A drying apparatus for processing plywood

Abstract

The utility model discloses a drying equipment is used in plywood processing, including mobile taking and putting bin and plywood, the one side of mobile taking and putting bin is equipped with fixed heating bin, the inside of mobile taking and putting bin and fixed heating bin is linked together, and the one side of mobile taking and putting bin is butt jointed to have the slope away from fixed heating bin, the one side of mobile taking and putting bin is hinged to have bin door, be provided with the lifting assembly for reducing fixed heating bin heat loss between mobile taking and putting bin and fixed heating bin, the utility model discloses a lifting assembly is set up and realizes the sealed isolation of mobile taking and putting bin and fixed heating bin, and electric push rod drives lifting baffle to lift, and sealing washer enhances the adhesion sealing property, reduces heat loss, reduces the preheating energy consumption, through setting the article component, its gyro wheel design, cooperate with the slide rail of slope, and the quick taking and moving of plywood is convenient, and the artificial labor intensity is alleviated, and the space utilization rate is improved to multilayer article rack, and the even heating of board is ensured.

Description

Technical Field

[0001] This utility model relates to the field of plywood processing technology, specifically to a drying device for plywood processing. Background Technology

[0002] Plywood, as an important type of engineered wood product, is widely used in furniture, construction, and packaging. Drying is a crucial step in its production that determines product quality. Drying not only accelerates adhesive curing to ensure a tight bond, but also prevents insect infestation, corrosion, and mold caused by excessive humidity, thus extending shelf life. If the moisture content is too high, it will lead to uneven glue application, reduced bond strength, and blistering during hot pressing, severely impacting quality. Therefore, precise and efficient drying is an essential step to reduce subsequent deformation and cracking and improve quality.

[0003] In the plywood production industry, box dryers are commonly used in small workshops, sample production scenarios, or multi-size plywood processing needs due to their simple structure, low cost, and flexibility in adapting to different plywood sizes. However, existing box dryers have significant drawbacks in practical applications: they operate intermittently, requiring a large opening of the drying chamber door each time plywood is loaded or unloaded, causing rapid heat loss and a sharp drop in internal temperature. When the next batch of plywood is loaded, the heating system must be restarted for extended preheating to restore the target drying temperature. This process not only prolongs the total drying time and reduces production efficiency but also wastes a significant amount of energy, substantially increasing production energy costs. Therefore, we need to propose a drying device for plywood processing. Utility Model Content

[0004] The purpose of this invention is to provide a drying device for plywood processing, which has the advantages of reducing heat loss, facilitating the handling of plywood, and ensuring uniform and efficient drying, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a drying device for plywood processing, comprising a movable loading and unloading chamber and plywood, wherein a fixed heating chamber is installed on one side of the movable loading and unloading chamber, the movable loading and unloading chamber and the fixed heating chamber are internally connected, a ramp is connected to the side of the movable loading and unloading chamber away from the fixed heating chamber, a chamber door is hinged to one side of the movable loading and unloading chamber, and a lifting assembly for reducing heat loss from the fixed heating chamber is provided between the movable loading and unloading chamber and the fixed heating chamber; The fixed heating chamber is equipped with a storage assembly for placing plywood. The fixed heating chamber is externally equipped with a drying assembly for drying the plywood.

[0006] Preferably, the lifting assembly includes a lifting baffle, which is slidably disposed between the movable loading / unloading compartment and the fixed heating compartment. Slider blocks are fixedly connected to both sides of the lifting baffle. A sliding groove adapted to the slider is provided at the connection between the movable loading / unloading compartment and the fixed heating compartment. The slider is slidably connected inside the sliding groove.

[0007] Preferably, the lifting assembly further includes a sealing gasket and a first electro-hydraulic rod. The sealing gasket is installed at the bottom of the lifting baffle, and a connecting block is installed at the top of the lifting baffle. The first electro-hydraulic rod is installed on both sides outside the connection between the movable loading / unloading chamber and the fixed heating chamber. Both ends of the connecting block are connected to the working end of the first electro-hydraulic rod.

