US2199243A - Elastic fluid turbine rotor - Google Patents

Description

A ril 30, 1940. G. w. MORTIMER ELASTIC FLUID TURBINE'ROTOR Filed March 1, 1939 v Inventorm i U wr /Mm o w /t W t M 5 if w Patented Apr. 30, 1940 UNITED STATES ELASTIC FLUID runnmn ino-ron George WQMortimer, Wakefield -Mass assignor to General Electric Company,

v New York a corporation of Application Marchl, 1939,- serial No. 259.146 1 Claims.

The present invention relates to the construction of rotors for elastic fluid turbines of the type having a peripheral ribtherein of dovetail cross-section upon which the bases of the buckets are mounted and secured in place thereby.- Such a construction requires modification of the shape of the rib at one or more places in its circumference to permit the buckets to be assembled in place. As a result ofthis, one or more spaces are left between groups of buckets which must be filled with a filling block or piece to lock the buckets in place. f

My invention has for its object an improved form of filling or looking piece or block for ture bine rotors which is so constructed that the wedging action of the locking piece when in place is confined to certain definite selected parts of the bucket bases andis itself provided with means whereby it is securely anchored against the effects of centrifugal force when the rotor is revolving at a high rate of speed.

For a consideration of what .I believe to be novel and my invention, attention is directed to the accompanying description .and the claims appended thereto.

In the accompanying drawing which is illustrative of my invention, Fig. .l is a perspective view of a part of a wheel'showing the bucketfilling slo't open; Fig. 2 is a similar view but with the locking piece or block in position, and Fig. 3 is a perspective view of the locking piece or block.

In the drawing, 5 indicates a rotor for an elasticv fluid turbine, such as a disk wheel for exrib 6' shaped to form the male member of a dovetail, the undercut shoulders I servingto hold the buckets 8 and their bases 9 against centrifugal forces. The bases are each provided with a dovetail slot to receive the rib B and conforming in shape thereto.

which engage the legs or skirts ll of the bucket bases and prevent them from spreading when the buckets are subjected to centrifugal forces. The

buckets are desirably integral with the bases and.

ample. The wheel is'p'rovided with an annular The rim. of the wheel is" also provided with small annular shouldersxlll.

to th at of the wheel, the slot extending entirely across the rim. It is generally desirable to slot the rib and rim at two or more angularly displaced regions to facilitate assembling the buckets on the wheel andto prevent undue wear of the faces of the rib, dovetail slots in the bucket bases and other surfaces subjected to wear as the bucketbases are moved circumferentially on the rib from a filling slot to their final positions. The efiect of these slots is to divide the buckets into group'slocatedzon opposite sides of .the slot or slots; Thebottom part of the slot I4 is in the form ofa dovetail while the outer part extending through the rib is or may be parallel or slightly inclined outwardly. In the slotting operationor operations, the distance between the adjacent .cutfe'nds of the rib is made slightly greater than the greatest Width of the filler block IE-measured vin the plane ofv the wheel. As a result, the bases of the'buckets on opposite sides of the slot extend slightly-beyond or overhang the said out ends 'as indicated at It. The purpose of this is to prevent the cut ends of the rib from contacting with-the filling block when the latter is-forced into place. The frontand rear ends'of the slot l4 are chamiered or cut away as at I! to permit peeni g, 0r riveting over the ends of the filler block into the cut-away portions so as to hold the same in place against endwise movement. Theupper edges of the dovetail part of the slot are also ,chamfered or beveled as indicated at l8. The filling block 15 is best shown in Fig. 3. It is provided with a foot or dovetail I9 which snug- 'ly fits into the 'dovetail portion of slot M. The sides of the block as a whole from the top to the dovetail-base l9 slightly taper toward the axis of the wheel in conformity with the slightly tapering bases of the buckets. It is also provided with What for convenience may be termed a head 20 having overhanging shoulders 2I on opposite sides. The side faces 22 thereof are the parts which engage selected portionsof the adjacent bucketrbases when the block is driven or forced into place under pressure. These selected portions are desirably located outside of the rib so that the fillingblock head cannot make contact with the cut ends 'of the rib. In other words, the'engaging surfaces of the fillingblock and bucket bases are'located in a region having a greater diameter than the rib. The block may be drilled as indicated at 23 to lighten it when so desired. The endsof the drilled hole are desirably slightly rounded to ensure smooth surfaces. The sides of the block adjacent the dovetail base are provided with small beveled shoulders 24 which when the block is inserted in place engage the chamfered or beveled surfaces I8 on opposite sides of the slot. The head has a slightly greater width measurement in the plane of the wheel than the distance between the assembled bases of the adjacent buckets so that when the block is driven or forced into place, it exerts its full wedging action or sidewise pressure on said bases and not on the cut ends of the rib, or

partly on one and partly on the other which would ultimately give rise to loose buckets. Because a steam turbine wheel is subjected to greatly varying temperatures which result in expansion and contraction tending to loosen the buckets, it is of paramount importance to have the bucket bases of each group firmly wedged into contact one with the other, and this is accomplished by the use of filling block of the character herein described.

