A borehole orienter load capacity testing device

Abstract

The present application belongs to the technical field of downhole tool testing, and particularly relates to a drilling orienter bearing capacity testing device. The drilling orienter bearing capacity testing device comprises a loading base, a measured tool fixedly arranged on the loading base, a bearing torque measuring cylinder fixedly arranged on the loading base, a torque sensor arranged on the bearing torque measuring cylinder, and a counter-torque loading assembly, axial two ends of the counter-torque loading assembly being respectively in torque transmission connection with the measured tool and the bearing torque measuring cylinder.

Description

Technical Field

[0001] This invention belongs to the field of downhole tool testing technology, specifically, it relates to a drilling directional tool load-bearing capacity testing device. Background Technology

[0002] Coiled tubing drilling is a technology that uses coiled tubing to complete drilling operations. It is widely used in offshore and onshore oil fields, and its operations include drilling, well workover, well completion, and well testing. Due to the low tensile, compressive, bending, and torsional stiffness of coiled tubing, it is difficult to perform directional operations on the surface. Therefore, a special directional tool needs to be designed downhole to achieve adjustment of the coiled tubing downhole tool face.

[0003] There are three operating modes for coiled tubing drilling directional systems: directional mode, sliding drilling mode, and combined drilling mode. The stress state of the directional system differs under each operating mode. To comprehensively evaluate the load-bearing capacity of the directional system and provide a basis for its structural design, load-bearing capacity tests need to be conducted indoors.

[0004] In actual drilling, the directional drilling tool is connected to the bottom of the directional drilling tool. When the directional drilling tool breaks the rock, it generates a counter-torque that acts on the output shaft of the directional drilling tool. Under the action of the counter-torque, the directional drilling tool has three working states: one is that it stops rotating and bears the counter-torque; the second is that it rotates in the direction of the counter-torque; and the third is that it rotates in the opposite direction of the counter-torque.

[0005] During the development of coiled tubing drilling directional systems, surface tests are required in conjunction with other downhole tools. However, fully replicating the downhole drilling assembly for testing requires complex equipment and a large testing area, resulting in high costs and a long development cycle. Summary of the Invention

[0006] In view of the technical problems mentioned above, the present invention aims to provide a drilling directional tester bearing capacity testing device, which can solve at least one of the above technical problems.

[0007] According to the present invention, a drilling directional tester bearing capacity testing device is provided, comprising:

[0008] The loading base is on which the test tool is fixedly mounted.

[0009] A load-bearing torsion measuring cylinder is fixedly mounted on the loading base, and a torque sensor is mounted on the load-bearing torsion measuring cylinder;

[0010] And an anti-torque loading component, one end of which is coaxially fixedly connected to the output end of the workpiece being tested, and the other end is connected to the torque-transmitting cylinder through a torque adjustment component.

[0011] In one specific embodiment, the anti-torque loading assembly includes a loading motor, the housing of which is coaxially fixedly connected to the tool under test, and the output shaft of which is coaxially connected to the load-bearing torque measuring cylinder for torque transmission.

[0012] In one specific embodiment, the anti-torque loading assembly further includes an outer cylinder, with a first end and a second end at its two axial ends. The first end is coaxially and fixedly connected to the workpiece under test via an adapter. The loading motor is coaxially and fixedly disposed inside the outer cylinder. The output shaft of the loading motor extends from the second end through a transmission mechanism and is connected to the load-bearing torsion measuring cylinder for torque transmission.

[0013] In one specific embodiment, a fixed base is fixedly installed inside the outer cylinder by an anti-rotation pin. The loading motor is located at the end of the fixed base near the tool being tested and is coaxially fixedly connected to the fixed base. The transmission mechanism is located at the end of the fixed base near the load-bearing torsion measuring cylinder.

[0014] In one specific embodiment, the transmission mechanism includes a reducer and a torque multiplier. The input shaft of the reducer is torque-transmittingly connected to the output shaft of the loading motor, the output shaft of the reducer is torque-transmittingly connected to the input shaft of the torque multiplier, and the output shaft of the torque multiplier is torque-transmittingly connected to the load-bearing torque measuring cylinder.

