IT201800009259A1 - METHOD OF PRODUCTION OF A METAL BELT, AND PRODUCTION PLANT IMPLEMENTING THIS METHOD - Google Patents

Description

Description of the invention having as title:

"METHOD OF PRODUCTION OF A METAL BELT, AND PRODUCTION PLANT THAT IMPLEMENTS SAID METHOD"

FIELD OF APPLICATION

The present invention refers to a method of producing a metal strip and to the production plant that implements this method.

In particular, the method according to the present invention allows to define the ways of making a metal strip and a constructive layout of a plant for the production of hot-rolled metal strips.

STATE OF THE TECHNIQUE

In the steel industry, metal strip production plants are known which usually comprise an ingot mold configured to cast slabs, extraction devices provided to extract the slabs from the mold, and a rolling line located downstream of the extraction devices, configured to reduce the thickness of the slab until a metal strip of desired thickness is obtained.

Depending on the thickness of the metal strip to be obtained, as well as the overall productivity that the plant must have, it is known to suitably size the entire plant so that it complies with the required parameters, at least as regards the productivity of the plant and the thicknesses. of tapes.

In relation to these requests, it is known to provide the customer with "endless" type systems, semi-continuous type systems, for example "coil to coil" and / or "semiendless", or combined "endless" and semi-continuous systems.

The endless-type plants provide for directly supplying, ie in direct drive, the product cast from the mold to the rolling line without cutting the product being processed unless before the final winding.

The semi-continuous type systems provide that downstream of the casting machine or roughing cages, the cast products are cut to size and placed in a heating and / or maintenance oven which also acts as an accumulation buffer for the cast products when it is required, for example, to interrupt downstream rolling due to minor accidents or scheduled cylinder changes.

If the cast product is cut, downstream of the casting machine or roughing stands, to a length such as to obtain, at the end of the rolling process, a single coil, the process is called "coil to coil". If, on the other hand, the cast product is cut, downstream of the casting machine or of the roughing stands, to a length such as to obtain, at the end of the rolling process, a plurality of reels, usually from two to five, the process is called "semiendless".

It is also known that, by means of suitable measures, a semi-continuous type plant can also be operated in endless mode, obtaining the advantages of this embodiment.

The choice of the type of plant to be adopted, as well as the number of components required, for example the number of rolling stands, or the choice of how many roughing stands and how many finishing stands to adopt, is usually determined on the basis of the experience of the technicians. sector. This sizing, or preparation of the tape production plant, however, sometimes does not allow to reach an effective compromise between the investments required to build the plant, also called Capex, and the operating costs of transformation, also called Opex. Therefore, situations arise in which the investments incurred for the construction of the production plant are too high compared to revenues and therefore a production plant that is oversized with respect to the customer's productivity is provided, or alternatively, situations arise in which regret of production is undersized and therefore does not allow the achievement of the production capacity requested by the customer.

It is therefore an object of the present invention to provide a production plant correctly sized according to the needs of the customer that works with a method of hot production of metal strips, for example steel, suitable for optimizing the productivity of a production plant for strips with the smallest number of cages possible while maintaining the maximum casting speed in relation to the various types of steel.

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 producing a hot-rolled metal strip which can selectively vary the thickness of the cast slab in relation to the final thickness of the strip. It is also an object of the invention to provide a method for producing metal strips which allows to obtain an extremely flexible system that can be adapted to specific customer needs.

It is also an object of the invention to provide a metal strip production plant which is competitive on the market.

In order to obviate the drawbacks of the known art and to obtain these and further objects and advantages, the Applicant has studied, tested and implemented the present invention.

EXPOSURE OF THE FOUND

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

In accordance with the aforementioned purposes, a method of producing metal strips, in accordance with the present invention, comprises the casting of a product through a casting machine equipped with a crystallizer to obtain a slab, and the hot rolling of the slab into a lamination station for obtaining metal strips having strip thicknesses different from each other.

The casting machine, during casting, exerts an action to reduce the thickness of the product cast out of the crystallizer.

According to an aspect of the present invention, the method provides for the casting machine to be selectively set, each time as the thickness of the strip varies, to exert a different action to reduce the thickness of the cast product.

This construction solution allows you to modulate the thickness of the slab exiting the casting machine, according to the final thickness of the strip to increase the efficiency of the strip production plant and increase the quality of the strip produced.

In particular, with the present invention it is also possible in some applications to reduce by at least one unit the number of rolling stands of the rolling station for the same productivity of a known plant. This results in an economic and efficiency advantage of the entire production plant.

The thickness reduction action induced on the strip, produced from time to time, is partly distributed in the casting machine and partly in the rolling station, allowing for an efficiency and higher quality of the produced strip.

In the event that, with the same productivity, the number of rolling stands of the rolling station is substantially the same as that of a known plant, with the present invention it is possible in any case to reduce the extent of the rolling crushes, as a part the reduction in thickness is carried out directly by the casting machine and not only in the rolling station as occurs in the known art.

This device allows to obtain an energy saving thanks to a reduction of the crushing pressure on the lamination slab, and to obtain a higher quality of the strip because, for example, the profile and the flatness of the same is improved and the risk of impressed scale is reduced. on its surface.

With the present invention, moreover, it is possible to reduce maintenance interventions at least in the rolling station.

ILLUSTRATION OF DRAWINGS

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

- figs. 1-9 show some of the possible embodiments of a plant for the production of a metal strip which implements a method in accordance with the present invention;

- fig. 10 graphically illustrates some curves, determined in relation to the thickness H of the cast product leaving the crystallizer, of the trend of the reduction ratio of the thickness of the cast product exerted by the casting machine as a function of the thickness of the strip; - fig. 11 illustrates curves, determined in relation to the thickness H of the product poured out of the crystallizer, which illustrate the trend of the thickness reduction ratio in the pulling unit as a function of the thickness of the strip;

- fig. 12 illustrates the criteria for choosing the lamination method;

- fig. 13 graphically illustrates a further criterion for choosing the lamination methods in relation to the thickness of the strip and the ability of a plant layout to adopt one and / or the other of the lamination methods;

- figs. 14 and 15 are graphs that correlate the nominal slab thickness, plant productivity and casting speed; both graphs relate to an operation of the casting equal to 7,200 hours / year;

- fig. 16 is a graph which correlates the thickness ratio to the number of rolling stands required;

- figs. 17-22 illustrate two embodiments of implementation of the teachings of the present invention.