[0008] Preferably, the storage assembly includes a movable compartment, which is slidably disposed inside the movable loading and unloading compartment and the fixed heating compartment, and on the upper surface of the slope. A second electro-hydraulic rod is installed on the outside of the fixed heating compartment. The working end of the second electro-hydraulic rod extends into the interior of the fixed heating compartment and is connected to the movable compartment on the side away from the compartment door. The interior of the movable compartment is equipped with multiple layers of shelves. Bearing seats are fixedly connected to both sides of the shelves. Rollers are rotatably installed inside the bearing seats. Plywood is placed on the top of the shelves, and the bottom of the plywood is in contact with the rollers.

[0009] Preferably, the storage assembly further includes pulleys and slide rails. The pulleys are installed on both sides of the bottom of the mobile compartment. The bottom of the mobile loading and unloading compartment and the fixed heating compartment, as well as the upper surface of the ramp, are all fitted with slide rails adapted to the pulleys. The pulleys and slide rails are slidably connected.

[0010] Preferably, the drying component includes an air inlet and an air return outlet. The air inlet is located on both sides of the fixed heating chamber, and the air return outlet is located at the bottom of one side of the fixed heating chamber and below the air inlet. An air outlet connected to the air inlet is installed on the inner wall of the fixed heating chamber, and the air outlet of the air outlet faces the shelf.

[0011] Preferably, the drying assembly further includes a hot air circulation mechanism, which is disposed outside the fixed heating chamber. The output end of the hot air circulation mechanism is connected to the air inlet through a pipe, and the input end of the hot air circulation mechanism is connected to the air return outlet through a pipe.

[0012] Compared with the prior art, the beneficial effects of this utility model are: This invention achieves sealed isolation between the movable loading / unloading chamber and the fixed heating chamber through a lifting assembly. An electric push rod drives the lifting baffle to rise and fall, and a sealing gasket enhances the seal, reducing heat loss and preheating energy consumption. The invention also features a storage assembly with rollers, ramps, and slide rails, facilitating quick loading, unloading, and movement of plywood, reducing manual labor intensity. Multi-layered shelves improve space utilization and ensure uniform heating of the boards. Finally, the invention incorporates a drying assembly to achieve hot air circulation and efficient heat utilization, ensuring uniform drying and improving drying quality. Attached Figure Description Figure 1 This is a schematic diagram of the structure of this utility model; Figure 2 This is a schematic diagram of the left side of the lifting component of this utility model; Figure 3 This is a schematic cross-sectional view of the movable loading and unloading chamber and the fixed heating chamber of this utility model; Figure 4 This is a schematic diagram of the left side of the storage component of this utility model; Figure 5 This is a schematic diagram showing the connection between the air outlet and the fixed heating chamber of this utility model.

[0013] In the diagram: 1. Moving loading / unloading chamber; 2. Fixed heating chamber; 3. Ramp; 4. Chamber door; 5. Lifting baffle; 6. Sliding block; 7. Slide groove; 8. Sealing gasket; 9. Connecting block; 10. First electro-hydraulic rod; 11. Moving chamber body; 12. Shelf; 13. Bearing seat; 14. Roller; 15. Plywood; 16. Pulley; 17. Slide rail; 18. Air inlet; 19. Air return outlet; 20. Air outlet; 21. Hot air circulation mechanism; 22. Second electro-hydraulic rod. Detailed Implementation

[0014] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0015] Please see Figure 1-5This utility model provides a technical solution: a drying device for plywood processing, including a movable loading and unloading chamber 1 and plywood 15. The movable loading and unloading chamber 1 serves as a transition area for loading and unloading plywood 15, reducing direct heat loss from the fixed heating chamber 2 during the loading and unloading process. A fixed heating chamber 2 is installed on one side of the movable loading and unloading chamber 1, serving as the core area for the drying operation. The fixed heating chamber 2 provides a closed space for heating and drying the plywood 15, preventing heat diffusion. The movable loading and unloading chamber 1 and the fixed heating chamber 2 are internally connected. A ramp 3 is connected to the side of the movable loading and unloading chamber 1 away from the fixed heating chamber 2. By setting the ramp 3, the movable chamber 11 can easily slide out to the outside, facilitating manual or mechanical loading and unloading of the plywood 15 and reducing operational difficulty. A door 4 is hinged to one side of the movable loading and unloading chamber 1, and a sealing strip is provided at the bottom edge of the door 4 to further isolate external cold air.