[0015] In one specific embodiment, the input shaft of the reducer is connected to the output shaft of the loading motor via a first coupling for torque transmission.

[0016] In one specific embodiment, the output shaft of the reducer is connected to the input shaft of the torque multiplier via a second coupling.

[0017] In one specific embodiment, the output shaft of the torque multiplier is connected to the torque-carrying torque measuring cylinder via the torque adjustment assembly.

[0018] In one specific embodiment, the torque adjustment assembly includes a torque transmission cylinder, one end of which is connected to the torque multiplier via a multi-faceted structure, and the other end of which is coaxially sleeved on the load-bearing torque measuring cylinder. A loading screw for transmitting and adjusting the torque is provided between the torque transmission cylinder and the load-bearing torque measuring cylinder.

[0019] In one specific embodiment, the first fixing component includes a first fixing plate, a first fixing stud, and a first fixing nut. The workpiece to be tested is located between the first fixing plate and the loading base. The first fixing stud passes through the first fixing plate and the loading base and is fastened by the first fixing nut.

[0020] Compared with the prior art, the advantages of this application are as follows.

[0021] Downhole power drilling tools generally consist of a directional tool, a screw, and a drill bit connected sequentially from top to bottom. This invention simulates the counter-torque effect of a downhole power drilling tool using a counter-torque loading assembly, thereby testing the actual load-bearing capacity of the tool under test (directional tool). The load-bearing torque measuring cylinder simulates the resistance of the formation to the drilling tool, while the counter-torque loading assembly simulates the forces exerted on the drilling tool by the screw and other components during drilling operations. The outer diameter of the counter-torque loading assembly is approximately equal to the diameter of the directional tool. After the directional tool is installed in the drilling directional tool load-bearing capacity testing device, its overall structure is similar to the wellbore, allowing it to be used as a whole to simulate directional operations during actual drilling. This simulation does not require drilling fluid to drive the power drilling tool in actual drilling, providing a user-friendly environment (liquid-free environment, pressure-free environment) for testing various performance characteristics of the directional tool. Furthermore, the counter-torque loading assembly of this invention is inexpensive, saving on testing costs and providing experimental support for optimizing the directional tool's structural design. Attached Figure Description

[0022] The invention will now be described with reference to the accompanying drawings.

[0023] Figure 1 A schematic diagram of an embodiment of the drilling directional tester bearing capacity testing device according to the present invention is shown;

[0024] Figure 2 A schematic diagram of a drilling directional test apparatus according to the present invention is shown.

[0025] The reference numerals in the figure are as follows:

[0026] 1. The instrument under test; 101. Output spindle;

[0027] 2. First fixing component; 201. First fixing stud; 202. First fixing nut; 203. First fixing pressure plate;

[0028] 3. Loading base; 4. Adapter;

[0029] 5. Anti-torque loading assembly; 501. Outer cylinder; 5011. First end; 5012. Second end; 502. Loading motor; 503. Anti-rotation pin; 504. Fixing seat; 505. First coupling; 506. Reducer; 507. Second coupling; 508. Torque multiplier; 509. Transmission mechanism;

[0030] 6. Torque transmission cylinder;

[0031] 7. Torque measuring cylinder; 701. Connecting part; 702. Detection part; 703. Fixing part;

[0032] 8. Torque sensor;

[0033] 9. Second fixing component; 901. Second fixing stud; 902. Second fixing nut; 903. Second fixing pressure plate;

[0034] 10. Loading screw; 100. Drilling directional bearing capacity testing device.

[0035] In this application, all drawings are schematic and are used only to illustrate the principles of the invention, and are not drawn to scale. Detailed Implementation

[0036] The invention will now be described with reference to the accompanying drawings.

[0037] It should be noted that the directional terms or qualifiers such as "up" and "down" used in this application are all specific to the referenced [reference]. Figure 1 Specifically, "above" refers to... Figure 1 The direction indicated by the arrow X in the image, "down" refers to... Figure 1 The arrow X points in the opposite direction. These are not used to define the absolute position of the components involved, but can vary depending on the specific circumstances.

