Bladed Rotor Structure For A Turbine Or A Compressor

Abstract

This invention comprises rotor structure for a turbine or compressor having an annular row of blades thereon, the rotor having a peripheral groove and the blades having root portions of the radial entry type received in the groove. The blade roots are machined to absolute pitch dimension or slightly less and the blades are disposed in groups, each group having an arcuate shroud segment riveted to the tenons of the blades in the group. Total accumulated deficiency due to undersize pitch dimensions in each group is made up by a thin liner member interposed between blade roots in adjacent groups.

Description

BACKGROUND OF THE INVENTION

Turbine and compressor rotor blades of the radial entry type, i.e., having roots of the type that are inserted in a peripheral locking groove on the rotor, are usually formed in such a manner that their root width is held to close tolerances. This is necessary because the width of the root establishes the pitch of the blade and any deviation from the absolute pitch dimension is troublesome, especially when the blades are of the shrouded type arranged in groups held together by arcuate shroud segments riveted to tenons on the blades.

Blades of the radial entry type are inserted in the locking groove through an enlarged entrance opening in the groove and after they are translated or rolled into abutment with each other, the gap left for the "closing" or "last" blade is measured. The last blade is then custom fitted by grinding down the width of the root to fit the gap and secured in any suitable manner. With this arrangement, the accumulated deviation from true pitch of the blades is compensated for at the last blade.

Previously to the above arrangement, the deviation from true blade pitch was made up by insertion of liners or shims between roots on a random basis in sufficient numbers and thickness to render unnecessary custom fitting of the last blade.

With both of the above arrangements, the spacing of the apertures in the arcuate shroud segments (for securement to mating tenons in the blades by riveting) cannot be predetermined nor can the apertures be "prepitched." Instead the aperture spacing is determined by calipering or otherwise measuring the individual spacing between adjacent blade tenons and drilling the apertures in the shroud segments to suit.

The above arrangements are expensive and involve considerable time to provide even at the manufacturing plant, where full facilities are available. However, when repairs in the field are subsequently required, the above arrangements are even more time consuming and difficult to provide, because of lack of proper facilities.

BRIEF SUMMARY

The present arrangement is an improvement over the above-described prior art and facilitates fabrication at the manufacturing plant and service in the field.

According to the invention, the radial entry blade roots are machined to a width as close as economically feasible to the theoretical pitch, but not exceeding such width. The blades are provided with tenons extending radially outwardly and are connected to each other in groups by arcuate shroud segments having apertures spaced equally from each other to coincide with the spacing between adjacent tenons. The shroud segments are secured to blades by riveting of the tenons.

The aggregate width of all of the blades in each blade group is measured and the deficiency is made up by a thin liner having a thickness substantially equal to such deficiency. The liners are disposed between adjacent blades at the ends of neighboring blade groups, so that they do not effect the pitch of the blade roots and therefore permit employment of shroud segments that have apertures that are prepunched to the theoretical pitch of the blades. With this arrangement, manufacture is facilitated, as well as service in the field where reblading of a rotor may be required, since individual blade width measurement for custom fitted shroud installation is eliminated.

THE DRAWINGS

The invention, along with its objects and advantages, will be more apparent from reading the following detailed description in connection with the accompanying drawings in which:

FIG. 1 is a fragmentary end view of a bladed rotor structure incorporating the invention, with portions cut away to show further detail;

FIG. 2 is an enlarged sectional view taken on line II-II of FIG. 1; and

FIG. 3 is a perspective fragmentary view of the rotor structure during fabrication.

PREFERRED EMBODIMENT

Referring to the drawings in detail, in FIG. 1 there is shown a portion of a rotor structure 10 for an axial flow elastic fluid turbine or compressor, formed in accordance with the invention.

The rotor structure 10, is only partially shown, since it may be of a well-known type. The rotor structure comprises a rotor disc 12 having an annular array of radially extending blades 14 connected to its circumferentially peripheral portion 15.

The blades 14 are unitarily connected to each other in groups (six blades to a group, in the example shown) by arcuate shroud segments 17, and the shroud segments are disposed in annular spaced end-to-end relation with each other.

The blades 14 are of the well-known "radial-entry" type and comprise an air foil or vane portion 18, a platform portion 19 and a root portion 20 of T-cross section The outer tips of the blades 14 are provided with radially extending tenon portions 21, which as illustrated are of circular cross section, but may be of any other suitable cross section, as known in the art.

The rotor disc 12 is provided with a peripheral groove 22 in its peripheral portion 15 and the groove is of T-shaped cross section to closely coincide with the T-shaped blade root portions 20. As illustrated, the groove 22 is slightly larger in cross section than the root portions to facilitate assembly, as will later be described, but a snug or sliding fit between the two may be provided, if desired.

As best seen in FIGS. 2 and 3 the T-shape cross section of the groove 22 is partially defined by a pair of circumferential flanges 24 disposed in mutually opposed and spaced relation with each other. These flanges extend across the T of the blade roots 20 and are effective to retain the blades in the groove.

