JP2001033174A - Lining structure of vacuum degassing furnace for molten steel and insulating plate used for it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent backside oxidation of magnesia-carbonaceous unfired brick lined in a vacuum degassing furnace. SOLUTION: In a lining structure of a vacuum degassing furnace for molten steel lined with a magnesia-carbonaceous unfired brick, a heat insulating plate whose outer side is covered with aluminum foil is arranged on a back surface of the magnesia-carbonaceous unfired brick. I do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lining structure of a vacuum degassing furnace for molten steel using magnesia-carbonaceous unfired brick, and a heat insulating plate used for the same.

[0002]

2. Description of the Related Art Magnesia-carbonaceous unburned bricks used as linings for molten steel containers and the like exhibit excellent durability due to the effects of magnesia such as corrosion resistance and carbon spalling resistance.

[0003] Vacuum degassing furnaces of the RH type, the DH type and the like are widely used as a molten steel refining treatment apparatus for performing degassing treatment of molten steel by a decompression operation. The lining of this vacuum degassing furnace is generally made of magnesia-chromium fired brick as a material that can withstand the reflux of molten steel, as disclosed in JP-A-62-255785 and JP-A-9-41031. As can be seen, the use of magnesia-carbonaceous unfired bricks has been attempted.

[0004]

The vacuum degassing furnace has an airtight structure for operation while reducing the pressure inside the furnace, but cannot completely prevent the invasion of the atmosphere. Atmosphere enters from refractory exposed places such as dip tubes or flange joints, etc.
After filling the back of the lining, it passes through brick joints and reaches the furnace.

[0005] Magnesia-carbonaceous unburned bricks are liable to undergo structural deterioration due to oxidation of carbon as a blending material. When a magnesia-carbonaceous unfired brick is used for tension in a vacuum degassing furnace, oxidation of the backside of the brick is remarkable due to the above-mentioned air flow accompanying the decompression operation. As a result, the durability of magnesia-carbonaceous unburned brick cannot be sufficiently exhibited.

[0006] As means for preventing the backside oxidation of magnesia-carbonaceous unburned brick in the tension of a vacuum degassing furnace, it is known that the backside of the brick is covered with a metal plate to prevent contact with the atmosphere. (Japanese Utility Model Laid-Open No. 61-120750).

[0007] However, covering the back surface with a metal plate is not effective in preventing air from entering the brick joint. If the entire brick is covered with a metal plate, oxidation prevention is effective, but since the metal plate has high thermal conductivity, use of more than necessary leads to furnace heat loss.
In addition, the metal plate causes a decrease in corrosion resistance due to the low melting point substance.

[0008] On the other hand, it is known that a heat insulating material is interposed in the back of the lining of a vacuum degassing furnace for the purpose of reducing the heat loss of the furnace or protecting the furnace shell. However, since the heat insulating material has a porous structure, it becomes a passage for the atmosphere, and the lining of the magnesia-carbonaceous unburned brick promotes oxidation of the back surface of the brick.

An object of the present invention is to solve the above-mentioned conventional problems in a lining structure of a vacuum degassing furnace for molten steel lined with magnesia-carbonaceous unburned brick.

[0010]

The lining structure of a vacuum degassing furnace for molten steel according to the present invention is a heat insulating lining of a vacuum degassing furnace for molten steel lined with magnesia-carbonaceous unburned brick, the outside of which is covered with aluminum foil. The plate is placed on the back of the magnesia-carbonaceous unfired brick.
Hereinafter, description will be given based on the drawings.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Magnesia-carbonaceous unfired bricks have high thermal conductivity due to the inclusion of carbon. According to the present invention, as shown in the vertical section of the furnace wall of a vacuum degassing furnace for molten steel shown in FIG. Protect the steel skin (3).

In the present invention, a heat insulating plate (2) whose outside is covered with an aluminum foil (4) is used. In the present invention, the aluminum foil (4) blocks the flow of air in the heat insulating plate (2) and has an effect of preventing oxidation of the back surface of the brick.

[0013] Thermal insulation plate (2) covered with aluminum foil (4)
Although not shown in the figure, if the outer periphery is further wrapped with a resin film, the aluminum foil (2) is prevented from being damaged when handling the heat insulating board, and the action of the aluminum foil to shut off the atmosphere is more reliable. .

[0014] Between the heat insulating plate (2) and the furnace shell (3), and further between the heat insulating plate (2) and the magnesia-carbonaceous unfired brick (1), if necessary, refractory mortar, An irregular shaped refractory such as a castable refractory may be filled.

It is known to arrange a permanent lining on the back of the lining as a general structure of a furnace lining.
The present invention can be applied to the case where the permanent lining is arranged.

