STATOR ASSEMBLY FOR A RADIAL-AXIAL EXPANSIONSTAGE OF A STEAM TURBINE

Description

PRIORITY CLAIM

[0001] This application claims priority from Italian Patent Application No. 102017000061762 filed on 06/06/2017.

[0002] The present invention relates to a stator assembly for a radial-axial expansion stage of a steam turbine.

[0003] As is known, steam turbines comprise several expansion stages wherein the thermodynamic energy of the flowing steam is converted into mechanical energy. Each stage is formed by an array of stator vanes and an array of rotor vanes. The first stage, in particular, may have different configurations depending on the design of the machine. In some steam turbines, the first stage has a radial-axial configuration: the steam entering the turbine flows through the stator vanes of the first stage in a substantially radial direction towards the inside and is axially diverted before it reaches the first array of rotor vanes. The stator vanes are shaped and arranged so as to accelerate the steam flow in the tangential direction. More precisely, the stator vanes of the radial-axial stage extend from respective anchoring portions to roof portions in a direction substantially parallel to the main axis of the steam turbine and from respective leading edges to respective trailing edges tangentially around the main axis.

[0004] The stator vanes of the first stage are individually manufactured and then mounted on the stator shell of the steam turbine. In detail, the anchoring and roof ends of each vane engage circumferential grooves formed in the shell of the steam turbine. To avoid vibrations during operation, the vanes are adjacent to each other, with the anchoring and roof adjacent surfaces touching each other, and with no clearance. Moreover, the vanes are mounted with a slight twist in the housing grooves. The interference thus generated produces a tight coupling between the vanes and reduces the risk of vibration occurrence. However, such twisting also causes high-intensity forces between the root and roof of the vanes and the respective housing grooves. In addition, the high operating temperatures favour the oxidation of the coupling surfaces between the roots and roofs of the vanes and the respective guides. Tightening by twisting and oxidation prevent free differential thermal expansion between the vanes and the shell during machine operation. As a result, the vanes are constantly subjected to stresses, which can compromise the structural integrity and reduce the service life of the vanes themselves.

[0005] EP 2 623 717 A1 discloses a stator assembly for a radial-axial expansion stage of a steam turbine, comprising an anchoring ring extending around an axis, guide ring, extending around the axis and a plurality of stator vanes, each having a respective airfoil connected to respective portions of the anchoring ring and of the guide ring. The stator vanes are arranged around the axis and configured to tangentially accelerate a steam flow entering from the outside toward the inside of the stator assembly. The stator vanes are formed in a single piece with the respective portions of the anchoring ring and of the guide ring.

[0006] Therefore, the object of the present invention is to provide a stator assembly for a radial-axial expansion stage of a steam turbine, which allows the limitations described above to be overcome, or at least mitigated.

[0007] According to the present invention, there is provided a stator assembly for a radial-axial expansion stage of a steam turbine, comprising:

an anchoring ring extending around an axis;

a guide ring extending around the axis;

a plurality of stator vanes, each having a respective airfoil connected to respective portions of the anchoring ring and of the guide ring, the stator vanes being arranged around the axis and configured to tangentially accelerate a steam flow entering from the outside toward the inside of the stator assembly;

wherein the stator vanes are formed in a single piece with the respective portions of the anchoring ring and of the guide ring;

characterized in that:

the stator vanes are tangential stator vanes;

the anchoring ring, the guide ring and the vanes define a cylindrical region around the axis;

in each stator vane, the airfoil has a leading edge and a trailing edge extending axially between the anchoring ring and the guide ring; and

the airfoil of each stator vane has a concave side facing the outside of the cylindrical region and a convex side facing the inside of the cylindrical region.

[0008] The anchoring ring and the guide ring can easily be inserted in the circumferential grooves, which, in steam turbines, are usually used to house individual vanes. Since in the present case the vanes are formed in a single piece with the anchoring ring and the guide ring, no twisting is needed to obtain an ideal tightening and effectively attenuate the vibrations. Furthermore, deformations due to thermal expansion may take place freely even in the presence of surface oxide layers, thus drastically reducing the mechanical stresses on the vanes. The risk of sudden breakage is thus reduced, while, in general, the service life of the vanes increases.

