Method for manufacturing bladed rings for radial turbomachines and bladed ring obtained by this method

Abstract

A method for the construction of bladed rings for radial turbomachines, including: preparing an annular block; roughing the annular block by removing material to define a first, second, third and fourth axial section, wherein the first axial section defines a reinforcement ring, wherein the third axial section defines a base ring; roughing the second axial section by removing material to delimit a plurality of separate elements, wherein the separate elements axially connect the base ring to the reinforcement ring; finishing each of the separate elements by removing material to provide the separate element with the shape of an airfoil blade, wherein a leading edge of the blade and a trailing edge of the blade develop substantially parallel to a central axis of the bladed ring; roughing the fourth axial section by removing material for delimiting an annular anchoring appendage of the base ring to a radial turbomachine.

Claims

1. Method for manufacturing bladed rings for radial turbomachines, comprising: preparing an annular block; roughing the annular block by removing material to define a first axial section, a second axial section, a third axial section and a fourth axial section, wherein the first axial section defines a reinforcement ring, wherein the third axial section defines a base ring; roughing the second axial section by removing material to delimit a plurality of separate elements, wherein the separate elements axially connect the base ring to the reinforcement ring, wherein the separate elements are prismatic; finishing each of the separate elements by removing material to provide the separate elements with the shape of an airfoil blade, wherein a leading edge of the blade and a trailing edge of the blade develop parallel to a central axis of the bladed ring.

2. The method of claim 1, wherein finishing each of the separate elements comprises: subjecting each of the separate elements to electrical discharge machining.

3. The method of claim 2, wherein subjecting each of the separate elements to electrical discharge machining comprises: applying to each of the separate elements at least two electrodes counter-shaped to the airfoil to be obtained.

4. The method of claim 3, wherein at least a first electrode is applied radially from inside and at least a second electrode is applied radially from outside.

5. The method of claim 1, wherein roughing the second axial section comprises: making grooves in the second axial section to form through openings, wherein two subsequent through openings delimit between them one of the separate elements.

6. The method of claim 5, comprising making first blind grooves radially from inside or from outside and making second grooves radially from outside or from inside to open the first blind grooves and to form the through openings.

7. The method of claim 5, wherein making grooves comprises: moving a milling cutter along rectilinear directions.

8. The method of claim 1, comprising: making a circumferential groove on the base ring and/or on the reinforcement ring at the trailing edges of the blades, wherein the circumferential groove delimits an annular wall.

9. The method of claim 8, comprising giving to a terminal edge of the annular wall a wavy shape, wherein crests of the terminal edge are placed at the trailing edges of the blades.

10. The method of claim 8, wherein a ratio between a radial depth of the circumferential groove and a radial chord is comprised between about 0.1 and about 0.9; wherein a ratio between a width of the circumferential groove and a radial depth is comprised between about 0.1 and about 2; wherein a ratio between a thickness of the circumferential annular wall and a width is comprised between about 0.1 and about 10.

11. The method of claim 1, comprising: making a fillet between each blade and the reinforcement ring and between each blade and the base ring.

12. Method for manufacturing bladed rings for radial turbomachines, comprising: preparing an annular block; roughing the annular block by removing material to define a first axial section, a second axial section, a third axial section and a fourth axial section, wherein the first axial section defines a reinforcement ring, wherein the third axial section defines a base ring; roughing the second axial section by removing material to delimit a plurality of separate elements, wherein the separate elements axially connect the base ring to the reinforcement ring; finishing each of the separate elements by removing material to provide the separate elements with the shape of an airfoil blade, wherein a leading edge of the blade and a trailing edge of the blade develop substantially parallel to a central axis of the bladed ring, wherein finishing each of the separate elements comprises: subjecting each of the separate elements to electrical discharge machining, and wherein subjecting each of the separate elements to electrical discharge machining comprises: applying to each of the separate elements at least two electrodes counter-shaped to the airfoil to be obtained.

13. Method for manufacturing bladed rings for radial turbomachines, comprising: preparing an annular block; roughing the annular block by removing material to define a first axial section, a second axial section, a third axial section and a fourth axial section, wherein the first axial section defines a reinforcement ring, wherein the third axial section defines a base ring; roughing the second axial section by removing material to delimit a plurality of separate elements, wherein the separate elements axially connect the base ring to the reinforcement ring; finishing each of the separate elements by removing material to provide the separate elements with the shape of an airfoil blade, wherein a leading edge of the blade and a trailing edge of the blade develop substantially parallel to a central axis of the bladed ring; making a circumferential groove on the base ring and/or on the reinforcement ring at the trailing edges of the blades, wherein the circumferential groove delimits an annular wall.

