Large size devolatilization extruder for post treatment of polymers

Abstract

This invention provides a large-size devolatilization extruder for polymer post-processing, belonging to the technical field of devolatilization machines. It includes a base, with a first motor fixedly connected to the left end of the upper surface of the base. A reducer is located on the right side of the first motor and fixedly connected to the base. The output end of the first motor is fixedly connected to the input end of the reducer. A cylinder is mounted on the upper surface of the base, and the output end of the reducer is fixedly connected to the input end of the mandrel inside the cylinder. In this invention, by setting up a first bearing, a rotating shaft, a large gear, a connecting head, a scraper, and a linkage drive assembly, the scraper is driven to rotate synchronously through the linkage drive assembly. The scraper adheres to the inner wall of the vacuum cylinder, which can promptly scrape away melt overflow and liquid film and crystals formed by the condensation of volatiles during the vacuuming process. This prevents the accumulation of overflow and condensate from clogging the vacuum cylinder, ensuring the continuity of the devolatilization operation and solving the problems of easy clogging and interruption of devolatilization in existing vacuum systems.

Description

Technical Field

[0001] This invention relates to the field of devolatilizer technology, and more particularly, to a large-size devolatilizer extruder for polymer post-processing. Background Technology

[0002] In the plastics processing industry, molten plastics generate a large amount of volatile substances during the melting and plasticizing process, including monomers, solvents, and low-molecular-weight additives. If these volatile substances are not effectively removed, they will remain inside the plastic products, leading to quality defects such as bubbles, shrinkage cavities, and embrittlement. Furthermore, the release of these volatiles into the air causes environmental pollution and harms the health of operators. Therefore, as a core auxiliary equipment in plastics processing, the devolatilization efficiency, stability, and adaptability of the devolatilization machine directly determine the quality of plastic products and the environmental friendliness of production.

[0003] A search revealed Chinese patent application CN202420159394.4, which discloses a twin-screw devolatilizer for biodegradable plastics, relating to the field of devolatilizer technology. The technical solution includes a twin-screw devolatilizer for biodegradable plastics, comprising a motor, a transmission box and coupling connected to the screw, and a jacket covering the screw with a feed inlet. A preheater is located at the feed inlet. This invention employs a combination of multiple heating methods, including electric heating, thermal oil heating, and steam pipeline heating, or a combination of several of these methods. This effectively solves the problems of incomplete devolatilization and high energy consumption in the devolatilization stage of biodegradable plastics with high solvent content. The above-mentioned patent still has the following shortcomings in use: 1. The vacuum system in the prior art is prone to clogging, and the melt overflow phenomenon is likely to occur during the vacuuming process, which leads to the blockage of the vacuum cylinder and reduces the continuity of devolatilization; 2. It is inconvenient to filter the volatiles, and the extracted volatiles contain solid impurities and condensate, which can easily cause damage to the vacuum equipment.

[0004] Therefore, there is an urgent need for large-size devouring extruders for polymer post-processing to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a large-size devolatilization extruder for polymer post-processing, in order to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A large-size devolatilization extruder for polymer post-processing includes a base. A first motor is fixedly connected to the left end of the upper surface of the base. A reducer is located on the right side of the first motor and is fixedly connected to the base. The output end of the first motor is fixedly connected to the input end of the reducer. A cylinder is mounted on the upper surface of the base. The output end of the reducer is fixedly connected to the input end of the mandrel inside the cylinder. A feed inlet is fixedly connected to the left end of the upper surface of the cylinder. A set of vacuum cylinders is uniformly fixedly connected to the upper surface of the cylinder. The upper surface of the vacuum cylinders is connected by screws... A top cover is fixedly connected to the bolt assembly. A first bearing is fixedly connected to the center of the upper surface of the top cover. A rotating shaft is fixedly connected to the inner side wall of the inner ring of the first bearing. The bottom end of the rotating shaft passes through the top cover and extends into the interior of the vacuum cylinder. A large gear is fixedly connected to the top end of the rotating shaft. A connector is fixedly connected to the bottom end of the rotating shaft through a bolt assembly. A scraper is fixedly connected to the bottom end of the connector. A linkage drive assembly is provided on the top cover. A connecting pipe communicating with the vacuum cylinder is fixedly connected to the side wall of the vacuum cylinder. A filter drainage assembly is provided at the outer end of the connecting pipe.

