CN116511247A

CN116511247A - Method for producing metal strip and production plant for carrying out said method

Info

Publication number: CN116511247A
Application number: CN202310746476.9A
Authority: CN
Inventors: 詹皮耶特罗·本尼迪蒂; 保罗·博比奇
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 2018-10-08
Filing date: 2019-09-25
Publication date: 2023-08-01
Also published as: RU2768955C1; KR20230084614A; WO2020075205A1; IT201800009259A1; US20220001442A1; KR20210102877A; KR102591941B1; US20230330740A1; EP3863781A1; CN113272084A

Abstract

The present application provides a method of producing a metal strip (N) and a production plant implementing said method, said method comprising: casting a cast product (P) by means of a casting machine (11) equipped with a crystallizer (15 a) to obtain a slab (B), and hot rolling said slab (B) in a rolling station (19) to obtain a metal strip (N). During casting, the casting machine (11) exerts an effect of reducing the thickness of the cast product (P) leaving the crystallizer (15 a).

Description

Method for producing metal strip and production plant for carrying out said method

The present application is a divisional application of application number CN201980080882.8 (PCT application number PCT/IT 2019/050210), application date 2019, 9, 25, and the name "method of producing metal strip and production apparatus for implementing the method".

Technical Field

The invention relates to a method for producing a metal strip and to a production plant for carrying out said method.

In particular, the method of the invention enables to define a pattern for obtaining a metal strip, as well as a layout of the architecture of the plant for producing hot rolled metal strips.

Background

In the steel industry, plants for producing metal strip are well known, these plants generally comprising: a mould for casting slabs (slabs), an extraction device for extracting the slabs from the mould, and a rolling line downstream of the extraction device, configured to reduce the total thickness of the slabs until a metal strip of the desired thickness is obtained.

It is known to suitably adjust the dimensions of the whole plant, at least in terms of plant productivity and strip thickness, according to the thickness of the metal strip to be obtained and to the overall productivity required by the plant, so as to conform to the required parameters.

With respect to these needs, it is known to provide customers with devices of the "headless" type, devices of the semi-continuous type, for example: "coil to coil" and/or "semi-endless" or "endless" and semi-continuous combined devices.

Headless equipment is used to provide cast product and to clamp the cast product directly from the die to the mill pass line, except that prior to final bending, there is no need to cut the product being processed.

The semi-continuous apparatus cuts the cast product into size downstream of the casting machine or roughing stands and processes it in a heating and/or maintenance furnace which may also act as a cumulative buffer (accumulation buffer) for the cast product if necessary, for example in the event of interruption of the downstream rolling due to small accidental or planned roll changes.

If the cast product is cut to length downstream of the casting or roughing machine in order to obtain a coil (coil) at the end of the rolling process, the process is called coil-to-coil. On the other hand, if the cast product is cut to length downstream of the casting machine or roughing stand, so as to obtain a plurality of coils (typically between 2 and 5) at the end of the rolling process, the process is called semi-headless.

It is known that by appropriate expedients, semi-continuous devices can also be operated in headless mode, so as to obtain the advantages of this solution.

The type of application device and the number of parts required are typically chosen according to the experience of the person skilled in the art, for example: the number of rolling stations, or the number of roughing stands and how many roughing stands are selected and how many finishing stands are used.

However, this scale, i.e. the preparation of the strip production plant, sometimes does not allow an effective compromise to be reached between the investment required for the plant construction (also called capital expenditure) and the cost of the operational transformation (also called operational expenditure). Thus, in some cases, the construction investment cost of the production facility is too high compared to the income, and thus the production facility provided is too large with respect to the productivity required by the customer, or the production facility is too small, and thus the throughput required by the customer cannot be achieved.

However, some known methods and apparatuses for producing metal strips have the above-mentioned problems, such as: the problems described above are found in documents WO 92/00815A1, JP S62248542A and WO 02/40201A 2.

It is therefore an object of the present invention to provide a production plant of the correct dimensions according to the needs of the customers who use hot manufacturing methods of metal strip (e.g. steel) so as to optimize the productivity of the strip production plant with the least possible number of strips, while maintaining the maximum casting speed associated with the various steels.

It is a further object of the present invention to provide an apparatus for producing hot rolled metal strip which requires only a limited investment (capital expenditure) and has a lower operational transformation cost (operational expenditure) than an apparatus for producing the same strip thickness.

It is a further object of the present invention to provide an apparatus and a corresponding method for perfecting the production of hot rolled metal strip that can selectively vary the thickness of the cast slab with respect to the final thickness of the strip.

Another object of the present invention is to provide a method for producing a metal strip that makes it possible to obtain a device that is extremely flexible and adaptable to the requirements of a specific customer.

Another object of the present invention is to provide an apparatus for producing metal strips that are competitive in the market.

The inventors have devised, tested and practiced the present invention to overcome the shortcomings in the art and to obtain these and other objects and advantages.

Disclosure of Invention

The invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.

