A small and medium-sized optical fiber preform drawing system and a preparation method thereof

Abstract

The application discloses a small and medium-sized optical fiber preform rod stretching system and a preparation method thereof. The preparation method is as follows: an intermediate to be stretched with an outer diameter of 170-210 mm is prepared by adopting an OVD process; the intermediate to be stretched is clamped in place, and outer diameter data and rod body information are detected in real time; the intermediate to be stretched is fed downward into a stretching furnace and is softened by melting; a traction wheel stretches the softened intermediate to be stretched into a finished preform rod with an outer diameter of 80-150 mm; the actual outer diameter of the finished preform rod is monitored in real time; and a PLC controller adjusts the feeding speed of the intermediate to be stretched and the discharging speed of the finished preform rod in real time according to received data. The application has the beneficial effect that the intermediate with an outer diameter of 180-210 mm is prepared by adopting the OVD process, and then the intermediate is stretched to obtain the small and medium-sized finished preform rod with an outer diameter of 80-150 mm, so that the fluctuation range of the outer diameter of the finished product is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber preform preparation technology, specifically relating to a stretching system and a method for preparing small and medium-sized optical fiber preforms. Background Technology

[0002] Optical fiber preforms are the core substrate for optical fiber drawing production, with 185mm outer diameter OVD preforms being the mainstream product in the industry. However, in some special optical fiber applications, preforms with smaller outer diameters (80mm to 150mm) are required.

[0003] Currently, the industry commonly uses OVD deposition technology to directly prepare 80mm-150mm preforms. However, existing OVD deposition equipment is designed for large preforms of 170mm and above. The internal structure, such as the torch arrangement and flame coverage, is poorly adapted to small-diameter target rods, easily leading to uneven powder deposition, large fluctuations in the outer diameter of the finished preforms (with a maximum deviation of up to 30mm), poor dimensional consistency, and difficulty in guaranteeing the quality of optical fiber products obtained through subsequent fiber drawing. Furthermore, the small temperature gradient between the small-diameter target rod and the flame results in low thermophoretic adhesion efficiency of silica powder and low raw material adhesion efficiency. This leads to slow weight gain per batch, long preparation cycles, and overall low production efficiency for the direct deposition process.

[0004] Therefore, there is an urgent need to provide a process for fabricating small-to-medium-sized optical fiber preforms ranging from 80mm to 150mm. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a stretching system and preparation method for small and medium-sized optical fiber preforms, aiming to solve the problem of large fluctuations in the outer diameter of finished small and medium-sized optical fiber preforms in existing technologies.

[0006] The technical solution adopted in this invention is: a method for preparing small and medium-sized optical fiber preforms, which includes the following steps: S1. Solid preforms with an outer diameter of 170~210mm are prepared using the OVD process and used as intermediates for stretching. S2. Position and clamp the intermediate body to be stretched onto the hanging rod device, and use the tower body diameter measuring instrument to detect the outer diameter data and rod information of the intermediate body to be stretched in real time online, and feed them back to the PLC controller. S3. Start the stretching process and feed the intermediate body to be stretched downwards. The intermediate body to be stretched enters the stretching furnace from the lower end to the upper end in sequence. Under the heating action of the stretching furnace, the intermediate body to be stretched melts and softens. S4. The molten and softened intermediate to be stretched is stretched into a finished preform with an outer diameter of 80mm to 150mm by a traction wheel. The finished preform is drawn out from the lower furnace opening of the stretching furnace. The actual outer diameter of the finished preform is monitored in real time by a diameter measuring instrument at the lower furnace opening, and the real-time outer diameter detection data is fed back to the PLC controller. The PLC controller adjusts the feeding speed of the intermediate to be stretched and the discharge speed of the finished preform in real time according to the received data.

[0007] According to the above scheme, the method by which the PLC controller adjusts the feeding speed of the intermediate body to be stretched in real time based on the received data is as follows: the tower diameter measuring instrument pre-scans the real-time outer diameter data and bar position information of the intermediate body to be stretched; the PLC controller receives and records the real-time outer diameter data and bar position information, and calculates the real-time feeding speed corresponding to the real-time outer diameter state of the intermediate body to be stretched based on the preset weight of the molten glass material fed per unit time; the real-time feeding speed is compared with the preset initial feeding speed, and if the difference between the real-time feeding speed and the initial feeding speed is within the set threshold range, then there is no need to adjust the real-time feeding speed; otherwise, the real-time feeding speed is adjusted.

