US2664268A - Overhung turbo-machine rotor arrangement - Google Patents

Description

Dec. 29, 1953 A. HOWARD RHUNG TURBQ MACHINE ROTOR ARRANGEMENT OVE Filed NOV. 27, 1948 Patented Dec. 29, 1953 OVERHUNG TURBO-MACHINE ROTOR ARRANGEMENT Alan Howard, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application November 27, 1948, Serial No. 62,373

2 Claims.

This invention relates to the construction and arrangement of high-speed turbo-machine rotors of the overhung type, particularly to such a rotor used as a turbine element in a gas turbine powerplant.

For mechanical simplicity, ease of access to the high temperature rotor, and for other reasons which arise in particular applications,.it is often desirable to use ina gas turbine powerplant a turbine rotor having one or perhaps at most two stages supported on a shaft in overhung relation to the shaft bearings. Thus there is no outboard bearing to make access to the turbine rotor difficult; Such an arrangement also permits a second low-pressure turbine element to be arranged in other bearings closely adjacent the discharge side of the first rotor. This is particularly advantageous in a compound gas turbine powerplant having a first turbine rotor driving one load device and a second turbine rotor in series fiow relation with the first and mechanically independent and driving a separate load device.

Because of the extremely high speeds and high temperature levels at which gas turbine power plants operate, it is always necessary in the design of such apparatus to consider the possibility that the rotor will experience a minor failure, such as the loss of a small portion of the bucket structure with resulting unbalance of the rotor and'increased danger of a major rotor failure. Accordingly, it is an object of the present invention to provide an overhung high temperature rotor arrangement which in the event of the loss of a small portion of the bucket structure will result in the production of a characteristic noise which will notify the operators that a failure has occurred and that the powerplant must be shut down immediately, simultaneously serving to exert a braking effect on the rotor so as to help prevent overspeed, and also acting as an emergency journal bearing to hold the overhung end of the rotor concentric so that any tendency to rotate about an eccentric axis due to the unbalanced dynamic forces resulting from loss of a bucket will be resisted, until the rotor can safely be brought to a stop.

"Other objects and advantages will be apparent fromthe following description taken in c0nnection with the accompanying drawing, in which the single figure represents a sectional view of a high temperature gas turbine rotor having a ing, the turbine rotor indicated generally at I consists of a two-stage welded wheel assembly comprising a first-stage disk 2 having a circurnferential row of buckets 3 and secured to, or as shown in the drawing, formed integral with the shaft 4. The disk '2 is actually a built-up welded construction consisting of the central web portion 2a and a rim portion 2b secured together by circumferential welds at 4a. This is the composite web construction as shown in my United States Patent No. 2,432,315, issued December 9, 1947, and assigned to the same assignee as the present application. With this construction, the web portion 2a and the shaft t may be formed of an inexpensive, easily worked, low-carbon steel, while the rim 2b, which is subjected to extremely high temperatures, may be formed of a more expene sive, and more diflicult to work, austenitic stainless steel. The buckets 3 may, with appropriate design of the bucket wheel, also be welded to the rim portion 2b, or they may be secured by any suitable dovetail arrangement, many of which are known to the art.

The second stage bucket wheel 5 likewise consists of a central web portion 5a, a rim portion 5b, secured by welds 6 and having a circumferential row of buckets I.

As will be apparent from the drawing, the buckets 3, l are provided with axial extensions 3a, la which cooperate to form the circumferential inner surface of the fluid flow path between the two bucket wheels. A slight axial clearance is provided between the circumferential edges of these extensions as indicated at 8 so that thermal expansion of these portions of the buckets is permitted without creating any stresses in the buckets or wheels. At the same time, the clearance space 8 is sufficiently small that no substantial amount of hot gas from the motive fluid fiow path will circulate into the circumferential space 9 between the two rim portions 2b, 5b.

The adjacent portions of the central wheel webs 2a, 5a are shaped to form an interfitting rabbet having a shrink lit at the circumferential surface It. It will be seen that the radial surfaces at l l abut, while a substantial clearance space is provided at H2. The wheel webs are provided with inclined surfaces l3, Hi forming a weld preparation groove in a manner which will be readily apparent from the drawing. At

, the bottom of the weld preparation groove, the

two-stage bucket wheel arranged in overhung relation to the supportingbearings.