[0038] Figure 1 The structure of the drilling directional tester load-bearing capacity testing device 100 according to the present invention is shown. Figure 1 As shown, the drilling directional tester bearing capacity testing device 100 mainly includes a loading base 3, an anti-torque loading component 5, and a bearing torsion measuring cylinder 7.

[0039] In this embodiment, the specific structure of the loading base 3 is not limited, as long as the length of the loading base 3 can at least accommodate the tested tool 1, the anti-torque loading component 5, and the load-bearing torsion measuring cylinder 7. Figure 1 As shown, the test tool 1 is fixedly mounted on the loading base 3 via the first fixing component 2. The load-bearing torque measuring cylinder 7 is fixedly mounted on the loading base 3 via the second fixing component 9, and a torque sensor 8 for measuring torque is installed on the load-bearing torque measuring cylinder 7. The two ends of the anti-torque loading component 5 are respectively connected to the test workpiece 1 and the load-bearing torque measuring cylinder 7 for torque transmission. One end of the anti-torque loading component 5 is coaxially fixedly connected to the output end of the test workpiece 1, and the other end is connected to the load-bearing torque measuring cylinder 7 for torque transmission through the torque adjustment component, thereby applying a torque in the opposite direction to the test tool 1 and the load-bearing torque measuring cylinder 7. The maximum torque between the anti-torque loading component 5 and the load-bearing torque measuring cylinder 7 can be adjusted by the torque adjustment component.

[0040] In one specific embodiment, the tool under test 1 is the orienteering device to be tested. It is easy to understand that the workpiece under test 1 can also be any other downhole tool whose torque carrying capacity needs to be measured.

[0041] like Figure 1 As shown, the test tool 1 is fixedly mounted on the upper part of the loading base 3 by the first fixing component 2. The load-bearing torsion measuring cylinder 7 is fixedly mounted on the lower part of the loading base 3 by the second fixing component 9. The anti-torque loading component 5 is coaxially disposed between the test tool 1 and the load-bearing torsion measuring cylinder 7. The torque sensor 8 is disposed on the load-bearing torsion measuring cylinder 7 and is located above the second fixing component 9.

[0042] When testing the torque load of the test tool 1, the anti-torque loading component 5 is activated, thereby applying a torque in the opposite direction to the test tool 1 and the load-bearing torque measuring cylinder 7. The test workpiece 1 and the load-bearing torque measuring cylinder 7 are subjected to the same torque. The torque carried by the test workpiece 1 at this time is known by the torque sensor 8 on the load-bearing torque measuring cylinder 7, thereby enabling the measurement of the maximum torque that the test tool 1 can carry.

[0043] Furthermore, the tested tool 1 and the anti-torque loading component 5 simulate the drill string's orienter and screw, while the load-bearing torsion measuring cylinder 7 simulates the resistance of the formation to the drill string. During the test, firstly, based on the required simulated formation environment, the maximum torque between the load-bearing torsion measuring cylinder 7 and the anti-torque loading component 5 is set using the torque adjustment component, making it the same as the resistance of the formation to the drill string. Then, the tested tool 1 is started, causing its output end to rotate. By reading the value from the torque sensor 8, the torque borne by the tested tool 1 at this time can be determined. Additionally, the anti-torque loading component 5 can also be started to simulate the rotation of the screw during drilling; by reading the value from the torque sensor 8, the torque borne by the tested tool 1 at this time can be determined.

[0044] In this embodiment, the first fixing component 2 includes a first fixing plate 203, a first fixing stud 201, and a first fixing nut 202. Holes for the first fixing stud 201 are provided on the loading base 3 and the first fixing plate 203. The workpiece 1 to be measured is located between the first fixing plate 203 and the loading base 3. The first fixing stud 201 passes through the holes in the first fixing plate 203 and the loading base 3, and is tightened by the first fixing nut 202 to increase the friction between the first fixing plate 203 and the workpiece 1 to be measured, thereby fixing the workpiece 1 to be measured on the loading base 3 and bearing torque.

