A vertical continuous casting machine strand and dummy bar lifting device

Abstract

The application discloses a kind of vertical continuous casting machine casting blank and dummy bar lifting device, belong to vertical continuous casting machine technical field, to solve the problem that the lifting device of the existing vertical continuous casting machine casting blank adopts sprocket and chain as transmission mechanism is not conducive to installation and maintenance, the vertical continuous casting machine casting blank and dummy bar lifting device include winch mechanism (100), lifting support (200), pulley assembly (300), support column (400) and steel wire rope (500), steel wire rope (500) passes pulley assembly (300), winch mechanism (100) can drive lifting support (200) moves up and down along support column (400). Steel wire rope and winch mechanism are used to drive lifting support to move up and down, the cooperation of steel wire rope and pulley not only facilitates installation and maintenance, but also can reduce production cost.

Description

Technical Field

[0001] This invention relates to the field of vertical continuous casting machine technology, specifically a lifting device for the billet and dummy bar of a vertical continuous casting machine. Background Technology

[0002] Vertical continuous casting technology was adopted before the now mainstream arc casting machine. Compared to vertical continuous casting machines, the main advantages of arc casting machines are reduced production costs and simplified operation. However, for very specialized steel grades, vertical continuous casting machines still have significant advantages. Because vertical continuous casting machines eliminate bending and straightening steps, there are virtually no restrictions on the types of steel that can be cast. Furthermore, the completely vertical casting direction creates optimal conditions for the flotation of non-metallic inclusions, ensuring excellent internal cleanliness of the cast billet.

[0003] In existing technology, the lifting device for the billet and dummy bar of a vertical continuous casting machine uses a motor and reducer as the drive mechanism, and a meshing sprocket and chain as the transmission mechanism to drive the lifting bracket up and down. Since the lifting device is located in a deep pit of about 40 meters, both the sprocket and the chain are very heavy, which has the disadvantages of being inconvenient to disassemble and assemble and difficult to maintain. Summary of the Invention

[0004] To address the problem that using sprockets and chains as transmission mechanisms in the aforementioned lifting devices is inconvenient for installation and maintenance, this invention provides a lifting device for the billet and dummy bar of a vertical continuous casting machine. The lifting device utilizes wire ropes and a winch mechanism to drive the lifting support up and down. The combination of wire ropes and pulleys not only facilitates installation and maintenance but also reduces costs.

[0005] The technical solution adopted by the embodiments of the present invention to solve its technical problem is as follows:

[0006] A lifting device for billet and dummy bar of a vertical continuous casting machine includes a winch mechanism, a lifting bracket, a pulley assembly, a support column and a wire rope. The pulley assembly is located on the upper part of the support column. One end of the wire rope is connected to the lifting bracket and the other end of the wire rope is connected to the winch mechanism. The wire rope passes around the pulley assembly, and the winch mechanism can drive the lifting bracket to move up and down along the support column.

[0007] The beneficial effects of the embodiments of the present invention are:

[0008] 1. It effectively solves the cumbersome problems of initial equipment installation, requiring less precise positioning; simply ensuring the two guide wheels are on the same center line is sufficient. Furthermore, the wire rope and pulley structure is simpler than the sprocket and chain structure, reducing the difficulty of maintenance for users during later use. The cost of wire rope guide wheels is much lower than that of sprocket and chain structures, reducing the buyer's initial investment and saving money. This significantly reduces costs both in terms of initial investment and subsequent maintenance.

[0009] 2. This invention can estimate the service life of the wire rope by recording the values ​​of the first encoder and the second encoder and comparing the two values. It can also detect whether the pulley rotation is obstructed, thus avoiding friction between the wire rope and the pulley. This can more intelligently remind future maintenance personnel to perform targeted equipment maintenance and improve work efficiency. Attached Figure Description

[0010] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0011] Figure 1 This is a schematic diagram of the lifting device for the billet and dummy bar of the vertical continuous casting machine described in this invention.

[0012] Figure 2 yes Figure 1 A schematic diagram of the middle pulley assembly.

[0013] Figure 3 yes Figure 1 A schematic diagram of the hoisting mechanism and the lifting support.

[0014] Figure 4 It is the hoisting mechanism along Figure 1 A schematic diagram of the direction A in the middle.