To facilitate understanding, identical reference numbers have been used wherever possible to identify identical common elements in the figures. It should be understood that elements and features of one embodiment can be conveniently incorporated into other embodiments without further specification.

DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to the various embodiments of the invention, of which one or more examples are illustrated in the attached figures. Each example is provided by way of example of the invention and is not intended as a limitation thereof. For example, the features illustrated or described as being part of an embodiment may be adopted on, or in association with, other embodiments to produce a further embodiment. It is understood that the present invention will include these modifications and variations.

Embodiments of the present invention refer to a method of producing a metal strip N in a production plant 10. In figs. 2-9 illustrates possible lay-outs of tape production plants 10 which implement the principles of the present invention. In particular, in the following reference will be made to fig. 1 illustrating a plurality of operating components mutually arranged along a processing line. These operating components illustrated in fig. 1 can be combined with each other to obtain one or more production layouts of belts illustrated in figs. 2-9. For this purpose, the constructional variants of the production plant 10 illustrated in figs. 2-9 refer to system components described with reference to fig. 1.

The production plant 10 of strips N includes at least one casting machine 11 in which the liquid metal is poured to be solidified and obtain a slab B.

In accordance with an aspect of the present invention, the production plant 10 also comprises a rolling station 19 located downstream of the casting machine 11 and configured to hot roll the slab B and obtain strips N.

The casting machine 11 comprises at least an ingot mold 15 equipped with a crystallizer 15a in which the formation of a cast product P takes place which passes through the entire casting machine 11.

The crystallizer 15a can comprise at least two wide plates facing each other and spaced apart, at least in the terminal portion, of a determined value which substantially corresponds to the thickness H of the cast product P leaving the crystallizer 15a.

Furthermore, the plates of the crystallizer 15a have a width which is determined in relation to the width of the web N which is to be obtained. At the outlet of the crystallizer 15a, the cast product P has a solidified outer shell, or skin, which allows the liquid metal to be contained also outside the crystallizer 15a.

In accordance with solutions of the present invention, the casting machine 11 can be provided with thickness reduction means located downstream of the crystallizer and which can be selectively set, each time as the thickness of the strip varies, in order to exercise a different action to reduce the thickness of the strip. thickness of the cast product P leaving the crystallizer 15a. The thickness reduction means can comprise a roller pre-lamination device and / or a group of rollers, for example for driving as described below.

In accordance with embodiments, the casting machine 11 comprises a roller pre-rolling device 16, also referred to hereinafter as a roller conveyor, located downstream of the mold 15 and configured to reduce the thickness of the cast product P leaving the crystallizer. 15a while his heart is still liquid or partially liquid.

In accordance with embodiments of the invention, the roller conveyor 16 is provided with a plurality of rollers grouped into segments that are opposite and aligned along the casting axis.

The rollers are selectively approached / moved away from each other to exert a selective action to reduce the thickness of the cast product.

Associated with the segments are adjustment devices 17 of a known type, for example hydraulic cylinders, to move the rollers of the roller conveyor 16 closer to each other and to carry out the aforementioned reduction in the thickness of the cast product P leaving the crystallizer 15a.

The reduction in overall thickness that the poured product P that comes out of the crystallizer 15a undergoes inside the roller conveyor 15a is carried out with a liquid core therefore does not generate elongation of the material.

The slab B, exiting the roller conveyor 16, is completely solidified and has a slab thickness SB1.

The thickness of the slab SB1 that is obtained at the end of the pre-rolling with liquid core determines the productivity of the casting machine 11 and therefore of the entire plant.

The compression carried out by the roller conveyor 16 allows the two half-skins to be joined in a junction point, called with the English term “Kissing Point” (KP), in which the cast product completely solidifies. The KP is also seen as the terminal vertex of the liquid cone which originates from the meniscus of the liquid metal in the crystallizer 15a.

In accordance with an aspect of the present invention, the position of the KP can be varied, along the longitudinal extension of the roller conveyor 16, by intervening on the intensity of the reduction in thickness at the liquid core obtained by adjusting the segments of the roller conveyor 16 and on the intensity secondary cooling. The position of the KP is also a function of the casting speed. The thickness of the cast product at the KP is equal to the thickness of the slab SB1 exiting the roller conveyor 16.

In accordance with an aspect of the present invention, the thickness of the slab SB1 is selectively set as a function of the final thickness of the strip N, in particular as a function of the product mix to be regretted, as will be better illustrated hereinafter.

In accordance with possible embodiments, the roller conveyor 16 can be associated with cooling devices of a known type, also called secondary cooling, and configured to cool the external surfaces of the slab and thus determine its further solidification. The cooling devices may include spray nozzles or water mixed with air ("air-mixed"). The action of the cooling devices also has an influence on the position of the KP.

In accordance with embodiments, the casting machine 11 comprises a pulling unit 18 located downstream of the roller conveyor 16 and configured to pull the slab B towards the rolling station 19.

The drawing assembly 18 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 B to be towed.

In accordance with embodiments, the drawing assembly 18 can also be configured to laminate the slab B which passes through it. By way of example only, 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 completely solidified slab B, as described below.

In accordance with possible embodiments, the towing unit 18 can comprise a first towing device 18a placed directly downstream of the roller conveyor 16, or in the vertical section of the casting machine 11. In accordance with a possible embodiment, possibly combinable with the previous embodiment, the towing unit 18 can comprise a second towing device 18b placed directly downstream of the curved portion of the casting machine 11.

The presence of the first pulling device 18a is provided only in the case of vertical casting.

The presence of the second towing device 18b is provided in the case of vertical and vertical-curved casting.

