CN210733296U - 3D printer of powder device is spread in area cooling - Google Patents

Abstract

The utility model discloses a 3D printer of powder device is spread in area cooling, including the work cylinder body, one side of work cylinder body is provided with the power air supply, the top of work cylinder body is provided with the heat preservation cavity, one side of heat preservation cavity is provided with the storage hopper, be provided with on the inside inclined plane of storage hopper and prevent blockking up the mechanism, and the outside of storage hopper is provided with and prevents blockking up mechanism matched with motor, the interior bottom front and back symmetry interlude of heat preservation cavity is provided with two sets of no pole cylinders, be provided with between the no pole cylinder and spread the powder groove, the top of spreading the powder groove is provided with the passage, the bottom of spreading the powder groove is provided with the powder bed, the bottom of powder bed is provided with. Has the advantages that: the powder can be spread bidirectionally by one-time powder falling, the powder spreading time is saved, the efficiency of laser printing is improved, and in addition, the rodless cylinder is adopted, so that the powder spreading structure of the whole machine is relatively simple, the precision is high, the work is reliable, and the cost is low.

Description

3D printer of powder device is spread in area cooling

Technical Field

The utility model relates to a 3D prints technical field, particularly, relates to a 3D printer of powder device is spread in area cooling.

Background

3D printing (additive manufacturing) is one of rapid prototyping technologies, and takes a mathematical model file as a basis, uses adhesive materials such as powdered metal or plastic, and adopts heat sources such as laser to manufacture products. The process of 3D printing can be classified into FDM (fused deposition), SLS (selective laser sintering), SLM (selective laser melt molding), and the like.

Wherein both SLS and SLM are directed to powder materials to directly manufacture products by melting powders in specific areas with a laser. The process is similar: the method comprises the steps of utilizing CAD software to model a specific object, then slicing a model through slicing software, transmitting section data of the sliced model to a control system, and controlling a laser with certain power by the control system to process and fuse metal powder or nonmetal powder of a specific layer. After the initial layer is processed and fused, the working platform descends by a distance of one layer thickness, the powder spreading device spreads unprocessed powder with a certain layer thickness, the next layer of powder is processed and fused continuously, the step is repeated until all the specific areas are fused, and a three-dimensional product is obtained.

From the above, the powder spreading device is a key part in the whole system, the reliability of the powder spreading device is related to the continuity of the whole printing process, and the final quality of the printed finished product is determined by the stable powder spreading and high precision. The printing medium is fine powder and is easy to raise dust, and the printing process of most materials needs to be heated to a certain temperature, so that the working condition and environment of the powder spreading device are severe.

The traditional powder spreading device is generally realized by combining a motor and a synchronous belt or combining the motor and a lead screw. The common motor, the synchronous belt and the lead screw are not suitable for working conditions of high temperature and high dust, and the high temperature resistant specially-made assembly is complex in process, high in cost and complex in maintenance, so that the motor, the synchronous belt or the lead screw and the like are required to be arranged outside the printing heat-insulation cavity in the traditional powder laying device, more extra parts are required to be added, the structure is complex, the cost is high, the precision is poor, and the printing quality is influenced.

An effective solution to the problems in the related art has not been proposed yet.

SUMMERY OF THE UTILITY MODEL

To the problem in the correlation technique, the utility model provides a 3D printer of whitewashed device is spread in area cooling to overcome the above-mentioned technical problem that current correlation technique exists.

Therefore, the utility model discloses a specific technical scheme as follows:

