Helium-free sintering device for low-water-peak optical fiber preform

Abstract

The utility model discloses a low water peak optical fiber preform rod helium-free sintering device which comprises a main furnace body and an exhaust pipeline system, the main furnace body comprises a loading cavity and an interlayer cavity outside the loading cavity, an optical fiber preform rod for production is arranged in the loading cavity, and a heating device for heating the optical fiber preform rod is arranged in the interlayer cavity. The pressure of the loading cavity is larger than that of the interlayer cavity, and the loading cavity and the interlayer cavity are both communicated with the exhaust pipeline system. The helium-free sintering device for the low-water-peak optical fiber preform, provided by the utility model, is simple in overall structure and convenient to use, can be used for efficiently completing the technological processes of dehydroxylation, degassing vitrification and pressurized rod taking, and can be used for obtaining a low-OH <-> cladding in a relatively shorter time, so that the production and manufacturing cycle and cost are greatly reduced, and the production efficiency is improved. The problem that the cleanliness of the cavity of the optical fiber preform sintering equipment is gradually deteriorated along with the increase of the service time is fundamentally solved, and meanwhile the problem that the dehydroxylation efficiency is low in the technical field of helium-free sintering is solved.

Description

Technical Field

[0001] The utility model belongs to the technical field of optical fiber communication, and particularly relates to a helium-free sintering device for a low-water-peak optical fiber preform. Background Art

[0002] In the field of sintering for manufacturing optical fiber preforms, sintering equipment is mainly divided into atmospheric-pressure and negative-pressure sintering equipment. The furnace body structure of both is basically that a sintering product container is arranged in the middle, heating components are installed around the sintering product container, heat insulation and thermal insulation devices are installed around the heating components, and corresponding contact or non-contact temperature measurement components are equipped. The heating method is mainly electric heating, and the heating components usually adopt graphite heating, induction heating, and plasma heating. Among them, graphite heating is the most used. Induction heating and plasma heating methods are used relatively less due to cost problems and current technical problems. However, there are the following defects in using graphite heating:

[0003] Most of the heat insulation materials of the sintering equipment adopt graphite materials. The heat insulation performance of graphite materials is excellent. However, as the use time increases, the graphite materials will gradually powder due to oxidation, resulting in an increase in graphite dust in the furnace, which not only affects the product quality, but also seriously may cause equipment short circuit and damage problems, seriously affecting the product quality and equipment stability.

[0004] In order to alleviate the above problems, a Chinese patent with the publication number CN211497392U and the patent name of a low-helium antioxidant device for a preform sintering furnace discloses that an inert gas input pipe and a helium input pipe are respectively arranged at the bottom left and top of the sintering furnace wall. The helium input pipe is connected to the left side of the furnace core tube. There are several branches with control valves on the connecting pipe, and the connecting pipe is respectively connected to the bottom of the preparation chamber, the top and bottom of the right side of the furnace core tube, and the right side of the sintering furnace wall. The connecting pipe is connected to a vacuum pump, and a gas flow field flowing from the bottom to the top is formed in the area between the inner wall of the sintering furnace wall and the outside of the graphite heat insulation part through vacuum suction. The lower end of the preparation chamber is connected to the upper end of the furnace core tube, and an isolation valve is arranged at the connection. It has the advantages of low helium consumption, high helium utilization rate, and the flow field can effectively isolate air to prevent oxidation of graphite parts and improve the service life of the equipment. However, the above patent only solves the problem of graphite part oxidation, cannot achieve helium-free sintering, and does not meet the requirements for producing low-water-peak optical fiber preforms.

[0005] In the field of optical fiber preform sintering, due to the shortage of helium energy, the unit price of helium continues to rise, resulting in a substantial increase in the manufacturing cost of optical fiber preforms. Therefore, helium-free sintering is a problem that must be overcome in the current field of optical fiber preform sintering. A Chinese utility model patent with the publication number CN114014532A and the patent name of a low-helium sintering device for the powder sintering process of an optical fiber preform discloses reducing the helium consumption of atmospheric-pressure sintering by improving the airtightness of the device, but this patent cannot fundamentally solve the problem of using helium.

