Microwave hot air mixed heating type pre-oxidation furnace adopting slot antenna

Abstract

The application discloses a microwave hot air mixed heating type preoxidation furnace adopting a slit antenna, which comprises a furnace body, a heater, a fan and a microwave heating device, a wire running area is formed in the furnace body, the wire running area has a width W, the microwave heating device comprises a microwave source and slit antennas, the number of the slit antennas is multiple, each slit antenna is connected with the microwave source, a wave leakage hole is arranged in the narrow surface of each slit antenna, the narrow surfaces of the slit antennas are distributed on the top surface or the bottom surface of the wire running area, the wave leakage holes are distributed along the length direction of the narrow surfaces, and the wave leakage holes of the multiple slit antennas are arranged in a matrix in the wire running area. The application can shorten the preoxidation time and reduce the reaction temperature.

Description

Technical Field

[0001] This invention relates to the field of pre-oxidation furnaces, and more specifically, to a microwave hot air hybrid heating type pre-oxidation furnace employing a slot antenna. Background Technology

[0002] Currently, the oxidation furnace is the core equipment in carbon fiber production, and the pre-oxidation of precursor fibers plays a crucial role in the process, directly affecting the final performance of carbon fibers.

[0003] Pre-oxidation is a crucial step in the preparation of polyacrylonitrile (PAN)-based carbon fibers. In a pre-oxidation furnace at 200℃–300℃, the PAN precursor fibers undergo cyclization, dehydrogenation, and oxygen absorption reactions, transforming the linear molecular chains into heat-resistant trapezoidal six-membered ring structures. The color of the PAN fibers changes from milky white to golden yellow, brownish-red, and finally black, ensuring that PAN-based carbon fiber products do not melt or burn during high-temperature carbonization. In the industrial production of carbon fibers, the pre-oxidation furnace heats the gas via electric heating tubes and then the fiber bundle via hot air, resulting in low energy efficiency. The entire process uses four to six pre-oxidation furnaces with gradient heating, and the pre-oxidation time is typically 60-90 minutes, accounting for approximately 90% of the entire carbon fiber production process. These multiple pre-oxidation furnaces consume about 65% of the total power of the production line.

[0004] Polyacrylonitrile (PAN) precursor fibers have very low dielectric constants and loss factors, making microwave heating of the fibers inefficient. Current research involves coating the surface of PAN precursor fibers with a highly stable microwave-absorbing coating, followed by microwave heating for pre-oxidation. For example, patent CN111691012A discloses an electrically controlled microwave pre-oxidation process for PAN precursor fibers, which involves coating the fiber surface with a carbon black coating for microwave pre-oxidation. The coating process often employs an impregnation and drying process, with the PAN precursor fibers impregnated for 20 minutes or using multiple short impregnations, increasing production line investment and subsequent production costs. Due to the inherent characteristics of microwaves, a distinct microwave field distribution exists within the cavity. Directly heating the microwave-absorbing coating for pre-oxidation places extremely high demands on the temperature detection and control of the fiber bundle within the furnace. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a microwave-hot-air hybrid heating pre-oxidation furnace using a slotted antenna. By heating with both hot air and microwaves, the pre-oxidation reaction process can be accelerated, the reaction time and temperature can be reduced, and lower energy consumption can be achieved.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A microwave-heated hot air hybrid heating pre-oxidation furnace employing a slotted antenna includes a furnace body, a heater for heating gas, a fan for conveying gas, and a microwave heating device. A wire-walking zone is formed inside the furnace body, with a length of L and a width of W. The furnace body includes an air inlet, an air outlet, a wire bundle inlet, and a wire bundle outlet. The wire-walking zone is located between the wire bundle inlet and the wire bundle outlet and connects the two. The fan conveys gas from the air inlet to the air outlet and discharges it from the air outlet. The microwave heating device includes a microwave source and multiple slotted antennas. Each slotted antenna is connected to the microwave source. One narrow facet of each slotted antenna has a leakage aperture. The narrow faces of the slotted antennas are distributed on the top or bottom surface of the wire-walking zone, and the leakage apertures are distributed along the length of the narrow faces. The leakage apertures of the multiple slotted antennas are arranged in a matrix within the wire-walking zone.

[0008] As a further setting, the center distance d between the leakage apertures in the width direction of the wire feeding area satisfies d≤0.405*λ^1.147, where λ is the microwave wavelength.

[0009] As a further setting, the number of slot antennas is n = floor(W / d), where d is the center distance between the leaky holes in the width direction of the wire-walking area.

[0010] As a further setting, the frequency of the microwave source is 915MHz or 2450MHz, with a wavelength λ corresponding to a frequency of 915MHz being 328mm and a wavelength λ corresponding to a frequency of 2450MHz being 122mm.

[0011] As a further setting, at a frequency of 2450MHz, the microwave input power deviation of each slit antenna is less than or equal to 15% when the positive and negative deviations are asymmetrical, and less than or equal to 20% when the positive and negative deviations are symmetrical; at a frequency of 915MHz, the microwave input power deviation of each slit antenna is less than or equal to 25% when the positive and negative deviations are asymmetrical, and less than or equal to 30% when the positive and negative deviations are symmetrical.

[0012] As a further setting, the phase deviation value fed into each slot antenna is less than or equal to pi / 15 or differs by 2n*pi on this basis.

[0013] As a further setting, each slot antenna has the same frequency, the same center distance d, and the same center distance c. The center distance d is the center distance between the leaky holes in the width direction of the wire-walking area, and the center distance c is the center distance between the leaky holes in the length direction of the wire-walking area.

[0014] As a further setting, the center distance c between the leakage holes in the length direction of the wire-feeding area satisfies 0.15λ≤c≤2λ, where λ is the microwave wavelength.

[0015] As a further feature, the leakage aperture is offset to one side in the width direction of the wire feeding area, with an eccentricity distance P≤0.025*λ^1.2, where λ is the microwave wavelength.

[0016] As a further configuration, the leakage aperture is centered on the narrow face of the slot antenna, and the entire slot antenna is shifted in the width direction of the wire-feeding area, thereby causing the leakage aperture to shift to one side in the width direction of the wire-feeding area; or the entire slot antenna is centered in the width direction of the wire-feeding area, but the leakage aperture is not centered on the narrow face of the slot antenna, thereby causing the leakage aperture to shift to one side in the width direction of the wire-feeding area.

[0017] As a further feature, the furnace body is provided with a feed port on the top or bottom surface of the wire feeding zone, and the feed port corresponds one-to-one with the leakage hole and the two have the same shape and size.

[0018] As a further feature, the shape of the leakage aperture is circular, waist-shaped, elliptical, or rectangular.

[0019] As a further configuration, the elliptical, waist-shaped, and rectangular slit holes are tilted as a whole on the narrow surface of the slot antenna at an angle of less than or equal to 2°.

[0020] As a further configuration, elliptical, waist-shaped, and rectangular slit holes are symmetrically and alternately tilted at an angle of less than or equal to 1° on the narrow surface of the slot antenna.

[0021] As a further setting, the diameter of the circular ripple hole is greater than or equal to 0.07*λ and less than or equal to 0.33*λ, where λ is the microwave wavelength.

[0022] As a further setting, the long side of the rectangular diaphragm aperture is greater than or equal to 0.2*λ and less than or equal to 0.75*λ, and the short side is greater than or equal to 0.006*λ and less than or equal to 0.366*λ. The long side of the diaphragm aperture is defined as the side parallel to the length direction of the wire feeding area, and the short side is defined as the side parallel to the width direction of the wire feeding area. The major axis of the elliptical diaphragm aperture is greater than or equal to 0.2*λ and less than or equal to 0.75*λ, and the minor axis is greater than or equal to 0.006*λ and less than or equal to 0.366*λ. The distance between the midpoints of the two arcs of the waist-shaped diaphragm aperture is greater than or equal to 0.2*λ and less than or equal to 0.75*λ, and the distance between the two parallel planes is greater than or equal to 0.006*λ and less than or equal to 0.366*λ, where λ is the microwave wavelength.

