Thermal insulation foaming furnace with trough transfer device
By adopting the trough transport device and heat recovery technology with inner and outer guide rail structures in the foam aluminum production equipment, the problem of uneven foaming caused by aluminum melt cooling is solved, and efficient and uniform foam aluminum production is achieved, which has improved the Production efficiency and product quality.
Patent Information
- Application Number
- CN202420864404.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-24
- Publication Date
- 2024-12-10
- Estimated Expiration
- 2034-04-24
AI Technical Summary
During the foam aluminum production process, the cooling of aluminum melt results in uneven foaming effect, affecting product quality, and existing equipment has problems of heat loss and low production efficiency in continuous production.
A thermal insulation foam furnace with a trough transfer device was designed, using the inner and outer guide rail structures to realize the continuous movement of the trough truck, and preheated the air through the heat recovery device, combining the ventilation combustion structure and thermistor detection to ensure that Temperature consistency and energy saving.
It achieves continuous production with uniform foaming, energy saving and efficient, and controllable process, improves product quality and production efficiency, and reduces energy consumption and space occupation.
Smart Images
Figure CN222133414U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the technical field of foam aluminum production, and more specifically relates to a heat-insulating foaming furnace with a material trough transfer device. Background Art
[0002] Foamed aluminum is a new type of material with randomly distributed holes in a metal matrix. It has the metallic characteristics of continuous phase aluminum and the characteristics of dispersed phase pores. It not only retains the electrical conductivity and ductility of metal, but also is lightweight. It has the characteristics of porous materials such as sound absorption, sound insulation, energy absorption and vibration reduction, electromagnetic shielding, and low thermal conductivity. It combines structural and functional characteristics and has become one of the important research and development topics in the field of materials science in the world today. An important step in the production process of foamed aluminum is the heat preservation foaming process. In the production process of the assembly line, the foamed aluminum must be transported away in time to meet continuous production. When the aluminum melt is poured into the trough, it is easy to cool when it contacts the bottom of the trough, which seriously affects the foaming effect at the bottom.
[0003] The invention patent with patent number 201310038972.5 discloses a complete set of equipment for producing foamed aluminum, which is equipped with a mold conveying device and a sealed box-type insulation furnace. A preheating zone, a casting zone, a shaping zone and a cooling zone are arranged in the sealed box-type insulation furnace, so that the heat of the foamed aluminum is continuously dissipated during the foaming process, thereby causing different degrees of foaming in the entire mold, resulting in uneven foam generation and affecting product quality.
[0004] Therefore, how to provide a heat-insulating foaming furnace with a material trough transfer device is a problem that technical personnel in this field urgently need to solve. Utility Model Content
[0005] In view of this, the utility model provides a heat-insulating foaming furnace with a material trough transfer device, which has the advantages of uniform foaming, energy saving and high efficiency, controllable process and continuous production.
[0006] In order to achieve the above purpose, the utility model adopts the following technical solutions:
[0007] A thermal insulation foaming furnace with a trough transfer device comprises a trough trolley, an inlet transfer device, an outlet transfer device and a thermal insulation foaming furnace body; the inlet transfer device and the outlet transfer device are used to transfer the trough trolley; the thermal insulation foaming furnace body comprises a furnace body, an inlet structure and an outlet structure, and a feed discharge port is provided on the top of the furnace body for conveying molten aluminum liquid; an inner guide rail for moving the trough trolley is provided inside the thermal insulation foaming furnace body, and an outer guide rail parallel to the inner guide rail is provided outside the body for rotating the trough trolley; the inlet transfer device is connected to the inlet structure through the inner guide rail; the outlet transfer device is connected to the outlet structure through the inner guide rail.
[0008] Furthermore, guide rail bases are provided below the inner guide rail and the outer guide rail for supporting the guide rails.
[0009] Furthermore, the material trough trolley includes a vehicle body, a material trough, a hanging plate and a roller; a mixing barrel is provided above the material trough; a groove with the same diameter as the mixing barrel is provided on the outer edge of the material trough, which is matched with the mixing barrel; the hanging plate is provided at the bottom of the vehicle body, and hook rings are provided at both ends of the hanging plate for connecting with the inlet transfer device and the outlet transfer device, and the vehicle body is rotatably connected to the roller.
