Connecting structure of casing coupling

Abstract

The invention relates to the technical field of couplings, and discloses a casing coupling connecting structure which comprises a coupling, an inner ring side of the coupling is provided with an inner conical thread, and the inner conical thread is in threaded fit with an outer conical thread arranged on the peripheral side of a casing; the base is fixedly connected to the side, away from the casing pipe, of the coupling in a sleeving mode, and the inner ring side of the base makes sealing contact with the peripheral side of the coupling; the float collar is annularly arranged on the inner ring side of the base, a hydraulic driving assembly is arranged on the base, the driving end of the hydraulic driving assembly is connected with the float collar, the float collar moves in the axial direction of the casing pipe, a step is arranged on the side, close to the casing pipe, of the float collar, and the step abuts against the casing pipe, so that the inner conical thread abuts against the outer conical thread in a sealed mode in the opposite direction. The sealing effect of the joint of the sleeve and the coupling can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of couplings, and in particular to a connection structure of a casing coupling. Background Art

[0002] In the process of mining and transporting oil, natural gas, coalbed methane, etc., casings need to be connected in series to form a transport pipeline, so casing couplings need to be used to connect them in a threaded manner.

[0003] The connection between the casing and the coupling requires higher torsion resistance and sealing performance. At present, most of the existing technologies are to install a rubber sealing ring at the threaded connection, and improve the sealing effect by contacting and squeezing the rubber sealing ring between the casing and the coupling. However, the rubber sealing ring will age and crack after long-term use, causing leakage of oil, gas and other transported materials from the gap, so there are certain usage defects. Summary of the invention

[0004] The object of the present invention is to provide a connection structure of a casing coupling to solve the problems existing in the above-mentioned prior art and to improve the sealing effect of the connection between the casing and the coupling.

[0005] To achieve the above object, the present invention provides the following solution: The present invention provides a connection structure of a casing coupling, comprising:

[0006] The coupling has an inner conical thread on its inner ring, and the inner conical thread cooperates with an outer conical thread on the outer peripheral side of the casing;

[0007] A base is sleeved and fixedly connected to a side of the coupling away from the sleeve, and an inner ring side of the base is in sealing contact with an outer peripheral side of the coupling;

[0008] A floating hoop is arranged on the inner ring side of the base, and a hydraulic drive assembly is arranged on the base. The driving end of the hydraulic drive assembly is connected to the floating hoop. The floating hoop moves axially along the casing. A step is provided on the side of the floating hoop close to the casing, and the step abuts against the casing so that the inner conical thread and the outer conical thread are sealed and abutted in opposite directions.

[0009] Preferably, the hydraulic drive assembly comprises:

[0010] A hydraulic pipe is provided in the base, one end of the hydraulic pipe is connected to the outside through a quick-release joint, the quick-release joint is fixed to the outer wall of the base, and the other end of the hydraulic pipe is provided with a driving part, the driving part is connected to the floating collar, and the driving part moves toward the adjacent casing under hydraulic drive;

[0011] A one-way valve is installed on a portion of the hydraulic pipe close to the quick connector and is configured to connect the hydraulic pipe along the quick connector to the driving unit.

[0012] Preferably, the driving unit comprises:

[0013] A piston ring, wherein a connecting seat is fixedly connected to the inner ring side of the base, a sealing cavity is provided in the connecting seat, the piston ring is slidably connected in the sealing cavity, and the hydraulic pipe is connected to a side of the sealing cavity away from the sleeve;

[0014] The piston rod is sealingly slidably connected to the side of the connecting seat close to the sleeve, one end of the piston rod extends into the sealing cavity and is fixedly connected to the piston ring, and one end of the piston rod close to the sleeve is fixedly connected to the floating collar.

[0015] Preferably, the connecting seat is an annular structure, the piston ring is arranged in the sealing cavity, and a bevel is provided on a side of the piston ring close to the hydraulic pipe, and the bevel faces the liquid outlet of the hydraulic pipe.

[0016] Preferably, it also includes:

[0017] A pressure regulating valve is installed on the portion of the hydraulic pipe close to the connecting seat.

