Method for Building stages of centrifugal radial turbines

Abstract

A method for building centrifugal radial stages of turbines, in which the first and the second end of each blade (4) are connected to respective two support rings (2, 3) joining, by means of laser welding, at least a first semi-portion (10) belonging to the respective end of the blade (4) to a respective second semi-portion (10) belonging to the respective support ring (2, 3) so as to form a resilient yielding connecting portion (10, 15) along a radial direction, and providing at least a stop portion (11) belonging to the end of the blade (4) facing, along the radial direction, at least a stop element (14) of the respective support ring (2, 3). The resilient yielding connecting portion (10, 15) enables the stop portion (11) to enter into contact with the stop element (14) when the stage (1) is subjected to the functioning loads of the turbine.

Claims

1. Method for building a stage of a centrifugal radial turbine, comprising: preparing a first support ring (2) and a second support ring (3); preparing a plurality of blades (4); connecting a first end of each blade (4) to the first support ring (2) and a second end of each blade (4) to the second support ring (3) in such a way that the blade (4) develops prevalently parallel to a rotation axis of the stage; wherein connecting the first or second end to the respective first or second support ring (2, 3) comprises: welding at least a first half-portion (10), resiliently yieldable along a radial direction and belonging to the respective end of the blade (4), to a second half-portion (15), resiliently yieldable along said radial direction and belonging to the respective support ring (2,3), to make a connecting portion resiliently yieldable (10, 15) along said radial direction; placing at least a stop portion (11) of said end of the blade (4) facing, along said radial direction, at least a stop element (14) of the respective support ring (2, 3); wherein the resiliently yieldable connecting portion (10, 15) allows the stop portion (11) to come into contact with the stop element (14) when the stage (1) is subjected to working loads of the radial turbine.

2. Method according to claim 1, wherein connecting the first or the second end to the respective first or second support ring (2, 3) comprises: placing two first half-portions (10) astride the stop element (14) and welding the two first half portions (10) to respective second half-portions (15) placed on sides of said stop element (14) and radially spaced from said stop element (14).

3. Method according to claim 2, comprising: placing two stop portions (11) of said first or second end facing, along said radial direction, on opposite sides of the stop element (14).

4. Method according to claim 2, wherein the first half-portion (10) is welded endwise to the second half-portion (15).

5. Method according to claim 1, wherein the welding is laser welding.

6. Method according to claim 1, wherein the welding is a pulsed laser welding.

7. Stage of a centrifugal radial turbine, comprising: a first support ring (2) and a second support ring (3); a plurality of blades (4) each presenting a first end and a second end; the blades (4) developing prevalently parallel to a rotation axis of the stage; first joints (7, 13), each interposed between the first end of each blade (4) and the first support ring (2), and second joints (8, 18), each interposed between the second end of each blade (4) and the second support ring (3); characterized in that each of the first joints (7, 13) and/or the second joints (8, 18) comprises: at least a connecting portion resiliently yieldable (10, 15) along a radial direction and linked to the respective blade (4) and to the respective support ring (2; 3); at least a stop element (14) integral with the respective support ring (2; 3); at least a stop portion (11) integral with the respective blade (4) and facing, along said radial direction, the stop element (14); wherein the resiliently yieldable connecting portion (10, 15) allows the stop portion (11) to come into contact with the stop element (14) when the stage (1) is subjected to the working loads of the radial turbine.

8. Stage according to claim 7, wherein, in a section plane including the rotation axis of the stage (1), each of the first joints (7, 13) and/or of the second joints (8, 18) exhibits two of said resiliently yieldable connecting portions (10, 15) placed on opposite sides of the stop element (14) and spaced from said stop element (14).

9. Stage according to claim 7, wherein each resiliently yieldable connecting portions (10, 15) comprises a first half-portion (10) joined to the blade (4) and a second half-portion (10) joined to the support ring (2; 3) and wherein the first half-portion (10) and the second half-portion (15) are mutually welded.

10. Stage according to claim 7, wherein each resiliently yieldable connecting portions (10, 15) presents a radial thickness (t1) comprised between about and about of a radial thickness (t2) of the stop element (14).

11. Method according to claim 1, wherein the welding is a full penetration laser welding.

Description

DESCRIPTION OF THE DRAWINGS

(1) The detailed description will be made in the following with reference to the accompanying drawings, provided by way of non-limiting example, wherein:

(2) FIG. 1 is a perspective view of an angular sector of a stage of a centrifugal radial turbine according to the present invention;

(3) FIG. 2 is the angular sector of FIG. 1 in a different perspective view;

(4) FIG. 3 is a section on an axial plane of a variant of the angular sector of FIG. 1.

