 38 and a finger follower 40b, sized to permit traverse motion of the finger member, was included to allow the finger member to rest adjacent either of two finger slots 42 or 43. The slots are spaced apart the width of a vane and position the finger member immediately adjacent the inner or outer annular rim. Thus, the traversely displaceable finger member ensures correct alignment with a circumferentially deformed assembly. A further feature of the finger member is that it is spring biased to permit one-way rotation of the bracket, i.e., clockwise rotation but not counterclockwise rotation of the bracket. A toggle clamp 44 is secured to the reverse side of the follower member is used to secure the nozzle assembly in a fixed aligned position when a desired alignment occurs. Placing a finger member adjacent the U-shaped cut 42 and bringing portion 40a to bear against the trailing edge of a vane aligns the connection between a damaged vane and the inner annular rim 9a with the upper electrode 32. Similarly, placing the finger member adjacent to U-shaped cut 43 and rotating the nozzle assembly counterclockwise places the trailing edge of the damaged vane abutting portion 40a and serves to align the lower electrode 33 with the connection between the damaged vane and the outer annular rim 9b allowing the burning thereof. After aligning either rim-vane connection with an electrode the thumb screw clamps 16 are tightened and the toggle clamp 44 is fastened to secure the aligned vane.

Operation of this invention is readily apparent by noting FIGS. 4 and 5 of the drawings showing the removal of the inner and the outer rim-vane connection of a damaged vane. For clarity the portion of the inner annular rim 9a that connects the assembly to bracket 13 has been removed and the vane next to the vane to be removed 9d is not shown for purposes of this disclosure. Portion 40a is brought to bear against the trailing side of a damaged vane 9d, as explained above, and the carriage is raised to bring the secured, aligned assembly to bear against the upper electrode 32 for its arc removal. Similarly the portion 40a is brought to bear against the damaged vane-outer annular rim connection in finger slot 43 and the carriage is lowered to bring the rim-vane connection against the electrode 33.

Because of the high currents involved and the nature of the materials it is necessary to immerse the invention and the nozzle assembly in a dielectric oil to prevent pock marking the nozzle assembly. The combined coaction of the secured X-shaped bracket mechanism coupled with the mechanical coaction of the follower member and toggle clamp enables a precise alignment of the burning alignment electrodes with the nozzle assembly and ensures the efficient, safe removal thereof.

From the foregoing it is apparent that novel and advantageous provision has been made for carrying out the desired end. However, attention is directed to the fact that variations may be made in the example method and apparatus disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

We claim:

1. Apparatus for precise arc removing welding a shaped end portion of a turbine vane from its supporting wheel assembly comprising: means for rotatably supporting the wheel assembly; electrode means affixed on a bed and configured to substantially correspond to said shaped portion; means supported on the bed for aligning said shaped portion with said electrode means including: an elongate guide member fixed on said bed and radially disposed with reference to said wheel assembly; a follower member movably carried on said guide member for adjustment to different sized turbine wheel assemblies; a finger carried on said guide member, said finger being radially displaceable for engaging selected portions of a vane to effect said alignment; and a holding member supported on said follower member and formed to engage said wheel assembly to maintain said alignment to enable the electrode means to engage precisely said shaped portion of the turbine vane.

2. An apparatus according to claim 1 in which said guide member includes: a guide carrier block electrically isolated from said bed; said follower member includes: a follower block formed with slots permitting only a longitudinal said displacement on said guide carrier block and further formed with a keeper groove retaining said finger element in a first and a second position along the trailing edge of said shaped portion for lateral alignment with said electrode means, and said holding member includes; an over center clamp securing said assembly to the aligning means to maintain said lateral alignment.

3. An apparatus according to claim 1 in which said securing means further includes; at least one guide bar pivotally mounted on said imparting means disposed to laterally displace said assembly thereby ensuring axial alignment of said shaped portion with said electrode means.

4. An apparatus according to claim 3 in which the securing means includes: a cross-shaped bracket pivotally carried on the imparting means to permit angular displacement; a latch mounted on each extremity of said bracket disposed to secure said assembly thereon; a disc element mounted on said imparting means; and at least one screw clamp carried on said bracket disposed for engaging said disc element to secure said assembly at a desired said angular displacement.

5. An apparatus according to claim 4 in which said guide member includes: a guide carrier block electrically isolated from said bed; said follower member includes; a follower block formed with slots permitting only a longitudinal displacement on said guide carrier block and having a keeper groove retaining said finger element in a first and second position along the trailing edge of said shaped portion for lateral alignment with said electrode means; and said holding member includes; an over center clamp securing said assembly to the aligning means to maintain said axial and said lateral alignment.

6. An apparatus according to claim 5 in which said finger element is spring biased to allow said angular displacement in one direction, upon said angular displacement in the opposite direction, said finger portion abuts said trailing edge ensuring said axial alignment.

7. An apparatus according to claim 6 in which said electrode means includes: a pair of opposed carbon electrodes spaced to allow the positioning of said shaped portion therebetween.

8. An apparatus according to claim 7 in which said imparting means is adapted for bidirectional displacement ensuring said electrical contact between one side of said shaped portion and one said carbon electrode and between the other side of said shaped portion and the other said carbon electrode.

9. An apparatus according to claim 8 in which said assembly is a turbine nozzle assembly having a pair of concentric rims and said shaped portion is one of a plurality of radially disposed nozzle vanes mounted therebetween.