US3378230A - Mounting of blades in turbomachine rotors - Google Patents

Description

A ril 16, 1968 M. D. TOOMEY 3,378,230

' MOUNTING OF BLADE-S IN TURBOMACHINE ROTORS Filed DeC. 16, 1966 2 Sheets-Sheet 1 IN VEN TOR.

gMW/mw jror April 16, 1968 M. o. TOOMEY MOUNTING OF BLADES IN TURBOMACHINE ROTORS Filed Dec. 16, 1966 2 Shees-Sheet 2 INVENTOR. Myron 0. foomey a ATTORNEY.

allll'll'l United States Patent 3,378,230 MOUNTING 0F BLADES as TURBO- MACHINE ROTUES Myron D. Tourney, Cincinnati, Ohio, assignor to General Electric Company, a corporation of New York Filed Dec. 16, 1966, Ser. No. 602,244 Claims. (Cl. 253-77) ABSTRACT OF THE DISCLOSURE The disclosure shows the mounting of turbomachinery blades on discs through the use of blade tangs and correspondingly shaped slots. The entrance to the slot is either narrower or wider than an intermediate portion and the slot depth is greater than that of the tang height so that the wider portion of the tang may be slid past the narrower portion of the slot and then the blade held in a radially outward position by a shim, whereby the blade is axially positioned relative to the disc and axial loadings are directly transmitted from the tang to the disc and the shim does not function as a load-bearing member. Where curved slots and tangs are used, the curvatures of opposite sides are different and selected to minimize stress concentrations by providing an essentially constant, projected, load-bearing section.

The present invention relates to turbomachincs and more particularly to improved means for mounting blade elements on a turbomachine rotor disc.

It has been conventional practice to mount the blade elements of a turbomachine rotor on a disc by forming tangs at the inner ends of the blade elements which are received by dovetail slots formed on the outer rim of the motor disc. The blade elements are then locked on the disc by clamping rings or straps which position the blade elements in an axial direction and function as loadbearing elements for axial loadings transmitted between the blade elements and the disc.

The straps or clamping rings employed for retaining the tangs in the slots represent a substantial expense since they must be designed and function as load-bearing members for transmitting axial loadings between the blade elements and the discs. Further, great care is required in the manufacture, not only of the blade elements and discs, but in the clamping means, to accurately position the blade elements in an axial sense.

One object of the invention is therefore to reduce the expense of turbomachine rotors by eliminating the need for axial load-bearing members to retain and position the tangs of blade elements in slots on the rotor disc.

Another difliculty encountered in mounting blade elements on rotor discs is encountered where curved tangs and slots are employed. The curvature of the tangs and slots approximates the curvature of the airfoil portion of the blade element and provides advantages in minimizing the stress levels in the tang due to transmission of radial loadings from the airfoil portion to the tang. The curvature of the slots in the disc create other stress problems due to the fact that the projected area of the disc, between slots, can vary substantially, from one radial face to the other and at intermediate portions.

Accordingly, another object of the invention is to obtain the above ends and further to minimize the stress levels in rotor discs where blade elements are mounted thereon through the use of curved slots and tangs.

The above objects are broadly attained by a mounting arrangement wherein tangs are formed on the blade element and received by slots in the rotor disc and characterized in that the slots and tangs have matching con- 3,378,230 Patented Apr. 16, 1968 figurations with their intermediate widths being different than at opposite ends thereof. Further, the slots have a greater depth than the tangs, permitting the wider dimension of the tang to pass through the narrower dimension of the slot as the tang is slid into the slot, and then permitting the blade element to be shifted radially outwardly of the disc so that the matching surfaces of the tang not only position the blade element in an axial sense, but transmit both axial and radial loadings from the blade element to the disc. Shim means are then provided for maintaining the tang in its outer load-bearing position. The shim means, however, simply functions as a spacer element and is not a load-bearing element, particularly for axial forces transmitted between the blade element and the disc.

Preferably these ends are attained by forming at least one side of the slot and tang respectively with matching convex or concave surfaces. Where curved slots and tangs are to be employed, it is preferable that the radius of curvature for one side of the slot and tang be formed on a different radius from the other sides thereof to provide either a larger or smaller Widthwise dimension to the slot and tang intermediate its length than at the opposite ends thereof. Further it is preferred that the matching concave tang and convex slot surfaces have a larger curvature and that the projected width between adjacent slots be approximately constant from one radial face of the disc to the other so that stress levels are minimized.

