Drying oven structure of coating machine
By improving the structural design of the coating machine oven, the problems of uneven airflow and electrode jitter were solved, a more efficient and safe electrode drying process was achieved, and the production quality of lithium batteries and equipment safety were improved.
Patent Information
- Application Number
- CN202422550640.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-21
- Publication Date
- 2025-09-16
- Estimated Expiration
- 2034-10-21
AI Technical Summary
The poor airflow uniformity and fluidity in the drying chamber of traditional coating machine ovens lead to the accumulation of NMP gas concentration, posing an explosion risk. In addition, the electrodes are prone to shaking and deviation, affecting production quality.
The structural design of a double-hull blowing vessel, multiple blowing nozzles, a return air cavity and a traction roller group is adopted, combined with the setting of an infrared heating device and cooling holes to ensure the uniformity and overall fluidity of the dry gas flow, prevent gas accumulation, reduce the uneven pressure on the electrode surface, use a wave-transparent plate to isolate corrosive gases, and improve heating efficiency and equipment safety.
The uniformity and overall fluidity of the gas flow in the drying chamber are achieved, the NMP gas concentration is reduced, the electrode vibration and deviation are prevented, the production quality and safety are improved, and the service life of the infrared lamp is extended.
Smart Images
Figure CN223337739U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of coating machines, in particular to an oven structure of a coating machine. Background Art
[0002] The baking process for lithium battery electrodes is a critical step in lithium battery manufacturing. Infrared ovens utilize infrared radiation to dry the electrodes. Compared to hot air ovens, they provide more uniform heating across the coating thickness, greater heating energy density, and improved baking efficiency, which can reduce dark marks on the coating. Because the coating material on the positive electrode contains NMP solvent, NMP evaporates into the air after baking. NMP is a flammable and explosive gas at high temperatures. NMP concentrations reaching the explosion limit can easily cause the oven to explode. Therefore, a return air structure is installed in the drying chamber to prevent excessive concentrations.
[0003] The current traditional hull structure has poor uniformity and fluidity in the pressure relief and return air areas on both sides of the hull and in the area between the two wind nozzles. If the pressure relief and return air are not timely, the concentration of NMP gas produced will increase, causing local accumulation of NMP gas. When the accumulated NMP gas concentration reaches the explosion limit, it is easy to cause explosion risks. In addition, the pole pieces are prone to "shaking" and "deviation" during operation, resulting in poor production quality. Utility Model Content
[0004] In response to the technical problems in the existing technology, the utility model provides a coating machine oven structure, which adopts a new hull structure, can increase the return air area and the pressure relief area without affecting the uniformity of the air outlet of the air nozzle, and can increase the overall fluidity inside the oven and reduce resistance, which is conducive to reducing costs and improving the safety and production quality of the oven.
[0005] The technical solution includes a drying chamber arranged inside a box body, wherein the drying chamber is provided with a blowing double hull, a plurality of blowing nozzles, a return air chamber and a traction roller group for pulling the pole piece through the drying chamber, the bottom of the blowing double hull is connected to the drying chamber through a plurality of blowing nozzles, the plurality of blowing nozzles are arranged at intervals along the moving direction of the pole piece, and the blowing nozzles are located above the pole piece, the top of the blowing double hull is connected to the air supply duct with a blowing fan, the return air chamber is installed above the blowing nozzle, and the return air chamber is connected to the drying chamber and the air supply duct with an exhaust fan The exhaust duct of the blowing nozzle includes a nozzle shell, a flow equalizing plate and an infrared heating device. The top of the nozzle shell is provided with a nozzle air inlet connected to the blowing double hull, and the bottom cross-section of the nozzle shell is in the shape of a bell mouth. The flow equalizing plate is installed in the nozzle shell and is located between the nozzle air inlet and the bell mouth. The infrared heating device is installed in the bell mouth and is located above the pole piece. Two nozzle slit air outlets are formed between the two sides of the nozzle shell and the infrared heating device. The nozzle shell is connected to the drying chamber through the nozzle slit air outlet.
[0006] Furthermore, the infrared heating device includes a lamp tube box, an infrared lamp tube and a wave-transmitting plate. The lamp tube box is installed in the bell mouth, and the infrared lamp tube is installed in the lamp tube box. The bottom of the lamp tube box is open and sealed with the wave-transmitting plate.
[0007] Furthermore, the infrared lamp tubes include two, and the two infrared lamp tubes are spaced apart and arranged on both sides of the lamp tube box.
