JP5598872B2 - Optical fiber preform manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing an optical fiber preform, and more particularly to a glass fine particle deposition step.

  As a method for producing a glass fine particle deposit for an optical fiber, there is an OVD method (Outside Vapor Deposition method). In the OVD method, a glass raw material containing silicon is introduced into a burner together with a combustion gas such as a flammable gas and an auxiliary combustible gas, and the glass raw material is subjected to a hydrolysis reaction or an oxidation reaction in a flame. (Hereinafter referred to as glass particulates) is generated and deposited on the outer periphery of a rotating and reciprocating target rod to form a glass particulate deposit.

  In this OVD method, clean air is supplied from the periphery of the burner toward the target material to rectify the flame of the burner, and the above-mentioned glass particles are efficiently deposited on the target material. Further, the reaction vessel is provided with an exhaust port or the like, and the supplied clean air is exhausted together with the glass fine particles that did not contribute to the synthesis of the glass fine particles.

  Here, a conventional apparatus for producing a glass fine particle deposit by the OVD method will be described. Patent Document 1 describes a vertical manufacturing apparatus in which a target material is arranged vertically in a reaction vessel and reciprocates in the vertical direction while rotating the target material. In this vertical manufacturing apparatus, a burner that jets a flame in the horizontal direction is provided on the side surface of the reaction vessel. Further, it is described that clean air is supplied in the horizontal direction from the periphery of the burner toward the target material, and the flame of the burner is stabilized by controlling the supply flow rate. In addition, by making the inner diameter of the clean air supply chamber provided on the side wall of the reaction vessel at least 1.5 times the finished outer diameter of the porous glass base material to be finally formed, the entire target material can be made uniform. It is described that fine glass particles can be deposited.

  However, since the clean air supply port is provided in the vicinity of the center in the vertical direction of the reaction vessel in the manufacturing apparatus of Patent Document 1, it is presumed that the wind speed of clean air is reduced at the upper end and the lower end of the reaction vessel.

  On the other hand, in Patent Document 2, in a vertical manufacturing apparatus in which a target material is arranged in the vertical direction (longitudinal direction), in order to prevent the occurrence of striae, the surface of the reaction vessel facing the burner in the vertical direction. There is a description that it is preferable to arrange a plurality of exhaust pipes so that the exhaust pipe located below and the exhaust air volume increase.

  Further, Patent Document 3 discloses that in the VAD (Vapor Phase Axial Deposition Method) method, the glass fine particles that did not adhere to the target material cannot be exhausted, and the glass fine particles adhere to the inner wall of the reaction vessel and peel off. It points out the problem that it enters into the glass particulate deposit, becomes transparent glass, and bubbles are generated in the optical fiber preform. Patent Document 3 describes that in order to eliminate this problem, it is better to reduce the amount of exhaust air below the target material. Thus, in the deposition process of glass fine particles, it is a problem to appropriately adjust the exhaust air volume.

  By the way, in the manufacturing apparatus in the OVD method as described in Patent Documents 1 and 2 described above, it is desired to reduce the supply air amount of clean air in order to reduce the processing cost of the gas exhausted from the exhaust port. When using a vertical manufacturing device and reducing the supply air volume of clean air, glass particles adhere to the gripping part at the upper end of the target material and fall as a lump, resulting in abnormal appearance of the glass particle deposit Sometimes occurred. This is presumed to be because glass particles that did not accumulate on the target material when the wind speed of the clean air was lowered floated and stayed on the upper part of the reaction vessel together with the flame without being exhausted. Note that in the VAD method as in Patent Document 3, the target material and the glass fine particle deposit are raised together with the progress of production, so that the problem that the glass fine particles adhere to the gripping portion of the target material does not occur.

JP 2006-24884 A JP 2008-081359 A Japanese Patent Laid-Open No. 03-040932

  However, if the amount of clean air supplied is increased in order to solve the above-described problem of appearance abnormality, the amount of exhausted gas increases, and the cost of processing exhaust gas containing chlorine increases. In addition, if the exhaust air volume is simply reduced, a gas containing chlorine stays in the reaction vessel, and there is a problem that the reaction vessel is corroded.

