US2025171A - Fastening means for turbine blades - Google Patents

Description

Dec. 24, 1935. F. LJUNGSTRGM FASTENING MEANS FOR TURBINE BLADES Filed Jan. 25, 1934 4 Sheets-Sheet 1 I IIIIII/lf 1935- F. LJUNGSTROM FASTENING MEANS FOR TURBINE BLADES Filed Jan. 25, 1934 4 Sheets-Sheet 2 1935- F. LJUNGSTRGM FASTENING MEANS FOR TURBINE BLADES Filed Jan. 25, 1934 4 Sheets-Sheet 3 D66. 24, F LJUNGSTRQM FASTENING MEANS FOR TURBINE BLADES Filed Jan. 25, 1954 4 Sheets-Sheet 4 Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE Aktiebolaget Spontan, corporation of Sweden Stockholm, Sweden, a

Application January 25, 1934, Serial No. 708,300 In Germany February 3, 1933 18 Claims. (Cl. 25377) This invention relates to that type of steam or gas turbines wherein the moving blades are fastened in grooves which extend obliquely across the periphery of the blade carrier, the object being to provide improved means for fastening blades of this character to the blade carrier.

It is customary, in this type of turbine, to dispose the blade grooves in the turbine disks-or carrier rings obliquely across the periphery in such manner that the grooves cut through or terminate in at least one side of the blade carrier, a construction which involves a subdivision of the material in the periphery of the disk or ring and thereby tends to insecurity and weakness of the blade carrier. This is also true where the obliquely disposed blade grooves are cut in specially provided raised portions on the supporting rim, because in both cases the outer peripheral portions of the blade carrier through which the grooves extend have to be supported by its inner portions. This requires a correspondingly larger, that is to say heavier, blade carrier in order to "obtain suiiiclent strength, a condition, however, which it is desired to avoid because of the resultant increased action of centrifugal force as well as for other reasons.

This difiiculty is obviated by means of the present invention whereby the simple production of a very light and stable turbine construction is made possible by causing both ends of the blade grooves to merge gradually into the rotatable peripheral surface of the blade carrier, so that successive, peripherally spaced sections through the carrier taken on radial planes show a constant gradual cross sectional change. Thus, the side surfaces of the blade carrier are not cut by the blade grooves, as in the case of prior grooves which extended to the sides. As a result of this, and of the constant change in cross section, a high degree of solidity and strength is imparted to the blade carrier.

The invention will be described in greater detail, referring to Figs. 1-20 of the accompanying drawings, in connection with so-called curved blades such as are disclosed, for example, in U. S. Patents Nos. 1,897,172 and 1,942,608. The invention is of particular advantage in connection with blades of this type. However, it is not limited to this type since it may obviously be applied to ordinary turbine blades, in so far as the blade carriers are provided with peripheral fastening grooves for moving blades disposed bliquely across the periphery of the blade carrier. Further features and advantages of the' invention will be apparent from the description of the illustrative embodiments.

Correlated Figs. 1-5 show various views and cross sections through a portion of a blade carrying ring having blade fastening means in accordance with the invention.

Fig, 6 illustrates the method of production of the fastening grooves.

Figs. '7 and 8 are two views of a portion of a blade rim provided with two-part curved blades.

Figs. 9 and 10 are enlarged views, in accordance with the invention, of fastening means for a compound curved blade such, for example, as that of Figs. 7 and 8.

Correlated Figs. 11-13 are various views of a portion of a blade rim having dished arched curved blades and fastening grooves in accordance with the invention.

Correlated Figs. 14-20 are various views and cross sections through a portion of a blade carrying ring, and illustrate fastening means in accordance with the invention, this construction having a particularly effective oscillation damping effect on curved blades.

In the drawings, reference numeral 2 designates a portion of a blade carrying ring provided with fastening grooves 3, constructed in accordance with the invention, said grooves being dovetail shaped in cross section (as shown in Figs. 3-6, 10 and 20) and being adapted to anchor the ends of curved blades which extend, preferably in the form of a catenary curve, between the carrier rings and which may be rigid or yieldable in-construction. The said blades may, for example, consist of thin sheet metal or the like, and may be engaged in the grooves 3 by means of straight ends which are enlarged to form blade roots 4. The bladerings 2 are interconnected in conventional manner by means of struts 5, which are in part supported by intermediate rings 6 (Figs. 7, 12, 15, 16).

