JP3023184B2 - Continuous tunnel furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a continuous tunnel furnace.

[0002]

2. Description of the Related Art Ceramic capacitors, ferrites,
A continuous tunnel furnace is used for firing ceramics for electronic components such as a thermistor. As a heating method of the continuous tunnel furnace, there are an electric heating method and a combustion heating method. When it is desired to control the furnace atmosphere strictly, an electric heating method is advantageous. On the other hand, the combustion heating method is advantageous from the viewpoint of energy cost and rapid firing, and a continuous tunnel furnace of this type is often used recently.

[0003]

However, in the conventional continuous tunnel furnace using the combustion heating method, it was difficult to set the atmosphere near the article to be fired to a desired atmosphere. For example, when the furnace temperature is 1000 ° C. or higher, it has been difficult to constantly maintain the oxygen concentration at a value of 12% or higher without taking special measures such as oxygen enrichment. In particular, when the combustion load capacity (eg, throughput, speed, furnace temperature, etc.) and the furnace exhaust capacity (eg, exhaust fan clogging, fan belt deterioration, etc.) fluctuate, the oxygen concentration and furnace pressure are stabilized. It was difficult to make it. In addition, unburned gas or incompletely burned gas may come into direct contact with the product to be fired, which may adversely affect the quality. Due to the above inconvenience, the yield in the firing process of the product has been reduced.

An object of the present invention is to provide a continuous tunnel furnace capable of precisely controlling a processing atmosphere.

[0005]

The continuous tunnel furnace of the present invention comprises a preheating section (11), a firing section (12) and a cooling section (1).
In the continuous tunnel furnace constituted by 3), the preheating portion (11) is provided with a refractory from a plurality of combustion chambers (17) formed inside the furnace wall (14) by the gas combustion heating device (42). (4) through a muffle (16) made of
1) is configured to be indirectly heatable, and a gas supply device (22) in which a number of pipes (24) for supplying an atmosphere gas into the muffle (16) is provided.
6) A first exhaust device (26) provided with a number of pipes (27) for exhausting the gas is provided in association with the gas supply into the muffle (16) to exhaust the combustion chamber (17). The second exhaust device (3) in which a number of pipes (32) of
The gist of the present invention is a continuous tunnel furnace characterized in that 1) is provided in association with gas supply into the muffle (16).

[0006] It is desirable to connect the binder combustion device to the first exhaust device so that the binder volatilized in the muffle can be completely ashed. It is desirable to provide pressure detecting means inside and outside the muffle, and in this case, it is desirable to control the pressure inside the muffle to be higher than the pressure outside the muffle (particularly the combustion chamber).

[0007]

FIG. 1 is a longitudinal sectional view showing one embodiment of a continuous tunnel furnace according to the present invention, and shows only an outline of the furnace for simplification. FIG. 2 is a longitudinal sectional view conceptually showing a part of the furnace, and FIG. 3 is a transverse sectional view taken along line AA of FIG.

The continuous tunnel furnace 10 comprises a preheating section 11, a firing section 12, and a cooling section 13. The preheating unit 11 employs a gas furnace type, and the firing unit 12 employs an electric furnace type.
The object to be heat-treated 41 is continuously or intermittently sent rightward in FIG. 1 through the processing chamber 18 provided in the furnace. In the process, a predetermined heat treatment is applied to the object to be heat-treated 41. The continuous tunnel furnace 10 has a generally rectangular furnace wall 14 having an elongated shape. Inside the furnace wall 14 is provided a processing chamber 18 formed along the longitudinal direction of the furnace, and a rail 15 is disposed at the bottom thereof. Workpiece 41
Is mounted on the base plate 40 and moves on the rail 15 together with the base plate 40.

