Stable anti-toppling pre-buried wall connecting piece

By designing limiting and locking mechanisms, the problem of wall ties being easily damaged in harsh environments is solved, achieving stable connection and safety of scaffolding, simplifying the installation process, and reducing construction costs.

CN224468763UActive Publication Date: 2026-07-07ROAD & BRIDGE SOUTH CHINA ENG CO LTD
View PDF 0 Cites 0 Cited by

Patent Information

Authority / Receiving Office
CN · China
Patent Type
Utility models(China)
Current Assignee / Owner
ROAD & BRIDGE SOUTH CHINA ENG CO LTD
Filing Date
2025-06-25
Publication Date
2026-07-07

AI Technical Summary

Technical Problem

Existing wall ties are easily damaged in harsh environments, which reduces the stability of the connection between the scaffolding and the building structure, posing a risk of collapse and threatening construction safety.

Method used

An embedded wall tie component including a limiting mechanism and a locking mechanism was designed. Through the engagement of the spiral rod and the spiral sleeve, and the sliding and clamping of the limiting block, the pipe body can be locked as it moves, thereby enhancing the binding force and preventing tipping.

Benefits of technology

It effectively prevents scaffolding from collapsing, simplifies the installation process, improves the lifespan and reliability of core components, and reduces construction costs.

✦ Generated by Eureka AI based on patent content.

Smart Images

  • Figure CN224468763U_ABST
    Figure CN224468763U_ABST
Patent Text Reader

Abstract

The utility model discloses a stable type anti -toppling pre -buried wall connecting piece relates to building engineering technical field, including pre -buried part, fixed part, cylinder one and cylinder two, the cylinder one is equipped with locking mechanism, and the cylinder two is equipped with limiting mechanism, and limiting mechanism includes rotating disc, and coaxial rotation is arranged in the cylinder two inside the one side close to cylinder one, in the utility model, when the scaffold appears toppling tendency, the pipe body will certainly move to the one side away from wall connecting piece, at this moment, locking mechanism passes through the meshing of screw rod and spiral sleeve, and the movement of pipe body is converted into driving force, makes limiting mechanism to pipe body and carries out more powerful clamping, realizes follow -up locking, can in time sense the toppling tendency of scaffold, and makes the reaction rapidly, effectively prevents the further movement of pipe body, thereby enhanced the restraint force to scaffold, reduced the risk of scaffold toppling, provided strong guarantee for construction safety.
Need to check novelty before this filing date? Find Prior Art

Description

Technical Field

[0001] This utility model relates to the field of building engineering technology, specifically to a stable, anti-tipping pre-embedded wall tie. Background Technology

[0002] Pre-embedded wall ties are connection devices in which specific components are pre-embedded inside the building structure (such as walls, columns, etc.) during construction. They are then used to connect scaffolding to the building structure. Through pre-embedding, the wall ties form a reliable connection with the building structure, providing stable support for the scaffolding, ensuring the safety of the scaffolding during construction, and preventing accidents such as scaffolding collapse. Pre-embedded wall ties generally have good load-bearing capacity and stability, and can adapt to different construction environments and scaffolding erection requirements.

[0003] In the construction industry, scaffolding is a common temporary facility used to provide working platforms and material storage space for construction workers. The connection between existing wall ties and scaffolding is usually achieved through connectors. However, in actual construction, the construction site environment is often harsh. Due to the influence of natural factors such as wind and rain erosion and high temperature and sunlight, connectors exposed to such environments for a long time are more susceptible to structural damage, such as rust. As the service time increases, the binding force of the connectors on the scaffolding will gradually decrease, resulting in a decrease in the stability of the connection between the scaffolding and the building structure, which poses a risk of collapse and seriously threatens the lives of construction workers and the smooth progress of the project.

[0004] In view of the above, this application is hereby submitted. Utility Model Content

[0005] The purpose of this utility model is to provide a stable, anti-tipping, pre-embedded wall tie to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, this utility model provides a stable anti-tipping pre-embedded wall tie, including a pre-embedded component, a fixing component, a first cylinder and a second cylinder. The first cylinder is equipped with a locking mechanism, and the second cylinder is equipped with a limiting mechanism. The limiting mechanism includes:

[0007] A rotating disk is coaxially rotatably disposed inside the second cylinder on the side close to the first cylinder. Multiple limiting blocks are slidably disposed on the side wall away from the first cylinder, arranged in a ring array about the axis of the rotating disk. The same fixed disk is slidably disposed on the side of the multiple limiting blocks away from the rotating disk. A sliding channel 1 that runs through the axis is opened on the side wall of the rotating disk and the fixed disk that are close to each other.

