Metal powder spreading device for additive manufacturing of rocket engine thrust chamber

Abstract

The invention discloses a metal powder spreading device for additive manufacturing of a rocket engine thrust chamber, and relates to the technical field of additive manufacturing. Comprising a machine body, a mounting base is slidably arranged on the inner wall of a cavity of the machine body through a rail, and the bottom of the mounting base is connected with a powder spreading head through an air cylinder; the powder spreading device further comprises a powder feeding pipe, the powder feeding pipe is fixed to the top of the powder spreading head in a penetrating mode, the powder feeding pipe is connected with a powder feeding mechanism, the top area of the powder spreading cavity is connected with a guide net plate through a first electric push rod, and a sealing plate is fixed to the bottom of the guide net plate through a connecting rod and arranged at an opening in the bottom of the powder spreading cavity. A paving assisting strip is vertically arranged in the mounting sleeve in a sliding mode, and a pressing plate is fixed to the bottom of the paving assisting strip and located on the sealing plate. According to the metal powder spreading device for additive manufacturing of the rocket engine thrust chamber, the powder spreading uniformity is guaranteed in the longitudinal direction, meanwhile, powder caking is avoided, and the powder spreading efficiency is improved in cooperation with vibration.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and particularly to a metal powder spreading device for additive manufacturing of a rocket engine thrust chamber. Background Art

[0002] The development direction of liquid rocket engines is high reliability, low cost, reusability, and short development cycles. Among them, the thrust chamber operates in harsh environments such as high temperature, high pressure, and high heat flux, and has to withstand extreme pressure and temperature gradients. Moreover, the improvement of engine performance will inevitably bring a more severe working environment to the thrust chamber. The mass of the thrust chamber generally accounts for more than 40% of the total mass of the entire engine, and it has a complex structure and many components, with extremely high requirements in terms of manufacturing accuracy, consistency, stability, and reliability. Traditional large-sized thrust chambers are composed of hundreds or thousands of components, and their production and manufacturing processes involve mechanical processing, welding, inspection, testing, etc. Not only is the production cycle long, but it is also difficult to detect certain steps, which affects the product reliability; advanced thrust chamber technologies will inevitably have material diversity and structural complexity, thus bringing difficulties in research, development, and production; Additive manufacturing technology has great advantages in complex structure forming, integrated design of multiple components, rapid production of small-batch customization, and cost reduction. Liquid rocket engine thrust chambers have the characteristics of a large number of parts, complex assembly and welding, and high production costs for small-batch customization; giving full play to the advantages of additive manufacturing technology helps liquid rocket engines achieve the development goals of "high reliability, low cost, and short development cycles". During the additive manufacturing process, using laser forming technology and cooperating with the layer-by-layer laying of metal powder, the workpiece is finally formed. However, the existing metal powder spreading devices have the following problems; For the metal powder spreading device, the powder is laid layer by layer through an opening at the bottom in cooperation with a scraper. However, the existing metal powder spreading devices are not convenient for overall uniform spreading. The powder is input into the spreading head through a powder feeding mechanism and a pipeline, and then exported by the spreading head. During this process, the longitudinal interval of powder spreading is relatively large. Merely using the pipeline powder feeding method, it is difficult to export the powder in time within the longitudinal interval, and it is easy to form accumulations in the middle, affecting the subsequent flatness. Further, the existing metal powder spreading devices are not convenient for powder dispersion operations, and some powders are agglomerated, etc. Directly exporting them is also one of the factors affecting the uniformity of powder spreading.

