STATIC BLADE FOR A TURBINE DIAPHRAGM AND ASSOCIATED TURBINE DIAPHRAGM

Abstract

Static blade for an axial flow turbine comprising an aerofoil portion having a leading edge, a trailing edge, a pressure side and a suction side and radially inner and outer reinforcement portions integral with said aerofoil portion. Each reinforcement portion closely follows the shape of the section of the aerofoil portion.

Claims

1. Static blade for an axial flow turbine comprising: an aerofoil portion having a leading edge, a trailing edge, a pressure side and a suction side, radially inner and outer reinforcement portions integral with said aerofoil portion, wherein each reinforcement portion (46, 48) closely follows the shape of the section of the aerofoil portion.

2. Static blade according to claim 1, wherein each reinforcement portion has a section substantially bigger than the section of the aerofoil portion, having a rounded and enlarged shape corresponding to the leading edge surrounding the leading edge of the aerofoil portion and a thinner part corresponding to the trailing edge surrounding the trailing edge of the aerofoil portion.

3. Static blade according to claim 1, made of an alloy steel material.

4. Static blade according to claim 3, wherein the alloy steel material comprises 12% of chrome.

5. An axial flow turbine diaphragm construction comprising: an annulus of a plurality of identical static blades according to claim 1, an inner and outer spacer bands having through-holes therein shaped to receive the inner and outer reinforcement portions of each static blade, and a radially inner and outer diaphragm rings surrounding the annular spacer bands.

6. Axial flow turbine diaphragm construction according to claim 5, wherein each reinforcement portions are welded to the corresponding spacer band by welds.

7. Axial flow turbine diaphragm construction according to claim 2, wherein of the welds are located at each leading and trailing edges of each reinforcement portions.

8. Axial flow turbine diaphragm construction according to claim 5, wherein the inner spacer band is welded to the inner ring and the outer band is welded to the outer ring.

Description

[0019] The present invention will be better understood from studying the detailed description of a number of embodiments considered by way of entirely non-limiting examples and illustrated by the attached drawings in which:

[0020] FIG. 1a illustrates the known spacer band turbine diaphragm type of construction;

[0021] FIG. 1b illustrates a fixed blade with integral platforms for use in the known platform turbine diaphragm type of construction;

[0022] FIG. 2 is a three-dimensional perspective view of a part of a steam turbine diaphragm according to an embodiment of the invention;

[0023] FIG. 3 is a three-dimensional perspective view of a static blade for use in the diaphragm construction of FIG. 2;

[0024] FIG. 4 is an upper view of the static blade of FIG. 3; and

[0025] FIG. 5 is a radial cross-section of a static blade of FIG. 3, welded onto spacer bands of the steam turbine diaphragm of FIG. 2.

[0026] The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale.

[0027] As illustrated on FIG. 2, a part of a steam turbine diaphragm 30 of a turbine comprises a nozzle unit having a plurality of identical static blade aerofoils 32 fixed radially to an inner ring 34 and to an outer ring 36 by means of inner and outer annular spacer bands 38, 40, which are folded from flat strip.

[0028] The inner and outer rings 34, 36, as well as the inner and outer spacer bands 38, 40 are concentric.

[0029] The inner and the outer spacer bands 38, 40 are each provided with through-holes 38a, 40a. As illustrated, the through-holes are open at both ends to receive the static blades. The through-holes 38a, 40a may be, for example, cut in said spacer bands 38, 40, for example by means of laser, to match the cross-section of the aerofoil shape. The ends of the aerofoils 32 are then inserted in said though-holes and fillet welded into place. The inner spacer band 38 is in turn welded to the inner ring 34 and the outer band 40 is in turn welded to the outer ring 36.

[0030] As illustrated on FIGS. 3 and 4, each static blade 32 has an aerofoil portion 44 having an elongated body having an inner end 32a brought into contact with the inner spacer band 38 and an outer end 32b, opposite to said inner end 32a, brought into contact with the outer spacer band 40.

[0031] The inner and outer ends 32a, 32b are connected respectively to the inner and outer spacer bands 38, 40 by wielding by way of a weld bead arranged between said ends and said spacer bands. In this way each static blade is welded both to the inner spacer band and to the outer spacer band.

[0032] Each static blade 32 has, for example, a section substantially in the shape of a vane, as shown on FIG. 4, having a rounded and enlarged shape corresponding to the leading edge 44a and a thinner part corresponding to the trailing edge 44b.

[0033] As illustrated on FIGS. 3 and 4, the inner and outer ends 32a, 32b of the each static blade 32 are provided respectively with an inner and outer reinforcement portion 46, 48. Each reinforcement portion 46, 48 has a section slightly bigger than the section of the aerofoil portion 44, as shown on FIG. 4, having a rounded and enlarged shape corresponding to the leading edge 46a, 48a and a thinner part corresponding to the trailing edge 46b, 48b.

[0034] Each reinforcement portion 46, 48 surrounds the periphery of the whole section of the corresponding end so as to have a section substantially bigger than the section of the aerofoil portion 44. The shape of the reinforcement portions 46, 48 thus approximates the shape of the section of the aerofoil portion 44 in its whole, i.e at and near the leading and trailing edges 44a, 44b, as well as the suction side and the pressure side of the aerofoil portion 44.

[0035] The first and second reinforcement portions 46, 48 are slid into their matching through-holes 38a, 40a of the spacer bands 38, 40 as shown on FIG. 5. Once all the static blades 32 have been assembled into the spacer bands 38, 40, they must be securely welded into position. Each leading and trailing edges of each reinforcement portions are welded to the corresponding spacer band by welds 50a, 50b and 52a, 52b. The welds 50a, 50b and 52a, 52b are shown in hatched lines on FIG. 4.

[0036] The static blades 32 are made of an alloy steel material, having for example, 12% of chrome.

[0037] Thanks to the reinforcement portions provided at each end of the aerofoil portions, the static blade is strengthen.

[0038] Thanks to the invention, the diaphragm construction has good mechanical strength, while being economical and easy to manufacture.