[0008] According to the above scheme, the method by which the PLC controller adjusts the discharge speed of the finished preform in real time based on the received data is as follows: Based on the real-time feeding speed, the target outer diameter of the finished preform, and the real-time outer diameter data of the intermediate to be stretched, the theoretical discharge speed of the finished preform is calculated. The theoretical outer diameter of the finished preform is calculated based on the axial temperature difference in the stretching furnace temperature zone, the theoretical discharge rate, the measured outer diameter of the intermediate body to be stretched, and the real-time feeding rate. The corrected discharge speed is calculated based on the theoretical outer diameter data of the finished preform, and the real-time speed of the traction wheel is adjusted so that the difference between the corrected discharge speed and the real-time speed of the traction wheel is controlled within a preset deviation threshold.

[0009] According to the above scheme, the method for calculating the corrected discharge speed of the finished preform is as follows: Calculation is performed using the following formula. ; In the formula, OF 1 represents the real-time outer diameter of the intermediate, in mm; V F The feed rate of the intermediate to be stretched is expressed in mm / s. OF 2 represents the theoretical outer diameter of the finished preform, in mm; V PΔT represents the corrected discharge speed of the finished preform, in mm / s; ΔT represents the temperature difference in the hot zone.

[0010] According to the above scheme, the heating power of the stretching furnace during the stretching process... P for: ; In the formula, A is a constant, ranging from 0.05 to 0.1; P 0 is the base power, with a value of 100kW; OF 1 represents the outer diameter of the intermediate body to be stretched; OF 0 is the reference outer diameter, which is 185mm.

[0011] According to the above scheme, the contact surface pressure between the traction wheel and the finished precast bar is... P m The condition of non-slippage must be met, that is: F 1= μ × P m × A m ≥ F 2; In the formula, P m The pressure at the contact surface between the traction wheel and the finished precast bar, in Pa; F 1 represents frictional force, in N; μ The coefficient of friction between the traction wheel and the finished preform; A m The contact area between the traction wheel and the finished precast bar is expressed in mm². F 2 represents the traction force required during the stretching process, in N.

[0012] According to the above scheme, the minimum pressure at the contact surface between the traction wheel and the finished precast bar is... P min for: P min = F 1 / ( μ × A m ).

[0013] The present invention also employs a small-to-medium-sized optical fiber preform stretching system to realize the small-to-medium-sized optical fiber preform preparation method described above; the system includes a rod hanging device, a stretching furnace, a traction wheel, a tower diameter gauge, a lower furnace opening diameter gauge, and a PLC controller; The hanging rod device is located above the inlet of the stretching furnace, and the hanging rod device is connected to the lifting mechanism, the two forming a feeding assembly; the top of the stretching furnace is provided with an upper furnace opening, and the bottom is provided with a lower furnace opening; the interior of the stretching furnace is equipped with heating elements; the traction wheel is installed below the lower furnace opening of the stretching furnace. The upper end of the intermediate body to be stretched is clamped and positioned by the hanging rod device, and the lower end of the intermediate body to be stretched extends into the furnace through the furnace opening at the top of the stretching furnace, where it melts and softens under the heating action of the heating element. The traction wheel pulls and stretches the molten and softened intermediate to be stretched into a finished preform, and the formed finished preform is vertically drawn out from the lower furnace opening of the stretching furnace. The tower diameter measuring instrument is located between the hanging rod device and the upper furnace opening of the stretching furnace; The lower furnace opening diameter measuring instrument is installed at the lower furnace opening of the stretching furnace; Both the tower diameter gauge and the lower furnace opening diameter gauge are connected to the PLC controller.

[0014] According to the above scheme, the heating element includes a graphite heating cylinder disposed above the inside of the stretching furnace, the outer periphery of the graphite heating cylinder is covered with a heat insulation layer, and an induction coil is installed outside the heat insulation layer; the inner diameter of the graphite heating cylinder is 240-300mm, and the axial height is 500-800mm; the inner diameter of the induction coil is 300-400mm, and the axial height is 300-400mm.

[0015] According to the above scheme, the heating temperature of the heating element is 1900~2100℃.

[0016] The beneficial effects of this invention are as follows: 1. This invention first uses OVD (Operational Vapor Deposition) technology to prepare solid preforms with an outer diameter of 170–210 mm as intermediates for stretching. Utilizing the mature and stable deposition characteristics of large-scale OVD equipment, the process achieves high efficiency and lower manufacturing costs. This large-size intermediate is then melt-stretched to obtain finished preforms with a size of 80–150 mm. Compared to the traditional process of directly depositing to prepare small-sized preforms, this method significantly reduces the fluctuation range of the finished product's outer diameter, significantly improves the overall uniformity of the finished preform's outer diameter, and achieves a high stretching success rate. This effectively increases the output and overall production capacity of the finished product, resulting in excellent geometric accuracy and fundamentally solving the problem of excessive dimensional deviations in existing processes.

