Double-ring cage-shaped multi-electrode combined plasma high-temperature furnace

Abstract

The invention provides a double-ring cage-shaped multi-electrode combined plasma high-temperature furnace. The device is characterized in that the device is composed of a heat insulation layer, a windproof cover, electrode bar sets and an annular electrode holder, based on arc discharge optical fiber hot working, electrode bars are embedded and fixed in the annular electrode holder, the number of the electrode bar sets is not less than two, needle tips of the electrode bars in each set are opposite in pairs, and a cage type high-temperature heating area defined by a plurality of plasma arcs is formed; different angles can be formed at the joint of the electrode bar group and the annular electrode holder according to different optical fibers, so that different longitudinal widths of the heating area are formed. Under the condition that the optical fiber is uniformly heated, the axial length of a temperature field is controlled by adjusting the needle point distance of the electrode bar group, and the heat insulation layer is rotated to drive the electrode bar group to twist a fire arc to form a local high-temperature area, so that the hot working requirements of different optical fiber types such as a large-core-diameter optical fiber drawing slowly-changing cone and large-pitch torsion are met; the method is suitable for the optical fiber processing field.

Description

Technical Field

[0001] The invention relates to a double-ring cage-shaped multi-electrode combined plasma high-temperature furnace, which can be used for thermal processing requirements of different optical fiber types such as large-diameter optical fiber drawing slowly variable tapers and large pitch twisting, and belongs to the field of optical fiber processing. Background Art

[0002] In the field of optical fiber thermal processing, arc plasma has a higher electrical-to-thermal conversion efficiency than laser, and reactive gases can be introduced for chemical removal. It can maintain the high quality of plasma processing while having the high efficiency of laser heat removal, which has important research significance for the processing of large-diameter and high-precision optical components.

[0003] Arc discharge is widely used in long-period fiber grating writing and melt taper. Long-period fiber gratings prepared by arc discharge have good thermal stability at high temperatures. The arc discharge method is that during the axial movement of the optical fiber, the electrode periodically discharges the optical fiber to form a long-period fiber grating. This method is simple and easy to control. It does not require doped optical fiber and optical fiber hydrogen loading. It can be adjusted by adjusting the size of the arc current and the size of the heated area of ​​the optical fiber. However, in the case of different optical fiber diameters such as optical fiber preform taper and large pitch torsion, the existing arc discharge based on plasma generation device has a small temperature zone and uncontrollable temperature, and cannot adapt to the thermal processing conditions of large core diameter optical fiber.

[0004] To solve the above problems, the method proposed in the patent of a large constant temperature zone four-electrode arc discharge high temperature optical fiber processing device (CN113820786A) widens the constant temperature zone by placing the axis of the electrode rod in the same plane as the axis of the optical fiber, overcoming the problem of a narrow constant temperature zone in the axial direction of the optical fiber due to arc discharge. However, it does not solve the problem that when the core diameter is too large and exceeds the plane of the temperature zone in the thermal processing of optical fibers with large core diameters, it is easy to cause uneven thermal processing. At the same time, when the external air flow fluctuates, the temperature of the plane temperature zone is easily disturbed. The method proposed in the patent of a multi-electrode system (CN200880008726) improves the problem of a narrow temperature zone and reduces air flow disturbance. However, when used, the electrodes need to be arranged in a partial vacuum or an absolute vacuum. The processing conditions are harsh and are not suitable for large pitch and long distance torsion processing. The patent of a multi-electrode AC arc discharge device, equipment and AC power supply (CN113727483A) mainly solves the problem of generating continuous and uniform large-volume plasma, but it is often used for powder material processing and preparation, and is not suitable for optical fiber thermal processing.

[0005] At present, the thermal processing requirements of different types of optical fibers such as slow-changing tapers and large pitch twisting for large-diameter optical fiber drawing are all based on oxyhydrogen flame optical fiber thermal processing, etc., and no large-diameter optical fiber thermal processing technology based on arc plasma has been found. However, the temperature of the oxyhydrogen flame may be difficult to accurately control, which may cause inconsistency in the optical fiber during processing. Due to the high temperature of the oxyhydrogen flame, optical fiber materials may be damaged, especially in high-power applications, where thermal damage or melting may occur. The use of oxyhydrogen flames may produce harmful byproducts and have potential negative impacts on the environment. At the same time, hydrogen is a flammable and explosive gas, and special attention should be paid to safety during operation, and the safety requirements for operators are high. As the requirements for precision and repeatability of optical fiber devices increase, oxyhydrogen flame processing may be difficult to meet the needs of high precision and high repeatability. In order to maintain stability during oxyhydrogen flame processing, a complex gas path system may be required, which may increase production costs.

