JP5907565B2 - Burner for manufacturing porous glass base material - Google Patents

Description

  The present invention relates to a burner for producing a porous glass preform in which a porous glass preform having a desired density distribution is obtained in accordance with a method for producing an optical fiber preform and the yield of the preform is improved.

Conventionally, various methods have been proposed for manufacturing an optical fiber preform.
Among them, the VAD method, which is a well-known method, attaches a starting member to a shaft that rises while rotating, hangs down in the reaction chamber, is installed in the reaction chamber, and has a predetermined angle with respect to the axial direction of the starting member. The porous glass base material composed of the core layer and the clad layer is produced by depositing and depositing the generated glass fine particles on the tip of the starting member by the core deposition burner and the clad deposition burner installed in the above. Although this method cannot be expected to be highly productive, it is a suitable method for obtaining an arbitrary refractive index distribution.

FIG. 1 is a diagram schematically showing an apparatus for producing a porous glass preform for an optical fiber by the VAD method.
The reaction vessel includes a deposition chamber 2 having an air supply port 4 and an exhaust port 5 and a storage chamber 3 for storing products, and the porous glass base material 1 is synthesized by a plurality of burners.
A starting member is inserted into the deposition chamber 2 and is raised while rotating. At the same time, a reaction gas is supplied to each burner and hydrolyzed in an oxyhydrogen flame to deposit synthesized glass particles on the starting member. Thus, the porous glass base material 1 is manufactured.
As a burner to be used, a quartz glass burner is generally used, and a core deposition burner 6 disposed toward the tip of the starting member, a first cladding deposition burner 7 disposed toward the side of the starting member, A plurality of burners such as the two-clad deposition burner 8 are arranged at a predetermined angle with respect to the pulling-up axis.
The produced porous glass base material is dehydrated and transparently vitrified in an electric furnace to form an optical fiber preform.

The porous glass base material is also manufactured by the OVD method. FIG. 3 is a diagram showing an outline of an apparatus for producing a porous glass base material by the OVD method.
The starting member is a member in which dummy rods 15 are welded to both ends of the core rod 14, and the core rod 14 is attached to the rotary chuck 17 via the dummy rod 15, and is supported rotatably around the axis. Burners 16 that are movable to the left and right are arranged in a row toward the starting member. Here, glass raw material gas (SiCl ₄ ), flammable gas, auxiliary combustion gas, and inert gas are sprayed from the burner 16 and hydrolyzed in an oxyhydrogen flame to synthesize glass particles, which are deposited on the starting member. By doing so, a porous glass base material is obtained. Reference numeral 19 denotes an exhaust hood.
In this way, the OVD method deposits and deposits glass particles generated in a flame of a plurality of burners arranged in a row along a horizontally installed starting member by reciprocating the burner or starting member. This is a method for producing a porous glass base material. This method provides high productivity.
The obtained porous glass base material is passed through a heating furnace body composed of a heater and a heat insulating material to be dehydrated and transparent glass to obtain an optical fiber base material.

Conventionally, a concentric multi-tube burner has been used in these production methods as a burner for synthesizing a glass fine particle deposit. The burner having such a structure is composed of a glass raw material gas, a combustible gas, and an auxiliary combustible gas. However, the glass particles were not sufficiently produced. As a result, the yield did not increase and high-speed synthesis was difficult.
In order to solve this problem, Patent Document 1 proposes a multi-nozzle burner in which a small-diameter auxiliary combustion gas ejection port is disposed in a combustible gas ejection port so as to surround a central raw material gas ejection port.

In recent years, the following problems have arisen as the size of the base material increases due to cost reduction.
In the method shown in FIG. 1 by the VAD method, the first cladding deposition burner 7 disposed on the upper portion of the core deposition burner 6 is disposed obliquely upward. Therefore, in the deposition region, as shown in FIG. 2, the soot density in the lower region 10 of the flame is high, and the soot density tends to be low in the upper region 11 of the flame. Reference numeral 9 denotes a central axis of the burner 7.
Here, when the amount of the combustible gas supplied to the first cladding deposition burner 7 is adjusted so that the density of the upper region 11 of the flame is appropriate, the soot density of the lower region 10 of the flame becomes too high, and vitrification occurs. Occasionally the problem of bubbles remaining. Conversely, if the amount of combustible gas is adjusted so that the soot density in the lower region 10 of the flame is appropriate, the soot density in the upper region 11 of the flame becomes too low, causing a problem of cracking during deposition. .

