Three-layer storage type head

Abstract

The application relates to a three-layer storage type machine head and relates to the technical field of plastic extrusion. In order to solve the problem of poor color layering of plastic products extruded from plastic raw materials of different colors, the machine head comprises a machine body, an annular insertion groove is formed in the machine body, a spiral body is inserted into the annular insertion groove, a sliding column is arranged in the spiral body, an annular groove is formed in the end wall of the spiral body, an annular movable column is arranged in the machine body, the sliding column is inserted into the spiral body, and the sliding column is inserted into the movable column; a first flow channel is formed in the outer side wall of the spiral body, a second flow channel is formed in the side wall of the sliding column, a third flow channel is formed in the movable column, one end of the movable column is connected with a driving assembly for driving the movable column to move, a glue injection flow channel in communication with the annular groove is further formed in the machine body; a first feeding port, a second feeding port and a third feeding port are formed in the outer side wall of the machine body, the first feeding port is in communication with the first flow channel, the second feeding port is in communication with the second flow channel, and the third feeding port is in communication with the third flow channel. The application has the effect of reducing the fusion between different plastic raw materials.

Description

Technical Field

[0001] This application relates to the field of extrusion technology, and in particular to a three-layer storage die head. Background Technology

[0002] A storage die head is a material storage and guiding device used in blow molding machines during plastic molding processes.

[0003] In existing blow molding processes, to improve the overall structural strength of plastic products, different types of plastic raw materials are melted and mixed, and then the mixed molten plastic is extruded. When different types of plastic raw materials are mixed, they first enter the die head through various feed ports of the storage die head. The die head has several flow channels, which are connected to the corresponding feed ports. After entering the die head through the various feed ports, the different types of plastic raw materials flow along different flow channels to the storage bins in the die head for internal mixing, and then are further extruded.

[0004] For some blow-molded products made of mixed materials, in order to obtain plastic products with color gradation, the different plastic raw materials mixed together only differ in color; however, after the different colored plastic raw materials melt and enter the storage silo, they will blend together, resulting in poor color gradation of the extruded plastic products. Summary of the Invention

[0005] To reduce the mixing of different plastic raw materials, this application provides a three-layer storage die head.

[0006] The technical solution for a three-layer storage type die head provided in this application is as follows: A three-layer material storage type machine head includes a body, an annular slot inside the body, a spiral body inserted into the annular slot, the spiral body being annular, the annular slot forming a sliding column within the spiral body, an annular groove penetrating the end wall of the spiral body, a movable column inside the spiral body being annular, the movable column being inserted into the annular groove, and the sliding column being inserted into the movable column; a first flow channel is formed on the outer wall of the spiral body, a second flow channel is formed on the side wall of the sliding column, and a third flow channel is formed within the movable column, one end of the movable column being connected to a drive assembly for moving the movable column; a glue injection channel communicating with the annular groove is also formed inside the body; a first inlet, a second inlet, and a third inlet are provided on the outer wall of the body, the first inlet communicating with the first flow channel, the second inlet communicating with the second flow channel, and the third inlet communicating with the third flow channel, the first flow channel and the second flow channel communicating with an opening at one end of the annular groove.

[0007] By adopting the above technical solution, during extrusion, three different colored molten plastics are injected into the machine body through the first, second, and third feed ports. The molten plastic entering from the first feed port further enters the first flow channel, the molten plastic entering from the second feed port further enters the second flow channel, and the molten plastic entering from the third feed port enters the third flow channel. After the first, second, and third flow channels are filled with molten plastic, the drive assembly is activated to move the movable column along the length of the annular groove. At this time, a storage bin is formed at the lower end of the annular groove. All the molten plastics in the first, second, and third flow channels enter the lower end of the annular groove. Then, the drive assembly is activated again to move the movable column back into the insertion slot. The movable column pushes the molten plastic in the annular groove, causing the molten plastic to be extruded from the injection channel, thus realizing extrusion. The design of the first, second, and third flow channels separates the molten plastics of different colors into layers. After the molten plastics of different colors are mixed, the moving column immediately moves down to extrude the mixed molten plastics of different colors, so that the mixed molten plastics are extruded immediately, reducing the fusion that occurs after the molten plastics of different colors are mixed and improving the color layering effect of the extruded products.

