JPH05212266A - Heater of molten zinc vessel - Google Patents

Abstract

PURPOSE:To reduce the microcracks resulting from thermal expansion and infiltration of zinc by forming the convection passage of molten zinc flowing in an induction field with aluminum titanate. CONSTITUTION:A coil 2 is provided close to a convection passage 4 through an iron core 3. The passage 4 is provided with a water-cooled jacket 5 and fixed to a molten zinc vessel by a flange 6. A current flows in the zinc in the passage 4 to generate Joule heat, the zinc is heated, whereas the passage itself as a sintered article is not heated since it does not transmit heat. The passage 4 of molten zinc flowing in an induction field is made with a U-tube in this way, hence the passage is not eroded by zinc or broken and has strength, and backup mortar is not needed. Further, when the heater is exchanged, a fresh one is connected to the vessel, and molten zinc can be immediately filled because the heater is resistant to rapid heating and cooling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating type molten zinc convection flow channel heating device in a molten zinc tank such as a zinc melting furnace.

[0002]

2. Description of the Related Art A molten zinc bath is used for heating and holding molten zinc inside, and is used in a hot dip galvanizing device for immersing a steel plate or steel pipe in molten zinc and coating the surface with zinc. There is. As a means for heating molten zinc, combustion heating (indirect heating) from the outer surface of the tank was previously performed by a burner, but since the tank wall is made of steel plate, it is eroded by zinc and periodical tank replacement is required. In particular, the electromagnetic induction heating method has been introduced in recent years due to the fact that a large amount of iron is dissolved in molten zinc and the coating quality of plated coating products is poor. In this heating method, the molten zinc is directly heated in the induction magnetic field, and the molten zinc itself does not have to be in direct contact with the heating body due to heat generation, and the inorganic material with good heat insulation and high corrosion resistance is attached to the tank wall. Can be used, the heat loss can be reduced, and the plating quality is good. In this heating device, a U-shaped flow path is generally provided on the outer wall of the tank so as to project, and an induction coil is wound around a part of the U-shaped flow path, or an iron core around which the induction coil is wound is provided. , U
Molten zinc flows between the molten zinc tank and the molten zinc tank by natural convection due to heating in the character-shaped channel. Molten zinc is usually about 400 to 500 ° C., but in the heating portion in the U-shaped channel, the temperature rises to about 700 ° C.

The material of the U-shaped flow path may be any material as long as it has good corrosion resistance to molten zinc and is not affected by the induced magnetic field (magnetic field loss, etc.), and is conventionally disclosed in Japanese Utility Model Publication No. 3-6299. An inorganic material mainly composed of graphite was used. For molten copper, Japanese Patent Laid-Open No. 49-106901
In the publication, it is proposed to use a product obtained by molding MgO and SiC with a binder. However, in a cast product using such a binder, as a result of an experiment with molten zinc,
It was confirmed that there was a risk of Zn leakage.

On the wall surface of the molten zinc tank, a cast product using such a binder is used. In this case, the permeated Zn solidifies in the wall surface by cooling from the outer surface, and Z
Although leakage does not occur, the permeated Zn does not solidify at the induction heating site and flows out.

For this reason, the U-shaped flow path has been formed by using the inorganic material mainly composed of graphite as disclosed above.
Since graphite is weak in strength and conductive (although resistance increases due to mixing with other inorganic agents, etc.), an induced current may be generated and self-heating may occur. Causes local unbalanced heat, which often causes breakage accidents and the like due to thermal stress. On the other hand, use of a fired ceramic article having excellent wettability and permeability of molten zinc as a heating body protective wall is disclosed in Japanese Patent Laid-Open No. 125898/1993. However, such a ceramic fired product
Since baking under high pressure is necessary, it becomes difficult to manufacture a complicated shape, especially a U-shaped product with a mold, so that the shape should be a cylindrical simple shape.
In addition, it is necessary to constantly monitor the leakage of the connecting portion such as the bottom.
Since the heating efficiency is better when the object to be heated is in the magnetic field due to the characteristic of induction heating, the immersion heating from the upper part is not adopted in a general melting tank.

The reason for forming the U-shape is that a heating device can be arranged outside the furnace to facilitate cooling of the coil and the like.
U-shaped that allows natural fluid to easily accompany heating (inlet and outlet are each open in the tank, and when a number of heating devices are connected in series, even a W-shaped inlet that shares an adjacent inlet) Good), and the mounting on the tank should be done with a slight upward slope to the inside of the tank.

[0007]

However, the conventional U-shaped channel has the following problems. It constantly receives temperature changes due to the power difference caused by tap switching during operation. Since it is desired to reduce the distance between the induction coil and the object to be heated because of the induction heating efficiency, a sufficient thickness cannot be secured. There is erosion due to high temperature Zn. There is a large temperature gradient on the inner and outer surfaces of the flow path, microcracks are generated due to thermal expansion, and zinc invades, resulting in a loss of secondary current, and the invading zinc generates heat. This will lead to an increase in the temperature of the device. In addition, there was no way to detect leakage or damage due to crack growth (due to the installation space and strong magnetic field), and it was impossible to make a replacement plan during operation. Further, when the apparatus itself uses fragile graphite or the like, it is necessary to pour the refractory mortar or the like into the outer periphery of the U-shaped tube to solidify it (strength reinforcement), and there is a problem that induction heating efficiency decreases and construction becomes complicated. there were. Therefore, there has been a demand for a heating device without such a defect, that is, a convection channel having a long life and high strength.

