The invention relates to a hollow-cast casting, which provides at least one core opening that is caused by the production technique and which has a closure device that closes the core opening.
The production of high-precision castings requires stable support for casting cores within a casting mold. In the course of the casting operation, the so-called chaplets required for this leave openings in the walls of the casting, which in most applications represent undesired weakening points of the casting, but in particular also undesired leakage points. In this connection, reference should be made in particular to the production of cooled turbine blades, in the interior of which complexly configured air channels are fashioned and these channels have to be formed in a gastight manner in the turbine blade to avoid undesired coolant losses. To produce the internal structure of such blades, casting cores have to be fixed in a very precise and stable manner in the casting mold, fixing the casting cores, which are oriented essentially in the longitudinal direction of the blade, on two sides, i.e. on the side of the blade root and on the side of the blade head, by means of chaplets of relatively large dimensions, which in turn result in large core openings in the casting once casting has been completed, but these are not all desired for proper functioning of the casting. For example, in the case of a cooled gas turbine blade, openings of relatively large dimensions are desired at the blade root in order to feed cooling air into the interior of the blade or remove it again, but particularly openings at the blade head or end of the airfoil of the blade represent undesired openings through which harmful cooling air leakages occur. Subsequent closing of such core openings caused by the casting technique, particularly in the end region of the airfoil of the blade, requires great care and consideration for the operating conditions to which the blade is exposed. For instance, the closure must be made resistant to heating and to temperature changes and stable enough with respect to the centrifugal forces occurring in the case of moving blades.
On the one hand, it would be desirable with respect to production considerations to use chaplets that are as large as possible, which however leads to large core openings also occurring in undesired regions of the casting, but on the other hand there is the need for these very core openings of large dimensions to be reliably closed. The closure mechanisms that have become known in the relevant literature are problematic when used on turbine blades, which undergo high thermal loads: for example, it is proposed in DE 39 36 171 A 1 to close core openings by means of buildup welding. Here, however, there is the latent risk of the placed-on closure piece, which is connected to the casting by a welded connection, becoming detached from the casting and exposing the previously closed opening again. Resultant consequential damage, in particular in connection with moving blades closed in such a way in rotor arrangements of gas turbine installations, is considerable.
In the documents U.S. Pat. No. 2,821,323 and DE 44 34 139 C1, closure plugs driven axially into the core opening are proposed for closing the core openings, but the associated risk of detachment of the corresponding closure plugs caused by centrifugal force, possibly additionally assisted by differential thermal expansions occurring between the closure plug and the casting, cannot be eliminated.
To avoid possible operationally caused detachment of a closure plug referred to above from the core opening of a casting, preferably a rotating gas turbine blade, it is proposed in DE 199 05 887 C1 to introduce a closure piece that closes the core opening in the casting along a clearance which extends transversely in relation to the core opening to be closed within the casting. However, apart from the already existing core opening within the casting, such a measure requires further local removal of material from said casting, causing it to be mechanically weakened further.
The disclosure is directed to a hollow-cast casting, including at least one core opening and a closure device that closes the at least one core opening. The closure device can be inserted into the core opening axially in relation to the at least one core opening and provides at least one surface region which, in axial projection in relation to the at least one core opening can be made to abut a surface region of the casting that is facing toward the casting. The surface region of the casting lies radially outside a cross-sectional area predetermined by the core opening.
In a second embodiment, the disclosure is directed to a hollow-cast casting, including at least one core opening and a closure device that closes the at least one core opening. The closure device can be inserted into the core opening axially in relation to the core opening and provides at least one surface region which, in axial projection of the core opening, can be made to abut a surface region of the casting that is facing away from the casting. The surface region lies radially outside a cross-sectional area predetermined by the core opening.
Without restricting the general idea of the invention, the invention is described below by way of example on the basis of exemplary embodiments with reference to the drawing, in which:
a, 1b show a plan view of the opening contour of a core opening and a perspective side view of a closure device,
a, 2b, 2c, 2d show a plan view of the opening contour of a core opening and a multi-sided representation through an alternative closure device,
a, 3b, 3c show a plan view of a core opening and a representation of a closure device that can be divided into two halves,
a, 4b show a cross-sectional representation and an exploded representation of a closure device comprising a screw, a shim and a nut element,
a, 5b show a representation of a closure device in the form of a shaped disk with an assembly aid,
a-c show various views of a closure device in the manner of a grub screw,
a, 7b show a representation of a securing pin, and
a, 8b show a plan view and a cross-sectional representation of a closure device formed as a strip.
Introduction to the Embodiments
The invention is based on the object of forming a hollow-cast casting, which provides at least one core opening that is caused by the production technique and which has a closure device that closes the core opening, in such a way that, on the one hand, the risk of operationally caused detachment of the closure device from the casting can be eliminated and, on the other hand, the measures required for this do not in any way allow the casting to be weakened. In particular, the aim is to avoid additional structural weakening within the casting for the purpose of securely anchoring the closing means within the core opening of the casting.
The solution achieving the object on which the invention is based is set forth in the appended independent claims. Features that can advantageously develop the hollow-cast casting formed according to the solution are the subject of the dependent claims and are described in the further description, in particular with reference to the exemplary embodiments.
