Disassembling and assembling tool for centralizer of logging-while-drilling instrument

Abstract

The utility model discloses a dismounting and mounting tool for a centralizer of a logging-while-drilling instrument, and solves the technical problem that the centralizer is difficult to dismount and mount quickly. The dismounting and mounting tool comprises a pushing sleeve which is used for being arranged on a logging instrument in a sleeving mode and abutting against a centralizer; the connecting rod is coaxially arranged in the pushing sleeve and used for being connected with a logging instrument; the hydraulic cylinder is arranged on the connecting rod; the piston end of the hydraulic cylinder can push the pushing sleeve to move in the axial direction of the connecting rod so that the pushing sleeve can push the centralizer to move in the axial direction of the logging instrument, and therefore the centralizer can be disassembled and assembled. According to the utility model, the centering device can be quickly disassembled and assembled, so that the working efficiency is improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of oil well logging instruments, and in particular relates to a disassembly and assembly tool for a centralizer of a logging while drilling instrument. Background Art

[0002] The development of marine oil and gas resources is a hot topic and focus of the current development of the world's marine economy. Marine oil and gas resources are not only abundant, but modern science and technology have also enabled them to be developed with great capabilities. The marine oil and gas industry has developed into an emerging and high-value-added leading industry in the marine economy.

[0003] Logging while drilling (LWD) instruments can effectively collect a variety of physical information in the underground environment, such as force, heat, and nuclear information, which is of great significance to oil exploration and development. The centralizer is an important component of the LWD instrument. Its function is to ensure that the instrument is centered in the wellbore. The centralizer is usually mounted on the logging instrument and has an interference fit with the logging instrument.

[0004] The stabilizer of the 675 density logging while drilling tool, a related art tool, is a split-body design. The stabilizer is secured to the drill collar using an interference fit. Because the PEEK source window is bonded to the stabilizer, it cannot be assembled using a shrink-fit method. Currently, the lack of a compatible disassembly and assembly tool hinders disassembly and assembly of the stabilizer, hindering operational efficiency and requiring improvement. Utility Model Content

[0005] In order to solve all or part of the above problems, the purpose of the present invention is to provide a tool for disassembling and assembling a centralizer of a logging while drilling instrument, which can realize rapid disassembly and assembly of the centralizer, thereby improving operation efficiency.

[0006] The utility model provides a disassembly and assembly tool for a centralizer of a logging while drilling instrument, comprising:

[0007] The push sleeve is used to be placed on the logging instrument and abut against the centralizer;

[0008] A connecting rod is coaxially arranged inside the thrust sleeve and is used to connect with the logging instrument;

[0009] a hydraulic cylinder, disposed on the connecting rod;

[0010] The piston end of the hydraulic cylinder can push the push sleeve to move along the axial direction of the connecting rod, so that the push sleeve can push the centralizer to move along the axial direction of the logging instrument, thereby realizing the disassembly and assembly of the centralizer.

[0011] Optionally, the push sleeve includes a propulsion sleeve, a support sleeve and a compression sleeve arranged in sequence, the end of the propulsion sleeve away from the support sleeve is used to abut against the stabilizer, and the end of the compression sleeve away from the support sleeve is used to abut against the piston end of the hydraulic cylinder.

[0012] Optionally, the propulsion sleeve and the compression sleeve are respectively provided with positioning ring grooves at one end facing the support sleeve, so that the corresponding ends of the support sleeve can be tightly clamped therein.

[0013] Optionally, the support sleeve includes an inner sleeve and an outer sleeve, the inner sleeve is coaxially arranged on the inner side of the outer sleeve and slidingly cooperates with the outer sleeve, a limiting member is arranged between the inner sleeve and the outer sleeve, and the limiting member is used to limit the relative sliding of the inner sleeve and the outer sleeve.

