Natural rubber crepe sheet automatic drying system and drying method

Abstract

The invention discloses an automatic drying system and method for natural rubber crepe sheets. Comprising a feeding system used for feeding incoming materials into a drying box body for drying; the drying box body comprises a feeding door, a box body conveying system and a discharging door; the box body conveying system is arranged at the top in the drying box body, and rubber materials can move in the drying box body through the box body conveying system; the vacuumizing system can vacuumize the interior of the drying box body; the heat supply system comprises an air inlet pipe and an air outlet pipe and is used for introducing hot air into the drying box body and then drying the film; and the discharging system is used for transferring the films conveyed by the box body conveying system to the finished product material conveying part, and finally the films are manually packaged and processed. Compared with an existing drying technology for the natural rubber crepe sheet, the method combining hot air heating with vacuum drying can dry the crepe sheet at the relatively low temperature, accurate control over the material temperature is facilitated, and the quality and performance of rubber are kept.

Description

Technical Field

[0001] The invention relates to the technical field of drying in the primary processing of natural rubber, and in particular to an automatic drying system and a drying method for a natural rubber crepe sheet. Background Art

[0002] In the production process of natural rubber crepe sheets, after the solidified rubber blocks are creped and hung, most production workshops need to manually hang them one by one on the rack and then push the rack as a whole into the drying furnace for drying, or manually hang the hanging rod from the feed port of the drying furnace to the drying box for drying, which has low production efficiency and high labor intensity. A small number of production workshops are equipped with mechanical grippers and traditional hanging rod conveyor belts for transportation, but the cost of using mechanical grippers is too high, maintenance is inconvenient, and the equipment covers a large area but a small area, which is not conducive to the use of production workshops and is not suitable for all production workshops; the traditional hanging rod conveyor belt evolved from the conveyor belt of the noodle conveyor device, but the weight of the film is very different from that of the noodles, and the inertia is large when the hanging rod moves and the equipment is handed over. In addition, the film to be dried still has a certain humidity and a certain viscosity. Unstable transmission can easily cause the films to stick together, or the hanging rod directly falls out of the conveyor device. At this time, it is necessary to stop the machine and intervene manually to correct it, otherwise the production quality will be reduced. Therefore, this production method is in urgent need of automation upgrade and transformation.

[0003] Moreover, in the traditional production process of crepe sheets, wood and coal are usually burned to heat the air to form hot air, and then the hot air is used to heat and dry the materials. According to current environmental protection requirements, the method of obtaining heat energy by combustion must be equipped with an environmental protection treatment device for combustion exhaust gas, resulting in high environmental protection treatment costs. At the same time, the use of combustion to obtain heat energy has problems such as the difficulty in accurately controlling the hot air temperature. The upgrading and transformation of green and environmentally friendly production in the production process of crepe sheets is imminent. Summary of the invention

[0004] In order to solve the problems of the prior art, the purpose of the present invention is to provide an automatic drying system and method for natural rubber crepe sheets. After the crepe sheet material is hung on the hanging rod, it is transported to the system by a chain. The transfer device in the system can automatically transfer the material. After being transferred into the drying box, the material can be dried in the drying box. The automation level of production and processing is greatly improved. At the same time, using electric energy as the energy source for drying can accurately control the temperature during the drying process. In addition, the hot air in the drying box can be recycled to recover the heat energy of the exhaust gas, which reduces energy consumption and solves the problem of environmental protection treatment of exhaust gas from combustion heating. The specific contents are as follows:

[0005] A natural rubber crepe sheet automatic drying system, comprising:

[0006] The feeding system is used to feed the materials into the drying box for drying;

[0007] The drying box body includes a feeding door, a flange pipe a, a flange pipe b, a flange pipe c, a box body conveying system, and a discharging door; the box body conveying system is installed at the top inside the drying box body, and the rubber material can move in the drying box body through the box body conveying system; the flange pipe a is installed on the side of the drying box body, and the flange pipe b and the flange pipe c are installed on the top of the drying box body;

[0008] The vacuum pumping system is connected to the flange pipe c on the drying box body and can pump the air inside the drying box body to create a vacuum;

[0009] The heating system includes an air inlet pipe and an air outlet pipe, which are respectively connected to the flange pipe a and the flange pipe b on the drying box body, and are used to introduce hot air into the drying box body to dry the film;

[0010] The blanking system is used to transfer the film conveyed by the box body conveying system to the finished product material conveying part, and finally it is manually packed; the blanking system has the same basic structure as the feeding system, the conveying height of the feeding system is higher than that of the box body conveying system, and the conveying height of the box body conveying system is higher than that of the blanking system.

