A wall section of a hot gas path part for a gas turbine and a method of additive manufacturing of a wall section

Abstract

A wall section (fig.1, WS) of a hot gas path part for a gas turbine, which wall section is additively manufactured by a powder based manufacturing process, comprising a first surface (fig.1, FS) and at least one first channel FC connected to a number of second channels SC (supply a coolant), which at respective junctions JS are branching off from the first channel. At least one of the second channels, preferably all second channels, comprises a shaped sub-section SN which merges into the at least one first channel and is funnel-shaped or comprises a continuously diverging cross section towards the first channel to improve the removal of excess powder during de-powdering. The first channel may have a larger cross section than the second channel. the sub-section may have an axial length one time of a diameter of the second channel. The wall section is manufactured in particular by laser powder bed fusion.

Description

[0081] The present invention relates to a wall section of a hot gas path part for a gas turbine and a method of additive manufacturing of a wall section.

[8802] In gas turbines the airfoils of turbine blades and vanes play a critical role in converting the energy of a hot working gas into mechanical work. The reliability and efficiency of the gas turbine depends highly on the reliability and efficiency of the turbine blades and vanes utilized in their turbine section.

[0083] With the trend of the recent decades to increase the turbine inlet temperatures new cooling designs of hot gas path parts like turbine blades and vanes have been established. In Example, the US 6,379,118 B2 discloses a so-called near wall cooling for a suction side and pressure side wall of a turbine blade airfoil with a main cooling channel, from which several cooling passages branches off and extents along the wall. In the meantime, further complex cooling geometries have been developed. As these complex cooling structures are hard to manufacture by an investment casting process, nowadays it is possible and typical to additively manufacture those structures. As the preferred additive manufacturing process for these metallic parts is the Laser-powder bed fusion process, the solid structures manufactured therewith had to be depowdered, which is a time-consuming process and when not performed accurately, may lead to failures of the parts when operated because of remaining powder which might blocks cooling passages.

[0004] With increasing complexity of the cooling channel network, the difficulty of powder removal after the solidification process increases as well. Therefore, new solutions are needed which supports the depowdering of those parts.

[0005] Based on this, the objective of the present invention is to provide a wall section of a hot gas path part for a gas turbine which comprises improved depowdering capabilities. Another objective of the invention is to provide a method for manufacturing such a wall section of the hot gas path part. [OGGS] The solution regarding the apparatus is a wall section in accordance with the features of claim 1. In detail the inventive wall section of a hot gas path part for a gas turbine, which wall section is manufactured by a powder based additive manufacturing process, in particular by a powder bed fusion process or a binder jetting additive manufacturing method, comprises a first surface designated to be subjected during operation to a hot working gas of the gas turbine, and at least one first channel, preferably to supply a coolant, connected with a number of second channels, which at junctions are branching off from the at least one first channel and which preferable are designated to cool the wall section during operation, wherein the at least one of the second channels, preferably all second channels, comprises at the respective junction a shaped sub-section which merges into at least one first channel, and the sub-section is funnel-shaped or comprises a continuously diverging cross section towards the first channel.

[0007] By adding a funnel-shaped or continuously diverging cross sections of subsections at the junction, where the second channel branches of from the first channel, the depowdering process step, which is part of the manufacturing process, is simplified. These features avoid the existence of corners, and / or dead-end areas. The invention is based on the knowledge, that after the fusion process for manufacturing the solid structure of the hot gas path part is completed, the residual powder, which is still in the hot gas path part, must be removed by a conventional depowdering process step. During depowdering the hot gas path part is shaken and rotated so that the residual powder is transported by gravity along the first and second channels towards cooling apertures through which the powder can finally fall out of the hot gas path part. These apertures are either coolant inlets or coolant outlets. In the following first and second channels will be mentioned together as cooling channels.

