Method of restoring a blade or vane platform

Abstract

A method for restoring a blade or vane platform of a gas turbine assembly configured for a power plant by: providing a blade or a vane having a platform with an edge deterioration zone; removing the deterioration zone by electro discharging machining technology; and rebuilding a removed zone by additive manufacturing technology. The removing can be performed to create a recessed plane along a platform edge, the recessed plane being connected to a platform plane by an enter inclined plane and an exit inclined plane arranged opposed along the platform edge.

Claims

1. A method for restoring a blade or vane platform of a gas turbine assembly configured for a power plant; the method comprising: a) providing a blade or a vane of a gas turbine assembly configured for the power plant, wherein the blade or vane includes a platform having a deteriorated edge zone; b) removing the deteriorated edge zone by electro discharging machining technology to create a removed zone; and c) rebuilding the removed zone by additive manufacturing technology, wherein the removing b) is performed to create a recessed main plane along a platform edge, the recessed main plane being connected to a platform outer surface by an enter inclined plane and an exit inclined plane arranged opposed along the platform edge, an angle between the recessed main plane and the enter and exit inclined planes is between 130° and 150°.

2. The method as claimed in claim 1, wherein the rebuilding c) is performed by using a five axes laser metal deposition technology.

3. The method as claimed in claim 2, comprising: delivering, during the rebuilding c), filler metal material in powder form.

4. The method as claimed in claim 2, wherein during the rebuilding c), a laser energy density is between 2000 J/cm.sup.2 and 5000 J/cm.sup.2.

5. The method as claimed in claim 4, wherein during the rebuilding c), the laser energy density is between 3000 J/cm.sup.2 and 4000 J/cm.sup.2.

6. The method as claimed in claim 5, comprising: selecting, during the rebuilding c), a powder feed rate to recreate a clad shape with an aspect ratio length/height between 3 and 6 and adhesion angles between 120° and 130°.

7. The method as claimed in claim 1, wherein a length of the removed zone is equal to or less than a length of the platform edge.

8. The method as claimed in claim 1, comprising: blending or machining the rebuilt zone.

9. A method for restoring a blade or vane platform of a gas turbine assembly configured for a power plant; the method comprising: a) providing a blade or a vane of a gas turbine assembly configured for the power plant, wherein the blade or vane includes a platform having a deteriorated edge zone; b) removing the deteriorated edge zone by electro discharging machining technology to create a removed zone; and c) rebuilding the removed zone by additive manufacturing technology, wherein the removing b) is performed to create a recessed main plane along a platform edge, the recessed main plane being connected to a platform outer surface by an enter inclined plane and an exit inclined plane arranged opposed along the platform edge, an angle between the recessed main plane and the enter and exit inclined planes is between 130° and 150°, and the recessed main plane and the enter and exit inclined planes are joined through a fillet radius of between 5 mm and 8 mm.

10. The method as claimed in claim 9, wherein the rebuilding c) is performed by using a five axes laser metal deposition technology.

11. The method as claimed in claim 10, comprising: delivering, during the rebuilding c), filler metal material in powder form.

12. The method as claimed in claim 10, wherein during the rebuilding c), a laser energy density is between 2000 J/cm.sup.2 and 5000 J/cm.sup.2.

13. The method as claimed in claim 12, wherein during the rebuilding c), the laser energy density is between 3000 J/cm.sup.2 and 4000 J/cm.sup.2.

14. The method as claimed in claim 13, comprising: selecting, during the rebuilding c), a powder feed rate to recreate a clad shape with an aspect ratio length/height between 3 and 6 and adhesion angles between 120° and 130°.

15. The method as claimed in claim 9, wherein a length of the removed zone is equal to or less than a length of the platform edge.

16. The method as claimed in claim 9, comprising: blending or machining the rebuilt zone.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.

