Sintering system based on powder rod plasma polarization and process thereof

Abstract

This invention discloses a sintering system and process based on plasma polarization of powder rods. The sintering system includes a transparent sealed cavity, a resonant cavity surrounding the transparent sealed cavity, and a high-frequency electromagnetic field supply system connected to the resonant cavity. The transparent sealed cavity is an uncoated transparent sealed cavity, and it is equipped with an air inlet and an air outlet. The sintering system based on plasma polarization of powder rods proposed in this invention, by employing a high-frequency electromagnetic field supply system for sintering the powder rods, significantly improves production efficiency compared to existing electric heating methods. Furthermore, it effectively avoids the problems of pre-densification and vitrification of the outer layer. This homogenized sintering method greatly reduces the problems of inner layer melt residue and bubbles during the vitrification process. Simultaneously, this sintering system also has the advantages of simple structure, stable operation, and ease of implementation.

Description

Technical Field

[0001] This invention relates to the field of preform manufacturing technology, and in particular to a sintering system and process based on powder rod plasma polarization. Background Technology

[0002] Preform manufacturing is the most cutting-edge and core technology in the entire optical fiber industry. Among them, the VAD (Vacuum Arc Degassing) process has high production efficiency, simple production control, low cost, and is conducive to large-scale production. It is currently the mainstream process route in the market.

[0003] Sintering is a crucial step in the VAD (Vacuum-Insulated Diameter) process, vital for improving production efficiency and process control. Currently, common sintering processes often use resistance furnaces or high-frequency induction furnaces for heating the transparent, sealed cavity. Because the silicon powder rod itself is made of porous silicon powder with very poor thermal conductivity, the temperature typically decreases gradually from the outer wall inwards, resulting in low heating efficiency. Furthermore, the heating process consumes helium resources, and existing technologies often suffer from uneven thermal distribution, leading to unstable process performance and impacting manufacturing efficiency and cost. Summary of the Invention

[0004] The main objective of this invention is to provide a sintering system and process based on powder rod plasma polarization, which aims to improve the heating efficiency of preform sintering and enhance the uniformity of internal heating.

[0005] This invention proposes a sintering system based on powder rod plasma polarization, comprising a lifting and rotating mechanism, a transparent sealed cavity, a resonant cavity, and a high-frequency electromagnetic field supply system, wherein...

[0006] The transparent sealed cavity is provided with an air inlet and an air outlet. The upper end of the transparent sealed cavity is provided with an opening for inserting a powder rod. A lifting and rotating mechanism is used to connect with the powder rod to drive it to rotate and move up and down in the transparent sealed cavity. A sealing device is installed on the opening to seal the end of the lifting and rotating mechanism inserted into the transparent sealed cavity. A resonant cavity is fitted outside the transparent sealed cavity to heat the powder rod inside. A high-frequency electromagnetic field supply system is connected to the resonant cavity.

[0007] Preferably, the high-frequency electromagnetic field supply system includes a waveguide and an antenna connected thereto, and the frequency of the electromagnetic waves supplied by the high-frequency electromagnetic field supply system exceeds 2450MHz.

[0008] Preferably, the transparent sealed cavity is made of a muffle tube.

[0009] The resonant cavity is a cylindrical resonant cavity, with a transparent, sealed cavity body aligned with the axis of the resonant cavity.

[0010] Preferably, the transparent sealed cavity is aligned with the axis of the resonant cavity.

[0011] Preferably, the height of the resonant cavity is 200mm~300mm.

[0012] This invention further proposes a sintering process based on the above-mentioned powder rod plasma polarization sintering system, comprising the following steps:

[0013] Place the powder stick inside a transparent, sealed cavity, and introduce gas into the cavity to pre-impregnate the powder stick.

[0014] Start the high-frequency electromagnetic field supply system and adjust the gas flow rate inside the transparent sealed cavity tube;

[0015] The powder rod is controlled to enter the corresponding internal space of the resonant cavity by a lifting and rotating mechanism, thereby performing step sintering of the powder rod.