Description

DESCRIPTION OF THE DRAWINGS

(1) This description will be set out below with reference to the attached drawings, provided solely for indicative and therefore non-limiting purposes, in which:

(2) FIG. 1 shows a meridian section of a radial turbomachine comprising bladed rings, according to the present invention;

(3) FIG. 2 is a partial cut-away perspective view of one of the bladed rings of FIG. 1;

(4) FIG. 3 is a section view along a radial and partial plane of the bladed ring of FIG. 2;

(5) FIG. 4 is a larger-scale portion of FIG. 3;

(6) FIG. 5 is a section view of a portion along a perpendicular plane to a central axis of the bladed ring of FIGS. 2, 3 and 4;

(7) FIG. 6 is an annular block used for constructing the bladed ring of FIGS. 2-5;

(8) FIG. 7, in a broken line, illustrates a sectioned portion according to the plane VI of FIG. 6 of the annular block and, in a continuous line, the corresponding sectioned portion of the block after a first roughing;

(9) FIG. 8 illustrates a machining to remove material according to a construction method of the bladed rings according to the present invention;

(10) FIG. 9 illustrates a machining step of FIG. 8;

(11) FIG. 10 illustrates a variant of the step of FIG. 9;

(12) FIG. 11 is a section view of a plane perpendicular to a central axis following the machining of FIGS. 8, 9 and 10;

(13) FIG. 12 illustrates a further machining step to remove material of the construction method according to the invention;

(14) FIG. 13 illustrates a variant of the machining step of FIG. 12;

(15) FIGS. 14A, 14B and 14C show variants of the machining step of FIG. 8.

DETAILED DESCRIPTION

(16) With reference to the above-mentioned figures, reference numeral 1 denotes in its entirety a radial turbomachine.

(17) The radial turbomachine 1 illustrated in FIG. 1 is an expansion turbine of a radial centrifugal type with a single rotor 2. For example, the turbine 1 can be used in the sector of plants for generation of electrical energy of the Rankine cycle type, either organic Rankine Cycle (ORC) or water steam, which exploit geothermal resources as sources.

(18) The turbine 1 comprises a fixed casing 3 in which the rotor 2 is housed so as to be able to rotate. To this end, the rotor 2 is rigidly connected to a shaft 4 which extends along a central axis X-X (which coincides with a rotation axis of the shaft 4 and the rotor 2) and is supported in the fixed casing 3 by appropriate bearings 5. The rotor 2 comprises a rotor disc 6 directly connected to the shaft 4 and provided with a front face 7 and an opposite rear face 8. The front face 7 projectingly bears a plurality of rotor bladed rings 9 that are concentric and coaxial to the central axis X-X.

(19) The fixed casing 3 comprises a front wall 10, located in front of the front face 7 of the rotor disc 6, and a rear wall 11, located in front of the rear face 8 of the rotor disc 6. The front wall 10 has an opening defining an axial inlet 12 for a work fluid. The axial inlet 12 is located at the central axis X-X and is circular and concentric to the axis X-X. The fixed casing 3 further has a transit volute 13 of the work fluid located in a radially peripheral position external to the rotor 2 and in fluid communication with an outlet, not illustrated, from the fixed casing 3.

(20) The front wall 10 projectingly bears a plurality of stator bladed rings 14 that are concentric and coaxial to the central axis X-X. The stator bladed rings 14 extend internally of the casing 3 towards the rotor disc 6 and are radially alternated with the rotor bladed rings 9 to define a radial path of expansion of the work fluid which enters through the axial inlet 12 and expands moving radially away towards the periphery of the rotor disc 2 up to entering into the transit volute 13 and then exiting from the fixed casing 3 through said outlet, not illustrated.

(21) The rotor bladed rings 9 and the stator bladed rings 14 are structurally similar to one another. In the following therefore a description will be made of the rotor bladed rings 9.

(22) With reference to FIGS. 2 and 3, the bladed ring 9 comprises a first support ring 15 or base ring destined to be anchored to the front face 7 of the rotor disc 6.

(23) As can be observed in FIGS. 2 and 3, the base ring 15 has a first annular central body 16, which in the above-mentioned section is rectangular or square, from which an annular anchoring appendage 17 extends axially on one side and comprises an elastically yielding ring 18 which terminates with a connecting foot 19. The elastically yielding ring 18 is directly connected to the base ring 15 and the connecting foot 19 is positioned at an end of the elastically yielding ring 18 opposite the first annular central body 16. The elastically yielding ring 18 enables a radial deformation thereof when subjected to loads (centrifugal force, temperature) of the turbomachine when operating. The connecting foot 19 is configured for stably engaging in an appropriate seating, not illustrated, fashioned in the rotor 2. The bladed ring 9 comprises a second support ring 20 or reinforcement ring. FIG. 3 illustrates the section, in an axial plane, of the reinforcement ring 20. As can be observed, the second support ring 20 has a second annular body 21, which in the above-mentioned section is rectangular or square.