[0016] A lifting assembly is installed between the movable loading / unloading compartment 1 and the fixed heating compartment 2 to reduce heat loss from the fixed heating compartment 2. The lifting assembly includes a lifting baffle 5, which is slidably positioned between the movable loading / unloading compartment 1 and the fixed heating compartment 2. A temperature and humidity sensor is installed on the outside of the fixed heating compartment 2, with its detection end extending into the interior of the fixed heating compartment 2. The lifting baffle 5 allows for connection or isolation between the two compartments; it closes during drying to prevent heat loss and opens during loading / unloading to allow passage of the movable compartment 11. Slider blocks 6 are fixedly connected to both sides of the lifting baffle 5. A groove 7, adapted to the slider 6, is provided at the connection point between the movable loading / unloading compartment 1 and the fixed heating compartment 2, and the slider 6 is slidably connected inside the groove 7. By setting the slider 6 and the groove 7, the movement trajectory of the lifting baffle 5 can be limited, while simultaneously providing stable support for the lifting baffle 5.

[0017] Meanwhile, the lifting assembly also includes a sealing gasket 8 and a first electro-hydraulic rod 10. The sealing gasket 8 is installed at the bottom of the lifting baffle 5. By setting the sealing gasket 8, it fits tightly against the contact surface when closed, enhancing the sealing performance and reducing heat leakage. The sealing gasket 8 is made of asbestos rubber, which is not easily affected by moisture, slight chemicals, etc. that may come into contact with the equipment during operation. It can maintain stable performance in humid and temperature-changing environments, ensuring the long-term effectiveness of the sealing reliability of the lifting assembly. A connecting block 9 is installed on the top of the lifting baffle 5. The first electro-hydraulic rod 10 is installed on both sides outside the connection between the movable loading / unloading chamber 1 and the fixed heating chamber 2. The stroke of the first electro-hydraulic rod 10 is greater than the height of the movable chamber 11, which facilitates the sliding passage of the movable chamber 11. A support frame is provided at the bottom of the first electro-hydraulic rod 10. Both ends of the connecting block 9 are connected to the working ends of the first electro-hydraulic rod 10.

[0018] Furthermore, the fixed heating chamber 2 is equipped with a storage assembly for placing plywood 15. This assembly includes a movable chamber 11, a square shell with two through-holes near the air outlet 20. The movable chamber 11 serves as a movable carrier for the plywood 15 and can slide between the movable loading / unloading chamber 1, the fixed heating chamber 2, and the ramp 3, enabling the "external loading / unloading - internal drying" transfer of the plywood 15. A handle is provided on the side of the movable chamber 11 near the door 4 for easy operation by the operator. The movable chamber 11 is slidably disposed inside the movable loading / unloading chamber 1 and the fixed heating chamber 2, and on the upper surface of the ramp 3. A second electro-hydraulic rod 22 is installed on the outside of the fixed heating chamber 2. The working end of the second electro-hydraulic rod 22 extends into the interior of the fixed heating chamber 2 and connects to the movable chamber 11 on the side away from the chamber door 4. The movable chamber 11 and the second electro-hydraulic rod 22 are detachably connected. By setting the second electro-hydraulic rod 22 to drive the movable chamber 11 to slide on the slide rail 17, automated transfer is achieved, reducing manual operation. The piston rod length of the second electro-hydraulic rod 22 is adapted to the stroke of the movable chamber 11.

[0019] Furthermore, the interior of the mobile storage unit 11 is equipped with multiple layers of shelves 12. Multiple ventilation holes are longitudinally opened inside the shelves 12 to improve hot air circulation, accelerate moisture removal, and prevent uneven drying caused by stacking. Bearing seats 13 are fixedly connected to both sides of the shelves 12. Rollers 14 are rotatably mounted inside the bearing seats 13. The bearing seats 13 and the rollers 14 reduce friction between the plywood 15 and the shelves 12, facilitating independent handling of individual plywood pieces and preventing surface scratches. The plywood 15 is placed on top of the shelves 12, with its bottom edge in contact with the rollers 14.

