US1187453A - Steam-turbine. - Google Patents

Description

C. E. SEARCH & I. W. MOORE.

STEAMTURBINE. APPLICATION FILED AUG'. I3. |913. RENEWED SEPT.2.' 1915.

Patented J une 13, 1916.

f .l i l liti @HABILES EDWIN' SEARCH AND JOSEH yW. MORE, OF MILWAUKEE, WISCONSIN, ASSIGNOBS T0 ALLIS-CHALMERS MANUAQTURXNG COMPANY, 0F MILWAUKEE,

WISCONSIN, A CORPORATION 0F DELAWARE.

' STEAM-TUINE;

ademas.

Application le August 13, 1913, Serial No. 784,779. Renewed. September 20, 1915. Serial No. 52,113.

To all 'whom t may concern Be it known that we, CHARLES EDWIN SEARCH and JOSEPH .W. MOORE, citizens of the United States, residing at Milwaukee and West- Allis, Milwaukee, respectively, .1n the county of Milwaukee and State of Wisconsin, have invented a certain new and use; ful improvement in Steam-Turblnes, of which the following is a specification.

This invention relates to improvements in steam turbines and more especially to a segment of blades designed for insertior` in or attachment to the spindle or cylinder of a steam turbine, and which is to be produced as a finished article of manufacture capable of withstanding the severe vibration stresses to which it will be subjected in the machine. y

rihe object of the invention is the production of a segment of blades for a turbine, which avoids the defects of the prior art structures, more especially being constructed to withstand vibration stresses.

yReferring to the drawings, Figure 1 is a plan view of a segment of turbine blades, the shroud strip being partly broken away. Fig. 2 is an elevation of same. Fig. 3 is a sectional view of a portion of a segment of blading, the section being taken in a plane of rotation. F ig. 4 is a transverse sectional view of same showing the detail of the 'securing means to the spindle or cylinder of the turbine.

in actual practice it has been found that a steam turbine constructed with segments of blades calked in the spindle and cylinder,

and having shroud strips fastened to thel ends of the blades by riveting-over integral tenons formed on the ends of the blades and preiiminarily inserted through holes punched therefor in the shroud strips,-has not vbeen able to withstand vthe vibration stresses imposed on the built-up structure by reason of the high speeds at which the turbine was designed to run. The result was disastrous and the vblades became detached.

As the result of an exhaustive study of the conditions entering into the construction and operation of such turbines, it has been found by actual test that there'is a definite law controlling the the built-up structures.

A segment of turbine blades made up with a Sankey foundation strip and with a pitch of vibration of riveted shroud strip as hereinbefore referred to, wasfastened securely in a vise at its foundation strip, a vibratory tachometer was placed on the segment of blades so held andthe segment was then vibrated manually by quickly running a piece of hard material over the blades in much the same manner asa bo would run a stick along a picket fence. The tachometer gave a certain reading for the pitch of the vibration thus produced, which reading it is unnecessary to state here in actual figures. A similar segment was experimented with in the saine way, except that the foundation strip was ycast-on to the ends of the blades, as a substitute for the Sankey foundation strip. When vibrated, the reading of the tachometer was substantially higher. Next, a

similar segment with the foundation strip cast-on was taken, but the shroud strip in this case, was soldered to the ends of the blades. Upon test, the tachometer again recorded a substantially higher figure as representing the pitch of vibration. Lastly, a tie-strip was soldered at one side of the segment of blades, intermediate their ends, the foundation strip being cast-on and the shroud strip being soldered on, and the tachorneter in this case again indicated a substantially higher figure than before.

This investigation clearly indicated the theory upon which the present invention is based. It has been found, in one case, where the blades had gone out on a turbine, where the shroud strip had been riveted on and without any tie-strip, that the vibration tachometer in a test of similar seg- 'ments of blading to those used in that tur- Specifieation of Letters Patent. Pfgnted Jun@ 139 1915 bine, indicated substantially the same figure diderent mechanicalfastenings of the prior art. It is believed that the trailing ends of the shroud strips, if not the trailing ends of the segment itself, whip during rotation,

I in much the same way as a flag whips in the wind. It was therefore found that a stiff and rigid, but comparatively inelastic, trusslike -se ment of blades is what is necessary to avoid this objectionable vibration and to raise the itch of vibration safely beyond the speed of) the turbine, so as not to be in resonance therewith. lt is found that the casting-in of the blades in the foundation strip, resulting in a softening and annealing of the blade near the cast-on foundation strip, is an importantl factor toward arriving at the accomplishing of the object of this invention. l Soldering a tie-strip to the blade at an intermediate point, and soldering a shroud strip at the end of the blade, are equally im ortant, factors for the attainment of thls result. Absence of any rojections whatever at the shroud strip asteningfsuch for instance a-s the rivetedover tenon ends of the prior art, it is be'- lieved additionally prevents the tendency Ato set up objectionable vibration. Incidentally' it might be stated that in ,the prior art riveting-over ofthe tenon to fasten the shroud strip causes either looseness, or distortion of the shroud strip itself, in Vthe case where a blade happens to be slightly shorter than it ought to be; and this looseness is, ofcourse, an element productive of vibration while' the distortion of the shroud is objectionable for other reasons, primarily failure to baffle properly;` additionally, the rivet heads serve as paddle brakes Vduring rotation.

