US2556890A - Turbine diaphragm arrangement and method of assembly - Google Patents

Description

B. c. THORN 2,556,890

TURBINE DIAPHRAGM ARRANGEMENT AND METHOD OF ASSEMBLY June 12, 1951 Filed May '7, 1946 Invent o1" B'e/r/wg'amin Thorn, HIS Attorneg.

Patented June 12, 1951 UNITE STATES ATENT FEEQE TURBINE DIAPHRAGM ARRANGEMENT AND- METHOD' OF ASSEMBLY Benjamin C. Thorn, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application May 7, 1946, Serial No. 667,743

9 Claims.

porting a turbo-machine diaphragm and its assoits ciated-shait packing means of the type described which will tend to eliminate abnormal leakage due to uneven wear of the shaft packing, occasioned by unequal thermal expansion of the component parts of the diaphragm and turbine cas-- perature multi-stage axial flow turbine which is less subject to leakage of the shaft packing than the diaphragm arrangements known to the prior art.

Other objects and advantages will appear from the following description taken in connection with the accompanying drawings, in which Fig. 1 shows a turbine diaphragm supported in its casing in accordance with the invention; Fig. 2 is a sectional view of the diaphragm assembly of Fig. 1, taken on the plane 22 in Fig. 1; Fig. 5

3 is a diagrammatic representation of a test set-up which maybe used in practicing the invention; and Fig. 4 is a diagrammatic representation, to an exaggerated scale, of the results obtained with the test set-up of Fig. 3.

Fig. 1 discloses a multistage steam turbine diaphragm of a type which has become familiar to those skilled in the turbine art. It comprises an annular disk i defining a central shaft opening 2 in which is located a shaft seal assembly indicated generally at 3. Concentric with disk 5- and radially spaced therefrom is a rim portion t. A plurality of circumferentially spaced blades 5 are secured to the outer circumference of disk 5 and the inner edge portion of rim d by any suitable method, as for instance by welding- Turbine diaphragm arrangements of this general type are disclosed, for instance, in U. S. Patents No. 2,282,894-Sheldon, issued May 12, 1942, No. 2,217,509-Spencer, issued October 8,

2 1940, and No. 2,102,416 Junggren, issued December 14, 1937.

To facilitate assembly, both the diaphragm and packing assembly are made of a plurality of sections. While in the drawing the diaphragm is shown as being divided into two halves along a diameter, it will be apparent that they conceivably could be made in three or more sections divided along radii.

The packing 3 mayconsist of two arcuate members 3a and 373 made of a suitable soft bearing metal and secured together to form a continuous ring by means of pairs of plates 6' secured to the packing ring members by suitable threaded iastenin s 1. also be made of carbon, in accordance with practice well known in the art. The packing rings to and 3b are provided on their exterior surface with a circumferential flange 9 which is received in a cooperating arcuate groove in the inner circumference of annular disk As may be seen in Fig. 2, there is a slight radial clearance at H] between disk I and the packing rings. The axial clearance between the circumferential flange 9 and the sides of the groove in disk 3 is sufiiciently small to prevent fluid leakage therethrough, yet large enough to prevent binding of the packing rings. The packing ring assembly is supported in the respective halves of the diaphragm by means of a transverse dowel pin it through the lower half of the diaphragm I and the flange 9 of packing ring member 3b. The upper packing ring 3a is held in proper position relative to disk l by means of a radially arranged dowel E2. It will be apparent that the packing 3 is supported at a fixed point B by the dowel I I, and is free to expand and contract relative to the diaphragm sections ta and H), by sliding axiall on dowel l2. The arcuate members 3a and 3b may also be adapted to serve as retainers for various types of segmental shaft packings which are well known to the art.