[0008] Furthermore, a plurality of cooling holes are provided on both sides of the top of the lamp tube box, and the plurality of cooling holes are spaced apart along the length direction of the lamp tube box. The cooling holes are connected to the slit air outlet of the ventilation nozzle, and cooling hole outlets are provided at both ends of the lamp tube box.
[0009] Furthermore, the blowing double hull includes two hollow hulls, a soft connection, a plurality of wind nozzle ducts and a plurality of hull air outlet slits. The two hulls are arranged at intervals, and the length of the hull extends along the moving direction of the pole piece. The tops of the two hulls are connected to the air supply duct through a soft connection, and the two hulls are connected through a plurality of wind nozzle ducts. The plurality of hull air outlet slits are arranged at intervals on the bottom of the two hulls, and the hull air outlet slits correspond one-to-one to the blowing nozzles. The two hulls are connected to the blowing nozzles through the hull air outlet slits.
[0010] Furthermore, a down blowing pipe is provided in the drying chamber, and the down blowing pipe is located below the traction roller group, the air outlet of the down blowing pipe faces the electrode, and the air inlet of the down blowing pipe is connected to the air supply duct.
[0011] Furthermore, a plurality of different rectangular return air openings are provided in the return air chamber along the width direction of the pole piece, and the rectangular return air openings are connected to the drying chamber and the return air chamber.
[0012] Beneficial effects:
[0013] 1. In the present invention, the setting of the blowing double hull, multiple blowing nozzles, return air chamber and traction roller group can ensure the uniformity of the flow of drying gas in the drying chamber, and increase the overall fluidity of the drying gas to prevent the occurrence of NMP accumulation due to small local dry gas flow, thereby achieving the purpose of eliminating the hidden dangers of oven explosion, corrosion, etc., combined with the setting of the flow equalizing plate and the nozzle slit air outlet, it can ensure the uniformity of the air outlet of the blowing nozzle, reduce the surface pressure of the electrode, ensure that the surface pressure of the electrode is evenly distributed and the return air resistance is small, prevent the electrode from shaking, curling, deviation and the like due to uneven force, and improve the production quality of the electrode.
[0014] 2. In the present invention, by configuring the lamp tube box, infrared lamp tube and wave-transmitting plate, the infrared lamp tube can be used to emit thermal radiation waves to uniformly heat the substrate on the surface of the electrode, thereby reducing the appearance of dark marks and increasing the drying efficiency. In addition, the wave-transmitting plate can isolate the infrared lamp tube from the exhaust gas containing NMP gas and related corrosive solutions, thereby avoiding the risk of explosion caused by NMP gas due to excessive surface temperature of the infrared lamp tube; combined with the configuration of two infrared lamp tubes, the drying efficiency can be further increased; through the configuration of the cooling hole, the cooling hole outlet and the cooling port connected to the slit air outlet of the vent nozzle, the dry gas entering the drying chamber can be diverted to cool the surface of the infrared lamp tube, thereby increasing the service life of the infrared lamp tube.
[0015] 3. In the present invention, the arrangement of two hulls, flexible connections, multiple nozzle ducts and multiple hull air outlet slits can ensure the uniformity of the air intake of the blowing nozzle; the arrangement of the lower blowing pipe can increase the air intake volume, reduce the NMP concentration, and prevent the accumulation of NMP gas under the electrode, further increase the overall fluidity of the drying gas, and further increase the drying efficiency.
[0016] 4. In the present invention, a plurality of different rectangular return air vents are provided along the width direction of the electrode and the rectangular return air vents are connected to the drying chamber and the return air chamber, so that the return air chamber can draw air from the drying chamber more evenly, thereby improving the uniformity of the overall dry gas flow in the oven and reducing the return air resistance. In addition, the exhaust gas concentration near the blowing nozzle can also be correspondingly reduced. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.
[0018] Figure 1 It is a partial cross-sectional view of the overall structure of the utility model;
[0019] Figure 2 This is a schematic diagram of the structure of the blower nozzle of the utility model;
[0020] Figure 3 for Figure 2 mid-section cutaway view;
[0021] Figure 4 This is a schematic diagram of the wind-blown double hull structure of the utility model.
