Drilling device for advanced drainage of soft rock stratum separation water body

Abstract

The invention provides a drilling device for advanced drainage of a soft rock stratum separation layer water body. According to the drilling device for advanced drainage and drainage of the soft rock stratum separation layer water, drilling is conducted through the drill bit, meanwhile, the first-stage sleeve and the second-stage sleeve are driven to move into a drill hole, slurry is conveyed through gaps of the sleeves, and the defect that traditional drainage and drainage are only drilled but not reinforced is overcome; when drilling to a soft water-resisting layer below the separation layer water body through the outer liquid spraying holes, grouting is conducted on soft rock damage gaps caused by drilling, and the water-resisting layer is reinforced; and if a large amount of separation layer water suddenly bursts into the drainage water, the grouting pressure of the slurry pump is increased, so that slurry enters the gap between the first-stage inner pipe and the drill rod from the inner liquid spraying hole, and hole sealing treatment is performed in time, so that water-resisting layer breakage caused by drilling is effectively prevented, and man-made separation layer water damage is avoided.

Description

Technical Field

[0001] The present application relates to the technical field of rock stratum drilling, and in particular to a drilling device for pre-draining water from stratified water bodies in weak rock strata. Background Art

[0002] During underground coal mining, the coal seam overburden produces delamination. Under the influence of factors such as hydrostatic pressure, stress or mining disturbance, a part of the water-filled delamination space ruptures and breaks into the mine in a short period of time, causing disasters.

[0003] The prevention of abscission water hazards mainly involves pre-drainage of abscission water bodies. Existing pre-drainage drilling equipment mainly reinforces the hole wall with cement slurry during the drilling process to ensure the integrity of the hole. When drilling holes in the relatively hard rock strata on the roof of the coal seam, the damage to the underlying impermeable layer of the abscission water body is relatively small, and the impermeable layer will not be damaged due to drilling, which will not cause the abscission water body to suddenly burst into the mining face.

[0004] However, when the overlying rock layer under the abscission water body is relatively soft, the existing drilling equipment will disturb the abscission layer during the drilling process, destroying the mechanical equilibrium state between the original rock layers, causing cracks in the abscission layer, and expanding with the continuous intrusion of the drill bit. Eventually, under the action of the hydrostatic pressure of the abscission water body, the abscission water body breaks through the abscission layer, thereby artificially causing abscission water damage. When faced with a drainage volume that exceeds expectations, the hole cannot be sealed in time, causing the working face to be flooded.

[0005] Therefore, there is an urgent need to provide a technical solution to the above-mentioned deficiencies in the prior art. Summary of the invention

[0006] The purpose of the present application is to provide a drilling device for pre-draining water from a detached water body in a soft rock layer, so as to solve or alleviate the problems existing in the above-mentioned prior art.

[0007] In order to achieve the above objectives, this application provides the following technical solutions: The present application provides a drilling device for pre-draining water from detached water bodies in weak rock strata, comprising: a drill bit, a rotating connection unit, a primary casing, a secondary casing and a drill rod; the bottom surface of the drill bit is provided with a mounting groove, and the rotating connection unit is installed in the mounting groove; the rotating connection unit comprises: a rotating ring, a fixed ring and a steel ball, there are two rotating rings, and the two rotating rings are symmetrically arranged on both sides of the fixed ring, and the end faces of the rotating ring facing the fixed ring are provided with rotating grooves, and a plurality of steel balls are installed in the rotating grooves; the primary casing comprises: a primary inner tube, a primary outer tube, a sealing cover plate and a thin film partition plate, the upper ends of the primary inner tube and the primary outer tube are both detachably connected to the bottom surface of the sealing cover plate, and steps are provided on the inner side wall of the primary outer tube and / or the outer side wall of the primary inner tube Boss; the film partition is located on the stepped boss, and a compression spring is arranged between the film partition and the sealing cover plate; wherein, the outer wall of the rotating ring is tightly matched with the mounting groove, and the inner wall of the fixing ring is connected with the outer wall of the first-level outer tube; the side wall of the first-level outer tube is provided with a plurality of external liquid spray holes, and the side wall of the first-level inner tube is provided with a plurality of internal liquid spray holes, and the external liquid spray holes and the internal liquid spray holes are respectively located on both sides of the film partition; the secondary casing is detachably connected to the lower end of the first-level casing, and the outer tube side wall of the secondary casing is provided with a plurality of the external liquid spray holes, and the bottom end of the secondary casing is axially provided with a liquid passing hole, and the liquid passing hole is located between the outer tube and the inner tube of the secondary casing; the drill rod passes through the inner tube of the secondary casing and the first-level inner tube in turn and is connected to the drill bit.

