US2992810A - Rotor construction and fabrication - Google Patents

Description

July 18, 1961 E. A. STALKER ROTOR CONSTRUCTION AND FABRICATION 2 Sheets-Sheet 1 Original Filed April 5, 1950 INV NTOR.

FIG. 5

y 1961 E. A. STALKER 2,992,810

ROTOR CONSTRUCTION AND FABRICATION Original Filed April 5, 1950 2 Sheets-Sheet 2 g E R 44 INVENTOR. A add/ 44 United States Patent ROTOR CONSTRUCTION AND FABRICATION Edward A. Stalker, Bay City, 'Mich., assignor to The Stalker Corporation, a corporation of Michigan Original application Apr. 5, 1950, Ser. No. 154,131, now

Patent No. 2,823,889, dated Feb. 18, 1958. Divided and this application Sept. 13, 1956, Ser. No. 609,710

10 Claims. (Cl. 253-39) This invention relates to bladed rotors adapted to the interchange of energy with a fluid as for instance compressor and turbine rotors.

An object is to provide a bladed rotor wherein the solidity near the tips approaches in magnitude the solidity near the roots of the blades.

Another object of the invention is to provide hollow blades having tapered wall thickness.

Another object of my invention is to provide an integral rotor construction in which the thickness of the Walls are tapered.

Still another object is to provide a means of fabricating hollow blades with tapered wall thickness.

Other objects will appear from the description, drawings and claims.

The above objects are accomplished by the means illustrated in the accompanying drawings in Which- FIG. 1 is a perspective cut-away view of a rotor according to this invention;

FIG. 2 is an axial view of a blank from which the blades are formed;

FIG. 3 is an edge view of the blank of FIG. 2;

FIG. 4 shows the manner of cutting a plate to provide integral blade blanks therein;

FIG. 5 is a perspective view of a blade isolated from the blade plate;

FIG. 6 is a fragmentary axial section of a rotor according to this invention;

FIG. 7 is a fragmentary section along line 7-7 in FIG. 6;

FIG. 8 is a cut-away perspective view of another form of rotor;

FIG. 9 is a blade section along line 9-9 in FIG. 8; and

FIG. 10 is a side view of a flanged side disk.

This application is a division of applicants copending Patent No. 2,823,889;

In a rotor the principal stresses are caused by the weight of the parts since the centrifugal force predominates. The weight of the hub for instance is largely determined by the weight of the blades. It is therefore desirable to make the blades hollow. In fact if the blades are made hollow the weight of the rotating parts of an axial flow compressor may be described by a percentage of the order of 40.

A further reduction in weight can be achieved or the rotor may be run at higher speeds by tapering the wall thickness of the blades. This is however difficult to achieve and the present invention is directed to a means of accomplishing this end by an economical structure and a process for making it.

In one form of the invention the blades or blade segments are to be made integral with a center disk as shown in FIG. 1. The plate 10, FIGS. 2 and 3, is decreased in thickness from the center to the periphery. This may be accomplished by pressing, grinding, machining, and the like. The plate is cut to form the plurality of blade parts 12 (of FIG. 1) about the periphery in a manner similar to that shown in FIG. 4 which shows only 4 blade blanks while the plate 10 in FIG. 1 has many more similar blade blanks forming the plurality of blades. The for- Ward extending tab 14 of each blade part 12 is then folded 2,992,810 Patented July 18, 1961 rearward about a suitable arbor by dies to form a blade 16 as shown in FIG. 5. The rear edge of the tab is bonded to the other edge 18 of the part to form a relatively sharp trailing edge 20.

Forlight loads the structure of FIG. 5 can be used as a'fan. For heavy duty two or more of the structures of FIG. 5 may be assembled as shown in FIG. 1.

The two plates with their blades, now indicated as 30 and 32 are fixed together in tandem on hub structure 44, 46 with the blades .16 of one plate interdigitating with the blades 17 of the other plate and with the plates being bonded together along faying surfaces thereof such as the contacting surfaces 30, 32 and 14, 18. See FIGS. 1 and 6. Suitable offsets of the blades with respect to their plate permit the leading edges of all the blades to lie in the same plane.

The side disks 36 and 38 with inward turned flanges 40 and 42 suitably notched as shown at 41 and 43 respectively enclose the blade plates. These with blade plates are fixed together by the hub elements 44 and 46.