[0023] As a further feature, the two ends of the wire feeding zone along its length are defined by perforated plates, the distance between the two perforated plates at both ends of the wire feeding zone is L, and the perforated plates are provided with through holes that pass through both ends.

[0024] As a further feature, the perforated plate has at least two perforated plates at each end of the wire feeding zone along its length, and the through holes of the multiple perforated plates at the same end are arranged in a staggered manner.

[0025] As a further feature, the diameter of the through hole is less than or equal to 0.25*λ, and the spacing between multiple mesh plates at the same end is less than or equal to λ, where λ is the microwave wavelength.

[0026] As a further feature, a wave-transparent plate is provided at the connection between the slot antenna and the feed port. The wave-transparent plate is made of fused silica, high-purity alumina, hexagonal boron nitride, or silicon nitride.

[0027] In summary, the present invention has the following beneficial effects: without any treatment of the polyacrylonitrile precursor fiber, the microwaves form a uniform electric field distribution in the direction perpendicular to the fiber bundle movement in the fiber-carrying zone through hot air microwave coupling technology, ensuring uniform pre-oxidation of the fiber bundle during operation; the microwave-enhanced acceleration of the pre-oxidation process can shorten the pre-oxidation time and reduce the reaction temperature, significantly improving production efficiency and thus reducing the production cost of the carbon fiber pre-oxidation process. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of an embodiment;

[0029] Figure 2 for Figure 1 Sectional view along the middle AA direction;

[0030] Figure 3 for Figure 1 Sectional view along the BB direction;

[0031] Figure 4 This is a schematic diagram showing the distribution of the perforated plate in an embodiment;

[0032] Figure 5 This is a partial top view of an embodiment;

[0033] Figure 6 A simulation diagram of a wave-leaking hole on a wide surface for an embodiment;

[0034] Figure 7 A simulation diagram using a circular ripple hole;

[0035] Figure 8 A simulation diagram showing the use of an elliptical ripple hole;

[0036] Figure 9 Simulation diagram of using a waist-shaped ripple hole;

[0037] Figure 10 The simulation diagram shows a rectangular ripple hole with an inclination angle of 2°.

[0038] Figure 11 The simulation diagram shows a rectangular ripple hole with an inclination angle of 30°.

[0039] Figure 12 A simulation diagram of a rectangular ripple hole with a symmetrical tilt angle of 1°;

[0040] Figure 13 A simulation diagram of a rectangular ripple hole with a symmetrical tilt angle of 2°;

[0041] Figure 14 A simulation diagram of a circular ripple hole with a diameter of 8.5 mm;

[0042] Figure 15 A simulation diagram of a circular ripple hole with a diameter of 8mm;

[0043] Figure 16 A simulation diagram of a circular ripple hole with a diameter of 40mm;

[0044] Figure 17 The simulation diagram shows the short side of the ripple hole is 2mm and the long side is 150mm.

[0045] Figure 18 The simulation diagram shows the short side of the ripple hole is 30mm and the long side is 246mm.

[0046] Figure 19 The simulation diagram shows the short side of the ripple hole is 99mm and the long side is 246mm.

[0047] Figure 20 The simulation diagram shows the short side of the ripple hole is 120mm and the long side is 246mm.

[0048] Figure 21 A simulation diagram showing a rectangular ripple hole with the longer side smaller than the shorter side;

[0049] Figure 22 The simulation diagram is for a frequency of 2450MHz and d=130mm;

[0050] Figure 23 The simulation diagram is for a frequency of 2450MHz and d = 110mm;

[0051] Figure 24 The simulation diagram is for a frequency of 2450MHz and d = 102mm;

[0052] Figure 25 The simulation diagram is for a frequency of 2450MHz and d=100mm;

[0053] Figure 26 The simulation diagram is for a frequency of 2450MHz and d=90mm;

[0054] Figure 27 The simulation diagram is for a frequency of 915MHz and d = 290mm;

[0055] Figure 28 The simulation diagram is for a frequency of 915MHz and d = 300mm;

[0056] Figure 29 The simulation diagram is for a frequency of 915MHz and d = 310mm;

[0057] Figure 30 The simulation diagram is for a frequency of 915MHz and d = 330mm;

[0058] Figure 31 The simulation diagram is for a frequency of 2450MHz and c = 244mm.

[0059] Figure 32 The simulation diagram is for a frequency of 2450MHz and c = 20mm.

[0060] Figure 33 The simulation diagram is for a frequency of 915MHz and c = 656mm.

[0061] Figure 34 The simulation diagram is for a frequency of 915MHz and c = 50mm.

[0062] Figure 35 The simulation diagram shows the reduction of the original requirement of 5 slot antennas to 4 by reducing one;

[0063] Figure 36 Simulation diagrams for microwave powers of 105W, 100W, 95W, 100W, and 100W;

[0064] Figure 37 Simulation diagrams for microwave powers of 110W, 100W, 100W, 90W, and 100W;

[0065] Figure 38 Simulation diagrams for microwave powers of 115W, 100W, 85W, 100W, and 100W;

[0066] Figure 39 Simulation diagrams for microwave powers of 105W, 100W, 100W, 100W, and 95W;

[0067] Figure 40 Simulation diagrams for microwave powers of 90W, 100W, 100W, 100W, and 110W;

[0068] Figure 41Simulation diagrams for microwave powers of 115W, 100W, 100W, 100W, and 85W;

[0069] Figure 42 Simulation diagrams for microwave powers of 100W, 80W, 100W, 120W, and 100W;

[0070] Figure 43 Simulation diagrams for microwave powers of 100W, 115W, 85W, 100W, and 100W;

[0071] Figure 44 Simulation diagrams for microwave powers of 100W, 125W, 100W, 100W, and 75W;

[0072] Figure 45 Simulation diagrams for microwave powers of 115W, 100W, 100W, 100W, and 85W;

[0073] Figure 46 Simulation diagrams for microwave powers of 125W, 100W, 100W, 100W, and 75W;

[0074] Figure 47 Simulation diagrams for microwave powers of 130W, 100W, 100W, 100W, and 70W;

[0075] Figure 48 The simulation diagram shows a frequency of 2450MHz and five phase ports: pi / 18, 0, 0, -pi / 18, and pi / 18.

[0076] Figure 49 The simulation diagram shows a frequency of 2450MHz and five phase ports: pi / 15, pi / 15, 0, -pi / 15, and 0.

[0077] Figure 50 The simulation diagram shows a frequency of 2450MHz and five phase ports: pi / 9, 0, -pi / 9, pi / 9, and 0.

[0078] Figure 51 The simulation diagram shows a frequency of 2450MHz and five phase ports: pi / 18, 0, 0, 0, and -pi / 18.

[0079] Figure 52 The simulation diagram shows a frequency of 2450MHz and five phase ports of 0, pi / 18, 0, -pi / 18, and 0.

[0080] Figure 53 The simulation diagram shows a frequency of 2450MHz and five phase ports: pi / 15, 0, 0, 0, and -pi / 15.

[0081] Figure 54 The simulation diagram shows a frequency of 2450MHz and five phase ports: pi / 9, 0, 0, 0, and -pi / 9.

[0082] Figure 55 The simulation diagram shows a frequency of 915MHz and five phase ports: pi / 18, 0, -pi / 18, pi / 18, and 0.

