IT201800006563A1 - PLANT AND PROCEDURE FOR THE PRODUCTION OF A HOT ROLLED METAL TAPE - Google Patents

Description

Description of the invention having as title:

"PLANT AND PROCEDURE FOR THE PRODUCTION OF A HOT ROLLED METALLIC TAPE"

FIELD OF APPLICATION

The field of application of the present invention is that of the steel industry and the production of metal semi-finished products, more particularly that of the production of metal strips, for example in steel, hot rolled by means of a rolling line located downstream of a continuous casting.

STATE OF THE TECHNIQUE

In the field of metal strip production, for example from US-B-5.307.864 a casting plant and method for the production of hot-rolled steel strips is known.

Document US-B-5.307.864 describes a steel strip production plant comprising a hot rolling line located downstream of a continuous casting machine equipped, in turn, with an ingot mold equipped with a crystallizer. The casting machine, of the vertical-curved type, also includes guiding devices for diverting the metal product from the vertical direction, leaving the crystallizer, to the horizontal direction following a curved path, with high radii of curvature.

This casting plant comprises, downstream of the guiding devices, a roughing stand for rolling the cast metal product, a shear for cutting the cast slab and a heating device for heating the cast slab before winding it into a winding device. / unwinder from which it is then unwound to be fed to the hot rolling line provided downstream.

An additional heating unit is interposed between the finishing rolling stands of the hot rolling line to restore the temperature of the rolling slab. Thereafter, a winding device, or reel winder, is provided.

However, the aforementioned system and the related procedure have the drawback of being rather rigid and not allowing you to easily adjust the hourly productivity. Their size requires substantial investments to make it and keep it operational, and it is uneconomical since it plans to carry out intermediate heating of the strip in the finishing train.

It is also known from US-B-7. 025.1 18 a machine and a vertical casting method designed to maintain the position of the kissing point, i.e. the point of complete solidification of the metal product, always in the same position along the containment devices, as the casting speed and the type of steel and secondary cooling modes. This allows, as now consolidated in the state of the art, to maintain constant the thickness of the cast product leaving the continuous casting machine. To keep the kissing point position unchanged, and therefore to keep the exit thickness of the cast product constant, at the different casting speeds, the thickness of the slab is varied in order to keep the growth of the solidification skin constant over time. This casting machine, however, is rigid as it is not capable of casting ultra-thin slabs and, above all, it is unable to adjust, with wide variability, the final thickness of the cast slabs and therefore adjust the productivity of the slab accordingly. 'plant.

An object of the present invention is to provide a plant and to develop the related process for the production of a hot rolled metal strip which, obviating the drawbacks of the prior art systems and processes, are very flexible and particularly suitable for production medium-low or up to a maximum of 1.1Mton / year, preferably to obtain an annual production of less than 800,000ton / year, and easily variable, for example between about 400,000ton / year and about 800,000ton / year.

Another object of the present invention is to provide a plant for the production of a hot-rolled metal strip which has very small overall dimensions, for example with a length of less than 130m, consequently reducing the investment and maintenance costs of the buildings. connected to them.

It is also an object of the present invention to provide a plant for the production of a hot-rolled metal strip that requires limited investments to make it (Capex) and has contained operating costs of transformation (Opex) if compared with a traditional plant to produce the same thicknesses. of tape.

A further object of the present invention is to provide a plant and to develop the related process for the production of a hot rolled metal strip which can easily vary the thickness of the cast slab in relation to the final thickness of the strip and optimize the productivity of the '' plant with the smallest number of cages possible while maintaining the maximum casting speed in relation to the steel grade of steel.

To obviate the drawbacks of the known art and to achieve these and further purposes and advantages, the Applicant has studied, tested and manufactured the equipment and perfected the method according to the present invention.

EXPOSURE OF THE FOUND

The present invention is expressed and characterized in the independent claims, while the dependent claims disclose other features of the present invention, or variants of the main solution idea.

In accordance with the aforementioned purposes, a plant for the production of a hot-rolled metal strip according to the present invention comprises:

- a continuous casting machine having a substantially vertical casting axis and having a containment length less than or equal to 6m, said continuous casting machine being configured to cast a metal product with a casting speed comprised between about 3.6m / min and about 6m / min and comprising an ingot mold, with relative crystallizer and a roller pre-rolling device configured to perform a liquid core pre-rolling and output an ultra-thin slab having selectively settable first thicknesses. Furthermore, the roller pre-rolling device has a length, measured in a direction parallel to the casting axis, less than or equal to 5m, and is configured to determine the complete solidification of the cast product in a solidification point contained in the device. roller pre-rolling device and selectively placed in an area between the output end of the latter and a distance from the output end of at least 80% of the length of the roller pre-rolling device, towards the 'entrance end of the latter.

In accordance with embodiments of the invention, the plant also comprises downstream of the roller pre-rolling device a towing unit configured to tow the slab and send it downstream.

After a curved section of the continuous casting machine, the plant also comprises, arranged along a substantially horizontal rolling plane:

- at least one roughing stand configured to transform said slab into a rough slab, also called X-bar, or transfer bar, having a second thickness,

- first cutting means configured to cut the rough slab to size,

- induction heating means configured to heat, or maintain, the rough slab at a given rolling temperature, a winding / unwinding device configured to selectively wind / unwind the blank and to keep it at the rolling temperature,

- second cutting means configured to carry out the head / tail trimming and possible scrapping in case of emergency of the rough slab,

- a continuous finishing rolling train to reduce the thickness of the rough slab to obtain a metal strip having a certain final thickness,

- cooling means configured to cool the metal strip,

- a reel configured to wind the metal strip. In accordance with a further embodiment of the invention, the roller pre-rolling device is configured to be adjustable so that the first thicknesses of the aforementioned slab are between about 28mm and about 48mm.

