Inverted V-shaped expansion shell anchor rod

Abstract

The invention relates to the technical field of surrounding rock supporting devices, in particular to an inverted-V-shaped expansion shell anchor rod which comprises a rod body, a shell sealing part, an expansion part and an expansion shell part, the rod body is provided with a first external thread section and a first connecting section which are connected, the expansion part is arranged on the first external thread section in a sleeving mode, and the expansion shell part is arranged on the first connecting section in a sleeving mode. The expansion shell part is arranged on the first connecting section and the first external thread section in a sleeving mode, the expansion part is in threaded connection with the first external thread section, the outer circumferential face of the expansion shell part is wrapped with the shell sealing part, and the shell sealing part is connected with the expansion part. According to the inverted-V-shaped expansion shell anchor rod, the probability that coal slime enters the threads of the rod body is reduced, and the anchoring stability is improved.

Description

Technical Field

[0001] The present application relates to the technical field of surrounding rock support devices, and in particular to an inverted V-shaped expansion shell anchor rod. Background Art

[0002] Mechanical expansion shell anchors are widely used in mining, slope, and tunnel support projects. Their basic principle is that the expansion shell at the anchor head expands and embeds into the tunnel opening. The anchor inside the surrounding rock changes the mechanical state of the surrounding rock, forming a cohesive and stable rock belt around the tunnel. The anchor and the surrounding rock work together to maintain tunnel stability. The main mechanical effects of the anchor include suspension, composite beam, composite arch, span reduction, and reinforcement. Proper use of the anchor not only improves support effectiveness, but also reduces material consumption, simplifies construction, and facilitates mechanized operation and rapid construction.

[0003] However, during the anchor support process, the threaded portion used for anchor pre-tightening is easily contaminated by coal slime or slurry, resulting in limited transmission during anchor pre-tightening, affecting the installation of the anchor and reducing the stability of the anchor. Summary of the Invention

[0004] The present application provides an inverted V-shaped expansion shell anchor rod to reduce the probability of coal slime entering the rod thread and improve anchoring stability.

[0005] The inverted V-shaped expansion shell anchor rod of the embodiment of the present application includes:

[0006] A rod body, wherein the rod body is provided with a first external thread section and a first connecting section connected to each other;

[0007] An expansion component and an expansion shell component, wherein the expansion component is sleeved on the first external thread segment, the expansion shell component is sleeved on the first connecting segment and the first external thread segment, and the expansion component is threadedly connected to the first external thread segment;

[0008] A shell sealing component is covered on the outer peripheral surface of the expansion shell component, and the shell sealing component is connected to the expansion component.

[0009] The present application provides an inverted V-shaped expansion shell anchor rod to reduce the probability of coal slime entering the rod thread and improve anchoring stability.

[0010] In some embodiments, the housing sealing component is made of any one of polytetrafluoroethylene and polyvinyl chloride.

[0011] In some embodiments, the expansion component includes an expansion piece, a first preset gap is defined between the expansion shell component and the first external thread segment, and the expansion piece is partially disposed within the first preset gap.

[0012] In some embodiments, the expansion member is provided with a gradual protrusion, which gradually increases in the direction of the radial dimension of the rod body away from the expansion shell component. There is a preset angle A between the inner straight line of the outer circumferential surface of the gradual protrusion and the axis of the rod body, and 5°≤A≤20°.

[0013] In some embodiments, the expansion shell component includes a smooth part, a damping plate and a wing part, the damping plate and the wing part extend along the direction of the rod body, the smooth part is sleeved on the first external thread segment, the smooth part is connected to the damping plate and the wing part, and the wing part and the damping plate are alternately arranged in the circumferential direction of the rod body.

[0014] In some embodiments, the expansion shell component includes an upper limit ring and a lower limit ring, the upper limit ring is arranged on the first connecting section, and the upper limit ring is connected to the end of the expansion shell component away from the expansion component, the lower limit ring is arranged in a first preset gap, and the lower limit ring is arranged on the side of the expansion shell component away from the expansion component.