Referring now more particularly to the drawwheel webs are recessed to form a circumferential chamber l5 in which is located a chill ring it. This ring it forms a rather snug fit'with the inner circumferential surfaces l3a, I ia but has an appreciable clearance space at i! relative to the second stage wheel web portion 50. With this arrangement the chill ring serves to back up the weld preparation groove and prevents weld metal penetrating into the wheel web portion 50. It should be particularly noted that the radial separationplane ll is displaced axially a substantial distance from the plane of theweld so that there is no possibility of weld metal pene trating as far as the surface H. sign removes the tendency for a crack to progress into a weld from a separation plane between two contiguous surfaces. Furthermore, during the welding and cooling process, the chill ring it is free to expand and contract in a radial direction without exerting any stresses on the wheel web portion 5c, the portions of the wheel webs immediately adjacent the surfaces'lli, i i being free to expand and contract somewhat in a radial direction relative to the more massive adjacent portions of the wheel webs.

.The shaft 4 is supported in a plurality of main bearings, one of which is shown as a plain babbitted journal bearing 58, secured to or formed integral with a support ring [9 which is free to slide axially at the surface in the main frame ring member 2|. The frame ringZi may be considered to be secured by casing structure, not shown, to an outer casing-22, the latter being welded toa continuous main frame ring 23. Supported between the frame ring 23 and the inner frame ring 2| is a turbine nozzle assembly indicated generally in elevation at 24. The details of this'nozzle structure are not material to an understanding of the present invention, but are 2:0

disclosed more fully in the copending application of C. J. Walker and Alan Howard, Serial No. 62,372, filed November 27, 19.48, now Patent No. 2,625,013 of January 13, 1953.

The details of the frame'ring 23 and, related outer casing structure 25 are not necessary to an understanding of thepresent invention, but it need only be noted that the members 23, 25 form the outer circumferential wall 25 of the motive fluid flow path. It will also be seen that the buckets 3, 'l are of the open-ended or shroudless type, defining a close clearance with the circumferential wall 26. The wall 26 carries the stationary interstage bladesZl, the tips of the blades 2? defining a close clearance With the axial extensionsfia, 1a of the buckets.

The exhaust passage from the second-stage buckets l i defined by inner and outer circumferential walls 28, 29.

In accordance with the present invention, the second-stage bucket. wheel is provided with a central axially extending portion forming a narrow smooth annular surface shown at 30, ordinarily defining a comparatively small radial clearance space with an adjacent-stationary ringmember 3 l, the latter being welded to the main frame cylinder 32, which is in turn supported-from-the casing 25 by any suitable means, for instance radial struts shown at 33 extending through streamline shrouds 3% across the hot-gas flow path. The clearance space between the members 36, 3! issufficiently large that there will beno contact under any normal operating conditions, being for instance of the order of .05 inch at a diameter on the order of 7 inches. It will be seen fromthe drawing that the bearing surface 353 is roughly the same diameter as the main journal portion of shaft l.

v.In order to removeheatfromthehigh-temperature wheel rims 2b, 5b, a pair of radiant cool- Thus this deing pads 35, 36 are provided. These may be provided with circumferential ribs or fins presenting an extended radiating surface facing the wheel rims, having interior passages 35a, 36a for the circulation of a suitable coolant such as water. Pad 35 may be conveniently secured by bolts 31 to frame ring 2|, while pad 36 may be. secured by bolts .38 to a ring 39 which i in turn bolted to the frame ring 3 I.

:Brief reference may also be made to the sealing member At which is bolted to th bearing support ring-l9, and defines a sealing air chamber '4l,'to--which sealing air at compressor discharge pressure is supplied by suitable conduits, not

I .shown. This high-pressure air flows in the direction indicated by the arrows in the drawing through one .or more radial passages as indicated at'42. Part of this air flows to the left through thelabyrinth seal 43 to resist the leakage of oil in the opposite direction from the bearing l8, while the other portion of the sealing air flows to the right through the labyrinth seal member id to resist the entrance of hot motive fluid into the annular space adjacent the first-stagewheel web. Such leakage of hot gas is also resisted by the circumferential lipformed by anaxial extension 3b on the bucket bases, which form a reduced clearance space with the adjacent stationary nozzle ring structure.

