CN108856667B - Method for receiving slabs during continuous casting - Google Patents

Abstract

The invention provides a method for receiving slabs during continuous casting, which provides casting a slab (S) along a casting axis (C), said slab (S) having a predefined width (W1), wherein the method provides for receiving the slab (S) with a plurality of rollers (11, 12), said rollers (11, 12) being arranged facing each other in pairs, and said rollers (11, 12) defining a passage for the cast slab (S) along the casting axis (C), wherein the plurality of rollers (11, 12) comprises electromagnetic rollers (12), the electromagnetic rollers (12) being provided with an electromagnetic stirrer (13) for stirring a liquid contained in the slab (S).

Description

Method for receiving slabs during continuous casting

Technical Field

The present invention relates to a method for receiving slabs (containing a slab) during continuous casting.

Background

Electromagnetic rolls have been widely used in the steel making industry since the 60's of the 20 th century. In fact, electromagnetic rollers are used to keep the molten steel stirred to increase the internal integrity of the slab.

Currently, thicker and thicker slabs are produced, resulting in longer metallurgical lengths. This makes the potential location for using an electromagnetic roller under the meniscus lower.

At the same time, slabs are becoming wider and wider due to the demand for higher production rates and more types of applications. The two aforementioned slab production trends present significant challenges to the electromagnetic rolls themselves. In fact, the electromagnetic rolls cannot undergo too great a mechanical deflection under the action of the hydrostatic pressure of the molten iron.

Generally, steel mills only accept very small mechanical deflections to ensure defect-free production of slabs. The high deflection of the slabs not only leads to surface and internal cracks, but may also affect the stability of the bath due to expansion effects.

This expansion behaviour disturbs the steel meniscus and leads to powder entrapment, which significantly affects the quality of the steel grade. This effect occurs even when the roller is far from the meniscus.

In this casting machine, therefore, it is necessary to design the electromagnetic rollers so as to ensure that the mechanical deflections of the slab are minimal, and in any case not greater than the limit set by the machine manufacturer.

Theory of the beam teaches that the deflection is determined by the loading conditions and the mechanical dimensions and properties of the electromagnetic roller; the load condition refers to the type of load and the location where the load is distributed on the beam.

The problem is how to mechanically design an electromagnetic roll that can withstand as much ferrostatic pressure as possible with the least possible deflection, while keeping in mind that the diameter of the roll remains comparable to the diameter of the adjacent roll. In addition to these considerations, the electromagnetic properties must be kept high to provide metallurgical benefits to the slab.

Typically, the load is distributed symmetrically on the slab. In a certain position down in the caster, for a slab of a certain thickness and width, with conventional one-piece rolls, the ferrostatic pressure may be so high that the roll deflection is too great to meet the machine manufacturer's needs.

In fact, three possible solutions are known and have been used in order to limit the flexing of the roll, each solution having specific drawbacks.

A first known solution is to increase the diameter of the electromagnetic roller in order to increase the resistance area of the roller cross section. This is possible in theory but generally not in practice, since the diameter of the electromagnetic roll should be coordinated with the adjacent roll and the nip roll of the segment. This may therefore have an influence on the expansion behaviour and the cracking rate of the slabs.

A second known solution is based on the length of the roller, since the length of the roller plays a major role in the deflection. For slabs with a width greater than 2500mm, the electromagnetic roller can be divided into two rollers with half the length to control mechanical deflection while ensuring a higher level of electromagnetic force on the molten steel.

This solution based on divided electromagnetic rollers is described in patent US2015/0290703 and has been used in industrial production for several years. However, if the length of the rolls becomes too short, i.e., the slab is shorter than 2500mm, the electromagnetic force is not sufficient to efficiently stir the molten steel and improve the internal soundness of the slab due to the half length of the electromagnetic rolls.

This occurs because the electromagnetic force is proportional to the pole pitch of the electromagnetic roller, which is related to the length of the electromagnetic roller. Therefore, the shorter the length of the electromagnetic roller, the weaker the electromagnetic force.

A third known solution is the embodiment known as a support roller. Instead of converting the roll barrel into two barrels, a support roller is installed in the middle of the electromagnetic roller to support the electromagnetic roller. This idea is attractive, but this simple solution presents major drawbacks in the practice of industrial production.

Under industrial production conditions, close and good contact cannot be ensured at all, since particles or objects of different sizes, such as mill scale, are introduced between the electromagnetic roll and the support roll. Therefore, both the electromagnetic roller and the support roller have signs of accelerated wear or are damaged in many cases.

With this solution, the service life of the electromagnetic roller and the support roller is greatly shortened, resulting in an excessively high maintenance cost. This solution is therefore not industrially reliable.

