CN220976239U - Automatic heavy hammer bolt overhead hoist - Google Patents

Abstract

The utility model discloses an automatic heavy hammer bolt lifting device, and relates to the technical field of lifting tools. Including handling bolt and spacing piece, its handling bolt is including the bolt pole and the rigid coupling in the bolt head of bolt pole first end tip, the bolt head is used for constituting spacing blocking at the first hole end of hanging hole, its spacing piece pin joint is in the second end of bolt pole, when spacing piece is in first state, spacing piece can stretch into in the hanging hole with the bolt pole, when spacing piece is in the second state, cooperation formation stop gear between spacing piece and the bolt pole, simultaneously, bolt pole and spacing piece pass through the round pin hub connection, when spacing piece is in the second state, the long tip portion of spacing piece is greater than the heavy moment of short tip portion to round pin axle. According to the utility model, in the process of lifting the base material, the lifting bolt is in any direction, the limiting piece of the lifting bolt can be always vertical to the bolt rod, the effect of preventing the hook from falling off is achieved, and the safety of the base material in the process of lifting is improved.

Description

Automatic heavy hammer bolt overhead hoist

Technical Field

The utility model relates to the technical field of lifting tools, in particular to an automatic heavy hammer bolt lifting device.

Background

At present, in the daily smelting operation procedure of the gas protection electroslag furnace, the lifting of the base metal of the electroslag furnace is an indispensable procedure in the preparation process of production, and plays a key role in adjusting the non-production time; at present, in the handling process of electroslag furnace parent metal, after the operating personnel is required to insert the bolt location, the locating hole of the bolt is vertically passed through again to artificially use long screw and nut and is taken as the unhooking stopper, however, the work is taken on the long screw of unhooking stopper and nut to artificial, its process is loaded down with trivial details not only, and when carrying out handling and in the short cycle many times, long screw and nut abandon at will on the scene, it also can increase the burden on manpower, material resources and time, the non-production time is prolonged, the purpose of yield increase and yield guarantee is not reached, simultaneously, on the people carry out unhooking stopper screw, get the work and also have following potential safety hazard: ① When an operator holds the lifting device and performs the work of lifting and taking the unhooking prevention gear, the operator can cause extrusion injury; ② The center of gravity of the base material is shifted due to neutral gear in the lifting and test lifting process of the lifting base material, and the lifting base material swings, so that the unhooking-preventing long screw is deformed; ③ The openings of the pins are not the same size as the long screws, and do not function as unhooking prevention devices to a certain extent, and unhooking is often caused.

For this purpose, an automatic weight plug lifting device is proposed to solve the above problems.

Disclosure of utility model

The utility model aims to provide an automatic heavy hammer bolt lifting device which is used for solving the problems in the background technology.

In order to achieve the above purpose, the present utility model provides the following technical solutions: an automatic heavy hammer bolt lifting device comprises a lifting bolt and a limiting piece, wherein the lifting bolt comprises a bolt rod and a bolt head fixedly connected to the end part of the first end of the bolt rod, the bolt rod is stretched into a lifting hole of a lifting base material along the second end of the bolt rod, and at the moment, the bolt head forms a limiting stop at the first hole end of the lifting hole; the limiting piece is in pin joint with the second end of the bolt rod, when the limiting piece is in a first state, the limiting piece and the bolt rod can extend into the hanging hole together, and when the limiting piece is in a second state, a limiting mechanism is formed by cooperation between the limiting piece and the bolt rod; the bolt rod is connected with the limiting piece through a pin shaft, when the limiting piece is in a second state, the limiting piece can be divided into a long end part and a short end part from the pin shaft, and the gravity moment from the long end part of the limiting piece to the pin shaft is larger than that from the short end part to the pin shaft.

Based on the technical characteristics, when the lifting device is used, the limiting piece is required to be adjusted to the first state, then the limiting piece adjusted to the first state and the bolt rod are stretched into the lifting hole of the base material to be lifted together, then the bolt head is rotated around the axis direction of the bolt rod, and after the bolt head is rotated to a certain angle, the weight moment from the long end part of the limiting piece to the pin shaft is far greater than the weight moment from the short end part to the pin shaft, so that the limiting piece can automatically rotate around the pin shaft, and finally the limiting piece and the bolt rod keep vertical to have the effect of preventing the hook from falling. The long end part of the limiting piece is always positioned at the lower part of the short end part due to the action of gravity, so that the limiting piece does not need to be manually adjusted in the process of lifting the base material, and the limiting piece always keeps a vertical angle with the axis of the bolt rod in the process of lifting the base material, thereby playing the effect of preventing the hook from falling off, and finally improving the safety of the lifting work of the base material.