According to the above object, the present invention provides a method for producing a metal strip, said method comprising: casting a cast product by a casting machine equipped with a crystallizer to obtain a slab, and hot rolling the slab in a rolling station (rolling station) to obtain metal strips having different strip thicknesses.

During casting, the casting machine exerts an effect of reducing the thickness of the cast product exiting the crystallizer.

According to one aspect of the invention, the method provides that the casting machine is selectively arranged in each case as the thickness of the strip varies, so as to exert a varying degree of reduction in thickness on the cast product.

In particular, in the case of equal sizes of the crystallisers, the method comprises: at least a first step of producing a first strip having a first thickness, wherein the caster applies a first reduction rate (first thickness reduction) to the cast product, and a second step of producing a second strip having a second thickness, less than the first thickness, wherein the caster applies a second reduction rate to the cast product, different from the first reduction rate, the reduction rate being defined as the difference between the thickness of the cast product exiting the crystallizer and the thickness of the slab exiting the caster, the difference being related to the thickness of the cast product exiting the crystallizer.

This solution makes it possible to adjust the relation between the thickness of the slab leaving the casting machine and the final strip thickness to increase the efficiency of the strip production plant and the quality of the strip produced.

In particular, in some application of the invention, it is also possible to reduce the number of rolling stands of the rolling station by at least one unit, but with the same productivity as the known devices. This determines the economic and efficiency advantages of the whole production plant.

The effect of reducing the thickness of the strip produced each time is partly carried out in the casting machine and partly in the rolling station, thus improving the efficiency and increasing the quality of the strip produced.

If the number of rolling stands of the rolling station is substantially the same as the number of rolling stands of the known plant at the same production rate, the number of rolling compressors can be reduced in any case, since the reduction of the partial thickness is carried out directly by the casting machine, instead of only at the rolling stations as in the prior art.

This expedient makes it possible to obtain energy savings due to the reduction of the compression pressure on the slab being rolled and to obtain a higher quality strip, since for example the profile and flatness of the strip are improved and the risk of scores being left on the surface of the strip is reduced.

Furthermore, the invention can reduce maintenance interventions at least in the rolling stations.

Drawings

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

figures 1 to 9 show some possible embodiments of an apparatus for producing metal strip for carrying out a method of the invention;

FIG. 10 graphically illustrates curves determined with respect to the thickness H of the cast product exiting from the crystallizer, the curves showing the reduction rate applied to the cast product by the casting machine as a function of the thickness of the strip;

FIG. 11 shows a plurality of curves determined by the thickness H of the cast product leaving the crystallizer, said curves showing the development of the reduction rate in the drawing unit as a function of the thickness of the strip;

FIG. 12 shows criteria for selecting a rolling mode;

FIG. 13 graphically illustrates further criteria for selecting a rolling mode, which criteria are related to strip thickness and capacity of the plant architecture applied to one and/or other rolling modes;

FIGS. 14 and 15 are graphs graphically showing the relationship of nominal slab thickness (nominal slab thickness) to plant productivity and casting speed; FIGS. 14 and 15 each indicate a 7200 hour/year casting operation;

FIG. 16 is a graph graphically showing the relationship of thickness ratio to the number of rolling stations required;

figures 17-22 illustrate two exemplary embodiments that implement the teachings of the present invention.

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

Detailed Description

Reference now will be made in detail to the various embodiments of the invention, one or more examples of which are illustrated in the figures. Each example is provided by way of explanation of the invention and should not be construed as limiting the invention. For example, portions may be used on or in conjunction with other embodiments to create another embodiment so long as the features illustrated or described in the figures are part of one embodiment. It is to be understood that the invention is intended to include all such modifications and alterations.

Embodiments of the present invention relate to a metal strip N produced in a production plant 10.

Fig. 2 to 9 show various possible architectures of the plant 10 for producing strips, said plant 10 implementing the principles of the present invention.

In particular, reference will be made hereinafter to fig. 1, fig. 1 showing a plurality of operating members reciprocally disposed along a working line. These components shown in fig. 1 may be combined with each other to obtain one or more architectures for producing the strip material, then as shown in fig. 2 to 9. For this purpose, the various variant embodiments of the production plant 10 shown in fig. 2 to 9 refer to the components of the plant described with reference to fig. 1.

The plant 10 for producing strip N comprises at least one casting machine 11 in which the liquid metal is cast into a solid state to obtain a blank B.

According to one aspect of the invention, the production plant 10 further comprises a rolling station 19 downstream of the casting machine 11, and the rolling station 19 is configured to hot-roll the slab B to obtain the strip N.

The casting machine 11 comprises at least one mould 15 provided with a crystallizer 15a, in which crystallizer 15a the cast product P is formed through the whole casting machine 11.

The crystallizer 15a may comprise at least two broad plates facing each other and spaced apart at least in the terminal section by a determined value substantially corresponding to the thickness H of the cast product P exiting from the crystallizer 15 a.

