KR20010040757A - Device for continuous casting in vertical charge of a melting metal - Google Patents

Abstract

The present invention relates to an apparatus for continuously casting in a molten metal molten metal portion in slab form using a copper ingot mold (1) extending along a transfer head (2) made of a refractory material, the transfer head (2) Is placed above the copper ingot mold 1 such that the liquid steel liquid level or meniscus S is suitably placed in the refractory transfer head 2 during the continuous casting operation but not in the copper ingot mold 1. Between the copper ingot mold 1 and the transfer head 2 are arranged connection elements made of refractory material comprising bars 3, 4, 5, 6, 7 and 8. The bar is arranged such that the assembly forms a joint element, the joint element of which the inner shape is similar to the inner shape of the ingot mold, the inner surface of which is an extension of the corresponding inner surface of the ingot mold, the dimension of which is the length of the bar (unit Mm), the ratio of the transverse cross section (in mm 2) of the bar to the bar is chosen to be less than 2.4 mm. In addition, the bar is parallel hexagonal in shape and its cross section has a height to length ratio of 0.4 to 0.6. Each bar (4, 6) is placed in full alignment with the ingot mold surface (each bar (4, 6) constitutes its extension), taking into account the mechanical assembly margin, and is directed backward by the slab. Supported against rear stops 12 and 13 that prevent pressurization, each bar 4 is machined to receive a retaining clamping claw 9, and the retaining clamping claw is ingot mold during its vibratory movement. The ability to press the bar vertically so that it is in continuous contact with the upper edge, and in particular by moving the bar towards the center of the slab at the beginning of the continuous casting operation in the vertical filling part, the bar being ingot mold surface (each bar 4 is its extension) It guarantees the dual function of the function of preventing the movement away from the alignment with.

Description

Device for continuous casting in vertical charge of molten metal

Continuous casting is a widespread technique that allows casting steel directly from a pouring vessel into a bottomless mold, where the steel exits from the bottomless mold in the form of a partially solidified continuous strand. The outflow vessel is usually an outflow ladle or tundish, which will be referred to herein as tundish for simplicity.

It is customary for the bottom of the tundish to be penetrated by a hole that cooperates with a closure member of known type. The outflow nozzle is fixed below the tundish coaxially with the taphole and suitably freely immersed in the upper part of the mold. These molds are made of copper and are water cooled. Also, the mold is usually subjected to vibratory motion in the longitudinal direction to prevent the steel from adhering to the wall, the amplitude of which is several millimeters.

In operation, liquid metal that flows from the tundish into the mold through a refractory nozzle disposed in the upper portion of the mold but may or may not be submerged below the liquid steel level or meniscus is recycled in the meniscus. It creates turbulence on the free surface of steel in the form of recirculation loops or waves. It is also known that in practice, it is very difficult to strictly maintain a constant level of steel in the mold when the steel flow rate is large and the mold has a small cross section. The combination of this phenomenon with the fact that steel begins to solidify in the meniscus, ie in contact with the walls of the copper mold, results in surface defects in the cast product.

This surface quality problem is serious in the continuous casting of flat products such as slabs, many of which are cast in so-called "specialty" fields such as sheet metal for bodywork or for drink cans. This is because it requires a basic cast product that is used for and is free of surface defects.

For many years, work has been done to remedy this problem, and most useful solutions currently employed in the pre-industrial development stage for the casting of long products or billets are the meniscus zone as the first coagulation zone. To separate from. It has been found that most of the surface defects of the product obtained by continuous casting may be healed by preventing meniscus from forming in the same zone where the solidification of the skin of the product begins. To do this, a copper mold is placed over the mold in such a way that a liquid steel liquid level or meniscus is located on the refractory transfer head but no longer on the actual copper mold and is called an element called a transfer head made of refractory. Thus upwards. Thus, the steel remains in liquid state in contact with the refractory constituting the transfer head and starts to solidify only when contacted with a metal mold formed from copper lying under the transfer head. The steel continuous casting method in which the fire resistant transfer head is placed on a copper mold is called thermal bath continuous casting.

In this regard, most of the research / development work was directly driven by horizontal thermal bath continuous casting technology, characterized in that the internal dimension of the refractory transfer head is smaller than the internal dimension of the mold, which is transferred because The wall of the head may not lie in the extension of the wall of the mold.