Accordingly, there is a need for a method and apparatus for receiving slabs for a continuous caster that overcomes at least one of the disadvantages of the prior art.

It is an object of the present invention to provide a method for bearing a slab against a continuous casting machine which allows limiting the lateral deflections of the slab, even in the bearing zone where the slab is subjected to significant ferrostatic pressure, while ensuring the necessary electromagnetic forces capable of ensuring high efficiency of stirring the liquid metal in the core or inside of the slab.

Another object of the present invention is to provide a method for receiving slabs during continuous casting which allows to ensure that the diameter of the electromagnetic rolls is coordinated with the diameter of the adjacent rolls, thus facilitating the joining of the electromagnetic rolls in the section located downstream of the casting plant.

Another object of the present invention is to provide a method for withstanding slabs during continuous casting, in which the electromagnetic stirring forces on the molten steel are more uniform along the slab width, resulting in better metallurgical results.

The applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain the advantages hereinafter described.

Disclosure of Invention

The present invention has been set forth in embodiments thereof and the principal features of the invention as well as other features of the invention or variations of the principal inventive concept have been described.

In accordance with the above purposes, the present invention relates to a method for receiving a slab during continuous casting, which provides for casting the slab along a casting axis. The blank has a predefined width.

The method also provides for receiving the slab with a plurality of rolls, the rolls being disposed facing each other in pairs and defining a channel for the cast slab along the casting axis.

The plurality of rollers includes electromagnetic rollers provided with an electromagnetic stirrer configured for stirring a liquid contained in the slab.

In use, the electromagnetic roller has a length less than the width of the slab, such that the slab projects with at least one projecting portion with respect to at least one end of said electromagnetic roller.

By means of the bearing method of the invention, the lateral deflection of the slab is limited, even in the bearing zone where the slab is subjected to significant ferrostatic pressure, while ensuring the necessary electromagnetic force of the liquid metal in the core or interior of the slab.

The present invention maintains the deflection of the electromagnetic rollers within acceptable values without the use of support rollers in wider slabs and/or when used in lower locations where ferrostatic pressure is higher.

According to another embodiment, the slab projects by an unsupported width of up to 300mm, preferably up to 250mm, with respect to one end of the electromagnetic roller, and said projecting portion is unsupported by the roller. In particular, the unsupported width of the slab is not in contact with or supported by the rollers, while other portions of the slab are adequately supported by the electromagnetic rollers.

According to one embodiment, each of the electromagnetic rollers is associated with a respective auxiliary bearing roller aligned and coaxial with the respective electromagnetic roller.

Embodiments of the present invention also relate to a casting apparatus comprising a mold configured to cast a slab and a plurality of rolls disposed in pairs facing each other along a casting axis to define a channel for the cast slab. The plurality of rollers includes electromagnetic rollers provided with an electromagnetic stirrer configured to stir the liquid contained in the slab. The electromagnetic roller has an in-use length smaller than the width of the slab so that the slab projects with respect to one end of said electromagnetic roller.

Drawings

These and other features of the invention will become apparent from the following description of some embodiments, given as non-limiting examples with reference to the accompanying drawings, in which:

FIG. 1 is a schematic view of a continuous caster according to the present invention;

FIG. 2 is a sectional view along section line II-II of FIG. 1;

FIG. 3 is a sectional view along section line III-III of FIG. 2;

FIG. 4 is a side view of FIG. 1;

FIG. 5 is a variation of FIG. 2;

FIG. 6 is a variation of FIG. 3;

FIG. 7 is a side view of FIGS. 5 and 6;

fig. 8 is a perspective view of an embodiment of the present invention.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is to be understood that elements and features of one embodiment may be readily incorporated into other embodiments without further recitation.

Detailed Description

Reference will now be made in detail to the various embodiments of the invention, one or more examples of which are illustrated in the figures. Generally, only the differences with respect to the respective embodiments are described. Each example is provided by way of illustration of the invention and is not intended to be limiting of the invention. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the present invention include such modifications and variations.

The embodiments described herein with reference to fig. 1 to 8 relate to a method for receiving slabs (conforming a slab) during continuous casting.

The method provides for casting a slab S along a casting axis C of the casting apparatus 10.

According to one embodiment of the invention, the slab S is cast in a mould 15.

At the outlet of the die 15, the slab S has a solidified outer skin and the inner or core of the slab S is still liquid.

The slab S has a predefined width W1. The width W1 of the slab S may be comprised between 1500mm and 3000mm, preferably between 1800mm and 2500 mm.

The method provides for the bearing of the slab S with a plurality of rollers 11, 12.

