The present disclosure relates to internally cooled turbine blades in gas turbines, such as cast blades that can facilitate removal of cores from cooling passages during manufacture.
Turbine blades in modern gas turbine engines can be exposed to high operational temperatures, such as temperatures in the high-pressure part of the turbine. For this reason, such turbine blades can be provided with internal passages through which cooling air is circulated. Cooling air which is bled from one or more compressor stages in the gas turbine engine, can impose a performance penalty on the engine. In such a case, the blade designer can seek to minimise cooling air consumption by designing the blades with complicated internal cooling passages. Modern high pressure turbine blades can be manufactured using the “lost wax” shell moulding process, in which the internal cooling passages are defined within the wax blade shape by cores made of a ceramic or other leachable material. When the wax is melted out of the shell mould and replaced by molten metal alloy, the ceramic cores remain in the solidified cast blade to define the internal cooling passages. The ceramic cores are removed during the last stages of the manufacturing process by, for example, a leaching process that dissolves the ceramic cores out of the blade internals using a caustic chemical composition.
It is known from EP-A-1 267 040 and other documents to define small openings in internal cooling passage walls of the casting by thin ancillary core portions that join one part of the ceramic core to another part. This can be done to provide support to cores during the casting process. After the part is cast and the core has been leached out, the opening can be closed off with a plug that is securely fixed into place.
A cast turbine blade is disclosed comprising: a blade root and a blade tip; at least one internal cooling passage that passes from an inlet in the blade root to an outlet in the blade tip, the cooling passage having a zone that is at a distance which is remote from the inlet of the cooling passage when the distance from the inlet is measured along the cooling passage, but that is closer to the inlet when the distance from the inlet is measured in a straight line; a supplementary passage that extends between the zone and the inlet through an internal wall of the cooling passage, wherein the supplementary passage is elongate and passes in a straight line from an aperture in an external surface of a base of the blade root, through the blade root, the inlet and the internal wall, to the zone; and a plug which obturates the supplementary passage wherein the plug is elongate and substantially co-extensive with the supplementary passage.
A method of manufacturing a turbine blade is disclosed using the lost wax casting process, the method comprising: casting a cooling passage that extends from an inlet in a root portion of the blade to an outlet in a tip portion of the blade, the cooling passage having a zone that is at a distance which is remote from the inlet of the cooling passage when the distance from the inlet is measured along the passage, but that is closer to the inlet when the distance from the inlet is measured in a straight line; and casting a supplementary passage for connecting the zone to the inlet during the manufacture of the blade, wherein the cooling passage and the supplementary passage are defined by at least one core comprising a leachable material.
Exemplary embodiments of the disclosure will be described herein, with reference to the accompanying drawings, in which:
According to the present disclosure, a cast turbine blade having a blade root and a blade tip is disclosed. According to an exemplary embodiment, at least one internal cooling passage passes (e.g., zig-zags, or meanders) through the blade from an inlet in the blade root to an outlet in the blade tip, the cooling passage having a zone that is remote from the inlet of the cooling passage when the distance from the inlet is measured around the passage, but that is closer to the inlet when the distance from the inlet is measured in a straight line. A supplementary passage extends between the remote zone and the inlet through an internal wall of the cooling passage, the supplementary passage being obturated by a (e.g., metallic) plug. The supplementary passage can be elongate, and pass in a straight line from an aperture in an external surface of the base of the blade root, through the blade root, the inlet and the internal wall, to the remote zone. The plug can also be elongate and substantially co-extensive with the supplementary passage.
The supplementary passage can possess an un-obturated state during a manufacturing process of the blade, such as during leaching out of ceramic cores from the cast blade, to connect the remote zone to the inlet and thereby improve access of leaching fluid to the remote zone. The supplementary passage can be obturated during a service life of the blade to prevent leakage of cooling air through the supplementary passage.
The remote zone of the cooling passage can be at a bend in the cooling passage.
The plug can be retained in a correct position in the supplementary passage against forces tending to push it further into the blade by a shoulder on the plug that bears against a complementary feature in the passage.
The plug can be retained in position against forces tending to remove it from the blade by an interference fit between the plug and the supplementary passage. For example, the interference fit can be obtained by deforming a feature on the plug to make it project into a recess of the supplementary passage. The feature on the plug can be a collar and the recess can include a wider part of the supplementary passage or an undercut in a wall of the supplementary passage. The collar can be caulked, swaged, or upset into a final position so as to grip the plug tightly and protrude into the recess in the passage.
