A double air channel up and down large circulation hot oven for tow

Abstract

The present application relates to a kind of double air ducts up and down large circulation heat ovens for tow, including two inner box bodies arranged up and down, inner box body is opened with front and rear extension air inlet, the air return duct that is circumferentially closed and extends front and rear is formed between two inner box bodies, and tow passes through air return duct front and rear, air inlet and air return are respectively opened in the front and rear ends of air inlet, and air return and air inlet are all set in the side of two air inlets close to each other and are all communicated with air return duct;Air inlet is equipped with front and rear arrangement fan and heater, and the air outlet of fan is set to front.This application realizes that tow is heated evenly on both sides by up and down double air ducts independent circulation, three-dimensional wrapping type heating, and the uniformity of temperature field is greatly improved, and heat efficiency can reach more than 85%, and upper and lower layers can be independently temperature-controlled, and the difference of heating process requirement of different tow specifications is adapted, effectively reduce broken filament rate and hairiness rate, and improve product quality.

Description

Technical Field

[0001] This invention relates to the field of filament processing technology, specifically to a dual-airflow, large-circulation hot drying oven for filaments. Background Technology

[0002] In the field of chemical fiber production, the heating and stretching of filament bundles is a key process that determines the mechanical properties and dimensional stability of the finished fibers. As the core equipment in this process, the uniformity of the temperature field and the rationality of the airflow organization of the hot drying oven directly affect the stretching quality, breakage rate, and final product quality of the filament bundles.

[0003] The existing heat drying ovens for heating filament bundles have the following main shortcomings: Firstly, unilateral heating leads to uneven heating of the filament bundle. Traditional drying ovens mostly adopt a single-duct, single-sided airflow structure, where hot air is only blown onto the filament bundle from one side. The leeward side of the filament bundle mainly relies on thermal radiation and air conduction to obtain heat, resulting in low heat exchange efficiency and a significant temperature gradient. This easily leads to a "hot on one side, cold on the other" phenomenon, causing uneven stretching of the filament bundle during the stretching process due to temperature differences. This, in turn, causes quality problems such as fluctuations in wire diameter, inconsistent elongation, broken filaments, and fuzzy fibers.

[0004] Secondly, the temperature gradient problem along the length of the oven is prominent. In existing ovens, hot air flows along the length of the oven body after being blown in through the air inlet. As heat is absorbed by the yarn bundles and lost through heat dissipation from the oven body, the air temperature gradually decreases along the way, creating a temperature gradient in the oven where the front end is hot and the back end is cool. The yarn bundles are in different temperature environments at the front and back ends, making it difficult to ensure consistent heating throughout the process, which seriously affects the tensile stability and the consistency of finished product quality.

[0005] Third, a single temperature zone design cannot meet the needs of differentiated processes. Different materials (such as PP, PE, PET) and different specifications (high denier network yarn, wide-width flat yarn, fine denier monofilament) of yarn bundles have different requirements for heating temperature curves and air volume. Traditional ovens can only provide a uniform temperature field and cannot perform segmented temperature control or independent upper and lower control according to process requirements. The equipment has poor process adaptability and cannot meet the needs of flexible production.

[0006] Fourth, the thermal efficiency is low and the energy consumption is high. Existing ovens generally have problems such as high air leakage rate, low hot air circulation frequency, and unreasonable heat distribution. The thermal efficiency is usually between 60% and 70%. A large amount of heat energy is lost through heat dissipation from the chamber and exhaust gas emissions, resulting in high energy consumption costs in the long term.

[0007] To address the aforementioned issues, the industry urgently needs a heat oven solution that can achieve uniform heating of both sides of the filament bundle, high temperature uniformity, independent zone temperature control capability, and excellent thermal efficiency. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a dual-airflow, large-circulation hot drying oven for filament bundles. Through an independent circulation heating structure with upper and lower dual airflow channels, it achieves three-dimensional, uniform heating of the filament bundles.

