Sintering process and sintering device for sintering a porous glass base material

Abstract

Sintering process for sintering a porous glass base material to produce a transparent glass by moving a hanging porous glass base material relative to a heating furnace and gradually heating the porous glass base material from one end to the other, with the steps: Measuring a feed rate V f of the porous glass base material and a movement speed V w a lower end of the porous glass base material; Performing a sintering treatment of the porous glass base material by presetting a ratio V based on a w / V f calculated setpoint α S (L), which is greater than 1, where the setpoint α S (L) is a stretching rate in a straight body section of the porous glass base material for each feed distance L of the porous glass base material; and Control at least one parameter from a temperature of the heating furnace and a feed rate of the porous glass base material such that a measured value α of the stretching rate of the porous glass base material corresponds to the target value α S (L) matches, whereby The sintering treatment is carried out by attaching a weight near the lower end of the hanging porous glass base material, the weight exerting a tension on the porous glass base material. Image processing is performed with respect to an image obtained by photographing a mark arranged on a side surface of the weight with a camera that follows the porous glass base material, and a speed of movement V w the lower end of the porous glass base material is calculated based on the position of the camera and the position of the marker in the image.

Description

[0001] The present invention relates to a sintering process and a sintering device for sintering a porous glass base material.

[0002] In JP 2005 - 8 452 A, a process for sintering a transparent glass with suppression of outer diameter changes in a porous glass base material was proposed. In JP 2003 - 81 642 A, a process for dewatering and heat-treating a porous glass preform is described, in which a uniform conversion to transparent glass without diameter variations along the longitudinal direction is achieved by position-dependent control of the furnace output during lowering and rotation.

[0003] The object of the invention is to provide a method for producing an optical fiber base material with a small change in diameter without increasing the number of processes.

[0004] This problem is solved by the subject matter of the independent patent claims. Further developments of the invention are found in the dependent claims.

[0005] According to a first aspect of the present invention, a sintering process for sintering a porous glass base material to produce a transparent glass is provided, wherein a suspended porous glass base material is moved relative to a heating furnace and the porous glass base material is gradually heated from one end to the other. The process comprises the steps of: measuring a feed rate V f of the porous glass base material and a movement speed V w a lower end of the glass base material, performing a sintering treatment of the porous glass base material, presetting a target value α S(L), which is greater than 1, a stretching rate in a straight body section of the porous glass base material, based on a ratio V w / V f is calculated for each feed distance L of the porous glass base material, and at least one parameter is controlled under a temperature of the heating furnace and the feed rate of the porous glass base material, such that a measured value α of the stretching rate of the porous glass base material is obtained with the target value α S (L) matches.

[0006] According to a second aspect of the present invention, a sintering device is provided for sintering a porous glass base material to produce a transparent glass, wherein a suspended porous glass base material is moved relative to a heating furnace and the porous glass base material is gradually heated from one end to the other. The device has a control section which, when the porous glass base material is sintered, sets a feed rate V. f of the porous glass base material and a movement speed V w measuring the lower end of the glass base material, a target value α is determined for each feed distance L of the porous glass base material. S (L), which is greater than 1, presets a stretching rate in a straight body section of the porous glass base material, based on a ratio V w / V fis calculated, and at least one parameter is calculated under a temperature of the heating furnace and the feed rate of the porous glass base material, such that a measured value α of the stretching rate of the porous glass base material matches the target value α S (L) matches. Fig. Figure 1 shows a schematic view of a glass lathe 10; Fig. Figure 2 shows a schematic view to describe the production of a porous glass base material by the glass lathe 10; Fig. Figure 3 shows a schematic cross-sectional view of a sintering device 29; Fig. Figure 4 shows a view illustrating a sintering process of a porous glass base material 18 carried out by the sintering device 29; Fig. Figure 5 shows a view illustrating an optical fiber base material 28 produced using the sintering device 29; Fig. Figure 6 shows a graph to represent the setpoint values ​​of an oven temperature in a heating oven 24; Fig. Figure 7 shows a graph to represent target values ​​of a stretching rate of the porous glass base material 18; Fig. Figure 8 shows a graph for representing the setpoint values ​​of a feed rate of the porous glass base material 18; and Fig. Figure 9 shows a view illustrating an optical fiber base material 38 produced using another sintering device 39;

[0007] The foregoing brief description of the invention does not necessarily describe all features of the embodiments of the present invention. The present invention may also be a partial combination of the features described above.