The flanges 40 and 42 are slotted inward from their free edges to jointly receive the blades for the depth thereof. The balance of the flange is unslotted.

The whole structure is bonded together preferably by brazing.

In FIG. 8 one group of the blades are formed by a set of two plates 50 and 52, the former carrying the upper blade parts 54 and the latter carrying the lower blade parts 56. These are joined together by brazing at the leading and trailing edges to form blades 58 as shown in FIG. 9.

A second group of blades 60 are formed by a set of plates 62 and 64.

The two groups are assembled with the blades interdigitating. Suitable hub elements 70 and side disks 72 are added to the assembly and the whole is bonded to gether to make the rotor of FIG. 8.

The local solidity of a bladed rotor is defined as the ratio of the sum of all the blade chord lengths at a given radius to the length of the circumference at the same radius.

Rotors in practice, for instance turbine rotors, have their blades very close together at the blade roots in order to achieve a satisfactorily high solidity at the tips. As a result the aerodynamic or flow efliciency at the blade roots is greatly impaired. This situation is largely brought about because the solid blades have to be reduced in thickness and chord toward the tip so that the root of the blade will not be subject to too great a centrifugal stress.

This is particularly true when the span or radial length of the blade exceeds twice the mean chord length, or the ratio of hub diameter to tip diameter is less than 0.8. This ratio is commonly called the hub ratio. In gas turbines for smaller hub ratios the top to root chord ratio is commonly about 0.6 since experience has shown that greater values lead to structural failure. The reduced tip chord obviously reduces the local solidity and it must be compensated for by placing the blades closer together. Then the roots which have larger chords are too close together for best flow efiiciency.

By making the blades hollow with tapered walls, a turbine rotor can be provided with tip chord lengths greater than 0.6 the root chord length or preferably equal to or exceeding the root chord with a root solidity no greater than 2.0. These proportions may be utilized even though the blade span is as great as twice the average chord length of the blade or the hub ratio less than 0.8.

By making the blades of an axial flow compressor hollow, they can be given a tip chord length greater than 0.8 the root chord length and preferably equal to or exceeding the root chord length even though the blade span 'ice is as great as twice the average chord length of the blade. The root solidity is preferably no greater than 1.5.

The solidity of a turbine is normally higher than a compressor because the flow through the former is accompanied by a pressure drop and through the latter by a pressure increase.

When the tip chord is large and especially if it is larger than the root chord, the torsional strength of the blade may need to be increased by increasing the thickness of the root section. In compressor blades the thickness of the root should be of the order of 12 to 15 percent of the root chord length for substantial tip to root chord ratios. In compressors, practice has been to make the blade root section with a maximum thickness of about of the chord length because it has been believed in the art that the thickness was largely responsible for the high drag. However the close spacing required because of the thinness of the blade has really been the cause of far greater drag increases.

As already pointed out thin spindly blades have required a small root chord ratio for structural integrity and the small tip chords have required close spacing at the tips leading to such close spacings at the root that no gain resulted from the blade thiness, but there were actually substantial drag losses.

The aerodynamic losses come about in large measure because at the root with the close spacing, each blade is in the disturbed flow of the other blade. In other words in a higher velocity flow. Since the blades are tapered to a large root chord the fraction of blade area in the higher velocity flow is increased. Furthermore the total blade area has also been increased because the close spacing means more blades in each rotor.

In this invention a practical means of fabricating a hollow blade of tapered wall thickness is disclosed and this construction and method of fabrication provides a rotor wherein the solidity at the periphery is large and approaches the solidity at the blade roots. The number of blades, the Weight of the whole rotor, and the costs are greatly reduced.

The steps in fabricating the rotor are substantially as follows. A plate is pressed or machined to have a decreasing thickness outward along the radii as in'FIGS. 2 and 3.

The individual plates are next Worked preferably by appropriate dies to form the blade segments. Since each plate was tapered along the radius the walls of the blades will decrease in thickness from the root outward.

The blade plate structures are placed together in axial tandem relation with the blades of one interdigitating with the blades of the other defining a nose portion of limited radius of curvature. Side disks. and hub elements are added. The assembly is bonded together preferably by brazing in a furnace.