[0015] In some embodiments, the expansion member is further provided with a guide protrusion, which is arranged on the expansion member or the gradual protrusion and extends along the radial direction of the rod body.

[0016] In some embodiments, a preset arc length B is provided between the wing member and the damping plate, and 1.5 mm ≤ B ≤ 5.0 mm.

[0017] In some embodiments, a plurality of fins are provided on the outer circumference of the fin member, the plurality of fins are spaced apart in the axial direction of the rod body, and the radial dimensions of the fins in the rod body gradually increase in a direction away from the expansion component.

[0018] In some embodiments, the inverted V-shaped expansion shell anchor rod also includes a tray, a ball pad and a fastener, and the rod body also includes a second connecting section and a third external threaded section, one end of the second connecting section is connected to the end of the first external threaded section away from the first connecting section, and the other end of the second connecting section is connected to the third external threaded section, and the radial dimensions of the second connecting section are both larger than the radial dimensions of the first external threaded section and the third external threaded section, and the tray, ball pad and fastener are sequentially arranged on the third external threaded section along the direction away from the second connecting section. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0020] Figure 1 A schematic diagram of an inverted V-shaped expansion shell anchor provided in an embodiment of the present application;

[0021] Figure 2 This is a cross-sectional schematic diagram of an inverted V-shaped expansion shell anchor rod according to an embodiment of the present application;

[0022] Figure 3 This is a schematic diagram of the first connecting section of an embodiment of the present application.

[0023] Figure 4 A schematic cross-sectional view of an expansion component provided in an embodiment of the present application;

[0024] Figure 5 This is a schematic diagram of the expansion shell component and the expansion component of an embodiment of the present application;

[0025] Figure 6 Schematic diagram of the rod body according to an embodiment of the present application.

[0026] Figure 7 This is a schematic diagram of the expansion shell component of an embodiment of the present application;

[0027] Figure 8 A schematic cross-sectional view of an expansion shell component and an expansion component provided in an embodiment of the present application;

[0028] Figure 9 This is a schematic top view of the expansion shell component provided in an embodiment of the present application.

[0029] Figure 10 A schematic diagram of the expansion component provided in an embodiment of the present application.

[0030] The above drawings include the following reference numerals:

[0031] Rod body 1, first external thread section 11, second connecting section 12, third external thread section 13, first preset gap 14, first connecting section 15,

[0032] Expansion component 2, guide protrusion 21, expansion piece 22, gradual protrusion 23,

[0033] Expansion shell component 3, smooth surface component 31, damping plate 32, wing component 33, wing 331, upper limit ring 34, lower limit ring 35,

[0034] Tray 4, ball pad 5, fastener 6. DETAILED DESCRIPTION

[0035] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0036] It should be noted that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating positions or positional relationships, are based on the positions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present application and simplifying the description. They do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present application. The terms "mounted", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be internal communication between two elements. The terms "parallel", "perpendicular", and "equal" include the situations described and situations similar to the situations described, and the range of the similar situations is within an acceptable deviation range, where the acceptable deviation range is determined by a person of ordinary skill in the art taking into account the measurement in question and the errors associated with the measurement of the specific quantity (i.e., the limitations of the measurement system). For example, "parallel" includes both absolute parallelism and approximate parallelism, where the acceptable deviation range for approximate parallelism may be, for example, within 5°; "perpendicular" includes both absolute perpendicularity and approximate perpendicularity, where the acceptable deviation range for approximate perpendicularity may also be, for example, within 5°. "Equal" includes both absolute equality and approximate equality, where the acceptable deviation range for approximate equality may be, for example, that the difference between the two is less than or equal to 5% of either. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0037] In order to enable those skilled in the art to better understand the present application, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0038] The inverted V-shaped expansion shell anchor rod of the embodiment of the present application includes:

[0039] The rod body 1 is provided with a first external thread section 11 and a first connecting section 15 connected to each other.

