A tensile and pressure resistant optical cable structure

Abstract

The utility model discloses a kind of tensile pressure-resistant optical cable structures, it includes outer sheath, inner sheath and optical fiber bundle. Annular reinforcing rib is equipped in outer sheath inner wall, buffer groove is equipped in inner sheath outer wall, optical fiber bundle is wrapped flexible protective layer outside and is embedded with buffer groove through protruding part. Outer sheath and inner sheath are detachably connected by elastic clamping tooth and groove, and the elastic core body in supporting column provides buffering and support, and positioning ring and positioning block ensure that optical fiber bundle is stable. The application can improve the tensile pressure-resistant performance of optical cable, enhance structural stability, facilitate maintenance replacement, prolong service life, and be suitable for complex laying environment.

Description

Technical Field

[0001] This utility model relates to the field of optical cable technology, and in particular to an optical cable structure that is tensile and pressure resistant. Background Technology

[0002] Optical fiber cables are crucial transmission media in modern communication systems, enabling long-distance, high-speed data transmission. Their structural design directly impacts their performance and lifespan in complex environments. Depending on the application, optical fibers require various properties such as tensile strength, pressure resistance, and moisture resistance to adapt to diverse laying conditions, including underground, aerial, and submarine installations. With the rapid development of communication networks, higher demands are placed on the reliability and durability of optical fibers. However, in practical applications, optical fibers are frequently damaged by external mechanical forces or environmental pressures, leading to decreased transmission performance or even interruptions.

[0003] Chinese patent CN219948515U discloses an easy-to-install ship collision avoidance device, including a mounting base. The mounting base has a working groove and an opening inside. A motor is installed inside the working groove, and a first gear is connected to the power drive end of the motor. A double-acting screw is connected inside the working groove, and a second gear is installed at the center of the outer side of the double-acting screw. Two symmetrical movable seats are connected to the outside of the double-acting screw. A connecting seat is connected inside the opening. A connecting plate is installed on the upper surface of the connecting seat, and a base is installed on the upper surface of the connecting plate. Two symmetrical buffer components are installed on the top of the base. A frame is installed on the top of the two buffer components, and several sets of collision avoidance rollers are connected to the top of the frame. Workers can quickly install and disassemble the collision avoidance device, improving work efficiency. The first and second springs ensure effective buffering, and the entire buffering process is stable.

[0004] However, during the process of conceiving and implementing the aforementioned application, the inventors discovered that the disclosed solution, which uses a motor to drive a bidirectional screw to insert the locking pin into the slot on the side wall of the connector for easy assembly and disassembly, requires a separate power source, resulting in relatively high costs. Similar design approaches also have limitations in the field of optical cable structure optimization, particularly in the comprehensive improvement of tensile and compressive strength; existing technologies still have room for improvement in this area. Utility Model Content

[0005] The purpose of this utility model is to provide a tensile and pressure-resistant optical cable structure, which solves the problems mentioned in the background art.

[0006] This invention is implemented as follows: a tensile and pressure-resistant optical cable structure includes an outer sheath, an inner sheath, and an optical fiber bundle. The inner wall of the outer sheath is provided with several annular reinforcing ribs, which are evenly distributed along the axial direction of the outer sheath and integrally formed with the outer sheath. The inner sheath is located inside the outer sheath, and its outer wall contacts the inner side of the annular reinforcing ribs. The inner wall of the inner sheath is provided with a spiral buffer groove, the cross-section of which is trapezoidal. The optical fiber bundle is located at the center of the inner sheath and is wrapped with a flexible protective layer. The outer wall of the flexible protective layer is provided with several protrusions, which are embedded in the buffer groove and fit against the inner wall of the buffer groove.

[0007] The outer sheath has retaining rings at both ends, and each retaining ring has a snap-fit ​​groove on its inner side. The inner wall of the snap-fit ​​groove has several elastic snap teeth, which are evenly distributed around the circumference of the snap-fit ​​groove and have their ends inclined inward. The inner sheath has retaining rings at both ends, and the outer wall of the retaining ring has several grooves, which correspond one-to-one with the elastic snap teeth. The width of the groove is slightly greater than the thickness of the elastic snap teeth. After the retaining ring is inserted into the snap-fit ​​groove, the elastic snap teeth are embedded in the groove, thus forming a detachable connection between the outer sheath and the inner sheath.

