JP5915028B2 - Method for sintering glass particulate deposit - Google Patents

Description

  The present invention relates to a method for sintering a glass fine particle deposit, in which the glass fine particle deposit is sintered in a heating furnace.

  Conventionally, as a sintering furnace which sinters a glass fine particle deposit body, what is described in patent document 1 is known, for example. As shown in FIG. 5, a sintering apparatus 100 as a sintering furnace includes a core tube 106 having a lid 109 and a heating furnace 105 having a heat source 104 disposed around the core tube 106. Further, the sintering apparatus 100 includes an inert gas introduction pipe 102 that supplies He gas or the like to the lower end of the furnace core tube 106, and an exhaust device 108 above the furnace core tube 106.

  In the sintering apparatus 100, an upper heat shield 107 is installed above the porous glass base material 111, and a lower heat shield 103 is installed below the sintering completion part 116 of the porous glass base material 111. ing. The upper heat shield 107 and the lower heat shield 103 are made of quartz glass, and are installed above and below the porous glass base material 111 to control the escape of radiant heat from the cone body 113 to control the temperature of the core tube 106. It suppresses unevenness and natural convection.

  In the sintering apparatus 100, the porous glass preform 111, which is a glass particulate deposit obtained by depositing glass particulates on the starting rod 112, which is a seed rod, is inserted into the core tube 106, and the porous glass preform is inserted. 111 is rotated while being rotated, heated by a heating furnace 105, and sintered.

JP 2000-219519 A

  However, in the process of sintering the porous glass base material 111, heat is not sufficiently transferred or dissipated, so the upper part of the porous glass base material 111 cannot be made completely transparent, A sintered part is formed. If an unsintered part is formed on the upper part of the porous glass base material 111, cracks may occur due to the difference in shrinkage from the sintered part, and the porous glass base material 111 may fall. Moreover, at the time of subsequent flame polishing, there may be a problem such as cracking and dropping due to the difference in thermal expansion coefficient at the boundary between the unsintered part and the sintered part.

  Furthermore, if the unsintered part during sintering is large, the unsintered part is sintered in the subsequent drawing process, so the porous glass base material 111 may be deformed or eccentric in the drawing furnace. There is.

  On the other hand, if the upper portion of the porous glass base material 111 is heated excessively to reduce the size of the unsintered portion, heat is excessively applied to the starting bar 112 and the starting bar 112 is stretched, and the porous glass base material is stretched. Problems such as 111 bending and dropping occur.

  The object of the present invention has been made in view of the above-mentioned circumstances, and by preventing the unsintered portion as small as possible during sintering, it prevents cracking and dropping of the porous glass base material, and also enables deformation during drawing. It is an object of the present invention to provide a method for sintering a glass fine particle deposit capable of minimizing inconveniences, such as eccentricity and eccentricity.

  The method for sintering a glass fine particle deposit according to the present invention that can solve the above-described problem is a glass fine particle deposit in which a glass fine particle deposit in which glass fine particles are deposited on a starting seed rod is heated and sintered by the heat of a heater. The sintering method is characterized in that the upper transparency rate in the tapered glass fine particle deposition portion above the sintered glass fine particle deposit is 0.4 or more.

  In the sintering method of the glass particulate deposit, a heat shielding jig capable of adjusting the position in the longitudinal direction of the glass particulate deposit is disposed near the upper portion of the tapered glass particulate deposit on the glass particulate deposit. Then, it is preferable to sinter the glass fine particle deposit while shielding heat transmitted from the heater and the tapered glass fine particle accumulation portion to the seed rod portion where the glass fine particles are not accumulated.

  According to the sintering method of the glass fine particle deposit according to the present invention, the upper transparency ratio indicating the ratio of the sintered portion in the tapered glass fine particle deposit on the upper part of the sintered glass fine particle deposit is 0.4. As described above, the porous glass preform can be prevented from being broken or dropped, and defects such as deformation and eccentricity during drawing can be minimized, and a high-quality optical fiber can be obtained.

It is the schematic which shows one Embodiment of the sintering method of the glass fine particle deposition body which concerns on this invention. It is a principal part enlarged view of the heat shield jig periphery of FIG. It is explanatory drawing of the upper transparency rate which concerns on this invention, (a) shows upper transparent length, (b) has shown the drawing deformation length. It is a graph which shows the relationship between the top transparency rate and defect incidence which concern on this invention. It is the schematic which shows the sintering furnace which sinters the conventional glass fine particle deposit.

