US20110182726A1 - As-cast shroud slots with pre-swirled leakage - Google Patents

Abstract

A system for forming a seal slot in a shroud assembly has a first element having a longitudinally extending slot and a second element having a longitudinally extending slot for receiving a portion of the first element. The first element has a pair of opposed surfaces and the second element has a pair of opposed surfaces which are oriented at an angle to the surfaces of the first element. The second element may have a planar portion and a curved portion adjacent the planar portion for forming a slot which allows a flow of fluid to exit the slot at a desired angle.

Description

BACKGROUND
• The present disclosure is directed to a refractory core assembly for forming cast shroud slots with pre-swirled leakage, a process for casting turbine engine components, such as turbine vane shrouds, having as-cast shroud slots with pre-swirled leakage, and to a cast turbine engine component having shroud slots for providing pre-swirled leakage.
• Co-pending U.S. patent application Ser. No. 11/639,455 addresses the use of refractory metal cores to cast slots into a turbine vane shroud, and avoid later manufacturing operations such as electro-discharge machining to cut the shrouds.
• It is desirable to manage turbine shroud leakage flows in ways that minimize leakage mixing and acceleration to rotational speed by injecting the leakage flow at a sharp angle to the shroud to accelerate it to the rotating flow next to the shroud. It is physically difficult to angle the segmentation line of the shroud, without interfering with the structural attachment of the airfoil to the shroud wall. It is desirable to have a variable shroud segmentation cut, that addresses the need for segmentation, and acceleration of the leakage flow associated with the segmentation cut.
SUMMARY
• In accordance with the present disclosure, there is provided a system for forming a seal slot in a shroud portion of a turbine engine component, which seal slot forming system broadly comprises a first element having a longitudinally extending slot and a second element having a longitudinally extending slot for receiving a portion of said first element.
• Further in accordance with the present disclosure, there is provided a turbine engine component which broadly comprises a plurality of airfoils, an as-cast shroud surrounding said airfoils, and said shroud having a tailored segmentation with a curvature which alters the leakage flow to be more aligned with the rotating flow.
• Still further in accordance with the instant disclosure there is provided a process for forming a turbine engine component comprising the steps of: placing a refractory core assembly comprising a first element and a second element with a non-planar position joined to said first planar element in a die; encapsulating said refractory core assembly in a wax pattern having the form of said turbine engine component; forming a ceramic shell mold about said wax pattern; removing said wax pattern; and pouring molten material into said ceramic shell mold to form said turbine engine component.
• Other details of the as-cast shroud slots with pre-swirled leakage are set forth in the following detailed description wherein like reference numerals depict like elements.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a top view of a portion of a turbine engine component having a segmented shroud;
• FIG. 2 is a top view of a portion of a turbine engine component having a segmented shroud which provides a pre-swirled leakage;
• FIG. 3 illustrates a refractory metal core system for forming the segmented shroud ofFIG. 2;
• FIG. 4 is a top view of the system ofFIG. 3;
• FIG. 5 is a side view of the system ofFIG. 3;
• FIG. 6 illustrates an as-cast turbine engine component having a segmented shroud;
• FIG. 7 is a sectional view taken along lines7-7 ofFIG. 6;
• FIG. 8 is a rear view of the as-cast turbine engine component ofFIG. 6; and
• FIG. 9 is a flow chart illustrating the process for forming the turbine engine component.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
• FIG. 1 illustrates a typicalturbine engine component10 having a plurality ofairfoils12 and a segmentedshroud ring14 having alinear slot16 between two of theairfoils12. The angle of theslot16 is constrained by the geometry of theairfoils12. Steep slot angles are not possible due to the airfoil geometry.
• FIG. 2 illustrates aturbine engine component10′ fabricated in accordance with the present invention. As can be seen fromFIG. 2, theturbine engine component10′ has a segmentedshroud ring14′ with a plurality ofairfoils12′. However, in this case, theslot16′ is not linear. Theslot16′ has a contour which is curved to turnleak flow18′ to match rotor motion and the flow of fluid around theturbine engine component10′ as exemplified by thearrow20′.
• One or more as-cast slots16′ may be produced in a wall of ashroud ring14′ in between two of theairfoils12′. Eachslot16′ may be cast integrally using the metalrefractory core system30′ shown inFIGS. 3-5.
• The refractorymetal core system30′ is formed from twothin plates32′ and34′. Thethin plates32′ and34′ are constructed so that they can be interlocked perpendicular to each other. As can be seen fromFIG. 3, theplate32′ may have a planar construction with twoopposed surfaces130′ and132′. Theplate32′ further may have a longitudinally extendingslot36′ for receiving theplate34′. Still further, theplate32′ may have a length which is shorter than the length of the plate longitudinally extending34′. While theplate32′ has been described as having a planar, it may also be non-planar if desired.