The method of operation and utility of the particular parts which constitute the present invention will be seen from the following. Itwill be readily apparent that the two bucket wheels comprise a considerable overhung mass. During manufacture the bucket wheels and related rotor parts are of course balanced with extreme care. However in spite of careful manufacture and the use .of the best available materials, it will sometimes happen that the highly stressed buckets deteriorate in service to the point where part or all of a bucket will fail and leave the bucket wheel. When this happens, even though .the mass of the fragment is small, considerable unbalance in the overhung rotor may result due to the extremely high rotational speeds, which may be, for instance, on the order ofl0,000 R. P. M. This dynamic unbalance will tend to cause the overhung rotor to vibrate to a degree which makes it imperative that the machine be immediately shut down to avoid serious damage. With the arrangement constituting the present invention, theclearance space between the central bucket wheel portion and the adjacent stationaryring is made sufficiently small that any abnormal unbalance will produce rubbing of the member 3%] .on the ring 3!, with the following results: (1) an ear-splitting squeal is 7 produced, which.immediatelynotifies the operator that a failure has occurred and that the machine must be immediately stopped;.(2).furthermore, this rubbing action produces acertain braking effect on the rotor tending toprevent overspeeding, or even to reduce the rotor speed; (3) finally, the presence of the rigid stationary ring 3| tends to hold the overhung rotor concentric so that it continues to rotate about its true axis. It will be apparent that if, due to a bearing failure or other serious accident, the rotor should get appreciably off center, the unbalanced forces would become so great as to wreck the entire machine. The strong guard ring 3! acts as an emergency journal bearing and insures that inthe event ofsuch a failure the rotor axiscannot move too far from its intendedposition, so that the unbalanced dynamic forces will be kept below a value which might result in destruction of the rotor or the entire machine. With the invention, it is entirely possible for the turbine rotor to lose most or all of one bucket without causing substantial damage to the turbine.

In order to perform these functions, it will be obvious that the cooperating cylindrical surfaces on the members 39, 3| must be of appreciable axial length in order to form a bearing surface capable of withstanding the loads imposed when the wheel assumes a sufficiently eccentric position as to produce rubbing.

It is also necessary that the diameter of these emergency journal bearing surfaces be on the order of the diameter of the main journal bearing surfaces of shaft l, in order that the rubbing velocities will not be so great as to generate friction heat sufiicient to cause failure of the parts.

Thus it will be seen that the invention provides an important safety feature in connection with powerplants having massive rotors supported in overhung relation to the shaft bearings.

While only one modification of the invention has been described in detail, it will be apparent to those skilled in the art that many modifications might be made, and it is desired to cover by the appended claims all such changes as fall within the true spirit and scope of the invention.

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

1. In a turbo-machine having a high-speed rotor with a disk portion connected to a shaft supported in main bearing means disposed at only one side of the disk, the combination of a casin supporting the bearing means, an axially extending hub member on the side of the disk remote from the bearing means and defining a smooth circumferential surface concentric with the axis of rotation and of a diameter substantially equal to that of the main bearing means, and a stationary guard ring member supported in the casing and having a circumferential surface forming a small annular clearance space with said hub portion of the disk, said cooperating spaced circumferential surfaces being of appreciable axial length to form a bearing surface whereby any substantial deviation of the disk from its true axis of rotation will result in rubbing on said bearing surface to produce a characteristic warning sound and a braking effect on the rotor While also acting as an emergency journal bearing to maintain the rotor concentric and thereby reduce the stresses resulting from dynamic unbalance of the rotor.

2. In a turbo-machine having a high-speed rotor with a disk portion connected to a shaft supported in main bearing means disposed at only one side of the disk, the combination of means supporting the bearing, an axially extending hub portion secured to the side of the disk remote from the main bearing and defining a smooth circumferential emergency bearing surface concentric with the normal axis of rotation and of a diameter substantially equal to that of the main bearing means, and a stationary guard ring member rigidly supported in fixed relation to said bearing support means, said guard defining an inner circumferential surface forming a small annular clearance space with said emergency bearing surface, said cooperating spaced circumferential surfaces being of appreciable axial length to form a bearing surface whereby abnormal deviation of the disk from its true axis of rotation produces rubbing on said bearing surface to produce a characteristic warning sound and a braking efiect on the rotor while also tending to maintain the rotor concentric and thereby reduce the stresses resulting from dynamic unbalance of the rotor.

ALAN HOWARD.

References Cited in the file Of this patent UNITED STATES PATENTS Number Name Date 1,469,045 MacMurchy Sept. 25, 1923 1,600,346 MacMurchy Sept. 21, 1926 2,277,333 Leopold Mar. 24, 1942 2,369,795 Planiol et al Feb. 20,1945 2,391,786 Kenney Dec. 25, 1945 2,459,519 Graham Jan. 18, 1949 2,557,747 Judson et al June 19, 1951 FOREIGN PATENTS Number Country Date 847,190 France June 26, 1939

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