A sensitized optical cable and its preparation method

Abstract

The application discloses a kind of sensitization sensing optical cable and preparation method thereof, the optical cable includes optical fiber, microtexture inner buffer layer, gradient foaming layer, outer buffer layer, damping layer, metal braiding layer and outer sheath arranged sequentially from inside to outside.The application realizes the efficient coupling and amplification of strain, temperature and vibration signal by the design of microtexture inner buffer layer and gradient foaming layer, greatly improves sensing sensitivity;Microtexture structure is introduced in the microtexture inner buffer layer, which not only ensures the protection of optical fiber surface, but also realizes controllable friction and signal coupling adjustment;The gradient foaming layer adopts radial density and pore size distribution gradient design, realizes efficient coupling of strain amplification and thermal / mechanical signal, and has better protection effect on the bending performance of optical fiber;Damping layer and metal braiding layer work together to significantly enhance the tensile, compression and impact resistance, while suppressing external vibration and noise interference;The optical cable has excellent weather resistance, high and low temperature resistance and corrosion resistance, to ensure long-term stable operation.

Description

Technical Field

[0001] This invention belongs to the field of optical cable technology, specifically relating to an enhanced-sensitivity optical cable and its preparation method. Background Technology

[0002] With the rapid development of fiber optic sensing technology, fiber optic-based temperature and strain monitoring has been widely used in power systems, geological disaster early warning, petrochemicals, and transportation infrastructure. As the carrier of sensing signals, special optical cables not only need to ensure the transmission performance of the optical fiber, but also must have excellent environmental adaptability and mechanical protection capabilities to ensure long-term stable operation.

[0003] Existing sensing optical cables have the following limitations due to their structure:

[0004] When strain and temperature are monitored in tight-buffered optical fibers, stresses such as tension, bending, and compression are easily transmitted directly to the optical fiber. The outer protective material of the optical fiber provides relatively poor mechanical protection, and the optical fiber is prone to breakage under high stress.

[0005] If the tight-buffered optical fiber has no buffer layer and the solid plastic structure is too rigid, the optical fiber is prone to micro-bending loss when used over long distances, which will shorten its service life.

[0006] For example, loose tube optical fibers have excess fiber length and grease, which makes the optical fiber insensitive to strain and temperature monitoring.

[0007] If the overall diameter of the loose sleeve is large, it is not conducive to miniaturization. At the same time, the pipe wall is relatively hard, which limits its bending performance.

[0008] The aforementioned shortcomings directly affect the monitoring quality, long-term operational stability, and laying environment limitations of the sensing optical cable. Therefore, it is urgent to achieve technological iteration and upgrading of the next generation of sensing optical cables through optimization of product structure and materials. Summary of the Invention

[0009] To address the problems in the prior art, the present invention aims to provide an enhanced-sensitivity optical cable and its preparation method.

[0010] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows:

[0011] An enhanced sensing optical cable includes, from the inside out, an optical fiber, a micro-textured inner buffer layer, a gradient foaming layer, an outer buffer layer, a damping layer, a metal braided layer, and an outer sheath.

[0012] Furthermore, the microtextured inner buffer layer has a microtextured structure on the side closest to the optical fiber.

[0013] Furthermore, the side of the gradient foamed layer near the microtextured inner buffer layer is a high-density closed-cell region with small pores, a pore size of 20-30 μm, and a density of 0.6-0.7 g / cm³. 3 The gradient foamed layer has a large-pore, low-density closed-cell region on the side near the outer buffer layer, with a pore size of 40-80 μm and a density of 0.4-0.5 g / cm³. 3 .

[0014] Furthermore, the thickness of the outer buffer layer is 100-160 μm.

[0015] Furthermore, the thickness of the damping layer is 0.1-0.3 mm, and the shear modulus is 0.1-10 MPa.

[0016] Furthermore, the thickness of the outer protective layer is 0.8-1.2 mm.