[0008] Optionally, the outer wall of the outer sheath is provided with a plurality of anti-slip strips, the anti-slip strips extending along the axial direction of the outer sheath, and the cross-section of the anti-slip strips being semi-elliptical; the interior of the anti-slip strips is provided with cavities, the cavities being filled with elastic material, the hardness of the elastic material being less than the hardness of the outer sheath.

[0009] Optionally, it also includes a support mechanism disposed between the outer sheath and the inner sheath. The support mechanism includes a plurality of support columns, one end of each support column being fixedly connected to the inner side of the annular reinforcing rib, and the other end being fixedly connected to the outer wall of the inner sheath. The support column has a through hole in the middle, and an elastic core is disposed in the through hole. The two ends of the elastic core are fixedly connected to the two ends of the through hole, respectively.

[0010] Optionally, the elastic core is made of rubber material, and its outer wall is provided with a plurality of annular protrusions. The annular protrusions are evenly distributed along the axial direction of the elastic core, and the height of the annular protrusions gradually decreases. The inner wall of the through hole is provided with an annular groove that matches the annular protrusions. The annular protrusions are embedded in the annular grooves and fit against the inner wall of the annular grooves.

[0011] Optionally, the outer surface of the optical fiber bundle is provided with several positioning rings, the inner wall of each positioning ring is fixedly connected to the outer wall of the flexible protective layer, and the outer wall of the positioning ring is provided with several positioning grooves, which are evenly distributed along the circumference of the positioning ring; the inner wall of the inner sheath is provided with several positioning blocks, which correspond one-to-one with the positioning grooves, and the width of the positioning block is slightly smaller than the width of the positioning groove; the positioning blocks are embedded in the positioning grooves, so that a limiting connection is formed between the optical fiber bundle and the inner sheath.

[0012] Optionally, the flexible protective layer is made of a multi-layer composite material, with an inner layer of polyurethane and an outer layer of polytetrafluoroethylene; the protrusion has a triangular cross-section and the height of the protrusion gradually decreases; the inner wall of the buffer groove is provided with a plurality of lubrication grooves, the lubrication grooves extend along the length of the buffer groove, and the cross-section of the lubrication grooves is rectangular.

[0013] Optionally, the cross-section of the annular reinforcing rib is T-shaped, and a plurality of reinforcing grooves are provided on its inner side. The reinforcing grooves are evenly distributed along the circumference of the annular reinforcing rib, and the cross-section of the reinforcing grooves is arc-shaped. The inner wall of the reinforcing groove is provided with a plurality of reinforcing rib strips, which extend along the length direction of the reinforcing groove, and the cross-section of the reinforcing rib strips is trapezoidal.

[0014] Optionally, the outer wall of the support column is provided with a plurality of heat dissipation holes, which are evenly distributed along the axial direction of the support column and have a circular cross-section; the inner wall of the heat dissipation holes is provided with a plurality of heat dissipation fins, which are evenly distributed along the circumference of the heat dissipation holes and have a gradually decreasing thickness.

[0015] Optionally, the outer wall of the anti-slip strip is provided with a plurality of anti-slip patterns, the anti-slip patterns extend along the length direction of the anti-slip strip, and the cross-section of the anti-slip patterns is wavy; the two ends of the anti-slip strip are provided with connecting parts, the cross-section of the connecting parts is L-shaped, and the two sets of connecting parts are respectively fixedly connected to the two ends of the outer sheath.

[0016] The technical advantages of this invention are as follows: By setting an annular reinforcing rib inside the outer sheath and a buffer groove outside the inner sheath, the overall tensile strength of the optical cable is improved through the cooperation of the annular reinforcing rib and the buffer groove. Simultaneously, by setting a flexible protective layer outside the fiber bundle and setting protrusions on the flexible protective layer, the compressive strength of the optical cable is further enhanced through the interlocking of the protrusions with the buffer groove. Furthermore, the outer and inner sheaths are detachably connected through the cooperation of elastic teeth and grooves, facilitating the maintenance and replacement of the optical cable. The elastic core and its annular protrusion design within the support column not only enhance the support strength of the optical cable but also provide good buffering performance. The cooperation of the positioning ring and positioning block ensures the stability and positioning accuracy of the fiber bundle within the inner sheath. The overall structural design is reasonable and can effectively cope with complex laying environments, extending the service life of the optical cable. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of this utility model.

