Turbine balancing

A turbine disk has an at least partially radially-extending first portion. An at least partially axially-extending circumferential flange has a root connecting the flange to the first portion. The flange extends to a rim and has a plurality of pairs of first and second weight-mounting fastener apertures. A plurality of first recesses are provided in the rim, each position between an associated first and second aperture of an associated one of the aperture pairs. A plurality of second recesses are provided in the rim each positioned between an adjacent two of the pairs.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to balancing of turbine rotors by the addition of weights, and more particularly to rotor flanges to which the weights are mounted.

(2) Description of the Related Art

The dynamic balancing of turbine rotors is a well-developed art. Each rotor may have, at one or more longitudinal locations, a circumferential array of mounting features permitting the installation of one or more balance weights.

It is known, for example, to balance a rotor by using a computer-controlled apparatus to spin the rotor about its rotational axis and measure the parameters of rotational displacements associated with imbalance. Based upon these measurements, the computer outputs an identification of a particular combination of balance weights to balance the rotor. Specifically, the computer may identify particular weight masses to be installed at one-to-all of the individual mounting locations defined by the mounting features.

BRIEF SUMMARY OF THE INVENTION

Accordingly, one aspect of the invention involves a turbine disk having an at least partially radially-extending first portion. An at least partially axially-extending circumferential flange has a root connecting the flange to the first portion. The flange extends to a rim and has a plurality of pairs of first and second weight-mounting fastener apertures. A plurality of first recesses are provided in the rim, each position between an associated first and second aperture of an associated one of the aperture pairs. A plurality of second recesses are provided in the rim each positioned between an adjacent two of the pairs.

Other aspects of the invention relate to remanufacturing a turbine disk. The disk initially has a plurality of recesses in its balancing flange rim, each positioned between a first aperture of one aperture pair and adjacent second aperture of an adjacent aperture pair. The method may involve broadening such recesses. The method may involve adding a plurality of additional recesses in the rim, each positioned between first and second mounting apertures of an associated mounting aperture pair. The method may also involve longitudinally trimming the rim.

DETAILED DESCRIPTION

FIG. 1shows a rotor20of a turbine engine high pressure compressor section. From fore to aft, the rotor includes three blade disks22,24,26and a rear disk or hub28secured to each other such as by welding. The rotor has a central longitudinal axis500which is a central longitudinal axis of the engine and an axis about which the rotor rotates. The periphery of each blade disk has mounting features30for mounting a circumferential array or stage of blades (not shown).

In the exemplary embodiment, the rear hub28has a frustoconical web40extending aft and radially inward from a junction with the rear blade disk26to a flange42for mounting to a high spool shaft (not shown). The rear hub28has a balance flange50extending generally longitudinally aft from the web40. The exemplary flange has inboard and outboard surfaces52and54and extends from a relatively thick root56at the web40to an aft rim58. A relatively thin distal or aft mounting portion60extends to the rim58and is provided with mounting apertures (discussed below) for the securing of weights62by means of fasteners64(e.g., rivets or threaded fasteners). In the exemplary embodiment, the flange inboard surface52has a smooth continuously curving transition to the outboard/aft surface of the web40and smoothly extends to a distal longitudinal portion along the mounting portion60. The flange outboard surface54has a shoulder or step70at the fore/proximal end of the mounting portion60, extending generally longitudinally fore and aft of the step. An intermediate portion72extends forward from the shoulder70with inboard and outboard surfaces initially parallel and then transitioning as described above. At the exemplary root56the outboard surface defines a slight channel74which facilitates machining of the surface54.

FIG. 3shows further details of the balance flange50with weights removed. The mounting apertures are provided in pairs.FIG. 3shows a first pair of first and second apertures80A and82A and a second pair of first and second apertures80B and82B. Each of the apertures is formed as a cylindrical radially-extending hole frustoconically beveled at the outboard surface54for accommodating an end (e.g., the head) of an associated one of the fasteners64. The exemplary flange rim58has two groups of recesses84and86, extending forward from a flat broken annular portion88, the unbroken part of which form flats of islands between adjacent recesses). Each recess84lies circumferentially between a pair of apertures for mounting a given weight. Each recess86lies between two adjacent pairs. The recesses may function to reduce weight and relieve hoop stress in the mounting portion60.

