US2958505A

US2958505A - Turbine bucket blades

Info

Publication number: US2958505A
Application number: US775330A
Authority: US
Inventors: Robert G Frank
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-11-20
Filing date: 1958-11-20
Publication date: 1960-11-01
Anticipated expiration: 1977-11-01

Description

Nov. 1, 1960 R. e. FRANK TURBINE BUCKET BLADES 2 Sheets-Sheet 1 Filed Nov. 20, 1958 M L WM m 'l l' il INVENTOR. X085? 6'. F/FM'A W4. A? Maw NOV. 1, 1960 R, G, FRANK 2,958,505

TURBINE BUCKET BLADES Filed Nov. 20, 1958 2 Sheets-Sheet 2 46 JNVENTOR.

fii 2,958,505

Patented Nov. 1, 1960 TURBINE BUCKET BLADES Robert G. Frank, Cincinnati, Ohio, assignor to the United v Filed Nov. 20, 1958, Ser. No. 775,330

2 Claims. (Cl. 253-39.15)

The present invention relates generally to turbine blades or buckets for use under high temperature conditions, and as illustrated herein, relates more particularly to turbine blades or buckets having cooling passages therein.

The high temperatures incident to the combustion of jet and rocket fuels has made it necessary to form turbine blades from metals or other materials which are substantially free from oxidation. However, new designs in reaction motors have resulted in highly increased inlet temperatures which are destructive of previously known turbine blades. Under earlier conditions the use of molybdenum and molybdenum alloys gave satisfactory results and destruction of the surfaces of the turbine blade due to high temperature oxidation was not a problem. However, gas temperatures may now range from about 2000 F. to about 2600 F. and solid molybdenum, molybdenum alloys and ceramic coated molybednum and molybdenum alloys corrode to such an extent that virtual destruction of the turbine blades may result.

It has been discovered, however, that hollow air cooled blades fabricated from conventional materials may be used in aircraft jet turbines. The strength of these blades or buckets is limited because of the inherent low strength of the materials of which the buckets are formed. It was found, however, that if the blades were fabricated from molybdenum wire clad or plated with a material highly resistant to oxidation would have sufficient strength, be of light weight and could be readily fabricated while still protecting the blades from oxidation at temperatures ranging from about 2000 F. to about 2600 F.

One object of the present invention, accordingly, is to provide turbine blades which are oxidation resistant at relatively high combustion temperatures. To this end and as illustrated, the invention contemplates the use of molybdenum wire clad or plated with an oxidation resistant material and encased in a sheath of oxidation resistant material.

With the above and other objects in view the invention will now be described with particular reference to the accompanying drawings in which:

Fig. 1 is a view in elevation of one form of turbine bucket embodying the present invention;

Fig. 2 is a view in section taken along the lines II-II of Fig. 1;

Fig. 3 is a view in section similar to that shown in Fig. 2 but illustrating another embodiment of the invention;

Fig. 4 illustrates another embodiment of the invention but before the parts of the sheet are secured together at their leading and trailing edges;

Fig. 5 illustrates another form of the invention with the sheath in the fiat; and

Fig. 6 is a view of the construction shown in Fig. 5 before the leading edges of the turbine bucket are welded together.

The purpose of the present invention is to provide aircooled turbine buckets which are able to withstand the high temperatures and high strains incident to the use of modern fuels in turbojet engines. Molybdenum wire or wires fabricated from tungsten, columbium, or nickel base alloys could be used so long as the intended operating temperature remains below the recrystallization temperature' of the material.

The present invention contemplates the use of high strength-high temperature wire as a supporting frame having suificient strength to withstand the high strains to which the buckets are subjected during use. Preferably molybdenum wire is used but any of the wire materials referred to just above will be satisfactory.

The construction shown in Fig. 1 comprises a root portion It) and a bucket or airfoil section 12. The root portion 10 is of usual shape and construction and need not be described in further detail herein. The airfoil section 12 is seated in a suitable shaped recess 14 in the root portion 10 and in which the completed airfoil is suitably brazed or welded. The airfoil section 12, as illustrated in Fig. 2, is composed of a plurality of rods or wires 16 of varying size which are coated with a suitable brazing alloy. The coated wires 16 are arranged parallel and contiguous to each other along the lateral center line of the blade and are assembled within a suitable sheath 18 formed preferably of chromium plate.

The shield 18 and the wires 16 assembled therewith are placed in an autoclave to fuse the brazing alloy to secure the wires 16 to each other and to the sheath 18 as shown at 20 and 22, respectively, in Fig. 2. It is to be noted that only sufiicient brazing alloy is used to permit the parts to be secured together without entirely filling the space be tween adjacent wires 16 and the sheath 18. Thus, a plurality of spaces 24 are provided which extend the entire length of the turbine buckets 12 and through which cooling air may be forced. It was previously stated that the root portion 10 was provided with a suitable shaped recess 14- in which the base portion of the airfoil section 12 is secured either by brazing or welding. There is provided an air duct 26 through which cooling air may be drawn and passed through the cooling passages 24.

