US2269200A - Method of manufacturing elastic fluid turbine buckets - Google Patents

Description

Patented Jam, 1942 mamon or muvracruamo sms'rrc raum 'rmmr Rudolph llillner, General El New York aucxirrs seheneeiedy, N. r., 'mignonto eetrio Company, acorponon of- Appiieetion renom is. im, serial No; 251,5

4 chime. (i. sii-15er) o 1 'I 'his invention relates to elastic huid 'turbine buckets and more particularly to removable bucket unitsfor turbines of the axial now type and methods of manufacturing same.

In axial noweiestie nuid turbines desienedes for high admission pressures, for example, of the order of 1200 pounds per square inch and above, and correspondingly high initial temperatures, it is required that the buckets, particularly vin n thehigh pressure stages, be of an extremelyfro strong and rigid #construction One form ofa suitable bucket arrangement consistsof a plurality of bucket units each having a base portion, a plurality of blades and a heavy cover portion bleek or metal er blank. considerable. diiiieuityY is experienced in accurately forming the lconcave and eon'vex surfaces denning the adjacent blade walls of the unit. This difficulty is primarily due to the particular arcuate configuration 'of `the passage which must be 'formed through the blank .from side in side. it beingof irregular shape and relatively narrow so that suiilcient clearances do not existfor cutting tools of suilicient rigidity to be passed into the cavity from either side for removingmetal therefrom in a satisfactory' manner. `In accordance with my "iiventigui, the passage defining the inner, adjacent walls of a pair of blade portions is maall machined from4 a single piece of forged steel. '515 chined out from the upper, or cover. end of the 'I'he base' of such bucket unitmay be provided with. a dovetail slot for removably positioning the unit onto the rotor rim. 'Ihe .manufacture of such bucket units from solid blocks of metal blank.

l In Fig. 1 is shown a solid block of metal or Ablank I preferably of forged steel of a proper alloy which will give suiilcient strength and rigidis exceedingly diiiicult. in that accurately finished '20 ity to the nished unit for withstanding the most transverse passages of arcuate cross-sectional shape must be formed through the block defining' the elastic uid channels between the adjacent'fblade portions.

It'isanfob'jct of this invention to provide a -25 new Tvand improved elastic fluid turbine bucket unitihaving a plurality ofblades and base and .cover portions rigidly connecting the opposite ends thereof.

It is a further object of this invention to pro- 3'0 vide a new and improved method of manufacturing elastic vfluid turbine bucket units comprising abase portion, a plurality of blades and a cover portion integrally united together in a rigid unit by which method the blade portions can be manufactured with comparative ease and with"great"aocuracy while the strength of the finished unit is such as will withstand the most extreme conditions of turbine operation.

e For a consideration of .what I believe to be novel and my invention, attention is directed 'A to the following description and the claims appended thereto taken in connection with the accompanying drawings.

'bucketinitmafactured in accordance with a methodv `ci.' lmy invention.

extreme conditions of operation when assembled in the high pressure stages of a turbine. o The iouter surfaces of the blank may be firstrough machined or'squared to some suitable preliminary shape,- such as that shown. y The, upper end or portion, which willconstitute the cover for the bucket unit, is indicated at -i if; the base or lower lportion in which the dovetailr fasteningmeans will be-formed'is indicated. at I2; while the interwill be formed is indicated at I3. The base portion i2 may be first slotted' as indicated at il in Figs. 3 and 5 as a preliminary rough milling operation to the formation ofthe dovetail which may becompleted later on in "the; sequence of the manufacturing steps. The rough slot I4 -is useful during the immediately succeeding steps in that the positioning of the blank in fthe work holder of the machine is thereby facilitated. In Fig. 2 is shown an end view of the'ablank having traced thereon in dotted lines'a layout-indicating a cross-section of a pair of blades i5 and'i dening an arcuately shaped passage il therev between which is to be milled out. Preliminary to the millingfof the passage itself, a chamfered groove il similar in shape to the passage il is milled in the. .upper end portion il of the blank as shown in Fig. 3, 'I'he chamfered'sides of this groove are desired for a later welding-operation The passage I1 is then formed by an en milling operation illustrated in Fig; 4 in which the mill- In the machining of turbine bucket units, eml -ing tool Il is shown extending downwardly into bodying a plurality of blades, from a single solid the blank through the upper end thereof and mediate section or portion from which the blades and also to enable an enlarged shank milling.` tool to be used inthe machining of the assage.

parallel with the side Walis 'f adjacent concave and con of lthe adjacent blade pori tively, may 'ce formed` as operation may be performer high degree of accuracy since may be of comparatively sho Iierigth and such a diameter as .to be r at ely inflexible. Asis well understood in the the adjacent surfaces of the blade portions are not truly parallel but are slightly spread apart at the upper ends so as to conform with the radius of curvas ture of the turbine rotor rim.

