A twin-screw extrusion equipment

Abstract

This invention relates to the technical field of twin-screw extrusion equipment and provides a twin-screw extrusion device, including a base, a first motor fixedly connected to the base, a threaded portion fixedly connected to the side of a first rotating shaft, the threaded portion having a sparse end and a dense end, an extrusion chamber disposed on the outer side of the threaded portion, and multiple scraping plates disposed on the extrusion chamber for scraping raw material from the threaded portion. A top cover is disposed at the upper end of the extrusion chamber, and the top cover is connected to the scraping plates via a pressing unit. A displacement unit is disposed at the upper end of the scraping plates for displacement within the threaded portion. In this invention, the first rotating shaft and the threaded portion rotate, and raw material enters the extrusion chamber through the feed inlet and is extruded forward under the action of the threaded portion. The scraping plates, under the action of the displacement unit, move along the threaded portion as it rotates, scraping the raw material from the surface of the threaded portion. The pressing unit ensures that the scraping plates maintain appropriate pressure with the threaded portion at all times, guaranteeing the scraping effect.

Description

Technical Field

[0001] This invention belongs to the technical field of twin-screw extrusion equipment, and particularly relates to a twin-screw extrusion equipment. Background Technology

[0002] Twin-screw extruders were developed based on single-screw extruders. Due to their excellent feeding performance, mixing and plasticizing performance, venting performance, and extrusion stability, they have been widely used in the molding and processing of extruded products. The molding and processing of color masterbatches is also carried out using twin-screw extruders. Waste plastics are one of the raw materials for the production of color masterbatches. Waste plastics go through recycling, mixing and crushing, granulation, blending, extrusion and molding steps to finally produce recycled black masterbatches or other types of color masterbatches.

[0003] A search revealed a Chinese patent titled "A Twin-Screw Extrusion Equipment," publication number CN220242339U. This patent utilizes an anti-sticking device. When in use, a rectangular bar rotates on the surface of a rotating rod, causing a rubber block to impact the surface of the feed hopper, effectively dislodging raw material adhering to the inner wall of the hopper. This solves the problem of raw material easily sticking to the inner wall of the feed hopper during actual use, making cleaning difficult and affecting the proportion of raw material entering the hopper next time, potentially impacting the molding and processing of the extruded product. However, this device has some shortcomings in practical use. After extrusion, residual raw material remains in the gaps between the twin screws, negatively impacting extrusion efficiency upon restarting and potentially causing blockages in the entire device. Therefore, this paper proposes a twin-screw extrusion equipment that solves these problems. Summary of the Invention

[0004] This invention provides a twin-screw extrusion device, which aims to solve the problem that after the twin screws extrude materials, residual raw materials remain in the gap between the twin screws. When the operation is restarted, this will have an adverse effect on the extrusion efficiency of the twin screws, and in severe cases, it will cause blockage of the entire device.

[0005] This invention is implemented as follows: a twin-screw extruder includes a base, on which a first motor is fixedly connected. A lubrication unit is fixedly connected to the output end of the first motor. The lubrication unit is connected to two first rotating shafts via a reducer connection. Threaded portions are fixedly connected to the sides of the first rotating shafts, the threaded portions having both sparse and dense ends. An extrusion chamber is provided outside the threaded portions. The extrusion chamber has multiple feed ports for feeding material and multiple scraper plates for scraping material from the threaded portions. A through-hole is opened at the upper end of the extrusion chamber, and a top cover is provided at the upper end of the extrusion chamber. The top cover is connected to the scraper plates via a pressing unit. A displacement unit for displacing material in the threaded portions is provided at the upper end of the scraper plates.

[0006] Preferably, the plurality of scraping plates are arranged vertically, and the thread pitch of the threaded part is 15 mils; a heating part for heating the raw material is fixedly connected to the extrusion box, a plurality of support legs are fixedly connected to the lower end of the base, an observation panel is provided on the extrusion box, a first scraping protrusion is fixedly connected to the side of the scraping plate, a first through groove for the scraping plate to pass through is provided on the upper cover, and the upper cover is connected to the extrusion box through an adjustment unit.