[0045] In a preferred embodiment, the first fixing plate 203 is adapted to the shape of the outer wall of the test tool 1. When the first fixing plate 203 fixes the test tool 1 on the loading base 3, the first fixing plate 203 fits against the outer wall of the test tool 1, so that the test tool 1 can be more firmly fixed on the loading base 3.

[0046] In this embodiment, the tool under test 1 is fixedly mounted on the loading base 3 by multiple first fixing components 2, thereby enabling the tool under test 1 to be more firmly fixed on the loading base 3. Figure 1 As shown, the three first fixing components 2 are distributed sequentially along the axial direction at the upper, middle and lower parts of the tool under test 1.

[0047] In this embodiment, the second fixing component 9 includes a second fixing plate 903, a second fixing stud 901, and a second fixing nut 902. Holes for the second fixing stud 901 are provided on the loading base 3 and the second fixing plate 903. The load-bearing torsion measuring cylinder 7 is located between the second fixing plate 903 and the loading base 3. The second fixing stud 901 passes through the holes in the second fixing plate 903 and the loading base 3, and is tightened by the second fixing nut 902 to increase the friction between the second fixing plate 903 and the load-bearing torsion measuring cylinder 7. This allows the second fixing plate 903 to fix the load-bearing torsion measuring cylinder 7 onto the loading base 3, enabling it to withstand torque.

[0048] In a preferred embodiment, the second fixing plate 903 is adapted to the shape of the outer wall of the load-bearing torsion measuring cylinder 7. When the second fixing plate 903 fixes the load-bearing torsion measuring cylinder 7 on the loading base 3, the second fixing plate 903 fits against the outer wall of the load-bearing torsion measuring cylinder 7, so that the test tool 1 can be more firmly fixed on the loading base 3.

[0049] In this embodiment, the load-bearing torsion measuring cylinder 7 is fixedly mounted on the loading base 3 by multiple second fixing components 9, thereby enabling the load-bearing torsion measuring cylinder 7 to be more firmly fixed on the loading base 3. Figure 1 As shown, the two second fixing components 9 are distributed sequentially along the axial direction, and the load-bearing torsion measuring cylinder 7 is fixedly mounted on the loading base 3.

[0050] According to the present invention, in this embodiment, the lower part of the workpiece 1 under test is an output shaft 101. The specific structure of the workpiece 1 under test is well known to those skilled in the art and will not be described in detail here. The anti-torque loading assembly 5 includes a loading motor 502. The housing of the loading motor 502 is coaxially and fixedly connected to the output shaft 101 of the tool under test. The output shaft of the loading motor 502 is coaxially and torque-transmittingly connected to the torque-bearing cylinder 7. After the loading motor 502 is started, it can provide torque in the opposite direction to the torque-bearing cylinder 7 and the tool under test.

[0051] In one specific embodiment, the anti-torque loading assembly 5 further includes an outer cylinder 501, with its upper axial end being a first end 5011 and its lower end being a second end 5012. The first end 5011 of the outer cylinder 501 is coaxially and fixedly connected to the output shaft 101 of the tool under test 1 via an adapter 4. Specifically, the first end 5011 is fixedly connected to the lower end of the adapter 4 via a threaded connection, and the upper end of the adapter 4 is fixedly connected to the output shaft 101 of the tool under test 1 via a threaded connection. The loading motor 502 is coaxially and fixedly disposed inside the outer cylinder 501. The output shaft of the loading motor 502 extends from the second end 5012 via a transmission mechanism 509 and is connected to the torque-bearing torque-measuring cylinder 7 for torque transmission. In this configuration, the housing of the loading motor 502 is connected to the output shaft 101 of the tool under test 1 via the outer cylinder 501, thereby enabling torque transmission between the housing of the loading motor 502 and the tool under test 1. The output shaft of the loading motor 502 is connected to the load-bearing torque measuring cylinder 7 through the transmission mechanism 509, thereby enabling the transmission of torque between the output shaft of the loading motor 502 and the load-bearing torque measuring cylinder 7.

