Guide vane tensioning tool

Abstract

The present invention discloses a guide vane tensioning tool, which is used to fix the guide vane of an aircraft engine to a turbine casing. The guide vane tensioning tool comprises: a support assembly, which is used to be connected to the turbine casing; a fixing assembly, which is connected to the support assembly; and a hook assembly, one end of which is connected to the fixing assembly, and the other end of which is used to fix the guide vane from the end of the guide vane. In the guide vane tensioning tool of the present invention, the hook assembly is connected to the support assembly through the fixing assembly, and the end of the guide vane is tightened by the hook assembly. In the process of installing the guide vane to the turbine casing, the end of the guide vane is tightened away from the turbine casing, so that the two ends of the guide vane are kept horizontal, so as to avoid the situation where the guide vane is stuck due to the different heights at the two ends of the guide vane, thereby improving the installation efficiency of the guide vane.

Description

Technical Field

[0001] The invention relates to the field of aero-engine assembly, and in particular to a guide vane tightening tool. Background Art

[0002] like Figure 1 As shown, the low-pressure turbine stator of the aircraft engine is composed of multiple stages of stators, and each stage of stator is composed of multiple guide vanes 3' (sector segments) to form a complete ring and then fixed on the turbine casing 1'. The fixing method of the guide vane 3' is as follows Figure 2 As shown, a slot is provided on one side of each guide vane 3' close to the front end of the turbine casing 1', and the guide vane 3' is mounted on the turbine casing 1' and the end edge plate of the front-stage outer ring. After the guide vane 3' of this stage forms a complete ring, the end of the guide vane 3' is pressed from the rear end direction of the turbine casing 1' by the retaining ring 4' to limit its axial movement along the turbine casing 1', and then the guide vane 3' is clamped on the turbine casing 1' through the slot of the rear-stage outer ring 5' to limit the radial movement of the guide vane 3' along the turbine casing 1'. The assembly mode of the guide vane 3' is piece by piece. After the complete ring is formed, the retaining ring 4' and the rear-stage outer ring 5' are installed in sequence to fix the guide vane 3' of this stage on the turbine casing 1'. Since the fixing structure of the guide vane 3' is similar to a cantilever beam, during the assembly of the guide vane 3', the inner side of the guide vane 3' is tilted toward the front end direction of the turbine casing 1' due to the influence of gravity, so that the guide vane 3' cannot be hung on the inner wall of the casing. In the conventional assembly process, a pad 2' needs to be placed on the front-stage guide vane 3' to support the rear-stage guide vane 3' from the inside. Since the profile of the guide vane 3' is an irregular plane, the pad 2' cannot be placed horizontally, so that each pad 2' is of different heights, resulting in the rear-stage guide vanes 3' being misaligned and uneven. The overlapping surfaces of adjacent guide vanes 3' are inclined overlaps. When the guide vanes 3' are of different heights, the adjacent guide vanes 3' will bite each other, making the guide vanes 3' unable to move. Once the guide vanes 3' are stuck in installation, the pad 2' needs to be replaced and the placement height of each guide vane 3' needs to be adjusted. The debugging cycle is long, making the installation efficiency of the guide vanes 3' low. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a guide vane tightening tool in order to overcome the defect in the prior art that the guide vanes are easily uneven in height and adjacent guide vanes are bitten into each other when the guide vanes are supported by pads.

[0004] The present invention solves the above technical problems through the following technical solutions:

[0005] A guide vane tightening tool is used to fix the guide vane of an aircraft engine to a turbine casing, and the guide vane tightening tool comprises:

[0006] a support assembly for connection to the turbine casing;

[0007] A fixing assembly, the fixing assembly being connected to the supporting assembly;

[0008] A hook assembly, one end of which is connected to the fixing assembly, and the other end of which is used to fix the guide vane from the end of the guide vane.

[0009] In the present solution, the hook assembly is connected to the supporting assembly via the fixing assembly, and the hook assembly is used to tighten the end of the guide vane. During the process of installing the guide vane to the turbine casing, after one end of the guide vane is fixed to the turbine casing, the hook assembly tightens the end of the guide vane away from the turbine casing to keep both ends of the guide vane level, thereby preventing the guide vane from biting each other due to one end being suspended in the air and the two ends of the guide vane being at different heights, thereby improving the guide vane installation efficiency.