A3D printer with a cooling powder spreading device comprises a working cylinder body, wherein a power air source is arranged on one side of the working cylinder body, a pneumatic control system matched with the power air source is arranged on the power air source, a heat preservation cavity is arranged at the top of the working cylinder body, a vibrating mirror is arranged at the top of the heat preservation cavity, a laser is arranged on one side of the vibrating mirror, a storage hopper is arranged on one side of the heat preservation cavity, an anti-blocking mechanism is arranged on an inner inclined plane of the storage hopper, a motor matched with the anti-blocking mechanism is arranged on the outer side of the storage hopper, an electric control discharge valve is arranged at the bottom of the storage hopper, a heating system is arranged at the inner top of the heat preservation cavity, two groups of rodless cylinders are symmetrically arranged at the front and back of the inner bottom of the heat preservation cavity in an inserting mode, one ends of the rodless cylinders are respectively, the powder spreading device is characterized in that a powder spreading groove is formed between the rodless cylinders, a material guide pipe is arranged above the powder spreading groove, the top end of the material guide pipe penetrates through the heat insulation cavity and is fixedly connected with the bottom end of the storage hopper, a powder bed is arranged at the bottom of the powder spreading groove, a piston is arranged at the bottom of the powder bed and is located at the inner top of the working cylinder body, a vertical movement device is arranged at the bottom of the piston, and the bottom end of the vertical movement device penetrates through the working cylinder body and extends to the bottom of the working cylinder body.

Furthermore, in order to achieve a good recycling effect on redundant powder and avoid the powder waste, the work cylinder body is provided with a powder recycling barrel between the power air source, and one side of the powder recycling barrel is fixedly connected with the side wall of the work cylinder body.

Furthermore, in order to realize the blanking of powder, the powder paving groove can pave the powder along the powder bed on the upper end of the working cylinder body along with the movement of the cylinder piston, the lower end of the powder paving groove is of a V-shaped structure, and the two ends of the powder paving groove are fixedly connected with the cylinder piston in the rodless cylinder through screws.

Furthermore, in order to achieve the anti-blocking effect, the anti-blocking mechanism comprises a fixed strip, the back surface of the fixed strip is fixedly connected with the inner wall of the storage hopper, an opening is formed in the middle of the fixed strip, a first arc strip is arranged in the opening, sliding rods are arranged on two sides of the first arc strip, sliding grooves matched with the sliding rods are formed in two sides of the opening, an arc groove penetrates through the middle of the first arc strip, a sliding block matched with the arc groove is arranged in the arc groove, a rotating rod is arranged in the middle of the sliding block, one end of the rotating rod is connected with a connecting block positioned on the back surface of the sliding block, a rotating shaft is arranged on the back surface of the connecting block, which is far away from one end of the sliding block, the other end of the rotating shaft penetrates through the fixed strip and the storage hopper in sequence and is, the surface of the first arc strip is provided with a second arc strip matched with the first arc strip, and the surface of the second arc strip is uniformly provided with a plurality of fixing columns.

Furthermore, in order to facilitate the rotation of the rotating shaft, a bearing matched with the rotating shaft is clamped in the middle of the fixing strip.

Further, in order to avoid separation between the sliding block and the arc-shaped groove, the two sides of the sliding block are provided with limiting blocks, and the limiting grooves matched with the limiting blocks are formed in the two sides of the inner portion of the arc-shaped groove.

Compared with the prior art, the beneficial effects of the utility model are that:

1. the utility model can realize bidirectional powder spreading by one-time powder falling, thereby saving the powder spreading time and improving the efficiency of laser printing; in addition, the cylinder adopted by the utility model can adopt a common rodless cylinder, the structure is simple and reliable, the cylinder can be directly arranged in the heat preservation cavity and is close to the powder laying platform, other transmission parts are not needed, the powder laying structure of the whole machine is relatively simple, and therefore, the precision is high, the work is reliable, and the cost is low;

2. the utility model has the advantages that as the working heat preservation cavity generally has a little temperature requirement, the working gas of the cylinder adopts low-temperature gas, generally nitrogen, which has cooling effect on the cylinder, prevents the cylinder part from being exposed in the heat preservation cavity, and ensures that printing is carried out smoothly because the cylinder part is too violent in expansion and contraction and loses efficacy; in addition, the cylinder is provided with the guide device, so that a guide rail required in the traditional 3D printer is omitted, the structure is simple, the operation is reliable, and the cost is low;

3. the utility model adopts the cylinder to drive the execution piston to be positioned inside the cylinder guide pipe, is not contacted with the high dust working condition, has reliable work, less maintenance and cost saving, in addition, the utility model adopts the cylinder control as the common left and right two-position electromagnetic valve, has simple control and reliable work;

