Optical fiber drawing furnace and optical fiber drawing method

Abstract

The present invention relates to an optical fiber drawing furnace and an optical fiber drawing method, comprising a furnace body, a graphite central tube extending vertically therethrough is installed in the middle of the furnace body, an insulation layer and a heating coil are provided on the periphery of the graphite central tube, the upper end of the graphite central tube is connected to an upper furnace opening, and the lower end of the graphite central tube is connected to a downwardly contracting lower furnace opening, the upper furnace opening is provided with a protective gas ring structure, a furnace opening sealing device is provided on the protective gas ring structure, and the protective gas ring structure is characterized in that the protective gas ring structure includes a metal flange installed on the upper furnace opening, a metal air inlet ring is provided at the upper end of the metal flange, an annular air inlet cavity is formed between the metal flange and the metal air inlet ring, and a graphite glass composite air ring is provided on the inner surface of the metal flange and the metal air inlet ring relative to the annular air inlet cavity. The present invention has a reasonable structural arrangement, the sealing port of the drawing furnace has strong high temperature resistance, small deformation, high working reliability, long equipment service life, and low processing cost, and is particularly suitable for the drawing processing of large-diameter optical fiber preform rods.

Description

Technical Field

[0001] The invention relates to an optical fiber drawing furnace and an optical fiber drawing method, belonging to the technical field of optical fiber manufacturing equipment. Background Art

[0002] Optical fibers are drawn from preform rods that are heated and melted in a drawing furnace. During the drawing process, the heat generated by the graphite heating element is induced by the heater inside the drawing furnace, melting the preform rod. Since graphite parts easily react with oxygen and burn at high temperatures, the drawing furnace mouth needs to have good sealing performance to extend the service life of the graphite parts. On the other hand, during drawing, the drawing furnace chamber also needs to be stably filled with inert process gas through the air ring structure installed at the furnace mouth. This can further isolate the ingress of external air and fully guarantee the quality of the optical fiber drawing. The diameter of existing optical fiber preform rods is getting larger and larger, and the diameter fluctuation of a single preform rod is also increasing. This places higher demands on the sealing of the drawing furnace. In addition, the existing drawing furnace air ring structure uses a single graphite air ring structure directly facing the optical fiber preform rod. Since the preform rod will continue to move downward during drawing and the outer diameter of the preform rod fluctuates, the single graphite air ring is easily oxidized and burned at the furnace mouth. The burned graphite air ring will affect the cleanliness of the preform rod surface and thus affect the optical fiber strength, and cause the surface of the graphite air ring to be uneven, affecting the stability of the airflow in the furnace, thereby affecting the processing quality of the optical fiber.

[0003] Existing sealing devices are either too simple, resulting in poor sealing effectiveness, especially when producing preforms with large outer diameter variations, which can easily cause blowby in the drawing furnace. They are also too complex and difficult to operate, or the sealing height is too high, which can prevent the preform from being fully drawn, leading to raw material loss. This affects quality parameters such as optical fiber roundness. Therefore, it is necessary to design a drawing furnace gas ring structure and sealing device to isolate the interior of the drawing furnace from the external air. This not only ensures the stability of the process gas inside the furnace, but also protects the graphite parts from oxidation and burning due to contact with the outside air, thereby extending their service life. Graphite parts are relatively expensive, and extending their service life can also significantly reduce production costs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an optical fiber drawing furnace and an optical fiber drawing method in view of the deficiencies in the above-mentioned prior art, which not only has a reasonable structure and good sealing performance, but also can effectively extend the service life of graphite parts and improve the drawing quality.

[0005] The technical solutions proposed by the present invention to solve the above-mentioned problems are as follows:

[0006] The invention comprises a furnace body, wherein a graphite central tube is installed in the middle of the furnace body and passes through the furnace body from top to bottom, an insulation layer and a heating coil are arranged on the periphery of the graphite central tube, the upper end of the graphite central tube is connected to the upper furnace mouth, and the lower end of the graphite central tube is connected to the downwardly contracted lower furnace mouth, the upper furnace mouth is provided with a protective gas ring structure, and a furnace mouth sealing device is arranged on the protective gas ring structure, which is characterized in that the protective gas ring structure comprises a metal flange installed on the upper furnace mouth, a metal air inlet ring is arranged at the upper end of the metal flange, and an annular air inlet cavity is formed between the metal flange and the metal air inlet ring, and a graphite glass composite air ring is arranged on the inner surface of the metal flange and the metal air inlet ring relative to the annular air inlet cavity.

