WO2018167632A1

WO2018167632A1 - Method for the construction of bladed rings for radial turbomachinery

Info

Publication number: WO2018167632A1
Application number: PCT/IB2018/051607
Authority: WO
Inventors: Stefano SALGAROLLO; Dario RIZZI
Original assignee: Exergy S.P.A.
Priority date: 2017-03-14
Filing date: 2018-03-12
Publication date: 2018-09-20
Also published as: HRP20211991T1; EP3612721A1; DK3612721T3; IT201700028266A1; LT3612721T; ES2901098T3; EP3612721B1

Abstract

The present invention relates to a method for constructing bladed rings for radial turbomachines. The method comprises: preparing a cylindrical block (M; M1, M2); making in the cylindrical block (M; M1, M2) a wavy circumferential cut (28, 28', 28") delimiting a first plurality of teeth (29) and a second plurality of teeth (30) meshing in one another; wherein the wavy circumferential cut (28, 28', 28") splits the cylindrical block (M; M1, M2) into a first annular body (31; 31 ', 31 ") provided with the first plurality of teeth (29) and into a second annular body (32; 32', 32") provided with the second plurality of teeth (30); separating the first annular body (31; 31 ', 31 ") from the second annular body (32; 32', 32"); removing material from each of the teeth (29, 30) of the first and second plurality to confer to each tooth (29, 30) the outline of at least one blade (22', 22") with an aerodynamic profile; joining coaxially the first annular body (31;31 ', 31 ") to the second annular body (32; 32', 32") by inserting the first blades (22') between the second blades (22").

Description

Title

"Method for the construction of bladed rings for radial turbomachinery"

DESCRIPTION

Field of the invention

The object of the present invention is a method for the construction of bladed rings for radial turbomachinery, a bladed ring and a bladed disc obtained by means of said method.

Radial turbomachinery means a turbomachine in which the flow of fluid with which it exchanges energy is directed in a radial direction for at least a part of the path followed in the turbomachine itself. The radial part of the path is delimited by at least one annular series of blades through which the fluid moves prevalently along a radial direction relative to an axis of rotation of the turbomachine.

A "bladed ring" comprises a plurality of blades arranged equally spaced from a central axis and joined to one another by two or more concentric rings axially spaced from one another. The blades extend between two rings with their leading and trailing edges turned radially towards the inside and towards the outside, respectively, (centrifugal radial ring) or vice versa (centripetal radial ring). The aforementioned leading and trailing edges may be parallel or substantially parallel to the central axis or curved (twisted blades). The bladed ring can have either a stator function (it is fixed with respect to a casing of the turbomachine and its blades are stator blades) or a rotor function (i.e. it rotates and its blades are rotor blades and therefore the central axis is the axis of rotation of the turbomachine). A "bladed disc" comprises a plurality of annular series of blades fixed onto a front face of a disc. The series are concentric and each series comprises a plurality of blades arranged at equal distances from a central axis of the disc. The blades extend away from the front face with their leading and trailing edges parallel or substantially parallel to the central axis. The bladed disc further comprises a plurality of reinforcement rings, each connected to all the blades of an annular series at one end of said blades opposite the one connected to the front face of the disc.

The bladed disc can also have either a stator function (it is also called a stator plate, it is fixed with respect to a casing of the turbomachine and its blades are stator blades) or a rotor function (it is also called a rotor disc, it rotates together with the turbomachine shaft and its blades are rotor blades and therefore the central axis is the axis of rotation).

A bladed disc can be seen as being formed by a plurality of concentric bladed rings fixed onto a support disc.

The present invention applies both to centrifugal radial turbomachines (out-flow) and centripetal radial turbomachines (in-flow). The present invention is applied both to drive turbomachines (turbines) and work turbomachines (compressors). Preferably but not exclusively, the present invention relates to expansion turbines. Preferably but not exclusively, the present invention relates to expansion turbines used in plants for the production of electrical and/or mechanical energy (power plants).

Background of the invention

Published document WO 2014/064567, in the name of the same Applicant, illustrates a method for constructing stages of centrifugal radial turbines, in which the first and the second ends of each blade are connected to respective support rings, joining, by laser welding, at least a first semi-portion belonging to the respective end of the blade and a respective second semi-portion belonging to the respective support ring, in order to form an resiliently yielding connecting portion along a radial direction, and placing at least a stop portion belonging to the end of the blade facing, along the aforementioned radial direction, at least a stop element of the respective support ring. The resiliently yielding connecting portion enables the stop portion to come into contact with the stop element when the stage is subjected to workloads of the turbine.

Published document GB 652 591 illustrates a bladed ring for radial turbines, in which the blades can be made in a single piece with a respective reinforcement ring.