The outer circumference of the diaphragm assembly is likewise provided with a flange I3 which is received in a circumferential groove in the casing i l. Casing it is divided into halves on a horizontal plane through the axis of the turnine, in a manner which will be understood by those skilled in the art and which is shown, for instance, in the above--mentioned Junggren patent. The axial clearance between the sides of flange portion I3 and the casing is is sufiiciently small to prevent fluid leakage, while there is some radial clearance at E5 to permit limited shifting of the diaphragm relative to the turbine The packing ring members may casing, such as may be caused by differential thermal expansion of the diaphragm and casing when the temperature of the motive fluid passing through the blades 5 changes suddenly. Radial keys, indicated by dotted lines at 35a, 35b, 35c, 35d in Fig. l, of flat rectangular cross section, are pressed, or otherwise secured, in a groove in the lower diaphragm section lb and extend into a similar groove in the upper section la, so as to form a tongue-and-groove joint therebetween. The complete diaphragm assembly is located in position in casing I4 by means of a plurality of key or dowel members, as described more particularly hereinafter.

The conventional turbine diaphragm and shaft packing assembly represented in Figs. 1 and 2 is well known in the art. Operating experience over long periods of time with pre-existing diaphragm structures of this general type has led to the discovery that in certain turbines, particularly those in which it is necessary to change the load (and therefore the operating temperatures) rapidly, there is a tendency for uneven heating of the diaphragm to cause it to deform so that the inner circumference 2 of disk I tends to assume the distorted shape indicated to an exaggerated scale by dotted lines 8 in Fig. 1. The result of such distortion is that the mid-portion of the packing ring member 31) is caused to be pressed into too close engagement with the shaft, thus causing excessive wear of the packing. When operating conditions change, or become uniform, and the packing resumes its normal shape, excessive clearances are opened at the places Where the abnormal wear has occurred. Leakage through these enlarged clearance spaces between the packing and its shaft may cause an appreciable loss in thermal efiiciency of the turbine.

My invention provides a novel means for locating and arranging the supporting devices for the diaphragm assembly so as to reduce, or prevent entirely, the above-described abnormal wear on the packing rings.

My invention specifically constitutes an improved method for supporting the separate sections of the diaphragm so that a given point adjacent the middle of the lower packing member 3b will be maintained fixed in space, relative to the turbine casing, regardless of thermal expansion and contraction of the diaphragm sections relative to the casing. This fixed point may, in the case of the lower half of the diaphragm assembly shown in Figs. 1 and 2, be taken as the point B, coincident with the axis of the dowel pin II.

It will be apparent that the above-described excessive wear of the packing will be prevented if the preselected point B can by some means be maintained fixed in space relative to the turbine casing, regardless of expansion or contraction of the sections of the diaphragm assembly relative to the casing. The means by which I accomplish this result will be seen from the following description of the method of installing the sections of a turbine diaphragm in accordance with my invention.

In assembling the diaphragm in accordance with my invention, the lower section I b of the diaphragm, without the packing assembly 3 is mounted as shown in Fig. 3, in either a horizontal or vertical plane. The mid-portion of the section is fixed in space by a suitabl device 16 secured to a test bed and engaging the diaphragm at the point B. Any suitable clamping device may b used, but the simplest is a C-clamp having a threaded jack-screw arranged to be turned by a handle I611. The diaphragm section is also engaged by a radially arranged dowel pin ll secured in a support l8, which is in turn fixed to the test bed. With this method of support, it will be seen that the diaphragm section is free to expand and contract in all directions from the fixed point B.

Spaced around the circumference of the rim 4 are a plurality of blocks 19, each having two surfaces 30 and 31 arranged at right angles to each other and perpendicular to the plane of the diaphragm. Secured to the test bed adjacent each block [9 is an angle member 28 arranged to support two micrometer dial indicators 2| and 22 having actuating spindles arranged to engage the respective surfaces 31] and 3! of the blocks [9.

Means are provided for subjecting the diaphragm section to conditions simulating those encountered in actual operation. In its simplest form, this means may comprise an arcuate pipe 23 having a row of holes drilled so as to project fluid jets onto the diaphragm blades 5, A suitable fuel gas is supplied through a valved conduit 24, mixed with compressed air from valved conduit 25, and led through branch conduits 25 to the respective ends of the nozzle pipe 23. With this arrangement, burning jets of gaseous fuel and air can be directed onto the diaphragm blades 5 so as to heat them to th temperatures to which they are subjected in an actual turbine installation. Of course if necessary, other means may be provided for heating or cooling other parts of the diaphragm in order to simulate as closely as may be desired the actual operating conditions.