[0010] Furthermore, the mixing barrel is a cylinder without seals at both ends, and two lifting ears are provided on the top; the lifting ears are connected with steel bars for suspending the mixing barrel; an asbestos pad is provided at the bottom of the groove for sealing the mixing barrel and the groove.
[0011] Furthermore, the thermal insulation foaming furnace body also includes a ventilation and combustion structure; the ventilation and combustion structure includes an air intake structure and an exhaust structure; the air intake structure includes an air duct, a gas duct, an air valve and an air inlet; the air duct and the gas duct are both connected to the air valve, the air valve is connected to the air inlet, and an electric spark is provided on the air valve; the air inlet is provided on the side wall of the furnace body, and the air inlet is provided in two rows, which are arranged in a centrally symmetrical manner; the exhaust structure includes an exhaust port and an exhaust blower, the exhaust port is provided on the side of the furnace body, and is connected to the exhaust blower through a pipe.
[0012] Furthermore, the thermal insulation foaming furnace body also includes a heat recovery device, which is arranged above the outlet structure and is used to collect heat and high-temperature gas emitted when the furnace is turned on; the heat recovery device includes a heat collection port and an air supply blower; the heat collection port is connected to the air supply blower through a pipe; the air supply blower is connected to the air duct through a pipe.
[0013] Furthermore, the structure of the entrance structure is the same as that of the exit structure, and the entrance structure includes an entrance furnace door, a slide rail, a motor and a bracket. Pulleys are provided on both sides of the entrance furnace door, and the pulleys cooperate with the slide rails; a bracket is provided on the upper part of the furnace body, a fixed pulley is provided above the bracket, and a winch is provided below the bracket; one end of a steel wire is fixedly connected to the top of the entrance furnace door, and the steel wire passes through the fixed pulley and is wound around the winch; the motor shaft is connected to the winch.
[0014] Furthermore, a plurality of thermistors are provided on the side of the furnace body for detecting the temperature inside the furnace.
[0015] Furthermore, the inlet transfer device and the outlet transfer device have the same structure and are symmetrically arranged relative to the insulation foaming furnace body; the inlet transfer device includes a transfer platform and a power assisting device; a transfer platform guide rail is arranged under the transfer platform for guiding the transfer platform to connect the inner guide rail and the outer guide rail; a platform track is arranged on the transfer platform for docking the inner guide rail and the outer guide rail for moving the material trough trolley; limit blocks are arranged on both sides of the platform track and the transfer platform guide rail; the power assisting device is arranged on the inner guide rail for controlling the movement of the material trough trolley.
[0016] Furthermore, the power assist device includes a hydraulic rod, a hook, a hook connecting rod and a guide rail for the hook, one end of the hydraulic rod is fixed on the guide rail base, and the other end is connected to the center position of the hook connecting rod; hooks are provided at both ends of the hook connecting rod, which cooperate with the hook ring at the bottom of the trough trolley; the guide rail for the hook is provided above the guide rail base, in the middle position of the inner guide rail, for limiting the movement of the hook.
[0017] The beneficial effects of the utility model are:
[0018] Compared with the prior art, the utility model is provided with a heat recovery device to collect the heat emitted by the furnace when it is turned on to preheat the incoming air, which can increase the combustion efficiency, thereby making the preheating effect of the furnace and the trough trolley better and being able to ensure the temperature in the furnace; by setting symmetrical air inlets, the furnace is made isothermal, and the bottom of the trough trolley is prevented from cooling down when the trough trolley moves, thereby affecting the foaming quality; by setting an inlet transfer device and an outlet transfer device, and connecting the inner guide rail and the outer guide rail, the foamed aluminum cell can be transferred out in time for the next process, and rotated through the outer guide rail, thereby realizing cyclic continuous production and improving production efficiency; the preheating and foaming processes are jointly set in the heat-insulating foaming furnace, which can ensure the consistency of temperature in the entire production process, save energy and space, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.