[0008] Some embodiments of the present invention are described below. The embodiments described below are not intended to limit the invention as defined in the claims, and not all combinations of the features described in connection with the embodiments are necessarily essential for aspects of the invention.

[0009] Fig. Figure 1 shows a schematic representation of a glass lathe 10, which can produce a sintered object from a porous glass base material. The glass lathe 10 has a pair of chucks 14 and several torches 16.

[0010] The porous glass base material can be produced, for example, by an OVD (Outside Vapor Deposition) process.

[0011] The pair of rotary chucks 14 grip shaft sections 12, which are welded to both ends of a core rod 11 in a target rod 13, and rotate the target rod 13, which is held horizontally. The multiple burners 16 are mounted on a common burner stand 15, which moves along a longitudinal direction of the target rod 13 and emits flames 17 over the entire length of the core rod 11 of the target rod 13.

[0012] In this process, oxygen and hydrogen are supplied to the burners 16 in addition to glass starting materials such as silicon tetrachloride, trichloromethylsilane, octamethylcyclotetrasiloxane, and the like. Therefore, glass microparticles are generated in the flames 17 through flame hydrolysis reactions. Consequently, the glass microparticles generated by the flames 17 adhere to a surface of the rotating target rod 13 due to a reciprocating movement of the burner stand 15 along the target rod 13.

[0013] Fig. Figure 2 shows a view illustrating a state in which the porous glass base material 18 is formed on the glass lathe 10. The glass microparticles adhering to the target rod 13 are deposited in layers. Furthermore, the outer diameter of the porous glass base material 18 increases due to the continuous deposition of the glass microparticles, so that the burner station 15 is positioned further away from the target rod 13. Once a predetermined deposition quantity of glass microparticles has been reached, the supply of the initial material gas to the burners 16 is stopped.

[0014] In this way, the porous glass base material 18, which contains the deposited glass microparticles, is formed. The porous glass base material 18 is sintered, for example in an electric furnace, to become a transparent glass material, and a fiber optic base material for drawing an optical fiber is obtained.

[0015] It should be noted that prior to the process described above for producing a transparent glass material, a dehydration treatment to remove impurities, such as an OH group, from the porous glass base material 18 can be carried out. The dehydration treatment is performed, for example, by heating the porous glass base material 18 to a temperature of approximately 1100°C in an atmosphere containing a dehydration gas, such as chlorine, thionyl, thionyl chloride, and the like.

[0016] Furthermore, the process for producing the porous glass base material 18 is not limited to an OVD process. For example, the porous glass base material 18 can also be produced by a VAD process (axial vapor deposition), an MCVD (modified chemical vapor deposition) process, a PCVD (plasma-enhanced chemical vapor deposition) process, and the like.

[0017] Fig. Figure 3 shows a schematic cross-sectional view of a sintering device 29 that can be used for sintering the porous glass base material 18. The sintering device 29 has a slide 20, a rotating shaft 21, a connecting element 22, a furnace core tube 23 and a heating furnace 24.

[0018] The furnace core tube 23 can be manufactured using transparent quartz glass and has a thickness sufficient to accommodate the porous glass base material 18. In the sintering device 29, the furnace core tube 23 is arranged vertically. The porous glass base material 18, to be sintered by the sintering device 29, is connected to the slide 20 via the rotating shaft 21 and the connecting element 22 and hangs downwards inside the furnace core tube 23.

[0019] The carriage 20 is positioned above the furnace core tube 23 and is driven in the direction shown in the drawing in an upward and downward motion, in which it engages one end of the rotating shaft 21 and suspends the rotating shaft 21 downwards. The rotating shaft 21 is connected to the carriage 20 at one upper end in the drawing, and the rotating shaft 21 is connected, via the connecting element 22 located at one lower end, inside the furnace core tube 23 to the shaft section 12, which is located on the upper surface of the porous glass base material 18 in the drawing. Therefore, the porous glass base material 18 moves upward and downward inside the furnace core tube 23 in the direction shown in the drawing, while rotating around the rotating shaft 21 as an axis of rotation.