4. the utility model is a single cylinder body printing structure, compared with the traditional three-cylinder structure of a powder spreading cylinder, a working cylinder and a recovery cylinder, the volume of the heat-insulating cavity is obviously reduced, which is beneficial to the stable control of a temperature field, thereby not only effectively ensuring the printing quality of a printer, but also effectively reducing the manufacturing cost of the cylinder body;

5. the utility model discloses a prevent the use of jam mechanism for it can play fine preventing blockking up the effect, thereby has avoided effectively because of the storage hopper blocks up the influence that brings for printing, and then provides assurance effectively for the printing of 3D printer.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a 3D printer with a cooling powder spreading device according to an embodiment of the present invention;

fig. 2 is a schematic diagram of an internal structure of a 3D printer with a cooling powder spreading device according to an embodiment of the present invention;

fig. 3 is one of schematic structural diagrams of an anti-clogging mechanism in a 3D printer with a cooling powder spreading device according to an embodiment of the present invention;

fig. 4 is a second schematic structural diagram of an anti-clogging mechanism in a 3D printer with a cooling powder spreading device according to an embodiment of the present invention;

fig. 5 is a cross-sectional view of a fixing strip in a 3D printer with a cooling powder spreading device according to an embodiment of the present invention;

fig. 6 is a schematic connection diagram of a first arc-shaped strip and a sliding block in a 3D printer with a cooling powder spreading device according to the embodiment of the present invention.

In the figure:

1. a working cylinder body; 2. a powder recovery barrel; 3. a power gas source; 4. a pneumatic control system; 5. a heat preservation cavity; 6. a galvanometer; 7. a laser; 8. a storage hopper; 9. an anti-clogging mechanism; 901. a fixing strip; 902. an opening; 903. an arc strip I; 904. a slide bar; 905. a sliding groove; 906. an arc-shaped slot; 907. a slider; 908. rotating the rod; 909. connecting blocks; 910. a rotating shaft; 911. a second arc strip; 912. fixing a column; 913. a limiting block; 914. a limiting groove; 10. a motor; 11. a heating system; 12. a rodless cylinder; 13. a conduit loop; 14. spreading a powder groove; 15. a material guide pipe; 16. a powder bed; 17. a piston; 18. a vertical movement device; 19. a cylinder piston.

Detailed Description

For further explanation of the embodiments, the drawings are provided as part of the disclosure and serve primarily to illustrate the embodiments and, together with the description, to explain the principles of operation of the embodiments, and to provide further explanation of the invention and advantages thereof, it will be understood by those skilled in the art that various other embodiments and advantages of the invention are possible, and that elements in the drawings are not to scale and that like reference numerals are generally used to designate like elements.

According to the utility model discloses an embodiment provides a 3D printer of whitewashed device is spread in area cooling.

Referring to the drawings and the detailed description, as shown in fig. 1-6, according to the embodiment of the present invention, a 3D printer with a cooling powder spreading device includes a working cylinder 1, a power air source 3 is disposed on one side of the working cylinder 1, and a pneumatic control system 4 is disposed on the power air source 3 and is matched with the power air source 3, so as to provide power and cool a rodless cylinder 12, and ensure that the temperature of the part exposed in the thermal insulation cavity 5 is within a rated working range, the power air source 3 uses liquefied nitrogen to provide power, a thermal insulation cavity 5 is disposed on the top of the working cylinder 1, a galvanometer 6 is disposed on the top of the thermal insulation cavity 5, a laser 7 is disposed on one side of the galvanometer 6, a storage hopper 8 is disposed on one side of the thermal insulation cavity 5, and an anti-blocking mechanism 9 is disposed on an inner inclined plane of the storage hopper 8, a motor 10 matched with the anti-blocking mechanism 9 is arranged on the outer side of the storage hopper 8, an electric control discharge valve is arranged at the bottom of the storage hopper 8, the electric control discharge valve is opened when the materials need to be discharged, the materials fall into the powder spreading groove 14 along the material guide pipe 15 at the tail of the storage hopper 8 under the action of gravity, the electric control discharge valve is closed after a period of time, the falling amount of the materials entering the powder spreading groove 14 can be roughly controlled according to the time, a heating system 11 is arranged at the inner top of the heat-insulating cavity 5, in order to ensure the effect of temperature field stabilization, the heating system 11 adopts four or eight groups of infrared lamp tubes for heating, a temperature control system is arranged in the heating system 11, two groups of rodless cylinders 12 are symmetrically inserted in the front and back of the inner bottom of the heat-insulating cavity 5, and one end of each rodless cylinder 12 is respectively connected with the pneumatic control system 4 and the power air source 3 through, a powder paving groove 14 is arranged between the rodless cylinders 12, a material guide pipe 15 is arranged above the powder paving groove 14, the top end of the material guide pipe 15 penetrates through the heat insulation cavity 5 and is fixedly connected with the bottom end of the storage hopper 8, a powder bed 16 is arranged at the bottom of the powder paving groove 14, a piston 17 is arranged at the bottom of the powder bed 16, the piston 17 is positioned at the inner top of the working cylinder body 1, in order to avoid powder leakage from a gap between the piston 17 and the inner wall of the working cylinder body 1, a sealing felt is arranged between the periphery of the piston 17 and the working cylinder body 1, one side of the sealing felt is fixedly connected with the piston, a vertical movement device 18 is arranged at the bottom of the piston 17, the bottom end of the vertical movement device 18 penetrates through the working cylinder body 1 and extends to the bottom of the working cylinder body 1, and the vertical movement device 18 is generally provided with a lead screw, the bearings, motor, etc. act to convert the rotary motion of the lead screw into vertical motion of the piston.

