US1770964A - Method of making die blocks for forging turbine blades - Google Patents

Description

Jul 22, 1930." R. c. ALLEN 1,770,964

METHOD OF MAKING DIE BLOCKS FOR FORGING TURBINE] BLADES Original Filed- 6- 1924 2 Sheets-Sheet l l o WITNESS INVENTOR RC. ALLEN.

@IVbIM ATTOR N EY July 22, 1930. R. c. ALLEN 1,770,964

METHOD OF MAKING DIE BLOCKS FOR FORGING TURBINE BLADES Original Filed Dec. 3, 1924 2 Sheets-Sheet 2 Fla. .5. Fla. 5.

INVENTOR R.C.ALLEN.. m. M

ATTORNEY .Fatented July 22, 1933 UNITED sTA TEs PATENT orriciz ROBERT c. ALLEN, or swan-Truman,rmvirsYLvANIA; assreivoaro wrisrrneriousn ELECTRIC & MANUFACTURING COMPANY, A CORPORATION or PENNSYLVANIA METHOD OF MAKING DIE BLOCKS FOR FORGING TURBINE BLADES Original application filed December 3, 1924, Serial No. 753,582. Divided and application filed. June 14, 1927. Serial No. 198,852. Again divided and this application filed April 30, 1929. Serial No. 359,304.

This application is a division of application Serial No. 198,852, filed June 14, 1927, which in turn is a divisionof application Serial No. 753,582, filed December 3, 1924.

The present invention relates to a method of making a die block, more particularly a die block as described in the first mentioned application, which die block is used for making turbine blades covered in the second mentioned application.

The object of the present invention is to provide an economical method of making a die block for forging turbine blades having varying blade tip. 1

Apparatus embodying features of my invention. is illustrated in the accompanying drawings forming a part of this specification in which:

Fig. 1 is a fragmentary sectional View of a turbine rotor and cylinder having my improved blading applied thereto;

Fig. 2 is a diagrammatic View descriptive of the motive fluid flow through the blades and showing in section a part of the blades illustrated in Fig. 1 along the lines 22 and 22 of Fig. 1; V

Fig; 3 is an elcvationof one of the blades, drawn to a larger scale than Fig. 1 and show ing in section the varying contour of the blade from rootrto tip;

Fig. 4 is a plan view of a milling machine with a die block for forging my improved turbine blade in process of being formed;

Fig. 5 is a side elevation of the die block shown in Fig. 1 and indicating the direction taken by the milling cutter shown in Fig. 4;

Fig. 6 is an end elevation of the die block illustrated in Fig. 4, drawn to a larger scale and showing the contour of the cut made by the milling cutter in Fig. 1 andthe contour of the cameo member of the die block employed in forging the blades;

Fig. 7 is a'view of the milling machine and die block shown in Fig. 4, the position of the die block being altered from the position shown in Fig. 4;

Fig. 8 is a side elevation of the die block showing from another View the position of the the block in Fig. 7 and also showing the cross section from blade root to direction of the cut made by the milling cutter illustrated in Fig. 7;

Fig. 9 is a view similar to Fig. 6 showing the contour of the cut made'by the milling cutter in Fig. 7, the altered position of the die blockin Fig. 7 from that shown in Fig. 4, and the contour of'the cameo member of the die block employed in forging the blades;

Fig. 10 is aper spective view of the completed die block and showing the surfaces of the blade devel-opedrthereby.

In turbines of the multi-stage type actuated by elastic fluid (hereinafter referred to as steam) the blade space between the rotor and the casing of the turbine increases from the end of the turbine where thehigh pressure steam is admitted to the exhaust end.

thereof in conformity, more or less, to the specific volume of the steam at the various pressures n the various stages of the turbine.

