SK1072014U1 - Process of continous casting of steel - Google Patents

Abstract

A method is described in which a liquid steel (2) is led from a tundish (3) to a crystallizer (5) via a submersible nozzle (4) having a main central channel (11) and two opposed discharge openings (8) therein bottom. A protective shield (12) is mounted on the immersion nozzle (4) to protect the lower portion thereof from the direct impact of the liquid steel (2) in the initial casting phase when the crystallizer (5) is empty, the protective shield (12) melting the surrounding liquid steel (2). In the casting process, the level of the liquid steel (6) in the crystallizer (5) is kept steady.

Description

Method of continuous casting of steel

Technical field

The technical solution relates to the continuous casting of steel into the gates, whereby the liquid steel is fed to the crystallizer from above via a dip nozzle (dip nozzle). The crystallizer itself consists of four water-cooled copper plates, which form a kind of "bottom-free container". The walls of the crystallizer are intensively water-cooled to ensure solidified surface crust formation around the perimeter of the casting and its integrity. At steady state, the surface solidified cast is drawn through the bottom opening of the crystallizer. The rate of withdrawal of the casting from below is in equilibrium with the introduction of the liquid steel into the crystallizer from above, thereby keeping the surface of the liquid steel in the crystallizer at a steady position.

BACKGROUND OF THE INVENTION

The continuous steel casting method is well known, with the cast rectangular slabs having cross sections from 50mm x 500mm up to 250mm x 2200mm. Square and round billets and other profiles are also produced by the continuous casting process.

Liquid steel flows from the ladle through the casting tube into the tundish. The flow of steel from the ladle to the tundish is controlled by a sliding shutter. The filling rate depends on the required stable level of the steel in the tundish or in the tundish. in a crystallizer.

Medzipanva is a metallurgical vessel constructed of steel sheets and is walled with refractory materials. Its primary function is to transport the steel from the ladle to the crystallizer and, due to its volume, performs the function of a temporary reservoir for liquid steel during the exchange of the ladles, enables its thermal and chemical homogenization and ensures proper removal of non-metallic inclusions from the metal. the volume of steel into the slag, as well as minimizing the mixed transition area of the chemical composition of the various fed grades.

During the casting of steel it is necessary to use several types of special shaped ceramics, which must be able to withstand besides the liquid steel exposure itself also sudden temperature changes, erosion of slag, but also high mechanical stress.

In the continuous steel casting process, the liquid steel is fed from the tundish to the crystallizer via an immersion tube (immersion nozzle). The sink is made of refractory ceramics and is attached to the tundish. In the case of casting of steel gates, the immersion nozzle is a ceramic tube with a central opening through which liquid steel flows from above the tundish into the immersion nozzle. The central opening is terminated at the bottom by two outlet openings perpendicular to the central opening. The flow of liquid steel from the tundish to the crystallizer through the immersion nozzle is provided by the gravitational gravity of the liquid steel, being controlled by a stopper rod or a slide valve, which controls the size of the opening cross-section.

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In a steady state casting, the dip nozzle is immersed in the liquid steel in the crystallizer, with the horizontal discharge openings being below the liquid steel level. The design of the submersible nozzle with two horizontal discharge openings ensures the desired dynamics and turbulence of the liquid steel flow in the crystallizer at steady state to ensure the desired quality of the cast slab.

The immersion nozzle protects the steel stream from the effects of the atmosphere as it flows from the tundish to the crystallizer. It must withstand high temperature changes, mechanical stress and also the corrosive effects of the slag in the crystallizer.

At the start of the casting process, the bottom of the crystallizer is clogged with a starter plug which is inserted into the crystallizer. The starter plug is of a flexible design and represents the temporary bottom of the crystallizer. The empty crystallizer is filled with melt as a conventional casting mold. As the liquid metal level rises to the steady state position, the starter plug carrying the casting is withdrawn from the bottom opening by means of pulling rollers. After the start of casting and the casting run to the horizontal part of the run-out section, the starting plug is separated from the casting.

