Traction device of covering net hook welding machine

Abstract

The utility model belongs to net covering hook welding equipment, and particularly relates to a traction device of a net covering hook welding machine. Comprising a front stand column and a rear stand column which are distributed on the two sides of the front end and the rear end of a material conveying channel, the front stand column and the rear stand column are in sliding fit with the synchronous and adjustable interval through a connecting frame and a movable frame, and the movable frame is in reciprocating fit with a main rack in the direction perpendicular to the material conveying channel; the air cylinder drives the front stand column and the rear stand column to do synchronous reciprocating motion in the material conveying direction through the crank-link mechanism and the linkage rod, the stroke of the crank-link mechanism is matched with the length of the main rib net unit grid and the auxiliary rib net unit grid, and self-resetting traction hooks are assembled on the inner sides of the front stand column and the rear stand column and fixing rods arranged on the outer side of the front stand column at intervals. The utility model effectively overcomes the problems of inaccurate transmission ratio, weak bearing capacity and the like in the prior art, and has the advantages of accurate transmission ratio, capability of processing net racks with different thickness specifications, convenience for realizing rapid standardized operation and the like.

Description

Technical Field

[0001] This utility model relates to mesh covering hook welding equipment, and specifically refers to a traction device for a mesh covering hook welding machine. Background Technology

[0002] The main structure of the composite steel mesh insulated exterior wall panel consists of main reinforcing meshes on both sides of a graphite polystyrene board, with secondary reinforcing meshes spaced apart on the outside of the main reinforcing meshes to form a frame. The two ends of the steel wires pass through the graphite polystyrene board and are welded to the main reinforcing meshes and secondary reinforcing meshes respectively. The steel wire mesh is attached to the surface of the secondary reinforcing meshes. The only difference between the composite steel mesh insulated interior wall panel and the composite steel mesh insulated exterior wall panel is that the latter does not contain graphite polystyrene board. Because of the impact of concrete during use, the steel wires are prone to detaching from the main and secondary reinforcing meshes. Therefore, bending the exposed ends of the steel wires on the surface of the secondary reinforcing mesh is an essential structure in existing products. This structure can maintain the stability of the product structure even after the steel wires detach from the main and secondary reinforcing meshes. Currently, there is no dedicated equipment to complete the bending operation. The bending operation is mainly completed manually using simple non-standard tools. If equipment is used to automate the production of composite steel mesh insulation wall panels, welding the steel wires to the secondary and main reinforcing meshes is an essential step in completing the above operation. Since there are many reports on wire breaking and welding equipment in existing literature, and the equipment is mature, the design of the matching traction device becomes the key technology to complete the above automated operation. At the same time, the design of the traction device also needs to consider the effective connection with the subsequent steel wire bending process.

[0003] The applicant has retrieved the following existing patent documents:

[0004] Patent document CN213564459U discloses a vertical steel wire mesh insulation board forming machine. The machine adopts a vertical structure. The conveying device 1 works by a drive motor 13 driving a belt 14 through a pulley, which in turn rotates rollers 12. When the polystyrene board is placed on the rollers 12, the rollers 12 move the board. The existing technology has several problems: First, the transmission ratio is not constant. Belt drives rely on friction, which leads to elastic slippage and inaccurate transmission ratios. Second, there is slippage loss and low efficiency. During operation, the belt slips due to the difference in tension and deformation on both sides of the pulley, causing speed loss and affecting transmission efficiency. Third, the belt life is short. The belt material is prone to aging and may stretch or crack after prolonged use, requiring regular inspection and replacement. Fourth, the load-bearing capacity is limited. Belt drives have low load-bearing capacity and are not suitable for heavy-duty or high-power transmission applications. Fifth, they are sensitive to environmental conditions. Belt drives are sensitive to ambient temperature and humidity, and their performance may degrade in high-temperature or humid environments. Sixth, the traction mechanism does not specify the compatibility of main rib meshes with different thicknesses, therefore this existing technology is not suitable for processing space frames with different thicknesses. Since subsequent welding and bending operations require high precision at the weld points and bends, the aforementioned existing technology cannot ensure that the feeding process meets the precision requirements of subsequent operations.