The first towing device 18a and / or the second towing device 18b can comprise a number of pairs of rollers comprised between 1 and 3.

As mentioned above, the rollers of the drawing assembly 18 are configured to effect a slight reduction of the solid core thickness on the slab B of thickness SB1 and therefore a real lamination, albeit of a slight entity, which determines an elongation of the material. The rolling, albeit light, of the pulling unit 18 generates a further reduction in the thickness of the slab B which assumes a further thickness SB2, less than SB1, thus allowing the rolling station 19 located downstream to reach thinner thicknesses. Since the pulling unit 18 is placed at the end of the casting machine 11, the thickness SB2 of the slab B exiting the pulling assembly 18 corresponds to the thickness of the slab B exiting the casting machine 11.

The pulling unit 18, together with the roller conveyor 16 and the crystallizer 15a, is an integral part of the casting machine 11 which, thanks to the rolling action carried out by the rollers, can be defined as a "Rolling Caster".

By Rolling Caster we mean a casting machine 11 capable of both casting the product and rolling it, partly with a liquid core and partly with a solid core.

The reduction in overall thickness that the cast product P undergoes that comes out of the crystallizer 15a inside the casting machine 11 is carried out partly with a liquid core and partly with a solid core.

According to an aspect of the present invention, the distribution of thickness reduction in the casting machine 11 can be advantageously modulated between the liquid core and the solid core according to specific production requirements.

In accordance with possible embodiments, the rolling station 19 comprises a roughing unit 12 configured to laminate the slab B.

The roughing unit 12 can be equipped with one or more roughing cages 20.

According to further embodiments of the invention, the rolling station 19 comprises a finishing unit 13 configured to laminate the slab B and bring the latter to its final dimensions, or to define the metal strip N.

The finishing unit 13 is located downstream of the roughing unit 12.

The finishing unit 13, in turn, can also include one or more finishing cages 21 each of which is configured to laminate and define the thickness of the SN strip.

According to possible embodiments, directly downstream of the roughing unit 12 there is a cutting shear 26 configured to cut the rough slab B and define a bar, also called in the transfer bar sector, which will be subjected to subsequent rolling to obtain of tape No.

The system 10 may include at least one induction heating device, in this case one, two, or three induction heating devices 22, 23, and 34 and configured to heat the slab B.

In accordance with a possible embodiment, the plant 10 comprises a first induction heating device 22 located downstream of the casting machine 11, in this case upstream of the roughing unit 12, and configured to restore the temperature of the slab before its introduction into the rolling station 19.

According to a possible embodiment, the plant 10 comprises a second induction heating device 23 placed upstream of the finishing unit 13, for example between the roughing unit 12 and the finishing unit 13, and configured to increase the temperature of the bar before its introduction into the finisher 13.

In accordance with a possible embodiment solution, the aforementioned second induction heating device 23 is placed directly downstream of the roughing unit 12.

According to a further embodiment solution, regret 10 comprises a third induction heating device 34 interposed between two of the aforementioned finishing cages 21 and configured to restore the temperature of the bar during the finishing process.

In accordance with a further embodiment, the production plant 10 can comprise at least a heating and / or maintenance unit, in this case two heating and / or maintenance units 32 and 33, configured to heat or maintain the temperature bar segments.

The heating and / or maintenance unit 32 and 33 can comprise a heating and / or maintenance tunnel furnace which also acts as a buffer for accumulating the bars in the event of interruption of the rolling process, due to accidents or due to programmed change of the cylinders. , thus avoiding loss of material and energy and, above all, avoiding an interruption of the casting.

According to a possible embodiment, the production plant 10 comprises a first heating and / or maintenance unit 32 placed directly upstream of the rolling station 19.

In accordance with a further implementation, the production plant 10 includes a second heating and / or maintenance unit 33 placed between the roughing unit 12 and the finishing unit 13.

In accordance with this embodiment, it is advantageous to provide that the production plant 10 is provided with a shear 35 interposed between the casting machine 11 and the rolling station 19 and configured to cut the slab B produced by the casting machine 11 into segments. In the event of an emergency, or for maintenance requirements due for example to the change of cylinders in the rolling station 19, the segments can be subsequently stored and maintained at temperature inside the first heating and / or maintenance unit 32.

In accordance with some embodiments, the production plant 10 comprises an intermediate winding / unwinding device 29 interposed between the cutting shear 26 and the finishing unit 13 and configured to wind the bar cut by the cutting shear 26 and to supply the finisher 13 the bar previously wound and cut.

In accordance with possible embodiments, Replant 10 can include both the second heating and / or maintenance unit 33 and the intermediate winding / unwinding device 29 located downstream from the heating unit 32.

The intermediate winding / unwinding device 29 can be for example of the type described in international application WO-A-2011/080300 in the name of the Applicant.

According to embodiments, the intermediate winding / unwinding device 29 comprises a first unit 30 and a second unit 31 which alternate in the winding function of the bar received from the roughing unit 12, and in the unwinding function of the previously wound bar, to feed it to the finisher 13.

In particular, while one of the two units 30, 31 wraps a bar, the other unit 31, 30 unwinds another rough bar supplying it downstream. This intermediate winding / unwinding device 29 also allows to define a temporary storage buffer to compensate for the different working speeds of the casting machine 11 and of the finishing unit 13. In this way the intermediate winding / unwinding device 29 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 intermediate winding / unwinding device 29 may include heating devices, not shown, to heat or maintain the bar contained inside at the temperature.

According to a further embodiment of the present invention, regress 10 can comprise a cutting member 28 placed between the roughing unit 12 and the finishing unit 13 and configured to cut the head or tail of the bar provided by the roughing 12, in this case from the intermediate winding / unwinding device 29, and to be fed to the finishing unit 13.

According to a further embodiment, between the rolling station 19 and the final winding unit 14 there is a cooling unit 24 configured to cool the strip N leaving the rolling station 19 and to allow it to be collected in the unit. final winding 14.