With this arrangement it will be apparent that when heated, the diaphragm assembly will expand with the mid-portion adjacent the shaft opening at point B remaining absolutely fixed in space, while the mid-portion of the rim 4 is constrained to expand in a purely radial direction by the dowel or key 11. Other portions of the rim 4 will expand freely in a manner dictated by the inherent design characteristics of the. diaphragm, and perhaps to some extent by the manner and rate at which heat is supplied to the nozzle blades 5. Throughout this heating process, periodic readings are taken of the micrometer dial indicators 21, 22 associated with each of the blocks I9. By taking frequent readings, it is possible to plot accurately the path in space followed by the respective points on the circumference of rim 4 to which the blocks l9 are attached.

Fig. 4 represents diagrammatically the diaphragm supported as in Fig. 3 with the deflections of the respective points on the circumference of rim 4 plotted, to a greatly enlarged scale. These deflection paths are indicated by the respective dot-dash lines 21. It will be observed that the points l9a adjacent the radial pin I! follow paths which are substantially radial, but have a slight tangential component in a direction away from key I7. The next points, labeled 1%, follow paths which are substantially horizontal. These points l9b are located in the neighborhood of the 45 position, substantially half way between dowel I! and the separation plane through the axis of the turbine. It is believed that with most, if not all, diaphragm sections of the general configuration shown in the drawings, the deflection at these 45 positions will occur in a substantially horizontal direction.

Instead of taking the deflection readings during the heating process, the diaphragm may be firstv heated uniformly byburning gases issuing from the jets in nozzle pipe 23, after which the fuel supplythrough conduit 24 may be discontinued and the blades 5 cooled by discharging only air from conduit 25 and nozzle pipe v23. It may also be desirable to take readings both during a heating and a cooling cycle. Generally it will be found that the paths-27 traversed during the cooling process will very closely approach those followed during the heating process.

Having determined the respective deflection paths 2! for the spaced points l-9a, I919, 190 around the circumference of the diaphragm section; the next step is 'to provide supporting means for the diaphragm section in the turbine casing which will permit expansion and contraction freely in the manner of the predetermined paths 2?. This may be accomplished very simply by using two or more dowel pins 28 (Fig. 1). These may besecured with a light press fit in holes 29 drilled in casing it. As shown in Fig. 1, the dowels 28 are located at the 45 position, corresponding to the points [92) in Fig. 4, .and are arranged at such an angle relative to the diaphragm-that the axis of the dowel is substantially parallel to the deflection paths followed by the points 1917. As shown in Figs. 1 and 2, the ends of the dowel pins form-a sufiicient clearancespace 32 with the bottoms, of the holes provided in the circumference of diaphragm rim so that the diaphragm is free to expand and contract in a direction parallel to the axis of the dowel. It will be understood that instead of round dowel pins, flat keys of rectangular cross section may be used. Furthermore, the separate key means at 28 may be dispensed with and suitable seats provided in the casing so as to engage mating'seats formed in the edge of the diaphragm. The upper diaphragm section in rests on the lower section lb, being held in proper alignment by the keys 35a, 351L350, 3dd, and a single radially arrangeddowel or key 36..

Tests have demonstrated that when the diaphragmlsections la and to are supported in the manner described above, the point B will remain absolutely. fixed in space relative to the turbine casing; and therefore there is no excessive wear produced at the mid-portion of the packing member 31).

It will be obvious that instead of using horizontal dowels 28 at the 45 position, other key means might be used at any convenient locationin rim i, the only requirement being that they may be arranged to permit movement of the rim at that point substantially in a direction corresponding to the deflection path 21 determined by the simulated operation test.

