Method capable of actively controlling hardening time of retard-bonded steel strand and steel strand embedded part

Abstract

The invention relates to a method capable of actively controlling the hardening time of a retard-bonded steel strand and a steel strand embedded part, and relates to the technical field of buildings. The method capable of actively controlling the hardening time of the retard-bonded steel strand comprises the following steps: providing a first cavity for containing a curing agent; providing a second cavity which is used for containing the slow binding agent and surrounds the first cavity; the embedded part is embedded in a reinforcement cage of the building beam, and the steel strand is tensioned; and the curing agent is controlled to flow into the second cavity from the first cavity and is mixed with the slow binder. The retard-bonded steel strand embedded part comprises a curing agent containing pipe, the curing agent containing pipe and the steel strand are jointly sleeved with a retard-bonded agent containing pipe, a second cavity is formed in the retard-bonded agent containing pipe, and rotating assemblies are arranged at the two ends of the curing agent containing pipe and can reversely rotate the two ends of the curing agent containing pipe correspondingly. The method capable of actively controlling the hardening time of the retard-bonded steel strand and the steel strand embedded part have the effect of controlling solidification of the retard-bonded agent according to needs.

Description

Technical Field

[0001] The invention belongs to the field of construction, and in particular relates to a method capable of actively controlling the hardening time of a slow-bonding slow-bonding steel strand and a steel strand embedded part. Background Art

[0002] Prestressed concrete has the advantages of improving the crack resistance of components, saving materials, increasing component stiffness, improving fatigue resistance, and adapting to large-span structures. It has been widely used in large public buildings and large-span bridges and other projects.

[0003] With the development of technology, a new type of prestressed steel strand has emerged. By coating a layer of retarding adhesive on the surface of the steel strand, it has the advantages of non-bonded prestressed steel strand during construction, and at the same time has the advantages of bonded prestressed steel strand during use, thus forming a retarded bonding steel strand. Retarded bonding steel strand can be widely used in construction projects, bridge projects, and water conservancy projects. In actual engineering use, due to the influence of construction period and environmental factors, the retarding adhesive will solidify and harden before the prestressed construction tensioning. This leads to the following problems: 1. Increase the tension resistance, resulting in prestress loss, so that the prestressed structure may not be able to meet the design stress requirements.

[0004] 2. Affect the prestressing effect, and thus affect the safety and service life of the structure.

[0005] 3. Premature hardening of the adhesive may cause changes in the bonding properties between the steel strands and concrete, affecting the overall performance of the structure.

[0006] 4. The difficulty and complexity of prestressed construction will increase, and the project will also need to take additional measures to solve the problem of increased tension resistance.

[0007] At present, there are no products and methods in China that can actively control the bonding of slow-bonding steel strand embedded parts. Therefore, there is an urgent need for a control method and steel strand embedded parts that can avoid the above-mentioned problems of slow-bonding steel strand embedded parts. Summary of the invention

[0008] We hope to reduce the tension resistance by actively controlling the hardening time of the slow-bonding steel strand, thereby meeting the stress requirement. The present application provides a method for actively controlling the hardening time of the slow-bonding steel strand and a steel strand embedded part.

[0009] In the first aspect, the present application provides a method for actively controlling the hardening time of a slow-bonding steel strand, using the following technical solution: A method for actively controlling the hardening time of a slow-bonding steel strand comprises the following steps: Providing a first cavity for containing a curing agent and distributed in the length direction of the steel strand; Providing a second cavity for containing the slow adhesive and surrounding the first cavity; The embedded slow-bonding steel strand to be released is embedded in the steel cage of the building beam, concrete is poured, and after the concrete reaches the design strength requirement, the steel strand is tensioned; The curing agent in the first cavity is controlled to flow from the first cavity into the second cavity, thereby mixing the curing agent and the slow-adhesive agent.

[0010] By adopting the above technical solution, the curing agent is placed in the first cavity in advance, and the retarding agent is placed in the second cavity. When the curing agent and the retarding agent do not need to be mixed, the two can be stored independently. When the two need to be mixed, it is only necessary to control the release of the curing agent in the first cavity into the second cavity, and then the curing of the coagulant can be controlled according to the curing time requirements, reducing the coagulation and hardening of the retarding agent before the prestressing construction tensioning. The prestressed structure can meet the requirements of stress design, ensure the overall performance of the structure, make the structure safer, and have a longer service life.