[0009] This invention is achieved through the following technical solution: a dual-air duct, top-bottom large-circulation hot drying oven for yarn bundles, comprising two inner chambers arranged vertically, each inner chamber having a front-to-back extending air inlet duct, and a circumferentially closed, front-to-back extending return air duct formed between the two inner chambers, through which the yarn bundle passes. The front and rear ends of the air inlet ducts have return air inlets and air outlets respectively, both located on the side of the two air inlets close to each other and connected to the return air ducts. The air inlet ducts are equipped with front-to-back arranged fans and heaters, with the fan outlets facing forward.

[0010] In operation, this solution involves starting both upper and lower fans. Air that has exchanged heat with the fiber bundle in the return air duct enters the rear section of the inlet air duct through the return air inlet. After being heated by the heater, it is pressurized and propelled forward by the fans, ultimately being blown into the return air duct from the inlet. This simultaneously wraps the heated fiber bundle from both upper and lower directions, and the hot air is then recycled through the return air inlet. This method achieves three-dimensional wrapping heating through independent circulation in the upper and lower dual air ducts, significantly improving the uniformity of heating in the circumferential direction of the fiber bundle. Simultaneously, the repeated circulation of hot air results in high thermal efficiency, and the upper and lower air ducts can operate independently, allowing for convenient adjustment according to different process requirements.

[0011] As an optimization, the heater is located at the rear end of the air inlet duct, and the air inlet is located on the side where the two heaters are close to each other. In this design, after the return air enters the rear section of the air inlet duct from the return air inlet, it first flows through the heater located at the rear end and is directly heated, and then is sent to the front air inlet by the fan. Because the heater is close to the return air inlet, the waste heat of the return air is effectively utilized for preheating, reducing heating power consumption; at the same time, the air inlet is located inside the heater, the path of the hot air from heating to blowing is the shortest, reducing heat loss during the transportation process, allowing the high-temperature hot air to act quickly on the filament bundle, and the heating response is more rapid.

[0012] As an optimization, the fans are axial flow fans with vertically oriented shafts. Each of the two fans has a fan inlet box on its side closest to the other. The rear end of the fan inlet box is connected to the front end of the heater, and the fan inlet is connected to the fan inlet box. In this design, the axial flow fan provides a large volume, low pressure, and uniform airflow, suitable for large circulation air volume requirements; the fan inlet box collects the heated air and guides it to the fan inlet.

[0013] As an optimization, the distance between the two fan inlet boxes gradually decreases from front to back. In this design, the distance between the two fan inlet boxes gradually decreases from front to back, thereby reducing the flow cross-section and increasing the flow velocity of the gas in the return air duct as it flows through the two fan inlet boxes. At the same time, it is easier to increase the connection cross-section with the heater end.

[0014] As an optimization, the air inlet duct is equipped with two fans arranged side by side, and the outlets of the fans are equipped with air guide plates. In this design, the two fans arranged side by side work simultaneously, increasing the air volume of a single-layer air duct. The air guide plates evenly diffuse the high-speed airflow from the outlet of each fan to the left and right sides, making the air velocity consistent throughout the width of the entire air inlet duct, avoiding airflow concentration in the middle, ensuring uniform transverse temperature in the return air duct, and ensuring that the filament bundle is heated evenly in the width direction.

[0015] As an optimization, a thermocouple is installed at the front end of the air inlet duct. In this solution, the thermocouple detects the temperature of the hot air about to be sent into the return air duct in real time and feeds the signal back to the temperature control system. The operator can then precisely adjust the heating power and fan speed based on the feedback to keep the filament bundle within the set process temperature range, ensuring the stability of the stretching quality.

[0016] As an optimization, the angle between the outlet tangent of the return air inlet and the gas flow direction in the return air duct is 0-30 degrees. Therefore, during use, the return airflow smoothly enters the return air inlet at a small angle, nearly parallel to the main flow direction of the return air duct. This avoids eddies and pressure losses caused by large-angle turns in the airflow, resulting in smoother return airflow, lower fan suction resistance, higher circulation efficiency, and reduced airflow pulsation, which helps maintain stable filament operation.