[0009] According to one aspect of the invention, the stator assembly comprises a plurality of annular sectors, each comprising a respective group of stator vanes, an anchoring ring sector and a guide ring sector, wherein the stator vanes of each sector have the respective airfoil connected to the respective anchoring ring sector and to the respective guide ring sector.

[0010] The division into annular sectors simplifies the mounting of the stator assembly on the shell of the steam turbine.

[0011] According to one aspect of the invention, the stator assembly comprises two annular sectors, each extending over an arc of 180°, wherein each group of stator vanes comprises half of the stator vanes and wherein the anchoring ring sectors and the guide ring sectors extend over arcs of 180°.

[0012] The division into only two annular sectors allows the deformations due to thermal expansion to be effectively accommodated, while maintaining an optimal distribution of the stresses and the advantages deriving from the simplicity of assembly.

[0013] According to one aspect of the invention, each annular sector is formed in a single piece.

[0014] According to one aspect of the invention, each annular sector comprises at least two respective stator vanes.

[0015] According to one aspect of the invention, a steam turbine comprises a radial-axial expansion stage provided with a stator assembly comprising:

an anchoring ring extending around an axis;

a guide ring extending around the axis;

a plurality of tangential stator vanes, each having a respective aerodynamic body, or airfoil, connected to respective portions of the anchoring ring and of the guide ring, the stator vanes being arranged around the axis and configured to tangentially accelerate a steam flow entering from the outside toward the inside of the stator assembly;

wherein the stator vanes are formed in a single piece with the respective portions of the anchoring ring and of the guide ring.

[0016] According to one aspect of the invention, the steam turbine comprises a shell housing a rotor rotatable about a rotation axis, the shell being provided with an anchoring circumferential groove and a guide circumferential groove; wherein the anchoring circumferential groove and the guide circumferential groove extend around the rotation axis and house the anchoring ring and the guide ring, respectively.

[0017] According to one aspect of the invention, the anchoring groove has a T-shaped cross-section and the anchoring ring has a base and a connection portion projecting from the base towards the guide ring. Moreover, the base has edges projecting radially inwards and radially outwards with respect to the connection portion, and wherein the anchoring ring is radially and axially retained inside the root guide.

[0018] The stator assembly is thus firmly locked in its seat of use and may also be removed for maintenance or replacement with relative ease. The guide ring may instead have a rectangular cross-section.

[0019] According to a further aspect of the invention, a process for manufacturing a stator assembly of a radial-axial expansion stage of a steam turbine comprises making:

an anchoring ring (13) extending around an axis (A);

a guide ring (15), extending around the axis (A);

a plurality of tangential stator vanes (17), each having a respective airfoil (18) connected to respective portions of the anchoring ring (13) and of the guide ring (15), the stator vanes (17) being arranged around the axis (A) and configured to tangentially accelerate a steam flow entering from the outside toward the inside of the stator assembly;

wherein the stator vanes (17) are formed in a single piece with the respective portions of the anchoring ring (13) and of the guide ring (15);

and further comprising obtaining a semi-finished block and making the anchoring ring (13), the guide ring (15) and the plurality of stator vanes (17) by subtractive manufacturing from the semi-finished block; and

cutting the anchoring ring and the guide ring to form a plurality of annular sectors, each comprising a respective group of stator vanes, a respective sector of the anchoring ring and a respective sector of the roof ring.

[0020] The present invention will now be described with reference to the accompanying drawings, which illustrate a non-limiting embodiment thereof, in which:

• Figure 1 is a section along an axial longitudinal plane of a steam turbine incorporating a stator assembly according to one embodiment of the present invention;
• Figure 2 is a perspective view of an enlarged detail of the steam turbine of Figure 1;
• Figure 3 is a perspective view of the stator assembly of Figure 1;
• Figure 4 is an exploded perspective view of the stator assembly of Figure 1; and
• Figure 5 is a front, partially sectioned view of the stator assembly of Figure 1.