(2) The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which:

(3) FIG. 1 is a schematic view of a gas turbine assembly for power plants;

(4) FIG. 2 is a schematic view of two adjacent turbine blades of the gas turbine of FIG. 1;

(5) FIG. 3 is a schematic view of the step of removing the deteriorated zone of the present invention;

(6) FIG. 4 is a schematic view of the electro discharging machining tool used in the present invention suitable for realizing a recessed zone on the platform;

(7) FIGS. 5 and 6 are schematic views of the recessed zone realized in the blade platform by using the tool of FIG. 5;

(8) FIG. 7 is a schematic view of the step of rebuilding the removed zone according to the present invention;

(9) FIGS. 8 and 9 are schematic views of the clad realized by using the technic of rebuilding of FIG. 7.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(10) In cooperation with attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to preferred embodiments, being not used to limit its executing scope. Any equivalent variation and modification made according to appended claims is all covered by the claims claimed by the present invention.

(11) Reference will now be made to the drawing figures to describe the present invention in detail.

(12) Reference is made to FIG. 1 which is a schematic view of a gas turbine assembly for power plants (in the following only gas turbine). FIG. 1 discloses a gas turbine 1 having an axis A and comprising in series along the main flow M:

(13) a compressor section 2, provided with an intake 11 for feeding air 10,

(14) a combustor section, provided with at least a burner unit 3; each burner being provided with a plurality of fuel nozzles 6 and being connected to a relative combustion chamber 4 wherein the compressed air is mixed with at least a fuel and this mixture is burnt to create a hot gas flow,
a turbine section 5 where the hot gas flow expands performing work on a rotor 7.

(15) Preferably, the rotor 7 is single piece of a plurality of rotor wheels welded together and extends from the compressor 2 to the turbine 5. As known, the combustor section can be provided with a single annular combustor or a plurality of can combustors. The exhaust gases leaving the turbine can be used, for instance, in a steam generator and the rotor 7 can be connected to load 9, i.e. an electrical generator in a power plant. As known, the compressor 2 and the turbine 5 comprises a plurality of stator vanes and a plurality of rotating blades. These rotating blades are connected to the rotor 7 and arranged in parallel circumferential rows centered in the axis A. Reference is made to FIG. 2 that is a schematic view of adjacent blades of the gas turbine of FIG. 1, in particular FIG. 2 refers to adjacent turbine blades 12. In particular, FIG. 2 discloses a legend of the main directions of the gas turbine field. In this legend the reference 13 refers to the axial direction that is parallel to the rotor 7, to the axis A and in general to the hot gas flow direction M. The terms downstream and upstream refer to the axial direction 13 along the hot gas flow direction M. The reference 14 refers to the radial direction centered in the axis A; the terms inner/inwardly and outer/outwardly refer to the distance from the axis A along the radial direction 14. The reference 15 refers to the circumferential direction centered in the axis A. FIG. 2 discloses an axial downstream view of two adjacent turbine blades 12 of a common row of blades. Blades 12 may be constructed of a metal, metal alloy, ceramic matrix composite (CMC), or other suitable material. Starting from the axis A and along the radial direction 14 each blade 12 comprises a foot 16 configured to be coupled with the rotor 7, a shank portion 17 provided with downstream or closing wall 18, a platform 19, and an airfoil 20. The channel for the hot gas is limited inwardly by the platforms and outwardly by the outer casing in form of a plurality a tales called heat shields. At the shank portion 17 between two adjacent blades a cavity is present, in particular a cooling air cavity. This cavity is outwardly limited along the radial direction 14 by the adjacent edges of the platforms 19 and downstream along the axial direction 13 by the adjacent edges of the closing walls 18. As known, in order to avoid losses of efficiency of turbine engine, the gap between two adjacent platforms 19 has to be sealed both in radial direction, i.e. to avoid leakages passing to the gap present between the adjacent platforms 19, and in axial direction, i.e. to avoid leakages passing to the gap present between the closing walls 18. The above axial and radial sealing are schematically represented in FIG. 2 with the reference 22 and 24.

(16) Even if the platform 19 (i.e. the inner face of the blade platform) is cooled as foregoing described, the outer surface of the platform is exposed to very high temperature due to the presence of the hot gas passing through the turbine. Due to this high temperature, the leading and the trailing platform edge are prone to deterioration in form of a corrosion or cracks due to thermomechanical fatigue.