[0015] Figure 5 This is a 3D schematic diagram of the lifting support.

[0016] Figure 6 This is a cross-sectional view of the lifting support.

[0017] Figure 7 yes Figure 6 An enlarged schematic diagram of the mid-position detection sensor.

[0018] Figure 8 It is the lifting support along Figure 1 A schematic diagram in the C direction.

[0019] Figure 9 It is the sliding base and the support base along Figure 1 A simplified diagram of the A-direction.

[0020] Figure 10 It is the pulley assembly along Figure 1 A schematic diagram of the direction A in the middle.

[0021] Figure 11 It is the support column edge Figure 1 Cross-sectional view along the BB direction.

[0022] The annotations in the attached figures are explained as follows:

[0023] 100. Hoisting mechanism; 200. Lifting support; 300. Pulley assembly; 400. Support column; 500. Wire rope;

[0024] 101. Motor; 102. Brake; 103. Reducer; 104. Coupling; 105. Wire rope drum; 106. First encoder;

[0025] 201. Sliding base; 202. Support base; 203. Buffer mechanism; 204. Support plate; 205. Guide wheel; 206. Rail cleaner; 207. Position detection sensor; 208. Wire rope tie rod;

[0026] 301. Pulley; 302. Lubrication hole; 303. Rope breakage detection sensor; 304. Shaft wheel; 305. Second encoder; 306. Pulley platform;

[0027] 401. Front upright; 402. Protective upright plate; 403. Rear upright; 404. Front guide rail; 405. Rear guide rail;

[0028] 2011. Front panel; 2012. Middle panel; 2013. Rear panel; 2014. Column installation space;

[0029] 2031, Buffer base; 2032, Top rod; 2033, Spring;

[0030] 2071. Contact; 2072. Touch switch; 2073. Wireless signal transmitter. Detailed Implementation

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] For ease of understanding and description, the following description of the present invention uses absolute positional relationships. Unless otherwise specified, the directional term "above" indicates... Figure 1 The direction above, the directional word "down" indicates Figure 1 The lower side of the middle, the directional word "left" indicates Figure 1 The left side of the direction, the directional word "right" indicates Figure 1 The right-hand direction in the text, the directional word "front" indicates perpendicular to. Figure 1 The direction of the paper and the direction pointing inwards; the directional word "back" indicates perpendicular to. Figure 1 The orientation of the paper is pointed outwards from the paper surface. This invention is described from the perspective of a reader or user, but the aforementioned directional terms should not be construed as limiting the scope of protection of this invention. Regarding the dimensions and angles of the components, those skilled in the art can determine them specifically according to actual needs.

[0033] like Figures 1 to 3 As shown in the embodiment of the present invention, a lifting device for the billet and dummy bar of a vertical continuous casting machine includes a hoisting mechanism 100, a lifting support 200, a pulley assembly 300, a support column 400, and a wire rope 500. The pulley assembly 300 is located on the upper part of the support column 400. The lifting support 200 can move up and down along the support column 400. One end of the wire rope 500 is connected to the lifting support 200, and the other end of the wire rope 500 is connected to the hoisting mechanism 100. The wire rope 500 passes around the pulley assembly 300, and the hoisting mechanism 100 can drive the lifting support 200 to move up and down along the support column 400.

[0034] This invention employs a coiled wire rope solution, effectively solving the cumbersome problems encountered during initial equipment installation. It eliminates the need for extremely high positioning precision, as the pulley assembly contains two pulleys, ensuring they are aligned on the same center line. Furthermore, the wire rope and pulley structure is simpler than the sprocket and chain structure, reducing the difficulty of maintenance for users during later operation. The cost of wire rope and pulleys is significantly lower than that of sprocket and chain structures, reducing the initial investment for the buyer and saving money. This results in substantial cost savings both in terms of initial investment and subsequent maintenance.

[0035] like Figures 3 to 4 As shown, the hoisting mechanism 100 is located at the lower part of the support column 400. The hoisting mechanism 100 includes a motor 101, a brake 102, a reducer 103, a coupling 104, and a wire rope drum 105 connected in sequence. The other end of the wire rope 500 is connected to the wire rope drum 105. The lifting device for the billet and dummy bar of the vertical continuous casting machine may contain two wire ropes 500, or it may contain three or four wire ropes 500.