[0016] Preferably, when the powder rod is placed inside a transparent sealed cavity and gas is introduced into the transparent sealed cavity for pre-impregnation treatment of the powder rod, the pressure inside the transparent sealed cavity is -100Pa to -300Pa, and the introduced gas is chlorine, helium, oxygen, or argon. When the introduced gas is chlorine, its flow rate is 50 to 200 sccm; when the introduced gas is helium, its flow rate is 0 to 2 slm; when the introduced gas is oxygen, its flow rate is 50 to 200 sccm; and when the introduced gas is argon, its flow rate is 1 to 2 slm. The pre-impregnation treatment time is 3 to 5 hours.

[0017] Preferably, when starting the high-frequency electromagnetic field supply system, the power of the antenna of the high-frequency electromagnetic field supply system is set to 4kW~15kW and the frequency is set to 2.4GHz~2.6GHz.

[0018] Preferably, when the powder rod is controlled to enter the internal space corresponding to the resonant cavity by the lifting and rotating mechanism, the stepping speed of the powder rod is 3mm / min to 6mm / min, and the rotation speed of the powder rod is 1rpm to 2rpm.

[0019] Preferably, after starting the high-frequency electromagnetic field supply system, the gas flow rate inside the transparent sealed cavity tube is reduced.

[0020] The sintering system based on powder rod plasma polarization proposed in this invention has the following beneficial effects:

[0021] 1. In cases using conventional electric heating equipment, the surface of the VAD powder rod is closest to the heat source and therefore often experiences the highest temperature, leading to densification and vitrification first. This results in insufficient vitrification of the inner layer, resulting in melt residue or bubbles. Using a high-frequency electromagnetic field supply system (in existing technologies, resonant cavities are used in the deposition process; this application is the first to propose its use in the sintering process) effectively avoids the problem of the outer layer densifying and vitrifying first. This homogenized sintering method significantly reduces the problems of melt residue and bubbles in the inner layer during the vitrification process.

[0022] 2. The plasma heat source can ensure that the inner and outer layers of the powder rod have basically the same temperature. At the same time, by adjusting the power of the high-frequency electromagnetic field, the residual gas in the loose body of the powder rod can be fully ionized, and the overall diffusion rate of the residual gas will be significantly improved. When the power is adjusted to the appropriate conditions, only a small amount of helium or zero helium is needed to finally achieve a transparent and bubble-free sintering result.

[0023] 3. Compared with electric heating equipment, plasma heat source has a faster and more uniform heating speed. The inside and outside of powder rod 3 can reach more than 1600°C simultaneously and quickly. Therefore, the speed of the vitrification process is increased by 60% compared with ordinary electric heating equipment, which greatly improves production efficiency.

[0024] 4. This sintering system also has the advantages of simple structure, stable operation and easy implementation. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a preferred embodiment of the sintering system based on powder rod plasma polarization of the present invention.

[0026] In the diagram, 1-transparent sealed cavity, 11-air inlet, 12-exhaust outlet, 13-sealing device, 2-resonant cavity, 3-powder rod, 4-lifting and rotating mechanism, 5-high frequency electromagnetic field supply system.

[0027] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0028] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0029] It should be noted that in the description of this invention, the terms "lateral," "longitudinal," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] This invention proposes a sintering system based on powder rod plasma polarization.

[0031] Reference Figure 1 In this preferred embodiment, a sintering system based on powder rod plasma polarization includes a lifting and rotating mechanism 4, a transparent sealed cavity 1, a resonant cavity 2, and a high-frequency electromagnetic field supply system, wherein...

[0032] The transparent sealed cavity 1 is provided with an air inlet 11 and an air outlet 12. The upper end of the transparent sealed cavity 1 is provided with an opening for inserting the powder rod 3. The lifting and rotating mechanism 4 is used to connect with the powder rod 3 to drive it to rotate and move up and down inside the transparent sealed cavity 1. A sealing device 13 is installed on the opening to seal the end of the lifting and rotating mechanism 4 inserted into the transparent sealed cavity 1. The resonant cavity 2 is fitted outside the transparent sealed cavity 1 to heat the powder rod 3 inside. The high-frequency electromagnetic field supply system is connected to the resonant cavity 2 (the high frequency of the high-frequency electromagnetic field supply system refers to the electromagnetic wave frequency exceeding 2450MHz).

[0033] The air inlet 11 is connected to a gas supply system, and the air outlet 12 is connected to a sintering exhaust system.

