Injection molding structure convenient to disassemble

Abstract

The injection molding structure comprises an injection molding box, a mounting hole is formed in the injection molding box, an injection molding barrel is arranged on one side of the mounting hole, a sealing disc is detachably arranged on the other side of the mounting hole, a screw rod is arranged at the injection molding barrel, and a main shaft of the screw rod penetrates through the mounting hole and the sealing disc; a pushing mechanism is detachably arranged on the side edge of the main shaft, meanwhile, the pushing mechanism is connected with an injection molding box, a motor is further arranged on the side edge of the injection molding box, and the motor is connected with the main shaft through a transmission belt; according to the utility model, the detachable sealing disc and the pushing mechanism are arranged, so that the screw rod can be detached and taken out for maintenance according to requirements, the current situation that the injection molding barrel needs to be detached for a long time is changed, and the situation that workers idle for maintaining the screw rod due to complicated detachment is avoided.

Description

Technical Field

[0001] The utility model relates to the field of injection molding equipment, in particular to an injection molding structure which is easy to disassemble. Background Art

[0002] In the production of plastic products, injection molding equipment is generally used to efficiently complete its production. Injection molding equipment is the main molding equipment that uses plastic molding molds to make plastic products of various shapes from thermoplastics or thermosetting plastics.

[0003] At present, there are many types of injection molding equipment. For example, a Chinese patent with patent publication number CN112677431A discloses an injection molding device of an injection molding machine, including a shooting platform base, a slide table is arranged on the shooting platform base, a sliding structure is arranged between the slide table and the shooting platform base, and a shooting platform front plate mechanism, a shooting platform middle plate mechanism and a shooting platform rear plate mechanism are arranged on the slide table in sequence. One end of the shooting platform front plate mechanism is used for discharging glue, and the other end of the shooting platform front plate mechanism is connected to the shooting platform middle plate mechanism, and the shooting platform middle plate mechanism can be driven to move relative to the shooting platform front plate mechanism. The shooting platform middle plate mechanism penetrates into the shooting platform front plate mechanism to extrude the shooting platform front plate mechanism, and the shooting platform rear plate mechanism penetrates into the shooting platform middle plate mechanism to drive the shooting platform middle plate mechanism to rotate. The present invention has the advantages of low energy consumption and high response.

[0004] Whether using the injection molding device provided by the above patent or other types of injection molding devices, during long-term operation, the screw rotates in the injection molding barrel, and the high-temperature material is pushed to move by the rotation of the screw. In the process of pushing the material to move, there is a large friction between the screw and the material, and the wear is relatively serious. Therefore, in order to ensure the good operation of the injection molding equipment, the screw needs to be maintained. The current injection molding equipment is relatively cumbersome to disassemble and assemble. If it is disassembled and assembled for screw maintenance, it is relatively not worth the loss. Therefore, the staff will not disassemble and assemble the injection molding equipment for screw maintenance unless they have to. This situation will be detrimental to the operation of the equipment and the production of plastic products. Utility Model Content

[0005] The utility model aims to provide an injection molding structure that is easy to disassemble, aiming to improve the problem that the disassembly of the injection molding equipment is cumbersome and not conducive to the maintenance of the screw.

[0006] The utility model is implemented as follows: an injection molding structure that is easy to disassemble comprises an injection molding box, a mounting hole is arranged on the injection molding box, an injection molding cylinder is arranged on one side of the mounting hole, a sealing disk is detachably arranged on the other side, a screw is arranged at the injection molding cylinder, and the main shaft of the screw passes through the mounting hole and the sealing disk; a pushing mechanism is detachably arranged on the side of the main shaft, and the pushing mechanism is connected to the injection molding box, and a motor is also arranged on the side of the injection molding box, and the motor is connected to the main shaft through a transmission belt.

[0007] Preferably, the diameter of the mounting hole is greater than or equal to the outer diameter of the screw, the sealing disk is connected to the injection molding box by bolts, and the outer diameter of the sealing disk is greater than the diameter of the mounting hole.

[0008] Preferably, a limiting groove is provided on the main shaft, and a driving wheel is sleeved thereon, a limiting column is fixedly provided on the inner side of the driving wheel, and the limiting column is located in the limiting groove.