[0010] Preferably, a plurality of mounting holes are provided on the outer side surface of the fixing component along the circumference of the fixing component, and the hook component is inserted into the mounting holes.

[0011] In the present solution, mounting holes are provided around the fixing component, and the hook component is connected to the fixing component through the mounting holes. The hook component is detachably connected to the fixing component through the mounting holes, rather than the hook component and the fixing component being integrally formed and unable to replace the hook component suitable for the turbine casing. Different hook components can be replaced according to the size of different turbine casings, thereby improving the versatility of the guide vane tensioning tool.

[0012] Preferably, the plurality of mounting holes are evenly distributed along the circumference of the fixing assembly.

[0013] In the present scheme, the mounting holes are evenly arranged along the circumferential direction of the fixing assembly. When the number of mounting holes is the same as the number of guide vanes of the corresponding stage of the rotor, the guide vanes are evenly distributed along the circumferential direction of the turbine casing. The mounting holes and the guide vanes are arranged one-to-one, and the hook assembly and the guide vanes are arranged one-to-one. The center of the hook assembly and the center of gravity of the guide vane are at the same position in the circumferential direction of the turbine casing, so that the hook can be aligned with the mid-section of the guide vane to meet the vertical fixation of the soft rope tied to the hook. The tensioning force of the hook assembly on the guide vane is applied to the center of gravity of the guide vane to avoid the tensioning force of the hook assembly on the guide vane and the gravity of the guide vane from being out of axial rotation to generate a rotational torque that causes the guide vane to overturn.

[0014] Preferably, multiple layers of the mounting holes are provided along the axial direction of the fixing assembly.

[0015] In this solution, multiple layers of mounting holes are arranged in the axial direction of the fixed component, and the number of mounting holes in each layer is different. The fixed component with multiple layers and different numbers of mounting holes can correspond to stator disks with different numbers of guide vanes. After the fixed component is installed once, it can be adapted to a turbine casing with different numbers of guide vanes in the circumferential direction, thereby improving the versatility of the fixed component.

[0016] Preferably, the fixing assembly includes a plurality of stacked fixing plates, and one end of the hook assembly is connected to the fixing plates.

[0017] In this solution, by providing stacked fixing plates, a stacked combination of fixing plates with different numbers of mounting holes can be selected according to needs during use, thereby improving the applicability of the guide vane tensioning tool.

[0018] Preferably, the fixing assembly further comprises a pivot shaft, and the pivot shaft penetrates the fixing plate and the supporting assembly.

[0019] In the present scheme, a pivot axis is provided to connect the fixed disk and the support assembly to achieve a detachable connection between the fixed disk and the support assembly. Each fixed disk can rotate around the pivot axis to adjust the circumferential position of the fixed disk and the turbine casing, so that the mounting hole and the mid-section of the guide vane are aligned, thereby aligning the hook assembly installed in the mounting hole and the mid-section of the guide vane, thereby satisfying the vertical fixation of the soft rope tied to the hook. The tensioning force of the hook assembly on the guide vane is applied to the center of gravity of the guide vane to avoid the tensioning force of the hook assembly on the guide vane and the gravity of the guide vane to generate a rotational torque on the same axis as the guide vane, which may cause the guide vane to overturn. Each fixed disk can be adjusted around the pivot axis separately to improve the flexibility of adjustment of the fixed assembly.

[0020] Preferably, the hook assembly includes an extension rod, one end of which is connected to the fixing assembly, and the extension rod is arranged along the radial direction of the fixing assembly.

[0021] In the present solution, an extension rod extending in the radial direction of the fixing assembly is provided, and the extension rod only extends on the mid-section of the guide vane. When multiple layers of fixing plates are respectively inserted with extension rods, the hooks located on the upper layer can pass between the extension rods of the lower layer, thereby avoiding interference between the hook assemblies connected to the mounting holes of different layers.

[0022] Preferably, the hook assembly further comprises a connecting member and a hook, and the hook is connected to an end of the extension rod away from the fixing assembly via the connecting member.