  Hereinafter, an embodiment of a method for sintering a glass fine particle deposit according to the present invention will be described in detail with reference to FIGS.

  As shown in FIG. 1, a sintering furnace 10 for sintering a glass particulate deposit 1 according to the present embodiment is closed at the top by a lid 13, and a glass particulate deposit in which glass particulates are deposited on a starting seed rod 3. 1 and a heater 12 which is a heat source for heating and sintering the glass particulate deposit 1 on the outer peripheral side of the core tube 11.

  The glass fine particle deposit 1 includes a cylindrical glass fine particle deposition unit 4, tapered glass particle deposition units 2 and 5 at the upper and lower ends of the glass fine particle deposition unit 4, and an upper tapered glass particle deposition unit 2. And a seed bar portion 8 in which glass fine particles are not deposited in the upper portion. The glass particulate deposit 1 is suspended in the furnace core tube 11 by a connecting member 14. A gas supply unit 15 that supplies an inert gas such as He gas and a gas discharge unit 16 are provided at the lower portion of the core tube 11 and the upper portion thereof.

  As shown in FIG. 2, the sintering furnace 10 is a heat shield made of carbon capable of adjusting the position of the glass fine particle deposit 1 in the longitudinal direction in the vicinity of the tapered glass fine particle deposit 2 at the top of the glass fine particle deposit 1. A jig 20 is provided. Note that the structure of the heat shield jig is not limited to the structure of FIG. 2 and may be a single plate as described in Patent Document 1, but it is necessary to be able to adjust the fixing position. is there. Next, an example of the heat shielding jig whose position can be adjusted will be described in detail.

  The heat shield jig 20 includes an upper jig 21 fixed to a predetermined position of the starting seed bar 3, a disk-shaped lower jig 22 having a heat shield function, three suspension bolts 23, and each suspension bolt. And adjustment nuts 26 </ b> A and 26 </ b> B screwed to 23.

  The upper jig 21 extends in three directions, has a bolt through hole in the vicinity of each tip, and has an attachment hole 27 through which the starting seed rod 3 is inserted.

  The lower jig 22 is composed of a first heat shield plate 24 having a notch for attaching to the seed rod portion 8 and a second heat shield plate 25 fitted to the first heat shield plate 24. . The first heat shield plate 24 has a seed rod through hole through which the seed rod portion 8 penetrates at the center, and has three bolt through holes through which the suspension bolts 23 are inserted. The second heat shield plate 25 has, for example, a fan shape so as to cover the notch portion by fitting from above the first heat shield plate 24.

  The outer diameter D1 of the heat shield jig 20 is set to an outer diameter dimension that falls within a range of 0.3D0 <D1 <0.98D0, where D0 is the inner diameter of the core tube 11. For example, when the inner diameter D0 is 200 mm, the substantially outer diameter D1 is set within a range of 60 mm to 196 mm. The height H1 of the heat shield jig 20 is set to about 400 mm when the position H0 of the lower jig 22 is, for example, 300 mm from the upper end of the starting seed bar 3.

Next, a procedure for mounting the heat shielding jig 20 to the glass particulate deposit body 1 and attaching the glass particulate deposit body 1 into the furnace core tube 11 will be described.
(Assembly of heat shield jig)
As shown in FIG. 2, three suspension bolts 23 are inserted from the lower side of the first heat shield plate 24 of the lower jig 22. Next, the first adjustment nut 26 </ b> A is screwed into each suspension bolt 23, and the suspension bolt 23 is inserted into the bolt through hole of the upper jig 21. Thereafter, the second adjustment nut 26 </ b> B is screwed into each suspension bolt 23. The screwing positions of the adjustment nuts 26A and 26B are such that when the heat shield jig 20 is engaged with the locking portion 15 of the connecting member 14, the first heat shield plate 24 at the lower end is a taper on the upper part of the glass particulate deposit 1. It adjusts so that it may arrange | position in the upper part vicinity of the glass-like fine particle deposition part 2. FIG.