[0007] As a preferred technical solution of this application, the linkage drive assembly includes a second bearing fixed to the upper end face of the top cover, a connecting shaft fixedly connected to the inner side wall of the inner ring of the second bearing, a small gear fixedly connected to the connecting shaft and meshing with a large gear, a driven bevel gear fixedly connected to the top end of the connecting shaft, two support plates symmetrically and fixedly connected to the upper end face of the top cover, a transmission shaft rotatably connected between the two support plates, a driving bevel gear fixedly connected to the transmission shaft and meshing with the driven bevel gear, a connecting shaft provided between adjacent transmission shafts, the two ends of the connecting shaft being fixedly connected to the transmission shafts respectively through couplings, a fixed seat fixedly connected to the upper end face of the end of the barrel near the first motor, a second motor fixedly connected to the upper end face of the fixed seat, and the drive end of the second motor being fixedly connected to its adjacent transmission shaft through a coupling.

[0008] As a preferred technical solution of this application, the filtration and drainage assembly includes a first control valve fixed to the outer end of a connecting pipe, a connecting pipe fixedly connected to the outer end of the first control valve, a filter housing fixedly connected to the outer end of the connecting pipe, a sealing plate fixedly connected to the outer end of the filter housing by a bolt assembly, a filter cylinder fixedly connected to the center of the inner sidewall of the sealing plate, a set of openings evenly distributed on the filter cylinder, and a filter screen fixedly connected to the openings, a vacuum pipe fixedly connected to the upper end face of the filter cylinder and communicating with it, a condensate drainage pipe fixedly connected to the bottom end of the filter cylinder and communicating with it, and a second control valve fixedly connected to the bottom end of the condensate drainage pipe.

[0009] As a preferred technical solution of this application, a first sealing ring is provided between the filter housing and the sealing plate, the filter cylinder is positioned corresponding to the connecting pipe, and a circular insertion port that mates with the filter cylinder is provided on the inner side wall of the filter housing.

[0010] As a preferred technical solution of this application, a protective cover is fixedly connected to the upper end face of the top cover, and the protective cover has an assembly port that matches the drive shaft.

[0011] As a preferred technical solution of this application, a second sealing ring is provided between the upper end face of the vacuum cylinder and the top cover, and a circular shell is fixedly connected to the center of the lower end face of the top cover, and a sealing ring that cooperates with the rotating shaft is fixedly connected inside the circular shell.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: In the scheme of this application: 1. By setting up a first bearing, a rotating shaft, a large gear, a connector, a scraper, and a linkage drive assembly, the scraper is driven to rotate synchronously through the linkage drive assembly. The scraper adheres to the inner wall of the vacuum cylinder, which can promptly scrape off the melt overflow and the liquid film and crystals formed by the condensation of volatiles during the vacuuming process. This prevents the overflow and condensate from accumulating and clogging the vacuum cylinder, ensuring the continuity of the devolatilization operation and solving the problems of easy clogging and interruption of devolatilization in the existing vacuum system. 2. By setting up a filtration and drainage component, the extracted volatiles are precisely filtered through the filter cylinder and filter screen, intercepting solid impurities and viscous substances, while achieving gas-liquid separation. The condensate is discharged through the condensate drain pipe, avoiding damage to the external vacuum equipment by impurities and reducing environmental pollution. This solves the problem of incomplete volatile treatment damaging the equipment in existing technologies. Attached Figure Description

[0013] Figure 1 One of the overall structural schematic diagrams of the large-size devolatilization extruder for polymer post-processing provided in this application; Figure 2 The second schematic diagram of the overall structure of the large-size devolatilization extruder for polymer post-processing provided in this application; Figure 3 A schematic diagram of the external overall structure of the vacuum cylinder of the large-size devolatilization extruder for polymer post-processing provided in this application; Figure 4 A schematic diagram of the internal structure of the vacuum cylinder of the large-size devolatilization extruder for polymer post-processing provided in this application; Figure 5 This is a schematic diagram of the filtration and drainage assembly of a large-size devolatilization extruder for polymer post-processing provided in this application.