Furthermore, the plates of the crystallizer 15a have a width determined with respect to the width of the strip N to be obtained.

At the outlet of the crystallizer 15a, the cast product P has a solidified shell or skin, which enables to contain liquid metal even outside the crystallizer 15 a.

According to some solutions of the invention, the casting machine 11 may have thickness reduction means downstream of the crystallizer, providing that in each case the thickness reduction means are selectively arranged as the thickness of the strip varies, so as to exert on the cast product P leaving the crystallizer 15a different degree of thickness reduction.

The thickness reduction device may include a pre-rolling device having a plurality of rollers and/or roller units (roller units), such as: the type of stretching as described below.

According to some embodiments, the casting machine 11 comprises a pre-rolling device 16 with a plurality of rolls, hereinafter also referred to as roll units, the pre-rolling device 16 being located downstream of the mould 15 and configured to reduce the thickness of the cast product P exiting from the crystallizer 15a, while its core is still liquid or partially liquid.

According to some embodiments of the invention, the roll unit 16 has a plurality of rolls grouped into sections opposite each other and aligned along the casting axis.

The plurality of rolls are selectively moved toward and away from each other to impart a reduced thickness selective action to the cast product.

An adjusting device 17 of a known type, for example a hydraulic cylinder, is associated with the plurality of sections so as to move the plurality of rolls of the roll unit 16 towards or away from each other and to reduce the thickness of the cast product P exiting from the crystallizer 15 a.

The overall reduction in thickness experienced by the cast product P leaving the crystallizer 15a in the roll unit 16 is the liquid core pressure (liquid core reduction), so that no lengthening of the material occurs.

The blank 16 exiting the roller unit 16 is fully cured and has a blank thickness SB1.

The slab thickness SB1 obtained at the end of the liquid core pre-rolling affects the productivity of the casting machine 11 and therefore the productivity of the overall plant.

The compression performed by the roller unit 16 enables joining of the two half-shells in a joint, also called "contact point" (KP), in which the cast product is fully solidified. The KP is also regarded as the terminal apex of the liquid cone (liquid cone) which originates from the meniscus of the liquid metal in the crystallizer 15 a.

According to one aspect of the invention, the position of KP may be varied along the longitudinal extension of the roll unit 16, thereby interfering with the strength of the reduced liquid core thickness and the secondary cooling strength obtained by adjusting the sections of the roll unit 16. The position of KP is also a function of casting speed. The thickness of the cast product corresponding to KP is equal to the slab thickness SB1 leaving the roll unit 16.

According to one aspect of the invention, the slab thickness SB1 is selectively set according to the final thickness of the strip N, in particular according to the product combination produced by the plant, as will be explained more clearly hereinafter.

According to a possible solution, a plurality of known types of cooling devices (also called secondary cooling) may be associated with the roller unit 16 and configured to cool the outer surface of the slab, determining its further solidification. The cooling means may comprise a plurality of nozzles for delivering atomized water or water mixed with air (air mist). The effect of the cooling means also has an influence on the position of KP.

According to some embodiments, the caster 11 comprises a stretching unit 18 downstream of the roller unit 16 and configured to stretch the slab B towards the rolling station 19.

The stretching unit 18 includes a plurality of pairs of stretching rollers, the number of which includes 1 to 6 stretching rollers.

Each pair of rollers is disposed on opposite sides of the blank B to be stretched.

According to some embodiments, the stretching unit 18 may also be configured to roll the slab B therethrough.

By way of example, each pair of rollers or at least one of them may be associated with a moving device, for example a hydraulic cylinder of a known type (not shown), for bringing the rollers towards or away from each other and determining a predetermined compression action on the fully solidified slab B, as described below.

According to a possible solution, the stretching unit 18 may comprise a first stretching device 18a located directly downstream of the roller unit 16, in other words in the vertical section of the casting machine 11. According to one possible solution (possibly in combination with the previous one), the stretching unit 18 may comprise a second stretching device 18b located immediately downstream of the bending section of the casting machine 11.

The presence of the first stretching means 18a is only provided in the case of vertical casting.

The presence of the second stretching means 18b is provided in the case of vertical and vertical bending casting (vertical-curved casting).

The first stretching device 18a and/or the second stretching device 18b may comprise a plurality of pairs of rollers, the number of rollers being between 1 and 3.

As mentioned above, the rollers of the stretching unit 18 are configured to perform a slight hydraulic core pressure on the blank B of thickness SB1, so that one real rolling determines the elongation of the material, although of a lesser amplitude. The rolling of the drawing unit 18, although very light, results in a further reduction of the thickness of the slab B, which has a further thickness SB2 smaller than SB1, so that the rolling station 19 located downstream reaches a thinner thickness. Because the stretching unit 18 is located at the end of the casting machine 11, the thickness SB2 of the blank B leaving the stretching unit 18 corresponds to the thickness of the blank B leaving the casting machine.