Document WO 2015/14071 1 , in the name of the same Applicant, illustrates a centrifugal radial turbine of the mono-rotating type and a centrifugal radial turbine of the counter-rotating type provided with bladed discs.

Public document US 4,306,833 illustrates a compressor with an impeller provided with a disc having two annular series of blades arranged at a peripheral zone and each on one of the faces of the disc itself. The blades of each series extend in a respective annular chamber. The disc with the blades can be realised through die casting. A ring is applied against each end of the blades of a series, to eliminate leaks due to the formation of vortexes at said ends. Each ring is fixed to the impeller through screws inserted in bosses fashioned on the impeller.

Public document US 6,508,631 illustrates a radial flow pump. The pump comprises a rotor and a plurality of blades arranged in concentric rings and extending from a first face of the rotor in a substantially parallel direction to a central axis of rotation. The rotor and the blades may be formed by a single block of material. A support ring that reduces deflection due to the centrifugal force may be arranged around the blades.

Summary

In such context, the Applicant perceived the need to improve the known methods for the construction of bladed rings for radial turbomachinery, in particular with a similar structure to those illustrated in the previous documents WO 2014/064567 and WO 2015/14071 1 , so as to speed up their production and reduce costs, while ensuring high quality such as to guarantee the reliability and efficiency of the turbomachinery in which they are installed.

The Applicant has noted that in the solutions that envisage the realisation of rotor bladed rings by direct joining between the blades and the support rings, as in WO 2014/064567, it is more difficult to separate the stresses due to the centrifugal force from those due to the weight of the blades. In particular, the Applicant has noted that the internal circumferential stresses due to centrifugal force have their points of maximum concentration at the connecting zones with the blades, in particular at the outlet edges thereof. These zones of maximum concentration of the stresses are structurally dangerous.

The Applicant has also noted that the machining from solid billet such as that suggested by GB 652 591 can be expensive and time consuming.

The Applicant has also noted that the realisation through the die casting of the disc illustrated in document US 4,306,833 does not allow blades to be obtained with precise geometries and therefore the high efficiencies required, for example, in power plants for energy generation. Furthermore, the compressor of such document substantially only has one stage split on the two faces of the disc of the impeller and is unsuitable for handling high enthalpy changes. Finally, the bosses of US 4,306,833 that allow the rings to be mounted on the rotor disc are located between two adjacent blades and therefore disturb the flow of the work fluid that flows over them.

The Applicant has also noted that the rotor described in document US 6,508,631 does not appear to display reinforcement rings and therefore would not allow leaks to be reduced or the desired performance to be obtained. Furthermore, none of these documents illustrates in detail the realisation process of the respective rotors.

The Applicant also highlights that document WO 2015/14071 1 does not illustrate any construction methods of the respective discs.

In this context, the Applicant pursues the following objectives:

^■ providing a method for the construction of bladed rings that is quick and relatively simple, so as to reduce production costs;

^■ providing a method for the construction of bladed rings that allows the waste material deriving from processing to be reduced to a minimum, so as to reduce the costs for the provision of the basic material and/or for the disposal of scraps;

^■ providing a method for the construction of bladed rings which enables the quality and constructive precision of the bladed rings to be improved and therefore the reliability and efficiency of the radial turbomachines in which they are installed.

The Applicant has found that the above-indicated and other objectives can be attained by realising blades of a ring from the blank, i.e. by removal of material from a starting block, in which the blades are sketched by dividing a cylindrical block in half through a wavy circumferential cut.

In particular, the stated and other objectives are substantially attained by a method for the construction of bladed rings for radial turbomachines, by a bladed ring, by a bladed disc and by a radial turbomachine according to one or more of the appended claims and/or according to one or more of the following aspects.

More specifically, according to an independent aspect, the present invention relates to a method for the construction of bladed rings for radial turbomachines, comprising:

preparing at least one cylindrical block;

making in the cylindrical block a wavy circumferential cut defining a first plurality of teeth and a second plurality of teeth meshing in one another; wherein the wavy circumferential cut splits the cylindrical block into a first annular body provided with the first plurality of teeth and into a second annular body provided with the second plurality of teeth;

separating the first annular body from the second annular body;

removing material from each of the teeth of the first plurality to confer to said tooth the outline of at least a first blade with an aerodynamic profile;

removing material from each of the teeth of the second plurality to confer to said tooth the outline at least of a second blade with an aerodynamic profile;

joining coaxially the first annular body to the second annular body by inserting the first blades between the second blades.

In the present description and the appended claims, the adjective "axial" means a definition of a direction running parallel to a central axis of the bladed ring or axis of rotation "X-X" of the turbomachine. The adjective "radial" is meant as a definition of a direction directed in radius-fashion perpendicularly from the central axis of the bladed ring or axis of rotation "X-X" of the turbomachine. The adjective "circumferential" is meant as a definition of directions tangential to circumferences coaxial to the central axis of the bladed ring or the axis of rotation "X-X" of the turbomachine.