[0017] As an optimization, both ends of the two inner chambers are equipped with hinged doors. Each door includes a fixed lower door panel, an upper door panel hinged to the lower door panel, and a cylinder that drives the upper door panel to swing up and down. During use, threading, or maintenance, the upper door panel is quickly flipped open by the cylinder, making operation convenient and quick. During the opening process, the control system automatically reduces the fan speed and heating power to minimize hot air leakage. After closing the door, the operating temperature is quickly restored, shortening process waiting time. This simplifies operation and reduces energy consumption.

[0018] As an optimization, the heater includes multiple front-to-back hot air ducts and two left-to-right duct fixing plates. Positioning sleeves through which the hot air ducts pass are fixed to the duct fixing plates, and set screws are threaded onto the positioning sleeves and fastened to the sides of the hot air ducts. In this design, the hot air ducts are fixed by the positioning sleeves and set screws. When a hot air duct ages or is damaged, it can be individually removed and replaced simply by loosening the corresponding set screw, without disassembling the entire heater. This allows for quick and easy maintenance, significantly reducing downtime and ensuring continuous operation of the production line.

[0019] As an optimization, the hot air duct is a U-shaped duct with adjacent hot air ducts staggered vertically. The U-shaped duct in this design increases the heating length of a single hot air duct, and the staggered arrangement forces the airflow to flow in an S-shape when passing through the heater, extending the contact time and contact area between the air and the hot air duct, making heat transfer more complete, the outlet hot air temperature more uniform, and the heating effect obtained by the filament bundle more stable.

[0020] The beneficial effects of this invention are as follows: Significantly improved temperature uniformity: Through independent circulation of upper and lower dual air ducts and three-dimensional enveloping heating design, combined with high-frequency circulation of high-flow axial fans, this invention can achieve an unloaded temperature uniformity of ≤±0.8℃ and a full-load temperature difference of ≤±1.2℃ in each area, which is far superior to the level of ±3-5℃ in traditional single-duct drying ovens. This fundamentally solves the problem of tensile quality defects caused by uneven heating of the filament bundles.

[0021] Significantly improved thermal efficiency: Hot air circulates repeatedly in a closed return air duct, and the heat is repeatedly utilized. Combined with a fully enclosed insulation structure, the thermal efficiency can reach over 85%, reducing energy consumption by 20%-30% compared to traditional ovens and significantly reducing long-term operating costs.

[0022] High process adaptability: The upper and lower air ducts have independent temperature control, and the upper and lower temperature curves and air volume parameters can be set separately for different materials and specifications of filaments, so as to realize multi-functionality and meet the needs of differentiated processes. At the same time, it can support the simultaneous processing of dual filaments, doubling the production capacity.

[0023] Good operational stability and high product quality: The uniform temperature field and gentle airflow organization make the tension fluctuation of the fiber bundle small and the operation stable during the heating process, effectively reducing the breakage rate and fuzz rate, and improving key quality indicators such as the breaking strength, breaking elongation and dimensional stability of the finished fiber. Attached Figure Description

[0024] Figure 1 This is an internal front view of the present invention; Figure 2 For the present invention Figure 1 Enlarged image; Figure 3 This is a top view of the present invention; Figure 4 This is a side view of the present invention; Figure 5 This is a side view of the door in the open state according to the present invention; Figure 6 This is a front view of the heater of the present invention; Figure 7 This is a top view of the heater of the present invention; Figure 8 This is a side view of the heater of the present invention; As shown in the figure: 1. Base frame, 2. Inner casing, 3. Air inlet duct, 4. Door switch, 41. Lower door panel, 42. Upper door panel, 43. Cylinder, 5. Return air inlet, 6. Return air duct, 7. Air inlet, 8. Heater, 81. Hot air duct, 82. Duct fixing plate, 83. Positioning sleeve, 84. Heat dissipation plate, 85. Connecting screw, 9. Fan, 10. Fan air inlet box, 11. Air guide plate, 12. Guide roller, 13. Thermocouple. Detailed Implementation

[0025] To clearly illustrate the technical features of this solution, the following detailed implementation method will be used to describe the solution.