(24) The bladed ring 9 comprises a plurality of blades 22 with an airfoil that extends between the base ring and the reinforcement ring 15, 20. The base ring and the reinforcement ring 15, 22 are coaxial and axially spaced from one another. Each blade 22 has a leading edge 23 and a trailing edge 24 parallel to the central axis X-X of the bladed ring 9. As the illustrated turbomachine 1 is a centrifugal radial turbine in which the work fluid moves radially towards the outside, the leading edge 23 of each blade 22 radially faces towards the inside, i.e. towards said central axis X-X, and the trailing edge 24 is facing radially towards the outside.

(25) The blades 22 are arranged equally spaced from the central axis X-X and circumferentially spaced by a constant pitch from one another. The blades 22 have a radial chord Cr defined by the difference between an external radius Re and an internal radius Ri of the bladed ring 9 measured at the blades 22 (FIG. 3). Each blade 22 has a first axial end 25 and a second axial end 26 that are opposite and respectively connected to the base ring 15 and the reinforcement ring 20 (FIG. 3).

(26) A circumferential groove 27 is fashioned on a radially external face of both the base ring 15 and the reinforcement ring 27, which circumferential groove 27 is located in proximity of the blades 22 so as to delimit an annular wall 28 (FIG. 4). The annular wall 28 extends radially outwards and has a terminal edge 29 which has a wavy shape, wherein the crests 30 of said terminal edge 29 are positioned at the trailing edges 24 of the blades 22 (FIGS. 2 and 5).

(27) By way of example, the radial chord Cr is about 10 mm. The ratio between an axial length L of the bladed ring 9 and said radial chord Cr is for example ten, so that the axial length L is about 100 mm. The ratio between an axial length Lp of each blade 22 and the radial chord Cr is, for example, five, so that said axial length Lp of each blade 22 is about 50 mm. The ratio between an axial length La1 of the reinforcement ring 20 and the radial chord Cr is for example two, so that said axial length La1 of the reinforcement ring 20 is about 20 mm. The ratio between an axial length La2 of the base ring 15 and the radial chord Cr is for example two, so that the axial length La2 of the base ring 15 is about 20 mm. The ratio between an axial length Le of the elastically yielding ring 18 and the radial chord Cr is for example about two, so that the axial length Le of the elastically yielding ring 18 is about 20 mm. The ratio between an axial length Lg of the elastically yielding ring 19 and the radial chord Cr is for example 0.5, so that the axial length Lg of the connecting foot 19 is about 5 mm. The ratio between a thickness s of the elastically yielding ring 18 and the radial chord Cr is for example about 0.125, so that said thickness s is about 1.25 mm. The ratio between a radial depth d of the circumferential groove 27 and the radial chord Cr is, for example, 0.5, so that the radial depth d is about 5 mm. The ratio between a width w of the circumferential groove 27 and the radial chord Cr is, for example, 0.15, so that said width w is about 1.5 mm. The ratio between a thickness t of the circumferential annular wall 28 and the radial chord Cr is for example about 0.08, so that said thickness t is about 0.8 mm.

(28) The bladed ring 9 is in a single piece, i.e. is made of a starting annular block 31 (FIG. 6) made of metal obtained, for example, by forging.

(29) According to the method for the construction of bladed rings for radial turbomachines of the invention, the starting annular block 31 is first roughed by removal of material (lathing or reaming) so as to define a first axial section 32, a second axial section 33, a third axial section 34 and a fourth axial section 35 (FIG. 7). The first axial section 32 and the second axial section 33, the third axial section 34 and the fourth axial section 35 are annular elements flanked in sequence one after another and forming a single body.

(30) The first axial section 32 defines the reinforcement ring 20, which in this step is practically already finished. The blades 22 will be fashioned from the second axial section 33, as described in detail in the following. The third axial section 34 defines the base ring 15, which in this step is practically already finished. The elastically yielding ring 18 and the connecting foot 19 will be fashioned from the fourth axial section 35.

(31) With the aim of forming the blades 22, the second axial section 33 is roughed by removing material so as to delimit a plurality of prismatic separate elements 36 which axially connect the base ring 15 to the reinforcement ring 20. Each of these prismatic separate elements 36 has a volume that is such as to each contain a final blade 22 or, in other terms, is characterised by transversal sections containing the aerodynamic profile of the blade 22 for each section. FIG. 11 illustrates a section of the second axial section 33 in a perpendicular plane to the central axis X-X after the definition of the plurality of prismatic separate elements 36. The transversal sections of said prismatic separate elements 36 are visible, as is the profile of the blade 22, in a broken line, which will be fashioned from each thereof.