[0006] The present invention discloses a double-ring cage-shaped multi-electrode combined plasma high-temperature furnace. The connection between the electrode rod group and the annular electrode seat can form different angles according to different optical fibers, thereby forming different longitudinal widths of the heating zone, and the optical fiber passes along the central axis of the annular electrode seat. The present invention can control the axial length of the temperature field by adjusting the needle tip distance of the electrode rod group and rotating the heat insulation layer to drive the electrode rod group to twist the fire arc to form a local high-temperature temperature zone while ensuring uniform heating of the optical fiber. The present invention is suitable for the field of optical fiber processing. Summary of the invention

[0007] The purpose of the present invention is to provide a double-ring cage-shaped multi-electrode combined plasma high-temperature furnace. This device can be used to meet the thermal processing requirements of different optical fiber types such as large-diameter optical fiber drawing slowly variable cones, large pitch torsion, etc., and can be widely used in optical fiber thermal processing systems.

[0008] The object of the present invention is achieved in that:

[0009] A double-ring cage-shaped multi-electrode combined plasma high-temperature furnace is invented, which is characterized in that the device includes: a heat insulation layer, a ring-shaped electrode seat, an electrode rod group, and a windproof cover.

[0010] The thermal insulation layer includes left and right thermal insulation layers, the left thermal insulation layer and the right thermal insulation layer are coaxially placed, the middle area between the two is a processing area, and the processing range of the processing area can be changed by adjusting the needle tip distance, the annular electrode seat is embedded and fixed inside the thermal insulation layer, the annular electrode seats on both sides are coaxially placed, the electrode rod group is embedded and fixed in the annular electrode seat, and the fixed position between the two has an angle biased towards the internal center, and the angle range is 0 degrees to 90 degrees

[0011] The electrode rod group is composed of no less than 2 groups of electrode rod groups, and each group of electrode rod groups is composed of a pair of electrode rods facing each other.

[0012] The electrode rod deflection angle θ can be set according to the diameter of the processed optical fiber, and its calculation formula is as follows:

[0013] Among them, L is the length of the electrode rod, R is the radius of the annular electrode holder, and r is the radius of the large core fiber. The corresponding electrode rod deflection angle is selected based on the known fiber diameter. The purpose is twofold: first, to prevent the processed fiber from being completely distributed in the temperature field due to the large deflection angle, resulting in uneven thermal processing; second, the size of the temperature field required for different fiber diameters is also different, and the size of the temperature field is determined by the spatial distribution of the electrode rod group.

[0014] When the processing area is determined, the thermal insulation layer can rotate coaxially relative to the processing optical fiber, and the rotation angle depends on the diameter of the processing optical fiber. The purpose is, firstly, when the thermal insulation layer rotates, it drives the internal electrode rod group to rotate. The rotation of the electrode rod group forms a single-leaf hyperbolic plasma distribution, and a higher temperature is achieved in the central area of ​​the processing area, which can be used for local heating of the optical fiber or drawing a steep cone. Secondly, the plasma fire arc rotates close to the processing optical fiber, and the optical fiber does not directly pass through the fire arc, which can reduce the metal splash of the electrode rod group affecting the optical fiber processing quality.

[0015] The coaxial relative rotation of the heat insulation layer satisfies the following rule.

[0016] When the heat insulation layer rotates, it drives the internal electrode rod group to rotate. Assuming that the plasma arc width is not considered, the surface generated by rotating the hyperbola around its main axis is called a single-leaf hyperboloid in geometry. A straight line passes through any point of the single-leaf hyperboloid.

[0017] A single-leaf hyperboloid (sometimes called a hyperboloid of revolution or a circular hyperboloid) is a surface produced by rotating a hyperbola about its major axis.