On the other hand, another recently developed technology, vertical thermal bath continuous casting, uses a fire-resistant transfer head in which the inner wall is in perfect alignment with the inner wall of the vertical continuous casting mold, within a mechanical fitting tolerance. The fire resistant transfer head is disposed above the vertical continuous casting mold. This type of casting prevents the typical defects present in horizontal warm bath continuous casting, such as "cold shuts," which are due to parasitic solidification of the refractory perpendicular to the casting axis and from horizontal to vertical. Because of the transformation of the transfer head technology, i.e., if only one, there is no alignment of the inner face of the mold and the inner face of the transfer head or seal between the transfer head and the mold, it also appears in vertical warm bath continuous casting.

The vertical warm bath continuous casting technique, in which the transfer head has an internal dimension equal to the internal dimension of the continuous casting mold, may be formed by the following elements.

The transfer head is configured such that its inner wall is in perfect alignment with the inner wall of the mold.

The fire resistant transfer head is placed on a continuous casting mold and acts as a "reservoir of liquid steel", the problem being mainly to meet the criteria for thermal shock resistance.

The presence of a fire resistant element called a "junction element" which lies between the transfer head and the continuous casting mold. The connection elements are placed directly above the mold and form thermal conductivity and thermal diffusivity, thermal shock resistance, mechanical wear resistance (due to contact with the solidified steel) and chemical resistance (due to contact with the liquid steel), and form the mold. The refractory is generally monoblock and seeps into the metal frame to increase the resistance to cracking as increasing thermal conditions are applied at the start of the casting. It must be prestressed.

Argon is injected between the copper continuous casting mold and the connection element to prevent the parasitic solidification of the steel from occurring at the bottom of the refractory.

Attempts made to industrially carry out the above technical development mainly apply to the vertical thermal bath continuous casting of products belonging to the billet form, ie products having small dimensions (up to 200 × 200 mm) and symmetrical (square or round) cross sections. This is usually done by a tubular mold formed as a single piece.

A number of problems have emerged in the practical construction of molds with transfer heads in an extension of the above development for vertical warm bath continuous casting of flat products, commonly called slabs. In particular, this problem is the practical implementation of fire resistant connection elements placed in direct contact with the upper edge of the copper mold which appears to be a major problem in industrial use.

This practical difficulty is related to the fact that there are major differences in construction between the molds used for billets and the molds used for slab or flat products. This means that compared to billet molds, slab molds have a large dimension, for example 200 × 2400 mm 2, a rectangular cross section with a long side to short side ratio of greater than 2, and are mechanically pressed in contact with each other and two small surfaces are separated between two large surfaces. This is because it is characterized by an assembly of four plates interposed therebetween. In this regard, the above dimensional features of the mold for vertical warm bath continuous casting of slabs can no longer be used in the case of vertical warm bath continuous casting in the form of billets for producing the connection elements. Once the composition of the component is provided, the component can no longer seep into the metal frame to fix the monoblock refractory, which technique leads to cracking of the connection element as increasing thermal conditions are applied at the start of casting. To increase the resistance.

The present invention relates to a device for continuous casting of molten metal, in particular for vertical hot-top continuous casting of flat steel products.

1 is a perspective view schematically showing a connection element formed from a bar;

An advantage of the apparatus according to the invention is that when used in connection with the vertical warm bath continuous casting of the slab, it is possible to:

To prevent cracking during the thermal shock at the start of casting in the refractory forming the connecting element.

Ensuring good alignment of the connection elements to the walls of the mold.

Ensuring that the connection elements are kept in place throughout the casting process.

Use minimum materials to limit the cost of manufacturing connection elements.

The apparatus described below provides the above advantages and provides a solution to the vertical warm bath continuous casting of the slab whose transfer head has the same internal dimensions as the copper mold.