[0006] Chinese utility model patent, with the publication number CN101781087A and the patent name of an integrated sintering and degassing device and method for a loose body optical fiber preform, discloses introducing chlorine gas in the dehydroxylation stage and introducing helium gas and deuterium gas in the vitrification stage. However, this patent cannot achieve helium-free sintering, cannot control the dehydroxylation pressure level, and has low dehydroxylation efficiency. At the same time, the above patent discloses that dehydroxylation needs to be preferentially carried out at a temperature of 1100°C to 1150°C. However, due to the height limitation of the temperature zone of the sintering device itself, it is necessary to carry out dehydroxylation while feeding the preform through a rod feeding mechanism. Since the residence time of the optical fiber preform in the chlorine gas atmosphere varies significantly, the chlorine content in the cladding varies greatly, resulting in a higher chlorine content at the rod tail than at the upper part. The above patent also discloses that it is necessary to raise the temperature during the vitrification process, control the evacuation pressure at 400 mbar to 500 mbar, and gradually control the rod feeding mechanism to lift to gradually complete the vitrification of the entire optical rod, which requires high furnace tube strength and has potential safety hazards. The above patent also discloses the use of a carbon furnace core tube, which has an oxidation problem as the service life extends. There is a trace amount of oxygen in the loose body during dehydroxylation and degassing, resulting in the gradual deterioration of the internal cleanliness of the furnace tube as the service life extends, and ultimately leading to poor product quality.

[0007] Therefore, achieving helium savings while taking into account the dehydroxylation efficiency of the cladding is a key issue urgently needed to be solved in the industry. Summary of the Utility Model

[0008] In order to solve the technical problems existing in the prior art, the purpose of the present utility model is to provide a helium-free sintering device for a low water peak optical fiber preform.

[0009] To achieve the above purpose and reach the above technical effects, the technical solution adopted by the present utility model is as follows:

[0010] A helium-free sintering device for a low water peak optical fiber preform, comprising a main furnace body and an exhaust air pipeline system. The main furnace body includes a loading cavity and an interlayer cavity outside it. A production optical fiber preform is arranged in the loading cavity, and a heating device for heating the optical fiber preform is arranged in the interlayer cavity. The pressure in the loading cavity is greater than the pressure in the interlayer cavity and the two are independent of each other. Both the loading cavity and the interlayer cavity are connected to the exhaust air pipeline system.

[0011] Further, the exhaust air pipeline system includes an exhaust pipe, an interlayer cavity air pipe, and a loading cavity air pipe. One end of the exhaust pipe is connected to the main air pipe, and the other opposite end of the exhaust pipe is respectively connected to the interlayer cavity air pipe and the loading cavity air pipe. The interlayer cavity air pipe is also connected to the interlayer cavity, and the loading cavity air pipe is also connected to the loading cavity.

[0012] Further, a sandwich chamber air duct is provided with a sandwich nitrogen inlet pneumatic valve, a sandwich chamber pressure control valve, a sandwich chamber vacuum pipeline pneumatic valve and a sandwich chamber exhaust pneumatic valve. The sandwich nitrogen inlet pneumatic valve is arranged between the sandwich chamber air duct and the gas mass flow controller. The sandwich chamber vacuum pipeline pneumatic valve is arranged between the sandwich chamber air duct and the sandwich chamber vacuum pump group. The sandwich chamber vacuum pump group is also communicated with an exhaust duct.

[0013] Further, the loading chamber air duct includes a main path and a branch path. The main path is provided with a loading chamber pressure control valve and a loading chamber exhaust pneumatic valve. The branch path is provided with a loading chamber vacuum pipeline pneumatic valve and a loading chamber vacuum pump group.

[0014] Further, the heating device is a molybdenum heating rod. A furnace body tungsten heat shield is arranged around the molybdenum heating rod inside the sandwich chamber.

[0015] Further, the loading chamber and the sandwich chamber are separated by a silicon carbide furnace tube.

[0016] Further, the optical fiber preform is connected to one end of a sintering guide rod through a connecting sleeve. The other opposite end of the sintering guide rod is arranged on an equipment tower. The sintering guide rod is hollow inside and communicated with the loading chamber. The feeding and lifting actions of the optical fiber preform can be realized from top to bottom or from bottom to top through the sintering guide rod, and the optical fiber preform can be driven to rotate.

[0017] Further, the loading chamber is communicated with a gas mixing device through the sintering guide rod. A loading upper inlet pneumatic valve is arranged between the sintering guide rod and the gas mixing device. The gas ratio of the gas entering the loading chamber is regulated through the gas mixing device.