In the technical scheme, the limiting piece is preferably pin-connected in the bolt rod through the pin shaft, the plate surface of the limiting piece is parallel to the axis of the bolt rod, and the axis of the pin shaft is perpendicular to the plate surface of the limiting piece.

Based on the technical characteristics, the limiting piece is free from blocking during the lifting of the base material and is required to be adjusted manually, so that the limiting piece can rotate more flexibly and has stronger practicability in the use process.

In this technical scheme, preferably, when the spacing piece is in the first state, stop gear is used for follow the circumference of round pin axle limited the bolt pole with the relative position between the spacing piece.

Based on the technical characteristics, when the limiting piece is in the first state, the limiting piece and the bolt rod can be limited to rotate mutually through the limiting mechanism, and then the limiting piece and the bolt rod can extend into the hanging hole conveniently.

In this technical scheme, preferred, its stop gear includes: a first oblique side formed at one end of the clamping area far away from the pin shaft and inclined to the direction of the bolt head, and a second oblique side formed in the bolt rod; when the limiting piece is switched to a first state, the first bevel edge is abutted with the second bevel edge.

Based on the technical characteristics, the first inclined edge and the second inclined edge which are mutually abutted are used as a limiting mechanism, so that the limiting piece is prevented from rotating with the bolt rod when in the first state, and the limiting piece can be conveniently converted from the first state to the second state.

In the technical scheme, when the limiting piece in the first state stretches into the second hole end of the hanging hole, the lifting bolt is rotated along the axial direction of the bolt rod, and in the rotation process of the lifting bolt, the limiting piece rotates from the first state around the pin shaft to the second state under the action of gravity.

Based on the technical characteristics, through rotatory handling bolt along the axis of bolt pole, and then just can realize the conversion of spacing piece from first state to second state, consequently, the use of being convenient for in parent metal handling work, and then improved the efficiency of its parent metal handling, make it play the critical effect to the regulation of non-production time.

Preferably in this technical solution, the latch head includes: the limiting column is fixedly connected to the first end part of the bolt rod; the handle is arranged opposite to the bolt rod and fixedly connected to the limit column; it is further preferred that the cross section formed by the stop post and the handle is parallel to the axis of the latch rod.

Based on the technical characteristics, the handle can facilitate the lifting device to extend into and out of the parent metal lifting hole, and simultaneously, the lifting device can also rotate in the parent metal lifting hole.

In the technical scheme, preferably, a waist hole is formed on the plate surface of the limiting plate, the limiting plate is in pin joint with the latch rod through a pin shaft penetrating through the waist hole, when the limiting plate is switched to a first state, the axis of the waist hole is parallel to the axis of the latch rod, and meanwhile, the pin shaft is positioned at the first end of the waist hole; when the limiting piece is switched to a second state, the axis of the waist hole is perpendicular to the axis of the bolt rod, and meanwhile, the pin shaft is positioned at the second end of the waist hole; preferably, a clamping hole is formed on a second oblique side in the bolt rod, and when the limiting piece is in the first state, one end of the short end part of the limiting piece, which is far away from the pin shaft, can pass through the clamping hole; further preferably, when the limiting piece in the first state extends into the second hole end of the hanging hole, the limiting piece is drawn along the axial direction of the waist hole, and in the drawing process of the limiting piece, the limiting piece rotates from the first state to the second state around the pin shaft under the action of gravity.

Based on the technical characteristics, the utility model belongs to another embodiment of the lifting device, when the base material is lifted and used, the limiting piece is required to be adjusted to the first state, then the limiting piece adjusted to the first state and the bolt rod are extended into a lifting hole of the base material to be lifted and used together, then the limiting piece arranged in the clamping hole is required to be pulled out along the axial direction of the bolt rod, and after the limiting piece is pulled out for a certain distance, the moment of gravity from the long end part of the limiting piece to the pin shaft is far greater than the moment of gravity from the short end part to the pin shaft, so that the limiting piece can automatically rotate around the pin shaft, and finally the limiting piece and the bolt rod keep vertical to play the effect of preventing the hook from falling.