In accordance with a further implementation of the present invention, the plant 10 comprises a final winding unit 14 of the tape N.

The final winding unit 14 may comprise a winding member 25 designed to wind the tape N.

In accordance with embodiments, the plant 10 comprises a cutting device 27 placed upstream of the final winding unit 14 and configured to cut the tape N to size, once a predefined weight of the tape reel N has been reached. cutting device 27 can be positioned between the cooling unit 24 and the final winding unit 14.

With reference to fig. 2 illustrates a variant embodiment of a production plant 10 which comprises, arranged in sequence, the casting machine 11 as defined above, the shear 35, the first induction heating device 22 and / or the first heating unit and / or holding 32, finisher 13, cooling unit 24 and final winding unit 14.

With reference to fig. 3 illustrates a further variant of the production plant 10 which in addition to the components provided in the production plant 10 in fig. 2 provides that the rolling station 19 comprises the roughing unit 12, the second induction heating device 23, the second heating and / or maintenance unit 33, and the cutting member 28 placed upstream of the finish 13.

With reference to fig. 4 illustrates a variant embodiment of a production plant 10 which comprises, arranged in sequence, the casting machine 11 as defined above, the roughing unit 12, the cutting shear 26, the second induction heating device 23, the intermediate winding / unwinding device 29, the cutting member 28, the finisher 13, the cooling unit 24 and the final winding unit 14.

With reference to fig. 5, production unit 10 comprises, arranged in sequence, the casting machine 11 as defined above, the rolling station 19 equipped with the roughing unit 12, the cutting shear 26, the second induction heating device 23, the second heating and / or holding unit 33, finisher 13, cooling unit 24 and final winding unit 14.

The production plants 10 described with reference to figs. 2-5, can be selectively set to work in coil to coil mode.

With reference to fig. 6, production unit 10 comprises, arranged in sequence, the casting machine 11 as defined above, the rolling station 19 equipped with the shear 35, the second induction heating device 23, the second heating and / or maintenance unit 33, finisher 13, cooler 24, cutter 27, and final take-up unit 14.

The production plant 10 described with reference to fig. 6 can be configured to work in coil to coil or semi-endless mode. With reference to fig. 7, the production plant 10 comprises, arranged in sequence, the casting machine 11 as defined above, the rolling station 19 equipped with the roughing unit 12, the cutting shear 26, the second induction heating device 23, of the finishing unit 13, of the third induction heating device 34 interposed between the finishing cages 21, of the cooling unit 24, of the cutting device 27 and of the final winding unit 14.

The production plant 10 described with reference to fig. 7 can be configured to work in endless mode.

With reference to fig. 8, production unit 10 comprises arranged in sequence, the casting machine 11 as defined above, the rolling station 19 equipped with the roughing unit 12, the cutting shear 26, the second induction heating device 23, the device intermediate winder / unwinder 29, of the cutting member 28, of the finishing unit 13, of the third induction heating device 34 interposed between the finishing cages 21, of the cooling unit 24, of the cutting device 27 and of the final winding unit 14.

The production plant 10 described with reference to fig. 8 can be configured to work in coil to coil or endless mode.

With reference to fig. 9, production unit 10 comprises arranged in sequence, the casting machine 11 as defined above, the rolling station 19 equipped with the shear 35, the first induction heating device 22, the first heating and / or maintenance unit 32, of the roughing unit 12, of the cutting shear 26, of the second induction heating device 23, of the finishing unit 13, of the third induction heating device 34 interposed between the finishing cages 21, of the cooling unit 24, the cutting device 27 and the final winding unit 14.

The production plant 10 described with reference to fig. 9 can be configured to work in coil to coil, semi-endless, or endless mode.

The embodiments of systems 10 described with reference to figs.

2-9, define examples of production plant layout families that the end user can choose in an optimized way according to the productivity, the produce mix, and the types of steel, also called "Steel grade", to be produced .

In accordance with an aspect of the present invention, a method of producing metal strips N comprises at least the casting of a cast product P through the casting machine 11 to obtain a slab B, and the hot rolling of the slab B in the rolling station 19 for obtaining N.

According to an aspect of the present invention, the casting machine 11, during casting, exerts an action to reduce the thickness of the cast product P at the outlet from the crystallizer 15 a.

According to a further aspect of the present invention, for each thickness dimension of the strip N that is produced, the casting machine 11 is selectively set to exert a different action to reduce the thickness of the cast product P leaving the crystallizer 15a.

In particular, it is envisaged that the thickness of the slab B produced by the casting machine 11 is, from time to time, adjusted according to at least the final thickness of the strip N to be obtained and possibly the variety of products, or "product mix" that you want to obtain.

This embodiment allows to reduce the crushing action that must be exerted in the rolling station 19, to reduce the required rolling power, to reduce the wear to which the rolling rolls are subjected and in some cases also to reduce, by at least one, the number of rolling stands with respect to known plants having the same overall productivity.

By way of example only, it can be envisaged that, with the same dimensions of the crystallizer 15a, the method comprises a first step of producing a first strip having a first strip thickness SN 'and in which the casting machine 11 exercises a first ratio reduction of thickness TAU A 'of the cast product leaving the crystallizer 15a, and a second phase of production of a second strip having a second strip thickness SN ", lower than the first thickness, and in which the casting machine 11 exercises a second reduction ratio TAU A "of the cast product P leaving the crystallizer 15 a, and in which the first reduction ratio of thickness TAU A 'is different from the second reduction ratio of thickness TAU A".

In accordance with an implementation solution, the first thickness reduction ratio TAU A 'is lower than the second thickness reduction ratio TAU A ".

The thickness reduction ratio TAU A is defined as the difference between the thickness H of the cast product P exiting the crystallizer 15a and the slab thickness SB2 exiting the casting machine 11, compared to the thickness H of the cast product P exiting from the crystallizer 15a.

