METHOD FOR THE MAINTENANCE OF A BLADED WHEEL OF A HIGH-PRESSURE TURBINE OF A TURBOMACH

Description

Technical field of the invention

[0001] The invention relates to a method for maintaining a high-pressure turbine bladed wheel of a turbomachine, such as a turbojet or aircraft turboprop. Prior art

[0002] There figure 1 represents a twin-spool, twin-body turbomachine 1. The axis of the turbomachine is referenced as X. In what follows, the terms axial and radial are defined with respect to the X axis.

[0003] The turbomachine 1 comprises, from upstream to downstream in the direction of gas flow within the turbomachine 1, a blower 2, a low pressure compressor 3, a high pressure compressor 4, a combustion chamber 5, a high pressure turbine 6 and a low pressure turbine 7.

[0004] The air from the blower 2 is divided into a primary flow A flowing into a primary vein 8, and a secondary flow B flowing into a secondary vein 9.

[0005] The low pressure compressor 3, the high pressure compressor 4, the combustion chamber 5, the high pressure turbine 6 and the low pressure turbine 7 are provided in the primary vein 8.

[0006] The high-pressure turbine 6 and the high-pressure compressor 4 are coupled in rotation via a first shaft 10 so as to form a high-pressure body.

[0007] The low-pressure turbine 7, the low-pressure compressor 3 and the blower 2 are coupled in rotation via a second shaft (not shown) so as to form a low-pressure body.

[0008] As this appears to the figure 2 The high-pressure turbine 6 conventionally comprises a disc 11 on which blades 12 are mounted. Each blade 12 comprises a blade 13 extending radially outwards from a blade root 14 mounted in a cavity 15 of the disc 11.

[0009] The apex 16 of the blade 12 is formed by the radially external end of the blade 12. The foot 14 and the blade 13 are here separated by a radially internal platform 17. The foot 14 has a general fir tree shape, here with four branches or lobes 18. The shape of the cavity 15 is complementary to the shape of the foot 14.

[0010] Each branch or lobe 18 rests on a complementary opposite surface of the disc 11. The surfaces of the foot 14 and the disc 11 resting on each other are called bearing surfaces 19. In the embodiment illustrated in the figure 4 , foot 14 has four supports 19, arranged symmetrically with respect to a median radial plane P.

[0011] The blades 12 are surrounded by an annular casing 20. A clearance j is formed between the vertices 16 of the blades 12 and the casing 20 surrounding the blades 12.

[0012] In order to maximize the turbomachine's efficiency, il It is necessary to limit the flow of gas flowing into the gaps located between the tips of the blades and the casing.

[0013] During operation, this play tends to increase over time due to two phenomena. The first phenomenon is the wear of the blade tip generated by the friction between the blade tip and the housing opposite it.

[0014] The second phenomenon is thermal erosion, i.e. oxidation, of the top of the blade, due to the high temperatures to which the blade is subjected in operation, particularly in the case of a high-pressure turbine.

[0015] Increasing this clearance leads to a degradation of turbomachine performance and, consequently, to an increase in fuel consumption and operating temperatures of the turbomachine, further aggravating the oxidation phenomenon.

[0016] Currently, when a turbine blade is too worn or too oxidized at its tip, it is replaced and discarded. Such maintenance is therefore very costly and / or leads to unplanned shutdowns of the turbomachine due to performance limits being reached.

[0017] Document US2009016890 discloses a shim to provide better protection to the bearing surfaces of the blades and disc. Presentation of the invention

[0018] The invention aims to remedy the aforementioned problems in a simple, reliable, and inexpensive manner. To this end, the invention proposes a method for maintaining a bladed high-pressure turbine wheel of a turbomachine, extending along an axis, comprising a disc with recesses, and radially extending blades, each blade comprising a blade and a radially internal root, the root of each blade being mounted in a recess of the disc, said root bearing on the disc via surfaces of the root and the disc forming bearing surfaces, characterized in that at least one shim is removably mounted between the root of at least one blade and the disc, at the level of the corresponding bearing surfaces, said method comprising the following steps: measure radial clearance between the apex of at least one blade, i.e. the radially external end of the blade, and a turbomachine housing located opposite the bladed wheel; if the radial clearance is greater than a specified value, remove said shim.

