JPH1149561A - Production of magnesia-carbon brick - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the falling of a reinforcing body from the surface of a magnesia.carbon brick as well as to enhance the high-temp. strength of the brick by putting the brick after forming in a hermetically sealable space, filling the space with one of an Mg vapor-contg. gas and a CO-contg. gas and then feeding the other gas into the space. SOLUTION: The Mg vapor-contg. gas is Mg vapor optionally diluted with a gas not reacting with Mg vapor, e.g. N2 or Ar. The CO-contg. gas is CO optionally diluted with a gas not reacting with CO. The Mg vapor and CO gas deposit magnesia and carbon in accordance with the reaction formula Mg+CO → MgO+C and a layer of the deposits is formed on the surface of the magnesia.carbon brick. The reaction is preferably carried out at >=700 deg.C. The gases are preferably introduced into the hermetically sealable space after preheating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing magnesia carbon brick.

[0002]

2. Description of the Related Art In general, bricks constituting the inner wall of an industrial furnace or a container for molten metal are mainly made of magnesia for use at high temperatures. Among them, magnesia-carbon bricks to which carbon is added in an appropriate amount are widely used in order to improve slag resistance and molten steel resistance against slag and molten steel erosion. Although the structure of the brick is densified by high-pressure molding, the pores still remain at the product stage, and the porosity is about 3%.

[0003] These bricks are heated before use. This is to prevent heat spalling by applying heat to the bricks and to operate smoothly. In addition, in the case of magnesia carbon brick, this heating is usually performed in the atmosphere. Therefore, carbon in the brick, that is, carbon is combined with oxygen in the atmosphere and escapes. As a result, the porosity increases to 9% after drying, and there is a problem that bricks are easily eroded through the pores. For example, when used for the inner wall of a container for molten metal, slag generated at the stage of producing the molten metal enters pores of the brick, reacts with silicon carbide and carbon inside the brick, and erosion of the brick proceeds.

[0004] Therefore, these bricks are used while repairing portions damaged during use. In general, as a method of reinforcing a brick, a method of spraying a mixture of refractory powder and water to a damaged portion, that is, a dry spraying method is known.

Further, as a method for repairing bricks, a thermal spraying method has been proposed. In this method, the refractory powder is brought into a semi-molten or molten state in a flame composed of oxygen and a fuel gas or by burning aluminum or silicon, and adheres to a damaged portion of the magnesia-carbon brick. For example, Japanese Unexamined Patent Publication (Kokai) No. 62-15508 discloses a flame sprayed material applied for such a purpose. These sprayed materials are melted by the flame, collide with the repaired portion and rapidly solidify to form a sprayed material mainly composed of a glass phase.

[0006]

However, there are various problems in the method of repairing and using bricks as in the prior art. For example, since the dry spraying method is performed after lowering the furnace temperature, it takes time to cool the furnace and raise the temperature after the reinforcing operation. Therefore, it is necessary to stop the operation of the furnace for a long period of time. Further, in the dry spraying method, since the sprayed refractory has no strength, it is easily peeled off by a slight impact.
Therefore, this method is only used as a temporary measure.

[0007] The sprayed material mainly composed of a glass phase described in Japanese Patent Application Laid-Open No. Sho 62-15508 crystallizes during the cooling process and changes to a crystal phase. Since the volume shrinks during this phase transition,
Cracks occur. For this reason, the thermal spray reinforcement becomes insufficiently bonded to the base material, and cannot be used for a long time. Especially when the base material is deteriorated and the strength is reduced,
Cracks develop from the base metal side, and the thermal spray reinforcing member falls off. Therefore, the life of the thermal spray reinforcing body is not determined only by the strength and spalling resistance of the thermal spray body itself. There is also a problem of such a thermal spray reinforcing body falling off, and the life is about 20 to 30 charges.

[0008] As described above, the conventional magnesia carbon brick has an increased porosity due to an increase in heat, and is liable to be damaged. Therefore, it is necessary to use the brick while repairing it. Also, the strength of the repaired brick was insufficient.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The present invention has been made to increase the strength of bricks during heating to prevent damage, and to remove and remove the surface material of bricks such as reinforcing members. It is an object of the present invention to provide a method for producing a magnesia carbon brick that can prevent the occurrence of cracks.

[0010]

According to the present invention, a magnesia-carbon brick is molded and then charged into a sealable space, and first of all, a gas containing magnesium vapor or a gas containing carbon monoxide. And supplying one of the gases into the space to fill the space, and then supplying the other gas into the space, the method for producing a magnesia-carbon brick.

The type of the space that can be sealed is not particularly limited as long as the gas used for the reaction can be prevented from leaking. Further, the gas containing magnesium vapor refers to a gas obtained by diluting magnesium vapor with magnesium vapor or a gas that does not react with magnesium vapor. For example, N ₂ or Ar may be used as the diluent gas. Similarly, a gas containing carbon monoxide refers to a gas obtained by diluting carbon monoxide with carbon monoxide or a gas that does not react with carbon monoxide. For example, N ₂ or Ar may be used as the diluent gas.