[0018] Figure 2 This is a cross-sectional view of the connection structure between the outer sheath and the inner sheath in this utility model.

[0019] Figure 3 This is a partially enlarged view of the present invention.

[0020] The reference numerals in the attached diagram are as follows: 1. Outer sheath; 2. Inner sheath; 3. Optical fiber bundle; 4. Annular reinforcing rib; 5. Buffer groove; 6. Flexible protective layer; 7. Protrusion; 8. Fixing ring; 9. Snap-fit ​​groove; 10. Elastic snap-fit ​​tooth; 11. Snap-fit ​​ring; 12. Support column; 13. Elastic core; 14. Positioning ring; 15. Positioning block. Detailed Implementation

[0021] like Figures 1 to 3 As shown, this utility model provides a tensile and pressure-resistant optical cable structure, the overall structure of which includes an outer sheath 1, an inner sheath 2, and an optical fiber bundle 3. The outer sheath 1 is located at the outermost layer of the entire optical cable structure, and its inner wall is provided with several annular reinforcing ribs 4. These annular reinforcing ribs 4 are evenly distributed along the axial direction of the outer sheath 1 and are integrally formed with the outer sheath 1. The inner sheath 2 is located inside the outer sheath 1, and its outer wall contacts the inner side of the annular reinforcing ribs 4. The inner wall of the inner sheath 2 is provided with a spiral buffer groove 5, and the cross-section of the buffer groove 5 is trapezoidal. The optical fiber bundle 3 is located at the center of the inner sheath 2, and its exterior is wrapped with a flexible protective layer 6. The outer wall of the flexible protective layer 6 is provided with several protrusions 7. These protrusions 7 are embedded in the buffer groove 5 and fit against the inner wall of the buffer groove 5.

[0022] The outer sheath 1 has retaining rings 8 at both ends, and each retaining ring 8 has a locking groove 9 on its inner side. The inner wall of the locking groove 9 has several elastic locking teeth 10, which are evenly distributed around the circumference of the locking groove 9, and the ends of the elastic locking teeth 10 are inclined inward. The inner sheath 2 has retaining rings 11 at both ends, and the outer wall of the retaining ring 11 has several grooves, which correspond one-to-one with the elastic locking teeth 10, and the width of the groove is slightly larger than the thickness of the elastic locking teeth 10. When the retaining ring 11 is inserted into the locking groove 9, the elastic locking teeth 10 are embedded in the groove, realizing a detachable connection between the outer sheath 1 and the inner sheath 2. This connection method facilitates the quick separation of the outer sheath 1 and the inner sheath 2 when maintenance or replacement of the optical cable is required.

[0023] The outer wall of the outer sheath 1 is provided with several anti-slip strips, which extend along the axial direction of the outer sheath 1 and have a semi-elliptical cross-section. The anti-slip strips have internal cavities filled with an elastic material whose hardness is less than that of the outer sheath 1. This design enhances the surface friction of the outer sheath 1 through the deformation capacity of the elastic material, thereby improving the ground grip of the optical cable during laying. Simultaneously, the outer wall of the anti-slip strips has several anti-slip patterns extending along the length of the strips, with a wavy cross-section. Connecting parts with an L-shaped cross-section are provided at both ends of the anti-slip strips, and the two sets of connecting parts are fixedly connected to the two ends of the outer sheath 1. This design further enhances the connection strength between the anti-slip strips and the outer sheath 1.

[0024] A support mechanism is provided between the outer sheath 1 and the inner sheath 2. This mechanism includes several support columns 12, one end of which is fixedly connected to the inner side of the annular reinforcing rib 4, and the other end is fixedly connected to the outer wall of the inner sheath 2. A through hole is provided in the middle of each support column 12, and an elastic core 13 is provided within the through hole. Both ends of the elastic core 13 are fixedly connected to the two ends of the through hole. The elastic core 13 is made of rubber, and its outer wall has several annular protrusions. These annular protrusions are evenly distributed along the axial direction of the elastic core 13, and their height gradually decreases. The inner wall of the through hole has an annular groove that matches the annular protrusions. The annular protrusions are embedded in the annular grooves and fit against the inner wall of the annular grooves. This design, through the elasticity of the elastic core 13 and the cooperation between the annular protrusions and the annular grooves, provides a buffering effect when the optical cable is subjected to radial pressure, while maintaining the structural stability of the support column 12. Furthermore, the outer wall of the support column 12 has several heat dissipation holes, which are evenly distributed along the axial direction of the support column 12, and the cross-section of each heat dissipation hole is circular. The inner wall of the heat dissipation hole is equipped with several heat dissipation fins, which are evenly distributed along the circumference of the heat dissipation hole, and the thickness of the heat dissipation fins gradually decreases. This design helps to dissipate the heat generated inside the optical cable to the external environment in a timely manner during operation, thereby improving the heat dissipation performance of the optical cable.