  The present invention has been made in view of such a problem, and an optical fiber preform manufacturing method capable of preventing the adhesion of glass particles to the gripping portion at the upper end of the target material and suppressing the occurrence of appearance abnormality, and An object is to provide a manufacturing apparatus.

  In order to achieve the above-described object, the present invention arranges a target material vertically in a reaction vessel provided with a clean air supply port and an exhaust port, and supplies clean air of a predetermined air volume from the clean air supply port. The exhaust gas is discharged from the exhaust port, the raw material gas and the combustible gas are ejected from the burner to generate glass particles, and the target material and the burner are moved relative to each other while rotating the target material, and the glass particles In the manufacturing method of the optical fiber preform in which the gas is deposited on the outer periphery of the target material, the ratio a / b between the wind speed a of the source gas ejected from the burner and the wind speed b of the exhaust gas at the upper end of the target material is less than 40 An optical fiber preform manufacturing method characterized by the above.

  According to the present invention, the ratio a / b between the wind speed a of the source gas ejected from the burner and the exhaust wind speed b at the upper end portion of the target material is adjusted to be less than 40, thereby depositing on the target material. It is possible to prevent a defect that the glass fine particles that have not adhered adhere to the upper end (gripping portion or the like) of the target material and the lump falls to cause an abnormal appearance of the glass fine particle deposit.

  In the present invention, it is desirable that an adjustment member for adjusting the wind speed or wind speed distribution of the exhaust gas is provided at the exhaust port, and the wind speed b of the exhaust gas is adjusted by the presence / absence, the shape change, or the position change of the adjustment member. .

  By providing an adjusting member at the exhaust port, the wind speed or wind speed distribution of the exhaust can be easily adjusted.

  Further, it is desirable that the lower opening width of the exhaust port is adjusted to be fully closed or partially opened by the adjusting member.

  Thereby, in the glass particle deposition apparatus in which the target material is vertically arranged in the reaction container, the wind speed distribution is changed by covering the lower part of the reaction container, and the glass particles remaining in the upper part of the reaction container can be easily discharged.

  In the present invention, the wind speed b of the exhaust gas may be adjusted by adjusting the inflow volume of the clean air.

  When the inflow volume of clean air is reduced, the cost required for exhaust processing can be reduced. In addition, when the flow rate of clean air is increased and the wind speed of the source gas is increased, the production rate of the glass particulate deposit can be increased.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and manufacturing apparatus of an optical fiber preform | base_material which can prevent adhesion of the glass fine particle to the holding part of the upper end of a target material, and can suppress generation | occurrence | production of an appearance abnormality can be provided.

The (a) sectional side view which shows the structure of the glass particle deposition apparatus 1, (b) Top view. The figure which shows the aspect of the adjustment member 9 attached to the exhaust nozzle 4. FIG. The figure which shows the flow of the exhaust_gas | exhaustion in the glass particulate deposition apparatus 1. FIG. The figure which shows the jig | tool for a wind speed measurement of the glass fine particle deposition apparatus.

  Hereinafter, an optical fiber glass fine particle deposition apparatus 1 according to an embodiment of the present invention will be described. FIG. 1 is a schematic configuration diagram of a glass particle deposition apparatus 1, FIG. 1 (a) is a side sectional view, and FIG. 1 (b) is a top view. The glass particulate deposition apparatus 1 mainly includes a reaction vessel 2, a burner 5, a target gripping portion 7, and the like.

  The reaction vessel 2 is shaped so that the target material 6 can be arranged vertically, and a pair of target gripping portions 7 are provided on the upper wall and the bottom of the reaction vessel 2. A target material 6 is gripped by the target gripping portion 7. The target material 6 includes, for example, a glass rod having a core and a part of a clad, and a support rod 8 fused on the top and bottom of the glass rod. The porous glass base material 11 is formed by further depositing glass fine particles serving as a clad on the outer periphery of the target material 6. Furthermore, an optical fiber preform is formed by sintering this in a high-temperature heating furnace.