In one embodiment, a powder recycling barrel 2 is arranged between the working cylinder body 1 and the power air source 3, and one side of the powder recycling barrel 2 is fixedly connected with the side wall of the working cylinder body 1. Through setting up like this for it can play fine recovery effect to unnecessary powder, thereby has avoided the emergence of the extravagant condition of powder effectively, has practiced thrift the printing cost of 3D printer.

In one embodiment, the lower end of the powder spreading groove 14 is arranged in a V-shaped structure, and both ends of the powder spreading groove 14 are fixedly connected with the cylinder piston 19 in the rodless cylinder 12 through screws. By this arrangement, not only the blanking of the powder is facilitated, but also the powder paving groove 14 can be made to pave the powder along the powder bed 16 at the upper end of the working cylinder 1 along with the movement of the cylinder piston 19. In a specific application, in order to further improve the paving effect, the bottom of the powder paving groove 14 is provided with an opening scraper.

In one embodiment, the anti-blocking mechanism 9 includes a fixing strip 901, the back of the fixing strip 901 is fixedly connected to the inner wall of the storage hopper 8, an opening 902 is formed in the middle of the fixing strip 901, an arc-shaped strip 903 is disposed in the opening 902, sliding rods 904 are disposed on both sides of the arc-shaped strip 903, sliding grooves 905 matched with the sliding rods 904 are formed on both sides of the opening 902, an arc-shaped groove 906 is formed through the middle of the arc-shaped strip 903, a sliding block 907 matched with the arc-shaped groove 906 is disposed inside the arc-shaped groove 906, a rotating rod 908 is disposed in the middle of the sliding block 907, one end of the rotating rod 908 is connected to a connecting block 909 disposed on the back of the sliding block 907, a rotating shaft 910 is disposed on the back of the connecting block 909, which is far away from one end of the sliding block 907, and the other end of the rotating shaft 910 sequentially penetrates through the fixing strip 901 and, the surface of the first arc strip 903 is provided with a second arc strip 911 matched with the first arc strip, and the surface of the second arc strip 911 is uniformly provided with a plurality of fixing columns 912. Through the use of preventing blockking up mechanism 9 for it can play fine preventing blockking up the effect, thereby has avoided effectively giving the influence that prints and bring because of storage hopper 8 blocks up, and then provides assurance effectively for the printing of 3D printer.

In one embodiment, a bearing is clamped in the middle of the fixing strip 901 and is matched with the rotating shaft 910. Through the use of bearings, effective assurance is provided for rotation of the rotating shaft 910.

In one embodiment, both sides of the slider 907 are provided with a stopper 913, and both sides of the inner portion of the arc-shaped groove 906 are provided with a stopper 914 matched with the stopper 913. The limiting block 913 and the limiting groove 914 are matched to use, so that a good limiting effect can be achieved on the sliding of the sliding block 907, the sliding block 907 is effectively prevented from being separated from the arc-shaped groove 906, and the sliding of the sliding block 907 is effectively guaranteed.