[0011] Optionally, after the step of controlling the curing agent in the first cavity to flow from the first cavity into the second cavity, the method further includes: using the cavity wall of the first cavity to stir the curing agent and the slow-adhesion agent.

[0012] By adopting the above technical solution, after the curing agent flows out from the first cavity, there is a situation where the curing agent and the binder retarder cannot be fully mixed. The cavity wall of the first cavity is used to stir the curing agent and the binder retarder. This can not only make the curing agent and the binder retarder mix evenly and reduce the occurrence of local uneven curing, but also does not require the setting of additional stirring tools, which is simple and convenient.

[0013] Optionally, the step of controlling the curing agent in the first cavity to flow from the first cavity into the second cavity includes: manipulating one end of the first cavity to rotate it forward, and simultaneously manipulating the other end of the first cavity to rotate it reversely, thereby causing multiple damage openings to appear on the first cavity and causing the curing agent to flow out from the damage openings.

[0014] By adopting the above technical solution, when the curing agent needs to flow out of the first cavity, the two ends of the first cavity are rotated in the forward and reverse directions respectively, so that the side wall of the first cavity is damaged, and the curing agent flows into the second cavity from the damaged part and contacts the slow-adhesive agent, thereby achieving the function of mixing the two.

[0015] Optionally, the step of using the cavity wall of the first cavity to stir the curing agent and the retarder includes: causing two ends of the first cavity to rotate in the same direction.

[0016] By adopting the above technical solution, the two ends of the first cavity are rotated in the same direction, so that the curing agent and the slow-adhesive agent can be stirred better.

[0017] In a second aspect, the present application provides a slow-bonding steel strand embedded part, using the aforementioned method for actively controlling the hardening time of the slow-bonding steel strand, and adopting the following technical solution: A retarding steel strand embedded part, using the above-mentioned method for actively controlling the hardening time of the retarding steel strand, comprises: a steel strand fixed by an anchor, a curing agent containing tube for forming a first cavity is arranged along the length direction of the steel strand, a retarding agent containing tube is jointly sleeved on the curing agent containing tube and the steel strand, a second cavity is formed inside the retarding agent containing tube, and rotating components are arranged at both ends of the curing agent containing tube, and the two rotating components can respectively rotate the two ends of the curing agent containing tube and make the rotation directions opposite.

[0018] By adopting the above technical solution, the retarding agent is filled between the inner wall of the retarding agent holding tube and the outer wall of the curing agent holding tube, so that the retarding agent can directly contact the outer wall of the curing agent holding tube and can contact the steel strand. When the rotating assembly is rotated, since the two ends of the curing agent holding tube rotate in opposite directions, the side wall of the curing agent holding tube will be damaged, and the curing agent released from the damaged part of the curing agent holding tube will directly contact the retarding agent, so that the curing agent and the retarding agent can be mixed as needed.

[0019] Optionally, the rotating components include an outer gear ring sleeved on the end of the steel strand, at least one gear is meshed on the outer teeth of the outer gear ring, an inner gear ring is arranged around the gear, and the outer gear ring is fixedly connected to the curing agent containing tube.

[0020] By adopting the above technical solution, the inner gear ring drives the gear to rotate, the gear drives the outer gear ring to rotate, and the outer gear ring drives the curing agent holding tube to rotate. The outer gear rings at both ends respectively drive the two ends of the curing agent holding tube to rotate in opposite directions, thereby damaging the side wall of the curing agent holding tube.

[0021] Optionally, there are multiple curing agent containing tubes which are spaced apart along the circumference of the steel strand, and each curing agent containing tube is fixedly connected to the outer gear ring.

[0022] By adopting the above technical solution, when there are multiple curing agent containing tubes that evenly surround the steel strands, the curing agent can be more fully mixed with the slow-adhesion agent around the steel strands.

[0023] Optionally, the curing agent containing tubes are arranged in an alternating grid pattern and adjacent grids have different thicknesses.

[0024] By adopting the above technical solution, due to the uneven thickness of the side wall of the curing agent containing tube, stress concentration will be generated at the junction of the thin and thick sides of the side wall, resulting in damage, but the stress concentration part of the curing agent containing tube will be completely twisted and broken.

