US3479009A - Blade retainer - Google Patents

Description

Nov. 18, 1969 F. D. BEAN 3,479,009

BLADE RETAINER Filed May 15, 1968 INVENTOR.

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ATTORN EY- United States Patent 3,479,009 BLADE RETAINER Fredrick D. Bean, Cincinnati, Ohio, assignor to General Electric Company, a corporation of New York Filed May 15, 1968, Ser. No. 729,153 Int. Cl. F01d /32 US. Cl. 416-216 4 Claims ABSTRACT OF THE DISCLOSURE A device for axially retaining a blade root within a slot formed in the periphery of a supporting rotor disc and having a pair of strips joined at one end by an integrally formed loop or head. The strips are adapted to be inserted within a passage extending across the disc between the blade root and the bottom surface of the slot. After insertion into the passage and with the loop abutting portions of one end of the disc and the blade root, the projecting ends of the strips are formed into generally oppositely extending tabs which abut portions of the other end of the disc and blade root to thereby axially lock the blade within its slot. The bottom surface of the blade root may be formed with a channel for engaging the strips and preventing contact between the strips and the slot side walls. The strips may be formed with means to yieldingly urge the blade radially outwardly of the slot and into radial locking abutment therewith.

This invention relates to blade locking means for retaining compressor blades, turbine blades and the like within the peripheral slots of a supporting rotor or disc.

In removal and replacement of turbomachinery rotor blades it is desirable that the blade locking means or retainer used to axially retain each blade within its respective rotor slot be adapted to be removed and replaced or reinserted without necessitating prior removal of the blade from the rotor slot. This is particularly important where the blades are formed with interlocking shrouds, each of which abuts and locks with the shroud of the immediately preceding and succeeding blade shroud. To remove one such interlocking shrouded blade from a fully assembled rotor, it is necessary to first remove the blade locking means or retainers for a sector of blades on either side of the blade to be removed. The lossened blades are then successfully fanned out axially and radially until the blade to be removed can be slipped axially, unimpaired by adjacent shrouds, out of its rotor slot. It will be noted, then, that if the blades within each loosened sector must first be removed from their rotor slots before they can be resecured, all blades would have to be removed in order to replace one blade. Accordingly, it is extremely desirable to provide blade locking means which can be removed and replaced without removing the blades from their slots.

A primary object of this invention, therefore, is to provide an improved retainer for axially securing a blade within a rotor or disc slot which can be removed and replaced without removing the blade from its slot.

Another object of this invention is to provide blade locking means as above which overcomes the problem of loose assembly of parts due to springback of bent tabs.

A further object of this invention is to provide blade locking means which facilitates balancing of the rotor blade assembly.

Other objects and advantages of this invention will become apparent upon reading the following description of the preferred embodimen Briefly stated, in accordance with one embodiment of this invention, means are provided to axially retain a blade within a slot formed in a supporting rotor disc in a manner which permits separate removal and replacement of a single blade from a fully assembled rotor and includes a pair of strips extending from one side of the disc and blade root to the other within a passage existing between the blade root and the slot bottom. The strips are suitably joined at one end, outwardly of the passage, by means which abut portions of one side of the disc and blade root. The other ends of the strips are formed into generally radially oppositely extending tabs, outwardly of the passage, which abut the other side of the disc and blade root and axially lock the blade within the slot.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of this invention, it is believed the invention will be better understood from the following description of the preferred embodiment taken in connection with the ac companying drawing wherein:

FIGURE 1 is a partially exploded perspective view showing a portion of an exemplary rotor blade assembly having one blade removed and employing the blade locking means of this invention;

FIGURE 2 is an enlarged plan view of the exemplary rotor blade of FIGURE 1;

FIGURE 3 is an enlarged cross-sectional view showing the blade locking means of FIGURE 1; and

FIGURE 4 is a cross-sectional view taken along lines 4-4 of FIGURE 3.

Referring now to FIGURE 1, a portion of a rotatable disc or rotor has been shown at 10 formed with a plurality of slots 12 at its periphery which extends from one side 14 of the disc 10 to the other side 16. Suitable turbine blades or buckets have been shown generally at 18 as having an airfoil portion 20, shroud means 22, a platform portion 24 and a root portion 26. The shroud means 22 have been shown in FIGURE 2 as comprising a sector 28, usually arcuate and formed with generally S-shaped inclined radial edges 30, each of which interlocks with the adjacent edge 30 of the preceding and succeeding shroud.

Each blade root 26 is formed with oppositely facing end surfaces 32 and 34, a bottom surface 36 and substantially oppositely directed side wall surfaces 38 and 40. As best seen in FIGURE 4, a channel 41, the function of which will be hereinafter described, may be provided in the root bottom surface 36 which extends from root end surface 32 to root end surface 34.

Each disc slot 12 is formed with a base surface 42 and side walls 44 and 46 and is sized in conjunction with the blade root 26 to enable the blade root portion to be slidably inserted into the slot in a generally axial direction relative to the rotational axis of the rotor. The slot side walls 44 and 46 and root side walls 38 and 40 are suitably shaped in a well known manner to abut and radially retain or lock each blade 18 within its slot 12 against centrifugal forces generated when the disc 10 rotates. Although a fir tree configured slot and root have been shown, it will be understood that other arrangements such as a dovetail configuration or the like may be employed. Additionally, as shown in FIGURE 4, the

blade root 26 and slot 12 are suitably sized so that when the root side walls 38, 40 are in radial locking abutmentwith slot side wall 44, 46, a passage 48 is formed between the root bottom surface 36 and the slot base surface 42' which extends across the disc 10 from side 14 to 16.

