US2823889A

US2823889A - Rotor construction and fabrication

Info

Publication number: US2823889A
Application number: US154131A
Authority: US
Inventors: Edward A Stalker
Original assignee: Stalker Development Co
Current assignee: Stalker Development Co
Priority date: 1950-04-05
Filing date: 1950-04-05
Publication date: 1958-02-18
Anticipated expiration: 1975-02-18

Description

Feb. 18, 1958 E. A. STALKER ROTOR CONSTRUCTION AND FABRICATION 2 Sheets-Sheet 1 Filed April 5, 1950 Fla. 4

IN VZN TOR.

FIG. 5"

Feb. 18, 1958 E. A. STALKER 2,823,889

ROTOR ons'mucnon AND FABRICATION Filed April 5, 1950 2 Sheets-Sheet 2 ///////////IIIIIIIIIIIll/1 as -4/ FIG. 8 36 7 46 if INVENTOR.

ijnited States atent ROTOR CONSTRUCTION AND FABRICATION Edward A. Stalker, Bay City, Mich., assignor to The Stalker Development Company, Bay City, Mich, a corporation of Michigan Application April 5, 1950, Serial No. 154,131

6 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. l 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 99 in Fig. 8; and

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

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 decreased 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 forward extending tab 14 of each blade part 12 is then folded ice 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. For light 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 disks 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 of the blade segments. 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 4t) and 42 are slotted inward from their free edges to receive the blades for a depth equal to their tapered length. 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 6d.

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 together 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 efficiency 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 tip to root chord ratio is commonly about 0.6 since experience has shown that greater values lea-d 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 efficiency.

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 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 or" the order of 12 to 15 percent for substantial tip to root chord ratios. In compressors, practice has been to make the root chord 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 tip chord ratio for structural integrity and the small tip chords have required close spacing at the tips leadin to such close spacings at the root in terms of gap-chord ratio or root solidity that no gain resulted from the blade thinness, 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 lar e 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. 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 in a rotor adapted for interchange of energy with a fluid, a plurality of blade plates each including a plurality of blades peripherally spaced there about, each said blade being formed integrally within its respective plate and twisted relative thereto to place each blade at a pitch angle, each said blade tapering in thickness along the span thereof, said plates being fixed axially in tandem with said blades interdigitating, and hub means positioned between said blades to restrain said blades from untwisting.

2. in combination in a rotor for an axial flow machine adapted for the interchange of energy between a fluid and said rotor, a hub structure comprising a pair of similarly shaped axially spaced side disks each having a rim flange of me same radius proiecting axially inward, each said flange having aplurality of peripherally spaced notches extending from a said flange edge toward its side disk and matching with the notch in the other said flange, blade plate means formed to provide a plurality of peripherally spaced blades, said plate means being positioned between said side disks with each said blade nested in matching notches of said flanges and projecting outward beyond said flanges, and means to hold said side disks and said blade plate means in selected relationship to define said rotor, said blade plate means having increasing thickness radially inward therealong.

3. In combination in a rotor adapted for interchange of energy with a fluid, a hub structure comprising axially spaced plates having their outer peripheries turned over and extending in a general axial direction defining a rim, and a plurality of hollow blades peripherally spaced about said hub structure, each of said blades having a wall extending radially inward beyond the outer perimeter of said hub structure and fixed to said hub structure inwardly of the inner Wall of said rim, each of said blades having another wall extending radially inward beyond said perimeter of said hub structure and terminating adjacent to said perimeter, the last said wall being substantially shorter than the first said wall.

4. In combination in a rotor adapted for interchange of energy with a fluid, a hub structure comprising axially spaced plates, and a plurality of hollow blades peripherally spaced about said structure, each said blade having a wall extending radially inward beyond the outer perimeter of said hub structure and fixed thereto inwardly of the radial thickness of said hub structure plates, each said blade having another wall extending radially inward be yond the outer perimeter of said hub structure and terminating adjacent to said perimeter, the last said wall being substantially shorter than the first said Wall, the portion of the first said Wall within said hub structure being twisted with respect to the portion of said wall positioned radially outward from said structure.

5. in combinationin a rotor adapted for interchange of energy with a fluid, a hub structure comprising a peripheral rim structure, and axially spaced plates fixed thereto, and a plurality of hollow blades peripherally spaced about said structure, each said blade having plate wall means forming a face of said blade and extending radially inward beyond said rim and fixed to said hub structure inwardly beyond said rim structure, each said blade having another wall extending radially inward through said rim and terminating short of the inner end of the first said wall, both said walls being bonded to said rim by fused metaL.

6. In combination in a rotor for an axial flow machine having an axis of rotation and adapted for the interchange of energy between a fluid and said rotor, a hub, axially spaced side disks integrally bonded to said hub and extending in a generally radial plane, rim means integrally carried by and located on the outer periphery of each of said disks, a single blade plate forming blade roots extending inwardly of said rim means and attached to said hub, said single blade plate extending integrally outward through said rim means and being formed to provide a plurality of peripherally spaced hollow blades outwardly of said rim means, said rim means extending over the entire space between said side disks and from blade to bladeadjacent the roots thereof to form a substantially closed rim perimeter, and fused metal means to intimately hold said side disks and said blade plate integrally bonded at said blade roots in predetermined relationship to form a unitary assembled rotor whereby said structure forms a lightweight rotor having high resistance to stresses set up by centrifugal force.

References Cited in the file of this patent UNITED STATES PATENTS 1,043,830 Heath Nov. 12, 1912 1,142,690 Francke June 8, 1915 1,363,692 Summers Dec. 8, 1920 1,707,463 Ford Apr. 2, 1929 ,(Qtherreferences on following page) 5 Bahr Ian. 20, 1942 Utz Nov. 23, 1943 Boerger Sept. 5, 1944 Upson Nov. 14, 1944 Redding Feb. 18, 1947 Watson Oct. 7, 1947 Waterval June 28, 1949 Hans Mar. 7, 1950 Oestrich er a1. July 3, 1951 Eastman et a1. July 1, .1952 Bachle July 22, 1952 6 FOREIGN PATENTS Great Britain of 1861 Sweden Dec. 24, 1895 Great Britain of 1892 Sweden Dec. 19, 1917 Great Britain May 7, 1925 Great Britain Dec. 21, 1931 France June 29, 1910 Great Britain Oct. 1, 1934 Great Britain July 3, 1940 Great Britain Nov. 2, 1948 Great Britain May 20, 1944