According to a possible embodiment of the present invention, the Applicant has determined that the casting machine 11 is selectively set to exert an action to reduce the thickness of the cast product P, defined by the relationship:

In which:

K: is a variable parameter between 0.8 and 1.1;

A: is a coefficient equal to 4689;

H: is the thickness of the cast product P leaving the crystallizer 15a, that is, it is the thickness of the crystallizer 15a;

a: is a coefficient equal to -0.37;

SN: is the thickness of the strip N to be obtained at the end of lamination.

The TAU A that derives from the expression above is a percentage value and, by way of example only, can normally be a value between 2% and 75%.

In fig. 10 illustrates some examples of curves, determined in relation to the thickness H of the cast product P, which illustrate the trend of the TAU A as a function of the thickness of the strip SN.

This relationship allows to optimize the setting of the casting machine 11, according to the thickness of the crystallizer 15a and the thickness of the strip SN to be obtained for efficient operation of the entire production plant, as defined above.

According to a possible embodiment of the invention, the casting machine 11 is configured to exercise:

i) an action of reducing the thickness of the cast product P by liquid core pre-lamination with the roller conveyor 16 referred to as the thickness reduction ratio in the roller conveyor TAU1;

ii) an action to reduce the thickness of the cast product P by the action of the towing group 18, referred to as the thickness reduction ratio in the towing group TAU2.

The reduction in thickness by means of the drive unit 18 can be optional.

The TAU A thickness reduction ratio is therefore given by the combination of TAU 1 and TAU 2 reductions.

The thickness reduction ratio in the roller conveyor TAU 1 is defined by the difference between the thickness H of the cast product P exiting the crystallizer 15a and the thickness of slab SB1 exiting the roller conveyor 16, compared to the thickness H of the cast product P exiting the crystallizer 15a.

The thickness reduction ratio in the towing unit TAU2, and is defined as the difference between the thickness of slab SB1 exiting the roller conveyor 16 and the thickness of slab SB2 exiting the towing assembly 18, compared to the thickness of slab SB1 in exit from the roller conveyor 16.

According to a possible embodiment of the present invention, the Applicant has determined that the pulling unit 18 is selectively set to exert an action to reduce the thickness SB1 of the solid core cast product P, defined by the relationship:

In which:

Q: it is a variable parameter between 0.8 and 1.1;

B: is a first coefficient equal to 10928;

H: is the thickness of the cast product P leaving the crystallizer 15a as defined above;

b: is a second coefficient equal to -1.659;

SN: is the thickness of the tape as defined above;

C: is a third coefficient equal to 10648;

c: is a fourth coefficient equal to -1.596.

In accordance with a possible embodiment solution, the reduction of the thickness of the solid core cast product P is applied for strip thicknesses SN between 0.6mm and 3.5mm. For these dimensions of the strip thickness SN, in fact, the reduction action with liquid core is relatively high in order to reduce the starting slab as much as possible, from the very beginning and therefore it is advantageous to couple the reduction action with liquid core also a further action of solid core thickness reduction exercised with the pulling unit 18.

In addition, the solid core rolling action exercised with the towing unit 18 allows to increase the production of the strips and this is particularly advantageous for thin strip thicknesses.

In flg. 11 illustrates some examples of curves, determined in relation to the thickness H of the poured product P leaving the crystallizer, which illustrate the trend of the TAU2 as a function of the thickness of the strip SN.

The reduction ratio in the roughing unit 12 is called TAU3 and is defined as the difference between the thickness SB2 of the slab B upstream of the roughing unit 12 and the thickness of the slab B downstream of the roughing unit 12, compared to SB2 thickness of slab B upstream of the roughing unit 12.

The reduction ratio in the finishing unit 21 is called TAU4 and is defined as the difference between the thickness of the slab B upstream of the finishing unit 21 and the thickness of the strip SN obtained, compared to the thickness of the slab B upstream of the finisher unit 21.

The overall reduction ratio of the rolling station 19 is defined as TAUB and is defined as the difference between the thickness of slab SB2 leaving the casting machine 11 and the thickness of the strip N obtained, in relation to the thickness of slab SB2 supplied by the machine of casting 11. The overall reduction ratio TAUB of the rolling station 19 can also be defined as the combination of the reduction ratios of the roughing unit 12 and the finishing unit 13, TAU 3 and TAU 4.

In accordance with a further aspect of the present invention, the method of producing metal strips comprises the supply, by a customer, of project data comprising at least:

- a PR productivity, for example annual, of the production plant 10,

- a range of thicknesses RS and an average belt width LN that the production plant 10 will have to produce;

- the respective distribution of productivity according to the thickness of the strip N produced;

- the types of products that can be poured with the casting machine, or the aforementioned “steel grade”

- the respective distribution of productivity according to the types of products that can be poured.

The set of the aforementioned parameters defines the so-called '' product mix of the plant, or the variety of products that the production regret 10 will have to produce and according to which it is sized to achieve the purposes of the present invention.

The supply of the range of thicknesses RS provides for the determination of a minimum thickness SMIN and a maximum thickness of SMAX obtainable tape.

In embodiments of the present invention, the rolling method provides for determining the optimal type of lamination method of slab B in relation to the mix required by the customer.

The lamination mode of slab B is chosen from endless, semi-endless and coil to coil lamination modes.

In fig. 12 shows a graph that illustrates the criteria for choosing one of the aforementioned lamination methods at least in relation to the thickness of the strip SN and of the castable Steel grades.

In general, for a construction of the production plant 10 which allows to work with several operating modes, the rolling method to be implemented from time to time will be defined by optimizing the operating conditions of the plant, on the basis of economic evaluations (energy consumption and yield of the process) and of the quality required for the final product (dimensional tolerances and mechanical characteristics of the belt).

By way of example, it can be foreseen that if in the production mix there is a prevalence of thin thicknesses without types of special steels, for example peritectic steels which are difficult to cast and require low casting speeds, an endless rolling method is chosen. , and therefore one of the plant layouts illustrated in figs can be chosen. 7, 8 or 9.