[0018] Further, a sintering upper sealing device is arranged at the top of the main furnace body for realizing the sealing with the sintering guide rod and the sealing with the furnace mouth of the main furnace body.

[0019] Further, the main furnace body is provided with a loading chamber pressure gauge, a sandwich chamber pressure gauge and an infrared thermocouple. The real-time monitoring of the pressure in the loading chamber is realized through the loading chamber pressure gauge. The real-time monitoring of the pressure in the sandwich chamber is realized through the sandwich chamber pressure gauge. The real-time monitoring of the temperature inside the main furnace body is realized through the infrared thermocouple.

[0020] Compared with the prior art, the beneficial effects of the utility model are as follows:

[0021] The utility model discloses a helium - free sintering device for low - water - peak optical fiber preforms, which comprises a main furnace body and an exhaust pipeline system. The main furnace body includes a loading cavity and an external sandwich cavity. A production - use optical fiber preform is arranged in the loading cavity, and a heating device for heating the optical fiber preform is arranged in the sandwich cavity. The pressure in the loading cavity is greater than that in the sandwich cavity, and both the loading cavity and the sandwich cavity are connected to the exhaust pipeline system. The helium - free sintering device for low - water - peak optical fiber preforms provided by the utility model has a simple overall structure and is convenient to use. By using this device, processes such as dehydroxylation, degassing vitrification, and pressurized rod - taking can be efficiently completed. A cladding with low OH - can be obtained in a relatively shorter time, greatly reducing the production and manufacturing cycle and cost. Fundamentally, the problem that the cleanliness of the chamber of the optical fiber preform sintering equipment deteriorates gradually with the increase of the use time is solved. At the same time, the problem of low dehydroxylation efficiency in the field of helium - free sintering technology is solved, and it is suitable for industrial promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic structural diagram of the present utility model;

[0023] Figure 2 is a flow chart of the present utility model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The following elaborates on the present utility model in detail so that the advantages and features of the present utility model can be more easily understood by those skilled in the art, thereby making the protection scope of the present utility model more clearly defined.

[0025] The following gives a brief overview of one or more aspects to provide a basic understanding of these aspects. This overview is not an exhaustive survey of all contemplated aspects, and is neither intended to identify key or decisive elements of all aspects nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description to follow.

[0026] As Figure 1 shown, the utility model discloses a helium - free sintering device for low - water - peak optical fiber preforms, which comprises a main furnace body and an exhaust pipeline system. The main furnace body includes a loading cavity and an external sandwich cavity. A production - use optical fiber preform 6 is arranged in the loading cavity, and a heating device for heating the optical fiber preform 6 is arranged in the sandwich cavity. The pressure in the loading cavity is greater than that in the sandwich cavity and the two are independent of each other, and both the loading cavity and the sandwich cavity are connected to the exhaust pipeline system.

[0027] As a specific embodiment, the exhaust air duct system includes an exhaust duct 17, an interlayer chamber air duct 18, and a loading chamber air duct 23. One end of the exhaust duct 17 is connected to the main air duct 14, and the main air duct 14 is used to transport the waste gas in the interlayer chamber and the loading chamber. The opposite end of the exhaust duct 17 is respectively connected to the interlayer chamber air duct 18 and the loading chamber air duct 23. The interlayer chamber air duct 18 is also connected to the interlayer chamber, and the loading chamber air duct 23 is also connected to the loading chamber. The exhaust duct 17 is used to achieve the exhaust transportation function, the interlayer chamber air duct 18 is used to achieve the exhaust function of the interlayer chamber, and the loading chamber air duct 23 is used to achieve the exhaust function of the loading chamber. The loading chamber air duct 23 includes a main path and a branch path. A loading chamber pressure control valve 24 and a loading chamber exhaust air pneumatic valve 25 are arranged on the main path, and a loading chamber vacuum pipeline pneumatic valve 26 and a loading chamber vacuum pump group 27 are arranged on the branch path. The loading chamber pressure control valve 24 is used to achieve the pressure control function of the loading chamber and the opening and closing functions of the loading air extraction. The loading chamber exhaust air pneumatic valve 25 is used to achieve the opening and closing functions of the loading chamber exhaust. The loading chamber vacuum pipeline pneumatic valve 26 is used to achieve the opening and closing function of the loading chamber exhaust, and the loading chamber vacuum pump group 27 is used to achieve the exhaust function of the loading chamber.