[0014] The image shows: 1. Base; 2. First motor; 3. Reducer; 4. Barrel; 5. Feed inlet; 6. Vacuum cylinder; 7. Top cover; 8. First bearing; 9. Rotating shaft; 10. Large gear; 11. Connector; 12. Scraper; 13. Linkage drive assembly; 1301. Second bearing; 1302. Connecting shaft; 1303. Small gear; 1304. Driven bevel gear; 1305. Support plate; 1306. Transmission shaft; 1307. Driven bevel gear; 1308. Connecting shaft; 1309. Coupling; 310. Fixed base; 1311. Second motor; 14. Connecting pipe; 15. Filter drainage assembly; 1501. First control valve; 1502. Connecting pipe; 1503. Filter housing; 1504. Sealing plate; 1505. Filter cylinder; 1506. Filter screen; 1507. Vacuum tube; 1508. Condensate drainage tube; 1509. Second control valve; 1510. First sealing ring; 16. Protective cover; 17. Assembly port; 18. Second sealing ring; 19. Round shell; 20. Sealing ring. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0016] like Figures 1-5 As shown, the large-size devolatilization extruder for polymer post-processing proposed in this embodiment includes a base 1. A first motor 2 is fixedly connected to the left end of the upper surface of the base 1. A reducer 3 is provided on the right side of the first motor 2. The reducer 3 is fixedly connected to the base 1. The output end of the first motor 2 is fixedly connected to the input end of the reducer 3. A cylinder 4 is installed on the upper surface of the base 1. The output end of the reducer 3 is fixedly connected to the input end of the mandrel inside the cylinder 4. A feed inlet 5 is fixedly connected to the left end of the upper surface of the cylinder 4. A set of vacuum cylinders 6 are uniformly fixedly connected to the upper surface of the cylinder 4. The upper surface of the vacuum cylinders 6 is connected to... A top cover 7 is fixedly connected to a bolt assembly. A first bearing 8 is fixedly connected to the center of the upper surface of the top cover 7. A rotating shaft 9 is fixedly connected to the inner side wall of the inner ring of the first bearing 8. The bottom end of the rotating shaft 9 passes through the top cover 7 and extends into the interior of the vacuum cylinder 6. A large gear 10 is fixedly connected to the top end of the rotating shaft 9. A connector 11 is fixedly connected to the bottom end of the rotating shaft 9 through a bolt assembly. A scraper 12 is fixedly connected to the bottom end of the connector 11. A linkage drive assembly 13 is provided on the top cover 7. A connecting pipe 14 communicating with the vacuum cylinder 6 is fixedly connected to the side wall of the vacuum cylinder 6. A filter drainage assembly 15 is provided at the outer end of the connecting pipe 14.

[0017] After the first motor 2 starts, the power output is reduced and increased in torque by the reducer 3 and transmitted to the mandrel inside the barrel 4. The mandrel rotates under the power drive, stirring and pushing the plastic raw material entering the barrel 4 from the feed port 5, so that the plastic raw material is fully melted and plasticized in the barrel 4 to form a uniform plastic melt, creating conditions for the subsequent removal of volatile substances and adapting to the melt processing needs of large-size plastic processing. The linkage drive component 13 synchronously drives all the rotating shafts 9 to rotate. The rotating shafts 9 drive the connector 11 and the scraper 12 to rotate. The scraper 12 adheres to the inner wall of the vacuum cylinder 6 and promptly scrapes away the melt overflow and liquid film and crystals formed by the condensation of volatile substances that may occur during the vacuuming process, preventing the overflow and condensate from accumulating and clogging the vacuum cylinder 6, and ensuring the volatilization efficiency.

[0018] like Figure 1 , Figure 2 and Figure 4 As shown, in a preferred embodiment, based on the above method, the linkage drive assembly 13 further includes a second bearing 1301 fixed to the upper end face of the top cover 7. A connecting shaft 1302 is fixedly connected to the inner side wall of the inner ring of the second bearing 1301. A small gear 1303 that meshes with the large gear 10 is fixedly connected to the connecting shaft 1302. A driven bevel gear 1304 is fixedly connected to the top end of the connecting shaft 1302. Two support plates 1305 are symmetrically connected and fixedly connected to the upper end face of the top cover 7. A transmission shaft 130 is rotatably connected between the two support plates 1305. 6. A drive bevel gear 1307 that meshes with the driven bevel gear 1304 is fixedly connected to the drive shaft 1306. A connecting shaft 1308 is provided between adjacent drive shafts 1306. The two ends of the connecting shaft 1308 are fixedly connected to the drive shaft 1306 through couplings 1309. A fixed seat 1310 is fixedly connected to the upper end face of the end of the barrel 4 near the first motor 2. A second motor 1311 is fixedly connected to the upper end face of the fixed seat 1310. The drive end of the second motor 1311 is fixedly connected to the drive shaft 1306 near it through couplings 1309.