[0083] Figure 56 The simulation diagram shows a frequency of 915MHz and five phase ports: pi / 15, 0, 0, -pi / 15, and pi / 15.

[0084] Figure 57 The simulation diagram shows a frequency of 915MHz and five phase ports: pi / 18, 0, 0, 0, and -pi / 18.

[0085] Figure 58 The simulation diagram shows a frequency of 915MHz and five phase ports with values ​​of 0, pi / 18, 0, -pi / 18, and 0.

[0086] Figure 59 The simulation diagram shows a frequency of 915MHz and five phase ports: pi / 15, 0, 0, 0, and -pi / 15.

[0087] Figure 60 The simulation diagram shows the offset of a slot antenna with a frequency of 2450MHz and an eccentricity of 5mm.

[0088] Figure 61 The simulation diagram shows the offset of a slot antenna with a frequency of 2450MHz and an eccentricity of 8mm.

[0089] Figure 62 The simulation diagram shows the offset of a slot antenna with a frequency of 2450MHz and an eccentricity of 9mm.

[0090] Figure 63 The simulation diagram shows the offset of a slot antenna with a frequency of 2450MHz and an eccentricity of 10mm.

[0091] Figure 64 The simulation diagram shows the offset of a slot antenna with a frequency of 915MHz and an eccentricity of 10mm.

[0092] Figure 65 The simulation diagram shows the offset of a slot antenna with a frequency of 915MHz and an eccentricity of 20mm.

[0093] Figure 66 The simulation diagram shows the offset of a slot antenna with a frequency of 915MHz and an eccentricity of 26mm.

[0094] Figure 67The simulation diagram shows the aperture offset at a frequency of 2450MHz and an eccentricity of 5mm.

[0095] Figure 68 The simulation diagram shows the aperture offset at a frequency of 2450MHz and an eccentricity distance of 8mm.

[0096] Figure 69 The simulation diagram shows the aperture offset at a frequency of 2450MHz and an eccentricity of 10mm.

[0097] Figure 70 The simulation diagram shows the aperture offset at a frequency of 915MHz and an eccentricity of 10mm.

[0098] Figure 71 The simulation diagram shows the aperture offset at a frequency of 915MHz and an eccentricity of 20mm.

[0099] Figure 72 The simulation diagram shows the aperture offset at a frequency of 915MHz and an eccentricity of 26mm.

[0100] Figure 73 The simulation diagram shows the aperture offset at a frequency of 915MHz and an eccentricity of 30mm.

[0101] Figure 74 The simulation diagram shows a frequency of 915MHz and two rows of leakage apertures.

[0102] Figure 75 The simulation diagram shows a frequency of 2450MHz and two rows of leakage apertures.

[0103] Figure 76 The simulation diagram shows the matrix shifted 10mm to the left at a frequency of 2450MHz.

[0104] Figure 77 The simulation diagram shows a matrix with a frequency of 2450MHz that is missing one column.

[0105] Figure 78 The simulation diagram shows the matrix shifted 20mm to the left at a frequency of 915MHz.

[0106] Figure 79 The simulation diagram shows a matrix with a frequency of 915MHz that is missing one column.

[0107] Figure labels: 1. Fan, 2. Heater, 3. Furnace body, 31. Air inlet, 32. Air outlet, 33. Wire bundle inlet, 34. Wire bundle outlet, 4. Feed port, 5. Slot antenna, 6. Microwave source, 7. Mesh plate, 71. Through hole, 8. Wave-transparent plate, 9. Wave-leaking hole. Detailed Implementation

[0108] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0109] Reference Figures 1-5 As shown, this embodiment discloses a microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna, referring to... Figure 1 It includes a furnace body 3, a heater 2 for heating the gas, a blower 1 for conveying the gas, and a microwave heating device. A fiber feeding zone is formed inside the furnace body 3. The fiber feeding zone is distributed along the length of the furnace body 3 and serves as a space for fiber pre-oxidation treatment. The length of the fiber feeding zone is L and the width is W.

[0110] Reference Figure 1 The furnace body 3 includes an air inlet 31, an air outlet 32, a filament inlet 33, and a filament outlet 34. The filament feeding zone is located between the filament inlet 33 and the filament outlet 34 and the filament feeding zone connects the filament inlet 33 and the filament outlet 34. The filament enters from the filament inlet 33, and after being heated by hot air and microwaves in the filament feeding zone, it leaves from the filament outlet 34.

[0111] Reference Figure 1 The wire feeding zone is located between the air inlet 31 and the air outlet 32, and the wire feeding zone connects the air inlet 31 and the air outlet 32. The blower 1 delivers gas from the air inlet 31 and exhausts it from the air outlet 32. The heater 2 heats the gas in the furnace body 3 so that the gas temperature reaches the temperature required for the pre-oxidation reaction. The blower 1 blows the heated gas into the air inlet 31 and heats the wire bundle in the wire feeding zone. The gas is finally discharged from the air outlet 32 ​​and is heated again and blown into the air inlet 31 by the blower 1. This cycle continues.

[0112] Reference Figure 2 , Figure 4 The wire feeding zone is defined at both ends by perforated plates 7 located within the furnace body 3. The distance between the two perforated plates 7 at both ends of the wire feeding zone is L. The perforated plates 7 have through holes 71 extending through both ends. The diameter of the through holes 71 is less than or equal to 0.25*λ, where λ is the microwave wavelength. The perforated plates 7 are made of metal and are used to evenly distribute hot air, ensuring that the hot air is evenly distributed and blown into the wire feeding zone parallel to the wire feeding direction. At the same time, the perforated plates 7 shield microwave energy from entering other areas through the through holes 71, thus protecting the normal operation of components such as the fan 1 and heater 2.

[0113] Reference Figure 2 , Figure 4At least two perforated plates 7 are provided at each end of the wire feeding zone along its length, and the through holes 71 of multiple perforated plates 7 at the same end are arranged in a staggered manner. Figure 4 The through-holes 71 with dark solid lines and those with light solid lines represent two staggered mesh plates 7. The spacing between multiple mesh plates 7 at the same end is less than or equal to λ. By setting multiple mesh plates 7 at the same end, the hot air distribution and microwave shielding functions can be better achieved.

[0114] Reference Figure 1 The microwave heating device includes a microwave source 6 and a slot antenna 5. The slot antenna 5 is connected to the microwave source 6. The slot antenna 5 is a purchased component and is a rectangular component. One of the narrow faces of the slot antenna 5 has a leakage aperture 9. The leakage aperture 9 is distributed along the length of the narrow face and is located on the top or bottom surface of the wire-running area. The microwaves fed by the microwave source 6 are fed into the wire-running area through the leakage aperture 9 of the slot antenna 5. The frequency of the microwave source 6 is 915MHz or 2450MHz. The wavelength λ corresponding to the frequency of 915MHz is 328mm, and the wavelength λ corresponding to the frequency of 2450MHz is 122mm.

[0115] Reference Figure 6 A leakage aperture 9 is provided on one of the wide faces of the slot antenna 5. At this time, the consistency of the electric field intensity in the same width direction does not meet the requirements. The wide face is a face with a larger area than the narrow face.

[0116] The fiber-carrying zone is the working area of ​​the microwave heating device. Microwaves create a uniform electric field distribution perpendicular to the fiber-carrying plane, ensuring uniform pre-oxidation of the fiber during its movement. Since the fiber-carrying plane is horizontal, microwaves are fed into the top or bottom surface of the fiber-carrying zone to ensure the microwave electric field is perpendicular to the fiber-carrying plane. Microwaves assist in heating the precursor fiber and accelerate the pre-oxidation reaction, shortening the reaction time and lowering the reaction temperature.