[0008] An internal gear ring is coaxially fixed to the side wall of the rotating disk away from the limiting block. Multiple gears are meshed on its inner side and arranged in a ring array about the axis of the rotating disk. A spiral sleeve is coaxially fixed on the side wall away from the rotating disk. The spiral sleeve passes through the second cylinder and is rotatably connected to each other. The spiral sleeve is connected to the locking mechanism inside the first cylinder. Each of the multiple limiting blocks has an arc-shaped notch on the side wall that is close to each other. The arc wall inside the notch is covered with a material to enhance friction.

[0009] Furthermore, the rotating disk has multiple arc-shaped grooves arranged in a circular array about the axial direction of the rotating disk on one side wall near the fixed disk. One end of the groove is oriented towards the axis of the sliding channel, and the other end is bent towards the outer edge of the rotating disk. The fixed disk has multiple grooves arranged in a circular array about the axial direction of the limiting blocks and extending radially along the fixed disk on one side wall near the rotating disk. The multiple grooves, grooves, and limiting blocks correspond one-to-one. The fixed disk is fixed to the inner arc wall of the cylinder. The cylinder has a sliding channel 2 extending through its axial side wall. The sliding channel 1 and sliding channel 2 are coaxial and interconnected. A sliding channel 3 is extending through the center of one side wall near the cylinder, and the length direction of the sliding channel 3 is consistent with that of the sliding channel 1.

[0010] Furthermore, the fixing member is fixed to the embedded part, the first cylinder and the second cylinder are fixedly connected to each other, the first cylinder is threaded to the outside of the fixing member, the tube is slidably disposed in the first sliding channel and the second sliding channel, the ends of the fixing member and the tube are coaxial and close to each other and abut against each other, and the locking mechanism disposed in the first cylinder includes a plurality of wedge-shaped blocks arranged in a ring array about the axis of the first cylinder and slidably disposed on the inner arc wall of the first cylinder.

[0011] Furthermore, multiple sliding grooves 3 are arranged in a ring array along the axial direction of the cylinder 1 on the inner arc wall of the cylinder 1. Each of the multiple sliding grooves 3 corresponds to one of the multiple spiral sleeves. A reset spring is fixed to the side of the wedge block near the inner wall of the sliding groove 3. A slider is fixed to the end of the reset spring away from the wedge block. Both the wedge block and the slider slide in the sliding groove 3. The sliding groove 3 and the sliding channel 3 are interconnected. A sliding channel 4 is opened through the side of the sliding groove 3 near the spiral sleeve. The sliding channel 4 is interconnected with the sliding groove 3 but not directly connected to the sliding channel 3. The length direction of the sliding channel 4 is consistent with the length direction of the sliding channel 3.

[0012] Furthermore, a fixing rod is fixed on the side wall of the wedge block near the second cylinder, and a spiral rod is coaxially fixed on the side wall of the fixing rod away from the wedge block. Both the fixing rod and the spiral rod are slidably disposed in the sliding channel four. The inner side of the spiral sleeve is provided with a spiral channel that is coaxial with the spiral rod and can mesh with each other. The end of the spiral rod away from the fixing rod meshes with the inner side of the spiral sleeve. Multiple limiting holes are provided on the outer arc wall of the tube near the fixing member, arranged in a ring array about the tube axis. The depth direction of the limiting holes is opened along the radial direction of the tube. The side of the wedge block near the axis of the first cylinder is inclined. The multiple wedge blocks correspond one-to-one with the multiple limiting holes, and the wedge blocks can be inserted into the limiting holes.