[0009] Preferably, the limiting groove is arranged along the length direction of the main shaft, and an opening is arranged at the end; the transmission belt is sleeved on the driving wheel.

[0010] Preferably, the pushing mechanism includes a support frame, a second telescopic cylinder, a vertical plate and a sleeve, the second telescopic cylinder is arranged on the support frame, the vertical plate is sleeved on the end of the second telescopic cylinder, and the sleeve is detachably arranged on the upper end of the vertical plate and sleeved on the end shaft of the main shaft.

[0011] Preferably, a convex plate is fixedly provided below the sleeve, a groove is provided at the upper end of the vertical plate, and the convex plate is connected by bolts and inserted into the groove.

[0012] Preferably, the end of the support frame is connected to the injection molding box, and a supporting arc plate is arranged above the support frame, a clamping arc plate is arranged above the supporting arc plate via bolts, and the second telescopic cylinder penetrates the space formed by the supporting arc plate and the clamping arc plate.

[0013] Preferably, a limiting mechanism is provided on the side of the driving wheel, and the limiting mechanism includes a main board and two first limiting plates. The main board is connected to the sealing disk. The two first limiting plates are arranged below the main board and located on both sides of the driving wheel. Balls are embedded on the adjacent side walls of the two first limiting plates, and the balls can contact the driving wheel.

[0014] Preferably, a limiting mechanism is provided on the side of the driving wheel, and the limiting mechanism includes a main board, a first limiting plate and a second limiting plate. The main board is connected to the sealing disk, the first limiting plate is provided below the main board, and a plug-in plate is fixedly provided at the end of the main board, a plug-in slot is provided at the upper end of the second limiting plate, an adjusting screw is provided at the plug-in slot, the plug-in plate extends into the plug-in slot, and the adjusting screw is threadedly inserted into the plug-in plate.

[0015] Compared with the prior art, the beneficial effects of the utility model are:

[0016] 1. The utility model is provided with a detachable sealing disk and a pushing mechanism, so that the sealing disk and the pushing mechanism can be disassembled as needed, and the screw can be taken out for maintenance, which changes the current situation that it takes a long time to disassemble the injection molding cylinder and avoids the staff from neglecting to maintain the screw due to the cumbersome disassembly.

[0017] 2. The utility model is provided with a pushing mechanism to push the screw to move, reduce the space at the end of the injection molding cylinder, and increase the pressure of the material output from the injection molding cylinder; a limiting mechanism is provided to limit the position of the driving wheel to provide support for the movement of the screw to avoid the transmission belt being detached due to the movement of the screw, which affects the rotation of the screw to transport the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a three-dimensional structural schematic diagram of an embodiment of the utility model;

[0019] Figure 2 It is a partial three-dimensional structural schematic diagram of the injection molding box of the utility model;

[0020] Figure 3 It is a three-dimensional structural schematic diagram of the screw of the utility model;

[0021] Figure 4 It is a three-dimensional structural schematic diagram of the push mechanism of the utility model;

[0022] Figure 5 It is a schematic diagram of the first three-dimensional structure of the limiting mechanism of the utility model;

[0023] Figure 6 It is a second three-dimensional structural diagram of the limiting mechanism of the utility model.

[0024] In the figure: 1. injection molding box; 11. injection molding cylinder; 12. injection molding stand; 13. first telescopic cylinder; 14. mounting hole; 15. sealing disk; 2. screw; 21. main shaft; 22. limiting groove; 23. end shaft; 24. driving wheel; 25. limiting column; 3. pushing mechanism; 31. bracket; 32. supporting arc plate; 33. second telescopic cylinder; 34. clamping arc plate; 35. vertical plate; 36. groove; 37. convex plate; 38. sleeve; 4. limiting mechanism; 41. main board; 42. first limiting plate; 43. ball; 44. second limiting plate; 45. plug-in plate; 46. plug-in groove; 47. adjusting screw. DETAILED DESCRIPTION

[0025] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] The following is a further description with reference to the accompanying drawings and specific embodiments:

[0027] Example 1

[0028] An injection molding structure that is easy to disassemble, which refers to the injection system in the injection molding machine (the entire injection molding machine includes the injection system, mold clamping system, hydraulic transmission system, electrical control system, lubrication system, heating and cooling system, safety monitoring system, etc.). Its working principle is similar to that of a syringe for injection. It uses the thrust of the screw (or plunger) to inject the plasticized molten state (i.e. viscous flow state) plastic into the closed mold cavity (this operation has an injection system), and the product is obtained after solidification and finalization.