Drawings

Fig. 1 is a schematic structural view of a lifting device limiting plate in a first state in an embodiment of the present utility model;

fig. 2 is a schematic structural view of a lifting device limiting plate in a second state according to an embodiment of the present utility model;

Fig. 3 is a schematic structural view of a lifting device limiting plate in a third state according to an embodiment of the present utility model;

FIG. 4 is a schematic view of another embodiment of the present utility model in which the trolley spacing tab is in a first state;

Fig. 5 is a schematic structural view of another overhead hoist limit tab in a second state according to an embodiment of the present utility model.

In the figure: 1. lifting the bolt; 12. a latch rod; 12A, a first oblique side; 13. a pin head; 13A, a limit column; 13B, carrying handles; 2. a limiting piece; 21. a long end portion; 22. a short end portion; 22A, a second oblique side; 23. waist holes; 3. and a pin shaft.

Detailed Description

The following description of the embodiments of the present utility model will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present utility model, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the utility model without making any inventive effort, are intended to be within the scope of the utility model.

It should be noted that, in the description of the present utility model, the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, only for convenience in describing the present utility model and simplifying the description, and do not indicate or imply that the apparatus or elements to be referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present utility model.

Furthermore, it should be understood that for ease of description, the dimensions of the various components shown in the figures are not drawn to actual scale.

It should be noted that like reference numerals and letters refer to like items in the following figures, and thus once an item is defined or illustrated in one figure, no further detailed discussion or description thereof will be necessary in the following description of the figures.

Before the utility model is known, it is clear that in the daily smelting operation process of the gas protection electroslag furnace, the lifting of the base metal of the electroslag furnace is an indispensable process in the preparation process to be produced, and plays a key role in adjusting the non-production time, so that the lifting of the base metal of the electroslag furnace plays a key role in adjusting the non-production time and increasing the smelting yield of a single furnace.

As shown in fig. 1 to 3, the present utility model provides a technical solution: an automatic heavy hammer bolt lifting device, wherein the lifting device comprises a lifting bolt 1 and a limiting piece 2; the lifting bolt 1 comprises a bolt rod 12 and a bolt head 13 fixedly connected to the end part of the first end of the bolt rod 12, the bolt rod 12 extends into a lifting hole of a lifting base material along the second end of the bolt rod 12, and at the moment, the bolt head 13 forms a limiting block at the first hole end of the lifting hole; the limiting piece 2 is in pin connection with the second end of the bolt rod 12, when the limiting piece 2 is in the first state, the limiting piece 2 and the bolt rod 12 can extend into the hanging hole, when the limiting piece 2 is in the second state, the limiting piece 2 and the bolt rod 12 are matched to form a limiting mechanism, specifically, fig. 1 is a schematic structural diagram of the lifting device in the first state of the limiting piece, and fig. 2 is a schematic structural diagram of the lifting device in the second state of the limiting piece; the latch rod 12 is connected with the limiting piece 2 through the pin shaft 3, when the limiting piece 2 is in the second state, the limiting piece 2 can be divided into a long end portion 21 and a short end portion 22 from the pin shaft 3, and the gravity moment from the long end portion 21 of the limiting piece 2 to the pin shaft 3 is larger than the gravity moment from the short end portion 22 to the pin shaft 3.

Further, as shown in fig. 1 and 2, the limiting piece 2 is pinned in the latch rod 12 through the pin shaft 3, the plate surface of the limiting piece 2 is parallel to the axis of the latch rod 12, and the axis of the pin shaft 3 is perpendicular to the plate surface of the limiting piece 2; preferably, in such a trolley embodiment of the application, the axis of the pin 3 intersects the axis of the bolt 12, the axis of the bolt 12 passing through the section of the limit piece 2; the technical characteristics can ensure that the limiting piece 2 can not be blocked when the base material is lifted and is required to be manually adjusted, so that the limiting piece can rotate more flexibly and has stronger practicability in the use process.