[0011] Furthermore, the feeding system includes a guide rail part, a support frame, and a rack; there are several drying box bodies arranged in parallel in the automatic drying system, and the guide rail part is installed at the feeding door of several drying box bodies; the support frame can move on the guide rail part, the rack can move on the support frame, and the moving directions of the support frame and the rack are perpendicular to each other on the horizontal plane; a conveying chain is installed inside the rack, and the conveying direction of the conveying chain is the same as the moving direction of the rack on the support frame; a rack conveying motor is arranged at the top of the rack, and the conveying chain is driven to rotate through a rack transmission chain.

[0012] Furthermore, the rack also includes a transition block, which is fixedly installed on the rack and is used to smoothly transfer the hanging rods conveyed on the conveying chain; a slideway is opened on the transition block, the width of the slideway is the same as the diameter of the hanging rod, and the hanging rod can slide through the slideway along the slideway.

[0013] Further, a bearing bracket, steel wheels, a drive shaft, and a drive motor are provided at the bottom of the support frame. The drive shaft is mounted on the bearing bracket through bearings. The steel wheels are installed at both ends of the drive shaft. The support frame is movably installed on the guide rail portion through the steel wheels. The drive motor can drive the drive shaft to rotate, thereby driving the steel wheels to rotate and enabling the support frame to move horizontally on the guide rail portion. A rack perpendicular to the guide rail portion in the horizontal direction is provided at the top of the support frame. The material rack is located above the support frame, and a gear cooperating with the rack is provided at the bottom. A material rack movement is installed on the material rack. The material rack movement motor is transmitted to the gear through a drive sprocket to drive the material rack to move longitudinally on the support frame.

[0014] Further, a flange pipe d is also provided on the drying box body. A plurality of the drying box bodies are arranged in parallel in the automatic drying system, and all the drying box bodies are interconnected through the flange pipe d.

[0015] Further, a heat preservation layer is provided on the outer wall of the drying box body. Positioning blocks are provided on the conveyor belts of the feeding system, the box body conveying system, and the discharging system. An arc hole with the same diameter as the hanging rod is opened at the top of the positioning block. An evacuation valve is provided in the flange pipe c. An air inlet valve and an air outlet valve are respectively provided in the flange pipe a and the flange pipe b.

[0016] Further, a hanging rod recovery device is also provided. The hanging rod recovery device is installed at the end of the discharging system and is used to convey the hanging rods to the hanging piece workshop.

[0017] A drying method for an automatic drying system of natural rubber crepe sheets, comprising the following steps: S1. Material warehousing. The material after hanging sheets is conveyed into the drying box body 1 through a feeding device. When warehousing, the support frame 22 bears the rack 23 and moves on the guide rail part 21 to the incoming material conveying end to pick up the material. After the conveying chain 231 is aligned with the incoming material conveying end, the rack 23 moves out through the rack conveying motor 232 to complete the docking of the conveying chain 231, and then all the rubber sheets are conveyed onto the conveying chain 231 on the rack 23. Then the rack 23 is retracted. The moving support part moves to the door of the drying box body 1, and the rack 23 is moved again. S2. The support frame 22 extends, so that the conveying chain 231 is docked with the conveyor belt of the box body conveying system 17 inside the drying box body 1, and the material is transferred into the interior of the drying box body 1. After the material enters the drying box body 1, the material is dried by the alternating use of the vacuum pumping system 4 and the heat supply system 3. S2.1. When the material is heated up, the flange pipe a13 and the flange pipe b14 inside the drying box body 1 are opened simultaneously. The heat supply system 3 supplies hot air at 80 °C to the drying box body 1 to heat up the material, and the flange pipe c15 is closed and maintained for 6 - 10 minutes. S2.2. After the hot air supply time is reached, the flange pipe a13 and the flange pipe b14 are closed simultaneously and maintained for 3 - 7 minutes. S2.3. Then the flange pipe c15 is opened, and the vacuum pumping system 4 is started, so that the absolute negative pressure inside the drying box body 1 is less than 30,000 Pa and maintained for 1 - 3 minutes. Then steps S1 to S3 are repeated. When the moisture content of the material is less than 1%, the time in step S1 is shortened to 1 - 3 minutes, and the time in step S3 is increased to 6 - 10 minutes. S3. Outbound. The dried material is conveyed to the finished product material conveying part 6 through the blanking system 5. The principle of the blanking system 5 is the same as that of the incoming system. Finally, it is processed by manual packing. The setting of the transition block 24 enables the hanging rod on the conveying chain 231 to move smoothly along the slide on the transition block 24 into the box body conveying system 17 inside the drying box body 1 and accurately fall into the arc hole opened on the positioning block 19 on the conveyor, preventing the dislocation of the material hanging rods during the handover. The cooperation between the transition block 24 and the positioning block 19 also facilitates the precise control of the distance between the materials by controlling the rotation of the motors of each part.

