JPH0545061A - Calcinating furnace - Google Patents

Abstract

PURPOSE:To provide a calcinating furnace capable of reducing a reaction between heavy metal vapor and a furnace core pipe without lowering the hot strength of the furnace core pipe. CONSTITUTION:A calcinating furnace comprises a cylindrical furnace core pipe 1, which pipe 1 includes an outer pipe 4 and a plurality of short pipes 5. The short pipes 5 are densely calcined using a high purity ceramic material, and abutted and coupled with each other and inserted into the outer pipe 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a calcining furnace used for calcining ceramic raw material powder such as a dielectric material and a piezoelectric material.

[0002]

2. Description of the Related Art A calcination furnace called a rotary kiln is used for calcination of ceramic raw material powder such as barium titanate-based dielectric material and lead titanate zirconate-based piezoelectric material. As shown in the cross-sectional view of FIG. 3, this calcination furnace has a cylindrical core tube 21 with a certain inclination,
The heater 22 is provided so as to surround this, and the raw material powder is transferred by rotating the core tube 21 at a constant speed. Reference numeral 23 in the figure is the outer wall of the calcining furnace.

The raw material powder to be calcined in this calcination furnace is charged from one end side of the furnace core tube 21 and is heated by the heater 22 while flowing toward the other end side by the rotation of the furnace core tube 21. It is supposed to be calcined by.

[0004]

By the way, such a calcination furnace is operated in a state where there is a large temperature difference between the end portion and the central portion along the longitudinal direction of the core tube 21, that is, a state where a large heat shock occurs. Therefore, the core tube 21
For this, it is necessary to have a material having excellent hot strength. Therefore, as the conventional furnace tube 21, it has been practiced to use a low-purity ceramic material such as Al ₂ O ₃ , MgO, or ZrO ₂ after firing it in a porous state.

However, when the ceramic raw material powders such as barium titanate and lead zirconate titanate are calcined by using the core tube 21, the lead and the like generated from these raw material powders are not used. Heavy metal vapor and core tube 21
Reacts violently with each other, the deterioration of the core tube 21 becomes remarkable, and the life is shortened. In addition, reaction products of lead glass, silica, alumina, etc. are generated by the reaction between the heavy metal vapor and the core tube 21, and these reaction products may be mixed as impurities into the ceramic raw material powder as a product. , Causing quality inconvenience.

In order to avoid the inconvenience caused by the reaction with the heavy metal vapor, it is conceivable that the core tube 21 is made of a high-purity ceramic material. However, in such a case, heat shock may occur. It is not practical because mechanical strength that can withstand is not obtained.

The present invention has been made in view of such conventional problems, and it is possible to reduce the reaction between the heavy metal vapor and the core tube without reducing the hot strength of the core tube. The purpose is to provide a kiln.

[0008]

A calcining furnace according to the present invention comprises:
In order to achieve such an object, a cylindrical core tube is constituted by an outer tube and a plurality of short tubes, the short tubes are densely fired using a high-purity ceramic material, and,
It is characterized in that they are butted and connected to each other and then inserted into the outer tube.

[0009]

According to the above construction, the heat shock generated by the temperature difference between the end portion and the central portion along the longitudinal direction of the core tube is a plurality of heat shocks inserted into the outer tube in a state of being butted and connected to each other. Will be absorbed by the short tubes. Further, since these short tubes are densely fired using the high-purity ceramic material, the reaction between these short tubes and the heavy metal vapor hardly occurs.

[0010]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view showing an overall structure of a calcining furnace according to an embodiment of the present invention, and FIG. 2 is a cutaway perspective view showing a sectional structure of a short tube constituting a core tube.

As shown in FIG. 1, the calcining furnace according to this embodiment is a rotary kiln, and is provided with a cylindrical core tube 1 having a certain inclination and a heater 2 surrounding the core tube 1. Since this is the same as the conventional example, detailed description thereof will be omitted. Reference numeral 3 in the figure is the outer wall of the calcining furnace.

The calcination furnace according to this embodiment is different from the conventional example in that the core tube 1 has a double tube structure composed of an outer tube 4 and a plurality of short tubes 5. A plurality of short tubes 5 are inserted in the inside of 4 in a state in which they are butted against each other and connected.

First, the outer tube 4 is formed as a long, integral tube by using a ceramic material having excellent hot strength such as SiC or Si ₃ N ₄ .