Thus the blades in the high-pressure end of the turbine are relatively short while the j blades in the low pressure end are relatively long. y r

The diameter of the rotor of a turbine plus the lengthof a blade, which is equivalent to a diameter measured across the rot-or between the midpoints of the blades on oppositesides thereof, is usually referred to in turbine practice as the mean diameter of the blades. The low-pressure blading in large condensing steam turbines has been made, in the past, as long as one-fifth of the mean diameter with a fair degree of eff-i ciency. .Thereis, of course, an a ipreciable' difference in peripheral speed atthe tip and at the base offa blade of this height, the tip having a peripheral speed 50% greater than the speed at the base in the case of a rotor blade, In past designs, wherethe length of the blade did not exceed one-fifth of the mean diameter, blades of parallel sections have been used for the reason that they may be more cheaply produced. Where the blades have been produced by drop-forging, the dies therefor have been machined by a planing or milling process. lVhere the blades have been cutfrom'a solid bar, elther milling or planing operations have been employed.

With blades of parallel sections as great as one-fifth the mean diameter in length, there is some disturbance to the steam flow at the tip and at the base portions of the blade, inasmuch as the blade inlet angle is only correct at one point, usually at the mean diameter or mid portion of the blade.

In recent turbines it has been found necessary to use blades greater in length than onefifth of the mean diameter and of higher peripheral speeds than those employed in the past. For such blades parallel sections can no longer be successfully employed as the centrifugal stresses in the rotor blades are entirely too high for the material usually employed in making the blades. It has therefore been found necessary to taper the blades from base to tip so that their cross sectional area increases from the tip toward the spindle at such rates that longer blades may be run at high speeds but with no higher stresses than when blades of parallel sections are employed.

As the blades increase in length from the high to the low-pressure end of the turbine, the speed of the tips of the moving blades relative to their root portions increases and the velocity of the motive fluid discharged from the moving blades, if considered relative to the stator or casing, is, in most practical applications, less at the tips than at the root portions of the moving blades. Assuming that'the motive fluid leaves a row of moving blades at a constant angle to the side of the blade row from the root to the tip of the blades the difference in speed of the blade at the root and the tip gives a resultant direction, or trajectory, to the steam leaving the blade row which varies progressively from the root to the tip, if the direction relative to the stator or casing be considered. Thus, the motive fluid may leave the root of the blade in a moving row, for example, with a trajectory at an acute angle relative to the stator, while at the tips of the blades the trajectory of the steam leaving the row may be at approximately a right angle, relative to the stator or even an obtuse angle, depending of course, upon the blade speed, the steam speed and the exit an gle relative to the side of the blade row.

From the above it is evident that in order to avoid eddying of the motive fluid as it enters the succeeding row of stationary blades the inlet angles of those blades should be such as to correspond with the varying trajectory of steam leaving the preceding row of moving blades in the example assumed in the preceding paragraph, the inlet angle of the succeeding stationary row of blades should be an acute angle at the base of the blade varying to approximately a right angle at the tip. Considering the relative motion of the stationary and moving blades it will be evident that the nest succeeding row of moving blades should have similar corresponding inlet angles.

It is obvious that variation in outlet angles will cause a radial displacement of the center of gravity of the steam flow so that special problems will be introduced if the outlet angles are varied. Considering the foregoing, therefore, it will be apparent that the most efiicient and desirable blade structure is one wherein the exit angles of the blades are constant and wherein the inlet angles vary from the roots to the tips of the blades in conformity to the varying trajectory of the entering steam.

In order to meet the requirements of a long ta ered blade which may accommodate itself to the varying conditions of steam flow through the turbine, the manufacture thereof has heretofore been a long, laborious and vary expensive process. It has been proposed to forge the blades and to thereafter warp or twist them by means of a suitable tool, in order to provide suitable inlet and leaving an gles. Blades have also been made, rough forged, and the steam passages afterward formed by several separate machining and hand processes. Either of these methods is obviously expensive and attended with many difficulties.