[0018] Preferably, a pair of the floating hoops are provided, and the pair of the floating hoops are symmetrically distributed relative to each other along the center of the base.

[0019] Preferably, a plurality of steps are provided, and the diameter of the steps gradually decreases in a direction away from the floating hoop.

[0020] Preferably, a shoulder is provided on the outer peripheral side of the step near one end of the sleeve, and a ridge is integrally formed and fixedly connected to the remaining portion of the outer peripheral side of the step away from the shoulder. The cross section of the ridge is a conical structure, and the tip of the ridge extends in a direction away from the step.

[0021] Preferably, a recess is provided on one end of the outer peripheral side of the coupling close to the base, the inner ring side of the base is in sealing contact with the recess, a limiting ring is fixedly provided on the end surface of the recess, and the outer wall of the limiting ring is a conical structure, a limiting groove is provided on the inner ring side of the base, and the limiting ring is snap-fitted with the limiting groove.

[0022] Preferably, the maximum diameter of the limiting ring is the same as the outer diameter of the coupling.

[0023] The present invention discloses the following technical effects:

[0024] The present invention utilizes a coupling and a casing thread connection, an inner conical thread is provided on the inner ring side of the coupling, and an outer conical thread is provided on the outer peripheral side of the casing, so that the inner conical thread and the outer conical thread can be threadedly connected, have a high degree of fit, and enhance the sealing performance, and a base is fixedly connected to the coupling to make the base and the coupling in sealing contact. In addition, a floating hoop is movably connected to the base, and the floating hoop ring is arranged on the inner ring side of the base, and a hydraulic driving component is arranged on the base, and a hydraulic driving force is provided by the hydraulic driving component to make the floating hoop move along the axial direction of the casing, and the step of the floating hoop is abutted against the casing. Since the base is fixedly connected to the coupling, the floating hoop drives the casing to move, so that the inner conical thread and the outer conical thread connected by the thread generate extrusion pressure each other, and the two abut in opposite directions, so that the connection sealing performance between the casing and the coupling is fully improved, and the sealing effect of the connection between the casing and the coupling is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 It is a connection relationship diagram between the base and the coupling in the present invention;

[0027] Figure 2 It is a connection relationship diagram between the base and the floating hoop in the present invention;

[0028] Figure 3 For the present invention Figure 2 A partial enlarged view of the middle A;

[0029] Figure 4 It is a connection relationship diagram between the casing and the coupling in the present invention;

[0030] Figure 5 For the present invention Figure 4 A partial enlarged view of point B in the middle;

[0031] Figure 6 It is a connection diagram between the shoulder and the ridge in the present invention;

[0032] Among them, 1. Coupling; 101. Internal conical thread; 102. Concave platform; 2. Casing; 201. External conical thread; 3. Base; 4. Floating hoop; 401. Step; 4011. Shoulder; 4012. Ridge; 5. Hydraulic pipe; 6. Quick connector; 7. Check valve; 8. Piston ring; 801. Bevel; 9. Connecting seat; 10. Piston rod; 11. Pressure regulating valve; 12. Limit ring. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] Reference Figure 1-Figure 6 The present invention provides a connection structure of a casing coupling, comprising:

[0036] The inner ring side of the coupling 1 is provided with an inner conical thread 101, and the inner conical thread 101 is threadably matched with an outer conical thread 201 provided on the outer peripheral side of the casing 2;

[0037] The base 3 is sleeved and fixedly connected to the side of the coupling 1 away from the casing 2, and the inner circle side of the base 3 is in sealing contact with the outer circumference side of the coupling 1;

[0038] The floating hoop 4 is arranged on the inner ring side of the base 3. A hydraulic drive assembly is arranged on the base 3. The driving end of the hydraulic drive assembly is connected to the floating hoop 4. The floating hoop 4 moves axially along the casing 2. A step 401 is provided on the side of the floating hoop 4 close to the casing 2. The step 401 abuts against the casing 2 so that the inner tapered thread 101 and the outer tapered thread 201 are sealed and abutted in opposite directions.