In the radial turbomachines according to the present invention, the leading edge faces radially towards the inside (centrifugal radial turbomachine) or towards the outside (centripetal radial turbomachine) and the trailing edge faces radially towards the outside (centrifugal radial turbomachine) or towards the inside (centripetal radial turbomachine).

"Cylindrical block" means a ring-shaped element comprising a single piece and not formed by various parts. Such cylindrical block may be a stand-alone element or may be part of a more complex element, such as a rotor disc that has on a face thereof one or more cylindrical blocks integrated into the rotor disc.

"Wavy circumferential cut" means a cut that passes through the thickness of the wall that defines the cylindrical body and that extends all around the cylindrical body along a wavy trajectory. The cut, therefore, identifies two plurality of teeth being complementary or counter-shaped to each other. A midline of said wavy trajectory is a circle coaxial to the central axis. Once completed, the wavy circumferential cut is necessarily a through cut so as to be able to divide the first annular body from the second annular body but it can be performed in various steps and possibly also with different methods.

The Applicant has verified that the present invention allows the realisation times of a radial bladed ring to be considerably reduced. In fact, the method allows the outline of the blades to be sketched (first plurality of teeth and second plurality of teeth) simultaneously on both annular bodies by making a single cut (wavy circumferential cut).

The Applicant has verified that the present invention allows the process necessary for obtaining blades to be simplified. In fact, once the two annular bodies have been separated, the space around each tooth necessary for processing it in order to define the aerodynamic profile is much larger than the available space if all the blades were realised on a single annular body. Furthermore, the stock to be removed in order to achieve the final shape of the blade is small compared to that to be removed in the realisation of the blades from the blank.

The Applicant has also verified that the present invention allows the waste material deriving from processing to be reduced to a minimum, in particular with respect to the realisation of the blades on two distinct annular bodies (two cylindrical blocks) from the blank and therefore the costs connected with the disposal and/or recycling thereof.

The Applicant has also verified that the present invention allows the quantity of the starting material to be reduced and therefore the costs, weight and difficulty of any transport and/or management of the semi-processing starting part(s).

The Applicant has also verified that the present invention allows savings to be made on the tools for the rough processing of the blades and machines with lower costs to be used for the roughing step (which is less precise in itself) because their performance is lower in terms of achievable tolerances.

The Applicant has also verified that the present invention allows good quality bladed rings and discs to be realised and therefore to ensure the reliability and efficiency of the radial turbomachines in which they are installed.

In one aspect, the cylindrical block is a stand-alone element.

In one aspect, the cylindrical block is an integral part of a starting disc and is arranged on a front face of said starting disc.

In one aspect, the starting disc comprises a plurality of concentric cylindrical blocks arranged on the front face. In one aspect, after the separation, the first annular body is still part of the starting disc.

In other words, the cylindrical block may be a stand-alone element and a bladed ring for radial turbomachines can be fashioned therefrom or one or more cylindrical blocks are integral parts of a disc and from the assembly a bladed disc for radial turbomachines bearing one or more bladed rings can be fashioned.

In one aspect, the cylindrical block or the disc provided with one or more cylindrical blocks is made by moulding, preferably by forging.

In one aspect, before performing the wavy circumferential cut, the cylindrical block is roughed.

In one aspect, the roughing is performed by turning.

In one aspect, the roughing envisages removing material to define a first axial section, a second axial section and a third axial section. Said axial sections are defined by respective circular portions of the cylindrical block axially flanked.

In one aspect, the first axial section defines a base ring. Once the bladed ring has been mounted in the turbomachine, the base ring is jointed to a support ring or to a casing of the turbomachine.

In one aspect, as well as the base ring, the first axial section also defines a resiliently yielding ring.

In one aspect, the first axial section defines a connecting foot placed at a terminal end of the resiliently yielding ring.

In one aspect, the third axial section defines a reinforcement ring. Once the bladed ring has been mounted in the turbomachine, the reinforcement ring is hung on the blades and supported in a cantilever fashion by the blades.

In one aspect, the wavy circumferential cut is performed in the second axial section. The second axial section is the one intended to generate the blades.

In one aspect, the wavy circumferential cut passes through a wall constituting said cylindrical block.

In one aspect, the wavy circumferential cut is performed through abrasive water jet (AWJ).

In one aspect, the wavy circumferential cut is performed through laser and/or electro discharge machining - sinker EDM and/or wire cut EDM and/or plasma and/or oxy cutting. In one aspect, the wavy circumferential cut is performed through the mechanical removal of chips.