[0008] Preferably, the inner wall of the annular slot near the glue injection channel is set as a sloping wall, and the sloping wall is inclined towards the glue injection channel; the end wall of the spiral near the glue injection channel is set as a mating sloping wall that is adapted to and inclined with the sloping wall.

[0009] By adopting the above technical solution, the inclined wall design prevents the molten plastic from accumulating on the inner bottom wall of the annular slot when it flows out of the first and second flow channels. Instead, it continues to flow downwards along the inclined wall, reducing the waste of molten plastic.

[0010] Preferably, the number of the first flow channels along the outer sidewall of the spiral body is at least two, and the number of the second flow channels along the sidewall of the sliding column is at least two.

[0011] By adopting the above technical solution, when the number of first and second flow channels is large, the rate at which the rated amount of molten plastic flows into the annular groove can be increased, and the working time of the overall extrusion process can be shortened.

[0012] Preferably, the first flow channel is spirally opened along the circumference of the outer wall of the spiral body, and the second flow channel is spirally opened along the circumference of the side wall of the sliding column.

[0013] By adopting the above technical solution, the spiral opening of the first and second flow channels can increase the flow mileage of the molten plastic in the first and second flow channels, allowing the molten plastics of different colors to be appropriately cooled during flow, reducing the situation where the molten plastics of different colors will rapidly merge after mixing due to high temperature, and improving the stratification of the molten plastics of different colors after mixing.

[0014] Preferably, the body of the machine has a plug-in groove, which is annular. One end of the plug-in groove is connected to the glue injection channel, and the other end is connected to the annular groove. One end of the movable column is inserted into the plug-in groove.

[0015] By adopting the above technical solution, the opening of the insertion slot can increase the length of the moving column's travel, increase the total amount of molten plastic that can be injected, and allow the operator to select the total amount of molten plastic to be injected into the machine body according to the required length of the extruded product, thereby improving the adjustability of the molten plastic injection amount.

[0016] Preferably, the inner bottom wall of the insertion groove near the glue injection channel is set as a limiting inclined wall, and the end wall of the movable column near the limiting inclined wall is adapted to the limiting inclined wall.

[0017] By adopting the above technical solution, the setting of the limiting inclined wall can support the position of the movable column in the insertion groove, reduce the component force of the insertion groove on the drive component, and at the same time allow the molten plastic entering the insertion groove to flow smoothly into the injection channel, reducing the accumulation of molten plastic on the bottom wall of the insertion groove.

[0018] Preferably, the end wall of the movable column is connected to a telescopic tube, the telescopic tube is connected to the third flow channel, and the end of the telescopic tube away from the third flow channel is connected to the third feed port.

[0019] Normally, molten plastic injected from the third inlet falls into the annular groove and then flows further into the third flow channel, leaving residue of molten plastic in the annular groove. By adopting the above technical solution, the molten plastic entering from the third inlet first enters the telescopic tube and then further enters the third flow channel. The telescopic tube can extend and retract with the up and down movement of the movable column, thus avoiding the residue of molten plastic in the annular groove.

[0020] Preferably, the outer wall of the telescopic tube is wavy, and a plurality of connecting rings are connected to the outer wall of the telescopic tube. The plurality of connecting rings are respectively connected to the corresponding troughs of the outer wall of the telescopic tube. The diameter of the connecting ring is larger than the diameter of the crest of the telescopic tube. The ring wall of the connecting ring has a plurality of through holes, and the through holes of adjacent connecting rings are positioned correspondingly. In all the connecting rings, the same elastic rope passes through the through holes coaxial along the length of the telescopic tube. The two ends of the elastic rope are respectively connected to the end wall of the movable column and the inner wall of the ring groove.

[0021] By adopting the above technical solution, when the elastic rope moves and expands synchronously with the movement of the movable column, several connecting rings will position the elastic rope along the length of the telescopic tube at the outer wall of the telescopic tube. Thus, after the molten plastic from the third feed port enters the telescopic tube, the elastic rope can support the wall of the telescopic tube, reducing the hydraulic pressure of the molten plastic on the telescopic tube and reducing the situation where the telescopic tube is deformed by compression, making it difficult to expand and contract.

