US2221679A - Method of making elastic fluid turbine buckets - Google Patents

Description

Nov. 12, 1940. W.C.HEI'CKMAN' 1221,679-

' MAKING ELA Filed Jan. 18, 1959 i Inventor":

Walter C. Heckman,

His Attorney.

AM a Patented Nov. 12,- 1940 UNITED STATES RIETHOD OF MAKING ELASTIC TURBINE BUCKETS Walter C. Heckman, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application January 18, 1939, Serial No. 251,579

2 Claims. (Cl. 29-15618) This invention relates to elastic fluid turbine buckets and more particularly to methods for manufacturing removable bucket units for turbines of the axial flow type.

In axial flow elastic fluid turbines designed 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 in the high pressure stages, be of an extremely strong and rigid construction. One form of a suitable bucket arrangement consists of a plurality of bucket units each having a base portion, a plurality of blades and a heavy cover portion all machined from a single piece of forged steel. The base of such bucket units may be provided with a dovetail slot for removably fastening the units onto the rotor rim. The manufacture of such bucket units fro-m solid blocks of forged metal is difficult in that accurately fin ished transverse passages of arcuate cross-sectional shape must be formed through the block defining the elastic fluid passages between the adjacent blade portions.

It is an object of this invention to provide a new and improved method of manufacturing elastic fluid turbine bucket units comprising a base portion, a plurality of blades and a cover portion from a solid piece of metal by which -method the bucket units can be manufactured with comparative ease and with great accuracy while the strength of the finished product is not impaired thereby.

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

Referring to the drawing, Fig. 1 illustrates a metal blank from which a bucket unit is to be made; Figs. 2 to 7, inclusive, are views illustrating the 'varioussteps according toone form 'of my invention; and Fig. 8 is a view in perspective illustrating the finished turbine bucket unit.

In the manufactureof turbine bucket units having a plurality of blades, from a single solid rigidity can be passed into the cavity from either side for removing metal therefrom at a satisfactory rate. The region of comparative inaccessibility in the central portion of the blank is relarated as by a layout traced on the upper surface of the blank as indicated at II and i2 defining the shape and position of the arcuate passage l3 therebetween. A portion of the, metal is then removed to form the central part of the passage 20 through an opening in the upper end of the blank. As indicated in Fig. 2, a hole It is drilled or end milled down into the blank extending through the upper surface thereof to a depth substantially equal to the lower boundary of the passage as shown more clearly in the vertical cross-sectional view, Fig. 3. The hole is of such cross-sectional shape that one wall thereof conforms accurately with the curvature of the convex surface l5 of the blade l2 while the oppo- 39 site wall conforms with the concave surface l6 of the blade I l. The width of this hole may be such that the convex wall I5 is formed to the point where it is substantially tangential of the sides ill and I8 of the blade l2. With the cen- 86 tral portion of the passage thus cleared out, it may readily be completed by the removal of metal through openings in the opposite side walls as by end milling operations substantially as indicated in the horizontal cross-sectional view, Fig. 4. Cuts l9 and 20 may first be taken along the tangents I1 and I8 of the blade l2, to be followed by milling through, as indicated at 2| and 22, into the hole It. After these rough milling operations are completed, the passage may be finished accurately to the proper curvature, as illustrated in Fig. 5, from the sides of the blank since the unfinished portions of the passage are readily accessible. The blank with the passage l3 completed is shown in Fig. 5, .it being noted that the upper and lower ends of the blank are still integrally united with the portions from which the blades are being formed.

After the passage l3 has beencompleted, the opening in the upper end of the blank may be r closed in any suitable manner. I prefer to weld a plug 23 therein substantially as shown in the vertical cross-sectional view, Fig. '7, the edges thereof and the edges of the opening being first suitably chamfered in order to secure a more perfect fusion of the metal in the welding operation. After the welding operation is completed it is preferred to heat-treat or anneal the blank in order to relieve any internal stresses caused by welding before the manufacture progresses through the succeeding stages.

The remaining steps to be performed upon the blank present no particular difficulties and may be carried out by well-known machine methods by anyone skilled in the art, since the remainder of surplus metal is removed from the outer surfaces of the blank. Such steps include the milling of a suitable dovetail slot 24 in the base of the unit, the milling of the outer convex and concave sides of the blades H and i2, respectively, the finishing .of the-cover portion 25 and the millingof the unit profile to the proper taper and the fitting of the unit to the wheel. The finished bucket unit is shown in Fig. 8. Though the bucket unit' shown and described in this instance is provided with but two blades, it is obvious that the method of this invention is equally applicable in the manufacture of bucket units 'of any number of blades. It is further understood that the dovetail type of fastening arrangement shown is merely illustrative of any suitable means for mounting the bucket units upon a turbine rotor rim.

From another viewpoint, the method ofmaking elastic fiuid turbine bucket units according to my invention includes the making of a block or blank from forged steel which has lower, intermediate and upper portions forming respectively upon machining a base, a plurality of bucket blades integral with the base and a, cover integral with the blades. An arcuate-shaped hole is formed through central parts of the outer and intermediate portions. Its width and curvature is substantially equal to the distance between and the curvature of adjacent sides of two bucket blades to be produced. In other words,

the wall of the arcuate hole forms part of the surface of the nozzle passages subsequently to be formed. Thereafter material is removed from opposite sides of the intermediate portion only towards the arcuate hole therein to form to-' gether with the latter a nomle passage through the intermediate portion. The arcuate hole in the outer portion is. then closed or plugged and the outer surfaces of the blank are machined to complete the formation of the unit.

Having described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof, I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

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

1. The method of manufacturing a bucket unit having two blades and a cover integral therewith which comprises the steps of producing a blank having lower intermediate and upper portions, forming an arcuate hole through the upper and intermediate portions, the arcuate hole having opposite wall portions defining surfaces of a nozzle passage subsequently to be produced removing material from opposite sides of the intermediate portion only towards the arcuate hole therein to form a curved nozzle passage through the intermediate portion, closing the arcuate hole in the outer portion, machining the lower portion to form a base, and machining the intermediate portion to form a. pair of bucket blades.

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