JPH0866748A - Mold coating material and method for starting casting - Google Patents

Abstract

PURPOSE: To uniformize the solidified shell and to prevent the surface flaw on a cast slab. CONSTITUTION: Mold coating material 2 protects the surface of a mold 1 at the time of starting continuous casting and lubricates at the time of drawing the cast slab, and fine powder for casting is suspended into rapeceed oil and the mold coating material can be applied onto the mold 1 by spraying. A dummy bar 3 for drawing the cast slab at the time of starting the continuous casting is set in the condition of plugging the lower end of the mold and the mold coating material 2 is applied on the surface of the mold. A tundish is set above the mold and molten steel is poured into the mold till reaching a fixed level, and after reaching the fixed level, the draw-out of the cast slab is started and the powder for lubricating the cast slab is started to charge at the time of starting the draw-out of the cast slab.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold coating material for continuous casting of steel and a casting start method.

[0002]

2. Description of the Related Art Conventionally, at the start of continuous casting, a dummy bar for pulling out a slab is set in a state where the lower end of the mold is closed. Set the tundish on the mold,
Molten steel is poured into the mold until it reaches a certain level, and after reaching the certain level, drawing of the slab is started. In this series of operations, the powder for lubricating the slab is started immediately after the molten steel injection is started, and thereafter, the powder is continuously supplied during casting.

[0003]

The powder introduced at the start of casting melts immediately and adheres to the mold surface to form a lubricating layer called a fixed layer. The fixed layer has a great influence on the heat transfer in the mold, and the thickness of the fixed layer has a great influence on the formation of the solidified shell of the slab. If there is a non-uniform thickness of the fixed layer in the mold, non-uniformity will occur in the solidified shell,
Defects such as cracks occur on the surface.

Further, the fixed layer moves as the cast piece is pulled out, but the moving speed is extremely slow as compared with the cast piece. Therefore, if the thickness of the fixing layer becomes nonuniform, the nonuniformity once formed remains for a long time, causing surface defects in the cast piece cast during that time. Since the flow of molten steel in the mold is not stable at the start of casting, unevenness is likely to occur in the fixed layer, and the reduction of slab defects immediately after the start has been a major issue.

[0005]

According to the present invention, a mold coating material is applied to the surface of a mold at the start of casting to prevent non-uniform formation of a fixed layer at the start of casting and to make the solidified shell uniform. The purpose is to

Specifically, at the start of continuous casting, a dummy bar for withdrawing a cast piece is set in a state where the lower end of the mold is closed, and the surface of the mold is covered with a mold coating material that replaces the fixing layer. Set the tundish on the mold,
Molten steel is poured into the mold until a certain level is reached, and after reaching the certain level, drawing of the slab is started. In this series of operations, the powder for lubricating the slab is started to be charged after the molten steel surface reaches a certain position in the mold, and thereafter the charging is continued during the casting.

As a substitute for the fixing layer covering the mold, the same material as the powder fixing layer is desirable, and it is optimal to uniformly stick the product obtained by melting the powder into a plate shape and uniformly adhering it to the mold surface. However, the solidified powder in the form of a plate is easily broken, and it is difficult to cover the entire surface of the mold, and the workability is extremely low.As an alternative to this, the powder is made into a fine powder and suspended in rapeseed oil. Invented

Although rapeseed oil burns when it comes into contact with molten steel, it does not change the powder material. By uniformly applying the mold coating material to the mold, a uniform fixed layer can be formed. When the molten steel surface reaches a certain position of the mold and the powder is charged again, the powder uniformly flows into the mold surface, and the fixed layer is uniformly formed. As a result, the occurrence of surface defects immediately after the start of casting is greatly reduced.

[0009]

EXAMPLE FIG. 1 is a schematic sectional view of a mold before the start of casting. Reference numeral 1 is a mold, 2 is a mold coating material according to the present invention, and 3 is a dummy bar. By directly covering the mold surface with the mold coating material, it is possible to prevent direct contact between the molten steel and the mold, and it is possible to pull out the cast slab due to the lubricating action.

[0010]

As shown in FIG. 2, the occurrence of vertical cracks at the start of casting was reduced to 68 when the conventional value was 100.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a mold before the start of casting in the present invention.

FIG. 2 is a comparison diagram of the occurrence rate of vertical cracks at the start of casting between the present invention and the conventional method.

[Explanation of symbols]

1: Mold, 2: Mold coating material, 3: Dummy bar.

Claims (2)

[Claims] 1. A mold coating material which protects the surface of a mold at the start of continuous casting and lubricates when a cast piece is drawn out. A fine powder of casting powder is suspended in rapeseed oil and applied to the mold by spraying. Mold coating material that can be. 2. A dummy bar for pulling out a slab at the start of continuous casting is set in a state where the lower end of the mold is closed, the mold coating material according to claim 1 is applied to the mold surface, and a tundish is set on the mold. , A casting start method in which molten steel is poured into a mold until a certain level is reached, and after reaching the certain level, withdrawal of the ingot is started and powder for lubricating the ingot is started at the beginning of withdrawal of the ingot.