SK500632009U1 - Continuous cast method - Google Patents

Abstract

Disclosed is a continuous cast method, wherein a melt (4) is supplied into a frame-shaped mould through a top opening of the mould by a nozzle (5) having at least two opposing ports (9), until a surface level (10) of the melt (4) reaches a steady state position above the ports (9), and wherein in a steady state condition, an at least superficially solidified casting (13) is drawn through a bottom opening of the mould opposite to the top opening, at a velocity corresponding to the flow rate of the melt (4), thus basically keeping the surface level (10) in the steady state position. In order to reduce spillings and related drawbacks during the starting procedure, the invention suggests that a splash shield (16) is mounted to the nozzle (5) and prevents spillings of the melt (4) protruding from the ports (9) from hitting the mould, and that the splash shield (16) is molten by the surrounding melt (4) at least in the steady state condition.

Description

Continuous casting method

Technical field

The invention relates to a continuous casting method, wherein the melt is fed into the frame mold through a die top opening having at least two opposing channels, until the surface level of the melt reaches a steady position above the channels and wherein at least a surface solidified casting is drawn through the lower mold orifice versus the upper orifice at a rate corresponding to the melt flow rate, thereby essentially maintaining the surface level in a stable position.

BACKGROUND OF THE INVENTION

The continuous strip casting process has been well known since the mid-19th century and is currently used for much of the steel production worldwide, including non-alloy carbon steel, alloys and stainless steel in various shapes and sizes. These include large rectangular "slabs (having a cross-section of 0.5 cm x 50 cm to 25 cm x 220 cm) and essentially square" billets "(up to 40 cm x 60 cm), small square or round" ingots " 10 cm to 20 cm) as well as others, such as sponge-shaped.

The melt flows into the tundish into the tundish and further through the ceramic nozzle, which is attached to the tundish, into the mold. When in the mold, the melt solidifies on the water-cooled copper bottom walls without a bottom to form a thin solidified casting envelope. Upon exiting the mold, the envelope forms a housing holding the remaining liquid melt in the casting. Since the tundish ensures a continuous flow of melt into the mold even during replacement of the ladle, the process takes place in a steady state.

In modern continuous slab casting machines, the mold is assembled from four separate copper walls: Two wide walls are attached to the device and two narrow walls are movable relative to the axis of symmetry of the mold, allowing the plate width to be adjusted even during the casting process. After machining and assembly of the mold, the gaps between the wide and narrow walls are limited to approximately 0.3 mm. In operation, thermal deformation as well as copper wall wear allows these gaps to grow up to 1.5 mm without impacting the casting process. In the steady state of the continuous casting process, the surface of the melt as well as the surface of the casting thin envelope are covered with liquid slag, on the one hand, thermally insulating the copper walls from the molten steel, and on the other.

The nozzle has lateral channels that force the melt flow to extend substantially at right angles to the narrow walls of the mold, thereby causing the melt flow to be forced. Opposite pairs of drive rollers underneath the lower mold aperture continuously pull the mold casting at a rate (or "casting speed") that corresponds to the melt flow rate into the mold and bend the casting from the initial vertical to the horizontal direction. Further solidification of the casting is controlled by spraying cooling water or aerosol between the rollers.

When starting the casting process, the bottom opening is plugged with a "false partition" and the empty mold is filled with melt, similar to conventional molding. As the surface of the melt rises to a predefined steady state between the nozzle ducts (also SEN), the envelope begins to solidify both on top of the false baffle and on the mold walls. When the surface level reaches a steady-state position, the false baffle is pulled out of the lower opening, the casting being carried by the drive rollers.

The most critical phase of the start-up procedure of the known process is the initial filling of the empty mold through up to 1.5 m of outside air: The melt is sprayed in the mold and poured onto the cooled copper walls, especially the narrow mold walls. By encountering cold walls, small overflows of the melt suddenly solidify, creating sharp-edged shapes that adhere particularly to the walls. A similar effect occurs regularly during the casting process when changing the "floating" tundish as provided by modern casting processes to significantly reduce equipment downtime: As the melt surface in the mold drops below the channel level, the newly initiated melt flow falls again up to 1.2 m through the outside air .

Because these solidified overflows are mostly embedded in the insulating slag instead of the flowing melt in a continuous casting process, they usually do not melt, but instead not only prevent relative movement between the mold and the casting, but scratch the thin solidifying envelope. When the resulting grooves are not closed, they continue along the length of the casting. In addition to the visible quality error, these grooves are the points of strong weakening of the casting thin envelope: in particular, when bending the casting from vertical to horizontal direction, the thin envelope may tear in these grooves, leaving liquid metal from inside both through the drive rollers and over adjacent parts of the casting device. This dreaded accident ("remelting") regularly involves not only interrupting the casting process, but damaging the equipment, requiring repair and cleaning, and overall causing a serious loss of productivity.

