US2625365A

US2625365A - Shrouded impeller

Info

Publication number: US2625365A
Application number: US78611A
Authority: US
Inventors: Moore Vincent
Original assignee: Curtiss Wright Corp
Current assignee: Curtiss Wright Corp
Priority date: 1949-02-26
Filing date: 1949-02-26
Publication date: 1953-01-13
Anticipated expiration: 1970-01-13

Description

Jan. 13, 1953 v, MOORE 2,625,365

SHROUDED IMPELLER Filed Feb. 26, 1949 2 SHEETS-SHEET l INVENTOR VINCENT MEIURE ATTORNEY Jan. 13, 1953 v. MOORE 2,625,365

SHROUDED IMPELiLER Filed Feb. 26, 1949 2 SHEETS-$HEET 2 I INVENTOR VINCENT MDDRE ATTORNEY Patented Jan. 13, 1953 SHROUDED IMPELLER Vincent Moore, Ridgewood, N. J., assignor to Curtiss-Wright Corporation, a. corporation of Delaware Application February 26, 1949, Serial No. 78,611

1 Claim.

This invention relates to bladed rotors for turbines, compressors, blowers or the like and is more particularly directed to such rotors having blades extending therefrom and having a shroud secured to and extending between or across the outer or tip ends of said blades.

Bladed rotors for turbines, compressors, blowers or the like have been provided with a shroud formed integral with the outer or tip ends of the rotor blades, for example by machining the rotor, with its blades and shroud, from one piece of metal. Such one piece constructions are obviously quite difficult to fabricate and expensive. An object of this invention comprises the provision of a novel shrouded rotor construction in which the shroud, after having been separately fabricated, is secured to the outer or tip ends of the rotor blades. In accordance with the present invention, separately formed shroud elements are disposed between the tip ends of the rotor blades, said shroud elements being welded or brazed to said blades in a manner to allow for shrinkage of the shroud following the welding or brazing operation without imposing undesirable stresses in said welded or brazed junctions.

Other objects of the invention will become apparent upon reading the annexed detailed description in connection With the drawing in which:

Figure 1 is an end view of a centrifugal compressor rotor embodying the invention;

Figure 2 is a sectional View taken along line 2--2 of Figure 1;

Figure 3 is a view taken along line 3-3 of Figure 1;

Figure 4 is a perspective view illustrating a, portion of the centrifugal compressor rotor of Figures 1-3;

Figure 5 is a sectional view, similar to Figure 2, but of an inducer or entrance section for the centrifugal compressor of Figures 1-4;

Figure 6 is an end view taken along line 6-45 of Figure 5;

Figure '7 is an enlarged view of a portion of Figure 3; and

Figures 8, 9, l0, and 11, are views similar to Figure 7 but of modified constructions.

Referring first to Figures 1 to 4, the invention is illustrated in connection with the bladed rotor of a centrifugal compressor [0. As will become apparent however, the invention is not limited to this type of bladed rotor. For example, the invention is equally applicable to axial flow compressors, to axial or centrifugal blowers and to turbines of the axial or radial flow types.

The compressor I0 is provided with a plurality of circumferentially'spaced fiat blades l2 extending radially from its hub 14, said hub being provided with internal splines Hi to which a driving shaft is adapted to be drivably connected. A plurality of shroud elements I8 are provided, each of said shroud elements being disposed between the outer or tip ends of a pair of adjacent blades I2. The construction of said shroud elements I8 is best seen in Figure 4.

Each shroud element l8 comprises adeck 20 having a pair of flanges 22 disposed along opposite edges of said deck 20, so that each shroud element l8 ha a channel-shaped cross-section. Each shroud element is shaped so that its deck 20 bridges the gap between the outer or tip ends of a pair of adjacent blades l2 between which said shroud element is disposed. In addition the flanges 22, of each shroud element 18, engage the sides of the outer or tip ends of its associated blades l2 and extend inwardly toward the root ends of said blades. The flanges 22 are secured to their engaged blades l2 by a, metallic fused junction, for example by welding or brazing, as hereinafter described. With a shroud element I8 secured in position between each pair of adjacent rotor blades l2, the tip ends of the rotor blades are provided with a shroud construction rigid with said blades.

Centrifugal compressors are commonly provided with an inducer or axial entrance section, for example as disclosed in Patent Number 2,399,852 issued to Campbell et a1. Figure 5 and 6 illustrate the application of the present invention to such an inducer section.

In Figures 5 and 6, there is illustrated an inducer or axial entrance section 30 for th centrifugal compressor Ill. The inducer section 30 comprises a hub 32 which is adapted to be coaxially secured to the hub M of the centrifugal compressor 10. In addition said inducer section 30 has a plurality of circumferentially spaced blades 34 extending substantially radially therefrom. The inducer blades 34 are designed to comprise continuations of the blades l2. Thus, the downstream ends of the blades 34 are adapted to abut against the upstream ends of the centrifugal compressor blades I2 and the upstream ends of the inducer blades 34 are curved into the direction of rotation of the compressor. The shape of the inducer blades 34 and their relation to the flat centrifugal compressor blades l 2 is conventional and is more fully described in the aforementioned patent of Campbell et al.