[0008] Preferably, a clamping end cap is detachably connected to the bottom of the drill bit, and a clamping boss is provided on the upper end surface of the clamping end cap, and the clamping boss presses the rotating connection unit axially.

[0009] Preferably, a threaded blind hole is provided on the bottom surface of the mounting groove, and the end of the drill rod is mounted in the threaded blind hole.

[0010] Preferably, the bottom surface of the sealing cover plate has a plurality of first spring grooves evenly distributed along the circumferential direction, and correspondingly, the top surface of the membrane diaphragm has a plurality of second spring grooves evenly distributed along the axial direction, the plurality of first spring grooves correspond one-to-one to the plurality of second spring grooves, and each of the first spring grooves and the corresponding second spring groove are respectively adapted to be connected with both ends of a compression spring.

[0011] Preferably, the primary sleeve further comprises: a guide bolt, which passes through the membrane diaphragm and the compression spring in sequence from the bottom surface of the membrane diaphragm and is then connected to the lower end of the sealing cover plate.

[0012] Preferably, a first connecting boss is provided at the lower end of the outer side wall of the first-stage outer tube, and a second connecting boss is provided at the upper end of the inner side wall of the outer tube of the second-stage sleeve, and the first connecting boss is threadedly adapted to the second connecting boss.

[0013] Preferably, the upper end surface of the inner tube of the secondary sleeve is flush with the bottom surface of the second connecting boss.

[0014] Preferably, a third connecting boss is provided at the lower end of the outer side wall of the outer tube of the secondary casing, the axial length of the third connecting boss is equal to the axial length of the second connecting boss, and the outer surface of the third connecting boss is provided with a connecting external thread.

[0015] Beneficial effects: In the drilling device for pre-draining water from detached water bodies in weak rock strata provided in an embodiment of the present application, an installation groove is provided on the bottom surface of the drill bit, and a rotating connection unit is installed in the installation groove. In the rotating connection unit, the outer wall of the rotating ring is tightly matched with the installation groove, and the inner wall of the fixed ring is connected to the outer wall of the first-level outer tube; since the upper ends of the inner tube in the first-level casing and the first-level outer tube are coaxially connected to the bottom surface of the sealing cover plate, relative rotation between the drill bit and the first-level outer tube is achieved, and at the same time, during the drilling process, the drill bit drives the first-level casing to move forward.

[0016] In the first-level casing, a stepped boss is provided on the inner wall of the first-level outer tube and / or the outer wall of the first-level inner tube, and a membrane partition compressed by a compression spring is arranged on the stepped boss; at the same time, a plurality of internal spray holes are provided on the first-level inner tube above the membrane partition. When the drill bit drills into the abscission water body, if a large amount of drainage water suddenly rushes into the abscission water body, the grouting pressure of the slurry pump can be increased. Under the action of the pressure of the slurry in the first-level casing, the membrane partition can be moved upward, and then the slurry can enter the gap between the first-level inner tube and the drill pipe from the internal spray holes, so as to seal the hole in time.