[0018] If you choose a Cartesian coordinate system whose axes are the axes of symmetry of the hyperboloid, and the origin is the center of symmetry of the hyperboloid, then the hyperboloid can be defined by one of the following two equations: or

[0019] Both equations approach the cone of the equation below.

[0020] If and only if a 2 =b 2 A rotational hyperboloid can be formed.

[0021] In the first case (where the right side of the equation is 1), it is a single-leaf hyperboloid, also called a hyperboloid.

[0022] The single-leaf hyperboloid temperature field representation satisfies the following rules.

[0023] By rotating the thermal insulation layer, the internal electrode rod group is driven to rotate, forming a temperature field that satisfies a single-leaf hyperboloid. This temperature field has the characteristics of high temperature in the middle and gradually decreasing toward both ends. It can realize thermal processing of different optical fiber types such as large-diameter optical fiber drawing, slowly variable cone, large pitch torsion, etc.

[0024] The arc discharge satisfies the following rules.

[0025] Arc discharge is an important form of gas discharge. It is difficult to give a strict definition of arc discharge. The most significant feature that distinguishes it from other gas discharge stages is that it will present an upward curved arc and produce a very high temperature hot plasma during the discharge process. The positive and negative electrodes are broken down by high voltage discharge to form a loop. The cathode emits an electron flow to the anode. The electron flow is constantly accelerated in the process of moving toward the anode, gaining extremely high energy, colliding with neutral gas molecules and atoms between the electrodes, transferring energy to neutral particles, and the gas is strongly ionized to produce ions and free electrons, accompanied by strong luminescence and heat release. The electrons generated by gas ionization further collide with non-ionized neutral gas particles, thereby producing avalanche ionization.

[0026] Gas breakdown is an important phenomenon in the gas discharge process. When the voltage across the gas discharge tube is small, the gas discharge current is very weak. On this basis, when the voltage across the two ends is increased, the current does not increase significantly. However, when the voltage increases to a certain level, the current passing through the gas gap will increase sharply, and the gas will show the characteristics of a conductor. This phenomenon is called gas breakdown, and the corresponding critical voltage is called breakdown voltage.

[0027] The breakdown voltage is an important parameter of gas discharge, which is related to factors such as electrode material, gas medium, inter-electrode distance, gas pressure, etc. Paschen derived a method for calculating the breakdown voltage of gas under uniform field strength, which is called Paschen's law. The calculation formula is as follows: Among them, P is the gas pressure, d is the inter-electrode distance, and A, B, and γ are all constants related to the gas type and the metal material. According to Paschen's law, when the metal material and the gas medium are determined, the breakdown voltage is a function of the product of the gas pressure and the inter-electrode distance. In addition, as the product of the gas pressure and the inter-electrode distance increases, the breakdown voltage first decreases and then increases. By setting the breakdown voltage parameters, the inter-electrode distance can be changed and the working range can be increased.

[0028] Compared with the prior art, the double-ring cage-shaped multi-electrode combined plasma high-temperature furnace proposed by the present invention has at least the following advantages:

[0029] (1) The device has high reliability, simple structure, simple electrode rod installation, high feasibility of optical fiber thermal processing, and is suitable for mass production.

[0030] (2) Improve temperature diversity. During the thermal processing of optical fibers, in addition to increasing the breakdown voltage parameters and increasing the power to increase the temperature of the processing area, the electrode rod group can also be rotated to form a single-leaf hyperbolic plasma distribution. The temperature of the middle section increases as the arcs get closer.

[0031] (3) The processing efficiency is stable. During the optical fiber thermal processing, because the processed optical fiber does not directly pass through the fire arc, when the breakdown voltage peak changes instantaneously, it will not directly affect the heating of the optical fiber.

[0032] (4) Improve processing quality. During the optical fiber thermal processing, because the processed optical fiber does not directly pass through the fire arc, the impact of metal splashing from the electrode rod is greatly reduced.