The rolls 11, 12 are arranged facing each other in pairs along the casting axis C.

The rolls 11, 12 define a passage for the cast slab S.

The rolls 11, 12 are free to rotate about respective axes of rotation perpendicular to the casting axis C.

According to one embodiment, the plurality of rolls includes a holding roll (holding roll)11 configured to exert only a holding action on the slab S during continuous casting. The resist roller 11 does not have an electromagnetic stirring function, that is, the resist roller 11 does not have a magnetic stirrer as described below.

The bearing rollers 11 can be arranged facing each other in pairs with respect to the casting axis C or the slab S.

The length of the receiving rolls 11 may be substantially equal to the width W1 of the cast slab S.

According to a solution not shown in the figures, the bearing roller 11 may comprise two or more parts. For example, the resist roller 11 may be defined by two or more cylinders: the two or more cylinders are axially aligned with each other and supported at their respective ends by a support element.

This solution allows increasing the resistance of the bearing rollers 11 to flexing, ensuring that the ferrostatic pressure of the slab S is borne.

Further, the plurality of rollers includes a plurality of electromagnetic rollers 12.

According to an embodiment, the electromagnetic rolls 12 can be arranged facing each other in pairs with respect to the casting axis C or the slab S.

According to another embodiment, the electromagnetic roller 12 or at least one of the electromagnetic rollers 12 may be disposed to face one of the receiving rollers 11.

According to other embodiments of the invention, the electromagnetic rollers 12 may be arranged on only one side with respect to the slab S.

The electromagnetic rollers 12 are arranged facing the core of the slab S along the casting axis C so as to stir the liquid.

The electromagnetic rollers 12 are provided with an electromagnetic stirrer 13, and the electromagnetic stirrer 13 stirs the liquid contained in the slab S.

According to one solution, the electromagnetic stirrer 13 is housed inside the electromagnetic roller 12.

In other embodiments (fig. 1), the electromagnetic rollers 12 are also arranged opposite one another in pairs with respect to the slab S along the casting axis C, so as to exert an action of bearing the slab S and also of stirring the liquid still present in the slab S.

Each electromagnetic stirrer 13 may comprise at least one electromagnetic inductor arranged within the respective electromagnetic roller 12.

In particular, the electromagnetic stirrer 13 generates a magnetic field and a corresponding electromagnetic force 17.

The electromagnetic force 17 generates a plurality of recirculation circuits 16 inside the liquid contained in the slab S, i.e. inside the surface layer.

According to a possible embodiment, the electromagnetic roller 12 has a length L greater than 1400mm and preferably less than 2500 mm.

The electromagnetic rollers 12 are supported at their ends by respective support elements 26, the support elements 26 being adapted so as not to interfere with the surface of the slab S.

During casting, the length L of the electromagnetic rolls 12 is less than the width W1 of the slab S, so that the slab S protrudes with respect to one end of said electromagnetic rolls 12.

Therefore, during casting, the slab S has the projecting portions 20 not in contact with the electromagnetic rolls 12.

Further, the projecting portion 20 projects in a direction parallel to the rotational axis of the electromagnetic roller 12 with respect to the electromagnetic roller 12.

In particular, it is provided that: the electromagnetic rolls 12 have a bearing surface configured to bear the slab S being cast during use and having said length L. The slabs S thus project with respect to the side edges of said bearing surface of the electromagnetic roller 12.

The bearing surface is the surface that is in direct contact with the slab S being cast during use. Therefore, the protruding portion 20 does not contact the receiving surface. The bearing surface has a cylindrical shape.

In this way, despite the presence of the projecting portion 20, the slabs S are supported in a stable manner, preventing excessive flexing and ensuring the necessary electromagnetic force of the electromagnetic stirrer 13.

According to one embodiment (fig. 2 to 4), the slab S projects with respect to one end of the electromagnetic roller 12 by an unsupported width W2 of up to 300mm, preferably up to 250 mm.

Therefore, only a small portion of the slab S is unsupported by the electromagnetic rollers 12. The steel located in the edges of the slab S solidifies almost completely at this position below the casting machine and this unsupported area is not a disadvantage in terms of quality.

According to another embodiment of the invention, the ratio between the unsupported width W2 of the slab S projecting outwards, i.e. transversely to the electromagnetic roller 12, and the width W1 of the slab S is comprised between 2% and 20%, preferably between 2.5% and 16%.

According to one embodiment of the invention (fig. 4, 7 and 8), the electromagnetic rolls comprise a first electromagnetic roll 12 and at least a second electromagnetic roll 12 spaced from each other along the casting axis C.