The invention, however, is not limited to the modification shown in Fig. 2 since the central portion of the bucket 12 may be hollow and provided with an internal lining formed of wires 28 which are substantially uniform in diameter and are so closely spaced that they are substantially in contact with each other. The wires 28 are coated with a suitable brazing or welding alloy. The wires 28 are assembled and supported in a suitable jig or fixture to form an airfoil section such as shown in Fig. 3. The shaped wire section has placed thereover a suitable sheath 30' which fits closely against the wires 28. The assembled wires 28 and sheath '30, together with jig with which they are supported are placed in an autoclave to permit the brazing or welding alloy to be fused to secure the wires 28 to each other and to the inner surface of the chromium coated sheath 30. After the brazing or welding operation has been completed the assembly is removed from the jig and surplus lengths of wire are trimmed at the top and bottom end portions of the sheath 30.

The bucket 12, as constructed above, is then placed in a recess 14 and suitably secured in place by brazing or welding. The bucket 12 shown in Fig. 3 has a hollow interior portion 32 which communicates with the air duct 26 through which suitable air or other fluid may be passed to maintain the temperature of the bucket 12 substantially below the high temperature of the inlet gases of the axial flow turbine.

There are shown in Figs. 4, 5 and 6 two other forms of the invention, which, however, when assembled display a cross-sectional area similar to the one shown in Fig. 3. In the modification shown in Fig. 4, a sheath 34 is shaped to form a root section 36 and a bucket section 38. The bucket or airfoil section 38 is coated with a suitable braz- 3 ing or welding alloy and high strength molybdenum or other high temperature alloy wires are suitably brazed or secured to the inner surface of at least one side of the sheath 38. Preferably, both sides of the sheath 38 are provided with e1ose1yspaced1wires 40 which are arranged in an airfoil section substantially similar to that shown in Fig. 3. It is to be noted that the airfoil section itself is of substantial thickness at the root section 36 and tapers from the root section toward the outer end of the blade or airfoil section 38. After the wire 40 has been secured in position the assembled bucket is placed in a suitable jig or fixture and maintained in shaped position to permit the leading and following edges of the airfoil section to be secured together by suitable brazing or weld- As illustrated, the construction shown in Fig. 4 has a root section which differs from that shown in Fig. l, but it is apparent that the hub of the turbine wheel may be suitably shaped to receive the substantially cylindrical root portion shown in Fig. 4. v V The construction shown in Fig. 5 is somewhat similar to the construction shown in Fig. 4, except that the portions of the sheath 42 are formed in one section and in side by side relation so that the right hand portion of the sheath 42 may be folded over the left hand portion of the sheath 42 and suitably shaped to form an airfoil turbine bucket section.

The modification shown in Fig. 5 is provided with a series of wires 44 which are coated with suitable alloy and secured to the sheath 42 in the same manner that the wires 40 are secured to the sheath 38, except that the wires extend from the top to the bottom of the sheath and thus extend into the root section 46 as shown in Figs. 5 and 6. Here again, it maybe necessary only to provide one side of the. sheath with wires. However, preferably both sides of the sheath are provided with wires so that the airfoil section is similar to the construction shown in Fig. 3, rather than to the construction shown in Fig. 2, which would be the case when only one side of the sheath 42 was provided with wires. After the sheath 42 has been provided with properly positioned wires it is folded along the line 48 which may form either the leading or followingedge ofthe bucket blade and is then placed in a suitable jig or die to bring the other longitudinal edges of the bucket close together to permit them to be secured by suitable brazing or welding to form a turbine bucket having the airfoil contours as shown in Fig. 3. At the same time the root section 46 is curved inwardly at the lower end to form a root portion for securing the bucket to a suitable hub.

Having thus described my invention what I claim as new and desire to secure by Letters Patent of the United States is:

..1. A fabricated blade for an axial flow rotor comprising a hollow metal sheath of airfoil cross section, a series of round metal rods within said sheath arranged contiguously with their centers along the chord of said airfoil, said rods being of diameters td'siibstanuan fill said sheath, and means to secure 'said'rods to .each other and to said sheath at their points of contact thereby allowing 'voids at the interstices between adjacent rods and said sheath.

2. n A fabricated blade of airfoil cross section comprising a hollow metallic sheath of said airfoil cross section, a reinforcingsection; s'aid reinforcing section comprising a series of'contighous, round metal rods arranged within said sheath with their centers along the chord of said airfoil cross section, the end rods in said sheath being in intimate contact with said sheath and one adjacent rod, the remainder of said rods being in intimate contact with adjacent rods and with opposite surfaces of said hollow metallic sheath, and means for securing said rods and said sheath together to allow voids at the interstices between the rods and said sheath.

References Cited in the file of this patent UNITED STATES PATENTS