[0019] After the second motor 1311 starts, it drives the adjacent transmission shaft 1306 to rotate through the coupling 1309. The adjacent transmission shafts 1306 are linked through the connecting shaft 1308 and the coupling 1309 to realize the synchronous rotation of all transmission shafts 1306. The driving bevel gear 1307 on the transmission shaft 1306 meshes with the driven bevel gear 1304 at the top of the connecting shaft 1302, which drives the connecting shaft 1302 to rotate stably. The rotation of the connecting shaft 1302 drives the small gear 1303 to rotate, and the rotation of the small gear 1303 drives the large gear 10 to rotate, thereby driving the rotating shaft 9 to rotate. The rotating shaft 9 drives the connecting head 11 and the scraper 12 to rotate. The scraper 12 is in contact with the inner wall of the vacuum cylinder 6 to scrape off the melt overflow and liquid film and crystals formed by the condensation of volatiles that may occur during the vacuuming process, preventing the overflow and condensate from accumulating and clogging the vacuum cylinder 6, and ensuring the devolatilization efficiency.

[0020] like Figure 1 , Figure 3 and Figure 5 As shown, in a preferred embodiment, based on the above method, the filtration and drainage assembly 15 further includes a first control valve 1501 fixed to the outer end of the connecting pipe 14, a connecting pipe 1502 fixedly connected to the outer end of the first control valve 1501, a filter housing 1503 fixedly connected to the outer end of the connecting pipe 1502, a sealing plate 1504 fixedly connected to the outer end of the filter housing 1503 by a bolt assembly, a filter cylinder 1505 fixedly connected to the center of the inner sidewall of the sealing plate 1504, a set of openings evenly provided on the filter cylinder 1505, and a filter screen 1506 fixedly connected inside the openings, a vacuum pipe 1507 fixedly connected to and communicating with the upper end face of the filter cylinder 1505, a condensate drain pipe 1508 fixedly connected to and communicating with the bottom end of the filter cylinder 1505, and a second control valve 1509 fixedly connected to the bottom end of the condensate drain pipe 1508.

[0021] The negative pressure environment inside the vacuum cylinder 6 extracts volatile substances from the plastic melt. The volatile substances are transported through the connecting pipe 14, enter the connecting pipe 1502 through the first control valve 1501 (which can control the on / off of the transport), and finally enter the filter housing 1503. After the volatile substances enter the filter cylinder 1505, the solid impurities or viscous substances in it are intercepted and filtered by the filter screen 1506. The purified volatile gases are extracted through the vacuum pipe 1507 (the vacuum pipe 1507 can be connected to external vacuum equipment), while the condensate formed by the condensation of the volatile substances is collected at the bottom of the filter cylinder 1505 and discharged through the condensate drain pipe 1508 and the second control valve 1509, thus realizing gas-liquid separation and impurity filtration.

[0022] like Figure 3 and Figure 5 As shown, in a preferred embodiment, based on the above method, a first sealing ring 1510 is provided between the filter housing 1503 and the sealing plate 1504, the filter cylinder 1505 is positioned corresponding to the connecting pipe 1502, and a circular insertion port that cooperates with the filter cylinder 1505 is provided on the inner side wall of the filter housing 1503.

[0023] The first sealing ring 1510 ensures the airtightness of the filter chamber and prevents gas leakage; the circular inlet on the inner wall of the filter housing 1503 matches the filter cartridge 1505 to improve the installation stability of the filter cartridge 1505.

[0024] like Figures 1-3 As shown, in a preferred embodiment, based on the above method, a protective cover 16 is fixedly connected to the upper end face of the top cover 7, and the protective cover 16 has an assembly port 17 that matches the drive shaft 1306.

