US2041699A - Steam turbine casing and method of manufacturing the same - Google Patents

Description

May 26, 1936. H. P. DAHLSTRAND Y I 2,041,699

`STEAM TURBINE CASING AND METHOD OF MANUFACTURING THE SAME Filed Aug. 23, 1935 Patented May 26, 1936 STEAM TUBBINE CASING AND BIETHOD OF MANUFACTURING THE SAME Hans P. Dahlstrand, Wanwatosa, Wis., assigner to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application August 23, 1933, Serial No. 686,374

13 Claims.

This invention relates to an improved casing for a steam turbine and to the method of manuiacturing the same.

The casings or cylinders of steam turbines are generally formed in separatel upper and lower sections bolted together along a longitudinal plane.

sections is cast integrally and is provided with `cored passages for admitting or withdrawing steam 'at various positions along the turbine axis. .During the casting operation, the cores which form these passages become solidified to such extent that it is difficult and expensive to remove them from the passages in the finished casting.

To facilitate the removal' of the cores, special openings are provided in the casing which openingsmust be closed in a permanent manner after the cores have been removed. lFurther, casings of this nature having inner and outer walls separated by cored passages are difiicult to cast successfully, in that the flow of molten metal into the complicated passages ofthe mold may not take place uniformly and the cooling of the vari- -ous irregular sections of the casting may occur unequally, resulting in blow holes, shrink cracks,

` or other imperfections in the casting.

It is an object of the present'invention to pro- .vide a steam turbine casing that may be manufactured readilyand inexpensively and that is of permanent and rigid construction.

A further object of the invention is to provide a method of manufacturing a steam turbine cas- I lowing parts oi this ing whereby a rigid unitary structure having vthe usual steam passages is made'without using cores to form the passages in the casing walls.

According to the present invention, the upper and lower halves of a turbine cylinder or casing are each formed of an outer casing wall cast in one piece and an inner casing wall cast in separate curved sections or ring segments which are secured within the outer wall in such manner as to provide the required steam passages therebetween. For supporting the inne'r wall segments, the outer wall is provided with inwardly project-v ing supporting elements. Each of the inner wall segments is provided with an opening by means of which a shrink-lit engagement with the corresponding supporting element is effected. The inner wall segments may be additionally secured to the supporting elements vby welding or they may be secured entirely vbyw'elding without the shrink-fit engagement.

The foregoing and other objects of the invention, which will become apparent from the folspecication taken in con- As usually made heretofore, each oi these (ci. :is-14am Fig. 1 is a view in vertical longitudinal secvs tion of portions of a steam turbine casing embodying the invention, parts of the inner casing being broken away to reveal the supporting elements onI the inner surface ofthe outer casing;

Fig. -2 is a view in transverse section of the turbine casing taken `on the plane represented by the line II-II in Fig. 1;

Fig. 3 is a view similar to Fig. 2 but taken on the plane represented by the line III-111 in Fig. l; and

Fig. 4 is a view. in vertical longitudinal section of a portion of a turbine casing embodying a modication of the invention, part of a turbine rotor being shown in operating position within the casing. i

The steam turbine casings or cylinders shown in the drawing are divided, as is the usual practice, into upper and lower half parts or sections lli and il, respectively, which 'are joined together in a horizontal longitudinal plane.

Referring to the embodiment of the invention shown in Figs. 1, 2 and 3, the upper and lower casing sections I0 and ii each comprises an outer casing shell or wall section i2 preferably formed in a single piece by casting, and an inner casing shell or wall section formed by a plurality of separately cast ring segments I3 positioned within the outer wall sections I2 in such manner as to prov-ide the required steam passages Il therebetween.

For supporting the inner wall segments i3, the outer wall i2 is provided with inwardly projecting supporting elements, which may' be clearly seen in the upper portion of Fig, l. These inner wall supporting elements comprise circumierentially 40 arranged ribs or webs i5 that are accurately machined on their inner edges to provide inwardly extending tongues I6 of predetermined dimensions. `The tongues I6 are each provided at one side with an undercut flange I1 which is shown greatlyv exaggerated inthe drawing to illustrate its function. Actually the iiange I1 is formed by undercutting the tongue I8 a few thousandths of an inch only.

