JP3944704B2 - heating furnace - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heating furnace .
[0002]
[Prior art]
In the production of an optical fiber, a heating furnace 101 as shown in FIGS. 4 and 5 is used in each process such as production of a base material, stretching, sintering, and drawing. In the heating furnace 101, an induction coil 103 is wound, and a heat insulating material 105 is provided inside the induction coil 103. A susceptor 111, which is a carbon conductive heating material, is attached inside the heat insulating material 105, and a heating region 113 is provided inside the susceptor 111.
[0003]
When a glass preform for an optical fiber is manufactured by the rod-in-tube method, a glass pipe into which a glass rod is inserted is inserted into the heating region 113, and an electric current is passed from the input terminal 115 attached to the upper portion of the casing 109 to the induction coil 103. To heat the susceptor 111 with an induced current, raise the temperature of the heating region 113, and integrate the glass pipe and the glass rod in the heating region 113.
[0004]
[Problems to be solved by the invention]
However, in order to manufacture the glass base material, it is required that the temperature distribution in the heating region is steep, and in the conventional technique as described above, an induced current is generated in the susceptor 111 and the heat insulating material 105. Since both of them generate heat and the heating area becomes wide, there is a problem that a steep temperature distribution cannot be obtained. Moreover, there is a possibility that power consumption will increase unnecessarily.
[0005]
The object of the present invention has been made by paying attention to the problems of the prior art as described above. By concentrating the power by narrowing the heating region, a steep temperature distribution can be obtained and the power consumption can be reduced. An object of the present invention is to provide a heating furnace that can be reduced.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the heating furnace of the invention according to claim 1 energizes the induction coil wound around the susceptor provided around the central portion of the internal space in the casing to cause the susceptor to flow. A heating furnace for generating heat by induction heating and heating the glass inserted into the internal space, wherein the length of the susceptor is shorter than the length of the internal space, and the susceptor is composed of silicon nitride at both ends thereof It is supported by a support member, and the internal space has a temperature gradient in which a temperature is high in a portion surrounded by the susceptor and a temperature is low in a portion surrounded by the support member.
[0007]
Therefore, since both sides of the heating element are supported by the support member, the heating element can be made small. In addition, since the support member is an insulator, no induction current is generated by the induction coil and no heat is generated. Therefore, a rapid temperature distribution can be obtained by concentrating the heat generation on the heat generation element made of carbon. In addition, since the induced current can be generated concentrated on the reduced heating element, the power consumption is reduced.
[0008]
The heating element support structure for a heating furnace as a reference example is characterized in that the support member can withstand high temperatures and thermal shocks in the range of 350 ° C to 2300 ° C.
[0009]
The heating element support structure for a heating furnace, which is a reference example, is characterized in that in the heating element support structure for a heating furnace, the support member is made of boron nitride. At this time, a state where the inside of the heating furnace is in a low oxygen region (inactive) is preferable.
[0010]
The support member made of boron nitride has heat resistance and insulation properties, and can support the heating element for a long time without being affected by high temperature and its thermal shock.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, taking as an example a heating furnace for manufacturing a glass preform for an optical fiber by a rod-in-tube method. FIG. 1 shows a cross-sectional view of a heating furnace 1 according to the present invention. In the heating furnace 1, an insertion portion 11, which is an internal space for passing the cladding glass pipe 5 in which the core glass rod 7 is inserted, is provided in the center of the casing 3 in the front-rear direction (left-right direction in FIG. 1). Openings 13F and 13R are provided at both front and rear end faces of the casing 3.
[0012]
A susceptor 15, which is a heating element made of carbon, is provided on the inner surface of the central portion of the insertion portion 11, and an induction coil 19 is wound around the susceptor 15 with a heat insulating material 17 interposed therebetween. Has been. Further, an inert gas such as nitrogen gas is jetted to the insertion portion 11 in order to discharge oxygen in the insertion portion 11 on the inner peripheral surface of the insertion portion 11 adjacent to both the front and rear sides of the susceptor 15. Inert gas outlets 21 are provided at predetermined intervals. A pipe 23 for supplying an inert gas is provided at the inert gas outlet 21 through the heat insulating material 17. The pipe 23 is connected to an inert gas ejection means (not shown).
[0013]
In order to consume oxygen in the insertion portion 11 and oxygen entering the insertion portion 11 inside the front and rear openings 13F and 13R in the insertion portion 11, an oxygen consumption ring 25 is provided as an oxygen consuming means. It is provided over the entire circumference of the inner circumferential surface of the. Furthermore, double shutters 27A and 27B are provided on the front and rear end faces 3F and 3R of the casing 3 outside the oxygen consumption ring 25 in the insertion portion 11 to prevent oxygen from entering the insertion portion 11 from the outside. The front chamber 29, which is a low oxygen region, is provided inside the double shutter 27B.