[0023] In the present scheme, an extension rod is radially arranged in the turbine casing, and a hook is hung on the extension rod. The hook hangs down vertically along the axial direction of the turbine casing, so that the pulling force of the hook on the guide vane is vertically upward. The pulling force of the hook on the guide vane is theoretically completely along the gravity direction of the guide vane, avoiding the pulling force of the hook on the guide vane to produce a component force not in the gravity direction of the guide vane, thereby improving the stability of the tensioning of the guide vane by the hook.

[0024] Preferably, the hook comprises a clamping portion and a connecting portion, the two sides of the connecting portion are respectively fixed with clamping portions, the cross section of the hook is in a side "U" shape, and the distance between the two clamping portions matches the width of the guide vane end.

[0025] In this solution, the hook is shaped like a side "U" and is clamped to one end of the guide vane when in use. The clamping of the hook and the guide vane is reliable and easy to disassemble. The hook can be quickly and conveniently clamped to the guide vane, thereby improving the installation efficiency of the guide vane.

[0026] Preferably, the support assembly includes a transverse plate and two longitudinal plates, the two longitudinal plates are fixedly connected to the two ends of the transverse plate, the support assembly is in an inverted "U" shape, and the longitudinal plate is provided with a snap-in groove at one end away from the transverse plate, and the snap-in groove matches the upper edge of the turbine casing.

[0027] In this solution, the support assembly is connected to the turbine casing through the snap-in grooves on the two longitudinal plates. The support assembly and the turbine casing are firmly installed and easy to disassemble, thereby improving the loading and unloading speed between the guide vane tensioning tool and the turbine casing.

[0028] The positive and progressive effects of the present invention are:

[0029] The guide vane tensioning tool of the present invention has a hook assembly connected to a supporting assembly via a fixing assembly, and the end of the guide vane is tightened by the hook assembly. During the process of installing the guide vane to the turbine casing, the end of the guide vane away from the turbine casing is tightened to keep the two ends of the guide vane level, thereby avoiding the situation where the guide vane is stuck due to different heights at the two ends of the guide vane, thereby improving the guide vane installation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the turbine stator mechanism.

[0031] Figure 2 It is a schematic diagram of fixing the stator guide vanes in the prior art.

[0032] Figure 3 It is a schematic diagram of the guide vane tightening tool of the present invention tightening the guide vane.

[0033] Figure 4 It is a schematic diagram of the overall structure of the guide vane tightening tool of the present invention for tightening the guide vane.

[0034] Figure 5 It is a schematic structural diagram of the guide vane tightening tool of the present invention.

[0035] Figure 6 It is a schematic cross-sectional view of the guide vane tightening tool of the present invention.

[0036] Description of reference numerals:

[0037] In the prior art:

[0038] Turbine case 1'

[0039] Pad 2'

[0040] Guide vane 3'

[0041] Retaining ring 4'

[0042] Post-stage outer ring 5'

[0043] In the present invention:

[0044] Turbine case 1

[0045] Guide vane 11

[0046] Guide vane tensioning tool 2

[0047] Support component 3

[0048] Card slot 31

[0049] Horizontal board 32

[0050] Vertical board 33

[0051] Fixing component 4

[0052] Mounting hole 41

[0053] Fixed plate 42

[0054] Pivot shaft 43

[0055] Hook component 5

[0056] Extension rod 51

[0057] Hook 52

[0058] Clamping portion 521

[0059] Connection part 522

[0060] Connector 53 DETAILED DESCRIPTION

[0061] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples.

[0062] like Figure 5 As shown, the present invention provides a guide vane tensioning tool 2 for fixing the guide vane 11 of an aircraft engine to a turbine casing 1 . The guide vane tensioning tool 2 includes a supporting component 3 , a fixing component 4 and a hook component 5 .

[0063] The support assembly 3 is used to be connected to the turbine casing 1 , and the guide vane tightening tool 2 is integrally fixedly connected to the turbine casing 1 via the support assembly 3 .

[0064] The fixing assembly 4 is connected to the supporting assembly 3 , and the fixing assembly 4 is fixedly connected to the turbine casing 1 through the supporting assembly 3 .