Each of the ring segments I3 forming the inne'l wall of the turbine casing is provided in its periphery with a circumferential groove I8 complementary to and-adapted to receive the tongue I8 of the cooperating supporting i web I5, but of slightly smaller dimensions. The groove I8 is likewise provided with a ange I8 that is formed vby slightly undercutting one side of the groove pass.the.complementary flange I9 in the groove I8 and permit the ring segment I3 to be placed in its proper position within the outer wallA I2 with the flanges I1 and I9 in overlapped relation. The ring segment I3 is then clamped in position and allowed to cool. As the heated ring segment 'cools to the temperature of the outer wall I2 the groove I8 shrinks into firm engagement with the tongue I6, thus bringing the flanges I1 and I9 into interlocking relation and'rmly securingthe inner wall ring segment to the inwardly projecting web I5.

Each of the ring segments I3 may be further secured to the cooperating web I5 by forming deposits 20 of weld metal in openings that extend through the ring segment into communication with the groove I8 and the inner surface of the supporting web I5. f

'I'he grooves I8 are preferably formed in the middle of each ring segment I3 in order that it may be symmetrically supported along one line only upon the cooperating supporting'web I5. However, in supporting certain of the ring segments, it is necessary to position the groove I8 near one edge of the segment in order to provide a steam passage I4 of the required dimensions between the ring segments and the outer wall I2 of the casing. In such instances the ring segments I3 are additionally supported and positioned, as illustrated by the end segments in Fig.

l and in Fig. 2, by inwardly projecting bosses 22 on the outer wall I2 which engage each ring segment near the edge thereof farthest from the supporting web I5.

The inner surfaces of the bosses 22 are accurately machined to cooperate with complementary machined surfaces on the peripheries of the ring segments I3. During the assembling process, the bosses 22 assist in properly positioning the in Fig. 4 the linner wall of the turbine casingl is formed by ring segments 23 which are fitted between inwardly projecting webs 2d of the outer walls of the casing halves and secured thereto by welding only. Preferably, the ring segments 23 are securely attached at each edge to the adjacent web-24 by a deposit 25 of weld metal. However, if a considerable difference in expansion is to be expected between the inner and the outer walls ofthe casing, the ring segments 23 may be secured in position by welding at one edge only, as illustratedgby the rings at the left end of the turbine casing in Fig. 4, leaving the other edge free to move relative to the adjacentrweb 2G. 'Ihe free edge of the segment may be supported lby bosses 22 :extending inwardly from the outer wall as in the of the end ringsegments in The turbine casings herein described may -be manufactured expeditiously and inexpensively without the dimculties usually encountered in forming complicated castings and in removing from such castings the cores necessary to form 5 the steam passages therein.

Although the specific embodiments ofthe inventin illustrated `by way of example have been described in detail in order to fully disclose the invention, it is to be understood that various modifications of the structures shown may be made by those skilled in the art without departing from the spirit and scope ofthe invention as defined in the subjoined claims.

It is claimed and desired to secure by Letters 15 Patent:

Y1. The method of making a steam turbine casing having .steam passages therein, comprising forming an outer casing'in a plurality of complementary sections having inwardly projecting Supporting elements, forming inner casing sections adapted to be carried within said outer casing sectionsin position to form steam passages therebetween and having openings complementary to said supporting elements, heating said 25 inner casing sections to expand said openings, shrinking said inner casing sections on to said supporting elements, and welding said inner casing sections to said supporting elements.

2. The method of constructing a steam turbine 30 casing, that comprises casting a pair of complementary outer casing sections having inwardly extending projections, forming a pluralityof inner casing sectionsvhaving grooves complementary to said projections and adapted to be carried within 35 said outer casing sections, fitting said inner sections within said outer sections by shrinking said grooved sections on to said projections, and further securing said inner sections within said outer sections by welding.

3. The method of manufacturing a steam turbine cylinder having steam passages therein, that comprises casting the outer casing wall in two halves divided longitudinally and having spaced internal circumferential webs, machining said 45 webs to provide inwardly projecting circular tongues of predetermined dimensions, forming half rings to constitute an inner casing wall, ma-

'chining grooves in the'peripheriesl of said half rings complementary to but slightly smaller than 50 the tongues in said outer casing, heating said half rings to expand said grooves, fitting said heated half rings into said outer casing halves in position to form steam passages therebetween and withv said expanded grooves engaging said 55 tongues, cooling said half rings to shrink said grooves into clamping engagement with said tongues, and welding said ringsto said casing webs.