[0028] As a more specific embodiment, a nitrogen inlet pneumatic valve 16 for the interlayer chamber, a pressure control valve 19 for the interlayer chamber, a vacuum pipeline pneumatic valve 21 for the interlayer chamber, and an air extraction pneumatic valve 20 for the interlayer chamber are arranged on the interlayer chamber air duct 18. The nitrogen inlet pneumatic valve 16 for the interlayer chamber is arranged between the interlayer chamber air duct 18 and the gas mass flow controller 15. The gas mass flow controller 15 is used to accurately control the intake air volume of the interlayer chamber. The nitrogen inlet pneumatic valve 16 for the interlayer chamber is used to achieve the opening and closing of the intake air of the interlayer chamber. The pressure control valve 19 for the interlayer chamber is used to achieve the pressure control function of the interlayer chamber and the opening and closing functions of the loading air extraction. The air extraction pneumatic valve 20 for the interlayer chamber is used to achieve the opening and closing of the main air extraction of the interlayer chamber. The vacuum pipeline pneumatic valve 21 for the interlayer chamber is used to achieve the opening and closing function of the exhaust. The vacuum pump group 22 for the interlayer chamber is used to achieve the exhaust function of the interlayer chamber. The vacuum pipeline pneumatic valve 21 for the interlayer chamber is arranged between the interlayer chamber air duct 18 and the vacuum pump group 22 for the interlayer chamber, and the vacuum pump group 22 for the interlayer chamber is also connected to the exhaust duct 17.

[0029] The fiber preform 6 is connected to the sintering leading rod 1 through the connecting sleeve 5. The sintering leading rod 1 is arranged on the equipment tower 11. Through the equipment tower 11, the support function for equipment installation and product transfer can be realized. Through the sintering leading rod 1, the feeding and lifting actions of the fiber preform 6 from top to bottom or from bottom to top can be realized. The rotation of the sintering leading rod 1 driven by the motor can also be used to drive the fiber preform 6 to rotate, and the rotation speed is 0.5 rpm to 20 rpm. The fiber preform 6 is generally suspended in the loading cavity. The sintering leading rod 1 is hollow inside and communicates with the loading cavity. The loading cavity is connected to the gas mixing device 13 through the sintering leading rod 1. An upper loading air inlet pneumatic valve 12 is arranged between the sintering leading rod 1 and the gas mixing device 13, which is used to realize the opening and closing functions of the loading cavity for air inlet, and the gas ratio of the air inlet to the loading cavity is regulated through the gas mixing device 13.

[0030] The loading cavity and the interlayer cavity of the main furnace body are separated by the silicon carbide furnace tube 9. A sintering upper sealing device 3 is arranged at the top of the main furnace body, which is used to realize the sealing with the sintering leading rod 1 and the sealing of the furnace mouth of the main furnace body. A loading cavity pressure gauge 2, an interlayer cavity pressure gauge 4 and an infrared thermocouple 10 are arranged on the main furnace body. The loading cavity pressure gauge 2 communicates with the loading cavity, and the real-time monitoring of the pressure in the loading cavity is realized through the loading cavity pressure gauge 2. The interlayer cavity pressure gauge 4 communicates with the interlayer cavity, and the real-time monitoring of the pressure in the interlayer cavity is realized through the interlayer cavity pressure gauge 4. The real-time monitoring of the temperature of the outer wall of the main furnace body is realized through the infrared thermocouple 10, that is, the real-time monitoring of the temperature inside the main furnace body is realized.

[0031] The heating device is a molybdenum heating rod 7, which is used to convert electrical energy into heat energy and heat the fiber preform 6 to the required temperature. A furnace body tungsten heat insulation screen 8 is arranged inside the interlayer cavity and around the molybdenum heating rod 7.