• Theplate34′ may have aplanar portion134′ withopposed surfaces136′ and138′. Still further, theplate34′ may have a longitudinally extendingslot38′ extending from a leadingedge40′, which slot receives a planar portion of theplate32′. Theplate34′ may have a curvedtrailing edge portion42′ in the shape of the desired configuration for thetrailing edge portion142′ of theslot16′. The exact curvature of thetrailing edge portion42′ and the angle are determined by the swirl needs and any airfoil limitations. If desired, thetrailing edge portion42′ may also have atwist portion144′ to tailor the radial swirl.
• Each of theplates32′ and34′ may be formed from any refractory metal or refractory metal alloy. While theplates32′ and34′ may be formed from molybdenum or a molybdenum alloy, they could also be formed from any other suitable refractory material. If desired, eachplate32′ and34′ may have a thin ceramic coating applied to the base refractory metal, refractory metal alloy, or refractory material forming the respective plate.
• When assembled, as shown inFIGS. 4 and 5, theplates32′ and34′ form an assembly in which thesurfaces130′ and132′ are at an angle with respect tosurfaces136′ and138′ and theplates32′ and34′ are interlocked. For example, thesurfaces130′ and132′ may be perpendicular to thesurfaces136′ and138′.
• Theturbine engine component10′ including theairfoils12′, and theshroud ring14′ may be formed using any suitable technique known in the art. For example, as set forth inFIG. 9, in astep202, the refractory core assembly comprising a first planar element, namelyplate32′, and a second non-planar element, namelyplate34′, joined to the first planar element may be placed in a die. Instep204, the refractory core assembly is encapsulated in a wax pattern having the form of theturbine engine component10′. Instep206, a ceramic shell mold is formed about the wax pattern. Instep208, the wax pattern is removed. Instep210, molten material is poured into the ceramic shell mold to form said turbine engine component. Instep212, the airfoils and the turbine engine component may be removed from the ceramic shell mold. Instep214, the refractory core assembly is removed after said molten material has solidified so as to form an as-cast slot in a shroud portion of the turbine engine component. The refractory core assembly removal step may be performed using an acid leach operation.
• Instep202, the refractory core assembly placing step preferably comprises placing a refractory core assembly wherein said first element is fitted into a slot in said second non-planar element and said second non-planar element is fitted into a slot in said planar element.
• If desired, instep202, a plurality of refractory core assemblies may be placed in the die. Further, each refractory core assembly may be placed in a portion of the die to be used to form an outer shroud ring and/or an inner shroud ring.
• If desired, instep210, the molten material pouring step may comprise pouring a molten material into said die to form a plurality of airfoils, such as pouring a nickel based superalloy.
• The resultantturbine engine component10′ formed by the foregoing process, as shown inFIG. 6, has an as-cast shroud14′ having a tailored segmentation in the form of an integralfeather seal slot16′ with a curvedtrailing edge portion50′.FIG. 7 is a sectional view taken along lines7-7 inFIG. 6 and shows the internal portion52′ of theslot16′ formed by theplate32′. The curved trailing edge portion52′ alters the leakage flow so that it is more aligned with the rotating flow. As can be seen fromFIG. 6, theslot16′ may have alinear portion53′ adjacent a first edge56′ and the curved orangled portion50′ adjacent asecond edge58′.
• FIG. 8 illustrates thesegmented shroud ring14′ with a flow offluid54′ being discharged from theslot16′. As can be seen from this figure, the fluid is pre-swirled and flows in the direction of rotation. Such a flow reduces losses.
• Separation (segmentation) of the shroud is useful because it relieves stress caused by the ring-strut-ring structure, i.e. a hot airfoil is overly constrained by cold inner and outer diameter rings.
• Using the refractory metal core plates such asplates32′ and34′ is advantageous because one can form complex slot shapes directly into the casting, without complex machining operations. The more complex the shape, the less likely the slot can be machined.
• The refractory metal core plates can be made very thin compared to a ceramic core. A ceramic core of similar thickness, i.e. 0.008 to 0.010″ or less, would likely result in low casting yield because it could easily break during handling, assembly, wax injection, or during the pour of molten metal. Ceramics are very fragile compared to metals.
• It is apparent that there has been described herein as-cast shroud slots with pre-swirled leakage. While the disclosure has been set out in the form of specific embodiments, other unforeseeable variations, modifications, and alternatives may become apparent to those skilled in the art having read the foregoing specification. Accordingly, it is intended to embrace those unforseseen alternatives, modifications, and variations as fall within the broad scope of the appended claims.