If in the production mix there is a prevalence of thin thicknesses but there is also the need to cast types of special steels, a coil-to-coil and semi-endless rolling method is generally chosen, and therefore one of the layouts can be chosen. of plant illustrated in figs. 6 and 9. Both coil-to-coil and semi-endless modes allow for the casting of special steels at low speed as the casting process is independent from the rolling process. The semi-endless mode is preferred for thin and ultra-thin N strip thicknesses, for example between 0.8mm and 1.4mm. The coil-to-coil mode is preferred instead for tape thicknesses greater than 1.4mm.

In fig. 13 graphically illustrates a further criterion for choosing the lamination methods in relation to the thickness of the strip and the ability of the plant layout chosen to adopt one and / or the other of the aforementioned lamination methods.

By way of example only, with reference to fig. 13, if the constructive layouts of figs. 2-5, the systems will be operated in coil-to-coil mode for strip thicknesses between about 1.2mm and about 12mm, while in the case in which the constructive layout of fig. 9, it is foreseen to operate the system in endless mode for strip thicknesses between about 0.6mm and about 1mm, in semi-endless mode for strip thicknesses between about 1mm and about 2mm and in coil-to- coil for tape thickness between about 2mm and about 12mm.

According to a further implementation solution, the production method provides for the setting of a casting speed VC which is chosen in a value between 4.5m / min and 6m / min.

In particular, for types of steel that are difficult to pour, such as API, peritectic and Corten steels, a lower casting speed is advantageously set, for example between 4.5 and 5m / min. For steels easier to cast such as Low Carbon, Medium Carbon, HSLA, DP, CP, HC, MnB, a higher casting speed is set, for example between 5m / min and 6m / min.

In the same way, the choice of casting speed VC can also be defined in relation to the chosen rolling modes, i.e. relatively low casting speeds for coil-to-coll and semi-endless modes, while higher casting speeds for endless mode. The production method then provides for the determination of a nominal slab thickness value SBN which, in relation to the casting speed VC and the average strip width LN, allows to reach the productivity PR.

This nominal slab thickness SBN can also be interpreted as the constant thickness of an equivalent slab which, for the same overall production for that given product-mix, corresponds to the average of the (variable) slab thicknesses after reduction to a weighted liquid core. (the average) on the respective hourly productions.

In accordance with a possible embodiment, the nominal slab thickness SBN is determined by the relation:

SBN = PR / HOURS OPERATED VE / (V C * LN * P S)

By operating hours, here and in the following of the description and claims, we mean the hours of operation, or of plant operation, in the calendar year, net of production stops for maintenance, accidents or the like.

Where PS is the specific weight of the steel which can usually be around 7.8kg / dm <3>.

With reference to figs. 14 and 15 graphs are shown that correlate the nominal slab thickness SBN, the annual productivity PR of the plant and the casting speed VC.

In particular, fig. 14 refers to a slab width of about 1300mm, while fig. 15 refers to a slab width of about 1400mm.

According to a possible implementation of the present invention, the method comprises the determination of the thickness H of the poured product P leaving the crystallizer 15a, or the determination of the distance between the plates of the crystallizer 15a at the outlet section of the latter. This thickness H of the cast product P is the one adopted for the entire product mix defined by the customer.

In a possible implementation of the invention, the thickness H of the cast product P leaving the crystallizer 15 a, is a number comprised between 10mm and 15mm more than the nominal slab thickness SBN.

The method then provides for the determination of a thickness ratio RSP applied by the rolling station 19 and which is calculated as the ratio between the value of the thickness of the slab SB2 entering the rolling station 19, when the strip N of minimum thickness SMIN is processed. , and the minimum thickness SMIN of the ribbon N obtainable.

The value of the thickness of the slab SB2 entering the rolling station 19 when the strip N of minimum thickness SMIN is processed, is calculated as the thickness H of the cast product P leaving the crystallizer 15a minus the maximum reduction in thickness impressed by the casting. According to a possible embodiment, this maximum thickness reduction induced by the casting machine 11 is at least equal to 31 mm, or greater.

Subsequently, the method provides for the determination of the number of rolling stands of the rolling station 19, in relation to this thickness ratio.

For a thickness ratio between 4 and 12, four rolling stands are provided.

For a thickness ratio between 12 and 21, five rolling stands are provided.

For a thickness ratio between 21 and 52, six rolling stands are provided.

For a thickness ratio between 52 and 110, seven rolling stands are provided.

This correlation between the number of rolling stands and the thickness ratio is illustrated in the graph of fig. 16.

The number of rolling stands of the rolling station 19 is intended as the sum of the number of finishing stands 21 and the number of blanking stands 20.

Subsequently, the method provides for setting a distribution mode of the liquid core and solid core reduction in the casting machine 11, carried out with the roller conveyor 16 and with the pulling unit 18, on the slab B leaving the crystallizer 15a, in relation to the final thickness of the strip N.

This distribution modality of the thickness reduction of the cast product P can be determined by means of the relations TAU A and TAU 2 defined above.

In accordance with a further possible embodiment solution, the casting machine 11 can be set to effect a thickness reduction of the cast product P equal to 5mm for a strip thickness equal to the aforementioned maximum thickness SMAX, and a thickness reduction comprised between 25mm and 3 Imm for a tape thickness equal to the aforementioned minimum thickness SMIN.

In accordance with a possible embodiment, the roller conveyor 16 can perform a maximum RCLMAX liquid core reduction of approximately 25mm. According to a possible embodiment, the roller conveyor 16 can perform a minimum reduction to the liquid core RCLMIN of about 5mm. This reduction allows to give higher quality to the cast metal product P.

According to an embodiment of the invention, the pulling unit 18 can perform a maximum reduction with a solid core of at least 7mm, while the minimum reduction is equal to zero.

In particular, each single pair of rollers of the drawing assembly 18 can produce, when necessary, a squeeze of an entity of between 0.5mm and 1.5mm.