[0026] like Figures 1-8 As shown, the present invention provides a dual-duct, top-bottom large-circulation hot drying oven for filament bundles, comprising two inner chambers 2 arranged vertically and vertically, fixedly mounted on a base frame 1. The base frame 1 is an integral welded steel frame, ensuring structural stability and vibration resistance during equipment operation, and preventing filament bundle shaking and deviation due to vibration. Both inner chambers 2 are elongated box structures extending in the front-to-back direction, arranged symmetrically vertically.

[0027] like Figure 1 , 2 As shown, each inner chamber 2 has a front-to-back extending air inlet duct 3 inside, which serves as the air supply channel for hot air circulation. A circumferentially enclosed, front-to-back extending return air duct 6 is formed between the two inner chambers 2. The return air duct 6 runs through the entire oven in the front-to-back direction, and its cross-section is rectangular. It is enclosed by the inner walls of the upper and lower inner chambers 2 and the side panels on both sides to form a closed space. The filament bundle passes through the return air duct 6 in the front-to-back direction for heating. Openings for the filament bundle to pass through are provided at both ends of the return air duct 6.

[0028] Each of the two inner casings 2 has a switch door 4 installed at both ends. Here, the two inner casings 2 are considered as a single unit. The switch doors 4 are installed at both ends of this single structure. Figure 4 , Figure 5 As shown, the opening and closing door 4 includes a lower door panel 41 fixed to the end of the lower inner housing 2, an upper door panel 42 hinged to the upper edge of the lower door panel 41, and a cylinder 43 that drives the upper door panel 42 to swing up and down and rotate. The lower door panel 41 is fixedly installed in the lower half of the end of the return air duct 6. When the door is closed, its top surface is flush with the bottom surface of the return air duct 6, and the wire bundle passes through the top of the lower door panel 41. The lower edge of the upper door panel 42 is hinged to the upper edge of the lower door panel 41 by a hinge, and can rotate in a vertical plane around the hinge axis. One end of the cylinder 43 is hinged to the inner housing 2, and the other end is hinged to the upper part of the upper door panel 42. When the door is closed, the upper door panel 42 and the lower door panel 41 together seal the end of the return air duct 6; when the door is opened, the piston rod of the cylinder 43 extends and pushes the upper door panel 42 to rotate upward (e.g., Figure 5As shown in the diagram, the end of the return air duct 6 is completely open, facilitating threading and maintenance operations for operators. When the door is open, the control system automatically reduces the speed of the fan 9 to minimize hot air leakage, while simultaneously pausing heating or switching to heat preservation mode. After the door is closed, the temperature quickly returns to the set temperature.

[0029] like Figure 1 , Figure 2 As shown, the air inlet duct 3 has a return air inlet 5 and an air inlet 7 at its front and rear ends, respectively. Both the return air inlet 5 and the air inlet 7 are located on the side of the two air inlets ducts 3 that are close to each other (i.e., the side facing the return air duct 6) and are connected to the return air duct 6. Specifically, the front end of the air inlet duct 3 (with the direction of the filament bundle's movement as the front, i.e....) Figure 1 A return air inlet 5 is provided on the right side of the inlet duct 3, located on the wall facing the return air duct 6 at the front of the inlet duct 3. Hot air enters the return air duct 6 from the inlet duct 3 through this inlet. The angle between the outlet tangent of the return air inlet 5 and the gas flow direction in the return air duct 6 (i.e., the direction opposite to the direction of the filament bundle) is 0-30 degrees. That is, the orientation of the return air inlet 5 is set at a small angle with the mainstream direction of the return air duct 6, so that the return airflow can enter the return air duct 6 in a smooth streamline direction, reducing flow resistance loss and vortex generation.

[0030] The rear end of air intake duct 3 ( Figure 1 An air inlet 7 is provided on the left side of the air inlet duct 3. The air inlet 7 is located on the wall facing the return air duct 6 at the rear section of the air inlet duct 3. The air that has exchanged heat with the silk bundle in the return air duct 6 returns to the air inlet duct 3 through this inlet duct.