The working principle is as follows: during printing, the power air source 3 provides power for the rodless cylinder 12, so that the rodless cylinder 12 drives the powder spreading groove 14 to move to the lower part of the material guide pipe 15, then the electric control discharge valve is opened, powder in the storage hopper 8 falls into the powder spreading groove 14 from the material guide pipe 15, then the electric control discharge valve is controlled to be closed, the rodless cylinder 12 drives the powder spreading groove 14 to move leftwards, powder with one layer thickness is horizontally spread, then the vibrating mirror 6 controls the laser 7 to irradiate the powder bed 16 with the spread powder, so that the powder with the current layer thickness is selectively melted and solidified, then the vertical movement device 18 is controlled to drive the powder bed 16 to descend by one layer thickness, the rodless cylinder 12 drives the powder spreading groove to move rightwards again, the powder with one layer thickness is spread, then the vibrating mirror 6 controls the laser 7 to irradiate the powder bed 16 with the spread powder again, and selectively melting and solidifying the powder with the current layer thickness, controlling the powder spreading groove 14 to move to the position below the material guide pipe 15 for material re-receiving, and finally repeating the steps to print a three-dimensional product. In addition, after the powder spreading groove 14 moves rightwards to spread powder with a certain thickness, the rodless cylinder 12 can be controlled to continue to drive the powder spreading groove 14 to move rightwards, so that redundant powder falls into the powder recycling barrel 2 to be recycled.

The working principle of the anti-blocking mechanism is as follows: when powder in the storage hopper 8 is placed for a long time and is affected with damp and take place to block up, this moment, alright drive axis of rotation 910 through motor 10 and rotate, thereby drive connecting block 909 and rotate, at arc groove 906, under the effect of slide bar 904 dwang 908, make slider 907 drive arc strip 903 and control cyclic motion, thereby make two 911 drive fixed column 912 and control cyclic motion, thereby make fixed column 912 can drive the powder in the storage hopper 8 and move, and then play fine effect of switching on.

In summary, by means of the above technical solution of the present invention, through the use of the present invention, the powder falling can be achieved in two directions, thereby saving the powder laying time and improving the efficiency of laser printing; the cylinder adopted by the utility model can adopt a common rodless cylinder, the structure is simple and reliable, the cylinder can be directly arranged in the heat preservation cavity and is close to the powder laying platform, other transmission parts are not needed, the powder laying structure of the whole machine is relatively simple, and therefore, the precision is high, the work is reliable, and the cost is low; the utility model has the advantages that as the working heat preservation cavity generally has a little temperature requirement, the working gas of the cylinder adopts low-temperature gas, generally nitrogen, which has cooling effect on the cylinder, prevents the cylinder part from being exposed in the heat preservation cavity, and ensures that printing is carried out smoothly because the cylinder part is too violent in expansion and contraction and loses efficacy; in addition, the cylinder is provided with the guide device, so that a guide rail required in the traditional 3D printer is omitted, the structure is simple, the operation is reliable, and the cost is low; the utility model adopts the cylinder to drive the execution piston to be positioned inside the cylinder guide pipe, and the execution piston is not contacted with the high dust working condition, thereby having reliable work, less maintenance and cost saving; the utility model adopts the cylinder control as a common left and right two-position electromagnetic valve, the control is simple, and the work is reliable; the utility model is a single cylinder body printing structure, compared with the traditional three-cylinder structure of a powder spreading cylinder, a working cylinder and a recovery cylinder, the volume of the heat-insulating cavity is obviously reduced, which is beneficial to the stable control of a temperature field, thereby not only effectively ensuring the printing quality of a printer, but also effectively reducing the manufacturing cost of the cylinder body; the utility model discloses a prevent the use of jam mechanism for it can play fine preventing blockking up the effect, thereby has avoided effectively because of the storage hopper blocks up the influence that brings for printing, and then provides assurance effectively for the printing of 3D printer.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "disposed," "connected," "fixed," "screwed" and the like are to be construed broadly, e.g., as meaning fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through an intermediate medium, and may be connected through the inside of two elements or in an interaction relationship between two elements, unless otherwise specifically defined, and the specific meaning of the above terms in the present invention will be understood by those skilled in the art according to specific situations.

