Turbine blade and diaphragm construction

Abstract

An axial flow turbine blade and diaphragm construction comprises an annulus of static turbine blades 20 and inner and outer spacer rings 40, 42 having apertures 41, 43 shaped to accommodate inner and outer platform portions 22, 23 of the blades, whereby the platform portions and the spacer rings together form inner and outer port walls of the turbine diaphragm. A particular feature of the blades is that the inner and outer platform portions 22 and 23 have straight side edges 22B, 22C and 23B, 23C, which are joined to each other by curved leading edges 22D and 23D that in plan view have a shape that follows the edge of the corner fillet 24 in the region of the leading edge 26 of the aerofoil 21.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention will now be described, with reference to the accompanying drawings, in which:

FIG. 1A illustrates the known spacer band type of turbine construction;

FIG. 1B illustrates a fixed blade with integral platforms for use in the platform type of construction, as already known;

FIG. 2 illustrates a single fixed blade according to the invention;

FIGS. 3A to 3D illustrate the blade of FIG. 2 from various viewpoints;

FIG. 4 illustrates the assembly of a steam turbine diaphragm according to the invention;

FIGS. 5A and 5B illustrate processes prior to a main welding operation by means of which the blades and the spacer rings are secured together, FIG. 5B being an enlarged portion of FIG. 5A within the dashed rectangle;

FIG. 6 illustrates the result of a machining operation prior to the main welding operation; and

FIG. 7 illustrates a group of the blades in the diaphragm after completion of the main welding operation.

Claims

1. A static blade for an axial flow turbine comprising: a) an aerofoil portion having a leading edge, a trailing edge, a pressure side, a suction side, and a chord line;b) radially inner and outer platform portions integral with the aerofoil portion;c) a corner fillet where the aerofoil portion meets each platform portion to form a smooth transition between the aerofoil portion and each platform portion;d) the platform portions in plan view comprising: i) a trailing edge formed to extend circumferentially of the turbine axis,ii) a straight side edge on each of the pressure side and the suction side of the aerofoil,iii) a curved leading edge that joins the side edges to each other and that in plan view has a shape that follows the edge of the corner fillet in the region of the leading edge of the aerofoil portion.

2. A static blade according to claim 1, in which the side edges of each platform portion are substantially parallel to each other and to the chord line of the aerofoil portion.

3. A static blade according to claim 1, in which the side edge of each platform portion on the pressure side of the aerofoil portion is tangential to the corner fillet at the leading and trailing edges of the aerofoil portion.

4. A static blade according to claim 1, in which the side edge of at least the inner platform portion is tangential to the corner fillet on the suction side of the aerofoil portion.

5. A static blade according to claim 4, in which the curved leading edge of the platform portion has a shape that follows an edge of the corner fillet between the leading edge of the aerofoil and a point at which the side edge of the platform portion on the suction side of the aerofoil is tangential to the corner fillet.

6. A static blade according to claim 4, the platform portion being the inner platform portion.

7. A static blade according to claim 1, in which the side edge and the curved leading edge of the outer platform portion on the suction side of the blade are spaced apart from the corner fillet.

8. An axial flow turbine diaphragm construction comprising an annulus of static turbine blades according to claim 1, andinner and outer spacer rings having apertures therein shaped to accommodate the inner and outer platform portions respectively,whereby the platform portions and the spacer rings together form inner and outer port walls of the turbine diaphragm.

9. An axial flow turbine diaphragm construction comprising: a) an annulus of static turbine blades having an aerofoil portion with integral inner and outer platform portions, andb) inner and outer spacer rings having apertures therein shaped to accommodate the inner and outer platform portions respectively, whereby the platform portions and the spacer rings together form inner and outer port walls of the turbine diaphragm,

10. An axial flow turbine diaphragm construction according to claim 9, in which the side edges of each platform portion are substantially parallel to each other and to the chord line of the aerofoil portion.

11. An axial flow turbine diaphragm construction according to claim 9, in which the side edge of each platform portion on the pressure side of the aerofoil portion is tangential to the corner fillet at the leading and trailing edges of the aerofoil portion.

12. An axial flow turbine diaphragm construction according to claim 9, in which the side edge of at least the inner platform portion is tangential to the corner fillet on the suction side of the aerofoil portion.

13. An axial flow turbine diaphragm construction according to claim 12, in which the curved leading edge of the platform portion has a shape that follows the edge of the corner fillet between the leading edge of the aerofoil and a point at which the side edge of the platform portion on the suction side of the aerofoil is tangential to the corner fillet.

14. An axial flow turbine diaphragm construction according to claim 13, the platform portion being the inner platform portion.

15. An axial flow turbine diaphragm construction according to claim 9, in which the side edge and the curved leading edge of the outer platform portion on the suction side of the blade are spaced apart from the corner fillet.

16. A method of manufacturing the axial flow turbine diaphragm construction of claim 8, comprising the steps of: a) assembling the static blades into the diaphragm by sliding the platform portions into the apertures in the spacer rings,b) locating an annular cover plate over the annulus of static turbine blades on each side thereof, the cover plates being sized such that inner and outer edges of the cover plates partly overlap the leading and trailing edges of the inner and outer platform portions,c) welding the inner and outer edges of each cover plate to the leading and trailing edges of the inner and outer platform portions and to intervening portions of the inner and outer spacer rings,d) machining weld preparation slots into the diaphragm around the inner and outer edges of each cover plate such that the leading and trailing edges of the inner and outer platform portions and any intervening portions of the inner and outer spacer rings are undercut,e) performing a welding process in the weld preparation slots to fill them and fix the inner and outer platform portions to the inner and outer spacer rings, andf) machining the inner and outer edges of the cover plates to remove them from the diaphragm.

17. A method according to claim 16, in which steps b) and c) are performed in a sequence comprising: i) locating a first annular cover plate over the annulus of static turbine blades on a first side thereof and performing the welding operation for the first annular cover plate; andii) locating a second annular cover plate over the annulus of static turbine blades on a second side thereof and performing the welding operation for the second annular cover plate.

18. A method according to claim 16, in which steps d) and e) are performed in a sequence comprising: i) machining a first weld preparation slot into the diaphragm around one of the inner and outer edges of a first cover plate and performing the welding operation in the first weld preparation slot;ii) machining a second weld preparation slot into the diaphragm around the other one of the inner and outer edges of the first cover plate and performing the welding operation in the second weld preparation slot;iii) machining a third weld preparation slot into the diaphragm around one of the inner and outer edges of a second cover plate and performing the welding operation in the third weld preparation slot; andiv) machining a fourth weld preparation slot into the diaphragm around the other one of the inner and outer edges of the second cover plate and performing the welding operation in the fourth weld preparation slot.