JPH0585761A - Porous glass base material - Google Patents

Abstract

PURPOSE:To provide the soot body which does not crack even when this soot body is formed to a larger size and can completely prohibit the progression of the crack even if such crack is generated with the porous glass base material (soot body) which is a precursor of synthetic silica glass. CONSTITUTION:This invention is identical to the prior art in that annular higher-density parts are formed at desired points on at least one of cone parts 5 of the above-mentioned soot body 10 by biscuit firing using heating burners 3, 4 but this invention consists in forming the above-mentioned higher density parts 20 in particular at >=2 points apart spacings in central parts 5C exclusive of both end positions 5A, 5B of the cone parts. More specifically, the positions where the above-mentioned higher density parts 20 are formed at >=2 points apart the spacings in the 70% central area 5C sandwiched by the 15% areas at both ends of the cone parts.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous glass base material which is a precursor of synthetic silica glass, and in particular, soot-like silica fine particles are deposited to form a cone portion having a tapered cross section on at least one axial end side. To a rod-shaped porous glass preform.

[0002]

2. Description of the Related Art Conventionally, SiCl ₄ or other silicon compounds are heated by an oxyhydrogen flame or other heat source, and soot-like silica fine particles produced by the flame hydrolysis reaction and high-temperature thermal oxidation reaction of alumina (Al ₂ O ₃ ) Or the like on a heat-resistant substrate or along the axial direction from the axial end of the substrate in a solid state to form a porous glass base material (hereinafter referred to as soot body) that is a precursor of a synthetic quartz glass body. A method for producing a synthetic quartz glass body by a so-called vapor phase, in which a transparent glass body is obtained by heating the soot body in a vacuum or an inert gas atmosphere to sinter / melt, is known.

Sulfur as a precursor of such synthetic silica glass
For example, SiCl may be manufactured by a method of manufacturing a sheet body. With silicon compounds such as 4
Silica fine particle forming bar capable of simultaneously supplying oxygen and hydrogen
And quartz glass, alumina, carbon, silicon carbide
The above-mentioned burner using a heat-resistant substrate with a rotatable shaft
Or, order at least one of the heat resistant substrates in the axial direction of the substrate.
While moving next, fine particles of silica on the rotating substrate
Method for producing soot body by stacking children (Japanese Patent Application No. 49-9)
No. 523)

In order to improve the deposition rate of silica fine particles on the heat-resistant substrate, the burners are arranged in a line in the axial direction of the heat-resistant substrate over substantially the entire length of the silica fine particle deposition site on the heat-resistant substrate. A method of manufacturing a soot body by uniformly laminating silica fine particles in the axial direction on the rotating substrate while reciprocating the burner row in the axial direction of the substrate (JP-A-53-70449). , Hereinafter referred to as radial growth method).

Furthermore, the burner is arranged toward the axial end of the heat-resistant substrate, and the silica fine particles are hemispherical on the substrate which is rotating while being moved in the direction in which the two members are relatively separated from each other in the axial direction of the substrate. A technique for producing a solid soot body by stacking the layers in a shape (Japanese Patent Laid-Open No. 52-143037 et al., Hereinafter referred to as axial growth method) has been developed.

However, since all of the above-mentioned production techniques are batch-type production methods of soot bodies, in order to increase the productivity of synthetic silica glass, it is essential to increase the size of the soot bodies. Since all the soot bodies are formed by simply depositing silica fine particles into a porous form, their mechanical strength is extremely brittle. Therefore, as the soot body becomes larger and its weight increases, the soot body becomes The generated load becomes large, and in the worst case, the soot body may be cracked and may fall and be damaged.