FIG. 4shows an exemplary prior art balance flange150wherein analogous portions to the flange50are shown with like numerals incremented by one hundred. The flange has a rim158and similar (identical in an exemplary embodiment) pairs of mounting apertures180A,182A,180B,182B. The flange only has recesses186between adjacent aperture pairs and not between apertures of a given pair. Accordingly, the rim flats of broken portion188are of greater circumferential extent than those of the flange50. Additionally, the recesses186are narrower than the recesses86. This narrowness may be measured at various longitudinal positions relative to the common plane of aperture centerlines (or intersections thereof with the projection of the flange outboard surface). Furthermore, the recesses186have a greater amount of aft-to-fore taper and the rim broken portion188is more rearwardly spaced stet the apertures (e.g., the mounting portion is longer in the flange150than in the flange50).

The flange150may be remanufactured in one or more ways to more closely resemble the flange50. The recesses186may be machined to broaden them and make them more blunt. The rim may be trimmed by machining to longitudinally shift the broken annular portion188forward. The second plurality of the recesses can be machined between adjacent apertures of each pair.

FIG. 5is a view of the circumferential outboard surface54of the flange50.FIG. 5shows slightly more than one cycle of mounting features along the flange, specifically showing apertures82A,80B and82B, each having an axis510. There is a circumferential spacing S1between axes of apertures of a given pair and a circumferential spacing S2between adjacent apertures of adjacent pairs. The spaces are advantageously different to prevent weights from erroneously being secured to one aperture each of an adjacent pair. In an exemplary embodiment, the spacing S2is slightly smaller than the spacing S1. The axes510are recessed forwardly of the rim annular portion88by a distance S3. An exemplary recess84has a uniform radius of curvature R1with a center of curvature offset rearwardly of the annular portion88by a distance S4so that a width W1of the recess at the annular portion88is slightly less than twice R1and a depth L1of the recess84ahead of the portion88is slightly less than R1. The exemplary recess86has more complex curvature. A central base portion200of the recess has a relatively large radius of curvature R2. Outboard aft portions202extending forward from the surface88are essentially straight and longitudinal. Transition portions204between the portion200and portion202have a relatively small radius of curvature R3. The recess86has a width W2at the surface88and a depth L2. As one parameter of the broadness of the recess86, the recess has a width W3at the longitudinal position of the axes510which is relatively close to W2. In the exemplary embodiment, the first recess depth L1is slightly less than the second recess depth L2, leaving a correspondingly greater mounting portion length L3ahead of the first recess than L4ahead of the second recess.

In an exemplary implementation, a flange radius along the outboard surface of the mounting portion60is 9.58 inches, a thickness of the mounting portion is 0.131 inches, a length of the mounting portion60is 0.5375 inch, and there are twenty pairs of mounting apertures. The mounting apertures have a nominal diameter of 0.11 inch, with a diameter at the chamfer of 0.16 inch. The separations S1, S2and S3are 0.719, 0.786, and 0.117 inch. The longitudinal spans L3and L4are 0.115 and 0.075 inch. The radius R1is 0.21 inch and the separation S4is 0.025 inch. The radii R2and R3are 0.575 and 0.13 inch. The widths W1, W2, and W3are 0.417, 0.490, and 0.478 inch. In the exemplary embodiment the depth and breadth of the recess86serves to reduce weight and hoop stresses at the circumferential ends of the weight mounting areas. The recesses84serve primarily for weight reduction as hoop stress reduction is not as great a concern within individual weight mounting areas. The partial circle shape of the recesses84reflects ease of machining (e.g., through use of simpler, less expensive, and/or more robust machining cutter and/or reduced use of the cutter). Although potentially advantageous from a weight reduction point of view, the benefits of making the recesses84similar to the recesses86might not be worth the additional manufacturing costs.

FIG. 5further shows, in broken line, the rim158of the prior art flange150. The mounting apertures and shoulder of such flange are coincident with those of the flange50and are not separately illustrated. The base of the recess186is forward of the base of the recess86. Accordingly, in the manufacturing process the rim flat portion188may be machined down to coincident with the rim flat portion88and additional recesses may be machined coincident with the recesses84. The recess186may be machined to provide a recess86′. The recess86′ is broader and substantially blunter than the baseline recess186. The width at the rim (same as W2) may be slightly larger than the corresponding baseline dimension W4(e.g., by 5-15%). The width between apertures (analogous to W3, but equal to W2in the illustrated embodiment) is advantageously substantially larger (e.g., by 30-80%) than the corresponding baseline dimension W5. The exemplary recess86′ is deeper than the recess86. In the exemplary embodiment, the depth of the recess86′ is chosen to be slightly deeper than the baseline recess186. The exemplary recess86is not so deep in order to limit manufacturing costs. Although potentially advantageous, the benefits of making the recesses86similar to the recesses86′ might not be worth the additional manufacturing costs.

One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the principles may be applied to various turbine configurations. Accordingly, other embodiments are within the scope of the following claims.