[0020] The heating furnace 24 is arranged such that it encloses a portion of the furnace core tube 23 longitudinally and comprises a heating element 25, a heat-insulating material 26, and a chamber 27. The heating element 25 radiates the generated heat through a tube wall of the furnace core tube 23 towards the interior of the furnace core tube 23. This allows the porous glass base material 18 running through the interior of the furnace core tube 23 to be heated. The heat-insulating material 26 encloses the heating element 25 distal to the furnace core tube 23 and thus prevents the heat generated by the heating element 25 from being emitted to the outside. The chamber 27 accommodates the heating element 25 and the heat-insulating material 26 and is integrated with the heating furnace 24.

[0021] The sintering device 29 further comprises a camera carriage 35 arranged laterally to the furnace core tube 23, as shown in the drawing. The camera carriage 35 moves along a guide rail 36 arranged in the longitudinal direction of the furnace core tube 23. Cameras 34 are mounted on the camera carriage 35. The cameras 34 can continuously photograph and monitor an optical fiber base material 28 inside the furnace core tube 23 from outside the furnace core tube 23 via a transparent furnace wall of the furnace core tube 23.

[0022] During the sintering of the porous glass base material 18 in the sintering device 29, a weight 30 can be attached to a lower end of the porous glass base material 18. This exerts a stress on the porous glass base material 18, causing it to stretch as it softens upon heating. In the illustrated example, the weight 30 comprises a quartz glass cylinder 32 sandwiched between a pair of carbon plates 31 on its top and bottom sides. Horizontal markings 33 are formed at the boundaries between the carbon plates 31 and the quartz glass cylinder 32, which can be observed by the cameras 34. Even in cases where the porous glass base material 18 becomes glass near its lower end, a desired stretching rate can be easily achieved at a comparatively low furnace temperature by attaching the weight to the lower end of the porous glass base material 18.Therefore, it is possible to prevent deformation caused by an excessive temperature increase in the furnace core tube 23.

[0023] In the sintering device 29, by photographing the markings 33, which can be photographed from the side surface of the weight 30 by the cameras 34, which are freely driveable in an upward and downward direction, the position of the weight 30 can be calculated based on the positions of the markings in a recorded image, obtained by image processing, and the positions of the cameras 34 themselves. Furthermore, a movement speed V can be determined. w The weight 30 can be calculated by continuously photographing the weight 30 with the cameras 34.

[0024] As described above, because the weight 30 is attached to the lower end of the porous glass base material 18, the position and speed of movement of the lower end of the porous glass base material 18 in the furnace core tube 23 are determined according to the position and speed of movement V. w of the weight 30 is known. In this way, the sintering device 29 can determine the position and the speed of movement V by photographing the markings 33 of the weight 30 attached to the porous glass base material 18 with the cameras 34. w of the lower end of the porous glass base material 18, which is itself transparent and difficult to photograph, safely and accurately measure.

[0025] It is noted here that in the weight 30 of the sintering device 29 shown in the drawings, the carbon plates and the quartz glass cylinder 32, which are two different types of material, are arranged in a vertical stack-like manner, and the markings 33 are formed by the boundaries of the materials. Therefore, the markings 33 can be designed so that they are easily recognizable in the image captured by the cameras 34 without wearing down. A material for forming the weight 30 is preferably both heat-resistant with respect to the heat inside the furnace core tube 23 and reaction-resistant, so that the material is not affected by chlorine or thionyl chloride used in the dehydration process.

[0026] Examples include carbon, silicon nitride, aluminum oxide, quartz glass, and the like. Furthermore, the side surface of the quartz glass starting material can be sandblasted. In the starting material described above, carbon and silicon nitride are dark-colored materials, while aluminum oxide and the sandblasted quartz glass are white materials. Therefore, by forming the weight 30 by combining such a dark-colored material and a white material, distinct boundaries can be obtained and the markings 33 can be formed, which are easily visually recognizable.