A shroud element 36 is secured between the outer or tip ends of each pair of adjacent inducer blades 34 in a manner similar to the mode of securement of the shroud element I8 to their blades l2. Thus, each shroud element 36 has a pair of flanges 38 extending from opposite edges of its deck 40 toward the roots of its pair of adjacent inducer blades 34. In addition said pair of flanges 38 are disposed against and secured to the outer or tip ends of the :pair of adjacent blades 34. With the shroud elements 36 secured in position between the inducer blades 34, said inducer blades are provided with a shroud construction rigid with the outer or tip ends of said blades and forming a continuation of the shroud OD- t tion provided by the shroud elements L8, 7

The shape of each said shroud element must obviously conform to the inter-blade space in which said shroud element is disposed. Accordingly except for their shape, the shroud elements [8 and 3B are similar. The shroud elements [8 are secured to the rotor blades .12 .of the main portion of a centrifugal compressor in which the fluid flow is primarily radial relative .to the rotor axis while the shroud elements .35 are secured to the rotor blades .34 .of said centrifugal compressor inducer section in which the flow is primarily axial relative to the rotor axis. Accordingly, it should be apparent that the rotor of any ,compressor, blower, turbine or the like, having a plurality of blades extending therefrom, can, in ac cordance with the present invention, be provided with a shroud construction rigid with the outer or tip-ends of the rotor blades.

The specific manner in which the shroud elements are secured to the rotor blades is best illustrated in Figures 7 to 10. Reference is first made to Figure 7. wh c comp i e a nl r ement of that portion of Figure 3 enclosed by the circular line 39. In Figure '7 the shroud element 18 is brazed to its pair of adjacent blades 12 as indicated by the brazed junction 40. Inaddition, the corner between each shroud flange 22 and its deck 20 is curved as indicated at 42 whereby the deck end of each flange 22 bends or diverges away from the tip of its adjacent blade ,I2 to provide an outwardly facing diverging groove 44 therebetween. The magnitude of this divergence is such that the brazed junction 43 between each blade l2 and its shroud flange 22 is disposed inwardly of the inner surface of its shroud deck 20. With this construction, any shrinkage of a shroud .deck 20, as it cools after the brazing operation, is taken up y bending between said deck 20 and its flanges 22. In this way, the brazed junction 40 between each shroud flange 22 and its blade 12, is not subjected to appreciable tensile stresses as a result of shrinkage of its deck 29 after the brazing operation. Obviously, if the brazed junction 48 were to extend to the outer surface of its deck 20, then any shrinkage of said deck would subject said brazed junction to high tensile stress. However, with the brazed junction M! disposed inwardly of the inner surface of its deck 26, shrinkage of said deck merely results in bending between said deck and its flanges 22 so as to increase the corner angle therebetween.

It has been found that, if the radius of curvature at the inside of the corner #2, between each flange 22 with its deck 2'8, is at least equal to the thickness of the shroud material, the groove 44 is sufiiciently wide so that the subsequently formed brazed junction 4!? will be disposed sufficiently inwardly of the inner surface of its deck 2.9 to avoid the creation of any appreciable tensile s r s s i tunction as a r sult of shrinkage of said deck after the brazing operation.

Figure 8 illustrates a modification of Figure 7. In Figure 8, a shroud element 50 comprises a deck 52 having a pair of inturned flanges 54 adapted to be secured against the sides of their respective adjacent blades I2 by brazing at 56. In Figure 8, the deck end of each flange 54 is reduced in thickness to provide a groove 58 between it'he .outer or tip end of the adjacent blade .12 and the deck .end of said flange. The grooves 58 are provided to prevent the formation of a brazed junction between a blade l2 and the adjacent reduced thickness portion of a flange 54.

The shroud elements l8 and 50 of Figures 7 and .8, respect ively, areotherwise similar.

The depth of each groove 58 is greater than the thickness of the adjacent deck 52 so that the brazed junction 58, securing each flange 54 to a blade l2, is disposed inwardly of the inner suriac of said deck. Thus the function of the grooves 58, in Figure 8, is the same as the function ,of the grooves 44, in Figure 7 Accordingly, shrinkage .of a deck .52 of a shroud element after the brazing operation, securing said shroud element .50 to the blades 12, is compensated for by bending between said deck .52 and its flange 5:, without imposing large tensile stresses on its brazed junctions 56. As ,a precautionary measure .or if necessary, astainless steel plate fill may be temporarily inserted in .each groove 58, during the brazing operation, to prevent the :formation of a "brazedjunction across the groove 56.