According to a further embodiment of the present invention, the aforementioned roughing stand and the aforementioned continuous finishing rolling train are configured to be adjustable so that the aforementioned final thickness of the metal strip is between about 0.8mm and about

12mm.

In accordance with a possible embodiment of the present invention, depending on the aforementioned casting speed, correlated to one of the first thicknesses of the slab, it is possible to obtain an hourly production of the casting machine comprised between about 80ton / h and about 160ton / h, corresponding at about 400.000ton / year and, respectively, at about 800.000ton / year.

In accordance with a further embodiment of the invention, the product poured out of the crystallizer has a certain thickness between 48mm and 56mm, preferably between 50mm and 54mm and still has a liquid core inside. In accordance with this embodiment, it can be provided that the crystallizer is defined by at least two plates facing each other and spaced apart by a distance, at least in the end portion, equal to the aforementioned thickness of the cast product. According to embodiments of the present invention, the size of the crystallizer can be substantially the same for each production condition imposed, for example linked to the thickness of the strip to be obtained, the casting speed and productivity.

In accordance with another embodiment of the present invention, immediately before the roughing stand a first descaling device is arranged which has the function of removing the scale from the surface of the slab.

In accordance with another embodiment of the present invention, a second descaling device is arranged between the aforementioned second cutting means and the aforementioned continuous finishing rolling train.

In accordance with an embodiment of the present invention, the continuous finishing rolling train comprises a number of finishing stands comprised between two and five.

According to possible embodiment solutions, the roughing stand is in direct contact with the casting machine, meaning by the term "direct grip" that there is no continuity solution between the cast product leaving the crystallizer and the ultra-thin slab that enters the roughing stand. . In other words, between the casting machine and the roughing stand the slab is not cut, so that these two machines work endlessly with each other.

In accordance with an embodiment of the present invention, the roughing stand is configured so that the second thickness of the rough slab is between about 8mm and about 25mm. Such dimensions of thickness of the blanked slab allow to wind the blanked slab in the winding / unwinding device.

Embodiments of the present invention also refer to a process for the production of a hot-rolled metal strip, which comprises:

- a step of continuous casting of a metal product with a casting speed between about 3.6m / min and about 6m / min and by means of a continuous casting machine having a substantially vertical casting axis, and a lower containment length or equal to 6m, the continuous casting machine comprising an ingot mold, with relative crystallizer, and a roller pre-rolling device having a length, measured in a direction parallel to the casting axis, less than or equal to 5m,

- a liquid core pre-rolling phase to achieve a thickness reduction of the cast product along the aforementioned casting axis and transform the cast product leaving the aforementioned crystallizer into a completely solidified ultra-thin slab having selectively settable first thicknesses, said phase of pre-rolling by providing for the complete solidification of the cast product in a solidification point contained in the roller pre-rolling device and selectively placed in an area between the exit end of the latter and a distance from the exit end of the roller pre-laminating device of at least 80% of the length of the roller pre-laminating device.

In accordance with possible embodiments of the invention, the process for producing a hot-rolled metal strip comprises:

- a phase of pulling the slab with a pulling unit which may also include a phase of reducing the thickness of the solidified slab,

- a roughing step of the aforesaid slab carried out along a substantially horizontal rolling plane, to transform the aforesaid slab into a rough slab having a second thickness. In accordance with a further aspect of the present invention, the following are carried out in sequence along the aforementioned rolling plane:

- a first cutting phase to cut the rough slab to size, - a heating / temperature maintenance phase, to heat, or maintain, the rough slab at a given rolling temperature,

- a winding / unwinding phase to selectively wind / unwind the rough slab,

- a second cutting phase to carry out the trimming of the head / tail of the rough slab and possible scrapping of the same in case of emergency,

- a finishing rolling step in a continuous train to reduce the thickness of the rough slab until the metal strip having a certain final thickness is obtained,

- a cooling phase of the metal strip e

- a winding phase to wind the metal tape.

In accordance with an implementation of the invention, the liquid core pre-lamination step reduces the thickness of the product poured out of the crystallizer so that the first thicknesses can be selectively set and included between about 28mm and about 48mm. In accordance with a further implementation of the invention, the aforementioned roughing step and the aforementioned continuous finishing rolling step take place so that the final thickness of the metal strip is between about 0.8mm and about 12mm.

In accordance with a further implementation of the present invention, the aforesaid method provides that, depending on the casting speed, correlated to the first selectively set thicknesses of the slab, it is possible to obtain an hourly production of the casting machine comprised between about 80ton / h and about 160ton. / h, corresponding to approximately 400,000 tons / year and, respectively, to approximately 800,000 tons / year.

According to possible embodiments of the present invention, the productivity of the casting machine can reach a maximum of 1.1Mton / year.

In accordance with a further implementation of the present invention, the process provides that the product poured out of the crystallizer has a thickness between 48mm and 56mm, preferably between 50mm and 54mm.

In accordance with a further implementation of the present invention, the process provides that before the roughing phase a phase of pulling the slab is carried out. This allows to facilitate the introduction and advancement of the slab through the subsequent roughing stand.

In accordance with a further implementation of the present invention, the process provides that immediately before the roughing step a first descaling step is carried out to remove the scale layer on the slab.

In accordance with a further implementation of the present invention, the process provides that between the second cutting step and the continuous finishing rolling step a second descaling step is carried out on the rough slab.

In accordance with a further implementation of the present invention, the process provides that the roughing step reduces the thickness of the slab so that the second thickness of the roughened slab is between about 8mm and about 25mm.

