Rotor stage of axial turbine with coak locking the vane roots

Abstract

Rotor stage of an axial turbine for the gas or steam expansion comprising a shaft, adapted to rotate around a main axis, and a plurality of vanes, the shaft having an annular recess extending around the main axis, said shaft further comprising an introduction slot extending laterally from the annular recess, the annular recess being adapted to engage the roots of the vanes and the introduction slot being adapted to allow the insertion of the roots of the vanes into the annular recess, said rotor stage further comprising a coak adapted to be inserted into the introduction slot through an exclusively radial movement, to constrain the roots of the vanes in an operative position inside the annular recess.

1 . Rotor stage of an axial turbine for gas or steam expansion comprising a shaft, adapted to rotate around a main axis, and a plurality of vanes, each of these having a root with at least one first tooth protruding in an axial direction, and a blade protruding from the top of the root in a substantially radial direction, the shaft having an annular recess extending around the main axis and comprising at least one first undercut adapted to accommodate the first tooth, said shaft further comprising an introduction slot extending laterally from the annular recess, the annular recess being adapted to engage the roots of the vanes and the introduction slot being adapted to allow the insertion of the roots of the vanes into the annular recess, said rotor stage further comprising a coak adapted to be inserted into the introduction slot to constrain the roots of the vanes in an operative position inside the annular recess, said coak being adapted to be inserted in an operative position into the introduction slot through an exclusively radial movement, characterized in that the shaft has a first fastening half-slot and the coak has a second fastening half-slot positioned such that, when the coak is inserted into the introduction slot, the two fastening half-slots and are facing one to another forming a fastening slot partially obtained in the shaft and partially in the coak, said rotor stage further comprising a fastening element adapted to be introduced inside said fastening slot and to lock the coak in the introduction slot. 
     
     
         2 . Rotor stage of an axial turbine according to  claim 1 , wherein the root of each vane comprises a second tooth departing axially and in a way opposite to the first tooth, the annular recess having a second undercut opposed to the first undercut, both the two undercuts being adapted to receive one between the first and the second tooth, the introduction slot cutting off the second undercut, said coak comprising a main body and a catching protuberance that, when the coak is arranged inside the introduction slot in an operative position, completes the second undercut so that to accommodate the second tooth of the root, preventing the radial movement thereof. 
     
     
         3 . Rotor stage of an axial turbine according to  claim 1 , wherein said coak arranged in an operative position inside the introduction slot, has a substantially “L”-shaped longitudinal section. 
     
     
         4 . Rotor stage according to  claim 1 , wherein characterized in that said fastening element comprises at least two separated parts. 
     
     
         5 . Rotor stage according to  claim 1 , wherein said fastening slot has an axially symmetric shape, with at least one annular widening and a neck, so that the fastening element can rotate inside the fastening slot. 
     
     
         6 . Rotor stage according to  claim 5 , wherein said fastening element comprises at least one body with at least one protuberance. 
     
     
         7 . Rotor stage according to  claim 6 , wherein said protuberance of the fastening element is an annular protuberance of axially symmetric shape, said fastening element being adapted to rotate around its own axis when inserted into the fastening slot. 
     
     
         8 . Rotor stage according to  claim 7 , wherein the body of the fastening element is divided in two parts along a plane comprising the axis thereof. 
     
     
         9 . Rotor stage of an axial turbine according to  claim 1 , wherein the roots of the vanes have a section with a plane perpendicular to the radial direction of a substantially lozenged shape.