(17) Once the deteriorated platform edge has been identified, the method of the present invention comprises the step of removing the deteriorated zone of the platform edge by means of electro discharging machining technology.

(18) FIG. 3 discloses schematically this step of removing the deteriorated zone of the platform edge wherein the reference 30 refers to an electro discharging machining tool working on the deteriorated platform edge.

(19) As disclosed in FIG. 4, the electro discharging machining tool 30 comprises a working surface comprising a straight plane surface 31 (in FIG. 3 acting along the platform edge) and two opposite angled plane surfaces 32. The length of the straight plane surface 31 can be varied in order to be applied only on the deteriorated zone and not necessary on the entire length of the platform edge.

(20) FIG. 5 discloses the recessed zone that can be realized on the platform edge by using the tool 30 of the previous FIG. 4. This FIG. 5 discloses a recessed zone 33 comprising a main recessed plane 34, realized by the straight plane surface 31 of the tool 30, and two angled opposite planes 35 realized by the angled plane surfaces 32 of the tool 30. These angled opposite planes 35 connect the main recessed plane 34 to the platform outer face. The main recessed plane 34 can be parallel to the outer platform surface or can be angled depending on the presence of a working angle between the tool 30 and the platform blade. The mentioned two angled opposite planes 35 can be also called as “enter” inclined plane and “exit” inclined plane because represent the starting and the ending point of the rebuilding step of the present invention. As disclosed in FIG. 6, preferably the angles β.sub.1 and β.sub.2 between the recessed main plane 34 and the enter and exit inclined plane 35 are between 130° and 150°. Moreover, the recessed main plane 34 and the enter and exit inclined plane 35 are joined through a fillet radius R between 5 mm and 8 mm.

(21) FIG. 7 discloses the rebuilding step of the removed zone by means of additive manufacturing technology. In particular, this step is performed by using a five axes laser metal deposition technology wherein the filler metal material is delivered in powder form. Preferably, the laser energy density is between 2000 J/cm.sup.2 and 5000 J/cm.sup.2, more preferably between 3000 J/cm.sup.2 and 4000 J/cm.sup.2.

(22) As known, the laser energy density is defined by the following equation wherein P is Laser Power, V is the scan velocity and D the Spot Laser diameter.

(23) $E=\frac{P}{v.Math.d}\left[\frac{J}{{\mathrm{cm}}^2}\right]$

(24) As disclosed in the last two FIGS. 8 and 9, the clad shape realized by using the method of the present invention discloses a ratio length/height (L/H) between 3 and 6 and an adhesion angles a between 120° and 130°.

(25) Although the invention has been explained in relation to its preferred embodiment(s) as mentioned above, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the present invention.

(26) In general, the present invention allows to repair the critical area of blade and vane platforms using the new laser metal deposition technology avoiding and eliminating the problems related to laser cladding process and increasing the repairability of parts also in critical areas such as the platform wedge faces, where the geometrical constraints of the repairable areas highly limit the use of the manual process. According to the invention a designed and optimized geometries are used during the removing step for the preparation before the rebuilding step. The invention allows to reach outstanding repair quality level by automatic method and very well controlled thermal input. The invention overcomes the following usual problems related to the laser cladding:

(27) the presence of porosity due to not optimized laser parameters that lead to a bad clad shape and not properly prepared rebuilding surfaces, in terms of angles between adjacent surfaces and fillet radii.

(28) the presence of cracks due to very high residual stresses generated by wrong process parameters.

(29) This aspect is particularly pronounced and easily to be found in Nickel based superalloy (usual base material for turbine blades and vanes).

(30) Moreover, the method of the invention can be applied to both blades and vanes platform geometries and doesn't necessary involves all the platform edges, but can be highly customized depending on the extension and the position of the defects in order to reduce the time and the costs for the repair. The invention minimizes the removal of blade or vane material reducing the impact of the repair on the base material and component strength. The invention allows to reaches an high flexibility, repeatability and selectivity of this automated process result in better quality products but also offer significant economic benefits.

(31) It is, therefore, contemplated that the appended claim or claims will cover such modifications and variations that fall within the true scope of the invention.