ILLUSTRATION OF DRAWINGS

These and other characteristics of the present invention will become clear from the following description of a preferred embodiment, provided only by way of non-limiting example, with reference to the attached drawings in which:

- fig. 1 is a schematic side view of a plant for the production of a hot rolled metal strip, according to the present invention;

- fig. 2 is a schematic section of a continuous casting machine of the plant of fig. 1, on an enlarged scale, in a first example of its operation;

- fig. 3 is a schematic section of the continuous casting machine of fig. 2 in a second example of its operation;

- fig. 4 is a schematic section of the continuous casting machine of fig. 2 in a third example of its operation;

- fig. 5 is a schematic section of the continuous casting machine of fig. 2 in a fourth example of its operation;

- fig. 6 is a diagram showing the progress of the operating field of the plant in fig. 1, with the thickness Sb in millimeters of the slab exiting the roller conveyor on the abscissa and the casting speed Ve in m / min on the ordinate, with iso-productivity curves correlated to different production capacities, respectively a = 80 ton / h, highlighted , b = 90 ton / h, c = 100 ton / h, d = 110 ton / h, e = 120 ton / h, f = 130 ton / h, g = 140 ton / h, h = 150 ton / h, i = 160ton / h, for a 1300mm wide belt.

It should be noted that in the present description and in the claims the terms vertical and horizontal with their declinations have the sole function of better illustrating the present invention with reference to the figures of the drawings and must not be used in any way to limit the scope of the invention itself. , or the scope of protection defined by the claims.

DESCRIPTION OF MANUFACTURING FORMS OF THE PRESENT

FOUND

With reference to fig. 1, a plant 10 for the production of a metal strip 11, for example in steel, hot rolled, according to the present invention, comprises a continuous casting machine 12, which in turn comprises an ingot mold 13 equipped with a crystallizer 14 (figs. 2-5), and a roller pre-rolling device, also referred to hereinafter with the term will radiate containment or, more simply, radiate 15 (figs. 1-5), arranged along a casting axis X substantially vertical.

The radius pre-rolling device 15 is configured to effect a reduction of the liquid core thickness of the metal product leaving the mold 13, to provide a selectively set first thickness Sb of the slab B.

Downstream of the radiator 15 there is a curved section 16 of the casting machine in which the cast product is diverted, along a curved path, from its substantially vertical condition to its substantially horizontal condition.

Downstream of the curved portion 16 there is a roughing stand 19 for roughing out the metal product coming out of the curved portion 16.

The height of the mold 13 is, for example, between 1000mm and 1200mm.

During use, the liquid metal is poured into the crystallizer 14 to maintain a filling level in the latter, also called meniscus M, which is substantially constant during casting.

In accordance with possible embodiments of the invention, the level of the meniscus M is placed lower than the inlet end of the crystallizer 14 at a distance between 50mm and 100mm, preferably between 80mm and 85mm.

According to possible embodiments, the roller conveyor 15 can have a length LR, measured in a direction parallel to the aforementioned casting axis X, less than or equal to 5m, preferably less than or equal to 4.2m.

The roller conveyor 15, according to possible embodiments, can comprise a plurality of pairs of segments 30a, 30b, 30c, 30d, 3 la, 31 b, 31 c, 31 d as described below, arranged on opposite sides with respect to the axis of casting X and each of which is provided with a plurality of rollers 32 for containing and / or compressing the metal product being cast. Each pair provides that a segment 30a, 30b, 30c, 3 Od, faces a corresponding segment 3 la, 31b, 31c, 3 1 d.

According to possible embodiments, the number of pairs of segments 30a, 30b, 30c, 30d, 31a, 31b, 31c, 31d is between four and eight.

At the outlet of the crystallizer 14, the cast product has a solidified outer shell having the function of containing the liquid metal still present inside it.

The roller conveyor 15 is configured to carry out a compression on the cast product (fig. 2) leaving the crystallizer 14, or to reduce the thickness of the cast product, while its internal core is still liquid, and to give it the thickness Sb, as it will be more forward described in detail.

In accordance with possible embodiment solutions, the roller conveyor 15 can be associated with cooling devices, not shown, also called secondary cooling, and configured to cool the external surfaces of the slab and to determine its further solidification.

The cooling devices may comprise spray nozzles or water mixed with air-mist air.

In accordance with an aspect of the invention, it is envisaged that the closing of the two half-skins which are formed in the crystallizer takes place inside the roller conveyor 15 and their point of union, which determines the complete solidification of the cast product, is called with the English term "Kissing Point" (KP). The KP can also be seen as the terminal vertex of the liquid cone that originates from the meniscus M in the crystallizer 14.

In accordance with an aspect of the present invention, the roller conveyor 15 is configured to determine the complete solidification of the cast product in a solidification point contained in the roller conveyor 15 and selectively placed in an area comprised between the outlet end of the latter and a distance from said outlet end of at least 80% of the length LR of the roller conveyor 15, that is towards and in direct proximity to the inlet end of the roller conveyor 15. This solidification point defines the aforementioned kissing point KP.

In other words, the invention makes it possible to use at least 80% of the length LR of the roller conveyor 15 to close the liquid cone and obtain corresponding thicknesses of slab exiting the roller conveyor.

This aspect can be explained still in another way through a characteristic quantity of the casting machine which is the solidification length.

The solidification length LS is defined as the distance between the level of the meniscus M of the molten material present in the crystallizer 13 and the position of the kissing point KP inside the roller conveyor 15.

In accordance with the above, the casting machine 12 is configured to have a solidification length LS which can be selectively set to a value selected between about 1.3m and about 5.9m, preferably between about 1.3m and 5.1m. The setting of the positioning of the kissing point inside the roller conveyor 15 is carried out by intervening on at least one of the following parameters: casting speed, secondary cooling intensity, and thickness reduction intensity at the liquid core by adjusting the segments of the roller conveyor 15, such as described below.