[0034] The transparent sealed cavity is made of a muffle tube. When using the high-frequency electromagnetic field supply system technology, heat is only generated in the ionized process gas area. No heat is generated in the tube wall and material of the transparent sealed cavity 1. Therefore, the temperature of the transparent sealed cavity 1 can be as low as below 1000℃. At this temperature, the transparent sealed cavity 1 made of glass will not experience high-temperature deformation or cracking. There is no need to use the muffle tube with the current coating technology. Conventional glass muffle tubes can meet the requirements.

[0035] Specifically, in this embodiment, the high-frequency electromagnetic field supply system includes a waveguide and an antenna connected to it. The antenna can be based on a common copper sheet resonant antenna. The waveguide introduces the high-frequency electromagnetic waves generated by the external antenna, generally exceeding 2450MHz, into the transparent sealed cavity 1. Since the transparent sealed cavity 1 is generally under low pressure, under the action of the high-frequency strong electromagnetic field, the powder rod 3 inside the transparent sealed cavity 1 is ionized by the process gas impregnated, forming a plasma-polarized powder rod 3. The overall maximum temperature of the powder rod 3 can reach 2000℃, thereby heating the silicon powder particles and ultimately completing the densification and glassization of the powder rod 3.

[0036] In this embodiment, the resonant cavity 2 is a cylindrical resonant cavity. The transparent sealed cavity 1 is aligned with the axis of the resonant cavity 2. The height of the resonant cavity 2 is 200mm~300mm.

[0037] The working process of this sintering system is as follows.

[0038] Step 1: Pre-dyeing treatment

[0039] The deposited powder rods, with outer diameters ranging from 150mm to 350mm and lengths from 400mm to 2500mm, are designed to be compatible with the dimensions of the transparent sealed cavity 1. The powder rod manufacturing process is not limited to VAD deposition. The bottom of the transparent sealed cavity 1 is purged with the desired process gas, including but not limited to chlorine, helium, oxygen, and argon. The pressure inside the transparent sealed cavity 1 is appropriately controlled at a slightly negative pressure, between -100pa and -300pa, to improve the impregnation effect. The process gas filling and impregnation time can be adjusted appropriately based on the powder rod dimensions. Generally, for powder rods with an outer diameter of 200mm and a length of approximately 1800mm, the time is controlled at 4 hours. For longer powder rods with larger outer diameters, the impregnation time can be appropriately extended. To ensure relatively uniform impregnation, the powder rod is rotated at a speed of 1-2 rpm.

[0040] Step 2: Activate the plasma resonant cavity 2

[0041] After the process gas impregnation of the rod is completed, the process gas flow rate can be appropriately reduced, and the pressure inside the transparent sealed cavity 1 is maintained at -100pa~-300pa. The plasma resonant cavity 2 is activated, and the antenna power is set at 4kW~15kW and the frequency is set at 2.49GHz. Generally, the larger the size of the powder rod 3, the higher the power required. The high-intensity electromagnetic field enters the resonant cavity 2 along the waveguide, penetrates the transparent sealed cavity 1, and enters the interior of the powder. The process gas impregnated inside the powder is polarized and ionized under the action of the high-intensity electromagnetic field, forming high-speed oscillating ions and electrons. This polarized gaseous substance containing high-speed oscillating electrons and ions is plasma. After these high-speed oscillating ions and electrons collide inside the powder, a large amount of energy is generated, and the local temperature can reach 2000℃.

[0042] After the high-temperature plasma is formed, the powder rod 3 begins to gradually shrink and soften, gradually vitrifying from a powder particle state to a transparent state.

[0043] Step 3: Control the powder rod to sinter in 3 steps until completion.

[0044] The powder rod 3 is controlled to pass through the resonant cavity 2 at a suitable stepping speed to complete the heating. The specific speed is about 3mm~6mm / min. At the same time, the powder rod 3 is kept rotating, and the speed can be set to 1~2 rpm. The powder rod 3 is controlled to pass through the plasma resonant cavity 2 from top to bottom through the lifting and rotating mechanism 4 to complete the overall glass sintering. The thicker the powder rod 3, the slower the stepping speed. Generally, it can be set according to the weight stepped per minute of 0.1~1kg. When the powder rod 3 steps to the end position, the power supply of the antenna of the resonant cavity 2 can be turned off. At this time, the process gas inlet can be turned off, nitrogen gas is added to maintain the negative pressure in the tube for replacement, and the sintered transparent glass rod is taken out of the transparent sealed cavity 1 and enters the next process.

