JP2008267704A - Induction heating furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an induction heating furnace installed with a furnace shell in the inside of an induction heating coil, capable of securing air-tightness with simple structure without increasing the size of the furnace and having furnace shell structure, without the risk of the occurrence of electrical discharges. <P>SOLUTION: Air-tightness of an inner furnace shell 2 is secured, by making the furnace shell that comprises a non-conductive and flame-resistant material into a multilayered structure of double or more and introducing an inert gas into the space between the inner furnace shell 2 and an outer furnace shell 3. In this case, pressure in the space between the inner and outer furnace shells 2, 3 can be made higher than pressure of atmosphere inside the furnace of the inner furnace shell 2 to prevent leakage of the atmosphere inside the furnace, and water vapor can be mixed in the inert gas to be introduced so as to further prevent the occurrence of leakage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a furnace for induction heating of a conductive material to be heated, and particularly to an induction heating furnace used when heating a material to be heated in an atmosphere containing a combustible gas such as hydrogen. This relates to the furnace wall structure.

  As a furnace structure of an induction heating furnace, for example, one shown in Patent Document 1 is known. In the furnace structure, since the furnace furnace is constructed using a fireproof board made of laminated material reinforced with ceramic fibers, when using a flammable gas such as hydrogen as the furnace atmosphere, the furnace atmosphere It is necessary to take measures to prevent leakage of gas so that it does not leak through the furnace shell.

  When the material to be heated is thin like a thin steel plate, the frequency is set high in order to increase the heating efficiency by reducing the current penetration depth. If it does so, the impedance in the electricity supply path from an induction heating coil and a power supply to an induction heating coil will each become high, and in order to flow a required electric current, the voltage of a power supply must be made high. Even in the case of a material to be heated having a low magnetic permeability, it is necessary to increase the frequency in order to increase the heating efficiency, and the voltage of the power source also increases. In these cases, the voltage of the power supply rarely reaches tens of thousands of volts, so that the induction heating furnace needs to take measures against electric discharge.

In Patent Document 1, as a countermeasure against these, a method is adopted in which the entire periphery of the furnace is surrounded by a case including an induction heating coil, and an inert gas such as nitrogen is circulated in the case.
However, in this method, it is necessary to enclose the entire structure including the induction heating coil, and since the case is enlarged, the leaked hydrogen gas is diluted on average by the inert gas. In such a region where the confidentiality is likely to be lowered, a portion having a high hydrogen concentration is locally generated. Since the portion having the high hydrogen concentration is naturally in the vicinity of the furnace or coil, there is a problem that discharge is likely to occur through the leaked hydrogen atmosphere.

  As another structure, the structure shown in Patent Document 2 is known. In the furnace shell structure, the hermeticity of the furnace shell is ensured by using a sheath made of a non-conductive material having an airtightness such as a resin. However, since the heat resistance of the sheath is low, the sheath It is necessary to reinforce the heat insulation, such as cooling the air and thickening the heat insulating material. For this reason, there arises a problem that the structure is complicated when the sheath is cooled, and when the thickness of the heat insulating material is increased, the heating coil is enlarged, and the interval between the heating coil and the material to be heated is widened. Thus, problems such as a decrease in heating efficiency, an accompanying increase in voltage, and occurrence of discharge due to the increase in voltage occur.

JP 2005-221132 A JP 2003-317912 A

  SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an induction heating furnace having a furnace shell structure that can ensure the hermeticity of the furnace with a simple structure without increasing the size and that does not cause a discharge. To do.

In the present invention, a furnace shell made of a non-conductive and refractory material has a double or more multiple structure, and the space between the inner furnace shell that surrounds the material to be heated and the outer furnace shell that surrounds it is not in the space. By introducing the active gas, the above-mentioned problems are solved. Further, by making the gas pressure in the space between the inner and outer furnace shells larger than the pressure in the furnace atmosphere in the inner furnace shell, leakage of the furnace atmosphere can be further prevented, Water vapor is mixed in the inert gas to be introduced so that the discharge is not generated more.
The gist of the present invention as described above is as follows.