[0022] Preferably, the movable column has a flared groove on the end wall near the glue injection channel. The flared groove is annular and connected to a ring plate. The inner wall of the flared groove has a receiving groove. The ring plate includes several arc-shaped plates, which are inserted into the receiving groove. A spring connects the arc plate to the bottom wall of the receiving groove, and a guide wall is provided on the top wall of the arc plate.

[0023] By adopting the above technical solution, when the molten plastic in the third flow channel passes through the flaring groove, the molten plastic contacts the guide wall, applies pressure to the guide wall, and pushes the arc-shaped plate to move and insert into the receiving groove under the guidance of the guide wall. At the same time, the spring is compressed, allowing the molten plastic to pass through the flaring groove. After the molten plastic has completely passed through the flaring groove, the spring force pushes the arc-shaped plate partly out of the receiving groove. The end of the arc-shaped plate away from the spring is attached to the inner wall of the flaring groove away from the receiving groove. When the movable column moves down to squeeze the molten plastic in the insertion groove, several blocking arc-shaped plates can block the flaring groove, further blocking the third flow channel, reducing the situation where the molten plastic in the insertion groove flows back into the third flow channel under the squeezing action.

[0024] In summary, this application includes at least one of the following beneficial technical effects: 1. The design of the first, second, and third flow channels allows for the stratification of molten plastics of different colors. After the molten plastics of different colors are mixed, the moving column immediately moves down to extrude the mixed molten plastics of different colors, so that the mixed molten plastics are extruded immediately, reducing the fusion that occurs after the molten plastics of different colors are mixed and improving the color stratification effect of the extruded products.

[0025] 2. The inclusion of elastic ropes and connecting rings reduces the likelihood of the telescopic tube being squeezed and deformed, making it difficult to extend or retract.

[0026] 3. The ring plate can block the third flow channel, reducing the possibility of molten plastic in the insertion groove flowing back into the third flow channel under the action of extrusion. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a three-layer storage head in an embodiment of this application.

[0028] Figure 2 This is a cross-sectional schematic diagram used in the embodiments of this application to illustrate the positional relationship between the first flow channel, the second flow channel, and the third flow channel.

[0029] Figure 3 yes Figure 2 An enlarged schematic diagram of part A in the middle.

[0030] Figure 4 yes Figure 2 Enlarged schematic diagram of part B.

[0031] Figure 5 This is a structural schematic diagram used in the embodiments of this application to illustrate the positional relationship between several arc-shaped plates.

[0032] Explanation of reference numerals in the attached drawings: 1. Machine body; 11. Annular slot; 111. Sloping wall; 12. Sliding column; 121. Second flow channel; 13. First feed port; 14. Second feed port; 15. Third feed port; 16. Glue injection channel; 17. Insertion groove; 171. Limiting sloping wall; 2. Spiral body; 21. First flow channel; 22. Annular groove; 3. Movable column; 31. Third flow channel; 32. Flared groove; 321. Receiving groove; 4. Telescopic tube; 41. Connecting ring; 411. Through hole; 42. Elastic rope; 5. Ring plate; 51. Arc plate; 511. Guide wall; 52. Spring; 6. Drive assembly; 61. Drive cylinder; 62. Connecting rod. Detailed Implementation

[0033] The following is in conjunction with the appendix Figure 1-5 This application will be described in further detail.

[0034] This application discloses a three-layer storage type die head. (Refer to...) Figure 1 and Figure 2 The three-layer storage type head includes a body 1. The outer wall of the body 1 is connected to a first feed port 13, a second feed port 14, and a third feed port 15. An annular slot 11 is provided inside the body 1. A spiral body 2 is inserted into the annular slot 11. The spiral body 2 is annular and adapted to the annular slot 11. The annular slot 11 forms a sliding column 12 inside the spiral body 2. The sliding column 12 is coaxial with the annular slot 11 and is inserted into the spiral body 2. An annular groove 22 is provided through the upper end wall of the spiral body 2 along the axial direction of the spiral body 2. The annular groove 22 extends through the spiral body 2 along the length direction of the spiral body 2. A movable column 3 is inserted into the annular groove 22. The movable column 3 is annular and adapted to the annular groove 22. The axial length of the annular groove 22 is greater than the axial length of the movable column 3. The movable column 3 is inserted into the annular groove 22 and can slide along the length direction of the annular groove 22.