The drawing unit 18 forms an integral part of the casting machine 11 with the Rolling unit and the crystallizer 15a, and can be defined as a "Rolling Caster" due to the Rolling action performed by the rolls.

The rolling caster is a casting machine 11 capable of casting a product and rolling a part of a liquid core and a part of a solid core.

The overall thickness reduction experienced by the cast product P exiting from the crystallizer 15a in the casting machine 11 is partly liquid core and partly solid core.

According to one aspect of the invention, the reduced thickness profile of the caster 11 can be advantageously adjusted between liquid and solid cores, depending on the specific production requirements.

According to a possible embodiment, the rolling station 19 comprises a roughing unit (rolling unit) 12 configured to roll the slab B.

The roughing unit 12 may have one or more roughing stations 20.

According to a further embodiment of the invention, the rolling station 19 comprises a finishing unit (finishing unit) 13, the finishing unit 13 being configured to roll the blank B and to process the blank B to its final dimensions, i.e. to define the metal strip N.

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

The finishing unit 13 may also include one or more finishing stations 21, each finishing station 21 being configured to roll and define a thickness SN of the strip.

According to a possible solution, a shear 26 is provided just downstream of the roughing unit 12, the shear 26 being configured to cut the rolled slab B and defining a bar, also called transfer bar, in a section, which will undergo subsequent rolling to obtain the strip N.

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

According to one possible solution, the plant 10 comprises a first induction heating device 22 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 it is introduced into the rolling station 19.

According to a possible solution, the apparatus 10 comprises a second induction heating device 23 located 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 it is introduced into the finishing unit 13.

According to a possible solution, the second induction heating device 23 is located immediately downstream of the roughing unit 12.

According to a further solution, the plant 10 comprises a third induction heating device 34 arranged between the two finishing stations 21, and the third induction heating device 34 is configured to restore the temperature of the bars during finishing.

According to a further embodiment, the production plant 10 may comprise at least one heating and/or maintenance unit, in which case two heating and/or maintenance units 32 and 33 are configured to heat or maintain the temperature of the bar segments.

The heating and/or maintenance units 32 and 33 may comprise heating and/or maintenance tunnel ovens which may act as accumulation buffers (accumulation buffer) for the bars in case of interruption of the rolling process due to accidents or programmed roll changes, avoiding losses of material and energy, in particular avoiding casting interruptions.

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

According to a further embodiment, the production plant 10 comprises a second heating and/or maintenance unit 33 located between the roughing unit 12 and the finishing unit 13.

According to this embodiment, it is advantageous to provide the production plant 10 with a shear 35, said shear 35 being arranged between said caster 11 and said rolling station 19 and configured to cut said slab B produced by said caster 11 into a plurality of pieces. In case of emergency, or in case of maintenance requirements (e.g. replacement of rolls in the rolling station 19), the plurality of segments may then be stored and maintained at a temperature within the first heating and/or maintenance unit 32.

According to some embodiments, the production apparatus 10 comprises an intermediate winding/unwinding device 29 arranged between the shears 26 and the finishing unit 13, and the intermediate winding/unwinding device 29 is configured to wind the bar cut via the shears 26 and to provide the previously wound and cut bar to the finishing unit 13.

According to a possible embodiment, the apparatus may comprise a second heating and/or maintenance unit 33 and an intermediate winding/unwinding device 29 located downstream with respect to said heating unit 32.

For example, the intermediate winding/unwinding device 29 may be of the type described in international application WO-A-2011/080300 in the name of the applicant.

According to some solutions, the intermediate winding/unwinding device 29 comprises a first unit 30 and a second unit 31, the first unit 30 and the second unit 31 alternately winding the bars received from the roughing unit 12 and unwinding the previously wound bars so as to feed the bars to the finishing unit 13.

In particular, when one of the two units 30, 31 winds one bar, the other unit 31, 30 unwinds the other rough rolled bar and supplies the bar downstream. Such intermediate winding/unwinding devices 29 can also define a temporary accumulation buffer to compensate for the different operating speeds of the casting machine 11 and of the finishing unit 13. In this way, the intermediate winding/unwinding device 29 is able to absorb (absorb) the downtime of the rolling mill in order to carry out small-scale maintenance or programmed roll changes, or to handle small accidents/jams, without interrupting the casting process and therefore without causing production losses and having an impact on the upstream steelworks.

According to a possible solution, said intermediate winding/unwinding device 29 can comprise heating means (not shown) to heat or maintain the temperature of the bars inside.

According to a further solution of the invention, the plant 10 may comprise a cutting member 28 arranged between the roughing unit 12 and the finishing unit 13, and the cutting member 28 is configured to cut the head or tail end of the bar provided by the roughing unit 12, in which case the bar is provided by the intermediate winding/unwinding device 29 and sent to the finishing unit 13.

According to a further solution, a cooling unit 24 is provided between the rolling station 19 and the final winding unit 14, the cooling unit 24 being configured to cool the strip N exiting from the rolling station 19 and to allow the collection of the strip N in the final winding unit 14.