[0027] Furthermore, several of the markings 33 can be spaced apart from one another in a vertical direction of the weight 30. Therefore, even if any object obstructing the cameras' fields of view, such as a connecting section, a retaining element, and the like, is arranged around the furnace core tube 23, one of the markings 33 will always be detectable by the cameras 34. For a similar reason, it is also preferred to photograph each of the multiple markings 33 with individual cameras 34.

[0028] The heating furnace 24 is attached approximately at the midpoint of the height of the furnace core tube 23 and has a height that is less than the length of the porous glass base material 18. Therefore, the heating furnace 24 cannot heat the entire porous glass base material 18 at once. In a case where the porous glass base material 18 passes through the inner surface of the heating furnace 24, the heating furnace 24 heats the porous glass base material 18 to a temperature of at least approximately 1500°C.

[0029] Fig. Figure 4 shows a schematic cross-sectional view illustrating a sintering process of the porous glass base material 18 carried out by the sintering device 29. Fig. 4 are elements that those in Fig. 3 items that have in common are designated by the same reference symbols and are not described repeatedly.

[0030] During sintering in the sintering device 29, the porous glass base material 18 to be sintered moves downwards by driving the carriage 20, while rotating inside the furnace core tube 23, which is filled with atmospheric gas, such as helium. Thus, the porous glass base material 18 is sintered by being gradually heated from the bottom up, and the sintered section becomes the optical fiber base material 28, which is a transparent glass. In the example shown, approximately the lower half of the porous glass base material 18 becomes the optical fiber base material 28, which is a transparent glass.

[0031] It is noted that at the point when the sintering process begins in the sintering device 29, the porous glass base material 18 becomes transparent glass from a tapered section formed near its lower end. However, this tapered section is a part that cannot be a product when an optical fiber is pulled. For this reason, monitoring the markings 33 using the cameras 34 is not necessary at the point when the sintering process begins to produce glass in the sintering device 29.

[0032] On the other hand, in the straight body section where the thickness of the porous glass base material 18 is approximately constant, control based on the position of the lower end of the porous glass base material 18 is performed by monitoring the markings 33 formed in the weight 30 by the cameras 34. Therefore, it is desirable for the markings 33 to be detected by the cameras 34, with the position of the camera carriage 35 being adjusted, before the heating by the heating oven 24 reaches the straight body section of the porous glass base material 18. The control that is performed while the markings 33 are being monitored by the cameras 34 is described below.

[0033] Fig. Figure 5 shows a schematic cross-sectional view to illustrate a state in which the sintering treatment performed by the sintering device 29 is complete. Fig. 5 are elements that those in the Fig. 3 and Fig. 4 items that have in common are designated by the same reference symbols and are not described repeatedly.

[0034] In the sintering device 29, the porous glass base material 18 is sintered along its entire length in the illustrated state, becoming the optical fiber base material 28, which is a transparent glass. However, a tapered section formed near the upper end of the porous glass base material 18 is a section that cannot be part of the fiber when it is drawn. For this reason, monitoring the markings 33 using the cameras 34 is not necessary in a final step of the sintering process performed by the sintering device 29.

[0035] During a sequence of sintering treatments performed by the sintering device 29, the following occurs, as described in the Fig. 3, Fig. 4 and Fig. As shown in Figure 5, the camera carriage 35 is attached to the weight 30 at the lower end of the porous glass base material 18 and moves along the guide rail 36. Therefore, a pair of cameras 34 can continuously capture images of a pair of markings 33 formed in the weight 30 at the boundaries of the carbon plates 31 and the quartz glass cylinder 32.

[0036] By continuously performing measurements of the position of the weight 30 from the upper and lower positions of the camera carriage 35 and the height positions of the markers 33 in the fields of view of the cameras 34, the movement speed V can be determined. w of the lower end of the glass base material. In the sintering device 29 shown in the drawings, a stretching rate α of the porous glass base material can be determined by a ratio V w / V f between a speed of movement V wat the lower end of the porous glass base material 18 and a feed rate V f at the upper end of the porous glass base material 18.