[0032] As Figure 2 shown, the present invention also discloses a use method of a helium-free sintering device for a low water peak fiber preform, including the following steps:

[0033] First, confirm that the hanging rod position is at zero point, that is, the sintering leading rod 1 and the connecting sleeve 5 are in the specified positions. Then, hang the optical fiber preform 6 on the connecting sleeve 5. Start entering the production state, control the optical fiber preform 6 to feed into the production position. During the feeding process, the molybdenum heating rod 7 is maintained at a temperature of 500°C to 1100°C, and the interlayer cavity is always kept in an inert gas protection atmosphere. After the optical fiber preform 6 feeds into the production position, at this time, the effective section of the optical fiber preform 6 enters the effective position of the temperature zone, located at the center position of the temperature zone. At this time, the upper sintering sealing device 3 forms a seal with the furnace mouth. First, control the sintering leading rod 1 to drive the optical fiber preform 6 to rotate through the motor, with a rotation speed of 0.5 rpm to 20 rpm. Secondly, synchronously open the interlayer cavity exhaust pneumatic valve 20 and the loading cavity exhaust pneumatic valve 25, and control the air pressure at -200 Pa to -600 Pa. Synchronously open the interlayer cavity pressure control valve 19 and the loading cavity pressure control valve 24. The loading cavity pressure is set at 50 Pa to 2000 Pa, monitored by the loading cavity pressure gauge 2. The interlayer cavity pressure set value is 200 Pa to 2000 Pa, and the interlayer cavity pressure is monitored by the interlayer cavity pressure gauge 4. The loading cavity and the interlayer cavity always maintain that the loading cavity pressure is greater than the interlayer cavity pressure, and the loading cavity and the interlayer cavity are independent of each other. Among them, the source for maintaining the pressure difference in the loading cavity is the process gas used in the loading cavity. By opening the lower loading air inlet pneumatic valve 12 and setting the ratio of the gas mixing device 13, the process gas contains 75% to 95% nitrogen and 5% to 25% chlorine. The main source of the interlayer cavity pressure control is nitrogen (99.999%). By opening the interlayer nitrogen inlet pneumatic valve 16 and the gas mass flow controller 15 to control the gas inlet volume, the interlayer cavity pressure is maintained. After maintaining for 30 min to 500 min, heat up to the target temperature (1100°C to 1300°C) at a set slope of 0°C / min to 8°C / min, and use the infrared thermocouple 10 to monitor the temperature of the loading cavity in real time. After the heating is completed, continue to maintain for 30 min to 600 min. After the above steps are completed, enter the degassing and vitrification stage:

[0034] First, close the extraction pneumatic valve 20 of the interlayer chamber, the exhaust pneumatic valve 25 of the loading chamber, and the nitrogen inlet pneumatic valve 16 of the interlayer chamber. Simultaneously open the vacuum pipeline pneumatic valve 21 of the interlayer chamber and the vacuum pipeline pneumatic valve 26 of the loading chamber. Simultaneously turn on the vacuum pump group 22 of the interlayer chamber and the vacuum pump group 27 of the loading chamber to synchronously reduce the pressure and evacuate the loading chamber and the interlayer chamber. Synchronously increase the furnace temperature to 1520 °C - 1560 °C at a set slope of 2 °C / min - 5 °C / min for vitrification of the optical fiber preform 6. The process gases are nitrogen (90% - 98%) and chlorine (2% - 10%). The vacuum degree of the loading chamber should be slightly lower than that of the interlayer chamber, and the control range is 0 Pa - 3000 Pa. PID control is performed through the pressure control valve 19 of the interlayer chamber and the pressure control valve 24 of the loading chamber. After vitrification is completed, simultaneously close the vacuum pipeline pneumatic valve 21 of the interlayer chamber and the vacuum pipeline pneumatic valve 26 of the loading chamber. Delay closing the vacuum pump group 22 of the interlayer chamber, the vacuum pump group 27 of the loading chamber, the pressure control valve 19 of the interlayer chamber, and the pressure control valve 24 of the loading chamber. Open the nitrogen inlet pneumatic valve 16 of the interlayer chamber. The intake volume of the interlayer chamber is variable, and the intake volume of the loading chamber is 1 L / min - 5 L / min. Then, regulate the flow rate of the gas mass flow controller 15 through PLC to ensure that the absolute value of the pressure difference between the pressure gauge 2 of the loading chamber and the pressure gauge 4 of the interlayer chamber is within 0 Pa - 3000 Pa. After pressurization is completed, start cooling synchronously until the standby temperature of 800 °C is reached. Lift the product to the rod hanging and picking point through the sintering lifting rod 1 and the connecting sleeve 5, and notify the production department to pick up the rod to complete this production.