[0003] In view of the above problems, there is an urgent need for innovative design on the original basis. Summary of the Invention

[0004] The purpose of the present invention is to provide a metal powder spreading device for additive manufacturing of a rocket engine thrust chamber, so as to solve the problems in the prior art proposed in the above background technology that the existing metal powder spreading device is not convenient for overall uniform spreading and is not convenient for powder dispersion operation. The technical solution of the present invention provides a solution significantly different from the prior art for the technical problem that the prior art solution is too single.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A metal powder spreading device for additive manufacturing of a rocket engine thrust chamber, including a machine body. An installation seat is slidably arranged on the inner wall of the cavity of the machine body through a track. The bottom of the installation seat is connected with a powder spreading head through a cylinder, and a powder spreading cavity is arranged in the powder spreading head; It further includes a powder feeding pipe. The powder feeding pipe is fixedly penetrated through the top of the powder spreading head and is connected with a powder feeding mechanism. The top area of the powder spreading cavity is connected with a guiding mesh plate through a first electric push rod. The bottom of the guiding mesh plate is fixed with a sealing plate through a connecting rod. The sealing plate is arranged at the bottom opening of the powder spreading cavity. A central rod is longitudinally penetrated and installed in the connecting rod. Installation sleeves are fixed on both sides of the central rod through cross bars. A powder assisting bar is vertically slidably arranged in the installation sleeve. The bottom of the powder assisting bar is fixed with a pressing plate, and the pressing plate is located on the sealing plate; A pushing mechanism is arranged in the central rod and on the inner wall of the cavity of the machine body, and the pushing mechanism is used to push the powder assisting bar to move vertically.

[0006] Preferably, the front and rear sides of the guiding mesh plate are inclined downward in the powder spreading cavity, and the powder spreading cavities are horizontally arranged at equal intervals in the powder spreading head.

[0007] Preferably, the left and right sides of the sealing plate are inclined upward to the outside, the two sides of the sealing plate are attached to the inner wall of the bottom of the powder spreading cavity, and the bottom of the sealing plate is designed as a triangular structure.

[0008] Preferably, a plurality of powder assisting bars are arranged in the longitudinal position, and the lengths of the plurality of powder assisting bars are adapted to the guiding mesh plate.

[0009] Preferably, the powder assisting bar and the pressing plate are inclined in the forward interval, and the pressing plate is parallel to the top of the sealing plate.

[0010] Preferably, the pushing mechanism includes a pushing strip, which is installed longitudinally through the powder spreading head, the front end of the pushing strip is elastically slidably arranged in the center rod by a spring, the rear end of the pushing strip is located outside the powder spreading head, the pushing strip slides vertically in close contact at the powder spreading head, a seal is sleeved on the pushing strip for preventing powder from overflowing from the powder spreading chamber, a pushing head is arranged above the rear end of the pushing strip, the pushing head is fixed to the inner wall of the body cavity, a pushing plate is fixed to the outside of the pushing strip, the pushing plate is located in the center rod, a tooth plate is arranged on the movable track of the pushing plate, the tooth plate is installed through the cross bar and the mounting sleeve, the outer end of the tooth plate is meshed with a tooth roller, and the tooth roller is arranged in the mounting sleeve through a torsion spring embedded rotation.

[0011] Preferably, the push heads are distributed at equal intervals on the inner wall of the cavity of the machine body, the distribution positions of the push heads are matched with the movable tracks of the mounting seat, and the push heads are designed as a hemispherical structure.

[0012] Preferably, the push plate slides within the center rod in a limited position, and the front end of the center rod is designed as an inclined structure to conflict with the tooth plate.

[0013] Preferably, the toothed roller is meshed with a paving-assisting strip of a rack structure, and the paving-assisting strip is staggered with the toothed plate.