[0039] The present invention utilizes a coupling 1 to be threadedly connected with a casing 2, an inner conical thread 101 is provided on the inner ring side of the coupling 1, and an outer conical thread 201 is provided on the outer peripheral side of the casing 2, so that the inner conical thread 101 and the outer conical thread 201 can be threadedly connected, have a high degree of fit, and enhance the sealing performance, and a base 3 is fixedly connected to the coupling 1, so that the base 3 and the coupling 1 are in sealing contact, and in addition, a floating hoop 4 is movably connected to the base 3, and the floating hoop 4 is arranged around the inner ring side of the base 3, and a hydraulic drive is arranged on the base 3. The hydraulic driving assembly provides a hydraulic driving force to make the floating collar 4 move axially along the casing 2, and the step 401 of the floating collar 4 abuts against the casing 2. Since the base 3 is fixedly connected to the coupling 1, the floating collar 4 drives the casing 2 to move, so that the internal tapered thread 101 and the external tapered thread 201 connected by the threads generate an extrusion force between each other, and the two abut in opposite directions, so that the connection sealing between the casing 2 and the coupling 1 is fully improved, thereby achieving the enhancement of the sealing effect of the connection between the casing 2 and the coupling 1.

[0040] Further, the hydraulic drive assembly includes:

[0041] A hydraulic pipe 5 is provided in the base 3. One end of the hydraulic pipe 5 is connected to the outside through a quick-release joint 6. The quick-release joint 6 is fixed to the outer wall of the base 3. A driving part is provided at the other end of the hydraulic pipe 5. The driving part is connected to the floating collar 4. The driving part moves toward the adjacent casing 2 under hydraulic drive.

[0042] The one-way valve 7 is installed on the portion of the hydraulic pipe 5 close to the quick connector 6 and is configured to connect the hydraulic pipe 5 along the quick connector 6 to the driving part.

[0043] In the present technical solution, hydraulic medium is transported through the hydraulic pipe 5 to provide driving force for driving the floating collar 4 to move. By installing a one-way valve 7 on the hydraulic pipe 5, the hydraulic medium is passed into the hydraulic pipe 5 from the quick connector 6, flows through the base 3 and finally passes into the driving part, so that the driving part drives the floating collar 4 to move along the end face direction of the adjacent casing 2, thereby achieving the situation that the step 401 on the floating collar 4 abuts against the casing 2, thereby enhancing the connection sealing between the casing 2 and the coupling 1.

[0044] Specifically, the one-way valve 7 prevents the hydraulic medium from flowing backwards, thereby achieving a long-term effect of maintaining a sealed connection between the casing 2 and the coupling 1 .

[0045] Furthermore, the driving unit includes:

[0046] The piston ring 8 is fixedly connected to a connecting seat 9 on the inner ring side of the base 3. A sealing cavity is provided in the connecting seat 9. The piston ring 8 is slidably connected in the sealing cavity. The hydraulic pipe 5 is connected to the side of the sealing cavity away from the sleeve 2.

[0047] The piston rod 10 is sealingly slidably connected to the side of the connecting seat 9 close to the sleeve 2. One end of the piston rod 10 extends into the sealing cavity and is fixedly connected to the piston ring 8. The end of the piston rod 10 close to the sleeve 2 is fixedly connected to the floating collar 4.

[0048] In the present technical solution, a connecting seat 9 is fixedly connected to the inner ring side of the base 3, a sealing chamber provided in the connecting seat 9 is used to accommodate the piston ring 8, and a hydraulic medium is introduced into the sealing chamber away from the side of the casing 2 through the hydraulic pipe 5, so that the piston ring 8 moves in the direction toward the casing 2 under the action of hydraulic pressure, and the floating collar 4 is driven to move through the piston rod 10, so that the step 401 is against the casing 2.