(1) In an induction heating furnace in which a furnace shell made of a non-conductive material is provided inside the induction heating coil, multiple furnace shells are arranged at intervals from each other outside the furnace shell surrounding the material to be heated. In addition, an induction heating furnace is characterized in that an inert gas is introduced into the space between the furnace shell and the furnace shell.
(2) The induction according to (1), wherein the pressure of the inert gas introduced between the furnace shell and the furnace shell is equal to or higher than the pressure of the atmospheric gas in the furnace shell surrounding the material to be heated. heating furnace.
(3) The water vapor is added to the inert gas introduced between the furnace shell and the furnace shell, and the temperature of the furnace shell disposed outside is set to 100 ° C. or higher (1) or ( The induction heating furnace described in 2).

According to the present invention, leakage of the furnace atmosphere to the outside can be prevented with a simple structure, and the occurrence of discharge and fire can be prevented.
In addition, since it is not necessary to increase the size of the furnace, it is possible to avoid the occurrence of discharge due to a decrease in heating efficiency and an increase in voltage due to an increase in the size of the induction heating coil.

Hereinafter, an embodiment of an induction heating furnace of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a view showing an embodiment when the present invention is applied to a horizontal induction heating furnace.

As shown in the figure, a furnace shell 1 made of a fire-resistant and non-conductive material has a double structure composed of an inner shell 2 surrounding a material to be heated 4 and an outer shell 3 surrounding the inner shell. A space 5 is provided between the outer shell 3 and the inner shell 2. An induction heating coil 6 is disposed outside the outer shell 3 so as to surround the material to be heated 4.
The outside of the induction heating coil 6 is surrounded by a coil case made of copper or aluminum (not shown), and leakage of magnetic flux generated from the induction heating coil 6 is prevented. A predetermined alternating current is supplied to the induction heating coil 6 from an induction heating power source (not shown), whereby the material to be heated 4 is heated.

  An atmosphere gas for introducing a predetermined furnace atmosphere is introduced into the space 7 in the inner shell, and an inert gas such as nitrogen is introduced into the space 5 between the outer shell 3 and the inner shell 2. . For this reason, for example, when the furnace atmosphere in the inner shell is a mixed atmosphere of nitrogen and hydrogen to prevent oxidation of the heated material during heating, the furnace atmosphere gas is between the inner shell and the outer shell. Even if it leaks into the space 5, it is diffused and diluted by the air flow of the inert gas existing between the outer shell and the inner shell, so that a portion having a high hydrogen concentration does not occur locally, and the induction heating coil Generation | occurrence | production of the discharge between 6 and combustible gas can be prevented.

The pressure P1 in the space 5 between the outer shell and the inner shell and the pressure P2 in the furnace atmosphere in the inner shell may be the same pressure. However, by setting P1> P2, the gas flow is between the outer shell and the inner shell. From the space 5 toward the space 7 in the inner shell, leakage of the furnace atmosphere containing a combustible gas such as hydrogen can be further prevented.
At this time, even if an inert gas introduced between the inner shell and the outer shell penetrates into the inner shell, the gas is an inert gas, and thus does not particularly affect the quality of the material to be heated 4, There is no problem in terms of safety.

Furthermore, water vapor may be added to the inert gas introduced into the space 5 between the inner shell and the outer shell.
Since water vapor has high resistance to discharge, by adding water vapor to the inert gas to be introduced, the occurrence of discharge between the induction heating coil and the combustible gas can be further suppressed, and safety can be further improved.
At that time, particularly when the heating temperature of the furnace is low, it is necessary to control the temperature between the outer shell and the inner shell to be equal to or higher than the dew point so that water vapor is not condensed. For this purpose, the surface temperature of the outer shell is monitored by a non-contact type thermometer such as a thermoviewer, and is controlled to a temperature of 100 ° C. or higher at which the added water vapor does not condense.

  A furnace shell can be comprised with the fireproof board which consists of an inorganic type laminated material, for example. For example, a fireproof board having a thickness of about 30 mm is used. In that case, a fire-resistant board having the same thickness as the inner shell and the outer shell may be used, or the inner shell directly exposed to a high temperature may be formed of a fire-resistant board having a thickness larger than that of the outer shell. When the operating temperature of the furnace is high, a ceramic fiber blanket for protecting the fireproof board from heat may be attached to the inner shell with a thickness of about 50 mm.