Figure 9 illustrates a still further modification of Figure 7. In Figure 9,, ,a shroud element 10 comprises a deck 72 and side flanges 14 spot welded to the blades 12 as indicated ,at 15. In spot Welding, the position of each spot weld junc- .tion 116 can be accurately controlled without regard to the shape of the space between each flange 7d and its associated blade l2. Accord ingly the shroud elements 70 need not .be formed to provide a groove between its side flangeslll and its adjacent blades 12 as in the case of the

grooves

44 and 58 of Figures 7 and v8 respectively. In "Figure ,9, the spot weld junctions 76 are located inwardly of the adjacent inner surface of its associated deck '72. With this arrangement, any shrinkage of said deck after the spot weld ng operation, merely causes bending between its flanges l4 and said deck without imposing large tensile stresses on the spot weld junctions.-

Figure 10 illustrates a structure similar to F ure 7 but the centrifugal compressor .blades l2 of Figure 10 diiTer from the blades 12 of .Ftigure 7 in that the blades 12' do not project beyond their brazed junctions 4-0 with the shroud elements [8. That is, the portion .of each vane l2 .of Figure? projecting beyond its brazed junction on, has been removed in Figure 10. The structure of Figures 7 and 10 are otherwise similar. With this ancture of Figure 10, a relatively large external groove is formed between each pair of shroud elements 12, thereby increasing the pumping losses caused by irregularities in the ,outer surface of the shroud construction above the corresponding losses with the shroud construction ,of Figure 7. If said pumpin losses are negligible or not objectionable then the structure of Figure ,10 may be preferred because it has the following advantage, namely that the outer edge of each yane 12' provides a positive outer limit for its brazed junction to. Accordingly, if the inner surface-of each shrouddeck 2D is disposed outwardiy-cf t outer edg o ts assoc ted vanes I1 its raz d auncticn to ,canpo r ssiblyext nd 011twardilybeyondsaidinner surface re ardless ,of the curvature of the corners 42 between said deck 20 and each of its flanges 22. Obviously the structure of Figure 8 may be modified in a similar manner by shortenin the compressor blades l2 so as not to extend beyond their brazed junctions with their shroud elements.

Figure 11 illustrates still another modification of the shroud elements. In Figure 11,

shroud elements

80 and 80' each comprise a deck 82 having side flanges 84 depending therefrom. Reference numeral 80 indicates the shape of a shroud element prior to welding or brazing said element to the rotor blades 12 and reference numeral 80' indicates the shape of said shroud element after welding or brazing said element to said blades. As indicated at 86, each shroud element is welded \ur brazed) to the adjacent blades l2 at the outer or tip ends of said blades and at the junction or its flanges 84 with its deck 82. Accordingly each welded or brazed junction 86 is disposed substantially in the plane of its associated deck 82 so that shrinkage of said deck, after said spot welding operation, cannot be compensated for by bending of its flanges 85 relative to said deck 82. As illustrated, however, each deck 82, as fabricated, is bowed slightly outwardly so that when said deck shrinks, after the welding operation, the deck merely straightens out as indicated at 89 thereby avoiding the creation of large tensile stresses in the welded or brazed junction 86. Obviously, this same result may be obtained by bowing the decks 82 inwardly instead of outwardly.

In each of the species of Figures '7 to 11 inclusive, the shroud elements and their brazed or welded junctions to the rotor blades are such that the shrinkage of said elements following the brazing or welding operation does not impose large stresses on the welded junction. It is possible to weld or braze each shroud element separately and to compensate for shrinkage of said shroud elements by deflection of the rotor blades. Thus, the deck of each shroud element could be made slightly larger than the gap between the tip ends of a pair of rotor blades. Then, prior to the securement of a shroud element between a pair of rotor blades, at least one of said rotor blades could be deflected slightly to widen the gap between said pair of blades such that the subsequent shrinkage of said shroud element merely undoes said deflection. Obviously, however, shrinkage at the last shroud element to be secured in place on a particular rotor could not be compensated for in this manner, but could be compensated for by one of the constructions illustrated in Figures '7 to 11 inclusive.

In all of the various species the tip end of the impeller blades I2 or l2 could obviously be notched to receive the side flanges of the shroud elements so that each said flange forms a smooth continuation of the adjacent surface of its associated impeller blades.

While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I aim in the appended claim to cover all such modifications.

I claim as my invention:

In a turbine, compressor, blower or the like having an annular fluid flow path; a rotor membar; a plurality of pircumferentially-spaced blades having a one-piece construction with said rotor member and extending therefrom into said fluid flow path; a plurality of shroud elements each disposed between a pair of adjacent blades, each of said shroud elements having a deck portion bridging the gap between the tip ends of its pair of blades from substantially the upstream to the downstream ends of said blades and having a pair of flanges extending inwardly only part way toward the root ends of said blades from opposite edges of said deck portion; and a brazed junction between each said flange and the adjacent blade and extending to the tip end of said blade, each shroud element deck portion bein disposed outwardly beyond the tip end of each adjacent blade.

VINCENT MOORE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,292,830 McCain Jan. 28,1919 2,390,504 Berger Dec. 11, 1945 FOREIGN PATENTS Number Country Date 563,458 Germany Nov. 5, 1932