(19)
(11)EP 2 628 905 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
09.09.2020 Bulletin 2020/37

(21)Application number: 13151515.7

(22)Date of filing:  16.01.2013
(51)International Patent Classification (IPC): 
F01D 11/24(2006.01)
F01D 5/18(2006.01)

(54)

Turbomachine hot-section blade outer air seal with turbulators, and corresponding method of augmenting a surface area

Schaufelaussenluftdichtung mit Turbulatoren im heißen Bereich einer Strömungsmaschine, und dazugehöriges Verfahren zur Flächenvergrösserung

Joint d'air extérieur d'aube avec turbulateurs dans la zone chaude d'une turbomachine, et procédé d'augmentation de surface associé


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 17.02.2012 US 201213399206

(43)Date of publication of application:
21.08.2013 Bulletin 2013/34

(73)Proprietor: United Technologies Corporation
Farmington, CT 06032 (US)

(72)Inventors:
  • Blaney, Ken F.
    Middleton, NH New Hampshire 03887 (US)
  • Lutjen, Paul M.
    Kennebunkport, ME Maine 04046 (US)

(74)Representative: Dehns 
St. Bride's House 10 Salisbury Square
London EC4Y 8JD
London EC4Y 8JD (GB)


(56)References cited: : 
EP-A2- 1 505 257
EP-A2- 1 676 981
US-A- 5 538 394
US-A1- 2005 123 401
US-A1- 2010 242 488
EP-A2- 1 533 475
EP-A2- 1 914 390
US-A- 5 738 493
US-A1- 2008 063 524
US-B1- 6 379 528
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    BACKGROUND



    [0001] This disclosure relates generally to a surface area augmentation feature and, more particularly, to a protrusion-type surface augmentation feature extending from a blade outer air seal and having a non-circular cross section.

    [0002] Turbomachines, such as gas turbine engines, typically include a fan section, a turbine section, a compressor section, and a combustor section. The fan section drives air along a core flow path into the compressor section. The compressed air is mixed with fuel and combusted in the combustor section. The products of combustion are expanded in the turbine section. Hot sections of the turbomachine are exposed to very high temperatures during operation. Cooling these areas of the engine is often difficult.

    [0003] Some surfaces of hot-section turbomachine engine components include surface area augmentation features. Typical features include cylindrical posts having circular cross-sections and spherical tops.

    [0004] A prior art blade outer air seal, having the features of the preamble of claim 1, is disclosed in US 6379528. Other prior art seals are shown in EP 1676981 and EP 1914390.

    SUMMARY



    [0005] According to the present invention, there is provided a turbomachine hot-section blade outer air seal as claimed in claim 1 and a method as claimed in claim 6.

    [0006] In a further non-limiting embodiment of the foregoing blade outer air seal embodiment, the profile may include at least three edges that are not curved.

    [0007] In a further non-limiting embodiment of either of the foregoing blade outer air seal embodiments, the at least three edges may each be spaced an equal distance from the axis.

    [0008] In a further non-limiting embodiment of any of the foregoing blade outer air seal embodiments, the profile may have a triangular shape.

    [0009] In a further non-limiting embodiment of any of the foregoing blade outer air seal embodiments, the radial cross-section of the protrusion may be parallel to the surface.

    [0010] In a non-limiting embodiment of the foregoing method of augmenting a surface area of a blade outer air seal, the radial cross-section may include four distinct linear portions.

    DESCRIPTION OF THE FIGURES



    [0011] The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the detailed description. The figures that accompany the detailed description can be briefly described as follows:

    Figure 1 shows a section view of an example turbomachine.

    Figure 2 shows a perspective view of an example blade outer air seal assembly.

    Figure 3 shows a perspective view of the Figure 2 blade outer air seal with an exposed inner cavity.

    Figure 4 shows a protrusion positioned on a surface of the Figure 3 blade outer air seal in an example outside the scope of the present invention.

    Figure 4A shows a section view at line 4A-4A in Figure 4.

    Figure 5 shows another example protrusion suitable for placement on the surface of the Figure 3 blade outer air seal.

    Figure 5A shows a section view at line 5A-5A in Figure 5.

    Figure 6 shows yet another example protrusion suitable for placement on the surface of the Figure 3 blade outer air seal.

    Figure 6A shows a section view at line 6A-6A in Figure 6.


