JP2002531273A - Equipment for vertical hot-top continuous casting of molten metal - Google Patents

Abstract

(57) [Summary] An apparatus for continuous hot-top casting of molten metal in the form of a slab uses a copper mold (1) extended by a supply head (2) made of a refractory material. 2) the mold (1) in such a way that the liquid steel level, or meniscus (S), is located in said refractory supply head (2) and no longer in the actual copper mold (1) during the continuous casting operation. ). A refractory connection element consisting of bars (3), (4), (5), (6), (7), (8) is placed between the copper mold (1) and the supply head (2). The bars are arranged in such a way that their assembly defines a connecting element of the same internal shape as the internal shape of the mold, and that the inner surface of said element is an extension of the inner surface of the corresponding mold. Additionally, the product of the cube of the bar width multiplied by the bar height and dividing by the cube of the bar tube length is greater than or equal to 0.025 mm, ie (l ³ * h * L ⁻³ )> = 0.025 mm. Furthermore, the bars are of the parallelepiped shape, their cross-section having a ratio of height to width between 0.4 and 0.6. On the one hand, each bar (4), (6) is pressed against the rear stop (12), (13), the function of which is to perfectly align the bar with the surface of the mold, which is an extension of the bar, within a mechanical fixing error. And to prevent the bars from being pushed backwards by the slab, while each bar (4) is machined (R) to accommodate a stop (9). The ability to press the bar vertically so that the bar remains in contact with the upper edge of the mold during the amplitude motion of the mold and the bar moves towards the center of the slab, especially at the beginning of a vertical hot-top continuous casting operation. To prevent movement from alignment with the surface of the extending mold.

Description

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL FIELD The present invention relates to an apparatus for continuous casting of molten metal, particularly in connection with vertical hot-top continuous casting of flat steel products.

Prior art Continuous casting is a popular technique, which allows steel to be cast directly from a casting vessel into a bottomless mold, from which it is extracted in the form of a partially solidified continuous strand. The casting vessel is usually a ladle or tundish; for simplicity it is generically designated here as a tundish.

[0003] The bottom of the tundish is usually perforated to cooperate with a closure member of a known type. The casting nozzle is fixed below the tundish coaxially with the tap hole, said nozzle being freely submerged in the upper part of the mold body. This mold is made of copper and cooled by water. In addition, the mold is normally driven in its longitudinal amplitude movement with an amplitude of a few millimeters to prevent the steel from sticking to the walls of the mold.

In operation, the liquid metal flowing from the tundish into the mold via a refractory nozzle submerged or unsubmerged below the level of the liquid steel located at the top of the mold or under the meniscus is recirculated in the meniscus Creates turbulence in the form of loops or waves on the free surface of steel. Further, it has proven very difficult to maintain a strictly constant level of steel in the mold, mainly when the steel flow rate is high and the mold has a small cross section. The combination of the above phenomena and the fact that the steel begins to solidify at the meniscus, ie in contact with the walls of the copper mold, results in the appearance of surface defects in the product casting.

[0005] This surface quality problem is particularly acute in the continuous casting of flat products such as slabs. Because many product castings of these types are intended for so-called "special" applications, such as sheet metal for bodywork or beverage cans, they require a base casting product without surface defects.

Although research has been carried out over the years to ameliorate the above problems, the most useful solution adopted at this time in the pre-industrial development phase for the casting of long products or billets is mainly the meniscus zone. Consists in separating from the coagulation zone. It has been found that most surface defects on products obtained by continuous casting can be rescued by preventing a meniscus from being established in the same region where solidification of the shell of the product begins. . To do this, the copper mold is extended upward by an element called a supply head made of a refractory material, and this element is a liquid steel level, or a meniscus, which is located in said refractory supply head and no longer contains the actual copper. It is placed on the mold in such a way that it is not located in the mold. Thus, the steel is kept in a liquid state in contact with the refractory material from which the feed head is made up, and begins to solidify only when in contact with a metal mold formed from copper which sits under the feed head. The latter method of continuous casting of steel with a refractory feed head placed on a copper mold is called hot-top continuous casting.

In connection with the foregoing, most research / development work has been directly inspired by the horizontal hot-top continuous casting technique, and the internal dimensions of the refractory feed head have been reduced to the interior of the mold (where they are located). It is characterized by being smaller than the dimensions, so that the wall of the supply head must not rest on an extension of the wall of the mold.