[0018] The present invention has the following beneficial effects compared with the prior art:

[0019] (1) Compared with the current drying technology for natural rubber crepe sheets, the method of using hot air heating combined with vacuum drying proposed by the present invention can dry the crepe sheets at a relatively low temperature, which is beneficial to the precise control of the material temperature and maintains the quality and performance of the rubber.

[0020] (2) The method of heating with hot air and then baking in the furnace and then carrying out the vacuum drying cycle proposed by the present invention can effectively improve the thermal energy utilization efficiency, reduce the waste of thermal energy, and meet the needs of the green and environmental protection industrial development by controlling the hot air supply time and the vacuum pumping time and connecting the reusable hot air to other drying box bodies.

[0021] (3) The automatic drying system for natural rubber crepe sheets provided by the present invention can automate the feeding, discharging, transfer and conveying, hot air supply, and drying process control of materials, greatly improving the working efficiency of manual feeding, discharging, and conveying in the current industry; the double-layer structure of the support frame and the material rack set in the feeding system facilitates docking with each drying box, and the setting of the transition block can ensure that the material hanging rod will not be misaligned or even fall during conveying. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the system described in the present invention;

[0023] Figure 2 Front view sectional schematic diagram of the drying box described in the present invention;

[0024] Figure 3 Left view sectional schematic diagram of the drying box described in the present invention;

[0025] Figure 4 Schematic diagram of the structure of the feeding system described in the present invention;

[0026] Figure 5 Front view of the feeding system described in the present invention;

[0027] Figure 6 Left view of the feeding system described in the present invention;

[0028] Figure 7 Schematic diagram of the usage state of the feeding system described in the present invention;

[0029] Figure 8 Schematic diagram of the usage state of the feeding system described in the present invention;

[0030] Figure 9 Three-dimensional schematic diagram of the usage state of the transition block described in the present invention;

[0031] Figure 10 Schematic diagram of the usage state of the transition block described in the present invention.

[0032] In the figure:

[0033] 1 - drying box, 11 - feed door, 12 - discharge door, 13 - flange pipe a, 14 - flange pipe b,

[0034] 15 - flange pipe c, 16 - flange pipe d, 17 - box conveying system, 18 - air distribution layer, 19

[0035] - positioning block;

[0036] 2 - feeding system, 21 - guide rail part, 22 - support frame, 221 - bearing frame, 222 - steel wheel,

[0037] 223 - drive shaft, 224 - drive motor, 225 - rack; 23 - rack, 231 - conveyor chain, 232 - rack conveyor motor, 233 - rack drive chain, 234 - gear; 24

[0038] — transition block, 241 - slideway;

[0039] 3 - heating system, 31 - air inlet pipe, 32 - air outlet pipe;

[0040] 4 - vacuum pumping system; 5 - blanking system; 6 - finished product material conveying section; 7 - hanging rod recycling device. Specific implementation mode

[0041] In order to make the technical means, creative features, and achievements of the present invention easy to understand, the following further describes the technical solutions of the invention in combination with one of the embodiments and specific implementation modes of an automatic drying system and drying method for natural rubber crepe sheets given by the present invention.