Further, the aforementioned solidified overflows typically occur around the narrow walls and in particular near the mechanically sensitive gaps between the narrow and wide walls of the mold. Gaps into the gaps not only accelerate the wear of the mold when adjusting the width of the plate, but in particular are the initiating cores for forming the solidified material in the mold.

-3 The technical solution intends to reduce overflows and associated deficiencies during the start-up procedure.

The essence of the technical solution

Based on the previously known continuous casting method, the technical solution suggests that a protective shield is mounted on the nozzle to prevent the melt from coming out of the channels from impinging on the mold and that the protective shield melts the surrounding melt at least in a steady state. The " lost " shield according to the invention is only effective during the most critical phase of the start-up procedure, namely when the melt initially fills the mold through the outside air. At this time, it protects the mold walls from melt spills coming from the nozzle channels. When the melt rises above the channels, the shield shield melts and becomes an unrecognizable part of the melt itself. For the following continuous process, the nozzle channels are unshielded, thereby inducing the necessary flow into the melt in the mold.

In a preferred embodiment of the invention, the shield shield deflects the melt flow substantially extending from one of the channels at right angles to the mold wall in a direction substantially parallel to the wall. The melt flow is thus led to a false baffle at the bottom of the mold, whereby the overflowing grooves do not strike the thin casting envelope.

Preferably, the shield further diverts the melt flow to the axis of symmetry of the mold. The melt flows emanating from the various nozzle channels are thus directed towards one another and reduce the flow rate and the motive energy of one another. The resulting steady melt flow creates less overflow and flows rather than spraying in the mold.

In a further preferred embodiment of the invention, the nozzle is attached to the bottom of the tundish which is filled with the melt of the ladle. The use of a tundish instead of filling the mold directly in the casting ladle makes it possible to ensure a continuous flow of melt into the mold, even during the casting ladle change.

In another preferred embodiment of the invention, the casting is withdrawn vertically from the mold and bent in a horizontal direction by paired support rollers. In this casting method according to the invention, the initial direction of the casting is equal to the direction of the gravitational force, which ensures the homogeneity of the forced melt flow within the mold and the finished casting.

The technical solution further proposes a protective shield for use in one of the above-described methods, comprising a barrier for penetrating opposing nozzle ducts

-4a thus mounting a protective shield on the nozzle. After inserting the baffle over the nozzle, the protective shield is fixed to the nozzle in a very simple manner.

In a preferred embodiment, the baffle has a tubular shape with a central melt inlet and melt outlets at both ends. The melt thus flows through the septum. When the baffle only constitutes a protective shield, handling in a particular nozzle shield holder is significantly simplified.

In another preferred embodiment of the invention, the shield shield has an annular for surrounding the nozzle above the channels and further has deflectors that are attached to the annular, wherein in the mounted shield position the deflectors are assigned to the channels to divert the melt flow from the channels to the axis of symmetry. This shield provides significant stabilization of the melt flow as described above.

The technical solution not only provides better surface quality of the cast product and increases process productivity by reducing the risk of tearing the envelope, but also greatly facilitates the start of the continuous strip casting process.

In addition to starting the continuous strip casting process, the shield of the present invention can also be effectively used to replace a "floating" tundish, allowing the surface of the melt to drop below the upper edge of the nozzle channels.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the technical solution will be illustrated by means of exemplary embodiments of the technical solution.

Figure 1a is a sketch of a continuous casting apparatus;

Figure 1b is a detail drawing of a casting apparatus showing a nozzle in a mold; and

Figure 1c is a perspective view of a detail of a nozzle in a mold;

Figure 2a is a first protective shield according to the invention;

Figure 2b is a first protective shield mounted on a nozzle; and

Figure 2c is a view of the melt flow through the first shield;

Figure 3a is a second protective shield according to the invention;

Figure 3b is a second protective shield mounted on the nozzle; and

Figure 3c is a view of the melt flow through the second shield.

EXAMPLES

The continuous casting apparatus shown in Figure 1a and in detail in Figures 1b and 1c comprises a ladle 2 and a tundish 3 below the ladle 2. The ladle 2 feeds the molten steel 4 to the tundish 3. The ceramic nozzle 5 is mounted on the tundish 3 and projects through the upper opening 6 of the frame mold 7, terminating between the copper, water-cooled walls 8 of the mold 7.

From the tundish 3, the melt 4 is fed to the mold 7 via two opposing nozzles 9 of the nozzle 5. In a steady state casting process (as shown in Figures 1a and 1b), the surface 10 of the melt 4 is substantially maintained at a defined steady state above In the mold 7 on the cold surface H of the walls 8, the melt 4 solidifies to form a thin envelope 12 of the casting 13.