[0025] Optionally, the curing agent is placed on the tube and a metal wire is arranged along the length direction of the tube.

[0026] By adopting the above technical solution, when the curing agent containing tube has a weak stirring function due to rupture, the metal wire can stir and mix the curing agent and the buffer binder.

[0027] Optionally, both ends of the steel strand are provided with bell-mouthed fixed ends, the inner gear ring is sleeved on the bell-mouthed fixed end and the two can rotate relative to each other, the gear is located inside the bell-mouthed fixed end, and the inner teeth of the inner gear ring pass through the bell-mouthed fixed end and mesh with the gear.

[0028] By adopting the above technical solution, the embedded part is fixed by the bell-mouth-shaped fixed end, and the inner gear ring is exposed at the bell-mouth-shaped fixed end, which can make it easier to apply force to rotate the inner gear ring and facilitate the inner gear ring to drive the gear to rotate.

[0029] In summary, the present application includes at least one of the following beneficial technical effects: when the curing agent and the retarding agent need to be mixed, the two ends of the curing agent holding tube are rotated in the opposite direction to damage the side wall of the curing agent holding tube, and the curing agent contained in the curing agent holding tube is released into the second cavity and contacts the retarding agent, and then the two are stirred, and the coagulant can be changed to solidify according to time control, which reduces the coagulation and hardening of the retarding agent before the prestressing construction tensioning. Avoid the stress loss caused by the tensioning resistance, so that the prestressed structure can meet the stress design requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the overall structure of the slow-bonding steel strand embedded part of the present application; Figure 2 is a perspective view of a slow-bonding steel strand embedded part embodying the present application; Figure 3 It is a schematic diagram of the internal structure of the slow-bonding steel strand embedded part of the present application; Figure 4 It is a schematic diagram of the structure of the curing agent release tube embodying the present application; Figure 5 It is a cross-sectional schematic diagram of a rotating assembly of a slow-bonding steel strand embedded part of the present application; Figure 6 It is a one-view diagram of the rotating assembly of the slow-bonding steel strand embedded part embodying the present application.

[0031] Description of reference numerals: 1. Steel strand; 2. Anchor; 3. Curing agent tube; 31. First cavity; 4. Retarding agent tube; 41. Second cavity; 5. Metal wire; 6. Bell-shaped fixed end; 10. Rotating assembly; 11. Outer gear ring; 12. Gear; 13. Inner gear ring. DETAILED DESCRIPTION

[0032] The following is combined with Figure 1-Figure 6 This application is described in further detail.

[0033] The embodiment of the present application discloses a method for actively controlling the hardening time of a slow-bonding steel strand.

[0034] Embodiment 1: See also Figure 1 , Figure 2 and Figure 3 , a method for actively controlling the slow bonding and hardening time of a steel strand embedded part, comprising the following steps: Step S1: providing a first cavity 31 for containing a curing agent and distributed along the length direction of the steel strand 1; Specifically, by providing a first cavity 31 along the length direction of the steel strand 1 and used to hold the curing agent, the curing agent can be pre-placed in an independent position to prevent the curing agent from contacting the slow-binder too early and causing it to solidify. The first cavity 31 can be set as one or more. When there are multiple first cavities 31 that evenly surround the steel strand 1, they can be in more sufficient contact with the slow-binder around the steel strand 1.

[0035] Step S2: providing a second cavity 41 for containing the slow adhesive and surrounding the first cavity 31; Specifically, the second cavity 41 for holding the retarder surrounds the first cavity 31. When the curing agent in the first cavity 31 flows out, it can directly contact and mix with the retarder in the second cavity 41, thereby achieving the curing of the retarder. By setting the second cavity 41, when there is no need to mix the curing agent and the retarder, the curing agent can be located in an independent position, so that the curing agent and the retarder are temporarily out of contact.

[0036] Step S3: embedding the slow-bonding steel strand embedded parts to be released in the steel cage of the building beam, pouring concrete, and tensioning the steel strand 1 after the concrete reaches the design strength requirement; Specifically, the steel strand is fixed by the anchor 2, and the steel strand provided with the first cavity 31 and the second cavity 41 is pre-buried in concrete. After the concrete reaches the design strength requirement, the steel strand is tensioned.