[0020] Furthermore, the storage assembly also includes pulleys 16 and slide rails 17. The pulleys 16 are installed on both sides of the bottom of the movable compartment 11. Slide rails 17, adapted to the pulleys 16, are embedded in the bottom of the movable loading / unloading compartment 1 and the fixed heating compartment 2, as well as on the upper surface of the ramp 3. The pulleys 16 and slide rails 17 are slidably connected. By setting up the pulleys 16 and slide rails 17, the movable compartment 11 is guided to slide smoothly, reducing movement resistance and ensuring smooth transfer between areas.

[0021] Based on this, a drying assembly for drying plywood 15 is provided on the outside of the fixed heating chamber 2.

[0022] The drying assembly includes an air inlet 18 and a return air inlet 19. The air inlets 18 are located on both sides of the fixed heating chamber 2, and the return air inlet 19 is located at the bottom of one side of the fixed heating chamber 2, below the air inlets 18. An air outlet 20, connected to the air inlet 18, is installed on the inner wall of the fixed heating chamber 2, with its outlet facing the shelf 12. By setting up the air inlet 18 and the air outlet 20, the air inlet 18 serves as a channel for hot air to enter the fixed heating chamber 2. The air outlet 20 has a conical structure with multiple air outlet holes on its surface, and its outlet faces the shelf 12, directionally blowing hot air onto the surface of the plywood 15, improving drying efficiency. The return air inlet 19 recovers the humid and hot air from the fixed heating chamber 2, achieving hot air recycling.

[0023] Furthermore, the drying assembly also includes a hot air circulation mechanism 21, which is located outside the fixed heating chamber 2. The output end of the hot air circulation mechanism 21 is connected to the air inlet 18 through a pipe, and the input end of the hot air circulation mechanism 21 is connected to the return air inlet 19 through a pipe.

[0024] In addition, the hot air circulation mechanism 21 includes a pre-air filter, a centrifugal fan, an electric heater, a heat exchanger, a temperature control valve, and a buffer air box. The pre-air filter is installed at the inlet of the circulating air and has multiple layers of filter screens and baffles to intercept impurities such as sawdust and dust generated during the drying process of plywood 15, preventing them from entering subsequent components and causing wear or blockage. The centrifugal fan, as the power source, is driven by a variable frequency motor, and the air volume can be adjusted by adjusting the speed to adapt to the needs of different drying stages. The air outlet is connected to the main air duct through a flange. The electric heating tube has adjustable power and is installed in the air duct between the centrifugal fan and the heat exchanger to heat the circulating air, raising the hot air temperature to 60-120℃ depending on the material of the plywood 15. The heat exchanger, as the core component for temperature regulation, allows air to flow through the tube side and cooling water or cold air to flow through the shell side. The cooling water flow rate is dynamically adjusted by the temperature control valve to precisely control the hot air temperature. The temperature control valve is linked to the temperature and humidity sensor inside the fixed heating chamber 2. It adjusts the cooling water flow rate according to the actual temperature setpoint inside the fixed heating chamber 2 within ±5℃ to avoid excessive fluctuations in hot air temperature. The buffer air box is located between the heat exchanger and the air inlet 18. It is equipped with a baffle plate inside to stabilize the air pressure and distribute the hot air evenly. A pressure sensor is installed inside the buffer air box to monitor air pressure fluctuations and control them within ±50Pa.

[0025] In summary, when the plywood 15 needs to be dried, the first electric hydraulic rod 10 is activated, extending its working end. This extends the lifting baffle 5 via the connecting block 9, causing it to rise vertically along the slide rail 7. Simultaneously, the chamber door 4 is opened, and the working end of the second electric hydraulic rod 22 extends, driving the movable chamber 11 along the slide rail 17 from the fixed heating chamber 2 through the movable pick-and-place chamber 1 to the ramp 3, pushing the movable chamber 11 outside the movable pick-and-place chamber 1. The operator uses the rollers 14 to place the plywood 15 layer by layer onto the shelf 12 for loading. After loading, the movable chamber 11 is moved in the opposite direction into the movable pick-and-place chamber 1, and the chamber door 4 is closed. The sealing strips on the edge of the chamber door 4 are ensured to fit tightly against the chamber body, reducing the entry of external cold air into the transition area and initially blocking the heat loss path. Activate the second electric hydraulic rod 22, shortening its working end to move the movable chamber 11 into the fixed heating chamber 2. Activate the first electric hydraulic rod 10, shortening its working end to lower the lifting baffle 5 until the bottom sealing gasket 8 is tightly fitted to the contact surface at the connection between the two chambers, achieving complete isolation between the fixed heating chamber 2 and the movable loading and unloading chamber 1, reducing heat loss during the drying stage, and ensuring no leakage during subsequent hot air circulation.