Below the lower opening 14 of the mold 7, the device 1 comprises a series of paired drive rollers 15 for pulling the casting 13 out of the mold 7 and for bending it from the vertical to the horizontal direction. Along the drive rollers 15, the casting 13 is cooled with water showers (not shown in the drawing).

In a first embodiment of the shield 16, as shown in Figure 2a, it is welded from 3 mm thick steel sheets to form a tubular partition 17. The shield 16 has a length 18 of 40 cm and a square section of height 19 of 64 mm and width 20 of 54 mm. The protective shield 16 has a brick-like stop 21 welded on the top surface 22, an inlet opening 23 on the top surface 22 and two outlet openings 24 on the bottom surface 25 at both ends 26.

Before the casting process begins, the shield 16 is inserted through the channels 9 into the nozzle until the stop 21 hits the surface 27 of the nozzle 5, as shown in Figure 2b _r After assembly, the slide (not shown) under tundish 3 opens, melt 4 flows through the inlet opening 23 into the shield 16 and flows from the shield 16 through the outlet openings 24, as shown in Figure 2c.

In an alternative second embodiment of the shield 28, as shown in Figure 3a, it is also welded from 3 mm steel sheets. The second shield 28 has an annular ring 29 of approximately 14 cm diameter and carrying two deflectors 31 The deflectors 31 are box-shaped, having a height 32 of 16 cm and a width 33 of 15 cm. The outer surfaces 34 of the deflectors 31 are arranged to have a distance of approximately 33 cm. The second protective shield 28 has a separate partition 30 of bevelled steel sheet of 3 mm thickness and a width of 5 cm. The deflectors 31 have slots 37 for inserting the partition 35 into the shield 28.

Prior to the casting process, the nozzle 5 is placed in the annulus 29 of the alternative shield 28 and the baffle 35 is inserted through the slots 37 and through the channels 9 into the nozzle 5,

The long stop 38 of the partition 35 does not strike the outer surface of the deflector 31 as shown in Figure 3b. Once mounted, the melt 4 first guides the baffle 35 to flow into the deflectors 31 and then to flow from the shield 28 as shown in Figure 3c.

Both the first shield 16 and the alternative second shield 28 will melt at least when they are below the surface 10 of the melt surface 4, thereby themselves becoming part of the melt 4.

Claims (8)

PROTECTION REQUIREMENTS A continuous casting method, wherein the melt (4) is fed into the frame mold (7) through an upper opening (6) of the mold (7) through a nozzle (5) having at least two opposing channels (9) until the level (10) the surface of the melt (4) does not reach a steady position above the channels (9) and wherein at steady state the least surface solidified casting (13) is drawn through the lower opening (14) of the mold (7) against the upper opening (6) at a speed corresponding to 4), thereby essentially maintaining the surface level (10) in a steady position, characterized in that the protective shield (16, 28) is mounted on the nozzle (5) and prevents the melt (4) coming out of the channels (9) ), the protective shield (16, 28) melts the surrounding melt (4) at least in a steady state. Continuous casting method according to the preceding claim, characterized in that the shield (16,28) deflects the melt flow (4) substantially extending from one of the channels (9) at right angles to the wall (8) of the mold (7). ) in a direction substantially parallel to the wall (8). Continuous casting method according to the preceding claim, characterized in that the protective shield (28) further deflects the flow of the melt (4) to the axis of symmetry of the mold (7). Continuous casting method according to one of the preceding claims, characterized in that the nozzle (5) is attached to the bottom of the tundish (3), which is filled with the melt (4) from the ladle (2). Continuous casting method according to one of the preceding claims, characterized in that the casting (13) is drawn vertically out of the mold (7) and bent in a horizontal direction by means of paired support rollers (15). Protective shield (16, 28) for use with one of the above claimed methods, characterized in that it comprises a partition (17, 35) for penetrating the opposing channels (9) of the nozzle (5) and hence attaching the protective shield (16). 16, 28) by a nozzle (5). Protective shield (16) according to the preceding claim, characterized in that the partition (17) has a tubular shape with a centered inlet opening (23) for the melt (4) and outlet openings (24) for the melt (4) at both ends (26). Protective shield (28) according to claim 6 or 7, characterized in that it comprises an annular ring (29) for surrounding the nozzle (5) above the channels (9) and further comprising deflectors (31) which are fixed o an annular ring (29), wherein in the mounted position of the shield (28) the deflectors (31) are assigned to the channels (9) to divert the melt flows (4) from the channels (9) to the axis of symmetry of the mold (7).