[0021] With reference to Figure 1, a steam turbine, for convenience shown only in part, is indicated with number 1 and comprises a shell 2 and a rotor 3, which is housed inside the shell 2 so as to be rotatable around a rotation axis A. The shell 2 encloses the rotor 3 and forms a scroll 4 for receiving steam into a flow path 5 defined between the shell 2 and the rotor 3.

[0022] The shell 2 and the rotor 3 are respectively provided with arrays of axial stator vanes 7 and arrays of axial rotor vanes 8, which are arranged in succession along the flow path 5 and form a plurality of expansion stages 10 of the axial type.

[0023] An input expansion stage 11, instead, is of the radial-axial type and comprises a radial stator assembly 11a and an axial rotor assembly 11b.

[0024] The axial rotor assembly 11b comprises an array of axial rotor vanes substantially like those previously described and for this reason indicated with the same reference number 8.

[0025] The radial stator assembly 11a, which is shown in greater detail in Figures 2-5, comprises an anchoring ring 13, a guide ring 15 and a plurality of tangential stator vanes 17.

[0026] The anchoring ring 13 and the guide ring 15 are coaxial and the stator vanes 17 each have a respective airfoil 18 (Figures 2 and 5) connected to respective portions of the anchoring ring 13 and of the guide ring 15. Furthermore, the stator vanes 17 are arranged around the axis of the anchoring ring 13 and of the guide ring 15 (Figures 3-5) and are configured to tangentially accelerate a steam flow entering from the outside toward the inside of the radial stator assembly 11a. In more detail, the anchoring ring 13, the guide ring 15 and the stator vanes 17 define a substantially cylindrical region around the axis of the anchoring ring 13 and of the guide ring. In each stator vane 17 (Figure 5), the airfoil 18 has a leading edge 18a and a trailing edge 18b extending in a substantially axial direction between the anchoring ring 13 and the guide ring 15. Moreover, the airfoil 18 of each stator vane 17 has a concave side 18c and a convex side 18d defined between the respective leading edge 18a and the respective trailing edge 18b. The concave side 18c faces the outside of the cylindrical region, whereas the convex side 18d faces the inside of the cylindrical region. The stator vanes 17 are formed in a single piece with the respective portions of the anchoring ring 13 and of the guide ring 15.

[0027] In one embodiment, the radial stator assembly 11a is defined by a plurality of annular sectors 20, each comprising a respective group of stator vanes 17, an anchoring ring sector 13a, and a guide ring sector 15a. The stator vanes 17 of each annular sector 20 have the airfoil 18 connected to the respective anchoring ring sector 13a and to the respective guide ring sector 15a.

[0028] In one embodiment, in particular, the radial stator assembly 11a comprises two annular sectors 20 (Figures 3-5), each extending over an arc of 180°. The anchoring ring sectors 13a and the guide ring sectors 15a also extend over arcs of 180° and each group of stator vanes comprises half of the total stator vanes 17. Moreover, each annular sector 20 is formed in a single piece. In further embodiments, not shown, the radial stator assembly 11a may be divided into a larger number of stator segments, for example three or four. Anyway, each annular sector comprises at least two respective stator vanes.

[0029] With reference to Figure 2, the shell 2 is provided with an anchoring circumferential groove 21 and a guide circumferential groove 22 extending around the rotation axis A. The anchoring ring 13 and the guide ring 15 are respectively housed in the anchoring circumferential groove 21 and the guide circumferential groove 22.

[0030] The anchoring circumferential groove 21 has a T-shaped cross-section and the anchoring ring 13 has a base 13b and a connection portion 13c projecting from the base 13b towards the guide ring 15. Furthermore, the base 13b has edges projecting radially inwards and radially outwards with respect to the connection portion 13c, so that the anchoring ring 13 is radially and axially retained inside the anchoring groove 21.

[0031] The guide circumferential groove 22 may have any cross section, just like the guide ring 15 (for example rectangular).

