US1763256A - Turbine blade - Google Patents

Description

June 10, 1930.

J. L. RAY

TURBINE BLADE Filed Jan. 16, 1929 M \3 Fig.3.

lNVEN TOR F 5. WITNESS lfil am ATTORN EY Patented June 10, 1930 UNETED STATES PATENT OFFICE.

JAMES L. BAY, OF SWAR'IHMORE, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA TURBINE BLADE Application filed January 16, 1929. Serial No. 332,926.

My invention relates to elastic iiuid turbines, and more particularly to the blading thereof, and it has for an object, to provide lmproved blading for apparatus of this character.

It is generally well recognized that the inlet and outlet edges of a turbine blade must be relatively thin, if eflicient flow of motive fluid is to be obtained. During the operation of a turbine, however, the blades are subjected to various bending stresses which attain their maximum value in the thin edge portions where the metal is thin and least able to withstand stresses. These bending stresses are either tension, or compression stresses, depending upon the direction of bending, or flexure about the root. The blades are also subjected to a direct tension due to their centrifugal force- Hence, When the bending results in a tension stress in the thin edge portions, the combined centrifugal and bending stresses may result in a relatively high tension stress, particularly in the thin edge portions where the bending stresses attain their 5 maximum value. This combination of circumstances has a tendency to produce small fractures, or cracks along either the inlet, or the outlet edge portions, and once a tracture occurs, it soon develops and causes failare of the blade.

It is a more particular object of this invention, therefore, to provide a blade having edge portions which shall be able to withstand greater stressing action.

Another object is to provide for certain improvement in the structure of the metal in the edge portions of a blade.

These and other objects are effected by my invention, as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. 1 is an elevation of a turbine blade:

Fig. 2 is a section on the line II-II of Fig.

' 1, showing'the neutral axes of this section;

Figs. 3, 4 and 5 are stress diagrams for a typical blade; and,

Figs. 6, 7 and 8 are stress diagrams for my improved blade. In accordance with my invention, after a from the wx axis.

turbine blade is fully formed the edge portions thereof are treated toimprove the structure of the'metal and to produce a greater concentration of internal compressive stresses in the edge portions. This treatment may be eflected by rolling, pressing, hammering, or like operations.

In Fig. 1 of the drawing, I show a typical turbine blade, indicated generally at 10, and comprising a blade portion 11 and a root portion 12. In Fig. 2, I show the major axis :ra and the minor axis y-y for the transverse section taken along the line IIII of Fig. 1, but for the purposes of illustration, Fig. 2 may be assumed to be any transverse section through the blade portion 11, of the blade 10. v

WVhile a turbine is in operation the centrifugal force of the blades themselves results in direct tension stresses, as indicated by the arrows 13 in Fig. 3. These stresses are substantially uniform across any transverse section, such as the section IIII, as indicated in Fig. 3. The blades are also subjected to bending stresses as indicated by the arrows 14 in Fig. 1, and from this figure it will be seen that the stresses due to bending increase from the central portion of a blade toward the thin edge portions thereof, attaining their maximum value inthese thin edge portions, since the latter are at the greater distance The arrows 14, which are above the line m4t, indicate tension stresses, while those below the same lineindioate compression stresses, itbeing under- 1 stood that both the inlet and the outlet edge portions will be either in tension, or compres .sion depending upon the direction ofbend- Fig. 5 is a combined stress diagram, the arrows 16 in this figure representing the algebraic sum of the tensionstresses, represented by the arrows 13 in Fig. 8, and the tension and compression stresses represented by the arrows 14 in Fig. 4. From Fig. 5,-it will be apparent that the maximum stress occurs in the edge portions of the blade when the bending produces a tensionin these edge portions, as

the tension stresses, so produced, add direct- 1y to the centrifugal stresses.

It is customary, in the manufacture of turbine blades, to give the blades a heat treatment after the forging, or other forming operations have been completed in order to improve the grain of the metal and to relieve any internal strains which may have originated during cooling, or which may have been caused by working. Such a treatment leaves the finished blades initially free from internal stresses, or strains.

In order to provide such a blade with edge portions which shall enable it to withstand greater stressing action, I subject the edge portions of the blade to a treatment consisting of rolling, pressing, hammering, or like operations which will produce compressive stresses in these edge portions. Heat treat ment may also be performed in such a way as to give the same effect, that is, by selective heating and cooling of the edges and body portions of the blade. Considering the blade 10 shown in Fig. 1, the portion of the blade from the inlet edge 17 to the line 18 parallel therewith, as well as that portion from the outlet edge 19 to the line 21 parallel therewith would be rolled in order to produce internal compressive stresses in the respective edge portions. It will be obvious that the same result may be had by pressing, hammer ing or like operations, and that these same operations will also produce a finer crystalline structure in these edge portions, and thus improve the structure of the metal.

After being treated in this manner, a blade will be initially stressed as shown in Fig. 6, wherein the stresses are indicated by the arrows 22, those below the line m-n indicating compression, while those above the same line indicate tension. From this diagram, it will be seen that a slight tension may be produced in the central portion of the blade, but this is not objectionable as the metal in this portion of the blade is better able to take care of such stress. While I prefer to treat both the inlet and the outlet edge portions in the manner just described, it will be obvious that only one of these edge portions may be so treated without departing from the spirit of my invention.

Fig. 7 is a combined stress diagram, the arrows 23 being the result of combining the stresses represented by the arrows 22 in Fig. 6 and the centrifugal stresses represented by the arrows 13 in Fig. 3. Fig. 8 is a combination of the stresses in Fig. 7 and the bending stresses represented by the arrows 14 in Fig.

4. Fig. 8, therefore, gives the final condition of maximum operating stresses. By comparing the stresses represented by the arrows 24 in Fig. 8 with the stresses shown in Fig. 5, it will readily be seen that the final operating stresses, particularly in the edge portions, in my improved blade are considerably less than those for corresponding conditions in other blades. Furthermore, not

only are the stresses lower in the edge portions, but the structure of the metal in these portions is also improved.

l/Vhile 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 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.

What I claim is:

1. A turbine blade having a greater concentration of internal compressive stresses in the respective inlet and outlet edge portions thereof than elsewhere.

2. A turbine blade having a finer crystalline structure in the respective inlet and outlet edge portions thereof than elsewhere.

3. A turbine blade having a greater concentration of internal compressive stresses in the respective inlet and outlet edge portions thereof than elsewhere, said stresses being formed'by working the material forming said edge portions.

In testimony whereof, I have hereunto subscribed my name this 10th day of January,

JAMES L. RAY.

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