Method for repairing a generator rotor blade connection

Abstract

A method for repairing a blade connection of a generator rotor is disclosed. The generator rotor includes an internally threaded hole formed in the generator rotor and an externally threaded blade root. The method includes the steps of removing the blade from the generator rotor, removing material of a first section of the root extending from an end of the root closest to the airfoil, and screwing the blade back into the threaded hole. Additionally, a reworked blade and a reworked blade generator rotor connection is disclosed.

Claims

1. A method for repairing a blade connection of a generator rotor comprising an internally threaded hole formed in the generator rotor and an externally threaded blade root, wherein a generator rotor blade comprises the externally threaded root and an airfoil, the method comprising the steps of: removing the blade from the generator rotor; removing material of a first section of the root extending from an end of the root closest to the airfoil; engaging the threads of a second section of the root furthest away from the airfoil into the threaded hole; removing a second material from the externally threaded blade root over a height of the first section (h.sub.1) which is larger than two times a pitch of the threads, wherein no material is removed from the externally threaded blade root in the second section having a height of the second section (h.sub.2) which is larger than three times the pitch of the threads; and screwing the blade into the threaded hole.

2. The method as claimed in claim 1, further comprising removing material in a first hole sector of the threaded holes closest to a surface of the generator rotor.

3. The method as claimed in claim 1, further comprising machining the first hole sector with an inclination such that the diameter decreases towards the bottom of the threaded hole.

4. The method as claimed in claim 2, further comprising splitting a ring into at least two sections and placed around the first section of the root before the blade is screwed back into the threaded hole.

5. The method as claimed in claim 4, further comprising pressing the ring between the blade and the generator rotor by screwing the blade into threaded hole.

6. The method as claimed in claim 5, further comprising pressing the ring in the direction parallel to the axis of the threaded hole by a platform of the blade and against an inclined side wall of the first hole sector which translates the axial movement of the ring sectors into a movement towards the first section of the root thereby creating a form fit between the generator rotor, the ring and the blade root.

7. The method as claimed in claim 1, further comprising removing material from the generator rotor at the bottom of the threaded hole before the blade is screwed back into the threaded hole to provide a free end below the root, and screwing back the blade into the threaded hole such that the blade comes to a rest on an outer surface of the generator rotor, a countersink machined on the outer surface of the generator rotor or on the ring.

8. A reworked blade comprising an airfoil and a threaded root, wherein the threaded root comprises a first section which is extending from an end of the threaded root closest to the airfoil having a diameter (d.sub.1) which is smaller than a minor diameter of a thread in a second section of the root wherein the thread of the second section of the root is further away from the airfoil than the first section, and in that a first plurality of threads of the threaded root engage into a second plurality of threads of a threaded hole in an outer section of the threaded hole extending for a height of at least two times the pitch of the second plurality of threads from a top of the threaded hole towards a bottom of the threaded hole.

9. The reworked blade as claimed in claim 8, wherein the first section is obtained by removing the thread from the root for a height of first section (h.sub.1) below the airfoil.

10. A reworked blade generator rotor assembly, comprising: a blade having an airfoil and a threaded root and a generator rotor with a threaded hole into which the blade is screwed in, wherein the threaded root comprises a first section which is extending from an end of the threaded root closest to the airfoil and which has a diameter (d.sub.1) which is smaller than a minor diameter of the threaded hole, and a threaded second section of the root which is further away from the airfoil than the first section, and in that a first plurality of threads of the threaded root engage into a second plurality of threads of the threaded hole in an outer section of the threaded hole extending for a height of at least two times the pitch of the second plurality of threads from a surface of the rotor towards a bottom of the threaded hole.

11. The reworked blade generator rotor assembly as claimed in claim 10, wherein the threaded hole of a first hole sector close to the surface of the generator rotor has a cylindrical shape or a conical shape free of threads, wherein a smallest diameter of the first hole sector (d.sub.3) is larger than a major diameter (d.sub.4) of the thread, and a ring which is split into at least two sections is placed in a space between the first section of the threaded root and the first hole sector.

12. The reworked blade generator rotor assembly as claimed in claim 10, wherein the ring is made of a first material having a higher coefficient of thermal expansion than a second material of the root.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure, its nature as well as its advantages, shall be described in more detail below with the aid of the accompanying schematic drawings. Referring to the drawings:

(2) FIG. 1 shows a partial view of a generator rotor with attached blade.

(3) FIG. 2 shows a partial view of a threaded hole in a generator rotor configured to receive a blade.

(4) FIG. 3A shows a partial view of a reworked threaded hole in a generator rotor configured to receive a blade.

(5) FIG. 3B shows a partial view of a generator rotor with attached reworked blade.

(6) FIG. 4 shows a partial view of a reworked generator rotor with attached reworked blade.

(7) FIG. 5 shows a partial view of a reworked generator rotor with attached reworked blade and a ring for supporting the blade.

(8) FIG. 6A shows the cross section VI-VI with a split ring.

(9) FIG. 6B shows the cross section VI-VI with a split ring consisting of 4 parts.