[0017] An external liquid spraying hole located below the membrane partition is arranged on the outer side wall of the first-level outer tube. The slurry in the first-level casing is sprayed into the cracks of the waterproof layer through the external liquid spraying hole to reinforce the waterproof layer. If the delamination water body does not burst into the drainage water in large quantities, the casing is screwed out step by step and the drill bit is withdrawn when the drilling is completed; if the delamination water body suddenly bursts into the drainage water in large quantities, the slurry enters the gap between the first-level inner tube and the drill rod through the internal liquid spraying hole, and the hole is sealed in time. The drill bit, drill rod and first-level casing remain in the borehole, and the other second-level casings are withdrawn step by step, thereby effectively avoiding man-made delamination water damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. Among them: Figure 1 A schematic diagram of the structure of a drilling device for pre-draining water from a stratified water body in a weak rock layer provided according to some embodiments of the present application; Figure 2 for Figure 1 an axial cross-sectional view of the illustrated embodiment; Figure 3 for Figure 2 A partial view at B in the view shown; Figure 4 A schematic diagram of a first-level outer tube and a first-level inner tube provided according to some embodiments of the present application; Figure 5 A schematic diagram of assembling a thin film separator on a sealing cover plate according to some embodiments of the present application; Figure 6 A schematic diagram of the structure of a sealing cover plate provided according to some embodiments of the present application; Figure 7 A schematic diagram of the structure of a drill bit provided according to some embodiments of the present application; Figure 8 An axial cross-sectional view of a thin film separator provided according to some embodiments of the present application; Fig. 9 It is a schematic diagram of assembling a rotating connection unit according to some embodiments of the present application; Fig.10 This is an axial cross-sectional view of a secondary casing provided according to some embodiments of the present application.

[0019] Description of reference numerals: 100, drill bit; 200, primary casing; 300, secondary casing; 400, rotary connection unit; 201, first-level outer tube; 202, first-level inner tube; 203, sealing cover plate; 204, film partition; 205, compression spring; 212, inner liquid spray hole; 301, liquid hole; 401. Fixed ring; 402. Rotating ring; 403. Steel ball. DETAILED DESCRIPTION

[0020] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments. Each example is provided by way of explanation of the present application and does not limit the present application. In fact, it will be clear to those skilled in the art that modifications and variations may be made in the present application without departing from the scope or spirit of the present application. For example, a feature shown or described as a part of an embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desired that the present application includes such modifications and variations within the scope of the appended claims and their equivalents.

[0021] In order to overcome the damage of the aquiclude to the soft rock stratum by the advance drainage of the aquiclude water body, the present application provides a drilling device for the advance drainage of the aquiclude water body in the soft rock stratum. When drilling to the estimated aquiclude, a coagulating liquid with good fluidity and fast coagulation time is released into the borehole to fill the cracks generated in the aquiclude during drilling, and timely reinforce the aquiclude, thereby effectively preventing the rupture of the aquiclude caused by drilling and avoiding man-made aquiclude water damage.

[0022] like Figures 1 to 10 As shown, the drilling device for pre-draining water from a soft rock layer detached water body comprises: a drill bit 100, a rotary connection unit 400, a primary casing 200, a secondary casing 300 and a drill rod. The drill bit 100 and the primary casing 200 are detachably connected via the rotary connection unit 400, the lower end of the primary casing 200 is detachably connected to the secondary casing 300, and the drill rod is detachably connected to the bottom of the drill bit 100 and passes through the primary casing 200 and the secondary casing 300.

[0023] The driving unit drives the drill rod to rotate, and the drill rod drives the drill bit 100 to rotate. The drill bit 100 and the primary casing 200 achieve relative rotation through the rotating connection unit 400. Thereby, while the drill rod and the drill bit 100 drill forward, they drive the primary casing 200 and the secondary casing 300 to move forward along the borehole. When drilling into the estimated waterproof layer, a solidifying liquid with good fluidity and fast solidification time is released into the borehole to fill the cracks generated in the waterproof layer during drilling, so as to reinforce the waterproof layer in time.

[0024] In the present application, a mounting groove is provided at the bottom of the drill bit 100, and a rotating connection unit 400 is installed in the mounting groove. Specifically, the outer diameter of the rotating connection unit 400 is matched with the radial dimension of the mounting groove, so that the rotating connection unit 400 and the mounting groove are tightly fitted; at the same time, a clamping end cover is detachably connected to the bottom end face of the drill bit 100. Specifically, the clamping end cover and the drill bit 100 are fastened together by fastening bolts (hexagonal cylindrical head bolts), and a clamping boss is provided on the upper end face of the clamping end cover, which presses the rotating connection unit 400 axially to clamp the rotating connection unit 400 in the mounting groove.