[0013] Compared with the prior art, the beneficial effects of this utility model are:

[0014] 1. Through the cooperation of the limiting mechanism and the locking mechanism, when the scaffolding shows a tendency to tilt, the pipe will inevitably move away from the wall tie. At this time, the locking mechanism converts the movement of the pipe into driving force through the engagement of the helical rod and the helical sleeve, so that the limiting mechanism can clamp the pipe more forcefully, achieving locking as it moves. It can detect the tendency of the scaffolding to tilt in time and react quickly, effectively preventing the pipe from moving further, thereby enhancing the binding force on the scaffolding, reducing the risk of scaffolding tilting, and providing strong protection for construction safety.

[0015] 2. Compared to the complex installation steps of traditional wall ties, this design simplifies the installation process, making it more convenient and efficient, saving construction time and labor costs. At the same time, the core components of this design are not directly exposed to the external environment, making them less susceptible to interference from harsh external environments, thereby improving the service life and reliability of the core components. This allows the wall tie to be disassembled and reused, further reducing construction costs. Attached Figure Description

[0016] Figure 1 An exploded view of the overall structure of a stable, anti-tipping embedded wall tie;

[0017] Figure 2 This is a schematic diagram showing the positional relationship between cylinder one and cylinder two in a type of stable, anti-tipping embedded wall tie.

[0018] Figure 3 This is a cross-sectional view of the internal structure of a core of a pre-embedded wall tie for a stable anti-tipping system.

[0019] Figure 4 Structural explosion of a limiting mechanism in a stable, anti-tipping pre-embedded wall tie. Figure 1 ;

[0020] Figure 5Structural explosion of a limiting mechanism in a stable, anti-tipping pre-embedded wall tie. Figure 2 ;

[0021] Figure 6 This is a schematic diagram of the overall structure of a stable, anti-tipping embedded wall tie.

[0022] In the picture:

[0023] 10. Embedded parts; 11. Fasteners; 12. Cylinder body one; 13. Cylinder body two; 14. Pipe body;

[0024] 141. Limiting hole;

[0025] 20. Wedge block; 21. Fixing rod; 22. Helical rod; 23. Helical sleeve; 24. Gear; 25. Internal gear ring;

[0026] 30. Rotating disc; 31. Limiting block; 32. Fixed disc. Detailed Implementation

[0027] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0028] Please see the appendix Figure 1 To be continued Figure 5 This utility model provides a stable anti-tipping pre-embedded wall tie: including a pre-embedded part 10, a fixing part 11, a first cylinder 12, and a second cylinder 13. The first cylinder 12 is provided with a locking mechanism, and the second cylinder 13 is provided with a limiting mechanism. The limiting mechanism includes:

[0029] The rotating disk 30 is coaxially rotatably disposed inside the second cylinder 13 on the side close to the first cylinder 12. Multiple limiting blocks 31 are slidably disposed on the side wall away from the first cylinder 12, arranged in a ring array about the axis of the rotating disk 30. The same fixed disk 32 is slidably disposed on the side of the multiple limiting blocks 31 away from the rotating disk 30. A sliding channel 1 that runs through the axis is opened on the side wall of the rotating disk 30 and the fixed disk 32 that are close to each other.

[0030] An internal gear ring 25 is coaxially fixed on the side wall of the rotating disk 30 away from the limiting block 31. Multiple gears 24 are meshed on its inner side and arranged in a ring array about the axis of the rotating disk 30. A spiral sleeve 23 is coaxially fixed on the side wall of the gear 24 away from the rotating disk 30. The spiral sleeve 23 passes through the second cylinder 13 and is rotatably connected to each other. The spiral sleeve 23 is connected to the locking mechanism inside the first cylinder 12.

[0031] The rotating disk 30 has multiple arc-shaped sliding grooves arranged in a circular array about the axial direction of the rotating disk 30 on one side wall near the fixed disk 32. One end of the sliding groove is set towards the axis of the sliding channel, and the other end is bent towards the outer edge of the rotating disk 30. The fixed disk 32 has multiple sliding grooves arranged in a circular array about the axial direction of the limiting block 31 and extending radially along the fixed disk 32 on one side wall near the rotating disk 30. The multiple sliding grooves, multiple sliding grooves, and multiple limiting blocks 31 correspond one-to-one.

[0032] The fixed plate 32 is fixed on the inner arc wall of the second cylinder 13. The second cylinder 13 has a sliding channel 2 through it along its axial side wall. The first sliding channel and the second sliding channel are coaxially arranged and interconnected. The first cylinder 12 has a sliding channel 3 through it at the center of one side wall near the second cylinder 13. The third sliding channel is in the same length direction as the first sliding channel.