[0020] Figure 1 It is a schematic diagram of the overall structure of the utility model.
[0021] Figure 2 It is a side view of the thermal insulation foaming furnace of the utility model.
[0022] Figure 3It is a structural schematic diagram of the entrance transfer device of the utility model.
[0023] Among them, in the figure:
[0024] 1- trough trolley; 2- entrance transfer device; 3- exit transfer device; 4- insulation foaming furnace body; 5- inner guide rail; 6- outer guide rail; 11- car body; 12- trough; 13- hanging plate; 14- mixing barrel; 21- transfer platform; 22- transfer platform guide rail; 23- platform track; 24- guide rail base; 25- limit block; 26- hydraulic rod; 27- hook; 28- hook connecting rod; 29- guide rail for hook; 30- plug; 41- furnace body; 42- entrance furnace door; 43- entrance structure; 44- exit structure; 45- exit furnace door; 46- feeding port; 47- air valve; 48- air inlet; 49- exhaust port; 50- exhaust blower; 51- heat collection port; 52- air supply blower; 53- thermistor. DETAILED DESCRIPTION
[0025] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.
[0026] Please see attached Figure 1 The utility model provides a heat preservation foaming furnace with a material trough transfer device, comprising: a material trough trolley 1, an inlet transfer device 2, an outlet transfer device 3 and a heat preservation foaming furnace body 4.
[0027] The trough trolley 1 includes a vehicle body 11, a trough 12, a hanging plate 13 and rollers; the trough 12 is fixedly arranged above the vehicle body 11, and a stirring barrel 14 is arranged above the trough 12; a groove with the same diameter as the stirring barrel 14 is arranged on the outer edge of the trough 12, which is matched with the stirring barrel 14; an asbestos pad is arranged at the bottom of the groove, which is used to seal the stirring barrel 14 and the groove; a guide column for limiting is arranged at the outer edge of the groove to ensure that when the stirring barrel 14 is lowered from the top of the insulation foaming furnace, the stirring barrel 14 just coincides with the position of the groove; the stirring barrel 14 is a cylinder without seals at both ends, and two lifting ears are arranged on the top; the lifting ears are connected with steel bars, which are used to suspend the stirring barrel 14 and limit the stirring barrel 14 to prevent it from shaking during the stirring process, resulting in leakage of aluminum melt.
[0028] The vehicle body 11 includes an insulating layer and heat-resistant bricks to ensure the stability of the trough trolley 1 during the movement process and the insulation effect during the stirring and foaming process; the hanging plate 13 is arranged at the bottom of the vehicle body 11, and hooks are provided at both ends of the hanging plate 13 for connecting with the inlet transfer device and the outlet transfer device to move the trough trolley 1; the vehicle body 11 is rotatably connected to the roller for the travel of the trough trolley 1.
[0029] The heat preservation foaming furnace body 4 includes a furnace body 41, a ventilation combustion structure, an inlet structure 43, an outlet structure 44, and a heat recovery device. A feed port 46 is provided on the top of the furnace body 41 for conveying molten aluminum liquid, and a heat preservation cover is provided above the feed port for sealing and heat preservation.
[0030] Please see attached Figure 2 The ventilation and combustion structure includes an air intake structure and an exhaust structure; the air intake structure includes an air duct, a gas duct, an air valve 47 and an air inlet 48; the air duct and the gas duct are both connected to the air valve 47, the air valve 47 is connected to the air inlet 48, and an electric spark is provided on the air valve 47; the air inlet 48 is provided on the side wall of the furnace body 41, and the air inlet 48 is provided in two rows, which are arranged in a central symmetrical manner to ensure that the temperature in the entire furnace is consistent; the air and the gas are mixed at the gas valve 47, and are ignited by the electric spark on the gas valve 47, so that the gas introduced into the furnace is burned, which is used for heating the inside of the thermal insulation foaming furnace.