[0014] Preferably, a scraper is connected to the bottom edge of the mounting seat via a second electric push rod.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. In the present invention, a plurality of powder spreading chambers are provided with guide mesh plates inclined forward and backward to guide the powder falling from the center, and the gravity of the powder is utilized to make the powder evenly enter the bottom of the guide mesh plate in the longitudinal interval and be guided out through the bottom space of the powder spreading chamber. In this process, the guide mesh plates and sealing plates in the corresponding powder spreading chambers are opened separately, and other powder spreading chambers are closed, so that powder spreading operations of different metal materials can be performed. On this basis, the corresponding pushing strips are forced to move upward, and during the movement of the powder spreading head, the pushing strips contact the pushing head, and the auxiliary spreading strips can be driven to move upward through the pushing plate, the tooth plate and the tooth roller to contact the guide mesh plate, so that the guide mesh plate vibrates, which, on the one hand, helps the guide mesh plate to guide the powder, and on the other hand, helps to guide the internal powder out and evenly disperse it. In this process, the bottom of the powder spreading chamber that needs to be spread with powder is opened, and only one group of pushing heads needs to be provided to realize internal vibration and powder guiding, which has a simple and practical structure and high operability. 2. In the present invention, a pressing plate is provided at the top of the sealing plate. It also uses the pushing bar and the pushing head to contact. Through the up and down movement of the powder assisting bar, the pressing plate is driven to move up and down. Cooperating with the inclined structure at the top of the sealing plate, on the one hand, it guides the falling powder, and on the other hand, it intermittently presses the powder through the pressing plate, which helps to disperse the powder and avoid powder caking. During this process, in cooperation with the vibration of the guiding mesh plate, vibration and dispersion operations are carried out inside, enabling the powder assisting bar to have multiple effects. On the basis of realizing efficient powder spreading inside, the structure is simplified, and it is applicable to the diversified powder spreading operations of different metal powders. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic front view structure diagram of the present invention; Figure 2 is a schematic side sectional view structure diagram of the powder spreading head of the present invention; Figure 3 is a schematic front sectional view structure diagram of the powder spreading head of the present invention; Figure 4 is of the present invention Figure 3 an enlarged structure diagram at position A in; Figure 5 is of the present invention Figure 4 an enlarged structure diagram at position B in; Figure 6 is a schematic top view structure diagram of the pushing plate of the present invention; Figure 7 is of the present invention Figure 4 an enlarged structure diagram at position C in.

[0017] In the figure: 1, machine body; 2, mounting seat; 3, powder spreading head; 4, powder spreading cavity; 5, powder feeding pipe; 6, first electric push rod; 7, guiding mesh plate; 8, connecting rod; 9, sealing plate; 10, central rod; 11, cross bar; 12, mounting sleeve; 13, powder assisting bar; 14, pressing plate; 151, pushing bar; 152, pushing head; 153, pushing plate; 154, toothed plate; 155, toothed roller; 16, second electric push rod; 17, scraper. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0019] Please refer to Figures 1-7, the present invention provides a technical solution: a metal powder spreading device for additive manufacturing of a rocket engine thrust chamber. An installation seat 2 is slidably arranged on the inner wall of the cavity of the body 1 through a track. The bottom of the installation seat 2 is connected with a powder spreading head 3 through a cylinder, and a powder spreading cavity 4 is arranged in the powder spreading head 3; As an implementation manner of the present invention, a powder feeding pipe 5 is fixedly penetrated through the top of the powder spreading head 3. The powder feeding pipe 5 is connected with a powder feeding mechanism. The top area of the powder spreading cavity 4 is connected with a guiding mesh plate 7 through a first electric push rod 6. The bottom of the guiding mesh plate 7 is fixed with a sealing plate 9 through a connecting rod 8. The sealing plate 9 is arranged at the bottom opening of the powder spreading cavity 4. A central rod 10 is longitudinally penetrated and installed in the connecting rod 8. Installation sleeves 12 are fixed on both sides of the central rod 10 through cross bars 11. A powder assisting bar 13 is slidably arranged vertically in the installation sleeve 12. The bottom of the powder assisting bar 13 is fixed with a pressing plate 14, and the pressing plate 14 is located on the sealing plate 9; As an implementation manner of the present invention, the front and rear sides of the guiding mesh plate 7 are inclined downward in the powder spreading cavity 4, and the powder spreading cavities 4 are transversely arranged at equal intervals in the powder spreading head 3; the left and right sides of the sealing plate 9 are inclined upward to the outside, and the two sides of the sealing plate 9 are attached to the inner wall of the bottom of the powder spreading cavity 4. The bottom of the sealing plate 9 is designed as a triangular structure; a plurality of powder assisting bars 13 are arranged in the longitudinal position, and the lengths of the plurality of powder assisting bars 13 are adapted to the guiding mesh plate 7; the powder assisting bars 13 and the pressing plate 14 are inclined in the forward interval, and the pressing plate 14 is parallel to the top of the sealing plate 9; the bottom edge of the installation seat 2 is connected with a scraper 17 through a second electric push rod 16; According to the powder spreading requirement, the corresponding powder spreading cavity 4 is selected to be opened. The first electric push rod 6 drives the guiding mesh plate 7 to move upward, so that the guiding mesh plate 7 drives the sealing plate 9 to move upward through the connecting rod 8, exposing the bottom opening space of the powder spreading cavity 4 here, and the corresponding metal powder is conveyed into the powder spreading cavity 4 through the powder feeding mechanism. The powder is guided and dropped through the front and rear inclined guiding mesh plate 7 and is led out through the bottom of the powder spreading cavity 4, so that the powder is evenly laid in the longitudinal position. After the powder spreading is completed, the first electric push rod 6 drives the guiding mesh plate 7 to move downward, so that the sealing plate 9 closes the bottom of the powder spreading cavity 4, and the second electric push rod 16 drives the scraper 17 to scrape the powder flat.