[0035] Reference Figure 1 and Figure 2A first flow channel 21 is provided on the outer wall of the spiral body 2, and a second flow channel 121 is provided on the side wall of the sliding column 12. The first flow channel 21 and the second flow channel 121 are connected to the opening at the lower end of the annular groove 22. The first feed port 13 is connected to the first flow channel 21, and the second feed port 14 is connected to the second flow channel 121. The number of first flow channels 21 along the outer wall of the spiral body 2 is at least two, and the number of second flow channels 121 along the side wall of the sliding column 12 is at least two. The first flow channels 21 are spirally opened along the circumference of the outer wall of the spiral body 2, and the second flow channels 121 are spirally opened along the circumference of the side wall of the sliding column 12. A third flow channel 31 is provided in the movable column 3. The third flow channel 31 passes through the movable column 3 axially. A telescopic tube 4 is connected between the third feed port 15 and the third flow channel 31.

[0036] Reference Figure 2 The body 1 has a plug-in groove 17, which is annular. One end of the plug-in groove 17 is connected to the glue injection channel 16, and the other end is connected to the annular groove 22 and has the same diameter as the annular groove 22. The end of the movable column 3 near the plug-in groove 17 is inserted into the plug-in groove 17. The first flow channel 21 and the second flow channel 121 are simultaneously connected to the plug-in groove 17.

[0037] Reference Figure 2 One end of the movable column 3 is connected to a drive assembly 6 that drives the movable column 3 to move. The drive assembly 6 includes a connecting rod 62 and a drive cylinder 61. The drive cylinder 61 is a pneumatic cylinder and is connected to the outer wall of the machine body 1. The telescopic rod of the drive cylinder 61 passes through the machine body 1 and is inserted into the annular groove 22 and connected to the connecting rod 62. The end of the connecting rod 62 away from the drive cylinder 61 is fixedly connected to the end wall of the movable column 3.

[0038] During extrusion, three different colored molten plastics are injected into the machine body 1 through the first feed port 13, the second feed port 14, and the third feed port 15. The molten plastic entering through the first feed port 13 further enters the first flow channel 21, the molten plastic entering through the second feed port 14 further enters the second flow channel 121, and the molten plastic entering through the third feed port 15 first enters the telescopic tube 4 and then further enters the third flow channel 31. After the first flow channel 21, the second flow channel 121, and the third flow channel 31 are filled with molten plastic, the start drive cylinder 61 drives the connecting rod 62 to move upward, further driving the movable column 3 to move upward along the length of the annular groove 22 and compressing the telescopic tube 4. The lower end of the movable column 3 moves out of the insertion groove 17. The insertion groove 17 then forms a storage bin, and all the molten plastic in the first flow channel 21, the second flow channel 121, and the third flow channel 31 enters the insertion groove 17. Then, the start drive cylinder 61 drives the connecting rod 62 to push the movable column 3 to re-insert into the insertion groove 17. At the same time, the telescopic tube 4 extends, and the movable column 3 pushes the molten plastic in the insertion groove 17, causing the molten plastic to be extruded from the injection channel 16, thus realizing extrusion.

[0039] Reference Figure 2 The inner wall of the annular slot 11 near the glue injection channel 16 is set as a sloping wall 111, which is inclined towards the glue injection channel 16; the end wall of the spiral body 2 near the glue injection channel 16 is set as a mating sloping wall that is adapted to and inclined with the sloping wall 111.

[0040] The sloped wall 111 ensures that when the molten plastic from the first flow channel 21 and the second flow channel 121 flows out, it will not stay and accumulate on the inner bottom wall of the annular slot 11, but will flow down along the sloped wall 111 into the insertion slot 17.

[0041] Reference Figure 2 The inner bottom wall of the insertion groove 17 near the glue injection channel 16 is set as a limiting inclined wall 171. The end wall of the movable column 3 near the limiting inclined wall 171 is adapted to the limiting inclined wall 171. The setting of the limiting inclined wall 171 can support the position of the movable column 3 in the insertion groove 17, reduce the component force of the insertion groove 17 on the drive component 6, and at the same time allow the molten plastic entering the insertion groove 17 to flow smoothly into the glue injection channel 16, reducing the accumulation of molten plastic on the inner bottom wall of the insertion groove 17.