[0017] 2. This invention considers the influence of axial temperature difference in the stretching furnace temperature zone on the outer diameter of the finished preform, and corrects the discharge speed of the finished preform to offset the molding error caused by temperature deviation, so that the outer diameter of the finished preform fits the preset target outer diameter, effectively improving the product molding quality and dimensional consistency.

[0018] 3. By adjusting the stretching power, this invention ensures consistent viscosity of the intermediate molten state during the stretching process, which can more effectively control the curvature and outer diameter stability, and further improve the quality of the finished product.

[0019] 4. This invention adjusts the clamping pressure and contact friction of the traction wheel, and matches the clamping force according to the change in the self-weight of the finished preform during the stretching process, so as to avoid the finished preform slipping or falling off during the stretching process and ensure the continuous and stable operation of the melt stretching process.

[0020] 5. Based on the traditional feeding and discharging speed matching formula, this invention compensates and corrects the discharging speed by incorporating the temperature difference of the graphite parts; through the coordinated use of multiple control methods such as feeding control, real-time discharging speed correction, and stretching power adjustment, the stability and uniformity of the outer diameter of the finished preform after stretching are significantly improved, so that the outer diameter of the finished product accurately matches the set target value. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the preform stretching system in this invention.

[0022] The components include: 1. Hanging rod device; 2. Tower body diameter gauge; 3. Intermediate body; 4. Stretching furnace; 5. Lower furnace opening diameter gauge; 6. Finished precast rod; 7. Traction wheel. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] In the description of the embodiments of this application, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0025] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0026] In the embodiments of this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0027] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, the term "a plurality of" indicates two or more.

[0028] like Figure 1 The system shown is a small-to-medium-sized optical fiber preform stretching preparation system, specifically a small-to-medium-sized optical fiber preform preparation system with an outer diameter of 80~150mm. The system includes a rod hanging device 1, a stretching furnace 4, a traction wheel 7, a tower diameter measuring instrument 2, a lower furnace opening diameter measuring instrument 5, and a PLC controller. The hanging rod device 1 is located above the inlet of the stretching furnace 4; the stretching furnace 4 is a vertical stretching furnace 4, with an upper furnace opening at the top and a lower furnace opening at the bottom; heating elements are installed inside the stretching furnace 4; the traction wheel 7 is installed below the lower furnace opening of the stretching furnace 4. The upper end of the intermediate body 3 to be stretched is clamped and positioned by the hanging rod device 1, and the lower end of the intermediate body 3 to be stretched enters the furnace through the furnace opening at the top of the stretching furnace 4, where it is melted and softened at high temperature under the heating action of the heating element. The traction wheel 7 pulls and stretches the molten and softened intermediate 3 into a finished preform 6, and the finished preform 6 is vertically drawn out from the lower furnace opening of the stretching furnace 4. The tower diameter measuring instrument 2 is located between the hanging rod device 1 and the upper furnace opening of the stretching furnace 4; The lower furnace opening diameter gauge 5 is installed at the lower furnace opening of the stretching furnace 4 and is used to detect the outer diameter data of the finished preform 6 after molding. Both the tower diameter measuring instrument 2 and the lower furnace opening diameter measuring instrument 5 are connected to the PLC controller.

[0029] In this invention, the intermediate body 3 to be stretched is prepared using the OVD process, with an outer diameter of 170-210 mm; the outer diameter of the finished preform 6 is 80-150 mm; the tower body diameter gauge 2 is used to scan the bar position information and corresponding outer diameter data of the intermediate body 3 to be stretched, and send them to the PLC controller; the lower furnace opening diameter gauge 5 is used to scan the outer diameter data of the finished preform 6, and send it to the PLC controller; the PLC controller adjusts the feeding speed of the intermediate body 3 to be stretched and the discharge speed of the finished preform 6 in real time according to the received data, so that the measured outer diameter of the finished preform 6 meets the design requirements.

[0030] Preferably, a cylindrical heating element is installed inside the stretching furnace 4; the heating element includes a graphite heating cylinder disposed above the inside of the stretching furnace 4, the outer periphery of the graphite heating cylinder is covered with a heat insulation layer, and an induction coil is installed outside the heat insulation layer. The inner diameter of the graphite heating cylinder is 240-300mm, and the axial height is 500-800mm; the inner diameter of the induction coil is 300-400mm, and the axial height is 300-400mm.

[0031] In this invention, the heating element has a heating temperature of 1900-2100℃ and is used to heat and melt the intermediate body 3 to be stretched.

[0032] In this invention, a sealing gas ring is installed at the upper furnace opening of the stretching furnace 4. The sealing gas ring is connected to an external inert pressure gas source. By introducing inert gas, a positive pressure environment is maintained inside the furnace, preventing outside air from entering the furnace cavity. At the same time, the inert atmosphere can protect the graphite heating cylinder inside the furnace, preventing the graphite components from being oxidized and burned by oxygen at high temperature.

