US3417964A - Shrouded blade arrangement - Google Patents

Description

. Dec. 24, 1968 R. J. ORTOLANO 3,417,964

2 Sheets-Sheet 2 Filed Nov. 20, 1967 United States Patent 3,417,964 SHROUDED BLADE ARRANGEMENT Ralph J. Ortolano, Saratoga, Calif., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 20, 1967, Ser. No. 684,124 7 Claims. (Cl. 25377) ABSTRACT OF THE DISCLOSURE This invention provides an improved shrouded blade arrangement of the riveted tenon type for an axial flow elastic fluid utilizing machine such as a turbine or a compressor. The improved structure is particularly advantageous when employed in a rotor because of its ability to withstand high centrifugal forces without loosening.

The novel feature resides in forming the holes in the shroud with a flared trumpet shape and riveting the tenons to the shroud in such a manner that the tenons are deformed into a flared trumpet shape complementary to the shape of the holes and in intimate compressive abutment therewith.

BACKGROUND OF THE INVENTION Shrouded blade arrangements have been employed in the axial flow turbine and compressor art for many years, primarily on the rotors. Typically, the blades are provided with integral tenon portions which are received in mating holes in the shroud and then riveted to the shroud to make a tight connection therewith. One such arrangement is shown in RI. Ortolano Patent 3,279,751, issued Oct. 18, 1966 and assigned to the same assignee as this invention. In this arrangement, the shroud holes are substantially unchamfered.

Another representative blade shrouding arrangement is shown in A. H. Redding Patent 2,315,655, issued Apr. 6, 1943 and assigned to the same assignee as this invention. In this arrangement the shroud holes are chamfered to a frusto-conical shape and the tenons are swollen by riveting, into tight and presumably complementary frustoconical shape with the chamfered portions of the holes.

SUMMARY In accordance with the teachings of this invention, frusto-conical chamfering of the shroud holes results in imperfect riveting of the tenon to the shroud because the tenon does not swell or expand to a truly frusto-conical shape. Accordingly, the expanded tenon does not attain a truly tight contiguous relationship with the chamfer and small gaps between the outer surface of the tenon and the inner surface of the chamfer are created that eventually may loosen with damaging results to the rotor blades and/ or the associated stator blades.

The invention provides an improved shrouded blade structure of the riveted type in which the riveted expanded tenon attains a truly tight and contiguous relation with the chamfered portion of the associated hole in the shroud. This is attained by forming the chamfered portion of the hole in the shroud with a flared trumpet shape, i.e., curved convex shape. The natural tendency for a riveted tenon has been discovered to expand to a flared trumpet shape, hence the resulting riveted connection is devoid of gaps or spaces between the outer surface of the tenon and the inner surface of the chamfered portion of the associated hole in the shroud.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a view of a portion of a shrouded blade turbine rotor having the invention incorporated therein;

FIG. 2 is an enlarged radial view taken on line II-II 3,417,964 Patented Dec. 24, 1968 of FIG. 1 and showing one of the blades with portions cut away;

FIG. 3 is a fragmentary plan taken on line IIIIII of FIG. 2 and looking in the direction of the arrows;

FIG. 4 is a fragmentary view showing a portion of the structure in FIG. 2, but before riveting;

FIG. 5 is a fragmentary View similar to FIG. 4, but after riveting;

FIGS. 6 and 7 are views similar to FIGS. 4 and 5, but showing another embodiment of the invention;

FIG. 8 is a plan similar to FIG. 3 but showing another embodiment of the invention in various stages of fabrication;

FIG. 9 is an enlarged sectional view taken on line IXIX of FIG. 8;

FIG. 10 is an enlarged sectional view taken on line X-X of FIG. 8;

FIG. 11 is a view similar to FIG. 10 but showing still another embodiment;

FIG. 12 is a fragmentary plan taken on line XIIXII and looking in the direction of the arrows; and

FIG. 13 is a fragmentary plan illustrating a still further embodiment.