While I have illustrated specific forms of the invention, it is to be understood that variations may be made therein and that I intend to claim my invention broadly as indicated by the appended claims.

I claim:

1. In combination to form an axial flow rotor adapted for the interchange of energy between a fluid and said rotor, a plurality of plates whose thicknesses decrease outward along the radius, each said plate having a plurality of peripherally spaced blade segments formed integrally of said plate, the segments of one plate being formed to register respectively with the segments of the other plate. to define a plurality of hollow blades, said plates being bonded together along faying surfaces of the leading and trailing edges respectively of said blade segments.

2. In combination to form an axial flow rotor adapted for the interchange of energy between a fluid and said rotor, a plurality of plates whose thicknesses decrease outward along the radius, each said plate having a plurality of peripherally spaced blade segments formed integrally of said plate, the segments of one plate being formed to register respectively with the segments of the other plate to define a plurality of hollow blades, said plates being bonded together along faying surfaces of the. leading and trailing edges respectively of said blade segments, and a hub structure bonded to said plates.

3. In combination in a rotor for the interchange of energy with a fluid, a set of blade plates each including a plurality of blade parts integral therewith spaced peripherally thereabout, said plates being tapered in thickness radially thereof, said plates being arranged axially in tan dem with said blade parts of a said plate in registration along their leading and trailing edges respectively with said parts of another said plate to form a. plurality of hollow blades of tapered wall thickness, said registering parts forming a blade being bonded together, and hub means to support said plates for rotation about the rotor axis.

4. In combination in a rotor adapted for the interchange of energy with a fluid, a set of sheet metal blade plates having blade parts formed therein and spaced peripherally thereabout, said plates being tapered in thickness radially thereof, said plates being arranged axially in tandem with said blade parts of a said plate in registration along their leading and trailing edges respectively with said parts of another said plate to form a plurality of hollow blades of tapered wall thickness, said registering parts forming a blade being bonded together, and hub means to support said plates for rotation about the rotor 3x18.

5. An axial flow turbine rotor as defined in claim 1 in which each said blade has a spanwise length no less than twice the mean chord length, each said blade having a tip chord length substantially as great as the root chord length, said blades being peripherally spaced to provide a root solidity less than 2.0

6. An axial flow compressor rotor as defined in claim 1 in which each said blade has a spanwise length no less than twice the mean chord length, each said blade having a tip chord length substantially as great as the root chord length, said blades being spaced peripherally to define a local solidity at the blade roots less than 1.5.

7. A bladed axial flow as defined in claim 1 in which each said blade has a longer chord at the tip than at the root thereof.

8. An axial flow compressor rotor as defined in claim 1 in which each said blade has a spanwise length no less than twice the mean chord length, each said blade having a tip chord length substantially as great as the root chord length, said blades being spaced peripheral-1y to define a local solidity at the blade roots no greater than 1.5, each said blade having a root maximum thickness not less than 12% of the root chord length.

9. A bladed axial flow gas turbine rotor as defined in claim 1 in which each said blade has a tip to root chord ratio greater than 0.8, said blades being peripherally spaced about said rotor to provide a root solidity no greater than 2.0.

10. A fluid turning blade for a fluid machine having an interchange of energy with a fluid as defined in claim 1 in which sheet metal blade plates are formed to define a blade wall having a nose portion of limited radius of curvature, said nose portion being tapered in thickness chordwise to provide for bending said portion to a small radius, another of said blade plates having -a blade wall juxtaposed with respect to the first said wall and having a nose portion nested in said nose portion of limited curvature, and means bonding said blade walls together to form hollow blades.

References Cited in the file of this patent UNITED STATES PATENTS 1,142,690 Francke June 8, 1915 (Other references on following page) UNITED STATES PATENTS Muller May 29, 1923 Hansen Dec. 6, 1927 Smith Mar. 27, 1934 Watson Oct. 7, 1947 Watson Dec. 9, 1947 Hans Mar. 7, 1950 Eastman et a1 Iulv 3. 1951 6 Bachle July 22, 1952 Stalker Aug. 18, 1953 Stalker Dec. 4, 1956 Stalker Dec. 4, 1956 Stalker Feb. 18, 1958 FOREIGN PATENTS Germany June 16, 1908

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