[0005] The applicant has not found any literature reports that are the same as or similar to this utility model in domestic patent databases. Summary of the Invention

[0006] The purpose of this invention is to provide a traction device for a wire mesh bending and welding machine, which can effectively achieve synchronous step-by-step traction of the main and secondary reinforcing meshes, ensuring the consistency of the forward frequency and amplitude of the main and secondary reinforcing meshes and the mesh sheet, and can perform traction operations on main and secondary reinforcing meshes of different thicknesses. This provides reliable structural support for the precise positioning and standardized rapid operation of subsequent wire feeding, welding wire, and bending.

[0007] The overall technical concept of this utility model is:

[0008] The traction device of the mesh bending and welding machine includes front and rear columns distributed on both sides of the front and rear ends of the material conveying channel. The front columns and the rear columns are arranged opposite each other and slide in a synchronously adjustable manner through a connecting frame and a movable frame. The movable frame reciprocates with the main frame in a direction perpendicular to the material conveying channel. The connecting frame rolls with the main frame through rollers. The cylinder drives the front and rear columns to reciprocate synchronously in the direction of the material conveying channel through a crank-connecting rod mechanism and a linkage rod. The stroke of the crank-connecting rod mechanism is an integer multiple of the length of the main or secondary rib mesh cell. Traction hooks with self-resetting function are installed on the inner side of the front column, the inner side of the rear column, and the fixed rods spaced apart on the outer side of the front column. The self-resetting direction is towards the material conveying channel, and the bending direction of the traction hook is towards the discharge direction and is adapted to the main or secondary rib mesh.

[0009] The applicant needs to explain that the main reason for the different positions of the traction hooks on the front and rear columns is that the steel wire has not yet welded the main and secondary reinforcing meshes together during feeding. The main and secondary reinforcing meshes can be connected by a simple connector. Once it enters the traction station, the subsequent traction action can be completed through a step-by-step traction operation. Therefore, the front columns on both sides of the material conveying channel have two layers of traction hooks on their inner and outer sides. This is mainly to ensure synchronous traction of the main reinforcing mesh and the secondary reinforcing meshes spaced apart from it, while reducing the traction load. The main reason for the single layer of traction hooks on the rear column is that the steel wire has already welded the main and secondary reinforcing meshes together and completed the bending operation of the exposed steel wires. Therefore, the traction operation can be achieved by hooking the secondary reinforcing mesh on the outside of the mesh frame. The main reason for designing the stroke of the crank connecting rod mechanism to be an integer multiple of the length of the main or secondary reinforcing mesh cells is to facilitate the standardized and rapid operation of subsequent welding and bending.

[0010] Other specific technical solutions of this utility model include:

[0011] The main purpose of the movable frame reciprocating with the main frame along a direction perpendicular to the material conveying direction is twofold: first, to accommodate main rib meshes of different thicknesses, thus broadening the product processing range; and second, to allow for traction operations on main and secondary rib meshes and mesh sheets of different thicknesses after the traction mechanism is adjusted. To achieve these objectives, and to ensure convenient adjustment of the distance between the movable frame and the main frame while allowing flexible coordination between adjacent components, the preferred technical implementation is that the movable frame reciprocates with the main frame via a first guide rail and guide wheels that roll with it. The relative movement between the movable frame and the main frame is achieved through a drive mechanism, which includes, but is not limited to, a screw feed mechanism, a rack and pinion mechanism, or a parallelogram mechanism.

[0012] The front columns are arranged opposite each other and slide together with a connecting frame and a movable frame to achieve synchronously adjustable spacing. The main purpose is to allow the front columns to effectively accommodate main ribs of different thicknesses, while the traction hook can pull the main and secondary ribs and mesh sheets of different thicknesses. The preferred technical means is that the front columns include front outer columns and front inner columns located on both sides of the front end of the material conveying channel. The front inner column is set on the movable frame and reciprocates with it along the direction of the material conveying channel. The front outer columns and the front inner columns slide together perpendicular to the direction of the material conveying channel through the guide rod on the connecting frame.

[0013] The main function of the cylinder, which drives the front and rear columns to reciprocate synchronously along the material conveying direction through the crank-connecting rod mechanism and linkage rod, is to provide structural support for subsequent welding and bending operations. To facilitate flexible cooperation between the front column and the movable frame, and to enable the front inner column to reciprocate flexibly under the action of the crank-connecting rod, the preferred technical means is that the front inner column reciprocates with the movable frame along the material conveying channel direction through a sliding sleeve and a guide rod set on the movable frame.