[0065] One end of the hook assembly 5 is connected to the fixing assembly 4, the hook assembly 5 is detachably connected to the fixing assembly 4, and the other end of the hook assembly 5 extends along the radial direction of the turbine casing 1. Figure 4 As shown, the turbine casing 1 is a cylindrical structure as a whole, and multiple stages of stators are installed along the axial direction of the turbine casing 1, and each stage of stators includes a guide vane 11 along the circumferential direction of the turbine casing 1. One end of the guide vane 11 is fixedly installed on the wall of the turbine casing 1, and the other end of the guide vane 11 extends along the radial direction of the turbine casing 1 toward the axial direction of the turbine casing 1, and the hook assembly 5 hooks one end of the guide vane 11 close to the axial direction of the turbine casing 1.

[0066] like Figure 3 As shown, a plurality of mounting holes 41 are provided on the outer surface of the fixing component 4 along the circumference of the fixing component 4. The fixing component 4 is cylindrical as a whole. The central axis of the fixing component 4 is coaxially arranged with the central axis of the turbine casing 1. A plurality of mounting holes 41 matching with the hook component 5 are provided along the circumference of the fixing component 4, and the hook component 5 is inserted into the mounting hole 41. A thread is provided in the mounting hole 41, and an external thread is provided at one end of the hook component 5 close to the fixing component 4. The hook component 5 is connected to the mounting hole 41 by a thread, thereby realizing a detachable connection between the hook component 5 and the fixing component 4. In the present embodiment, the hook component 5 is connected to the mounting hole 41 by a thread. In other embodiments, the hook component 5 may also be connected to the mounting hole 41 by an interference fit, or the hook component 5 may also be connected to the mounting hole 41 by a fixing pin.

[0067] Along the circumferential direction of the fixing assembly 4, at the same height in the axial direction of the fixing assembly 4, a plurality of mounting holes 41 of the same size are provided. The plurality of mounting holes 41 are evenly distributed along the circumference of the fixing assembly 4, and the angles between two adjacent mounting holes 41 located at the same layer of the fixing assembly 4 and the axis of the fixing assembly 4 are the same. The mounting holes 41 are arranged in this way because the guide vanes 11 installed on the same stage of the stator on the turbine casing 1 are also evenly distributed along the circumference of the turbine casing 1. When installing the guide vanes 11, each mounting hole 41 corresponds to a guide vane 11, and each mounting hole 41 is installed with a hook assembly 5, so that one hook assembly 5 corresponds to a guide vane 11. The mounting holes 41 and the guide vanes 11 are arranged in a one-to-one correspondence, so that the hook assembly 5 and the guide vanes 11 are arranged in a one-to-one correspondence, and the center of the hook assembly 5 and the center of gravity of the guide vane 11 are at the same position in the circumferential direction of the turbine casing 1, so that the hook 52 can be aligned with the mid-section of the guide vane 11 to meet the vertical fixation of the soft rope tied to the hook 52. The tensioning force of the hook assembly 5 on the guide vane 11 is applied to the center of gravity of the guide vane 11, so as to avoid the tensioning force of the hook assembly 5 on the guide vane 11 and the gravity of the guide vane 11 from generating a rotational torque on different axes, which may cause the guide vane 11 to overturn.

[0068] Multiple layers of mounting holes 41 are provided along the axial direction of the fixing assembly 4. Each layer of mounting holes 41 is evenly distributed along the axial direction of the fixing assembly 4, and the number of mounting holes 41 in each layer is different to adapt to stators of different stages with different numbers of guide vanes 11. The mounting holes 41 have the same shape, and the hook assembly 5 can be installed in any mounting hole 41 on the fixing assembly 4.

[0069] The fixing assembly 4 includes a plurality of stacked fixing disks 42, and one end of the hook assembly 5 is connected to the fixing disk 42. The fixing disk 42 is in the shape of a circular disk. The thickness of each layer of the fixing disks 42 is the same. The axial direction of the fixing disk 42 is the same as the axial direction of the turbine casing 1, and the fixing disk 42 is arranged at the axis of the turbine casing 1. On each layer of the fixing disk 42, mounting holes 41 are opened along the radial direction of the fixing disk 42, and the mounting holes 41 on each fixing disk 42 are evenly distributed along the circumferential direction of the fixing disk 42. The number of mounting holes 41 on each layer of the fixing disk 42 is different to adapt to each stage of the stator with different numbers of guide vanes 11.