[0026] At this time, the centrifugal fan draws in air from the return air inlet 19 of the fixed heating chamber 2 at a pressure of 500-800Pa. After being purified by the pre-air filter, the air is sent to the electric heater to be heated to the set temperature, such as 80-120℃, which is adjusted according to the material of the plywood 15. The heated hot air is calibrated by the cooling water in the tube side and shell side of the heat exchanger. The temperature control valve adjusts the cooling water flow according to the temperature and humidity sensor signal in the fixed heating chamber 2 to stabilize the hot air temperature within the set value ±5℃ range. The stabilized hot air enters the buffer air box and is divided into each air outlet 20 by the internal guide plate, blowing onto the surface of the plywood 15 on the shelf 12 to accelerate the evaporation of moisture.

[0027] During the drying process, the humid and hot air carrying moisture flows back from the return air inlet 19 at the bottom of the fixed heating chamber 2 through the return air duct to the hot air circulation mechanism 21, forming a closed loop. During the process, the temperature and humidity sensor continuously monitors the environment inside the chamber, and the controller dynamically matches the drying requirements of the plywood 15 by adjusting the power of the electric heater and the speed of the centrifugal fan, so as to avoid over-drying or under-drying.

[0028] After drying, the controller activates the extension of the first electro-hydraulic rod 10, causing the lifting baffle 5 to rise and open the passage; simultaneously, the second electro-hydraulic rod 22 is activated, its working end extending to push the movable chamber 11 along the slide rail 17 from the fixed heating chamber 2 to the movable loading and unloading chamber 1. At this point, the restriction between the second electro-hydraulic rod 22 and the movable chamber 11 is released, and the second electro-hydraulic rod 22 retracts back into the fixed heating chamber 2. At this time, the first electro-hydraulic rod 10 retracts, and the lifting baffle 5 descends to seal the fixed heating chamber 2, reducing residual heat loss; furthermore, the chamber door 4 is opened, and the movable chamber 11 slides to the ramp 3 position. After the movable chamber 11 is moved out, the operator pushes the movable chamber 11 to the designated unloading area, and the dried plywood 15 is easily removed using the rollers 14, completing a single drying operation.

[0029] It should be noted that the temperature and humidity sensors, electro-hydraulic rods, air filters, centrifugal fans, electric heaters, heat exchangers, temperature control valves, buffer boxes, pressure sensors, and controllers mentioned above are all devices with relatively mature existing technologies. Specific models can be selected according to actual needs. At the same time, the power supply for the temperature and humidity sensors, electro-hydraulic rods, air filters, centrifugal fans, electric heaters, heat exchangers, temperature control valves, buffer boxes, pressure sensors, and controllers can be powered by built-in power supplies or by mains power. The specific power supply method should be selected according to the situation, and will not be elaborated here.

[0030] In addition, the following components, due to direct contact with hot air at 60-120℃ or long-term exposure to high-temperature environments, must possess reliable high-temperature resistance. This is a core prerequisite for ensuring long-term stable operation of the equipment and preventing equipment failure due to high-temperature aging or damage: The filter screen of the pre-filter must be made of glass fiber material with a temperature resistance of ≥150℃, and the frame must be made of galvanized steel plate with a temperature resistance of ≥200℃; the impeller of the centrifugal fan must be made of aluminum alloy with a temperature resistance of ≥120℃, and the motor bearings must use high-temperature lubricating grease with an applicable temperature range of -30℃ to 180℃; the heating element of the electric heater must be made of 316 stainless steel with a temperature resistance of ≥600℃, and the outer fins must be made of corrosion-resistant aluminum alloy with a temperature resistance of ≥200℃; the tube side of the heat exchanger must be made of seamless steel pipe with a temperature resistance of ≥300℃, and the shell side seals must be made of silicone rubber with a temperature resistance of ≥200℃; the connecting duct and buffer air box must be made of galvanized steel plate with a thickness of ≥1.5mm with a temperature resistance of ≥200℃, and the interface sealing gasket must be made of asbestos rubber gasket with a temperature resistance of ≥300℃.