[0045] Table 1 Sintering results of conventional electric heating equipment

[0046]

[0047] The specific structure after sintering using this sintering system is shown in Table 2 below.

[0048] Table 2 Sintering results of this sintering system

[0049]

[0050] A comparison of Tables 1 and 2 shows that using this sintering system can improve the sintering quality of the preforms while reducing gas consumption.

[0051] The sintering system based on powder rod plasma polarization proposed in this invention has the following beneficial effects:

[0052] 1. In cases using conventional electric heating equipment, the surface layer of the VAD powder rod 3 is closest to the heat source and therefore often experiences the highest temperature, leading to densification and vitrification first. This results in insufficient vitrification of the inner layer, resulting in melt residue or bubbles. Using a high-frequency electromagnetic field supply system (in existing technologies, resonant cavities are used in deposition processes; this application is the first to propose its use in sintering processes) effectively avoids the problem of the outer layer densifying and vitrifying first. This homogenized sintering method significantly reduces the problems of melt residue and bubbles in the inner layer during the vitrification process.

[0053] 2. The plasma heat source can ensure that the inner and outer temperatures of the powder rod 3 are basically the same. At the same time, by adjusting the power of the high-frequency electromagnetic field, the residual gas in the loose body of the powder rod 3 can be fully ionized, and the overall diffusion rate of the residual gas will be significantly improved. When the power is adjusted to the appropriate conditions, only a small amount of helium or zero helium is needed to finally achieve a transparent and bubble-free sintering result.

[0054] 3. Compared with electric heating equipment, plasma heat source has a faster and more uniform heating speed. The inside and outside of powder rod 3 can reach more than 1600°C simultaneously and quickly. Therefore, the speed of the vitrification process is increased by 60% compared with ordinary electric heating equipment, which greatly improves production efficiency.

[0055] 4. This sintering system also has the advantages of simple structure, stable operation and easy implementation.

[0056] The present invention further proposes a sintering process based on powder rod plasma polarization.

[0057] In this preferred embodiment, a sintering process based on the above-described powder rod plasma polarization sintering system includes the following steps:

[0058] Step S10: Place the powder rod 3 inside the transparent sealed cavity 1, and introduce gas into the transparent sealed cavity 1 to pre-impregnate the powder rod 3.

[0059] Step S20: Start the high-frequency electromagnetic field supply system and adjust the gas flow rate inside the transparent sealed cavity 1 tube;

[0060] In step S30, the powder rod 3 is controlled to enter the internal space corresponding to the resonant cavity 2 by the lifting and rotating mechanism 4, thereby performing step sintering on the powder rod 3.

[0061] In step S10, the powder rod 3 is placed inside the transparent sealed cavity 1. When the transparent sealed cavity 1 is purged with gas to pre-impregnate the powder rod 3, the pressure inside the transparent sealed cavity 1 is -100Pa to -300Pa. The gas purged is chlorine, helium, oxygen, or argon. When the gas purged is chlorine, its flow rate is 50 to 200 sccm; when the gas purged is helium, its flow rate is 0 to 2 slm; when the gas purged is oxygen, its flow rate is 50 to 200 sccm; and when the gas purged is argon, its flow rate is 1 to 2 slm. The pre-impregnation treatment time is 3 to 5 hours.

[0062] In this sintering process, by pre-impregnation, the powder rod 3 is impregnated in the process gas environment for 3 to 5 hours, thereby fully diffusing the process gas into the interior of the powder. After entering the high-frequency electromagnetic field resonance region, the process gas inside the powder rod 3 is ionized, and the temperature distribution of the inner and outer layers of the powder rod 3 is nearly uniform, effectively avoiding the problem of the outer layer becoming dense and vitrified first. This homogenization sintering method greatly reduces the problems of inner layer melting residue and bubbles in the vitrification process.

[0063] In step S20, when starting the high-frequency electromagnetic field supply system, the antenna power of the high-frequency electromagnetic field supply system is set to 4kW~15kW, and the frequency is set to 2.4GHz~2.6GHz. The larger the size of the powder rod, the higher the power required.