To permit insertion of the blades 14 in the groove 22, arcuate opposed portions of the flanges 24 are cut away (see FIG. 3) thereby forming an entrance slot or opening 26 permitting "radial entry" of the blades 14, one at a time, into the groove 22. After entry, the blades 14 are "rolled" or translated laterally to form the annular array that completely fills the peripheral extent of the groove.

Since the entrance opening 26 is devoid of the locking flanges 24, a special blade called a "closing" blade or "last" blade is employed to complete the annular array and blades. This blade is not shown, since it may be of any well-known type and forms no part of this invention. However, it may be pointed out that the "last" blade employs locking means that do not rely on the shape of the groove 22.

As thus far described, the structure is substantially conventional.

In accordance with the invention, the width A of the roots 20 is machined as closely as economically feasible to the theoretical pitch dimension taken to three decimal places, but not to exceed this dimension. Hence when the total required number of blades 14 are inserted and rolled into abutment with each other, a void or gap in the blade row will remain that normally is of a width equal to the total number of blades multiplied by the average deficiency or negative departure per blade root from the theoretical pitch dimension.

This gap is preferably resolved on a blade group basis and may be divided by the number of blade groups in the blade array to arrive at a gap B per blade group. The gap B is preferably expressed as a linear measurement carried to three decimal places. To take up the gap B between blade groups, a shim or liner member 29 is inserted between adjacent blade roots at the ends of neighboring blade groups. The liners 29 are of T-shape as best seen in FIG. 2 and are of a thickness equal to the thickness of the gap B. They may be inserted at any point in the periphery of the groove 22 by turning sideways during insertion, thereby their facilitating assembly at the ends of each blade group.

With this arrangement the accumulation of individual deviations from the theoretical width A is limited to each blade group and compensated for by the liners 29. Since the liners 29 are disposed between adjacent blade groups the shroud segments 17 may be preformed with uniform pitch dimensions or spacing between the apertures 30. The number of blades in each group is generally equal to the number of blades that can mate with the preformed apertures of the shroud segment and remain in end-to-end abutment when the width A of a blade root is expressed in a measurement carried to three decimal places, thereby facilitating manufacture and assembly of the shroud segments onto the tenons 21 of the blades. This factor becomes even more significant when repair in the field is required since equipment and special tools are lacking to make the shroud segments with the customized or individually fitted apertures.

Also, since the liners are uniformly distributed about the circumference of the rotor disc 12, balance of the rotor (both dynamic and static) is maintained.

In the example shown, the blades 14 are initially loose fitting in the groove 22 to facilitate positioning, but after positioning the root portions 20 are wedged against the annular flanges 24 by suitable caulking strips 31, as well known in the art.

To more clearly explain the invention, the following examples is given:

Assuming 24 groups of blades in a row, each group consisting of six blades, the total number of blades equals 6 .times. 24 or 144 blades.

Assuming a linear dimension of 0.500 inch for pitch A and manufacture of the blades with a 0 plus tolerance and a 0.003 inch negative tolerance, expressed as:

+ 0.000

- 0.003

0.500

If the blades are formed with the greatest acceptable deficiency, their width A= 0.0497 inch and the total accumulated negative error per group is 6 .times. 0.003 inch or 0.018 inch. Accordingly, the thickness of the liners in this instance should be 0.018 inch. However, in actual manufacture the width A is usually maintained closer than the maximum tolerance prescribed, so that the liner thickness may be somewhat less than 0.018 inch in this example.

It will be seen that, in this example, the total accumulated error for the entire blade row can be as great as 144 .times. 0.003 or 432 inch, which is almost the width of another blade and would have undesirable effects if compensated for by a single liner at a single gap.

It will also be seen that the accumulated error of 0.018 for a blade group if compensated for by insertion of a liner between blades within the group would prevent installation of a prepunched liner with uniform spacing between apertures.

Although only one embodiment of the invention has been shown, it will be seen that the invention is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

Claims

I claim:

1. A turbine rotor, comprising,

a rotor disc having a circumferential groove,

an annular array of blades carried by said disc and having root portions of the radial entry type,

said root portions engaging said groove,

said blades being disposed in arcuate groups having generally an equal number of blades in each group,

said blades being provided with tenons,

an arcuate shroud segment having equally spaced apertures adapted to mate with said tenons for joining the blades of each group so that the associated root portions of the blades within each group are disposed in end-to-end abutment,

the number of blades in each group being generally equal to the number of blades that can mate with the equally spaced apertures of said shroud segment and remain in end-to-end abutment,

said tenons being firmly connected to their associated shroud segments, and

thin liner members interposed between the root portion of adjacent blade groups to adjust the thickness of the groups to a predetermined thickness.

2. The structure recited in claim 1, wherein

the groove is provided with an enlarged opening to permit entry of the roots of the blades in the groove,

the last blade is disposed in said enlarged opening, and

means is provided for securing the last blade to the disc.

3. The structure recited in claim 1, wherein

the arcuate segments are disposed in spaced end-to-end relation with each other and jointly encompass the annular array of blades.

4. The structure recited in claim 1, wherein

the groove is of T-shaped cross section and the liners are of similar shape and size.

5. The structure recited in claim 1, wherein

the thickness of at least some of the blade roots in each group is less than the theoretical predetermined thickness, and

the thickness of the liner members is chosen in a manner to make up the difference.