  A burner 5 is disposed inside the reaction vessel 2. The number of burners 5 may be one or plural.

  The upper end portion and the lower end portion of the target material 6 are fixed to the target gripping portion 7. The target material 6 can rotate about the axis A as a rotation axis. The target material 6 and the burner 5 can reciprocate relative to the axial direction of the target material 6 (in the direction of arrow B in the figure). Thereby, the flame of the burner 5 can be uniformly applied to the longitudinal direction of the target material 6.

  The burner 5 is provided with a raw material gas flow path for jetting a raw material gas at the center, a raw material seal gas flow path is provided around the raw material gas flow path, and an auxiliary combustion gas is jetted to the outer periphery of the raw material seal gas flow path. An auxiliary combustion gas flow path is provided, a flammable gas flow path for injecting flammable gas is formed on the outer periphery thereof, and a burner seal gas flow path is provided on the outermost periphery. By supplying the raw material gas into the flame composed of the auxiliary combustion gas and the combustible gas ejected from the burner 5, the glass fine particles are synthesized, and the glass fine particles can be deposited on the outer peripheral surface of the target material 6. The glass fine particles are baked and hardened by the heat of the burner 5. Thereby, a high-density porous glass base material is formed.

The gas supplied to the burner 5 is, for example, SiCl ₄ and O _{2 in} the source gas channel, N _{2 in the} source seal gas channel, O _{2 in the} auxiliary combustion gas channel, H ₂ in the combustible gas channel, N ₂ may flow through the burner seal gas flow path.

  Further, the burner 5 may be moved away from the target material 6 with the growth (increase in diameter) of the porous glass base material that is a glass fine particle deposit. By doing so, glass particles can be deposited while the distance between the flame of the burner 5 and the surface of the porous glass base material 11 is always constant.

  The reaction container 2 has a side wall on the side where the burner 5 is disposed as a full opening and serves as a clean air supply port 3. An exhaust nozzle 4 is provided on the side surface facing the clean air supply port 3. The exhaust nozzle 4 is formed at the center of the reaction vessel 2 in the width direction (the depth direction in FIG. 1A), and has a full opening from the upper end to the lower end of the target material 6. The flame ejection direction of the burner 5, the axis of the target material 6, and the left and right position center lines of the exhaust nozzle 4 are arranged on the center line C of the reaction vessel 2.

  In the present invention, the configuration of the burner 5, the gas used, and the arrangement of each component inside the reaction vessel 2 are not limited to the examples described above.

  2A and 2B are diagrams showing an aspect of adjusting the opening of the exhaust nozzle 4. FIG. 2A shows a state in which the adjusting member 9 is removed and the exhaust nozzle 4 is fully opened, and FIG. FIG. 2C shows a state in which the adjustment member 9 a is installed below the exhaust nozzle 4, and FIG. 2C shows a state in which the adjustment member 9 b without a slit is installed below the exhaust nozzle 4.

  In the following description, adjustment members having different shapes are described with reference numerals 9a and 9b, respectively. However, when there is no need to distinguish the adjustment members 9a and 9b, the reference numeral 9 is assigned. To do.

  The exhaust nozzle 4 is provided with an adjustment member 9 that adjusts the opening width thereof. The adjustment member 9 is, for example, plate-shaped and covers the lower side of the opening of the exhaust nozzle 4. The adjustment member 9 is detachable from the exhaust nozzle 4. By attaching an adjustment member 9 having a desired size or shape to the opening of the exhaust nozzle 4 at a desired position, the wind speed and the wind speed distribution of the exhaust gas in the reaction vessel 2 can be adjusted.

  FIG. 3 is a view showing the flow of exhaust (including clean air and flame) in the reaction vessel 2 when the adjusting member 9 is attached to the exhaust nozzle 4 as shown in FIGS. 2 (b) and 2 (c). It is. Arrows D, E, and F in FIG. 3 indicate the flow directions of the exhaust gas in the upper, middle, and lower portions of the reaction vessel 2, respectively.