In accordance with possible implementations of the method, if a coil to coil type production mode is set, and the use of a winding / unwinding device 29 is envisaged, the number of roughing stands 20 is determined so as to supply a bar with a thickness of between 8mm and 25mm at the input to the winding / unwinding device 29. Bar thicknesses less than 8mm would lead to problems of transport and introduction of the bar into the winding / unwinding device, while bar thicknesses greater than 25mm would entail operational and / or dimensional difficulties with possible generation of surface defects on the bar itself. In accordance with further possible implementations of the method, if a coil to coil type production mode is set, and the use of a heating unit 33 is envisaged, the number of roughing stands 20 is determined in a manner a bar with a thickness greater than or equal to 30mm to be supplied to the heating unit. Dimensions lower than these thickness values would require the use of an extremely long heating unit, difficult to manage and uneconomical.

In accordance with a possible embodiment, the number of finishing stands 21 is expected to be at least two.

REALIZATION EXAMPLES

With reference to figs. 17-22 two embodiments of implementation of the teachings of the present invention are now illustrated. Specifically, with reference to figs. 17-19, a first case is illustrated in which a PR production of approximately 1.1 Mton / year is required, a range of thicknesses RS between 1.2mm and 8mm and an average width of the LN strip of approximately 1300mm;

With reference to figs. 20-22, on the other hand, illustrates a second case in which a PR production of approximately 1.4 Mton / year is required, a range of thicknesses RS between 0.8mm and 3mm and an average width of the LN belt of approximately 1400mm.

With reference to the tables shown in figs. 17 and 20 it is possible to appreciate at least in the last four columns on the right a comparison on the distribution of productivity in relation to the "product mix" in the case of a conventional casting and in the case of a casting with thickness reduction according to the teachings of the present invention. The values of produce mix, and annual productivity (see the eleventh and twelfth columns of the tables) are parameters required by the customer and set according to his needs for use of the system.

Again with reference to the tables shown in figs. 17 and 20 it is possible to appreciate how in the sixth column the thickness of the slab SB2 exiting the casting machine 11 is not a constant value as the thickness of the strip varies, but is a value that decreases with the reduction of the thickness in the strip. In the conventional or known technique, on the other hand, the thickness of the SBN slab exiting the casting machine is always equal to the variation in the thickness of the strip as reported in the second column from the left. This consideration is also illustrated graphically in figs. 18 and 21.

This variation of the thickness of the slab in relation to the thickness of the final strip is obtained by the fact that the casting machine 11 gives the product being cast a reduction in the core of liquid RCL of the thickness which is reported in column three of the tables of figs. 17 and 20.

These tables also show the thickness reductions made with the drive unit 18 (fifth column), with the roughing unit 12 (seventh column), and with the finishing unit 13 (ninth column), and how these actions are divided according to the thickness of the final strip to be obtained.

In figs. 19 and 22, on the other hand, graphically illustrates the divisions of the hourly productivity of the plant according to the thickness of the strip to be obtained, in the case of a known conventional casting, and of a casting with variable thickness reduction in accordance with the present invention.

In particular, in both flgs. 19 and 22 it is possible to note that, in the case of a known conventional casting, the hourly productivity is maintained unchanged for any thickness of strip to be obtained, while with the casting according to the present invention the hourly productivity is varied in relation to the tape thicknesses to be obtained.

From an analysis of figs. 19 and 22 it can be appreciated that for low web thickness values the present invention admits a lower productivity with respect to conventional solutions, while for high web thickness values the present invention provides a higher productivity than conventional solutions. Overall, however, the annual productivity of the plant in the case of conventional casting and casting in accordance with the present invention are the same, and in the solution in accordance with the present invention it is possible to obtain the aforementioned advantages with respect to the known solution.

With reference to the first case illustrated in figs. 17-19 now illustrates a method of choosing the type of plant and the number of rolling stands of the rolling station 19.

In particular, on the basis of the range of belt thicknesses varying between 1.2mm and 8mm, and in relation to the graph in fig. 12, it is advantageous to adopt a plant layout capable of implementing a coil-to-coil type lamination mode.

The setting of a casting speed of about 5.5m / min is then envisaged which corresponds, for an average width LN of the strip of 1300mm and a productivity of l, lMton / year, a nominal thickness of SBN slab of about 45mm. as can also be graphically derived from fig. 14.

On the basis of this SBN value it is possible to determine the thickness H of the cast product P which is from 10mm to 15mm greater than the nominal slab value SBN, in this case equal to 55mm, as shown in the table in fig. 17.

The determination of the thickness reduction to be impressed by the rolling station 19 is then envisaged.

The thickness of the slab SB2 entering the lamination station 19 when the minimum thickness is processed is 24mm.

The ratio of thicknesses RSP of the rolling station 19 is therefore a total of 24 / 1.2 = 20.

With reference to fig. 16 it is possible to appreciate that for this thickness ratio corresponds a number of cages equal to 5.

With reference to conventional casting, on the other hand, the conventional thickness ratio is given by the ratio between the nominal slab thickness SBN and the minimum thickness SMIN of the strip, in this case 45 / 1.2 = 37.5. With reference to fig. 16, this thickness ratio corresponds to a number of cages equal to 6. From this example it is possible to appreciate how with the same annual productivity of the plant it is possible, compared to the conventional production method, to reduce the number of cages by one unit Laminating.

With reference to the second case illustrated in figs. 20-22 a further method of choosing the type of plant and the number of rolling stands of the rolling station 19 is now illustrated.

In particular, on the basis of the range of belt thicknesses varying between 0.8mm and 3.0mm and in relation to the graph in fig. 12 it is advantageous to adopt a plant layout capable of implementing an endless rolling mode.

The setting of a casting speed of about 6.0m / min is then envisaged which corresponds, for an average width LN of 1400mm and a productivity of 1.4Mton / year, a nominal thickness of SBN slab of about 50mm as derivable also graphically from fig. 15. On the basis of this value SBN it is possible to determine the thickness H of the cast product P which is from 10mm to 15mm greater than the nominal slab value SBN, in this case equal to 65mm, as shown in the table in fig. 20.

The determination of the thickness ratio to be impressed by the rolling station 19 is then envisaged.

The thickness of slab SB2 entering the lamination station 19 when the minimum thickness is processed is 34mm.