[0007] Preferably, the pressing unit includes a plurality of first guide rods symmetrically arranged and fixedly connected to the upper cover. A pressing plate is sleeved on the outer side of the plurality of first guide rods. A first connecting plate is fixedly connected to the upper end of each of the first guide rods on both sides. The upper end of the pressing plate is connected to the first connecting plate through a plurality of first springs for providing elastic force. The first springs are sleeved on the outer side of the first guide rods. A barrier plate for blocking the scraping plate is fixedly connected to the side of the extrusion box.

[0008] Preferably, the displacement unit includes multiple sets of symmetrically arranged second through slots formed on the lower pressure plate. The length of the second through slot is divided into long slots and short slots, and the long slots and the short slots correspond one-to-one with the sparse end and the dense end, respectively. A second guide rod is fixedly connected in the second through slot. A moving block is sleeved on the outer side of the second guide rod. The side wall of the moving block contacts the side wall of the second through slot. The moving block is connected to the side wall of the second through slot through a second spring for providing elastic force. The second spring is sleeved on the outer side of the second guide rod. The lower end of the moving block is fixedly connected to the scraping plate. The scraping plate is divided into a wide plate and a narrow plate, and the wide plate and the narrow plate correspond one-to-one with the sparse end and the dense end, respectively.

[0009] Preferably, the upper cover is provided with a lifting unit for lifting the scraper.

[0010] Preferably, the lifting unit includes a second motor, which is fixedly connected to the upper cover via a first connecting rod. A rotating gear is fixedly connected to the output end of the second motor, and the rotating gear is provided with incomplete gear teeth. A second connecting plate is fixedly connected to the side of the lower pressure plate, and the side of the second connecting plate is provided with spur gear teeth that mesh with the incomplete gear teeth. The incomplete gear teeth can drive the spur gear teeth to move in the vertical direction.

[0011] Preferably, the adjustment unit includes symmetrically arranged third connecting plates fixedly connected to both sides of the extrusion box. A third motor is fixedly connected to one of the third connecting plates, and a reciprocating lead screw is fixedly connected to the output end of the third motor. The end of the reciprocating lead screw is rotatably connected to the third connecting plate. A reciprocating slider is sleeved on the outside of the reciprocating lead screw. The reciprocating slider is fixedly connected to the upper cover. A limit rod is fixedly connected between the two third connecting plates. The limit rod passes through the reciprocating slider, and the reciprocating slider can drive the upper cover to move in the horizontal direction.

[0012] Preferably, the scraping plate has a scraping unit on its side, the scraping unit including a plurality of second scraping protrusions symmetrically arranged on both sides of the scraping plate, the scraping plate having a groove adapted to the second scraping protrusions, a third guide rod fixedly connected in the groove, the third guide rod being inserted into a movable groove on the second scraping protrusion, the second scraping protrusion being connected to the groove by a third spring for providing elasticity, the third spring being sleeved on the outside of the third guide rod.

[0013] Compared with the prior art, the embodiments of this application have the following main advantages:

[0014] 1. By setting up the pressing unit and the elastic force of the first spring, it is ensured that when the material scraping operation is not performed, the lower end of the scraping plate is in contact with the barrier plate. When the material scraping operation is performed, the scraping plate is in contact with the first rotating shaft and the threaded part to scrape the material.

[0015] 2. By setting the displacement unit, when the threaded part rotates, it will bring the scraper plate a horizontal feed, which will drive the moving block to move in the direction of the second guide rod. Under the action of the second spring, the scraper plate can contact the side of the threaded part, so as to better perform the material scraping operation.

[0016] 3. With the lifting unit, when the equipment needs maintenance or scraper replacement, the scraper can be lifted up by the lifting unit. In addition, because the displacement unit has a limited displacement distance, the lifting unit can adapt to the rotation of the threaded part and drive the scraper to move up and down to ensure the normal operation of the scraper. The adjustment unit can adjust the position of the top cover to facilitate cleaning and maintenance of the equipment.