[0035] Example 1

[0036] First, confirm that the hanging rod position is at zero point, that is, the sintering leading rod 1 and the connecting sleeve 5 are in the specified positions. Then, hang the optical fiber preform 6 on the connecting sleeve 5. Start entering the production state. Drive the optical fiber preform 6 into the production position by controlling the servo motor through the PLC. During the process of feeding the rod, the molybdenum heating rod 7 is maintained at a temperature of 900 °C, and the interlayer cavity is always kept in an inert gas protection atmosphere. After the optical fiber preform 6 is fed into the production position, at this time, the effective section of the optical fiber preform 6 enters the effective position of the temperature zone, which is located at the center of the temperature zone. At this time, the upper sealing device 3 of the sintering and the furnace mouth form a seal. First, drive the optical fiber preform 6 to rotate by controlling the sintering leading rod 1 with the motor, with a rotation speed of 5 rpm. Synchronously open the extraction pneumatic valve 20 of the interlayer cavity and the exhaust pneumatic valve 25 of the loading cavity, and control the wind pressure at -350 Pa. Synchronously open the pressure control valve 19 of the interlayer cavity and the pressure control valve 24 of the loading cavity. The pressure of the loading cavity is set at 280 Pa and monitored by the pressure gauge 2 of the loading cavity. The pressure of the interlayer cavity is set at 260 Pa and the pressure of the interlayer cavity is monitored by the pressure gauge 4 of the interlayer cavity, always keeping the pressure of the loading cavity greater than that of the interlayer cavity. Among them, the source for maintaining the pressure difference of the loading cavity is the process gas used in the loading cavity. By opening the lower intake pneumatic valve 12 of the loading and setting the ratio of the gas mixing device 13, the process gas contains 85% nitrogen and 15% chlorine. The main source of the interlayer cavity pressure control is nitrogen (99.999%). By opening the nitrogen intake pneumatic valve 16 of the interlayer and controlling the gas input amount with the gas mass flow controller 15, the pressure of the interlayer cavity is maintained. After maintaining for 150 min, heat up to the target temperature of 1250 °C at a set slope of 4 °C / min, and monitor with the infrared thermocouple 10. After the heating is completed, continue to maintain for 200 min. After the above dehydroxylation step is completed, continue with the degassing and vitrification stages:

[0037] First, close the extraction pneumatic valve 20 of the interlayer chamber, the exhaust pneumatic valve 25 of the loading chamber, and the nitrogen intake pneumatic valve 16 of the interlayer chamber. Synchronously open the vacuum pipeline pneumatic valve 21 of the interlayer chamber and the vacuum pipeline pneumatic valve 26 of the loading chamber. Synchronously turn on the vacuum pump group 22 of the interlayer chamber and the vacuum pump group 27 of the loading chamber to synchronously decompress and evacuate the loading chamber and the interlayer chamber. Synchronously heat the furnace temperature to 1520 °C at a set slope of 2 °C / min for vitrification of the optical fiber preform 6. The process gas is 98% nitrogen and 2% chlorine. The vacuum degree of the loading chamber should be slightly lower than that of the interlayer chamber, and the control range is 1600 Pa. PID control is performed through the pressure control valve 19 of the interlayer chamber and the pressure control valve 24 of the loading chamber. After vitrification is completed, synchronously close the vacuum pipeline pneumatic valve 21 of the interlayer chamber and the vacuum pipeline pneumatic valve 26 of the loading chamber. Delay closing the vacuum pump group 22 of the interlayer chamber, the vacuum pump group 27 of the loading chamber, the pressure control valve 19 of the interlayer chamber, and the pressure control valve 24 of the loading chamber. Open the nitrogen intake pneumatic valve 16 of the interlayer chamber. The intake air volume of the interlayer chamber is a variable, and the intake air volume of the loading chamber is a fixed value of 1.5 L / min. Then, adjust the flow rate of the gas mass flow controller 15 through PLC to ensure that the absolute value of the pressure difference between the pressure gauge 2 of the loading chamber and the pressure gauge 4 of the interlayer chamber is within 1600 Pa. After pressurization is completed, synchronously start to cool down to the standby temperature of 800 °C. Lift the product to the rod hanging and picking point through the sintering guide rod 1 and the connecting sleeve 5, and notify the production department to pick up the rod to complete this production. The hydroxyl content of the test sample is ≤ 6.50 μg / g.