[0037] Step S4: Control the curing agent in the first cavity 31 to flow from the first cavity 31 into the second cavity 41, thereby mixing the curing agent and the slow-binder.

[0038] Specifically, when it is necessary to mix the curing agent and the retarding agent, the curing agent is controlled to flow out of the first cavity 31 and flow into the second cavity 41, so that the two are mixed, so as to realize the need to control the curing of the coagulant according to time, and reduce the coagulation and hardening of the retarding agent before the prestressing construction. On the one hand, it can reduce the stress loss caused by the tensioning resistance, so that the prestressed structure can meet the requirements of the stress design. On the other hand, it ensures the effect of the prestressing, and ensures the safety and service life of the structure. On the other hand, reducing the premature hardening of the retarding agent may cause changes in the bonding properties between the steel strands and the concrete, affecting the overall performance of the structure. On the other hand, it avoids the difficulty and complexity of prestressed construction, and also avoids the need to take additional measures to solve the situation of increased tensioning resistance.

[0039] Embodiment 2: The difference between this embodiment and the first embodiment is that after the step of controlling the curing agent in the first cavity 31 to flow from the first cavity 31 into the second cavity 41, the following steps are further included: Step S5: using the cavity wall of the first cavity 31 to stir the curing agent and the slow-acting binder.

[0040] Specifically, after the curing agent flows out of the first cavity 31, there is a situation where the curing agent and the binder retarder cannot be fully mixed. Using the cavity wall of the first cavity 31 to stir the curing agent and the binder retarder can not only make the curing agent and the binder retarder mix evenly and reduce the occurrence of local uneven curing, but also eliminate the need to set up additional stirring tools.

[0041] Embodiment 3: Compared with Embodiment 2, the step of controlling the curing agent in the first cavity 31 to flow from the first cavity 31 into the second cavity 41 in this embodiment includes: Step S41: controlling one end of the first cavity 31 to rotate forwardly, and controlling the other end of the first cavity 31 to rotate reversely, so that a plurality of broken openings 32 appear on the first cavity 31 and the curing agent flows out from the broken openings.

[0042] Specifically, when the curing agent needs to flow out of the first cavity 31, the two ends of the first cavity 31 are rotated in the forward and reverse directions respectively, so that the side wall of the first cavity 31 is damaged, and the curing agent flows into the second cavity 41 from the damaged part and contacts the slow-adhesive agent, thereby achieving the function of mixing the two.

[0043] Embodiment 4: Specifically, the difference between this embodiment and embodiment 3 is that after step S41, the following steps are further included: Step S42: Make the two ends of the first cavity 31 rotate in the same direction.

[0044] Specifically, after the curing agent and the bonding retarder are mixed, there is uneven mixing. Without adding any additional stirring tools, the first cavity 31 continues to rotate along the circumference formed by all the steel strands 1 to stir the curing agent and the bonding retarder at the same time.

[0045] The embodiment of the present application also discloses a slow-bonding steel strand embedded part used in the above-mentioned method capable of actively controlling the slow-bonding and hardening time of the steel strand embedded part.

[0046] Embodiment 1: See also Figure 3 , Figure 4 and Figure 5 A retarding steel strand embedded part comprises: a steel strand 1, wherein the steel strand 1 has a plurality of strands and forms a bundle, and both ends are fixed by anchors 2. A curing agent containing tube 3 for forming a first cavity 31 is arranged along the length direction of the steel strand 1, and a retarding agent containing tube 4 is sleeved on the curing agent containing tube 3 and the steel strand 1, and a second cavity 41 is formed inside the retarding agent containing tube 4. The second cavity 41 is filled with a retarding agent, and the retarding agent is filled between the inner wall of the retarding agent containing tube 4 and the outer wall of the curing agent containing tube 3, so that the retarding agent can directly contact the outer wall of the curing agent containing tube 3 and can contact the steel strand 1.

[0047] The curing agent containing tube 3 and the slow-binder containing tube 4 may be made of plastic tubes, specifically polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), polybutylene (PB), acrylonitrile-butadiene-styrene (ABS), etc.