  As shown in FIG. 3, clean air is uniformly supplied from the clean air supply port 3 into the reaction vessel 2 with a predetermined air volume. Clean air is the atmosphere from which dust and the like have been removed through a filter. Further, glass fine particles are ejected from the burner 5 together with the flame. The flame of the burner 5 is rectified by clean air, and the ejected glass particles accumulate on the target material 6. The target material 6 rotates and reciprocates relative to the burner 5. Furthermore, since clean air flows uniformly from the upper part to the lower part of the target material 6, glass particles can be uniformly deposited on the target material 6. Glass particulates that have not contributed to deposition float in the reaction vessel 2 but are exhausted from the exhaust nozzle 4 as exhaust together with clean air.

  When the adjustment member 9a having the slit 42 partially covers the lower side of the exhaust nozzle 4 as shown in FIG. 2 (b), the reaction vessel is compared with the case where the adjustment member 9 is not attached as shown in FIG. 2 (a). The exhaust air volume at the top of 2 is large and the exhaust air volume at the bottom of the reaction vessel 2 is small. 2C, when the entire lower side of the exhaust nozzle 4 is covered with the adjusting member 9b having no slit, the amount of exhaust air at the upper part of the reaction vessel 2 is larger than that in FIG. The exhaust air volume at the bottom of the reaction vessel 2 is further reduced.

  The lengths of the adjusting members 9a and 9b in the longitudinal direction and the width of the slit 42 are adjusted according to the set exhaust air speed. In the present invention, the exhaust wind speed is determined by the ratio with the wind speed of the raw material gas ejected from the burner 5. Specifically, when the wind speed of the source gas ejected from the burner 5 is “a” and the exhaust wind speed at the upper end of the target material 6 is “b”, the ratio “a” between the wind speed a of the source gas and the exhaust wind speed b is “a”. / B "is adjusted to be less than 40. The exhaust wind speed at the upper end of the target material 6 is the wind speed at the traverse upper end position of the burner 5, that is, the position of the measurement point 10 shown in FIG.

FIG. 4 is an example of a measurement jig installed in the reaction vessel 2. FIG. 4 is a front view of the reaction vessel 2 as viewed from the clean air intake side of FIG. As shown in FIG. 4, an anemometer 15 is installed at a position corresponding to the measurement point 10 in the reaction vessel 2 shown in FIG. That is, the position of the anemometer 15 (measurement point 10) is set to the traverse upper end position of the burner 5, as shown in FIG. The anemometer 15 may be supported by the mount 13 installed so as not to affect the reciprocating movement of the target material 6 and the burner 5.
Using such a measuring jig, clean air is supplied from the clean air supply port and exhaust gas is exhausted from the exhaust duct under the same conditions as those for manufacturing the porous glass base material. Since it is difficult to measure the wind speed during manufacture of the porous glass base material, the wind speed measured by the anemometer 15 is used as the wind speed during manufacture.

  The wind speed a of the raw material gas is adjusted by the raw material input amount, the opening area of the burner 5 and the like. The exhaust wind speed b is adjusted by changing the presence or absence of the adjusting member 9 and the shape or position of the adjusting member 9. Alternatively, the exhaust air speed b may be adjusted by adjusting the inflow air amount of clean air.

In addition, it is desirable that the wind speed “a” of the source gas to be ejected and the exhaust wind speed “b” at the upper end of the target material 6 are set in view of the following points.
(A) It is desirable to reduce the inflow volume of clean air as much as possible. This is because if the inflow air volume of clean air is large, the exhaust air volume also increases and the cost required for processing the exhaust gas increases.
(B) The raw material wind speed is preferably larger. This is because the deposition rate of the glass particles increases as the amount of the glass particles ejected from the burner 5 is increased.

