JPH0477234B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a combustion type continuous firing tunnel furnace (hereinafter also referred to as a roller hearth kiln) suitable for firing soft ferrite and the like.

(Prior art and its problems) Electric furnaces have traditionally been the mainstream furnace for firing this type of soft ferrite, but electric furnaces require extremely long firing times (25 to 40 hours). Further, since the fired bodies are stacked in multiple stages, there are problems such as variations in firing quality tend to occur and the firing cost increases.

Therefore, a new kiln was needed, and a roller hearth kiln was considered as a quick kiln that was extremely effective in saving energy. However, with this roller hearth kiln, ordinary fired products can be fired in the atmosphere, but when heated by gas combustion, for example, combustion gas and heated air flow toward the entrance and exit of the furnace, and the roller Because outside air flows in through holes made in the side wall for driving, the atmosphere inside the furnace is disturbed, making it extremely difficult to control the atmosphere in the cooling zone, which affects the characteristics of the fired product. For example, it was considered impossible to sinter Mn-Zn ferrite.

However, compared to other types of kilns, this roller hearth kiln can reduce fuel costs, ensure stable firing quality, and have uniform dimensions and characteristics, so there is a strong demand for being able to adjust the atmosphere. It was big and warm.

The general structure of this roller hearth kiln is as shown in Figure 5.
(these constitute a heating zone) and a cooling zone C, and between the inlet 1 and the outlet 2 on both sides, there is a fired body W (for convenience of explanation, the molded body before and after firing is included). A hearth roller 3 in which roller members for conveyance are arranged at predetermined intervals is horizontally arranged, and the hearth roller 3 moves the fired body W placed on the tray 4 from the inlet 1 side to the outlet 2.
It is fired in the process of being transported to the side. In the preheating zone A, the fired body is heated by gas combustion in the burner 6 in the firing zone B. The combustion gas used for heating passes through the damper 7 and the input duct 8 and is discharged to the outside by the inlet fan 9. In the cooling zone C after firing, cooling air is supplied from a large number of outlets 10, and this cooling air is discharged to the outside by an outlet fan 11 through a damper 12 and an outlet duct 13.

Temperature T and oxygen concentration distribution O2% in the furnace of this roller hearth kiln (inside the kiln body 14)
An example of this is shown in FIG. That is, when entering the cooling zone C, the oxygen concentration increases rapidly, and as a result, the fired body W is oxidized, and in particular,
At present, it is not possible to obtain the desired properties of Mz--Zn ferrite through oxidation, and in fact, it has been difficult to fire soft ferrite such as Mn--Zn ferrite in a roller hearth kiln. The present invention has been made to solve the above-mentioned conventional technical problems, and includes a roller that can prevent oxidation of the fired body in the cooling zone when the fired body is rapidly cooled from the firing temperature to, for example, about 500°C. The purpose is to provide a hearth kiln.

(Means for Solving the Problems) The gist of the present invention is to provide a roller hearth kiln (combustion-type In the continuous firing tunnel furnace), a low oxygen partial pressure chamber with a low oxygen partial pressure is provided in the cooling zone. For example, nitrogen gas is ejected to keep the oxygen partial pressure, or in other words, the oxygen concentration, low.

When lowering the oxygen partial pressure with nitrogen gas as described above, for example, the temperature, furnace pressure, oxygen partial pressure, etc. in the low oxygen partial pressure chamber are measured, and the amount of nitrogen gas jetted into the chamber is thereby controlled. By doing so, the oxygen partial pressure and furnace pressure can be adjusted.

Note that the number of low oxygen partial pressure chambers is not limited to one, but it is also possible to provide two or more.

(Operations and Effects) According to the present invention, the fired body fired by a combustion source such as a burner in the firing zone is transferred to the cooling zone where it is rapidly cooled (for example, to around 500°C), and
The presence of the low oxygen partial pressure chamber prevents oxidation of the fired body. In addition, by adjusting the nitrogen injection amount and always maintaining the furnace pressure in the low oxygen partial pressure chamber higher than atmospheric pressure, the system is not affected by disturbances such as the flow of combustion gas, heated air, or the inflow of outside air. In addition, a stable atmosphere with low oxygen partial pressure can be provided in the hypoxic partial pressure chamber.