4. The method of making a steam turbine cas- 60 ing, that comprises forming an outer wall in a plurality of longitudinally divided complementary sections each provided with an inwardly projecting circumferential rib, machining an undercut iiange in said rib, forming an inner wall in g5 arcuate sections, machining in each section a circumferential groove shaped complementary to and adapted tocooperate with the inwardly projecting rib of the corresponding outer wall section, heating said inner wall section to expand 70 r into mm engagement with the nb of the outer ywall section.

5. The method of making a steam turbine casing, that comprises forming an outer wall in a plurality of longitudinally divided complementary sections'each provided with an inwardly projecting circumferential rib, machining atongue having ashallow undercut flange in said rib, formingan inner wall in arcuate sections, machining in each of said sectlons-a-circumferen tial groove shaped complementary to and adapted to cooperate with the inwardly projecting rib of the corresponding outer wall section, drilling welding holes through said inner wall section in communication with said groove, heating said inner wall section toexpand the groove therein, fitting the expanded groove over the complementary tongue with the undercut flanges thereof overlapping to place the inner wall section in predetermined position within the outer wall secy tion, permitting the inner wallV section to cool to shrink the groovejtherein into firm interlocking engagement withgthe tongue of the outer wall section, and securing said inner wall section -to said rib by welding it thereto through said welding holes. l

6. A steam turbine casing, comprising an outer wall including a plurality of complementary parts each having inwardly projecting circumferential ribs, and an inner wall including a pluralityi of arcuate'segments corresponding in angular extent to the parts of the outer wall and eachhavl ing a groove complementary to the corresponding rib, said inner wall segments being positioned within said outer wall parts.with the grooves therein in rigid engagement with the corresponding ribs of the outer wall parts.

7. A steam turbine casing, comprising an outer shell including a plurality of complementary parts, an inner shell including a plurality of arcuate segments disposed within said outer shell, and a body of fused weld metal securing each of said inner shell segments to said Aouter shell.

8. A steam turbine casing, comprising anouter I shell including a plurality of longitudinally divided complementary sections each provided with an inwardly projecting circumferential web having an undercut flange, an inner shell including arcuate sections each having a circumferential groove provided with an undercut flange said groove being complementary to and disposed to cooperate with the inwardly projecting web of the corresponding outer section, and means for securing said sections to said webs.

y 9. A steam turbine casing, comprising an outer shell, an inner shell formed in a plurality of parts, and a deposit of fused weld metal securing each part of saidV inner shell within said outer shell along only one line of attachment.

10. A steam turbine casing, comprising an outer shell section having inwardly projecting circumferential webs. a plurality of inner shell seg'- ments disposed within said outer shell section in position to form therewith between said webs circumferential steam passages, and means rigidly securing each of -said. inner shell segmentsl to one of said webs.

11. A steam turbine casing, comprising the combination with an outer shell section having l a plurality of inwardly extending circumferential comprising a plurality of complementaryonepiece outer shell sections each having spaced integ-ral inwardly projecting circumferential ribs each rib presenting at its inner end a tongue provided at one side with an` undercut flange, and a plurality of arcuate inner shell segments corresponding in angular extent to the outer shell sections each presenting in its outer surface a groove complementary to-'the flanged tongue of one of said ribs, said inner shell segments being mounted within said outer shell sections with the groove of each inner shell segment rigidly engaging the complementary tongue of its cooperating rib and disposed in position to constitute with said rib and other portions of the outer shell a circumferential steam passage.

13. A steam turbine casing of the type divided longitudinally into separable parts and having formed therein circumferential steam passages, comprising a plurality of complementary onepiece outer shell sections each having spaced integral inwardly projecting circumferential ribs each rib presenting at its inner end a tongue provided at one side with an undercut flange, a plurality of arcuate inner shell segments corresponding 'in angular extent to the outer shell sections each presenting in 'its outer surface a groove complementary to the flanged tongue of oneof said ribs and having spaced openingsextending radially from said groove inwardly through the segment, said inner shell segments .being mounted within said outer shell sections with the groove of each inner shell segment rigidly engaging the complementary tongue of its cooperating rib and disposed in position to constitute with said rib and other portions of the y"ing each inner segment to its cooperating rib.

HANS P. DAHLSTRAND.

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