[0014] Optionally, the limiting member includes:

[0015] A guide groove is provided on the outer side wall of the inner sleeve and is arranged along the axial direction of the inner sleeve;

[0016] A limit block is provided on the inner side wall of the outer sleeve and is slidably engaged with the guide groove;

[0017] There are multiple limit grooves, which are respectively arranged on the outer side wall of the inner sleeve. The multiple limit grooves are arranged in sequence along the axial direction of the inner sleeve. The multiple limit grooves are respectively connected to the guide grooves, and after the inner sleeve and the outer sleeve rotate relative to each other, the limit block can be tightly stuck in any of the limit grooves.

[0018] Optionally, an indicator groove connected to the guide groove is provided on a side of the inner sleeve close to the compression sleeve, and the indicator groove and the limiting groove are distributed on different sides of the guide groove.

[0019] Optionally, the limiting block can be tightly snapped into the indicating groove.

[0020] Optionally, the connecting rod includes a connecting screw and a connecting head, the connecting head is arranged at the end of the connecting screw and is used to be threadedly connected to the corresponding end of the logging instrument, the connecting screw passes through the hydraulic cylinder and slides with the hydraulic cylinder, a locking member is provided between the connecting screw and the hydraulic cylinder, and the locking member is used to limit the relative sliding of the hydraulic cylinder and the connecting screw.

[0021] Optionally, the locking element includes:

[0022] There are two locking pieces, each in a semicircular shape. The two locking pieces are spliced ​​together to form a locking ring that is sleeved on the connecting screw, and the locking ring abuts against the end of the hydraulic cylinder away from the push sleeve;

[0023] There are two half-thread grooves, each provided on the inner side wall of the corresponding locking piece. The two half-thread grooves are joined to form a full-thread groove that matches the external thread of the connecting screw, so as to achieve position limiting between the locking piece and the connecting screw.

[0024] A locking sleeve tightly sleeved on the locking ring formed by splicing the two locking pieces;

[0025] There are two limit bars, which are respectively arranged at one end of the corresponding locking piece close to the hydraulic cylinder, and one end of the locking sleeve facing the hydraulic cylinder is respectively in contact with the two limit bars.

[0026] Optionally, the inner side wall of the locking sleeve and the outer side walls of the two locking pieces are respectively provided with mutually matching limiting inclined surfaces.

[0027] As can be seen from the above technical solution, the utility model provides a tool for disassembling and assembling a centralizer of a logging while drilling instrument, which has the following advantages:

[0028] This disassembly and assembly tool can be used in conjunction with logging instruments to quickly disassemble and assemble the centralizer, thereby improving operational efficiency. Furthermore, because the push sleeve is a telescopic structure with adjustable length, and the relative position of the hydraulic cylinder and connecting screw can be fine-tuned, the disassembly and assembly tool can utilize a hydraulic cylinder with a shorter extension stroke and disassemble and assemble the centralizer through multiple pushes. This allows the disassembly and assembly tool to utilize a smaller hydraulic cylinder, reducing the tool's cost, overall size, and improving its compactness.

[0029] Other features and advantages of the present invention will be described in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0031] Figure 1 Schematic diagram of the user state of the tool for disassembling and assembling the centralizer of the logging while drilling instrument in the embodiment of the present utility model;

[0032] Figure 2 This is an exploded view of a disassembly and assembly tool for a centralizer of a logging while drilling instrument in an embodiment of the present utility model;

[0033] Figure 3 This is an exploded view of the push sleeve in the embodiment of the present utility model;

[0034] Figure 4This is a schematic structural diagram of the support sleeve in an embodiment of the present utility model;

[0035] Figure 5 This is an exploded view of the locking member in the embodiment of the present utility model;

[0036] Figure 6 It is a cross-sectional view of the locking member in the embodiment of the present utility model.

[0037] Description of reference numerals:

[0038] 1. Push sleeve; 11. Propulsion sleeve; 12. Support sleeve; 121. Inner sleeve; 122. Outer sleeve; 13. Compression sleeve; 14. Positioning ring groove; 2. Connecting rod; 21. Connecting screw; 22. Connecting head; 3. Hydraulic cylinder; 4. Limiting piece; 41. Guide groove; 42. Limiting block; 43. Limiting groove; 5. Indicating groove; 6. Locking piece; 61. Locking plate; 62. Locking ring; 63. Half thread groove; 64. Full thread groove; 65. Locking sleeve; 66. Limiting strip; 67. Limiting inclined plane. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention more clear, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other in any way.