[0008] On the other hand, another recently developed technique, vertical hot-top continuous casting, is a method in which the inner wall of the refractory feed head is placed within a vertical continuous casting mold (on which it is positioned) within mechanically fixed tolerances. Use a refractory supply head that is perfectly aligned with the inner wall. This aspect of casting prevents typical defects present in horizontal hot-top continuous casting, such as "cold shut". Cold shuts can be attributed to parasitic solidification on the surface of the refractory perpendicular to the casting axis, which is also due to the horizontal to vertical conversion of feed head technology, i.e. the feed head on the inner surface of the mold or if present. The lack of alignment with the inner surface of the seal between the feed head and the mold will also appear in vertical hot top continuous casting.

The above described technique of vertical hot-top continuous casting with a feed head having the same internal dimensions as the continuous casting mold can be defined by the following factors:-its inner wall is perfectly aligned with the inner wall of the mold. A supply head configured to:-the refractory supply head is positioned above a continuous casting mold and acts as a "liquid steel reservoir"; the supply head in question is primarily based on thermal shock resistance; The presence of a refractory element called a "connecting element" located between the feed head and the continuous casting mold, the connecting element being located just above the mold and having thermal conductivity and heat Certain criteria for the degree of diffusion, thermal shock resistance, mechanical wear resistance (contact with solidified steel) and chemical resistance (contact with liquid steel) and the permissible machinability to form it. And the refractory is generally a monoblock, necessarily inevitably by setting in a metal frame to increase its resistance to cracking when subjected to increasing thermal conditions at the start of casting. Prestressed; argon is injected between the continuous copper casting mold and the connecting element to prevent parasitic solidification of the steel at the bottom of the refractory.

[0010] The tests carried out to carry out the above technical development industrially have mainly consisted of products of the billet type, ie of small dimensions (maximum 200 × 200 mm) and of symmetrical (square or round) cross section. Applied to vertical hot top continuous casting, this was generally done by a tubular mold formed as a single piece.

[0011] The extension of the above development to vertical hot-top continuous casting of flat products (commonly referred to as slabs) has revealed a number of problems with the actual configuration of molds with feed heads. In particular, it is a practical realization of a refractory connecting element placed directly in contact with the upper edge of the copper mold, which seems to pose a major problem in its industrial implementation.

The practical difficulties described above are related to the fact that there is a great difference in the configuration between the billet mold and the slab or flat product mold. This is characterized in that, compared to the billet mold, the slab mold has a large dimension (for example 200 × 2400 mm ² ) due to the rectangular cross-section where the ratio of the long side to the short side is greater than ² , and is further mechanically pressed against each other. Because it is characterized by an assembly of four plates (two small faces sandwiched between two large faces). In this context, the above-mentioned dimensional features of the mold for vertical hot-top continuous casting of slabs make use of the technology defined in the case of billet-type vertical hot-top continuous casting to make connecting elements. No longer possible. Given the shape of the elements, they can no longer be sewn into a metal frame to secure the monoblock refractory-this technique requires that the connecting element be subjected to increasing thermal conditions at the start of casting. To increase the crack resistance.

The advantages of the device according to the invention include its use in connection with vertical hot-top continuous casting of slabs:-Prevents the refractory of which the connecting element is made from cracking upon thermal shock at the start of casting -Ensuring that there is a good alignment of the connecting element with the mold wall;-ensuring that the connecting element is held in place throughout the casting operation; Using a minimum amount of material to limit the cost of making;

[0014] The apparatus described below provides the above-mentioned advantages, and thus provides a solution for vertical hot-top continuous casting of slabs with a feed head having the same internal dimensions as the copper mold.

According to the present invention, copper extended by a supply head made of a refractory material
Apparatus for vertical hot-top continuous casting of molten metal in slab form using a mold
Wherein the feed head is a liquid steel level, or the meniscus is during a continuous casting operation.
One that is located in the refractory supply head described above and is no longer located in the actual copper mold
Wherein the copper mold is disposed above the mold in a formula.
Including a refractory connection element located between the flammable supply heads, wherein said connection element is reduced.
And four long elements (hereinafter referred to as bars), said elements being
The stand defines a connecting element having the same internal shape as that of the mold, and the inner surface of the element is cast.
Being arranged in such a way as to be an extension of the corresponding inner surface of the mold, and the width of the bar
Is multiplied by the height of the bar and divided by the cube of the length of the bar.
Product is greater than or equal to 0.025 mm, ie (l³* H * L ^-3 )> = 0.025 mm (where h is substantially parallel to the direction of travel of the slab)
Represents the height, which is the cross-sectional dimension of a simple bar, and l is a bar approximately perpendicular to the direction of travel of the slab.
Represents the width, which is the dimension of the cross-section of L, where L is the length of the bar and all these dimensions are m
m).