[0033] Preferably, there are two sets of traction wheels 7, with their axles spaced apart and arranged in parallel; the two traction wheels 7 rotate in opposite directions at the same speed, and the finished preform 6 after stretching is located between the two traction wheels 7; a radial constant pressure device is provided between the two traction wheels 7.

[0034] In this invention, the traction speed of the traction wheel 7 is 500-800 mm / min. During operation, the radial constant pressure device causes a pair of traction wheels 7 to form a circumferential radial constant pressure clamp on the finished preform 6 after melting and stretching. The two traction wheels 7 rotate in opposite directions at the same speed to generate friction, which applies a constant downward traction force to the finished preform 6, pulling the finished preform 6 downward.

[0035] In this invention, the hanging rod device 1 is connected to the lifting mechanism, and the two form a feeding assembly; the lifting mechanism drives the hanging rod device 1 and the intermediate body 3 to be stretched to feed downward, and feeds the intermediate body 3 to be stretched into the stretching furnace 4 at a uniform speed; the PLC controller is connected to the lifting mechanism and is used to control the feeding speed of the intermediate body 3 to be stretched through the lifting mechanism.

[0036] In this invention, the tower diameter gauge 2 is installed above the stretching furnace 4, and includes an optical lens portion and an electrical component. The lower furnace opening diameter gauge is installed inside the stretching furnace 4 and located at the lower furnace opening, and includes an optical lens portion and an electrical component. Both the tower diameter gauge 2 and the lower furnace opening diameter gauge are existing mature structures. The tower diameter gauge 2 is composed of a Keyence 120 model dual-unit tester, which can be used for testing the outer diameter of preforms with an outer diameter of less than 300mm.

[0037] In this invention, the lifting mechanism, hanging rod device 1, stretching furnace 4, traction wheel 7, etc. are all mature equipment in the industry, and will not be described in detail here.

[0038] A method for fabricating small-to-medium-sized optical fiber preforms, specifically a method for fabricating small-to-medium-sized optical fiber preforms with an outer diameter of 80mm~150mm, is based on the preform stretching system described above; the method includes the following steps: S1. Solid preforms with an outer diameter of 170~210mm are prepared using the OVD process and used as intermediates to be stretched 3; S2. Position and clamp the intermediate body 3 to be stretched on the hanging rod device 1 of the precast rod stretching system. The outer diameter data and rod position information of the intermediate body 3 to be stretched are detected in real time online by the tower body diameter measuring instrument 2 and fed back to the PLC controller. S3. Start the stretching process. The lifting mechanism drives the hanging rod device 1 and the intermediate body 3 to be stretched to move downward. The intermediate body 3 to be stretched enters the stretching furnace 4 from the lower end to the upper end in sequence. Under the heating action of the stretching furnace 4, the intermediate body 3 to be stretched melts and softens. S4. The molten and softened intermediate body 3 with an outer diameter of 170~210mm is stretched into a finished preform 6 with an outer diameter of 80mm~150mm by the traction wheel 7. The finished preform 6 is continuously drawn out from the lower furnace opening of the stretching furnace 4. The actual outer diameter of the finished preform 6 after stretching is monitored in real time by the lower furnace opening diameter measuring instrument 5, and the real-time outer diameter detection data is fed back to the PLC controller. The PLC controller adjusts the feeding speed of the intermediate body 3 and the discharge speed of the finished preform 8 in real time according to the received data.

[0039] In this invention, the method by which the PLC controller adjusts the feeding speed of the intermediate body 3 to be stretched in real time based on the received data is as follows: the tower diameter gauge 2 pre-scans the real-time outer diameter data and rod position information of the intermediate body 3 to be stretched; the PLC controller receives and records the real-time outer diameter data and the corresponding rod position information, and calculates the real-time feeding speed corresponding to the real-time outer diameter state of the intermediate body 3 to be stretched based on the preset weight of the molten glass fed per unit time; the real-time feeding speed is compared with the preset initial feeding speed. If the difference between the real-time feeding speed and the initial feeding speed is within the set threshold range, then there is no need to adjust the real-time feeding speed; otherwise, the real-time feeding speed is adjusted. The larger the outer diameter of the intermediate body 3 to be stretched, the faster the matching feeding speed, thereby ensuring a constant amount of molten material fed per unit time, so as to ultimately improve the uniformity of the outer diameter of the 80mm~150mm preform after stretching.