[0033] The fixing member 11 is fixed to the embedded part 10. The first cylinder 12 and the second cylinder 13 are fixedly connected to each other. The first cylinder 12 is threaded to the outside of the fixing member 11. The tube 14 is slidably disposed in the first sliding channel and the second sliding channel. The ends of the fixing member 11 and the tube 14 are coaxial and close to each other. The locking mechanism disposed in the first cylinder 12 includes a plurality of wedge blocks 20 arranged in a ring array about the axis of the first cylinder 12 and slidably disposed on the inner arc wall of the first cylinder 12.

[0034] It should be noted that the limiting mechanism is used to form a stable clamp on the tube 14 and can adapt to tubes 14 of different diameters. It has a wide range of applications. Reducing the tube 14 of a specific size requires a specific type of connector.

[0035] The embedded part 10 and the fastener 11 can be regarded as an integral structure. The end of the outer arc wall of the fastener 11 away from the embedded part 10 is provided with a thread for threaded connection with the cylinder 12. The thread has a good self-locking effect, and since the overlap length of the fastener 11 and the cylinder 12 is large after connection, the connection here is stable.

[0036] When the tube body 14 moves away from the fixed part 11 and tends to tilt, the wedge block 20 in the locking mechanism will be moved by the action of the tube body 14, which will drive the spiral rod 22 to rotate. The spiral rod 22 meshes with the spiral sleeve 23 to drive the spiral sleeve 23 to rotate. The spiral sleeve 23 drives the gear 24 to rotate. The gear 24 meshes with the internal gear ring 25, thereby driving the rotating disk 30 to rotate.

[0037] When the rotating disk 30 rotates, since the first sliding groove on it is arc-shaped and the second sliding groove is arranged radially along the fixed disk 32, the first sliding groove cooperates with the limiting block 31, so that the limiting block 31 slides along the second sliding groove on the fixed disk 32. That is, the rotation of the rotating disk 30, together with the first sliding groove, provides power for the movement of the limiting block 31. The movement trajectory of the fixed disk 32 and the two-dimensional limiting block 31 of the sliding groove is limited and guided, thereby causing multiple limiting blocks 31 to converge towards the center synchronously, clamping the tube 14 more forcefully, preventing it from moving further, and achieving the effect of locking as it moves.

[0038] Please see the appendix Figure 1 To be continued Figure 5 This utility model provides a technical solution: multiple sliding grooves 3 are provided on the inner arc wall of the cylinder 12 in a ring array about the axial direction of the cylinder 12. The multiple sliding grooves 3 correspond one-to-one with the multiple spiral sleeves 23. A reset spring is fixed on the side of the wedge block 20 near the inner wall of the sliding groove 3. A slider is fixed on the end of the reset spring away from the wedge block 20. The wedge block 20 and the slider slide in the sliding groove 3. The sliding groove 3 and the sliding channel 3 are interconnected. A sliding channel 4 is provided through the side of the sliding groove 3 near the spiral sleeve 23. The sliding channel 4 is interconnected with the sliding groove 3 but not directly connected to the sliding channel 3. The length direction of the sliding channel 4 is consistent with the length direction of the sliding channel 3.

[0039] A fixing rod 21 is fixed on the side wall of the wedge block 20 near the cylinder 2 13. A spiral rod 22 is coaxially fixed on the side wall of the fixing rod 21 away from the wedge block 20. The fixing rod 21 and the spiral rod 22 are slidably arranged in the sliding channel 4. The inner side of the spiral sleeve 23 is provided with a spiral channel that is coaxial with the spiral rod 22 and can mesh with each other. The end of the spiral rod 22 away from the fixing rod 21 meshes with the inner side of the spiral sleeve 23.

[0040] Multiple limiting holes 141 are provided on the outer arc wall of the tube body 14 near the end of the fixing member 11, arranged in a ring array about the axial direction of the tube body 14. The depth direction of the limiting holes 141 is opened radially along the tube body 14. The end of the wedge block 20 near the axis of the first cylinder 12 is inclined on the side near the second cylinder 13. The multiple wedge blocks 20 correspond one-to-one with the multiple limiting holes 141 and the wedge blocks 20 can be inserted into the limiting holes 141.