[0017] This invention also discloses a method for preparing an enhanced-sensitivity optical cable, comprising the following steps:

[0018] 1) Provide optical fiber;

[0019] 2) Fabricate a microtextured inner buffer layer on the outside of the optical fiber;

[0020] 3) A gradient foaming layer is prepared outside the microtextured inner buffer layer;

[0021] 4) An outer buffer layer is prepared outside the gradient foaming layer;

[0022] 5) Prepare a damping layer outside the outer buffer layer;

[0023] 6) Prepare a metal braided layer outside the damping layer;

[0024] 7) Prepare an outer protective layer outside the metal braided layer.

[0025] Furthermore, in step 2), the step of fabricating a microtextured inner buffer layer on the outside of the optical fiber includes:

[0026] The raw materials for preparing the microtextured inner buffer layer are fed into a single-screw extruder with an aspect ratio greater than 25. The die of the single-screw extruder adopts a microtextured die core. When the optical fiber passes through the microtextured die core, a microtextured structure is formed on the outer surface of the optical fiber. After exiting the die, it immediately enters a vacuum sizing sleeve for preliminary shaping. The vacuum degree is 0.06-0.08 MPa.

[0027] Furthermore, the microtextured mold core includes a mold core seat, the central position of which is raised to form a material flow channel, the material flow channel has an optical fiber hole for passing through the optical fiber, and the material flow wall of the material flow channel is processed with several regularly spaced microtextured bumps. The mold core seat is also provided with several shaft pins and positioning holes.

[0028] Furthermore, in step 3), the step of preparing a gradient foaming layer outside the microtextured inner buffer layer includes:

[0029] (1) Preparation of functional masterbatch for high-density closed-cell region with small pores and functional masterbatch for low-density closed-cell region with large pores:

[0030] The functional masterbatch for the high-density closed-cell region comprises the following components by weight percentage:

[0031] PA12 foaming material: 89.6-94.2%;

[0032] Nucleating agent 0.4-0.8%;

[0033] Al2O3 or BN filler 5-10%;

[0034] The functional masterbatch for the macroporous, low-density closed-cell region comprises the following components by weight percentage:

[0035] PA12 foam material 94.85-99.6%;

[0036] Nucleating agent 0.15-0.4%;

[0037] Thermally conductive filler 0-5%;

[0038] Both the functional masterbatch of the small-pore high-density closed-cell region and the functional masterbatch of the large-pore low-density closed-cell region are prepared by mixing and granulation using a twin-screw extruder. The functional masterbatch needs to be fully dried.

[0039] (2) The functional masterbatch of small-pore high-density closed-cell region and the functional masterbatch of large-pore low-density closed-cell region are respectively fed into different dies of twin-screw extruder. Combined with the high-pressure physical foaming injection system, the pore size and density gradient from the inside to the outside is formed through the radial flow channel of the die and the local temperature difference induction.

[0040] (3) The vacuum sizing sleeve, air cooling section and water cooling section are used for shaping in sequence. The vacuum degree is -0.06~-0.09MPa, the length of the air cooling section is controlled at 1-3m, and the traction ratio is 1.2-1.5.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] a. Enhanced sensing performance: Through the design of micro-textured internal buffer layer and gradient foaming layer, efficient coupling and amplification of strain, temperature and vibration signals are achieved, significantly improving the sensitivity of fiber optic sensing.

[0043] b. Structural optimization: A microtextured structure design is introduced into the microtextured inner buffer layer to ensure the protection of the fiber surface and achieve controllable friction and signal coupling adjustment. The gradient foaming layer adopts a radial density and pore size distribution gradient design to achieve efficient coupling of strain amplification and thermo / mechanical signals. It has both lightweight and buffering functions, avoiding the excessive constraint or excessive slippage problems of traditional tight / loose sleeve structures, and at the same time, it has a better protection effect on the bending performance of the fiber.

[0044] c. Superior mechanical performance: A damping layer is designed between the outer buffer layer and the metal braid layer to effectively reduce external vibration and noise transmission and improve signal purity. This is a design rarely seen in traditional sensing optical cables. The damping layer and the metal braid layer work together to significantly enhance tensile, compressive and impact resistance, while suppressing external vibration and noise interference.