[0037] Furthermore, in the sintering device 29 at least one parameter is controlled under a temperature of the heating furnace and a feed rate such that the elongation rate α measured by the porous glass base material 18 to be sintered corresponds to a predetermined setpoint α S (L) of the stretching rate. For example, if the measured stretching rate α was smaller than the setpoint, a control is executed to increase the temperature of the heating furnace 24 or to decrease the movement speed of the porous glass base material 18 through the carriage 20.

[0038] Therefore, because the softening progresses due to the increased temperature of the porous glass material 18, the elongation rate α increases. If the outer diameter of the core rod 11 is constant, the target value α S (L) the stretching rate of the core rod 11 as a constant value α S The outer diameter of the core rod 11 is set to a constant value, independent of the feed distance L. By setting this value, the manufacturing processes for the core rod 11 are simplified, and the glass microparticle deposition process can be streamlined.

[0039] Furthermore, by setting the target value of the stretching rate to a value greater than 1 and causing the porous glass base material 18 to become glass while being actively stretched, the porous glass base material 18 can become a transparent glass at a higher temperature. Therefore, even the center of the porous glass base material 18 can be made sufficiently transparent.

[0040] However, in the porous glass base material 18, a different setpoint can be set, if necessary, for the section that cannot be a product. To control the drive of the carriage 20, a PID feedback controller, a table controller where a table of deviations and setpoints is provided in advance as a reference, and the like can be used.

[0041] Furthermore, the setpoint α can be Sthe stretching rate of the porous glass base material 18 is calculated as shown in the following equation 1, where an outer diameter of the core rod 11 is determined by D T The figure shows a diameter ratio between the diameter of the core rod 11 and the diameter of the porous glass base material 18, represented by r, and a target outer diameter after the porous glass base material 18 has become a transparent glass, represented by D. P is shown. Target value αS of the stretching rate = (DT / r / DP)2

[0042] However, in a case where the outer diameter D T the core rod 11 has a distribution in the longitudinal direction, the target value α S the stretching rate as a function α S (L) defines the feed distance L.

[0043] In this case, if the stretching rate α of the porous glass base material 18 is controlled by adjusting the temperature of the heating furnace 24, a furnace temperature T0(L) can be preset for each feed length L of the porous glass base material, and a temperature deviation ΔT can be determined based on a deviation or ratio between the measured value α of the stretching rate and the setpoint α described above. S (L) are obtained to perform the sintering treatment at an oven temperature set to T0(L)+ΔT. By presetting the oven temperature T0(L) such that the deviation of the measured value α of the stretching rate from the target value α S (L) becomes smaller or the ratio between the measured value α of the stretching rate and the target value α S If (L) is close to 1, the temperature deviation ΔT can be made small and the control stability improved.

[0044] Furthermore, in the case of controlling the sintering treatment of the porous glass base material 18 by adjusting the temperature of the heating furnace 24, when the porous glass base material 18 is used with the same shape, the temperature change relative to the feed distance L is essentially the same for each batch. Therefore, by setting the furnace temperature to T0(L)+ΔT, presetting the furnace temperature T0(L) for each feed distance L of the porous glass base material, and obtaining the temperature deviation ΔT based on the deviation or the ratio between the measured value α of the stretching rate and the setpoint α S (L) also the section at both ends of the porous glass base material where the change in outer diameter is large can be appropriately controlled.

[0045] On the other hand, if the stretching rate is controlled by adjusting the feed rate, it is advantageous if sintering occurs at a speed of V f0 (L)+ΔVf The set feed rate is executed, with a feed rate V f0 (L) is set for each feed distance L of the porous glass base material and a feed rate deviation ΔV is set. f based on a deviation or ratio between the measured value α of the stretching rate and the target value α S (L) is obtained by presetting the feed rate V f0 (L) such that the deviation between the measured value α of the stretching rate and the target value α S (L) becomes smaller, the feed rate deviation ΔV f reduced and tax stability improved.