Further, since the manufacturing method is a batch method, the silica fine particle forming burner is extinguished every time the deposition of a predetermined amount of silica glass fine particles on each of the heat-resistant substrates is finished, and after cooling once below a predetermined temperature. When a batch treatment method is adopted such that the soot body moves to the sintering and melting step of the next step, the soot body has a significantly smaller heat capacity than the transparent glass body. It is cooled rapidly, and the contraction of the cooled surface causes tensile stress on the surface of the soot body, causing cracking. Further, with respect to the above-mentioned defects, the larger the diameter of the soot body is, the larger the temperature difference between the cooled surface and the inside becomes, and the above-mentioned defects are amplified.

Since the heat-resistant substrate for supporting the soot body is made of alumina, carbon, or silicon carbide as described above, the heating position of the burner after the burner is extinguished or at the start of the deposition site is As the distance from the starting end increases, heat shrinkage occurs due to the temperature decrease of the heat resistant substrate, while the soot body hardly forms heat shrinkage due to the temperature decrease because it is formed of silica fine particles as described above, and as a result, the heat shrinkage occurs. Misalignment and peeling easily occur between the formed substrate.

On the other hand, in any of the above-mentioned techniques, silica fine particles are inevitably deposited on the heat resistant substrate while one or more silica fine particle forming burners are relatively moved along the axial direction of the heat resistant substrate. A cone portion having a tapered cross-section is formed on the axial end side of the soot body deposited on the substrate, but since the cone portion is thinned toward the edge, its mechanical strength is extremely fragile, For this reason, when a slight physical impact is applied to the cone portion, cracking is more likely to occur as compared with other straight body portions, the cracking progresses throughout the soot body axial direction, and the above-mentioned drop occurs. Problems such as breakage easily occur.

In order to eliminate this drawback, FIG. 3 (A)
After forming the cone portion 5 or the soot body 10 as shown in FIG. 3, the boundary portion between the cone portion 5 and the base body 1 is baked by a heating burner 3 to form a ring-shaped densified portion, Techniques for preventing the occurrence are disclosed. (JP-A-63-206324)

[0011]

However, when the cone boundary portion 5A, which is extremely thinned, is sintered with a flame to have a high density, the amount of heat supplied per density becomes extremely large. A large contraction also occurs in the circumferential direction to generate a strain, and therefore, not only the end portion 5A is likely to be cracked in the axial direction, but also the soot body 10 is increased in size to be applied to the heat resistant substrate 1. As the weight burden is increased, the amount of bending also increases, and a large stress is applied to the boundary portion. If the portion to which the stress is most applied is densified, cracks are likely to occur due to stress concentration.

In view of the drawbacks of the prior art, the present invention does not cause cracks even when the soot body is upsized, and even if cracks occur, the progress thereof can be completely prevented. The purpose is to provide a possible suit.

[0013]

The present invention provides the soot body 10 described above.
It is the same as the above-mentioned prior art in that at least one desired portion of the cone portion 5 is heated and tightened using the heating burners 3 and 4 to form a ring-shaped densified portion, but the present invention particularly The conversion part 20 is placed at both end positions 5A, 5B of the cone part.
It is characterized in that it is formed in two or more places at intervals in the central portion 5C except for, and more specifically, the formation position of the densified portion 20 is sandwiched between 15% areas on both ends of the cone portion. % It is characterized in that it is formed in two or more places in the central region 5C at intervals. The densification section 2
0 may be formed only on the cone portion 5 of the soot body 10 on the shaft start end side, but it is preferably formed on both the start end side 5 and the end side 5'if necessary. Further, the present invention is applicable to both the radial growth method in which the heat-resistant substrate 1 extends horizontally and the axial growth method in which the heat-resistant substrate 1 is vertically provided.

[0014]

[Function] The small-diameter end portion 5 of the cone portion 5 on the heat-resistant substrate side
As described above, when the density of A is increased, the defect shown in FIG.