Blade carrier ring 2, which may of course constitute part of a disk or drum, terminates, radially and outwardly thereof, in a. surface I which may be cylindrical or conical. Said blade grooves 3 are preferably cut to a, chord of the circle defining the periphery of the carrier rim, and therefore they merge gradually into peripheral surface I, as may clearly be seen from Fig. 1. This merging of the grooves into the peripheral surface is, as above stated, of great significance as far as the solidity and strength of the carrier ring is concerned. If, as in prior constructions, the grooves terminated in the lateral surfaces of the carrier ring, the outer portion of the carrier ring would thereby be rendered discontinuous in the direction of the periphery. The outer portions would then no longer be self supporting and would have to be supported by the inner portions of the ring or other rotatable blade support, so that a correspondingly heavier construction would result. If, on the other hand, the grooves terminate in the peripheral surface of the rim, a constant and gradual variation in the cross section is obtained, so that the strength and solidity of the rim is considerably improved.

in comparison with prior constructions, and the peripheral portions of the rim are self supporting.

The merging of the fastening grooves in the outer peripheral surface I of carrier rim 2, as shown in Fig. 1, is facilitated by the character of the narrow blade roots 4 which overlap each other at a small blade angle. This makes it easily possible to select a width of blade rim such that the grooves terminate in the peripheral surface and not in the lateral surfaces of the rim. The aforementioned curved blades are particularly adapted to fastening means in accordance with the invention, since they may be made with very narrow roots and with comparatively small blade angles, which makes it possible for the grooves to terminate in the peripheral surface of the carrier ring even if the rim is relatively narrow.

The construction and arrangement of the blade grooves is clearly apparent from Figs. 3-5, which represent cross sections on lines 33, 4-4 and 5-5 of Fig. 2. These views also show that the blade root 4 does not entirely fill groove 3, which makes it possible easily to insert and withdraw the blades. For example, if a blade is to be removed, it is first pressed downwardly into the groove, whereby it is liberated and can then be easily withdrawn. Figs. 2 and 3 show packing or looking pieces 8 packed, in conventional manner, into the blade grooves at both ends of the blade root 4. These packing pieces prevent longitudinal displacement of the blades in the grooves, serving therefore to retain the blades in proper position therein.

Fig. 6 shows a suitable method of making the fastening grooves 3. It is preferred to first cut a straight groove having parallel walls perpendicular to the outer surface 1. Then, as the drawings show, the dovetail configuration of the groove is produced in two operations by means of suitable inclined cutters 9. In this connection, the cutters may be of such shape that the resultant inner portion of the groove is semicircular, which is advantageous from the standpoint of solidity. It is apparent from the drawings that, as a result of the inclination of the cutters B, the cross section of the blade groove is somewhat enlarged at the mouth thereof. A saving in material, that is to say in weight, may be effected by removing the material which has been rendered ineffective as a support for the blade because of the enlargement and widening of the mouth of the groove. This may be accomplished, for instance, by making the ends of the effective blade holding portion of the groove substantially coincident with the starting points or lateral extremities of a hollow rabbet groove extending around the blade simplicity, but one double curved blade 10, i I being shown, and only the sections through carrier rings 2 and '8 parallel to a strut 5. One edge 12 of blade H is disposed, along the entire length thereof, in contact with the inner surface of blade 5 l0, whereby the two blade elements 10 and II overlap to a certain extent. A composite blade of this character is advantageous, among other things, in that the resultant double arched form of the blade produces considerable rigidity. 10

Fig. 10 is a section taken along X-X of Fig. 9. The two views show blade halves l3 and 14, which are disposed at an inclination within groove 3, and retained in the dovetail shaped groove by means of wedge-shaped filler pieces 15. Packing 15 pieces 8 are again used to retain the blades longitudinally of the groove.