[0025] The protective cover 16 protects the gears and shafts of the linkage drive assembly 13 to prevent debris from getting in or people from accidentally touching them. The assembly port 17 is used to adapt to the installation and rotation of the drive shaft 1306.

[0026] like Figure 1 , Figure 3 and Figure 4 As shown, in a preferred embodiment, based on the above method, a second sealing ring 18 is provided between the upper end face of the vacuum cylinder 6 and the top cover 7, and a circular shell 19 is fixedly connected to the center of the lower end face of the top cover 7, and a sealing ring 20 that cooperates with the rotating shaft 9 is fixedly connected inside the circular shell 19.

[0027] The second sealing ring 18 can prevent the negative pressure inside the vacuum cylinder 6 from leaking, ensuring a stable negative pressure environment required for degassing. The sealing ring 20 can prevent the gas inside the vacuum cylinder 6 from leaking from the gap between the rotating shaft 9 and the top cover 7, while also preventing external impurities from entering the vacuum cylinder 6.

[0028] Specifically, the large-size devolatilization extruder used for polymer processing operates as follows: First, the first motor 2 is started. The power output of the first motor 2 is reduced and increased in torque by the reducer 3, and then transmitted to the mandrel inside the barrel 4, driving the mandrel to rotate stably. At the same time, the plastic raw material is fed into the barrel 4 at a uniform speed from the feed port 5. During the rotation of the mandrel, the plastic raw material is continuously stirred and pushed, so that the plastic raw material is fully melted and plasticized in the barrel 4 to form a uniform plastic melt. While the plastic melt is being plasticized and pushed, the external vacuum equipment is started, in conjunction with the vacuum cylinder 6 and the filter and drainage assembly 15, to form a stable negative pressure environment inside the vacuum cylinder 6. The negative pressure is used to quickly extract the volatile substances volatilized in the plastic melt. At the same time, the linkage drive assembly 13 and the second motor 131 are started. 1. The adjacent drive shaft 1306 is driven to rotate through the coupling 1309. The adjacent drive shaft 1306 is linked with the connecting shaft 1308 and the coupling 1309 to realize the synchronous rotation of all drive shafts 1306. The driving bevel gear 1307 on the drive shaft 1306 meshes with the driven bevel gear 1304 at the top of the connecting shaft 1302, driving the connecting shaft 1302 to rotate. The small gear 1303 on the connecting shaft 1302 meshes with the large gear 10 at the top of the rotating shaft 9, driving the rotating shaft 9 to drive the scraper 12 to rotate synchronously. The scraper 12 is in contact with the inner wall of the vacuum cylinder 6 to promptly scrape off the melt overflow and liquid film and crystals formed by the condensation of volatiles that may occur during the vacuuming process, preventing the overflow and condensate from accumulating and blocking the vacuuming channel, and ensuring the continuous and efficient operation of the devolatilization process. The volatiles extracted from the vacuum cylinder 6 are transported through the connecting pipe 14. The first control valve 1501 is opened, and the volatiles are sent into the filter housing 1503 through the connecting pipe 1502. The filter cylinder 1505, which is set corresponding to the connecting pipe 1502, filters the volatiles. Solid impurities and viscous substances are intercepted by the filter screen 1506. The purified volatile gases are extracted through the vacuum pipe 1507 and can be recycled or discharged in compliance with standards as needed. The condensate formed by the condensation of volatiles during the filtration process is collected at the bottom of the filter cylinder 1505. The second control valve 1509 is opened periodically, and the condensate is discharged through the condensate drain pipe 1508, realizing gas-liquid separation and impurity filtration.