[0020] As an embodiment of the present invention, a pushing mechanism is arranged in the center rod 10 and on the inner wall of the cavity of the machine body 1, and the pushing mechanism is used to push the auxiliary laying strip 13 to move vertically; the pushing mechanism includes a pushing strip 151, and the pushing strip 151 is installed longitudinally through the powder laying head 3. The front end of the pushing strip 151 is elastically slidably arranged in the center rod 10 through a spring, and the rear end of the pushing strip 151 is located outside the powder laying head 3. The pushing strip 151 vertically fits and slides at the powder laying head 3, and a seal for preventing the powder in the powder laying cavity 4 from overflowing is sleeved on the pushing strip 151. A pushing head 152 is arranged above the rear end of the pushing strip 151, and the pushing head 152 is fixed on the inner wall of the cavity of the machine body 1. A pushing plate 153 is fixed on the outside of the pushing strip 151. The push plate 153 is located in the center rod 10, and a tooth plate 154 is arranged on the moving track of the push plate 153. The tooth plate 154 is installed in the cross bar 11 and the mounting sleeve 12, and the outer end of the tooth plate 154 is meshed with a tooth roller 155, and the tooth roller 155 is arranged in the mounting sleeve 12 through the embedded rotation of the torsion spring; the push heads 152 are evenly spaced on the inner wall of the cavity of the body 1, and the distribution position of the push heads 152 is adapted to the moving track of the mounting seat 2, and the push heads 152 are designed as a hemispherical structure; the push plate 153 is limited and slidable in the center rod 10, and the front end of the center rod 10 is designed as an inclined structure to conflict with the tooth plate 154; the tooth roller 155 is meshed with the auxiliary laying strip 13 of the rack structure, and the auxiliary laying strip 13 and the tooth plate 154 are staggered; The connecting rod 8 drives the push strip 151 to move upward through the center rod 10, so that the push strip 151 here moves upward to the position of the push head 152. When the powder spreading head 3 moves, the push strip 151 moves with it, and the push strip 151 contacts the push head 152, so that the push strip 151 is forced to move longitudinally in the center rod 10. The inclined surface of the push plate 153 on the push strip 151 contacts the tooth plate 154, pushing it to move toward the installation sleeve 12, and the tooth plate 154 and the tooth roller 15 5 meshes, driving the toothed roller 155 to rotate, and then the toothed roller 155 meshes with the auxiliary laying strip 13, driving the auxiliary laying strip 13 to move up, so that it contacts with the guide mesh plate 7, and the guide mesh plate 7 is forced to vibrate, which helps to guide the powder thereon to fall evenly. At the same time, when the pushing strip 151 is separated from the pushing head 152, the pushing strip 151 is reset under the action of the spring, so that the auxiliary laying strip 13 moves down and resets, and the pressing plate 14 contacts with the top inclined surface of the sealing plate 9 to squeeze the fallen powder.