[0031] The exhaust structure includes an exhaust port 49 and an exhaust blower 50. The exhaust port 49 is arranged on the side of the furnace body 41 and is connected to the exhaust blower 50 through a pipeline. The exhaust blower 50 is connected to a cooling system through a pipeline to suck out the exhaust gas, cool it, and then pass it into the exhaust gas treatment device.
[0032] The entrance structure 43 has the same structure as the exit structure 44, and includes an entrance furnace door 42, a slide rail, a motor and a bracket. Pulleys are arranged on both sides of the entrance furnace door 42, and the pulleys cooperate with the slide rails. A bracket is arranged on the upper part of the furnace body 41, and a fixed pulley is arranged above the bracket, and a winch is arranged below the bracket. One end of a steel wire is fixedly connected to the upper part of the entrance furnace door 42, and the steel wire passes through the fixed pulley and is wound on the winch. The motor shaft is connected to the winch. The motor controls the lifting of the furnace door, and the setting of the pulley and the slide rail makes the heavy furnace door stable when lifting and lowering, reducing shaking and friction.
[0033] The heat recovery device is arranged above the outlet structure 44, and is used for collecting the heat and high-temperature gas emitted when the furnace is turned on; the heat recovery device includes a heat collection port 51 and an air supply blower 52; the heat collection port 51 is arranged above the outlet furnace door 45, and is connected to the air supply blower 52 through a pipeline; the air supply blower 52 is connected to the air duct through a pipeline; the air supply blower 52 sends the hot air collected by the heat collection port 51 into the air duct, and the preheated air is then mixed with the fuel gas, which can make the combustion more complete and reduce heat loss.
[0034] The furnace body 41, the inlet furnace door 42 and the outlet furnace door 45 are all provided with a heat-insulating layer to reduce heat loss. A plurality of thermistors 53 are also provided on the side of the furnace body 41 to detect the temperature inside the furnace.
[0035] A stopper is provided on the outside of the entrance structure 43 to prevent the rear vehicle from moving forward and hitting the furnace door after the front vehicle enters during the transfer of the trough trolley 1.
[0036] Please see attached Figure 3 The inlet transfer device 2 and the outlet transfer device 3 have the same structure and are symmetrically arranged relative to the thermal insulation foaming furnace body 4; the inlet transfer device 2 is connected to the inlet of the thermal insulation foaming furnace body 4; the outlet transfer device 3 is connected to the outlet of the thermal insulation foaming furnace body 4.
[0037] The heat-insulating foaming furnace body 4 is provided with an inner guide rail 5 for moving the trough trolley 1 , and is provided with an outer guide rail 6 parallel to the inner guide rail 5 for rotating the trough trolley 1 .
[0038] The entrance transfer device 2 includes a transfer platform 21 and a power assist device; a transfer platform guide rail 22 is arranged under the transfer platform 21, which is used to guide the transfer platform 21 to connect the inner guide rail 5 and the outer guide rail 6; a platform track 23 is provided on the transfer platform 21, which is connected to the inner guide rail 5 and the outer guide rail 6 and is used to move the trough trolley 1; when the transfer platform 21 reaches the entrance of the insulation foaming furnace through the transfer platform 21 guide rail, the platform track 23 is connected to the inner guide rail 5, and the trough trolley 1 moves to the inner guide rail 5 through the platform track 23 and enters the insulation foaming furnace.
[0039] Bolts 30 are provided on both sides of the inner guide rail 5 and the outer guide rail 6 for fixing the transfer platform 21 to ensure stable movement of the trough trolley 1.
[0040] A guide rail base 24 is disposed below the inner guide rail 5 and the outer guide rail 6 for supporting the guide rails.
[0041] Limiting blocks 25 are provided on both sides of the platform track 23 and the guide rail of the transfer platform 21 to prevent the trough trolley 1 and the transfer platform 21 from deviating from the track. A latch is provided on the transfer platform 21 to fix the trough trolley 1 to prevent the trough trolley 1 from moving on the platform track 23 when the transfer platform 21 moves.
