Retention system and method for the blades of a rotary machine

This is a continuation of application Ser. No. 09/466,900, filed Dec. 20, 1999, now abandoned, the entire content of which is hereby incorporated by reference in this application.

This invention was made with Government support under Contract No. DE-FC21-95MC-31176 awarded by the Department of Energy. The Government has certain rights in this invention.

This invention relates to turbo machinery rotor construction and, more particularly, to structure for axially retaining the rotor blades on the rotor disk of a turbo machine.

Turbo machinery such as high performance gas turbine engines have a compressor and turbine that each includes one or more annular banks or rows of axially spaced fixed stator vanes that are positioned between rows of rotatable rotor blades. Each rotor blade is formed with a rotor tip, an airfoil and a dovetail-shaped base or root that mounts within a mating, generally axial slot formed between adjacent dovetail posts on the web of the rotor disk.

In order to prevent axial movement of the rotor blades, i.e., along the longitudinal axis of the rotor disk and engine, one or more blade retainers are mounted adjacent the axial slots in the rotor disk. Conventional retention systems, however, have inadequate retention capabilities for gas turbines with large axial aerodynamic loads on the blades caused by, for example, compressor stalls, blade rubs, ingestion of objects, and the like.

In an exemplary embodiment of the invention, a blade retention system is provided for a rotating machine having a hub with a plurality of shaped, generally axially extending openings at circumferentially spaced positions about the hub. A plurality of blades having complementary-shaped base portions are received in the openings, and each of the blades is provided with a blade retention slot therein. A circumferential hub slot is formed about a circumference of the hub, wherein the blade retention slots are substantially aligned with the circumferential hub slot when the blades are received in the openings. At least one ring segment is secured in the blade retention slots and the circumferential hub slot. The circumferential hub slot is preferably substantially U-shaped such that an open end of the circumferential hub slot faces a center of the hub, and the blade retention slots are similarly substantially U-shaped such that open ends thereof face the center of the hub. The ring segments preferably extend between 20° and 360° and preferably 24° in one embodiment and 180° in another embodiment.

A key may be provided for securing the ring segment in the blade retention slots and the circumferential hub slot. The key includes a hook portion at one end of the key engageable with the ring segment and a threaded portion at an opposite end of the key. In this context, the blade retention system further includes a nut that is cooperatively engageable with the threaded portion of the key. The key is preferably disposed in a hole in the hub that includes a key receiving portion of a first diameter that receives the key and a nut receiving portion of a second diameter, larger than the first diameter to thereby define a shoulder, that receives the nut. The nut is structurally supported by the shoulder to pull the key into locking engagement with the ring segment. An inside diameter of the nut receiving portion may be threaded, and the blade retention system may further include a cap threaded into engagement with the hole in the hub. In an alternative arrangement, the key is disposed in a hole in at least one of the complementary-shaped base portions of the blades.

In another exemplary embodiment of the invention, a blade retention system is provided for a rotating machine including a turbo machinery blade with a dovetail portion shaped to fit into a complementary-shaped opening in a hub for rotation about a hub axis. The blade retention system includes a securing slot defined by (1) a blade retention slot in the turbo machinery blade and (2) a circumferential hub slot formed about a circumference of the hub and substantially aligned with the blade retention slot when the dovetail portion is fit into the complementary-shaped opening in the hub. The blade retention system also includes at least one ring segment engageable with the securing slot to thereby retain the blade from axial displacement.

In yet another exemplary embodiment of the invention, a method of retaining blades in a rotating machine includes the steps of (a) machining a blade slot in each of the plurality of blades, (b) machining a circumferential hub slot about a circumference of the hub such that the blade retention slots are substantially aligned with the circumferential hub slot when the blades are received in the openings, (c) positioning the blades in the openings, and (d) securing at least one ring segment in the blade retention slots and the circumferential hub slot. Step (d) may be practiced by inserting at least one key having a key opening adjacent the blade retention slots and the circumferential hub slot, fitting the at least one ring segment into the key opening, and urging the key toward the blade retention slots and the circumferential hub slot. Step (d) may further be practiced by forming a hole in one of the hub or base portions of the blades, and inserting the key into the hole prior to fitting the ring segment into the key opening. Step (d) may be still further practiced by forming threads at an inside diameter of the hole and threading the cap to the hole.

FIG. 1 is an axial view of the retention system of the invention;

FIG. 2 is a cross sectional view along line II—II in FIG. 1;

FIG. 3 is an axial view of an alternative embodiment retention system of the invention;

FIG. 4 is a cross sectional view along line IV—IV in FIG. 3;

FIG. 5 is an axial view of another alternative embodiment retention system of the invention; and

FIG. 6 is a cross sectional view along line VI—VI in FIG. 5 .

With reference to FIGS. 1 and 2, a hub 10 of a rotor or other rotary machine is provided with dovetail or like-shaped openings 12 for receiving a dovetail or base portion 14 of a turbo machinery blade. The dovetail 14 and complementary-shaped opening 12 in the hub 10 serve to retain the turbo machinery blades radially. As noted, since the dovetails are oriented in an axial direction, a retention system such as the retention system of the present invention is required to prevent axial movement of the blades. Typically, the dovetail axis forms an angle with the engine centerline that ranges from 0° to about 50°, and the retention system of the invention is useful for the entire range of dovetail angles.

