Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
1995-06-07
2001-06-05
Hail, III, Joseph J. (Department: 3205)
Metal founding
Process
Shaping liquid metal against a forming surface
C134S152000, C134S16600C
Reexamination Certificate
active
06241000
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the removal of a core, such as a ceramic core, from inside of a casting, such as an investment casting.
BACKGROUND OF THE INVENTION
In the manufacture of gas turbine engine components, such as gas turbine engine blades and vanes, an appropriate alloy, such as a nickel or cobalt based superalloy, is investment cast in a ceramic investment mold. One or more ceramic cores may be present in the ceramic investment mold in the event the cast component is to include one or more internal passages. For example, gas turbine blades and vanes for modern, high performance gas turbine engines typically include internal cooling passages extending through the airfoil and root portions and through which passages compressor bleed air is conducted to cool the airfoil portion during engine operation. In this event, the ceramic core positioned in the investment mold will have a configuration corresponding to the internal cooling passage(s) to be formed through the airfoil and root portions of the cast turbine blade or vane. The blade or vane component may be cast by well known techniques to have an equiaxed, columnar, or single crystal microstructure.
In the past, the ceramic core has been removed from the investment cast component by an autoclave technique or an open kettle technique. One autoclave technique involves immersing the cast component in an aqueous caustic solution (e.g. 45% KOH) at elevated pressure and temperature (e.g. 250 psi and 177° C.) for an appropriate time (e.g. 4-10 hour cycles) to dissolve the core from the casting. U.S. Pat. Nos. 4,134,777 and 4,141,781 disclose autoclave caustic leaching of yttria ceramic cores and beta alumina ceramic cores from directionally solidified superalloy castings. An exemplary open kettle technique involves immersing the cast component in a similar aqueous caustic solution at ambient pressure and elevated temperature (e.g. 132° C.) with agitation of the solution for a time (e.g. 90 hours) to dissolve the core from the casting. These core removal techniques are quite slow and time-consuming.
SUMMARY OF THE INVENTION
The present invention provides method and apparatus for removing a core from inside a casting in a relatively rapid manner as compared to the aforementioned autoclave and open kettle techniques. One embodiment of the method comprises disposing the casting and a fluid spray means, such as for example only a fluid spray nozzle, in a manner to expose a region of the core to a core dissolving fluid discharge of the fluid spray means, supplying a core dissolving fluid to the fluid spray means for discharge toward the exposed core region, and discharging the fluid from the fluid spray means to contact the core region and remove core material therefrom and progressively from further regions of the core within the casting as they become exposed as core material is progressively removed.
The discharge of fluid from the fluid spray means can be interrupted periodically to allow dissolved core material and spent fluid to drain from inside the casting or, alternately, the casting and fluid spray means can be relatively moved so that the casting can drain to this same end at a drain location apart from the fluid spray means. In a particular embodiment of the invention, the casting and a plurality of fluid spray nozzles are relatively moved so that the casting is moved from one fluid spray nozzle to the next to receive core dissolving fluid at each nozzle and to drain dissolved core material and spent fluid when moved to a drain location between the nozzles. A plurality of castings can be carried on a linearly movable carrier, such as a transport conveyor, or on a rotatable carrier, such as a carousel, past a plurality of fixed or stationary core dissolving fluid spray nozzles to remove the core from each casting.
In practicing the invention to remove a ceramic core from turbine blade or vane investment castings having an airfoil portion and root portion with the core exposed at the root portion, the castings and one or more core dissolving fluid spray means, such as fluid spray nozzles, are positioned so that a caustic solution (e.g. 45% KOH) at elevated temperature (e.g. 100 to 150° C.) and pressure (e.g. 50 to 450 psi) is supplied to the nozzles and discharged at the exposed core region at the root portion to dissolve the core from the root portion progressively through the airfoil portion in a relatively short time (e.g. typically 1 to about 10 hours) depending upon the configuration of the casting and core therein. One or more additional core dissolving fluid spray nozzles may be positioned to discharge core dissolving fluid at the blade or vane casting tips where another region of the core may be exposed at a tip plenum cavity of the castings.
The invention will be described in more detail by the following drawings and detailed description.
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Das Reingen von Druckgub in Wäbrigen Lösungenals Altermativr zur Reingung mit Lösemittein H. D. Heidenblutt, Glesserei 75, pp. 110-113, 1988.
Hochdruck-Nabentkernungs maschine für Glesserei 73, pp. 515-516, 1986.
Conroy Patrick L.
McRae Michael M.
Pierson Harold C.
Hail III Joseph J.
Howmet Research Corporation
Lin I.-H.
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