It isunderstood that, in the prior art, a structure has been proposed to which thin supporting strips have been welded to the blades and then stout stiening rings have been soldered to the strips, or equivalent fastening means have'been used, but in all of these constructions the stout stifening ring is always present in addition to the 1t is as well applicable to a radial'low tur-l thin supporting strip. lf these were used in an axial flow turbine with which the resent invention primarily deals, although bine, it would be impossible -on account of the heavy structure to practicably baille the leakage ilowof steam around the ends of the blades of the segments, which the shroud strip in the` present invention is designed to accomplish. The weight of this heavy' structure is supported from the 'blades and this isobjectionable on account of the excessive centrifugal force during rotation. It

should 'also be pointed out that those proposed constructions are primarily applicable to gas turbines of the radial flow type. In such a turbine ,very high temperatures exist and soldering must be exceedingly questionable as a practicable fastening. Also in the prior art is to be found a turbine havinga few end blades of a segment brazed to a shroud strip, but there the segment is mechanically fastened to the foundation strip, and moreover thel shroudstrip is located adjacent the ends of the blades leaving projecting blade ends to objectionably serve as paddles during rotation. Also, it has been proposed to cast-0n both ffundation strip and shroud strip, but in such construction the shroud strip would be entirely too heavy to serve as a battle to prevent leakage of steam and its weight supported from the blades wouldlbe objectionable; it would also be not uniform in texture if castV thin enough tobe a practicable baiiler.

Referring more particularly to the drawing, a series of blades l is shown cast-in in the foundation strip 2, and has fastened to its ends a single, light shroud strip 4, by soldering the parts directly together. This mode of securing the shroud strip is preferable to welding as it is difficult to prevent distortion of the partsin order to make a weld, Whereas such a high heat is not necessary in soldering. The solder 5 is clearly shown in Figs. 3 and 4. The klight shroud ing the tenon 6 preferably With two parallel sides and two sides with a curvature corresponding to the surface of the blades. These tenons 6 are short, preferably only of sufcient length to fairly enter the holes punched in the shroud strip 4. They. are shown of length equal to the thickness of the shroud strip 4 so as to be Hush with the surface of the shroud strip between the sides of the channel, which shape the shroud strip 4 assumes. The object of extending the tenons` 6 into correspondingly shaped holes in the shroud strip 4 is twofold, first, to properly space the blades, and second, to properly set the same at their theoretical angle about their axes. The strip having been properly set against theextreme ends of the blades l, the same is soldered thereto preferably by placing the-segment of blades in a position where the shroud strip 4 is at the bottom; but, in the case of very small blades set close together, the segment lmay be so placed as to have the shroud strip 4 at the top and thesolder 5 may be applied strong enough to rupture the blade itself I before pulling oil the shroud strip. After solderingthe shroud strip 4 tothe ends of blades 1, the structure' about this fastening is then a smooth surface throughout the full extent of the shroud strip. This is important as presenting no paddle brake action during rotation.

A tie-strip 7 is soldered to the blades 1 at a point intermediate thereof, and preferably in notches provided in the blades. This feature alone, is not, of course, intended to be represented as novel. This strip may be omitted in the case of short ilades or Where the speed is comparatively The segment of blades as thus far con- 'structed, is then machined as ,to its foundation strip 2 and the shroud strip 4, so as finally to produce an article of manufacture which is applicable to a turbine spindle or cylinder without any further machining. The finished segment is designed to be calked into a recess formed in the spindle or cylinder 3 of the steam turbine, as indicated in Fig. 4.

It should be understood that it is not desired to be limited to the exact details of construction shown and described, for obvious modifications Will occur to a person skilled in the art.

It is claimed and desired to secure by Letters Patent,-

1. The combination of a plurality of blades, a cast-on foundation strip for said blades, a single shroud strip soldered to the eXtreme ends of said blades, a tie strip soldered to intermediate portions of saidblades, and means for fastening said foundation strip to a support.

2. The combination of a plurality of blades, a cast-on foundation strip for said blades, a shroud strip soldered to the extreme ends of said blades, a tie strip soldered to intermediate portions of said blades, and means for fastening said foundation strip to a support.

3. The combination of a plurality of blades, and a foundation strip, a single light shroud strip, and a tie strip each united to said blades by `fusion of metal, and means 'for-fastening said foundation strip to a spindle or cylinder.

4. As an article of manufacture, la Segment of blading having a foundation strip, a single light shroud strip and a tie strip each secured to said blading by fusion of metal.

5. As an article of manufacture, a segment of blading having a foundation strip cast-on, a shroud strip soldered to the extreme ends of said blading and a tie strip soldered to intermediate portions of said blading. l 4

6. As an article of manufacture, a segment of'blading having a foundation strip, a single light shroud strip and a tie strip each secured to said blading by fusion of vmetal and said shroud strip being smooth throughout at its connection to said blading.

7. As an article of manufacture, a segment of blading having a foundation strip cast-on, a shroud strip soldered to the extreme ends of said blading and a tie strip soldered to intermediate portions of said blading, said shroud strip being smooth throughout at its connection to said blading.

8. As an article of manufacture, a seg-V ment of blading having a foundation strip and a previously formed single light rshroud strip each secured to said blading by fusion of metal and said shroud strip being smooth .throughout at its connection to said blading.

9. rlhe combination of a plurality of blades, a cast-on foundation strip for said blades, a previously formed shroud strip soldered to the eXtreme ends of said blades, and means for fastening said foundation strip to a support.

In testimony whereof, the signatures of the inventors are aliixed hereto in the presence of two Witnesses.

CHARLES EDWIN SEARCH. JOSEPH W. MOORE. Witnesses:

W. H. LmBER, Gr. F. DE WEIN.

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