[0014] To improve the synchronization of the up-and-down movements of the front outer column and the front inner column, and to facilitate the synchronous operation of the traction hook for the main and auxiliary reinforcing mesh and mesh panels, thereby meeting the requirements of the same frequency and amplitude for the conveying of the main and auxiliary reinforcing mesh and mesh panels, and also to facilitate the synchronous and effective transmission of the rear column, the preferred technical implementation is that the lower ends of the front outer column and the front inner column are respectively connected to the power output end of the first crank-connecting rod mechanism arranged opposite to each other, the power output of the cylinder is connected to the power input end of the first crank-connecting rod mechanism, and the upper ends of the front outer column and the front inner column are respectively connected to the power output end of the second crank-connecting rod mechanism arranged opposite to each other. The first crank-connecting rod mechanism and the second crank-connecting rod mechanism are linked through the first connecting rod.

[0015] To ensure the synchronization of the crank-connecting rod mechanism's movements, the preferred technical approach is to link the opposing second crank-connecting rod mechanisms through a second connecting rod.

[0016] To enable the traction hook on the rear column to perform traction operations on the main and secondary reinforcing meshes and mesh sheets of different thicknesses, and to improve the flexibility of movement between adjacent components, the preferred technical means is that the rear column includes an outer rear column and an inner rear column located on both sides of the front end of the material conveying channel. The inner rear column is set on the movable frame and reciprocates with it along the direction of the material conveying channel. The outer rear column and the inner rear column are slidably assembled perpendicular to the direction of the material conveying channel through the guide rod on the connecting frame. The inner rear column reciprocates with the movable frame along the direction of the material conveying channel through the sliding sleeve and the guide rod set on the movable frame.

[0017] To facilitate the assembly of the traction hook with the front and rear columns, and to effectively achieve the self-resetting function of the traction hook, the preferred technical means is that a fixing plate is installed on the inner side of the front and rear columns, the end of the traction hook is rotatably assembled with the fixing plate, and a reset spring is provided at the junction of the middle of the traction hook and the fixing plate.

[0018] The main function of the linkage is to ensure the synchronization of the front and rear columns while ensuring effective power transmission. The preferred technical implementation is that the linkage adopts a third link between the connecting frame assembled at the junction of the front outer column and the front inner column, and between the connecting frame at the junction of the outer column and the rear inner column.

[0019] To ensure effective coordination between the traction hooks and the main and secondary reinforcing meshes, the preferred technical means are that the traction hooks on the inner side of the front column and the inner side of the rear column are adapted to the main reinforcing mesh; and the traction hooks installed on the fixed rods spaced apart on the outer side of the front column are adapted to the secondary reinforcing mesh.

[0020] This invention works as follows:

[0021] The main rib mesh is placed between the front inner column and the front outer column. By adjusting the drive mechanism between the main frame and the movable frame, the distance between the main frame and the movable frame is adjusted to the correct position under the action of the drive mechanism, the first guide rail and the guide wheel. The front inner column is driven by the movable frame and moves to the correct position on the connecting frame along the direction perpendicular to the material conveying direction to complete the adjustment of the front inner column and the front outer column. The principle of adjusting the distance between the rear inner column and the rear outer column is the same. The mesh and secondary reinforcing mesh are placed from the inside out in the gap between the front inner column and the fixed rod. The secondary reinforcing mesh is fixed to the front end of the main reinforcing mesh using fasteners. The cylinder is then activated to reciprocate. The cylinder's power output drives the lower end of the front column via the first crank-connecting rod mechanism. The sliding sleeve on the outer side of the lower end of the front column reciprocates along the guide rod. The rollers on the connecting frame at the lower end of the front column roll along the lower surface of the material conveying channel. The upper end of the front column is synchronously driven by the first connecting rod and the second crank-connecting rod mechanism. The rear column is driven by the third connecting rod. The upper end of the front column, the upper end of the rear column, and the outer side of the lower end of the rear column are all affected. The sliding sleeve reciprocates along the guide rod. The rollers on the connecting frames at the upper and lower ends of the front and rear columns roll along the second guide rail or the surface of the material conveying channel, respectively. The traction hook retracts to the end of its stroke in the opposite direction to the material conveying. Under the action of the return spring, the traction hook springs back to its original position, hooks the main rib mesh and the secondary rib mesh, and drives them to be conveyed along the direction of the material conveying channel to the end of its stroke. Under the action of the front and rear columns, the traction hook retracts. The pressure of the main rib mesh and the secondary rib mesh causes the return spring to contract, completing one working cycle. The traction hook returns to the end of its stroke to start the next working cycle.