  As described above, according to the present invention, the ratio a / b between the wind speed a of the source gas ejected from the burner 5 and the wind speed b of the exhaust gas at the upper end of the target material 6 is adjusted to be less than 40. Thus, it is possible to prevent the defect that the glass fine particles that did not contribute to the deposition adhere to the upper end (gripping portion or the like) of the target material 6 and the lump falls to cause an appearance abnormality. When determining the raw material air speed a and the exhaust air speed b (inflow air volume), the ratio a / b may be determined so as to be less than 40. From various viewpoints such as cost reduction and product manufacturing speed. An optimum value can be selected. Further, by installing the adjustment member 9 in the exhaust nozzle 4, the exhaust wind speed b can be adjusted by changing the shape and arrangement of the adjustment member 9.

  Hereinafter, the vertical glass fine particle deposition apparatus 1 in which the target material 6 is vertically arranged in the reaction vessel 2 is used by adjusting the opening amount of the exhaust nozzle 4, the raw material wind speed, or the inflow air amount of clean air. The number of appearance anomalies in the glass particulate deposits was investigated. In the following evaluations, the same glass particle deposition apparatus 1 as in FIG. 1 is used, the burner 5 and the target material 6 reciprocate relatively, and clean air is uniformly supplied from the side wall on the burner 5 side. Shall be. The manufacturing conditions are as follows. The results are shown in Table 1.

Target: A cylinder having a core part and a part of the clad part, having a diameter of 50 mm and a total length of about 3000 mm. As a constituent material, the clad part is mainly SiO ₂ and the core part is doped with SiO ₂ in Ge.
・ Combustion gas: O ₂ , H ₂
・ Glass raw material: SiCl ₄
・ Clean air: Air that has been filtered to remove dust.
・ Raw material wind speed adjustment method: Adjust by the amount of raw material sent to the burner.
Wind speed adjustment method at wind speed measurement points: (a) No adjustment member (FIG. 2 (a)), (b) Slit adjustment member 9a (FIG. 2 (b)), (c) No slit adjustment member 9b (FIG. 2 (c)).
・ Reaction vessel volume: 3 m ³

  In each condition, five evaluations were performed, and the number of appearance defects was counted. The determination was “◯” when no defect occurred, “Δ” when only one defect occurred, and “X” when two or more defects occurred.

Glass fine particle deposition equipment No. In No. 1, the adjusting member was used in the form of FIG. 2A (without the adjusting member), the raw material wind speed a was set to 30 [m / s], and the clean air inflow rate was set to 50 [m ³ / min]. At this time, the wind speed b at the measurement point 10 was 0.8 [m / s], and the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “38”.

Glass fine particle deposition equipment No. 2 uses the adjusting member in the mode of FIG. 2B (the adjusting member 9a having the slit 42 is disposed below the exhaust nozzle 4), the raw material wind speed a is 30 [m / s], and the clean air inflow rate is 50. [M ³ / min]. At this time, the wind speed b at the measurement point 10 was 1 [m / s], and the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “30”.

Glass fine particle deposition equipment No. 3 uses the adjusting member in the mode shown in FIG. 2C (the adjusting member 9b having no slit 42 is disposed below the exhaust nozzle 4), the raw material wind speed a is 30 [m / s], and the clean air inflow amount is 50. [M ³ / min]. At this time, the wind speed b at the measurement point 10 was 1.2 [m / s], and the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “25”.

  Glass fine particle deposition equipment No. 1-No. When 3 is compared, as shown in Table 1, the number of occurrences of defects is 0 in all of the five uses. The judgment results were all “◯”.

Glass fine particle deposition equipment No. In No. 4, the adjusting member was used in the form shown in FIG. 2A (without the adjusting member), the raw material wind speed a was set to 40 [m / s], and the inflow volume of clean air was set to 50 [m ³ / min]. At this time, the wind speed b at the measurement point 10 was 0.8 [m / s], and the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “50”.

Glass fine particle deposition equipment No. 5 uses the adjusting member in the mode of FIG. 2B (the adjusting member 9a having the slit 42 is disposed below the exhaust nozzle 4), the raw material wind speed a is 40 [m / s], and the clean air inflow rate is 50. [M ³ / min]. At this time, the wind speed b at the measurement point 10 was 1 [m / s], and the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “40”.