DESCRIPTION OF THE EMBODIMENT SHOWN IN FIGS. 1-5, INCLUSIVE Referring to the drawings in detail, in FIG. 1 there is shown a portion of a turbine rotor 10 comprising a rotor spindle 11 having an array of radially extending blades 12 supported therein and connected to each other in suitable arcuate groups (four per group, as illustrated) by arcuate shroud members 13. Although the entire rotor 10 is not shown, it will be understood that the spindle 11 is of circular cross-section and the blades 12 are arranged in an annular array about the rim 14 of the spindle.

The blades 12 may be connected to the rotor rim 14 in any desired manner. However, as best illustrated in FIG. 2, the blades are formed with bulbous T-shaped roots 15 received in a mating peripheral groove 16 formed in the spindle rim 14.

The blades are provided with air foil vane portions 17 extending radially outwardly from the roots 15 and are further provided with tenons 18 extending through uniformly spaced holes 19 formed in the shroud members 13 and secured thereto by deformation of the tenons 18, as by riveting.

As thus far described, the structure is substantially conventional.

The invention comprises a method of manufacture and the resulting tenon and joint structure which will now be described. Since all of the blades 12 are substantially identical and are joined to the shroud 13 in the same manner, only one of the blades will be described.

As best shown in FIG. 4, the tenon 18 is formed integrally with the vane portion 17 of the blade 12 and of substantially circular cross-section, so that it is initially of substantially cylindrical shape. The associated hole 19 in the shroud member 13 is also of circular cross-section but of flared trumpet shape. More particularly, the outer surface 13a of the shroud is chamfered to a depth at least half of its radial thickness in a manner to provide the hole 19 with an inner wall 20 having an arcuate, convex cross sectional surface portion 21. The wall surface portion 21 defines a circular arc of about having a radius R at most equal to the thickness T of the shroud 13, but preferably slightly less than the thickness T. Expressed in another manner, the surface portion 21 is toroidal in shape, since it may be deemed to include the inner quadrant of a torus. Viewed in its entirety the hole is of flared trumpet shape, as previously stated and the tenon 18 extends snugly therethrough to a suitable height above the upper surface 13a of the shroud.

The tenon 18 is then deformed by riveting blows directed parallel to its central axis 22 to secure the blade 17 to the shroud 13 by mutually compressive abutment. As viewed in FIG. 5, the deformation of the tenon attained by riveting causes radial swelling and axial shortening of the tenon to provide a preferably flush relation between the tenon 18 and the shroud surface 13a, but, most importantly the tenon assumes an outer flared trumpet shape 24 exactly concavely complementary to the flared trumpet shape of the convex inner wall portion 21 of the hole. It must be pointed out that the natural or inherent deforming characteristics of the tenon 18 during riveting cause deformation to the flared shape. Hence, after riveting is completed to the degree required for mutually compressive relationship of the thus formed joint structure, no voids between the two complementary surfaces are formed which could otherwise cause loosening of the joint structure due to the stresses incurred in operation.

If desired, after the riveting operation is completed, a peripheral rib portion 25 may be provided on the outer surface of the shroud member 13 by machining or otherwise cutting away the portions 26 and 27 of the shroud to the depth indicated by the dot-dash line 13b in FIG. 5. Although a portion of the riveted tenon is also cut away to provide the rib 25, the remaining flared portion of the tenon is completely adequate to prevent subsequent loosening of the shroud member 13.

In this embodiment, the shroud member 13 is of rectangular cross-section as best seen in FIG. 2, and the tenon 18 extends in a direction normal to the surface 13b.

EMBODIMENT SHOWN IN FIGS. 6 AND 7 FIG. 7 illustrates a completed shrouded blade structure 30 comprising a shroud member 31 and blades 32 (only one shown). This structure is similar to the structure shown in FIG. 5 and differs therefrom only in that the shroud member 31 is of generally wedge-shaped crosssection and the blade 33 has an integral tenon 33 whose central axis 34 is normal to the finished outer surface 31a of the shroud but inclined with respect to the inner surface 31b of the shroud.

FIG. 6 illustrates the above components before riveting of the tenon 33 to the shroud member 31. Although the shroud 31 is of wedge-shaped cross section, and therefore of unsymmetrical cross-sectional shape, the hole 34 in the shroud is normal to the unfinished outer surface 310 of the shroud and the flared trumpet shaped wall portion 36 of the hole is of uniform cross-sectional shape throughout its entire periphery.