[0117] Reference Figure 2 , Figure 3 The furnace body 3 has a feed port 4 on the top or bottom surface of the wire-feeding area. The feed port 4 corresponds one-to-one with the leakage aperture 9 and the two are the same in shape and size. The microwave of the slot antenna 5 is fed into the wire-feeding area through the feed port 4. The leakage aperture 9 is arranged in a matrix in the wire-feeding area.

[0118] Feed port 4 coincides with ripple hole 9. Ripple hole 9 is circular in shape (see reference). Figure 7 ) or oval (refer to) Figure 8 ) or waist-shaped (refer to) Figure 9 (or rectangular)

[0119] Elliptical, oblong, or rectangular ripple holes 9 can be tilted as a whole on the narrow surface of the slot antenna 5 at an angle of less than or equal to 2°. Taking a rectangular hole as an example, refer to... Figure 10 The overall tilt angle is 2°, and the consistency of the electric field intensity along the width of the same column meets the requirements; therefore, the rectangle is a slanted rectangle. (Refer to...) Figure 11 The overall tilt angle is 30°, which does not meet the requirements.

[0120] Elliptical, oblong, and rectangular ripple holes 9 can be symmetrically and alternately tilted at an angle of less than or equal to 1° on the narrow surface of the slot antenna 5. Taking the rectangular one as an example, refer to... Figure 12 The symmetrical tilt angle is 1°, which meets the requirements. At this point, the rectangle is a slanted rectangle, and the tilt direction of each column of leakage holes 9 is consistent along the width of the wire feeding area; along the length of the wire feeding area, adjacent leakage holes 9 are symmetrically distributed in each row. (Refer to...) Figure 13 The symmetrical tilt angle is 2°, which does not meet the requirements.

[0121] The diameter of the circular ripple hole 9 is greater than or equal to 0.07*λ and less than or equal to 0.33*λ. (Refer to...) Figure 14 When λ is 122mm and the diameter of the circular ripple hole 9 is 8.5mm, the requirements are met. (Refer to...) Figure 15 When λ is 122mm and the diameter of the circular leakage aperture 9 is 8mm, the consistency of the electric field intensity in the same column width direction begins to deform, failing to meet the requirements. (Refer to...) Figure 16 When λ is 122mm and the diameter of the circular ripple hole 9 is 40mm, the requirements are met.

[0122] The long side of the rectangular ripple hole 9 is greater than or equal to 0.2*λ and less than or equal to 0.75*λ, and the short side is greater than or equal to 0.006*λ and less than or equal to 0.366*λ. (Refer to...) Figure 17 The frequency is 915MHz, the wavelength is 328mm, and the short side of the leakage aperture 9 is 2mm and the long side is 150mm, which meets the requirements. (Refer to...) Figure 18 The frequency is 915MHz, the wavelength is 328mm, the short side of the leakage aperture 9 is 30mm, the long side is 246mm, and the center distance c between the leakage apertures 9 along the length of the wire-running area is 437mm, i.e., c is 1.333λ, which meets the requirements. (Refer to...) Figure 19 The frequency is 915MHz, the wavelength is 328mm, the short side of the leakage aperture 9 is 99mm, the long side is 246mm, and the center distance c between the leakage apertures 9 along the length of the wire-feeding area is 437mm, i.e., c is 1.333λ, which meets the requirements. (Refer to...) Figure 20 The frequency is 915MHz, the wavelength is 328mm, the short side of the leakage aperture 9 is 120mm, the long side is 246mm, and the center distance c between the leakage apertures 9 in the length direction of the wire-feeding area is 437mm, that is, c is 1.333λ, which meets the requirements.

[0123] Two sides of the leakage aperture 9 (which can be the two long sides or the two short sides) are parallel to the width direction of the wire feeding area, and the other two sides of the leakage aperture 9 (which can be the two short sides or the two long sides) are parallel to the length direction of the wire feeding area, as shown in the reference. Figure 21 The horizontal axis represents the length of the wire feeding area in the furnace, and the vertical axis represents the width. This figure shows the electric field distribution of the wire feeding area on a plane at a certain height. The different colors of the legend on the far right indicate the magnitude of the electric field intensity on this plane. In the microwave-enhanced pre-oxidation process, the uniformity of the electric field distribution directly affects the thermal oxidation reaction process of the wire bundle. Areas with higher electric field intensity have a higher degree of oxidation. Uneven electric field distribution will cause inconsistent pre-oxidation degrees of the wire bundles in different width directions, and may even cause wire breakage, seriously restricting the consistency control of the final product. Therefore, it is necessary to ensure the consistency of the electric field intensity in any "column" width direction on any plane at any height of the furnace. Let the furnace length be the X-coordinate, the width be the Y-coordinate, and the height be the Z-coordinate; that is, the electric field intensity must be consistent on the line where the XY plane and the YZ plane intersect at any height of the furnace. Figure 21 In the middle, the long side of the rectangular leakage hole 9 is smaller than the short side. Therefore, the long side of the leakage hole 9 is defined as the side parallel to the length direction of the wire feeding area, and the short side is defined as the side parallel to the width direction of the wire feeding area.

[0124] The major axis of the elliptical ripple hole 9 is greater than or equal to 0.2*λ and less than or equal to 0.75*λ, and the minor axis is greater than or equal to 0.006*λ and less than or equal to 0.366*λ, which is consistent with that of the rectangular ripple hole 9.

[0125] The distance between the midpoints of the two arcs of the waist-shaped ripple hole 9 is greater than or equal to 0.2*λ and less than or equal to 0.75*λ, and the distance between the two parallel planes is greater than or equal to 0.006*λ and less than or equal to 0.366*λ, which is consistent with the rectangular ripple hole 9.

[0126] Reference Figure 2 , Figure 3 A wave-transparent plate 8 is provided at the connection between the slot antenna 5 and the feed port 4. The wave-transparent plate 8 is made of fused silica, high-purity alumina, hexagonal boron nitride, or silicon nitride. The wave-transparent plate 8 ensures microwave feeding while preventing hot air from entering the slot antenna 5.

[0127] The furnace body 3, where the slot antenna 5 and the feed port 4 are located, is detachably connected for easy maintenance. Alternatively, the furnace body 3, where the slot antenna 5 and the feed port 4 are located, is welded together for reliable connection.

[0128] Multiple slotted antennas 5 are connected to a single microwave source 6 via a power divider, meaning one microwave source 6 inputs microwaves to the corresponding multiple slotted antennas 5. Alternatively, each slotted antenna 5 is connected to a microwave source 6, meaning one microwave source 6 inputs microwaves to the corresponding slotted antenna 5. The microwave source 6 is a solid-state microwave source, each equipped with its own phase-locked loop (PLL), which ensures the consistency of each solid-state microwave source.

[0129] Reference Figure 5 The center distance d between the leakage holes 9 in the width direction of the wire feeding zone is ≤0.405*λ^1.147.

[0130] When the frequency is 2450MHz and the wavelength is 122mm, d≤100mm.

[0131] Figure 22 The diameter d = 130mm, which does not meet the requirements.

[0132] Figure 23 The value d = 110mm does not meet the requirements.

[0133] Figure 24 In the middle section, d = 102 mm, the electric field strength in the same column width direction is slightly inconsistent, which does not meet the requirements.

[0134] Figure 25 The middle d = 100mm, which meets the requirements.

[0135] Figure 26 The diameter d = 90mm, which meets the requirements.

[0136] When the frequency is 915MHz and the wavelength is 328mm, d≤311mm.

[0137] Figure 27 The middle d = 290mm, which meets the requirements.

[0138] Figure 28 The diameter d = 300mm, which meets the requirements.