(Installation of heat shield jig)
The heat shielding jig 20 is fixed to the connecting member 14 in advance before the connecting member 14 connecting the starting seed bar 3 is inserted into the core tube 11. The connecting member 14 has a locking portion 15 that engages the upper jig 21 of the heat shield jig 20. In the heat shield jig 20, the mounting hole 27 of the upper jig 21 is engaged with the locking portion 15 from above the connecting member 14 with the second heat shield plate 25 removed.

(Installation of glass particulate deposit)
The glass particulate deposit 1 is suspended in the core tube 11 with the heat shield jig 20 fixed to the connecting member 14. That is, the second heat shield plate 25 of the lower jig 22 is detached, and the glass particulate deposit 1 integrated with the starting seed rod 3 is connected to the connecting member 14 and suspended in the core tube 11.

  At this time, the boundary portion between the tapered glass particulate depositing portion 2 and the seed rod portion 8 on the upper portion of the glass particulate depositing body 1 is in the vicinity of the notch portion of the first heat shield plate 24 engaged in the core tube 11 in advance. Be placed. Fine adjustment of the position is performed by the three sets of adjustment nuts 26A and 26B so that the first heat shield plate 24 is not in contact with the glass particulate deposit 1 and is accurately disposed at the boundary portion. Finally, the second heat shield plate 25 is fitted onto the first heat shield plate 24 to complete the attachment of the glass particulate deposit 1 before sintering.

Next, a method for sintering the glass particulate deposit will be described.
(Sintering process of glass particulate deposits)
By heating the inside of the furnace tube 11 to about 1600 ° C. by the heater 12, the glass fine particle deposit 1 is sintered and made transparent. At this time, the lower jig 22 of the heat shield jig 20 is disposed at the boundary portion between the tapered glass fine particle accumulation portion 2 and the seed rod portion 8 above the glass fine particle accumulation body 1. As a result, the glass fine particle deposit 1 is sintered while heat transmitted from the heater 12 and the transparent glass base material to the seed rod portion 8 is shielded.

  Thereby, the area | region of the unsintered part of glass fine particle deposit 1 upper part can be made small, preventing the elongation of the starting seed | rod 3 by the heat | fever of the heater 12. FIG.

  According to the sintering method of the glass fine particle deposit of the present embodiment, the sintering in the tapered glass fine particle deposition portion 2 on the upper portion of the sintered glass fine particle deposit 1 is performed using the heat shield plate having the above-described configuration. The upper transparency ratio indicating the proportion of the part is set to 0.4 or more. By reducing the proportion of unsintered parts, it is possible to prevent cracking and dropping of the porous glass base material, and to minimize defects such as deformation and eccentricity during drawing, and to produce high-quality optical fibers. Can be obtained.

  The upper transparency rate can be calculated by (upper transparent length L1) / (drawing deformation length L2). As shown in FIG. 3, the upper transparent length L1 is a distance from the lower end of the unsintered portion 9 in the tapered glass fine particle deposition portion 2 to the upper end of the core portion 7 at the center of the glass fine particle deposit 1, and visually This is the length of the part (transparent part) where light can be seen through. Further, the drawing deformation length L2 is such that the outer diameter of the glass fine particle deposit 1 from the melting start end P0 of the glass fine particle deposit 1 at the time of drawing is an effective part diameter E0 (at the start end position of the base material melting at the time of drawing). This is the distance to the position P1 where E0 / 2 is half of the outer diameter. The upper transparency rate referred to here is 0.4 or more, for example, when a drawing furnace having a drawing deformation length L2 of 100 mm is used, the upper transparent length L1 of the glass particulate deposit 1 is 40 mm. That means that.

  The drawing deformation length L2 is proportional to the length of the heat zone of the drawing furnace. Therefore, even when the upper transparent length L1 (depending on the volume ratio of the unsintered portion 9) is the same, when the drawing deformation length L2 is long, the unsintered portion 9 is easily applied to the heat zone, and the unfired The influence (occurrence of defects) is likely to occur. That is, even if the upper transparent length L1 is the same, the influence differs depending on the drawing deformation length L2, and the upper transparency rate indicates the degree of this influence.