The ratio of thicknesses RSP of the rolling station 19 is therefore a total of 34 / 0.8 = 42.5.

With reference to fig. 16 it is possible to appreciate that for this thickness ratio corresponds a number of cages equal to 6.

With reference to conventional casting, however, the conventional thickness ratio is given by the ratio between the nominal slab thickness SBN and the minimum thickness SMIN of the strip, in this case 50 / 0.8 = 62.5. With reference to fig. 16 to this thickness ratio corresponds a number of cages equal to 7. From this example it is possible to appreciate how with the same annual productivity of the plant it is possible, compared to the conventional production method, to reduce the number of cages by one unit. lamination.

It is clear that modifications and / or additions of parts may be made to the production method of a metal strip, and to the production plant that implements this method described above, without thereby departing from the scope of the present invention.

It is also clear that, although the present invention has been described with reference to some specific examples, a person skilled in the art will certainly be able to realize many other equivalent forms of production method for a metal strip, and of a production plant that implements such method, having the characteristics expressed in the claims and therefore all falling within the scope of protection defined by them.

In the following claims, the references in brackets are for the sole purpose of facilitating reading and should not be considered as limiting factors as regards the scope of protection underlying the specific claims.

Claims (13)

CLAIMS 1. Method of producing metal strips (N) comprising casting a cast product (P) through a casting machine (11) equipped with a crystallizer (15a) to obtain a slab (B), and hot rolling of said slab (B) in a rolling station (19) for obtaining metal strips (N) having strip thicknesses (SN) different from each other, in which said casting machine (11), during casting, exerts a action of reducing the thickness of the cast product (P) leaving the crystallizer (15a), characterized by the fact that said casting machine (11) is selectively set, each time as the thickness of the strip (SN) varies, to exert a different action to reduce the thickness of the cast product (P). 2. Method as in claim 1, characterized in that for the same dimensions of the crystallizer (15a), the method comprises a first step of producing a first strip having a first thickness (SN '), in which the casting machine ( 11) exerts a first thickness reduction ratio (TAU A ') of the cast product (P), and a second production step of a second strip having a second thickness (SN "), lower than the first thickness (SN'), in which the casting machine (11) exercises a second thickness reduction ratio (TAU A ") of the cast product (P) different from the first thickness reduction ratio (TAU A '). 3. Method as in claim 2, characterized by the fact that the first thickness reduction ratio (TAU A ') is lower than the second thickness reduction ratio (TAU A "). 4. Method as in any one of the preceding claims, characterized in that said casting machine (11) is selectively set to exert an action to reduce the thickness of the cast product (P) leaving the crystallizer (15a), defined by relation: in which: K: is a variable parameter between 0.8 and 1.1; A: is a coefficient equal to 4689; H: is the thickness of the cast product (P) leaving the crystallizer a: is a coefficient equal to -0.37; SN: is the thickness of the strip to be obtained at the end of the lamination. 5. Method as in any one of the preceding claims, characterized in that said casting machine (11) comprises a roller pre-rolling device (16) which exerts an action to reduce the thickness of the cast product (P) leaving the crystallizer (15a) by pre-lamination with a liquid core. 6. Method as in claim 5, characterized in that said roller pre-rolling device (16) is provided with a plurality of opposite rollers and between which said cast product (P) passes and said rollers are selectively approached / moved away between them to exert a selective action of reducing the thickness of said cast product (P) to a liquid core. 7. Method as in claim 5 or 6, characterized in that said casting machine (11) comprises a pulling unit (18) which exerts an action to reduce the thickness of the cast product (P) at the outlet from said device roller pre-rolling (16), by means of solid core rolling of the cast product (P). 8. Method as in claim 7, characterized by the fact that the pulling unit (18) is selectively set to exercise an action to reduce the thickness of the solid core cast product (P), defined by the relationship: in which: Q: is a variable parameter between 0.8 and 1.1; B: is a first coefficient equal to 10928; H: is the thickness of the cast product (P) leaving the crystallizer (15a); b: is a second coefficient equal to -1.659; SN: is the thickness of the tape; C: is a third coefficient equal to 10648; c: is a fourth coefficient equal to -1.596. 9. Method as in claim 7 or 8, characterized in that the reduction of the thickness of the solid core cast product (P) is applied for strip thicknesses (SN) between 0.6mm and 3.5mm. 10. Method as in any one of the preceding claims, characterized in that it comprises the determination of the thickness (H) of said product cast out of the crystallizer (15a) which is a number between 10mm and 15mm more than a thickness of nominal slab (SBN) defined by the relation SBN = PR / OPERATING HOURS / (VC * LN * PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5m / min and 6m / min , LN is the average width of the strip, and PS is the specific gravity of the steel. 11. Method as in any one of the preceding claims, characterized in that it comprises the determination of a thickness ratio (RSP) applied by the rolling station (19) calculated as the ratio between the value of the slab thickness (SB2) in input to said laminating station (19), when the strip (N) of minimum thickness (SMIN) is processed, and the value of said minimum thickness (SMIN) of the strip (N). Method as in claim 11, characterized in that it comprises determining the number of rolling stands of the rolling station (19), wherein: - for a thickness ratio between 4 and 12, four rolling stands are provided; - five rolling stands are provided for a thickness ratio between 12 and 21; - six rolling stands are provided for a thickness ratio between 21 and 52; - for a thickness ratio between 52 and 110, thirst rolling stands are provided. 13. Metal strip production plant (N) comprising a casting machine (11) equipped with a crystallizer (15a) configured to pour a cast product (P) and obtain a slab (B), and a rolling station ( 19) of said slab (B) for obtaining metal strips (N) having strip thicknesses (SN) different from each other, in which said casting machine (11), during casting, is configured to exert an action thickness reduction of the cast product (P) leaving the crystallizer (15a), characterized by the fact that said casting machine (11) can be selectively configured, each time, as the thickness of the strip (SN) varies, in order to exercise a different action to reduce the thickness of the cast product (P).