[0022] The technological advancements achieved by this utility model are as follows:

[0023] 1. This utility model uses a traction hook with a self-resetting function as the action execution component of the traction device. First, it can realize unidirectional traction of the main and secondary ribs and mesh, thereby ensuring smooth material conveying. Second, the action execution mechanism uses mechanical components as the main structure, with good component assembly reliability, stable structure and low failure rate. Third, the traction hook is easy to cooperate with the main and secondary ribs, improving the reliability of traction action and facilitating automated control.

[0024] 2. This utility model adopts a structural and assembly design of front and rear columns, movable frame and main frame. First, it facilitates the arrangement of the traction hook while meeting the load requirements. Second, it facilitates cooperation with the main frame and movable frame to meet the requirements of motion transmission. Third, the structural design of the front and rear columns in conjunction with the crank connecting rod mechanism and linkage rod facilitates synchronous action to reduce the conveying load of the traction hook.

[0025] 3. The front column of this utility model adopts an inner and outer column structure with a double-layer traction hook. First, it can be designed according to the material conditions to ensure the synchronous traction of the main reinforcement mesh and the secondary reinforcement mesh. Second, it effectively reduces the load on the traction hook and reduces the possibility of damage to the main reinforcement mesh or the secondary reinforcement mesh due to excessive tension.

[0026] 4. This utility model adopts a cylinder-driven structure with an auxiliary crank connecting rod stroke. Firstly, it simplifies the drive and transmission mechanism while ensuring the reliability of the drive. Secondly, it has a relatively accurate transmission ratio, ensuring the accuracy of transmission and providing structural protection for operations such as traction, wire welding, and bending. Attached Figure Description

[0027] The accompanying drawings of this utility model are as follows:

[0028] Figure 1 This is a schematic diagram of the structure of this utility model.

[0029] Figure 2 yes Figure 1 Top view.

[0030] Figure 3 This is a perspective view of the present invention.

[0031] Figure 4 This is a schematic diagram showing the connection between this utility model and the frame.

[0032] Figure 5 yes Figure 4 Top view.

[0033] Figure 6 This is a perspective view of the present invention connected to the frame.

[0034] Figure 7 yes Figure 4 A magnified view of part A.

[0035] Figure 8 yes Figure 5 A magnified view of part B in its non-operating state.

[0036] Figure 9 yes Figure 5 A magnified view of part B in operation.

[0037] The reference numerals in the attached figures are as follows:

[0038] 1. Cylinder; 2. Main frame; 3. Movable frame; 4. Guide wheel; 5. First guide rail; 6. Sliding sleeve; 7. Guide rod; 8. Front column; 8A. Front outer column; 8B. Front inner column; 9. Rear column; 9A. Rear outer column; 9B. Rear inner column; 10. Fixing plate; 11. Return spring; 12. Traction hook; 13. First crank-connecting rod mechanism; 14. Second crank-connecting rod mechanism; 15. First connecting rod; 16. Second connecting rod; 17. Third connecting rod; 18. Connecting frame; 19. Fixing rod; 20. Second guide rail; 21. Roller; 22. Main rib mesh; 23. Secondary rib mesh. Detailed Implementation

[0039] The embodiments of this utility model are further described below with reference to the accompanying drawings, but this is not intended to limit the utility model. The scope of protection of this utility model is determined by the contents of the claims. Any equivalent technical means substitutions made based on the description do not depart from the scope of protection of this utility model. The terms "front end," "rear end," "both sides," "inner side," and "outer side" in this utility model are based on the orientation in the accompanying drawings and should not be construed as limiting the utility model. The terms "first," "second," and "third" are used only to describe distinctions and should not be construed as implying importance.