[0040] An expansion component 2 and an expansion shell component 3, wherein the expansion component 2 is sleeved on the first external thread segment 11, and the expansion shell component 3 is sleeved on the first connecting segment 15 and the first external thread segment 11, and the expansion component 2 is threadedly connected to the first external thread segment 11;

[0041] A shell sealing component is covered on the outer peripheral surface of the expansion shell component 3 , and the shell sealing component is connected to the expansion component 2 .

[0042] The inverted V-shaped expansion shell anchor rod of the embodiment of the present application reduces the probability of coal slime entering the thread of the rod body 1 and improves the anchoring stability.

[0043] The rear end of the first connecting section 12 is connected to the front end of the first external thread section 11. The first connecting section 12 and the first external thread section 11 are sleeved with an expansion shell component 3.

[0044] The expansion shell component 3 and the expansion component 2 extend in the forward and backward directions. Before pre-tightening, there is a first preset gap 14 between the expansion shell component 3 and the first external thread segment 11. The outer shell sealing component is covered on the outer peripheral surface of the expansion shell component 3, and the rear end part of the outer shell sealing component is in contact with the front end of the expansion component 2. The expansion component 2 is threadedly connected to the first external thread segment 11. During pre-tightening, the expansion component 2 moves forward to squeeze the expansion shell to expand and deform the expansion shell component 3. The expansion shell component 3 expands in the radial direction of the rod body 1 to break the outer shell sealing component, and then extends into the surrounding rock to complete the anchoring.

[0045] Before the anchor rod is extended into the anchoring position, the outer shell sealing component covers the outer circumference of the expansion shell component 3 and the outer circumference of the expansion component 2 to prevent mud and coal slime from entering the first external thread section 11 within the first preset gap 14. That is, during the process of the anchor rod being extended into the borehole, the mud and coal slime in the borehole may contaminate the various components of the anchor rod. The outer shell sealing component covers the outer circumference of the expansion shell component 3 and the expansion component 2 to prevent mud and coal slime from entering the gap between the expansion shell component 3 and the expansion component 2, thereby keeping these components clean. This reduces the probability of mud and coal slime entering the thread gap during the pre-tightening process, thereby reducing the problem of pre-tightening problems or reduced anchoring effect caused by impurities.

[0046] The inverted V-shaped expansion shell anchor rod of the embodiment of the present application is provided with a shell sealing component. The shell sealing component can effectively prevent mud and coal slime from entering the gap between the expansion shell component 3 and the expansion component 2 by covering the outer peripheral surface of the expansion shell component 3 and the expansion component 2, thereby keeping these components clean. It prevents mud and coal slime from entering the thread gap before pre-tightening, thereby reducing the problem of uneven pre-tightening or reduced anchoring effect caused by impurities. The shell sealing component can ensure that the expansion shell component 3 and the expansion component 2 can work normally during the pre-tightening process, thereby improving the stability and reliability of the anchoring. Clean components can better contact the surrounding rock and achieve more effective anchoring. It prevents mud and coal slime from entering the thread, thereby extending the service life of the anchor rod. The protective effect of the shell sealing component can significantly reduce component damage caused by impurities, avoid or reduce the probability of mud entering the thread before or during pre-tightening, resulting in uneven anchoring rotation, resulting in poor anchoring effect, thereby improving the stability and safety of the anchoring, and reducing maintenance costs.

[0047] In some embodiments, the housing sealing component is made of either polytetrafluoroethylene or polyvinyl chloride. Polytetrafluoroethylene has a certain degree of chemical stability and can resist corrosion from most chemical substances, including strong acids, strong bases, and organic solvents. This can prevent the mud in the borehole from corroding the housing sealing component and entering the first preset gap 14. Polyvinyl chloride is relatively low in cost and is used in cost-sensitive applications with low environmental requirements. Based on specific application requirements and working conditions, a suitable material can be selected to ensure the sealing performance and reliability of the anchor rod. It is understandable that the housing sealing component can be a multi-layer raw tape.