[0048] In this embodiment, there are multiple steel strands 1, which are spliced ​​into a cylindrical shape. There can be multiple curing agent containing tubes 3. In the embodiment, there are four curing agent containing tubes 3, which surround all steel strands 1 in a ring shape, and one curing agent containing tube 3 is set every 90 degrees. There are multiple curing agent containing tubes 3, which can make the curing agent flow out evenly along the circumferential interval of the bundle of steel strands 1, and can be more fully integrated with the slow-adhesive agent around the steel strands. Please also read Figure 6 A rotating assembly 10 is provided at both ends of the curing agent containing tube 3. The two rotating assemblies 10 can respectively rotate the two ends of the curing agent containing tube 3 and make the rotation directions of the two ends opposite. The structures of the two rotating assemblies 10 are the same.

[0049] Each rotating assembly 10 includes an outer gear ring 11 sleeved on the end of the steel strand 1, and a gear 12 is meshed on the outer teeth of the outer gear ring 11. An inner gear ring 13 meshing with the gear 12 is arranged around the gear 12, and the number of gears 12 is multiple and evenly spaced along the outer gear ring 11, and the outer gear ring 11 is fixedly connected to the curing agent containing tube 3.

[0050] When the inner gear rings 13 at both ends of the curing agent holding tube 3 are rotated in the opposite direction, the inner gear ring 13 drives the gear 12 to rotate, the gear 12 drives the outer gear ring 11 to rotate, and the outer gear ring 11 drives the curing agent holding tube 3 to rotate. The outer gear rings 11 at both ends drive the two ends of the curing agent holding tube 3 to rotate in the opposite direction, thereby damaging the side wall of the curing agent holding tube 3, and the curing agent contained in the curing agent holding tube 3 is released into the second cavity 41 and contacts the slow-adhesive agent.

[0051] See also Figure 4 , the side wall thickness of the curing agent containing tube 3 is uneven, and the thinner part is the part that is easily damaged, that is, the outflow port of the curing agent. Specifically, the curing agent containing tubes 3 of the present embodiment are arranged in an alternating grid shape, and of course can also be set in other shapes such as triangles, circles, etc., not limited to grid shapes. When the rotating components 10 at both ends of the steel strand 1 are rotated (the two rotating components 10 rotate in opposite directions), the outer gear ring 11 in the rotating component 10 generates a torsional force on each curing agent containing tube 3. Due to the uneven thickness of the side wall of the curing agent containing tube 3, stress concentration will occur at the junction of the thin and thick side walls, resulting in damage, but the stress concentration part of the curing agent containing tube 3 will be completely twisted and broken.

[0052] The side wall of the curing agent holding tube 3 is damaged, and the curing agent inside is released and enters the second cavity 41 of the slow-binder holding tube 4 to contact the slow-binder. After the curing agent is released into the second cavity 41, the two rotating components 10 rotate in the same direction, driving each damaged curing agent holding tube 3 to stir the mixture of the curing agent and the slow-binder, so that the two reagents are fully integrated.

[0053] There is a 1mm wide metal wire 5 in the middle of the outer wall of the curing agent containing tube 3. The number of the metal wire 5 can be one, or multiple metal wires 5 can be evenly spaced on the curing agent containing tube 3. When the curing agent containing tube 3 is broken and the stirring function is weak, the metal wire 5 can stir and mix the curing agent and the buffer binder.

[0054] Both ends of the steel strand 1 are provided with a bell-shaped fixed end 6, which can fix the entire embedded part, and the bell-shaped shape is more convenient for fixing. The inner gear ring 13 is sleeved on the bell-shaped fixed end 6 and the two can rotate relative to each other. The gear 12 is located inside the bell-shaped fixed end 6, and the inner teeth of the inner gear ring 13 pass through the bell-shaped fixed end 6 and mesh with the gear 12.

[0055] In order to make the meshing accurate, the gear 12 can be positioned, that is, the gear 12 can only rotate on its own. The gear 12 can also be positioned without being positioned, and a housing is provided outside to prevent the gear 12 from running off.