[0042] As Figures 1-9 shown, the specific embodiments given for the invention are as follows:

[0043] An automatic drying system for natural rubber crepe sheets, comprising:

[0044] A feeding system 2 for feeding incoming materials into the drying box body 1 for drying;

[0045] The drying box body 1 includes a feeding door 11, a flange pipe a13, a flange pipe b14, a flange pipe c15, a box body conveying system 17, and a discharging door 12; the box body conveying system 17 is installed at the top inside the drying box body 1, and the rubber material can move in the drying box body 1 through the box body conveying system 17; the flange pipe a13 is installed on the side of the drying box body 1, and the flange pipes b14 and c15 are installed on the top of the drying box body 1; the drying box body 1 is also provided with a flange pipe d16, and a plurality of drying box bodies 1 are arranged in parallel in the automatic drying system, and all the drying box bodies 1 are interconnected through the flange pipe d16.

[0046] A vacuum pumping system 4 is connected to the flange pipe c15 on the drying box body 1 and can evacuate the inside of the drying box body 1;

[0047] A heating system 3 includes an air inlet pipe 31 and an air outlet pipe 32, which are respectively connected to the flange pipe a13 and the flange pipe b14 on the drying box body 1, and are used to dry the film by introducing hot air into the drying box body 1;

[0048] The blanking system 5 is used to transfer the film conveyed by the box conveying system 17 to the finished product material conveying section 6, and finally it is manually packed; the basic structure of the blanking system 5 is the same as that of the feeding system 2. The conveying height of the feeding system 2 is higher than that of the box conveying system 17, and the conveying height of the box conveying system 17 is higher than that of the blanking system 5.

[0049] The feeding system 2 includes a guide rail section 21, a support frame 22 and a rack 23; several drying boxes 1 are arranged in parallel in the automatic drying system, and the guide rail section 21 is installed at the feeding door 11 of several drying boxes 1; the support frame 22 can move on the guide rail section 21, and the rack 23 can move on the support frame 22. The moving direction of the support frame 22 and the moving direction of the rack 23 are perpendicular to each other on the horizontal plane; a conveying chain 231 is installed inside the rack 23, and the conveying direction of the conveying chain 231 is the same as the moving direction of the rack 23 on the support frame 22; a rack conveying motor 232 is arranged on the top of the rack 23, and the conveying chain 231 is driven to rotate by a rack transmission chain 233. The rack 23 also includes a transition block 24, which is fixedly installed on the rack 23 and is used to smoothly transfer the hanging rods conveyed on the conveying chain 231; a slideway 241 is opened on the transition block 24, and the width of the slideway 241 is the same as the diameter of the hanging rod, and the hanging rod can slide through the slideway 241 along the slideway 241. A bearing frame 221, steel wheels 222, a driving shaft 223 and a driving motor 224 are arranged at the bottom of the support frame 22. The driving shaft 223 is installed on the bearing frame 221 through bearings, and the steel wheels 222 are arranged at both ends of the driving shaft 223. The support frame 22 is movably installed on the guide rail section 21 through the steel wheels 222, and the driving motor 224 can drive the driving shaft 223 to rotate, and then drive the steel wheels 222 to rotate to make the support frame 22 move horizontally on the guide rail section 21; a rack 225 perpendicular to the guide rail section 21 in the horizontal direction is arranged on the top of the support frame 22. The rack 23 is located above the support frame 22, and a gear 234 cooperating with the rack 225 is arranged at the bottom. A rack 23 movement is installed on the rack 23, and the rack 23 movement motor can drive the rack 23 to move longitudinally on the support frame 22 through driving sprockets to the gear 234.

[0050] A heat-insulating layer is provided on the outer wall of the drying box body 1; positioning blocks 19 are provided on the conveyor belts of the feeding system 2, the box body conveying system 17, and the discharging system 5. An arc hole with the same diameter as the hanging rod is opened at the top of the positioning block 19; an evacuation valve is provided in the flange pipe c15; an air inlet valve and an air outlet valve are respectively provided in the flange pipes a13 and b14. Air distribution layers 18 are respectively provided at the bottom and top of the drying box body 1. The hot air entering the drying box body 1 through the flange pipe a13 rises evenly through the bottom air distribution layer 18, passes through the material, and then enters the flange pipe b14 through the top air distribution layer 18 and is output from the drying box body 1. A hanging rod recycling device 7 is also provided. The hanging rod recycling device 7 is installed at the end of the discharging system 5 and is used to convey the hanging rods to the hanging piece workshop.