In accordance with a further aspect of the present invention, the casting machine 12 has a containment length LC, which is defined as the distance between the inlet end of the crystallizer 14, i.e. the end through which the molten material is introduced. , and the exit end of the roller conveyor 15, that is the end from which the ultra-thin slab B protrudes. According to a possible embodiment, the containment length LC is less than or equal to about 6m, preferably less than or equal to about 5.2m. This containment length LC is very limited with respect to known embodiments. Furthermore, the containment length LC is a fixed value of the casting machine 12, set for example in the design phase of the casting machine itself.

A reduced containment length LC, as defined above, allows to reduce the height, and therefore the overall dimensions, of the casting machine 12, thus also reducing the size of the production plant.

In accordance with a possible embodiment solution, the product poured out of the crystallizer 14 has a certain initial thickness Se (fig. 2) which is between 48mm and 56mm, preferably between 50mm and 54mm, in this case, of about 52mm.

In accordance with a possible embodiment, the crystallizer 14 is defined by at least two plates facing each other and spaced, at least in the terminal portion, by the aforementioned determined initial thickness Se.

According to an embodiment of the invention, the same crystallizer 14 can be used for the entire range of belt thicknesses and productivity defined in the introduction thanks to the flexibility of the containment roller conveyor, thus allowing to simplify the management of the plant. The slab B exiting the roller conveyor 15, due to a reduction in the thickness obtained by means of pre-rolling with a liquid core, can have first thicknesses Sb between about 28mm and about 48mm, so slab B is of the ultra-thin type and in output from the roller conveyor 15 is completely solidified.

This allows to have the curved portion 16 (fig. 1) of the casting machine 12 with a very reduced radius of curvature R compared to known solutions.

In accordance with a possible embodiment, the radius of curvature R can be comprised between about 1.5m and 2.5m, even more preferably 1.7m and 2.2m.

This allows to obtain the following advantages:

- bring the casting axis X closer to the roughing stand 19,

- reduce the spaces, and the overall dimensions of the system 10;

- arrive with an ultra-thin slab B at the roughing stand 19 at a sufficiently high temperature to allow the rolling, in the roughing stand 19, in direct contact with the casting (i.e. in endless) and allowing lower crushing forces with the same reductions with consequent energy saving;

- drastically reduce, if not completely eliminate, the containment and guide rollers of the curved section, with a reduction in components and heat losses due to the heat exchange between rollers and slab.

In accordance with a possible embodiment of the present invention, downstream of the roller conveyor 15 there is a towing unit 17 configured to tow the slab B downstream, or rather towards the roughing stand 19.

The drawing assembly 17 comprises a number of pairs of drawing rollers, comprised between one and six.

The rollers of each pair are arranged on opposite sides with respect to the slab to be towed. The rollers of each pair, or at least one of them, can be associated with handling devices, for example hydraulic cylinders of a known type (not shown), to bring the rollers closer to / away from each other and also to determine a predefined crushing action on the slab. B completely solidified, as described below. In accordance with possible embodiments, the towing unit 17 can comprise a first towing device 16a placed directly downstream of the roller conveyor 15, or in the vertical section of the casting machine 12, and a second towing device 16b placed directly downstream of the curved section 16 of the casting machine 12. The first towing device 16a and the second towing device 16b can comprise a number of pairs of rollers comprised between 1 and 3.

As mentioned above, the rollers of the drawing assembly 17 are configured to effect a slight reduction in thickness on the slab with a solid core and therefore a real lamination. In particular, each single pair of drawing rollers can produce, when necessary, a squeeze of an entity between 0.5mm and 1.5mm so as to obtain, overall, a reduction in thickness of between about 2mm and about 7mm.

This rolling already carried out in casting involves a further reduction in the thickness of the slab B thus allowing the roughing stand 19 located downstream to reach second thicknesses Sz of the roughened slab Z thinner.

The towing unit 17 is an integral part of the casting machine 12 which, thanks to the rolling action carried out by its rollers, can be defined as a "Rolling Caster".

By Rolling Caster we mean a casting machine 12 capable of performing both the casting of the product and its rolling, partly with a liquid core and partly with a solid core.

Downstream of the roller pre-rolling device 15, in this case downstream of the pulling unit 17 are arranged, in sequence, along the same rolling plane P:

- an optional first descaling device 18 to remove the scale from the surface of the slab B,

- the aforementioned roughing stand 19, from which a rough slab Z, also called X-bar or transfer bar, comes out,

- first cutting means 20, for example comprising a shears for cutting to size,

- induction or inductor heating means, 21, preferably of the modular type,

- a winding / unwinding device 22, for example of the type described in the international application WO-A-201 1/080300 in the name of the Applicant,

- second cutting means 24, for example comprising a shear, for trimming the head / tail 24 and scrapping the rough slab Z in the event of an emergency,

- a possible second descaling device 25,

- a continuous finishing rolling train 26 configured to roll the rough slab Z until the aforementioned metal strip 11 is obtained,

- cooling means 28 configured to cool the metal strip 11, preferably of the modular type, e

- a reel 29 configured to wind the metal strip 11 on a reel.

According to possible embodiments, the roughing stand 19 is configured to reduce the thickness of the slab B in relation to the winding and containment capacity of the winding / unwinding device.

According to possible embodiments, the rough slab Z, or transfer bar, exiting the roughing stand 19 has a thickness between 8mm and 25mm, preferably between 10mm and 25mm.

In accordance with possible embodiments of the present invention, the first cutting means 20 are configured to cut to size the rough slab Z to a length equivalent to the weight of a reel complete with metal strip 11 which is wound in the winder 29.

According to possible embodiments of the present invention, the induction heating means 21, positioned upstream of the winding / unwinding device 22, are configured to heat the rough slab Z to a temperature between about 1000 ° C and about 1200 ° C, or a temperature suitable for the subsequent rolling of the rough slab and thus allow to restore the temperature of the rough slab Z which has been dissipated in the roughing stand 19.