FIGS. 2 and 3 show an embodiment of the present invention in which a permanent lining is arranged. Figure 2 shows the insulation plate (2) with a permanent lining (6) on the back.
In the embodiment shown in FIG. 3, a permanent lining (6) is provided between the magnesia-carbonaceous unburned brick (1) and the heat insulating plate (2). Also in the embodiment of FIGS. 2 and 3, the front and rear of the heat insulating plate (2) are fireproof mortar,
Irregular refractories such as castable refractories may be interposed and filled.

Although not shown, the present invention may be combined with conventional lining construction techniques. For example, the heat insulating plate used in the present invention, whose outside is covered with aluminum foil, and the conventional heat insulating plate which does not cover the outside may be combined so as to be multilayered in the thickness direction of the furnace wall. Also,
The back of each magnesia-carbonaceous unfired brick may be covered with a metal plate.

The material of the heat insulating plate is glass, silica, alumina,
A ceramic fiber or a microporous ceramic containing silica-alumina as a main component is used. The microporous ceramic can be provided with a shape retaining ability by a metal foil described later, and it is not necessarily required to be a molded body, but may be a powder composed of fine ceramic particles.

The thermal conductivity of the heat insulating plate body is 0.02 to 0.08 w / w at a temperature of 500 ° C. corresponding to the use condition of the heat insulating plate.
(Mk) is preferred. The thickness of the aluminum foil is not particularly limited. For example, it is preferably 0.1 mm or less. The coating of the aluminum foil may be one layer or multiple layers.

The material of the resin film for further covering the outer periphery of the heat insulating plate covered with the aluminum foil is vinyl chloride, polystyrene, polyethylene or the like. In order to achieve close contact with the aluminum foil, the resin film may be formed into a bag shape, and the heat insulating plate may be formed into a vacuum pack with the resin film. Alternatively, the heat insulating plate may be covered after coating or bonding a resin film on the aluminum foil in advance.

The shape and thickness of the heat insulating material are not particularly limited. If the heat insulating material has high heat insulation, the thickness can be reduced accordingly. The shape is, for example, a square or a rectangle with a side of 100 to 1000 mm, and the thickness is preferably 3 to 50 mm from the viewpoints of ease of production of the heat insulating material, handling during furnace wall construction, and the like. Further, thin heat insulating plates may be used in a multi-layered manner.

The specific material of the magnesia-carbonaceous non-fired brick used for the lining is not particularly different from the conventional product. For example, the magnesia of the aggregate is electromagnetized or sintered magnesia, magnesia-calcia or natural magnesia. Carbon to be combined with magnesia is phosphorus graphite, earth graphite,
Examples include expanded graphite, electrode waste, carbon black, pitch coke, and anthracite. The proportion of carbon in the aggregate is 1-3
0 wt% is preferred.

It is customary to add an antioxidant to the magnesia-carbonaceous unfired brick. As the antioxidant, Al, Si, Mg, or an alloy of Al
-Mg, Al-Si and the like are typical examples. If necessary, glass powder, titanium, titanium compound, boride,
Antioxidants such as carbides, nitrides, aluminum fibers, and carbon fibers, sintering agents, and tissue strengthening agents may be added.

[0024] The magnesia-carbonaceous unfired brick is produced by adding, for example, a phenol resin as a binder to the above-mentioned blend, press-molding, and heat-treating at about 100 to 500 ° C.
The permanent lining is, for example, brick of magnesia, magnesia-chromium, alumina-silica, or the like.
In repairing the lining, only the magnesia-carbonaceous unfired brick is replaced while leaving the permanent lining, so that the permanent lining is preferably a fired product having excellent mechanical strength.

Although not shown, the backside of the magnesia-carbonaceous unburned brick may be covered with an iron plate to further improve oxidation prevention. In order to cover the iron plate, the iron plate is put into a brick forming mold, and then the refractory compound is charged, and the iron plate and the refractory compound are integrally formed.

[0026]

EXAMPLES Examples of the present invention and comparative examples are shown below. Each example is for the lining of the lower tank of the RH type vacuum degassing furnace. The thickness of the entire lining including the heat insulating material was 400 mm in each case.

Example 1: Wacker Ch as a heat insulating material
“Wacker super” manufactured by emie GmbH
FLEX "(registered trademark) was used. The material is a microporous molded body mainly composed of volatile silica, and the thermal conductivity is 0.031602.
w / (mk). The size is 300 height × 700 width × 3 thickness
mm. In this embodiment, the surface of the heat insulating material was covered with an aluminum foil having a thickness of 0.05 mm.

[0028] As shown in Fig. 1, the above-mentioned heat insulating material was spread all over the inside of the furnace shell without any gap, and then a magnesia-carbonaceous unfired brick was lined. The magnesia-based mortar was used to bond between the furnace shell, the heat insulating material, and the magnesia-carbonaceous unfired brick.