According to a preferred embodiment of the device according to the invention, the bar can be composed of at least two elements placed longitudinally end to end.

According to one embodiment of the device of the invention, the bar has a parallelepiped shape as an outer surface and the cross section of the bar has a height to width ratio between 0.3 and 2.0.

With respect to the function of the connection between the mold and the supply head, which is entrusted to a connecting element composed of bars, each bar is preferably such that it has a height-to-width ratio close to 0.5. It is chosen to have a cross-section, which is to optimize its ability to withstand thermal shock. This is on the one hand because the solidification shell of the slab that "rises" with respect to the mold during the amplitude cycle must not be too low in height so that the upper refractory formation of the feed head is mechanically weaker than the connecting element. On the other hand, the height must not be too large so as not to introduce excessive costs with regard to the refractory material consumed to make the connection element.

According to another embodiment of the device of the invention, each bar is pressed against a rear stop. The function of the rear stop is to position the bar within mechanical seating tolerances in perfect alignment with the face of the mold at the extension of the bar, and to prevent the bar from being pushed back by the slab.

According to yet another embodiment of the device of the invention, each bar is machined to accommodate a stop, for example by providing a fixing groove in it, the stop having two functions. On the one hand, the function of vertically pressing the bar so that the bar during the amplitude movement of the mold remains in contact with the upper edge of the mold, and on the other hand the mold in which the bar is extended by the bar moving towards the center of the slab To prevent the bar from moving out of alignment with the surface and possibly preventing the bar from falling into the steel at the beginning of the continuous casting operation.

Another important feature relates to the operating conditions of the connection element. In fact, the refractory material used to make the connection element has a coefficient of thermal expansion of about 4 × 10 ⁻⁶ K ⁻¹ ,
And given the operating temperature is close to 1000 ° C., the longitudinal expansion of the bar on one side of the 2 m long slab mold will be close to 8 mm. Therefore, each bar must be inflatable, and the means described below are used to achieve this.

According to a preferred embodiment of the device according to the invention, for the purpose of allowing the bar to expand, a thin film of boron nitride (BN) is placed on the upper surface of the copper mold on which the connecting elements formed from the bar are supported. Coated.

According to another preferred embodiment of the device according to the invention, for the purpose of making the bar expandable, a thin layer of graphite paper is placed between the upper surface of the bar on which the stop acts and the stop. Inserted.

According to yet another preferred embodiment of the device of the invention, means are used for ensuring that the individual bars remain in contact with each other for the purpose of allowing the bars to expand, Is independent of the operating temperature of the bars; preferably the means exerts a pressure in the direction of the longitudinal axis of the individual bars juxtaposed along one side of the mold to keep the individual bars in contact, this effect Is obtained, for example, by a compression spring.

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

According to another preferred embodiment of the device of the invention, fine (<0.1 mm) SiA
Alumina with 1ON binder is used as a material to make the bar.

Further features and advantages of the present invention are given in the following detailed description of actual illustrative examples.
This description is illustrated by the accompanying FIG. 1, which is a schematic representation without any particular scale, in which only those elements necessary for understanding the invention have been reproduced. In addition, to better show the dimensional characteristics of the bars as well as their arrangement with respect to each other,
First, certain elements are not consciously depicted, and second, connecting elements are shown by separating some of the bars.

FIG. 1 is a perspective view schematically showing a connecting element formed from a bar, the connecting element being a continuous steel slab such that the liquid steel level or meniscus (S) is located in the supply head (2). It is located between a casting mold (1) for casting and a feeding head (2) associated with a continuous casting method having a feeding head, both said casting mold (1) and the feeding head (2) complicating FIG. They are simply drawn in dashed lines for the purpose of indicating their relative position with respect to the connecting elements in order to avoid confusion.

The connecting elements are bars (3), (4), (5), (6) placed on top of the mold (1).
, (7) and (8). The bars are held in place by respective stops (9), (10), (11) supported in grooves (R) machined into the individual bars. Other stops are not shown to simplify the figure and make it easier to understand. In addition, the figure shows two elements (12) which serve to secure the stops (9) and (11) and to hold the bar in place to prevent movement both towards the center of the slab and in the opposite direction. ) And (13) are shown. Other elements of the same type have also been omitted to simplify the drawing and make it easier to understand.