[0070] The fixing assembly 4 also includes a pivot shaft 43, which is inserted through the fixing plate 42 and the supporting assembly 3. The bottom end of the pivot shaft 43 has a positioning plate, and the top end of the pivot shaft 43 has a threaded portion. A through hole matching the outer diameter of the pivot shaft 43 is provided at the center of each fixing plate 42. During installation, the pivot shaft 43 passes through the fixing plates 42 and the supporting assembly 3 at each level from bottom to top, and the pivot shaft 43 and the supporting assembly 3 are tightened by nuts at the upper part of the supporting assembly 3. The positioning plate below the pivot shaft 43 abuts against the fixing plate 42 at the bottom, and the positioning plate at the bottom and the nut at the top fix the supporting assembly 3 and the fixing plates 42 at each level. When the nut is not tightened on the threaded portion at the top of the pivot shaft 43, the fixed disk 42 can rotate along the axis of the pivot shaft 43 to adjust the circumferential position of the mounting hole 41 on the fixed disk 42. After the mounting hole 41 and the guide vane 11 are circumferentially aligned, the nut and the pivot shaft 43 are tightened to achieve the circumferential positioning of the fixed disk 42.

[0071] like Figure 6As shown, the hook assembly 5 includes an extension rod 51, which is a rigid straight rod. One end of the extension rod 51 is connected to the fixing assembly 4. In this embodiment, the end of the extension rod 51 connected to the fixing assembly 4 is provided with an external thread, and the mounting hole 41 on the fixing assembly 4 is processed with an internal thread. The extension rod 51 is inserted into the mounting hole 41 and rotated around the axial direction of the mounting hole 41 to tighten and install the extension rod 51 and the fixing assembly 4. In other embodiments, the extension rod 51 and the mounting hole 41 can also be fixed by interference fit or by fixing the extension rod 51 and the fixing assembly 4 with a fixing pin. The extension rod 51 is arranged along the radial direction of the fixing assembly 4, and the fixing assembly 4 is arranged at the central axis of the turbine casing 1, and the central axes of the fixing assembly 4 and the turbine casing 1 are coaxially arranged, and the radial direction of the fixing assembly 4 is the same as the radial direction of the turbine casing 1. The lengths of the guide vanes 11 at each stage are different, and the radii of the turbine casing 1 along the axial direction are also different, resulting in different radii of the inner rings formed by the guide vanes 11 at the same stage. The length of the extension rod 51 is greater than the maximum radius of the inner ring formed by the guide vanes 11, and hooks 52 are provided at different radial positions of the extension rod 51 to meet the inner fixation of the guide vanes 11 at each stage.

[0072] The hook assembly 5 further includes a connecting member 53 and a hook 52, and the hook 52 is connected to one end of the extension rod 51 away from the fixing assembly 4 through the connecting member 53. The top end of the hook 52 is fixedly connected to the connecting member 53. One end of the connecting member 53 is connected to the hook 52, and the other end of the connecting member 53 is wound and connected to the extension rod 51. In this embodiment, the connecting member 53 is a soft rope, and in other embodiments, the connecting member 53 can also be a rope made of other flexible materials such as a wire rope or a cotton rope.

[0073] The hook 52 includes a clamping portion 521 and a connecting portion 522. The clamping portions 521 are fixedly provided on both sides of the connecting portion 522. When the hook 52 is fixedly connected to the inner side of the guide vane 11, the two clamping portions 521 are respectively fixedly connected to the upper and lower parts of the inner side of the guide vane 11. The cross section of the hook 52 is in a side "U" shape. The distance between the two clamping portions 521 matches the width of the end of the guide vane 11, so that the two clamping portions 521 can be clamped to the end of the guide vane 11.

[0074] The support assembly 3 includes a transverse plate 32 and two longitudinal plates 33. The two longitudinal plates 33 are fixedly connected to the two ends of the transverse plate 32, and the two longitudinal plates 33 extend vertically downward from the two ends of the transverse plate 32 respectively. The support assembly 3 is in an inverted "U" shape. A snap-in groove 31 is provided at one end of the longitudinal plate 33 away from the transverse plate 32. The snap-in groove 31 matches the upper edge of the turbine casing 1. The distance between the two snap-in grooves 31 is the same as the diameter of the turbine casing 1. The support assembly 3 is positioned and installed with the edge of the top of the turbine casing 1 through the snap-in groove 31, ensuring that the support assembly 3 can be quickly placed on the edge of the top of the turbine casing 1, and the snap-in groove 31 ensures that the fixing assembly 4 located at the center of the support assembly 3 is located at the central axis of the turbine casing 1.