Claims

1. A large-size devolatilization extruder for polymer post-processing, comprising a base (1), characterized in that, A first motor (2) is fixedly connected to the left end of the upper surface of the base (1). A reducer (3) is provided on the right side of the first motor (2). The reducer (3) is fixedly connected to the base (1). The output end of the first motor (2) is fixedly connected to the input end of the reducer (3). A cylinder (4) is installed on the upper surface of the base (1). The output end of the reducer (3) is fixedly connected to the input end of the spindle inside the cylinder (4). A feed inlet (5) is fixedly connected to the left end of the upper surface of the cylinder (4). A set of vacuum cylinders (6) are evenly fixedly connected to the upper surface of the cylinder (4). A top cover (7) is fixedly connected to the upper surface of the vacuum cylinder (6) by bolt assembly. A first bearing (8) is fixedly connected to the center of the upper end face of the vacuum cylinder (6). A rotating shaft (9) is fixedly connected to the inner side wall of the inner ring of the first bearing (8). The bottom end of the rotating shaft (9) passes through the top cover (7) and extends into the interior of the vacuum cylinder (6). A large gear (10) is fixedly connected to the top end of the rotating shaft (9). A connector (11) is fixedly connected to the bottom end of the rotating shaft (9) by a bolt assembly. A scraper (12) is fixedly connected to the bottom end of the connector (11). A linkage drive assembly (13) is provided on the top cover (7). A connecting pipe (14) communicating with the vacuum cylinder (6) is fixedly connected to the side wall of the vacuum cylinder (6). A filter drainage assembly (15) is provided at the outer end of the connecting pipe (14).

2. The large-size devolatilization extruder for polymer post-processing according to claim 1, characterized in that, The linkage drive assembly (13) includes a second bearing (1301) fixed to the upper end face of the top cover (7). A connecting shaft (1302) is fixedly connected to the inner side wall of the inner ring of the second bearing (1301). A small gear (1303) that meshes with the large gear (10) is fixedly connected to the connecting shaft (1302). A driven bevel gear (1304) is fixedly connected to the top end of the connecting shaft (1302). Two support plates (1305) are symmetrically and fixedly connected to the upper end face of the top cover (7). A transmission shaft (1306) is rotatably connected between the two support plates (1305). A fixed drive shaft (1306) is fixed to the transmission shaft (1306). A drive bevel gear (1307) is connected to the driven bevel gear (1304). A connecting shaft (1308) is provided between adjacent transmission shafts (1306). The two ends of the connecting shaft (1308) are fixedly connected to the transmission shaft (1306) through couplings (1309). A fixed seat (1310) is fixedly connected to the upper end face of the end of the barrel (4) near the first motor (2). A second motor (1311) is fixedly connected to the upper end face of the fixed seat (1310). The drive end of the second motor (1311) is fixedly connected to the transmission shaft (1306) near it through a coupling (1309).

3. The large-size devolatilization extruder for polymer post-processing according to claim 1, characterized in that, The filtration and drainage assembly (15) includes a first control valve (1501) fixed to the outer end of the connecting pipe (14). The outer end of the first control valve (1501) is fixedly connected to a connecting pipe (1502). The outer end of the connecting pipe (1502) is fixedly connected to a filter housing (1503). The outer end of the filter housing (1503) is fixedly connected to a sealing plate (1504) by a bolt assembly. A filter cylinder (1505) is fixedly connected to the center of the inner side wall of the sealing plate (1504). A set of openings are evenly provided on the filter cylinder (1505), and a filter screen (1506) is fixedly connected inside the openings. A vacuum tube (1507) communicating with the upper end face of the filter cylinder (1505) is fixedly connected to the upper end face of the filter cylinder (1505). A condensate drain pipe (1508) communicating with the lower end of the filter cylinder (1505) is fixedly connected to the lower end face of the filter cylinder (1505). A second control valve (1509) is fixedly connected to the lower end of the condensate drain pipe (1508).

4. The large-size devolatilization extruder for polymer post-processing according to claim 3, characterized in that, A first sealing ring (1510) is provided between the filter housing (1503) and the sealing plate (1504). The filter cylinder (1505) is positioned corresponding to the connecting pipe (1502). A circular insertion port that matches the filter cylinder (1505) is provided on the inner side wall of the filter housing (1503).

5. The large-size devolatilization extruder for polymer post-processing according to claim 1, characterized in that, The top cover (7) is fixedly connected to a protective cover (16), and the protective cover (16) has an assembly port (17) that matches the drive shaft (1306).

6. The large-size devolatilization extruder for polymer post-processing according to claim 1, characterized in that, A second sealing ring (18) is provided between the upper end face of the vacuum cylinder (6) and the top cover (7). A round shell (19) is fixedly connected at the center of the lower end face of the top cover (7). A sealing ring (20) that cooperates with the rotating shaft (9) is fixedly connected inside the round shell (19).

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