[0139] Figure 29 The value of d = 310 mm meets the requirements.

[0140] Figure 30 In the middle section, d = 330 mm, the electric field strength in the same column width direction is slightly inconsistent, which does not meet the requirements.

[0141] Reference Figure 5 The center distance c between the leakage holes 9 in the length direction of the wire-feeding zone satisfies 0.15λ≤c≤2λ.

[0142] Reference Figure 31 When the frequency is 2450MHz and the wavelength is 122mm, c is 244mm, which meets the requirements.

[0143] Reference Figure 32 When the frequency is 2450MHz and the wavelength is 122mm, c is 20mm, which meets the requirements.

[0144] Reference Figure 33 When the frequency is 915MHz and the wavelength is 328mm, c is 656mm, which meets the requirements.

[0145] Reference Figure 34 When the frequency is 915MHz and the wavelength is 328mm, c is 50mm, which meets the requirements.

[0146] The number of leakage holes 9 in the width direction of the wire feeding zone is n = floor(W / d), that is, rounding down W / d. With a frequency of 2450MHz, d = 100mm, and furnace width W = 500mm, we get n = 5. (Refer to...) Figure 35 Reducing the number of slot antennas from 5 to 4, which originally required 5, does not meet the requirements. It is also impossible to add one more slot antenna while keeping the center distance d constant, as this would exceed the width of the wire-feeding zone.

[0147] At a frequency of 2450MHz, the microwave power deviation is less than or equal to 15% when the positive and negative deviations are asymmetrical, and less than or equal to 20% when the positive and negative deviations are symmetrical. At a frequency of 915MHz, the microwave power deviation is less than or equal to 25% when the positive and negative deviations are asymmetrical, and less than or equal to 30% when the positive and negative deviations are symmetrical.

[0148] Reference Figure 36 The frequency is 2450MHz, the microwave power of the main port is 100W, the deviation port has a deviation of 5%, namely 95W and 105W, the positive and negative deviations of the 5 ports are asymmetrical, namely 105W, 100W, 95W, 100W and 100W respectively, which meets the requirements.

[0149] Reference Figure 37 The frequency is 2450MHz, the main microwave power is 100W, the deviation port has a deviation of 10%, namely 90W and 110W, the positive and negative deviations of the 5 ports are asymmetrical, namely 110W, 100W, 100W, 90W and 100W respectively, which meets the requirements.

[0150] Reference Figure 38 The frequency is 2450MHz, the main microwave power is 100W, the deviation port has a deviation of 15%, namely 85W and 115W, the positive and negative deviations of the 5 ports are asymmetrical, namely 115W, 100W, 85W, 100W and 100W respectively, which meets the requirements.

[0151] Reference Figure 39The frequency is 2450MHz, the main microwave power is 100W, the deviation port has a deviation of 5%, namely 95W and 105W, the positive and negative deviations of the five ports are symmetrical, namely 105W, 100W, 100W, 100W and 95W respectively, which meets the requirements.

[0152] Reference Figure 40 The frequency is 2450MHz, the main microwave power is 100W, the deviation port has a deviation of 10%, namely 90W and 110W. The positive and negative deviations of the five ports are symmetrical, namely 90W, 100W, 100W, 100W and 110W, which meets the requirements.

[0153] Reference Figure 41 The frequency is 2450MHz, the main microwave power is 100W, the deviation port has a deviation of 15%, namely 85W and 115W, the positive and negative deviations of the five ports are symmetrical, namely 115W, 100W, 100W, 100W and 85W respectively, which meets the requirements.

[0154] Reference Figure 42 The frequency is 2450MHz, the main microwave power is 100W, the deviation port has a deviation of 20%, namely 80W and 120W, the positive and negative deviations of the 5 ports are symmetrical, namely 100W, 80W, 100W, 120W and 100W respectively, which meets the requirements.

[0155] Reference Figure 43 The frequency is 915MHz, the main microwave power is 100W, the deviation port has a deviation of 15%, namely 85W and 115W, the positive and negative deviations of the 5 ports are asymmetrical, namely 100W, 115W, 85W, 100W and 100W respectively, which meets the requirements.

[0156] Reference Figure 44 The frequency is 915MHz, the main microwave power is 100W, the deviation port has a deviation of 25%, namely 75W and 125W, the positive and negative deviations of the 5 ports are asymmetrical, namely 100W, 125W, 100W, 100W and 75W respectively, which meets the requirements.

[0157] Reference Figure 45 The frequency is 915MHz, the main microwave power is 100W, the deviation port has a deviation of 15%, namely 85W and 115W, the positive and negative deviations of the 5 ports are symmetrical, namely 115W, 100W, 100W, 100W and 85W respectively, which meets the requirements.

[0158] Reference Figure 46 The frequency is 915MHz, the main microwave power is 100W, the deviation port has a deviation of 25%, namely 75W and 125W, the positive and negative deviations of the five ports are symmetrical, namely 125W, 100W, 100W, 100W and 75W respectively, which meets the requirements.

[0159] Reference Figure 47 The frequency is 915MHz, the main microwave power is 100W, the deviation port has a deviation of 30%, namely 70W and 130W, the positive and negative deviations of the 5 ports are symmetrical, namely 130W, 100W, 100W, 100W and 70W respectively, which meets the requirements.

[0160] The phase deviation value fed into each slot antenna 5 is less than or equal to pi / 15, i.e., 12°, and can differ by 2n*pi on this basis.

[0161] Reference Figure 48 The frequency is 2450MHz, the phase has an irregular deviation, the main phase aperture is 0, the deviation aperture is pi / 18, i.e. 10°, and the five apertures are pi / 18, 0, 0, -pi / 18, and pi / 18, which meets the requirements.

[0162] Reference Figure 49 The frequency is 2450MHz, the phase has an irregular deviation, the main phase aperture is 0, the deviation aperture is pi / 15, i.e. 12°, and the five apertures are pi / 15, pi / 15, 0, -pi / 15, and 0, which meets the requirements.

[0163] Reference Figure 50 The frequency is 2450MHz, the phase is irregularly deviated, the main phase aperture is 0, the deviation aperture is pi / 9, that is, 20°, the five apertures are pi / 9, 0, -pi / 9, pi / 9, 0, the consistency of electric field intensity on the same width has begun to shift, although only slightly, which is slightly unsatisfactory.

[0164] Reference Figure 51 The frequency is 2450MHz, the phase has a regular symmetrical deviation, the main phase aperture is 0, the deviation aperture is pi / 18, i.e. 10°, and the five apertures are pi / 18, 0, 0, 0 and -pi / 18 respectively, which meets the requirements.

[0165] Reference Figure 52 The frequency is 2450MHz, the phase has a regular symmetrical deviation, the main phase aperture is 0, the deviation aperture is pi / 18, i.e. 10°, and the five apertures are 0, pi / 18, 0, -pi / 18, and 0 respectively, which meets the requirements.

[0166] Reference Figure 53 The frequency is 2450MHz, the phase has a regular symmetrical deviation, the main phase aperture is 0, the deviation aperture is pi / 15, i.e. 12°, and the five apertures are pi / 15, 0, 0, 0 and -pi / 15 respectively, which meets the requirements.

[0167] Reference Figure 54The frequency is 2450MHz, the phase is regularly symmetrically deviated, the main phase aperture is 0, the deviation aperture is pi / 9, that is, 20°, and the five apertures are pi / 9, 0, 0, 0, and -pi / 9 respectively. The consistency of the electric field intensity on the same width has begun to shift, although only slightly, which is slightly unsatisfactory.