In accordance with the invention set forth in the above mentioned application, Serial No. 753,582, I provide a relatively long, tapered blade, each surface of the port section of which is defined by plane surfaces and cylindrical'or curved surfaces, the axes of which diverge longitudinally and laterally of the blade from the tip to the root thereof, and which provides a constant leaving angle and a varying inlet angle from tip to root of the blade in accordancewith varying conditions of steam flow in the turbine.

In accordance with the present invention, I provide a method of making a die block for forging blades of this character. The cylindrical or curved surface of one of the die block members, preferably the cameo member, is out along a straight line which is inclined to the cameo member. The intaglio member may be made of uniform cross section. A die block is thus produced for forging the blades, whereby blades of the greatest eiiiciency may be produced at a minimum cost, and which require no twisting or warping to accommodate varying conditions of steam flow.

Referring now to the drawings for a better understanding of my invention, I show in Fig. 1, at 10, a fragment of a turbine rotor and at 11 a fragment of a cylinder. At 12 is shown a row of moving blades carried by the rotor 10 and at 13-13 rows of stationary blades carried by the cylinder 11. The rows of blades 12 and 13 are of parallel section as they are of lesser height than rows 16 and 17 following and therefore may not require the tapering or working for the reasons stated above. They are followed bymoving rows of tapered blades1616 and stationary rows of tapered blades 1717, said blades being made in accordance with my invention. The direction offlow of steam through the blades is from right to left and may be better understood by reference to Fig. 2, wherein a typical steam flow condition through rows 13, 16 and 17 is shown.

In Fig. 2 the blade sections in the upper part of the figure represent the stationaryv rows of blades 13 and 17 and the moving rov. 16 along the line 22 of Fig. 1', while the lower blade sections represent the same rows along the line 22* of Fig. 1. lllccon'ipanying the rows 13 and 16 are velocity diagrams in which Vs represents steam velocity, which is constant from the root to the tips of the blades; V represents blade velocity along theline 2 2 of Fig. 1; V represents blade velocity along the line 2'-2 of Fig. 1; T and T represent the trajectory of the steam leaving a blade row relative to the succeeding row of blades along the lines, 22 and 22, respectively, of Fig. 1. The ankle '6 represents the leaving angle of the steam from each row of blades, which angle is constant throughout the blade length for both the stationary and moving blades. The varying trajectory T and T is determined by, and is a component of, the leaving angle of the steam relative to the blade row, the velocity of the steam and the velocity of the moving blade row at the point considered. The angles made by T and T with the side of the blade row determine the'inlet angle of the next succeeding row of blades atthat point. Inasmuch as the blade velocity along the line 22 is much greater than the blade velocity along the line 2-2 the inlet angle along the line 22 as determined by the trajectory T is 1' uch greater than the inlet angle along the line 22' as determined by T in order to avoid disturbanc s in the steam flow as hereinbefore pointed out.

Referring to Fig. 3, I show in further detail a blade made in accordance with my invention. In this figure 18 represents the port, or working section, of the blade and 19 the root or holding section which may be of any form known in the art. Sectional views of the port section 1.8 are shown in 21,

22, 28, 24 and 25, said sectional views show ing the inlet-and leaving angles of the blade at the respective points selected. It'will be noted that the port section 18 of the blade decreases in cross section from the root to the ti) thereof and that the leavin an le 6 is l is.

constant from the root to the tip. The inlet edge of the blade makes an angle with the side of the blade row as shown at ca, 0. or, a and a said angles being relatively small near the root of the blade. and increasing toward the tip in order to accommodate the surface 51 define theback of the blade.

varying trajectory of the steam from the next preceding row of blades as shown in Fig. 2 and prevent disturbances in the steam flow. In accordance with my invention the blade is so produced that the inlet angles increase progressively from the root to the tips of the blades asma-y best be understood by reference to the method of making the blade which will now be described.