[0029] like Figure 1 , Figure 2 As shown, the specific, easily disassembled injection molding structure includes an injection molding box 1, an injection molding barrel 11, a sealing disk 15, a screw 2 and a pushing mechanism 3. A mounting hole 14 is provided on the injection molding box 1. The sealing disk 15 and the injection molding barrel 11 are respectively provided on both sides of the mounting hole 14. At the same time, the sealing disk 15 is connected to the injection molding box 1 by bolts. The main part of the screw 2 is located in the injection molding barrel 11 and the mounting hole 14, and the main shaft 21 of the screw 2 penetrates the sealing disk 15. The pushing mechanism 3 is provided at the end of the main shaft 21, and the screw 2 can be controlled to move in the injection molding barrel 11, so as to increase the pressure of the molten material outputting the injection molding barrel 11 through the movement of the screw 2. In addition, a motor is also provided on the side of the injection molding box 1, and the motor is connected to the main shaft 21 through a transmission belt, and then the screw 2 can be controlled to rotate through the operation of the motor, so as to control the material to move slowly in the injection molding barrel 11. This arrangement allows the screw 2 to be removed by disassembling the push mechanism 3 and the sealing disk 15 when it is necessary to maintain the screw 2, thereby removing the restriction on the screw 2, and making it easier for the staff to remove the screw 2 from the injection cylinder 11 and the injection molding box 1 for maintenance, thus changing the current situation where it takes a long time to disassemble the injection cylinder 11, and avoiding the staff from neglecting to maintain the screw due to the cumbersome disassembly. In order to facilitate the output of the screw 2 from the mounting hole 14, the diameter of the mounting hole 14 is greater than or equal to the outer diameter of the screw 2. At the same time, in order to facilitate the conveying of materials, the outer diameter of the sealing disk 15 is greater than the diameter of the mounting hole 14. The mounting hole 14 is sealed and blocked under the action of the sealing disk 15, and the sealing disk 15 is movably connected to the main shaft 21 in a sealing manner.

[0030] like Figure 1 As shown, in addition, an injection molding stand 12 is movably sleeved below the injection molding box 1, and a first telescopic cylinder 13 is arranged on the injection molding box 1. The telescopic end of the first telescopic cylinder 13 is connected to the mold clamping system to control the movement of the injection molding box 1 and the injection molding cylinder 11, and provide support for the connection and disconnection between the injection molding cylinder 11 and the mold clamping system.

[0031] like Figure 3As shown, in order to avoid the screw 2 from rotating and affecting the screw 2 from moving along the length direction of the injection molding cylinder 11, a limiting groove 22 is provided on the main shaft 21, and the limiting groove 22 is provided along the length direction of the main shaft 21, and the end is provided with an opening, and a driving wheel 24 is sleeved on the main shaft 21, and a limiting column 25 is fixedly provided on the inner side of the driving wheel 24, and the limiting column 25 is located in the limiting groove 22, and the transmission belt is sleeved on the driving wheel 24. Under the cooperation of the limiting column 25 and the limiting groove 22, the driving wheel 24 can rotate synchronously with the main shaft 21, and then the driving wheel 24 and the screw 2 can be controlled to rotate under the operation of the motor to realize the conveying of materials. Because the length of the limiting groove 22 is greater than the length of the limiting column 25, when the pushing mechanism 3 controls the screw 2 to move along the length direction of the injection molding cylinder 11, the screw 2 can move relative to the driving wheel 24, so as to avoid the driving wheel 24 moving away from the transmission belt, resulting in the transmission belt being separated.

