JPH0781958A - Small-sized electric furnace for optical fiber processing and production thereof - Google Patents

Abstract

PURPOSE:To improve durability by forming closely the metallic layer being a heat generating body on a ceramic supporting body, then applying a pasty ceramic layer on the surface of the metallic layer to form a closed structure. CONSTITUTION:After burning the ceramic supporting body 1 such as a specific shaped high purity Al2O3, the thin film of the heat generating body metal 2 of a Rh/Pt alloy, etc., is formed on the surface by a rotating sputtering, etc. Then, a Pt wire is wrapped at its both ends, and a Pt paste is applied at the Joint part of the heat generating body metal 2 and the Pt wire to form a terminal 4. Then, the ceramic such as pasty high purity Al2O3 is applied uniformly on the surface of the heat generating body metal 2, and air-dried to form the ceramic coating layer having a specific thickness, and a closed structure is formed. Moreover, the around of the closed structure is enclosed with a foamed Al2O3, and a refractory cement 6 is inserted at the end parts to fix, and the small-sized electric furnace for the optical fiber processing is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small electric furnace for processing an optical fiber used for heating an optical fiber and a method for manufacturing the same.

[0002]

2. Description of the Related Art A small electric furnace for processing an optical fiber, in which a metal layer which is a heating element is provided on the surface of a ceramic support, is disclosed in, for example, Japanese Patent Laid-Open No. 3-187937. Unlike the carbon heater, this metal thin film heater does not need to be used in an inert gas, so that the heating device has a simple structure and has excellent temperature responsiveness. However, in the metal thin film heater, at the same time as heat generation, the evaporation pressure of the heating element itself rises, and the heating element metal evaporates and is consumed. For example, in a heater having an 80-20 platinum rhodium sputtered film having a thickness of 30 μm, an outer diameter of 3 mm and a length of 30 mm as a heating element, the heating element is broken in about 35 hours when the central temperature is 1550 degrees.

On the other hand, although not for optical fiber processing, a hermetically sealed heater having a heating element metal sandwiched between two ceramics has been commercialized in order to suppress evaporation of the heating element metal. As a method of making it, a sheet-shaped ceramic is made by adding polyvinyl alcohol or the like as a binder to the ceramic powder, kneading the mixture, and pressing it. A paste-like metal to be a heating element is applied or printed on the ceramic sheet. The same ceramic sheet is superposed on it and integrated, and finally fired. The maximum operating temperature of this hermetic heater is less than 1200 degrees, 1450
It cannot be used as a furnace for optical fiber processing that requires a temperature of more than 10 degrees. The reason for this low use temperature is the purity of the ceramics.

For example, in the case of alumina, the firing of ceramics is 1750 in a high purity region of 99.5% or more in purity.
Sintering can only be done under firing conditions of about 24 hours.
On the other hand, if the purity is around 92%, SiO ₂ , MgO, Ca
By adding O and other additives, the sintering temperature is lowered, and it becomes possible to sinter under a firing condition of 1300 ° C. for about 4 hours. Here, FIG. 3 shows a heating element hermetically sealed structure of a conventional hermetically sealed heater.

In the figure, in this manufacturing method, the ceramic support 1 and the heating element metal 2 sandwiched by the ceramic support 1 are simultaneously sintered. At this time, the diffusion layer 7 which is a compound of the ceramic support 1 and the heating element metal 2 is always formed along with the mutual diffusion of the ceramic support 1 and the heating element metal 2. Since the pure heating element metal layer is lost accordingly, the heating element metal 2 must be thickly applied or printed in anticipation thereof. However, if the layer of the heating element metal 2 is thickened, cracking is likely to occur due to strain due to a difference in thermal expansion coefficient and baking with the ceramic support 1. Diffusion and cracking become more severe as the firing temperature increases and the time increases. Therefore, the ceramic support 1
In this manufacturing method in which the heating element metal 2 and the heating element metal 2 are simultaneously sintered, it is not possible to use high-purity ceramics that need to be fired at a high temperature for a long time. In other words, ceramics of reduced purity had to be used so that it could be sintered at a low temperature in a short time, and the maximum operating temperature of the furnace was low.