[0168] Reference Figure 55 The frequency is 915MHz, the phase has an irregular deviation, the main phase aperture is 0, the deviation aperture is pi / 18, i.e. 10°, and the five apertures are pi / 18, 0, -pi / 18, pi / 18, and 0, which meets the requirements.

[0169] Reference Figure 56 The frequency is 915MHz, the phase has an irregular deviation, the main phase aperture is 0, the deviation aperture is pi / 15, i.e. 12°, and the five apertures are pi / 15, 0, 0, -pi / 15, and pi / 15, which meets the requirements.

[0170] Reference Figure 57 The frequency is 915MHz, the phase has a regular symmetrical deviation, the main phase aperture is 0, the deviation aperture is pi / 18, i.e. 10°, and the five apertures are pi / 18, 0, 0, 0 and -pi / 18 respectively, which meets the requirements.

[0171] Reference Figure 58 The frequency is 915MHz, the phase has a regular symmetrical deviation, the main phase aperture is 0, the deviation aperture is pi / 18, i.e. 10°, and the five apertures are 0, pi / 18, 0, -pi / 18, and 0 respectively, which meets the requirements.

[0172] Reference Figure 59 The frequency is 915MHz, the phase has a regular symmetrical deviation, the main phase aperture is 0, the deviation aperture is pi / 15, i.e. 12°, and the five apertures are pi / 15, 0, 0, 0 and -pi / 15 respectively, which meets the requirements.

[0173] The slot antennas 5 are distributed on the top or bottom surface of the wire-walking area. Each slot antenna 5 has the same frequency, center distance d, and center distance c.

[0174] The leakage aperture 9 is offset to one side along the width of the wire feeding zone, with an eccentricity P ≤ 0.025*λ^1.2. The eccentricity P is within... Figure 5This illustrates that if all slot antennas 5 are centered as a whole, and the aperture 9 is also centered on the narrow face of the slot antenna 5, with its center point being n, then the entire slot antenna 5 is shifted upwards, causing its center point to become m. The distance P between m and n is the eccentricity distance. Alternatively, if all slot antennas 5 are centered as a whole, but the aperture 9 is not centered on the narrow face of the slot antenna 5, the aperture 9 is shifted upwards, causing it to deviate from the center of the narrow face of the slot antenna 5.

[0175] Frequency 2450MHz, wavelength 122mm, eccentricity P≤8mm. Frequency 915MHz, wavelength 328mm, eccentricity P≤26mm.

[0176] Reference Figure 60 The frequency is 2450MHz and the eccentricity is 5mm, which meets the requirements.

[0177] Reference Figure 61 The frequency is 2450MHz and the eccentricity is 8mm, which meets the requirements.

[0178] Reference Figure 62 With a frequency of 2450MHz and an eccentricity of 9mm, the consistency of the electric field strength on the same width has begun to shift, which does not meet the requirements.

[0179] Reference Figure 63 The frequency is 2450MHz and the eccentricity is 10mm, which does not meet the requirements.

[0180] Reference Figure 64 The frequency is 915MHz and the eccentricity is 10mm, which meets the requirements.

[0181] Reference Figure 65 The frequency is 915MHz and the eccentricity is 20mm, which meets the requirements.

[0182] Reference Figure 66 The frequency is 915MHz and the eccentricity is 26mm, which meets the requirements.

[0183] Figures 60-66 All of these cases involve the leakage aperture 9 being centered on the narrow surface of the slot antenna 5.

[0184] Reference Figure 67 The frequency is 2450MHz and the eccentricity is 5mm, which meets the requirements.

[0185] Reference Figure 68 The frequency is 2450MHz and the eccentricity is 8mm, which meets the requirements.

[0186] Reference Figure 69 The frequency is 2450MHz and the eccentricity is 10mm, which does not meet the requirements.

[0187] Reference Figure 70 The frequency is 915MHz and the eccentricity is 10mm, which meets the requirements.

[0188] Reference Figure 71 The frequency is 915MHz and the eccentricity is 20mm, which meets the requirements.

[0189] Reference Figure 72 The frequency is 915MHz and the eccentricity is 26mm, which meets the requirements.

[0190] Reference Figure 73 With a frequency of 915MHz and an eccentricity of 30mm, the consistency of the electric field strength in the same column width has begun to deviate, which does not meet the requirements.

[0191] Figures 67-73 All of these cases involve the leakage aperture 9 being offset upwards on the narrow surface of the slot antenna 5.

[0192] The leakage apertures 9 are arranged in a matrix in the wire-feeding area. The minimum size of this matrix is ​​two columns, as shown in the reference. Figure 74 At a frequency of 915MHz, the leakage aperture 9 has two rows, which meets the requirements. (Refer to...) Figure 75 At a frequency of 2450MHz, the leakage aperture 9 has two rows, which meets the requirements. (Refer to...) Figure 76 The frequency is 2450MHz, the wavelength is 122mm, and the entire matrix is ​​shifted 10mm to the left, which meets the requirements. (Refer to...) Figure 77 The frequency is 2450MHz, the wavelength is 122mm, and although it is missing one column, it is still a matrix and meets the requirements. (Refer to...) Figure 78 The frequency is 915MHz, the wavelength is 328mm, and the matrix is ​​shifted 20mm to the left, which meets the requirements. (Refer to...) Figure 79 The frequency is 915MHz and the wavelength is 328mm. It is missing one column, but it is still a matrix and meets the requirements.

[0193] Example 1

[0194] 12k polyacrylonitrile precursor fibers were tensioned at both ends and passed through a pre-oxidation furnace at a temperature of 220℃. The wind speed in the fiber-carrying zone was 3 m / s. A microwave heating device was in operation. Two rows of leakage apertures (9) were distributed on the top surface of the fiber-carrying zone. The frequency was 915 MHz, the center distance (d) was 300 mm, and the center distance (c) was 400 mm. The microwave input power of a single slot antenna (5) was 800 W. Phase consistency was ensured at the entrance of each slot antenna (5). The dwell time was 10 minutes. The fiber bundle was brown in color, and the bulk density of the prepared fiber was 1.243 g / cm³. 3 .

[0195] Comparative Example 1

[0196] 12k polyacrylonitrile precursor fibers were subjected to tension at both ends and passed through a pre-oxidation furnace at a temperature of 220℃. The air velocity in the fiber-carrying zone was 3m / s. Microwave heating was not used; only hot air heating was employed. The residence time was 10 minutes. The resulting fiber bundle was golden yellow in color, and the bulk density of the prepared fibers was 1.228g / cm³. 3 Compared to Example 1, the pre-oxidation degree of Comparative Example 1 was significantly insufficient, resulting in a golden-yellow color in the filament bundle. Therefore, using a microwave heating device can accelerate the pre-oxidation process and improve production efficiency.

[0197] Example 2

[0198] 12k polyacrylonitrile precursor fibers were tensioned at both ends and passed through a pre-oxidation furnace at 220℃. The wind speed in the fiber-carrying zone was 3m / s. A microwave heating device was in operation. Eight rows of leakage apertures (9) were distributed on the top surface of the fiber-carrying zone. The frequency was 915MHz, with a center distance d of 290mm and a center distance c of 400mm. The microwave input power of a single slot antenna (5) was 2000W, with a 5% asymmetry in positive and negative deviations to ensure phase consistency at the entrance of each slot antenna (5). The dwell time was 7 minutes. The fiber bundle was golden yellow, and the bulk density of the prepared fiber was 1.233g / cm³. 3 .