[0025] The outer surface of the fiber optic bundle 3 is provided with several positioning rings 14. The inner wall of each positioning ring 14 is fixedly connected to the outer wall of the flexible protective layer 6. The outer wall of the positioning ring 14 is provided with several positioning grooves, which are evenly distributed along the circumference of the positioning ring 14. The inner wall of the inner sheath 2 is provided with several positioning blocks 15, which correspond one-to-one with the positioning grooves, and the width of the positioning block 15 is slightly smaller than the width of the positioning groove. The positioning blocks 15 are embedded in the positioning grooves, so that the fiber optic bundle 3 and the inner sheath 2 form a limiting connection. This design can effectively prevent the fiber optic bundle 3 from shifting in the inner sheath 2 and ensure the stability of the position of the fiber optic bundle 3 in the optical cable. The flexible protective layer 6 is made of multi-layer composite material, with an inner layer of polyurethane material and an outer layer of polytetrafluoroethylene material. The outer wall of the flexible protective layer 6 is provided with several protrusions 7, the cross-section of which is triangular and the height of which gradually decreases. The inner wall of the buffer groove 5 is provided with several lubrication grooves, which extend along the length of the buffer groove 5 and have a rectangular cross-section. This design, through the cooperation of the protrusion 7 and the buffer groove 5, as well as the presence of the lubrication groove, reduces the friction of the fiber bundle 3 when it moves in the inner sheath 2, while enhancing the overall compressive strength of the optical cable.

[0026] The annular reinforcing rib 4 has a T-shaped cross-section, with several reinforcing grooves evenly distributed along its circumference. The grooves themselves have arc-shaped cross-sections. The inner wall of each groove is provided with several reinforcing ribs extending along its length, each with a trapezoidal cross-section. This design, through the combination of the reinforcing grooves and ribs, significantly enhances the structural strength of the annular reinforcing rib 4, effectively dispersing stress when the optical cable is subjected to tensile force and preventing structural damage caused by localized stress concentration.

[0027] In practical applications, the optical cable structure of this invention is suitable for various complex laying environments. For example, during underground pipeline laying, the optical cable may be subjected to pressure from the soil and impact from external construction equipment. In this case, the annular reinforcing rib 4 of the outer sheath 1 and the buffer groove 5 of the inner sheath 2 work together to absorb external pressure through the rigid support of the annular reinforcing rib 4 and the elastic deformation of the buffer groove 5, preventing damage to the optical fiber bundle 3. At the same time, the anti-slip strip design makes the optical cable less prone to slippage during laying, improving construction efficiency. In high-altitude installation scenarios, the optical cable may be affected by wind and temperature changes. In this case, the role of the support column 12 and the elastic core 13 is particularly critical. The support column 12 ensures the relative positional stability between the outer sheath 1 and the inner sheath 2 through its rigid connection, while the elastic core 13 alleviates the internal stress changes caused by thermal expansion and contraction of the optical cable through its elastic deformation. In addition, the cooperation of the positioning ring 14 and the positioning block 15 ensures the stable position of the optical fiber bundle 3 in the inner sheath 2, preventing the optical fiber bundle 3 from shifting due to changes in the external environment and affecting the quality of optical signal transmission.

[0028] This invention achieves tensile and compressive strength of optical cables through the connection, position, and cooperation relationships between the various components, while facilitating maintenance and replacement. It also exhibits good adaptability and reliability in complex environments, meeting the demands of modern communication networks for high-performance optical cables.

[0029] To enable those skilled in the art to fully understand and implement this utility model, the following supplementary explanation of the implementation principle of this utility model is provided in conjunction with specific application scenarios.