On the other hand, each of the short tubes 5 is densely formed by using a ceramic material (Al ₂ O ₃ , MgO, ZrO _2, etc.) having a high purity, specifically, a purity of 99.5% or more. It has been baked. That is, as shown in the cross-sectional view of FIG. 2, an annular protrusion 6 is formed on one edge of each short tube 5, and an annular recess 7 is formed on the other edge.
The short pipes 5 are coaxially butted and connected to each other by fitting the protrusions 6 and the recesses 7. The short tubes 5 are inserted into the outer tube 4 in a state of being butted and connected to each other, so that the outer tube 4 and the outer tube 4 constitute the double-tube-structured core tube 1. A space between the short pipe 5 and the outer pipe 4 is filled with a heat-resistant blanket-shaped padding 8 such as Al ₂ O ₃ . Further, at this time, if necessary, the same filling material (not shown) is also filled between the short tubes 5.

That is, the outer tube 4 and the plurality of short tubes 5 described above are configured as a core tube 1 having a double tube structure, and, for example, as in the case of the conventional calcination furnace, for example, 2 °
It will be driven to rotate integrally with a certain degree of inclination. Therefore, the ceramic raw material powder to be calcined is transferred to the inside of the short tubes 5 which are connected to each other.
After being charged from one end side, the core tube 1 is calcinated by the heating of the heater 2 while flowing toward the other end side by the rotation of the core tube 1. And in this case
A large heat shock acts on the core tube 1 due to the temperature difference between the end portion and the central portion along the longitudinal direction of the core tube 1, but the heat shock constitutes the core tube 1. It will be absorbed by the space between the plurality of short tubes 5 inserted inside the outer tube 4. Further, since these short tubes 5 are densely fired using a high-purity ceramic material, the reaction between these short tubes 5 and heavy metal vapor hardly occurs.

By the way, the inventors of the present invention have provided a calcination furnace equipped with the core tube 1 having a double tube structure according to the present embodiment,
A calcination furnace equipped with the core tube 21 according to the conventional example is prepared, and Pb _{0 · 93} (Sr _{0 · 07} ) {Zr _{0 · 51} Ti _{0 · 49} (Nb
The life of each of the core tubes 1 and 21 was examined by calcining the ceramic raw material powders having the composition of _0.001 )} O ₃ respectively. The core tube 21 according to the conventional example can be calcined at about 3000 kg per one. However, it was confirmed that the life of the core tube 1 according to the present example was extended to about 10 times because it can be calcined up to about 30,000 kg. Further, when a reaction product is generated by the reaction with the heavy metal vapor generated from the ceramic raw material powder, and this is mixed as an impurity in the calcined ceramic raw material powder, a sintered body created using this raw material powder Since pinholes are generated, the inventors made a sintered body from the ceramic raw material powder having the above composition and examined the number of pinholes. As a result, it was calcined by the core tube 21 according to the conventional example. The sintered body made of the raw material powder had 8 pinholes / cm ² , whereas the sintered body made of the raw material powder calcined by the core tube 1 according to this example had ² pinholes / cm ² . It was found to decrease to about 1/4.

[0017]

As described above, according to the calcining furnace of the present invention, a plurality of short tubes densely fired using a high-purity ceramic material are inserted into the outer tube. Since the core tube having the heavy tube structure is used, the reaction between the heavy metal vapor and the core tube can be reduced without lowering the hot strength of the core tube. As a result, it is possible to significantly suppress the deterioration of the core tube and prolong the service life, and at the same time prevent the reaction product from being mixed as an impurity in the ceramic raw material powder, which is a product, and improve the quality. The effect that can be obtained is obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing the overall structure of a calcination furnace according to an embodiment of the present invention.

FIG. 2 is a cutaway perspective view showing a cross-sectional structure of a short tube forming a core tube.

FIG. 3 is a sectional view showing an overall structure of a calcination furnace according to a conventional example.

[Explanation of symbols]

 1 Core tube 4 Outer tube 5 Short tube

Claims (1)

[Claims] 1. A calcination furnace comprising a cylindrical core tube (1), said core tube (1) comprising an outer tube (4) and a plurality of short tubes (5). The temporary tube (5) is densely fired using a high-purity ceramic material, and is inserted into the outer tube (4) after being butt-connected to each other. Firing furnace.