Claims (17)

1. A system for forming a seal slot in a shroud assembly, said system comprising a first element having a longitudinally extending slot and a second element having a non-planar portion and a longitudinally extending slot for receiving a portion of said first element.

2. The system ofclaim 1, wherein said first element has a pair of opposed surfaces and said second element has a pair of opposed surfaces which are oriented at an angle with respect to said surfaces of said first element.

3. The system ofclaim 1, wherein said second element has a planar portion and said non-planar portion comprises a curved portion adjacent said planar portion.

4. The system ofclaim 1, wherein said first element has a first length and said second element has a second length greater than said first length.

5. The system ofclaim 1, wherein each of said first and second elements is formed from a refractory metal material.

6. The system ofclaim 1, wherein said second element has a portion with a twist.

7. A turbine engine component comprising:

a plurality of airfoils;

an as-cast shroud surrounding said airfoils; and

said as-cast shroud having a tailored segmentation with a curvature which alters the leakage flow to be more aligned with the rotating flow.

8. The turbine engine component ofclaim 7, wherein said tailored segmentation has a linear portion adjacent a first edge of said shroud and an angled portion adjacent a second opposed edge of said shroud.

9. The turbine engine component ofclaim 8, wherein said angled portion of said slot has an angle sufficient to turn said fluid flow to match a rotational flow about said turbine engine component.

10. A process for forming a turbine engine component comprising the steps of:

placing a refractory core assembly comprising a first element and a second element having a non-planar portion joined to said first element in a die;

encapsulating said refractory core assembly in a wax pattern having the form of said turbine engine component;

forming a ceramic shell mold about said wax pattern;

removing said wax pattern; and

pouring molten material into said ceramic shell mold to form said turbine engine component.

11. The process ofclaim 10, wherein said refractory core assembly placing step comprises placing a refractory core assembly wherein said first element is fitted into a slot in said second element and said second element is fitted into a slot in said first element.

12. The process ofclaim 10, further comprising removing said refractory core assembly after said molten material has solidified so as to from a slot in a wall of a portion of said turbine engine component.

13. The process ofclaim 12, wherein said removing step comprises removing said refractory core assembly using an acid leach operation.

14. The process ofclaim 10, wherein said placing step comprises placing a plurality of refractory core assemblies in said die.

15. The process ofclaim 10, wherein said placing step comprises placing said refractory core assembly in a portion of said die to be used to form at least one of an outer shroud ring and an inner shroud ring.

16. The process ofclaim 10, wherein said molten material pouring step comprises pouring a nickel based superalloy.

17. The process ofclaim 10, further comprising removing said turbine engine component with said airfoils from said ceramic shell mold.

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