[0031] like Figure 1 , 2 As shown, the air inlet duct 3 is equipped with a fan 9 and a heater 8 arranged in a front-to-back configuration, with the air outlet of the fan 9 facing forward. The heater 8 is located at the rear end of the air inlet duct 3, and the air inlet 7 is located on the side where the two heaters 8 are close to each other. After the air enters the rear section of the air inlet duct 3 through the air inlet 7, it first flows forward through the heater 8 and is heated, then is pressurized by the fan 9 and continues to flow forward, finally returning to the return air duct 6 through the return air inlet 5 to exchange heat with the filament bundle.

[0032] The fan 9 is an axial flow fan with its shaft vertically arranged, such as... Figure 2 As shown, the fans 9 inside the two inner casings 2 are arranged symmetrically, with their rotating shafts vertically positioned. Each fan 9 has a fan inlet box 10 on the side closest to it (i.e., the lower side of the upper fan 9 and the upper side of the lower fan 9). The fan inlet box 10 is a closed shell structure, forming an airflow channel inside. The rear end of the fan inlet box 10 is connected to the front end of the heater 8, and the air inlet of the fan 9 is connected to the fan inlet box 10. That is, the hot air from the heater 8 first enters the fan inlet box 10 and is then drawn in by the fan 9 through its inlet. The fan inlet box 10 collects and guides the incoming airflow, ensuring that the airflow enters the air inlet of the fan 9 evenly, preventing airflow deviation that could lead to decreased fan efficiency and vibration noise.

[0033] like Figure 2 As shown, the distance between the two fan inlet boxes 10 gradually decreases from front to back. That is, the upper and lower walls of the fan inlet box 10 are inclined in a tapering manner in the front-to-back direction, with a larger opening at the front and a smaller opening at the rear, forming a tapering airflow channel. This tapering structure has a compression and rectification effect on the airflow, making the velocity distribution of the airflow tend to be uniform before entering the fan 9, while reducing flow separation and eddy current losses.

[0034] like Figure 3 As shown, two fans 9 are installed side-by-side in each air inlet duct 3, forming a dual-fan parallel air supply structure within a single-layer air duct. The two fans 9 are arranged in a left-right direction, drawing air from the fan inlet box 10 and delivering it forward. Each fan 9 has a guide vane 11 installed at its outlet. The guide vane 11 consists of arc-shaped or flat guide blades, fixed at the outlet of the fan 9, and is used to guide the high-speed airflow from the fan 9 outlet to diffuse evenly in a left-right direction, preventing airflow from concentrating in the central area.

[0035] like Figure 1 , Figure 6 As shown, the heater 8 includes multiple front-to-back hot air ducts 81 and two left-to-right duct fixing plates 82. The duct fixing plates 82 are vertically arranged metal plates, one on each side, fixed within the air inlet duct 3. The hot air ducts 81 are arranged in multiple rows along the front-to-back direction (i.e., multiple rows of ducts along the airflow direction), with each hot air duct 81 passing through the left and right duct fixing plates 82 on either side. Figure 7 As shown, a positioning sleeve 83 is fixedly connected to the duct fixing plate 82, through which the hot air duct 81 passes. The positioning sleeve 83 is a circular sleeve structure, welded or embedded in a through hole opened on the duct fixing plate 82, and the end of the hot air duct 81 passes through the inner hole of the positioning sleeve 83. Figure 8 As shown, the positioning sleeve 83 has a radial threaded hole, and a set screw is threaded into the threaded hole. The end of the set screw is screwed into the inner hole of the positioning sleeve 83 and pressed against the outer circumferential surface of the hot air pipe 81, thereby fixing the hot air pipe 81 inside the positioning sleeve 83. Loosening the set screw allows the hot air pipe 81 to be pulled out from the positioning sleeve 83, realizing the quick disassembly and replacement of a single hot air pipe.