According to a further embodiment of the invention, the apparatus 10 comprises a final winding unit 14 of the strip material N.

The final winding unit 14 may comprise a winding member 25, said winding member 25 being adapted to wind the strip N into coils (coils).

According to some embodiments, the apparatus 10 comprises a cutting device 27 upstream of the final winding unit 14, the cutting device 27 being configured to cut the strip N to size once a predetermined weight of the coil of strip N is reached. The cutting device 27 may be located between the cooling unit 24 and the final winding unit 14.

Referring to fig. 2, fig. 2 shows a variant embodiment of the production plant 10, said production plant 10 comprising, in succession, said casting machine 11, said shear 35, said first induction heating device 22 and/or said first heating and/or maintenance unit 32, said finishing unit 13, said cooling unit 24 and said final winding unit 14, as defined above.

Referring to fig. 3, fig. 3 shows a further variant embodiment of the production plant, the production plant 10 of fig. 2 providing, in addition to the components provided by the production plant 10, the rolling station 19 comprising the roughing unit 12, the second induction heating device 23, the second heating and/or maintenance unit 33, and the cutting member 28 upstream of the finishing unit 13.

Referring to fig. 4, fig. 4 shows a further variant embodiment of the production plant 10, the production plant 10 comprising, in succession, the casting machine 11, the roughing unit, the shear 26, the second induction heating device 23, the intermediate winding/unwinding device 29, the cutting member 28, the finishing unit 13, the cooling unit 24 and the final winding unit 14 as defined above.

Referring to fig. 5, the production plant 10 comprises, in succession, the casting machine 11, the rolling station 19 provided with the roughing unit 12, the shears 26, the second induction heating device 23, the second heating and/or maintenance unit 33, the finishing unit 13, the cooling unit 24 and the final winding unit 14, as defined above.

The production apparatus 10 described with reference to fig. 2-5, the production apparatus 10 may optionally be configured to operate in a roll-to-roll mode.

Referring to fig. 6, the production plant 10 comprises, in succession, the casting machine 11, the rolling station 19 provided with the shears 35, the second induction heating device 23, the second heating and/or maintenance unit 33, the finishing unit 13, the cooling unit 24, the cutting device 27 and the final winding unit 14, as defined above.

The production facility 10 described with reference to fig. 6 may be configured to operate in a roll-to-roll or semi-headless mode.

Referring to fig. 7, the production apparatus 10 includes the casting machine 11, the rolling station 19 provided with the rough rolling unit 12, the shears 26, the second induction heating device 23, the finish rolling unit 13, the third induction heating device 34 provided between the plurality of finish rolling stations 21, the cooling unit 24, the cutting device 27, and the final winding unit 14, which are sequentially arranged as defined above.

The production facility 10 described with reference to fig. 7 may be configured to operate in headless mode.

Referring to fig. 8, the production apparatus 10 includes the casting machine 11, the rolling station 19 provided with the roughing unit 12, the shears 26, the second induction heating device 23, the intermediate winding/unwinding device 29, the cutting member 28, the finishing unit 13, the third induction heating device 34 provided between the finishing stations 21, the cooling unit 24, the cutting device 27, and the final winding unit 14, which are sequentially provided as defined above.

The production facility 10 described with reference to fig. 8 may be configured to operate in a roll-to-roll or headless mode.

Referring to fig. 9, the production plant 10 comprises, in order, the casting machine 11, the rolling station 19 provided with the shears 35, the first induction heating device 22, the first heating and/or maintenance unit 32, the roughing unit 12, the shears 26, the second induction heating device 23, the finishing unit 13, the third induction heating device 34 provided between a plurality of finishing stations 21, the cooling unit 24, the cutting device 27 and the final winding unit 14, as defined above.

The production facility 10 described with reference to fig. 9 may be configured to operate in a roll-to-roll or semi-headless or headless mode.

The embodiment of the apparatus 10 described with reference to fig. 2 to 9 defines an example of a series of production apparatus architecture in which the end user can select in an optimal manner the productivity, the product combination and the type of steel to be produced, also called "steel grades".

According to one aspect of the invention, a method for producing a metal strip N comprises: casting a cast product P at least by means of said casting machine 11 to obtain a slab B, and hot rolling said slab B in said rolling station 19 to obtain a metal strip N.

According to one aspect of the invention, during casting, the casting machine 11 exerts an effect of reducing the thickness of the cast product P leaving the crystallizer 15 a.

According to another aspect of the invention, the casting machine 11 is selectively set to exert a different action for reducing the thickness of the cast product P exiting from the crystallizer 15a, for each thickness dimension of the strip N produced.

In particular, the thickness of the slab B produced by the casting machine 11 is adjusted in each case at least according to the final thickness of the strip N to be obtained and to the type of product or combination of products that may be obtained.