[0036] Motor 101 serves as the driving energy source for the equipment. It also includes rotor and stator temperature detection components to monitor the motor's operating status and wear, thus protecting it. Brake 102, as the equipment's braking unit, protects motor 101 and reducer 103, ensuring a smooth stop when the equipment reaches the designated position. The brake primarily consists of wear plates, an on / off switch, and a switch to detect wear on the wear plates, promptly reminding the user to replace them and ensuring reliable equipment operation.

[0037] The reducer 103 converts the high-speed output of the motor 101 to a low-speed output, increasing the torque according to the reduction ratio, thereby enabling the wire rope drum 105 to be driven with a larger driving force. The coupling 104 connects the reducer 103 and the wire rope drum 105. The wire rope drum 105 winds the wire rope 500, and the rotation of the drum controls the lifting and lowering of the lifting bracket 200. The drum has two types of wire rope grooves to suit different directions of rotation.

[0038] The lifting device for the billet and dummy bar of the vertical continuous casting machine also includes a control unit. The motor 101 is connected to a first encoder 106. Both the first encoder 106 and the motor 101 are connected to the control unit. The control unit can control the operation of the lifting device for the billet and dummy bar of the vertical continuous casting machine. The first encoder 106 can measure the number of rotations of the motor 101.

[0039] The number of rotations of the motor 101 is directly proportional to the rotation of the wire rope drum 105. The first encoder 106 can measure the number of rotations of the motor 101, thereby obtaining the number of rotations of the wire rope drum 105. Multiplying the number of rotations of the wire rope drum 105 by the diameter of the wire rope drum 105 gives the distance the lifting support 200 moves in the vertical direction. Thus, the control unit can calculate the position of the lifting support 200 in the vertical direction, enabling real-time monitoring of the position of the lifting support 200.

[0040] like Figures 5 to 9 As shown, the lifting bracket 200 includes a sliding base 201 and a support base 202 connected in sequence. The sliding base 201 has a U-shaped cross-section and includes a front side plate 2011, a middle plate 2012, and a rear side plate 2013 connected in sequence from front to back. The front side plate 2011, middle plate 2012, and rear side plate 2013 are all in an upright position. The front side plate 2011, middle plate 2012, and rear side plate 2013 enclose a column installation space 2014. The column installation space 2014 is located to the left of the middle plate 2012, and the support base 202 is located to the right of the middle plate 2012. The support column 400 is located within the column installation space 2014. The sliding base 201 and the support base 202 are the main load-bearing components, mainly bearing the weight of the billet and / or the dummy bar, as well as supporting the installation of other related equipment.

[0041] like Figure 6 As shown, the lifting bracket 200 also includes a buffer mechanism 203. The buffer mechanism 203 includes a buffer base 2031 and a top rod 2032 connected vertically. The buffer base 2031 is located above the support base 202. A support plate 204 is connected to the outside of the support base 202. The support plate 204 is roughly horizontal. The top rod 2032 passes through the support base 202 and the support plate 204 from top to bottom. A spring 2033 is sleeved on the lower part of the top rod 2032. The spring 2033 can provide an upward restoring force to the buffer base 2031 and the top rod 2032. Spring 2033 is located above support plate 204. Spring 2033 is provided with a protective sleeve. The protective sleeve includes an upper protective sleeve and a lower protective sleeve arranged vertically. The lower end of the upper protective sleeve is sleeved over the upper end of the lower protective sleeve. The upper end of the upper protective sleeve is snapped and fixed to the top rod 2032. The upper end of spring 2033 abuts against the upper end of the upper protective sleeve. The lower end of spring 2033 abuts against support plate 204.

[0042] The buffer base 2031 and the top rod 2032 can move up and down synchronously. When the buffer base 2031 is at its upper limit position, there is a gap between the buffer base 2031 and the support base 202 in the vertical direction; when the buffer base 2031 is at its lower limit position, the buffer base 2031 is in contact with the support base 202. A convex-concave guide structure can be provided between the buffer base 2031 and the support base 202. For example, the buffer base 2031 has a groove, and the support base 202 has a protrusion, and the groove and the protrusion can be matched and inserted vertically.