It will now be readily apparent that, with the lower diaphragmsection supported infixed relation to thecasing'by the method described above, the'lower shaft packing segment 32) willlikewise be held in the desired. fixed space relation to the shaft by reason of the connecting dowel pin vI l. Likewise the upper packing segment 3a will be supported in proper relation. to the shaft, since it is connected to thelower packing segment and is free to shirt slightly relative to the upper diaphragm section. Thus both packing segments are positively located in desired relation to the shaft, wholly independent of erratic thermal distortions of either diaphragm section concomitant with sudden large changes in temperature of the operating fluid. Localized wear of the packings,

6 with resulting excessive leakage-of motive fluid is thereby avoided.

While the invention has been .described as being particularly applicable to high temperature fluid pressure turbines, it will be appreciated by those skilled in the art that it may also be applied to similar 'diaphragms used in other turbo-machines, such as" multi-stage axial flow compressors.

My invention provides a simple improved method for assembling and supporting sectional turbine diaphragms which eliminates much trouble with the uneven wear of, and abnormal leakage through, the shaft packings associated with the diaphragms.

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

1. The method of assembling an axial flow multi stage fluid pressure turbo-machine having a casing and diaphragrns for separating the respective-stages,each diaphragm being fabricated mat least two sections divided substantially along radii thereof, which includes supporting a diaphragm section with a mid-portion adjacent the central shaft opening fixed in space and with a corresponding portion at the circumference of the section constrained to expand and contract in a substantially radial direction, subjecting the section to conditions simulating those encountered in actual service and meanwhile determining the paths in space described by a plurality of spaced points around the circumference of the section, and mounting the diaphragm section in the turbo-machine casing by means which constrain the section to expand and contract at said points so as to describe paths relative to the turbine casing similar to those determined by said simulated operation.

2. In a method of assembling an axial flow multi-stage fluid pressure turbo-machine having a casingand diaphragms for separating the respective stages, each diaphragm being fabricated in-at least two sections divided substantially along radii thereof, the steps which include supporting one section of a diaphragm with a first midportion adjacent the central shaft opening fixed in space and with a second mid-portion at the circumference of the section constrained to expand and contract in a substantially radial direction, subjecting the section to temperature conditions simulating those of actual service, meanwhile determining the paths in a plane normal to the axis of the diaphragm described by a plurality of points spaced around the circumference of the section, and mounting the section in the turbo-machine casing in such a manner that the section is free to expand and contract with the respective points on the circumference describing paths relative to the casing similar to those observed during said simulated operation, whereby said first mid-portion remains substantially stationary in space relative to the casing regardless of differential thermal expansion during operation.

3. In a method of assembling an axial flow 1 multi-stage fluid pressure turbo-machine having a casing and diaphragms for separating the respective stages, each diaphragm being fabricated in at least two sections divided substantially along radii thereof, the steps which include supporting a section of a diaphragm with a first portion adjacent thecentral shaft opening fixed in space with a second portion at the circumference of the section constrained to expand and contract in a substantially radial. direction, heating and cooling vthe section in a manner simulating the temperature conditions of actual service, meanwhile determining the path described in the plane of the section by a third portion of the circumference, and mounting the section in the casing by means engaging said second and third circumferential portions in a manner permitting the section to expand and contract with said second and third portions describing paths in space relative to the casing similar to those observed during the simulated operation, whereby said first portion remains substantially stationary in space relative to the casing regardless of differential thermal expansion during operation.

4. In an axial flow multi-stage fiuid pressure turbo-machine, the combination of a casing and a transverse diaphragm supported in the casing and having a central shaft opening and portions subjected to heating and cooling in operation, the diaphragm being divided substantially along a diameter thereof into two separate sections, and means for supporting one of the sections in the casing including first key means engaging the mid-portion of the circumference of the section and constructed and arranged to constrain said portion to expand and contract in a substantially radial direction relative to the casing, and second and third key means engaging circumferential portions of the section spaced substantially 45 degrees on either side of said first key, said second and third key means being substantially parallel to said diameter, whereby the mid-portion of the section adjacent the central shaft opening remains substantially stationary in space relative to the casing during differential thermal expansion of the casing and diaphragm.