[0040] The overall structure of this embodiment is shown in the figure. The traction device of the mesh hook welding machine includes front columns 8 and rear columns 9 distributed on both sides of the front and rear ends of the material conveying channel. The front columns 8 and the rear columns 9 are arranged opposite each other and achieve a synchronously adjustable sliding fit through the connecting frame 18 and the movable frame 3. The movable frame 3 reciprocates with the main frame 2 along the direction perpendicular to the material conveying channel. The connecting frame 18 rolls with the material conveying channel or the second guide rail 20 on the main frame 2 through the roller 21. The cylinder 1 is connected by a crank-connecting rod mechanism and The linkage drives the front column 8 and the rear column 9 to reciprocate synchronously along the material conveying channel. The stroke of the crank-connecting rod mechanism is an integer multiple of the length of the main rib mesh 22 or the secondary rib mesh 23 cell, and corresponds to the spacing of the steel wires subsequently welded on the mesh frame. Traction hooks 12 with self-resetting function are installed on the inner side of the front column 8, the inner side of the rear column 9, and the fixed rods 19 spaced apart on the outer side of the front column 8. The self-resetting direction is towards the material conveying channel, and the bending direction of the traction hooks 12 is towards the discharge direction and is adapted to the main rib mesh 22 or the secondary rib mesh 23.

[0041] The movable frame 3 reciprocates with the main frame 2 via the first guide rail 5 and the guide wheel 4 that rolls with it. The movable frame 3 and the main frame 2 move relative to each other through a drive mechanism. The drive mechanism is a lead screw feed mechanism, which is existing technology and is not shown in the figure to avoid too many lines, and will not be described further.

[0042] The front column 8 includes an outer front column 8A and an inner front column 8B located on both sides of the front end of the material conveying channel. The inner front column 8B is mounted on the movable frame 3 and reciprocates with it along the direction of the material conveying channel. The outer front column 8A and the inner front column 8B are slidably assembled perpendicular to the direction of the material conveying channel through the guide rod on the connecting frame 18.

[0043] The front inner column 8B achieves reciprocating cooperation with the movable frame 3 along the material conveying channel direction through the sliding sleeve 6 and the guide rod 7 set on the movable frame 3.

[0044] The lower ends of the front outer pillar 8A and the front inner pillar 8B are respectively connected to the power output end of the first crank-connecting rod mechanism 13 arranged opposite to each other. The power output of the cylinder 1 is connected to the power input end of the first crank-connecting rod mechanism 13. The upper ends of the front outer pillar 8A and the front inner pillar 8B are respectively connected to the power output end of the second crank-connecting rod mechanism 14 arranged opposite to each other. The first crank-connecting rod mechanism 13 and the second crank-connecting rod mechanism 14 are linked by the first connecting rod 15. The second crank-connecting rod mechanisms 14 arranged opposite to each other are linked by the second connecting rod 16.

[0045] The rear column 9 includes an outer rear column 9A and an inner rear column 9B located on both sides of the front end of the material conveying channel. The inner rear column 9B is mounted on the movable frame 3 and reciprocates with it along the direction of the material conveying channel. The outer rear column 9A and the inner rear column 9B are slidably assembled perpendicular to the direction of the material conveying channel through the guide rod on the connecting frame 18. The inner rear column 9B reciprocates with the movable frame 3 along the direction of the material conveying channel through the sliding sleeve 6 and the guide rod 7 mounted on the movable frame 3.

[0046] A fixing plate 10 is installed on the inner side of the front column 8 and the inner side of the rear column 9. The end of the traction hook 12 is rotatably assembled with the fixing plate 10. A return spring 11 is provided at the junction of the middle part of the traction hook 12 and the fixing plate 10.

[0047] The linkage rod adopts a third link 17, which is assembled between the connecting frame 18 at the junction of the front outer column 8A and the front inner column 8B, and between the connecting frame 18 at the junction of the front outer column 9A and the rear inner column 9B.

[0048] The traction hooks 12 on the inner side of the front column 8 and the inner side of the rear column 9 are adapted to the main reinforcement mesh 22; the traction hooks 12 installed on the fixing rods 19 spaced apart on the outer side of the front column 8 are adapted to the secondary reinforcement mesh 23.