[0017] 4. With the setting of the scraping unit, when the scraping plate performs scraping operation, the second scraping protrusion can move out of the groove in the direction of the third guide rod under the elastic force of the third spring. Thus, multiple second scraping protrusions can adapt to the curvature of the threaded part, and can further scrape the material of the threaded part. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a twin-screw extrusion device provided by the present invention. Figure 1 ;

[0019] Figure 2 This is a schematic diagram of the structure of a twin-screw extrusion device provided by the present invention. Figure 2 ;

[0020] Figure 3 yes Figure 2 Enlarged structural diagram at point A;

[0021] Figure 4 This is a schematic diagram of the threaded section in a twin-screw extruder provided by the present invention;

[0022] Figure 5 This is a partial structural schematic diagram of a twin-screw extrusion device provided by the present invention;

[0023] Figure 6 yes Figure 5 Enlarged structural diagram at point B;

[0024] Figure 7 yes Figure 5 Enlarged structural diagram at point C;

[0025] Figure 8 This is a schematic diagram of the scraping unit in a twin-screw extruder provided by the present invention.

[0026] Figure reference numerals: 1. Base; 2. First motor; 3. Lubrication unit; 4. Reducer connection unit; 5. First rotating shaft; 6. Loose end; 7. Dense end; 8. Extrusion box; 9. Feed inlet; 10. Scraper plate; 11. Through-hole; 12. Top cover; 13. Heating unit; 14. First through-groove; 15. First guide rod; 16. Lower pressure plate; 17. First connecting plate; 18. First spring; 19. Barrier plate; 20. Second through-groove; 21. Second guide rod; 22. Moving block 23. Second spring; 24. Second motor; 25. First connecting rod; 26. Rotating gear; 27. Incomplete gear teeth; 28. Second connecting plate; 29. ​​Spur gear teeth; 30. Third connecting plate; 31. Third motor; 32. Reciprocating lead screw; 33. Reciprocating slider; 34. Limiting rod; 35. Support leg; 36. Observation panel; 37. First scraping protrusion; 38. Second scraping protrusion; 39. Groove; 40. Third guide rod; 41. Moving groove; 42. Third spring. Detailed Implementation

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, not to describe a particular order.

[0028] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0029] This invention provides a twin-screw extrusion device, such as... Figures 1-8As shown, the device includes a base 1, on which a first motor 2 is fixedly connected. A lubrication part 3 is fixedly connected to the output end of the first motor 2. The lubrication part 3 is connected to two first rotating shafts 5 via a reducer connection part 4. A threaded part is fixedly connected to the side of each first rotating shaft 5. The threaded part consists of a sparse end 6 and a dense end 7. An extrusion box 8 is provided on the outside of the threaded part. The extrusion box 8 is provided with multiple feed ports 9 for feeding materials. The extrusion box 8 is provided with multiple scraping plates 10 for scraping raw materials from the threaded part. A through-hole 11 is opened at the upper end of the extrusion box 8. A top cover 12 is provided at the upper end of the extrusion box 8. The top cover 12 is connected to the scraping plates 10 via a pressing unit. A displacement unit for displacement of the threaded part is provided at the upper end of the scraping plate 10.

[0030] The thread gap in this application is increased from the international standard of 50 microns to 15-20 microns, achieving non-additive ultrafine dispersion, so that pigment particles can be effectively dispersed to their original particle size, and can be processed into higher quality masterbatch raw materials.

[0031] Multiple scraper plates 10 are vertically arranged; a heating part 13 for heating the raw material is fixedly connected to the extrusion box 8; multiple support legs 35 are fixedly connected to the lower end of the base 1; an observation panel 36 is provided on the extrusion box 8; a first through groove 14 for the scraper plates 10 to pass through is provided on the upper cover 12; and the upper cover 12 is connected to the extrusion box 8 through an adjustment unit.

[0032] In actual use, the above-mentioned device starts when the first motor 2 is activated, driving the first rotating shaft 5 and the threaded part to rotate through the lubrication part 3 and the reducer connection part 4. The raw material enters the extrusion box 8 through the feed port 9 and is extruded forward under the action of the threaded part. At the same time, the scraper plate 10 is displaced on the threaded part as the threaded part rotates under the action of the displacement unit, scraping off the raw material on the surface of the threaded part. The pressing unit ensures that the scraper plate 10 always maintains appropriate pressure with the threaded part to ensure the scraping effect.