  In order to achieve this upper transparency ratio (0.4 or more), as described above, in the longitudinal direction of the glass particulate deposit 1 near the upper portion of the tapered glass particulate deposit 2 on the glass particulate deposit 1. A heat shielding jig 20 that can be adjusted in position is disposed on the glass particle sintering body 1 while the heat transmitted from the heater 12 and the tapered glass particle deposition unit 2 to the seed bar unit 8 is shielded. Thereby, even if the seed rod part 8 is brought close to the heat zone, which is the heating region in the sintering furnace 10 by the heater 12, heat transmitted to the seed rod part 8 side can be shielded, and the elongation of the seed rod part 8 is prevented. However, the volume of the unsintered portion 9 of the tapered glass fine particle deposition portion 2 can be reduced.

  In addition, this invention is not limited to each embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably. In addition, the material, shape, dimension, numerical value, form, number, location, and the like of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.

  For example, although the sintering process has been described in the above embodiment, it can also be applied to a drawing furnace in the drawing process. Further, the mounting position of the heat shield jig may be a core tube or a lid part of a sintering furnace in addition to the starting seed bar and the connecting member.

  Next, examples carried out for confirming the effects of the sintering method of the glass fine particle deposit according to the present invention will be described.

(Sintering furnace)
・ Used sintering furnace inner diameter D0: 200 mm
・ Sintering temperature: 1600 ℃
(Heat shield jig)
-Heat shield used: carbon type fixed to the connecting member-Heat shield jig outer diameter D1: 185mm
・ Heating shield height H1: 400mm
-Lower jig position H0: 300 mm from the upper end of the starting seed bar
(Glass base material)
・ Porous glass base material: Glass fine particle deposit with an outer diameter of 180 mm

  The upper transparent length L1 is changed by adjusting the position of the heat shield jig, etc., and the glass base material having a different size of the upper unsintered portion is placed in the same drawing furnace (the drawing deformation length L2 is about The frequency of occurrence of defects such as core eccentricity at the end of drawing when 100 mm) is drawn is totaled. The results are shown in FIG.

  As shown in FIG. 4, when the upper transparency rate is between 0.1 and 0.2, the failure rate is as high as 50% or more, and when the upper transparency rate is between 0.2 and 0.3, a failure occurs. It can be seen that the rate drops from about 40 percent to about 10 percent. It can be seen that when the upper transparency ratio is around 0.4, the defect occurrence rate is about 10% or less, and when the upper transparency ratio is 0.4 or more, almost no failure occurs.

  As described above, by setting the upper transparent ratio of the sintered glass fine particle body to 0.4 or more, it is possible to minimize defects such as deformation and eccentricity in the drawing process, and to produce high-quality light. A fiber can be obtained.

DESCRIPTION OF SYMBOLS 1 ... Glass particulate deposit body, 2 ... Tapered glass particulate deposit part, 3 ... Starting seed rod, 8 ... Seed rod part, 10 ... Sintering furnace, 11 ... Reactor core tube, 12 ... Heater, 14 ... Connecting member, 20 ... Heat shield jig, 21 ... upper jig, 22 ... lower jig, 23 ... suspension bolt, 24 ... first heat shield plate, 25 ... second heat shield plate, 26 ... adjustment nut, 27 ... mounting hole, L1 ... Upper transparent length, L2 ... Drawing deformation length

Claims (2)

A method for sintering a glass particulate deposit, in which a glass particulate deposit obtained by depositing glass particulate on a starting seed bar is heated and sintered by the heat of a heater,
The drawing deformation length proportional to the length of the heating zone of the same drawing furnace as the drawing furnace for drawing the sintered glass fine particle deposit is set to L2,
When the upper transparent length in the tapered glass fine particle deposit part on the upper part of the glass fine particle deposit after sintering is L1, the upper transparency defined by L1 / L2 is 0.4 or more. A method for sintering a glass particulate deposit, which comprises sintering the glass particulate deposit. In the sintering method of the glass fine particle deposit according to claim 1,
A heat shielding jig capable of adjusting the position of the glass particulate deposit in the longitudinal direction is disposed near the upper portion of the tapered glass particulate deposit on the glass particulate deposit, and the heater and the tapered glass particulate are arranged. A method for sintering a glass particulate deposit, wherein the glass particulate deposit is sintered while shielding heat transmitted from the deposit to the seed rod portion where the glass particulate is not deposited.

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