[0042] Reference Figure 2 and Figure 3 The outer wall of the telescopic tube 4 is wavy, and a connecting ring 41 is connected to each trough of the outer wall of the telescopic tube 4. The diameter of the connecting ring 41 is larger than the diameter of the crest of the telescopic tube 4. Several through holes 411 are opened in the ring wall of the connecting ring 41. In this embodiment, there are 4 through holes 411. The positions of the several through holes 411 of adjacent connecting rings 41 are corresponding. In all the connecting rings 41, the same elastic rope 42 passes through the through holes 411 that are coaxial along the length direction of the telescopic tube 4. The two ends of the elastic rope 42 are connected to the end wall of the movable column 3 and the inner wall of the ring groove 22, respectively.

[0043] When the telescopic tube 4 moves and extends with the movement of the movable column 3, it will drive the elastic rope 42 to extend and extend synchronously. Several connecting rings 41 will position the elastic rope 42 along the length of the telescopic tube 4 at the outer wall of the telescopic tube 4. Thus, after the molten plastic from the third feed port 15 enters the telescopic tube 4, the elastic rope 42 can support the tube wall of the telescopic tube 4, reduce the pressure of the hydraulic pressure of the molten plastic on the telescopic tube 4, and reduce the situation where the telescopic tube 4 is squeezed and deformed, thus preventing it from extending and retracting.

[0044] Reference Figure 2 , Figure 4 and Figure 5The movable column 3 has a flared groove 32 on one end wall near the glue injection channel 16. The flared groove 32 is annular and a ring plate 5 is connected inside the flared groove 32. A receiving groove 321 is provided on the inner wall of the flared groove 32. The ring plate 5 includes several arc-shaped plates 51. Several arc-shaped plates 51 are inserted into the receiving groove 321. A spring 52 is connected between the arc-shaped plates 51 and the bottom wall of the receiving groove 321. A guide wall 511 is provided on the top wall of the arc-shaped plates 51. The guide wall 511 is a downward inclined wall.

[0045] When the molten plastic in the third flow channel 31 passes through the flared groove 32, the molten plastic comes into contact with the guide wall 511. The molten plastic applies pressure to the guide wall 511 and, under the guidance of the guide wall 511, pushes the arc plate 51 to move and insert into the receiving groove 321. At the same time, the spring 52 is compressed, allowing the molten plastic to pass through the flared groove 32. After the molten plastic has completely passed through the flared groove 32, the spring 52 pushes the arc plate 51 partially out of the receiving groove 321. The end of the arc plate 51 away from the spring 52 is attached to the inner wall of the flared groove 32 away from the receiving groove 321. When the movable column 3 moves down to squeeze the molten plastic in the insertion groove 17, several blocking arc plates 51 can block the flared groove 32 and further block the third flow channel 31, reducing the possibility of the molten plastic in the insertion groove 17 flowing back into the third flow channel 31 under the squeezing action.

[0046] The implementation principle of a three-layer storage type die head in this application embodiment is as follows: Three different colored molten plastics are injected into the machine body 1 through the first feed port 13, the second feed port 14 and the third feed port 15. The molten plastic entering through the first feed port 13 further enters the first flow channel 21, the molten plastic entering through the second feed port 14 further enters the second flow channel 121, and the molten plastic entering through the third feed port 15 first enters the telescopic tube 4 and then further enters the third flow channel 31. After the first flow channel 21, the second flow channel 121, and the third flow channel 31 are filled with molten plastic, the start drive cylinder 61 drives the connecting rod 62 to move upward, further driving the movable column 3 to move upward along the length of the annular groove 22 and compressing the telescopic tube 4. The lower end of the movable column 3 moves out of the insertion groove 17. The insertion groove 17 then forms a storage bin, and all the molten plastic in the first flow channel 21, the second flow channel 121, and the third flow channel 31 enters the insertion groove 17. Then, the start drive cylinder 61 drives the connecting rod 62 to push the movable column 3 to re-insert into the insertion groove 17. At the same time, the telescopic tube 4 extends, and the movable column 3 pushes the molten plastic in the insertion groove 17, causing the molten plastic to be extruded from the injection channel 16, thus realizing extrusion. The arrangement of the first flow channel 21, the second flow channel 121, and the third flow channel 31 allows for the stratification of molten plastics of different colors. After the molten plastics of different colors are mixed, the movable column 3 immediately moves down to extrude the mixed molten plastics of different colors, allowing the mixed molten plastics to be extruded immediately. This reduces the fusion that occurs after the molten plastics of different colors are mixed and improves the color stratification effect of the extruded products.