As a result, the firing of soft ferrites (e.g. Mz-Zn ferrites), which cannot achieve the desired properties unless under a stable, low-oxygen atmosphere,
The roller hearth kiln has made it possible to fire materials that were said to be impossible with gas-heated roller hearth kilns, which are based on direct combustion. Additionally, compared to electric furnaces, firing time can be significantly shortened (for example, 1/5 to 1/8), and firing costs such as fuel costs are much lower (for example, 1/8).
2 to 1/4).

(Example) Next, an example of the present invention will be described with reference to the drawings.

Note that the roller hearth kiln shown in Fig. 1 etc. has a cooling zone C as its main part, and the rest of the structure is the same as the conventional kiln shown in Fig. 5, so the same symbols are given. Cooling zone C will be explained in detail.

The cooling zone C that is continuous to the firing zone B is the first cooling zone C.
1 and a second cooling zone C2, and a low oxygen partial pressure chamber 15 is formed in the first cooling zone C1. As is clear from FIG. 3, in the kiln main body 14, a first partition wall 16 and a second partition wall are provided at each end of the first cooling zone C1 on the firing zone B side and the second cooling zone C2 side.
A partition wall 17 is formed to protrude inward, and a low oxygen partial pressure chamber 15 is defined by these partition walls 16, 17 and the kiln body 14. The first partition wall 16 and the second partition wall 17 allow the tray 4 on which the fired body is placed to pass. A first passage 18 and a second passage 19 having a relatively small cross-sectional area are formed.

A wall portion of the kiln body 14 corresponding to the low oxygen partial pressure chamber 15 is provided with a plurality of nitrogen (N2) gas ejection passages 20, 21, and 22 on the inlet side, outlet side, and intermediate portion, respectively. These spout passages 2
0, 21, and 22 penetrate the wall of the kiln main body 14 from the outside to the inside, and face the hearth roller 3 from the top and bottom directions (furnace ceiling and hearth), or from four directions, top, bottom, left, right, or more. It is formed from the radial direction. Each jet passage 20 on the inlet side opens into the first passage 18 through the first partition 16, while each jet passage 21 on the outlet side opens into the second passage 19 through the second partition 17, and also opens into the second passage 19 through the second partition 17. Each of the ejection passages 22 of the section opens to the inner wall surface of the low oxygen partial pressure chamber 15.

A nitrogen gas introduction passage 23 is provided in the group of injection passages 20 on the inlet side, a similar introduction passage 24 is provided in the group of injection passages 21 on the outlet side, and a nitrogen gas introduction passage 24 is provided in the group of injection passages 22 on the intermediate portion. The paths 25 are branched and connected to each other. These introduction channels 23, 24 and 2
5 are aggregated on the upper and lower sides, for example,
It is connected to an unillustrated supply source (for example, a compressor) of nitrogen gas. In addition, the introduction path 23,
24 and 25 are provided with control valves 26, 27, and 28 that control the amount of nitrogen gas ejected into the first cooling zone C1, respectively.

Further, on the inner wall surface of the low oxygen partial pressure chamber 15, a temperature measuring device 29 such as a thermocouple for measuring the temperature inside the chamber (furnace temperature), a furnace pressure measuring device 30 for measuring pressure, and an oxygen partial pressure In other words, an oxygen amount measuring device 31 (more precisely, a detection section thereof) for measuring the amount of oxygen is provided.

Next, the effect will be explained.

The fired body W, which has been preheated to, for example, about 400 to 500°C in the preheating zone A, is fired at a high temperature of, for example, 1300 to 1400°C by gas combustion in the burner 6 in the firing zone B. This fired body W is then transferred to the cooling zone C, and reaches the first cooling zone C1.

Here, nitrogen gas is blown in from the injection passage 20 on the inlet side, the injection passage 22 in the center, and the injection passage 21 on the exit side, thereby reducing the oxygen partial pressure (oxygen concentration) in the low oxygen partial pressure chamber. It will be done. The degree of decline is
Although it cannot be generalized because it varies depending on the type of fired body, it is generally between a few ppm and a few percent, especially Mn-Zn.
In the case of soft ferrite such as ferrite, the number
It is estimated to be around ppm to 100ppm. In fact, when comparing the oxygen concentration graph shown in FIG. 2 with the conventional graph shown in FIG.
It can be seen that the oxygen concentration in No. 1 is significantly lower.

