Cooled Turbine Rotor And Its Manufacture

Abstract

An integral cast turbine rotor wheel includes a disk and porous blades extending from the disk and into the rim of the disk, the disk defining cooling air entrance ports communicating with the porous blades so that cooling air may be circulated through them. The method of manufacture of the wheel includes providing cores defining air ports and blades, the blade portion of each core being porous, placing the cores in a mold shaped to conform to the wheel and pouring metal to define the cast body. The cores are then removed and any necessary machining of the wheel is performed.

Description

My invention relates to turbine wheels and the like and to a method of manufacturing them; it is particularly directed to unitarily cast wheels having porous blades which may be cooled by air circulated through the blades. The primary object of the invention is to provide a wheel, particularly one for small turbines, which may be economically manufactured and which is well adapted to stand up to the rigors of service in a gas turbine engine. The structure and method of manufacture may have other applications, however.

It is well known that turbine rotor elements including a wheel or disk and blades cast integral with the disk are an article of commerce. So far as I am aware, however, such wheels have not included blades of a porous nature.

Certain United States patents may be mentioned as background of the detailed description of my invention. Porous blades for turbomachines are disclosed or suggested by Smith et al. U.S. Pat. No. 2,665,881, Jan. 12, 1954, Erwin U.S. Pat. No. 2,720,356, Oct. 11, 1955, and Endres U.S. Pat. No. 2,970,807, Feb. 7, 1961. Markus et al. U.S. Pat. No. 3,523,766, Aug. 11, 1970, is directed to a process for making porous cast structures. Paul U.S. Pat. No. 2,611,161, Sept. 23, 1952, Bly et al. No. 3,635,791, Jan. 18, 1972, and McLaren U.S. Pat. No. 3,648,756, Mar. 14, 1972, are directed to the casting of turbine wheels or other bladed turbine structures.

While the practice of my invention involves the use of known technology in carrying out the manufacture of the rotor element, it involves a new combination of steps effective to produce a product which I believe to be new.

The nature of my invention and its advantages will be clear to those skilled in the art from the succeeding detailed description and accompanying drawings of the preferred embodiment of the invention.

FIG. 1 is a sectional view of a turbine rotor element taken on a plane containing the axis of rotation thereof.

FIG. 2 is an enlargement of a portion of FIG. 1 with seal rings mounted on the rotor.

FIG. 3 is an elevation view taken on the plane indicated by the line 3--3 in FIG. 2.

FIG. 4 is an axonometric view of a core element.

FIG. 5 is a transverse sectional view of a mold for casting the turbine rotor element.

Referring first to FIG. 1, a turbine rotor element or wheel 2 comprises a disk 3 having a rim portion 4. The wheel bears an annular cascade of blades 6 extending from the rim of the wheel. The wheel may be of conventional overall outline and may be suitably machined for connection to a shaft (not shown) or connection to other turbine disks to form a multistage rotor.

As indicated in FIGS. 2 and 3, seal rings or seal plates 7 and 8 are mounted in circumferential grooves 10 and 11 machined in the outer face of the rim 4. This is a somewhat schematic showing of the seal rings, but the details of such are well known to those skilled in the art and are immaterial to my present invention.

The disk, including the rim, is substantially all a solid, that is, non-porous structure, but each blade 6 includes an airfoil portion 12 and a base portion 14 extending into the rim, the portions 12 and 14 being porous. A cooling air port 15 extends into the rim from the forward face of the wheel under the base portion of each blade. As shown, the cooling air port extends to the rear face of the rim. Drilled or cast passages 16 through the rim at the forward side of disk 3 admit cooling air behind seal plate 7 to the ports 15, and thus into the porous blade base 14 and on into the porous airfoil portion 12 from which it is discharged through the porous blade structure into the hot gas stream flowing past the blades. This is known as transpiration cooling, the cooling being effected by the flow of the cooling air through small pores in the structure and out through the surface, where it additionally forms a film of cooler air to isolate the blade to some extent from the hot motive fluid.

Means for conducting cooling air to the face of the wheel need not be described, since such is very well known and is widely employed in turbine engines. The flow of the cooling air through the rotor may be effected by a pumping action due to centrifugal force or to a difference in pressure between the cooling air supplied and the motive fluid passing the turbine, or in any other suitable manner.