[0042] The power assist device is arranged on the inner guide rail 5, and includes a hydraulic rod 26, a hook 27, a hook connecting rod 28 and a hook guide rail 29. One end of the hydraulic rod 26 is fixed on the guide rail base 24, and the other end is connected to the center position of the hook connecting rod 28; hooks 27 are arranged at both ends of the hook connecting rod 28, which cooperate with the hook ring at the bottom of the trough trolley 1; the hook guide rail 29 is arranged above the guide rail base 24, in the middle position of the inner guide rail, and is used to limit the movement of the hook 27; the hydraulic rod 26 is used to control the movement of the hook 27 and the hook guide rail 29, thereby controlling the movement of the trough trolley 1.
[0043] The working principle of the utility model is as follows: air and gas are mixed after passing through the air pipe and the gas pipe into the gas valve 47, and the mixed gas is passed into the heat preservation foaming furnace through the air inlet 48, and the gas is ignited by electric spark ignition to preheat the furnace body 41 and the material tank on the upper part of the material tank trolley 1. When the entrance furnace door 42 of the heat preservation foaming furnace is opened, the exhaust blower 50 is turned on at the same time. The material tank trolley 1 is transported to the entrance by the transfer platform 21, the bolt 30 is pulled, the transfer platform 21 is fixed, the hook 27 of the power assist device is fixed to the hook ring at the bottom of the material tank trolley 1, and the material tank trolley 1 is pulled to be sent into the heat preservation foaming furnace. After preheating inside the insulation foaming furnace, the trough trolley 1 moves to the designated position below the discharge port 46, aligns the bottom of the stirring barrel 14 with the groove at the bottom of the trough 12 from the discharge port 46, and guides the molten aluminum liquid into the stirring barrel 14 after placement. After stirring and foaming, the stirring barrel 14 is lifted out of the insulation foaming furnace and covered with an insulation cover; after foaming, the entrance furnace door 42 and the exit furnace door 45 of the insulation foaming furnace are opened, and the power assist device drives the trough trolley 1 into the furnace, and the trough trolley 1 with the foamed aluminum cell in front is pushed out, and the hydraulic rod 26 of the exit transfer device drives the trough trolley 1 out of the insulation foaming furnace and transports it to the transfer platform 21. After the subsequent cooling step, the foamed aluminum is taken away, and the trough trolley 1 is transported to the outer guide rail 6 through the exit transfer device, and rotated to the entrance transfer device to continue the next process.
[0044] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.
[0045] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A heat preservation foaming furnace with a trough transfer device, characterized in that: It comprises a material trough trolley (1), an inlet transfer device (2), an outlet transfer device (3) and a heat preservation foaming furnace body (4); The inlet transfer device (2) and the outlet transfer device (3) are used to transfer the trough trolley (1); The heat-insulating foaming furnace body (4) comprises a furnace body (41), an inlet structure (43) and an outlet structure (44); a feed port (46) is provided at the top of the furnace body (41) for conveying molten aluminum liquid; The heat-insulating foaming furnace body (4) is provided with an inner guide rail (5) for moving the trough trolley (1), and an outer guide rail (6) parallel to the inner guide rail (5) is provided on the outside for rotating the trough trolley (1); The inlet transfer device (2) is connected to the inlet structure (43) via an inner guide rail (5); the outlet transfer device (3) is connected to the outlet structure (44) via an inner guide rail (5).
2. The heat-insulating foaming furnace with a trough transfer device according to claim 1, characterized in that: A guide rail base (24) is provided below the inner guide rail (5) and the outer guide rail (6) for supporting the guide rails.
3. The heat-insulating foaming furnace with a trough transfer device according to claim 1, characterized in that: The trough trolley (1) comprises a vehicle body (11), a trough (12), a hanging plate (13) and a roller; a stirring barrel (14) is arranged above the trough (12); a groove having the same diameter as the stirring barrel (14) is arranged on the outer edge of the trough (12) and is matched with the stirring barrel (14); the hanging plate (13) is arranged at the bottom of the vehicle body (11), and hooks are arranged at both ends of the hanging plate (13) for connecting with the inlet transfer device and the outlet transfer device, and the vehicle body (11) is rotatably connected with the roller.