[0045] d. The optical cable has excellent weather resistance, high and low temperature resistance and corrosion resistance, ensuring long-term stable operation;

[0046] e. High applicability: It adopts three-layer co-extrusion, supercritical CO2 foaming and high-precision weaving process, and the parameters are adjustable, which can take into account multiple sensing needs such as strain, temperature or vibration. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the structure of the present invention;

[0048] Figure 2 This is a schematic diagram of the structure of the microtextured mold core of the present invention;

[0049] Among them, 1-optical fiber; 2-microtextured inner buffer layer; 3-gradient foaming layer; 4-outer buffer layer; 5-damping layer; 6-metal braided layer; 7-outer protective layer; 8-shaft pin; 9-mold core seat; 10-microtextured bumps; 11-optical fiber hole; 12-positioning hole; 13-material flow wall. Detailed Implementation

[0050] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0051] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it 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 to prepare for the more detailed descriptions that follow.

[0052] like Figure 1-2As shown, the present invention discloses an enhanced sensing optical cable, comprising an optical fiber 1, a micro-textured inner buffer layer 2, a gradient foaming layer 3, an outer buffer layer 4, a damping layer 5, a metal braided layer 6, and an outer sheath 7 arranged sequentially from the inside to the outside.

[0053] In some implementations, fiber 1 is a standard communication or sensing fiber (such as G.652, G.657, etc.), and the appropriate type is selected according to the actual monitoring requirements.

[0054] In some implementations, the microtextured inner buffer layer 2 forms a regular microtextured structure on the side close to the optical fiber 1, forming a "local stick-slip zone". This ensures sufficient coupling to transfer static / low-frequency strain, while allowing local slippage to occur under transient or high stress conditions to avoid stress concentration and micro-damage.

[0055] In some implementations, the gradient foam layer 3 adopts a radial density and pore size distribution gradient design to achieve efficient coupling of strain amplification and thermo / mechanical signals. The inner region has a small-pore, high-density structure to ensure stable coupling between the optical fiber 1 and external stress and temperature, while the outer region has a large-pore, low-density structure to provide buffering and lightweighting.

[0056] In some specific embodiments, the side of the gradient foamed layer 3 near the microtextured inner buffer layer 2 is a high-density closed-pore region with small pores (pore size 20-30 μm, density 0.6-0.7 g / cm³). 3 This enhances the transmission of strain and temperature signals. The side closest to the outer buffer layer 4 is a large-pore, low-density closed-pore region (pore size 40-80μm, density 0.4-0.5g / cm³). 3 This provides excellent cushioning and shock resistance. The thickness of the gradient foam layer 3 is 200-350 μm.

[0057] In some embodiments, the outer buffer layer 4 has a thickness of 100-160 μm, providing surface abrasion resistance, end clamping strength and overall protection, and providing closed protection for the gradient foaming layer 3, limiting the exposure of the foam cell surface.

[0058] In some implementations, the damping layer 5 is used to absorb high-frequency noise and instantaneous impacts, improve the signal-to-noise ratio, and prevent unwanted vibrations from interfering with the optical fiber. It has a thickness of 0.1-0.3 mm and a shear modulus of 0.1-10 MPa, balancing damping performance and overall flexibility of the optical cable.

[0059] In some embodiments, the metal braided layer 6 is uniformly distributed outside the damping layer 5, providing protection against external lateral pressure, biting, and bending. It also amplifies and conducts local strain, dispersing external lateral pressure, resisting biting, and serving as an electrical shielding grounding layer. In terms of materials, it is preferably woven from 304 / 316 stainless steel wire, galvanized steel wire, or tin-plated copper wire, with a wire diameter of 0.12-0.15 mm and a braiding coverage of 40-60%. After braiding, the finished product must undergo quality inspection for appearance and dimensions. The outer diameter should be maintained within a tolerance of ±0.05 mm, the braiding coverage must meet design requirements, and the braided mesh should be uniform and gap-free. Tensile and lateral pressure performance must be verified through mechanical testing, requiring the optical cable to withstand a tensile force of 1000 N and a lateral pressure of 1000 N / 100 mm, with an fiber attenuation increase not exceeding 0.05 dB / km.

[0060] In some implementations, the outer protective layer 7 serves as an environmental barrier, including moisture protection, abrasion resistance, UV protection, and final mechanical protection. Materials such as PU, PE, or PVDF are selected, with a thickness of 0.8-1.2 mm, and the surface can be marked / printed.