[0046] It is noted that in the case of controlling the sintering treatment by adjusting the feed rate of the porous glass base material 18, if the porous glass base material 18 is used with the same shape, similar to the case of temperature, the change in feed rate relative to the feed distance L of the porous glass base material 18 is essentially the same for each batch. For this reason, sintering at a temperature of V f0 (L)+ΔV f set feed rate, where the feed rate V f0 (L) is set for each feed distance L of the porous glass base material and the feed rate deviation ΔV f based on the deviation or ratio between the measured value α of the stretching rate and the target value α S(L) is obtained, also the tapered section where the change in outer diameter at both ends of the porous glass base material is 18 can be appropriately controlled.

[0047] In this way, by controlling the temperature of the heating oven or the feed rate, the measured value α of the stretching rate can be adjusted to match the target value α. S (L) the elongation rate is the same, the outer diameter of the straight body section of the porous glass base material 18 is kept constant. [First embodiment]

[0048] A porous glass base material 18 with an outer diameter of 360 mm was produced by depositing glass microparticles onto a target rod 13, resulting in a diameter ratio r between the diameter of the core rod 11 and the diameter of the glass base material of 0.305 (r = 0.305). The target rod 13, with a total length of 4000 mm, comprised a straight body section with an outer diameter of 55 mm along its entire length, the core rod 11 with a length of 2000 mm, and dummy sections serving as shaft sections 12. A weight 30, in which a quartz glass cylinder 32 with a height of 200 mm and an outer diameter of 200 mm was sandwiched between two carbon plates 31, each 10 mm thick and with an outer diameter of 200 mm, was attached to a lower end of this porous glass base material 18.

[0049] A sintering treatment was carried out by arranging the above-described porous glass base material 18 in the sintering device 29. Fig. Figure 6 shows a graph to represent a relationship between the furnace temperature T0(L) and the feed distance L (mm) of the porous glass base material 18 during this sintering treatment. Fig. Figure 7 shows a graph to represent a relationship between the target value α S (L) the stretching rate of the porous glass base material 18 and the feed distance L (mm) of the porous glass base material 18 during this sintering treatment. As shown in the drawing, the target value α was S (L) the stretching rate is set to a constant value. Fig. Figure 8 shows a graph to represent a relationship between the feed rate V f0(L) of the porous glass base material 18 and the feed distance (L) during the sintering treatment. As shown in the drawing, the feed rate V was f0 (L) set to a constant value.

[0050] By measuring the position of the lower end of the glass base material according to the positions of the markings 33 of the weight 30 using the cameras 34, the elongation rate α of the porous glass base material 18 was measured during sintering. Furthermore, the deviation between the respective feed distance L and the target value α was determined. S (L) the temperature deviation ΔT was calculated by a PID operation, and the temperature of the heating oven 24 was set to T0(L)+ΔT.

[0051] The difference between the stretching rate α of the straight body section of the porous glass base material 18 during sintering and the target value α S(L) The stretching rate was a maximum of 0.020. Furthermore, the distribution range of the outer diameter of the glass base material in the straight body section of the porous glass base material 18 was 158.7 mm to 161.0 mm and was therefore satisfactory. The porous glass base material 18 became transparent glass throughout the entire straight body section and became the optical fiber base material 28, without any apparent problems in its appearance. [Second embodiment]

[0052] A porous glass base material 18 with an outer diameter of 360 mm was produced by depositing glass microparticles onto a target rod 13 such that the diameter ratio r between the diameter of a core rod 11 and the diameter of the glass base material was 0.305 (r = 0.305). The target rod 13, with a total length of 4000 mm, comprised a straight body section with an outer diameter of 55 mm along its entire length, a core rod 11 with a length of 2000 mm, and dummy sections 12 configured as shaft sections. A weight, having a shape in which a quartz glass cylinder 32 with a height of 200 mm and an outer diameter of 200 mm was sandwiched between two carbon plates 31, each 10 mm thick and with an outer diameter of 200 mm, was attached to a lower end of this porous glass base material 18.