The tubular shape is optimal for use as a furnace for processing optical fibers. However, in the manufacturing method in which the ceramics and the heating element metal are simultaneously sintered, at the time of firing,
Shape distortion due to the use of a tube was likely to occur and the metal of the heating element was likely to break, which made manufacturing difficult. If the firing of ceramics and the formation of the heating element metal are performed in separate steps, problems such as diffusion, cracking, and breakage can be individually solved, but it is extremely difficult to solve them by a manufacturing method in which sintering is simultaneously performed.

[0007]

As described above, the conventional small electric furnace using the ceramics and the heating element metal has respective characteristics, but one has a short durability life,
The other one could not be used because its operating temperature was low. That is,
None of them satisfy all the required performances that can be used as a furnace for heating an optical fiber.

It is an object of the present invention to provide a small electric furnace for processing an optical fiber, which has a high operating temperature and an excellent durable life, and a manufacturing method thereof.

[0009]

According to a first aspect of the present invention, in a small electric furnace for processing an optical fiber in which a metal layer which is a heating element is closely formed on a surface of a ceramic support, the metal layer which is a heating element is formed. The surface is coated with a ceramic layer to form a closed structure.

According to a second aspect of the present invention, there is provided a method for manufacturing a small electric furnace for processing an optical fiber, which has a step of closely forming a metal layer which is a heating element on a surface of a ceramic support body. The method has a step of coating the surface of the metal layer, which is the body, with a paste-like high-purity ceramic layer.

[0011]

In the method for manufacturing a small electric furnace for processing an optical fiber according to the present invention, a thick high-purity ceramic that has been main-fired in advance is used as a support, and a metal layer is closely formed on the surface of the support to form a heating element. A high-purity paste-like ceramic layer that does not require heat treatment is thinly coated and naturally dried. As a result, the heating element metal is hermetically sealed with ceramics having excellent heat resistance and shielding properties, so that it is possible to realize a small electric furnace for processing an optical fiber, which has a high maximum operating temperature and a long durable life.

Further, the sintering of the high-purity ceramic serving as the support and the formation of the heating element metal are separately performed, and the high-purity ceramic layer is formed on the heating element metal layer without thin firing. As a result, there is no adverse effect of diffusion due to high temperature firing. Furthermore, since the heating element metal layer and the high-purity ceramics layer can be thinned, thermal strain is alleviated and cracking is less likely to occur.

[0013]

1 is a perspective view showing the construction of an embodiment of a small electric furnace for processing an optical fiber according to the present invention. In addition, here
The state where some small electric furnaces for optical fiber processing were cut away is shown.

First, the structure of each part will be described according to the manufacturing process. Outside diameter 3 mm, inside diameter 2 mm, length 35 mm, purity 99.5
The ceramic support 1, which is a% alumina insulation, is fired. Then, a platinum alloy containing 20% by weight of rhodium is sputtered on the surface thereof to form a heating element metal 2 having a thickness of 30 μm. Next, a platinum wire having a thickness of 1 mm and a length of 80 mm is wound around each of the ends twice, and a platinum paste is applied to a contact portion between the heating element metal 2 and the platinum wire to form the terminal 4. next,
A paste-like alumina having a purity of 99.5% is uniformly applied to the surface of the heating element metal 2 and naturally dried to form a ceramic coating layer 3 having a thickness of about 50 μm. Next, the periphery thereof is surrounded by expanded alumina 5 having an outer diameter of 15 mm, an inner diameter of 7 mm and a length of 35 mm, and a refractory cement 6 is inserted and fixed at the end. The small electric furnace A for processing an optical fiber of this embodiment can be manufactured by the above steps.

FIG. 2 shows the heating element sealing structure in this embodiment. As shown in the figure, the heating element metal 2 is sealed by the ceramic support 1 and the ceramic coating layer 3.

On the other hand, for the purpose of comparison, a conventional small electric furnace B for processing an optical fiber was also manufactured except the step of forming the ceramic coating layer 3. For these two types of small electric furnaces for optical fiber processing, when the peak temperature of the furnace is set to 1550 degrees, the heating element metal 2 formed of a platinum alloy thin film is used.
The durability life until the wire was broken was evaluated. The results are shown in FIGS. 4 and 5. In addition, the peak temperature of the furnace is obtained by measuring the temperature distribution in the longitudinal direction of the furnace, and at the same time, the peak temperature of 90% is measured to evaluate the flatness of the temperature distribution.
"Width 90" is the length in the longitudinal direction of the furnace that reaches a temperature of at least%.
And standardized.