A plurality of combustion chambers 17 are formed inside the furnace wall 14 in the preheating section 11. The combustion chamber 17 is provided with a gas burner as a combustion heating device 42. A muffle 16 is provided inside the combustion chamber 17 so as to surround a heat treatment target moving in the processing chamber 18. The muffle 16 is formed of a refractory. Depending on the use of the furnace, it may be made of stainless steel or the like. In the preheating unit 11, an outer wall of the processing chamber 18 is formed by the muffle 16 and the rail 15. The inside of the processing chamber 18 (muffle 16) may be configured to be airtight. In this case, high-temperature gas does not flow between the processing chamber 18 and the combustion chamber 17. On the other hand, when the muffle 16 is not configured to be airtight, it is necessary to prevent gas from flowing from the combustion chamber in order to maintain the atmosphere in the muffle at a predetermined atmosphere. For this purpose, the exhaust devices 26 and 31 to be described later are controlled so that the pressure in the muffle 16 is kept equal to the pressure in the combustion chamber, preferably higher than the pressure in the combustion chamber. In other words, the pressure in the combustion chamber is maintained at a negative pressure relative to the pressure in the muffle. In order to detect the pressure, pressure gauges 20 and 2 are provided in the muffle 16 (processing chamber 18) and the combustion chamber.
1 is set. Then, the exhaust devices 26 and 31 are controlled while monitoring the pressure. In some cases, the air supply device 22 is controlled together with the exhaust devices 26 and 31 described above.

An exhaust device 31 is provided on the furnace wall of the preheating section 11 to exhaust the inside of the combustion chamber 17. The exhaust device 31
It comprises a pipe 32, a valve 33, and a fan 34. Since the valves 33 are provided in the individual combustion chambers, the exhaust intensity can be set for each combustion chamber.

The muffle 16 is provided with an air supply device 22 and an exhaust device 26 for supplying and exhausting air into the processing chamber 18. The exhaust device 26 is provided independently of the exhaust device 31 for the combustion chamber 17. The air supply device 22 includes a supply unit 2
5, a pipe 23 and a valve 24. The exhaust device 26 includes a pipe 27, a valve 30, a fan 29, and a binder combustor 28. Binder combustion device 28
Is to completely incinerate the binder indirectly heated by the muffle 16 and volatilized.

By means of the air supply device 22 (and the exhaust device 26), for example, oxygen in the processing chamber 18 (muffle 16) can be kept at a high concentration and stably. For example, as shown in Table 1, in the example, the oxygen concentration could be set to a maximum of 20.6%, and this could be controlled in the range of 20.2 to 20.6%. On the other hand, in the conventional furnace, the maximum oxygen concentration that can be set is about 12%, and the control range is 8 to 12%.
%.

The baking section 12 is provided with a normal electric heater (not shown). FIG. 4 shows an example of a heat treatment temperature pattern for firing the thermistor. In the figure, X, Y, and Z are preheating, heating, and cooling regions.

[0014]

According to the continuous tunnel furnace of the present invention, the atmosphere near the object to be heat-treated, for example, the firing atmosphere can be stably maintained at a predetermined atmosphere regardless of the product throughput. For example, the oxygen concentration can be maintained constantly and at a high concentration.

Further, since the inside of the muffle and the combustion chamber are independently exhausted, it is possible to prevent the volatile binder and unburned gas from flowing from the pre-tropical zone to the main sintering zone. Therefore, the sintering quality yield of the product can be significantly improved. For example, when a thermistor is manufactured using the furnace of the present invention, the yield which was 89% in the past can be increased to 98%.

Further, in the embodiment of the present invention, since the binder combustion device is provided, the binder component volatilized from the processed material is discharged to the outside of the furnace in a completely burned state, and the environment can be maintained clean. Was.

[0017]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of one embodiment of a continuous tunnel furnace.

FIG. 2 is a longitudinal sectional view conceptually showing a part of a continuous tunnel furnace.

FIG. 3 is a lateral sectional view taken along line AA of FIG. 2;

FIG. 4 is a graph showing an example of a pattern of a heat treatment temperature.

[Explanation of symbols]

 16 Muffle 22 Atmospheric gas supply device 27 Exhaust device 31 Exhaust device 42 Combustion heating device

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Japanese Utility Model Sho 62-55092 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F27B 9/04

Claims (1)

(57) [Claims] In a continuous tunnel furnace comprising a preheating section (11), a firing section (12) and a cooling section (13), the preheating section (11) is connected to a gas combustion heating device (42).
Therefore, a plurality of combustion chambers formed inside the furnace wall (14)
(17) Reinforced from inside via refractory muffle (16)
The processing object (41) can be heated indirectly, and the atmosphere
Multiple pipes to supply gas into muffle (16)
A gas supply device (22) in which (24) is arranged is provided.
Many pipes (27) for exhausting the inside of the full (16)
Place the arranged first exhaust device (26) in the muffle (16).
The combustion chamber (17) is provided in connection with the gas supply to the
The second exhaust in which a number of pipes (32) are arranged
Device (31) associated with gas supply into muffle (16)
A continuous tunnel furnace characterized by being additionally provided .