As shown in fig. 1, when the limiting piece 2 is in the first state, the limiting mechanism is used for limiting the relative position between the latch rod 12 and the limiting piece 2 along the circumferential direction of the pin shaft 3; preferably, in this trolley embodiment of the application, the limit mechanism comprises a first oblique edge 12A formed at the end of the short end portion 22 remote from the pin 3 and inclined in the direction of the latch head 13, and a second oblique edge 22A formed in the latch rod 12, the first oblique edge 12A abutting against the second oblique edge 22A when the limit tab 2 is switched to the first state; preferably, in the embodiment of the lifting device of the present application, two ends of the pin shaft 3 are welded to the latch rod 12, the plate surface of the limiting plate 2 is provided with the waist hole 23, when the pin shaft 3 is placed at the second end of the waist hole 23, the limiting plate 2 can rotate relative to the pin shaft 3, when the pin shaft 3 is placed at the first end of the waist hole 23, the limiting plate 2 is clamped with the latch rod 12 (the limiting plate 2 cannot rotate relative to the pin shaft 3), the second end of the latch rod 12 is provided with a right trapezoid opening with a second inclined edge 22A, the thickness of the right trapezoid opening is slightly larger than that of the limiting plate 2, so that the limiting plate 2 can rotate smoothly around the pin shaft 3, and meanwhile, the inclination angle of the first inclined edge 12A and the second inclined edge 22A is 30 ° to 60 °, in this embodiment of the present application, the limiting plate 2 can be satisfied with the limit of the latch rod 12 in the first state, the sliding of the first inclined edge 12A on the second inclined edge 22A of the latch rod 12 is facilitated, and simultaneously, the first inclined edge 2 is prevented from being scratched by the operator when the first inclined edge 2 rotates.

As shown in fig. 1 and 2, when the limiting piece 2 in the first state extends into the second hole end of the hanging hole, the lifting bolt 1 is rotated along the axial direction of the bolt rod 12, and during the rotation of the lifting bolt 1, the limiting piece 2 rotates from the first state to the second state around the pin shaft 3 under the action of gravity.

Specifically, as shown in fig. 1 and 2, when the lifting device of the present utility model is used, the second oblique side 12A on the limiting plate 2 needs to slide to the first state along the matching direction of the sliding opening (i.e. the second oblique side 12A), then the limiting plate 2 adjusted to the first state and the bolt rod 12 extend into the lifting hole of the base material to be lifted together, then the bolt head 13 is rotated around the axis direction of the bolt rod 12, after the bolt head is rotated to a certain angle, the limiting plate 2 automatically rotates around the pin shaft 3 because the gravitational moment from the long end part 21 of the limiting plate 12 to the pin shaft 3 is far greater than the gravitational moment from the short end part 22 to the pin shaft 3, and finally the limiting plate 2 and the bolt rod 12 keep vertical to play the role of preventing the hook from falling.

Further, as shown in fig. 3, in the third state where the limiting plate 2 is matched with the latch rod 12, the pin shaft 3 is disposed at the first end of the waist hole 23, and at this time, the limiting plate 2 is clamped with the latch rod 12 (the limiting plate 2 cannot rotate relative to the pin shaft 3), so that the limiting plate 2 is in the third state, the second inclined edge 12A on the limiting plate 2 cannot slide to the first state along the matching direction of the sliding opening (i.e., the second inclined edge 12A), and the limiting plate 2 and the latch rod 12 can always keep vertical to have the effect of preventing the unhooking gear, so that the potential safety hazard is smaller than that of the second state.

As shown in fig. 1 to 3, the latch head 13 includes a limit post 13A and a handle 13B, wherein the limit post 13A is fixedly connected to a first end of the latch rod 12, the handle 13B is opposite to the latch rod 12 and is fixedly connected to the limit post 13A, and further, a section formed by the limit post 13A and the handle 13B is parallel to an axis of the latch rod 12; in the embodiment of the present application, the limiting post 13A is cylindrical, and the cross-sectional dimension is slightly larger than that of the latch rod 12, and at the same time, the limiting post 13A may be configured as a strip structure with the cross-sectional dimension slightly larger than that of the latch rod 12 under the condition of saving materials or reducing the dead weight of the lifting device.