  On the other hand, in the method using the OVD method, glass particles are deposited on the core rod 14 using an apparatus as shown in FIG. 3, but they are arranged in a line as shown in FIGS. 4 (a) and 4 (b). The inter-burner region 20 is strongly heated from both sides by the flame of the adjacent burner, so that the soot density at that portion tends to increase locally. Therefore, if the amount of combustible gas supplied to the burner is adjusted so that the density of the entire porous glass base material is appropriate, the soot density in the inter-burner region 20 becomes too high locally, and bubbles remain during vitrification. The problem occurs. On the contrary, when the amount of combustible gas is adjusted so that the soot density in the region 20 between the burners is appropriate, the density of the entire porous glass base material is lowered, and there is a problem that it breaks during deposition.

Patent No. 1,773,359

  According to the present invention, a porous glass base material having a desired density distribution can be obtained according to the manufacturing method, without cracking during deposition, and without bubbles remaining during sintering vitrification of the porous glass base material. An object of the present invention is to provide a burner for producing a porous glass base material capable of improving the yield.

As a result of repeated studies to achieve the above object, it has been found that it is important to appropriately arrange a small-diameter auxiliary combustion gas ejection port having an appropriate diameter in order to obtain a desired density distribution. It came to.
The burner for producing the porous glass base material of the present invention is arranged in one or more rows concentrically with respect to the glass raw material gas jet port outside the central glass raw material gas jet port, and the same row of jet ports Is a glass particle synthesis burner having a combustible gas ejection port containing a small-diameter auxiliary combustion gas ejection port having the same focal length, and the inner diameter of the small-diameter auxiliary combustion gas ejection ports in the same row is the same as the circumference of the same row. Characterized by different directions.

The small-diameter auxiliary combustion gas ejection ports in the same row are arranged with ejection ports having a large inner diameter in one semicircular region, and in the other semicircular region, the inner diameter is larger than that of the one semicircular side. It is preferable to arrange a small ejection port.
Further, the small-diameter auxiliary combustible gas ejection ports in the same row are arranged with ejection ports having a large inner diameter on the upper and lower sides, and on the left and right sides, ejection ports having a smaller inner diameter than the upper and lower sides. It is preferable to arrange.

  According to the present invention, a porous glass base material with less variation in density distribution can be obtained, and the yield can be improved without cracking during production and without leaving bubbles in the base material after vitrification. It has excellent effects such as being able to.

It is a schematic diagram which shows an example of the manufacturing apparatus of the optical fiber preform by VAD method. It is a deposition schematic diagram explaining the deposition state by the 1st clad deposition burner. It is a schematic diagram which shows an example of the manufacturing apparatus of the optical fiber preform | base_material by OVD method. (A) which shows typically deposition by OVD method is a front view, (b) is a side view. It is a schematic diagram which shows the example of arrangement | positioning of the ejection port of small diameter auxiliary | assistant combustible gas suitable for the VAD method of this invention. It is a schematic diagram which shows the example of arrangement | positioning of the injection port of small diameter auxiliary | assistant combustible gas suitable for the OVD method of this invention. It is a schematic diagram which shows arrangement | positioning of the conventional small aperture auxiliary | assistant combustible gas ejection port.

Hereinafter, although embodiment of this invention is described, this invention is not limited to these, Various aspects are possible.
In the burner for producing the porous glass base material of the present invention, in the combustible gas ejection port, the small-diameter auxiliary combustion gas ejection ports are arranged in one or more rows concentrically with respect to the glass raw material gas ejection port, The inner diameter of the small-diameter auxiliary combustion gas ejection ports in the same row is different in the circumferential direction of the same row.
More specifically, in the manufacturing method, in the region where the soot density is likely to increase, a small-diameter auxiliary combustion gas ejection port having a smaller inner diameter than the region where the soot density is difficult to increase is arranged, and the supply amount of the auxiliary combustion gas is reduced. By lowering the firepower, the soot density can be selectively lowered.
Conversely, in the region where the soot density is difficult to increase, a small-diameter auxiliary combustion gas injection port with a larger inner diameter than the region where the soot density is likely to increase can be arranged to increase the supply amount of auxiliary combustion gas and increase the thermal power. The soot density can be selectively increased.