The above and other related objects and features of the invention will be apparent from a reading of the following description of the disclosure found in the accompanying drawings and the novelty thereof pointed out in the appended claims.

In the drawings:

FIGURE 1 is a fragmentary perspective view, partially exploded and partially in section, showing a turbomachine rotor;

FIGURE 2 is a top plan view of a portion of the rotor seen in FIGURE 1;

FIGURE 3 is a section taken on line 3-3 in FIG- URE 1;

FIGURES 4 and 5 are similar elevations of a portion of the radial face of the turbomachine rotor;

FIGURE 6 is a fragmentary perspective view of a turbomachine rotor embodying a modified form of the invention;

FIGURE 7 is a top plan view of a portion of the rotor seen in FIGURE 6;

FIGURE 8 is a top plan view of the turbomachine rotor embodying another alternate embodiment of the invention; and

FIGURE 9 is an elevation of a modified embodiment of the invention seen in FIGURE 8.

Referring now more particularly to FIGURES 1-5, inclusive, in the accompanying drawing, a turbomachine rotor 10 is shown having a plurality of angularly spaced slots 12 opening into the outer surface of the rotor disc and extending from one radial face 13 to the opposite radial face 14. These slots are of undercut, generally dovetail form, angled relative to the axis of the rotor. The inwardly divergent side walls 15, 16 of the slots 12 are also concave relative to their lengthwise direction, preferably having maximum spacing or width at the midpoint of the slots, as is best seen in FIGURES 1 and 3. The side walls 15, 16 blend, through curved sections, with the outer circumference of the disc and with the base 36 of the slot.

Each slot 12 mounts a blade element 20 of the turbomachine rotor 19, the blade element 20* having an airfoilshaped portion 21 at its outer end and a tang 22 at its inner end. The narrow shank 24 of the tang 22 joins with a platform 26 which defines the inner flow path of the a gas stream through the turbomachine and from which the airfoil-shaped portion 21 projects.

Each tang 22 is formed with divergently tapered sides 30, 31 which are convexly curved along their lengths so that the tang is thickest intermediate its length as is best shown in the detached tang portion of FIGURE 1. The sides 30, 31 are curved at their lower portions to blend with the base 35 of the tang.

Slot 12 is of greater depth than the tang 22. Consequently the width of the slot opening into the radial face of the rotor disc is sufiicient for the widest portion of the tang (at its midpoint) to pass therethrough when the base of the tang is at approximately the same level as the base of the slot. The tang 22 can thus be longitudinally inserted in the slot 12 (FIGURE 4) and then shifted radially outwardly (FIGURE 5). The tapered walls of the slot and tang are of corresponding slope and curvature so that when the blade is so positioned, they serve as bearing surfaces for both radial and axial loads which are transmitted between the blade elements and the rotor disc in operation.

After blade element has been so positioned, a shim 40 is introduced in the gap between the base 35 of the tang and the base 36 of the slot. The shim 40 simply maintains the blade position so that the registered curved surfaces of the tang and slot are maintained in a load bearing position. When the rotor is rotating, the loads thereon are primarily in a radial direction, thus positively wedging the tang against the slot walls so that any axial loadings thereon are likewise carried by the longitudinally curved portions of the tang and slot. The blade element is also positively positioned on the disc in an axial as well as a radial direction.

It will thus be apparent that the shim 40 is not in any sense a load-bearing member and may be economically formed of lightweight material. Preferably the shim is maintained in the slot 12 by having tabs 40a at its ends which may be bent up to prevent the shim from falling from the rotor. The tabs 40a take little or no force loading since there is no force transmission from the blade elements, in an axial sense, thereto. This is to say that while the tab 46a is shown engaging both the rotor 11 and tang 22, it could simply engage one or the other and perform its function equally as well.

In the alternate embodiment of the invention illustrated in FIGURES 6 and 7 the tang 22 is formed with concavely curved divergent sides a, 31a, and the slot 12' for receivig this tang is similarly formed with divergent side Walls 15', 16' which are convexly curved in a lengthwise direction. Whereas in the previous embodiment the central portion of the tang and slot was widest, in the present embodiment the narrowest dimensions are found at this point. Again the depth of the slot 12' is greater than the depth of the tang 22. This enables the wide end portion of the tang 22 to be introduced into the slot 12 when the base of the tang is at approximately the same level as the base 36 of the slot. Again, the slope and longitudinal curvature of the tang and slot are matching so that when the blade element is displaced outwardly, the tang will transmit both radial and axial loadings directly to the turbomachine rotor 11. The same shim (not illustrated) may be employed to maintain the blade element in its radially outwardly displaced position for the transmission of both radial and axial loads.