[0021] Working principle: According to the powder spreading requirement, select to open the corresponding powder spreading chamber 4. The first electric push rod 6 drives the guiding mesh plate 7 to move upward, so that the guiding mesh plate 7 drives the sealing plate 9 to move upward through the connecting rod 8, exposing the opening space at the bottom of the powder spreading chamber 4 here. The corresponding metal powder is conveyed into the powder spreading chamber 4 through the powder feeding mechanism. The powder is guided and dropped through the guiding mesh plate 7 that is inclined forward and backward, and is discharged through the bottom of the powder spreading chamber 4, so that the powder is evenly laid in the longitudinal position. At the same time, the connecting rod 8 drives the pushing strip 151 to move upward through the central rod 10, so that the pushing strip 151 here moves upward to the position of the pushing head 152, and the pushing strip 151 moves upward in the space penetrated by the rear end of the powder spreading head 3. Through the sealing strip on the pushing strip 151, the connection between the space penetrated by the rear end of the powder spreading head 3 and the powder spreading chamber 4 is sealed to prevent powder overflow. At the same time, the mounting seat 2 and the powder spreading head 3 are driven to move horizontally through the track, and the powder spreading head 3 is driven to move upward by the cylinder on the mounting seat 2, so that the bottom of the powder spreading head 3 is separated from the internal powder layer. The powder spreading head 3 performs powder spreading operations during the movement; During this process, the pushing strip 151 moves along, and the pushing strip 151 contacts the pushing head 152, so that the pushing strip 151 is forced to move longitudinally in the central rod 10. The inclined surface of the pushing plate 153 on the pushing strip 151 abuts against the toothed plate 154, pushing it to move in the direction of the mounting sleeve 12. Through the engagement of the toothed plate 154 and the toothed roller 155, the toothed roller 155 is driven to rotate, and then the toothed roller 155 engages with the assisting spreading strip 13 to drive the assisting spreading strip 13 to move upward, so that it contacts the guiding mesh plate 7. The guiding mesh plate 7 is stressed and vibrates, which helps the powder on it to be evenly guided and fall. At the same time, when the pushing strip 151 is separated from the pushing head 152, the pushing strip 151 resets under the action of the spring, so that the assisting spreading strip 13 moves downward and resets. The pressing plate 14 contacts the inclined surface at the top of the sealing plate 9 to squeeze the falling powder to prevent caking. After powder spreading is completed, the first electric push rod 6 drives the guiding mesh plate 7 to move downward, so that the sealing plate 9 closes the bottom of the powder spreading chamber 4, and the second electric push rod 16 drives the scraper 17 to scrape the powder flat.

[0022] The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art. In the description of the present invention, unless otherwise specified, the meaning of "a plurality of" is two or more; the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention. In addition, terms such as "first", "second", "third", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0023] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A metal powder spreading device for additive manufacturing of a rocket engine thrust chamber, comprising a machine body (1). An installation seat (2) is slidably arranged on the inner wall of the cavity of the machine body (1) through a track. A powder spreading head (3) is connected to the bottom of the installation seat (2) through a cylinder. A powder spreading cavity (4) is arranged in the powder spreading head (3). It is characterized in that: It further includes a powder feeding pipe (5). The powder feeding pipe (5) is fixedly penetrated through the top of the powder spreading head (3). The powder feeding pipe (5) is connected to a powder feeding mechanism. A guiding mesh plate (7) is connected to the top area of the powder spreading cavity (4) through a first electric push rod (6). A sealing plate (9) is fixed to the bottom of the guiding mesh plate (7) through a connecting rod (8). The sealing plate (9) is arranged at the bottom opening of the powder spreading cavity (4). A central rod (10) is longitudinally penetrated and installed in the connecting rod (8). Installation sleeves (12) are fixed to both sides of the central rod (10) through cross bars (11). A powder assisting bar (13) is slidably arranged vertically in the installation sleeve (12). A pressing plate (14) is fixed to the bottom of the powder assisting bar (13). The pressing plate (14) is located on the sealing plate (9). A pushing mechanism is arranged inside the central rod (10) and on the inner wall of the cavity of the machine body (1). The pushing mechanism is used to push the powder assisting bar (13) to move vertically.