The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (6)

1. The 3D printer with the cooling powder spreading device is characterized by comprising a working cylinder body (1), wherein a power air source (3) is arranged on one side of the working cylinder body (1), a pneumatic control system (4) matched with the power air source is arranged on the power air source (3), a heat-insulating cavity (5) is arranged at the top of the working cylinder body (1), a vibrating mirror (6) is arranged at the top of the heat-insulating cavity (5), a laser (7) is arranged on one side of the vibrating mirror (6), a storage hopper (8) is arranged on one side of the heat-insulating cavity (5), an anti-blocking mechanism (9) is arranged on an inner inclined plane of the storage hopper (8), a motor (10) matched with the anti-blocking mechanism (9) is arranged on the outer side of the storage hopper (8), an electric control discharge valve is arranged at the bottom of the storage hopper (8), a heating system (11) is arranged at the inner top of the heat-insulating cavity (, the inner bottom of the heat-insulation cavity (5) is symmetrically and alternately provided with two groups of rodless cylinders (12) in a front-back penetrating mode, one ends of the rodless cylinders (12) are respectively connected with the pneumatic control system (4) and the power air source (3) through guide pipe loops (13), powder paving grooves (14) are formed between the rodless cylinders (12), material guide pipes (15) are arranged above the powder paving grooves (14), the top ends of the material guide pipes (15) penetrate through the heat-insulation cavity (5) and are fixedly connected with the bottom end of the storage hopper (8), powder beds (16) are arranged at the bottom of the powder paving grooves (14), pistons (17) are arranged at the bottoms of the powder beds (16), the pistons (17) are located at the inner top of the working cylinder body (1), vertical movement devices (18) are arranged at the bottom ends of the pistons (17), and the bottom ends of the vertical movement devices (18) penetrate through the working cylinder body (1) and extend to the working cylinder body (1) ) The bottom of (a).

2. The 3D printer with the cooling powder spreading device according to claim 1, wherein a powder recovery barrel (2) is arranged between the working cylinder body (1) and the power air source (3), and one side of the powder recovery barrel (2) is fixedly connected with the side wall of the working cylinder body (1).

3. The 3D printer with the cooling powder spreading device is characterized in that the lower end of the powder spreading groove (14) is of a V-shaped structure, and two ends of the powder spreading groove (14) are fixedly connected with a cylinder piston (19) in the rodless cylinder (12) through screws.

4. The 3D printer with the cooling powder spreading device according to claim 1, wherein the anti-blocking mechanism (9) comprises a fixing strip (901), the back of the fixing strip (901) is fixedly connected with the inner wall of the storage hopper (8), an opening (902) is formed in the middle of the fixing strip (901), a first arc strip (903) is arranged in the opening (902), sliding rods (904) are arranged on both sides of the first arc strip (903), sliding grooves (905) matched with the sliding rods (904) are formed in both sides of the opening (902), an arc groove (906) is formed in the middle of the first arc strip (903) in a penetrating manner, a sliding block (907) matched with the arc groove (906) is arranged in the arc groove (906), a rotating rod (908) is arranged in the middle of the sliding block (907), and one end of the rotating rod (908) is connected with a connecting block (909) located on the back of the sliding block (907), the back of one end, far away from the sliding block (907), of the connecting block (909) is provided with a rotating shaft (910), the other end of the rotating shaft (910) sequentially penetrates through the fixing strips (901) and the storage hopper (8) and is connected with the motor (10), the surface of the first arc strip (903) is provided with a second arc strip (911) matched with the first arc strip, and the surface of the second arc strip (911) is uniformly provided with a plurality of fixing columns (912).

5. The 3D printer with the cooling and powder spreading device is characterized in that a bearing matched with the rotating shaft (910) is clamped in the middle of the fixing strip (901).

6. The 3D printer with the cooling powder spreading device according to claim 4, wherein two sides of the sliding block (907) are provided with limiting blocks (913), and two sides of the inner portion of the arc-shaped groove (906) are provided with limiting grooves (914) matched with the limiting blocks (913).

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