[0033] Combination Figure 5 and Figure 7 The pressing unit includes a plurality of first guide rods 15 symmetrically arranged and fixedly connected to the upper cover 12. A pressing plate 16 is sleeved on the outer side of the plurality of first guide rods 15. A first connecting plate 17 is fixedly connected to the upper end of the first guide rods 15 on both sides. The upper end of the pressing plate 16 is connected to the first connecting plate 17 through a plurality of first springs 18 for providing elastic force. The first springs 18 are sleeved on the outer side of the first guide rods 15. A barrier plate 19 for blocking the scraper plate 10 is fixedly connected to the side of the extrusion box 8.

[0034] When the aforementioned pressing unit is actually in use, the elastic force of the first spring 18 ensures that the lower end of the scraping plate 10 is in contact with the barrier plate 19 when the material scraping operation is not being performed. When the material scraping operation is being performed, the scraping plate 10 is in contact with the first rotating shaft 5 and the threaded part to perform the material scraping operation.

[0035] The displacement unit includes multiple symmetrically arranged second through slots 20 formed on the lower pressure plate 16. The length of the second through slot 20 is divided into long slots and short slots. The long slots and the short slots correspond one-to-one with the sparse end 6 and the dense end 7, respectively. A second guide rod 21 is fixedly connected inside the second through slot 20. A moving block 22 is sleeved on the outside of the second guide rod 21. The side wall of the moving block 22 contacts the side wall of the second through slot 20. The moving block 22 is connected to the side wall of the second through slot 20 through a second spring 23 for providing elastic force. The second spring 23 is sleeved on the outside of the second guide rod 21. The lower end of the moving block 22 is fixedly connected to the scraping plate 10. The scraping plate 10 is divided into a wide plate and a narrow plate, and the wide plate and the narrow plate correspond one-to-one with the sparse end 6 and the dense end 7, respectively.

[0036] When the aforementioned displacement unit is actually used, the rotation of the threaded part will bring a horizontal feed to the scraper 10, which will drive the moving block 22 to move in the direction of the second guide rod 21. Under the action of the second spring 23, the scraper 10 can contact the side of the threaded part to better perform the material scraping operation.

[0037] The upper cover 12 is provided with a lifting unit for lifting the scraper 10.

[0038] The lifting unit includes a second motor 24, which is fixedly connected to the upper cover 12 via a first connecting rod 25. A rotating gear 26 is fixedly connected to the output end of the second motor 24. The rotating gear 26 is provided with incomplete gear teeth 27. A second connecting plate 28 is fixedly connected to the side of the lower pressure plate 16. The side of the second connecting plate 28 is provided with spur gear teeth 29 that mesh with the incomplete gear teeth 27. The incomplete gear teeth 27 can drive the spur gear teeth 29 to move in the vertical direction.

[0039] The lifting unit has two functions. When it is necessary to maintain the equipment or replace the scraper 10, the scraper 10 can be lifted up by the lifting unit. Secondly, because the displacement unit has a limited displacement distance, the lifting unit can adapt to the rotation of the threaded part and drive the scraper 10 up and down to ensure the normal operation of the scraper 10. The adjustment unit can adjust the position of the top cover 12 to facilitate cleaning and maintenance of the equipment.

[0040] Combination Figure 3 The adjustment unit includes symmetrically arranged third connecting plates 30 fixedly connected to both sides of the extrusion box 8. A third motor 31 is fixedly connected to one of the third connecting plates 30. A reciprocating screw 32 is fixedly connected to the output end of the third motor 31. The end of the reciprocating screw 32 is rotatably connected to the third connecting plate 30. A reciprocating slider 33 is sleeved on the outside of the reciprocating screw 32. The reciprocating slider 33 is fixedly connected to the upper cover 12. A limiting rod 34 is fixedly connected between the two third connecting plates 30. The limiting rod 34 passes through the reciprocating slider 33. The reciprocating slider 33 can drive the upper cover 12 to move in the horizontal direction.