On the other hand, when the large-diameter end portion 5C located at the boundary with the soot body straight body portion 8 is densified, a recess is formed as shown in FIG. 3B, and the straight body portion 8 is caused by the recess. A ring-shaped edge 29 is generated in the vicinity of the boundary with and a crack 28 is generated in that portion along the circumferential direction, and stress concentration is likely to occur in a part of the crack 28 due to the bending of the soot body 10. As a result, an axial crack 27 is generated from that portion, and the above-mentioned defects cannot be eliminated.

For this reason, it is preferable to densify the central region 5C of the cone portion, but if the densification portion is only one and the soot body is enlarged, in the unlikely event that a crack occurs, the progress is completely completed. I can't stop you.

Therefore, by forming the densified portion 20 in two or more places in the central region 5C except the both end positions 5A and 5B of the entire length of the cone portion at intervals, stress concentration can be prevented even if the soot body bends. It is possible to disperse by that amount, and the cause of cracking can be greatly reduced, and even if cracking occurs, the densified portion 20 is at two or more locations, so the crack progress inhibiting force is greatly reduced. improves.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail below as an example with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. Not too much.

FIG. 1 shows a soot body manufacturing apparatus according to an embodiment of the present invention. First, in this embodiment, as shown in FIG. 1, a tube made of alumina (Al ₂ O ₃ ) (outer diameter 40 mm, thickness 5 mm, length 1.5 m) is installed horizontally, and both ends thereof are rotated by a support body 9. A heat-resistant substrate 1 is formed by supporting the substrate 1 as much as possible, and a silica fine particle forming burner 2 disposed vertically from the lower position of the substrate 1 toward the peripheral surface of the substrate 1 is provided.
The forming burner 2 is configured to be relatively movable in the axial direction of the base body. Since these configurations are already well known, detailed description thereof will be omitted, but the soot body 10 manufactured by the apparatus has a total length of 1.2 m and a straight body portion 8 length of 0.
A soot body having a length of 4 m and cone portions 5 and 5'formed on both ends thereof set to 0.4 m can be manufactured.

As shown in FIG. 2, the heating burners 3, 4, 3 ', 4'for baking the soot body are heat-resistant substrates having an inclination angle of ± 20 ° to 70 ° with respect to the silica fine particle forming burner 2. And the heating burner 3,
As shown in FIG. 2, 4, 3, ′ and 4 ′ are arranged at positions shifted inward from the soot body deposition site start end 5 by desired sites. The heating burners 3, 4, 3 ′ and 4 ′ are generally constituted by oxyhydrogen burners, but the present invention is not limited thereto.

In such a structure, first, the silica fine particle forming burner 2 is traversed from the deposition site starting end 5 side along the axial direction of the heat-resistant substrate 1 while the silicon compound is fed into the combustion flame of H ₂ and O _2, and the combustion is performed. By depositing the silica fine particles generated in the heat-resistant substrate 1, and then heating the burner 3, 4, 3 ', 4'at a predetermined time, the predetermined positions 6, 7 of the cone portion of the soot body 8, The heating portion is baked in a ring shape to form the densified portion 20. At this time, the heating positions and heating temperatures of the heating burners 3, 4, 3 ', 4'are substantially the same as those of the silica fine particle forming burner 1.
The temperature is set to about 000 to 1500 ° C.

The heating timings of the heating burners 3, 4, 3 ', 4'disposed on the axial end side of the soot body are such that silica fine particles are deposited on the heat resistant substrate 1 after the cone formation is started and after the cone formation is completed. The burners 3, 4 and
3'and 4'are ignited to form the ring-shaped densified portion 20.

Next, in order to confirm the action and effect of the present invention,
The following experiment was tried. First, when the number of heating burners is limited to one, and the heating position is heated within the cone narrow end position (hereinafter referred to as 5A position) within 15% of the boundary between the cone portions 5 and 5 ′ and the heat-resistant substrate 1 ( Comparative Example 1), cone portion 5,
When the cone thick end position (hereinafter referred to as 5B position) within 15% area from the boundary between 5'and the straight body portion 8 (hereinafter referred to as 5B position) is heated (comparative example 2), the central area 70% (hereinafter 5C
When the soot body 10 of 15 kg and 30 kg is manufactured respectively, the cracks are generated in both the soot bodies 10 of 15 kg and 30 kg. However, in Comparative Example 2, 3
Cracking was observed only in the 0 kg soot body.