5. In a multi-stage fluid pressure turbo-machine, the combination of a casing, a transverse diaphragm having a central shaft opening and portions subjected to heating and cooling during operation, the diaphragm being divided substantially along a horizontal diameter thereof into an upper and a lower section, annular shaft packing means associated with the central diaphragm opening, means pivotally connecting said packing to the lower diaphragm section at a point adjacent the mid-portion thereof, diaphragm supports associated with the casing and engaging the lower section, said supports comprising key means engaging circumferential portions of the lower section spaced substantially 45 degrees from said diameter, said key means being substantially parallel to said horizontal diameter, and means retaining the lower section in centered relation to the casing on said key means, whereby said pivot point remains substantially stationary in space relative to the casing regardless of differential thermal expansion of the casing and diaphragm during actual operation.

6. In an axial flow multi-stage fluid pressure turbo-machine, the combination of a casing and a transverse diaphragm supported in the casing and having a central shaft opening and a portion adjacent the circumference defining a motive fluid flow path axially therethrough, the diaphragm being divided substantially along a diameter thereof into two separate sections, and means in the casing for supporting one of the sections in the casing and including a first key member restraining a mid-portion of the circumference of said section against displacement in a tangential direction while efiecting limited relative displacement between said casing and section along a radial path, and second and third locating seat members engaging circumferential portions of the section spaced substantially l5 degrees on either side of said first key member, said second and third members having diaphragm supporting surfaces substantially parallel to said diameter, whereby the mid-portion of the section adjacent the central shaft opening remains substantially stationary in space relative to the casing during differential thermal expansion of the casing and diaphragm.

7. In a high temperature turbine having a casing with a rotor shaft supported therein and a diaphragm divided substantially along radii into at least two sections with a segmental shaft packing for the central shaft opening therein, the combination of means supporting one diaphragm section in the casing in substantially fixed space relation to the shaft, means supporting at least one of the shaft packing segments on said fixed diaphragm section, and means connecting the other packing segments to said first segment, whereby the segmented shaft packing is accurately located relative to the shaft regardless of thermal distortion of the other diaphragm sections.

8. In a multi-stage fluid pressure turbo-machine having a casing, a transverse diaphragm with a central shaft opening and shaft packing means associated with the diaphragm surrounding the shaft opening, both diaphragm and shaft packing means being divided into at least two segments substantially along radii thereof, at least some of the diaphragm sections being subjected to strong heating and cooling effects by changes of temperature of the motive fluid during operation, the combination of means supporting at least one diaphragm section in the casing in substantially fixed relation to the shaft, means supporting at least one of the shaft packing segments from said fixed diaphragm section, and means supporting the remaining shaft packing segments from said first-mentioned segment whereby the shaft packing means is maintained in proper location relative to the shaft regardless of thermal distortion of the other diaphragm sections during rapid changes in temperature of the operating fluid.

9. In a high temperature turbo-machine having a casing with a rotor supported therein and a diaphragm construction including at least one upper and one lower section and segmental shaft packing means associated with the respective sections, the combination of means supporting at least one diaphragm section in the casing in substantially fixed space relation to the shaft, said diaphragm support means including spaced circumferential portions defining seat means cooperating with guide means in the casing for efiecting movement of said diaphragm portion relative to the casing along paths similar to the respective paths which said portions follow when the section is supported freely in space with a mid-portion thereof adjacent the shaft opening fixed and the section is subjected to temperature conditions similar to those of actual operation, m ans supporting at least one of the shaft packing segments on said fixed diaphragm section, and means connecting the other packing segments to said first segment, whereby the shaft packing assembly is accurately located relative to the shaft and casing regardless of distortion of the other diaphragm sections resulting from sudden and extreme changes in temperature of 9 the operating medium flowing through the sections.

BENJAMIN C. THORN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 392,442 Logan Nov. 6, 1888 830,393 Wilkinson Sept. 4, 1906 Number 10 Name Date Junggren Sept. 7, 1920 Duran Feb. 10, 1925 Baumann Nov. 20, 1928 Doran Aug. 23, 1932 Junggren Dec. 14, 1937 Spencer Oct. 8, 1940 Webster July 1, 1941 Sheldon May 12, 1942 Wert Dec. 15, 1942

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