[0032] In use, a steam flow fed to the steam turbine 1 through the scroll 4 enters the flow path 5 substantially in a radial direction through the radial stator assembly 11a. The steam flow is tangentially accelerated by the stator vanes 17 of the radial stator assembly 11a and is further axially diverted before it reaches the axial rotor assembly 11b. Thereafter, the steam flow passes through the expansion stages 10 of the steam turbine 1, where part of the available thermodynamic energy is converted into mechanical energy.

[0033] The radial stator assembly 11a may be manufactured (for example and not exclusively) with any subtractive manufacturing technique starting from a semi-finished block in the form of a disk, a cylinder or more generally a plate, made of steel or even a high-nickel alloy. The manufacturing may be carried out, for example, by milling or spark erosion in order to obtain the anchoring ring 13, the guide ring 15, and the stator vanes 17 described above. Alternatively, the radial stator assembly 11a can also be manufactured with additive manufacturing techniques, in any case so that the stator vanes form a single piece with the respective portions of the anchoring ring 13 and of the guide ring 15.

[0034] The radial stator assembly 11a is then cut, for example by wire spark erosion, into the desired number of annular sectors (e.g. two, each of 180°).

[0035] Lastly, it is evident that the stator assembly described above can be subject to modifications and variations without departing from the scope of the present invention, as defined in the appended claims.

Claims

1. A stator assembly for a radial-axial expansion stage of a steam turbine, comprising:

an anchoring ring (13) extending around an axis (A);

a guide ring (15), extending around the axis (A);

a plurality of stator vanes (17), each having a respective airfoil (18) connected to respective portions of the anchoring ring (13) and of the guide ring (15), the stator vanes (17) being arranged around the axis (A) and configured to tangentially accelerate a steam flow entering from the outside toward the inside of the stator assembly;

wherein the stator vanes (17) are formed in a single piece with the respective portions of the anchoring ring (13) and of the guide ring (15);

characterized in that:

the stator vanes (17) are tangential stator vanes (17) ;

the anchoring ring (13), the guide ring (15) and the vanes define a cylindrical region around the axis (A);

in each stator vane (17), the airfoil (18) has a leading edge (18a) and a trailing edge (18b) extending axially between the anchoring ring (13) and the guide ring (15); and

the airfoil (18) of each stator vane (17) has a concave side (18c) facing the outside of the cylindrical region and a convex side (18d) facing the inside of the cylindrical region.

2. The stator assembly according to claim 1, comprising a plurality of annular sectors (20), each comprising a respective group of stator vanes (17), an anchoring ring sector (13a) and a guide ring sector (15a), wherein the stator vanes (17) of each annular sector (20) have the respective airfoil (18) connected to the respective anchoring ring sector (13a) and to the respective guide ring sector (15a).

3. The stator assembly according to claim 2, comprising two annular sectors (20), each extending over an arc of 180°, wherein each group of stator vanes (17) comprises half of the stator vanes (17) and wherein the anchoring ring sectors (13a) and the guide ring sectors (15a) extend over arcs of 180°.

4. The stator assembly according to claim 2 or 3, wherein each annular sector (20) is formed in a single piece.

5. The stator assembly according to any one of claims 2 to 4, wherein each annular sector (20) comprises at least two respective stator vanes (17).

6. A steam turbine comprising a radial-axial expansion stage provided with a stator assembly (11a) according to any one of the foregoing claims.

7. The steam turbine according to claim 6, comprising a shell (2) housing a rotor (3) rotatable about a rotation axis (A), the shell (2) being provided with an anchoring circumferential groove (21) and a guide circumferential groove (22); wherein the anchoring circumferential groove (21) and the guide circumferential groove (22) extend around the rotation axis (A) and house the anchoring ring (13) and the guide ring (15), respectively.

8. The steam turbine according to claim 7, wherein:

the anchoring circumferential groove (21) has a T-shaped cross-section and the anchoring ring (13) has a base (13b) and a connection portion (13c) projecting from the base (13b) towards the guide ring (15);

the base (13b) has edges projecting radially inwards and radially outwards with respect to the connection portion (13c), and wherein the anchoring ring (13) is radially and axially retained inside the anchoring circumferential groove (21).