[0064] After starting the high-frequency electromagnetic field supply system, reduce the gas flow rate inside the transparent sealed cavity tube 1. Specifically, set the chlorine flow rate to 30 sccm~100 sccm, the helium flow rate to 0~1 slm, the oxygen flow rate to 30 sccm~100 sccm, and the argon flow rate to 0.5 slm~1 slm.

[0065] In step S30, when the powder rod 3 is controlled to enter the internal space corresponding to the resonant cavity 2 by the lifting and rotating mechanism 4, the stepping speed of the powder rod 3 is 3mm / min~6mm / min, and the rotation speed of the powder rod 3 is 1rpm~2rpm.

[0066] The sintering process proposed in this invention involves the powder rod 3 being driven by a stepper motor to gradually pass through a high-frequency electromagnetic field region at a predetermined speed. Under the set electromagnetic wave power, the process gas inside the powder rod 3 is gradually ionized to form a plasma polarization heat source. When the heat source temperature reaches above 1450°C, the powder rod 3 gradually densifies and vitrifies, ultimately completing the sintering process. This significantly improves production efficiency and effectively avoids the problem of the outer layer densifying and vitrifying first. This homogenized sintering method greatly reduces the problems of inner layer melting residue and bubbles during the vitrification process.

[0067] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A sintering system based on powder rod plasma polarization, characterized in that, It includes a lifting and rotating mechanism, a transparent sealed cavity, a resonant cavity, and a high-frequency electromagnetic field supply system, among which, The transparent sealed cavity is provided with an air inlet and an air outlet. An opening for inserting a powder rod is provided at the upper end of the transparent sealed cavity. A lifting and rotating mechanism is connected to the powder rod to drive its rotation and vertical movement within the transparent sealed cavity. A sealing device is installed on the opening to seal the end of the lifting and rotating mechanism inserted into the transparent sealed cavity. A resonant cavity is fitted outside the transparent sealed cavity to heat the powder rod inside. A high-frequency electromagnetic field supply system is connected to the resonant cavity. The high-frequency electromagnetic field supply system includes a waveguide and an antenna connected to it. The electromagnetic wave frequency supplied by the high-frequency electromagnetic field supply system exceeds 2450MHz. The resonant cavity is a cylindrical resonant cavity, and the axis of the transparent sealed cavity is flush with the axis of the resonant cavity.

2. The sintering system based on powder rod plasma polarization as described in claim 1, characterized in that, The transparent, sealed cavity is made of muffle tube.

3. The sintering system based on powder rod plasma polarization as described in claim 1, characterized in that, The height of the resonant cavity is 200mm~300mm.

4. A sintering process based on the powder-rod plasma polarization sintering system according to any one of claims 1 to 3, characterized in that, Includes the following steps: Place the powder stick inside a transparent, sealed cavity, and introduce gas into the cavity to pre-impregnate the powder stick. Start the high-frequency electromagnetic field supply system and adjust the gas flow rate inside the transparent sealed cavity tube; The powder rod is controlled to enter the corresponding internal space of the resonant cavity by a lifting and rotating mechanism, thereby performing step sintering of the powder rod.

5. The sintering process as described in claim 4, characterized in that, When pre-impregnating the powder rod by purging it into a transparent, sealed cavity with gas, the pressure inside the cavity is -100Pa to -300Pa. The gas used is chlorine, helium, oxygen, or argon. The flow rate is 50 to 200 sccm when chlorine is used, 0 to 2 slm when helium is used, 50 to 200 sccm when oxygen is used, and 1 to 2 slm when argon is used. The pre-impregnation time is 3 to 5 hours.

6. The sintering process as described in claim 4, characterized in that, When starting the high-frequency electromagnetic field supply system, the power of the antenna of the high-frequency electromagnetic field supply system is set to 4kW~15kW.

7. The sintering process as described in claim 4, characterized in that, When the powder rod is controlled to enter the corresponding internal space of the resonant cavity by the lifting and rotating mechanism, the stepping speed of the powder rod is 3mm / min~6mm / min, and the rotation speed of the powder rod is 1rpm~2rpm.

8. The sintering process as described in claim 4, characterized in that, After starting the high-frequency electromagnetic field supply system, reduce the gas flow rate inside the transparent sealed cavity tube.

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