According to the solution, a hollow-cast casting, which provides at least one core opening that is caused by the production technique and which has a closure device that closes the core opening, is distinguished by the fact that the closure device can be inserted into the core opening axially in relation to the core opening and provides at least one surface region which, in axial projection of the core opening, can be made to abut a surface region of the casting that is facing toward the casting. As this happens, the closure device abuts a surface region of the casting that extends radially outside a cross-sectional area predetermined by the core opening.
The idea on which the invention is based concerns the closure of a core opening caused during production without at the same time weakening the region of the casting around the core opening by additional removal of material, a closure device being inserted axially into the core opening and ensuring that the core opening is closed off in a secure and gas-tight manner by a pressed connection. In a particularly preferred configurational variant of the hollow-cast casting according to the solution, the core opening and the closure device are formed in such a way that the core opening is closed and sealed by way of a bayonet closure.
As an alternative to the closure taking the form of a bayonet closure, a way in which the closure for a core opening can be obtained that is similarly effective and particularly simple is by providing a thread structure surrounding the core opening on the inner wall, with a screw means that can be brought into engagement with said structure, preferably in the form of a grub screw. Like the closure device formed above as a bayonet closure, this may likewise also be secured in the course of an additional material-bonded connection between the closure device and the casting, for example by a welded or brazed connection.
A further preferred configurational variant provides a closure device in the manner of a shaped disk, on one side of which a nozzle-like elevation is provided, the form and size of which are made to match the core opening volume that is radially enclosed by the core opening. The closure device is inserted into the core opening axially from inside, i.e. from the cavity enclosed by the casting, the nozzle-like elevation at least partially filling the core opening and the shaped disk lying against the inner wall of the casting that directly surrounds the core opening radially. There are, in principle, several possibilities for fixing a closure device formed in such a way in the core opening, for example by way of clamping, preferably in the form of a press fit, and/or by a welded or brazed connection. In particular with regard to the closure of core openings in the region of the tip of a moving blade, the centrifugal forces occurring act in a manner additionally assisting intimate closure of the core opening. Detachment of a closure device formed as a projecting shaped disk can be ruled out, with the centrifugal forces indeed acting with a closure-inducing effect on the closure device. Further details of a form this may take can also be taken from the description of actual exemplary embodiments.
A further alternative according to the solution for the closure of a core opening caused by the production technique in a hollow-cast casting, in which the core opening preferably has a rectangular opening cross section, provides as the closure element a strip-like means, preferably produced from metallic material, which, while undergoing deformation, can be pressed against an abutting surface adjoining the core opening on the casting in such a way that the core opening is closed off in a largely fluid-tight manner by the closure element, the closure mechanism being based on the intrinsic deformability of the strip-like closure element and the pressing force that can be produced thereby. Further details of this as well as with respect to the idea of the solution outlined above can be taken from an exemplary embodiment illustrated below.
a shows the plan view of a core opening 1, which is provided on the surface of a casting G. In particular, it should be assumed that the core opening 1 is provided on the surface on the end face of a moving or stationary blade of a rotary turbo-engine. The core opening 1 has in the exemplary embodiment shown a cross-sectional area which is made up of a circular area 1′ and in each case two ring sector areas 1″ adjoining symmetrically on both sides of the circular area 1′. The core opening 1 shown in
Serving for closing the core opening 1 shown in
The middle part 5 of the closure device 3 is formed in the manner of a solid or hollow cylinder and, as a consequence, has a circular cross section, which coincides with the circular cross section 1′ that can be inscribed in the core opening 1. The base part 4 comprises one or more, for example two collars 4′ as illustrated, which are formed in the manner of ring segments and, together with the middle part 5 formed in the manner of a cylinder, produce in axial projection an overall cross section which corresponds to the cross-sectional area of the core opening 1 represented in
For closing the core opening 1 represented in
The closure mechanism according to the solution is consequently based on an intimate form or force fit between the axially upwardly oriented surface areas 4″ of the collars 4′, which are made to abut the surface regions of the joining areas 2 that are directed axially toward the casting. It is consequently impossible for the closure device 3 to be able to become detached from the core opening 1 even when centrifugal forces occur.
a shows the plan view of an alternative form for a core opening 1 which, as in the case of the example according to
The closure device 3 has two collars 4′, which are formed like ring segments and, as a difference from the exemplary embodiment according to
A further embodiment for forming a closure device according to the solution is represented in
As a safeguard against turning, the two halves 13, 14 are brazed or welded to the casting, at least at the groove-like clearances 9 provided in the head part 6.
As a difference from the closure device explained above, which are based on the bayonet closure principle, an alternative closure mechanism is explained in
The embodiment represented in
a shows a shaped disk 15, which as it were provides the shaped disk 15 represented in
a shows a closure device formed as a grub screw 20, which for the closure of a core opening 1 is inserted into an internal thread 21, as shown in
a and b show a further measure for securing against uncontrolled turning of a closure device 3 introduced into a core opening 1. Thus it should be assumed in
Number | Date | Country | Kind |
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365/08 | Mar 2008 | CH | national |
This application is a continuation of International Application No. PCT/EP2009/052524 filed Mar. 4, 2009, which claims priority to Swiss Patent Application No. 00365/08, filed Mar. 11, 2008, the entire contents of all of which are incorporated by reference as if fully set forth.
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Number | Date | Country | |
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20110056648 A1 | Mar 2011 | US |
Number | Date | Country | |
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Parent | PCT/EP2009/052524 | Mar 2009 | US |
Child | 12878691 | US |