9. A process for manufacturing a stator assembly of a radial-axial expansion stage of a steam turbine according to claim 1, comprising making:

an anchoring ring (13) extending around an axis (A);

a guide ring (15), extending around the axis (A);

a plurality of tangential stator vanes (17), each having a respective airfoil (18) connected to respective portions of the anchoring ring (13) and of the guide ring (15), the stator vanes (17) being arranged around the axis (A) and configured to tangentially accelerate a steam flow entering from the outside toward the inside of the stator assembly;

wherein the stator vanes (17) are formed in a single piece with the respective portions of the anchoring ring (13) and of the guide ring (15);

and further comprising obtaining a semi-finished block and making the anchoring ring (13), the guide ring (15) and the plurality of stator vanes (17) by subtractive manufacturing from the semi-finished block; and

cutting the anchoring ring (13) and the guide ring (15) to form a plurality of annular sectors (20), each comprising a respective group of stator vanes (17), a respective sector of the anchoring ring (13) and a respective sector of the guide ring (15).

Ansprüche

1. Statoranordnung für eine Radial-/Axial-Erweiterungsstufe einer Dampfturbine, die Folgendes umfasst:

einen Ankerring (13), der um eine Achse (A) verläuft;

einen Führungsring (15), der um die Achse (A) verläuft; und

mehrere Statorschaufeln (17), die jeweils ein entsprechendes Schaufelblatt (18) besitzen, das mit entsprechenden Abschnitten des Ankerrings (13) und des Führungsrings (15) verbunden ist, wobei die Statorschaufeln (17) um die Achse (A) angeordnet sind und

konfiguriert sind, einen Dampfstrom, der von außerhalb ins Innere der Statoranordnung eintritt, tangential zu beschleunigen; wobei

die Statorschaufeln (17) einteilig mit den entsprechenden Abschnitten des Ankerrings (13) und des Führungsrings (15) gebildet sind;

dadurch gekennzeichnet, dass

die Statorschaufeln (17) tangentiale Statorschaufeln (17) sind;

der Ankerring (13), der Führungsring (15) und die Schaufeln einen zylindrischen Bereich um die Achse (A) definieren;

in jeder Statorschaufel (17) das Schaufelblatt (18) eine Vorderkante (18a) und eine Hinterkante (18b) besitzt, die zwischen dem Ankerring (13) und dem Führungsring (15) axial verlaufen; und

das Schaufelblatt (18) jeder Statorschaufel (17) eine konkave Seite (18c), die der Außenseite des zylindrischen Bereichs zugewandt ist, und eine konvexe Seite (18d), die der Innenseite des zylindrischen Bereichs zugewandt ist, besitzt.

2. Statoranordnung nach Anspruch 1, die mehrere ringförmige Sektoren (20), die jeweils eine entsprechende Gruppe Statorschaufeln (17) umfassen, einen Ankerringbereich (13a) und einen Führungsringbereich (15a) umfasst, wobei die Statorschaufeln (17) jedes ringförmigen Sektors (20) das entsprechende Schaufelblatt (18), das mit dem entsprechenden Ankerringbereich (13a) und dem entsprechenden Führungsringbereich (15a) verbunden ist, besitzen.

3. Statoranordnung nach Anspruch 2, die zwei ringförmige Sektoren (20), die jeweils über einen Bogen von 180° verlaufen, umfasst, wobei jede Gruppe Statorschaufeln (17) die Hälfte der Statorschaufeln (17) umfasst und die Ankerringbereiche (13a) und die Führungsringbereiche (15a) über Bögen von 180° verlaufen.

4. Statoranordnung nach Anspruch 2 oder 3, wobei jeder ringförmige Sektor (20) einteilig gebildet ist.

5. Statoranordnung nach einem der Ansprüche 2 bis 4, wobei jeder ringförmige Sektor (20) mindestens zwei entsprechende Statorschaufeln (17) umfasst.