Thus, by selecting the inner diameter of the small-diameter auxiliary combustible gas ejection port so as to correct it according to the soot density characteristics of the manufacturing method, a porous glass base material deposited with a more uniform density is obtained. And problems such as bubbles and cracks are less likely to occur.
In particular, as shown in FIG. 2, the soot density in the lower region of the burner is likely to increase when it is disposed at a certain angle with respect to the growth axis, as in the first cladding deposition burner of the VAD method, On the contrary, since the soot density in the upper region of the opposite burner tends to decrease, the small-diameter auxiliary combustible gas ejection port arranged concentrically as shown in FIG. ) Side is provided with a small-diameter auxiliary combustion gas ejection port having a large inner diameter, and the lower semicircular region, that is, the position A (0 deg) side, has a small-diameter auxiliary combustion property having a relatively smaller inner diameter than the position E side. By arranging the gas ejection port, the unevenness of the soot density can be effectively reduced. The position below the burner center is 0 deg position A, and every 90 deg clockwise, position C is 90 deg, position E is 180 deg, and position G is 270 deg.

  Furthermore, in the case of the OVD method, as shown in FIGS. 4A and 4B, when the soot density between adjacent burners tends to increase due to the influence of the flame of the adjacent burners, as shown in FIG. The small-diameter auxiliary combustible gas ejection ports arranged concentrically are arranged in the vertical direction, that is, the 0-deg position A side and the 180-deg position E side, and the small-diameter auxiliary-combustible gas ejection port is arranged in the left-right direction, ie 90 deg. By arranging a small-aperture auxiliary gas ejection port having a smaller inner diameter than the positions A and E on the position C side and the position G side of 270 degrees, soot density unevenness can be effectively reduced.

[Conventional example 1]
A porous glass base material was manufactured by the VAD method using the reaction apparatus shown in FIG. A concentric quadruple burner was used for the core deposition burner 6 and appropriate amounts of raw material gases (SiCl ₄ , GeCl ₄ ), combustible gas, auxiliary gas, and inert gas were supplied. In the clad deposition burners 7 and 8, as shown in FIG. 7, eight small-diameter auxiliary combustion gas ejection ports 13 having the same diameter and the same diameter are arranged concentrically in the combustible gas ejection port 12. A multi-nozzle burner with a nozzle focal length of 100 mm was used.
Here, as shown in Table 1, among the glass raw material gas (SiCl ₄ ) and the combustible gas, the auxiliary combustible gas, and the inert gas to be supplied, the first clad deposition burner 7 is supplied with the combustible gas H ₂ . The second cladding deposition burner 8 was supplied with appropriate amounts of glass raw material gas (SiCl ₄ ), combustible gas, auxiliary gas, and inert gas. Deposition was performed under four conditions A to D in which the supply amount of the combustible gas H ₂ was changed. The deposition time is 24 hours. Subsequently, 10 pieces of optical fiber preforms were produced by sintering glass. The deposition conditions and deposition results are summarized in Table 1.

As a result, in the conventional A and the conventional B, since the amount of the flammable gas supply is small, the soot density in the region above the flame of the burner is excessively lowered, and cracking occurs during the deposition.
On the other hand, in conventional C and conventional D, since the amount of flammable gas supplied is large, the soot density in the upper area of the flame of the burner was appropriate and it did not crack during deposition. As a result, since the soot density in the area under the flame was too high, degassing was insufficient during vitrification, and bubbles remained.

[Example 1]
Therefore, as shown in FIG. 5, a small-diameter auxiliary combustion gas ejection port having a large inner diameter is disposed in the upper D to F region (135 to 225 deg) centered on E, and the lower center centered on A on the opposite side. A multi-nozzle burner in which a small-aperture auxiliary gas injection port having a relatively smaller inner diameter than the E side is arranged in the B to H region (45 to 315 deg) on the side, and this is used as the first cladding deposition burner , Deposition was carried out with the E (180 deg) side facing up.
This is because the soot density is increased by arranging a small-diameter auxiliary gas injection port with a small auxiliary gas supply amount on the A (0 deg) side in the lower flame area where the soot density tends to increase. On the other hand, in the area on the upper side of the flame where the soot density tends to decrease, because the inner diameter is large, the small-diameter auxiliary combustion gas injection port with a large auxiliary combustion gas supply amount is arranged on the E (180 deg) side, Increase soot density. As a result, the soot density distribution in the deposition region is reduced.
In this manner, similarly to Conventional Example 1, only the amount of the flammable gas H ₂ supplied was changed, supplied 24 hours, deposited for 24 hours, formed into sintered glass, and 10 optical fiber preforms were manufactured.
Table 2 shows the inner diameter of the small-diameter auxiliary combustion gas ejection port arranged at each angular position, and Table 3 shows the deposition result.
As a result, under any conditions, there was no problem of cracking during production or bubbles remaining in the base material after vitrification.