[0038] Example 2

[0039] First, confirm that the hanging rod point is at zero, that is, the sintering guide rod 1 and the connecting sleeve 5 are in the specified positions. Then, hang the optical fiber preform 6 onto the connecting sleeve 5. Start entering the production state. Drive the optical fiber preform 6 into the production position by controlling the servo motor through the PLC. During the process of feeding the rod, the molybdenum heating rod 7 is maintained at a temperature of 900 °C, and the interlayer cavity is kept in an inert gas protection atmosphere all the time. After the optical fiber preform 6 is fed into the production position, the effective section of the optical fiber preform 6 enters the effective position of the temperature zone, which is located at the center of the temperature zone. At this time, the upper sintering sealing device 3 forms a seal with the furnace mouth. First, drive the optical fiber preform 6 to rotate by controlling the sintering guide rod 1 with the motor at a rotation speed of 5 rpm. Synchronously open the pneumatic valve 20 for exhausting air from the interlayer cavity and the pneumatic valve 25 for exhausting air from the loading cavity. Control the air pressure at -350 Pa. Synchronously open the pressure control valve 19 for the interlayer cavity and the pressure control valve 24 for the loading cavity. Set the pressure of the loading cavity at 280 Pa and monitor it through the pressure gauge 2 of the loading cavity. Set the pressure of the interlayer cavity at 260 Pa and monitor the pressure of the interlayer cavity through the pressure gauge 4 of the interlayer cavity, and always keep the pressure of the loading cavity greater than that of the interlayer cavity. Among them, the source for maintaining the pressure difference of the loading cavity is the process gas used in the loading cavity. By opening the pneumatic valve 12 for inlet air at the lower part of the loading cavity and setting the ratio of the gas mixing device 13, the process gas contains 85% nitrogen and 15% chlorine. The main source for controlling the pressure of the interlayer cavity is nitrogen (99.999%). Control the gas inlet amount by opening the pneumatic valve 16 for inlet nitrogen into the interlayer cavity and the gas mass flow controller 15 to maintain the pressure of the interlayer cavity. After maintaining for 200 min, heat up to the target temperature of 1250 °C at a set slope of 4 °C / min and monitor it with the infrared thermocouple 10. After the heating is completed, continue to maintain for 300 min. After the above dehydroxylation step is completed, continue with the degassing and vitrification stages:

[0040] First, close the extraction pneumatic valve 20 of the interlayer chamber, the exhaust pneumatic valve 25 of the loading chamber, and the nitrogen inlet pneumatic valve 16 of the interlayer chamber. Synchronously open the vacuum pipeline pneumatic valve 21 of the interlayer chamber and the vacuum pipeline pneumatic valve 26 of the loading chamber. Synchronously turn on the vacuum pump group 22 of the interlayer chamber and the vacuum pump group 27 of the loading chamber to synchronously decompress and evacuate the loading chamber and the interlayer chamber. The furnace temperature is increased to 1520 °C at a set slope of 2 °C / min for vitrification of the optical fiber preform 6. The process gas is 98% nitrogen and 2% chlorine. The vacuum degree of the loading chamber should be slightly lower than that of the interlayer chamber, and the control range is 1600 Pa. PID control is performed through the pressure control valve 19 of the interlayer chamber and the pressure control valve 24 of the loading chamber. After vitrification is completed, synchronously close the vacuum pipeline pneumatic valve 21 of the interlayer chamber and the vacuum pipeline pneumatic valve 26 of the loading chamber. Delay closing the vacuum pump group 22 of the interlayer chamber, the vacuum pump group 27 of the loading chamber, the pressure control valve 19 of the interlayer chamber, and the pressure control valve 24 of the loading chamber. Open the nitrogen inlet pneumatic valve 16 of the interlayer chamber. The intake volume of the interlayer chamber is a variable, and the intake volume of the loading chamber is a fixed value of 1.5 L / min. Then, the PLC is used to control the input amount of the gas mass flow controller 15 to ensure that the absolute value of the pressure difference between the pressure gauge 2 of the loading chamber and the pressure gauge 4 of the interlayer chamber is within 1600 Pa. After pressurization is completed, start cooling synchronously. Cool down to the standby temperature of 800 °C. Lift the product to the rod hanging and picking point through the sintering lifting rod 1 and the connecting sleeve 5, and notify the production department to pick up the rod to complete this production. The hydroxyl content of the test sample is ≤0.50 μg / g. Since the chlorination time in this embodiment is extended, the hydroxyl content in this embodiment is lower than that in Embodiment 1, indicating that the chlorination time will affect the hydroxyl content of the sample.