[0043] like Figures 6 to 7 As shown, a position detection sensor 207 is provided below the support plate 204. The position detection sensor 207 includes a contact 2071, a touch switch 2072, and a wireless signal transmitter 2073. The touch switch 2072 is connected to the wireless signal transmitter 2073, and the contact 2071 is connected to the lower end of the push rod 2032. The wireless signal transmitter 2073 and the control unit can communicate wirelessly. When the push rod 2032 moves downward, the contact 2071 can touch the touch switch 2072, and the wireless signal transmitter can transmit a wireless signal to the control unit, which can receive the wireless signal.

[0044] The buffer mechanism 203 primarily serves a buffering function, and through the up-and-down movement of the push rod 2032, the contact 2071 can touch the touch switch 2072. After the billet and / or the dummy bar falls onto the buffer base 2031, the push rod 2032 moves downward, and the touch switch 2072 is activated. The wireless signal transmitter then emits a wireless signal, which is received by the control unit in the control room, indicating that the lifting bracket 200 has received the billet and / or the dummy bar. A protective cover may be provided around the position detection sensor 207.

[0045] like Figures 8 to 9 As shown, both the front side plate 2011 and the rear side plate 2013 are connected to two guide wheels 205 arranged vertically. A rail cleaner 206 is installed above each guide wheel 205. A wire rope tie rod 208 is connected to the left side of the middle plate 2012, and one end of the wire rope 500 is fixedly connected to the wire rope tie rod 208. The lifting bracket 200 slides up and down along the support column 400 via the guide wheels 205, ensuring stable and reliable equipment movement. The rail cleaner 206 can clean debris from the guide rails, ensuring smooth rail operation. The wire rope tie rod 208 is used to fix the wire rope 500.

[0046] like Figure 10 As shown, the pulley assembly 300 includes a pulley platform 306, a pulley 301, a shaft wheel 304, a rope breakage detection sensor 303, and a second encoder 305. The pulley 301 is fitted over the shaft wheel 304. The shaft wheel 304 is connected to the pulley platform 306 via bearings and bearing seats. The bearing seats have lubrication holes 302 to ensure smooth pulley operation, stable lifting support movement, and extended wire rope life. The pulley 301 is a fixed pulley, corresponding one-to-one with the wire rope 500. The rope breakage detection sensor 303 is located on the outer circumference of the pulley 301. The second encoder 305 measures the number of rotations of the pulley 301. Both the rope breakage detection sensor 303 and the second encoder 305 are connected to the control unit. The rope breakage detection sensor 303 is a proximity switch; when the wire rope suddenly breaks, it sends a signal to the control unit, alerting maintenance personnel to check the wire rope condition and stop the machine for inspection.

[0047] The second encoder 305 measures the number of rotations of the pulley 301. Multiplying the number of rotations of the pulley 301 by its diameter yields the vertical distance the lifting support 200 has moved. The control unit can then calculate the vertical position of the lifting support 200, enabling real-time monitoring. Simultaneously, the control unit compares the vertical positions of the lifting support 200 calculated by the first encoder 106 and the second encoder 305. On one hand, the distance between these two positions indicates the tension of the wire rope 500 and indirectly the lubrication and rotation of the pulley 301. On the other hand, when the distance between the two positions exceeds a set value, such as 70% of the maximum tensile deformation of the wire rope 500 (the specific deformation is given by the wire rope manufacturer), the control unit issues an alarm signal and stops the lifting device of the vertical continuous casting machine's billet and dummy bar. Maintenance personnel are then required to perform maintenance.

[0048] like Figure 11 As shown, the support column 400 includes a front column 401 and a rear column 403 spaced apart. A front guide rail 404 is connected to the front of the front column 401, and a rear guide rail 405 is connected to the rear of the rear column 403. Both the front column 401 and the rear column 403 have water-cooled cavities filled with cooling water. Due to the harsh working environment, the water-cooled structure of the front column 401 and the rear column 403 protects the equipment from deformation after prolonged use. The guide wheel 205 on the front side of the lifting bracket 200 contacts the front guide rail 404, and the guide wheel 205 on the rear side of the lifting bracket 200 contacts the rear guide rail 405, ensuring smooth vertical movement of the lifting bracket 200.