[0030] During the fiber optic cable laying process, the outer sheath 1 and inner sheath 2 are first assembled using the engagement ring 11 and engagement slot 9. When the engagement ring 11 is inserted into the engagement slot 9, the elastic locking teeth 10 retract inward due to the pressure from the outer wall of the engagement ring 11 until the engagement ring 11 is fully inserted. The elastic locking teeth 10 then embed into the grooves on the outer wall of the engagement ring 11, thus achieving a quick connection. This design requires no additional tools or power source, simplifying the installation process while ensuring the reliability of the connection. Disassembly is only required by applying appropriate external force to disengage the elastic locking teeth 10 from the grooves, facilitating later maintenance.

[0031] In underground pipeline laying scenarios, optical cables may be subjected to soil pressure or impact from external construction equipment. In this case, the annular reinforcing rib 4 of the outer sheath 1, through its T-shaped cross-section and internal reinforcing grooves and ribs, effectively disperses the tensile force and radial pressure applied externally, preventing structural damage caused by stress concentration. Simultaneously, the buffer groove 5 of the inner sheath 2, through its trapezoidal cross-section design, undergoes elastic deformation under compression, absorbing some of the impact energy. The protrusions 7 within the buffer groove 5, in conjunction with the flexible protective layer 6, further enhance the compressive strength, protecting the fiber bundle 3 from direct damage.

[0032] In high-altitude installation scenarios, optical cables may experience thermal expansion and contraction due to wind or temperature changes. In this case, the support column 12, with its two ends fixedly connected to the annular reinforcing rib 4 and the inner sheath 2 respectively, maintains the relative positional stability between the outer sheath 1 and the inner sheath 2. The elastic core 13 in the middle of the support column 12 undergoes elastic deformation under external force, mitigating internal stress changes caused by thermal expansion and contraction. Furthermore, the annular protrusion on the outer wall of the elastic core 13 cooperates with the annular groove on the inner wall of the through hole, providing cushioning while ensuring the structural stability of the support column 12. The heat dissipation holes and their internal heat sinks help dissipate the heat generated during the optical cable's operation to the external environment in a timely manner, thereby improving the cable's heat dissipation performance.

[0033] During the operation of the optical cable, the positional stability of the fiber bundle 3 is achieved by the cooperation of the positioning ring 14 and the positioning block 15. The positioning groove on the outer wall of the positioning ring 14 corresponds one-to-one with the positioning block 15 on the inner wall of the inner sheath 2, and the width of the positioning block 15 is slightly smaller than the width of the positioning groove, allowing the two to fit tightly together. This limiting connection method effectively prevents the fiber bundle 3 from shifting in the inner sheath 2, thereby ensuring the stability of optical signal transmission. The flexible protective layer 6 is made of multi-layer composite material, with the inner polyurethane material providing good flexibility and the outer polytetrafluoroethylene material having excellent corrosion resistance and wear resistance. The cooperation between the protrusion 7 and the buffer groove 5, as well as the presence of the lubrication groove, reduces the friction of the fiber bundle 3 when moving in the inner sheath 2, further improving the overall performance of the optical cable.

[0034] The anti-slip strip plays a crucial role in the installation process. Extending axially along the outer sheath 1, the anti-slip strip has a semi-elliptical cross-section. The elastic material inside deforms under pressure, increasing the friction on the surface of the outer sheath 1 and thus improving the optical cable's grip. The wavy anti-slip texture on the outer wall of the anti-slip strip further enhances the friction effect, while the L-shaped connectors at both ends ensure a secure connection between the anti-slip strip and the outer sheath 1, preventing it from detaching due to external forces in complex environments.

[0035] Through the synergistic effect of the above-mentioned components, the optical cable structure of this utility model can exhibit excellent tensile and compressive strength in various complex laying environments, while also possessing good heat dissipation and stability, meeting the needs of modern communication networks for high-performance optical cables.