[0041] For the parts or structures not specifically described in the present invention, existing technologies or existing products can be adopted, and no further elaboration will be made here.

[0042] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A low water peak optical fiber preform helium-free sintering device, characterized in that: The invention comprises a main furnace body and an exhaust pipe system. The main furnace body comprises a loading chamber and an interlayer chamber outside the loading chamber. An optical fiber preform for production is arranged in the loading chamber. A heating device for heating the optical fiber preform is arranged in the interlayer chamber. The pressure of the loading chamber is greater than that of the interlayer chamber and the two are independent of each other. The loading chamber and the interlayer chamber are both connected to the exhaust pipe system.

2. The low water peak optical fiber preform helium-free sintering device according to claim 1, characterized in that: The exhaust pipe system includes an exhaust duct, an interlayer chamber air duct and a loading chamber air duct. One end of the exhaust duct is connected to the main air duct, and the other end of the exhaust duct is respectively connected to the interlayer chamber air duct and the loading chamber air duct. The interlayer chamber air duct is also connected to the interlayer cavity, and the loading chamber air duct is also connected to the loading cavity.

3. The low water peak optical fiber preform helium-free sintering device according to claim 2, characterized in that: The interlayer chamber air duct is provided with an interlayer nitrogen air intake pneumatic valve, an interlayer chamber pressure control valve, an interlayer chamber vacuum pipeline pneumatic valve and an interlayer chamber exhaust pneumatic valve. The interlayer nitrogen air intake pneumatic valve is arranged between the interlayer chamber air duct and the gas mass flow controller, the interlayer chamber vacuum pipeline pneumatic valve is arranged between the interlayer chamber air duct and the interlayer chamber vacuum pump group, and the interlayer chamber vacuum pump group is also connected to the exhaust pipe.

4. The low water peak optical fiber preform helium-free sintering device according to claim 2, characterized in that: The loading chamber air duct includes a main circuit and a branch circuit. The main circuit is provided with a loading chamber pressure control valve and a loading chamber exhaust pneumatic valve. The branch circuit is provided with a loading chamber vacuum pipeline pneumatic valve and a loading chamber vacuum pump group.

5. The low water peak optical fiber preform helium-free sintering device according to claim 1, characterized in that: The heating device is a molybdenum heating rod, and a furnace tungsten heat insulation screen is arranged in the interlayer cavity and around the molybdenum heating rod.

6. The low water peak optical fiber preform helium-free sintering device according to claim 1, characterized in that: The loading chamber and the interlayer chamber are separated by a silicon carbide furnace tube.

7. The low water peak optical fiber preform helium-free sintering device according to claim 1, characterized in that: The optical fiber preform is connected to one end of a sintering guide rod through a connecting sleeve, and the other end of the sintering guide rod is arranged on the equipment tower. The interior of the sintering guide rod is hollow and communicates with the loading chamber. The sintering guide rod can realize the feeding and lifting actions of the optical fiber preform from top to bottom or from bottom to top and drive the optical fiber preform to rotate.

8. The low water peak optical fiber preform helium-free sintering device according to claim 7, characterized in that: The loading chamber is connected to the gas mixing device through the sintering guide rod, and an upper loading air intake pneumatic valve is arranged between the sintering guide rod and the gas mixing device. The gas ratio of the loading chamber intake is regulated by the gas mixing device.

9. The low water peak optical fiber preform helium-free sintering device according to claim 7, characterized in that: The top of the main furnace body is provided with a sintering upper sealing device for achieving sealing with the sintering guide rod and sealing with the furnace mouth of the main furnace body.

10. The low water peak optical fiber preform helium-free sintering device according to claim 1, characterized in that: The main furnace body is provided with a loading chamber pressure gauge, an interlayer chamber pressure gauge and an infrared thermocouple. Real-time monitoring of the loading chamber pressure is achieved through the loading chamber pressure gauge, real-time monitoring of the interlayer chamber pressure is achieved through the interlayer chamber pressure gauge, and real-time monitoring of the temperature inside the main furnace body is achieved through the infrared thermocouple.

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