According to possible embodiments, the winding / unwinding device 22 comprises a first unit 22a and a second unit 22b which alternate with each other in the winding function of the rough slab Z received from the roughing stand 19, and in the unwinding function of the rough slab Z , previously wound, to feed it to the continuous finishing rolling mill 26. In particular, while one of the two units 22a, 22b winds a blank slab Z supplied by the upstream casting machine, the other unit 22b, 22a unwinds another slab roughly, supplying it downstream. This winding / unwinding device 22 also allows to define a temporary accumulation buffer to compensate for any slowdowns and non-synchronization between the continuous casting machine 12 and the continuous finishing rolling train 26. The winding / unwinding device 22 allows to absorb the downtime of the rolling mill for small maintenance or for the programmed change of cylinders or for small accidents / grounding, without the need to interrupt the casting process, and therefore without loss of production and without penalizing the upstream steel mill.

In accordance with possible embodiments, the above-mentioned winding / unwinding device 22 can comprise one or more heating devices, such as burners, which can be selectively activated to keep the rough slab Z at the temperature. The winding / unwinding device 22 can also comprise devices for entry and exit of the blank slab Z, for example guiding devices for the introduction and exit of the blank slab Z.

In accordance with embodiments of the invention, the continuous finishing rolling train 26 can comprise a plurality of rolling stands 27, for example between two and five in number, for example four, as illustrated in fig. 1.

According to a possible embodiment of the present invention, the cooling means 28 can comprise cooling devices of the laminar type.

The plant 10 is advantageously very compact and has an overall length LT less than or equal to 130m.

In accordance with the embodiments illustrated in figs. 2-5, the roller conveyor 15 can comprise segments of intrados 30a, 30b, 30c and 30d, in this case four segments which in the figures are on the right with respect to the casting axis X, and respective and opposite extrados segments 3 1a, 31b, 3 1e and 31d, which in the figures are on the left with respect to the casting axis X. In particular, the soffit segments 30a, 30b, 30c, 30d, are arranged on the same side as the soffit side of the curved section 16, while the extrados segments 3 la, 3 lb, 3 le, 3 ld are placed on the same side of the extrados side of the curved section 16.

According to a possible embodiment, each segment 30a, 30b, 30c, 30d, 31a, 31b, 31e and 31d can be provided with a plurality of rollers, in this case five rollers 32.

The extrados segments 31 a, 31 b, 31c and 31 d are configured to remain in a fixed position, normally aligned parallel to the casting axis X.

The soffit segments 30a, 30b, 3 Oc and 3 Od are instead configured to be individually and selectively inclined by a certain angle a with respect to the casting axis X by means of actuators, such as hydraulic cylinders, not shown in the drawings. The actuators can be controlled by position transducers, also not shown in the drawings.

The inclination of one or more intrados segments 30a, 30b, 3 Oc and 3 Od is performed to reduce the thickness of the cast product when the latter is not yet completely solidified and therefore contains a liquid core. The angle a of inclination of the segments 30a, 30b, 30c and 30d can be comprised between about 15 degrees (fig. 2) and zero degrees (fig. 5), and can be different for each segment 30a, 30b, 30c and 30d as a function of its position in the roller conveyor 15, of the casting speed and of the desired final thickness of the slab B.

In accordance with embodiments illustrated in figs. 2, 3 and 4, the first three segments 30a, 30b, 3 0c are inclined to squeeze, and therefore reduce the thickness, so that the kissing point is substantially located in the transition zone between one segment and another, more in in particular in the area between the last roller of one of the segments and the first roller of the next segment. This ensures that the sloping segments always crush in the presence of a liquid heart. In fact, if within the segment there were even only a section of solid core slab, this would prevent said segment from tilting and therefore from crushing or, if forced to do so, the rollers and the thrust cylinders would be damaged.

In accordance with further embodiments, it can be envisaged that the KP is positioned not only in the transition zone between the segments 30a, 30b, 30c, 30d, 3 1a, 3 lb, 31c, 31d but in any position along the extension of the roller conveyor 15 comprised between the last roller of the first segment 30a and the last roller of the last segment 30d. In this way it is possible to obtain, in a desired manner, the closure of the liquid cone in any position along the entire length LR of the roller conveyor 15, with the exception of the first segment 30a.

The soffit segments 30b, 30c and 30d, which are found below KP, i.e. inside which the KP is positioned, are kept substantially parallel to the casting axis X since the slab is already completely or partially solidified and therefore cannot perform any crushing as there is no longer a liquid heart, or a completely liquid heart.

The segments are however approached parallel to the casting axis X to keep them in contact with the surface of the slab obtained by the reduction in thickness performed by the overlying segments. The position of the aforementioned kissing point KP can also be adjusted according to the casting speed and the amount of secondary cooling that is carried out along the roller conveyor 15.

Normally the fourth segment of the soffit 30d (fig. 5) is not inclined since, being the last segment, the KP falls inside it. In fact, the KP cannot position itself below the last segment as there is no longer any containment and cooling, therefore the presence of a liquid core would cause the slab to swell with the risk of breaking the skin and escaping the steel contained. within it, causing the so-called breakout.

The lower limit position of the KP, which determines the maximum achievable solidification length LS, is in correspondence with the last roller 32 of the last segment 30d: in this case, the fourth segment 3 0d can also assume a slightly inclined position.

In other words, in the roller conveyor 15 the extrados segments 31a, 31b, 31c and 3 1d are fixed and parallel to the casting axis X, while the intrados segments 30a, 30b, 30c, 30d are configured to work in this way: the segments that “see” liquid steel in all their height are inclined so as to crush and reduce the thickness of the cast product containing the liquid core. Instead, all the segments below the KP, or within which the KP is positioned, are not inclined and are kept parallel to the casting axis X, so as not to perform any crushing of the cast product.