[0036] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A tensile and pressure resistant optical cable structure, comprising an outer sheath (1), an inner sheath (2), and an optical fiber bundle (3), characterized in that: The inner wall of the outer sheath (1) is provided with a plurality of annular reinforcing ribs (4), which are evenly distributed along the axial direction of the outer sheath (1) and integrally formed with the outer sheath (1). The inner sheath (2) is located inside the outer sheath (1), and its outer wall is in contact with the inner side of the annular reinforcing rib (4). The inner wall of the inner sheath (2) is provided with a spiral buffer groove (5), and the cross section of the buffer groove (5) is trapezoidal. The fiber bundle (3) is located at the center of the inner sheath (2), and is wrapped with a flexible protective layer (6). The outer wall of the flexible protective layer (6) is provided with several protrusions (7). The protrusions (7) are embedded in the buffer groove (5) and fit against the inner wall of the buffer groove (5). The outer sheath (1) is provided with fixing rings (8) at both ends. Each fixing ring (8) is provided with a snap-fit ​​groove (9) on its inner side. The inner wall of the snap-fit ​​groove (9) is provided with a number of elastic snap teeth (10). The elastic snap teeth (10) are evenly distributed along the circumference of the snap-fit ​​groove (9) and their ends are inclined inward. The inner sheath (2) is provided with snap rings (11) at both ends. The outer wall of the snap ring (11) is provided with a number of grooves. The grooves correspond one-to-one with the elastic snap teeth (10), and the width of the grooves is greater than the thickness of the elastic snap teeth (10). After the snap ring (11) is inserted into the snap groove (9), the elastic snap teeth (10) are embedded in the groove, so that a detachable connection is formed between the outer sheath (1) and the inner sheath (2).

2. The tensile and pressure resistant optical cable structure as described in claim 1, characterized in that: The outer wall of the outer sheath (1) is provided with a plurality of anti-slip strips. The anti-slip strips extend along the axial direction of the outer sheath (1) and have a semi-elliptical cross section. The anti-slip strips have cavities inside, and the cavities are filled with elastic material. The hardness of the elastic material is less than that of the outer sheath (1).

3. The tensile and pressure resistant optical cable structure as described in claim 1, characterized in that: It also includes a support mechanism disposed between the outer sheath (1) and the inner sheath (2). The support mechanism includes a plurality of support columns (12). One end of each support column (12) is fixedly connected to the inner side of the annular reinforcing rib (4), and the other end is fixedly connected to the outer wall of the inner sheath (2). The support column (12) has a through hole in the middle, and an elastic core (13) is disposed in the through hole. The two ends of the elastic core (13) are fixedly connected to the two ends of the through hole, respectively.

4. The tensile and pressure resistant optical cable structure as described in claim 3, characterized in that: The elastic core (13) is made of rubber material, and its outer wall is provided with a number of annular protrusions. The annular protrusions are evenly distributed along the axial direction of the elastic core (13) and their height gradually decreases. The inner wall of the through hole is provided with an annular groove that matches the annular protrusions. The annular protrusions are embedded in the annular grooves and fit against the inner wall of the annular grooves.

5. The tensile and pressure resistant optical cable structure as described in claim 1, characterized in that: The outer side of the optical fiber bundle (3) is provided with several positioning rings (14), the inner wall of each positioning ring (14) is fixedly connected to the outer wall of the flexible protective layer (6), and the outer wall of the positioning ring (14) is provided with several positioning grooves; the inner wall of the inner sheath (2) is provided with several positioning blocks (15), the positioning blocks (15) correspond one-to-one with the positioning grooves, and the width of the positioning blocks (15) is smaller than the width of the positioning grooves; the positioning blocks (15) are embedded in the positioning grooves, so that the optical fiber bundle (3) and the inner sheath (2) form a limiting connection.

6. The tensile and pressure resistant optical cable structure as described in claim 1, characterized in that: The flexible protective layer (6) is made of multi-layer composite material, with the inner layer being polyurethane and the outer layer being polytetrafluoroethylene; the protrusion (7) has a triangular cross-section and its height gradually decreases; the inner wall of the buffer groove (5) is provided with several lubrication grooves, which extend along the length of the buffer groove (5) and have a rectangular cross-section.

7. The tensile and pressure resistant optical cable structure as described in claim 1, characterized in that: The cross-section of the annular reinforcing rib (4) is T-shaped, and a number of reinforcing grooves are provided on its inner side. The reinforcing grooves are evenly distributed along the circumference of the annular reinforcing rib (4) and have an arc-shaped cross-section. The inner wall of the reinforcing groove is provided with a number of reinforcing rib strips. The reinforcing rib strips extend along the length direction of the reinforcing groove and have a trapezoidal cross-section.

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