US1890581A - Blades for turbine rotors - Google Patents

Description

Dec. 13, 1932. s. KOHLER BLADES FOR TURBINE ROTORS Filed Jan. 18, 1930 2 Sheets-Sheet 1 I Dec. 13, 1932. G. KOHLER BLADES FOR TURBINE ROTORS Filed Jan. 18, 1930 2 Sheets-Sheet 2 Patented Dec. 13, 1932 UNETE I ma GUSTAV KGHLER, OE IVIULHEIM-RUHR, GERMANY, .ASSIGNOR 'IO SIEMENS-SCHUCKERT- WERKE AKTIENGESELLSCHAET, 0F BERLIN SIEMENSSTADT, GERMANY, A CORPO- RATION' OF GERMANY BLADE$ FOB, TURBINE ROTORS Application filed January 18, 1920, Serial No.

Myinvention relates to improvements in blades for turbine rotors and the method of their manufacture.

The thick bead, flange or broadened edge at the periphery of the largest diameter disk ing them in radial direction.

Quite a number of different forms of blade bases, insertable into the wheel rim in the direction of the wheel axis, have been suggested in the prior art. Notwithstanding the great advantage accruing to this mode of blade attachment by way of a decrease in the centrifugal stresses in the disk periphery, and thus the possibility of increasing the peripheral speed, this construction, so far as I am aware, has not been favored by turbine manufacturers up to the present.

he reason becomes obvious when one considers that in this type ofconstruction it had always been proposed to provide the disk at its periphery'with slots opening into axially directed cylindrical recesses. The blades corresponding to the shape of the slots are provided with thin stems or shanks, each stem terminating at the inner end in a cylindrical base to fit the cylindrical recess in the disk.

In this proposed form the blade has a considareas is uite unsuitable for the reat stresses b developing in modern turbines.

My invention while making use of the 421,721, and in Germany December 29, 1928.

meritorious idea of inserting the blades in axial direction, does away at the same time With the thickened disk rim, and also eliminates the defects which up to the present have adversely afiectedthe general introduction of this typeof-blading into practical turbine construction. According to my invention the blades have a Wedge-shaped base, the load supporting crosssectional area of which progressively decreases from the extreme end portion of the base toward the beginning of the blade proper, where it emerges from the disk periphery. A form of blade is thus obtained which has a cross-section conforming with the shape requirements for withstanding the great stresses developing in modern turbines, and being free from any sudden clianges in cross-sectional area, undercuts, notches, thickened portions or beads, such as are present in the prior art suggestions of axially insertedbladebases,with their incident internal stresses and the stresses upon the material at the disk periphery.

The beneficial results obtained by the blade base form of continuously increasing'thickness according to the present invention are of particular importance for the low pressure blading of steam turbines.

It would=appear from contemporary art and" publications that the limit has been reached regarding the size of the loW pressure wheels and blades for a given speed, and that the present day steam turbine design has reached the upper limit of the critical output which latter is the maximum output which can be obtained from any kind of turbine at a given speed.

Since the first turbines were constructed, this critical output has been gradually raised. At present, so far as I am aware, for instance not more than 85,000 k. w. can be developed by a turbine running at 3,000

B. P. M. From the foregoing it will be obvious that this value is determined by the blade and disk stresses occurring in the last low pressure wheel. It would thus seem that the critical output-of a turbine set could be further raised only by an extensive subdivision of the low pressure stage, or by emterial at the circumference of the disk, present in modern turbines can be removed with out adversely affecting the strength of the blades as proposed by my present invention, it becomes possible to considerably raise the critical output. Such blades have the most favorable design if, according to my invention, the boundary surfaces of the blade base located in the wheel rim and the adjoining portions of the blade, which face in the direction of the wheel plane, have the contour, or

.constituteportions of the contour, of symmetrical bodies produced by rotation, more particularly conical surfaces, which possess a common axis. I Blades constructed on this principle establish, as calculations have shown, exteremely favorable conditions as regards strength when moving at high peripheral wheel speeds, and permit of a substantial raising of the capacity limit of a turbine, having such rotor blade construction.

I will now describe my new and improved .form of blading with conical blade bases and the mode of its manufacture with reference to the examples illustrated in the accompanying drawings, in which 'Fig. 1 represents the face view of a portion of the disk periphery with the blade bases inserted into the slots, the blades being indicated in transverse section taken at a distance from the base,

Figs. 2 and 3 represent transverse sections of the disk rim with a portion of a blade, these figures showing different modes of locking the blade bases to the rim,

Fig. 4 shows in a developed face view of the disk periphery a further modification of securing the blades on the disk.

Fig. 5 represents a sectionof a multi-disk rotor portion, showing the relative position between the rotor and stator blades, and

Fig. 6 represents in side elevation a portion of the disk rim with the blades in place.

One embodiment'of my invention is illustrated in Fig. 1 of the drawings which shows a portionof the wheel periphery face with.:

several bladesinserted into'their respective slots, the blades themselves appearing in transverse section, on about the line d-d in Fig. 6. I The slot for the blade is designed as a portion of a conical ring more clearly shown at C in Fig. 6, with the common axis m for,

the radius r for the inner boundary surface,

' and the radii 1 for the outer surface, which latter radii become larger and larger with increasing depth of the slot. In Fig. 1 radius r prevails at the intersection of the outer boundary surface with the disk periphery. The axis 17?. is spaced from the central plane 29 through the disk at right angles to its axis, by the distance Z. The base of the blade inserted into such a slot is milled with cutters having correspondingly similar shaped cutting surfaces. The concave face of the blade proper is milled at the radius 71, and its convex face at the radius 1",, with the center m. This mode of manufacture of the blading has the advantage that drawn material may be used for the blades which requires only very little finishing work. After milling the blade profile it is only necessary to finish the edges a and b in the manner indicated. A number of complete blades assembled on the rim are shown in Fig. 6 in side elevation. From this figure the gradually increasing thickness of.