[0019] The method according to the invention aims to determine the state of wear or deformation of the high-pressure turbine by measuring the radial clearance between the blade tip and the housing and, if the aforementioned radial clearance is too large, removing the shims. Removing the shims then reduces the radial clearance between the blade tip and the housing, thus restoring acceptable performance at a lower cost, without replacing or repairing the blades or the housing.

[0020] At least one shim can be mounted between the foot of each blade and the disc, at the level of the corresponding bearings, all shims being removed if the radial clearance is greater than said determined value.

[0021] This method avoids creating disparities or steps formed by differences in the positioning of the blade tips around the circumference of the turbomachine. Such steps can generate aerodynamic disturbances affecting the proper functioning of the turbomachine.

[0022] The tinsel can be mounted removably on the paddle foot.

[0023] The shim can be mounted removably on the disc, for example in the cavity or on a tooth of the disc delimited between two adjacent cavities.

[0024] The shim may include a radial stop surface, bearing against a complementary stop surface of the blade foot or disc.

[0025] This feature makes it easier to achieve the correct axial positioning of the shim and also helps to keep the shim axially in position during the operation of the turbomachine.

[0026] The tinsel can have a thickness of between 0.1 and 0.9 mm.

[0027] The tinplate can be made from a cobalt-based alloy.

[0028] Several shims can be mounted removably between the foot of at least one blade and the disc. Brief description of the figures

[0029] [ Fig. 1 ] is a schematic cross-sectional view of a prior art turbomachine; [ Fig. 2 ] is a schematic view of part of a prior art high-pressure turbine; [ Fig. 3 ] is a view illustrating the mounting of a blade foot in a recess of a bladed wheel disc according to one embodiment of this document; [ Fig. 4 ] is a perspective view of a cell fitted with a tinsel, according to the embodiment of the figure 3 ; Fig. 5 ] is a perspective view of a paddle wheel equipped with two lateral clappers, according to another embodiment; [ Fig. 6 ] is a perspective view of a paddle wheel fitted with a single shim, according to another embodiment; [ Fig. 7 ] is a view corresponding to the figure 3 , in which the tinsel was removed following a maintenance operation. Detailed description of the invention

[0030] THE figures 3 et 4 illustrate a bladed high-pressure turbine rotor wheel 6 according to one embodiment.

[0031] This form of realization differs from that illustrated in the figure 2 in that a shim 21 is removably mounted in each cavity 15 and covers, entirely or almost entirely, the inner surface of each cavity 15 of the bladed wheel. The shim 21 thus has a general U-shaped form and includes recesses adapted to accommodate the lobes 18 of the foot 14 of the corresponding blade 12. The shim 21 therefore has surfaces 22 intended to come into contact with the bearing surfaces of the foot 14 of the blade 12. These surfaces are called the bearing surfaces 22 of the shim 21.

[0032] The 21 clinquant is formed by a sheet of metal with a thickness between 0.1 and 0.9 mm, and made from a cobalt-based alloy.

[0033] The foot 14 of the dawn 12 rests on the supports 22 of the shim 21 after assembly in the alveolus 15.

[0034] It should be noted that the radial position of the apex 16 of the blade 12 takes into account the thickness of the shim 21 in its specifications in order to obtain the desired clearance j.

[0035] It is also possible to use two shims 21, located on either side of the median plane P and arranged symmetrically, said shims 21 covering the spans 19 of the cell 15. Each shim 21 covers only half, or less, of the cell 15.

[0036] THE figures 4 And 5 illustrate two forms of embodiment in which the tinplates 21 are mounted in a removable manner, not in the alveoli 15, but on the feet 14 of the blades 12.