2. The metal powder spreading device for additive manufacturing of a rocket engine thrust chamber according to claim 1, characterized in that: Both the front and rear sides of the guiding mesh plate (7) are inclined downward in the powder spreading cavity (4). The powder spreading cavities (4) are transversely arranged at equal intervals in the powder spreading head (3).

3. The metal powder spreading device for additive manufacturing of a rocket engine thrust chamber according to claim 2, characterized in that: Both the left and right sides of the sealing plate (9) are inclined upward to the outside. Both sides of the sealing plate (9) are in contact with the inner wall of the bottom of the powder spreading cavity (4). The bottom of the sealing plate (9) is designed as a triangular structure.

4. A metal powder spreading device for additive manufacturing of a rocket engine thrust chamber according to claim 3, characterized in that: A plurality of powder assisting bars (13) are arranged in the longitudinal position. The lengths of the plurality of powder assisting bars (13) are adapted to the guiding mesh plate (7).

5. A metal powder spreading device for additive manufacturing of a rocket engine thrust chamber according to claim 4, characterized in that: The powder assisting bar (13) and the pressing plate (14) are inclined in the forward interval. The pressing plate (14) is parallel to the top of the sealing plate (9).

6. A metal powder spreading device for additive manufacturing of a rocket engine thrust chamber according to claim 5, characterized in that: The pushing mechanism includes a pushing bar (151). The pushing bar (151) is longitudinally penetrated and installed in the powder spreading head (3). The front end of the pushing bar (151) is elastically slidably arranged inside the central rod (10) through a spring. The rear end of the pushing bar (151) is located outside the powder spreading head (3). The pushing bar (151) is vertically and slidably attached to the powder spreading head (3). A sealing strip for preventing the powder in the powder spreading cavity (4) from overflowing is sleeved on the pushing bar (151). A pushing head (152) is arranged above the rear end of the pushing bar (151). The pushing head (152) is fixed to the inner wall of the cavity of the machine body (1). A pushing plate (153) is fixed to the outside of the pushing bar (151). The pushing plate (153) is located inside the central rod (10). A toothed plate (154) is arranged on the moving track of the pushing plate (153). The toothed plate (154) is penetrated and installed in the cross bar (11) and the installation sleeve (12). A toothed roller (155) is meshed with the outer end of the toothed plate (154). The toothed roller (155) is rotationally arranged in the installation sleeve (12) through a torsion spring in an embedded manner.

7. A metal powder spreading device for additive manufacturing of a rocket engine thrust chamber according to claim 6, characterized in that: The push heads (152) are evenly distributed on the inner wall of the cavity of the body (1). The distribution positions of the push heads (152) are adapted to the movement trajectories of the mounting seats (2). The push heads (152) are designed as hemispherical structures.

8. A metal powder spreading device for additive manufacturing of a rocket engine thrust chamber according to claim 7, characterized in that: The push plate (153) is limited and slides within the central rod (10). The front end of the central rod (10) is designed as an inclined structure and abuts against the toothed plate (154).

9. A metal powder spreading device for additive manufacturing of a rocket engine thrust chamber according to claim 8, characterized in that: The toothed roller (155) meshes with the auxiliary paving strip (13) of a rack structure. The auxiliary paving strip (13) and the toothed plate (154) are staggeredly distributed.

10. A metal powder spreading device for additive manufacturing of a rocket engine thrust chamber according to claim 9, characterized in that: A scraper (17) is connected to the bottom edge of the mounting seat (2) through a second electric push rod (16).

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