[0007] According to the above solution, the furnace mouth sealing device is a glass ring quartz wool floating sealing device.

[0008] According to the above scheme, the graphite glass composite air ring includes a graphite air ring tightly configured with the inner hole of the metal flange, and radial air inlet holes spaced circumferentially are provided on the outer periphery of the upper end of the graphite air ring corresponding to the annular air inlet cavity, and an inserted glass air guide ring is arranged in the inner hole of the graphite air ring corresponding to the radial air inlet holes, and the outer periphery of the upper end of the inserted glass air guide ring is configured with the inner surface of the upper end of the metal air inlet ring.

[0009] According to the above solution, a gap is maintained between the outer peripheral surface of the inserted glass gas guide ring and the inner hole of the graphite gas ring and extends downward for a distance to form an annular air gap.

[0010] According to the above solution, radial air inlet holes are evenly spaced along the circumference on the outer periphery of the upper end of the graphite air ring. The radial air inlet holes are downwardly inclined and radially deflected. When air is admitted, a protective air ring layer is formed that rotates downward and surrounds the optical fiber preform.

[0011] According to the above solution, the downward tilt angle α of the radial air inlet is 10 to 40°, and the radial deflection angle β (to the right or left) is 15 to 45°.

[0012] According to the above solution, the diameter of the radial air inlet holes is 1.5 to 3 mm, and the number of air inlet holes uniformly distributed along the circumference is 20 to 50.

[0013] According to the above solution, the lower end of the graphite air ring extends downward for a distance, axially intersecting with the graphite central tube, and the outer periphery is configured with the inner hole of the graphite central tube.

[0014] According to the above scheme, the glass ring quartz wool floating sealing device includes a glass sealing seat installed on the upper end of the metal air inlet ring, the annular sealing groove set in the inner hole of the glass sealing seat is filled with sealing quartz wool, a radial floating glass tightening ring is installed on the top of the glass sealing seat, a quartz wool sealing layer covering the optical fiber preform rod is set in the radial floating glass tightening ring, and an upper glass pressure ring is installed on the upper end of the radial floating glass tightening ring.

[0015] According to the above scheme, the radial floating glass tightening ring includes 2 to 4 glass arc blocks, and a clamping groove is opened on the outer circumferential surface of the glass arc block. The glass arc blocks are spliced ​​into a ring along the circumferential direction and the annular spring is clamped through the clamping groove, which surrounds the outer circumference of the quartz wool sealing layer to form a radial floating glass tightening ring.

[0016] According to the above solution, the metal air inlet ring is connected to the shielding gas source through the connecting pipe and the control valve, so that the shielding gas enters the annular air inlet cavity.

[0017] According to the above solution, cooling water tanks are respectively provided in the metal flange and the metal air inlet ring.

[0018] The technical solution of the optical fiber drawing method of the present invention is: using the above-mentioned drawing furnace, the optical fiber preform rod clamped on the lifting feed bracket device is passed through the furnace mouth sealing device and the protective gas ring structure into the upper furnace mouth of the drawing furnace and into the furnace cavity, the protective gas is turned on to enter the furnace cavity through the protective gas ring structure, and the heating coil is turned on to heat the graphite center tube. When the drawing furnace is heated to above 1700°C, the optical fiber preform rod is drawn into an optical fiber through high-temperature melting.

[0019] According to the above solution, the flow rate of the protective gas is 20-40 L / min, and the protective gas is helium or argon.

[0020] According to the above solution, the outer diameter of the optical fiber preform is 120 to 240 mm.

[0021] According to the above solution, the fluctuation of the outer diameter of each optical fiber preform (the difference between the maximum outer diameter and the minimum outer diameter) is less than 20 mm, and further the fluctuation is less than 40 mm.

[0022] According to the above solution, the feeding speed of the optical fiber preform is 0.5-2 mm / min, and the maximum drawing speed is 3500 m / min.