Accordingly, here again the tenon 33 is deformed into a shape truly complementary to the inner surface of the hole to provide a joint structure free of voids or gaps between the two complementary surfaces.

EMBODIMENT SHOWN IN FIGS. 8-12, INCLUSIVE FIGS. 11 and 12 illustrate a completed shrouded blade structure 40 comprising an arcuate shroud member 41 and blades 42. This structure is similar to the structure shown in FIG. 7 and differs therefrom only in that the tenon 44 and the mating hole 44 in the shroud 41 are of non-circular cross section.

FIG. 8 illustrates the shrouded blade structure 40 in various stages of fabrication, for ease of comprehension. In this view and in accompanying FIG. 9, the uppermost blade 42 is illustrated in position in its mating hole before riveting; the next lower blade 42 and the accompanying FIG. 10 illustrate the blade after riveting; and below the above two blades an unbladed opening is illustrated.

The blade 44 is preferably for-med from strip metal of air foil shape and the tenon 44 is provided by cutting away opposite portions of the strip metal, thereby to impart a parallelogram cross-section to the tenon.

To accommodate the parallelogram cross section of the tenon 44, the mating holes 45 in the shroud member 41 are punched or otherwise cut out to the same parallelogram shape. However, the trumpet shaped flared portion 47 of the hole 45 is formed in the same manner as in the previously described embodiments and during the riveting operation, the tenon 44 is deformed radially to a complementary concave trumpet shape of circular cross section to completely engage the flared portion 47. Here again the resulting joint structure is truly complementary to the shape of the hole 19 to obviate voids, gaps and irregularities that could otherwise lead to loosening of the blade in service.

If desired, after riveting, the shroud 44 may be machined, as previously described, to provide a peripheral upstanding rib 49.

EMBODIMENT SHOWN -IN FIG. 13

FIG. 13 illustrates a shrouded blade structure 50 similar to the shroud structure 40 and comprising a blade 51 and a shroud 52 disposed in assembled relation, but before riveting, for clarity. In this embodiment, the blade 51 is provided with a tenon portion 53 of generally parallelogram cross-section and the shroud 52 is provided with a mating hole 55 of complementary parallelogram shape to receive the tenon 53. However, in this embodiment the flared portion 56 (of the shroud) surrounding the hole 55 is also of complementary parallelogram shape.

In the riveting operation, the tenon 53 is deformed radially to a complementary shape (not shown) to completely engage the flared portion 56 in the same manner as described in connection with the other embodiments.

Although several embodiments have been shown, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

I claim as my invention:

1. A shrouded blade group for an axial fluid flow machine, comprising a plurality of blades having an air foil shaped portion,

each of said blades having a tenon extending from said air foil shaped portion,

an arcuate elongated shroud member having a plurality of longitudinally spaced holes extending transversely therethrough,

said tenons being received in said holes and rivetedly secured to said shroud,

said holes being defined by peripheral inner wall surface portions of flared trumpet shape of arcuate convex cross-section, and

said tenons having outer peripheral surface portions of flared trumpet shape of arcuate concave cross-section complementary to said inner wall surface portions and in intimate compressive abutment therewith.

2. The structure recited in claim 1, wherein the tenons and holes are of complementary non-circular cross-section.

3. The structure recited in claim 1, wherein the cross-sectional shape of the inner and outer complementary wall surfaces defines an arc of a. circle, and

the tenons, the holes and the flared surface portions are of circular peripheral shape.

4. The structure recited in claim 3, wherein the circular arc is less than 5. The structure recited in claim 1, wherein the flared trumpet shape is of circular peripheral configuration, and

the tenons and holes have portions of non-circular peripheral configuration.

6. The structure recited in claim 1, wherein the flared trumpet shape is of circular peripheral configuration and has an arcuate cross-section defining an arc of a circle.

7. The structure recited in claim 6, wherein the arc is less than 90 and the tenons extend through the holes in flush relation with the surrounding surface of the shroud.

References Cited UNITED STATES PATENTS 2,237,121 4/1941 Stine et al.

FOREIGN PATENTS 344,297 3/ 1931 Great Britain.

EVERETT A. POWELL, JR., Primary Examiner.

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