METHOD FOR FABRICATING A FRANCIS-TYPE RUNNER FOR A HYDRAULIC MACHINE, AND RUNNER FABRICATED USING SUCH A METHOD
The method relates to the fabrication of a Francis-type runner for a hydraulic machine. The Francis-type runner includes: a runner band including at least two elements partially defining the runner band, a runner crown including at least two elements partly defining the runner crown, and a plurality of blades extending between the runner crown and the runner band. The blades are each fitted in between two elements of the runner band and between two elements of the runner crown. The method includes fabricating separately the blades, the elements of the runner band and the elements of the runner crown. All the elements of the runner band are then welded to the blades using an electron beam welding method. All the elements of the runner crown are then welded to the blades using an electron beam welding method.
1 . A method of fabricating a Francis-type runner for a hydraulic machine; THE Francis-type runner including
a runner band with symmetry of revolution about a central axis of the runner, the runner band including at least two elements partially defining the runner band,
a runner crown with symmetry of revolution about the central axis, the runner crown including at least two elements partly defining the runner crown, and
a plurality of blades extending between the runner crown and the runner band, the blades each being fitted in between two elements of the runner band and between two elements of the runner crown,
the method comprising:
a) fabricating separately the blades, the elements of the runner band and the elements of the runner crown, then
b) electron beam welding all the elements of the runner band to the blades, and then
c) electron beam welding all the elements of the runner crown to the blades.
2 . The method as claimed in claim 1 , wherein the blades lie flush with the exterior surfaces of the runner band and of the runner crown.
3 . The method as claimed in claim 1 , wherein during step b) and/or during step c) the electron beam is applied on the outside of the runner.
4 . The method as claimed in claim 1 , wherein during step b) a method of welding with the addition of filler material, notably of the TIG or MIG type, is also used for welding the elements of the runner band to the blades.
5 . The method as claimed in claim 1 , wherein during step c) a method of welding with the addition of filler material is also used for welding the elements of the runner crown to the blades.
6 . The method as claimed in claim 4 , wherein during step b) and/or during step c) the welding with the addition of filler material precedes the electron beam welding.
7 . The method as claimed claim 4 , wherein a first welded seam resulting from the welding with the addition of filler material is situated on the inside of the runner whereas a second welded seam resulting from the electron beam welding is situated on the outside of the runner.
8 . The method as claimed in claim 4 , wherein the welds involving an addition of filler material and the electron beam welds interpenetrate.
9 . The method as claimed in claim 1 , wherein the electron beam welds are complete joint penetration welds.
10 . A Francis turbine runner for a hydraulic machine, characterized in that it is fabricated using a method as claimed in claim 1 .