[0023] The beneficial effects of the present invention are: 1. The provision of a graphite glass composite air ring can effectively prevent the graphite air ring from contacting and oxidizing with air, greatly extending the service life of the graphite air ring, reducing the impact on the optical fiber drawing quality caused by the burning of graphite parts, extending the life of graphite parts and saving equipment maintenance costs; 2. The furnace mouth sealing device is a glass ring quartz wool floating sealing device, which not only improves the dynamic sealing performance of the drawing furnace, but also ensures a good sealing effect when the outer diameter of the preform fluctuates; 3. The protective gas first enters the annular air inlet cavity from the metal air inlet ring for uniform mixing and preheating, and then enters the annular air gap between the graphite air ring and the inserted glass air guide ring through the circumferentially arranged air inlet holes at the upper end of the graphite air ring, forming a downward rotating protective air ring layer surrounding the optical fiber preform, which can reduce the flow rate of the protective gas entering the furnace, allowing the protective gas to flow evenly and smoothly through the annular air gap, forming a uniform and smooth air flow in the furnace. The flow layer prevents the air holes of the shielding gas from directly facing the preform rod when it enters the furnace, thus avoiding the air flow from directly scouring the preform rod. The high-temperature surface of the preform rod will wrinkle when it suddenly encounters the cold air flow, thereby affecting the strength and roundness of the optical fiber. The shielding gas entering the furnace is guided downward in the annular air gap between the graphite gas ring and the inserted glass air guide ring before entering the preform rod area to fill the entire furnace. This process not only preheats the shielding gas that has just entered to reduce the temperature difference between the shielding gas and the preform rod, but also allows the shielding gas to be evenly mixed to form a shielding gas ring, providing a stable and good processing condition for the melt drawing of the optical fiber preform rod, thereby further improving the drawing quality of the optical fiber; 4. The present invention has a reasonable structural arrangement and adopts a glass part structure and a metal part cooling water trough structure, so that the sealing port of the drawing furnace has strong high temperature resistance, small deformation, high working reliability, and low processing cost, and is particularly suitable for the drawing processing of large-diameter optical fiber preform rods. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a front cross-sectional structural diagram of an embodiment of the present invention.

[0025] Figure 2 This is a front cross-sectional structural diagram of a glass ring quartz wool floating sealing device in one embodiment of the present invention.

[0026] Figure 3 This is a front cross-sectional structural diagram of the graphite glass composite air ring portion in one embodiment of the present invention.

[0027] Figure 4 This is a three-dimensional structural diagram of a glass arc block in one embodiment of the present invention.

[0028] Figure 5 This is a front cross-sectional structural diagram of a graphite gas ring in one embodiment of the present invention.

[0029] Figure 6 for Figure 5 A top view of the structure. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are further described below with reference to the accompanying drawings.