As shown in fig. 4 and 5, in another embodiment of the lifting device provided by the application, a waist hole 23 is formed on the plate surface of the limiting plate 2, the limiting plate 2 is pinned in the latch rod 12 by a pin shaft 3 penetrating through the waist hole 23, when the limiting plate 2 is switched to the first state, the axis of the waist hole 23 is parallel to the axis of the latch rod 12, and meanwhile, the pin shaft 3 is positioned at the first end of the waist hole 23; when the limiting piece 2 is switched to the second state, the axis of the waist hole 23 is perpendicular to the axis of the bolt rod 12, and meanwhile, the pin shaft 3 is positioned at the second end of the waist hole 23; preferably, in this embodiment of the lifting device according to the application, the second oblique edge 22A of the latch rod 12 is formed with a clamping hole, and when the limiting plate 2 is in the first state, the end of the short end portion 22 of the limiting plate 2, which is far away from the pin shaft 3, can extend into the clamping hole.

Further, as shown in fig. 4 and 5, when the limiting piece 2 in the first state extends into the second hole end of the hanging hole, the limiting piece 2 is extracted along the axial direction of the waist hole 23, and during the extracting process of the limiting piece 2, the limiting piece 2 rotates from the first state to the second state around the pin shaft 3 under the action of gravity.

Specifically, as shown in fig. 4 and 5, when the lifting device of the utility model is used, the limiting piece 2 needs to be stretched into the clamping hole first so that the limiting piece 2 is adjusted to the first state, then the limiting piece 2 adjusted to the first state and the bolt rod 12 are stretched into the lifting hole of the base material to be lifted, then the limiting piece 2 placed in the clamping hole needs to be pulled out along the axial direction of the bolt rod 12, and then the limiting piece 2 is pulled out for a certain distance, because the gravity moment from the long end part 21 of the limiting piece 2 to the pin shaft 3 is far greater than the gravity moment from the short end part 22 to the pin shaft 3, the limiting piece 2 automatically rotates around the pin shaft 3, and finally the limiting piece 2 and the bolt rod 12 keep vertical to play the effect of preventing the hook from falling.

In the embodiment of the application, the lifting devices have two types: 15T parent metal can be lifted and 25T parent metal can be lifted; the lifting device capable of lifting 15T base materials is characterized in that the length dimension of a plug rod 12 is 480mm, the radius of a section is 20mm, the height of a limiting column 13A is 20mm, the radius of a section is 35mm, when a limiting plate 2 is in a first state and a second state, the distance from the topmost end 22 of the limiting plate 2, which is far away from a pin shaft 3, to the axis of the pin shaft 3 is 80mm, the distance from the topmost end 21 of the limiting plate 2, which is far away from the pin shaft 3, to the axis of the pin shaft 3 is 100mm, and the dimension of a waist hole 23 is 15mm x 40mm; the lifting device capable of lifting 25T parent metal, the length dimension of the bolt rod 12 is 580mm, the radius of the section is 30mm, the height of the limiting column 13A is 20mm, the radius of the section is 45mm, when the limiting sheet 2 is in a first state and a second state, the distance from the top end of the limiting sheet 2, which is far away from the pin shaft 3, to the axis of the pin shaft 3 is 100mm, the distance from the top end of the limiting sheet 2, which is far away from the pin shaft 3, to the axis of the pin shaft 3 is 120mm, and the dimension of the waist hole 23 is 15 mm; preferably, in the embodiment of the application, the bolt rod 12, the bolt head 13 and the limiting piece 2 in the lifting device are all made of high-strength, high-hardness and high-wear-resistance high-chromium structural steel.

In summary, the application provides an automatic weight bolt lifting device, which is characterized in that a limiting piece 2 is pinned at a second end of a bolt rod 12, so that the limiting piece 2 and a lifting bolt 1 are integrated, long screws and nuts are prevented from being discarded at will on site, and the non-production time is prolonged; meanwhile, the three using states of the limiting piece 2 are flexibly switched, so that not only is the function of preventing unhooking gear realized, but also the non-production time is shortened, and the purposes of increasing yield and protecting yield are further achieved.

Although embodiments of the present utility model have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the utility model, the scope of which is defined in the appended claims and their equivalents.