[0008]

In view of the above circumstances, the inventors of the present invention have completed the heating device of the present invention as a result of diligent experimental research. A heating device provided by an induction heating method,
The point is that the molten zinc convection flow channel that flows in the induction magnetic field is made of aluminum titanate.

Here, the convection flow passage means a pipe through which molten zinc passes for heating, and a plurality of convection passages are usually provided in a molten zinc bath. The present invention lies in the point that this flow path is made of aluminum titanate, and the shape and size are not particularly limited. In the present invention, the U-shaped tube made of aluminum titanate eliminates the need for mortar for backup because it has no corrosion or destruction by zinc and has strength. Also, since replacement work is resistant to rapid heating and cooling, after connecting to the main tank,
Molten zinc can be quickly filled.

The aluminum titanate is obtained by mixing powders of titanium dioxide and aluminum oxide and sintering them at a high temperature. The mixing ratio of titanium dioxide and aluminum oxide and the manufacturing method do not need to be special and may be ordinary ones. Since aluminum titanate can be molded at a relatively low temperature during this firing, it is not necessary to use a mold like conventional fine ceramics, and a core made of gypsum or the like can be used.
It is possible to mold even a complicated U-shaped shape.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail based on the embodiments shown in the drawings. FIG. 1 is a perspective view showing an outline of a heating device 1 of the present invention. The coil 2 is provided in the vicinity of the convection flow path 4 via the iron core 3. The convection channel 4 has a water cooling jacket 5 for cooling and is attached to the molten zinc bath by a flange 6. This itself is similar to the conventional heating device. The electromagnetic induction from the coil 2 causes a current to flow in the zinc in the convection flow path to generate Joule heat and heat the zinc.
Of course, the flow path itself, which is a sintered product, is not conductive and is not heated.

Example 1 A crucible for experiments was manufactured from the material shown in Table 1 having a cylindrical shape with a bottom inside an induction coil. After filling the inside with zinc powder, 700 ° C.
After heating and melting until the temperature was maintained for a certain period of time, zinc was removed and the inner surface was visually observed. A is an example of the present invention, and B, C, D and E are comparative examples. Next, after heating and melting to 700 ° C. by the same procedure, the temperature was naturally cooled to 450 ° C., and the temperature was raised to 700 ° C. again, and a 24-hour durability test was performed. Further, an inner cylinder of the same material was connected to the upper part of the test inner cylinder, and the connection strength was also checked. The results are shown in Table 2.

[Table 1]

[Table 2]

In Table 2, ◯ in the heat-up test indicates no abnormality, and X indicates crack generation. In the durability test, ○ indicates no abnormality,
X indicates cracking, and Δ indicates that zinc penetrates into the structure. Regarding the connection strength, ◯ indicates that there is no abnormality, Δ indicates that the connection strength has deteriorated, and x indicates that there is almost no connection strength and zinc leakage may occur.

B and C were made of fine ceramics and had good results, but there was no adhesive strength after heating of the connection part. The aluminum titanate of the present application had no adhesive strength at all, but mechanical bonding was maintained because the surface of the connecting portion was machined. Also,
Although D is used conventionally, a crack was generated due to rapid heat (the test device has a small capacity, so the temperature changes more rapidly than the actual device). In addition, E is a castable (unshaped refractory material) used for the inner wall surface of the tank for the purpose of comparison and confirmation, but as a result of observing the cross-section after the durability test, zinc intrusion was recognized. In a water cooling test after rapid heating with a test piece (rectangular cross section) different from this test product, only E was broken and A to
D was normal.

Example 2 A U-shaped tube made of the aluminum titanate of the present invention was attached to an inductor heating device of a hot dip galvanizing facility for thin steel sheets, and durability was tested. The equipment specifications are 250 tons of zinc and 35 of production.
A T / Hr molten zinc bath, which is a zinc flow path (U-shaped tube) in an inductor with a heating capacity of 300 Kw, and the components are the same as those in A of Example 1 above, and a pipeline with an inner diameter of 100 mm and a thickness of 35 mm. Formed. In the experiment, after using the actual machine for about 3 months, detailed inspection was conducted, but no abnormality such as damage was found at all.
For comparison, the graphite U-shaped tube, which was replaced at the same time, was damaged in 3 months.

[0016]

The present invention described in detail above has the following great advantages. It has excellent thermal shock resistance and almost no cracks even when the temperature changes suddenly. Therefore, various troubles caused by cracks do not occur. Since it has higher strength and heat resistance than graphite, the wall thickness of the conduit can be reduced, and the induction heating efficiency can be improved. Further, no castable reinforcement is required, and the work of assembling the U-shaped conduit and the coil is facilitated. Since there is no oxidative damage such as graphite in the atmosphere, it is not necessary to adjust the atmosphere at the start of melting, which simplifies the work. The life is extended and the time loss due to replacement can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a heating device of the present invention.

[Explanation of symbols]

 1 Induction heating device 2 Coil 3 Iron core 4 Convection flow path 5 Water cooling jacket 6 Flange

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshihiro Hara 4-53 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries, Ltd. (72) Inventor Atsushi Kubota 4-53 Kitahama, Chuo-ku, Osaka Sumitomo Metal Industries Co., Ltd. (72) Inventor Seiki Kayama 4-53-3 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries Co., Ltd. (72) Inventor Kenji Imae 1-7 Tomita-cho, Takatsuki-shi, Osaka Prefecture No. 12 Inmae Industrial Co., Ltd.

Claims (1)

[Reference number] P92020302 [Claims] 1. A heating device for a molten zinc tank, wherein the heating device is provided in a molten zinc tank by a dielectric heating method, and a convection channel of molten zinc flowing in an induction magnetic field is formed of aluminum titanate.