After the filling blocks are firmly wedged into place, the ends thereof are so peened or riveted over as to fill the chamfer l1, after which the wheel rim may be lightly machined so as topresent smooth side faces, as indicated in Fig. 2. After the buckets are properly assembled and anchored as above described, the cover l3 having openings registering with the tenon I2 is applied and the tenons 2 riveted over to secure the cover in place.

Mention has been made of the fact that the head 28 has a greater dimension in the plane of the wheel than the portion directly under it, and this difference in dimension or clearance resulting therefrom has been exaggerated in Fig. 3. The amount that these dimensions differ is usually small. In the case of relatively small diameter steam turbine wheels, the clearance on each of the opposite sides of the block below the head may be of the order of a few thousandths of an inch, and the head may have a radial depth of the order of one-quarter of an inch.

An importnt feature of my improved construction resides in the fact that the filling block cannot be inserted in place in such manner as to make contact with the cut ends of the rib, nor can it be inserted at all if the bucket bases are not positioned as they should be. This is due to the fact that the slot M definitely positions the block l5, and to the further fact that the distance between the cut ends of the rib is somewhat greater than the width of the head of the block. From a manufacturing standpoint, this means that faulty assembly of the block cannot be made by a careless workman. Another important feature of the construction resides in the fact that the dovetail base of the filling block securely anchors it in place and results in a simplification in the structure as a whole and a reduction in the cost of manufacture.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A turbine rotor having a rim, a peripheral rib thereon of dovetail shape, the rim and rib being through slotted in a plane perpendicular to the plane of the rotor to form a filling slot-for buckets, the portion of the slot in the rim being of dovetail shape and that of the rib being wider than the thickness of a bucket base, buckets having bases mounted on the rib and secured thereby, and a filling block having a foot located in the slot in the rim and held by the walls thereof and also a portion located between the adjacent bucket bases and exerting sidewise pressure on selected portions thereof having a diameter greater than that of the rib.

2. A bucket wheel for an elastic fluid turbine having ,a rim, a peripheral rib thereon of dovetail shape, a slot extending through the rim and rib located in a plane perpendicular to the plane of the wheel and forming a filling slot for buckets, the portion of the slot in the rim being of dovetail shape and that in the rib being of greater width than that of a bucket base and also of greaterwidth than the filling block, and a filling block having a foot anchored in the dovetail slot in the rim and a head of less width than that of the slot in the rib, the dovetail foot serving to prevent circumferential movement of the buckets on the rib.

3. A turbine element comprising a carrier hav ing a rib thereon of dovetail shape in cross-section, the carrier and rib being cut through at right angles to the plane of the carrier to form a bucket assembling slot, buckets having bases mounted on the rib on opposite sides of the slot, and held in position by the rib, a block located in the slot having an enlarged head, the sides of which exert a wedging action only on the bucket bases outside of the rib, the side portion of the block below the head being separated by a clearance from the adjacent cut ends of the rib, and means for anchoring the block.

4. A turbine rotor having a rim, an annular rib thereon of dovetail shape in cross-section, the rim and rib being transversely cut through to form an open slot which is wider than a bucket base, the lower end of the slot being of dovetail formation, buckets having bases mounted upon and secured in place by the rib and located on opposite sides of the slot therein, the bases of the buckets adjacent the slot slightly overhanging the cut ends of the rib, and a filling block anchored in the dovetail slot in the rim and exerting a wedging action limited to the bucket bases, the sides of the block being separated from the walls of the cut in the rib by a small clearance.

5. A turbine wheel having a rim, an annular rib located on the peripheral surface thereof of dovetail shape in cross-section, the rim and rib that of the wheel to forma bucket assembling slot, the portion of the slot in the rim being of dovetail formation, buckets having baseswhich taper toward the axis of the wheel and engage the rib and are securely held thereby against centrifugal forces, the bases'being located on opposite sides of the slot and overhanging the sides thereof, and a filling block for the slot having a dovetail foot at its inner end securely fitted into the slot in the rim and a slightly enlarged head GEORGE W. MORTIMER.

being cut through in a plane perpendicular to

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