[0048] In some embodiments, the expansion component 2 includes an expansion member 22, and a first preset gap 14 is defined between the expansion shell component 3 and the first external threaded section 11, and the expansion member 22 is partially disposed within the first preset gap 14. During the pretightening process, the expansion member 22 moves forward, squeezing the expansion shell component 3. This squeezing action causes the expansion shell component 3 to expand in the radial direction of the rod body 1, thereby achieving an anchoring function. Part of the size of the expansion member 22 is disposed within the first preset gap 14, ensuring that the expansion member 22 can directly contact the expansion shell component 3, applying uniform pressure, and enabling the expansion shell component 3 to expand and deform smoothly.

[0049] In some embodiments, the expansion member 22 is provided with a gradually changing protrusion 23, which gradually increases in the radial dimension of the rod body 1 in the direction away from the expansion shell member 3. A predetermined angle A is formed between the inner line of the outer circumference of the gradually changing protrusion 23 and the axis of the rod body 1, and 5°≤A≤20°. The gradually changing protrusion 23 gradually increases in the radial dimension of the rod body 1 from front to back.

[0050] Specifically, the gradually varying protrusion 23 is used to expand the expansion shell component 3 during pre-tightening, extending it into the surrounding rock to achieve anchoring. Furthermore, since the gradually varying protrusion 23 is partially located within the first predetermined gap 14, setting the size of A prevents an excessively large A from causing deformation of the expansion shell component 3 and impacting the sealing effect between the inner wall of the expansion shell component 3 and the cylindrical member. This also prevents a too small predetermined angle from causing the expansion component 2 to squeeze the expansion shell component 3 less than expected during anchoring, thereby ensuring effective anchoring.

[0051] When the angle A is 5°, the slope of the gradually changing protrusion 23 is relatively small, which can ensure that the expansion shell component 3 can expand evenly during the pre-tightening process, avoiding sealing problems caused by excessive extrusion deformation. When the angle A is 20°, the slope of the gradually changing protrusion 23 is moderate, which can ensure that the expansion shell component 3 is expanded more during the pre-tightening process to improve the anchoring effect, while avoiding excessive deformation of the expansion shell component 3 due to an excessively large angle, which may cause damage to the expansion shell and affect the anchoring effect. By reasonably setting the angle A, it is possible to avoid excessive deformation of the expansion shell component 3, which may cause premature damage to the outer shell sealing component and affect the sealing effect, and ensure the stability and reliability of the anchoring effect.

[0052] In some embodiments, the expansion shell component 3 includes a smooth member 31, a damping plate 32, and a wing member 33. The damping plate 32 and the wing member 33 extend along the direction of the rod body 1. The smooth member 31 is sleeved on the first external thread segment 11. The smooth member 31 is connected to the damping plate 32 and the wing member 33, and the wing member 33 and the damping plate 32 are alternately arranged in the circumferential direction of the rod body 1. The smooth member 31, the damping plate 32, and the wing member 33 all extend in the front-to-back direction.

[0053] Specifically, the smooth member 31 is arranged at the front end of the rod body 1, and the damping plate 32 and the wing member 33 are connected to the rear end of the smooth member 31, and the number of the wing members 33 and the damping plate 32 is multiple, and the multiple wing members 33 and the damping plate 32 are alternately arranged at the rear end of the smooth member 31 along the circumference of the rod body 1. A plurality of wings 331 are provided on the wing member 33 so as to extend into the surrounding rock during anchoring. However, before anchoring, the wings 331 on the wing member 33 will cause the space of the borehole after grouting to be squeezed more. For example, after grouting in the borehole, the slurry in the borehole is squeezed when the anchor rod is extended. The wing members 33 and the damping plates 32 are alternately arranged, so that the mud on the wing member 33 can flow outward from between the damping plates 32 between the two wing members 33 when the anchor rod is extended into the anchoring position, thereby reducing the force of the slurry impacting the wing member 33 and the gap between the wing member 33 and the damping plate 32, reducing the probability of mud or coal slime entering the first external threaded section 11 in the first preset gap 14, and thereby improving the stability of the anchoring.