[0022] Description of reference numerals:
[0023] 10. Blowing nozzle; 101. Nozzle air inlet; 102. Flow equalizing plate; 103. Infrared lamp tube; 104. Cooling hole; 105. Cooling hole outlet; 106. Wave-transparent plate; 107. Nozzle shell; 108. Nozzle slit air outlet; 20. Drying chamber; 30. Return air chamber; 40. Pole piece; 50. Oven insulation layer; 60. Blowing double hull; 601. Hull; 602. Flexible connection; 603. Nozzle duct; 604. Hull air outlet slit; 70. Downblowing duct; 80. Traction roller group. DETAILED DESCRIPTION
[0024] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.
[0025] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.
[0026] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.
[0027] In this application, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.
[0028] In this application, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.
[0029] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.
[0030] The utility model provides a coating machine oven structure, such as Figure 1 、 Figure 2 and Figure 3As shown, it includes a drying chamber 20 arranged inside the box body. In order to improve the heat preservation effect in the drying chamber 20, an oven heat insulation layer 50 can be set on the surface of the box body. The drying chamber 20 is provided with a blowing double hull 60, a plurality of blowing nozzles 10, a return air chamber 30 and a traction roller group 80 for pulling the pole piece 40 through the drying chamber 20. The bottom of the blowing double hull 60 is connected to the drying chamber 20 through a plurality of blowing nozzles 10. The plurality of blowing nozzles 10 are arranged at intervals along the moving direction of the pole piece 40, and the blowing nozzles 10 are located above the pole piece 40. The top of the blowing double hull 60 is connected to the air supply duct with a blowing fan. The return air chamber 30 is installed above the blowing nozzle 10, and the length of the return air chamber 30 extends along the width direction of the pole piece 40. Specifically, it can be set at the top of the box body. In order to increase the contact area between the return air chamber 30 and the gas in the drying chamber 20 and increase the overall flow area inside the drying chamber 20, the return air chamber 30 can be used to improve the heat preservation effect in the drying chamber 20. The length of the wind chamber 30 is equal to the width of the drying chamber 20. The return air chamber 30 connects the drying chamber 20 and the exhaust duct with the exhaust fan. The blowing nozzle 10 includes a nozzle shell 107, a flow equalizing plate 102 and an infrared heating device. The top of the nozzle shell 107 is provided with a nozzle air inlet 101 connected to the blowing catamaran 60. The bottom cross-section of the nozzle shell 107 is a bell mouth. The flow equalizing plate 102 is installed in the nozzle shell 107 and is located between the nozzle air inlet 101 and the bell mouth. The infrared heating device is installed in the bell mouth and is located above the pole piece 40. Two nozzle slit air outlets 108 are formed between the two sides of the nozzle shell 107 and the infrared heating device. The nozzle shell 107 is connected to the drying chamber 20 through the nozzle slit air outlet 108. The length of the nozzle slit air outlet 108 is not less than the width of the pole piece 40, ensuring that the dry gas can cover the entire pole piece 40.
[0031] In this embodiment, by setting up the blowing double hull 60, multiple blowing nozzles 10, return air chamber 30 and traction roller group 80, the uniformity of the flow of drying gas in the drying chamber 20 can be ensured, and the overall fluidity of the drying gas can be increased to prevent the occurrence of NMP aggregation due to small local dry gas flow, thereby achieving the purpose of eliminating hidden dangers such as oven explosion and corrosion. In addition, the production efficiency of the electrode 40 can also be improved. Specifically, since the exhaust gas concentration generated near the blowing nozzle 10 in the drying chamber 20 is the highest, and the saturated gas pressure generated by excessive concentration will cause the evaporation rate of the solution in the electrode 40 to slow down, thus improving the fluidity can avoid this problem. Combined with the setting of the flow equalizing plate 102 and the nozzle slit air outlet 108, the uniformity of the air outlet of the blowing nozzle 10 can be ensured, the surface pressure of the electrode 40 can be reduced, and the surface pressure distribution of the electrode 40 can be uniform and the return air resistance can be small, thereby preventing the electrode 40 from shaking, curling, deviation and the like due to uneven force, thereby improving the production quality of the electrode 40.
[0032] In the present invention, preferably, Figure 1 、 Figure 2 and Figure 3 As shown, the infrared heating device includes a lamp tube box, an infrared lamp tube 103 and a wave-transmitting plate 106. The lamp tube box is installed in the bell mouth, and the infrared lamp tube 103 is installed in the lamp tube box. The bottom of the lamp tube box is open and sealed with the wave-transmitting plate 106; the infrared lamp tubes 103 include two, and the two infrared lamp tubes 103 are spaced apart on both sides of the lamp tube box; a plurality of cooling holes 104 are provided on both sides of the top of the lamp tube box, and the plurality of cooling holes 104 are spaced apart along the length direction of the lamp tube box, and the cooling holes 104 are connected to the slit air outlet 108 of the ventilation nozzle, and cooling hole outlets 105 are provided at both ends of the lamp tube box.