6. Dampfturbine, die eine Radial-/Axial-Erweiterungsstufe, die mit einer Statoranordnung (11a) nach einem der vorhergehenden Ansprüche versehen ist, umfasst.

7. Dampfturbine nach Anspruch 6, die eine Hülle (2) umfasst, die einen Rotor (3) aufnimmt, der um eine Drehachse (A) drehbar ist, wobei die Hülle (2) mit einer umlaufenden Verankerungsnut (21) und einer umlaufenden Führungsnut (22) versehen ist; wobei die umlaufende Verankerungsnut (21) und die umlaufende Führungsnut (22) um die Drehachse (A) verlaufen und den Ankerring (13) bzw. den Führungsring (15) aufnehmen.

8. Dampfturbine nach Anspruch 7, wobei
die umlaufende Verankerungsnut (21) einen T-förmigen Querschnitt besitzt und der Ankerring (13) eine Basis (13b) und einen Verbindungsabschnitt (13c), der von der Basis (13b) zum Führungsring (15) vorsteht, besitzt; und die Basis (13b) Kanten besitzt, die in Bezug auf den Verbindungsabschnitt (13c) radial nach innen und radial nach außen vorstehen, und wobei der Ankerring (13) in der umlaufenden Verankerungsnut (21) radial und axial festgehalten wird.

9. Verfahren zum Herstellen einer Statoranordnung einer Radial-/Axial-Erweiterungsstufe einer Dampfturbine nach Anspruch 1, das das Bilden von Folgendem umfasst:

eines Ankerrings (13), der um eine Achse (A) verläuft;

eines Führungsrings (15), der um die Achse (A) verläuft;

und

mehrerer tangentialer Statorschaufeln (17), die jeweils ein entsprechendes Schaufelblatt (18) besitzen, das mit entsprechenden Abschnitten des Ankerrings (13) und des Führungsrings (15) verbunden ist, wobei die Statorschaufeln (17) um die Achse (A) angeordnet sind und

konfiguriert sind, einen Dampfstrom, der von außerhalb ins Innere der Statoranordnung eintritt, tangential zu beschleunigen; wobei

die Statorschaufeln (17) einteilig mit den entsprechenden Abschnitten des Ankerrings (13) und des Führungsrings (15) gebildet sind;

und der ferner Folgendes umfasst: Erhalten eines halb fertiggestellten Blocks und ein Herstellen des Ankerrings (13), des Führungsrings (15) und der mehreren Statorschaufeln (17) durch subtraktive Fertigung aus dem halb fertiggestellten Block und

Schneiden des Ankerrings (13) und des Führungsrings (15),

um mehrere ringförmige Sektoren (20) zu bilden, die jeweils eine entsprechende Gruppe Statorschaufeln (17),

einen entsprechenden Sektor des Ankerrings (13) und einen entsprechenden Sektor des Führungsrings (15) umfassen.

Revendications

1. Ensemble de stator pour un étage d'expansion radial - axial d'une turbine à vapeur comprenant :

une bague d'ancrage (13) s'étendant autour d'un axe (A) ;

une bague de guidage (15) s'étendant autour de l'axe (A) ;

une pluralité de pales de stator (17), chacune ayant une surface portante (18) respective raccordée aux parties respectives de la bague d'ancrage (13) et de la bague de guidage (15), les pales de stator (17) étant agencées autour de l'axe (A) et configurées pour accélérer de manière tangentielle un écoulement de vapeur entrant de l'extérieur vers l'intérieur de l'ensemble de stator ;

dans lequel les pales de stator (17) sont formées d'un seul tenant avec les parties respectives de la bague d'ancrage (13) et de la bague de guidage (15) ;

caractérisé en ce que :

les pales de stator (17) sont des pales de stator tangentielles (17) ;

la bague d'ancrage (13), la bague de guidage (15) et les pales définissent une région cylindrique autour de l'axe (A) ;

dans chaque pale de stator (17), la surface portante (18) a un bord d'attaque (18a) et un bord de fuite (18b) s'étendant axialement entre la bague d'ancrage (13) et la bague de guidage (15) ; et

la surface portante (18) de chaque pale de stator (17) a un côté concave (18c) faisant face à l'extérieur de la région cylindrique et un côté convexe (18d) faisant face à l'intérieur de la région cylindrique.