[0049] Specifically, a plurality of piston rods 10 may be fixedly connected along the axial direction of the piston ring 8 at equal intervals to improve the driving stability of the floating collar 4, and a sealing hole is opened on the side wall of the connecting seat 9, and the sealing holes are corresponding to the piston rods 10 one by one. The piston rod 10 is sealed and slidably connected with the sealing holes to prevent the hydraulic working medium from flowing out of the sealing holes.

[0050] Furthermore, the connecting seat 9 is an annular structure, the piston ring 8 is arranged in the sealing cavity, and a bevel 801 is provided on a side of the piston ring 8 close to the hydraulic pipe 5 , and the bevel 801 faces the liquid outlet of the hydraulic pipe 5 .

[0051] In this technical solution, the piston ring 8 is arranged in the annular connecting seat 9 to effectively separate the sealing cavity. After the hydraulic medium enters the sealing cavity, the bevel 801 of the piston ring 8 guides the hydraulic medium so that the hydraulic medium flows into the side of the piston ring 8 away from the sleeve 2, thereby hydraulically pushing the piston ring 8, and the piston ring 8 is in sliding contact with the inner wall of the sealing cavity. The piston ring 8 is preferably but not limited to rubber material to seal and separate the sealing cavity, which can prevent the hydraulic medium from flowing into the sealing hole. .

[0052] Furthermore, it also includes:

[0053] The pressure regulating valve 11 is installed on the portion of the hydraulic pipe 5 close to the connecting seat 9.

[0054] In the present technical solution, a pressure regulating valve 11 is also provided on the hydraulic pipe 5. Since a plurality of hydraulic pipes 5 are axially opened on the base 3, after the hydraulic medium is introduced into the hydraulic pipe 5 and passes through the one-way valve 7, the hydraulic medium is introduced into the sealing cavity and squeezed and matched with the piston ring 8 to provide a driving force for the floating hoop 4. At the same time, the hydraulic action also acts on the one-way valve 7 in the opposite direction. In order to avoid the reaction force supporting the floating hoop 4 and the casing 2 to be borne entirely by the one-way valve 7, a pressure regulating valve 11 is added to the end of the hydraulic pipe 5 near the sealing cavity to share part of the hydraulic reaction force, thereby improving the service life of the overall connection structure.

[0055] Furthermore, a pair of floating hoops 4 are provided, and the pair of floating hoops 4 are symmetrically distributed relative to each other along the center of the base 3 .

[0056] It can be understood that two coupling collars 1 are symmetrically fixed with the base 3 as the center, so that the two casings 2 can be connected in series. Correspondingly, a pair of floating collars 4 are provided, so that the pair of floating collars 4 can move and contact with the casings 2 on both sides respectively, so as to realize the connection of the two casings 2 in series and the sealing fixation with the coupling collar 1.

[0057] Furthermore, a plurality of steps 401 are provided, and the diameter of the steps 401 gradually decreases in a direction away from the floating collar 4 .

[0058] By gradually reducing the number of steps 401 in the direction away from the floating collar 4, a stepped structural protrusion facing the casing 2 is formed. As the floating collar 4 moves, the steps 401 are driven to move in the direction of the casing 2. The steps 401 with a small diameter first extend into the casing 2. As the steps 401 continue to move, the steps 401 that match the inner diameter of the casing 2 are in contact with the inner wall of the casing 2 along the circumferential direction, thereby stabilizing the structure of the casing 2. The steps 401 that are larger than the inner diameter of the casing 2 are pressed against the end of the casing 2, thereby achieving uniform and sufficient extrusion force on the casing 2, thereby improving the sealing and stability of the connection between the coupling 1 and the casing 2.

[0059] Furthermore, a shoulder 4011 is provided on the outer peripheral side of the step 401 close to one end of the sleeve 2, and a ridge 4012 is integrally formed and fixedly connected to the remaining portion of the outer peripheral side of the step 401 away from the shoulder 4011. The cross-section of the ridge 4012 is a conical structure, and the tip of the ridge 4012 extends in a direction away from the step 401.