The roller conveyor 15, thanks to the fact that it is divided into several segments, albeit in a small space, allows to increase the degree of freedom of the crushing in the formation of the slab B operated by the rollers 32, also being able to close the liquid cone immediately below. the crystallizer 14. In this way the range of variability of the solidification length LS usable on the casting machine 12, which corresponds to a range of variability of the thickness of the slab B coming out of the roller conveyor 15, is advantageously extended by increasing the operating capacity of the casting itself.

In the embodiment illustrated in Figures 2 to 5, a roller conveyor 15 has been considered having four pairs of segments of equal length.

In accordance with other embodiments, the number of pairs of segments, with the same containment length LC, can be increased up to 8.

In accordance with other embodiments, the segments of the roller conveyor 15 can be of different lengths from each other. In particular, it can be envisaged that the first pair of segments 30a, 3 1a, located at the inlet end of the roller conveyor 15, has a shorter length than the length of the segments 30b, 30c, 30d, 31b, 31c, 3 1 d placed downstream. In this way, the first pair of segments allows you to crush the metal product in an area even closer to the outlet end of the crystallizer 14 and then move the upper limit position of the KP upwards. Therefore, the minimum value of the solidification length LS is further reduced or the range of use of the solidification length LS is further extended. By way of example only, each segment 30a, 30b, 30c, 30d, 31a, 31b, 31c, 31d can have a length comprised between 0.4m and 1.5m, preferably between 0.5m and 1m.

The casting machine 12 according to the invention is therefore characterized by a so-called "two-dimensional flexibility" since, with a given crystallizer 14 it is possible to choose a wide range, with respect to the known technique, both of casting speed and thickness of the slab B.

In the plant 10 the solidification length LS is advantageously very reduced, compared to the plants of the known art, and is preferably between about 1.3 m, in the operating condition represented in fig. 2, and about 5.9 m, in the operating condition shown for example in fig. 5.

The plant 10 described up to now allows to obtain a production of a metal strip 11 having a very thin thickness, for example between about 0.8mm and about 12.0mm, preferably between 1.2mm and 12mm and for example an average width about 1300mm.

In the diagram of fig. 6 shows the operating capacity of the casting machine 12 in which the casting speed Ve can vary from about 3.6m / min to about 6.0m / min and the first thickness of slab B after the pre-rolling action a liquid core can vary from 28 mm to 48 mm. The curves a, b, c, d, e, f, g, h, i shown in the diagram of fig. 6 are curves of iso-productivity per hour expressed in tons / hour (tons / h), from about 80 tons / h to about 160ton / h, which correspond to an annual productivity between about 400,000 tons / year and about 800,000 tons / year.

These curves refer to an average web width of 1300mm.

The contour line, or perimeter, of the diagram of fig. 6 defines the limit conditions of use of the casting machine 12 as a function of the degree of cast steel, also called “steel grade” and of the geometric and constructive characteristics of the crystallizer 14 and of the containment roller conveyor 15.

The diagram has been drawn considering the casting of a low carbon steel.

From the diagram in fig. 6 it is evident how the casting machine 12, with the same crystallizer 14, can advantageously cover a wide range of variation of the hourly productivity, however within the limits of a medium-low productivity.

This flexibility is made possible thanks to:

- being able to vary the solidification length LS for the same crystallizer, substantially exploiting the entire length of the roller conveyor 15, which translates into the possibility of choosing the aforementioned first thicknesses Sb in an interval between 28mm and 48mm;

- being able to vary the casting speed over a wide range, that is from 3.6m / min to 6.0m / min.

In particular, figures 2 to 5, read together with the diagram of fig.

6, refer to four different working conditions in terms of the range of the casting speed Ve and the aforementioned first thicknesses Sb of the slab B obtained after the liquid core pre-rolling action by means of the roller conveyor 15.

The minimum thickness value Sb of 28.0mm (fig. 2) is obtained in a high and narrow range of casting speed Ve, ie between about 5.2m / min and about 6.0m / min (fig. 6). This is the condition in which there is the minimum solidification length LS, and therefore the position of the highest KP, as well as the maximum angle of inclination, and therefore the maximum crushing of the slab B exerted by the first segment 30a.

The maximum value of the first thickness Sb of slab B of 48.0mm (fig. 5) is obtained, on the other hand, at the casting speed Ve of 5.5m / min. This is the condition in which there is substantially the maximum solidification length LS, and therefore the position of the lowest KP, with the minimum inclination angle of the soffit segments.

Figs. 3 and 4 illustrate two intermediate situations in which the first two and the first three segments are respectively inclined. Other intermediate situations, not illustrated, are possible in which, by inclining one or more segments with different crushing angles, the KP is selectively positioned at any point between the limit positions to obtain, at the various casting speeds illustrated in fig. 6, the intermediate thickness range between the extreme values.

The operation of the plant 10 described so far, which also defines the process for the production of the hot rolled metal strip 11, is as follows.

First of all, the characteristics of the steel strip in rolls that must be produced are established by defining: minimum thickness, width, and Steel grade, that is, the type of steel to be cast.

Subsequently, the productivity of the steel mill that feeds the continuous casting machine 10 must be established as a function of how many rolls of strip, with the aforementioned characteristics, must be produced.

In this way it is determined on the diagram of fig. 6, or on the equivalent diagram relating to the steel-grade and the belt width chosen, the iso-productivity curve for the continuous casting machine. The Steel grade also determines the maximum casting speed that can be used (VcMAX) to cast that steel grade to quality. In fact, there are steels that are "easier" to cast, for example steels with low carbon content, which allow high casting speeds, and steels that are more "difficult" to cast, for example peritectic steels, which require low casting speeds. .

Setting the VcMAX therefore limits the usable iso-productivity curve to a portion.

As described below, the casting parameters (slab thickness Sb and casting speed Ve) are determined on the defined iso-productivity curve based on the configuration of the finishing train.