[0056] The inner gear ring 13 can be arranged to form a certain thickness of outward protrusion at the part of the bell-shaped fixed end 6, and a groove for inserting a hand is formed on the side to facilitate its rotation. Specifically, during operation, the inner gear ring 13 can be rotated manually, or driven by a motor to rotate the inner gear ring 13, the inner gear ring 13 drives the gear 12 to rotate, the gear 12 drives the outer gear ring 11 to rotate, and the outer gear ring 11 drives the curing agent holding tube 3 to rotate, so that the curing agent holding tube 3 moves between the steel strand and the slow-adhesive holding tube 4.

[0057] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for actively controlling the hardening time of a slow-bonding steel strand, characterized in that: The steps include: Providing a first cavity (31) for containing a curing agent and distributed in the length direction of the steel strand (1); Providing a second cavity (41) for containing the slow adhesive and surrounding the first cavity (31); The slowly-bonded steel strand embedded parts to be released are embedded in the steel cage of the building beam, concrete is poured, and after the concrete reaches the design strength requirement, the steel strand (1) is tensioned; The curing agent in the first cavity (31) is controlled to flow from the first cavity (31) into the second cavity (41), thereby causing the curing agent and the slow-adhesive agent to mix.

2. The method for actively controlling the hardening time of slow-bonding steel strands according to claim 1, characterized in that: After the step of controlling the curing agent in the first cavity (31) to flow from the first cavity (31) into the second cavity (41), the step also includes: using the cavity wall of the first cavity (31) to stir the curing agent and the slow-adhesive agent.

3. The method for actively controlling the hardening time of slow-bonding steel strands according to claim 1, characterized in that: The step of controlling the curing agent in the first cavity (31) to flow from the first cavity (31) into the second cavity (41) comprises: controlling one end of the first cavity (31) to rotate it in a forward direction, and simultaneously controlling the other end of the first cavity (31) to rotate it in a reverse direction, thereby causing a plurality of broken openings (32) to appear on the first cavity (31) and causing the curing agent to flow out from the broken openings.

4. The method for actively controlling the hardening time of slow-bonding steel strands according to claim 2, characterized in that: The step of using the cavity wall of the first cavity (31) to stir the curing agent and the slow-adhesive agent comprises: causing the two ends of the first cavity (31) to rotate in the same direction.

5. A slow-bonding steel strand embedded part, using the method for actively controlling the hardening time of a slow-bonding steel strand as claimed in any one of claims 1 to 4, characterized in that: include: A steel strand (1) is fixed by an anchor (2), and a curing agent containing tube (3) for forming a first cavity (31) is arranged along the length direction of the steel strand (1). A retarding agent containing tube (4) is sleeved on the curing agent containing tube (3) and the steel strand (1), and a second cavity (41) is formed inside the retarding agent containing tube (4). Rotating assemblies (10) are arranged at both ends of the curing agent containing tube (3), and the two rotating assemblies (10) can rotate the two ends of the curing agent containing tube (3) respectively and make the rotation directions opposite.

6. The slow-bonding steel strand embedded part according to claim 5 is characterized in that: The two rotating assemblies (10) each comprise an outer gear ring (11) sleeved on the end of the steel strand (1), at least one gear (12) being meshed on the outer teeth of the outer gear ring (11), an inner gear ring (13) being arranged around the gear (12), and the outer gear ring (11) being fixedly connected to the curing agent containing tube (3).

7. The slow-bonding steel strand embedded part according to claim 6 is characterized in that: The curing agent containing tubes (3) are in plurality and are arranged at intervals along the circumference of the steel strand (1), and each curing agent containing tube (3) is fixedly connected to the outer gear ring (11).

8. The slow-bonding steel strand embedded part according to any one of claims 5 to 7, characterized in that: The curing agent containing tubes (3) are arranged in an alternating grid pattern, and adjacent grids have different thicknesses.

9. The slow-bonding steel strand embedded part according to claim 8, characterized in that: A metal wire (5) is arranged on the curing agent containing tube (3) and along its length direction.

10. The slow-bonding steel strand embedded part according to claim 6, characterized in that: Both ends of the steel strand (1) are provided with a bell-mouth-shaped fixed end (6), the inner gear ring (13) is sleeved on the bell-mouth-shaped fixed end (6) and the two can rotate relative to each other, the gear (12) is located inside the bell-mouth-shaped fixed end (6), and the inner teeth of the inner gear ring (13) pass through the bell-mouth-shaped fixed end (6) and mesh with the gear (12).

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