[0031] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A drying device for plywood processing, comprising a movable loading and unloading chamber (1) and plywood (15), wherein a fixed heating chamber (2) is installed on one side of the movable loading and unloading chamber (1), the movable loading and unloading chamber (1) and the fixed heating chamber (2) are internally connected, a ramp (3) is connected to the side of the movable loading and unloading chamber (1) away from the fixed heating chamber (2), and a chamber door (4) is hinged to one side of the movable loading and unloading chamber (1), characterized in that: A lifting assembly is provided between the movable loading and unloading compartment (1) and the fixed heating compartment (2) to reduce heat loss from the fixed heating compartment (2); The fixed heating chamber (2) is equipped with a storage component for placing plywood (15); The fixed heating chamber (2) is provided with a drying assembly for drying the plywood (15) on its exterior.

2. The drying equipment for plywood processing according to claim 1, characterized in that: The lifting assembly includes a lifting baffle (5), which is slidably disposed between the movable pick-up and place compartment (1) and the fixed heating compartment (2). Slider blocks (6) are fixedly connected to both sides of the lifting baffle (5). A groove (7) adapted to the slider (6) is provided at the connection between the movable pick-up and place compartment (1) and the fixed heating compartment (2). The slider (6) is slidably connected inside the groove (7).

3. The drying equipment for plywood processing according to claim 2, characterized in that: The lifting assembly also includes a sealing gasket (8) and a first electric hydraulic rod (10). The sealing gasket (8) is installed at the bottom of the lifting baffle (5). A connecting block (9) is installed on the top of the lifting baffle (5). The first electric hydraulic rod (10) is installed on both sides outside the connection between the movable loading and unloading chamber (1) and the fixed heating chamber (2). Both ends of the connecting block (9) are connected to the working end of the first electric hydraulic rod (10).

4. The drying equipment for plywood processing according to claim 3, characterized in that: The storage assembly includes a movable compartment (11), which is slidably disposed inside the movable loading and unloading compartment (1) and the fixed heating compartment (2) and on the upper surface of the ramp (3). A second electric hydraulic rod (22) is installed on the outside of the fixed heating compartment (2). The working end of the second electric hydraulic rod (22) extends into the interior of the fixed heating compartment (2) and is connected to the movable compartment (11) on the side away from the compartment door (4). The movable compartment (11) is equipped with multiple layers of shelves (12). Bearing seats (13) are fixedly connected to both sides of the shelves (12). Rollers (14) are rotatably installed inside the bearing seats (13). Plywood (15) is placed on the top of the shelves (12) and the bottom of the plywood (15) is in contact with the rollers (14).

5. A drying device for plywood processing according to claim 4, characterized in that: The storage assembly also includes pulleys (16) and slide rails (17). The pulleys (16) are installed on both sides of the bottom of the mobile compartment (11). The bottom of the mobile loading and unloading compartment (1) and the fixed heating compartment (2) as well as the upper surface of the ramp (3) are all fitted with slide rails (17) that are compatible with the pulleys (16). The pulleys (16) and slide rails (17) are slidably connected.

6. The drying equipment for plywood processing according to claim 5, characterized in that: The drying assembly includes an air inlet (18) and an air return outlet (19). The air inlet (18) is located on both sides of the fixed heating chamber (2). The air return outlet (19) is located at the bottom of one side of the fixed heating chamber (2) and below the air inlet (18). The inner wall of the fixed heating chamber (2) is equipped with an air outlet (20) that communicates with the air inlet (18), and the air outlet of the air outlet (20) faces the shelf (12).

7. A drying device for plywood processing according to claim 6, characterized in that: The drying assembly also includes a hot air circulation mechanism (21), which is located outside the fixed heating chamber (2). The output end of the hot air circulation mechanism (21) is connected to the air inlet (18) through a pipe, and the input end of the hot air circulation mechanism (21) is connected to the return air inlet (19) through a pipe.

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