Claims

1. A traction device for a wire mesh bending hook welding machine, characterized in that... The system includes front columns (8) and rear columns (9) distributed on both sides of the front and rear ends of the material conveying channel. The front columns (8) and rear columns (9) are arranged opposite each other and slide in a synchronously adjustable manner through a connecting frame (18) and a movable frame (3). The movable frame (3) reciprocates with the main frame (2) in a direction perpendicular to the material conveying channel. The connecting frame (18) rolls with the main frame (2) through rollers (21). The cylinder (1) drives the front columns (8) through a crank-connecting rod mechanism and a linkage rod. The rear column (9) moves synchronously back and forth along the material conveying channel. The stroke of the crank connecting rod mechanism is an integer multiple of the length of the main rib mesh (22) or the secondary rib mesh (23). The inner side of the front column (8), the inner side of the rear column (9), and the fixed rod (19) spaced apart on the outer side of the front column (8) are equipped with a traction hook (12) with a self-resetting function. The self-resetting direction is towards the material conveying channel. The bending direction of the traction hook (12) is towards the discharge direction and is adapted to the main rib mesh (22) or the secondary rib mesh (23).

2. The traction device of the wire mesh bending and welding machine according to claim 1, characterized in that... The movable frame (3) reciprocates with the main frame (2) through the first guide rail (5) and the guide wheel (4) that rolls with it. The movable frame (3) and the main frame (2) achieve relative motion through the drive mechanism. The drive mechanism includes, but is not limited to, a lead screw feeding mechanism, a gear rack mechanism, and a parallelogram mechanism.

3. The traction device of the wire mesh bending and welding machine according to claim 1 or 2, characterized in that... The front column (8) includes a front outer column (8A) and a front inner column (8B) located on both sides of the front end of the material conveying channel. The front inner column (8B) is set on the movable frame (3) and reciprocates with it along the direction of the material conveying channel. The front outer column (8A) and the front inner column (8B) are slidably assembled perpendicular to the material conveying direction through the guide rod on the connecting frame (18).

4. The traction device of the wire mesh bending hook welding machine according to claim 3, characterized in that... The front inner column (8B) achieves reciprocating cooperation with the movable frame (3) along the material conveying channel direction through the sliding sleeve (6) and the guide rod (7) set on the movable frame (3).

5. The traction device of the wire mesh bending hook welding machine according to claim 3, characterized in that... The lower ends of the front outer column (8A) and the front inner column (8B) are respectively connected to the power output end of the first crank-connecting rod mechanism (13) which is arranged opposite to each other. The power output of the cylinder (1) is connected to the power input end of the first crank-connecting rod mechanism (13). The upper ends of the front outer column (8A) and the front inner column (8B) are respectively connected to the power output end of the second crank-connecting rod mechanism (14) which is arranged opposite to each other. The first crank-connecting rod mechanism (13) and the second crank-connecting rod mechanism (14) are linked through the first connecting rod (15).

6. The traction device of the wire mesh bending hook welding machine according to claim 5, characterized in that... The two crank-connecting rod mechanisms (14) are linked by a second connecting rod (16).

7. The traction device of the wire mesh bending hook welding machine according to claim 1 or 2, characterized in that... The rear column (9) includes an outer rear column (9A) and an inner rear column (9B) located on both sides of the front end of the material conveying channel. The inner rear column (9B) is mounted on the movable frame (3) and reciprocates with it along the direction of the material conveying channel. The outer rear column (9A) and the inner rear column (9B) are slidably assembled perpendicular to the direction of the material conveying channel through the guide rod on the connecting frame (18). The inner rear column (9B) reciprocates with the movable frame (3) along the direction of the material conveying channel through the sliding sleeve (6) and the guide rod (7) mounted on the movable frame (3).

8. The traction device of the wire mesh bending hook welding machine according to claim 1 or 2, characterized in that... A fixing plate (10) is installed on the inner side of the front column (8) and the inner side of the rear column (9). The end of the traction hook (12) is rotatably assembled with the fixing plate (10). A return spring (11) is provided at the junction of the middle part of the traction hook (12) and the fixing plate (10).

9. The traction device of the wire mesh bending hook welding machine according to claim 1, characterized in that... The linkage adopts a third link (17) between the connecting frame (18) assembled at the junction of the front outer column (8A) and the front inner column (8B) and the connecting frame (18) at the junction of the outer column (9A) and the rear inner column (9B).

10. The traction device of the wire mesh bending hook welding machine according to claim 1, characterized in that... The traction hooks (12) on the inner side of the front column (8) and the inner side of the rear column (9) are adapted to the main reinforcement mesh (22); and the traction hooks (12) installed on the fixing rods (19) spaced apart on the outer side of the front column (8) are adapted to the secondary reinforcement mesh (23).

Images