This solution makes it possible to reduce the compression action exerted in said rolling station 19, thus reducing the rolling power required, reducing the wear of the rolling rolls, and in some cases also the number of at least one rolling stand with respect to known devices having the same overall productivity.

By way of example only, a crystallizer 15a of the same size may be provided, the method comprising a first step of producing a first strip having a first thickness SN ', wherein the caster 11 applies a first reduction ratio TAU a' to the cast product P leaving the crystallizer 15a, and a second step of producing a second strip having a second thickness SN "smaller than the first thickness SN ', wherein the caster 11 applies a second reduction ratio TAU a" to the cast product P leaving the crystallizer 15a, the second reduction ratio TAU a "being different from the first reduction ratio TAU a'.

According to one solution, the first thinning ratio TAU a 'is smaller than the second thinning ratio TAU a'.

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

According to a possible solution of the invention, the inventors have determined that the casting machine 11 is selectively set to exert an effect of reducing the thickness of the cast product P, said effect being defined by the formula:

TAUA＝K·A·H ^-1 ·e ^a·SN

wherein:

k is a variable parameter between 0.8 and 1.1;

a is a coefficient approximately equal to 4689;

h is the thickness of the cast product P exiting from the crystallizer 15a, i.e. the thickness of the crystallizer 15 a;

a is a coefficient equal to-0.37;

SN is the thickness of the strip obtained at the end of rolling.

The TAU a derived from the formula is a percentage value and can typically be a value between 2% and 75% by way of example only.

Fig. 10 shows some examples of curves determined with respect to the thickness H of the cast product P, which show the development of TAU a as a function of the strip thickness SN.

This formula enables to optimize the relation between the settings of the casting machine 11 and the thickness of the crystalliser 15a and the thickness SN of the strip, so as to achieve an efficient operation of the whole production plant, as described above.

According to a possible solution of the invention, the casting machine 11 is configured to apply:

(i) An action of reducing the thickness of the cast product P by liquid core pre-rolling using a roll unit 16, in which is called a reduction ratio TAU1;

(ii) The action of reducing the thickness of the cast product P by using the action of the stretching unit 18, in which it is called the thinning ratio TAU2.

The thickness reduction via the stretching unit 18 is optional.

Therefore, the thinning ratio TAU a is given by a combination of thinning ratios TAU 1 and TAU2.

The reduction rate TAU 1 in the roll unit is defined as the difference between the thickness H of the cast product P leaving the crystallizer 15a and the thickness SB1 of the slab leaving the roll unit 16, said difference being associated with the thickness H of the cast product P leaving the crystallizer 15 a.

The thinning ratio TAU2 in the stretching unit is defined as the difference between the thickness SB1 of the blank leaving the roller unit 16 and the thickness SB2 of the blank leaving the stretching unit 18, which is associated with the thickness SB1 of the blank leaving the roller unit 16.

According to a possible solution of the invention, the applicant has determined that the stretching unit 18 is selectively set to exert on the solid cast product P an effect of reduced thickness SB1, defined by the formula:

TAU2＝Q·(-B·H ^b ·lnSN+C·H ^c )

wherein:

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 as defined above;

b is a second coefficient equal to-1.659;

SN is the thickness of the ribbon;

c is a third coefficient equal to 10648;

c is a fourth coefficient equal to-1.596.

According to a possible solution, the solid reduction of the thickness of the cast product P is suitable for strips with a thickness SN comprised between 0.6 and 3.5 mm. In fact, for strip thicknesses SN of these dimensions, the action of the liquid core pressure is relatively high in order to minimize the initial slab from the beginning, so that the further action of solid core reduction of the thickness applied by the stretching unit 18 is advantageous in combination with the action of the liquid core pressure.

Furthermore, the solid-core rolling action exerted by the stretching unit 18 enables an increase in the productivity of the strip, thus being particularly advantageous for thin strip thicknesses.

Fig. 11 shows an example of a plurality of curves determined by the thickness H of the cast product P leaving the crystallizer, said curves showing the development of TAU2 as a function of the strip thickness SN.

The reduction rate of the roughing unit 12 is referred to as 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, which is correlated with the thickness SB2 of the slab B upstream of the roughing unit 12.

The reduction rate at 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 strip thickness SN obtained, which is correlated with the thickness of the slab B upstream of the finishing unit 21.

The total reduction rate of the rolling station 19 is defined as TAUB and as the difference between the slab thickness SB2 exiting from said casting machine 11 and the obtained strip thickness N, said difference being related to the slab thickness SB2 provided by the casting machine 11. The total reduction TAUB of the rolling station 19 can also be defined as a combination of the reduction TAU3 and TAU4 of the roughing unit 12 and the finishing unit 13.