[0049] A protective plate 402 is installed between the front column 401 and the rear column 403. The front end of the protective plate 402 is welded to the right end of the front column 401, and the rear end of the protective plate 402 is welded to the right end of the rear column 403. During normal production, the cutting slag from the flame cutting machine splashes severely. The benefit of the protective plate 402 is to protect the equipment, wire rope, switches, etc.

[0050] The following describes the working process of the lifting device for the billet and dummy bar of the vertical continuous casting machine.

[0051] During production on a vertical continuous casting machine, molten steel is cooled by the tundish, the crystallizer, the fan-shaped section, and by the straightening force of the vertical machine's straightening machine and the weight of the dummy bar. This ensures that the billet can move downwards at a certain speed. After passing through multiple straightening machines, the billet reaches the vertical fire cutter. At this point, the billet head needs to be cut, and the dummy bar is supported by the lifting bracket 200 of the lifting device to prevent it from suddenly falling onto the lifting bracket 200 after the dummy bar head is cut.

[0052] When the billet is about to reach the vertical flame cutting machine, the PLC (control unit) issues a command, and the hoisting mechanism 100 of the aforementioned lifting device starts working. The motor 101 rotates, and through the reducer 103, coupling 104, and wire rope drum 105, the wire rope 500 on the drum is driven to pass through the pulley assembly 300, converting the rotational motion of the drum into the linear motion of the wire rope 500. The lifting speed can be steplessly controlled according to the motor speed. The first encoder 106 at the motor calculates the lifting speed and position of the wire rope 500 by calculating the drum diameter and the speed ratio of the reducer. The end of the wire rope 500 is connected to the lifting bracket 200 through the wire rope tie rod 208. The entire equipment structure connects the hoisting mechanism 100 and the lifting bracket 200 together through the wire rope. The lifting support 200 can move upward along the guide rails (front guide rail 404 and rear guide rail 405) of the lifting support column 400. When it reaches the position of the dummy bar, the motor can apply an upward force to the dummy bar in advance according to the change in torque. At the same time, the lifting support 200 contains a touch switch 2072. When the buffer mechanism 203 of the lifting mechanism is under pressure, the contact 2071 contacts the touch switch 2072, and the wireless signal transmitter emits a wireless signal. The control unit in the control room receives the wireless signal. These two measures can ensure that the dummy bar and wire rope will not be subjected to a large impact force when the billet head is cut off. At the same time, the main control room will also receive the signal to ensure the service life and reliability of the equipment.

[0053] During the cutting process of the vertical flame cutting machine, a large amount of cutting slag will be splashed out. The protective plate 402 can prevent slag from splashing onto the motor 101 and the wire rope 500. At the same time, the front column 401 and the rear column 403 are water-cooled structures, which are more conducive to protecting the equipment and preventing it from deforming in the high-temperature working environment, thus facilitating the smooth operation of the equipment.

[0054] The lifting position of the lifting bracket 200 can be determined by the values ​​recorded by the first encoder 106 at the rear of the motor and the second encoder 305 on the pulley assembly 300. After calculation of the equipment parameters, a set of values ​​can be obtained to record the position of the lifting bracket 200. By processing these two numbers, the position of the equipment can be more accurately guaranteed. At the same time, when the interpolation of the two numbers exceeds a certain value, it indicates that the pulley assembly 300 is jammed or the wire rope has been stretched to its limit and needs to be replaced. This can more intelligently remind future maintenance personnel to perform targeted equipment maintenance and improve work efficiency.

[0055] After the lifting support 200 reaches the bottom, the billet delivery system of the vertical machine can transport the ingot rod out. At the same time, the billet continues to descend, and the lifting support moves up to drag the billet and prevent it from falling suddenly. Then the vertical fire cutter performs the cutting action. By repeating the above equipment actions, the billets of the vertical machine can be produced one by one.

[0056] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical solutions, and embodiments of the present invention can be freely combined and used together.