[0040] like Figures 1-6 The present invention illustrates an embodiment of the present invention, which discloses a tool for disassembling and assembling a centralizer for a logging-while-drilling instrument. The tool comprises a thrust sleeve 1, a connecting rod 2, and a hydraulic cylinder 3. The thrust sleeve 1 can be mounted on the logging instrument, with its end abutting the centralizer. The connecting rod 2 is coaxially disposed within the thrust sleeve 1, movably connected to the thrust sleeve 1, and configured to connect to the logging instrument. The hydraulic cylinder 3 is disposed on the connecting rod 2, and the piston end of the hydraulic cylinder 3 can propel the thrust sleeve 1 axially along the connecting rod 2, thereby enabling the thrust sleeve 1 to propel the centralizer axially along the logging instrument, thereby enabling assembly and disassembly of the centralizer.

[0041] In one embodiment, Figure 1 、 Figure 2 、 Figure 3As shown, the thrust sleeve 1 includes a thrust sleeve 11, a support sleeve 12, and a compression sleeve 13, which are arranged in sequence. The thrust sleeve 11, support sleeve 12, and compression sleeve 13 can be sequentially sleeved on the well logging instrument. The end of the thrust sleeve 11 away from the support sleeve 12 is used to abut the centralizer, and the end of the compression sleeve 13 away from the support sleeve 12 is used to abut the piston end of the hydraulic cylinder 3. At the same time, the ends of the thrust sleeve 11 and the compression sleeve 13 facing the support sleeve 12 are respectively provided with positioning ring grooves 14, which allow the corresponding ends of the support sleeve 12 to be tightly engaged, thereby improving the limiting effect between the thrust sleeve 11, support sleeve 12, and compression sleeve 13.

[0042] In one embodiment, Figure 3 、 Figure 4 As shown, the support sleeve 12 includes an inner sleeve 121 and an outer sleeve 122. The inner sleeve 121 is coaxially arranged on the inner side of the outer sleeve 122 and slides with the outer sleeve 122. At the same time, a limiting member 4 is arranged between the inner sleeve 121 and the outer sleeve 122, and the limiting member 4 is used to limit the relative sliding of the inner sleeve 121 and the outer sleeve 122 so that the length of the support sleeve 12 can be adjusted.

[0043] In one embodiment, Figure 3 、 Figure 4 As shown, the limiting member 4 includes a guide groove 41 provided on the outer wall of the inner sleeve 121, and the guide groove 41 is arranged along the axial direction of the inner sleeve 121. A limiting block 42 is integrally formed on the inner wall of the outer sleeve 122, and the limiting block 42 slides in cooperation with the guide groove 41. A plurality of limiting grooves 43 are provided on the outer wall of the inner sleeve 121, and the plurality of limiting grooves 43 are arranged in sequence along the axial direction of the inner sleeve 121, and the plurality of limiting grooves 43 are respectively connected to the guide groove 41. When the inner sleeve 121 and the outer sleeve 122 rotate relative to each other, the limiting block 42 can be tightly snapped into any limiting groove 43, thereby achieving the limiting of the inner sleeve 121 and the outer sleeve 122.

[0044] Because the overall length of the support sleeve 12 is adjustable, the disassembly and assembly tool can use a hydraulic cylinder 3 with a shorter extension stroke and achieve disassembly and assembly of the centralizer through multiple thrusts. Specifically, when the piston end of the hydraulic cylinder 3 is extended to the limit, the piston end of the hydraulic cylinder 3 is controlled to return to its original position. At this time, the overall length of the support sleeve 12 is adjusted, and the clamping sleeve 13 is again brought into contact with the piston end of the hydraulic cylinder 3. Subsequently, the piston end of the hydraulic cylinder 3 can once again push the thrust sleeve 1 forward. This design allows the disassembly and assembly tool to use a smaller hydraulic cylinder 3, reducing the cost of the disassembly and assembly tool, reducing the overall size of the disassembly and assembly tool, and improving the design compactness.