FIGURES 8 and 9 illustrate an embodiment of the invention employing curved slots and tangs which provide for more eificient transmission of radial force loadings from the airfoil-shaped portion of the blade element to the rotor disc. The slot 12" again has divergently tapered walls 15 and 16". The wall 16" is curved lengthwise of the slot on a given radius of curvature. The wall 15" is also curved lengthwise of the slot about a radius of curvature which is shorter than that of the wall 16". This means that the slot has a wider dimension at its midpoint than at its opposite ends which open into the radial faces 13 and 14- of the rotor disc 11.

The tang 22" is formed correspondingly to the slot 12", having divergent walls 30 and 31" which are curved in a lengthwise direction on curvatures respectively corresponding to those employed in generating slot surfaces l5, 316'. It will be seen that the con-cave tang wall 31" and the convex slot wall 16 have a greater curvature, as by being generated on a longer radius, than the convex tang wall 30" and concave slot wall 15'. This gives a wider central dimension x to the slot and tang than the dimensions y at the opposite ends thereof, as related to the nominal, curved axes thereof.

Again, the depth of the tang 22 is greater than the depth of the slot 12" so that when the base 35 of the tang is at approximately the same level as the base 36 of the slot, the tang may be slid into the slot and the blade element then shifted radially outwardly as indicated in FIGURE 9 so that the load-bearing surfaces of the tang and slot are capable of transmitting both radial and axial loads. A shim 40 is again employed to maintain the tang in its load-bearing position.

The projected width of the disc material between the slots 12" is the prime factor determining the stress loading therein. With the illustrated, preferred configuration, the projected width w may be maintained a constant from one radial face 13 to the opposite radial face 14. It is also possible to maintain the same type of relationship in the tang 12" and the shank 24 thereof. Unequal stress loadings in the disc and blade elements may thus be minimized and the mass of metal required for a given load condition reduced, all of which leads to a lighter construction particularly desirable in the propulsion of aircraft.

While reference here has been made to turbom-achine rotors, it will be appreciated that this term covers both compressor and turbine rotors and therefore modifications of the embodiments described will occur to those skilled in the art. It is thus to be understood that these embodiments are not illustrative and not limiting.

Having thus described the invention, what is claimed as novel and desired to be secured by Letters Patent of the United States is:

1. A turbomachine rotor comprising,

a disc having at least one blade element mounted theresaid disc having a dovetail slot opening into the outer circumference of the disc and extending from one radial face thereof to the other,

said blade element having a tang at its lower end which is to be received by said slot characterized in that,

the lengthwise portions of the slot and tang having a matching configuration with their widths being larger or smaller at intermediate portions than at the opposite ends thereof,

said slot having a greater depth than the tang, permitting the wider dimension of the tang to pass through the narrower dimension of the slot as the tang is slid into the slot and then permitting the blade ele ment to be shifted radially outwardly so that the matching surfaces of the slot and tang transmit both axial and radial loadings from the blade element to the disc, and

means are provided for maintaining the blade in its outward load-bearing position.

2. A turbomachine rotor as in claim 1 wherein,

the slot and tang walls are divergent in a direction inwardly of the rotor disc and are smoothly curved in a direction lengthwise of the slot.

3. A turbomachine rotor as in claim 2 wherein,

the slot has an axis of single curvature, whereby the slot has concave and convex surfaces respectively engaged by corresponding convex and concave tang surfaces.

4. A turbomachine rotor as in claim 3 wherein,

the concave tang surface and the convex slot surface have a gretaer curvature than the convex tang surface and concave slot surface.

5. A turbomachine rotor as in claim 4 wherein,

the disc has a plurality of slots angularly spaced about its circumference,

blade elements are mounted in each slot, said blade elements having tangs received by said slots, said slots and tangs being formed with the same configuration as said one slot, and

the projected width (w) between adjacent slots being substantially a constant from one radial face of the disc to the other.

6 References Cited UNITED STATES PATENTS 8/ 1954 Schorner 253-77 11/1965 Schoenborn 25 3-77 11/1966 Stanley 253-77 FOREIGN PATENTS 12/1954 France.

3/1952 Germany.

EVERETTE A. POWELL, 111., Primary Examiner. L

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