[0075] like Figure 4 As shown, the guide vane 11 is fixed on the turbine casing 1 according to the following steps:

[0076] S1, mounting a plurality of fixing plates 42 with different numbers of evenly distributed mounting holes 41 on the pivot shaft 43;

[0077] S2, install the pivot shaft 43 into the central hole of the support assembly 3, fix it with a locking member, and do not tighten the locking member temporarily, so that the fixed plate 42 can rotate around the axis;

[0078] S3, installing the support assembly 3 to the upper edge of the turbine casing 1;

[0079] S4, such as Figure 2 As shown, the guide vane 11 is installed on the turbine casing 1, and the front clamping groove of the guide vane 11 clamps the front stage outer cover and the casing mounting groove;

[0080] S5. According to the installation position of the guide vane 11, select the corresponding fixing plate 42 and rotate it so that the axis of a circumferential installation hole 41 is aligned with the middle section of the guide vane 11;

[0081] S6, tighten the locking piece so that the fixing plate 42 is pressed and cannot rotate;

[0082] S7, screw the extension rod 51 into the mounting hole 41 corresponding to the fixing plate 42;

[0083] S8, after hooking the hook assembly 5 with the soft rope onto the inner side of the guide vane 11, the soft rope is wound around the extension rod 51 to achieve the inner side suspension fixation of the guide vane 11;

[0084] S9, repeat S4, S7 and S8 to complete the installation of all guide vanes 11 of this stage;

[0085] S10, repeat S1-S9 until all guide vanes 11 of this stage are installed.

[0086] Although the specific embodiments of the present invention are described above, it should be understood by those skilled in the art that this is only for illustration and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A guide vane tightening tool for fixing the guide vane of an aircraft engine to a turbine casing, characterized in that: The guide vane tightening tool comprises: a support assembly for connecting to an upper edge of the turbine casing; A fixing assembly, the fixing assembly being connected to the supporting assembly; A hook assembly, one end of which is connected to the fixing assembly, and the other end of which is used to fix the guide vane from the end of the guide vane away from the turbine casing; A plurality of mounting holes are provided on the outer side surface of the fixing assembly along the circumference of the fixing assembly, and the hook assembly is inserted into the mounting holes; The fixing assembly includes a plurality of stacked fixing plates, and one end of the hook assembly is connected to the fixing plates; The fixing assembly further comprises a pivot shaft, and the pivot shaft is penetrated through the fixing plate and the supporting assembly.

2. The guide vane tightening tool according to claim 1, characterized in that: A plurality of the mounting holes are evenly distributed along the circumference of the fixing assembly.

3. The guide vane tightening tool according to claim 1, characterized in that: Multiple layers of mounting holes are arranged along the axial direction of the fixing assembly.

4. The guide vane tightening tool according to claim 1, characterized in that: The hook assembly comprises an extension rod, one end of which is connected to the fixing assembly, and the extension rod is arranged along the radial direction of the fixing assembly.

5. The guide vane tightening tool according to claim 4, characterized in that: The hook assembly further comprises a connecting member and a hook, wherein the hook is connected to an end of the extension rod away from the fixing assembly through the connecting member.

6. The guide vane tightening tool according to claim 5, characterized in that: The hook comprises a clamping portion and a connecting portion, the two sides of the connecting portion are respectively fixed with clamping portions, the cross section of the hook is in a side "U" shape, and the distance between the two clamping portions matches the width of the guide vane end.

7. The guide vane tightening tool according to claim 1, characterized in that: The support assembly includes a transverse plate and two longitudinal plates, the two longitudinal plates are fixedly connected to the two ends of the transverse plate, the support assembly is in an inverted "U" shape, and a snap-in groove is provided at one end of the longitudinal plate away from the transverse plate, and the snap-in groove matches the upper edge of the turbine casing.

Images