[0033] In this embodiment, by configuring the lamp tube box, the infrared lamp tube 103 and the wave-transmitting plate 106, the infrared lamp tube 103 can be used to emit thermal radiation waves to uniformly heat the substrate on the surface of the electrode 40, thereby reducing the appearance of dark marks and increasing the drying efficiency. In addition, the wave-transmitting plate 106 can isolate the infrared lamp tube 103 from the exhaust gas containing NMP gas and related corrosive solutions, thereby avoiding the risk of explosion caused by NMP gas due to excessive surface temperature of the infrared lamp tube 103; combined with the configuration of two infrared lamp tubes 103, the drying efficiency can be further increased; by configuring the cooling hole 104, the cooling hole outlet 105 and the cooling port connected to the slit air outlet 108, the drying gas entering the drying chamber 20 can be diverted to cool the surface of the infrared lamp tube 103, thereby increasing the service life of the infrared lamp tube 103.
[0034] In the present invention, preferably, Figure 1 and Figure 4 As shown, the blowing double hull 60 includes two hollow hulls 601, a soft connection 602, a plurality of nozzle ducts 603 and a plurality of hull air outlet slits 604. The two hulls 601 are arranged at intervals, and the length of the hull 601 extends along the moving direction of the pole piece 40. The tops of the two hulls 601 are connected to the air supply duct through the soft connection 602, and the two hulls 601 are connected through the plurality of nozzle ducts 603. The plurality of hull air outlet slits 604 are arranged at intervals on the bottom of the two hulls 601. The hull air outlet slits 604 correspond one-to-one to the blowing nozzles 10, and the two hulls 601 are connected to the blowing nozzles 10 through the hull air outlet slits 604.
[0035] In this embodiment, the uniformity of the air intake of the blowing nozzle 10 can be ensured by the arrangement of two hulls 601, a flexible connection 602, a plurality of nozzle ducts 603 and a plurality of hull air outlet slits 604.
[0036] In the present invention, preferably, Figure 1As shown, a lower blowing pipe 70 is further provided in the drying chamber 20. The lower blowing pipe 70 is located below the traction roller group 80. The air outlet of the lower blowing pipe 70 faces the electrode 40. The air inlet of the lower blowing pipe 70 is connected to the air supply duct. The width of the lower blowing pipe 70 is also not less than the width of the electrode 40, ensuring that the blown dry gas can cover the entire electrode 40.
[0037] In this embodiment, the provision of the downblowing pipe 70 can increase the air intake volume, reduce the NMP concentration, and prevent NMP gas from gathering under the electrode 40, further increasing the overall fluidity of the drying gas and further improving the drying efficiency.
[0038] In the present invention, preferably, Figure 1 As shown, a plurality of different rectangular return air openings are provided in the return air chamber 30 along the width direction of the pole piece 40 , and the rectangular return air openings connect the drying chamber 20 and the return air chamber 30 .
[0039] In this embodiment, by providing a plurality of different rectangular return air vents along the width direction of the pole piece 40 and connecting the rectangular return air vents to the drying chamber 20 and the return air chamber 30, the return air chamber 30 can be made to draw air more evenly from the drying chamber 20, thereby improving the uniformity of the overall dry gas flow in the oven and reducing the return air resistance. In addition, the exhaust gas concentration near the blowing nozzle 10 can also be correspondingly reduced.
[0040] Working principle:
[0041] like Figures 1 to 4 As shown, 1. The dry gas in the air supply duct enters the hull 601 from the flexible connection 602 of the blowing double hull 60, and the dry gas is evenly distributed to the multiple blowing nozzles 10 through the blowing double hull 60 structure;
[0042] 2. The drying gas enters the nozzle housing from the nozzle air inlet 101 and passes through the flow equalizer 102 to evenly reach the two nozzle slit air outlets 108. Then, the gas reaches the drying chamber 20 to dry the electrode 40.
