JPH06142899A - Lower nozzle for casting molten steel - Google Patents

Abstract

PURPOSE:To prolong the life of the lower nozzle by constituting the circumference of a molten steel flow hole of shaped refractories, constituting the circumference thereof of monolithic refractories and protecting the outermost peripheral part with a shell case. CONSTITUTION:The lower nozzle for casting molten steel is used for a ladle or tundish. The circumference of the molten steel flow hole d of such lower nozzle for casting the molten steel is constituted of the shaped refractories c. The circumference of the shaped refractories c is constituted of the monolithic refractories b to form a two-layered construction. The outermost peripheral part is protected with the iron shell case. The shaped refractories are formed of >=1 kinds among alumina graphitic, magnesium graphitic, alumina zirconia graphitic or zirconia refractories. A heat insulating material is embedded between the shaped refractories and the monolithic refractories, The shaped refractories are molded by a hydrostatic press. As a result, the corrosion resistance and spalling resistance are improved and the expansion and loosening of the iron shell are prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten steel casting nozzle, and more particularly to a molten steel casting lower nozzle for use in ladle and tundish slide valve devices.

[0002]

2. Description of the Related Art Molten steel casting nozzles, particularly lower nozzles used in ladle and tundish slide gate devices, have conventionally been of a standard fire resistance of high Al ₂ O ₃ quality, Al ₂ O ₃ -C quality, zircon quality, etc. Or high Al ₂ O ₃ castable (undefined) refractories are applied, and these refractories are generally protected and restrained by a steel case before use.

[0003]

It is known that the lower nozzle of the one-piece structure made of various refractory materials as described above has the following drawbacks depending on the material thereof: (1) Lower nozzle made of zircon-shaped regular refractory material Has the advantage of being excellent in spall resistance and relatively inexpensive, but it is inferior in corrosion resistance, however, so that melting loss increases when it is used many times and it cannot be used.

(2) A lower nozzle made of a high Al ₂ O ₃ type regular refractory or a high Al ₂ O ₃ irregular type refractory has good corrosion resistance, but on the other hand is poor in spall resistance and is difficult to cast when molten steel is cast. Due to the thermal shock of, the crack that reaches from the molten steel flow hole to the steel case of the back part is likely to occur, and there is a case where the molten steel is inserted into this crack and local melting loss due to intake from the crack occurs. In some cases, it is known that a steel leak accident may result.

(3) The lower nozzle made of Al ₂ O ₃ -C quality refractory has the best corrosion resistance and can be used many times, but it has the same resistance as the high Al ₂ O ₃ quality refractory. There is a problem of crack generation due to lack of spalling property. Further, since this refractory has a high thermal conductivity, the iron shell case on the outer periphery is significantly deteriorated by heat when used many times, and the original functions of protection and restraint are also significantly reduced.

[0006]

The inventors of the present invention have developed the present invention as a result of various studies and experiments in order to solve various defects of the prior art as described above, and the technical constitution of the present invention is as follows. In the molten steel casting lower nozzle used for ladle or tundish, the surroundings of the molten steel flow hole are composed of a standard refractory,
The fixed refractory has a two-layer structure composed of an irregular refractory, and the outermost peripheral portion is protected by a steel case, which is a lower nozzle for molten steel casting, wherein the fixed refractory is Al ₂
O ₃ -C quality, MgO-C protein, Al ₂ O ₃ -ZrO ₂ -C
Quality or ZrO ₂ quality refractory made of one or more
Further, a heat insulating material is embedded between the regular refractory material and the irregular refractory material, and by adopting such a technical configuration, a lower nozzle of an integral structure made of a conventional refractory material of the same material is formed. Compared with this, the occurrence of melting loss and cracks is suppressed, and the service life is extended to more than double.

A detailed example of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a vertical cross-sectional view showing an example of a lower nozzle to which the present invention is applied, where a is an iron skin case for protecting and restraining the nozzle body, b is an indefinite (castable) refractory, and c is the nozzle. It is a standard refractory arranged around the hole d, and in this example, a convex projection or ridge c ′ is provided on the outer periphery of the standard refractory to prevent displacement.

FIG. 2 is a vertical cross-sectional view showing an example in which a fixed refractory c arranged around the nozzle hole d is provided with a taper (tapered downward), and the other parts are as shown in FIG. The same member is shown.