In one aspect, the wavy circumferential cut is performed in one or more steps/phases.

In one aspect, the wavy circumferential cut crosses the cylindrical block along radial directions.

In one aspect, the wavy circumferential cut, in at least some stretches, crosses the cylindrical block along tangent directions to virtual circumferences coaxial to the cylindrical block.

In one aspect, the wavy circumferential cut is performed in part through interrupted cuts performed starting from a radially internal surface of the cylindrical block and in part through interrupted cuts performed starting from a radially outer surface of the cylindrical block. Interrupted cut means a cut that penetrates into the material of the cylindrical block without exiting from the opposite side, i.e. it is not a through cut.

In one aspect, on a radially outer surface of the cylindrical block, the wavy circumferential cut has the shape of a square wave.

In one aspect, each tooth has, in a front view, a substantially polygonal outline, e.g. substantially quadrilateral, preferably substantially parallelogram shaped.

In one aspect, the number of teeth of the first plurality is equal to the number of teeth of the second plurality.

In one aspect, the number of teeth of the first plurality is different from the number of teeth of the second plurality.

In one aspect, removing material from each of the teeth of the first plurality and of the second plurality comprises: roughing each tooth to define in a front view an outline proximal to that of a blade, preferably but not necessarily substantially polygonal. In other words, starting from the quadrilateral, material is removed to realise an outline, for example but not necessarily a polygon, closer to the definitive outline of the blade.

In one aspect, the roughing of each tooth is performed by removing blocks of material.

In one aspect, the blocks are removed from the tooth with a quadrilateral section to confer to it the polygonal section. In one aspect, the blocks are removed from the tooth to confer to it an outline that traces the shape of the blade but with stock to be removed in a subsequent finishing step.

In one aspect, the roughing of each tooth is performed through abrasive water jet and/or laser and/or mechanical removal of chips and/or electro discharge machining and/or sinker EDM and/or wire cut EDM and/or plasma and/or oxy cutting.

In one aspect, removing material from the first plurality and the second plurality comprises: performing a finishing step until the tooth is conferred the aerodynamic outline of the blade.

In one aspect, the finishing of each blade is performed through the mechanical removal of chips and/or electrical discharge machining and/or electrochemical machining - ECM.

In one aspect, coaxially jointing the first annular body with the second annular body comprises: joining terminal ends of the first blades to the second annular body.

In one aspect, each first blade is inserted between two second blades until a terminal end of the first blade is brought against a bottom surface of the second annular body lying between the two second blades.

In one aspect, coaxially jointing the first annular body with the second annular body comprises: joining terminal ends of the second blades to the first annular body.

In one aspect, each second blade is inserted between two first blades until a terminal end of the second blade is brought against a bottom surface of the first annular body lying between the first two blades.

In one aspect, coaxially jointing the first annular body with the second annular body comprises: fixing terminal ends of the first blades to the second annular body.

In one aspect, coaxially jointing the first annular body with the second annular body comprises: fixing terminal ends of the second blades to the first annular body.

In one aspect, the terminal ends of the first blades are fixed to the second annular body and/or the terminal ends of the second blades are fixed to the first annular body through screws and/or pins. In one aspect, a leading edge and/or a trailing edge of said first blade extend parallel or substantially parallel to a central axis of the first annular body.

In one aspect, a leading edge and/or a trailing edge of said second blade extend parallel or substantially parallel to a central axis of the second annular body.

In one aspect, a leading edge and/or a trailing edge of said first blade have a curved profile (twisted blades).

In one aspect, a leading edge and/or a trailing edge of said second blade have a curved profile (twisted blades).

In one aspect, the present invention relates to a bladed ring for radial turbomachines realised according to one or more of the aspects listed above and/or according to one or more of the appended claims and/or embodiments illustrated below.

In one aspect, the present invention relates to a bladed disc for radial turbomachines comprising one or more bladed rings according to the previous aspect.

In one aspect, the bladed rings are realised individually and then joined to a support disc.

In one aspect, a starting disc is prepared integrating one or more concentric cylindrical blocks arranged on the front face of the starting disc and realising the bladed ring(s) from said one or more concentric cylindrical blocks.

According to one aspect, the present invention relates to a radial turbomachine comprising at least one bladed ring and/or a bladed disc according to the preceding aspect.

In one aspect, the bladed ring is a rotor ring.

In one aspect, the bladed ring is a stator ring.

In one aspect, the radial turbomachine is a centrifugal or centripetal radial turbine, preferably with a single rotor disc or with two counter-rotating rotor discs.

Further characteristics and advantages will more fully emerge from the detailed description of a radial turbomachine, of a bladed ring for radial turbomachines, of a bladed disc for radial turbomachines and of a method for construction thereof according to the present invention.