The upper end of the passage il is then closed by welding a suitably shaped insert 22 into the charnfered groove in the upper end or cover portion II-. The welded cover .portion reuniting the upper ends of .the blade portions is shown milling tc-ol i@ v rirn.

more clearly in Fig. 6, the welds are V-shaped in'oross section as indicated at`23. Because the welding operation is likely to set up internal Astresses within the metal of the blank, it is pre ferred that the blank be heat treated or annealed at this stage in order that such stresses be relieved before the manufacture of the unit progresses through the succeeding stages.

The remaining steps to be performed upon the 'blank present no particular diillcultiesV and may be carried out by well-known methods by anyo'ne skilled in the art by simply machining or milling the remaining surplus of metal `from the outer surfaces of the blank. The outerfconvex assenso bucket units having any greater number ,of blades. t is further understood that the dovetype of fastening arrangement shown is merely illustrative of any suitable meansfcr mounting the bucket units upon the turbine rotar Having describec' the principle of operation of my invention together with the apparatus' which now consider to represent the best em bodirnent thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention can be carried out by other means.

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

l., The method of making an elastic fluid turbine bucket unit from forged steel which comprises the steps of making a blank having lower intermediate and upper portions, removing material from the upper portion to form a groove tapered towards the intermediate portion and of y a width and curvature near the intermediate porand concave sides of the blade portions -IS and V I6 maybe milled olf leaving the cover and base portions Il and I2 intact for separate machine operations to be performed thereon. The dovc4 tailslot in the base portion Il may .thenben lcompleted giving itthe suitable curvatureI for fitting onto the turbine rotor. vThe cover portion of the unit may be machined to the proper thickness in accordance with the' degree of ri'- gidity required for the upper ends ofthe blade portions. The opposite sidesV of the unit may be Y tapered in accordance with the radius of curvature of the vturbine wheel 'and properly finished in order that adjacent bucket units will ilt snugly between the adjacent blades.

The nished bucket unit, as shown in Fig. 7, is of an extremely strong andA rugged construction, the lower ends of the Ablades being integrally united with the baseA and being relatively immovable with respect to each other. The upagainst each other and withthe proper spacing i 'V-shaped welds.

tion substantially equal to the width and curvature of a bucket passage to be produced thereafter, removn'materlalfrom the intermediate portion to detlne a curved bucket passage. forming a curved strip V-shaped in cross section, and fusing the strip to the walls of the groove by l A2. A method of producing a turbine blade unit consisting of a plurality of blades integral with a single root, comprising providing a blank of rectangular cross-section; .said blank having side, end, top, and bottom faces; forming a nuid passage in the top face thereof; said passage having its ends opening through the opposite side faces of the blank; permanently securing a.

shroud piece in'closing relation to the open top of the passage; heat-treating the structure to remove stresses therein; Aand machining the blank to nal form.

3. AA method of producing a turbine blade unit consisting of a plurality of blades integral with a single root, comprising providing a blankof rectangular cross-section; said blank having side,

end, top and bottom faces; forming'a fluid passage in an end thereof; said passage having its ends opening through the oppositeifaces of the blank; welding a shroud piece in closing relation vto the open top of the passage; heattreating the structure to remove stresses therein; and

I machining the blank to final form.

per ends of the blades being integrally unitedv through the bridging .cover Vportion Il further insures the complete rigidity of the blades with respectto eachother, the bucket unit shown possessing substantially the same strength as regards distortional stresses Vas though the slot il extending between the adjacentzblade portions had been formed therethrough from theopposite sides Without disturbing the integral cover portion.

Though the bucket unit shown and describedin this instance .is provided with but twolbades. it is obvious that the method of this invention is equally applicable in the manufacture -of 4. A method of producing a turbine blade unit consisting of a plurality of blades integral with a single root, comprising providing a blank of rectangular cross-section; said blank having side, end, top and bottom faces; milling a uid passage in an end thereof, said passage having its vends opening through the opposite faces oi the blank; forming a shroud piece to ft'in the open top of the passage; welding said shroud piece to the walls of the passage adjacent the upper edges of the latter; heat-treating the structure to remove stresses therein resulting from the welding; andv machining the blank to y Y final form.

RUDOLPH HILLNER.

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