[0031] The furnace comprises a cylindrical furnace body 1, with a cylindrical graphite center tube 4 extending vertically through the center. An insulation layer 2 and a heating coil 3 are disposed around the outer periphery of the graphite center tube for induction heating and heat preservation. The upper end of the graphite center tube is connected to an upper furnace opening, while the lower end of the graphite center tube is connected to a downwardly converging lower furnace opening 19. A protective gas ring structure is mounted on the upper furnace opening. The protective gas ring structure comprises a metal flange 5 mounted on the upper furnace opening, and a metal inlet ring 6 disposed at its upper end. An annular concave cavity is formed on the upper end surface of the metal flange, which is aligned with an annular boss on the lower end surface of the metal inlet ring. Cooling water grooves 17 and 7 are respectively disposed within the metal flange and the metal inlet ring. An annular inlet cavity 20 is formed between the metal flange and the inner cavity below the metal inlet ring. The metal inlet ring is connected to a protective gas source via a pipe and a control valve, allowing protective gas to enter the annular inlet cavity. A graphite glass composite air ring is installed on the inner surface of the metal flange and the metal air inlet ring relative to the annular air inlet cavity. The graphite glass composite air ring includes a graphite air ring 8 tightly configured with the inner hole of the metal flange. The outer periphery of the upper end of the graphite air ring corresponds to the annular air inlet cavity and has radial air inlet holes evenly spaced along the circumference. The radial air inlet holes are downwardly inclined and radially deflected air inlet holes. The downward inclination angle α is 25°, and the radial deflection (to the left) angle β is 30°. The aperture of the radial air inlet holes is 2mm, and there are 32 air inlet holes evenly distributed along the circumference. When air is admitted, a protective air ring layer will be formed that rotates downward and surrounds the optical fiber preform rod 18. The lower end of the graphite air ring extends downward for a distance, axially intersecting with the graphite center tube, and the outer periphery is configured with the inner hole of the graphite center tube. An inserted glass gas guide ring 9 is arranged in the radial air inlet hole corresponding to the inner hole of the graphite gas ring. The outer periphery of the upper end of the inserted glass gas guide ring is arranged with the inner surface of the upper end of the metal gas inlet ring. The outer periphery of the inserted glass gas guide ring maintains a gap with the inner hole of the graphite gas ring and extends downward for a distance. The gap is 0.5 to 2 mm to form an annular air gap. The protective gas ejected from the circumferentially arranged air inlet holes at the upper end of the graphite gas ring enters the annular air gap between the graphite gas ring and the inserted glass gas guide ring, forming a protective gas ring layer that rotates downward and surrounds the optical fiber preform rod. The protective gas is an inert gas.A furnace mouth sealing device is arranged on the top of the protective gas ring structure, and the furnace mouth sealing device is a glass ring quartz wool floating sealing device, and the glass ring quartz wool floating sealing device includes an annular glass sealing seat 10 installed on the upper end of the metal air inlet ring, and the annular boss on the lower end face of the glass sealing seat is configured with the annular cavity provided on the upper end face of the metal air inlet ring. The annular sealing groove provided in the inner hole of the glass sealing seat is filled with sealing quartz wool 11, which constitutes the second-level sealing of the optical fiber preform rod. A radial floating glass tightening ring 12 is arranged on the top of the glass sealing seat, and the radial floating glass tightening ring includes two glass arc blocks, and the glass arc blocks are semicircular or nearly semicircular, and the outer circumference of the glass arc blocks is opened. A card slot 21 is provided, and two glass arc blocks are spliced ​​into a ring along the circumferential direction and clamped with an annular spring 14 through the card slot, which surrounds the outer circumference of the quartz wool sealing layer 13 to form a radial floating glass tightening ring. A quartz wool sealing layer covering the optical fiber preform is provided in the radial floating glass tightening ring, and the quartz wool sealing layer can be bundled by a quartz rope 15. An upper glass pressure ring 16 is installed on the upper end of the radial floating glass tightening ring, thereby forming the first-level seal for the optical fiber preform. When the outer diameter of the optical fiber preform fluctuates, the radial floating glass tightening ring will tighten or loosen the quartz wool sealing layer under the action of the annular spring, so that the adaptive surface sealing layer always tightly covers the optical fiber preform, ensuring the axial feed dynamic seal of the optical fiber preform during drawing.

[0032] The above-mentioned drawing furnace is used to pass the optical fiber preform rod clamped on the lifting feed bracket device into the upper furnace port of the drawing furnace through the furnace port sealing device and the protective gas ring structure and enter the furnace cavity. The protective gas is turned on to enter the furnace cavity through the protective gas ring structure. The heating coil is turned on to heat the graphite center tube. When the drawing furnace is heated to about 1950°C, the optical fiber preform rod is drawn into an optical fiber through high-temperature melting. During operation, the protective gas flow rate is 30L / min, the protective gas is helium or argon, the outer diameter of the optical fiber preform rod is 220mm, and the fluctuation of the outer diameter of each optical fiber preform rod (the difference between the maximum outer diameter and the minimum outer diameter) is 30mm. The feed speed of the optical fiber preform rod is 1.6mm / min, and the drawing speed is 3500m / min.