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

^■ figure 1 shows a meridian section of a radial turbomachine comprising a single bladed disc;

■ figure 2 is a partial perspective view of a detail of a bladed ring belonging to the disc of figure 1 ;

^■ figure 3 illustrates a cylindrical block from which the bladed ring of figure 2 is fashioned;

^■ figure 4 illustrates the view of figure 2 in a processing step of the cylindrical block;

^■ figure 5 illustrates a sectional view of the cylindrical block appearing in figure 4;

^■ figure 5A illustrates the sectional view of figure 5 according to a variant of the processing step of figure 4;

■ figure 6 illustrates a lateral view of the cylindrical block in the processing step of figures 4 or 5;

^■ figure 7 illustrates a perspective view of the cylindrical block in a subsequent processing step;

^■ figure 8 illustrates a front view of one of the two parts of the cylindrical block in a further processing step;

^■ figure 8A illustrates a variant of the further processing step of figure 8;

^■ figure 8B illustrates a tool used in the processing step of figure 8A;

^■ figure 9 illustrates a front view of the other side of the cylindrical block in a further processing step;

■ figure 10 illustrates an assembly step of the method according to the present invention;

^■ figure 1 1 illustrates a sectional view of the bladed ring appearing in figure 2;

^■ figure 12 illustrates a processing step of a starting disc according to a variant of the method according to the invention.

Detailed description

With reference to the above-mentioned figures, reference numeral 1 denotes in its entirety a radial turbomachine. The radial turbomachine 1 illustrated in figure 1 is an expansion turbine of a radial centrifugal type (out-flow) 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 vapour, or even other types of cycles with different work fluids.

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 an axis of rotation of the shaft 4 and of the rotor 2) and is supported in the fixed casing 3 by appropriate bearings 5. The rotor 2 comprises a rotor disc 6 connected to the aforementioned shaft 4 and provided with a front face 7 and an opposite rear face 8. The rotor disc 6 is of the overhung type, i.e. it is connected in a cantilever fashion to an end of the shaft 4. The front face 7 of the rotor disc 6 bears in a cantilever fashion a plurality of rotor bladed rings 9 that are concentric and coaxial to the central axis "X-X".

The fixed casing 3 comprises a front wall 10, located opposite the front face 7 of the rotor disc 6, and a rear wall 1 1 , located opposite 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 same 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.

An internal face of the front wall 10 bears in a cantilever fashion a plurality of stator bladed rings 14 that are concentric and coaxial to the central axis "X-X". The stator bladed rings 14 extend inside 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.

The rotor bladed rings 9 and the stator bladed rings 14 are structurally similar to one another.

The structure of the rotor disc 6 is described below, as is an example of a method for the construction of the bladed rings 9 of the rotor disc 6. The same method can also be used for realising the stator rings 14. In general, such method is used to build bladed rings and discs (stator and/or rotor) for radial turbomachines.

A portion of the bladed ring 9 realised with such method is illustrated in figure 2. With reference to figure 2, the bladed ring 9 comprises a first support ring 15 or base ring intended to be anchored to the front face 7 of the rotor disc 6. As can be observed in figures 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 a resiliently yielding ring 18 which terminates with a connecting foot 19. The resiliently yielding ring 18 is directly connected to the base ring 15 and the connecting foot 19 is positioned at an end of the resiliently yielding ring 18 opposite the first annular central body 16.

The resiliently 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 disc 6.

The bladed ring 9 comprises a second support ring 20 or reinforcement ring. Figure 2 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.

The bladed ring 9 comprises a plurality of blades 22', 22" with an aerodynamic profile that extend between the base ring and the reinforcement ring 15, 20. The base ring and the reinforcement ring 15, 20 are coaxial and axially spaced from one another. Each blade 22', 22" of the illustrated example 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', 22" radially faces towards the inside, i.e. towards said central axis "X-X", and the trailing edge 24 faces radially towards the outside.

The blades 22', 22" are arranged equally spaced from the central axis "X-X" and circumferential ly spaced by a constant pitch from one another.

Each blade 22', 22" has a first axial end and a second axial end that are opposite and respectively connected to the base ring 15 and to the reinforcement ring 20. The method according to the present invention for the realisation of the bladed ring 9 envisages starting from a cylindrical block "M" made of forged metal which in figure 3 is illustrated as a stand-alone element. A half-section of the cylindrical block "M", sectioned by the radial plane IV of figure 3, is illustrated in figure 4 in broken lines.

The cylindrical block "M" is first subjected to rough turning through which material is removed until a first axial section 25, a second axial section 26 and a third axial section 27 are defined. The axial sections 25, 26, 27 are defined by respective circular portions of the cylindrical block "M" axially flanked and forming a single body (figure 4).