Moreover, the above-described blowing of nitrogen gas not only reduces the oxygen concentration but also serves to rapidly cool the fired body W. That is, as is clear from comparing the furnace temperature T shown by the solid line in the graph of FIG. 2 with that of FIG. (in this example, from around 1300℃ to 600℃)
℃) in a short period of time).

In addition, the oxygen amount partial pressure device 31 in the low oxygen partial pressure chamber 15 continues to measure the oxygen partial pressure in the chamber, and the control valve 28 is operated to control the central By controlling the amount of nitrogen gas blown from the ejection passage 22, the oxygen concentration in the low oxygen partial pressure chamber 15 is maintained at a substantially constant low level. The group of jetting passages 22 can also be called an oxygen amount regulating blow.

Furthermore, the furnace pressure is constantly measured by the furnace pressure measuring device 30. In order to keep this furnace pressure almost constant, the amount of nitrogen gas ejected from the injection passage 20 on the inlet side is controlled by the control valve 26, and the amount of injection from the injection passage 21 on the outlet side is controlled by the control valve 27. and are controlled respectively. The furnace pressure is adjusted by controlling the ejection amount, and is set at a substantially constant furnace pressure. In other words, the ejection passages 20, 2
The furnace pressure is adjusted by the shielding function based on the nitrogen gas injection from the injection passage 2. In this sense, the injection passage 20 is connected to the inlet air curtain blow,
1 can also be referred to as an outlet side air curtain blow.

Note that it is desirable that the amount of ejection from the ejection passage 20 on the inlet side is set to be about 10 to 30% larger than the amount of ejection from the ejection passage 21 on the outlet side. This is because the nitrogen gas blown into the low oxygen partial pressure chamber 15 easily flows toward the outlet 2 of the kiln body 14.

The fired body W that has passed through the first cooling zone C1 further moves to the second cooling zone C2, where it is finally heated to a temperature of, for example, 100°C by blowing out cooling air from the air outlet 10.
After being cooled down to a certain degree, it is discharged from the outlet 2 to the outside. In this second cooling zone C2, the oxygen concentration becomes considerably high as shown in the graph of FIG. 2, but since it has been cooled to around 500°C in the first cooling zone C1,
Oxidation is also difficult to occur, and the properties of the fired body W are substantially not adversely affected.

As described above, the oxygen concentration in the first cooling zone C1 is suppressed to a low level, and rapid cooling is performed in a stable atmosphere.
- Zn ferrite etc. can now be fired using a roller hearth kiln.

In the embodiment described above, the number of low oxygen partial pressure chambers is one, but for example, as shown in FIG.
the first, second, third and fourth cooling zones C1, C
2, C3, and C4.

In addition, the nitrogen gas ejection passages 21 and 22 on the inlet side and outlet side in the embodiment explained in FIG. It is also possible to configure an oxygen partial pressure chamber.

It goes without saying that the present invention can be implemented with various other modifications based on the knowledge of those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing a roller hearth kiln according to an embodiment of the present invention, FIG. 2 is a graph showing the temperature and oxygen concentration inside the kiln, and FIG.
The figure is an enlarged sectional view showing a part of FIG. 1, FIG. 4 is a sectional view simply showing the main part of another embodiment of the present invention, and FIG. 5 is an example of a conventional roller hearth kiln. The sectional view shown in FIG. 6 is a graph showing the temperature and oxygen concentration inside the kiln, and corresponds to FIG. 2. 3... Hearth roller, 4... Tray, 6... Burner, 14... Kiln body, 15... Low oxygen partial pressure chamber, 2
0, 21, 22...Nitrogen gas ejection path, 23, 24,
25... Nitrogen gas introduction path, 26, 27, 28... Control valve, 29... Temperature measuring device, 30... Furnace pressure measuring device, 31... Oxygen amount measuring device.

Claims (1)

[Scope of Claims] 1. A combustion type continuous firing tunnel furnace comprising at least a heating zone and a cooling zone, in which a fired body fired by a combustion source in the heating zone is rapidly cooled in the cooling zone, wherein the cooling zone contains an oxygen component. A combustion type continuous firing tunnel furnace characterized by a low pressure, low oxygen partial pressure chamber.