In Fig. 4, I show a milling machine 27 which may be driven by any suitable means as by a belt pulley 28. Mounted upon the machine bed is a block 29 to be machined for forming the intaglio member ofthe die block which I employ in forging the turbine blades. A milling cutter 31 is carried by journal bear ings 32 and 33, the latter being fitted to guides and 36 so that theymay be movedback Feed and forth in the cutting operation. mechanism for the milling cutter 31 is associated with the bearings 32 and 33,-such for example, as sets'of beveled gears at 37 and 38, feed screws 39 and 40, a drive shaft 42 and a hand-operating-wheel 48. e

In the operationillustrated in Fig. 4 the block 29 is placed at right angles to the cutter 31 and the cut is made straight througl'i the face of the block as indicated bythe dotted line 44 in Fig. 5. The contour of the cut which I have found desirable for reaction blades is illustrated in Fig. 6 and comprises a cylindrical surface 45 supple1nented by a flat tangential surface 46. The surfaces 45 and 46 definethe contour of the cameo member of the die block which is illustratedat 47 and consequentlythe contour of theconcave or workingface of the blade. The flat surface 46 is at the leaving side of the blade,while the curved surface 45 is at the inlet side. Each of these edges may be progressively changed from root to tip of the blade in the operation about to be described iii) and which constitutes one of the most impor tant features of my invention.

Referring to Figs. 7, 8 and 9, I show the next operation inmaking the die block. In the operation here illustrated, I show a milling cutter 48 which makes a cut in the bloclr 29 having a contour as illustrated in Fig. 9, comprising a curved surface 49 supplemented by a flat, tangential surface 51. It is to be understood, however, that the particular contour of either of the cuts illustrated will vary with the area and'configuration of the required steam passages between adjacent blades. The curved surface49 and the flat In making the cuthere illustrated the block :29 is shifted at one end to one side from the position illustrated in Fig. 4, and as illustrated by the dotted line 52 in Figs. 7 and 9 and also raised at one end as shown at 53,

Figs. 8 and 9. The cutter 48 is now driven straight through the block 29, whiohhas been shifted to the position indicated, and in transversing said block the right side of the surface 49, as shown in the drawing, approaches and cuts the right edge of the surface l5 considered in the direction from the blade tip forming portion to the blade base forming portion. In proceeding through the block 29 a different part of the curved surface of the milling cutter el8 cuts across the curved surface. describing therewith a skew curve, or a curve of double curvature.

As is well understood in the art, when producing an article byforging, it is necessary that a space be left along the inner edges of the striking surfaces of the die members for the flow of metal. This is necessary in order to produce an article of definite dimensions. I accordingly show spaces 56-56 at each side of the die block to accommodate the before mentioned flow of metal. These spaces or grooves may be formed by any suitable process. When the metal for forming the blade is forged, therefore. there will be at each side thereof a fringe of rough metal extending the length of the blade. In the final completion of the blade this fringe is cut by any suitable process, preferably in a straight line along the edges of the blade. The resultant inlet edge of the blade then is finally resolved into a plane curve, the curvature of which depends upon the curvature of the cylindrical surface 45 and the direction of the cut diagonally across said surface.

The inlet edge of the blade being defined by a plane-curve extending from end-to-end of the port section 18 of the blade, results in a flattening out of the inlet angle or causing it to become progressively greater from the base to the tip as will be more particularly described later. In making the out last described the block 29 is raised at its lower end as indicated at 53 in Figs. 8 and 9. The milling cutter 48 is driven straight through the face of the block 29 so that the curved surface 49 is cutdeeper at the lower end of the block than at the upper end and gradually approaches the curved surface 45 of the cameo member 4 as it approaches the top, the two surfaces 45 and i9 thus defining an area of progressively decreasing cross section from base to top. Referring to Fig. 9 the axis of the surface 49 is indicated at O and the axis of the surface 45 at X, said axes lying in different horizontal planes. Upon considering the paths of the milling cutters 31 and d8 in describing these two surfaces as illustrated in Figs. 4 and 7, it will be seen that the axes O and X converge longitudinally and laterally from the base to the top of the area defined.