[0012] Magnesia MgO and carbon C can be deposited by the reaction between magnesium vapor and carbon monoxide gas. The reaction is shown below. Mg + CO → MgO + C

[0013] Here, C on the right side of the reaction formula is solid carbon precipitated together with magnesia.
The main constituent of magnesia carbon brick is obtained.

The reaction temperature is desirably 700 ° C. or higher. This is because if the temperature is lower than 700 ° C., part of the Mg vapor tends to be condensed at the stage of transfer to the reaction site, so that Mg cannot be effectively used for the intended reaction.

The Mg vapor may be generated by heating molten Mg. In this case, the heating temperature is 700 to 1200
It is desirable to be in the range of ° C. This is because Mg below 700 ° C
This is because the rate of generation of steam is too low.
If the temperature exceeds ℃, the generation of Mg vapor becomes intense, and it becomes difficult to control the flow rate and pressure of a gas containing the same.

Mg as a starting material for the Mg vapor may be ingot or powder. When Mg is a powder, it may be a single Mg or a mixed powder of Mg-CaO and Mg-Al. Since Mg powder easily ignites, mixed powder is more desirable.

In order to generate Mg vapor, MgO and Al
May be generated by reacting as follows. 3MgO + 2Al → 3Mg + Al ₂ O ₃

In this case, the reaction temperature is 850 to 1700 ° C.
Is preferably within the range. This is because if the temperature is lower than 850 ° C., the reaction rate is too slow. On the other hand, if the temperature exceeds 1700 ° C., the generation of Mg vapor becomes intense, and it becomes difficult to control the flow rate and pressure of the gas containing the same.

The concentration of the Mg vapor contained in the gas containing the Mg vapor (diluent gas) is 0.1 vol. % Is desirable. This corresponds to 0.1 vol. If the amount is less than 10%, the reaction rate is too slow.

The concentration of carbon monoxide gas contained in the gas (diluent gas) containing carbon monoxide gas is 1 vol.
l. % Is desirable. This corresponds to 1 vol.
If the amount is less than 10%, the reaction rate is too slow.

Next, the reaction on the surface and the surface of the brick will be described. The magnesium vapor (containing gas) that has also penetrated into the pores of the brick reacts with the above-mentioned carbon monoxide gas. This reaction is catalyzed on the solid surface and proceeds preferentially on the brick surface. If this reaction continues, the gas containing magnesium chloride is consumed, so that the carbon monoxide gas gradually penetrates into pores and the like. In this manner, magnesia and carbon are deposited inside the pores while the reaction interface of the two types of gas proceeds deep inside the pores and the like, and the pores are filled up.

In the present invention, the brick (magnesia
By precipitating magnesia and carbon, which are the main components of the carbon brick, the reinforcing body and the brick are integrated, and problems such as falling off from the reinforcing portion can be solved.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In practice, a furnace that can be covered with an industrial furnace or a ceramic furnace may be used as a hermetically sealable space. The magnesia carbon brick molded in this is inserted. Next, heating is performed to remove moisture contained in the brick after molding. The heating of the brick is also desirable from the viewpoint of accelerating the gas reaction on the surface of the brick, that is, the precipitation of magnesia and carbon.

The gas containing magnesium vapor is introduced into the furnace after preheating. After the gas fills the furnace,
Introduce carbon monoxide gas. It is desirable that the carbon monoxide gas is preheated as much as possible from the viewpoint of securing the reaction temperature. Thus, by reacting the two gases, a layer composed of magnesia and carbon precipitates is formed on the surface of the magnesia-carbon brick.

[0025] If vacuuming is performed using a vacuum furnace as a space that can be sealed, when the atmosphere gas in the furnace is replaced with a gas containing magnesium vapor, the loss of the latter gas can be reduced. The use of a vacuum furnace is also desirable from the viewpoint of preventing oxidation of the carbon constituting the magnesia-carbon brick charged therein.

When it is desired to increase the thickness of the magnesia layer on the surface of the brick, this operation is repeated a plurality of times.
You can achieve your goals.

[0027]

According to the present invention, a magnesium vapor gas or a gas containing the same is reacted with a carbon monoxide gas,
Since the brick is protected by depositing magnesia on the surface of the magnesia-carbon brick, the strength during hot work is reinforced. Further, by precipitating magnesia and carbon, which are the main components of the brick, the reinforcing body and the magnesia-carbon brick are integrated, and the problem of the reinforcing body falling off from the brick surface can be solved.

Claims (1)

[Claims] Claims 1. A magnesia carbon brick is molded and then charged into a sealable space. First, of a gas containing magnesium vapor or a gas containing carbon monoxide,
A method for manufacturing a magnesia-carbon brick, comprising supplying one of the gases into the space to fill the space, and then supplying the other gas into the space.