According to the invention, a copper mold is used which extends along a transfer head made of refractory material, the transfer head being no longer a real copper mold, although a liquid steel level or meniscus is placed on the refractory transfer head during a continuous casting operation. An apparatus for vertical warm bathing continuous casting of molten metal in slab form disposed over a mold in such a way that it is not positioned, the refractory connection element lying between a copper mold and the refractory transfer head, wherein the connection element is then And at least four elongated elements, referred to as bars, wherein the assembly forms a connection element of an internal shape that is identical to the internal shape of the mold while being arranged in such a way that the inner surface of the connection element is an extension of the corresponding inner surface of the mold. , (the width of the bar) ³ × (height of bar) ÷ (the length of the bar) ³ is less than 0.025 ㎜ inde, i.e. (l ³ and h × L ^-3) ≥ 0.025 ㎜, where h denotes the dimension of the height of the bar substantially parallel to the direction of movement of the slab cross-section, l is the width of the substantially vertical bars in the direction of movement of the slab cross-section Where L represents the length of the bar, the units of all dimensions being mm.

According to a preferred embodiment of the device of the invention, the bar may comprise at least two elements lying longitudinally between the ends.

According to one embodiment of the device of the invention, the bar has a equilateral hexagonal shape as the outer surface, and the cross section of the bar has a height to width ratio of 0.3 to 0.2.

For the connection function between the mold and the transfer head over the connecting element including the bar, each bar is preferably chosen to have a cross section with a height to width ratio of about 0.5, which is to optimize the ability to withstand thermal shocks. will be. This is because, on the one hand, the solidified sheath of the slab that "raises" against the mold during the oscillation cycle should not be too small so as not to damage the upper refractory formed in the part of the transfer head which is mechanically weaker than the connecting element, Is not to be so large that it does not incur excessive costs in terms of refractory materials consumed to manufacture the connection elements.

According to another embodiment of the device of the present invention, each bar places the bar in perfect alignment within the mechanical mounting tolerances with the surface of the mold where the bar is an extension and prevents the bar from being pushed back by the slab. It is pressed against the rear stop which functions.

According to another embodiment of the device of the invention, each bar is processed by, for example, providing a fixed groove to receive a holdfast, the holdfast being in contact with the upper edge of the mold during the vibrational movement of the mold. The ability to press the bar vertically so that it remains in the center and move towards the center of the slab to prevent the bar from falling into the steel during the start of the continuous casting operation, thereby preventing the bar from moving out of alignment with the surface of the extending mold It provides a dual function of function.

Another non-essential embodiment relates to the working conditions for the connection elements. In fact, if the coefficient of thermal expansion of the refractory material used to make the connection element is about 4 × 10 ⁻⁶ K ⁻¹ , and the working temperature is about 1000 ° C., the bar on one surface of the slab mold, 2 m long, The longitudinal expansion will be about 8 mm. Thus, it is necessary to allow each bar to expand freely, and the means may be used for this purpose.

According to a preferred embodiment of the device of the present invention, a thin film of boron nitride (BN) is coated on the top surface of the copper mold supported by the connection element formed from the bar to allow the bar to expand.

According to another preferred embodiment of the device of the present invention, a thin layer of graphite paper is interposed between the holdfast and the top surface of the bar on which the holdfast acts.

According to another preferred embodiment of the device of the present invention, to allow the bars to expand, means are used to ensure that the various bars remain in contact with each other and are independent of the operating temperature, preferably various bars. The means for applying pressure in the longitudinal axis direction of is arranged in parallel along one surface of the mold to maintain contact with the various bars.

According to a preferred embodiment of the device of the invention, a high performance ceramic is used as the material for producing the bar, preferably the high performance ceramic is SiAlON + BN (SiAlON = silicon aluminum oxynitride; BN = boron nitride).

According to another preferred embodiment of the device of the invention, a SiAlON binder with fine particles (<0.1 mm) is used as the material for producing the bar.

Additional features and advantages of the invention are provided in the detailed description of the following examples. This description is illustrated and described by the schematic diagram of FIG. 1 attached without specific accumulation, in which only the elements necessary to understand the invention have been reproduced. Further, in order to better represent the dimensional characteristics of the bars as well as the positioning of the bars relative to each other, firstly some elements are not intentionally shown, and secondly the connection elements are shown by separating some of the bars.