[0045] In one embodiment, Figure 3 、 Figure 4As shown, the inner sleeve 121 is provided with an indicator groove 5 connected to the guide groove 41 on one side close to the compression sleeve 13, and the indicator groove 5 and the limit groove 43 are distributed on different sides of the guide groove 41, that is, multiple limit grooves 43 are located on one side of the guide groove 41, and the indicator groove 5 is located on the other side of the guide groove 41. When the staff adjusts the length of the support sleeve 12, they can confirm the rotation direction of the inner sleeve 121 and the outer sleeve 122 by observing the position of the indicator groove 5, so as to achieve the rapid locking of the inner sleeve 121 and the outer sleeve 122, thereby improving the convenience of operation. In addition, the limit block 42 can be tightly inserted into the indicator groove 5 to achieve the limit of the inner sleeve 121 and the outer sleeve 122, so as to increase the adjustment range of the support sleeve 12.

[0046] In one embodiment, Figure 1 、 Figure 2 As shown, the connecting rod 2 includes a connecting screw 21 and a connector 22. The connector 22 is connected to the end of the connecting screw 21 and is used to threadably connect to the corresponding end of the logging instrument. The connecting screw 21 passes through the hydraulic cylinder 3 and slides with the hydraulic cylinder 3. At the same time, a locking member 6 is provided between the connecting screw 21 and the hydraulic cylinder 3 to limit the relative sliding of the hydraulic cylinder 3 and the connecting screw 21.

[0047] In this embodiment, the connector 22 is threadedly connected to the end of the connecting screw 21 so that the model of the connector 22 can be replaced to adapt to well logging instruments of different specifications. Of course, in other embodiments, the connector 22 can also be fixedly connected to the connecting screw 21.

[0048] In one embodiment, Figure 5 、 Figure 6 As shown, the locking member 6 includes two semicircular locking pieces 61, the openings of which are disposed opposite each other. When joined, the two locking pieces 61 form a locking ring 62 that can be sleeved onto the connecting screw 21, and the locking ring 62 abuts against the end of the hydraulic cylinder 3 away from the thrust sleeve 1. The inner sidewalls of the two locking pieces 61 are respectively provided with a semi-threaded groove 63. When the two locking pieces 61 are joined to form the locking ring 62, the two semi-threaded grooves 63 form a full threaded groove 64 that matches the external thread of the connecting screw 21, thereby limiting the position between the locking piece 61 and the connecting screw 21.

[0049] In one embodiment, Figure 5 、 Figure 6As shown, the locking member 6 also includes an annular locking sleeve 65, which fits snugly over the locking ring 62 formed by joining the two locking pieces 61. Semicircular retaining bars 66 are integrally formed on the ends of the two locking pieces 61 proximal to the hydraulic cylinder 3, and the end of the locking sleeve 65 facing the hydraulic cylinder 3 abuts against the two retaining bars 66. Furthermore, matching retaining bevels 67 are integrally formed on the inner sidewall of the locking sleeve 65 and the outer sidewalls of the two locking pieces 61 to ensure the retaining effect between the locking pieces 61 and the locking sleeve 65.

[0050] The use process of the logging while drilling instrument centralizer disassembly and assembly tool in this embodiment is as follows:

[0051] Put the centralizer on the logging instrument and align the positioning key on the logging instrument with the positioning groove on the inner wall of the centralizer. Then, thread the corresponding end of the logging instrument to the connector 22, and then put the propulsion sleeve 11, support sleeve 12 and clamping sleeve 13 on the logging instrument in sequence, and make the end of the propulsion sleeve 11 away from the support sleeve 12 to abut against the centralizer. Next, put the hydraulic cylinder 3 on the connecting screw 21, and make the piston end of the hydraulic cylinder 3 abut against the clamping sleeve 13, and then respectively snap the two locking plates 61 onto the connecting screw 21, and ensure that the two locking plates 61 abut against the tail of the hydraulic cylinder 3. Then, put the locking sleeve 65 on the two locking plates 61, and make the locking sleeve 65 abut against the two limit bars 66 respectively.