[0061] This invention also discloses a method for preparing an enhanced-sensitivity optical cable, comprising the following steps:

[0062] 1) Provide fiber optic cable 1;

[0063] 2) A microtextured inner buffer layer 2 is fabricated on the outside of optical fiber 1;

[0064] 3) A gradient foaming layer 3 is prepared outside the microtextured inner buffer layer 2;

[0065] 4) An outer buffer layer 4 is prepared outside the gradient foaming layer 3;

[0066] 5) A damping layer 5 is prepared outside the outer buffer layer 4;

[0067] 6) Prepare a metal braided layer 6 outside the damping layer 5;

[0068] 7) Prepare an outer protective layer 7 outside the metal braided layer 6.

[0069] Step 2), the step of fabricating the microtextured inner buffer layer 2 outside the optical fiber 1 includes:

[0070] The micro-textured inner buffer layer 2 is extruded using a small single-screw extruder with an aspect ratio greater than 25 and a compression ratio controlled at approximately 2.5:1. The raw materials for preparing the micro-textured inner buffer layer 2 are fed into this small single-screw extruder. The die head uses a specially customized micro-textured die core, which includes a die core seat 9. A frustum-shaped or other shaped material flow channel is formed by a central protrusion in the die core seat 9. An optical fiber hole 11 for passing through the optical fiber 1 is opened inside the material flow channel. Several regularly spaced micro-textured protrusions 10 are machined on the material flow wall 13 of the material flow channel. The height / depth of the protrusions is 30-50μm and the spacing is 100-200μm. The microtexture protrusions 10 are in direct contact with the molten melt and are replicated to the inner surface of the microtexture inner buffer layer 2 during cooling and solidification, thereby forming a "local stick-slip zone" interface between the optical fiber and the microtexture inner buffer layer 2. The core holder 9 is also provided with two shaft pins 8 and positioning holes 12. The two shaft pins 8 are symmetrically arranged on opposite sides of the optical fiber hole 11 for radial / angular positioning and locking of the core in the mold, which facilitates assembly, concentric adjustment and subsequent disassembly and maintenance.

[0071] When fiber 1 passes through the microtextured mold core, a microtextured structure is formed on the outer surface of fiber 1. After exiting the mold, it immediately enters the vacuum sizing sleeve for preliminary shaping, with a vacuum degree of 0.06-0.08 MPa.

[0072] In some embodiments, the raw materials for preparing the microtextured inner buffer layer 2 include the following components by weight percentage:

[0073] Extrusion grade PA12 97.5-99% (extrusion grade PA12 can be replaced with PEEK under high temperature conditions);

[0074] Siloxane micro powder 0.3-1.5%;

[0075] Antioxidant 0.05-1.5%.

[0076] Incorporating siloxane micropowder helps improve the friction and peel performance between optical fiber 1 and the microtextured inner buffer layer 2.

[0077] Step 3), the step of preparing a gradient foaming layer 3 outside the microtextured inner buffer layer 2 includes:

[0078] (1) Preparation of functional masterbatch for high-density closed-cell region with small pores and functional masterbatch for low-density closed-cell region with large pores:

[0079] The functional masterbatch for high-density closed-cell regions with small pores comprises the following components by weight percentage:

[0080] PA12 foaming material: 89.6-94.2%;

[0081] Nucleating agent 0.4-0.8%;

[0082] Al2O3 or BN filler 5-10%;

[0083] The functional masterbatch for the macroporous, low-density closed-cell region comprises the following components by weight percentage:

[0084] PA12 foam material 94.85-99.6%;

[0085] Nucleating agent 0.15-0.4%;

[0086] Thermally conductive filler 0-5%;

[0087] Both the small-pore high-density closed-cell functional masterbatch and the large-pore low-density closed-cell functional masterbatch are produced by mixing and granulation using a twin-screw extruder. The functional masterbatch needs to be fully dried.