[0053] The porous glass base material 18 with the weight 30 attached to it was arranged in the sintering device 29, and the sintering treatment was carried out at a constant feed rate V. f0 (L) with the in the Fig. 6, Fig. 7 and Fig. The settings shown in section 8 were implemented. During sintering, the position of the lower end of the porous glass base material 18 was measured according to the positions of the markings on the weight 30 using the cameras 34, and the stretching rate α during sintering was measured. Furthermore, the deviation between the respective feed distance L and the target value α was used. S (L) of the stretching rate the velocity deviation ΔV f calculated by a PID operation, and the feed rate of the porous glass base material 18 through the slide 20 was set to V f0 (L) + ΔV f set.

[0054] The difference between the stretching rate α of the straight body section of the porous glass base material 18 during sintering and the target value α S (L) The maximum stretching rate was 0.022. Furthermore, the distribution range of the outer diameter in the straight body section of the porous glass base material 18 was 158.8 mm to 161.3 mm, which was satisfactory. The porous glass base material 18 became transparent glass throughout the entire straight body section and became the optical fiber base material 28, without any apparent problems in its appearance.

[0055] In this way, by changing the furnace temperature or the feed rate in the sintering device 29 according to the feed distance L of the porous glass base material 18, the outer diameter of the optical fiber base material 28 obtained from the sintered porous glass base material 18 can be kept stable, and a good transparent state can be maintained. In the example described above, although the control was carried out by controlling either the furnace temperature of the heating furnace 24 or the feed rate of the carriage 20, the control can also be carried out by simultaneously controlling the change of both parameters.

[0056] Fig.Figure 9 shows a schematic view to represent a form of the porous glass base material 18 sintered using a sintering device 39, which does not have the weight 30, the cameras 34 and the like, without the control described above according to the deviation with respect to the setpoint α S (L) of the stretching rate is carried out. In the sintering device 39, the elements that are common to those of the sintering device 29 are designated by the same reference numerals and are not described again.

[0057] In the porous glass base material 18, in which a transparent glass is gradually produced by heating in the furnace 24, a contraction force caused by surface tension of the welded glass becomes essentially constant at every position of the feed path L. However, a gravitational force acting on the porous glass base material 18, where a part is softened or welded, and which pulls the porous glass base material 18, depends on the weight of the optical fiber base material 38 located below the position where the furnace 24 heats the material in the sintering device 39. For this reason, if the measured stretching rate α does not correspond to the deviation from the target value α S (L) the stretching rate is controlled as the sintering treatment progresses, an upper part of the porous glass base material 18 thin and a lower part of the porous glass base material 18 thick.

[0058] It is noted that in a process for producing transparent glass by sintering, even if the deviation in the feed rate of the porous glass base material 18 is controlled to zero by measuring the movement speed of the lower end of the porous glass base material 18, if the sintering process is carried out by controlling the elongation of the porous glass base material to zero, the temperature of the heating furnace near the upper end of the glass base material must be reduced. Therefore, in a case where a larger size of the glass base material is sintered, the elongation near the upper end of the porous glass base material will be greater due to gravity, and the heating temperature must be reduced.Therefore, if the temperature is controlled in such a way that the elongation of the porous glass base material 18 becomes zero, the heating cannot be carried out to the heating temperature at which the porous glass base material 18 gradually becomes transparent glass to a sufficient extent.

[0059] Even if a core rod 11 is manufactured that has been pre-set along its entire longitudinal direction such that its outer diameter depends on a longitudinal distribution of the stretching factor during the glass manufacturing process, the processing must be carried out in such a way that the outer diameter of the core rod 11 changes in the longitudinal direction. Furthermore, the deposition rate of the glass microparticles must be adjusted to correspond to the outer diameter of the core rod 11. For this reason, controlling the processing of the core rod 11 and the OVD process becomes complex, and the productivity of an optical fiber base material decreases.

[0060] Although specific embodiments of the present invention have been described, the technical scope of the invention is not limited to the embodiments described above. It is apparent to those skilled in the art that various modifications and improvements can be made to the embodiments described above. Furthermore, it is evident from the content of the claims that the embodiments to which such modifications or improvements have been made are included within the technical scope of the invention.