Alternatively, after assembly of the blade into a turbine rotor, the plug can be retained in position against forces tending to remove it from the blade by abutment of an external end of the plug with a surface of the rotor.
An exemplary method of manufacture can include, during casting of the blade, defining the cooling passage by a core or cores having a leachable material, the supplementary passage being likewise defined by a leachable core, or machined into the blade after casting. After casting of the blade, the core material can be removed from the blade by a leaching process, during which the supplementary passage can facilitate quicker and more thorough removal of core material from the remote zone of the cooling passage, the supplementary passage being obturated by insertion of the plug after conclusion of the leaching process.
Referring to
A first leg 12a of passage 12 extends longitudinally through the blade's trailing edge region between the air inlet 14 in the root R and a bend 20 at the tip T of the blade. At the tip, the passage 12 doubles back on itself to form its second leg 12b, which extends longitudinally through the mid-chord region of the blade from the blade tip T to a bend zone 18 near the root. Here, the passage doubles back on itself again to form its third leg 12c, which extends longitudinally through the mid-chord region of the blade from the zone 18 to the outlet 16 in the blade tip.
After casting of the blade, the ceramic cores or the like that define the cooling passages 12 and 13 of the exemplary
Referring to
During casting of the blade, the supplementary passage 22 can conveniently be defined by cores, which after casting can, for example, be easily removed mechanically, or leached out (e.g., during the initial stages of the leaching process). Alternatively, passage 22 can be readily machined into the blade after casting, but before the core removal process commences.
Referring to
During operation of turbine blade 10 when installed on a gas turbine rotor, the blade can be retained to the rotor against powerful centrifugal forces by industry standard features provided on, or associated with, root R and the rotor. However, such centrifugal forces, acting in the direction shown by the arrow C (
An additional shoulder or flange 39 can be located as a fail-safe feature on the plug's stem 36, just under the bulbous portion 32. Flange 39 can have a greater diameter than the diameter of the supplementary passage 22 where it penetrates the cooling passage wall 26. Consequently, in the unlikely event that the stem 36 breaks during the service lifetime of the blade 10, flange 39 can prevent the bulbous portion 32 from being displaced into the bend zone 18 under the influence of centrifugal forces.
Before, during and after installation of the turbine blade 10 on the gas turbine rotor, the plug 30 should be retained in position against forces tending to remove it from the blade. In an exemplary embodiment, such retention can be achieved by means of an interference fit between a feature on the cylindrical end portion 44 of plug 30 and an feature in the supplementary passage portion 22a. As shown, the feature in the supplementary passage can be a recess in the passage wall, having a shallow groove 40 that forms a wider part of the passage (an undercut portion of the passage wall would perform a similar function). The feature on the plug can be a cylindrical collar 42. After the plug 30 has been inserted into the supplementary passage 22, collar 42 can be slid over the cylindrical end portion 44 of the plug until it abuts the flange 34. The collar can be then deformed into position as shown, e.g., by a caulking, swaging, or upsetting operation, so that it tightly grips the cylindrical end portion 44 and portions of it (indicated by reference numerals 46 in
The present disclosure has been described above purely by way of example, and modifications can be made within the scope of the disclosure as claimed. The disclosure also encompasses any individual features described or implicit herein or shown or implicit in the drawings or any combination of any such features or any generalisation of any such features or combination, which extends to equivalents thereof. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Each feature disclosed in the specification, including the claims and drawings, may be replaced by alternative features serving the same, equivalent or similar purposes, unless expressly stated otherwise.
Any discussion of the prior art throughout the specification is not an admission that such prior art is widely known or forms part of the common general knowledge in the field.
Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.
Thus, it will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
Number | Date | Country | Kind |
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07110385.7 | Jun 2007 | EP | regional |
This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/EP2008/056051, which was filed as an International Application on May 16, 2008 designating the U.S., and which claims priority to European Application 07110385.7 filed in Europe on Jun. 15, 2007. The entire contents of these applications are hereby incorporated by reference in their entireties.
Number | Date | Country | |
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Parent | PCT/EP2008/056051 | May 2008 | US |
Child | 12638580 | US |