(32) To define the prismatic separate elements 36, a milling cutter 37 is positioned in a radially internal position relative to the second axial section 33 and orientated along a radial direction (FIGS. 8, 9 and 10). The milling cutter 37 is radially moved towards the outside up to being engaged with a radially internal surface 38 of the second axial section 33. Thereafter the milling cutter 37 is displaced axially over the whole axial length Lp of the second axial section 33, i.e. of each blade 22, and then extracted from the second axial section 33. These steps are carried out one (as in FIG. 9) or more times (as in FIG. 10) for realising a radially internal groove 39 which is blind (i.e. which does not pass through the thickness of the second axial section 33). The milling cutter 37 is then displaced by one step along a circumferential direction in order to realise another groove 39. The radially internal grooves 39 are realised in a same number as the blades 22.

(33) The same milling cutter 37 or a further milling cutter 40 is positioned in a radially external position relative to the second axial section 33 and orientated in an oblique direction with respect to a radial direction (FIG. 8). The further milling cutter 40 is moved towards the inside along said oblique direction up to being engaged with a radially external surface 41 of the second axial section 33. Thereafter the further milling cutter 40 is displaced axially over the whole axial length Lp of the second axial section 33, i.e. of each blade 22, and then extracted from the second axial section 33. These steps are carried out one or more times for realising a radially external groove 42 (FIG. 8). The milling cutter 40 is then displaced by one step along a circumferential direction in order to realise another groove 42. The radially external grooves 42 realised are in a same number as the blades 22. As can be observed in FIG. 8, each radially external groove 42 is located at a respective radially internal groove 40 and said two radially external groove 42 and radially external groove 40 co-penetrate so as to open a through opening or radial passage 43 (FIG. 11).

(34) The milling cutters 37, 40 are moved along rectilinear directions, i.e. without complicated interpolations of movements. During this roughing step of the blades 22 the roughness Ra of the surfaces is usually greater than 0.8 and the precision is for example comprised between +/0.05 mm and 2 mm.

(35) The functioning parameters of the milling cutters 37, 40 are for example reported in following table 1.

(36) TABLE-US-00001 TABLE 1 Advancement velocity 1000 mm/min Cutting depth 1 mm Tangential velocity 20 m/min Rotation velocity 5000 RPM Torque 50 Nm Axial speed 30 m/min

(37) The prismatic separate elements 36 are therefore machined removing material for forming the blades 22 with the desired airfoil profile and with a desired surface quality (roughness Ra for example comprised between 0.02 and 32) and precision (for example comprised between +/0.01 mm and +/0.5 mm).

(38) According to a method, the finishing is carried out by frontal milling with a spherical milling cutter 44 (FIG. 12). The functioning parameters of the milling cutter 44 are for example reported in following table 2.

(39) TABLE-US-00002 TABLE 2 Advancement velocity 500 mm/min Cutting depth 0.1 mm Tangential velocity 100 m/min Rotation velocity 20000 RPM Torque 5 Nm Axial speed 15 m/min

(40) Alternatively, finishing is carried out by electrical discharge machining (FIG. 13). For this purpose, two electrodes 45, 46 are applied to each of the separate elements 36, counter-shaped to the airfoil to be obtained. A first electrode 45 is applied radially from inside according to a radial direction and at least a second electrode 46 is applied radially from outside according to a radial direction. As can be noted, the first electrode 45 has a first operating surface 47 counter-shaped to the lower surface of the blade 22 and the second electrode 46 has a second operating surface 48 counter-shaped to the upper surface of the blade 22. The functioning parameters of the electrodes are for example reported in following table 3.

(41) TABLE-US-00003 TABLE 3 Working/peak current 600 A Advancement velocity 20 mm/min

(42) During the finishing of the blades 22 described above, a fillet 49 is made between the first axial end 25 of each blade 22 and the reinforcement ring 20 and between the second axial end 26 of each blade 22 and the base ring 15. This fillet 49, visible in FIG. 4, can have a circular or elliptical profile and extends all about the blade 22 in the joining area between a surface of the blade 22 and the respective base ring 15 or reinforcement ring 20.

(43) Following the finishing of the blades 22, the circumferential grooves 27 on the base ring 15 and reinforcement ring 20 and each annular wall 28 is fashioned about the blades 22 in proximity of the trailing edge 24 so as to give the terminal edge 29 of each annular wall 28 the above-described wavy shape.

(44) At this point, the fourth axial section 35, which still has the shape of FIG. 7, is lathed or reamed to obtain the elastically yielding ring 18 and the connecting foot 19.

(45) Lastly the blades 22 are polished, for example for further reducing the surface roughness and/or for eliminating any working micro-defects in the machining of the preceding steps.