[0051] A drying method for an automatic drying system of natural rubber crepe sheets includes the following steps. S1. Material storage: The material after hanging sheets is conveyed into the drying box body 1 through the feeding device; when storing, the support frame 22 bears the rack 23 and moves on the guide rail part 21 to the incoming material conveying end to pick up the material. After the conveying chain 231 is aligned with the incoming material conveying end, the rack 23 moves out through the rack conveying motor 232 to complete the docking of the conveying chain 231, and then all the rubber sheets are conveyed onto the conveying chain 231 on the rack 23; then the rack 23 is retracted; the moving support part is moved to the door of the drying box body 1, and the rack 23 is moved again. S2. The support frame 22 is extended to connect the conveying chain 231 with the conveyor belt of the box body conveying system 17 inside the drying box body 1, and the material is transferred to the inside of the drying box body 1. After the material enters the drying box body 1, the material is dried by alternately using the vacuum pumping system 4 and the heat supply system 3. S2.1. When the material is heated up, the flange pipes a13 and b14 inside the drying box body 1 are opened simultaneously, and the heat supply system 3 supplies hot air at 80°C to the drying box body 1 to heat up the material, and the flange pipe c15 is closed and maintained for 6 - 10 minutes. S2.2. After the hot air supply time is reached, the flange pipes a13 and b14 are closed simultaneously and maintained for 3 - 7 minutes. S2.3. Then the flange pipe c15 is opened, and the vacuum pumping system 4 is started to make the absolute negative pressure inside the drying box body 1 less than 30,000 Pa and maintained for 1 - 3 minutes; then S1 to S3 are repeated. When the moisture content of the material is less than 1%, the time in step S1 is shortened to 1 - 3 minutes, and the time in step S3 is increased to 6 - 10 minutes. S3. Outbound: The dried material is conveyed to the finished product material conveying part 6 through the discharging system 5. The principle of the discharging system 5 is the same as that of the incoming system; finally, it is manually packed. The setting of the transition block 24 enables the hanging rods on the conveying chain 231 to smoothly move along the slide on the transition block 24 into the box body conveying system 17 inside the drying box body 1 and accurately fall into the arc holes opened on the positioning blocks 19 on the conveyor, preventing misalignment during the handover of the material hanging rods. The cooperation between the transition block 24 and the positioning block 19 also facilitates the precise control of the distance between materials by controlling the rotation of the motors of each part.

[0052] It should be understood that the above specific embodiments are only used for exemplary illustration or explanation of the principles of the present invention, and do not constitute a limitation to the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention shall be included within the protection scope of the present invention. The appended claims of the present invention are intended to cover all variations and modifications that fall within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A natural rubber crepe sheet automatic drying system, characterized in that: include: A feeding system (2) is used to feed the material into the drying box (1) for drying; A drying box (1) comprises a feed door (11), a flange pipe a (13), a flange pipe b (14), a flange pipe c (15), a box conveying system (17), and a discharge door (12); the box conveying system (17) is arranged and installed on the top of the drying box (1), and the rubber material can move in the drying box (1) through the box conveying system (17); the flange pipe a (13) is arranged and installed on the side of the drying box (1), and the flange pipe b (14) and the flange pipe c (15) are arranged and installed on the top of the drying box (1); A vacuum system (4) connected to the flange pipe c (15) on the drying box (1) and capable of vacuuming the interior of the drying box (1); The heating system (3) comprises an air inlet pipe (31) and an air outlet pipe (32), which are respectively connected to the flange pipe a (13) and the flange pipe b (14) on the drying box (1), and are used to dry the film after hot air is introduced into the drying box (1); The unloading system (5) is used to transfer the film delivered by the box conveying system (17) to the finished material conveying section (6), and finally to manually pack the film; the unloading system (5) has the same basic structure as the loading system (2), the loading system (2) has a higher conveying height than the box conveying system (17), and the box conveying system (17) has a higher conveying height than the unloading system (5).

2. The automatic drying system for natural rubber crepe sheets as claimed in claim 1, characterized in that: The feeding system (2) comprises a guide rail portion (21), a support frame (22) and a material rack (23); a plurality of drying boxes (1) are arranged in parallel in the automatic drying system, and the guide rail portion (21) is arranged and installed on the feeding doors (11) of the plurality of drying boxes (1); the support frame (22) can move on the guide rail portion (21), and the material rack (23) can move on the support frame (22), and the moving direction of the support frame (22) and the moving direction of the material rack (23) are perpendicular to each other on a horizontal plane; a conveying chain (231) is arranged and installed inside the material rack (23), and the conveying direction of the conveying chain (231) is consistent with the moving direction of the material rack (23) on the support frame (22); a material rack conveying motor (232) is arranged on the top of the material rack (23), and the conveying chain (231) is driven to rotate through the material rack transmission chain (233).