[0041] In actual use, in order to ensure the normal operation of the extrusion operation, the upper cover 12 is positioned above the through-hole 11 under the drive of the reciprocating slider 33 during the extrusion operation, thus blocking it. When it is necessary to scrape the threaded part by the scraper plate 10, the third motor 31 rotates to drive the reciprocating screw 32 to rotate, which in turn drives the reciprocating slider 33 to move, thereby moving the upper cover 12 so that the position of the first through groove 14 corresponds to that of the through-hole 11, which facilitates the scraping operation.

[0042] The scraping plate 10 has a first scraping protrusion 37 fixedly connected to its side.

[0043] Combination Figure 6 and Figure 8 To further scrape away the raw material from the threaded portion and improve the adaptability of the scraper plate 10, a scraping unit is provided on the side of the scraper plate 10. The scraping unit includes a plurality of second scraping protrusions 38 symmetrically arranged on both sides of the scraper plate 10. The scraper plate 10 is provided with a groove 39 that is adapted to the second scraping protrusions 38. A third guide rod 40 is fixedly connected in the groove 39. The third guide rod 40 is inserted into a moving groove 41 provided on the second scraping protrusion 38. The second scraping protrusion 38 is connected to the groove 39 by a third spring 42 for providing elasticity. The third spring 42 is sleeved on the outside of the third guide rod 40.

[0044] When the scraping plate 10 is performing scraping operations, the second scraping protrusion 38 can move out of the groove 39 in the direction of the third guide rod 40 under the elastic force of the third spring 42. Thus, the multiple second scraping protrusions 38 can adapt to the curvature of the threaded part, and can further scrape the material from the threaded part.

[0045] In summary, the working principle of this invention is as follows: During operation, the first motor 2 starts, driving the first rotating shaft 5 and the threaded part to rotate through the lubrication part 3 and the reducer connection part 4. Raw material enters the extrusion chamber 8 through the feed inlet 9 and is extruded forward under the action of the threaded part. Simultaneously, the scraper plate 10, under the action of the displacement unit, moves along the threaded part as it rotates, scraping the raw material from the surface of the threaded part. The pressing unit ensures that the scraper plate 10 maintains appropriate pressure with the threaded part to guarantee the scraping effect. To ensure the normal operation of the extrusion process, during extrusion, the upper cover 12, driven by the reciprocating slider 33, is positioned above the through-hole 11, blocking it. The scraper plate 10 is needed to scrape the raw material from the threaded part. During the scraping operation, the third motor 31 rotates, driving the reciprocating lead screw 32 to rotate, which in turn drives the reciprocating slider 33 to move, thereby moving the upper cover 12 so that the first through groove 14 corresponds to the through opening 11, facilitating the scraping operation. When the scraping plate 10 is performing the scraping operation, the second scraping protrusion 38 can move out of the groove 39 in the direction of the third guide rod 40 under the elastic force of the third spring 42. Thus, the multiple second scraping protrusions 38 can adapt to the curvature of the threaded part, enabling further scraping of the material from the threaded part.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A twin-screw extruder, comprising a base (1), characterized in that, A first motor (2) is fixedly connected to the base (1). A lubrication part (3) is fixedly connected to the output end of the first motor (2). The lubrication part (3) is connected to two first rotating shafts (5) through a reducer connection part (4). A threaded part is fixedly connected to the side of the first rotating shaft (5). The threaded part has a sparse end (6) and a dense end (7). An extrusion box (8) is provided on the outside of the threaded part. A plurality of feed ports (9) for feeding are provided on the extrusion box (8). A plurality of scraping plates (10) for scraping raw materials from the threaded part are provided on the extrusion box (8). A through-hole (11) is opened at the upper end of the extrusion box (8). A top cover (12) is provided at the upper end of the extrusion box (8). The top cover (12) is connected to the scraping plate (10) through a pressing unit. A displacement unit for displacement of the threaded part is provided at the upper end of the scraping plate (10). The pressing unit includes a plurality of first guide rods (15) symmetrically arranged and fixedly connected to the upper cover (12). A pressing plate (16) is sleeved on the outer side of the plurality of first guide rods (15). A first connecting plate (17) is fixedly connected to the upper end of the first guide rods (15) on both sides. The upper end of the pressing plate (16) is connected to the first connecting plate (17) through a plurality of first springs (18) for providing elastic force. The first springs (18) are sleeved on the outer side of the first guide rods (15). A barrier plate (19) for blocking the scraper plate (10) is fixedly connected to the side of the extrusion box (8). The displacement unit includes multiple sets of symmetrically arranged second through slots (20) opened on the lower pressure plate (16). The length of the second through slot (20) is divided into long slots and short slots. The long slots and the short slots correspond one-to-one with the sparse end (6) and the dense end (7), respectively. A second guide rod (21) is fixedly connected inside the second through slot (20). A moving block (22) is sleeved on the outside of the second guide rod (21). The side wall of the moving block (22) contacts the side wall of the second through slot (20). The moving block (22) is connected to the side wall of the second through slot (20) through a second spring (23) for providing elastic force. The second spring (23) is sleeved on the outside of the second guide rod (21). The lower end of the moving block (22) is fixedly connected to the scraping plate (10). The scraping plate (10) is divided into a wide plate and a narrow plate. The wide plate and the narrow plate correspond one-to-one with the sparse end (6) and the dense end (7), respectively.