Glass fine particle deposition equipment No. 6 uses the adjusting member in the mode shown in FIG. 2C (the adjusting member 9b having no slit 42 is disposed below the exhaust nozzle 4), the raw material wind speed a is 40 [m / s], and the clean air inflow amount is 50. [M ³ / min]. At this time, the wind speed b at the measurement point 10 was 1.2 [m / s], and the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “33”.

Glass fine particle deposition equipment No. 4-No. 6 is compared, as shown in Table 1, the number of occurrences of defects among the five uses is as follows. No. 4 3 times, glass fine particle deposition apparatus No. No. 5 once, glass fine particle deposition apparatus No. 6 is one time. That is, under the conditions of the raw material wind speed of 40 [m / s] and the air volume of 50 [m ³ / min], when the adjusting member 9b having no slit in FIG. 2C is used (a / b = 33), The number of defects is small, which is preferable.

Glass fine particle deposition equipment No. In No. 7, the adjusting member was used in the form shown in FIG. 2A (without the adjusting member), the raw material wind speed a was set to 60 [m / s], and the inflow amount of clean air was set to 50 [m ³ / min]. At this time, the wind speed b at the measurement point 10 was 0.8 [m / s], and the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “75”.

Glass fine particle deposition equipment No. 8 uses the adjusting member in the mode of FIG. 2 (b) (the adjusting member 9a having the slit 42 is disposed below the exhaust nozzle 4), the raw material wind speed a is 60 [m / s], and the inflow air amount of clean air is 50. [M ³ / min]. At this time, the wind speed b at the measurement point 10 was 1 [m / s], and the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “60”.

Glass fine particle deposition equipment No. 9 uses the adjusting member in the mode of FIG. 2 (c) (the adjusting member 9b without the slit 42 is disposed below the exhaust nozzle 4), the raw material wind speed a is 60 [m / s], and the clean air inflow amount is 50. [M ³ / min]. At this time, the wind speed b at the measurement point 10 was 1.2 [m / s], and the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “50”.

Glass fine particle deposition equipment No. 7-No. When the results of use of No. 9 are compared, as shown in Table 1, the number of occurrences of defects out of the five uses is the glass fine particle deposition apparatus No. 7 and no. No. 8 5 times, glass fine particle deposition apparatus No. No. 9 was twice, and all the judgments were “x”. That is, under the conditions of the raw material wind speed of 60 [m / s] and the air volume of 50 [m ³ / min], the ratio a / b between the raw material wind speed a and the exhaust wind speed b is both “50” or more, and the appearance abnormality is poor. There has occurred.

Glass fine particle deposition equipment No. 10-No. 12, the wind speed b at the measurement point 10 is 1.3 [m / s], the exhaust air volume is 80 [m ³ / min], and the adjustment member is used in the mode of FIG. The raw material wind speed was changed for each.

  Under such conditions, the glass fine particle deposition apparatus No. 10, the raw material wind speed a was set to 30 [m / s]. At this time, the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “23”. As a result of the five evaluations, the number of defects was 0.

  Further, under the same conditions, the glass fine particle deposition apparatus No. 11, the raw material wind speed a was set to 40 [m / s]. At this time, the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “31”. As a result of the five evaluations, the number of defects was 0. Further, the glass fine particle deposition apparatus No. 12, the raw material wind speed a was set to 60 [m / s]. At this time, the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “46”. As a result of five evaluations, the number of defects was 2.

That is, the glass fine particle deposition apparatus No. 10-No. From the result of use 12, when the inflow air volume is 80 [m ³ / min], a good result cannot be obtained when the ratio a / b between the raw material air speed a and the exhaust air speed b is “46”. It was found that good results were obtained.

Furthermore, the glass fine particle deposition apparatus No. 1 and No. 10 is compared, even if the inflow air volume is changed from 50 [m ³ / min] to 80 [m ³ / min], the ratio a / b between the raw material air speed a and the exhaust air speed b is less than “40”. Due to the range, good results are obtained. From the viewpoint of the exhaust treatment cost, the glass fine particle deposition apparatus No. It is preferable to use 1.