[0061] The operations, procedures, steps, and stages of each process performed by a device, system, program, and method, as described in the claims, embodiments, or diagrams, may be performed in any order, provided that the order is not specified by "before," "previous," or the like, and provided that the output of a preceding process is not used in a subsequent process. Even if the process flow is described in the claims, embodiments, or diagrams using phrases such as "first" or "next," this does not necessarily mean that the process must be performed in that order.

Claims

[1] Sintering process for sintering a porous glass base material to produce a transparent glass by moving a hanging porous glass base material relative to a heating furnace and gradually heating the porous glass base material from one end to the other, comprising the steps: Measuring a feed rate V f of the porous glass base material and a movement speed V w a lower end of the porous glass base material; Performing a sintering treatment of the porous glass base material by presetting a ratio V based on a w / V f calculated setpoint α S (L), which is greater than 1, where the setpoint α S (L) is a stretching rate in a straight body section of the porous glass base material for each feed distance L of the porous glass base material; and Control at least one parameter from a temperature of the heating furnace and a feed rate of the porous glass base material such that a measured value α of the stretching rate of the porous glass base material corresponds to the target value α S (L) matches, whereby The sintering treatment is carried out by attaching a weight near the lower end of the hanging porous glass base material, the weight exerting a tension on the porous glass base material. Image processing is performed with respect to an image obtained by photographing a mark arranged on a side surface of the weight with a camera that follows the porous glass base material, and a speed of movement V w the lower end of the porous glass base material is calculated based on the position of the camera and the position of the marker in the image. [2] Sintering process according to claim 1, wherein The sintering treatment of the porous glass base material is carried out by presetting a temperature T0(L) of the heating furnace for each feed length L of the porous glass base material, and The sintering is carried out at a furnace temperature of T0(L) + ΔT, where ΔT is a temperature deviation based on a deviation or ratio between the measured value α and the setpoint α. S (L) is obtained. [3] Sintering process according to claim 1, wherein The sintering treatment is carried out by presetting a feed rate V f0 (L) of the porous glass base material for each feed distance L of the porous glass base material, and sintering at a feed rate V f0 (L) + ΔV f , is executed, where ΔV fa feed rate deviation of the porous glass base material, which is based on a deviation or ratio between the measured value α and the target value α S (L) is obtained. [4] Sintering process according to claim 1, wherein the porous glass base material has a core rod with a constant outer diameter in a longitudinal direction and glass microparticles deposited on an outer circumference of the core rod, and The sintering treatment is carried out by setting the target value α. S (L) as a constant value α S , which is greater than 1 and does not depend on the feed distance L of the porous glass base material. [5] Sintering process according to one of claims 1 to 4, wherein the marking has boundaries of several elements in the weight, wherein the boundaries are formed and configured by stacking the several elements. [6] Sintering process according to claim 5, wherein the marking has several markings spaced apart from each other in the longitudinal direction of the porous glass base material. [7] Sintering process according to claim 6, wherein the multiple markings are photographed individually using multiple cameras. [8] Sintering device for sintering a porous glass base material to produce a transparent glass by moving a hanging porous glass base material relative to a heating furnace and gradually heating the porous glass base material from one end to the other, comprising: a control section that sets a feed rate V during the sintering of the porous glass base material f of the porous glass base material and a movement speed V wmeasuring the lower end of the porous glass base material, for each feed distance L of the porous glass base material, one based on a ratio V w / V f calculated setpoint α S (L), which is greater than 1 preset, where the setpoint α S (L) is a stretching rate in a straight body section of the porous glass base material for each feed distance L of the porous glass base material, and controls at least one parameter from a temperature of the heating furnace and a feed rate of the porous glass base material such that a measured value α of the stretching rate of the porous glass base material corresponds to the setpoint α S (L) matches, whereby The sintering treatment is carried out by attaching a weight near the lower end of the hanging porous glass base material, the weight exerting a tension on the porous glass base material. Image processing is performed with respect to an image obtained by photographing a mark arranged on a side surface of the weight with a camera that follows the porous glass base material, and a speed of movement V w the lower end of the porous glass base material is calculated based on the position of the camera and the position of the marker in the image.

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