The first axial section 25 defines the base ring 15, which in this step may be practically already finished, and the resiliently yielding ring 18 with the connecting foot 19. The blades 22', 22" will be fashioned from the second axial section 26, as will be described in detail in the following. The third axial section 27 defines the reinforcement ring 20.

The rough turning can be followed by finish turning.

At the end of the finish turning, the cylindrical block "M" has the reinforcement ring 20 practically already finished, the second axial section with a radial thickness slightly less than the radial thickness of the first 25 and third 27 axial section, the base ring 15 also practically already finished, the resiliently yielding ring 18 and the connecting foot 19.

As can be noted in figure 4, since the second axial section 26 has a radial thickness slightly less than the first 25 and the third 27 axial section adjacent thereto, respective steps are defined both on a radially internal surface and on a radially outer surface of the semi-processed cylindrical block "M". The lower thickness of the second axial section 26 allows less material to be cut and furthermore to have less material removed during the blade finishing step, according to what is described below.

In the second axial section 26, in one or more steps and with one or more processing tools, a wavy circumferential cut 28 is performed, which extends along the entire circumference of said second axial section 26.

In the preferred and illustrated embodiment, the cut is performed through abrasive water jet (AWJ) and has, seen on a radially outer surface of the axial section 26, a square wave outline with peaks and troughs arranged at the mentioned steps. In a different embodiment, the cut can be performed through laser or mechanical removal of chips (or also sinker EDM, wire cut EDM, plasma, oxy cutting). As can be seen in figures 4 and 6, the wavy circumferential cut 28 extends in a zig-zag fashion between the two steps. Peaks and troughs of the wavy cut are defined by circumferential stretches of the cut parallel to the two steps and connected to each other by axial stretches parallel to each other.

The wavy circumferential cut 28 passes through the wall of the second axial section 26 of the cylindrical block "M". The aforementioned axial stretches of the cut extend along directions " and in tangent planes to virtual circumferences coaxial to the cylindrical block "M", as illustrated in figure 5. The aforementioned stretches of the cut parallel to the two steps (radial cuts at the base of the blades) extend in substantially perpendicular planes to the central axis "X-X" or slightly inclined with respect to a perpendicular plane to said central axis "X-X".

It follows that, in a sectional view on a perpendicular plane to the central axis "X-X" (such as that of figure 5), the through cuts belonging to the wavy circumferential cut 28 delimit in the thickness of the second axial section 26 shapes that resemble quadrilaterals. More precisely, each of said shapes is delimited by the radially outer surface of the second axial section 26, by the radially internal surface of the second axial section 26 and by two of the directions "T" tangent to virtual circumferences coaxial to the cylindrical block "M".

The wavy circumferential cut 28 therefore defines a first plurality of teeth 29 and a second plurality of teeth 30 meshing in one another and each having a parallelepiped outline with a substantially quadrilateral section.

In the variant of figure 5A, the aforementioned axial stretches of the cut extend along two directions "TV and "T2". In other words, each of the axial stretches of the wavy circumferential cut 28 is formed through a first cut performed starting from a radially outer surface of the second axial section 26 along a first direction "TV. Such first cut penetrates about half way into the thickness of the second axial section 26 (interrupted cut). Each of the axial stretches of the wavy circumferential cut 28 is completed by performing a second cut in a radially internal surface of the second axial section 26 along a second direction "T2". Such second cut penetrates about half way into the thickness of the second axial section 26 (interrupted cut) until it connects with the first cut. Although not illustrated, each of the circumferential stretches of the wavy cut is formed through a first cut performed starting from the radially outer surface of the second axial section 26 and through a second cut performed in the radially internal surface of said second axial section 26.

In other embodiments not illustrated, the teeth 29, 30 may also have different outlines. For example, the cuts may be performed on radial planes.

The wavy circumferential cut 28 further divides the cylindrical block "M" into a first annular body 31 provided with the first plurality of teeth 29 and into a second annular body 32 provided with the second plurality of teeth 29.

After the wavy circumferential cut 28 has been performed, the first annular body 31 and the second annular body 32 are separated from one another by distancing them axially as illustrated in figure 7. The first annular body 31 therefore comprises the base ring 15 with the first plurality of teeth 29 and the resiliently yielding ring 18 with the connecting foot 19. The second annular body 32 comprises the reinforcement ring 20 with the second plurality of teeth 30.

The first annular body 31 and the second annular body 32 may be processed separately.

Each tooth 29 of the first plurality is processed by removing material to confer to said tooth 29 the outline with the aerodynamic profile of a first blade 22'. Each tooth 30 of the second plurality is processed by removing material to confer to said tooth 30 the outline with the aerodynamic profile of a second blade 22". As can be noted, the available space between the teeth 29, 30 of each annular body 31 , 32 is sufficient for processing the teeth 29, 30 easily and quickly, in particular since a small amount of stock is to be removed.