According to a further aspect of the invention, a method of producing a metal strip comprises providing, by a customer, design data comprising at least:

productivity PR, for example: annual yield of production facility 10;

a series of thicknesses RS and average widths LN of the strip that must be produced by the production plant 10;

the respective distribution of the productivity is related to the thickness of the produced strip N;

the type of product that can be cast by the casting machine, namely the above steel grade;

the respective distribution of productivity versus type of castable product;

The above set of parameters defines the so-called "product mix" of the plant, i.e. the kind of product that the production plant 10 will have to produce, and determines its dimensions according to said kind, in order to achieve the object of the invention.

The thickness range RS is provided to determine the minimum thickness SMN and the maximum thickness SMAX of the strip that can be obtained.

In some embodiments of the invention, the rolling method provides for determining the type of optimal rolling pattern of slab B based on the combination of products required by the customer.

The rolling mode of the slab B is selected from headless, semi-headless and roll-to-roll (coil) modes.

Fig. 12 shows a graph of criteria for selecting one of the above rolling modes, at least in relation to the strip thickness SN and the castable steel grade.

In general, in order to enable the production plant 10 to use a plurality of modes of operation, the rolling mode implemented in each case will be determined by optimizing the operating conditions of the plant, based on economic evaluations (process energy consumption and yield) and on the quality required of the final product (dimensional tolerances and mechanical characteristics of the strip).

By way of example only, it may be provided that if a thinner thickness (not including a particular type of steel, e.g., peritectic steel that is difficult to cast and requires a low casting speed) is prevalent in the product combination, then the endless rolling mode is selected, and thus one of the various equipment layouts shown in fig. 7, 8, or 9 may be selected.

If a relatively thin thickness is prevalent in the product combination and a particular type of steel is to be cast, a roll-to-roll and semi-endless rolling mode is typically selected, so that one of the plant layouts shown in fig. 6 and 9 can be selected. Both the roll-to-roll and semi-endless rolling modes are capable of casting special steels at low speeds, and therefore the casting process is not limited by the rolling process. The semi-headless mode is suitable for thin and ultra-thin strip N thicknesses, for example, between 0.8 mm and 1.4 mm. For tapes with a thickness greater than 1.4 mm, the roll-to-roll mode is preferred.

Fig. 13 graphically illustrates further criteria for selecting a rolling mode, which criteria are related to strip thickness and capacity for selecting an equipment layout employing one of the various rolling modes described above and/or other modes.

By way of example only, referring to fig. 13, if the constructive layout of fig. 2-5 is selected, the apparatus operates in a roll-to-roll mode for a strip having a thickness of between about 1.2 mm and about 12 mm, if the constructive layout of fig. 9 is selected, the apparatus operates in a headless mode for a strip having a thickness of between about 0.6 mm and about 1 mm, the apparatus operates in a semi-headless mode for a strip having a thickness of between about 1 mm and about 2 mm, and a roll-to-roll mode for a strip having a thickness of between about 2 mm and about 12 mm.

According to a further solution, the production method is used to set a casting speed VC selected from values between 4.5 m/min and 6 m/min.

In particular, for steel types that are difficult to cast (e.g., API, peritectic, and Cowden), it is advantageous to set a lower casting speed, such as: the casting speed was between 4.5 m/min and 5 m/min. For steels that are easier to cast, for example: low carbon, medium carbon, HSLA, DP, CP, HC, mnB steel, set higher casting speeds, for example: the casting speed was between 5 m/min and 6 m/min.

In the same way, the choice of casting speed VC can also be defined in relation to the chosen rolling mode, i.e. with a relatively low casting speed for the reel-to-reel and semi-headless modes and a higher casting speed for the headless modes.

The production method is then used to determine the value of the nominal blank thickness SBN, which is related to the casting speed VC and the average strip width LN, so that the production rate PR can be reached.

For the same total production of a given product combination, the nominal slab thickness SBN, which corresponds to the average value of the slab thickness (variable) after liquid core depression weighting (average value) of the production per hour, can also be interpreted as a constant thickness of an equivalent slab (equivalent slab).

According to a possible solution, the nominal blank thickness SBN is defined by the following formula:

sbn=pr/operation time/(VC LN PS)

In this and in the following description and in the claims, the operating time refers to the running time, i.e. the running time of the device in calendar years (deducting production interruption times due to maintenance, accidents, etc.).

Wherein PS is the specific gravity of the steel, typically about 7.8kg/dm ³ 。

Referring to fig. 14 and 15, the correlation between the nominal blank thickness SBN and the annual yield PR of the plant and the casting speed VC is shown.

In particular, fig. 14 refers to a width of the plate blank of about 1300 mm, while fig. 15 refers to a thickness of the plate blank of about 1400 mm.

According to one possible embodiment of the invention, the method comprises: the thickness H of the cast product P leaving the crystallizer 15a is determined, i.e. the distance between the plates of the crystallizer 15a is determined in correspondence with the outlet portion of the latter. This thickness H of the cast product P is the thickness taken by the customer for the whole product combination.

In a possible embodiment of the invention, the thickness H of the cast product P leaving the crystallizer 15a is 10 to 15 mm greater than the nominal slab thickness SBN.