[8888] By the utilization of the new shaped sub-sections at the junction the powder is not caught anymore in or by the junctions, corners or in dead ends. During depowdering process step comprising the rotational or shaking motions of the hot gas path part the powder can move continuously towards the openings so that the powder is not caught in any indentations or any so-called dead water areas, which might appear in limited locations, when in general a fluid, e.g., coolant flows through the first and second channels. The new junction structure supports the complete removal of any powder from the solid hot gas path part. Hence, the main difference between the invention and known solutions is the avoidance and elimination of indentations at channel junctions, so that the likelihood of powder getting caught in the hot gas path part after the completion of the depowdering process step is reduced. Consequently, the likelihood of clogged cooling channels because of powder remaining behind in the hot gas path part is reduced as well. This ensures the full capability of the part as intended. Additionally, the time for the depowdering process step might be reduced, which will reduce the process cost, manual labour and increase the output of the depowdering apparatus.

[8888] Furthermore, the design of the sub-sections at the junctions will enable more sophisticated or complex second channel network structures, which leads to improved cooling capabilities and the efficient utilization of coolant.

[0018] According to a first preferred embodiment a size of the cross section of the first channel is larger than a size of the cross section of the second channel, wherein the cross section of the second channel is determined offside the subsection. As typically additively manufactured (AM) designs of second channels comprises a larger number of parallel arranged second channels, which are all connected to the same first channel, the first channel must be able to provide appropriate amount of coolant with lowest pressure drop or loss to the said parallel arranged second channel.

[0011] Another preferred alternative of the invention proposes that the sub-section has an axial length of at least one times of a diameter of the second channel, the diameter is determined offside the sub-section. This enables a suitable and stepless adaption between the different diameters and avoids a stepwise change, which otherwise could have led to unwanted indentations.

[0012] A further aspect of the present invention relates to the first channel is designated to cool the wall section as well. Hence, the first channel can be arranged with the same distance to the first surface like the second channel and con contribute to the cooling of the wall of the hot gas path part.

[0013] According to another preferred embodiment the wall section comprises opposingly located to the first surface a second surface, which is during operation, not subjected to the hot gas. This embodiment advantageously provides an opportunity to utilize the invention in multiple areas of a hot gas path part and as well in a so called near-wall-cooling configuration, in which the wall section has a thickness of approx. 3 mm to 10 mm and the second channels have diameter in the range of approximately 0,3 mm and 3 mm of the thickness, which is typical for airfoils of turbine blades or turbine vanes of heavy duty gas turbines.

[0014] Preferably, the hot gas path part is embodied as a ring segment, or a heat shield, or as a gas turbine blade, a gas turbine vane, and the wall section is part of an airfoil or a platform of the gas turbine blade or gas turbine vane.

[0015] Regarding the manufacturing method, the solid structure of the wall section of the hot gas path part is produced by a powder based additive manufacturing method, in particular by a powder bed fusion process or a binder jetting additive manufacturing method. In the powder bed fusion process, a suitable powder of metal or alloy is successively deposited in layers, whereby each powder layer is fused with the underlying solid structure after it has been deposited. Further, the manufacturing method further comprises a step of depowdering the hot gas path part.

[8818] Advantages and embodiments relating to the described method may as well pertain or be valid regarding the wall section or the hot gas path part itself, or vice versa.

[8817] Other embodiments, features, and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate by way of example the principles of the invention. SR^EF DESCRIPTION OF DRAWINGS

[8818] FIG 1 is a cross section through an airfoil as a wall section of a hot gas path part in accordance with a first exemplary embodiment of the invention,

[8818] FIG 2 shows in a lateral view multiple second channels branching of from a first cooling channel in accordance with a first exemplary embodiment,

[8820] FIG 3 shows in a top view the junction of one of the second channels merging into the first channel in accordance with a first exemplary embodiment.