3. The automatic drying system for natural rubber crepe sheets as claimed in claim 2, characterized in that: The material rack (23) also includes a transition block (24), which is fixedly mounted on the material rack (23) and is used to allow the hanging rods transported on the conveying chain (231) to be smoothly transferred; a slideway (241) is provided on the transition block (24), the width of the slideway (241) is the same as the diameter of the hanging rod, and the hanging rod can slide through the slideway (241) along the slideway (241).

4. The automatic drying system for natural rubber crepe sheets as claimed in claim 2, characterized in that: The bottom of the support frame (22) is provided with a bearing frame (221), a steel wheel (222), a driving shaft (223) and a driving motor (224); the driving shaft (223) is mounted on the bearing frame (221) via a bearing; the steel wheel (222) is mounted on both ends of the driving shaft (223); the support frame (22) is movably mounted on the guide rail portion (21) via the steel wheel (222); the driving motor (224) can drive the driving shaft (223) to rotate and then drive the steel wheel (222) to rotate so that the support frame (22) (22) moves horizontally on the guide rail portion (21); a rack (225) is arranged at the top of the support frame (22) and is perpendicular to the guide rail portion (21) in the horizontal direction; the material rack (23) is located at the upper part of the support frame (22), and a gear (234) is arranged at the bottom for use with the rack (225); a material rack (23) moving motor is arranged on the material rack (23), and the material rack (23) moving motor can drive the material rack (23) to move longitudinally on the support frame (22) by driving a sprocket to the gear (234).

5. The automatic drying system for natural rubber crepe sheets as claimed in claim 1, characterized in that: The drying box (1) is also provided with a flange pipe d (16); a plurality of the drying boxes (1) are arranged in parallel in the automatic drying system, and all the drying boxes (1) are interconnected via the flange pipe d (16).

6. The automatic drying system for natural rubber crepe sheets as claimed in claim 1, characterized in that: The outer wall of the drying box (1) is provided with a heat-insulating layer; the conveyor belts of the feeding system (2), the box conveying system (17) and the unloading system (5) are all provided with positioning blocks (19), and the top of the positioning blocks (19) is provided with a circular arc hole with the same diameter as the hanging rod; the flange pipe c (15) is provided with an evacuation valve; the flange pipe a (13) and the flange pipe b (14) are respectively provided with an air inlet valve and an air outlet valve.

7. The automatic drying system for natural rubber crepe sheets as claimed in claim 1, characterized in that: A hanging rod recovery device (7) is also provided. The hanging rod recovery device (7) is installed at the end of the unloading system (5) and is used to transport the hanging rods to the hanging film workshop.

8. A drying method based on the natural rubber crepe sheet automatic drying system according to claim 1, characterized in that: The following steps are involved: S1, material storage, the material after hanging is transported to the drying box (1) through the loading device; S2, drying, after the material enters the drying box (1), the material is dried by the vacuum system (4) and the heating system (3) alternately used; S3, storage out, the dried material is transported to the finished material conveying part (6) through the unloading system (5), and finally packaged manually.

9. The drying method of the natural rubber crepe sheet automatic drying system as claimed in claim 8, characterized in that: The step S2 comprises S2.1, when the temperature of the material is increased, the flange pipe a (13) and the flange pipe b (14) in the drying box (1) are opened at the same time, the heating system (3) supplies hot air at 80°C to the drying box (1) to increase the temperature of the material, and the flange pipe c (15) is closed and maintained for 6-10 minutes; S2.2, after the hot air supply time is reached, the flange pipe a (13) and the flange pipe b (14) are closed at the same time and maintained for 3-7 minutes; S2.3, then the flange pipe c (15) is opened, and the vacuum system (4) is started to make the absolute negative pressure in the drying box (1) less than 30000Pa, and maintained for 1-3 minutes; then S1 to S3 are repeated, and when the moisture content of the material is less than 1%, the time in step S1 is shortened to 1-3 minutes, and the time in step S3 is increased to 6-10 minutes.

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