[0036] like Figure 6 , Figure 7 As shown, the hot air duct 81 is a U-shaped duct, that is, a single hot air duct 81 is bent into a U-shape, and its two ends are respectively fixed to the duct fixing plates 82 on the left and right sides, as shown. Figure 6As shown, adjacent hot air ducts 81 are staggered vertically, meaning that adjacent rows of hot air ducts 81 are arranged alternately in the vertical direction, with one row slightly higher and the next slightly lower. This creates an S-shaped, meandering flow path for the air as it passes through the multiple rows of hot air ducts 81, increasing the contact area and contact time with the outer wall of the hot air ducts 81. Multiple heat dissipation plates 84, which are thin metal sheets, are also fitted onto the hot air ducts 81 at intervals along their length to increase the heat dissipation area and enhance convective heat transfer between the hot air ducts 81 and the air. The left and right duct fixing plates 82 are also tightened and fixed together by multiple connecting screws 85 to ensure the rigidity and stability of the overall structure of the heater 8.

[0037] like Figure 1 , Figure 3 As shown, a thermocouple 13 is installed at the front end of the air inlet duct 3 to collect the temperature of the hot air that will be sent into the return air duct 6 in real time. The signal output terminal of the thermocouple 13 is connected to the temperature control system. The temperature control system controls the heating power output of the heater 8 and the speed of the fan 9 according to the temperature feedback signal through a PID algorithm. In addition, multiple auxiliary temperature measuring points can be set in the return air duct 6, the rear end of the air inlet duct 3, etc., to realize multi-point temperature monitoring.

[0038] Between the two inner housings 2, guide rollers 12 are installed at the front and rear ends of the return air duct 6. The guide rollers 12 are used to guide the yarn bundle to smoothly enter and exit the return air duct 6, reducing frictional damage between the yarn bundle and the edge of the equipment. The guide rollers 12 are rotatably installed at the yarn bundle inlet and outlet at the end of the return air duct 6.

[0039] The method of using this invention is as follows: Before starting the equipment, the operator opens the door panels at both ends of the oven using the pneumatic switch door 4, passes the filament bundle through the return air duct 6 in the front-to-back direction, and guides the filament bundle direction using the guide roller 12. After the filament bundle is passed through, the switch door 4 is closed, so that the return air duct 6 forms a circumferentially closed heating chamber.

[0040] After the equipment is started, the axial flow fans 9 in the upper and lower air inlets 3 operate simultaneously, creating negative pressure suction within the air inlets 3. The air that has completed heat exchange with the filament bundle in the return air duct 6 enters the rear section of the air inlet duct 3 through the air inlet 7. The small angle setting of the return air inlet 5 allows the return airflow to enter the return air duct 6 smoothly, with low flow resistance and few turbulences.

[0041] After the gas enters the rear section of the air inlet duct 3, it flows forward through the heater 8. The U-shaped hot air pipes 81 in the heater 8, which are staggered vertically, force convection heating of the air. The air flows in an S-shaped meandering manner between the staggered pipe rows, fully exchanging heat with the hot air pipes 81 and the heat sink 84, and the temperature rises rapidly to the set value.

[0042] The heated high-temperature hot air continues to flow forward, and after being collected and guided by the fan inlet box 10, it enters the inlet of the axial flow fan 9 evenly. The axial flow fan 9 pressurizes the hot air and sends it out at high speed from the outlet, and it is evenly distributed along the width of the inlet duct 3 by the air guide plate 11, and finally enters the return air duct 6 from the return air port 5.

[0043] Hot air is blown simultaneously from both above and below onto the filament bundle traveling through the return air duct 6, forming a three-dimensional, wrap-around heating system. The two independent upper and lower air ducts can be set to the same temperature, or they can be set to different temperatures according to process requirements, such as segmented temperature zone control for preheating in the front section and stretching and shaping in the rear section. After the hot air completes convective heat exchange with the filament bundle, its temperature drops slightly. Driven by the forward movement of the filament bundle and the pressure difference, it flows towards the rear end of the return air duct 6, and re-enters the rear section of the inlet air duct 3 through the air inlet 7, starting a new cycle.