[8821] FIG 4 shows in a lateral view multiple second channels branching of from a first cooling channel in accordance with a second exemplary embodiment,

[8822] FIG 5 shows in a top view the junction of one of the second channels merging into the first channel in accordance with a second exemplary embodiment. DESCRIPTION OF EMBODIMENTS

[0823] FIG 1 shows as one exemplary embodiment of the invention of a hot gas path part HP comprising a wall section WS schematically a cross section through an airfoil AF. The plane of the cross section plane is arranged perpendicular to a radial direction RD (FIG. 2). With that, FIG 1 shows as the outer contour of the airfoil AF a profile, which represents the surface of the airfoil AF as well. The surface is during operation in contact with the hot working gas of the gas turbine.

[0024] Like conventional airfoils of prior known turbine blades or turbine vanes of gas turbines, the airfoil comprises a suction side wall SW and a pressure side wall PW, which are merging into one another at a leading edge LE and at a trailing edge TE of the airfoil AF, whereas the terms leading and trailing refers to the flow direction of the hot gas working of the gas turbine. Both, the pressure side wall PW and the suction side wall SW comprise a first surface SF, which is subjected, during operation of the airfoil, to the hot working medium of the gas turbine.

[0025] Perpendicular to this, in radial direction, the airfoil AF and with that, the suction side wall SW and the pressure side wall PW, the leading edge LE and the trailing edge as well extent with a span direction from an inner end IE to an outer end OE. When the airfoil AF is part of a turbine blade (not shown), at the inner end IE usually a platform is arranged. In the same manner, when the airfoil AF is part of a turbine vane (not shown as well), usually at the inner end IE and at the outer end OE comprises a platform. Those platforms are also known as shrouds. A chord direction CD extends from the leading edge LE to the trailing edge TE and is arranged in the plane of the cross section. [0Q2S] In or directly adjacent to the leading edge LE a first channel FC is arranged, which can be supplied with a coolant, e.g., compressor air, in a conventional manner. In accordance with the first exemplary embodiment, the airfoil AF comprises four - a first, a second, a third and a fourth -cooling circuits CC1, CC2, CC3, CC4, although the fundamental idea of the invention can be realized only in one cooling circuit. Each of them comprises a number of second channels SC. The cooling circuits CC1, CC2, CC3, CC4 are located on the pressure side of the airfoil AF and with that, in the pressure side wall PW, as a near-wall cooling configuration. The second channels SC in general extend in chord direction CD. For the sake of clarity, it is mentioned that the terms “radial direction”, “axial direction”, and “circumferential direction” are in reference to the machine axis of the gas turbine. The “cord direction” is usually a combination of the axial and circumferential direction and depends on a predetermined cross section of the airfoil and its blade angle. The span direction of the airfoil is identical to the radial direction RD.

[0027] Although second channel SC of different cooling circuits are shown in FIG. 1 as lines with distinctive styles, it has to be understood that the lines shall represent conventional cooling passages in the airfoil AF of preferably circular, elliptical or rectangular shapes. A typical diameter of the cooling channels is in the range between 0,3 and 3,00 mm, depending on the size of the airfoil and the local cooling requirements. Rectangular shapes offer larger surfaces and larger cross sections. [002S] The most upstream arranged second channels SC of the four cooling circuits CC1-CC4 are connected with the first channel FC. These second channels extend in the pressure side wall directly underneath the surface of the airfoil along the chord. In such a case and during operation, the coolant flowing through these sections are effectively cooling respective side wall sections. [002S] Contrary to this, some segments of the second channels SC of the third and fourth cooling circuits CC3, CC4 are arranged on a larger distance to the surface than second channels SC of the first and second cooling circuits CC1, CC2. Those segments are designated to not cool the side walls effectively. Their objective is to forward already heated up coolant, without or with lowest possible heating, to chord regions where said coolant is again utilized to cool the side wall.

[0030] Each of a most downstream arranged second channels SC of the four cooling circuits CC1-CC4 ends in an outlet OT, which is arranged in the surface of the airfoil AF. Preferably, the outlets OT can be embodied as a conventional film cooling hole. The outlets OT of the different cooling circuits CC1-CC4 are distributed along the chord direction CD. The arrangement of second channels SC as displayed in FIG 1 is multiple times present on different span levels of the airfoil AF.