DETAILED DESCRIPTION

(10) Embodiments of the invention may be beneficial in that they reestablish life time in a threaded blade generator rotor connection.

(11) FIG. 1 shows a partial view of a generator rotor 16 with an attached blade 10. The shown generator utilizes single-stage blowers comprising a row of blades 10. Embodiments of the invention may be used with multi-stage blowers. The blade has an externally threaded root 14 configured to mate with an internally threaded hole 17 formed within rotor 16. In the example of FIG. 1 the blade has a platform 19 arranged between the root 14 and the airfoil 15. The platform is arranged in a countersink 18 plane with the outer surface of the rotor 16. A plurality of blades 10 may be circumferentially disposed around rotor 16 to form a row of blades

(12) FIG. 2 shows a partial view of a threaded hole 17 in the generator rotor 16 with the blade removed. The threaded hole 17 as a thread with a minor diameter d.sub.2 and a major diameter d.sub.4.

(13) FIG. 3A is based on FIG. 2. The threaded hole 17 in the generator rotor 16 is reworked and now comprises a cylindrical first hole sector 21. It is delimited by a wall of the first sector hole wall 26 and has a diameter of first hole sector d.sub.3 which is larger than the major thread diameter d.sub.4. The first hole sector 21 extends from the surface of the rotor towards the bottom of the threaded root hole 17 and has a length of first sector l.sub.1. This length of the first sector l.sub.1 can for example be larger than two times the pitch of the thread. In the example shown it is larger than three times the pitch of the thread.

(14) A second hole sector 22 remains with the original thread and has a length of second sector l.sub.2. The length of second sector l2 should be long enough to carry the load of a blade 15. Typically it is longer than 3 times the pitch of the thread, in this example it is longer that eight times the pitch of the thread.

(15) FIG. 3B is based on FIG. 1. The blade 10 is replaced by reworked blade 10 and the rotor 16 is further cut away to better indicate the dimension of the root 14. The root 14 is reworked and now comprises a cylindrical first section 11 with a diameter of first section d.sub.1 which is smaller than the minor thread diameter d.sub.2. The first section 11 extends from the platform 19 of the blade towards the bottom of the root 14 and has a height of first section h.sub.1. This length of the first section h.sub.1 can for example be larger than two times the pitch of the thread. In the example shown it is larger than three times the pitch of the thread.

(16) FIG. 4 shows a partial view of a reworked generator rotor 16 with an attached reworked blade 10. It is based on the reworked rotor of FIG. 3A and combined with the reworked blade of FIG. 3B. Between the cylindrical first section 11 of the root 14 and the cylindrical first hole sector 21 a gap 20 remains open. The treads of the root 14 engage with the threads of the threaded hole below the gap 20.

(17) FIG. 5 shows a further embodiment and is based on FIG. 4. In this embodiment the first sector hole wall 26 is inclined with an angle and opens towards the outer surface rotor, respectively to the countersink 18. Thus the first hole sector has a truncated conical shape. A split ring 23 (split is not shown in this Figure) is inserted between the root 14 and threaded hole. In this example the outer wall of the ring is inclined with the same angle as the first sector hole wall 26. When screwing the blade 15 into the generator rotor the ring 23 is pressed against the inclined first sector hole wall 26. Due to the inclination the ring is then also pressed against the cylindrical outside of the first section 11 of the root 14 thereby forming a force fit which support the blade 10 and suppresses vibrations. Also rings with cylindrical inner and outer walls are conceivable which would fit into a gap 20 as shown in FIG. 4.

(18) When reworking the threaded hole can be elongated to provide a free end 25 below the root to assure that the blade 10 comes to a rest on the ring 23 and presses the ring onto the inclined first sector hole wall 26.

(19) FIG. 6A shows the cross section VI-VI of FIG. 5 with a first example for a ring 23. Here, the ring 23 is split into 2 parts. The two parts can be placed around the first section of the root before reassembly of the blade into the rotor.

(20) FIG. 6B shows the cross section VI-VI with a split ring which consists of four parts. The four parts can be obtained by cutting a ring. In a circular arrangement as shown around the root 14 the four parts are separated by a slit 24. The slit 24 has a thickness of slit t which allows the four parts to be pressed onto the root when installing the blade into the root. The slit prevents the parts to rest on the abutting faces of the ring 23. The slit t can for example be in the range of 0.1% to 5% of the diameter of first section d.sub.1 of the root 14.

(21) Electrical generators used in gas turbines may be subjected to different operating conditions and blades 10 may have different designs and operating characteristics. Therefore the blades 10 are subjected to varying loads and stresses. The threaded roots 14 used for attaching a blade 10 to a rotor 16 may vary from generator-to generator, and even from blade-to-blade in a single generator.

(22) It is to be understood that even though numerous characteristics and advantages of various embodiments have been set forth in the foregoing description, together with details of the structure and functions of various embodiments, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the embodiments to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings disclosed herein can be applied to other systems without departing from the scope and spirit of the application.