Although in the following reference is made to a first electromagnetic roller and a second electromagnetic roller, it is not excluded that the same teachings can be applied to more than two electromagnetic rollers.

According to an embodiment, a first electromagnetic roller 12 may face another first electromagnetic roller 12 so as to define a first pair 18 of electromagnetic rollers 12.

According to other embodiments, the second electromagnetic roller 12 may face another second electromagnetic roller 12 so as to define a second pair 19 of electromagnetic rollers 12.

A plurality of the receiving rollers 11 may be disposed between the first electromagnetic roller 12 and the second electromagnetic roller 12 to receive and support the slab S.

According to an embodiment, the first electromagnetic roller 12 and the second electromagnetic roller 12 are arranged such that: a first edge 21 of the slab S projects with respect to the first electromagnetic roller 12, while a second edge 22, opposite the first edge 21, projects with respect to the second electromagnetic roller 12.

This arrangement of the electromagnetic rollers 12 allows to maximize and homogenize as much as possible the molten steel recirculation circuit 16 as shown in figures 4 and 7.

In fact (fig. 4), this particular arrangement of the first electromagnetic roller 12 and of the second electromagnetic roller 12 allows to obtain the following distribution of the recirculation circuit 16: the recirculation loops 16 are evenly distributed in the area between the first electromagnetic roller 12 and the second electromagnetic roller 12.

In particular, to generate these recirculation circuits 16, the electromagnetic force 17 generated in the first electromagnetic roller 12 is directed in a first direction, which is opposite to a second direction: the electromagnetic force 17 generated in the second electromagnetic roller 12 is guided in the second direction.

Preferably, the unsupported width W2 of the projecting portion 20 projecting outside the first electromagnetic roller 12 is equal to the unsupported width W2 of the projecting portion 20 projecting outside the second electromagnetic roller 12.

According to a possible solution of the invention, one of said electromagnetic rollers 12 is positioned directly below the mould 15.

According to another embodiment (fig. 5 to 8), each of the electromagnetic rollers 12 is associated with a respective auxiliary backup roller 14 if the unsupported width W2 of the slab S is excessively long, wherein the auxiliary backup rollers 14 are aligned and coaxial with the respective electromagnetic rollers 12.

Thus, the electromagnetic rollers 12 support most of the slab S, and the auxiliary receiving rollers 14 support the remaining portion of the slab S, i.e., the overhang portion 20.

The auxiliary receiving roller 14 does not have an active electromagnetic inductor inside, but has only a supporting function.

The length K of the auxiliary bearing roller 14 may be equal to or greater than the unsupported width W2.

Preferably, it is provided to use the auxiliary bearing rollers 14 in the case where the ratio between the unsupported width W2 and the width W1 of the slab S is comprised between 10% and 40%.

According to a possible embodiment, the length K of the auxiliary backing roll 14 is comprised between 10% and 40% of the length L of the respective electromagnetic roll 12.

According to a possible solution of the invention (fig. 5 to 8), each electromagnetic roller 12 and the respective auxiliary bearing roller 14 associated with this electromagnetic roller 12 are supported by said supporting element 26.

In particular, the supporting elements 26 are configured to support one of the electromagnetic rollers 12 and the respective auxiliary bearing roller 14 one after the other along the axis and directly adjacent to each other.

According to a possible embodiment (fig. 7 and 8), the first electromagnetic roller 12 comprises a respective auxiliary bearing roller 14 arranged in alignment with the first electromagnetic roller 12, and the second electromagnetic roller 12 comprises a respective auxiliary bearing roller 14 arranged in alignment with the second electromagnetic roller 12.

The auxiliary receiving roller 14 associated with the first electromagnetic roller 12 is located in a position opposite to the auxiliary receiving roller 14 associated with the second electromagnetic roller 12.

In other words, the auxiliary backing rolls 14 associated with the first electromagnetic rolls 12 are located on a first side with respect to the casting axis C, while the auxiliary backing rolls 14 associated with the second electromagnetic rolls 12 are located on a second side opposite the first side with respect to the casting axis C.

As can also be observed in fig. 8, in this variant of the casting installation 10 too the following applies: the electromagnetic force 17 generated in the first electromagnetic roller 12 is guided in a first direction, which is opposite to a second direction that is: the electromagnetic force 17 generated in the second electromagnetic roller 12 is guided in the second direction.

Embodiments of the invention also relate to a casting plant 10 comprising said mould 15 configured to cast the slab S and said plurality of rollers 11, 12 arranged facing each other in pairs along the casting axis C to define a passage for the cast slab S.