[0052] In one specific embodiment, a fixing seat 504 is fixedly installed inside the outer cylinder 501 by an anti-rotation pin 503. The anti-rotation pin 503 is arranged radially, with one end inside the outer cylinder 501 and the other end inside the fixing seat 504, thereby fixing the fixing seat 504 inside the outer cylinder 501. The loading motor 502 is located at the end of the fixing seat 504 near the measured tool 1, that is, the loading motor 502 is located above the fixing seat 504, and the housing of the loading motor 502 is coaxially fixedly connected to the fixing seat 504 by fastening bolts. The transmission mechanism 509 is located at the end of the fixing seat 504 near the load-bearing torsion measuring cylinder 7, that is, the transmission mechanism 509 is located below the fixing seat 504. The fixing seat 504 is constructed as a ring structure, and the output shaft of the loading motor 502 passes through the fixing seat 504 and is connected to the transmission mechanism 509.

[0053] In one specific embodiment, the transmission mechanism 509 includes a reducer 506 and a torque multiplier 508. The housing of the reducer 506 is coaxially fixed to the mounting base 504 by fastening bolts, and the input shaft of the reducer 506 is torque-transmittingly connected to the output shaft of the loading motor 502. In this embodiment, the input shaft of the reducer 506 is torque-transmittingly connected to the output shaft of the loading motor 502 via a first coupling 505.

[0054] The torque multiplier 508 is located below the reducer 506. The housing of the torque multiplier 508 is fixedly connected to the outer cylinder 501 by fastening screws. The output shaft of the reducer 506 is connected to the input shaft of the torque multiplier 508 for torque transmission. In this embodiment, the output shaft of the reducer 506 is connected to the input shaft of the torque multiplier 508 for torque transmission through the second coupling 507.

[0055] The output shaft of the torque multiplier 508 is connected to the load-bearing torque measuring cylinder 7 for torque transmission. In this embodiment, the output shaft of the torque multiplier 508 is connected to the load-bearing torque measuring cylinder 7 for torque transmission via a torque adjustment assembly.

[0056] In one specific embodiment, the torque adjustment assembly includes a torque transmission cylinder 6. The upper end of the torque transmission cylinder 6 is connected to the torque multiplier 508 via a polygonal structure. For example, the inner wall of the upper end of the torque transmission cylinder 6 is constructed as a polygon, and the output shaft of the torque multiplier 508 is constructed as a polygon that adapts to the inner wall of the upper end of the torque transmission cylinder 6. The output shaft of the torque multiplier 508 is inserted into the upper end of the torque transmission cylinder 6, thereby realizing the torque transmission connection.

[0057] The lower end of the torque transmission cylinder 6 is coaxially sleeved on the load-bearing torque measuring cylinder 7. The torque transmission cylinder 6 can be sleeved inside or outside the load-bearing torque measuring cylinder 7. A loading screw 10 for transmitting torque is provided between the torque transmission cylinder 6 and the load-bearing torque measuring cylinder 7. In this embodiment, the torque transmission cylinder 6 is sleeved inside the load-bearing torque measuring cylinder 7. A threaded hole is opened on the side wall of the load-bearing torque measuring cylinder 7, and the loading screw 10 is installed in the threaded hole. The loading screw 10 is screwed onto the load-bearing torque measuring cylinder 7, and its end face contacts the torque transmission cylinder 6. The load torque is generated by the tightening force of the loading screw 10 against the outer wall of the torque transmission cylinder 6. The maximum torque between the load-bearing torque measuring cylinder 7 and the torque transmission cylinder 6 is adjusted by adjusting the tightness of the loading screw 10.

[0058] The torque measuring cylinder 7 includes a connecting part 701, a detection part 702, and a fixing part 703 arranged coaxially from top to bottom. The wall thickness of the detection part 702 is less than the wall thickness of the connecting part 701 and the fixing part 703. The torque sensor 8 is mounted on the detection part 702 to facilitate torque measurement. The connecting part 701 is used to connect to the torque transmission cylinder 6. The fixing part 703 is fixedly connected to the loading base 3 via a second fixing assembly 9.