[0041] Each of the multiple limiting blocks 31 has an arc-shaped recess on one side wall that is close to each other, and the arc wall inside the recess is covered with a material to enhance friction.

[0042] It should be noted that: the end of the tube 14 with the limiting hole 141 is inserted into the second cylinder 13 and then into the first cylinder 12 until it abuts against the end of the fixing member 11. Since the wedge block 20 is fixed with a reset spring on the side near the inner wall of the slide groove 3, and the end of the reset spring away from the wedge block 20 is fixed with a slider, and both the wedge block 20 and the slider slide in the slide groove 3, when the tube 14 is inserted, the inclined surface of the end of the wedge block 20 abuts against it, forcing the wedge block 20 to retract. At this time, the reset spring is compressed and stores energy until the limiting hole 141 aligns with the wedge block 20. The wedge block 20 loses its restriction, and the reset spring releases the stored energy to drive the wedge block 20 into the limiting hole 141. Since the side wall of the wedge block 20 near the sliding channel 3 away from the second cylinder 13 is a vertical plane, this side wall of the wedge block 20 can form a stable abutment with the limiting hole 141.

[0043] At this time, the limiting mechanism has not yet clamped the tube 14. Therefore, after confirming that the connection is completed, pull the tube 14 out in the opposite direction so that the limiting mechanism can retract to initially clamp the tube 14.

[0044] During disassembly, simply remove the entire assembly that is fixedly connected to the first cylinder 12 from the fixing member 11. Then, continue to push the tube 14 toward one end of the limiting hole 141 to remove the tube 14 from the assembly that is fixedly connected to the first cylinder 12 and the second cylinder 13. The operation is simple and can be reused.

[0045] Working principle:

[0046] During installation, the tube body 14 is inserted into the second cylinder 13 and then into the first cylinder 12, abutting against the fixing part 11. The inclined surface at the end of the wedge block 20 is compressed and retracts, the reset spring stores force, and after the limiting hole 141 is aligned with the wedge block 20, the reset spring is released, allowing the wedge block 20 to be inserted into the limiting hole 141. At this time, the limiting mechanism does not clamp the tube body 14. Pulling the tube body 14 out in the opposite direction allows the limiting mechanism to initially clamp it.

[0047] When the tube body 14 moves away from the fixed part 11 (causing a tilting tendency), the wedge block 20 is squeezed to move it, which drives the fixed rod 21 and the spiral rod 22 to slide in the sliding channel four. The spiral rod 22 meshes with the spiral sleeve 23 to drive the gear 24 to rotate. The gear 24 meshes with the internal gear ring 25 to drive the rotating disk 30 to rotate. Through the first sliding groove, it cooperates with the limiting block 31, so that the limiting block 31 slides and gathers along the second sliding groove. The tube body 14 is clamped by the arc-shaped notch and the friction-enhancing material to prevent it from moving further, thus achieving locking as it moves.

[0048] During disassembly, remove the cylinder body 12 and cylinder body 2 13 as a whole, and push the tube body 14 to remove it.

Claims

1. A stable anti-tipping pre-embedded wall tie, comprising an embedded part (10), a fixing part (11), a first cylinder (12) and a second cylinder (13), characterized in that: The first cylinder (12) is provided with a locking mechanism, and the second cylinder (13) is provided with a limiting mechanism. The limiting mechanism includes: The rotating disk (30) is coaxially rotatably disposed inside the second cylinder (13) on the side close to the first cylinder (12). Multiple limiting blocks (31) are slidably disposed on the side wall away from the first cylinder (12), arranged in a ring array about the axis of the rotating disk (30). The same fixed disk (32) is slidably disposed on the side of the multiple limiting blocks (31) away from the rotating disk (30). A sliding channel 1 that runs through the axis is opened on the side wall of the rotating disk (30) and the fixed disk (32) that are close to each other. An internal gear ring (25) is coaxially fixed on the side wall of the rotating disk (30) away from the limiting block (31). Multiple gears (24) arranged in a ring array about the axial direction of the rotating disk (30) are meshed on its inner side. A spiral sleeve (23) is coaxially fixed on the side wall of the gear (24) away from the rotating disk (30). The spiral sleeve (23) is set through the second cylinder (13) and rotates and is connected to each other. The spiral sleeve (23) is connected to the locking mechanism in the first cylinder (12).