[0033] (5) There are a variety of optical fiber processing types, which can be applied to the thermal processing needs of different optical fiber types such as slow-changing cones, large pitch twisting, etc. for drawing different large-diameter optical fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of a double-ring cage-shaped multi-electrode combined plasma high-temperature furnace;

[0035] Figure 2 It is a schematic diagram of the parallel arc structure of a double-ring cage-shaped six-electrode combination plasma high-temperature furnace;

[0036] Figure 3 It is a simulation diagram of a single-blade hyperbolic type based on a rotating fire arc;

[0037] Figure 4 It is a schematic diagram of the rotating arc structure of a double-ring cage-shaped six-electrode combination plasma high-temperature furnace;

[0038] Figure 5 It is a schematic diagram of the structure of a double-ring cage-shaped four-electrode combination plasma high-temperature furnace;

[0039] Figure 6 It is a schematic diagram of the parallel arc structure of a double-ring cage-shaped four-electrode combination plasma high-temperature furnace;

[0040] Figure 7 It is a double-ring cage-shaped four-electrode combination plasma high-temperature furnace arc heating optical fiber temperature map;

[0041] In the figure:

[0042] 1-insulation layer, 2-annular electrode holder, 3-electrode rod group, 4-wind shield, 101 right side insulation layer, 102 left side insulation layer. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with specific embodiments. In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0044] The invention discloses a double-ring cage-shaped multi-electrode combined plasma high-temperature furnace.

[0045] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] Figure 2 The invention is a schematic diagram of a parallel arc structure of a double-ring cage-shaped six-electrode combination plasma high-temperature furnace. It comprises: an insulation layer 1, an annular electrode holder 2, and an electrode rod group 3. The electrode rod group 3 is composed of three groups of electrode rods. The insulation layer 1 is composed of a right insulation layer 101 and a left insulation layer 102. The insulation layers on both sides are coaxially placed. The middle area between the two is a processing area. The processing area can change the processing range by adjusting the distance. The annular electrode holder 2 is embedded and fixed inside the insulation layer 1. The annular electrode holders 2 on both sides are coaxially placed. The electrode rod group 3 is embedded and fixed in the annular electrode holder 2. The fixed position between the two has an angle deviated to the inner center. Assuming that the diameter r of the processed optical fiber is 2 cm, the radius R of the annular electrode holder is 5 cm, and the length of the electrode rod L = 5 cm, according to formula (1), θ = 36.87° is calculated. By using the known optical fiber diameter, the corresponding electrode rod deflection angle is selected. The purpose is to prevent the processing optical fiber from being completely distributed in the temperature field due to the large deflection angle or the optical fiber being too far from the arc, resulting in uneven thermal processing. In the system, two electrode rods in each of the three groups of electrode rods are opposite to each other, forming a triangular three-dimensional processing temperature zone centered on the processing optical fiber, so that the temperature zone distribution is more uniform. And according to formula (5), by increasing the breakdown voltage, the arc length can be increased, and the axial and radial temperature field expansion can be achieved.

[0047] Figure 3It is a simulation diagram of a single-leaf hyperboloid type based on a rotating fire arc. The simulation diagram is a surface generated by rotating a single-leaf hyperboloid (sometimes called a rotating hyperboloid or a circular hyperboloid) around its principal axis. A hyperboloid is a surface that can be obtained from a rotating parabola by deforming it using directional calibration. A hyperboloid is a quadratic surface, which can be defined as the surface of a set of points of a two-dimensional polynomial in three variables. Among quadratic surfaces, the hyperboloid is characterized in that it not only has a center of symmetry, but also allows planes to intersect it to form cones, cylinders, etc. The hyperboloid also has three pairs of vertical symmetry axes and three pairs of vertical symmetry planes. The single-leaf hyperboloid parameter representation approximately satisfies formula (4). The single-leaf hyperbolic temperature field is formed by rotating the arc straight line. The purpose is, firstly, that when the insulation layer rotates, it drives the internal electrode rod group to rotate. The electrode rod group rotates to form a single-leaf hyperbolic plasma distribution, so that a higher temperature is achieved in the central area of ​​the processing area, which can be used for local heating of optical fiber or drawing of steep cones. Secondly, the plasma arc rotates close to the processed optical fiber, and the optical fiber does not directly pass through the arc, which can reduce the metal splash of the electrode rod group affecting the optical fiber processing quality.

[0048] Figure 4 The invention is a schematic diagram of a rotating arc structure of a double-ring cage-shaped six-electrode combination plasma high temperature furnace. It includes: a heat insulation layer 1, a ring electrode holder 2, and an electrode rod group 3. The heat insulation layer 1 is composed of a right heat insulation layer 101 and a left heat insulation layer 102, and the heat insulation layers on both sides are coaxially placed.