The connection element lies between the mold 1 and the transfer head 2 for the continuous casting of the slab in connection with the transfer head and the continuous casting process such that the liquid steel liquid level or the meniscus S is located in the transfer head 2. . The mold 1 and the transfer head 2 are both drawn with broken lines to indicate their relative position to the connecting element without complicating and confusing FIG. 1.

The connection element is formed from bars 3, 4, 5, 6, 7 and 8 that sit on top of the mold 5. The bar is held in place by respective holdfasts 9, 10, 11 supporting the grooves R machined into the various bars. Other holdfasts are not shown for simplicity and ease of understanding of the drawings. The figure also shows only two elements 12, 13 which serve to engage the holdfasts 9, 11 and also hold the bar in position in order to prevent movement towards the center of the slab and in the opposite direction. It is showing the bay. Other elements of the same kind have been omitted for simplicity and ease of understanding of the drawings.

Therefore, the apparatus embodying the present invention has a good surface finish and very good internal soundness, so that the steel slab meets the standards required for specialty fields such as sheet metal for bodywork and beverage cans by means of vertical thermal bath continuous casting operation. To get it.

Claims (13)

Using a copper mold 1 extending along a transfer head 2 made of a refractory material, the transfer head 2 is a liquid steel liquid level or a meniscus S during the continuous casting operation. In a device for vertical warm bathing continuous casting of molten metal in the form of slabs, which is arranged on the mold 1 in such a way that it is located on the mold but is no longer located on the actual copper mold 1, A refractory connection element lying between a copper mold (1) and said refractory transfer head (2), The connection element comprises at least four elongated elements 3, 4, 5, 6, 7, 8, hereinafter referred to as bars, wherein the assembly of connection elements forms a connection element of an internal shape identical to the internal shape of the mold. The inner surface of the element is arranged to be an extension of the corresponding inner surface of the mold, (Width of the bar) ³ × (bar height) ÷ (length of the tube of the bar) ³ is 0.025 mm or less, ie (l ³ × h × L ^-3 ) ≥ 0.025 mm, where h is the progression of the slab The height is the dimension of the cross section of the bar approximately parallel to the direction, l represents the width, which is the dimension of the cross section of the bar approximately perpendicular to the advancing direction of the slab, and L represents the length of the bar, all dimensions being mm Device. The device of claim 1, wherein the bar comprises at least two elements disposed end to end in the longitudinal direction. The device according to claim 1 or 2, wherein the bar has a equilateral hexagonal shape as the outer surface and the cross section of the bar has a height to width ratio of 0.3 to 2.0. 4. The bar according to one or more of the preceding claims, wherein each bar (4, 6) places the bar and the surface of the mold in which the bar is an extension in complete alignment within the mechanical mounting tolerances and the bar And pressurizes against the rear stop (12, 13) which functions to prevent pressurization to the rear. The method according to claim 1, wherein each bar 4 is machined to receive a hold fast 9 (R), the hold fast 9 being adapted to the mold during vibration of the mold. The ability to press the bar vertically so that it remains in contact with the upper edge, and move it towards the center of the slab to prevent the bar from moving out of alignment with the surface of the extending mold so that the bar can be And providing a dual function of preventing the fall into the device. 6. The boron nitrite (BN) thin film is coated on the top surface of the copper mold supported by the connection element formed from the bar to allow the bar to expand. Device. 6. A device according to one or more of the preceding claims, wherein a thin layer of graphite paper is interposed between the holdfast and the top surface of the bar on which the holdfast acts to allow the bar to expand. 8. Apparatus according to one or more of the preceding claims, wherein means are used to allow the various bars to remain in contact with each other regardless of the operating temperature in order to allow the bars to expand. The device of claim 8, wherein the pressure application means in the longitudinal direction of the various bars are arranged in parallel along one surface of the mold to keep the various bars in contact. 10. The device of claim 9, wherein the pressure applying means in the longitudinal direction of the various bars is a compression spring. Device according to one or more of the preceding claims, characterized in that a high performance ceramic is used as the material for producing the bar. The device of claim 11, wherein the high performance ceramic is SiAlON + BN (SiAlON = silicon aluminum oxynitride; BN = boron nitride). The device according to one or more of claims 1 to 10, which is used as a material for producing alumina bars containing SiAlON binders having fine particles (<0.1 mm).