    DETAILED DESCRIPTION



    [0012] Referring to Figure 1, an example turbomachine, such as a gas turbine engine 10, is circumferentially disposed about an axis 12. The gas turbine engine 10 includes a fan section 14, a low-pressure compressor section 16, a high-pressure compressor section 18, a combustion section 20, a high-pressure turbine section 22, and a low-pressure turbine section 24. Other example turbomachines may include more or fewer sections.

    [0013] During operation, air is compressed in the low-pressure compressor section 16 and the high-pressure compressor section 18. The compressed air is then mixed with fuel and burned in the combustion section 20. The products of combustion are expanded across the high-pressure turbine section 22 and the low-pressure turbine section 24.

    [0014] The low-pressure compressor section 16 and the high-pressure compressor section 18 include rotors 26 and 28, respectively, that rotate about the axis 12. The high-pressure compressor section 18 and the low-pressure compressor section 16 also include alternating rows of rotating airfoils or rotating compressor blades 30 and static airfoils or static vanes 32.

    [0015] The high-pressure turbine section 22 and the low-pressure turbine section 24 include rotors 34 and 36, respectively, which rotate in response to expansion to drive the high-pressure compressor section 18 and the low-pressure compressor section 16. The high-pressure compressor section 18 and the low-pressure compressor include alternating rows of rotating airfoils or rotating compressor blades 38 and static airfoils or static vanes 40.

    [0016] In this example, rotating the rotor 36 drives a shaft 42 that provides a rotating input to a geared architecture 44. The example geared architecture 44 drives a shaft to rotate fan 46 of the fan section 14. The geared architecture 44 has a gear ratio that causes the fan 46 to rotate at a slower speed than the shaft 42.

    [0017] The examples described in this disclosure are not limited to the two-spool gas turbine architecture described, however, and may be used in other architectures, such as the single spool axial design, a three-spool axial design, and still other architectures. That is, there are various types of gas turbine engines, and other turbomachines, that can benefit from the examples disclosed herein.

    [0018] Referring to Figures 2 and 3 with continuing reference to Figure 1, an example blade outer air seal 50 is arranged circumferentially about the blades 38 of the high-pressure turbine section 22. The blade outer air seal 50 includes a predominantly cylindrical sealing surface 52 proximate to the tip of the blades 38. During rotation of the high-pressure turbine section rotor, the surface 52 creates a seal with the blades 38.

    [0019] During operation, the blade outer air seal 50 is exposed to significant thermal energy. Cooling air 56, such as bleed air from the engine 10, is moved into cavities 62 and 64 within the blade outer air seal 50 to cool the blade outer air seal 50. The blade outer air seal 50 is considered a hot-section component of the engine 10 due to its exposure to the hot gas flow path of the engine 10. The blade outer air seal 50 is an investment cast component in this example. The blade outer air seal 50 typically requires the use of parasitic cooling air to meet its life requirements. The blade outer air seal 50 is considered a hot section part because it requires the cooling air. Other hardware requiring cooling flow is considered a hot section part. Furthermore, adjacent or supporting hardware or other hardware that directs or delivers cooling air may also be considered hot section parts.

    [0020] In this example, an impingement plate 66 covers the cavities 62 and 64. The cooling air 56 moves through apertures 68 in the impingement plate 66 to the cavities 62 and 64. The air exits the cavities 62 and 64 through apertures 70 in the blade outer air seal 50.

    [0021] A floor surface 72 and sidewalls 74 establish portions of the cavity 64. An array of protrusions 76 extend from the floor surface 72 of the blade outer air seal 50. The floor surface 72 of the blade outer air seal 50 is considered a base surface of a hot-section component in this example.

    [0022] The array of protrusions 76 are surface area augmentation features that effectively increase the surface area of the blade outer air seal 50 interacting with air moving through the cavity 64. The array of protrusions 76 thus facilitates thermal energy transfer from the blade outer air seal 50 to the air moving through the cavity 64.

    [0023] Referring to Figures 4 and 4A with continuing reference to Figure 3, an example, outside the scope of the present invention, of one of the protrusions 76A within the array of protrusions 76 extends longitudinally along an axis W1 away from the floor surface 72. A radial cross-section 80 of the protrusion 76a has a profile that is noncircular. The radial cross-section 80 is parallel to the floor surface 72 and perpendicular to the axis W1 in this example.