Claims (10)

1. An automatic weight bolt overhead hoist, characterized in that it overhead hoist includes:

the lifting bolt (1) comprises a bolt rod (12) and a bolt head (13) fixedly connected to the end part of the first end of the bolt rod (12), the bolt rod (12) is stretched into a lifting hole of a lifting base material along the second end of the bolt rod (12), and at the moment, the bolt head (13) forms a limiting stop at the first hole end of the lifting hole;

The limiting piece (2) is in pin joint with the second end of the bolt rod (12), when the limiting piece (2) is in a first state, the limiting piece (2) and the bolt rod (12) can extend into the hanging hole, and when the limiting piece (2) is in a second state, the limiting piece (2) and the bolt rod (12) are matched to form a limiting mechanism;

The bolt rod (12) is connected with the limiting piece (2) through the pin shaft (3), when the limiting piece (2) is in the second state, the limiting piece (2) can be divided into a long end part (21) and a short end part (22) from the pin shaft (3), and the gravity moment from the long end part (21) of the limiting piece (2) to the pin shaft (3) is larger than the gravity moment from the short end part (22) to the pin shaft (3).

2. The automatic weight plug pin lifting device according to claim 1, wherein the limiting piece (2) is pinned in the plug pin rod (12) through a pin shaft (3), the plate surface of the limiting piece (2) is parallel to the axis of the plug pin rod (12), and the axis of the pin shaft (3) is perpendicular to the plate surface of the limiting piece (2).

3. An automatic weight bolt handling device according to claim 2, characterized in that the limit mechanism is adapted to define the relative position between the bolt bar (12) and the limit plate (2) in the circumferential direction of the pin (3) when the limit plate (2) is in the first state.

4. An automated weight plug overhead hoist according to claim 3, wherein the limit mechanism comprises:

A first oblique side (12A) formed at an end of the short end portion (22) remote from the pin shaft (3) and inclined to the direction of the latch head (13);

A second oblique side (22A) formed in the latch rod (12);

when the limit plate (2) is switched to a first state, the first oblique side (12A) is abutted with the second oblique side (22A).

5. An automatic weight bolt handling device according to claim 4, characterized in that when the limit piece (2) in the first state is extended into the second hole end of the hanging hole, the handling bolt (1) is rotated in the axial direction of the bolt rod (12), and during the rotation of the handling bolt (1), the limit piece (2) is rotated from the first state to the second state around the pin shaft (3) by gravity.

6. An automatic weight bolt handling device according to claim 5, characterized in that the bolt head (13) comprises:

The limiting column (13A) is fixedly connected to the first end part of the bolt rod (12);

And the carrying handle (13B) is arranged opposite to the bolt rod (12) and fixedly connected to the limiting column (13A).

7. An automatic weight bolt handling device according to claim 6, characterized in that the cross section of the limit post (13A) and handle (13B) is parallel to the axis of the bolt bar (12).

8. The automatic weight bolt lifting device according to claim 4, wherein a waist hole (23) is formed on the plate surface of the limiting piece (2), the limiting piece (2) is pinned in the bolt rod (12) through a pin shaft (3) penetrating into the waist hole (23), when the limiting piece (2) is switched to the first state, the axis of the waist hole (23) is parallel to the axis of the bolt rod (12), and meanwhile, the pin shaft (3) is positioned at the first end of the waist hole (23); when the limiting piece (2) is switched to the second state, the axis of the waist hole (23) is perpendicular to the axis of the bolt rod (12), and meanwhile the pin shaft (3) is located at the second end of the waist hole (23).

9. The automatic weight bolt lifting device according to claim 8, wherein a clamping hole is formed on the second oblique side (22A) in the bolt rod (12), and when the limiting piece (2) is in the first state, one end of the short end portion (22) on the limiting piece (2) away from the pin shaft (3) can extend into the clamping hole.

10. The automatic weight plug pin lifting device according to claim 9, wherein when the limiting piece (2) in the first state extends into the second hole end of the lifting hole, the limiting piece (2) is extracted along the axial direction of the waist hole (23), and during the extracting process of the limiting piece (2), the limiting piece (2) rotates from the first state to the second state around the pin shaft (3) under the action of gravity.