Further, the glass fine particle deposition apparatus No. 4 and no. 11, the inflow air volume is changed from 50 [m ³ / min] to 80 [m ³ / min]. Glass fine particle deposition equipment No. 4, the ratio a / b between the raw material wind speed a and the exhaust wind speed b was as large as “50”. In this case, out of the five evaluations, the number of defects occurred three times. On the other hand, the glass fine particle deposition apparatus No. In No. 11, the ratio a / b between the raw material wind speed a and the exhaust wind speed b was “31”, and the number of occurrences of defects was 0. Thus, good results were obtained.

Further, the glass fine particle deposition apparatus No. 7 and no. 12 is compared, the inflow air volume is changed from 50 [m ³ / min] to 80 [m ³ / min]. Glass fine particle deposition equipment No. 7, the ratio a / b between the raw material wind speed a and the exhaust wind speed b was as large as “75”. In this case, five defects out of the five evaluations occurred. Further, the glass fine particle deposition apparatus No. 12, the ratio a / b between the raw material wind speed a and the exhaust wind speed b was as large as “46”, and two of the five evaluations were defective, and good results could not be obtained.

Considering the above results in view of the number of defects generated, the exhaust treatment cost, and the generation rate of the glass particle deposit, the glass particle deposition apparatus No. It can be seen in 6 that the best results are obtained.
In addition, even if the inflow air volume is 50 [m ³ / min], that is, the inflow air volume per minute / the volume of the reaction vessel is 17 or less, occurrence of abnormal appearance can be suppressed.

  As described above, it is possible to prevent the appearance abnormality from occurring by setting the ratio a / b between the wind speed a of the source gas ejected from the burner and the exhaust wind speed b at the upper end of the target material to be less than 40. In addition, the exhaust processing cost can be reduced.

  As mentioned above, although embodiment of this invention was described referring an accompanying drawing, the technical scope of this invention is not influenced by embodiment mentioned above. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs.

DESCRIPTION OF SYMBOLS 1 ......... Glass particulate deposition apparatus 2 ......... Reaction container 3 ......... Clean air supply port 4 ......... Exhaust nozzle 5 ...... Burner 6 ......... Target material 7 ......... Target gripping part 8 ......... Support rod 9, 9a, 9b ......... Adjusting member 10 ......... Measurement point 11 ......... Porous glass base material 13 ...... Base 15 ......... Anemometer 42 ......... Slit

Claims (6)

A target material is arranged vertically in a reaction vessel provided with a clean air supply port and an exhaust port,
Supplying clean air of a predetermined air volume from the clean air supply port, and exhausting exhaust gas from the exhaust port, the raw material gas and combustible gas are ejected from the burner to generate glass particles,
In the method of manufacturing an optical fiber preform in which the target material and the burner are relatively moved while rotating the target material, and the glass particles are deposited on the outer periphery of the target material.
A method of manufacturing an optical fiber preform, wherein a ratio a / b between a wind speed a of a source gas ejected from the burner and a wind speed b of the exhaust gas at an upper end of the target material is less than 40.   2. The method of manufacturing an optical fiber preform according to claim 1, wherein a wind speed b of the exhaust gas is adjusted depending on the presence / absence of an adjusting member for adjusting a wind speed or a wind speed distribution of the exhaust gas at the exhaust port. An adjustment member for adjusting the wind speed or wind speed distribution of the exhaust is provided at the exhaust port,
The method of manufacturing an optical fiber preform according to claim 1, wherein the wind speed b of the exhaust gas is adjusted by changing the shape of the adjusting member. An adjustment member for adjusting the wind speed or wind speed distribution of the exhaust is provided at the exhaust port,
The method of manufacturing an optical fiber preform according to claim 1, wherein the wind speed b of the exhaust gas is adjusted by changing the position of the adjusting member.   5. The method of manufacturing an optical fiber preform according to claim 2, wherein the lower opening width of the exhaust port is adjusted to be fully closed or partially opened by the adjusting member.   The method for manufacturing an optical fiber preform according to any one of claims 1 to 5, wherein the wind speed b of the exhaust gas is adjusted by adjusting an inflow amount of the clean air.

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