[0199] Comparative Example 2

[0200] 12k polyacrylonitrile precursor fibers were subjected to tension at both ends and passed through a pre-oxidation furnace at a temperature of 220℃. The air velocity in the fiber-carrying zone was 3m / s. Microwave heating was not used; only hot air heating was employed. The residence time was 10 minutes. The resulting fiber bundle was golden yellow, and the bulk density of the prepared fibers was 1.230 g / cm³. 3 Compared to Example 2, the time required for the filaments to turn golden yellow during the pre-oxidation process in Comparative Example 2 was longer than that in Example 2. Therefore, using a microwave heating device can reduce the pre-oxidation time, increase the speed of the production line, and improve production efficiency.

[0201] Example 3

[0202] 12k polyacrylonitrile precursor fibers were tensioned at both ends and passed through a pre-oxidation furnace at a temperature of 240℃. The wind speed in the fiber-carrying zone was 3 m / s. A microwave heating device was in operation. Ten rows of leakage apertures (9) were distributed on the top surface of the fiber-carrying zone. The frequency was 2450 MHz, the center distance (d) was 100 mm, and the center distance (c) was 160 mm. The microwave input power of a single slit antenna (5) was 1000 W. Phase consistency was ensured at the entrance of each slit antenna (5). The dwell time was 10 minutes. The fiber bundle was brownish-black, and the bulk density of the prepared fiber was 1.249 g / cm³. 3 .

[0203] Comparative Example 3

[0204] 12k polyacrylonitrile precursor fibers were tensioned at both ends and passed through a pre-oxidation furnace at room temperature without heating. The air velocity in the fiber-carrying zone was 3 m / s. A microwave heating device was in operation. Ten rows of perforations (9) were distributed on the top surface of the fiber-carrying zone. The frequency was 2450 MHz, the center distance (d) was 100 mm, and the center distance (c) was 160 mm. The microwave input power of a single slit antenna (5) was 1000 W. Phase consistency was ensured at the entrance of each slit antenna (5). The dwell time was 10 minutes. The fiber bundle color was predominantly white with a slight yellow tint. The bulk density of the prepared fibers was 1.206 g / cm³. 3 Compared to Example 3, the pre-oxidation process in Comparative Example 3 resulted in a predominantly white to slightly yellowish fiber bundle color, indicating that the effect of using only a microwave heating device without turning on the hot air is negligible in the pre-oxidation process.

[0205] Example 4

[0206] 12k polyacrylonitrile precursor fibers were tensioned at both ends and passed through a pre-oxidation furnace at a temperature of 230℃. The wind speed in the fiber-carrying zone was 3 m / s. A microwave heating device was in operation. Twelve rows of leakage apertures (9) were distributed on the top surface of the fiber-carrying zone. The frequency was 2450 MHz, the center distance (d) was 90 mm, and the center distance (c) was 140 mm. The microwave input power of a single slit antenna (5) was 1000 W. Phase consistency was ensured at the entrance of each slit antenna (5). The dwell time was 12 minutes. The fiber bundle was brownish-black, and the bulk density of the prepared fiber was 1.253 g / cm³. 3 .

[0207] Comparative Example 4

[0208] 12k polyacrylonitrile precursor fibers were subjected to tension at both ends and passed through a pre-oxidation furnace at a temperature of 240℃. The air velocity in the fiber-carrying zone was 3m / s, and the microwave heating device was not used. The residence time was 14 minutes. The fiber bundle was brownish-black in color, and the bulk density of the prepared fibers was 1.250g / cm³. 3 Compared to Example 4, Comparative Example 4 has a higher hot air temperature and a longer process time. Therefore, using a microwave heating device can significantly reduce the hot air temperature and energy consumption.

[0209] Example 5

[0210] 12k polyacrylonitrile precursor fibers were subjected to tension at both ends and pre-oxidized in five pre-oxidation furnaces at temperatures set at 220℃ / 230℃ / 240℃ / 250℃ / 260℃. The hot air velocity in the fiber-carrying zone was 2.5 m / s. A microwave heating device was activated. Eight rows of leakage apertures (9) were distributed on the top surface of the fiber-carrying zone at a frequency of 2450 MHz, with a center-to-center distance (d) of 90 mm and a center-to-center distance (c) of 160 mm. The microwave input power of a single slit antenna (5) was 1000 W, ensuring phase consistency at the entrance of each slit antenna (5). The dwell time in each pre-oxidation furnace was 7 minutes. The fiber bundle was black, and the bulk density of the prepared pre-oxidized fiber was 1.370 g / cm³. 3 .

[0211] Comparative Example 5

[0212] 12k polyacrylonitrile precursor fibers were subjected to tension at both ends and pre-oxidized in five pre-oxidation furnaces at temperatures set at 220℃ / 230℃ / 240℃ / 250℃ / 260℃. The hot air velocity in the fiber-carrying zone was 2.5 m / s. Microwave heating was not used; only hot air heating was employed. The residence time in each pre-oxidation furnace was 7 minutes. The resulting fiber bundle was black, and the bulk density of the prepared fiber was 1.342 g / cm³. 3 Compared to Example 5, Comparative Example 5 had insufficient pre-oxidation time and a lower bulk density. Therefore, using a microwave heating device can reduce the pre-oxidation time, increase the speed of the production line, and improve production efficiency.

[0213] Example 6

[0214] 12k polyacrylonitrile precursor fibers were subjected to tension at both ends and pre-oxidized in five pre-oxidation furnaces at temperatures set at 220℃ / 230℃ / 240℃ / 250℃ / 260℃ respectively. The hot air velocity in the fiber-carrying zone was 3.0 m / s. A microwave heating device was activated. Eight rows of leakage apertures (9) were distributed on the top surface of the fiber-carrying zone at a frequency of 915 MHz, with a center-to-center distance (d) of 280 mm and a center-to-center distance (c) of 360 mm. The microwave input power of a single slit antenna (5) was 2000 W, ensuring phase consistency at the entrance of each slit antenna (5). The dwell time in each pre-oxidation furnace was 10 minutes. The fiber bundle was black, and the bulk density of the prepared pre-oxidized fiber was 1.386 g / cm³. 3 .

[0215] Comparative Example 6

[0216] 12k polyacrylonitrile precursor fibers were subjected to tension at both ends and pre-oxidized in five pre-oxidation furnaces at temperatures set at 230℃ / 240℃ / 250℃ / 260℃ / 270℃. The hot air velocity in the fiber-carrying zone was 3.0 m / s. Microwave heating was not used; only hot air heating was employed. The residence time in each pre-oxidation furnace was 10 minutes. The resulting fiber bundle was black, and the bulk density of the prepared fiber was 1.370 g / cm³. 3Compared to Example 6, Comparative Example 6 has a higher hot air temperature, but the degree of pre-oxidation is significantly lower than that of Example 6. Therefore, using a microwave heating device can significantly reduce the hot air temperature and energy consumption.

[0217] Example 7

[0218] 12k polyacrylonitrile precursor fibers were subjected to tension at both ends and pre-oxidized in five pre-oxidation furnaces at temperatures set at 230℃ / 240℃ / 250℃ / 260℃ / 270℃. The hot air velocity in the fiber-carrying zone was 3.5 m / s. A microwave heating device was activated. Eight rows of leakage apertures (9) were distributed on the top surface of the fiber-carrying zone at a frequency of 915 MHz, with a center-to-center distance (d) of 300 mm and a center-to-center distance (c) of 420 mm. The microwave input power of a single slit antenna (5) was 2500 W, ensuring phase consistency at the entrance of each slit antenna. The dwell time in each pre-oxidation furnace was 8 minutes. The fiber bundle was black, and the bulk density of the prepared pre-oxidized fiber was 1.379 g / cm³. 3 .