For that purpose, each tooth 29, 30 is first roughed by cutting and removing, through AWJ or through laser (or by sinker EDM, wire cut EDM, plasma, oxy cutting), blocks of material for defining, in a front view of the tooth 29, 30, a substantially polygonal outline that virtually contains the aerodynamic outline of the blade 22', 22" that it is to form (figures 8 and 9).

In one embodiment, the roughing of the blades is performed through electrodes with a rigid frame (hollow electrode) having the most appropriate shape. Figure 8A shows the removal of material through a hollow electrode 100 so as to have a roughed shape of the blades 22 that traces the final shape of the blades but with a stock 101 to be removed later in the finishing step. Such hollow electrode 100 is better illustrated in figure 8B and comprises a support foot 102 configured to be coupled to electrical discharge machining EDM equipment. A frame extends from the support foot 102 and is defined by a frame made of wire-shaped or rod-shaped elements. The frame comprises two curved rods 103, 104 and a rectilinear rod 105. The frame delimits/surrounds, together with the support foot 102, a window/opening/passage 106 which, seen from the front, is substantially rectangular but which lies on a curved surface, the one in which the two curved rods 103, 104 lie. The support foot 102 therefore delimits a side of the window 106.

In a further embodiment, the roughing of the blades is performed through wire or rigid electrodes but not closed in a frame. For example, the electrode has a single wire-shaped or rod-shaped element with an outline like one 104 of the curved rods of figure 8A (without the other curved rod 103 and without the rectilinear rod 105) or comprises one 104 of the curved rods and the rectilinear rod 105 of figure 8A but not the second curved rod 103.

Subsequently, each tooth is finished by removing further material until it is conferred the aerodynamic outline of the blade 22', 22" (figures 8 and 9, broken lines). The finishing of each blade 22', 22" can be performed through the mechanical removal of chips and/or EDM. In the latter case, one or more electrodes counter-shaped to the aerodynamic outline of the blade 22', 22" to be obtained can be used.

Bottom surfaces 33', 33" placed between adjacent blades 22', 22" respectively of the first annular body 31 and of the second annular body 32 and head surfaces of the blades 22', 22", where the stock is present, are subjected to finishing, e.g. through EDM, milling, ECM.

On the bottom surfaces 33', 33" placed between adjacent blades 22', 22" respectively of the first annular body 31 and of the second annular body 32 (figures 8 and 9) holes 34 are performed (figure 10), threaded or not, configured to receive connecting elements, such as screws or pins not illustrated. The holes 34 in the first annular body 31 and in the second annular body 32 pass axially through the first support ring 15 and the second support ring 20, respectively.

A terminal end, in particular the head surface, of each blade 22', 22" is finished and processed to perform a hole 35 (figure 10), threaded or not, configured to receive the aforementioned connecting elements. According to what is illustrated in figure 10, the first annular body 31 and the second annular body 32 are positioned coaxially (the central axes "X-X", Ύ-Υ" coincide) opposite one another and moved towards each other by advancement along the central axes "X-X", Ύ-Υ" (arrows F1 and F2 in figure 10) so as to insert the first blades 22' between the second blades 22".

Head surfaces of the first blades 22' are approached or brought against the bottom surfaces 33" of the second annular body 32 and head surfaces of the second blades 22" are moved towards each other or brought against the bottom surfaces 33' of the first annular body 31 so as to arrange the holes 34 in the bottom surfaces 33', 33" in alignment with the holes 35 on the head surfaces. The insertion and tightening of the screws, not illustrated, in the holes 34, 35, allows the first annular body 31 to be jointed coaxially with the second annular body 32. In this way, the bladed ring of figure 2 is obtained, represented in the section of figure 1 1 .

The bladed rotor disc 6 of figure 1 is obtained by mounting a plurality of bladed rings realised as described above on the front face 7 of said rotor disc 6 through the engagement of the connecting feet 19 in appropriate seatings, not illustrated in detail.

In one embodiment, the concentric bladed rings are realised in part as integrating parts of the bladed disc 6.

More precisely, as illustrated in figure 12, each cylindrical block "M1 , M2" is an integral part of a starting disc "D" and is arranged on a front face of said starting disc "D".

The wavy circumferential cut 28', 28" performed in every cylindrical block "M1 , M2" determines the separation of the second annular bodies 32', 32" from the starting disc "M1 , M2" while the first annular bodies 31 ', 31 " remain integrated into the disc.

In this case, the connecting foot 19 is absent because the first annular bodies 31 ',

31 " are conceived as integrated parts in the starting disc "D".