To look the blade bases against axial displacement, the wheel disks 1 may, for instance as shown in Fig. 2, be slightly undercut at a distance from the periphery, so that the bases of the blades 2 project by a small amount into this undercut position. These projectingbase portions may be conveniently upset or peened over the slot edges. Another way of locking the blades in position is to provide the bases with a bore close to the wheel periphery, through which is threaded a wire 3, which rests in a central peripheral groove provided in the wheel as shown in Fig. 3 of the drawings. The slot for the blade base may also be made so that it enters at one side of the rim,

but stops short of the other rim side, so that a small amount of material remains standing,

against which the blade is able to abut, as shown in Fig. 4 which represents a face view of a portion of the wheel rim developed into a straight plane. 4 is the outer wheel periphery, 5 are the milled slots which do not extend across the entire width of the wheel. The blades may be held in position similar to the manner shown in Fig. 3.

It will be understood that the novel kind of blading is not only of special advantage for turbines composed of individual wheel disks but also for turbine constructions in which a plurality of disks are combined into a unit. In the constructions used heretofore it was necessary either to combine the individual disks into a very thick disk with correspondingly strengthened hub or, if this accumulation of material was to be avoided the disks, cut out of a blank cylinder, had to be spaced far apart to enable the intermediate material to be machined out by the turning tool. Very broad stationary guide blades are then required, however. If, on the other hand, my improved blading is made use of in which enlarged rims, or the like are omitted, the disks lot) iiu

may be machined out of a blank cylinder, with normal spacing. A construction is then obtained in which the diameter of the blade wheel may be increased far beyond the dimensions permissible now, due to the absence of large accumulations of material on the largest circumference of the disk.

In turbines equipped with my improved blading a special packing for the clearance is necessary. This packing may in very simple manner be produced by providing the disks with projections which form the counter faces for the usual packing sheets on the stationary guide blades. This construction is by way of example illustrated in Fig. of the drawings. Referring to this figure, are the impeller blades, 11 the stationary guide blades. The impeller blades 10 are axially inserted into the disks 12 machined out of a blank cylinder. The disks 12 are provided with small projecting annular rims 13 which may be integral with the disks and be machined out of them or may be attached by suitable means not shown here. These 1 rims form the counter faces for the packing sheets 14 of the guide blades 11. The slots which hold the blade bases may be cut into the wheel periphery by any suitable means known in the art, such as for instance by milling, a feature which forms no part of the present invention and has therefore been omitted from the description and drawings.

I claim:

1. A turbine rotor disk having rigid blades extending radially from the disk periphery and having at least one curved medium guide surface, each blade having a solid base integral with the blade and being insertable into the disk rim in the direction of the disk axis, said base having a thickness, measured in the circumferential direction of the disk, which gradually increases from the blade thickness measured at the disk periphery, toward the extreme base end, whereby the transverse sectional area of the base is gradually increased toward the base end in amounts to form together with the blade a structure of substantially uniform strength.

the shape of the blade bases to permit the insertion of the blades into the disk in the direction of the disk axis. V

3. A turbine rotor disk having radially extending axially inserted blades, each blade having a base forming on one side a continuation of one blade surface, said base, measured in the circumferential direction of the disk, having a thickness gradually increasing from the blade thickness at the disk periphery toward the extreme base end, the longitudinal sides of said base forming parts of the inner and outer surface of an annular rotary body.

4. A turbine rotor disk having radially extending axially inserted blades, each blade having a base forming on the blade side facing against the direction of rotation a continuation of the blade surface, said base, measured in the circumferential direction of the disk, having a thickness gradually increasingfrom the blade thickness at the disk periphery toward the extreme base end in amounts to form a blade body of substantially constant strength, the longitudinal sides of said base forming parts of the inner and outer surface of a cone-shaped ring.

5. A turbine rotor disk having radially extending axially inserted blades, each blade having a base forming on the blade side facing against the direction of rotation a continuation of the blade surface, said base, measured in the circumferential direction of the disk, having a-thickness gradually increasing from the blade thickness at the disk periphery toward the extreme base end in amounts to form a blade body of substantially constant strength, the longitudinal sides of said base forming parts of the inner and outer surfaces of a cone-shaped ring, whose center of rotation is located outside of the rotor disk periphery.

In testimony whereof I affix my signature.

GUSTAV KGHLER.

2. A turbine rotor disk having rigid blades extending radially from the disk periphery and having at least one curved medium guide surface, each blade having a solid base integral with the blade and being insertable into the disk rim in the direction of the disk axis, said base having a thickness, measured in the circumferential direction of the disk, which gradually increases from the blade thickness, measured at the disk periphery, toward the extreme base end, whereby the transverse-sectional area of the base is gradually increased toward the base end in amounts to form together with the blade a structure of substantially uniform strength, said disk having substantially axially di rected slots in its periphery conforming with

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