[0052] Next, the piston end of the hydraulic cylinder 3 extends, causing the compression sleeve 13, support sleeve 12, and propulsion sleeve 11 to move synchronously. At this time, the propulsion sleeve 11 pushes the centralizer to move axially along the well logging instrument. When the piston end of the hydraulic cylinder 3 extends to its limit position, the piston end of the hydraulic cylinder 3 is controlled to return to its original position. At this time, the inner sleeve 121 or the outer sleeve 122 is rotated to allow the limit block 42 to enter the guide groove 41. The inner sleeve 121 is then pulled toward the hydraulic cylinder 3 until the limit block 42 aligns with the first-stage limit groove 43. The inner sleeve 121 or the outer sleeve 122 is then rotated further to allow the limit block 42 to form a snap fit with the first-stage limit groove 43.

[0053] When the length of the support sleeve 12 is adjusted, if the compression sleeve 13 is in contact with the piston end of the hydraulic cylinder 3, the centralizer can be pushed again. If there is a large gap between the compression sleeve 13 and the piston end of the hydraulic cylinder 3, or if the limit block 42 has not reached the position of the first-stage limit groove 43, the compression sleeve 13 and the two locking plates 61 can be removed. Then, the position of the hydraulic cylinder 3 can be readjusted to ensure that the piston end of the hydraulic cylinder 3 is in contact with the compression sleeve 13, and the centralizer can be pushed again. Repeat this process several times until the centralizer is properly installed.

[0054] Similarly, when the centralizer needs to be disassembled, the other end of the logging instrument is threadedly connected to the connector 22, and the above steps are repeated until the centralizer is completely disassembled.

[0055] The disassembly and assembly tool in this embodiment has the following advantages:

[0056] (1) The disassembly and assembly tool can be used in conjunction with the logging instrument to realize the disassembly and assembly of the centralizer through mechanical pushing. The operation is simple and fast, which can not only reduce the burden on the staff but also improve the operation time.

[0057] (2) Because the push sleeve 1 is a telescopic structure with adjustable length, and the relative position of the hydraulic cylinder 3 and the connecting screw 21 can be fine-tuned, the disassembly and assembly tool can use a hydraulic cylinder 3 with a shorter extension stroke and disassemble the centralizer by multiple pushes. In this way, the disassembly and assembly tool can use a smaller hydraulic cylinder 3, reducing the cost of the disassembly and assembly tool, reducing the overall size of the disassembly and assembly tool, and improving the compactness of the design.

[0058] (3) The disassembly and assembly tool adopts a split design, that is, each component can be disassembled, which is convenient for the staff to maintain each component separately, reducing maintenance costs and improving maintenance convenience.

[0059] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in the present invention should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0060] In addition, the terms "first," "second," etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. In the description of this utility model, "plurality" means more than two, unless otherwise specifically defined.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A tool for disassembling and assembling a centralizer of a logging while drilling instrument, characterized in that: include: A push sleeve (1) is used for being sleeved on the logging instrument and abutting against the centralizer; A connecting rod (2) is coaxially arranged inside the push sleeve (1) and is used to connect to a well logging instrument; A hydraulic cylinder (3) is arranged on the connecting rod (2); The piston end of the hydraulic cylinder (3) can push the push sleeve (1) to move axially along the connecting rod (2), so that the push sleeve (1) can push the centralizer to move axially along the logging instrument, thereby realizing the disassembly and assembly of the centralizer.

2. The logging while drilling instrument centralizer assembly and disassembly tool according to claim 1, characterized in that: The thrust sleeve (1) comprises a propulsion sleeve (11), a support sleeve (12) and a compression sleeve (13) which are arranged in sequence. The end of the propulsion sleeve (11) away from the support sleeve (12) is used to abut against the stabilizer, and the end of the compression sleeve (13) away from the support sleeve (12) is used to abut against the piston end of the hydraulic cylinder (3).