[0088] In terms of materials, PA12 foaming material with the same system as the microtextured inner buffer layer 2 is preferred to maintain the matching of thermal expansion and moisture absorption properties. Thermally conductive fillers (Al2O3 or BN fillers) are added to improve temperature response capability, but the dosage needs to be controlled to avoid foam collapse and embrittlement.

[0089] (2) The gradient foam layer 3 is formed by a twin-screw extruder combined with a high-pressure physical foaming injection system. The foaming gas is supercritical CO2. The injection system includes a high-pressure pump, a mass flow meter and a safety valve. The injection pressure is 12-18 MPa. The amount of CO2 added is set according to 0.1-0.5 wt% of the mass flow rate of molten PA12 and is precisely adjusted to ±0.01 g / s by the mass flow meter. The extruder adopts a multi-path parallel co-extrusion method, which feeds the functional masterbatch of small-pore high-density closed-pore area and the functional masterbatch of large-pore low-density closed-pore area into different dies of the twin-screw extruder. Combined with the high-pressure physical foaming injection system, a pore size and density gradient is formed from the inside to the outside through the radial flow channel of the die and the local temperature difference induction.

[0090] (3) After the molten PA12 is demolded, it passes through a vacuum sizing sleeve, an air-cooling section, and a water-cooling section for shaping. The vacuum degree is -0.06~-0.09MPa to ensure the outer diameter and the integrity of the closed pores. The length of the air-cooling section is controlled at 1-3m to allow the surface to cool down slowly and promote the closing of pores. Then it enters the water-cooling tank for rapid shaping. The traction ratio is 1.2-1.5 to ensure dimensional stability and prevent the bubbles from being torn apart. By adjusting the gas injection volume, nucleating agent ratio, die head temperature difference, and cooling rate, the inner bubble pore diameter is 20-30μm and the density is 0.6-0.7g / cm³. 3 The outer pore size is 40-80μm, and the density is 0.4-0.5g / cm³. 3 The overall closed-cell rate is greater than 90%.

[0091] In step 4), the raw materials for preparing the outer buffer layer 4 include the following components by weight percentage:

[0092] PA12 base material 97-99%;

[0093] Antioxidant 0.05-0.2%;

[0094] Heat stabilizer 0.05-0.5%;

[0095] Carbon black / light stabilizer 0-3%.

[0096] Step 5), the step of fabricating the damping layer 5 outside the outer buffer layer 4, includes:

[0097] There are two main production methods:

[0098] The first method involves bonding a separately prepared damping film to the surface of the outer buffer layer 4 via hot pressing or roll pressing. In this method, plasma surface treatment or mechanical micro-roughening is employed to improve the surface activity and roughness of the outer buffer layer 4, facilitating the formation of a stable interface between the damping film and the outer buffer layer 4. The bonding equipment is a hot press roller or a laminating machine, and temperature control depends on the glass transition temperature of the damping film material and the softening point of the adhesive. The damping film comprises the following components by weight percentage:

[0099] Polyurethane elastomer: 89.5-94.5%;

[0100] Internal plasticizer (phthalates) 5.3-10.1%;

[0101] Antioxidant 0.1-0.5%;

[0102] The second method involves co-extruding the damping material directly through a multi-layer co-extrusion device after the outer buffer layer extrusion process. In this method, the damping material is fed through a separate small extruder and merges with the outer buffer layer material flow within the co-extrusion die to form a tightly fitted double-layer structure. A small amount of compatibilizer, such as maleic anhydride-grafted polyolefin or polyurethane-polyamide copolymer, can be added to the damping material formulation. The damping material comprises the following components by weight percentage:

[0103] Vinyl acetate 91.5-96.5%;

[0104] Plasticizer 2-5%;

[0105] Compatibilizer 1-3%;

[0106] Heat stabilizer or light stabilizer 0.1-0.6%.

[0107] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0108] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A sensing optical cable with enhanced sensitivity, characterized in that, The optical fiber cable comprises, from inside to outside, an optical fiber, a micro-texture inner buffer layer, a gradient foaming layer, an outer buffer layer, a damping layer, a metal braid layer and an outer protective layer. The micro-texture inner buffer layer has a micro-texture structure on the side close to the optical fiber. The gradient foaming layer has a small-hole high-density closed-cell area with a pore size of 20-30 μm and a density of 0.6-0.7 g / cm 3 , and the gradient foaming layer has a large-hole low-density closed-cell area with a pore size of 40-80 μm and a density of 0.4-0.5 g / cm 3 .