[0040] In this invention, the discharge speed of the finished preform 6 is controlled by the traction wheel 7. The method by which the PLC controller adjusts the discharge speed of the finished preform 6 in real time based on the received data is as follows: Based on the real-time feeding speed, the target outer diameter of the finished preform 6, and the real-time outer diameter data of the intermediate body 3 to be stretched, the theoretical discharge speed of the finished preform 6 is calculated; then, based on the axial temperature difference of the temperature zone of the stretching furnace 4, the theoretical discharge speed, and the measured outer diameter and real-time feeding speed of the intermediate body 3 to be stretched, the theoretical outer diameter data of the finished preform 6 is calculated; based on the theoretical outer diameter data of the finished preform 6, the corresponding corrected discharge speed is calculated, and the real-time speed of the traction wheel is adjusted so that the difference between the corrected discharge speed and the real-time speed of the traction wheel 7 is controlled within a preset deviation threshold. The specific process is as follows: The PLC controller calculates the theoretical discharge speed of the finished preform 6 based on the feeding speed of the intermediate body 3 to be stretched, the target outer diameter of the finished preform 6, and the real-time outer diameter of the intermediate body 3 to be stretched measured by the tower diameter measuring instrument 2, using the classic formula (1): V F × OF 1× OF 1= OF 2× OF2× V P (1); In the formula, OF 1 represents the measured outer diameter of the intermediate body 3 to be stretched, in mm; V F The feed rate of intermediate 3 to be stretched is expressed in mm / s. OF 2 represents the target outer diameter of the finished preform 6 after stretching, in mm; V P The theoretical discharge speed of the finished precast bar 6 is also the linear speed of the traction wheel 7, expressed in mm / s.

[0041] Comparison revealed a significant deviation between the measured outer diameter of the finished preform 6 and the target outer diameter after stretching. Therefore, the discharge speed of the finished preform 5 needs to be corrected. Extensive data comparison showed that the axial temperature difference ΔT within the stretching furnace 4 affects the actual outer diameter of the finished preform 6. For example, if the stretching temperature is set to 2000℃, the length of the temperature zone from the middle to the bottom of the heating element in the stretching furnace 4 is approximately 200mm, and there is an axial temperature difference ΔT of approximately 150℃ between the middle and bottom of the heating element. The outer diameter error of the finished preform 6 is directly related to this axial temperature difference ΔT. Therefore, the theoretical discharge speed of the finished preform 6 needs to be corrected to calculate the corrected discharge speed.

[0042] In this invention, the method for calculating the corrected discharge speed of the finished preform 6 is as follows: based on the axial temperature difference of the temperature zone of the stretching furnace 4, the theoretical discharge speed, and the measured outer diameter and real-time feeding speed of the intermediate body 3 to be stretched, the theoretical outer diameter data of the finished preform 6 is calculated using formula (2). Then, based on the theoretical outer diameter data of the finished preform 6, the measured outer diameter of the intermediate body 3 to be stretched, and the real-time feeding speed, the corresponding corrected discharge speed is calculated using formula (3), and the real-time speed of the traction wheel 7 is adjusted so that the difference between the corrected discharge speed and the real-time speed of the traction wheel 7 is controlled within the preset deviation threshold.

[0043] In this invention, the theoretical outer diameter of the finished preform 6 is calculated using formula (2): (2); In formula (2), The theoretical discharge velocity of the finished preform 6 obtained by formula (1) is mm / s; ΔT is the theoretical outer diameter of the finished preform 6, in mm; ΔT is the axial temperature difference in the stretching furnace temperature zone, and also the axial temperature difference between the middle and bottom areas of the heating element, in °C, with a value of 100~200 °C. OF 1 represents the measured outer diameter of the intermediate body 3 to be stretched, in mm; VF The feed rate of the intermediate body 3 to be stretched is in mm / s.

[0044] In this invention, the corrected discharge rate of the finished preform 6 is calculated using formula (3): (3); In formula (3), The theoretical outer diameter of the finished preform 6 is calculated using formula (2), in mm; The corrected discharge speed of the finished preform 6 obtained by using formula (3) is expressed in mm / s. OF 1 represents the measured outer diameter of the intermediate body 3 to be stretched, in mm; V F The feed rate of the intermediate body 3 to be stretched is in mm / s.

[0045] To more effectively control the outer diameter of the stretched precast bar 6 within a set threshold range, this invention further optimizes the discharge speed of the stretched precast bar 6 at the discharge end. The optimization method is as follows: For a target outer diameter of a certain precast bar 6 (which falls within the range of 80-150mm), when the furnace mouth diameter gauge 5 detects that the deviation between the measured outer diameter of the stretched precast bar 6 and the target outer diameter exceeds the allowable deviation threshold, the outer diameter is corrected by adjusting the discharge speed: if the measured outer diameter is greater than the target outer diameter and the difference exceeds the preset deviation threshold, the discharge speed is increased at a rate of 1mm / s; if the measured outer diameter is less than the target outer diameter and the difference exceeds the preset deviation threshold, the discharge speed is decreased at a rate of 1mm / s, thereby offsetting the outer diameter deviation and ensuring that the dimensions of the precast bar 6 meet the specifications. For example, if the target outer diameter is 120mm, when the measured outer diameter of the finished preform 6 detected by the furnace mouth diameter measuring instrument 5 reaches below 119mm or above 121mm, that is, when the outer diameter deviation exceeds the ±1mm set threshold, the discharge speed will decrease or increase at a speed of 1mm / s to correct the outer diameter deviation and make the outer diameter of the stretched finished preform 6 return to the target range.