[8831] Besides the first channel FP, in the coolable wall section WS comprises further radially extending first channels FFC. Those interconnects second channels SC which belongs to the same cooling circuits CC1, CC2, CC3 or CC4.

[0032] Each second channel SC merges at a junction JS into the first channel FC, as shown in the following figures. Contrarily to a conventional junction and in accordance with the first exemplary embodiment, the second channels comprise a shaped sub-suction SN at its junction. As displayed in FIGs. 2 and 3 the subsections are funnel-shaped, i.e., with a constant opening angle. Furthermore, the central axes of the first and second channels of arranged in an offset manner such the second channel SC tangentially merges the first channel FC. This is shown in FIG. 3.

[0033] Preferably, the sub-section SN has an axial length of at least one times of a diameter of the second channel, wherein the diameter of the second channel is determined offside its sub-section SN. The cross section of the first channel FD is, as being a supply channel of the coolant for the second channels, larger than the cross section of the second channels.

[0834] In accordance with a second exemplary embodiment of the invention, as displayed in FIGs. 4 and 5, the sub-sections comprise a continuously diverging cross section towards the first channel in form like a diffusor or nozzle, i.e., with a continuously changing opening angle. With that, the first difference between the first and second exemplary embodiment is related to the shape of the sub-section SN of the second channels SC. Another difference is related to the orientation of the central axes of both cooling channels. The central axes of the second and first cooling channels are not offset but intersect (FIG 5).

[8833] The utilization of the funnel-shaped or continuously diverging sub-section at the junctions of second and first channels SC, FC allows an easier removal of powder after the completion of the solidification process of the hot gas path part HP. Of course, the sub-sections of the second cooling channels can be located at both endings, in their inlet ending and / or their outlet ending, in regard to the direction of flow of the coolant that flows through them.

[0833] It should be noted that the term "comprising" does not exclude other elements or steps and "a" or "an" does not exclude a plurality. Also, elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims. Although the invention is illustrated and described in detail by the preferred embodiments, the invention is not limited by the examples disclosed, and other variations can be derived therefrom by a person skilled in the art without departing from the scope of the invention.

Claims

1. A wall section (WS) of a hot gas path part (HP) for a gas turbine, which wall section (WS) is additively manufactured by a powder based additive manufacturing process, comprising:- a first surface (FS) designated to be subjected to a hot working gas during operation of the gas turbine, and- and at least one first channel (FC) connected with a number of second channels (SC), which at junctions (JS) are branching off from the at least one first channel (FC), characterized in thatthe at least one of the second channels (SC), preferably all second channels (SC), comprises at the respective junction a shaped sub-section (SN) which merges into the at least one first channel (FD), andthe sub-section (SN) is funnel-shaped or comprises a continuously diverging cross section towards the first channel (FC).

2. The wall section (WS) according to claim 1,wherein a size of the cross section of the first channel (FC) is larger than a size of the cross section of the second channel (SC), the cross section of the second channel is determined offside the sub-section (SN).

3. The wall section (WS) according to one of the preceding claims, wherein the sub-section (SN) has an axial length of at least one (1) times of a diameter of the second channel (SC), the diameter is determined offside the sub-section.

4. The wall section (WS) according to one of the preceding claims, wherein the at least one first channel (FD) is designated to cool the wall section as well5. The wall section (WS) according to one of the preceding claims, wherein the wall section (WS) comprises a second surface (ES) opposingly located to the first surface (FS), wherein the second surface (ES) is during operation not subjected to the hot gas.5 6. A method of manufacturing a wall section (WS) of a hot gas path part (HP)according to one of the preceding claims, wherein the solid structure of the wall section is produced by a powder based additive manufacturing method, in particular by a Laser-powder bed fusion process or a binder jetting additive manufacturing method.10 7. The method according to claim 6,comprising a step of depowdering of the hot gas path part (HP).

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