The blade retention system of the invention includes a circumferential groove or slot 16 machined or otherwise formed about a circumference of the hub in the forward or aft face of the rotor structure for the stage where axial retention is desired. The circumferential hub slot 16 is preferably U-shaped such that an open end thereof faces a center of the hub 10 as shown. A correspondingly U-shaped blade retention slot 18 is machined or otherwise formed in the dovetail portions 14 of the turbo machinery blades. The blade retention slots 18 are similarly oriented such that open ends thereof face the center of the hub 10 . When the dovetail portions 14 of the turbo machinery blades are fit into the complementary-shaped openings 12 in the hub 10 , the blade retention slots 18 are substantially aligned with the circumferential hub slot 16 to define a securing slot 20 that spans the circumference of the hub 10 .

In order to axially retain the blades, at least one ring segment 22 is secured in the aligned blade retention slots 18 and circumferential hub slot 16 , i.e., the securing slot 20 . Preferably, each ring segment 22 spans between 20° and 360° of the hub circumference. Of course, each blade must be retained from axial movement such that, for example, with a rotor incorporating fifteen blades evenly spaced about the circumference thereof, a minimum of fifteen ring segments 22 would be required, each spanning about 24°. A typical rotor stage could include up to 100 blades. In a preferred arrangement, however, the retention system is provided with two ring segments 22 , each extending 180°.

In order to tighten and secure the ring segments 22 in the securing slot 20 , a key assembly 30 is provided for at least each of the ring segments 22 . (With longer ring segments, more than one key assembly may be desirable.) The key assembly 30 includes a key 32 having a hook portion 34 at one end of the key, a key opening 36 at an intermediate portion of the key, and a threaded portion 38 at an opposite end of the key. A hole is drilled in the hub with a drill or the like of a first diameter to define a key receiving portion 40 . Subsequently, using a drill of a second diameter, larger than the first diameter, a nut receiving portion 42 of the hole is formed. Because the nut receiving portion 42 has a larger diameter than the key receiving portion 40 , a shoulder 44 is defined in the hole.

In order to secure the ring segments 22 in the securing slot 20 , after machining the circumferential hub slot 16 and the blade retention slots 18 and after drilling the key receiving portion 40 and nut receiving portion 42 , the key 32 is inserted into the hole as far as possible into an extended key receiving area 40 a. The ring segments 22 are then placed over the hook portion 34 into the key opening 36 of the key 32 , partially within the securing slot 20 . To facilitate placement of the ring segments 22 , each ring segment or at least each portion of the ring segments configured for receiving a key assembly 30 , is provided with a tab area 46 including a slot 48 to facilitate seating of the ring segments 22 .

With this configuration, a nut 50 having internal threads is inserted into the nut receiving portion 42 of the hole over the threaded portion 38 of the key 32 . As the nut 50 is rotated, once supported by the shoulder 44 , the key 32 is driven radially outward (upward in FIG. 2) via the action of the threads, and the ring segments 22 are brought into secure engagement within the securing slot 20 .

The ring segments 22 are preferably formed of a strong material such as steel or nickel-steel, depending on the operating temperature of the machine. The key 32 carries considerably less load than the ring segments 22 , and a preferred material for the key 32 is titanium. Of course, those of ordinary skill in the art will contemplate other materials that may be suitable for a particular application, and the invention is not meant to be limited to a specific material.

FIGS. 3 and 4 illustrate an alternative embodiment of the present invention. In this embodiment, the threaded portion 38 a of the key 32 is slightly shorter than the threaded portion 38 in the first embodiment. Additionally, the nut receiving hole 42 a is modified to incorporate internal threads. In this embodiment, in order to provide a redundant back-up load path for centrifugal loads on the key 32 , a cap 52 is threaded into the nut receiving hole 42 a. Otherwise, the function configuration of the arrangement in this embodiment is the same as that of the first embodiment, and further description thereof will be omitted.

In still another alternative embodiment, referring to FIGS. 5 and 6, the hole previously formed in the rotor structure for the key assembly is rather formed in the dovetail sections 14 of the blades. In this embodiment, a modified key 32 a is provided without the threaded portion 38 but includes the key opening 36 and hook portion 34 . A key extension 54 is provided at a radially inward end of the key 32 a to secure the key 32 a in the hole 53 . That is, during assembly, after inserting the ring segments 22 into the key opening 36 of the key 32 a, the key 32 a is manually driven radially outward or using a tool designed for this purpose, and the key extension 54 is bent into the hole extension 40 a to secure the key and ring segments. This configuration provides an integrated back-up load path for the key.

With the construction of the present invention, retainer sections with high axial load capacity can be installed and removed easily. Each retainer segment and its key assembly can be configured to provide retention for one-half or fewer of the blades in a stage. As such, a retainer section can be removed and reinstalled without requiring access to the entire circumference of the stage. Moreover, the system requires no machining between stages in the axial direction, and installation and removal does not require pin insertion, staking or bolting between stages in the axial direction.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.