The device for carrying out the invention therefore has a good surface finish and a very good internal soundness, and consequently the necessary standards for specific applications such as bodywork and sheet metal for beverage cans Steel slabs conforming to the above can be obtained by a vertical hot-top continuous casting operation.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically illustrating a connecting element formed from a bar placed between a mold and a supply head.

────────────────────────────────────────────────── ─── [Continuation of summary] Pressed against (12), (13), the function is to place the bar in perfect alignment with the mold surface, which is an extension of the bar, within the mechanical fixing error, and the bar is The purpose of this is to prevent the slab from being pushed back backwards, while on the other hand each bar (4) is machined (R) to accommodate the stop (9), which stop is the mold stop. The ability to vertically press the bar so that it remains in contact with the upper edge of the mold during amplitude movement and the bar is extended by moving it towards the center of the slab, especially at the start of a vertical hot-top continuous casting operation It provides two functions, one to prevent movement from alignment with the mold surface.

Claims (13)

[Claims] An apparatus for continuous hot-top casting of molten metal in the form of a slab using a copper mold (1) extended by a supply head (2) made of a refractory material, the apparatus comprising: Supply head (2) is liquid steel level or meniscus (S
) Is positioned on said mold (1) in such a way that it is located in said refractory supply head (2) during the continuous casting operation and is no longer located in the actual copper mold (1); It comprises a refractory connection element placed between said copper mold (1) and said refractory supply head (2), said connection element comprising at least four long elements (
(3), (4), (5), (6), (7), (8) (hereinafter referred to as a bar), wherein the element has a connection element whose internal shape is the same as the internal shape of the mold. And that the inner surface of the element is arranged in such a way that it is an extension of the inner surface of the corresponding mold, and the cube of the bar tube is multiplied by the cube of the bar width to the height of the bar. The product of the length divided by the cube of 3 must be greater than or equal to 0.025 mm, that is, (l ³ * h * L ^-3 )> = 0.025 mm (where h is the direction of travel of the slab) Represents the height, which is the dimension of the cross-section of the substantially parallel bar, l represents the width, which is the dimension of the cross-section of the bar substantially perpendicular to the direction of travel of the slab, L is the length of the bar, all these dimensions Is expressed in mm). 2. Apparatus according to claim 1, wherein the bar can be composed of at least two longitudinally end-to-end elements. 3. The bar according to claim 1, wherein the outer surface has a parallelepiped shape and the cross section of the bar has a height to width ratio of between 0.3 and 2.0.
Or the apparatus according to 2. 4. Each bar (4), (6) has its function placed in perfect alignment with the face of the mold, which is an extension of the bar within mechanical seating error, and the bar is pushed back by the slab backwards. 4. Device according to one or more of the preceding claims, characterized in that it is pressed against a post-stop (12), (13), which is to prevent indentation. 5. Each bar (4) is machined (R) to accommodate a stop (9), this stop having two functions, one of which allows the bar to move during the amplitude movement of the mold. The ability to press the bar vertically to remain in contact with the upper edge of the slab, and on the other hand to prevent the bar from moving out of alignment with the surface of the extending mold by moving the bar towards the center of the slab, and continuous casting Apparatus according to one or more of the preceding claims, characterized in that it provides the function of possibly preventing the bar from falling into the steel at the start of the operation. 6. A bar for inflatable purposes, characterized in that a thin film of boron nitride (BN) is coated on the upper surface of the copper mold on which the connecting elements formed from the bar are supported. An apparatus according to one or more of claims 1 to 5. 7. A bar for inflatable purposes, characterized in that a thin layer of graphite paper is inserted between the upper surface of the bar on which the stop and the stop work. An apparatus according to one or more of the preceding claims. 8. Means are used to ensure that the individual bars remain in contact with each other, which is independent of the operating temperature and is characterized by the purpose of making the bars inflatable. An apparatus according to one or more of clauses 1 to 7. 9. The method of claim 8, wherein said means exerts pressure in the direction of the longitudinal axis of the individual bars juxtaposed along one side of the mold to keep the individual bars in contact. apparatus. 10. Apparatus according to claim 9, wherein the means for exerting pressure in the direction of the longitudinal axis of the individual bar is a compression spring. 11. The device according to claim 1, wherein a high-performance ceramic is used as a material for making the bar. 12. The high performance ceramic is made of SiAlON + BN (SiAlON =
12. The device according to claim 11, wherein silicon aluminum oxynitride; BN = boron nitride). 13. The bar according to claim 1, wherein alumina having fine (<0.1 mm) SiAlON binder is used as material for making the bar.
An apparatus according to one or more of the preceding claims.