The number of stands 27 required in the finishing train 26 is determined with the minimum final thickness of the strip and therefore the aforementioned second thickness Sz of the transfer bar Z exiting the roughing stand 19 which is most suitable for feeding the continuous finishing rolling train 26.

According to the second thickness Sz that the transfer bar Z must have, the aforementioned first thickness Sb is established, which must have the slab B coming out of the roller conveyor 15.

By way of example, the following Table 1 shows the minimum values of the final thickness Sf of the metal strip 11 as a function of the assigned values of the first thickness Sb of the slab exiting the roller conveyor 15, of the second thickness Sz of the rough slab Z and of the number of paving stands 27.

Table 1 - Minimum final thickness Sf of the metal strip as a function of the thickness Sz of the rough slab Z.

With reference to fig. 6 and Table 1 describes a possible method of determining the operating parameters of the system.

By way of example only, if you want to obtain a metal strip of the low carbon content type and with a minimum thickness Sf equal to 1.8mm, width equal to 1300mm and a productivity of 110ton / h, in fig. 6 the isoproductivity curve "d" is taken into consideration, which corresponds to the desired productivity. This isoproductivity curve extends over a thickness range of the cast slab comprised between about 32mm and 48mm.

From Table 1, it is possible to identify adoptable production ranges of slab thicknesses Sb equal to 38mm and 48mm.

In the first case, ie thickness Sb of the slab equal to 38 mm, 4 rolling stands are required to obtain the desired minimum thickness of 1.8 mm. In the second case, ie thickness Sb of the slab equal to 48mm, 5 rolling stands are required.

It is convenient to identify a configuration with the minimum number of rolling mill stands in the train, therefore a train with four rolling stands will be chosen.

With the value Sb = 38mm you then enter the diagram of figure 6 until you intercept the iso-productivity curve "d" previously established and thus obtain the casting speed Ve to be used, which in this specific case is approximately 4.75m / min.

If the surrounding conditions change, the implant 10 can be easily adapted to the changed situation. For example, the availability of liquid steel for a given casting sequence could be changed due to delays in the upstream steel plant due to problems during the steel treatment phases in the secondary metallurgy phases.

In this case, the choice of the iso-productivity curve is modified and the casting parameters are redetermined.

The system 10 described so far is therefore very versatile and easy to control and set up in the field.

It is clear that modifications and / or additions of parts and / or phases may be made to the plant 10 for the production of a hot-rolled metal strip and to the relative process described up to now, without thereby departing from the scope of the present invention. .

For example, along the curved section 16 insulating panels can be arranged to avoid and / or reduce the cooling of the bar B between the exit of the radiator 15 and the towing unit 17.

It is also clear that, although the present invention has been described with reference to a specific example of an embodiment, a person skilled in the art will certainly be able to realize many other equivalent forms of plants and / or processes for the production of a hot rolled metal strip having the characteristics expressed in the attached claims and therefore all falling within the scope of protection defined therein.

Claims (21)