[0060] In the present technical solution, the step 401 can be extended into the sleeve 2, and a shoulder 4011 is provided on the outer peripheral side of the step 401 to form a bevel 801 facing the inner wall of the sleeve 2, so as to facilitate guiding when the step 401 moves, so that steps 401 of different diameters can smoothly transition and extend into the sleeve 2, and because the convex ridge 4012 is fixedly connected to the outer peripheral side of the step 401, and the convex ridge 4012 smoothly transitions with the side wall of the step 401, as the step 401 extends into the sleeve 2, the inner wall surface of the sleeve 2 slides along the outer peripheral side of the step 401, and the structural protrusion generated by the convex ridge 4012 can relatively tighten the step 401 and further improve the fixing stability of the sleeve 2.

[0061] Furthermore, a recess 102 is provided at one end of the outer peripheral side of the coupling 1 close to the base 3, and the inner ring side of the base 3 is in sealing contact with the recess 102. A limiting ring 12 is fixedly provided on the side end surface of the recess 102, and the outer wall of the limiting ring 12 is a conical structure. A limiting groove is provided on the inner ring side of the base 3, and the limiting ring 12 is snap-fitted with the limiting groove.

[0062] The coupling 1 is fixed to the base 3 by a limiting ring 12, and the limiting ring 12 is fixed to the end face of the recessed platform 102 on the outer peripheral side of the coupling 1, and the inner conical thread 101 is provided on the inner ring side of the coupling 1. After the floating collar 4 abuts against the casing 2, the casing 2 is threadedly connected to the coupling 1, and the coupling 1 is pulled in a direction away from the base 3, and the base 3 is used to provide a fixing force for the coupling 1.

[0063] Furthermore, the maximum diameter of the limiting ring 12 is the same as the outer diameter of the coupling 1 .

[0064] Reference Figure 1 Under the clamping action of the limiting ring 12, the base 3 and the coupling 1 are fixed. When the floating collar 4 and the end of the casing 2 are squeezed, the casing 2 and the base 3 form a force acting on the coupling 1 in the opposite direction. The outer diameter of the limiting ring 12 is the same as the outer diameter of the coupling 1 away from the base 3, so that the two forces are balanced and the damage to the structure of the coupling 1 caused by the external force is reduced.

[0065] The working principle of the connection structure of the casing coupling of the present invention is as follows:

[0066] The base 3 is separated along the center to form two semicircular hoops, corresponding to the positions of the limiting groove and the limiting ring 12, and the two semicircular hoops are embraced to form the base 3, and the seams are welded, so that the base 3 is sleeved outside the coupling 1, and the limiting ring 12 is fixed to the limiting groove. A plurality of hydraulic pipes 5 are pre-opened on the base 3, and the sleeve 2 is threadedly connected to the coupling 1, and then the oil circuit is connected with the quick-release connector 6, and hydraulic oil is introduced into the hydraulic pipe 5. As the hydraulic oil enters the sealing cavity, the piston ring 8 can be squeezed, so that the piston ring 8 drives the piston rod 10 moves the float collar 4, and then moves the float collar 4 toward the casing 2, utilizes a plurality of stepped steps 401 provided on the float collar 4 to adapt to the inner diameter of the casing 2, utilizes the steps 401 to extend into the casing 2, and the casing 2 moves along the shoulder 4011 and is clamped and abutted against the adapted convex ridge 4012, thereby relatively fixing the float collar 4 and the casing 2, and under the action of hydraulic pressure, the outer conical thread 201 provided on the side wall of the casing 2 and the inner conical thread 101 provided on the inner ring side of the coupling 1 are closely fitted, so that the casing 2 and the coupling 1 are sealed, connected and fixed.

[0067] The one-way valve 7 provided on the hydraulic pipe 5 is used to maintain constant hydraulic pressure. Compared with the method of providing a rubber gasket in the traditional technology, it can effectively avoid the situation where the sealing effect is reduced due to rubber aging, and improve the sealing connection effect between the casing 2 and the coupling 1.