Correlated Figs. 11-13 show, as another embodiment, the fastening of dished arched curved blades l6, which form the subject matter of the 20 application of Fritz Alexander Wettstein. Serial No. 708,290, filed of even date herewith, in grooves 3 which are formed in accordance with the invention. Blades I6, which are preferably made of ground sheet metal of suitable thickness, 25 are converted into dished form by pressing, drawing over a form, or by hammering. This dished configuration is indicated in the drawings by means of lines l8, which represent intersections of the blades with planes passing through the 30 axis of rotation; also by lines l9, which represent intersections of the blades with planes parallel to the plane of the drawing of Fig. 13; and finally, by lines 20, in Fig. 11, which represent intersections of the blades with planes perpendicular to 35 the axis of rotation. In the illustrated embodiment, the double curvature of the blades disappears gradually toward the blade ends, so that the blades may be inserted into rectilinear grooves 3.

Using the fastening arrangement of the invention, it is possible to make the blade grooves 3 and blade roots 4 very long, so that a very small number of the double curved blades need be used. The invention also makes it possible to extend blade roots in adjacent grooves beyond each other in overlapping relationship, as shown in broken lines 2| in Fig. 11. This results in a very effective damping of the oscillation of sheet metal blades, as will be explained in greater detail in connection with Figs. 14-20.

It is of extreme importance in the construction of high speed and high load radial admission turbines, e. g., 140,000 kw. at 3,000 revolutions per minute, to maintain the weight of the rotating mass as small as possible. This is made possible by the use of curved blades of the aforementioned type, such as described, for example, in U. S. Patents Nos. 1,897,172 and 1,942,608. These curved blades need be but about 1 mm. thick in the middle thereof, the thickness increasing three to five fold toward the ends. As a result of the small wall thickness thereof, blades of this type may safely be exposed to a certain oscillation. On the other hand, however, the blades, because of their light weight, are sensitive to oscillation impulses which are due to fluctuations in the regularity of flow of the steam or gas through the turbine.

With curved blades. which overlap laterally to a greater or less extent without, however. touching each other, the passageway for outwardly flowing steam or gas which is formed between the overlapping blade portions is subjected to a periodic variation in the flow velocity, as soon as the oscillations of the blades cause a transverse movement of this portion of the blades. The alternate narrowing and widening of the flow passageway ,eifects variations in velocity of the steam, uses up energy from the blade oscillations, and therefore produces an effective damping action on the blade oscillations so that theamplitude thereof may be reduced and becomes dependent upon the magnitude of the impulse and on the damping. It is obvious that the damping action In accordance with Fig. 14, the front and-rear blade edges do not form fiat curves, but are doubly curved in such manner that, in side view, the front edge 22 is concave and the rear edge 23 is convex. These may be produced, for example, by forming the blade, spread out in a single plane as shown in Fig. 17, with arcuate front and rear edges 22 and 23. The double curved configuration is advantageous in that the catenary are produced by centrifugal force is somewhat narrower at the front edge'22 than at the rear edge 23 of the blade (see Fig. 16) which is favorable to the shape of the passageway defined between the blades. This provides means, independent of the blade length and the angle of fastening, for influencing the form of the catenary line in the direction most favorable to the conditions of flow, even in the case of thin sheet metal blades.

Figs. 18 and 19 show details of Figs. 14 and 15 on an enlarged scale. Fig. 20 is a section along line 2020 of Fig. 18.

Although the invention is of particular advantage in connection with curved blades of the character above described, the advantages desclibed in general in the introduction apply also to fastening arrangements in accordance with the invention in connection with other forms and types of blades.

It will be obvious that the invention is not limited to the construction shown in the drawings, but is capable of a variety of mechanical embodl merits. While the drawings illustrate several preferred forms of the invention, it is to be expressly understood that they are for the purpose of illustration only and are not to be construed as defining the limits of the invention since various changes, which will now be apparent to those skilled in the art, may be made in the form, details of construction and arrangement of the parts without departing from the inventive concept. Reference is therefore to be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. In a turbine, axially spaced blade carrying members, each of said members having a series of grooves formed in the circumferential portion thereof, said grooves lying wholly within the confines of said members with their ends merging gradually into the circumferential surfaces thereof whereby the peripheries of the blade. carrying portions of said members have uninterrupted lattial portion thereof oblique to both the plane and axis of rotation of said member, said grooves lying wholly within the confines of said members with their ends merging gradually into the circumferential surfaces thereof whereby the pe- 10 ripheries of the blade carrying portions of said members have uninterrupted lateral edges, and

a series of curved blades spanning said members and having their ends fastened in said grooves.