The blade locking means for retaining each blade 18 axially within its respective slot 12 has been shown gen shown in FIGURE 4, to thereby prevent chafing between the strips and the side walls 44, 46. The strips 52, 54 have a length greater than the length of the passage 48 so that after insertion into passage 48 and with the loop or head 56 abutting substantially radially aligned portions of the disc side 14 and the root end surface 32, sutficient material projects beyond the blade root end surface 34 and the disc side 16 to enable tabs 58 and 60 to be formed. As best shown in FIGURE 3, the tabs 58 and 60 are formed generally normal to the plane of their respective strips 52 and 54 and abut, respectively, generally radially aligned portions of the disc side 16 and the blade root end surface 34, to thereby retain the blade against axial movement within its slot 12.

Accordingly, initial installation of the turbine blades or buckets 18 in the rotatable disc may be readily ac; complished by slidably inserting each blade root 26 into its respective slot 12, inserting the retainer 50 of this invention into each passage 48 and forming the tabs 52 and 54.

Normally, in forming the interlocking slot and blade root side walls 44, 46 and 38, 40 respectively, sufficient clearance is left to enable the blade root to be easily slipped into the slot. This, of course, results in some radial play of the turbine blade 18 relative to the disc 10, which, in operation, is taken up by the action of centrifgual force which urges each turbine blade or bucket radially outwardly and into radial locking abutment with the slot side walls 44 and 46. However, to facilitate balancing of a blade disc assembly, it is necessary that the blades be in the position they will assume during operation. Accordingly, each retainer 50 is preferably formed with means to yieldingly urge each blade 18 radially outwardly within its slot 12 and into radial locking abutment with the slot side walls 44 and 46. To this end, for example, and as shown in FIGURES 3 and 4, one strip 54 may be formed with a dimple or depression 62, intermediate the loop 56 and the tab 60, which is sized in depth to provide an overall radial thickness to the strips 52, 54 slightly greater than the radial depth of passage 48. Due to the elasticity of the metal of the dimple, the retainer can be forced into place, thereby holding the blade radially tight in its slot to facilitate handling and balancing of the assembled rotor disc.

Since the blade locking means or retainer 50 of this invention is insertable within the passage 48, it is possible to remove and replace one turbine blade 18 without removal of every blade on the disc 10.

In replacing shroud interlocked blades or buckets of the type shown generally at 18 and previously described, it is first necessary to remove the blade locking means or retainer 50 for a sector of blades on either side of the blade to be removed. The blades within such sectors are then axially and radially fanned out until the interlocking shroud edges 30 are free, whereupon the blade is axally removed and replaced. The replaced blade and each loosened blade 18 may then be axially resecured by simply inserting a blade retainer within each passage 48 and forming the tabs 58 and 60 are previously described.

The retainer 50 may be conveniently formed of one continuous metallic member which is bent or folded back on itself to define the loop or head 56 and strips 52, 54. Because of such one piece construction, assembly and stocking problems are greatly reduced.

As will be understood by those skilled in the art, blade retainers which rely on bent tabs may result in some degree of axial looseness due to tab springback or the inherent resiliency of the tab material. This is, of course, undesirable and is overcome in the blade retainer 50 of this invention by providing the preformed head or loop 56 which, during installation and forming of the tabs 58 and 60, may be axially and resiliently deformed so that after the tabs are formed they will be tensioned or yieldingly urged to maintain their abutment with the blade root end 34 and the disc side 16 by the springback of the head or loop 56.

The foregoing is a description of an illustrative embodiment of the invention and it is applicants intention in the appended claims to cover all forms which fall within the scope of the invention.

I claim:

1. In a turbomachine including a rotatable disc member having a first side surface and a second side surface and at least one root-receiving slot extending transversely of said disc member at its periphery, and a blade member having a root portion engaged in said slot, said root portion having a first end surface and a second end surface, said slot and said root portion being shaped to abut and radially lock the blade member to said disc form a passage therebetween extending transversely of.

said disc member, locking means for axially retaining said blade root within said slot, said locking means comprising:

a pair of generally fiat strips axially positionable within said passage,

means joining said strips at one end thereof outwardly of said passage, said joining means comprising an integral extension of said strips formed as a loop and adapted for locking abutment with generally radially aligned portions of said disc first side surface and said root first end surface,

the other ends of said strips projecting out of said passage and formable into oppositely extending tabs abutting generally radially aligned portions of said disc second side surface and said root second end surface.

2. The structure of claim 1 further characterized in that said joining means is resiliently deformable along the axis of said passage when said tabs are formed, whereby after said tabs have been formed said joining means is operative to yieldingly urge said tabs into locking abutment with said disc second side surface and said root second end surface and thereby prevent axial looseness of said blade due to tab springback.

3. The structure of claim 1 further characterized in that said locking means further includes means to yieldingly urge said blade root radially outwardly into radial locking abutment with said slot.

4. The structure of claim 3 further characterized in that said yielding means comprise a dimple formed in at least one said strip intermediate said joining means and said tab, with said dimple having a depth sized to provide an overall radial thickness to said strips greater than the radial depth of said passage.

References Cited UNITED STATES PATENTS 791,564 6/1905 Lynch. 2,297,770 10/1942 Jcpson. 2,753,149 7/1956 Kurti.

2,786,648 3/ 1957 Ledwith. 2,971,744 2/1961 Szydlowski.

FOREIGN PATENTS 202,682 2/ 1955 Australia. 1,031,802 3/1953 France.

691,380 5/1953 Great Britain.

EVERETTE A. POWELL, JR., Primary Examiner

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