[0054] In some embodiments, the expansion shell component 3 includes an upper limit ring 34 and a lower limit ring 35, the upper limit ring 34 is arranged on the first connecting section 15, and the upper limit ring 34 is connected to the end of the expansion shell component 3 away from the expansion component 2, the lower limit ring 35 is arranged in the first preset gap 14, and the lower limit ring 35 is arranged on the side of the expansion shell component 3 away from the expansion component 2. The upper limit ring 34 is arranged on the first connecting section 15, and is connected to the end of the expansion shell component 3 away from the expansion component 2. The lower limit ring 35 is arranged in the first preset gap 14 and is located at the front end of the expansion shell component 3. The function of the lower limit ring 35 is to further limit the position of the expansion shell component 3 to ensure that the expansion shell component 3 can be evenly expanded during the expansion process. The upper and lower limit rings 35 cooperate with each other to prevent the expansion shell component 3 from excessive movement during the expansion process.

[0055] In some embodiments, the expansion member 22 is further provided with a guide protrusion 21, which is disposed on the expansion member 22 or the gradual protrusion and extends radially along the rod body 1. The guide protrusion 21 is disposed on the outer circumference of the gradual protrusion or the expansion member 22, and at least partially extends into the gap between the wing member 33 and the damping plate 32 to prevent the expansion member 22 from rotating during pretightening, guide the expansion member 22, and improve the stability of the expansion member 22 and the anchoring effect.

[0056] In some embodiments, a preset arc length B is provided between the wing member 33 and the damping plate 32 , and 1.5 mm ≤ B ≤ 5.0 mm.

[0057] Specifically, the gap between the fin member 33 and the damping plate 32 has a preset arc length B. When the preset arc length B is 1.5 mm, the gap width is small, effectively controlling the flow velocity and flow rate of the slurry. This prevents the slurry from rapidly impacting the gap between the fin member 33 and the damping plate 32 when the anchor rod is extended into the anchoring position, thereby reducing the probability of mud or coal slime entering the first externally threaded section 11 within the first preset gap 14. When the preset arc length B is 5.0 mm, friction between the fin member 33 and the damping plate 32 is reduced, thereby keeping the threads clean and ensuring a smooth preload process.

[0058] In some embodiments, a plurality of fins 331 are provided on the outer circumference of the fin member 33 , the plurality of fins 331 are spaced apart in the axial direction of the rod body 1 , and the radial size of the fins 331 in the rod body 1 gradually increases in the direction away from the expansion component 2 .

[0059] That is, the wing 331 is triangular, and the radial size of the wing 331 on the rod body 1 gradually decreases in the direction away from the expansion component 2, that is, the radial size of the wing 331 on the rod body 1 gradually increases from front to back, so that during anchoring, the wing 331 on the wing member 33 can better contact with the surrounding rock, thereby improving the anchoring effect.

[0060] By providing a plurality of triangular fins 331 on the outer peripheral surface of the fin member 33 and arranging them at intervals in the axial direction of the rod body 1, and allowing the radial size of the fins 331 to gradually increase from front to back in the rod body 1, it is convenient for the slurry to flow backward when the anchor rod is extended, reducing the concentrated impact force of the slurry on the fin member 33, and reducing the probability of mud or coal slime entering the thread gap, thereby keeping the thread clean and ensuring a smooth pre-tightening process.

[0061] In some embodiments, the inverted V-shaped expansion shell anchor rod also includes a tray 4, a ball pad 5 and a fastener 6, and the rod body 1 also includes a second connecting section 12 and a third external thread section 13. One end of the second connecting section 12 is connected to the end of the first external thread section 11 away from the first connecting section 15, and the other end of the second connecting section 12 is connected to the third external thread section 13. The radial dimensions of the second connecting section 12 are greater than the radial dimensions of the first external thread section 11 and the third external thread section 13. The tray 4, ball pad 5 and fastener 6 are arranged on the third external thread section 13 in sequence along the direction away from the second connecting section 12.