[0059] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0060] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0061] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0062] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A drilling directional instrument load-bearing capacity testing device, characterized in that, include: Loading base (3), the test tool (1) is fixedly mounted on the loading base (3); A load-bearing torsion measuring cylinder (7) is fixedly mounted on the loading base (3), and a torque sensor (8) is mounted on the load-bearing torsion measuring cylinder (7); and The anti-torque loading component (5) has one end coaxially fixedly connected to the output end of the workpiece (1) being tested, and the other end is connected to the torque-carrying torque measuring cylinder (7) via a torque adjustment component.

2. The drilling directional tester bearing capacity testing device according to claim 1, characterized in that, The anti-torque loading component (5) includes a loading motor (502), the housing of which is coaxially fixedly connected to the test tool (1), and the output shaft of which is coaxially connected to the load-bearing torque measuring cylinder (7) for torque transmission.

3. The drilling directional tester bearing capacity testing device according to claim 2, characterized in that, The anti-torque loading assembly (5) also includes an outer cylinder (501), with the two axial ends of the outer cylinder (501) being a first end (5011) and a second end (5012), respectively. The first end (5011) is coaxially fixedly connected to the workpiece (1) under test via an adapter (4). The loading motor (502) is coaxially fixedly installed inside the outer cylinder (501), and the output shaft of the loading motor (502) extends from the second end (5012) through a transmission mechanism (509) and is connected to the load-bearing torsion measuring cylinder (7) for torsion transmission.

4. The drilling directional tester bearing capacity testing device according to claim 3, characterized in that, A fixed base (504) is fixedly installed inside the outer cylinder (501) by an anti-rotation pin (503). The loading motor (502) is located at one end of the fixed base (504) near the test tool (1) and is coaxially fixedly connected to the fixed base (504). The transmission mechanism (509) is located at one end of the fixed base (504) near the load-bearing torsion measuring cylinder (7).

5. The drilling directional tester bearing capacity testing device according to claim 4, characterized in that, The transmission mechanism (509) includes a reducer (506) and a torque multiplier (508). The input shaft of the reducer (506) is connected to the output shaft of the loading motor (502) for torque transmission. The output shaft of the reducer (506) is connected to the input shaft of the torque multiplier (508) for torque transmission. The output shaft of the torque multiplier (508) is connected to the load-bearing torque measuring cylinder (7) for torque transmission.

6. The drilling directional tester bearing capacity testing device according to claim 5, characterized in that, The input shaft of the reducer (506) is connected to the output shaft of the loading motor (502) via a first coupling (505) for torque transmission.

7. The drilling directional tester bearing capacity testing device according to claim 5, characterized in that, The output shaft of the reducer (506) is connected to the input shaft of the torque multiplier (508) via a second coupling (507).

8. The drilling directional tester bearing capacity testing device according to claim 5, characterized in that, The output shaft of the torque multiplier (508) is connected to the load-bearing torque measuring cylinder (7) via the torque adjustment component.

9. The drilling directional tester bearing capacity testing device according to claim 8, characterized in that, The torque adjustment assembly includes a torque transmission cylinder (6), one end of which is connected to the torque multiplier (508) via a multi-faceted structure, and the other end of which is coaxially sleeved on the load-bearing torque measuring cylinder (7). A loading screw (10) for adjusting the torque is provided between the torque transmission cylinder (6) and the load-bearing torque measuring cylinder (7).

10. The drilling directional tester bearing capacity testing device according to any one of claims 1 to 9, characterized in that, The first fixing component (2) includes a first fixing plate (203), a first fixing stud (201) and a first fixing nut (202). The workpiece (1) to be tested is located between the first fixing plate (203) and the loading base (3). The first fixing stud (201) passes through the first fixing plate (203) and the loading base (3) and is fastened by the first fixing nut (202).

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