4. The heat-insulating foaming furnace with a trough transfer device according to claim 3, characterized in that: The mixing barrel (14) is a cylinder without seals at both ends, and is provided with two hanging ears on the top; the hanging ears are connected with steel bars for suspending the mixing barrel (14); an asbestos pad is provided at the bottom of the groove for sealing the mixing barrel (14) and the groove.
5. The heat-insulating foaming furnace with a trough transfer device according to claim 1, characterized in that: The heat-insulating foaming furnace body (4) also includes a ventilation and combustion structure; the ventilation and combustion structure includes an air intake structure and an exhaust structure; the air intake structure includes an air duct, a gas duct, an air valve (47) and an air intake port (48); the air duct and the gas duct are both connected to the air valve (47), the air valve (47) is connected to the air intake port (48), and the air valve (47) is provided with an electric spark; the air intake port (48) is provided on the side wall of the furnace body (41), and the air intake port (48) is provided in two rows and is arranged in a central symmetrical manner; the exhaust structure includes an exhaust port (49) and an exhaust blower (50), the exhaust port (49) is provided on the side of the furnace body (41), and is connected to the exhaust blower (50) through a pipeline.
6. The heat-insulating foaming furnace with a trough transfer device according to claim 5, characterized in that: The heat-insulating foaming furnace body (4) further comprises a heat recovery device, which is arranged above the outlet structure (44) and is used to collect heat and high-temperature gas emitted when the furnace is turned on; the heat recovery device comprises a heat collection port (51) and an air supply blower (52); the heat collection port (51) is connected to the air supply blower (52) via a pipeline; the air supply blower (52) is connected to the air duct via a pipeline.
7. The heat-insulating foaming furnace with a material trough transfer device according to claim 1, characterized in that: The inlet structure (43) has the same structure as the outlet structure (44), and the inlet structure (43) comprises an inlet furnace door (42), a slide rail, a motor and a bracket. Pulleys are provided on both sides of the inlet furnace door (42), and the pulleys cooperate with the slide rails. A bracket is provided on the upper part of the furnace body (41), a fixed pulley is provided above the bracket, and a winch is provided below the bracket. One end of a steel wire is fixedly connected to the top of the inlet furnace door (42), and the steel wire passes through the fixed pulley and is wound around the winch. The motor shaft is connected to the winch.
8. The heat-insulating foaming furnace with a material trough transfer device according to claim 1, characterized in that: A plurality of thermistors (53) are also provided on the side of the furnace body (41) for detecting the temperature inside the furnace.
9. The heat-insulating foaming furnace with a material trough transfer device according to claim 2, characterized in that: The inlet transfer device (2) and the outlet transfer device (3) have the same structure and are symmetrically arranged relative to the heat-insulating foaming furnace body (4); the inlet transfer device (2) comprises a transfer platform (21) and a power-assisting device; a transfer platform guide rail (22) is arranged below the transfer platform (21) for guiding the transfer platform (21) to connect the inner guide rail (5) and the outer guide rail (6); a platform track (23) is arranged on the transfer platform (21) for docking the inner guide rail (5) and the outer guide rail (6) for moving the trough trolley (1); both sides of the platform track (23) and the transfer platform (21) guide rail are provided with limit blocks (25); the power-assisting device is arranged on the inner guide rail (5) for controlling the movement of the trough trolley (1).
10. The heat-insulating foaming furnace with a material trough transfer device according to claim 9, characterized in that: The power assist device comprises a hydraulic rod (26), a hook (27), a hook connecting rod (28) and a hook guide rail (29); one end of the hydraulic rod (26) is fixed on the guide rail base (24), and the other end is connected to the center position of the hook connecting rod (28); hooks (27) are arranged at both ends of the hook connecting rod (28) and cooperate with the hook ring at the bottom of the trough trolley (1); the hook guide rail (29) is arranged above the guide rail base (24) and in the middle position of the inner guide rail (5) to limit the movement of the hook (27).