3. In a turbine, axially spaced blade carrying 15 members, each of said members having a series of grooves formed in the circumferential portion thereof, said grooves lying wholly within the confines of said members with their ends merging gradually into the circumferential surfaces there- 20 of whereby the peripheries of the blade carrying portions of said members have uninterrupted lateral edges, said grooves being dovetail shaped in cross section, and a series of blades spanning said members and having enlarged roots formed 25 on the ends thereof, said enlarged roots being housed within said grooves and thereby anchoring said blades to said carrying members.

4. In a turbine, axially spaced blade carrier rings, each of said rings having a series of grooves 3 formed in the periphery thereof oblique to both the plane and axis of rotation of said ring, said grooves lying wholly within the confines of said rings with their ends merging gradually into the peripheral surfaces thereof whereby the periph- 35 cries of the blade carrying portions of said members have uninterrupted lateral edges, said grooves being dovetail shaped in cross section,- and a series of sheet metal blades extending in catenary form between said carrier rings, said blades having 40 enlarged roots formed on the ends thereof and housed within said grooves, thereby anchoring said blades to said carrier rings.

5. In a turbine, axially spaced blade carrier rings, each of said rings having a series of grooves 45 formed in the periphery thereof oblique to both the plane and axis of rotation of said ring, said grooves lying wholly within the confines of said rings with their ends merging gradually into the peripheral surfaces thereof whereby the periph- 50 cries of the blade carrying portions of said members have uninterrupted lateral edges, said grooves being dovetail shaped in cross section, and a series of curved blades of dish-like configuration extending between said carrier rings, said blades having enlarged roots formed on the ends thereof and housed within said grooves, thereby anchor.- ing said blades to said carrier rings.

6. In a turbine, axially spaced blade carrying members, each of said members having a series 60 of grooves formed in the circumferential portion thereof, said grooves lying wholly within the confines of said members with their ends merging gradually into the peripheral circumferential sur-- faces thereof whereby the peripheries of the blade 05 carrying portions of said members have uninterrupted lateral edges, blades spanning said members and having their ends housed within said grooves, and means for locking said blade ends in their proper positions within said grooves.

7. In a turbine, a blade carrying member having a series of grooves formed in the circumferential portion thereof, said grooves lying wholly within the confines of said member with their ends merging gradually into the circumferential surfaces thereof whereby the peripheries of the blade carrying portions of said member have uninterrupted lateral edges, and blades mounted on said member and having their ends housed within said grooves.

8. In a turbine, axially spaced blade carrying members, each of said members having a series of grooves formed in the periphery thereof, said grooves lying wholly within the confines of said members with their ends merging gradually into the peripheral surfaces thereof whereby the peripheries of the blade carrying portions of said members have uninterrupted lateral edges, and a series of curved blades extending. between said carrying members with their ends fastened in said grooves, said grooves being so constructed and arranged that the anchored ends of adjacent blades overlap each other by a predetermined amount.

9. In a turbine, axially spaced blade carrying members, each of said members having a series of grooves formed in the periphery thereof, said grooves lying wholly within the confines of said members with their ends merging gradually into the peripheral surfaces thereof, and a series of curved blades extending between said carrying members with their ends fastened in said grooves, said grooves being so constructed and arranged that adjacent blades overlap each other by a constant amount throughout the span between said members.

10. In a turbine, axially spaced blade carrying members, each of said members having a series of grooves formed in the periphery thereof, said grooves lying wholly within the confines of said members with their ends merging gradually into the peripheral surfaces thereof, and a series of curved blades extending in catenary form between said carrying members with their ends fastened in said grooves, each of said blades being formed from a fiat metal strip having arcuate front and rear edges which, when the blade assumes a catenary form, become curved in side view.