The vertical axes of FIGS. 4 and 5 are the heater current (A) and the heater voltage (V) indicating the applied current voltage of the furnace,
It represents the length (mm) of Width90. The horizontal axis is time (Hr)
Represents FIG. 4 shows the result of a life test of the small electric furnace A for processing an optical fiber according to the present embodiment, and shows that the heating element metal 2 is broken at the time when it exceeds 62 hours. FIG. 5 shows a result of a life test of the conventional small electric furnace B for processing an optical fiber, and shows that the heating element metal 2 is broken at the time when it exceeds 34 hours.

In each of the furnaces, the Width 90 decreased during the test while keeping the peak temperature at 1550 ° C., which means that the evaporation proceeds more toward the center of the furnace and the temperature distribution becomes narrower. There is. Small electric furnace A for optical fiber processing of this embodiment
In comparison with the conventional small electric furnace B for processing an optical fiber, the decrease in Width 90 is obviously smaller, and it can be seen that the evaporation and consumption of the heating element metal 2 is suppressed. As described above, in the small electric furnace for processing an optical fiber according to the present embodiment,
Since the sealed structure that suppresses the evaporation of the heating element metal 2 can be formed of high-purity ceramics, the maximum operating temperature is high and the durable life can be significantly extended.

It should be noted that it is not always necessary to have a structure in which the ceramic heat generating element is surrounded by the hollow expanded alumina 5 as in this embodiment. In that case, refractory cement 6
Becomes unnecessary. Further, the terminal 4 does not need to be wound with a platinum wire around the heating element metal 2 and fixed with a platinum paste as long as it has heat resistance and has a low electric resistance and heat conduction. Further, the ceramic support 1 is not limited to the tubular one, and may have a shape according to the application.

[0020]

As described above, in the small electric furnace for processing an optical fiber according to the first aspect of the present invention, since the heating element metal can have a closed structure in which it is wrapped with high-purity ceramic excellent in heat resistance and shielding property, It is possible to suppress the evaporation and consumption of the heating element metal that occurs with the generation of heat and to extend the durable life.

In the method for manufacturing a small electric furnace for processing an optical fiber according to a second aspect of the present invention, the ceramics serving as the support are separately sintered and the heating element metal is formed, and the ceramics that do not require high temperature treatment are coated. The method forms a hermetically sealed structure of heating element metal. Therefore, high-purity ceramics can be used, and the operating temperature of the furnace can be increased. Moreover, the furnace can be configured in a tubular shape most suitable for optical fiber processing without causing problems such as diffusion, cracking, and breakage.

[Brief description of drawings]

FIG. 1 is a perspective view showing the configuration of an embodiment of a small electric furnace for processing an optical fiber according to the present invention.

FIG. 2 is a cross-sectional view showing a heating element sealing structure in the present embodiment.

FIG. 3 is a cross-sectional view showing a heating element sealing structure of a conventional heater having a sealed structure.

FIG. 4 is a graph showing the results of a life test of the small electric furnace for processing an optical fiber according to the present embodiment.

FIG. 5 is a graph showing the results of a life test of a conventional small electric furnace for processing an optical fiber.

[Explanation of symbols] 1 ceramics support 2 heating element metal 3 ceramics coating layer 4 terminals 5 expanded alumina 6 refractory cement 7 diffusion layer

Claims (2)

[Claims] 1. A small electric furnace for optical fiber processing, wherein a metal layer as a heating element is closely formed on the surface of a ceramic support, and a ceramic layer is coated on the surface of the metal layer as a heating element to form a closed structure. A small electric furnace for optical fiber processing. 2. A method for manufacturing a small electric furnace for optical fiber processing, which comprises a step of closely forming a metal layer, which is a heating element, on the surface of a ceramics support, the surface of the metal layer, which is the heating element, after the step. A method for manufacturing a small electric furnace for processing an optical fiber, which comprises a step of coating a paste-like high-purity ceramics layer on the substrate.