In the particular blade heretofore des ribed, which blade represents the preferred embodiment of my invention, the axes O and X do not, at any time, intersect, the axis 0 passing beneath and beyond the axis X. It is entirely possible, however, that a blade might be developed in the manner described in which the relative inclination of the two curved surfaces 45 and 49 be such as to result in intersecting axes.

In Fig. 10, I show a perspective view of the completed die block wherein the port section 18 of the blade is lying in the intaglio member 29, the resulting concave surface of the intaglio member and of the blade being substantially conjugate to the convex surface of the cameo member. The direction of the inlet edge of the blade with respect to the cylindrical surface 45 is indicated at 541-. It will be plain that the line 54 cutting the curved surface 45 defines an inlet edge for the port section 18 of the blade, said inlet edge being such as to present a progressively increasing angle to the side of the blade row from the base to the tip. It will be further evident that the two flat surfaces Q6 and 51 cooperate to provide a leaving edge which presents a constant angle to the side of the blade row.

In the foregoing description, the manner of developing the cameo member l7 of the die block has not been described. Inasmuch as the cross sectional area of the cameo member is constant throughout it may be produced by any suitable machining process known in the art and which will not be necessary to describe here. The intaglio member may also be produced by other machining processes than milling. For example, the operations described may also be carried out by a planing process and it is to be understood that the particular machining process therein described is for the purpose of illustration and is that which appears to me to be the best suited for the operation. It is further to be understood that the cooperating surfaces defining the blade may be developed in the reverse to that described; that is, the area defined by the surface of the intaglio member might be of aconstant cross section and the area defined by the cameo might be variable without departing from the spirit of my invention.

IVhile I have shown my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications, without departing from the spirit thereof, and I desire, therefore. that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims.

In this connection. it is desired particularly to point out that, while I show my invention embodied in a method of forming a die block for forging a turbine blade, each working face of which is formed along a single axis for the entire length of the blade, the invention is not so limited, and the claims are intended to cover my invention where embodied in a method of forming a die blockfor forging any substantial length of a turbine blade.

WVhat I claim is: r r

1. The method of forming one member of a die block for forging turbine blades, which comprises setting the member at an angle both vertically and laterally to the direction of travel of a cutter and then moving the cutter in a straight path, relative to the memher, to produce therein a cutof the contour of one side of the blade to be forged.

2. The method of forming a die block coinprising cameo and intaglio members for forging turbine blades, which includes machining one of the members to form a curved surface having a straight line axis for form ing one side of the blade and cutting the other member in straight path which is at an angle laterally to the first mentioned axis to produce a curved surface for forming the other side of the blade. g

3. The method of forming a die block comprising cameo and intaglio members for forging turbine blades, which includes machining one of the members to form a curved surface having a straight line axis for forming one side of the blade and cutting the other member in straight path which is at an angle 7 both vertically and laterally to the first mentioned axis to produce a curved surface for forming the other side of the blade.

l. The method of forming a die block for forging a turbine blade having concave and convex cylindrical surfaces,- which comprises forming a convex surface on the cameo member to form the concave surface of the blade,

then cutting the intaglio member to register with the cameo and then driving a cutter straight through the intaglio member in a direction which is inclined both vertically and laterally to the direction of the first cut, thereby producing a concave surface for forming the convex surface of the blade.

5. The method of cutting the intaglio member of a die block for forging turbine blades which comprises forming a cut of uniform contour longitudinally of the member, then setting the member at an angle both vertically and laterally to the direction of travel of a cutter and then producing in the member a cut of the'contour of the convex a side of the blade to be forged.

6. The method of forming a die block for forging a turbine blade, comprising cutting a cameo member to form a convex cylindrical surface of uniform cross section, and driving a cutter straight through the intaglio member to produce a concave cylindrical surface, the axes of said surfaces being in- ROBERT C. ALLEN.

clined toward each other and non-intersecti mg.. V

7. The method'of cutting a die block for forging a turbine blade having concave and convex cylindrical surfaces whose axes diverge, which comprises forming a' cameo

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