[0025] The bottom surface of the mounting groove is provided with a threaded blind hole for connecting the upper end of the drill rod, so that the drill rod and the drill bit 100 can realize power transmission through the threaded connection. In addition, the drill rod connected to the drill bit 100 can also be fixedly connected to the drill bit 100 by other fixed connection methods such as welding to further enhance the firmness of the connection between the drill rod and the drill bit 100.

[0026] In the present application, the rotating connection unit 400 includes: a rotating ring 402, a fixed ring 401 and steel balls 403. There are two rotating rings 402, which are symmetrically arranged at the two end faces of the fixed ring 401, and a rotating groove is provided on the end faces of the rotating ring 402 and the fixed ring 401, and a plurality of steel balls 403 are installed in the rotating groove.

[0027] The outer wall of the rotating ring 402 is tightly matched with the installation groove. At the same time, under the action of the compression end cap, the rotating connection unit 400 is compressed and fixed in the installation groove as a whole; the inner wall of the fixed ring 401 is connected to the primary casing 200. Specifically, a detachable connection method such as threaded connection can be adopted, or a fixed connection method such as welding can be adopted. In this way, the relative rotation movement between the rotating ring 402 and the fixed ring 401 is realized. At the same time, the axial force between the rotating ring 402 and the fixed ring 401 is transmitted through the steel ball 403, so that the primary casing 200 can move into the borehole with the drill bit 100, and at the same time, it does not rotate with the drill bit 100.

[0028] In the present application, the primary casing 200 includes: a primary inner tube 202, a primary outer tube 201, a sealing cover plate 203 and a membrane partition 204. Among them, the primary outer tube 201 and the primary inner tube 202 are both tubular structures, and the upper ends of the primary outer tube 201 and the primary inner tube 202 can be detachably connected to the bottom surface of the sealing cover plate 203 coaxially, specifically, connected to the sealing cover plate 203 by threaded connection.

[0029] The inner wall of the primary outer tube 201 and the outer wall of the primary inner tube 202 are both provided with stepped bosses, and during normal drilling, a film partition 204 is placed on the stepped bosses. Specifically, a compression spring 205 is provided between the film partition 204 and the sealing cover plate 203. When the upper ends of the primary outer tube 201 and the primary inner tube 202 are screwed onto the sealing cover plate 203, the film partition 204 is compressed onto the stepped bosses by the compression spring 205.

[0030] Furthermore, the bottom surface of the sealing cover plate 203 is uniformly provided with a plurality of first spring grooves along the circumferential direction, and correspondingly, the top surface of the film diaphragm 204 is uniformly provided with a plurality of second spring grooves along the axial direction, and the plurality of first spring grooves correspond to the plurality of second spring grooves one by one, and each first spring groove and the corresponding second spring groove are respectively adapted to the two ends of a compression spring 205. In other words, the two ends of a compression spring 205 are respectively located in the first spring groove and the second spring groove arranged correspondingly, thereby making the compression force of the compression spring 205 act uniformly on the film diaphragm 204, and uniformly compressing the film diaphragm 204 on the stepped boss, avoiding the film diaphragm 204 from being subjected to an unbalanced load, and enhancing the stability of the film diaphragm 204.

[0031] In a specific example, the guide bolt passes through the bottom surface of the film diaphragm 204 and the compression spring 205 in sequence, and is connected to the lower end of the sealing cover plate 203. Specifically, a mounting countersunk hole and a coaxial mounting through hole are axially arranged on the bottom surface of the film diaphragm 204, and a compression threaded blind hole is axially arranged on the bottom surface of the sealing cover plate 203. The mounting countersunk hole, the mounting through hole, and the compression threaded blind hole are all coaxial with the corresponding first spring slot and second spring slot. After the rod of the guide bolt passes through the mounting through hole, it passes through the compression spring 205 and is threadedly connected to the compression threaded blind hole. The pre-compression force of the compression spring on the film diaphragm 204 can be adjusted by adjusting the guide bolt.