[0043] 3. Part of the drying gas is diverted at the nozzle slit outlet 108 to enter the cooling hole 104 to cool the surface of the infrared lamp 103. After cooling, the drying gas flows into the drying chamber 20 from the cooling hole outlet 105. At the same time, the infrared lamp 103 emits thermal radiation waves that penetrate the wave-transmitting plate 106 to evenly heat the substrate on the surface of the electrode 40.
[0044] 4. After the dry gas in the drying chamber 20 bakes the electrode 40, the waste gas evaporated from the surface of the electrode 40 mixes with the dried gas to form exhaust gas and is stored in the drying chamber 20;
[0045] 5. The exhaust duct draws the exhausted air in the drying chamber 20 into the return air chamber 30 for recovery and discharge.
[0046] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0047] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.
Claims
1. A coating machine oven structure, comprising a drying chamber (20) arranged inside a box body, wherein a blowing double hull (60), a plurality of blowing nozzles (1), a return air chamber (30) and a traction roller group (80) for pulling the pole piece (40) through the drying chamber (20) are provided in the drying chamber (20), the bottom of the blowing double hull (60) is connected to the drying chamber (20) through a plurality of blowing nozzles (1), the plurality of blowing nozzles (1) are arranged at intervals along the moving direction of the pole piece (40), and the blowing nozzles (1) are located above the pole piece (40), the top of the blowing double hull (60) is connected to an air supply duct with a blowing fan, the return air chamber (30) is installed above the blowing nozzle (1), and the return air chamber (30) is connected to the drying chamber (20) and an exhaust duct with an exhaust fan, characterized in that The blowing nozzle (1) includes a nozzle shell (107), a flow equalizing plate (102) and an infrared heating device. The top of the nozzle shell (107) is provided with a nozzle air inlet (101) connected to the blowing double hull (60). The bottom cross-section of the nozzle shell (107) is in the shape of a bell mouth. The flow equalizing plate (102) is installed in the nozzle shell (107) and is located between the nozzle air inlet (101) and the bell mouth. The infrared heating device is installed in the bell mouth and is located above the pole piece (40). Two nozzle slit air outlets (108) are formed between the two sides of the nozzle shell (107) and the infrared heating device. The nozzle shell (107) is connected to the drying chamber (20) through the nozzle slit air outlet (108).
2. A coating machine oven structure according to claim 1, characterized in that: The infrared heating device comprises a lamp tube box, an infrared lamp tube (103) and a wave-transmitting plate (106); the lamp tube box is installed in the bell mouth; the infrared lamp tube (103) is installed in the lamp tube box; the bottom of the lamp tube box is open and sealed to the wave-transmitting plate (106).
3. A coating machine oven structure according to claim 2, characterized in that: The infrared lamp tubes (103) include two, and the two infrared lamp tubes (103) are arranged at intervals on both sides of the lamp tube box.
4. A coating machine oven structure according to claim 3, characterized in that: A plurality of cooling holes (104) are provided on both sides of the top of the lamp tube box. The plurality of cooling holes (104) are spaced apart along the length direction of the lamp tube box. The cooling holes (104) are connected to the slit air outlet (108) of the ventilation nozzle. Cooling hole outlets (105) are provided at both ends of the lamp tube box.
5. A coating machine oven structure according to any one of claims 1 to 4, characterized in that: The blowing double hull (60) comprises two hollow hulls (601), a soft connection (602), a plurality of nozzle ducts (603) and a plurality of hull air outlet slits (604). The two hulls (601) are arranged at intervals, and the length of the hulls (601) extends along the moving direction of the pole piece (40). The tops of the two hulls (601) are connected to the air supply duct through the soft connection (602). The two hulls (601) are connected to each other through the plurality of nozzle ducts (603). The plurality of hull air outlet slits (604) are arranged at intervals at the bottoms of the two hulls (601). The hull air outlet slits (604) correspond one-to-one to the blowing nozzles (1). The two hulls (601) are connected to the blowing nozzles (1) through the hull air outlet slits (604).
6. The coating machine oven structure according to claim 5, characterized in that: A lower blowing pipe (70) is further provided in the drying chamber (20). The lower blowing pipe (70) is located below the traction roller group (80). The air outlet of the lower blowing pipe (70) faces the electrode (40), and the air inlet of the lower blowing pipe (70) is connected to the air supply duct.
7. The coating machine oven structure according to claim 1, characterized in that: A plurality of different rectangular return air openings are provided in the return air chamber (30) along the width direction of the pole piece (40), and the rectangular return air openings are connected to the drying chamber (20) and the return air chamber (30).