The critical moment for loading the sink, especially its lower part, is the initial discharge of the liquid steel from the tundish into the crystallizer via the sink (start of casting). The design of the lower part of the sink (weakening of the structure due to the side outlet openings), its thermal and mechanical load at the initial moment of casting, when the liquid steel falls freely on the bottom of the sink, is one of the factors limiting the service life of the sink.

The essence of the technical solution

The technical solution proposes a method of continuous casting of steel through an immersion nozzle, with a protective shield mounted on the immersion nozzle that protects the bottom of the immersion nozzle from liquid steel in the initial casting phase. The shape of the shield ensures that the liquid steel stream is diverted directly from the central vertical channel into the side outlets, thereby preventing extreme thermal and mechanical overload of the bottom of the sink in the initial casting phase. After the crystallizer has been filled with liquid steel above the level of the outlet openings of the sink, the protective shield melts and becomes part of the melt. During the subsequent steady-state casting, the holes of the immersion nozzle are unprotected to achieve the desired liquid steel flow in the crystallizer.

Image overview

In FIG. 1 shows a sketch of a continuous steel casting device for gates.

In FIG. 2 is a perspective view showing an immersion nozzle in a crystallizer.

In FIG. 3 shows a protective shield according to the invention.

In FIG. 4 shows an immersion nozzle with a protective screen.

In FIG. 5 is a view of the flow of liquid steel through the dip nozzle using a protective shield.

EXAMPLES

Example 1

The continuous steel casting apparatus shown in Figure 1 and in detail in Figure 2 comprises a ladle 1 and a tundish 3. From the ladle 1, the liquid steel 2 is fed to the tundish 3. The tans 3 liquid steel 2 flows due to its gravity gravity through Submerged nozzle 4 into the crystallizer 5. The submerged nozzle 4 has two opposing openings 8 at the bottom, through which liquid steel flows from the central channel 11 of the submerged nozzle 4 into the space of the crystallizer 5. In steady state casting (as shown in Figure 1) In the crystallizer 5 on the cold wall surface, the liquid steel 2 solidifies and forms the solid crust of the slab 7, the core of the slab remaining liquid and solidifying gradually in the secondary cooling section 10. Partially (on the surface) ) the solidified endless slab is pulled out from below the crystallizer 5 by a series of paired pulling rollers 9, which thus ensuring the bending of the slab from the vertical direction to the horizontal direction. Along the drawing rollers 9 in the secondary cooling section 10, the slab is cooled with water showers (not shown in the drawing).

The shield 12 shown in Figure 3 is made of a steel sheet 13 that is bent into the shape of Figure 3. To enhance the effect of the shield 12, a steel sheet 14 is welded to its lower portion as shown in Figure 3. 3. For handling and inserting the shield 12 into the sink 4, the shield 12 is provided with a holder 15.

Before starting the pouring of the liquid steel, the protective shield 12 is inserted through the holes 8 into the sink nozzle 4. After assembly, the slide (not shown) at the tundish drain outlet 3 opens, the liquid steel 2 flows from the tundish 3 through the central channel of the sink. The inclined walls of the shield 12. After the inclined walls of the shield 12, the liquid steel flows to the outlet openings of the sink nozzle 8 and flows into the space of the crystallizer 5.

The protective shield 12 melts after the level of liquid steel 6 in the crystallizer 5 rises above the level of the outlet openings of the sink nozzle 8.

Claims (1)

Protection claims A continuous steel casting process in which liquid steel (2) is fed to a crystallizer (5) via an immersion nozzle (4) having a main central channel (11) and two oppositely disposed apertures (8) in the lower part of the immersion spout (4), until the liquid steel level (6) has reached a steady position above the discharge holes (8) of the immersion spout (4), wherein in a steady state casting the surface solidified cast is drawn through the lower opening of the crystallizer (5) at a speed corresponding to (2) for maintaining a steady level of liquid steel (6) in the crystallizer (5), characterized by the fact that a protective shield (12), which is made of steel to protect its lower part from direct impact of the liquid steel (2) in the initial casting phase, the protective shield (12) melting the surrounding liquid steel