[0032] In the present application, a plurality of external liquid spraying holes are arranged on the side wall of the primary outer tube 201, and a plurality of internal liquid spraying holes 212 are arranged on the side wall of the primary inner tube 202, and the external liquid spraying holes and the internal liquid spraying holes 212 are respectively located on both sides of the film partition 204. That is, the external liquid spraying holes on the side wall of the primary outer tube 201 are located below the film partition 204, and the internal liquid spraying holes 212 on the side wall of the primary inner tube 202 are located above the film partition 204. Thereby, when drilling into the estimated waterproof layer, a solidifying liquid with good fluidity and fast solidification time is released into the borehole through the external liquid spray hole to fill the cracks generated in the waterproof layer during drilling, so as to reinforce the waterproof layer in time; when the drill bit 100 drills into the abscission water body, if there is no large amount of drainage water intruding into the abscission water body, the casing is screwed out step by step when the drilling is completed, and the drill bit 100 is withdrawn; if the abscission water body suddenly intrudes into the drainage water in large quantities, the grouting pressure of the slurry pump can be increased to make the membrane diaphragm 204 move upward, and then the slurry enters the gap between the first-level inner tube 202 and the drill pipe from the internal liquid spray hole 212, so as to perform the hole sealing treatment in time.

[0033] If the abscission water body suddenly bursts into the drainage water in large quantities, the grouting pressure of the slurry pump can be increased. Under the pressure of the slurry in the primary casing 200, the membrane partition 204 moves upward, and then the slurry enters the gap between the primary inner tube 202 and the drill pipe from the inner spray hole 212, and the hole is sealed in time. The drill bit 100, drill pipe and primary casing 200 remain in the borehole, and the other secondary casings 300 are withdrawn step by step, thereby effectively avoiding man-made abscission water damage.

[0034] In the present application, the secondary sleeve 300 is detachably connected to the lower end of the primary sleeve 200. Specifically, a first connection boss is provided at the lower end of the outer side wall of the primary outer tube 201, and a second connection boss is provided at the upper end of the inner side wall of the outer tube of the secondary sleeve 300. The first connection boss and the second connection boss are threadedly adapted and connected. In other words, the outer side wall of the first connection boss is provided with an external thread, and the inner side wall of the second connection boss is provided with an internal thread. The primary outer tube 201 and the secondary sleeve 300 are connected together through threaded connection.

[0035] Furthermore, the upper end surface of the inner tube of the secondary casing 300 is flush with the bottom surface of the second connecting boss, that is, when the first connecting boss and the second connecting boss are in place through threaded connection, the lower end surface of the primary inner tube 202 abuts against the upper end surface of the inner tube of the secondary casing 300, thereby limiting the threaded connection between the first connecting boss and the second connecting boss through the abutment between the lower end surface of the primary inner tube 202 and the upper end surface of the inner tube of the secondary casing 300, and at the same time, effectively isolating the drill pipe and the casing, allowing the slurry to flow along the casing.

[0036] As the drill bit 100 drives the primary casing 200 to move in the borehole, another secondary casing 300 is connected by threading at the lower end (tail) of the secondary casing 300, and the cycle is repeated until the target waterproof layer is drilled. The connection between the secondary casings 300 is achieved by threading the second connecting boss provided at the upper end of the secondary casing 300 and the third connecting boss provided at the lower end of the outer wall of the outer tube of the secondary casing 300. The axial length of the third connecting boss is equal to the axial length of the second connecting boss, and the outer surface of the third connecting boss is provided with a connecting external thread, which is threadedly connected to the internal thread of the second connecting boss.

[0037] The outer tube side wall of the secondary casing 300 is provided with a plurality of external liquid spray holes, and the bottom end of the secondary casing 300 is provided with a liquid passing hole 301 along the axial direction, and the liquid passing hole 301 is located between the outer tube and the inner tube of the secondary casing 300, thereby allowing the slurry to pass through the liquid passing hole 301 into the gap between the outer tube and the inner tube of the secondary casing 300 and be transported to the primary casing 200.

[0038] In the present application, drilling is performed through the drill bit 100, while driving the primary casing 200 and the secondary casing 300 to move into the borehole, and slurry is transported through the gaps between the casings to improve the shortcomings of traditional drainage water only drilling without reinforcement; through the external spray hole, when drilling into the soft impermeable layer below the abscission water body, grouting is performed into the soft rock damage gaps caused by drilling to reinforce the impermeable layer; if the abscission water body suddenly bursts into a large amount of drainage water, the grouting pressure of the slurry pump is increased, so that the slurry enters the gap between the primary inner pipe 202 and the drill pipe from the internal spray hole 212, and the hole is sealed in time, thereby effectively preventing the working face from being flooded due to excessive water exceeding the expected drainage capacity.