It should be noted that the base portion 14 of the blades preferably terminates at some small axial distance from the forward and rear face of the rim so that the forward and rear face of the rim is solid, with the blade base portions constituting plugs of porous material integral with the solid portion of the rim extending into the periphery of the rim.

It will be apparent to those skilled in the art that the structure described is very simple and suitable one for a turbine engine where it is desired to cool the blades to make use of higher temperature motive fluid than would otherwise be possible. It is particularly suited to small turbines in which the economy of casting the entire rotor element in one piece may be a very important consideration in the economic suitability of a gas turbine engine.

FIGS. 4 and 5 illustrate steps in the manufacture of the rotor element.

FIG. 5 shows more or less schematically a mold which may be employed in a casting process following known technology as exemplified by the teachings of the patents referred to above. The mold 22 includes a drag 23 and a cope 24 which define a mold cavity 25 into which metal is introduced through a sprue 26. The mold may be ceramic, and it may be prepared by investment of a suitable permanent or disposable pattern. The mold cavity 25 has the overall contour or form of the rotor element prior to any machining which may take place after casting. It defines pockets 27 which are of the form of the portion of the blade which projects from the rotor rim. A blade core 28 is disposed in each pocket 27.

The blade core (FIG. 4) comprises a porous portion 30 having the form of the blade and a solid portion 31 having the form of the cooling air port 15. The porous portion is of a fibrous nature such that, when metal is cast into and penetrates the porous portion of the core and the core is subsequently dissolved out by suitable agent, the blade portion is relatively full of small capillary passages which intercommunicate. The solid base part 31 of the core 28 may, of course, be formed by any usual technique of forming of solid ceramic bodies. The porous blade portion 30 might be provided by sintering together granules of suitable size, much as porous objects are produced by powder metallurgy. It might also be made by dipping a polyurethane foam pad of proper shape into a leachable ceramic such as that disclosed in U.S. Pat. No. 3,576,653 of Miller et al., Apr. 27, 1971, and then squeezing out the excess ceramic. The foam is dipped and squeezed until the polyurethane foam fibers are completely covered with the ceramic. The foam may then be air dried and fired to gasify the polyurethane and leave a ceramic foam. The porous and solid parts of the blade 28 may then be united by a suitable cement.

The manner in which the cores 28 are disposed in mold 22 will be obvious. Once the mold is assembled with the cores in place, the pouring of the metal may follow the usual casting processes, such as vacuum casting preferably. The wheel is preferably of a high nickel base alloy, for example, Inco 713C (trademark) or Mar M246 (trademark). After the metal is solidified and cooled, the mold is disassembled, the casting is removed, and the ceramic cores 28 are leached out of the metal, after which any necessary machining is accomplished in the usual manner.

It should be apparent to those skilled in the art that the described method is highly suitable for the economical and feasible production of the turbine rotor element described and that the rotor element is particularly suited to the requirements of gas turbine engines.

The term "disk," as used in the appended claims, is intended to mean any annular body mounting the blades.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.

Claims

I claim:

1. A bladed turbine rotor element comprising, in combination, a solid disk having a rim portion and an annular row of porous blades integral with the disk, each blade including a porous airfoil portion projecting from the rim and a porous base portion extending into the rim; the rim defining circumferentially spaced air entrance ports each coummunicating with the exterior of the disk and with the base portion of a blade; the said rotor element being unitarily cast as an integral piece.

2. A bladed turbine rotor element comprising, in combination, a solid disk having a rim portion and an annular row of porous blades integral with the disk, each blade including a porous airfoil portion projecting from the rim and a porous base portion extending into the rim; the rim surrounding the base portion and defining circumferentially spaced air entrance ports each communicating with the exterior of the disk and with the base portion of a blade; the said rotor element being unitarily cast as an integral piece.

3. A method of manufacturing an integral bladed turbine rotor element with a solid disk, porous blades, and air entrance ports in the disk communicating with the blades, the method comprising providing a mold with a cavity corresponding in form to the rotor element; providing cores each corresponding in form to at least one blade and a corresponding port, each core having a porous portion corresponding to the blade and a solid portion defining the port; disposing the cores in place in the mold; and pouring molten metal into the mold so as to fill the pores in the porous portions of the core and fill the remainder of the mold cavity around the solid portion of the cores and the base portion of the porous blades to provide the solid disk integral with the blades; removing the cast element from the mold; and removing the core material from the blades and the ports to leave porous blades extending from the disk and into the disk communicating with the ports.