3. The logging while drilling instrument centralizer assembly and disassembly tool according to claim 2, characterized in that: The propulsion sleeve (11) and the compression sleeve (13) are respectively provided with positioning ring grooves (14) at one end facing the support sleeve (12), so that the corresponding ends of the support sleeve (12) can be tightly clamped therein.

4. The logging while drilling instrument centralizer assembly and disassembly tool according to claim 2, characterized in that: The support sleeve (12) comprises an inner sleeve (121) and an outer sleeve (122), wherein the inner sleeve (121) is coaxially arranged on the inner side of the outer sleeve (122) and is slidably matched with the outer sleeve (122), and a limiting member (4) is arranged between the inner sleeve (121) and the outer sleeve (122), and the limiting member (4) is used to limit the relative sliding of the inner sleeve (121) and the outer sleeve (122).

5. The logging while drilling instrument centralizer assembly and disassembly tool according to claim 4, characterized in that: The limiting member (4) comprises: A guide groove (41) is provided on the outer side wall of the inner sleeve (121) and is arranged along the axial direction of the inner sleeve (121); A limit block (42) is provided on the inner side wall of the outer sleeve (122) and is slidably engaged with the guide groove (41); There are a plurality of limiting grooves (43) which are respectively arranged on the outer side wall of the inner sleeve (121). The plurality of limiting grooves (43) are arranged in sequence along the axial direction of the inner sleeve (121). The plurality of limiting grooves (43) are respectively connected to the guide groove (41). After the inner sleeve (121) and the outer sleeve (122) rotate relative to each other, the limiting block (42) can be tightly inserted into any of the limiting grooves (43).

6. The logging while drilling instrument centralizer assembly and disassembly tool according to claim 5, characterized in that: An indicator groove (5) connected to the guide groove (41) is provided on one side of the inner sleeve (121) close to the compression sleeve (13), and the indicator groove (5) and the limiting groove (43) are distributed on different sides of the guide groove (41).

7. The logging while drilling instrument centralizer assembly and disassembly tool according to claim 6, characterized in that: The limiting block (42) can be tightly inserted into the indicating groove (5).

8. The logging while drilling instrument centralizer assembly and disassembly tool according to claim 1, characterized in that: The connecting rod (2) includes a connecting screw (21) and a connecting head (22), wherein the connecting head (22) is arranged at the end of the connecting screw (21) and is used for being threadedly connected to the corresponding end of the logging instrument, the connecting screw (21) passes through the hydraulic cylinder (3) and is slidably matched with the hydraulic cylinder (3), and a locking member (6) is provided between the connecting screw (21) and the hydraulic cylinder (3), and the locking member (6) is used to limit the relative sliding of the hydraulic cylinder (3) and the connecting screw (21).

9. The logging while drilling instrument centralizer assembly and disassembly tool according to claim 8, characterized in that: The locking member (6) comprises: There are two locking pieces (61) and each of them is semicircular. The two locking pieces (61) are spliced ​​together to form a locking ring (62) sleeved on the connecting screw (21), and the locking ring (62) abuts against the end of the hydraulic cylinder (3) away from the push sleeve (1); Two half-thread grooves (63) are respectively provided on the inner side walls of the corresponding locking pieces (61); the two half-thread grooves (63) are spliced ​​together to form a full-thread groove (64) that matches the external thread of the connecting screw (21), so as to achieve position limiting between the locking piece (61) and the connecting screw (21); A locking sleeve (65) is tightly sleeved on the locking ring (62) formed by splicing the two locking pieces (61); There are two limit bars (66) and they are respectively arranged at one end of the corresponding locking piece (61) close to the hydraulic cylinder (3), and the end of the locking sleeve (65) facing the hydraulic cylinder (3) is respectively in contact with the two limit bars (66).

10. The logging while drilling instrument centralizer assembly and disassembly tool according to claim 9, characterized in that: The inner side wall of the locking sleeve (65) and the outer side walls of the two locking pieces (61) are respectively provided with mutually matching limiting inclined surfaces (67).

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