CLAIMS 1. Plant for the production of a hot rolled metal strip (11), comprising a continuous casting machine (12) having a substantially vertical casting axis (X) and having a containment length (LC) less than or equal to 6m , said continuous casting machine (12) being configured to cast a metal product with a casting speed (Ve) between about 3.6m / min and about 6m / min and comprising an ingot mold (13), with relative crystallizer (14 ), and a roller pre-lamination device (15) configured to carry out a liquid core pre-lamination and output an ultra-thin slab (B) having selectively settable first thicknesses (Sb), said pre-laminating device a rollers (15) having a length (LR), measured in a direction parallel to said casting axis (X), less than or equal to 5m, and being configured to determine the complete solidification of the cast product in a solidification point contained in d this roller pre-rolling device (15) is selectively placed in an area comprised between the output end of the latter and a distance from said output end of at least 80% of the length (LR) of said device roller pre-lamination (15). 2. Plant as in claim 1, characterized in that said casting machine (12) is configured to have a selectively settable solidification length (LS) in a value chosen between about 1.3m and about 5.9m. 3. Plant as in claim 2, characterized in that said plant further comprises, downstream of said roller pre-rolling device (15), a towing unit (17) configured to tow said slab (B), and that after a curved section (16) of said continuous casting machine (12), said plant comprises arranged along a substantially horizontal rolling plane (P), - at least one roughing stand (19) configured to transform said slab (B) into a rough slab (Z) having a second thickness (Sz), - first cutting means (20) configured to cut said rough slab (Z) to size, - induction heating means (21) configured to heat, or maintain, said blank slab (Z) at a given rolling temperature, a winding / unwinding device (22) configured to selectively wind / unwind said blank slab (Z) and to maintain it at said rolling temperature, - second cutting means (24) configured to carry out the head / tail trimming and possible scrapping in case of emergency of said rough slab (Z), - a continuous finishing rolling train (26) to reduce the thickness of said rough slab (Z) until said metal strip (11) having a certain final thickness (Sf) is obtained, - cooling means (28) configured to cool said metal strip (11), - a reel (29) configured to wind said metal strip (11). 4. Plant as in claim 3, characterized by the fact that said drive unit (17) is an integral part of the casting machine (12) and is composed of a number of pairs of driving rollers comprised between one and three, the rollers of each torque being configured to carry out a solid core reduction of said slab (B) with a thickness decrease between about 2mm and about 7mm. 5. Plant as in claim 3 or 4, characterized in that said curved section (16) of said casting machine (12) has a radius of curvature (R) comprised between about 1.5m and 2.5m, and that said roughing stand (19) is in direct contact with said casting machine (12). 6. Plant as in any one of the preceding claims, characterized in that said roller pre-rolling device (15) comprises a plurality of pairs of segments (30a, 30b, 3 Oc, 3 Od, 3 la, 3 lb, 3 le, 3 ld), arranged on opposite sides with respect to said casting axis (X) and each of which is provided with a plurality of containment and / or compression rollers (32) for the cast metal product, and that the number of pairs of segments (30a, 30b, 30c, 30d, 3 la, 3 lb, 3 le, 31 d) is between four and six. 7. Plant as in claim 6, characterized in that it comprises intrados segments (30a, 30b, 30c, 30d) arranged on the same side as the intrados side of said curved portion (16) and selectively inclinable with respect to said casting axis ( X) by means of actuators, and extrados segments (3 la, 3 lb, 3 le, 3 ld) arranged on the same side as the extrados side of said curved section (16) and configured to remain in a fixed position and aligned parallel to said casting axis (X) 8. Plant as in claim 6 or 7, characterized in that said segments (30a, 30b, 30c, 30d, 31a, 31b, 31c, 31d) have the same length. 9. Implant as in claim 6 or 7, characterized in that said segments (30a, 30b, 30c, 30d, 31a, 3 1b, 3 1c, 3 1 d) have different lengths, and that the first pair of segments (30a, 3a), located at the inlet end of said roller pre-rolling device (15), has a shorter length than the length of the segments (30b, 30c, 30d, 31 b, 31 c, 31 d ) placed downstream. 10. Plant as in any one of the preceding claims, characterized in that said roller pre-rolling device (15) is configured to be adjustable so that said first thicknesses (Sb) are comprised between about 28.0mm and about 48 , 0mm. 11. Plant as in any one of claims 3 to 5, characterized in that said roughing stand (19) and said continuous finishing rolling train (26) are configured to be adjustable so that said final thickness (Sf) of said metal tape (1 1) is between about 0.8mm and about 12mm. 12. Plant as in any one of the preceding claims, characterized in that according to said casting speed (Ve), correlated to said first thickness (Sb) of said slab (B), the casting machine (12) allows to obtain an hourly production between about 80 tons / h and about 160 tons / h, corresponding to about 400,000 tons / year and, respectively, about 800,000 tons / year. 13. Plant as in any one of the preceding claims from 3 to 5, characterized in that said continuous finishing rolling train (26) comprises a number of finishing stands (27) comprised between two and five. 14. Plant as in any one of the preceding claims 3 to 5, characterized in that said roughing stand (19) is configured so that said second thickness (Sz) is comprised between about 8mm and about 25mm. 15. Process for the production of a hot rolled metal strip (11), comprising: - a step of continuous casting of a metal product with a casting speed (Ve) between about 3.6m / min and about 6m / min and by means of a continuous casting machine (12) having a casting axis (X) substantially vertical, and a containment length (LC) less than or equal to 6m, said continuous casting machine (12) comprising an ingot mold (13), with relative crystallizer (14) and a roller pre-rolling device (15) having a length (LR), measured in a direction parallel to said casting axis (X), less than or equal to 5m, - a liquid core pre-rolling step to achieve along said casting axis (X) a thickness reduction of said cast product and transform the cast product leaving said crystallizer (14) into a completely solidified ultra-thin slab (B) having a first thickness (Sb) which can be selectively set, said pre-lamination phase providing for the complete solidification of the cast product in a solidification point contained in said roller pre-lamination device (15) and selectively placed in an area between the outlet end of the latter and a distance from said outlet end of at least 80% of the length (LR) of said roller pre-rolling device (15). 16. Process as in claim 15, characterized in that it comprises: - a towing phase of said slab (B) with a towing unit (17), - a roughing step of said slab (B) carried out along a substantially horizontal rolling plane (P), to transform said slab (B) into a rough slab (Z) having a second thickness (Sz), and in which the following are carried out in sequence along said rolling plane (P): - a first cutting phase to cut the rough slab (Z) to size, - a heating / temperature maintenance phase, to heat or maintain said blank slab (Z) at a given rolling temperature, - a winding / unwinding phase to selectively wind / unwind said rough slab (Z), - a second cutting phase to carry out the trimming of the head / tail of the rough slab (Z) and possible scrapping of the same in case of emergency, - a finishing rolling step in a continuous train to reduce the thickness of said rough slab (Z) until said metal strip (11) having a certain final thickness (Sf) is obtained, - a cooling phase of said metal strip (11) e - a winding step for winding said metal strip (11). 17. Process as in claim 15 or 16, characterized in that according to said casting speed (Ve), correlated to said first thickness (Sb) of said slab (B), it is possible to obtain an hourly production of said casting machine casting (12) between about 80 tons / h and about 160 tons / h, corresponding to about 400,000 tons / year and, respectively, about 800,000 tons / year. 18. Process as in any one of claims 15 to 17, characterized in that the cast product leaving said crystallizer (14) has a certain initial thickness (Se) between 48mm and 56mm, and said pre-lamination step with rollers, it carries out an adjustable reduction of the thickness of said cast product which at the end of said roll pre-rolling step assumes a first thickness (Sb) which can be selectively set to a value chosen in the range between about 28.0 mm and about 48, 0mm. 19. Process as in claim 16, characterized in that during said drawing step said slab (B) is subjected to a solid core reduction with a thickness reduction of between about 2mm and about 7mm. 20. Process as in any one of claims 15 to 19, characterized in that during said roller pre-rolling step, intrados segments (30a, 30b, 30c, 30d) of a roller pre-rolling device (15) are selectively inclined with respect to said casting axis (X), and extrados segments (3 la, 31b, 3 le, 31 d) of said roller pre-rolling device (15) and opposed to said intrados segments (30a , 30b, 30c, 30d) remain in a fixed position and aligned parallel to said casting axis (X). 21. Process as in claim 16, characterized in that said roughing step reduces the thickness (Sb) of said slab (B) so that said second thickness (Sz) of said rough slab (Z) is between about 8mm and about 25mm.