[0047] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A three-layer storage type feed head, comprising a body (1), wherein an annular slot (11) is provided inside the body (1), a spiral (2) is inserted into the annular slot (11), the spiral (2) is annular, and a sliding column (12) is provided inside the spiral (2), characterized in that, The end wall of the spiral (2) is provided with an annular groove (22). A movable column (3) is provided inside the spiral (2). The movable column (3) is annular and is inserted into the annular groove (22). The sliding column (12) is inserted into the spiral (2). A first flow channel (21) is provided on the outer wall of the spiral (2). A second flow channel (121) is provided on the side wall of the sliding column (12). A third flow channel (31) is provided inside the movable column (3). One end of the movable column (3) is connected to a drive mechanism that drives the movable column (3) to move. Moving component (6); the body (1) is also provided with a glue injection channel (16) communicating with the annular groove (22); the outer wall of the body (1) is provided with a first inlet (13), a second inlet (14) and a third inlet (15), the first inlet (13) is communicating with the first flow channel (21), the second inlet (14) is communicating with the second flow channel (121), the third inlet (15) is communicating with the third flow channel (31), and the first flow channel (21) and the second flow channel (121) are communicating with one end of the annular groove (22); The end wall of the movable column (3) is connected to a telescopic tube (4), which is connected to the third flow channel (31). The end of the telescopic tube (4) away from the third flow channel (31) is connected to the third feed inlet (15). The outer wall of the telescopic tube (4) is wavy. Several connecting rings (41) are connected to the outer wall of the telescopic tube (4). The connecting rings (41) are respectively connected to the corresponding troughs of the outer wall of the telescopic tube (4). The diameter of the connecting ring (41) is larger than the diameter of the crest of the telescopic tube (4). Several through holes (411) are opened in the ring wall of the connecting ring (41). The positions of the several through holes (411) of adjacent connecting rings (41) are corresponding. In all the connecting rings (41), the same elastic rope (42) passes through the through hole (411) coaxial along the length direction of the telescopic tube (4). The two ends of the elastic rope (42) are respectively connected to the end wall of the movable column (3) and the inner wall of the ring groove (22).

2. The three-layer storage type die head according to claim 1, characterized in that, The inner wall of the annular slot (11) near the glue injection channel (16) is set as a sloping wall (111), which is inclined towards the glue injection channel (16); the end wall of the spiral body (2) near the glue injection channel (16) is set as a mating sloping wall that is adapted to and inclined with the sloping wall (111).

3. The three-layer storage type die head according to claim 1, characterized in that, The number of the first flow channels (21) along the outer side wall of the spiral (2) is at least two, and the number of the second flow channels (121) along the side wall of the slide column (12) is at least two.

4. The three-layer storage type die head according to claim 3, characterized in that, The first flow channel (21) is spirally opened along the circumference of the outer sidewall of the spiral body (2), and the second flow channel (121) is spirally opened along the circumference of the sidewall of the slide column (12).

5. The three-layer storage type die head according to claim 1, characterized in that, The body (1) has a plug-in groove (17) inside. The plug-in groove (17) is annular. One end of the plug-in groove (17) is connected to the glue injection channel (16), and the other end is connected to the annular groove (22). One end of the movable column (3) is inserted into the plug-in groove (17).

6. The three-layer storage type die head according to claim 5, characterized in that, The inner bottom wall of the insertion groove (17) near the glue injection channel (16) is set as a limiting inclined wall (171), and the end wall of the movable column (3) near the limiting inclined wall (171) is adapted to the limiting inclined wall (171).

7. The three-layer storage type die head according to claim 1, characterized in that, The movable column (3) has a flared groove (32) on one end wall near the glue injection channel (16). The flared groove (32) is annular and connected to a ring plate (5). The inner wall of the flared groove (32) has a receiving groove (321). The ring plate (5) includes several arc-shaped plates (51). Several arc-shaped plates (51) are inserted into the receiving groove (321). A spring (52) is connected between the arc-shaped plate (51) and the bottom wall of the receiving groove (321). A guide wall (511) is provided on the top wall of the arc-shaped plate (51).

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