[0032] like Figure 5 As shown, in order to limit the position of the driving wheel 24, a limiting mechanism 4 is arranged on the side of the driving wheel 24, and the limiting mechanism 4 includes a main board 41 and two first limiting plates 42. The main board 41 is connected to the sealing disk 15. The two first limiting plates 42 are arranged below the main board 41 and located on both sides of the driving wheel 24. Balls 43 are inlaid on the adjacent side walls of the two first limiting plates 42, and the balls 43 can contact the driving wheel 24. Since the first limiting plates 42 are distributed on both sides of the driving wheel 24, the driving wheel 24 can be limited to be placed stably relative to the injection molding box 1, thereby providing support for the screw 2 to move relative to the driving wheel 24. The setting of the ball 43 facilitates reducing the resistance between the driving wheel 24 and the first limiting plate 42 by rolling. When the screw 2 needs to be maintained, the limiting mechanism 4 is disassembled by rotating the bolts connecting the main board 41 and the sealing disk 15.

[0033] like Figure 4 As shown, in order to control the movement of the screw 2 relative to the injection molding cylinder 11, the pushing mechanism 3 includes a support frame 31, a second telescopic cylinder 33, a vertical plate 35 and a sleeve 38. The end of the support frame 31 is connected to the injection molding box 1, and a supporting arc plate 32 is arranged above the support frame 31. A clamping arc plate 34 is arranged above the supporting arc plate 32 through bolts. The second telescopic cylinder 33 penetrates the space formed by the supporting arc plate 32 and the clamping arc plate 34. The vertical plate 35 is sleeved at the end of the second telescopic cylinder 33. A groove 36 is arranged at the upper end of the vertical plate 35. The sleeve 38 is sleeved on the end shaft 23 of the main shaft 21 through a bearing connection. A convex plate 37 is fixedly arranged below the sleeve 38. The convex plate 37 is connected by bolts and inserted into the groove 36. Under the action of the support frame 31, the first telescopic cylinder 33 is stably installed relative to the injection molding box 1. At the same time, under the action of the first telescopic cylinder 33, the movement of the screw 2 can be controlled so as to increase the pressure of the material output from the injection molding cylinder 11 through the movement of the screw 2. When the screw rod 2 needs to be maintained, the bolts connecting the convex plate 37 and the vertical plate 35 are rotated to release the restrictions of the sleeve 38 and the vertical plate 35.

[0034] Example 2

[0035] An injection molding structure that is easy to disassemble, which refers to the injection system in the injection molding machine (the entire injection molding machine includes the injection system, mold clamping system, hydraulic transmission system, electrical control system, lubrication system, heating and cooling system, safety monitoring system, etc.). Its working principle is similar to that of a syringe for injection. It uses the thrust of the screw (or plunger) to inject the plasticized molten state (i.e. viscous flow state) plastic into the closed mold cavity (this operation has an injection system), and the product is obtained after solidification and finalization.

[0036] like Figure 1 , Figure 2 As shown, the specific, easily disassembled injection molding structure includes an injection molding box 1, an injection molding barrel 11, a sealing disk 15, a screw 2 and a pushing mechanism 3. A mounting hole 14 is provided on the injection molding box 1. The sealing disk 15 and the injection molding barrel 11 are respectively provided on both sides of the mounting hole 14. At the same time, the sealing disk 15 is connected to the injection molding box 1 by bolts. The main part of the screw 2 is located in the injection molding barrel 11 and the mounting hole 14, and the main shaft 21 of the screw 2 penetrates the sealing disk 15. The pushing mechanism 3 is provided at the end of the main shaft 21, and the screw 2 can be controlled to move in the injection molding barrel 11, so as to increase the pressure of the molten material outputting the injection molding barrel 11 through the movement of the screw 2. In addition, a motor is also provided on the side of the injection molding box 1, and the motor is connected to the main shaft 21 through a transmission belt, and then the screw 2 can be controlled to rotate through the operation of the motor, so as to control the material to move slowly in the injection molding barrel 11. This arrangement allows the screw 2 to be removed by disassembling the push mechanism 3 and the sealing disk 15 when it is necessary to maintain the screw 2, thereby removing the restriction on the screw 2, and making it easier for the staff to remove the screw 2 from the injection cylinder 11 and the injection molding box 1 for maintenance, thus changing the current situation where it takes a long time to disassemble the injection cylinder 11, and avoiding the staff from neglecting to maintain the screw due to the cumbersome disassembly. In order to facilitate the output of the screw 2 from the mounting hole 14, the diameter of the mounting hole 14 is greater than or equal to the outer diameter of the screw 2. At the same time, in order to facilitate the conveying of materials, the outer diameter of the sealing disk 15 is greater than the diameter of the mounting hole 14. The mounting hole 14 is sealed and blocked under the action of the sealing disk 15, and the sealing disk 15 is movably connected to the main shaft 21 in a sealing manner.