    [0024] In this example, the profile includes three edges 84a-84c that are not curved. That is, the edges 84a-84c are linear. In this example, each of the edges 84a-84c is spaced an equal distance d from the axis W1. In other examples, some of all of the edges 84a-84c are not equally spaced from the axis W1.

    [0025] Also, in this example, a radiused area 86a transitions the edge 84a to the edge 84b, a radiused area 86b transitions the edge 84b to the edge 84c, and a radiused area 86c transitions the edge 84c to the edge 84a.

    [0026] The protrusion 76a includes three sides 88a-88c facing outwardly away from the axis W1. The sides 88a-88c are not planar. Concave portions 90 transition the floor surface 72 into convex portions 92. The convex portions 92 transition the concave portions 90 into a planar portion 94. The planar portion 94 has a triangular shape and is parallel to the floor surface 72 in this example.

    [0027] In one specific example, the concave portions 90 and the convex portions 92 have a 0.015 inch radius (0.381 mm), and a distance D from the floor surface 72 to the top surface 94 is 0.030 inches (0.762 mm). Thus, the protrusion 76a can be said to have a height of 0.030 inches (0.762 mm). The total surface area of the protrusion 76a is about 0.0029 inches2 (1.871 mm2).

    [0028] Although the example array of protrusions 76 is shown in the blade outer air seal 50, many other components of the engine 10 could benefit from the use the array of the protrusions 76. For example, the combustor panels in the combustion section could also benefit from the increased surface area provided by the array of protrusions 76.

    [0029] In this example, all the protrusions 76a in the array of protrusions 76a are shaped similarly to the protrusion 76a. In other examples, some or all of the protrusions in the array of protrusions 76a have different shapes.

    [0030] An example protrusion 76b forming part of the array of protrusions of the blade outer air seal according to the invention is shown in Figures 5-5A. The protrusion 76b includes a radial cross-section 82 similar to the radial cross-section 80 of the protrusion 76a. Notably, the protrusion 76b includes planar side walls 98a-98c each positioned radially the same distance from the axis W2.

    [0031] The protrusion 76b includes concave portions 100 transitioning the floor surface 72 into the side walls 98a-98c, and convex portions 104 transitioning the side walls 98a-98c to a planar top surface 106. The example top surface 106 is planar, has a triangular profile, and is parallel to the floor surface 72. The example protrusion 76b has a total surface area of 0.0035 inches2 (2.258 mm2).

    [0032] Yet another example protrusion 76c suitable for use within the array of protrusions 76 instead of, or in addition to, other protrusions is shown in Figures 6-6A. The protrusion 76c has a rectangular or diamond-shaped radial profile 102. In this example, the radial profile 102 of the protrusion 76c is generally rhombic. The radial profile 102 is square in other examples.

    [0033] The profile 102 of the example protrusion 76c includes four noncurved (or linear) sides 108a-108d. Each of the sides 108a-108d is positioned the same distance away from the axis W3. Radial portions transition the sides of the profile into one another.

    [0034] The protrusion 76c includes concave portions 110 transitioning the floor surface 72 into respective side walls 112a-112d. The protrusion 76c includes convex portions 114 transitioning the side walls 112a-112d to a planar portion 116. The planar portion 116 is has a square profile and is parallel to the floor surface 72 in this example. In other examples, the planar portion 116 is not parallel to the floor surface 72. The total surface area of the protrusion 76c is 0.0038 inches2 (2.452 mm2) in this example.

    [0035] The example protrusions 76b, and 76c may be used alone or in combination within the array of protrusions 76. Other example protrusions could also be used.

    [0036] Features of the disclosed examples include a protrusion having an increased surface area for transferring thermal energy away from a hot-section component. The protrusion is a type of surface area augmentation feature.

    [0037] The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the scope of this disclosure. Thus, the scope of legal protection given to this disclosure can only be determined by studying the following claims.