According to the invention, the electromagnetic force 17 generated by the travelling magnetic field is more uniform along the slab width W1, because the shortening of the electromagnetic roller 12 compared to the slab width W1 smoothes the electromagnetic edge effect while ensuring a sufficient stirring action.

It is clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of the present method for receiving slabs during continuous casting, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claims (13)

1. A method for receiving slabs during continuous casting, providing casting a slab (S) along a casting axis (C), the slab (S) having a predefined width (W1), wherein the method provides for receiving the slab (S) with a plurality of rollers (11, 12), the rollers (11, 12) being arranged in pairs facing each other and the rollers (11, 12) defining a passage for the cast slab (S) along the casting axis (C), wherein the plurality of rollers (11, 12) comprises electromagnetic rollers (12), the electromagnetic rollers (12) being provided with an electromagnetic stirrer (13) stirring a liquid contained in the slab (S), and wherein, during casting, the electromagnetic rollers (12) have a length (L) smaller than the width (W1) of the slab (S) such that the slab (S) protrudes with respect to at least one end of the electromagnetic rollers (12) at least one of the ends thereof -an extension (20), said slab (S) extending with respect to one end of said electromagnetic roller (12) by an unsupported width (W2) of up to 300mm, and said extension (20) being unsupported by said roller.

2. The method for receiving slabs during continuous casting according to claim 1, characterized in that said slab (S) projects with respect to one end of said electromagnetic rolls (12) by an unsupported width (W2) of up to 250 mm.

3. Method for receiving slabs during continuous casting according to claim 2, characterized in that the ratio between the unsupported width (W2) of the slab (S) and the width (W1) of the slab (S) is comprised between 2% and 20%.

4. Method for receiving slabs during continuous casting according to claim 3, characterized in that the ratio between the unsupported width (W2) of the slab (S) and the width (W1) of the slab (S) is comprised between 2.5% and 16%.

5. The method for receiving slabs during continuous casting according to claim 1, characterized in that each of said electromagnetic rollers (12) is associated with a respective auxiliary receiving roller (14), said auxiliary receiving roller (14) being aligned and coaxial with the respective electromagnetic roller (12), said auxiliary receiving roller (14) supporting said projecting portion (20).

6. The method for receiving slabs during continuous casting according to any one of the preceding claims, characterized in that said rolls comprise a first electromagnetic roll (12) and a second electromagnetic roll (12) spaced from each other along said casting axis (C).

7. Method for receiving slabs during continuous casting according to claim 6, characterized in that a plurality of receiving rolls (11) are provided between the first electromagnetic roll (12) and the second electromagnetic roll (12) to receive and support the slab (S).

8. Method for receiving slabs during continuous casting according to claim 6, characterized in that said first electromagnetic roll (12) is arranged so that a first edge (21) of said slab (S) projects with respect to said first electromagnetic roll (12) and a second edge (22) opposite to said first edge (21) projects with respect to said second electromagnetic roll (12).

9. Casting apparatus comprising a mould (15) and a plurality of rollers (11, 12), the mould (15) being configured to cast a slab (S), the plurality of rollers (11, 12) being arranged facing each other in pairs along a casting axis (C) to define a channel for the cast slab (S), wherein the plurality of rollers (11, 12) comprises electromagnetic rollers (12), the electromagnetic rollers (12) being provided with an electromagnetic stirrer (13) configured to stir liquid contained in the slab (S), wherein, in use, the electromagnetic rollers (12) have a length (L) that is less than a width (W1) of the slab (S) such that the slab (S) protrudes with respect to one end of the electromagnetic rollers (12), the slab (S) protruding with respect to one end of the electromagnetic rollers (12) by an unsupported width (W2) of up to 300mm, and the projecting portion (20) is unsupported by the roller.

10. The casting plant according to claim 9, characterized in that each of the electromagnetic rolls (12) is associated with a respective auxiliary bearing roll (14), the auxiliary bearing roll (14) being aligned and coaxial with the respective electromagnetic roll (12).

11. Casting plant according to claim 9 or 10, characterized in that said rolls comprise a first electromagnetic roll (12) and a second electromagnetic roll (12) spaced from each other along said casting axis (C).

12. The casting plant according to claim 11, characterized in that the auxiliary bearing rolls (14) associated with the first electromagnetic rolls (12) are located on a first side with respect to the casting axis (C) and the auxiliary bearing rolls (14) associated with the second electromagnetic rolls (12) are located on a second side opposite to the first side with respect to the casting axis (C).

13. The casting plant according to claim 11, characterized in that a plurality of receiving rolls (11) are provided between the first electromagnetic roll (12) and the second electromagnetic roll (12) to receive and support the slab (S).

Images