[0046] In order to more effectively control the viscosity of the finished preform 6 after stretching and stabilize the outer diameter, the temperature during the stretching process needs to be comprehensively evaluated based on the outer diameter of the intermediate body 3 to be stretched and the torque of the traction wheel 7 during the stretching process.

[0047] In this invention, the stretching of the solid preform (i.e., the intermediate body 3 to be stretched) involves high-temperature viscous deformation, and the heating power of the heating element during the stretching process... P It can be calculated using formula (4): (4); In formula (4), A is a constant with no unit. It is used in the correction formula and takes a value between 0.05 and 0.1. It is mainly related to the usage status and resistance of the heating element (specifically the graphite heating cylinder) of the stretching furnace 4. The value can be obtained through experience. P 0 is the base power, taken as 100Kw, referencing the power of glass softening during the stretching of OVD185 preforms of this type; OF 1 represents the outer diameter of the intermediate body 3 to be stretched, in mm; OF 0 is the reference outer diameter, which is 185mm.

[0048] In this invention, the feeding speed of the feeding assembly and the speed of the traction wheel 7 are both controlled by a control program. The faster the feeding speed, the larger the outer diameter of the intermediate body 3 to be stretched. During the stable stretching process, the outer diameter of the finished preform 6 is controlled by small adjustments to the speed of the traction wheel 7. During the stretching process, as the material is continuously discharged and formed, the weight of the finished preform 6 drawn from the lower opening of the stretching furnace 4 gradually increases. At this time, the clamping pressure of the traction wheel 7 needs to be adaptively increased to ensure reliable clamping and positioning of the finished preform 6 by the traction wheel 7, and to avoid slippage or falling of the rod due to its own weight. If the clamping force of the traction wheel 7 is too small, the finished preform 6 will fall directly, causing the entire preform stretching mode to fail, and ultimately making it impossible to control the outer diameter.

[0049] According to the principles of tribology, the contact surface pressure between the traction wheel 7 and the finished precast bar 6... P m It must meet the condition of non-slippage, that is: F 1= μ × P m × A m ≥ F 2(5); In formula (5), P m The pressure at the contact surface between the traction wheel 7 and the finished precast bar 6 is expressed in Pa. F 1 represents frictional force, in N; μ The coefficient of friction between the traction wheel 7 and the preform (0.60 for a silicone wheel and 0.50 for a polyurethane wheel). A m The contact area between the traction wheel 7 and the precast bar is expressed in mm². F 2 represents the traction force required during the stretching process, in N, which is related to the stretching speed, the weight of the preform, and the tension setting.

[0050] In this invention, the minimum pressure at the contact surface between the traction wheel 7 and the finished precast bar 6 is... P min for: P min = F 1 / ( μ × A m (6).

[0051] In this invention, the traction wheel 7 can be a V-shaped or circular arc-shaped grooved wheel structure; if it is a single wheel with double-sided contact, the contact area... A m The calculation formula is: A m =2× L × B (7); In formula (7), L The axial contact length between the traction wheel 7 and the precast bar is in mm and is equal to the wheel width. B The radial contact width between the traction wheel 7 and the precast bar is measured in mm and is determined by the pressing depth.

[0052] Example In this embodiment, the above-described stretching method is used to stretch a batch of solid preforms with an outer diameter of 185mm prepared by the OVD process as intermediate bodies 3 to be stretched to a finished preform 6 with a target outer diameter of 120mm. First, a batch of intermediate bodies 3 with rod numbers X1 to X7 and an outer diameter range of 170 to 190mm are prepared using OVD (External Vapor Deposition). Then, the intermediate bodies 3 are directly placed into the stretching furnace 4. The tower diameter gauge 2 pre-scans the outer diameter data and rod position information of the entire intermediate body 3. The intermediate body 3 is then melted and stretched in the stretching furnace 4 to obtain a finished preform 6 with an outer diameter of 120mm. The relevant parameters are as follows: the target outer diameter of the finished preform 6 is 120mm; the weight of the glass feed per unit time is set; the feed rate is calculated and adjusted based on the rod position information and corresponding outer diameter data of the intermediate body 3. Taking the feeding of one intermediate body 3 as an example... Figure 1 As shown, when the measured outer diameter of the intermediate body 3 to be stretched is 187.51 mm during feeding, the feeding speed is calculated to be 11.94 mm / s based on the weight of the molten glass material fed per unit time. The real-time feeding speed is then adjusted to meet the set threshold requirement. The theoretical linear velocity of the traction wheel 7, which is also the theoretical discharge speed of the finished preform 6, is then calculated using the classic formula (1). V P = V F × OF 1× OF 1 / ( OF 2× OF2)=11.94×187.51×187.51 / (120×120)≈29.14mm / s.