Claims

1. A strand and dummy bar lifting device for a vertical continuous casting machine, characterized in that, The vertical continuous casting machine billet and dummy bar lifting device includes a winch mechanism (100), a lifting support (200), a pulley assembly (300), a support column (400), and a steel wire rope (500). The pulley assembly (300) is located at the upper part of the support column (400). One end of the steel wire rope (500) is connected with the lifting support (200), and the other end of the steel wire rope (500) is connected with the winch mechanism (100). The steel wire rope (500) passes through the pulley assembly (300). The winch mechanism (100) can drive the lifting support (200) to move up and down along the support column (400). The winch mechanism (100) includes a motor (101), a brake (102), a speed reducer (103), a shaft coupling (104), and a steel wire rope drum (105) connected in sequence. The vertical continuous casting machine billet and dummy bar lifting device further includes a control unit. The motor (101) is connected with a first encoder (106). The first encoder (106) and the motor (101) are both connected with the control unit. The first encoder (106) can measure the number of rotations of the motor (101). The lifting support (200) includes a sliding base (201) and a support base (202) connected in sequence. The cross section of the sliding base (201) is in a concave shape structure. The sliding base (201) includes a front side plate (2011), an intermediate plate (2012), and a rear side plate (2013) connected in sequence from front to back. The front side plate (2011), the intermediate plate (2012), and the rear side plate (2013) surround a column mounting space (2014). The column mounting space (2014) is located at the left side of the intermediate plate (2012). The support base (202) is located at the right side of the intermediate plate (2012). The front side plate (2011) and the rear side plate (2013) are both connected with two guide wheels (205) arranged in an up-down manner. Above the two guide wheels (205), a rail cleaner (206) is arranged. The left side of the intermediate plate (2012) is connected with a steel wire rope pull rod (208). One end of the steel wire rope (500) is connected and fixed with the steel wire rope pull rod (208). The pulley assembly (300) includes a pulley (301), a shaft wheel (304), a broken rope detection sensor (303), and a second encoder (305). The broken rope detection sensor (303) is located outside the outer circumferential surface of the pulley (301). The second encoder (305) can measure the number of rotations of the pulley (301). The broken rope detection sensor (303) and the second encoder (305) are both connected with the control unit.

2. The billet and dummy bar lifting device of a vertical continuous casting machine according to claim 1, characterized by, The winch mechanism (100) is located at the lower part of the support column (400). The other end of the steel wire rope (500) is connected with the steel wire rope drum (105).

3. The billet and dummy bar lifting device for a vertical continuous casting machine according to claim 1, characterized in that, The lifting support (200) further comprises a buffering mechanism (203), which comprises a buffering base (2031) and a top rod (2032) connected in sequence, the buffering base (2031) is located above the supporting base (202), the supporting base (202) is connected with a supporting flat plate (204), the top rod (2032) passes through the supporting base (202) and the supporting flat plate (204) in sequence, the lower part of the top rod (2032) is provided with a spring (2033), and the spring (2033) can provide upward restoring force for the buffering base (2031) and the top rod (2032).

4. The billet and dummy bar lifting device of a vertical continuous casting machine according to claim 3, wherein A position detection sensor (207) is arranged below the supporting flat plate (204), the position detection sensor (207) comprises a contact head (2071), a touch switch (2072) and a wireless signal transmitter (2073), the touch switch (2072) and the wireless signal transmitter (2073) are connected, the contact head (2071) is connected with the lower end of the top rod (2032), the wireless signal transmitter (2073) and the control unit can communicate wirelessly, when the top rod (2032) moves downward, the contact head (2071) can touch the touch switch (2072), and the wireless signal transmitter (2073) can transmit wireless signals to the control unit.

5. The billet and dummy bar lifting device for a vertical continuous casting machine according to claim 1, wherein The supporting column (400) comprises a front column (401) and a rear column (403) arranged in sequence, the front column (401) is connected with a front guide rail (404) in front, the rear column (403) is connected with a rear guide rail (405) at the back, a water cooling cavity is arranged in the front column (401) and the rear column (403), and cooling water is arranged in the water cooling cavity.

6. The billet and dummy bar lifting device of a vertical continuous casting machine according to claim 5, wherein A protection column (402) is arranged between the front column (401) and the rear column (403), the front end of the protection column (402) is connected with the right end of the front column (401), and the rear end of the protection column (402) is connected with the right end of the rear column (403).

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