2. The twin-screw extruder as described in claim 1, characterized in that, Multiple scraping plates (10) are vertically arranged, and the thread pitch of the threaded part is 15-20 mils.

3. The twin-screw extruder as described in claim 1, characterized in that, The extrusion box (8) is fixedly connected to a heating part (13) for heating the raw material. The lower end of the base (1) is fixedly connected to a plurality of support legs (35). The extrusion box (8) is provided with an observation panel (36). The side of the scraper (10) is fixedly connected to a first scraping protrusion (37).

4. The twin-screw extruder as described in claim 1, characterized in that, The upper cover (12) is provided with a first through groove (14) for the scraper (10) to pass through, and the upper cover (12) is connected to the extrusion box (8) through an adjustment unit.

5. A twin-screw extruder as described in claim 1, characterized in that, The upper cover (12) is provided with a lifting unit for lifting the scraper (10).

6. A twin-screw extruder as described in claim 5, characterized in that, The lifting unit includes a second motor (24), which is fixedly connected to the upper cover (12) via a first connecting rod (25). A rotating gear (26) is fixedly connected to the output end of the second motor (24). The rotating gear (26) is provided with incomplete gear teeth (27). A second connecting plate (28) is fixedly connected to the side of the lower pressure plate (16). The side of the second connecting plate (28) is provided with straight gear teeth (29) that mesh with the incomplete gear teeth (27). The incomplete gear teeth (27) can drive the straight gear teeth (29) to move in the vertical direction.

7. A twin-screw extruder as described in claim 4, characterized in that, The adjustment unit includes symmetrically arranged third connecting plates (30) fixedly connected to both sides of the extrusion box (8). A third motor (31) is fixedly connected to one of the third connecting plates (30). A reciprocating screw (32) is fixedly connected to the output end of the third motor (31). The end of the reciprocating screw (32) is rotatably connected to the third connecting plate (30). A reciprocating slider (33) is sleeved on the outside of the reciprocating screw (32). The reciprocating slider (33) is fixedly connected to the upper cover (12). A limiting rod (34) is fixedly connected between the two third connecting plates (30). The limiting rod (34) passes through the reciprocating slider (33). The reciprocating slider (33) can drive the upper cover (12) to move in the horizontal direction.

8. A twin-screw extruder as described in claim 6, characterized in that, The scraping plate (10) has a scraping unit on its side. The scraping unit includes a plurality of second scraping protrusions (38) symmetrically arranged on both sides of the scraping plate (10). The scraping plate (10) has a groove (39) adapted to the second scraping protrusions (38). A third guide rod (40) is fixedly connected in the groove (39). The third guide rod (40) is inserted into the moving groove (41) provided on the second scraping protrusion (38). The second scraping protrusion (38) is connected to the groove (39) by a third spring (42) for providing elasticity. The third spring (42) is sleeved on the outside of the third guide rod (40).

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