Example 2: As shown in FIG. 2, on the back of the heat insulating plate,
A magnesia-chromium mineral fired brick was provided with a permanent lining, and the others were the same as in Example 1. The layer thickness of the permanent lining was 30 mm, and the thickness of the magnesia-carbonaceous unfired brick layer was reduced accordingly. The magnesia-based mortar was used to bond between the furnace skin, the permanent lining, the heat insulating material, and the magnesia-carbonaceous unfired brick.

Example 3: As shown in FIG. 3, a permanent lining made of magnesia-chromium mineral fired brick was provided between the magnesia-carbonaceous unfired brick and the heat insulating plate, and the other parts were the same as in Example 1 above. I made it. The layer thickness of the permanent lining was 30 mm, and the thickness of the magnesia-carbonaceous unfired brick layer was reduced accordingly. The magnesia mortar was used to bond between the furnace skin, heat insulating material, permanent lining, and magnesia-carbonaceous unburned brick.

Example 4 The heat insulating plate covered with aluminum foil was further covered with a polyethylene film on the surface, and the other conditions were the same as in Example 1 above. Comparative Example 1: The heat insulating plate was used without being covered with aluminum foil. Others are Example 1.
Same as.

Comparative Example 2 A heat insulating layer having a thickness of 20 mm made of an alumina castable refractory was provided in place of the heat insulating plate. The test results for the lining structure of each example are shown in the following table.

[0033]

【table 1】

[0034] For the heat insulation, the surface temperature of the furnace shell was measured. The lower the temperature, the better the heat insulation. Insulation is not only the magnitude of heat loss,
It also has a significant effect on the adhesion of metal in the furnace. When the heat insulating property is high, the temperature of the furnace inner wall surface is high, and the adhesion of the metal is prevented. If the adhesion of the metal is remarkable, the metal falls into the molten steel and is impeded from purifying the steel.

The oxidation resistance is obtained by determining the ratio of the oxidized portion to the magnesia-carbonaceous unfired brick after use. The durability was determined by treating the molten steel stored in one 100-ton molten steel ladle once, and determining how many times the lining was used.

As shown in the table, in Examples 1 to 4, results excellent in heat insulation, oxidation resistance and durability were obtained. Among them,
In Example 4, in which the surface of the heat insulating plate covered with the aluminum foil was covered with the resin film, the aluminum foil was prevented from being damaged, the air was more reliably shut off, and the oxidation resistance was further improved.

On the other hand, Comparative Example 1 has excellent heat insulating properties,
Since the heat insulating material is not covered with aluminum foil, it has poor oxidation resistance. Comparative Example 2 using an alumina castable refractory as the heat insulating layer is inferior in both heat insulating properties and oxidation resistance.

In the above embodiment, even in the RH vacuum degassing furnace,
Although the lining of the lower tank is shown, the same effect can be obtained in any part such as the intermediate tank and the upper tank.

[0039]

The lining structure according to the present invention can be used under the operating conditions peculiar to a vacuum degassing furnace in which the pressure inside the furnace is reduced.
The magnesia-carbonaceous unfired brick can fully exhibit the durability effect of the unburned brick. As a result, as in the tests of the examples, the lining structure of the vacuum degassing furnace for molten steel according to the present invention has improved durability as compared with the conventional structure.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a lining structure according to an embodiment of the present invention.

FIG. 2 shows another embodiment of the present invention.

FIG. 3 shows another embodiment of the present invention.

[Explanation of symbols]

 1 Magnesia-carbon non-fired brick 2 Insulating plate 3 Furnace shell 4 Aluminum foil

Claims (6)

[Claims] Claims: 1. In a lining structure of a vacuum degassing furnace for molten steel lined with magnesia-carbonaceous unfired bricks, a heat insulating plate whose outer side is covered with aluminum foil is arranged on the back of the magnesia-carbonaceous unfired bricks. Lining structure of vacuum degassing furnace for molten steel. 2. The lining structure of a vacuum degassing furnace for molten steel according to claim 1, wherein a permanent lining is provided on a back surface of the heat insulating plate. 3. The lining structure of a vacuum degassing furnace for molten steel according to claim 1, wherein a permanent lining is provided between the magnesia-carbonaceous unfired brick and the heat insulating plate. . 4. The lining of a vacuum degassing furnace for molten steel according to any one of claims 1 to 3, wherein a thermal conductivity of the heat insulating plate body under heating at 500 ° C. is 0.02 to 0.08 w / (mk). Construction. 5. The lining structure of a vacuum degassing furnace for molten steel according to any one of claims 1 to 4, wherein a heat insulating plate whose outer side is covered with aluminum foil is further covered with a resin film on its outer periphery. 6. A heat insulating plate for use in a lining structure of a vacuum degassing furnace for molten steel according to any one of claims 1 to 5.