[0053] The theoretical outer diameter of the finished preform 6 is 120.84 mm, calculated using formula (2). Then, the discharge speed is corrected using formula (3), and the corrected discharge speed of the finished preform 6 is 29.53 mm / s.

[0054] = ; .

[0055] In this embodiment, the relevant parameters are shown in Table 1. As the material is continuously fed in, the feed rate is adjusted accordingly as the measured outer diameter of the intermediate body 3 to be stretched changes, and the discharge rate is also adaptively corrected accordingly.

[0056] Table 1 shows the feed rate and discharge rate in the embodiments.

[0057] In this embodiment, the discharge speed is further optimized and adjusted during the stretching process: when the furnace mouth diameter gauge detects that the actual measured outer diameter of the finished preform 6 is below 119mm, the speed is reduced; when the actual measured outer diameter of the finished preform 6 is above 121mm, the speed is increased, as shown in Table 2.

[0058] Table 2 Optimization and Adjustment of Discharge Speed

[0059] This embodiment also optimizes the heating power of the heating element during the stretching process. The heating power of the heating element corresponds to the stretching power. The relevant parameters are shown in Table 3. The outer diameter of the base material is also the feed outer diameter of the intermediate body 3 to be stretched.

[0060] Table 3. Relevant parameters of the embodiments

[0061] Comparative Example This comparative example uses the conventional process mentioned in the background art to prepare a finished preform 6 with a target outer diameter of 120 mm.

[0062] The finished preform 6 obtained in the comparative example was compared with the finished preform 6 obtained in the example. The average outer diameter of the finished preform 6 obtained by conventional OVD deposition in the comparative example was 123 mm, with an outer diameter fluctuation range of 10~20 mm; while the average outer diameter of the finished preform 6 obtained in the example was 121 mm, with an outer diameter fluctuation range of no more than 7 mm. The process of the present invention can significantly reduce the outer diameter fluctuation of the finished product, greatly improve the uniformity of the outer diameter of the preform, and effectively improve the yield of stretch forming.

[0063] Table 4 Comparison of finished product dimensions obtained from the examples and comparative examples.

[0064] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0065] Finally, it should be noted that the above are merely preferred embodiments of this application and are not intended to limit this application. Although this application has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for fabricating small-to-medium-sized optical fiber preforms, characterized in that, The method includes the following steps: S1. Solid preforms with an outer diameter of 170~210mm are prepared using the OVD process and used as intermediates for stretching. S2. Position and clamp the intermediate body to be stretched onto the hanging rod device, and use the tower body diameter measuring instrument to detect the outer diameter data and rod information of the intermediate body to be stretched in real time online, and feed them back to the PLC controller. S3. Start the stretching process and feed the intermediate body to be stretched downwards. The intermediate body to be stretched enters the stretching furnace from the lower end to the upper end in sequence. Under the heating action of the stretching furnace, the intermediate body to be stretched melts and softens. S4. The molten and softened intermediate to be stretched is stretched into a finished preform with an outer diameter of 80mm to 150mm by a traction wheel. The finished preform is drawn out from the lower furnace opening of the stretching furnace. The actual outer diameter of the finished preform is monitored in real time by a diameter measuring instrument at the lower furnace opening, and the real-time outer diameter detection data is fed back to the PLC controller. The PLC controller adjusts the feeding speed of the intermediate to be stretched and the discharge speed of the finished preform in real time according to the received data.

2. The method for preparing small-to-medium-sized optical fiber preforms as described in claim 1, characterized in that, The method by which the PLC controller adjusts the feeding speed of the intermediate material to be stretched in real time based on the received data is as follows: The tower diameter measuring instrument pre-scans the real-time outer diameter data and bar position information of the intermediate body to be stretched; The PLC controller receives and records the real-time outer diameter data and bar position information, and calculates the real-time feeding speed corresponding to the real-time outer diameter state of the intermediate body to be stretched based on the weight of the molten glass material fed per unit time. The real-time feeding speed is compared with the preset initial feeding speed. If the difference between the real-time feeding speed and the initial feeding speed is within the set threshold range, then there is no need to adjust the real-time feeding speed; otherwise, the real-time feeding speed is adjusted.