[0014]
Next, the principal part of the optical fiber glass preform manufacturing apparatus 1 according to the present invention will be described in more detail. As shown in FIG. 2, both front and rear (left and right in FIGS. 1 and 2) sides of the susceptor 15 are supported by edge portions 31 ′ at the end of the support member 31. The support member 31 has a thermal conductivity smaller than that of carbon and is an insulator. Further, since the support member 31 can withstand a thermal shock that rises from 400 ° C. to 2300 ° C. in 10 minutes in the range of 350 ° C. to 2300 ° C., the support member 31 is made of, for example, boron nitride. It is used.
[0015]
The temperature distribution of the susceptor 15 and the support member 31 at this time is shown in FIG. 3, and the center position of the susceptor 15 is set to the zero point. When the susceptor 15 is supported by the support member 31 as in this embodiment (indicated by a solid line in FIG. 3), the susceptor made of carbon over the entire insertion portion as in the prior art (indicated by a broken line in FIG. 3). ), The temperature of the support member 31 which is both the front and rear sides of the susceptor 15 is lower, and the temperature distribution is steep.
[0016]
With the above configuration, when the glass preform for the optical fiber is manufactured, the clad glass pipe 5 into which the core glass rod 7 is inserted is relatively inserted from the left side in FIG. . At this time, the front and rear double shutters 27A and 27B open and close in accordance with the shape of the glass base material 9, and oxygen enters the insertion portion 11 from between the double shutters 27A and 27B and the glass base material 9. To prevent.
[0017]
Then, inert gas, for example, nitrogen gas, is jetted into the insertion portion 11 from the inert gas outlets 21 provided on both the front and rear sides of the susceptor 15, and oxygen inside the insertion portion 11 is changed to both front and rear openings 13 </ b> F. The gas is discharged from 13R together with nitrogen gas. Further, while consuming oxygen remaining in the insertion portion 11 or oxygen entering the insertion portion 11 from the openings 13F and 13R by the oxygen consumption ring 25, a current is passed through the induction coil 19 to cause the susceptor 15 to generate heat. The inner region is heated to heat the glass rod 7 and the glass pipe 5 inserted in the region. Furthermore, the glass pipe 5 is crushed by setting the inside of the glass pipe 5 to a negative pressure, and the glass rod 7 and the glass pipe 5 are integrated to form a glass preform for an optical fiber. At this time, both the front and rear sides (left and right in FIG. 1) of the susceptor 15 are supported by the support member 31 that is an insulator, so that power can be concentrated on the susceptor 15.
[0018]
When the size of the susceptor 15 is about 55-60% of the conventional size and the other is the support member 31, the power consumption can be reduced by about 10% compared to the conventional size. Further, since the support member 31 is made of boron nitride, it can withstand a thermal shock caused by a rapid temperature change without causing cracks and the like, so that the susceptor 15 can be supported for a long time.
[0019]
The heating element support structure of the heating furnace of the present invention is not limited to the above-described embodiment, and appropriate modifications and improvements can be made. That is, in the above-described embodiment, the support member 31 is provided only in the vicinity of the susceptor 15, but it may be provided up to both ends of the insertion portion 11.
[0020]
Although using boron nitride to the support member 31, otherwise, silicon nitride (Si ₃ N _4), aluminum nitride (AlN), cordierite ceramics _{(2MgO · 2A 2 lO 3 ·} 5SiO 2), alumina ( Al ₂ O ₃ ), zirconia (ZrO ₂ ), etc., or a mixture of two or more components among them may be used. In the above example, the production of the optical fiber glass preform is shown, but the heating furnace of the present invention is not limited to this. It may be used in other processes in the production of optical fibers, and can also be used in other cases.
[0021]
【The invention's effect】
As described above, the heating furnace according to the present invention can achieve the following effects.
(1) The heating element can be made small.
(2) A steep temperature distribution can be obtained.
(3) Power consumption can be reduced.
(4) By using a support member that can withstand thermal shock, the heating element can be supported for a long time.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a heating element support structure for a heating furnace according to the present invention.
FIG. 2 is a schematic cross-sectional view showing a heating member support member.
FIG. 3 is a graph showing a temperature distribution in a base material insertion portion.
FIG. 4 is a cross-sectional view showing an example of a heating element support structure of a conventional heating furnace.
5 is a side view as seen from the direction V in FIG. 4;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Heating furnace 5 Clad glass pipe 7 Core glass rod 11 Insertion part 15 Susceptor (heating element)
19 Induction coil 31 Support member

Claims (1)

  Heating the glass inserted into the internal space by energizing the induction coil wound around the susceptor provided around the central portion of the internal space in the casing to inductively heat the susceptor to generate heat. A furnace,
  The length of the susceptor is shorter than the length of the internal space, the susceptor is supported by support members made of silicon nitride at both ends thereof, and the temperature of the internal space is high at the portion surrounded by the susceptor. A heating furnace characterized by having a temperature gradient that the temperature is low in the enclosed part.

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