[0062] Tray 4 supports and secures the anchor rod, ensuring it can stably bear the load after installation. Ball pad 5 adjusts the contact angle between tray 4 and the anchor rod, ensuring it evenly bears the load and reducing stress concentration. Fastener 6, a nut, secures tray 4 and ball pad 5 to the anchor rod, ensuring the stability of the entire anchor rod system.

[0063] The radial dimension of the second connecting section 12 is greater than the radial dimension of the first external thread section 11 and the third external thread section 13, which is convenient for limiting the expander and preventing the expander or the expansion shell component 3 from moving backward when the anchor rod is extended into the drill hole. At the same time, it also prevents the tray 4 from moving forward and disengaging from the third external thread, resulting in a decrease in the anchoring effect.

[0064] The above is a detailed introduction to the method provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core ideas of the present application. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. An inverted V-shaped expansion shell anchor, characterized in that: include: A rod body, wherein the rod body is provided with a first external thread section and a first connecting section connected to each other; An expansion component and an expansion shell component, wherein the expansion component is sleeved on the first external thread segment, the expansion shell component is sleeved on the first connecting segment and the first external thread segment, and the expansion component is threadedly connected to the first external thread segment; A shell sealing component is covered on the outer peripheral surface of the expansion shell component, and the shell sealing component is connected to the expansion component.

2. The inverted V-shaped expansion shell anchor according to claim 1, characterized in that: The shell sealing component is made of any one of polytetrafluoroethylene and polyvinyl chloride.

3. The inverted V-shaped expansion shell anchor according to claim 1, characterized in that: The expansion component includes an expansion piece, a first preset gap is defined between the expansion shell component and the first external thread segment, and the expansion piece is partially disposed within the first preset gap.

4. The inverted V-shaped expansion shell anchor according to claim 1, characterized in that: The expansion member is provided with a gradual protrusion, which gradually increases in the direction of the radial dimension of the rod body away from the expansion shell component. A preset angle A is formed between the inner straight line of the outer circumferential surface of the gradual protrusion and the axis of the rod body, and 5°≤A≤20°.

5. The inverted V-shaped expansion shell anchor according to claim 4, characterized in that: The expansion shell component includes a smooth component, a damping plate and a wing component, the damping plate and the wing component extend along the direction of the rod body, the smooth component is sleeved on the first external thread segment, the smooth component is connected to the damping plate and the wing component, and the wing component and the damping plate are alternately arranged in the circumferential direction of the rod body.

6. The inverted V-shaped expansion shell anchor according to claim 5, characterized in that: The expansion shell component includes an upper limit ring and a lower limit ring. The upper limit ring is arranged on the first connecting section and is connected to the end of the expansion shell component away from the expansion component. The lower limit ring is arranged in a first preset gap and is arranged on the side of the expansion shell component away from the expansion component.

7. The inverted V-shaped expansion shell anchor according to claim 6, characterized in that: The expansion member is further provided with a guide protrusion, which is arranged on the expansion member or the gradual protrusion and extends along the radial direction of the rod body.

8. The inverted V-shaped expansion shell anchor according to claim 6, characterized in that: A preset arc length B is provided between the wing member and the damping plate, and 1.5 mm ≤ B ≤ 5.0 mm.

9. The inverted V-shaped expansion shell anchor according to claim 6, characterized in that: A plurality of fins are provided on the outer circumferential surface of the fin member. The plurality of fins are spaced apart in the axial direction of the rod body, and the sizes of the fins in the radial direction of the rod body gradually increase in a direction away from the expansion component.

10. The inverted V-shaped expansion shell anchor according to claim 1, characterized in that: It also includes a tray, a ball pad and a fastener. The rod body also includes a second connecting segment and a third external thread segment. One end of the second connecting segment is connected to the end of the first external thread segment away from the first connecting segment, and the other end of the second connecting segment is connected to the third external thread segment. The radial dimensions of the second connecting segment are greater than the radial dimensions of the first external thread segment and the third external thread segment. The tray, ball pad and fastener are sequentially arranged on the third external thread segment in a direction away from the second connecting segment.

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