The other processing steps are substantially identical to those described above and illustrated in figures 5 - 10 for the individual bladed ring 9.

List of elements

1 radial turbomachine

2 rotor fixed casing

shaft

bearings

rotor disc

front face

rear face

rotor bladed rings

front wall

rear wall

axial inlet

transit volute

stator bladed rings

first support ring

first annular central body

annular anchoring appendage

resiliently yielding ring

connecting foot

second support ring

second annular body

', 22" blades

leading edge

trailing edge

first axial section

second axial section

third axial section

, 28', 28" wavy circumferential cut first plurality of teeth

second plurality of teeth

, 31 ', 31 " first annular body

, 32', 32" second annular body ', 33" bottom surfaces

holes in the bottom surfaces holes in the head surfaces0 hollow electrode 101 stock

102 support foot

103 curved rod

104 curved rod

105 rectilinear rod

106 window

D starting disc

M, M1 , M2 cylindrical block

Claims

1 . A method for the construction of bladed rings for radial turbomachinery, comprising:

preparing at least one cylindrical block (M; M1 , M2);

making in the cylindrical block (M; M1 , M2) a wavy circumferential cut (28, 28', 28") defining a first plurality of teeth (29) and a second plurality of teeth (30) meshing in one another; wherein the wavy circumferential cut (28, 28', 28") splits the cylindrical block (M; M1 , M2) into a first annular body (31 ; 31 ', 31 ") provided with the first plurality of teeth (29) and into a second annular body (32; 32', 32") provided with the second plurality of teeth (30);

separating the first annular body (31 ; 31 ', 31 ") from the second annular body (32; 32', 32");

removing material from each of the teeth (29) of the first plurality to confer to said tooth (29) the outline of at least a first blade (22') with an aerodynamic profile;

removing material from each of the teeth (30) of the second plurality to confer to said tooth (30) the outline of at least a second blade (22") with an aerodynamic profile;

joining coaxially the first annular body (31 ; 31 ', 31 ") to the second annular body (32; 32', 32") by inserting the first blades (22') between the second blades (22").

2. The method according to claim 1 , wherein, on a radially outer surface of the cylindrical block (M; M1 , M2), the wavy circumferential cut (28, 28', 28") has the shape of a square wave.

3. The method according to claim 1 or 2, wherein the wavy circumferential cut (28, 28', 28") passes through the cylindrical block (M; M1 , M2) along radial directions or directions tangent to virtual circumferences coaxial to said cylindrical block (M; M1 , M2).

4. The method according to claim 1 , 2 or 3, wherein each tooth (29, 30) presents a substantially polygonal outline in a front view.

5. The method according to one of the preceding claims 1 to 4, comprising, before making the wavy circumferential cut (28; 28', 28"), roughing the cylindrical block (M; M1 , M2) by removing material to define a first axial section (25), a second axial section (26), a third axial section (27), wherein the first axial section (25) defines a base ring (15), wherein the third axial section (27) defines a reinforcement ring (20), wherein the wavy circumferential cut (28; 28', 28") is made in the second axial section (26).

6. The method according to one of the preceding claims 1 to 5, wherein removing material from each of the teeth (29, 30) of the first plurality and the second plurality comprises: roughing each tooth (29, 30) and then performing a finish to give the tooth (29, 30) the aerodynamic outline of the blade (22', 22").

7. The method according to the preceding claim, wherein the roughing of each tooth (29, 30) is performed by removing blocks of material.

8. The method according to one of the preceding claims 1 to 7, wherein joining coaxially the first annular body (31 ; 31 ', 31 ") to the second annular body (32; 32',

32") comprises fixing terminal ends of the first blades (22') to the second annular body (32; 32', 32") and fixing terminal ends of the second blades (22") to the first annular body (31 ; 31 ', 31 ").

9. The method according to one of the preceding claims 1 to 8, wherein the wavy circumferential cut (28; 28', 28") is performed by abrasive water jet or laser.

10. The method according to one of the preceding claims 1 to 9, wherein the cylindrical block (M; M1 , M2) is an integral part of a starting disc (D) and is disposed on a front face of said starting disc (D), wherein, after separation, the first annular body (31 ; 31 ', 31 ") is still part of said disk (D)

1 1 . The method according to claim 10, wherein the starting disc (D) comprises a plurality of cylindrical blocks (M1 ; M2) concentrically arranged on the front face.

12. The method according to one of the preceding claims from 1 to 9, wherein the cylindrical block is a stand-alone element.

13. A bladed ring for radial turbomachinery realised according to one of claims 1 to 12.

14. A bladed ring for radial turbomachinery comprising one or more bladed rings according to claim 13.

15. A radial turbomachine comprising at least one bladed ring according to claim 13 or a bladed disc according to claim 14.