[0037] The assembly formed by the paddle foot 14 and the shim(s) 21 is then mounted in the corresponding alveolus 15 of the disc 11.

[0038] There figure 5 illustrates in particular a form of embodiment in which two lateral shims 21 are mounted on either side of the foot 14, symmetrically with respect to the median radial plane P. Each shim 21 has a form complementary to the lateral side of the foot 14, each shim 21 thus covers the two relevant lateral spans 19 of the foot 14 of the blade 12.

[0039] There figure 6 illustrates a form of realization in which a single tinsel 21 covers both lateral sides of the foot 14 of the awl 12, that is to say covers all the spans 19 of the foot 14.

[0040] The shim 21 has a shape complementary to that of the foot 14 and includes a radial wall 23 suitable for forming an axial stop bearing against a radial end surface 24 of the foot 14, which can be an upstream or a downstream surface of the foot 14.

[0041] Note that the shim 21 does not cover the radially internal end surface 25 of the foot 14. This is because cooling air circulation channels for the blade 12 open onto this end surface 25, and it is necessary to keep these channels unobstructed. Alternatively, the shim 21 can cover the radially internal end surface 25 of the foot 14, but in this case, it must have openings or ports opposite the outlets of these channels to allow the passage of cooling air.

[0042] As previously stated, this document proposes a method for maintaining such a high-pressure turbine bladed wheel 6, said method comprising a step in which the radial clearance j between the tip 16 of the blade 12 and the casing 20 is measured and, if this radial clearance j is greater than a predetermined value, the shim(s) 21 are removed, as illustrated in the figure 7This has the effect of bringing the blade apex 16 closer to the housing 20, and therefore reducing the clearance j by the value of the thickness of the shim 21.

[0043] It is therefore possible to reduce the play j in a simple, quick and inexpensive way, in order to improve the performance of the turbomachine and compensate for the aforementioned wear or corrosion phenomena.

Claims

1. Method for maintaining a bladed wheel (6) of a high-pressure turbine of a turbomachine, extending along an axis, comprising a disc (11) comprising cavities (15), and blades (12) extending radially and each comprising an airfoil (13) and a radially internal root (14), the root (14) of each blade (12) being mounted in a cavity (15) of the disc (11), said root (14) being supported by the disc (11) by means of surfaces of the root (14) and of the disc (11) which form bearing surfaces (19), characterized in that at least one foil (21) is removably mounted between the root (14) of at least one blade (12) and the disc (11), at the corresponding bearing surfaces (19), said method comprising the following steps: - measuring a radial clearance (j) between the tip (16) of at least one blade (12), meaning the radially external end of the blade (12), and a shroud (20) of the turbomachine situated facing the bladed wheel, - if the radial clearance (j) is greater than a determined value, removing said foil (21).

2. Method according to the preceding claim, wherein at least one foil (21) is mounted between the root (14) of each blade (12) and the disc (11), at the corresponding bearing surfaces (19), all foils (21) being removed if the radial clearance (j) is greater than said determined value.

3. Method according to one of the preceding claims, wherein the foil (21) is removably mounted on the blade root (14).

4. Method according to one of claims 1 or 2, wherein the foil (21) is removably mounted on the disc (11), for example in the cavity (15) or on a tooth of the disc (11) defined between two adjacent cavities (15).

5. Method according to one of the preceding claims, wherein the foil (21) comprises a radial abutment surface (23) bearing against a complementary abutment surface (24) of the root (14) of the blade (12) or of the disc (11).

6. Method according to one of the preceding claims, wherein the foil (21) has a thickness of between 0.1 and 0.9 mm.

7. Method according to one of the preceding claims, wherein the foil (21) is made of a cobalt-based alloy.

8. Method according to one of the preceding claims, wherein several foils are removably mounted between the root (14) of at least one blade (12) and the disc (11).