[0068] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0069] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A connection structure of a casing coupling, characterized in that: include: The coupling (1) has an inner conical thread (101) on its inner ring side, and the inner conical thread (101) is threadably matched with an outer conical thread (201) on the outer peripheral side of the casing (2); A base (3) is sleeved and fixedly connected to a side of the coupling (1) away from the sleeve (2), and an inner ring side of the base (3) is in sealing contact with an outer peripheral side of the coupling (1); A floating hoop (4) is arranged on the inner ring side of the base (3). A hydraulic drive assembly is arranged on the base (3). The drive end of the hydraulic drive assembly is connected to the floating hoop (4). The floating hoop (4) moves axially along the casing (2). A step (401) is provided on the side of the floating hoop (4) close to the casing (2). The step (401) abuts against the casing (2) so that the inner conical thread (101) and the outer conical thread (201) are sealed and abutted in opposite directions.

2. The connection structure of the casing coupling according to claim 1, characterized in that: The hydraulic drive assembly comprises: A hydraulic pipe (5) is provided in the base (3), one end of the hydraulic pipe (5) is connected to the outside through a quick-release joint (6), the quick-release joint (6) is fixed to the outer wall of the base (3), and the other end of the hydraulic pipe (5) is provided with a driving part, the driving part is connected to the floating collar (4), and the driving part moves toward the adjacent casing (2) under hydraulic drive; A one-way valve (7) is installed on a portion of the hydraulic pipe (5) close to the quick connector (6) and is configured to connect the hydraulic pipe (5) along the quick connector (6) to the driving unit.

3. The connection structure of the casing coupling according to claim 2, characterized in that: The driving unit comprises: A piston ring (8), a connecting seat (9) is fixedly connected to the inner ring side of the base (3), a sealing cavity is defined in the connecting seat (9), the piston ring (8) is slidably connected in the sealing cavity, and the hydraulic pipe (5) is connected to a side of the sealing cavity away from the sleeve (2); The piston rod (10) is sealingly slidably connected to the side of the connecting seat (9) close to the sleeve (2), one end of the piston rod (10) extends into the sealing cavity and is fixedly connected to the piston ring (8), and the end of the piston rod (10) close to the sleeve (2) is fixedly connected to the floating collar (4).

4. The connection structure of the casing coupling according to claim 3, characterized in that: The connecting seat (9) is an annular structure, the piston ring (8) is arranged in the sealing cavity, and a bevel (801) is provided on a side of the piston ring (8) close to the hydraulic pipe (5), and the bevel (801) faces the liquid outlet of the hydraulic pipe (5).

5. The connection structure of the casing coupling according to claim 2, characterized in that: Also includes: A pressure regulating valve (11) is installed on the portion of the hydraulic pipe (5) close to the connecting seat (9).

6. The connection structure of the casing coupling according to claim 1, characterized in that: A pair of the floating hoops (4) are provided, and the pair of the floating hoops (4) are symmetrically distributed relative to each other along the center of the base (3).

7. The connection structure of the casing coupling according to claim 1, characterized in that: A plurality of steps (401) are provided, and the diameter of the steps (401) gradually decreases in a direction away from the floating collar (4).

8. The connection structure of the casing coupling according to claim 1, characterized in that: A shoulder (4011) is provided on the outer peripheral side of the step (401) close to one end of the sleeve (2), and a ridge (4012) is integrally formed and fixedly connected to the remaining portion of the outer peripheral side of the step (401) away from the shoulder (4011), wherein the cross section of the ridge (4012) is a conical structure, and the tip of the ridge (4012) extends in a direction away from the step (401).

9. The connection structure of the casing coupling according to claim 1, characterized in that: A recessed platform (102) is provided at one end of the outer peripheral side of the coupling (1) close to the base (3), and the inner ring side of the base (3) is in sealing contact with the recessed platform (102). A limit ring (12) is fixedly provided on the side end surface of the recessed platform (102), and the outer wall of the limit ring (12) is a conical structure. A limit groove is provided on the inner ring side of the base (3), and the limit ring (12) is snap-fitted with the limit groove.

10. The connection structure of the casing coupling according to claim 9, characterized in that: The maximum diameter of the limiting ring (12) is the same as the outer diameter of the coupling (1).

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