[Conventional example 2]
A porous glass base material was manufactured by the OVD method using a reactor as shown in FIG.
A multi-nozzle burner is prepared in which eight small-diameter auxiliary combustion gas ejection ports 13 having an inner diameter of 1.5 mm are arranged in the combustible gas ejection port 12 as shown in FIG. 7, and the focal length of the nozzle is 100 mm. These were arranged in a row at intervals of 150 mm.
The burner supplies a combustible gas H ₂ only changing gas as shown in Table 4, the outer diameter of 50mm, a dummy rod having an outer diameter of 50mm on a starting member which is welded to both end portions of the core rod length 2000mm Depositing, 10 pieces of 100 kg of porous glass base material were produced.

As a result, in conventional E and conventional F, since the amount of flammable gas supplied is small, the soot density of the entire porous glass base material becomes too low, and cracking occurs from the edge of the porous glass base material during deposition. It was.
On the other hand, the conventional G and the conventional H have a large supply amount of combustible gas, so that the soot density of the entire porous glass base material can be made appropriate, but the burner corresponding to the reference numeral 20 in FIG. In the area between them, due to the influence of the density becoming too high, gas could not escape during the vitrification and remained as bubbles.

[Example 2]
Therefore, a multi-nozzle burner in which a small-diameter auxiliary combustion gas ejection port having a large inner diameter is arranged at positions A and E as shown in FIG. 6 and a small-aperture auxiliary gas ejection port having a small inner diameter is arranged at positions C and G. Were prepared with the position C, G side facing the burner.
This is because in the region between the burners where the soot density is likely to increase, the soot density is lowered by placing the soot density at the position C and position G where the small-diameter auxiliary combustion gas injection port with a small inner diameter is arranged. In addition, in the regions on the A and E sides where the soot density tends to decrease, a small-aperture auxiliary gas injection port with a larger inner diameter than the positions C and G is arranged to increase the soot density, soot density distribution in the deposition region It arrange | positions so that may become small.
Thus, it manufactured on the same conditions as the prior art example 2. Table 5 shows the inner diameter of the small-diameter auxiliary combustion gas ejection port arranged at each angular position, and Table 6 shows the deposition result.
Under any condition, there was no problem of cracking during production or bubbles remaining in the base material after vitrification.

1. Porous glass base material,
2. Reaction chamber,
3. Storage room,
4). Air inlet,
5. exhaust port,
6). Core deposition burner,
7). First cladding deposition burner,
8). Second cladding deposition burner,
9. The central axis of the burner,
10. The lower area of the flame,
11. The upper area of the flame,
12 Flammable gas ejection port,
13. Small-diameter auxiliary combustion gas ejection port,
14 Core rod,
15. Dummy rod,
16. Burner,
17. Rotating chuck,
18. Porous glass base material,
19. Exhaust hood,
20. Interburner area,
21. An area where the density is not particularly high except between the burners.

Claims (3)

A small-diameter auxiliary combustion gas ejection port that is arranged in one or more rows concentrically with the glass raw material gas ejection port outside the central glass raw material gas ejection port, and the ejection ports in the same row have the same focal length. In a burner for synthesizing glass fine particles having a combustible gas ejection port that encloses a gas, a porous glass base material characterized in that inner diameters of small-diameter auxiliary combustion gas ejection ports in the same row are different in the circumferential direction of the same row Burner. The small-diameter auxiliary combustion gas ejection ports in the same row are arranged with ejection ports having a large inner diameter in one semicircular region, and in the other semicircular region, the ejection having a smaller inner diameter than the one semicircular side The burner for producing a porous glass base material according to claim 1, wherein a port is disposed. In the same row, small-diameter auxiliary combustion gas ejection ports are arranged with an ejection port having a larger inner diameter on the upper and lower sides, and on the left and right sides, ejection ports with an inner diameter smaller than those on the upper and lower sides are arranged. The burner for producing a porous glass base material according to claim 1.

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