[0039] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A drilling device for pre-draining water from a soft rock layer, characterized in that: include: Drill bit, rotary connection unit, primary casing, secondary casing and drill pipe; The bottom surface of the drill bit is provided with a mounting groove, and the rotating connection unit is mounted in the mounting groove; The rotating connection unit comprises: a rotating ring, a fixed ring and steel balls. There are two rotating rings, which are symmetrically arranged on both sides of the fixed ring. The end faces of the rotating ring and the fixed ring facing each other are both provided with rotating grooves, and a plurality of steel balls are installed in the rotating grooves. The first-level casing comprises: a first-level inner tube, a first-level outer tube, a sealing cover plate and a film partition plate, the upper ends of the first-level inner tube and the first-level outer tube are both detachably connected to the bottom surface of the sealing cover plate, and a stepped boss is arranged on the inner side wall of the first-level outer tube and / or the outer side wall of the first-level inner tube; the film partition plate is located on the stepped boss, and a compression spring is arranged between the film partition plate and the sealing cover plate; The outer side wall of the rotating ring is tightly matched with the mounting groove, and the inner side wall of the fixed ring is connected with the outer side wall of the first-level outer tube; the side wall of the first-level outer tube is provided with a plurality of outer liquid spray holes, and the side wall of the first-level inner tube is provided with a plurality of inner liquid spray holes, and the outer liquid spray holes and the inner liquid spray holes are respectively located on both sides of the film partition; The secondary sleeve is detachably connected to the lower end of the primary sleeve, and a plurality of external liquid spraying holes are arranged on the side wall of the outer tube of the secondary sleeve, and a liquid passing hole is arranged along the axial direction at the bottom end of the secondary sleeve, and the liquid passing hole is located between the outer tube and the inner tube of the secondary sleeve; The drill rod passes through the inner tube of the secondary casing and the primary inner tube in sequence and is connected to the drill bit.

2. The drilling device for advanced drainage of water in soft rock strata according to claim 1 is characterized in that: The bottom of the drill bit is detachably connected with a clamping end cover, and the upper end surface of the clamping end cover is provided with a clamping boss, and the clamping boss presses the rotating connection unit in the axial direction.

3. The drilling device for pre-draining water from soft rock layer delamination water body according to claim 1, characterized in that: A threaded blind hole is provided on the bottom surface of the installation groove, and the end of the drill rod is installed in the threaded blind hole.

4. The drilling device for advanced drainage of water in soft rock strata according to claim 1 is characterized in that: The bottom surface of the sealing cover plate is uniformly distributed with a plurality of first spring grooves along the circumferential direction, and correspondingly, the top surface of the film diaphragm is uniformly distributed with a plurality of second spring grooves along the axial direction, the plurality of first spring grooves correspond one-to-one with the plurality of second spring grooves, and each of the first spring grooves and the corresponding second spring groove are respectively adapted to be connected with the two ends of a compression spring.

5. The drilling device for advanced drainage of water in soft rock strata according to claim 4 is characterized in that: The primary sleeve also includes: a guide bolt, which passes through the film diaphragm and the compression spring in sequence from the bottom surface of the film diaphragm and is connected to the lower end of the sealing cover plate.

6. The drilling device for advanced drainage of water in soft rock strata according to claim 1 is characterized in that: A first connection boss is disposed at the lower end of the outer side wall of the primary outer tube, and a second connection boss is disposed at the upper end of the inner side wall of the outer tube of the secondary sleeve. The first connection boss is threadedly adapted to the second connection boss.

7. The drilling device for advanced drainage of water in a soft rock layer according to claim 6 is characterized in that: The upper end surface of the inner tube of the secondary sleeve is flush with the bottom surface of the second connecting boss.

8. The drilling device for advanced drainage of water in soft rock strata according to claim 1 is characterized in that: A third connecting boss is provided at the lower end of the outer side wall of the outer tube of the secondary casing, the axial length of the third connecting boss is equal to the axial length of the second connecting boss, and the outer surface of the third connecting boss is provided with a connecting external thread.

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