2. The sensing optical cable according to claim 1, wherein The outer buffer layer has a thickness of 100-160 μm.

3. The sensing optical cable according to claim 1, wherein The damping layer has a thickness of 0.1-0.3 mm and a shear modulus of 0.1-10 MPa.

4. The sensing optical cable according to claim 1, wherein The outer protective layer has a thickness of 0.8-1.2 mm.

5. A method of manufacturing a sensitized sensing optical cable according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: 1) providing an optical fiber; 2) preparing a micro-texture inner buffer layer outside the optical fiber; 3) preparing a gradient foaming layer outside the micro-texture inner buffer layer; 4) preparing an outer buffer layer outside the gradient foaming layer; 5) preparing a damping layer outside the outer buffer layer; 6) preparing a metal braid layer outside the damping layer; 7) preparing an outer protective layer outside the metal braid layer. The micro-texture inner buffer layer has a micro-texture structure on the side close to the optical fiber. The gradient foaming layer has a small-hole high-density closed-cell area with a pore size of 20-30 μm and a density of 0.6-0.7 g / cm 3 , and the gradient foaming layer has a large-hole low-density closed-cell area with a pore size of 40-80 μm and a density of 0.4-0.5 g / cm 3 .

6. The method of claim 5, wherein the step of applying a coating of a light- absorbing material to the outer surface of the optical fiber is performed by a process selected from the group consisting of: dip coating, spin coating, and spray coating. In step 2), the step of preparing the micro-texture inner buffer layer outside the optical fiber comprises: feeding the raw material for preparing the micro-texture inner buffer layer into a single-screw extruder with a length-diameter ratio greater than 25, wherein a micro-texture die core is used for the die head of the single-screw extruder, and the micro-texture structure is formed on the outer surface of the optical fiber when the optical fiber passes through the micro-texture die core, and the extruded product is immediately introduced into a vacuum sizing sleeve for preliminary sizing, and the vacuum degree is 0.06-0.08 MPa.

7. The method of claim 6, wherein the method further comprises the step of: The micro-texture die core comprises a die core seat, wherein a flow channel is formed by protruding in the central position of the die core seat, an optical fiber hole for passing through the optical fiber is opened in the inside of the flow channel, and a plurality of regular micro-texture protrusions are processed on the flow wall of the flow channel, and a plurality of shaft pins and positioning holes are further arranged on the die core seat. ​ 8. The method of claim 5, wherein the optical fiber is a single mode fiber. In step 3), the step of preparing the gradient foaming layer outside the micro-texture inner buffer layer comprises: (1) preparing a functional master batch for a small-hole high-density closed-cell zone and a functional master batch for a large-hole low-density closed-cell zone: The functional master batch for the small-hole high-density closed-cell zone comprises the following components by weight percentage: PA12 foaming material 89.6-94.2%; Nucleating agent 0.4-0.8%; Al2O3 or BN filler 5-10%; The functional master batch for the large-hole low-density closed-cell zone comprises the following components by weight percentage: PA12 foaming material 94.85-99.6%; Nucleating agent 0.15-0.4%; Thermal conductive filler 0-5%; Both the functional master batch for the small-hole high-density closed-cell zone and the functional master batch for the large-hole low-density closed-cell zone are prepared by twin-screw extruder mixing and granulation, and the functional master batch needs to be sufficiently dried; (2) feeding the functional master batch for the small-hole high-density closed-cell zone and the functional master batch for the large-hole low-density closed-cell zone into different die heads of a twin-screw extruder respectively, combining with a high-pressure physical foaming injection system, and forming a pore size and density gradient from inside to outside through radial shunt channels and local temperature difference induction of the die head; (3) sequentially passing through a vacuum sizing sleeve, an air cooling section and a water cooling section for sizing, wherein the vacuum degree is -0.06~-0.09 MPa, the length of the air cooling section is controlled to be 1-3 m, and the draw ratio is 1.2-1.5.

Images