Turbine blade retention system and method

A retention system retains a turbine blade dovetail in a retention ring dovetail slot. The retention system includes a retention opening formed in the blade dovetail. A through hole is formed in the retention ring, wherein the through hole is positioned such that it is aligned with the retention opening when the dovetail is assembled in the dovetail slot. A connector is disposed in the through hole and engages the retention opening. In this manner, undesirable relative movement of parts can be reduced or eliminated, thereby preventing excessive wear.

BACKGROUND OF THE INVENTION

The invention relates to a retention system used to prevent axial and/or radial movement of a shaped object in a correspondingly shaped slot and, more particularly, to a retention system and method for retaining a turbine blade dovetail in a retention ring dovetail slot.

In a conventional turbine compressor component, stator blades are held in a retaining ring by means of a dovetail connection (i.e., a dovetail on the blade is received in a complimentary slot in the retaining ring), and the retaining ring, in turn, is secured within a circumferential slot in the compressor casing.

The fit between the blade and the dovetail slot in the ring is loose to allow for assembly and tolerances. Therefore, if the blades are not properly retained, the loose fit may allow the hardware to move in the slot, leading to excessive wear. The excessive wear would eventually fail the part, requiring the unit to be shut down until a repair can be made.

Additionally, radial movement of the blade in the dovetail slot allows for a variation of the tip radius during the machining process. Reduced variation in radial clearance could potentially increase performance and avoid excessive tip rubs.

Typically, each stator blade is retained in the ring to limit motion along the ring dovetail slot by one or more stakes. This is a process where material at the edge of the ring slot is plastically deformed and displaced into a void created by a local chamfer of the stator dovetail. This is a manual and highly variable process which can in some cases provide inadequate retention of the stator blade in the ring slot. Vibratory forces acting on the stator can produce wear on the stake leading to eventual failure of the retention feature. Once the stake is worn, the blade can then slide freely in the ring slot. At very high amplitudes, this motion can lead to wearing of the ring dovetail and eventual failure of the ring. This could then lead to blade liberation and subsequent collateral damage to the gas turbine. This problem has been addressed in recent designs of the assignee via a set screw solution, disclosed in commonly-owned, pending application Ser. No. 11/282,603, filed Nov. 21, 2005. There have also been many documented instances of stators being installed incorrectly either by inserting the airfoil in the ring backwards or inserting the stator or ring in the wrong axial position (stage). Some of these mis-assemblies have been identified as causes of subsequent failure of machine equipment.

There remains a need, however, for a reliable, mistake-proof retention technique for securing airfoil stator blading in turbo-machinery.

BRIEF DESCRIPTION OF THE INVENTION

In one exemplary embodiment, the invention relates to a retention system for use in assembling a turbine blade dovetail a mating dovetail slot in a retaining ring, the retention system comprising: a first retention slot formed in the blade dovetail; a second retention slot formed in a retaining ring, the second slot in open communication with the first retention slot, wherein the first retention slot is positioned such that it is aligned with the second retention slot when the dovetail is assembled in the dovetail slot; and a locking member disposed in the first and second retention slots.

In another aspect, the invention relates to a method of retaining a turbine blade dovetail in a retention ring dovetail slot comprising: forming a retention slot in the blade dovetail; forming a locking slot in the retention ring such that the locking slot opens into the retention slot; and inserting a locking member in the retention slot and the locking slot.

The invention will now be described in detail in connection with the drawings identified below.

The following detailed description of an exemplary, non-limiting embodiment of the present invention is applied to gas turbine compressor stator blades that are retained in the compressor casing via a retaining ring (typically comprised of plural arcuate segments). This embodiment, however, is exemplary only, and the invention is intended to embrace any other application where it is desired to retain a part within a slot.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a simplified cross section showing turbine stator blades10in a conventional compressor, represented by a static casing12. The blades are typically secured via a dovetail section (not shown) engaging a correspondingly shaped dovetail slot (not shown) in a stator retaining ring14. The retaining rings, in turn, are slidably received and secured within circumferential slots16in the casing12. The stator blades10alternate in an axial direction with blades18extending radially outwardly from the rotor20. Radially inner ends of the stator blades may be shrouded or unshrouded, but that aspect is not important for purposes of this invention. It will be appreciated that ring14may be composed of two or more arcuate segments.

FIG. 2illustrates one stator ring assembly22wherein a plurality of (gas turbine) stator blades10are secured within the stator retaining ring14.

FIG. 3is an exploded perspective view of a blade retention system for securing a gas turbine compressor stator blade24within a retaining ring26in accordance with an exemplary, non-limiting embodiment of the invention. Each turbine blade24includes an airfoil28and a blade dovetail30at one end thereof which is assembled into a correspondingly-shaped dovetail slot32in a retaining ring26that is similar to the ring14(FIGS. 1,2) except as noted below.

In the exemplary embodiment, a retention slot34is formed in the blade dovetail30, with the slot oriented substantially perpendicular to an axial insertion direction A of the dovetail30into the dovetail slot32. In other words, retention slot34extends in substantially the same circumferential direction as the retaining ring26, that is substantially perpendicular to the length dimension of the blade dovetail30. A lock wire slot36is formed in the retaining ring26, also in the circumferential direction, and in open communication with the dovetail slot32that receives the stator blade dovetail30, and thus also substantially perpendicular to the blade dovetail30. Thus, upon assembly, the retention slot32and the lock wire slot36are aligned in a radial direction such that a lock wire38may be inserted into both slots36and32to thereby retain the stator blade dovetail30in the ring26(seeFIG. 4). Note that the lock wire38provides both radial and axial positioning and retention. In this regard, the wire38pressed into the slot36takes up any radial slack between the dovetail30and slot32while at the same time, preventing any movement of the dovetail30axially along the slot32. Moreover, by placing the slot34asymmetrically along the length of the dovetail30, mistake-proof assembly of stator blade insertion into the ring slot32is assured.

Turning now toFIGS. 5Aand B, the locking wire38, when fully inserted within the lock wire slot36, may be staked at opposite sides40,42thereof to retain the lock wire in place. When fully inserted, the lock wire may provide a gap or recess44above the wire and within the ring26. This arrangement leaves room for a locating pin46placed in the case (see12inFIG. 1) to provide mistake-proofing of the ring-stator assembly within the case. In this way, it is possible to assemble the stators within the ring in only one fashion, and to assemble the stator ring assembly within the case in only one fashion.

Note that inFIG. 5A, both axial and radial retention are achieved while inFIG. 5B, absent staking at40,42, only axial retention is provided. However, in the case ofFIG. 5B, a radially oriented set screw or the like, inserted through the vane ring44(adjacent the lock wire), could be employed to provide radial retention. Note that inFIG. 5B, the lock wire need not be fully inserted as shown inFIG. 5A, and it may have a loose or tight fit within the lock wire slot36.