Claims

1. An optical fiber drawing furnace, comprising a furnace body, a graphite central tube extending vertically through the furnace body, an insulation layer and a heating coil disposed on the periphery of the graphite central tube, the upper end of the graphite central tube being connected to an upper furnace opening, and the lower end of the graphite central tube being connected to a downwardly contracting lower furnace opening, the upper furnace opening being provided with a protective gas ring structure, and a furnace opening sealing device disposed above the protective gas ring structure, characterized in that The protective gas ring structure includes a metal flange installed on the upper furnace mouth, a metal air inlet ring is arranged at the upper end of the metal flange, and an annular air inlet cavity is formed between the metal flange and the metal air inlet ring, and a graphite glass composite air ring is arranged on the inner surface of the metal flange and the metal air inlet ring relative to the annular air inlet cavity; the graphite glass composite air ring includes a graphite air ring tightly arranged with the inner hole of the metal flange, radial air inlet holes spaced along the circumferential direction are provided on the outer periphery of the upper end of the graphite air ring corresponding to the annular air inlet cavity, an inserted glass air guide ring is arranged at the inner hole of the graphite air ring corresponding to the radial air inlet holes, and the outer periphery of the upper end of the inserted glass air guide ring is arranged with the inner surface of the upper end of the metal air inlet ring; the outer peripheral surface of the inserted glass air guide ring maintains a gap with the inner hole of the graphite air ring and extends downward for a distance to form an annular air gap.

2. The optical fiber drawing furnace according to claim 1, characterized in that The furnace mouth sealing device is a glass ring quartz wool floating sealing device.

3. The optical fiber drawing furnace according to claim 1, characterized in that The outer periphery of the upper end of the graphite air ring is provided with radial air inlet holes spaced evenly along the circumferential direction. The radial air inlet holes are downwardly inclined and radially deflected. When air is admitted, a protective air ring layer is formed that rotates downward and surrounds the optical fiber preform.

4. The optical fiber drawing furnace according to claim 3, characterized in that The downward tilt angle α of the radial air inlet is 10 to 40°, and the radial deflection angle β is 15 to 45°.

5. The optical fiber drawing furnace according to claim 3 or 4, characterized in that The diameter of the radial air inlet holes is 1.5 to 3 mm, and the number of air inlet holes uniformly distributed along the circumference is 20 to 50.

6. The optical fiber drawing furnace according to claim 1, characterized in that The lower end of the graphite air ring extends downward for a distance, the axial direction is staggered with the graphite central tube, and the outer periphery is configured with the inner hole of the graphite central tube.

7. The optical fiber drawing furnace according to claim 2, characterized in that The glass ring quartz wool floating sealing device includes a glass sealing seat installed on the upper end of the metal air inlet ring, an annular sealing groove set in the inner hole of the glass sealing seat is filled with sealing quartz wool, a radial floating glass tightening ring is installed on the glass sealing seat, a quartz wool sealing layer covering the optical fiber preform rod is set in the radial floating glass tightening ring, and an upper glass pressure ring is installed on the upper end of the radial floating glass tightening ring.

8. The optical fiber drawing furnace according to claim 7, characterized in that The radial floating glass tightening ring includes 2 to 4 glass arc blocks, each of which has a clamping groove on its outer circumferential surface. The glass arc blocks are spliced ​​into a ring along the circumferential direction and an annular spring is clamped through the clamping groove, which surrounds the outer circumference of the quartz wool sealing layer to form a radial floating glass tightening ring.

9. The optical fiber drawing furnace according to claim 1 or 2, characterized in that The metal air inlet ring is connected to the protective gas source through a connecting pipe and a control valve, so that the protective gas enters the annular air inlet cavity.

10. The optical fiber drawing furnace according to claim 1 or 2, characterized in that The metal flange and the metal air inlet ring are respectively provided with cooling water tanks.

11. A method for drawing an optical fiber, characterized in that Using any one of claims 1-10, the optical fiber preform rod clamped on the lifting feed bracket device is passed through the furnace mouth sealing device and the protective gas ring structure into the upper furnace mouth of the drawing furnace and into the furnace cavity, the protective gas is turned on to enter the furnace cavity through the protective gas ring structure, and the heating coil is turned on to heat the graphite center tube. When the drawing furnace is heated to above 1700°C, the optical fiber preform rod is drawn into an optical fiber by high-temperature melting.

12. The optical fiber drawing method according to claim 11, characterized in that The protective gas flow rate is 20-40 L / min, and the protective gas is helium or argon.

13. The optical fiber drawing method according to claim 11, characterized in that The outer diameter of the optical fiber preform is 120-240 mm.

14. The optical fiber drawing method according to claim 11, characterized in that The fluctuation of the outer diameter of each optical fiber preform is less than 40 mm.

15. The optical fiber drawing method according to claim 11, characterized in that The feeding speed of the optical fiber preform is 0.5-2 mm / min, and the maximum drawing speed is 3500 m / min.

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