3. The method for preparing small-to-medium-sized optical fiber preforms as described in claim 2, characterized in that, The method by which the PLC controller adjusts the discharge speed of the finished preform in real time based on the received data is as follows: Based on the real-time feeding speed, the target outer diameter of the finished preform, and the real-time outer diameter data of the intermediate to be stretched, the theoretical discharge speed of the finished preform is calculated. The theoretical outer diameter of the finished preform is calculated based on the axial temperature difference in the stretching furnace temperature zone, the theoretical discharge rate, the measured outer diameter of the intermediate body to be stretched, and the real-time feeding rate. The corrected discharge speed is calculated based on the theoretical outer diameter data of the finished preform, and the real-time speed of the traction wheel is adjusted so that the difference between the corrected discharge speed and the real-time speed of the traction wheel is controlled within a preset deviation threshold.

4. The method for preparing small-to-medium-sized optical fiber preforms as described in claim 3, characterized in that, The method for calculating the corrected discharge speed of the finished preform is as follows: Calculation is performed using the following formula. ； In the formula, OD 1 represents the real-time outer diameter of the intermediate body to be stretched, in mm; V F The feed rate of the intermediate to be stretched is expressed in mm / s. OD 2 represents the theoretical outer diameter of the finished preform, in mm; V P ΔT represents the corrected discharge speed of the finished preform, in mm / s; ΔT represents the axial temperature difference in the stretching furnace temperature zone.

5. The method for preparing small-to-medium-sized optical fiber preforms according to any one of claims 1 to 4, characterized in that, Heating power of the stretching furnace during the stretching process P for: ； In the formula, A is a constant, ranging from 0.05 to 0.1; P 0 is the base power, with a value of 100kW; OD 1 represents the outer diameter of the intermediate body to be stretched; OD 0 is the reference outer diameter, which is 185mm.

6. The method for preparing small-to-medium-sized optical fiber preforms as described in claim 3, characterized in that, The contact surface pressure between the traction wheel and the finished preform bar P m The condition of non-slippage must be met, that is: F 1= μ × P m × A m ≥ F 2； In the formula, P m The pressure at the contact surface between the traction wheel and the finished precast bar, in Pa; F 1 represents frictional force, in N; μ The coefficient of friction between the traction wheel and the finished preform; A m The contact area between the traction wheel and the finished precast bar is expressed in mm². F 2 represents the traction force required during the stretching process, in N.

7. The method for preparing small-to-medium-sized optical fiber preforms as described in claim 6, characterized in that, Minimum pressure at the contact surface between the traction wheel and the finished preform. P min for: P min = F 1 / （ μ × A m ）。 8. A stretching system for small-to-medium-sized optical fiber preforms, used to implement the method for preparing small-to-medium-sized optical fiber preforms as described in any one of claims 1 to 7; characterized in that, The system includes a hanging rod device, a stretching furnace, a traction wheel, a tower diameter gauge, a lower furnace opening diameter gauge, and a PLC controller. The hanging rod device is located above the inlet of the stretching furnace, and the hanging rod device is connected to the lifting mechanism, the two forming a feeding assembly; the top of the stretching furnace is provided with an upper furnace opening, and the bottom is provided with a lower furnace opening; the interior of the stretching furnace is equipped with heating elements; the traction wheel is installed below the lower furnace opening of the stretching furnace. The upper end of the intermediate body to be stretched is clamped and positioned by the hanging rod device, and the lower end of the intermediate body to be stretched extends into the furnace through the furnace opening at the top of the stretching furnace, where it melts and softens under the heating action of the heating element. The traction wheel pulls and stretches the molten and softened intermediate to be stretched into a finished preform, and the formed finished preform is vertically drawn out from the lower furnace opening of the stretching furnace. The tower diameter measuring instrument is located between the hanging rod device and the upper furnace opening of the stretching furnace; The lower furnace opening diameter measuring instrument is installed at the lower furnace opening of the stretching furnace; Both the tower diameter gauge and the lower furnace opening diameter gauge are connected to the PLC controller.

9. The small-to-medium-sized optical fiber preform stretching system as described in claim 8, characterized in that, The heating element includes a graphite heating cylinder disposed above the inside of the stretching furnace. The graphite heating cylinder is covered with an insulation layer, and an induction coil is installed outside the insulation layer. The inner diameter of the graphite heating cylinder is 240-300 mm, and the axial height is 500-800 mm. The inner diameter of the induction coil is 300-400 mm, and the axial height is 300-400 mm.

10. The small-to-medium-sized optical fiber preform stretching system as described in claim 8, characterized in that, The heating element has a heating temperature of 1900–2100°C.

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