[0044] During the above process, thermocouple 13 collects the hot air temperature at the front end of the air inlet duct 3 in real time and feeds it back to the temperature control system. The temperature control system uses a PID algorithm to precisely control the heating power of heater 8 and the speed of fan 9 to maintain a dynamic balance of the set temperature. When wire threading or maintenance is required, the pneumatic door 4 opens quickly, and the control system simultaneously reduces the fan speed and heating power to reduce heat loss. After closing the door, it quickly returns to the working state.

[0045] Of course, the above description is not limited to the examples above. Technical features not described in this invention can be implemented by or using existing technology, and will not be repeated here. The above embodiments and drawings are only used to illustrate the technical solutions of this invention and are not intended to limit this invention. This invention has been described in detail with reference to preferred embodiments. Those skilled in the art should understand that any changes, modifications, additions or substitutions made by those skilled in the art within the scope of this invention do not depart from the spirit of this invention and should also fall within the scope of protection of the claims of this invention.

Claims

1. A dual-airflow, top-bottom large-circulation hot drying oven for yarn bundles, characterized in that: It includes two inner boxes (2) arranged vertically, with an air inlet (3) extending forward and backward inside the inner box (2). A circumferentially closed return air duct (6) is formed between the two inner boxes (2). The filament bundle passes through the return air duct (6) forward and backward. The air inlet (3) has a return air port (5) and an air inlet (7) at its front and rear ends, respectively. The return air port (5) and the air inlet (7) are both located on the side of the two air inlets (3) that are close to each other and are connected to the return air duct (6). The air inlet duct (3) is equipped with a fan (9) and a heater (8) arranged in front and behind, with the air outlet of the fan (9) facing forward.

2. The dual-airflow, large-circulation hot drying oven for filament bundles according to claim 1, characterized in that: The heater (8) is located at the rear end of the air inlet duct (3), and the air inlet (7) is located on the side where the two heaters (8) are close to each other.

3. The dual-airflow, top-bottom large-circulation hot drying oven for filament bundles according to claim 1, characterized in that: The fan (9) is an axial flow fan with the shaft vertically arranged. Each of the two fans (9) has a fan inlet box (10) on the side close to each other. The rear end of the fan inlet box (10) is connected to the front end of the heater (8), and the air inlet of the fan (9) is connected to the fan inlet box (10).

4. A dual-airflow, top-bottom large-circulation hot drying oven for filament bundles according to claim 3, characterized in that: The distance between the two fan inlet boxes (10) gradually decreases from front to back.

5. A dual-airflow, top-bottom large-circulation hot drying oven for filament bundles according to claim 1, characterized in that: The air inlet duct (3) is equipped with two fans (9) arranged on the left and right sides, and the outlet of the fans (9) is equipped with a guide plate (11).

6. A dual-airflow, top-bottom large-circulation hot drying oven for filament bundles according to claim 1, characterized in that: The front end of the air inlet duct (3) is equipped with a thermocouple (13).

7. A dual-airflow, top-bottom large-circulation hot drying oven for filament bundles according to claim 1, characterized in that: The angle between the outlet tangent of the return air inlet (5) and the gas flow direction in the return air duct (6) is 0-30 degrees.

8. A dual-airflow, top-bottom large-circulation hot drying oven for filament bundles according to claim 1, characterized in that: Both ends of the two inner boxes (2) are equipped with switch doors (4), which include a fixed lower door panel (41), an upper door panel (42) hinged to the lower door panel (41), and a cylinder (43) that drives the upper door panel (42) to swing up and down.

9. A dual-airflow, top-bottom large-circulation hot drying oven for filament bundles according to claim 1, characterized in that: The heater includes multiple front-to-back hot air ducts (81) and two left-to-right duct fixing plates (82). The duct fixing plates (82) are fixed with positioning sleeves (83) through which the hot air ducts (81) pass. The positioning sleeves (83) are threaded with set screws that are fastened to the side of the hot air ducts (81).

10. A dual-airflow, top-bottom large-circulation hot drying oven for filament bundles according to claim 9, characterized in that: The hot air duct (81) is a U-shaped duct and adjacent hot air ducts (81) are staggered vertically.

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