In FIG. 3, the shape of the regular refractory material is the same as that of FIG. 2 described above, and further, at the boundary between the regular refractory material c and the irregular refractory material b on the outer periphery thereof, a heat insulating material e made of a ceramic fiber molding or the like. FIG. 4 is a vertical cross-sectional view showing an example in which the layers are embedded in a layered (continuous or discontinuous) state. With such a configuration, deterioration of the outermost peripheral part of the steel case a due to heat reception is reduced and the life of the lower nozzle is extended. The structure is designed to achieve.

[0011]

The two-layer lower nozzle of the present invention achieves the following operational effects in detail: (1) Since the nozzle itself has a two-layer structure, the fixed refractory around the hole or the outer peripheral portion Even if a crack occurs in the castable refractory, the crack often stops at the boundary between the two materials, so that a crack that penetrates from the hole side to the back iron skin side is less likely to occur. Therefore, the risk of local melt damage from a crack and inhalation was greatly reduced, and the risk of causing local melt loss to leakage steel was also greatly reduced.

(2) Further, by adopting the above-mentioned two-layer structure, it is difficult to apply MgO-C or ZrO _{2 having} a high corrosion resistance due to its large thermal expansion and poor spall resistance. It has become possible to use it as a regular refractory material that constitutes the surrounding area.

(3) Further, Al ₂ O ₃ --C and Mg are formed around the holes.
Even if a carbon-based high thermal conductivity material such as OC is applied, the thermal conductivity of the castables around it is low, so the deterioration of the iron case is greatly reduced, and the iron case thickness should be 3 mmt or more. By setting to, the iron case can be used many times.

(4) Al ₂ O ₃ forming the periphery of the nozzle hole
When the material such as -C is manufactured by hydrostatic molding using a rubber press, the effect of the present invention is further exhibited. That is, the conventional casting nozzle was generally molded by uniaxial pressing using a mold frame, but when the nozzle becomes long, uniaxial pressing causes non-uniform filling and It also has a drawback that cracks are likely to occur during use because the density of is likely to be non-uniform. On the other hand, this non-uniform density is greatly improved by isostatic molding with a rubber press,
Manufacturing costs increase due to material costs and processing costs after molding. However, in the nozzle according to the present invention, since the periphery of the regular refractory which constitutes the periphery of the nozzle hole is further surrounded by the castable layer, the refractory material inside the nozzle hole has a simple cylindrical or cylindrical shape. Since it has a similar shape and does not require precise processing of the outer surface, the advantages of rubber press molding can be utilized more easily.

The compositional examples and various properties of the product of the present invention and the conventional integrated structure are compared as follows: The lifespan of the above composition example is as a result of the experiment as follows: (1) Conventional integrated structure a. In the case of zircon refractory, the use of 2 charges is the limit because of its corrosion resistance.

B. In the case of alumina refractory, cracks occur and use of 3 charges is the limit.

C. In the case of Al ₂ O ₃ -C quality refractory, the iron shell becomes brittle and the use of 4 charges is the limit.

D. In the case of a one-layered ZrO ₂ -based and MgO-C-based refractory material, it could not be used as a lower nozzle because of cracking due to thermal shock.

(2) The above table of the product of the present invention can use 7 charges. The lower nozzle of the composition could be used for 6 charges.

[0020]

EFFECT OF THE INVENTION By adopting the technical constitution of the present invention,
Corrosion resistance and spall resistance are improved, expansion of the iron case,
Loosening can be prevented, and the life of the lower nozzle can be extended to about twice or more.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a lower nozzle to which the present invention is applied.

FIG. 2 is a vertical sectional view of a lower nozzle of another example to which the present invention is applied.

FIG. 3 is a vertical cross-sectional view showing an example in which a heat insulating material is embedded between a standard refractory and an irregular peripheral refractory.

[Explanation of symbols]

 a Iron case b Unshaped refractory c Fixed refractory c'Convex protrusion or ridge d Nozzle hole e Heat insulating material

Claims (4)

[Claims] 1. A lower nozzle for molten steel casting used in a ladle or a tundish has a two-layer structure in which the molten steel circulation hole is formed of a regular refractory and the surrounding of the regular refractory is formed of an irregular refractory. A lower nozzle for molten steel casting, characterized in that the outermost peripheral part is protected by a steel case. 2. The lower nozzle for molten steel casting according to claim 1, wherein the regular refractory material is one or more of alumina / graphite, magnesia / graphite, alumina / zirconia / graphite or zirconia refractory. . 3. The lower nozzle for molten steel casting according to claim 1, wherein a heat insulating material is embedded between the regular refractory material and the irregular refractory material. 4. The lower nozzle for casting molten steel according to claim 1, wherein the regular refractory material is formed by isostatic pressing.