DETAILED DESCRIPTION

(5) With reference to the figures, 1 denotes in its entirety a stage of a centrifugal radial turbine of the Ljungstrom type (though only an angular sector is illustrated which subtends by an angle of a few degrees). In the stage 1 of the invention, the structure of the angular sector illustrated in FIG. 1 is extended by 360 to form a complete ring (not illustrated). The stage 1 comprises a first support ring 2, a second support ring 3 and a plurality of blades 4 which extend between the two support rings 2, 3 and connect the two support rings 2, 3. In the appended figures, only respective angular sectors of the two rings 2, 3 and the three blades 4 interposed between the angular portions are illustrated. The complete stage 1 comprises various tens of blades 4.

(6) The first ring 2 is connected to the rest of the turbine by means of a slim wall 5 which leaves the rings free to translate radially and elastically by a certain quantity when subjected to work loads of the turbine. In this way the stress level is considerably lowered in the hot zone of the machine (rings and blades). This translation prevents fluid-dynamic problems on the blades: the bladed part remains aligned, problems such as vortices at the base of the blade, variations in incidence, are avoided; these are problems which might have a determinant influence on the machines' performance. FIGS. 1 and 3 show different geometrical structures of the slim wall 5.

(7) The blades 4 are connected to the first ring 2 at an opposite edge to the edge connected to the turbine. Each blade 4 comprises a central portion 6 provided with an aerodynamic profile, a first semi-joint 7 arranged on a first end of the blade 4 and a second semi-joint 8 arranged on a second end of the blade 4.

(8) Each of the semi-joints 7, 8 seen in a section performed on an axial plane (a plane containing the rotation axis of the stage, FIG. 3), exhibits a substantially U-shaped profile, with a central element 9 and two first resilient yielding semiportions 10 which develop from the central element 9 parallel and reciprocally distanced. The first resilient yielding semiportions 10 are further substantially parallel to the development of the forward edge 4a and the rear edge 4b of the respective blade 4. The seatings delimited by the U-shaped profile of each of the semi joints 7, 8 are facing on opposite sides. Seen in the section performed on the axial plane (FIG. 3), each first semiportion 10 exhibits a proximal zone 11 (close to the central element 9) with a thickness 5 that is greater and a distal zone 12 (further from the central element 9) with a smaller thickness. The two proximal zones 11 are facing one another and closed to one another with respect to the two distal zones 12 of each semi-joint 7, 8.

(9) On the opposite side to the one connected to the turbine, the first ring support 2, seen in the second made along the axial plane of FIG. 3, exhibits a third semijoint 13 formed by a central body 14 and two second resilient yielding semiportions 15 which develop parallel to the central body 14, along opposite sides thereof and distanced from the central body 14. The second resilient yielding semiportions 15 exhibit an axial development (parallel to the rotation axis of the stage 1) that is smaller than the axial development of the central body 14.

(10) The central body 14 of the first support ring 2 is housed between the first resilient yielding semiportions 10 of the first semijoint 7 with a distal end 16 thereof positioned between the two proximal zones 11. Each of the two second resilient yielding semiportions 15 is jointed at a head to a respective first semiportion 10.

(11) The joint is obtained by laser welding of the complete-penetration pulsed type. The frequency of pulsation is about 50 Hz with a weld time of about 10 ms. As can be seen in FIGS. 1 and 2, along the width (along the circumferential development of the stage) of each first resilient yielding semiportion 10, two weld beads 17 are made and a closing crater 17a is situated between the two weld beads 17.

(12) In an embodiment that is not illustrated, in the zone of the closing crate 17a a through-opening is fashioned (hole, milling), through the resilient yielding first and second semiportions 10, 15, so as to avoid the notch effect, present between a blade and another on the welded surface.

(13) The first semijoint 7 and the third semijoint 13 form a first joint 7, 13 interposed between the first end of the blade 4 and the first support ring 2. Each first semiportion 10 together with the second semiportion 15 to which it is welded form a single resilient yielding portion 10, 15.

(14) The second semi-joint 8 of each blade 4 is connected to a fourth semi-joint 18 located on an edge of the second support ring 3. The second semijoint 8 and the fourth semijoint 18 form a second joint 8, 18 which, as visible in the figures, exhibits the same structural characteristics as the first joint 7, 13.

(15) The resilient yielding portions 10, 15 of each joint enable, when the stage is subjected to the loads of the turbine when functioning, a relatively radial displacement between the blades 4 and the support rings 2, 3 which is limited by the contact between the proximal zone 11 of the respective first semiportion 10, which performs the function of a stop portion, with the distal end 16 of the respective central body 14, which functions as a stop element. The displacement is about 0.1 mm.

(16) In the section made along the axial plane (FIG. 3), each resilient yielding portion 10, 15 exhibits a radial thickness t1 of about of the radial thickness t2 of the stop element 14. Further, the proximal zone 11 exhibits a radial thickness t3 of about double the radial thickness t1 of the resilient yielding portion 10, 15.

(17) The above-described stage 1 is constructed by realising the blades and the two support rings 2,3 separately and then positioning each blade 4 on the stages 2, 3 and welding it after positioning it.