[0037] like Figure 1 As shown, in addition, an injection molding stand 12 is movably sleeved below the injection molding box 1, and a first telescopic cylinder 13 is arranged on the injection molding box 1. The telescopic end of the first telescopic cylinder 13 is connected to the mold clamping system to control the movement of the injection molding box 1 and the injection molding cylinder 11, and provide support for the connection and disconnection between the injection molding cylinder 11 and the mold clamping system.

[0038] like Figure 3As shown, in order to avoid the screw 2 from rotating and affecting the screw 2 from moving along the length direction of the injection molding cylinder 11, a limiting groove 22 is provided on the main shaft 21, and the limiting groove 22 is provided along the length direction of the main shaft 21, and the end is provided with an opening, and a driving wheel 24 is sleeved on the main shaft 21, and a limiting column 25 is fixedly provided on the inner side of the driving wheel 24, and the limiting column 25 is located in the limiting groove 22, and the transmission belt is sleeved on the driving wheel 24. Under the cooperation of the limiting column 25 and the limiting groove 22, the driving wheel 24 can rotate synchronously with the main shaft 21, and then the driving wheel 24 and the screw 2 can be controlled to rotate under the operation of the motor to realize the conveying of materials. Because the length of the limiting groove 22 is greater than the length of the limiting column 25, when the pushing mechanism 3 controls the screw 2 to move along the length direction of the injection molding cylinder 11, the screw 2 can move relative to the driving wheel 24, so as to avoid the driving wheel 24 moving away from the transmission belt, resulting in the transmission belt being separated.

[0039] like Figure 6 As shown, a limiting mechanism 4 is provided on the side of the driving wheel 24, and the limiting mechanism 4 includes a main board 41, a first limiting plate 42 and a second limiting plate 44. The main board 41 is connected to the sealing disk 15, the first limiting plate 42 is arranged below the main board 41, and a plug-in plate 45 is fixedly arranged at the end of the main board 41, and a plug-in slot 46 is arranged at the upper end of the second limiting plate 44, and an adjusting screw 47 is arranged at the plug-in slot 46, and the plug-in plate 45 extends into the plug-in slot 46, and the adjusting screw 47 is threadedly inserted into the plug-in plate 45. The first limiting plate 42 and the second limiting plate 44 are respectively arranged on both sides of the driving wheel 24, and the adjacent side walls are inlaid with balls 43. With the cooperation of the first limiting plate 42 and the second limiting plate 44, the driving wheel 24 is limited to be stably placed relative to the injection molding box 1, providing support for the movement of the screw 2. The adjusting screw 47 is arranged, and the relative positions of the first limiting plate 42 and the second limiting plate 44 can be adjusted according to needs, which provides convenience for adapting to driving wheels 24 of different sizes.

[0040] like Figure 4As shown, in order to control the movement of the screw 2 relative to the injection molding cylinder 11, the pushing mechanism 3 includes a support frame 31, a second telescopic cylinder 33, a vertical plate 35 and a sleeve 38. The end of the support frame 31 is connected to the injection molding box 1, and a supporting arc plate 32 is arranged above the support frame 31. A clamping arc plate 34 is arranged above the supporting arc plate 32 through bolts. The second telescopic cylinder 33 penetrates the space formed by the supporting arc plate 32 and the clamping arc plate 34. The vertical plate 35 is sleeved at the end of the second telescopic cylinder 33. A groove 36 is arranged at the upper end of the vertical plate 35. The sleeve 38 is sleeved on the end shaft 23 of the main shaft 21 through a bearing connection. A convex plate 37 is fixedly arranged below the sleeve 38. The convex plate 37 is connected by bolts and inserted into the groove 36. Under the action of the support frame 31, the first telescopic cylinder 33 is stably installed relative to the injection molding box 1. At the same time, under the action of the first telescopic cylinder 33, the movement of the screw 2 can be controlled so as to increase the pressure of the material output from the injection molding cylinder 11 through the movement of the screw 2. When the screw rod 2 needs to be maintained, the bolts connecting the convex plate 37 and the vertical plate 35 are rotated to release the restrictions of the sleeve 38 and the vertical plate 35.