2. Ensemble de stator selon la revendication 1, comprenant une pluralité de secteurs annulaires (20), chacun comprenant un groupe respectif de pales de stator (17), un secteur de bague d'ancrage (13a) et un secteur de bague de guidage (15a), dans lequel les pales de stator (17) de chaque secteur annulaire (20) ont la surface portante (18) respective raccordée au secteur de bague d'ancrage (13a) respectif et au secteur de bague de guidage (15a) respectif.

3. Ensemble de stator selon la revendication 2, comprenant deux secteurs annulaires (20), chacun s'étendant sur un arc de 180°, dans lequel chaque groupe de pales de stator (17) comprend la moitié des pales de stator (17) et dans lequel les secteurs de bague d'ancrage (13a) et les secteurs de bague de guidage (15a) s'étendent sur des arcs de 180°.

4. Ensemble de stator selon la revendication 2 ou 3, dans lequel chaque secteur annulaire (20) est formé d'un seul tenant.

5. Ensemble de stator selon l'une quelconque des revendications 2 à 4, dans lequel chaque secteur annulaire (20) comprend au moins deux pales de stator (17) respectives.

6. Turbine à vapeur comprenant un étage d'expansion radial - axial prévu avec un ensemble de stator (11a) selon l'une quelconque des revendications précédentes.

7. Turbine à vapeur selon la revendication 6, comprenant une coque (2) logeant un rotor (3) pouvant tourner autour d'un axe de rotation (A), la coque (2) étant prévue avec une rainure circonférentielle d'ancrage (21) et une rainure circonférentielle de guidage (22) ; dans laquelle la rainure circonférentielle d'ancrage (21) et la rainure circonférentielle de guidage (22) s'étendent autour de l'axe de rotation (A) et logent la bague d'ancrage (13) et la bague de guidage (15), respectivement.

8. Turbine à vapeur selon la revendication 7, dans laquelle :

la rainure circonférentielle d'ancrage (21) a une section transversale en forme de T et la bague d'ancrage (13) a une base (13b) et une partie de raccordement (13c) faisant saillie de la base (13b) vers la bague de guidage (15) ;

la base (13b) a des bords faisant saillie radialement vers l'intérieur et radialement vers l'extérieur par rapport à la partie de raccordement (13c), et dans laquelle la bague d'ancrage (13) est radialement et axialement retenue à l'intérieur de la rainure circonférentielle d'ancrage (21).

9. Procédé pour fabriquer un ensemble de stator d'un étage d'expansion radial - axial d'une turbine à vapeur selon la revendication 1, comprenant l'étape consistant à fabriquer :

une bague d'ancrage (13) s'étendant autour d'un axe (A) ;

une bague de guidage (15) s'étendant autour de l'axe (A) ;

une pluralité de pales de stator tangentielles (17), chacune ayant une surface portante (18) respective raccordée aux parties respectives de la bague d'ancrage (13) et de la bague de guidage (15), les pales de stator (17) étant agencées autour de l'axe (A) et configurées pour accélérer de manière tangentielle un écoulement de vapeur entrant de l'extérieur vers l'intérieur de l'ensemble de stator ;

dans lequel les pales de stator (17) sont formées d'un seul tenant avec les parties respectives de la bague d'ancrage (13) et de la bague de guidage (15) ;

et comprenant en outre l'étape consistant à obtenir un bloc semi-fini et réaliser la bague d'ancrage (13), la bague de guidage (15) et la pluralité de pales de stator (17) par fabrication soustractive du bloc semi-fini ; et

couper la bague d'ancrage (13) et la bague de guidage (15) afin de former une pluralité de secteurs annulaires (20), chacune comprenant un groupe respectif de pales de stator (17), un secteur respectif de la bague d'ancrage (13) et un secteur respectif de la bague de guidage (15).

Drawing