2. The pre-embedded wall tie for stable anti-tipping as described in claim 1, characterized in that: On one side wall of the rotating disk (30) near the fixed disk (32), there are multiple arc-shaped grooves arranged in a ring array about the axial direction of the rotating disk (30). One end of the groove is set towards the axis of the sliding channel, and the other end is bent towards the outer edge of the rotating disk (30). On one side wall of the fixed disk (32) near the rotating disk (30), there are multiple grooves arranged in a ring array about the axial direction of the limiting block (31) and extending radially along the fixed disk (32). The multiple grooves, the multiple grooves and the multiple limiting blocks (31) correspond one to one.

3. The pre-embedded wall tie for stable anti-tipping as described in claim 1, characterized in that: The fixed plate (32) is fixed on the inner arc wall of the second cylinder (13). The second cylinder (13) has a sliding channel 2 through it along its axial side wall. The first sliding channel and the second sliding channel are coaxially arranged and interconnected. The first cylinder (12) has a sliding channel 3 through it at the center of the side wall near the second cylinder (13). The third sliding channel is in the same length direction as the first sliding channel.

4. The pre-embedded wall tie for stable anti-tipping as described in claim 1, characterized in that: The fixing member (11) is fixed on the embedded part (10). The first cylinder (12) and the second cylinder (13) are fixedly connected to each other. The first cylinder (12) is threaded to the outside of the fixing member (11). The tube (14) is slidably disposed in the first sliding channel and the second sliding channel. The ends of the fixing member (11) and the tube (14) are coaxial and close to each other. The locking mechanism disposed in the first cylinder (12) includes a plurality of wedge blocks (20) arranged in a ring array about the axis of the first cylinder (12) and slidably disposed on the inner arc wall of the first cylinder (12).

5. A stable anti-tipping embedded wall tie as described in claim 4, characterized in that: Multiple sliding grooves 3 are arranged in a ring array along the axial direction of the cylinder 1 (12) on the inner arc wall of the cylinder 1 (12). Each of the multiple sliding grooves 3 corresponds to one of the multiple spiral sleeves (23). A reset spring is fixed on the side of the wedge block (20) near the inner wall of the sliding groove 3. A slider is fixed on the end of the reset spring away from the wedge block (20). The wedge block (20) and the slider slide in the sliding groove 3. The sliding groove 3 and the sliding channel 3 are interconnected. A sliding channel 4 is opened through the side of the sliding groove 3 near the spiral sleeve (23). The sliding channel 4 is interconnected with the sliding groove 3 but not directly connected to the sliding channel 3. The length direction of the sliding channel 4 is consistent with the length direction of the sliding channel 3.

6. A stable anti-tipping embedded wall tie as described in claim 4, characterized in that: A fixing rod (21) is fixed on one side wall of the wedge block (20) near the second cylinder (13). A spiral rod (22) is coaxially fixed on one side wall of the fixing rod (21) away from the wedge block (20). The fixing rod (21) and the spiral rod (22) are slidably arranged in the sliding channel four. The inner side of the spiral sleeve (23) is provided with a spiral channel that is coaxial with the spiral rod (22) and can mesh with each other. The end of the spiral rod (22) away from the fixing rod (21) meshes with the inner side of the spiral sleeve (23).

7. A stable anti-tipping embedded wall tie as described in claim 4, characterized in that: Multiple limiting holes (141) are provided on the outer arc wall of the tube (14) near the fixing member (11) at one end. They are arranged in a ring array about the axial direction of the tube (14). The depth direction of the limiting holes (141) is opened radially along the tube (14). The wedge block (20) near the axis of the first cylinder (12) has an inclined surface on the side near the second cylinder (13). The multiple wedge blocks (20) correspond one-to-one with the multiple limiting holes (141) and the wedge blocks (20) can be inserted into the limiting holes (141).

8. A stable anti-tipping embedded wall tie as described in claim 1, characterized in that: Each of the multiple limiting blocks (31) has an arc-shaped recess on one side wall that is close to each other, and the arc wall inside the recess is covered with a material that enhances friction.