    Claims

    1. A turbomachine hot-section blade outer air seal (50) comprising an array of protrusions (76b; 76c) that each extend away from a base surface (72) of the blade outer air seal (50) along a longitudinal axis (W2; W3) into a cavity (64) of the blade outer air seal (50), wherein a radial cross-section of each protrusion (76b; 76c) has a profile (80; 82; 102) that is non-circular and each protrusion (76b; 76c) includes at least three distinct planar surfaces (98a, 98b, 98c; 112a, 112b, 112c) facing away from the axis (W2; W3) and at least one planar surface (106; 116) facing axially away from the base surface (72),
    characterised in that:
    each protrusion includes radii that transition one of the at least three distinct planar surfaces (98a, 98b, 98c; 112a, 112b, 112c) into another of the at least three distinct planar surfaces (98a, 98b, 98c; 112a, 112b, 112c), convex portions (104; 114) that transition the at least one planar surface (106; 116) facing axially away from the base surface (72) into the at least three distinct planar surfaces (98a, 98b, 98c; 112a, 112b, 112c) facing away from the axis (W2; W3), and concave portions (100; 110) that transition the at least three distinct planar surfaces (98a, 98b, 98c; 112a, 112b, 112c) facing away from the axis (W2; W3) into the base surface (72).
     
    2. The blade outer air seal (50) of claim 1, wherein the profile (82; 102) comprises at least three edges (84a, 84b, 84c) that are not curved.
     
    3. The blade outer air seal (50) of claim 2, wherein the at least three edges (84a ... 108c) are each spaced an equal distance from the axis (W2; W3).
     
    4. The blade outer air seal (50) of any of claims 1 to 3, wherein the profile (80; 82; 102) has a triangular shape.
     
    5. The blade outer air seal (50) of any preceding claim, wherein the radial cross-section of each protrusion (76b; 76c) is parallel to the base surface (72).
     
    6. A method of augmenting a surface area of a turbomachine hot-section blade outer air seal (50), comprising:
    increasing a surface area of a turbomachine hot-section blade outer air seal (50) using an array of protrusions (76b; 76c), wherein the protrusions each extend longitudinally along an axis (W2; W3) away from a base surface (12) of the blade outer air seal (50) into a cavity (64) of the blade outer air seal (50), and each of the protrusions (76b; 76c) has a radial cross-section having a profile (82; 102) that is non-circular and each protrusion (76b; 76c) includes at least three distinct planar surfaces (98a, 98b, 98c, 112a, 112b, 112c) facing away from the axis (W2; W3) and at least one planar surface (106; 116) facing axially away from the base surface (72), characterised in that:
    each protrusion includes radii that transition one of the at least three distinct planar surfaces (98a, 98b, 98c) into another of the at least three distinct planar surfaces (98a, 98b, 98c; 112a, 112b, 112c), convex portions (104; 114) that transition the at least one planar surface (106; 116) facing axially away from the base surface (72),
    into the at least three distinct planar surfaces (98a, 98b, 98c; 112a, 112b, 112c) facing away from the axis (W2; W3), and concave portions (100; 110) that transition the at least three distinct planar surfaces (98a, 98b, 98c; 112a, 112b, 112c) facing away from the axis (W2; W3) into the base surface (72).
     
    7. The method of claim 6, wherein the radial cross-section includes four distinct linear portions (108a, 108b, 108c, 108d).
     


    Ansprüche

    1. Äußere Laufschaufelluftdichtung (50) des heißen Bereichs einer Strömungsmaschine, umfassend eine Anordnung von Vorsprüngen (76b; 76c), die sich jeweils weg von einer Grundfläche (72) der äußeren Laufschaufelluftdichtung (50) entlang einer Längsachse (W2; W3) in einen Hohlraum (64) der äußeren Laufschaufelluftdichtung (50) erstrecken, wobei ein radialer Querschnitt jedes Vorsprungs (76b; 76c) ein Profil (80; 82; 102) aufweist, das nicht kreisförmig ist und jeder Vorsprung (76b; 76c) mindestens drei unterschiedliche ebene Flächen (98a, 98b, 98c; 112a, 112b, 112c), die von der Achse (W2; W3) wegzeigen und mindestens eine ebene Fläche (106; 116) einschließt, die axial von der Grundfläche (72) wegzeigt,
    dadurch gekennzeichnet, dass:
    jeder Vorsprung Folgendes einschließt: Radien, die eine der mindestens drei unterschiedlichen ebenen Flächen (98a, 98b, 98c; 112a, 112b, 112c) in eine andere der mindestens drei unterschiedlichen ebenen Flächen (98a, 98b, 98c; 112a, 112b, 112c) übergehen lassen, konvexe Abschnitte (104; 114), die die mindestens eine ebene Fläche (106; 116), die axial von der Grundfläche (72) wegzeigt, in die mindestens drei unterschiedlichen ebenen Flächen (98a, 98b, 98c; 112a, 112b, 112c) übergehen lassen, die von der Achse (W2; W3) wegzeigen, und konkave Abschnitte (100; 110), die die mindestens drei unterschiedlichen ebenen Flächen (98a, 98b, 98c; 112a, 112b, 112c), die von der Achse (W2; W3) wegzeigen, in die Grundfläche (72) übergehen lassen.
     