For example, when heating a steel plate having a width of 1200 to 1300 mm, the width of the inner shell is set to about 1500 mm that is 100 mm wider than the width of the steel plate.
The distance between the inner shell and the outer shell is about 10 mm. Narrower spacing is desirable to reduce the overall size and ensure the pressure of the inert gas to be introduced, but if it is too narrow, it is difficult to ensure work accuracy when inserting the inner shell into the outer shell. become.
There may be no space between the inner and outer shells, but unless the structure prevents the introduction of inert gas, a ceramic fiber blanket is inserted and the pressure of the introduced inert gas is reduced. It may have an enhancing effect.

  When the furnace shell having the above structure is used, when the furnace temperature in the inner shell is about 850 ° C., the outer surface temperature of the inner shell is insulated by the 50 mm fiber blanket and the 30 mm inner shell wall. Therefore, it becomes about 400 degreeC. Further, the outer surface temperature of the outer shell is about 250 ° C., which is a sufficiently low temperature, and it can be seen that heat insulation is excellent due to multiple furnace shells.

  The furnace pressure P1 in the inner shell and the furnace pressure P2 between the outer shell and the inner shell are usually set to about 5 to 10 mmAq. For example, when the pressure P1 in the inner shell is about 5 mmAq, the pressure P2 in the outer shell is preferably set to 7 mmAq, which is higher than the furnace pressure. In particular, by setting P2 to be higher than P1 by 2 mmAq or more, the effect of preventing leakage of furnace atmosphere gas in the inner shell is enhanced.

  The amount of the inert gas introduced between the outer shell and the inner shell varies depending on the distance between the outer shell and the inner shell and the presence or absence of a fiber blanket, but is about 5 to 10 liters / min, and water vapor is added to the inert gas. In this case, since a predetermined effect cannot be obtained if the concentration is low, management is performed so that the concentration is 50% by volume or more. However, if the concentration is high, the cost increases.

FIG. 2 shows an embodiment of the present invention between radiant heating furnaces 9 and 10 using a radiant tube or the like in order to rapidly heat a steel plate 8 as a material to be heated during the heat treatment. It is a figure which shows the example at the time of inserting the induction heating furnace 11 which concerns.
An inert gas introduced between the outer shell 3 and the inner shell (not shown) is introduced from the outside of the coil case 12 through the gas supply port 13 and discharged to the outside of the coil case 12 through the gas discharge port 14.
When exhausting inert gas, there is a risk that combustible gas may be discharged together. Therefore, a gas detector that can detect combustible gas is installed to control the concentration of combustible gas in the exhaust gas. It is better to place a flame near the gas outlet 14 and burn it to prevent explosion.

In the above embodiment, the furnace shell has a double structure of the inner shell and the outer shell, but the outer shell may be multiplexed to have a triple structure or more as a whole.
The induction heating furnace is not limited to the horizontal type shown in the above embodiment, and can be implemented in the same manner even in a vertical type. Moreover, as shown in the said embodiment, it can also provide continuously with another heating furnace, and can also be used independently.
The material to be heated is typically a steel plate, but in general, the present invention can be applied to any metal having magnetism, and the shape is not necessarily limited to a plate shape.

It is a figure which shows one Embodiment at the time of applying this invention to a horizontal induction heating furnace. It is a figure which shows the example at the time of inserting the induction heating furnace which concerns on this invention between the normal radiant heating type heating furnaces.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Furnace shell 2 Inner shell 3 Outer shell 4 Heated material 5 Space between outer shell 3 and inner shell 2 6 Induction heating coil 7 Space in inner shell 8 Steel plate (heated material)
9, 10 Radiation heating furnace 11 Induction heating furnace 12 Coil case 13 Gas inlet 14 Gas outlet

Claims (3)

  In an induction heating furnace provided with a furnace shell made of a non-conductive material inside the induction heating coil, the furnace shells are arranged in multiple layers at intervals from each other outside the furnace shell surrounding the material to be heated. An induction heating furnace characterized in that an inert gas is introduced into the space between the furnace shell and the furnace shell.   The induction heating furnace according to claim 1, wherein the pressure of the inert gas introduced between the furnace shell and the furnace shell is equal to or higher than the pressure of the atmospheric gas in the furnace shell surrounding the material to be heated.   The water vapor is added to the inert gas introduced between the furnace shell and the furnace shell, and the temperature of the furnace shell disposed outside is set to 100 ° C or more. Induction furnace.

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