[0041] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may be modified and varied in various ways. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An injection molding structure that is easy to disassemble, characterized in that: The invention comprises an injection molding box (1), a mounting hole (14) is arranged on the injection molding box (1), an injection molding cylinder (11) is arranged on one side of the mounting hole (14), and a sealing disk (15) is detachably arranged on the other side, a screw rod (2) is arranged at the injection molding cylinder (11), and a main shaft (21) of the screw rod (2) passes through the mounting hole (14) and the sealing disk (15); a pushing mechanism (3) is detachably arranged on the side of the main shaft (21), and the pushing mechanism (3) is connected to the injection molding box (1); a motor is also arranged on the side of the injection molding box (1), and the motor is connected to the main shaft (21) through a transmission belt.

2. The easily disassembled injection molding structure according to claim 1, characterized in that: The diameter of the mounting hole (14) is greater than or equal to the outer diameter of the screw (2); the sealing disk (15) is connected to the injection molding box (1) via bolts, and the outer diameter of the sealing disk (15) is greater than the diameter of the mounting hole (14).

3. The easily disassembled injection molding structure according to claim 1, characterized in that: The main shaft (21) is provided with a limiting groove (22) and is sleeved with a driving wheel (24). A limiting column (25) is fixedly provided on the inner side of the driving wheel (24), and the limiting column (25) is located in the limiting groove (22).

4. The easily disassembled injection molding structure according to claim 3, characterized in that: The limiting groove (22) is arranged along the length direction of the main shaft (21), and an opening is arranged at the end thereof; the transmission belt is sleeved on the driving wheel (24).

5. The easily disassembled injection molding structure according to claim 1, characterized in that: The pushing mechanism (3) comprises a support frame, a second telescopic cylinder (33), a vertical plate (35) and a sleeve (38); the second telescopic cylinder (33) is arranged on the support frame; the vertical plate (35) is sleeved on the end of the second telescopic cylinder (33); the sleeve (38) is detachably arranged on the upper end of the vertical plate (35) and sleeved on the end shaft (23) of the main shaft (21).

6. The easily disassembled injection molding structure according to claim 5, characterized in that: A convex plate (37) is fixedly arranged below the sleeve (38), a groove (36) is arranged at the upper end of the vertical plate (35), and the convex plate (37) is connected by bolts and inserted into the groove (36).

7. The easily disassembled injection molding structure according to claim 5, characterized in that: The end of the support frame is connected to the injection molding box (1), and a supporting arc plate (32) is arranged above the support frame, and a clamping arc plate (34) is arranged above the supporting arc plate (32) via bolts, and the second telescopic cylinder (33) penetrates the space formed by the supporting arc plate (32) and the clamping arc plate (34).

8. The easily disassembled injection molding structure according to claim 3, characterized in that: A limiting mechanism (4) is arranged on the side of the driving wheel (24), and the limiting mechanism (4) comprises a main board (41) and two first limiting plates (42). The main board (41) is connected to the sealing disk (15). The two first limiting plates (42) are arranged below the main board (41) and located on both sides of the driving wheel (24). Balls (43) are embedded on the adjacent side walls of the two first limiting plates (42), and the balls (43) can contact the driving wheel (24).

9. The easily disassembled injection molding structure according to claim 3, characterized in that: A limiting mechanism (4) is arranged on the side of the driving wheel (24), and the limiting mechanism (4) comprises a main board (41), a first limiting plate (42) and a second limiting plate (44). The main board (41) is connected to the sealing disk (15). The first limiting plate (42) is arranged below the main board (41), and a plug-in plate (45) is fixedly arranged at the end of the main board (41). The upper end of the second limiting plate (44) is provided with a plug-in slot (46), and an adjusting screw (47) is arranged at the plug-in slot (46). The plug-in plate (45) extends into the plug-in slot (46), and the adjusting screw (47) is threadedly inserted into the plug-in plate (45).

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