    2. Äußere Laufschaufelluftdichtung (50) nach Anspruch 1, wobei das Profil (82; 102) mindestens drei Kanten (84a, 84b, 84c) umfasst, die nicht gebogen sind.
     
    3. Äußere Laufschaufelluftdichtung (50) nach Anspruch 2, wobei die mindestens drei Kanten (84a...108c) jeweils in einem gleichen Abstand von der Achse (W2; W3) beabstandet sind.
     
    4. Äußere Laufschaufelluftdichtung (50) nach einem der Ansprüche 1 bis 3, wobei das Profil (80; 82; 102) eine dreieckige Form aufweist.
     
    5. Äußere Laufschaufelluftdichtung (50) nach einem der vorhergehenden Ansprüche, wobei der radiale Abschnitt jedes Vorsprungs (76b; 76c) zu der Grundfläche (72) parallel ist.
     
    6. Verfahren zur Flächenvergrößerung einer äußeren Laufschaufelluftdichtung (50) des heißen Bereichs einer Strömungsmaschine, umfassend:
    Vergrößern einer Fläche einer äußeren Laufschaufelluftdichtung (50) des heißen Bereichs einer Strömungsmaschine unter Verwendung einer Anordnung von Vorsprüngen (76b; 76c), wobei sich die Vorsprünge jeweils längs entlang einer Achse (W2; W3) weg von einer Grundfläche (12) der äußeren Laufschaufelluftdichtung (50) in einen Hohlraum (64) der äußeren Laufschaufelluftdichtung (50) erstrecken, und jeder der Vorsprünge (76b; 76c) einen radialen Querschnitt aufweist, der ein Profil (82; 102) aufweist, das nicht kreisförmig ist und jeder Vorsprung (76b; 76c) mindestens drei unterschiedliche ebene Flächen (98a, 98b, 98c, 112a, 112b, 112c), die von der Achse (W2; W3) wegzeigen und mindestens eine ebene Fläche (106; 116) einschließt, die axial von der Grundfläche (72) wegzeigt, dadurch gekennzeichnet, dass:

    jeder Vorsprung Folgendes einschließt: Radien, die eine der mindestens drei unterschiedlichen ebenen Flächen (98a, 98b, 98c) in eine andere der mindestens drei unterschiedlichen ebenen Flächen (98a, 98b, 98c; 112a, 112b, 112c) übergehen lassen, konvexe Abschnitte (104; 114), die die mindestens eine ebene Fläche (106; 116), die axial von der Grundfläche (72) wegzeigt,

    in die mindestens drei unterschiedlichen ebenen Flächen (98a, 98b, 98c; 112a, 112b, 112c) übergehen lassen, die von der Achse (W2; W3) wegzeigen, und konkave Abschnitte (100; 110), die die mindestens drei unterschiedlichen ebenen Flächen (98a, 98b, 98c; 112a, 112b, 112c), die von der Achse (W2; W3) wegzeigen, in die Grundfläche (72) übergehen lassen.


     
    7. Verfahren nach Anspruch 6, wobei der radiale Querschnitt vier unterschiedliche lineare Abschnitte (108a, 108b, 108c, 108d) einschließt.
     