11. In a turbine, axially spaced blade carrying members, each of said members having a series of grooves formed in the periphery thereof, said grooves lying wholly within the confines of said members with their ends merging gradually into the peripheral surfaces thereof, and a series of curved blades extending between said carrying members with their ends fastened in said grooves, said grooves being so constructed and arranged that each groove houses the ends of two blades in overlapping relationship, the configuration of said overlapping blades being such that one side edge of one blade is in contact with a surface of the other blade throughout the span between said carrying members, thereby forming a composite curved blade.

12. In a turbine, axially spaced blade carrying members, each of said members having a series of grooves formed in the periphery thereof, said grooves lying wholly within the confines of said members with their ends merging gradually into the peripheral surfaces thereof, a series of curved blades extending between said carrying members with their ends fastened in said grooves, saidgrooves being so constructed and arranged that each groove houses the ends of two blades in overlapping relationship, and packing means within said grooves for maintaining each pair of overlapping blade ends'in proper position.

13. In a turbine, axially spaced blade carrying members, each of said members having a series of grooves formed in the periphery thereof oblique to both the plane and axis of rotation of ,said member, said grooves lying wholly within '6 the confines of said members with their ends merging gradually into the peripheral surfaces thereof, a series of blades spanning said members and having their ends anchored in said grooves, said grooves being longer than the associated blade ends, means for locking said blade ends in positions intermediate the ends of said grooves, and a relatively shallow, annular rabbet groove extending around the periphery of each of said members, the boundaries of said rabbet 15 grooves passing through the extremities of the blade holding portions of said first mentioned grooves.

14. In a turbine of the type wherein the moving blades are secured at their ends to axially spaced rotatable blade carrying members, means for fastening said blades to said members comprising enlarged roots formed on the ends of said blades, and grooves formed in the circumferential portions of said members and adapted to receive said blade roots, said grooves lying wholly within the confines of said members with their ends merging gradually into the circumferential surfaces thereof, whereby the peripheries of the blade carrying portions of said members have uninterrupted lateral edges and successive peripherally spaced sections through said members taken on radial planes show a constant gradual cross sectional change. 35

15. In a turbine of the type wherein the moving blades are secured at their ends to axially spaced rotatable blade carrying members, means for fastening said blades to said members comprising enlarged roots formed on .the ends of 0 said blades, grooves formed in the circumferential portions of said members and adapted to receive said blade roots, and packing means within said grooves for maintaining said blade roots in proper position therein, said grooves lying wholly within the confines of said members with their ends merging gradually into the circumferential surfaces thereof, whereby the peripheries of the blade carrying portions of said members have uninterrupted lateral edges and successive peripherally spaced sections through said members taken on radial planes show a constant gradual cross sectional change.

16. In a turbine of the type wherein the moving blades are secured at their ends to axially spaced rotatable blade carrying members by means of grooves oblique to both the planes and axis of rotation of said members, the formation of said grooves in such a manner that they lie wholly within the confines of the circumferential portions of said members with their ends merging gradually into the circumferential surfaces thereof and terminating short of the sides of said members, whereby the peripheries of the blade carrying portions of said members have .ofsaidgroovesinsuchamannerthattheyare'll dovetail shaped in cross section, are rectilinear in a longitudinal direction and lie wholly within the confines of the circumferential portions of said members with their ends merging gradually into the circumferential surfaces thereof and terminating short of the sides of said members, whereby the peripheries of the blade carrying portions of said members have uninterrupted lateral edges and successive peripherally spaced sections through said members taken on radial planes show a constant cross sectional variation without abrupt change.

18. In a turbine, axially spaced blade carrying members, each of said members having a series of grooves formed in the circumferential portion thereof, said grooves lying wholly within the confines of said members with their ends merging gradually into the circumferential surfaces thereof, whereby the peripheries of the blade carrying portions of said members have uninterrupted lateral edges, and a series of curved blades extending between said carrying members with their ends fastened in said grooves, said grooves being so constructed and arranged that adjacent blades have predeterminately spaced overlapping relationship with each other adjacent the end portions of said blades.

FREDRIK LJUNGSTRGM.

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