Next, using two heating burners, as shown in FIG. 4, the heating positions are 5A and 5B (Comparative Example 4), 5A and 5C (Comparative Example 5), 5B and 5C (Comparative Example 6), And 5C
When heating was performed so as to form two densified portions 20 spaced apart from each other in the regions (Examples), 15 kg and 30 kg soot bodies were produced in the same manner as described above, and Comparative Example 4 was obtained. In No. 6, cracking was observed in both soot bodies of 15 kg and 30 kg, but in Comparative Examples 4 and 5, it was 30
Cracking was observed only for the Kg soot body. Further, in Example 1 in which two baked portions were formed in the 5C region at intervals, no cracks were found in both soot bodies of 15 kg and 30 kg.

Next, in order to confirm whether the same effect can be obtained in the axial growth method, as shown in FIG.
A heat-resistant substrate 1 made of a seed rod made of alumina (Al ₂ O ₃ ) rotatable around an axis is hung, and a position slightly shifted in the radial direction from the axis on the lower end side of the seed rod 1. The silica fine particle forming burner 2 and the pair of heating burners 3 and 4 are vertically arranged on the starting end side of the soot deposition position of the seed rod 1 along the horizontal direction. The silica fine particle forming burner 2 is configured to be vertically movable by a driving means (not shown).

In such a structure, first, while rotating the heat-resistant substrate 1, the forming burner 2 is gradually lowered along the axial direction, and is jetted from the forming burner 2 H ₂
A silicon compound is fed into the combustion flame of the heat treatment and O ₂ to deposit the silica fine particles generated in the combustion flame on the heat-resistant substrate 1, and at the time when the silica fine particles are deposited on the heat-resistant substrate 1, heating is performed. A pair of ring-shaped high-density portions 20 are formed by igniting the burners 3 and 4 and heating the central portion 5C of the cone portion 5 at two locations with a space therebetween. It was confirmed that also in the large soot body 10 formed in this way, no deviation occurred between the large soot body 10 and the heat resistant substrate 1, and no cracks were generated in the cone portion 5 on the lower end side of the shaft.

[0027]

As described above, according to the present invention, it is possible to prevent the heat-resistant substrate from cracking, or to completely prevent the progress of the crack even if the cone portion cracks. This makes it possible to easily accommodate larger soot bodies. And so on.

[Brief description of drawings]

FIG. 1 is a schematic front view showing a glass base material manufacturing apparatus according to an embodiment of the present invention.

FIG. 2 is a side view of FIG.

FIG. 3 is a schematic view of a main part of a soot body in the process of reaching the present invention and the prior art in which a ring-shaped densified portion is formed in a cone portion.

FIG. 4 is a schematic view of a main part of a soot body showing a comparative example and an example in which two ring-shaped densified portions are formed at predetermined positions of a cone portion.

FIG. 5 is an overall schematic diagram showing a glass base material manufacturing method according to another embodiment of the present invention.

[Explanation of symbols]

 1 heat resistant substrate 2 silica fine particle forming burner 34 heating burner 20 densification section

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location C03B 37/018 Z 7224-4G

Claims (2)

[Claims] 1. A ring-shaped densified portion is formed in at least one cone portion of a porous glass base material in which soot-shaped silica fine particles are deposited to form a cone portion having a tapered cross-section on at least one axial end side. At the same time, the densified portion is formed at two or more locations in the central portion excluding the both end positions of the cone portion with a space therebetween, 2. The porous glass base material according to claim 1, wherein the densified portion forming position is a 70% central area sandwiched between 15% areas on both ends of the cone portion.