    Revendications

    1. Joint d'étanchéité à l'air extérieur de pale de la zone chaude d'une turbomachine (50) comprenant un ensemble de protrusions (76b ; 76c) qui s'étendent chacune à l'opposé d'une surface de base (72) du joint d'étanchéité à l'air extérieur de pale (50) le long d'un axe longitudinal (W2 ; W3) dans une cavité (64) du joint d'étanchéité à l'air extérieur de pale (50), dans lequel une section transversale radiale de chaque protrusion (76b ; 76c) présente un profil (80 ; 82 ; 102) qui est non circulaire et chaque protrusion (76b ; 76c) comporte au moins trois surfaces planes distinctes (98a, 98b, 98c ; 112a, 112b, 112c) orientées à l'opposé de l'axe (W2 ; W3) et au moins une surface plane (106 ; 116) orientée axialement à l'opposé de la surface de base (72),
    caractérisé en ce que :
    chaque protrusion comprend des rayons qui font la transition entre l'une des au moins trois surfaces planes distinctes (98a, 98b, 98c ; 112a, 112b, 112c) dans une autre des au moins trois surfaces planes distinctes (98a, 98b, 98c ; 112a, 112b, 112c), des parties convexes (104 ; 114) qui font la transition entre l'au moins une surface plane (106 ; 116) orientée axialement à l'opposé de la surface de base (72) dans les au moins trois surfaces planes distinctes (98a, 98b, 98c ; 112a, 112b, 112c) orientées à l'opposé de l'axe (W2 ; W3), et des parties concaves (100 ; 110) qui font la transition entre les au moins trois surfaces planes distinctes (98a, 98b, 98c ; 112a, 112b, 112c) orientées à l'opposé de l'axe (W2 ; W3) dans la surface de base (72).
     
    2. Joint d'étanchéité à l'air extérieur de pale (50) selon la revendication 1, dans lequel le profil (82 ; 102) comprend au moins trois bords (84a, 84b, 84c) qui ne sont pas incurvés.
     
    3. Joint d'étanchéité à l'air extérieur de pale (50) selon la revendication 2, dans lequel les au moins trois bords (84a ... 108c) sont chacun espacés d'une distance égale par rapport à l'axe (W2 ; W3).
     
    4. Joint d'étanchéité à l'air extérieur de pale (50) selon l'une quelconque des revendications 1 à 3, dans lequel le profil (80 ; 82 ; 102) présente une forme triangulaire.
     
    5. Joint d'étanchéité à l'air extérieur de pale (50) selon une quelconque revendication précédente, dans laquelle la section transversale radiale de chaque protrusion (76b ; 76c) est parallèle à la surface de base (72).
     
    6. Procédé d'augmentation d'une surface d'un joint d'étanchéité à l'air extérieur de pale de la zone chaude d'une turbomachine (50), comprenant :
    l'augmentation d'une surface d'un joint d'étanchéité à l'air extérieur de pale de la zone chaude d'une turbomachine (50) à l'aide d'un réseau de protrusions (76b ; 76c), dans lequel les protrusions s'étendent longitudinalement le long d'un axe (W2 ; W3) à l'opposé d'une surface de base (12) du joint d'étanchéité à l'air extérieur de pale (50) dans une cavité (64) du joint d'étanchéité à l'air extérieur de pale (50), et chacune des protrusions (76b ; 76c) présente une section transversale radiale ayant un profil (82 ; 102) qui est non circulaire et chaque protrusion (76b ; 76c) comporte au moins trois surfaces planes distinctes (98a, 98b, 98c ; 112a, 112b, 112c) orientées à l'opposé de l'axe (W2 ; W3) et au moins une surface plane (106 ; 116) orientée axialement à l'opposé de la surface de base (72), caractérisé en ce que :

    chaque protrusion comprend des rayons qui font la transition entre l'une des au moins trois surfaces planes distinctes (98a, 98b, 98c) dans une autre des au moins trois surfaces planes distinctes (98a, 98b, 98c ; 112a, 112b, 112c), des parties convexes (104 ; 114) qui font la transition entre l'au moins une surface plane (106 ; 116) orientée axialement à l'opposé de la surface de base (72),

    dans les au moins trois surfaces planes distinctes (98a, 98b, 98c ; 112a, 112b, 112c) orientées à l'opposé de l'axe (W2 ; W3), et des parties concaves (100 ; 110) qui font la transition entre les au moins trois surfaces planes distinctes (98a, 98b, 98c ; 112a, 112b, 112c) orientées à l'opposé de l'axe (W2 ; W3) dans la surface de base (72).


     
    7. Procédé selon la revendication 6, dans lequel la section transversale radiale comporte quatre parties linéaires distinctes (108a, 108b, 108c, 108d).
     




    Drawing

















    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description