[0049] In the system, the two electrode rods in each of the three groups of electrode rods are opposite to each other, forming a triangular three-dimensional processing temperature zone centered on the processed optical fiber. Then the relative positions of the insulation layers 1 on the left and right sides remain unchanged, and the insulation layer 102 on the left side is rotated, while increasing the breakdown voltage. The purpose is to prevent arc breaking and damage to the power supply as the needle tip distance increases. During the rotation of the insulation layer, the left electrode rod group follows the rotation, the needle tip distance increases, and the needle tip potential changes from A+, B+, C+ to A-, B-, C-. The fire arc is elongated, and at the same time, the three different fire arcs continue to approach the central optical fiber position, forming a higher temperature area in the axial center. When the optical fiber passes through the central area axially, it will not be affected by the fire arc plasma. Based on this temperature field, optical fiber thermal processing such as large-diameter optical fiber taper and twisting can be achieved.

[0050] Example 2

[0051] Figure 5 The present invention is a schematic diagram of the structure of a double-ring cage-shaped four-electrode combination plasma high-temperature furnace, which includes: a heat insulation layer 1, a ring electrode seat 2, and an electrode rod group 3, wherein the electrode rod group 3 is composed of two groups of electrode rods.

[0052] Figure 6It is a schematic diagram of the parallel arc structure of a double-ring cage-shaped four-electrode combination plasma high-temperature furnace. Assuming that the radius r of the processed optical fiber is 2 cm, the radius R of the ring electrode holder is 5 cm, and the length of the electrode rod is L = 5 cm, according to formula (1), θ = 44.612°.

[0053] Figure 7 This is a temperature diagram of the arc heating optical fiber in a simple embodiment of a double-ring cage-shaped four-electrode combination plasma high-temperature furnace. (a) in the figure shows a double-ring cage-shaped four-electrode combination plasma high-temperature furnace electrode rod and optical fiber distribution position. The distance between the two sets of electrode rods is 3mm. The optical fiber is located in the center area of ​​the two sets of electrode rods. The breakdown voltage is started to generate an arc. (c) in the figure shows the temperature distribution of the optical fiber during the optical fiber thermal processing. The highest temperature fluctuates around 1100 degrees. The temperature diagram can reasonably arrange the electrode rod position, which provides feasibility for multi-electrode combination.

[0054] The present invention and its implementation methods are described schematically above, and the description is not restrictive. The drawings show only one implementation method of the present invention, and the actual structure and method are not limited thereto. Therefore, if a person skilled in the art is inspired by the invention and designs a structure and implementation method similar to the technical solution without creativity without departing from the purpose of the invention, they all fall within the protection scope of the present invention.

Claims

1. A double-ring cage-shaped multi-electrode combined plasma high-temperature furnace, It is characterized in that The device includes: A heat insulation layer (1), an annular electrode seat (2), an electrode rod group (3), and a wind shield (4).

2. According to claim 1, a double-ring cage-shaped multi-electrode combined plasma high-temperature furnace, Features: The thermal insulation layer (1) comprises left and right thermal insulation layers, the left thermal insulation layer (102) and the right thermal insulation layer (101) are coaxially arranged, the middle area between the two is a processing area, and the processing range of the processing area can be changed by adjusting the needle tip distance, the annular electrode seat (2) is embedded and fixed inside the thermal insulation layer (1), the annular electrode seats (2) on both sides are coaxially arranged, the electrode rod group (3) is embedded and fixed in the annular electrode seat (2), and the fixed position between the two has an angle biased towards the inner center, and the angle range is 0 degrees to 90 degrees.

3. According to claim 1, a double-ring cage-shaped multi-electrode combined plasma high-temperature furnace, Features: The number of the electrode rod groups (3) is n, and the relationship between n and the center angle of the circle is a multiple relationship, n is not less than 2, and each electrode rod group consists of two electrode rods facing each other.

4. According to claim 1, a double-ring cage-shaped multi-electrode combined plasma high-temperature furnace, Features: When the processing area is determined, the heat insulation layer (1) can rotate coaxially relative to the processing optical fiber, and the rotation angle depends on the diameter of the processed optical fiber. When the heat insulation layer (1) rotates, it drives the internal electrode rod group (3) to rotate.

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