[0219] Comparative Example 7

[0220] 12k polyacrylonitrile precursor fibers were subjected to tension at both ends and pre-oxidized in five pre-oxidation furnaces at temperatures set at 235℃ / 245℃ / 255℃ / 265℃ / 275℃. The hot air velocity in the fiber-carrying zone was 3.5 m / s. Microwave heating was not used; only hot air heating was employed. The residence time in each pre-oxidation furnace was 12 minutes. The resulting fiber bundle was black, and the bulk density of the prepared fiber was 1.378 g / cm³. 3 Compared to Example 7, Comparative Example 7 has a higher hot air temperature and a longer process time. Therefore, using a microwave heating device can significantly reduce the hot air temperature and energy consumption.

[0221] As can be seen from the examples and comparative examples, the pre-oxidation furnace of this application has a significant strengthening effect compared with hot air pre-oxidation and microwave pre-oxidation alone. In the process of preparing polyacrylonitrile pre-oxidized fibers, it can reduce the pre-oxidation time and reduce the production cost of carbon fiber pre-oxidation process, which has important application value for the actual production process of carbon fiber.

[0222] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A microwave hot air hybrid heating pre-oxidation furnace employing a slotted antenna, characterized in that, The system includes a furnace body (3), a heater (2) for heating gas, a fan (1) for conveying gas, and a microwave heating device. A wire-feeding zone is formed inside the furnace body (3). The length of the wire-feeding zone is L, and the width is W. The furnace body (3) includes an air inlet (31), an air outlet (32), a wire bundle inlet (33), and a wire bundle outlet (34). The wire-feeding zone is located between the wire bundle inlet (33) and the wire bundle outlet (34) and connects the wire bundle inlet (33) and the wire bundle outlet (34). The wire-feeding zone is also located between the air inlet (31) and the air outlet (32) and connects to the air inlet (31). The fan (1) delivers gas from the air inlet (31) and exhaust vent (32). The microwave heating device includes a microwave source (6) and a slot antenna (5). There are multiple slot antennas (5). Each slot antenna (5) is connected to the microwave source (6). One of the narrow faces of each slot antenna (5) is provided with a leakage hole (9). The narrow faces of the slot antennas (5) are distributed on the top or bottom surface of the wire-running area. The leakage holes (9) are distributed along the length direction of the narrow face. The leakage holes (9) of multiple slot antennas (5) are arranged in a matrix in the wire-running area.

2. The microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 1, characterized in that, The center distance d between the leakage holes (9) in the width direction of the wire feeding area satisfies d≤0.405*λ^1.147, where λ is the microwave wavelength.

3. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 1, characterized in that, The number of slot antennas (5) is n = floor(W / d), where d is the center distance between the leakage holes (9) in the width direction of the wire-feeding area.

4. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 1, characterized in that, The microwave source (6) has a frequency of 915MHz or 2450MHz. The wavelength λ corresponding to the frequency of 915MHz is 328mm, and the wavelength λ corresponding to the frequency of 2450MHz is 122mm.

5. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 4, characterized in that, The frequency is 2450MHz. When the microwave input power deviation of each slit antenna (5) is asymmetrical, it is less than or equal to 15%. When the microwave input power deviation of each slit antenna (5) is symmetrical, it is less than or equal to 20%. The frequency is 915MHz. When the microwave input power deviation of each slit antenna (5) is asymmetrical, it is less than or equal to 25%. When the microwave input power deviation of each slit antenna (5) is symmetrical, it is less than or equal to 30%.

6. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 1, characterized in that, The phase deviation value fed into each slot antenna (5) is less than or equal to pi / 15 or differs by 2n*pi on this basis.

7. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 1, characterized in that, Each slot antenna (5) has the same frequency, the same center distance d, and the same center distance c. The center distance d is the center distance between the leakage holes (9) in the width direction of the wire-walking area, and the center distance c is the center distance between the leakage holes (9) in the length direction of the wire-walking area.

8. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 1, characterized in that, The center distance c between the leakage holes (9) along the length of the wire-feeding area satisfies 0.15λ≤c≤2λ, where λ is the microwave wavelength.

9. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 1, characterized in that, The leakage aperture (9) is offset to one side in the width direction of the wire feeding area, and its eccentricity distance P≤0.025*λ^1.2, where λ is the microwave wavelength.

10. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 9, characterized in that, The ripple hole (9) is centered on the narrow face of the slot antenna (5). The slot antenna (5) as a whole is shifted in the width direction of the wire-feeding area, which causes the ripple hole (9) to shift as a whole towards one side of the width direction of the wire-feeding area. Alternatively, the slot antenna (5) may be centered in the width direction of the wire-feeding area, but the ripple hole (9) may not be centered in the narrow face of the slot antenna (5), thus causing the ripple hole (9) to shift to one side of the width direction of the wire-feeding area.

11. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 1, characterized in that, The furnace body (3) has a feed port (4) on the top or bottom surface of the wire feeding zone. The feed port (4) corresponds one-to-one with the leakage hole (9) and the two have the same shape and size.

12. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 1, characterized in that, The shape of the ripple hole (9) is circular, waist-shaped, elliptical, or rectangular.

13. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 12, characterized in that, The elliptical, waist-shaped, and rectangular slit holes (9) are tilted as a whole on the narrow surface of the slot antenna (5) at an angle of less than or equal to 2°.

14. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 12, characterized in that, Elliptical, waist-shaped, and rectangular slit holes (9) are symmetrically and alternately arranged on the narrow surface of the slot antenna (5) at an angle of less than or equal to 1°.

15. A microwave hot air hybrid heating pre-oxidation furnace employing a slotted antenna according to claim 12, characterized in that, The diameter of the circular ripple hole (9) is greater than or equal to 0.07*λ and less than or equal to 0.33*λ, where λ is the microwave wavelength.

16. A microwave hot air hybrid heating pre-oxidation furnace employing a slotted antenna according to claim 12, characterized in that, The long side of the rectangular ripple hole (9) is greater than or equal to 0.2*λ and less than or equal to 0.75*λ, and the short side is greater than or equal to 0.006*λ and less than or equal to 0.366*λ. The long side of the ripple hole (9) is defined as the side parallel to the length direction of the wire feeding area, and the short side is defined as the side parallel to the width direction of the wire feeding area. The major axis of the elliptical ripple hole (9) is greater than or equal to 0.2*λ and less than or equal to 0.75*λ, and the minor axis is greater than or equal to 0.006*λ and less than or equal to 0.366*λ. The distance between the midpoints of the two arcs of the waist-shaped ripple hole (9) is greater than or equal to 0.2*λ and less than or equal to 0.75*λ, and the distance between the two parallel planes is greater than or equal to 0.006*λ and less than or equal to 0.366*λ, where λ is the microwave wavelength.

17. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 1, characterized in that, The two ends of the wire feeding area along its length are defined by a perforated plate (7), and the distance between the two perforated plates (7) at both ends of the wire feeding area is L. The perforated plate (7) is provided with through holes (71) that pass through both ends.

18. A microwave hot air hybrid heating pre-oxidation furnace employing a slotted antenna according to claim 17, characterized in that, The perforated plate (7) has at least two perforated plates at each end of the wire feeding zone along its length, and the through holes (71) of the multiple perforated plates (7) at the same end are arranged in a staggered manner.

19. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 18, characterized in that, The diameter of the through hole (71) is less than or equal to 0.25*λ, and the spacing between multiple mesh plates (7) at the same end is less than or equal to λ, where λ is the microwave wavelength.

20. A microwave hot air hybrid heating pre-oxidation furnace using a slotted antenna according to claim 11, characterized in that, A wave-transparent plate (8) is provided at the connection between the slot antenna (5) and the feed port (4). The wave-transparent plate (8) is made of fused silica, high-purity alumina, hexagonal boron nitride, or silicon nitride.

Images