The method is then provided for determining a thickness ratio RSP applied by the rolling station 19, and said thickness ratio RSP is calculated as the ratio between the values of the thicknesses SB2 of the blanks entering the rolling station 19, when processing a strip N of minimum thickness SMIN, a minimum thickness SMIN of the strip N is obtained.

When working the strip N of minimum width SMIN, the value of the thickness SB2 of the slab entering the rolling station 19 is calculated as the thickness H of the cast product P leaving the crystallizer 15a minus the maximum thinning imposed by the casting machine. According to one possible solution, the maximum thinning caused by the casting machine 11 is at least equal to 31 mm or more.

Subsequently, the method is used to determine the number of rolling stands of the rolling station 19 in relation to the thickness ratio.

When the thickness ratio is between 4 and 12, four rolling stands are provided.

Five rolling stands are provided when the thickness ratio is between 12 and 21.

When the thickness ratio is between 21 and 52, six rolling stands are provided.

Seven rolling stands are provided when the thickness ratio is between 52 and 110.

The relationship between the number of rolling stands and the thickness ratio is shown in the graph of fig. 16.

The number of rolling stands of the rolling station 19 is the sum of the number of finishing stations 21 and the number of roughing stations 20.

Subsequently, the method is provided for setting a mode for distributing the liquid core pressure and the solid core pressure in the casting machine 11 with the roller unit 16 and the stretching unit 18 on the slab B exiting from the crystallizer 15a with respect to the final thickness of the strip N (solid core reduction).

Such a pattern of thickness reduction of the cast product P distributed can be determined by the TAU a and TAU 2 formulas defined above.

According to a further possible solution, the casting machine 11 can be set to perform a thickness reduction of the cast product P equal to 5 mm, corresponding to the strip thickness of the maximum thickness SMAX, and a thickness reduction between 25 mm and 31 mm, corresponding to the strip thickness of the minimum thickness SMIN.

According to one possible solution, the roller unit 16 may perform a maximum liquid core pressure RCLMAX of about 25 mm. According to one possible solution, the roller unit 16 may perform a minimum liquid core pressure RCLMIN of about 5 mm. This reduction gives the cast metal product P a higher quality.

According to one solution of the invention, the stretching unit 18 may perform a maximum solid core reduction of at least 7 mm, while the minimum reduction is 0.

In particular, each pair of rollers of the stretching unit 18 may achieve a compression of between 0.5 mm and 1.5 mm when desired.

According to various possible embodiments of the method, if a reel-to-reel production mode is set and a winding/unwinding device 29 is used, the number of roughing stations 20 is determined so as to provide bars with a thickness comprised between 8 mm and 25 mm when entering the winding/unwinding device 29. A bar thickness of less than 8 mm would lead to problems of transporting and introducing the bar into the winding/unwinding device, while a bar thickness of more than 25 mm would lead to difficulties of handling and/or sizing, possibly creating surface defects on the bar itself.

According to a further possible embodiment of the method, if a roll-to-roll production mode has been set and a heating unit 33 is used, the number of roughing stations 20 can be determined so as to provide bars with a thickness greater than or equal to 30 mm when entering the heating unit. Dimensions smaller than these thickness values require the use of very long heating units, which are difficult to manage and uneconomical.

According to one possible solution, the number of finishing stations 21 is at least 2.

Examples:

with reference to fig. 17-22, examples of two embodiments of the teachings of the present invention will now be described.

Specifically, referring to fig. 17-19, in the first instance, the production rate PR is about 1.1 metric tons/year, the thickness range RS is between 1.2 mm and 8 mm, and the desired average width LN of the strip is about 1300 mm.

Referring to fig. 20 to 22, on the other hand, in the second case, the production rate PR is about 1.4 metric tons/year, the thickness range RS is between 0.8 mm and 3 mm, and the average width LN of the desired strip is about 1400 mm.

Referring to the tables shown in fig. 17 and 20, a comparison of productivity versus distribution of product combinations with conventional casting and reduced thickness casting can be observed in at least the last four columns on the right in accordance with the teachings of the present invention.

The product combination and annual output values (see columns 11 and 12 of the table) are parameters required by the customer and are set according to the requirements of the customer for using the equipment.

Meanwhile, referring to the tables shown in fig. 17 and 20, it can be observed that in the sixth column, the slab thickness SB2 exiting from the casting machine 11 is not a constant value that varies with the thickness of the strip, but a value that decreases with the decrease in the thickness of the strip. In conventional or known techniques, on the other hand, the thickness SBN of the blank leaving the caster is always the same as the thickness of the strip variation, as indicated in the second column from the left. Fig. 18 and 21 also graphically illustrate this consideration.

This variation of the slab thickness with respect to the final strip thickness is obtained by the fact that: the casting machine 11 applies a thickness of liquid core pressure RCL on the cast product as shown in the third column of the tables of fig. 17 and 20.

The table also shows the thickness reduction performed with the stretching unit 18 (fifth column), the roughing unit 12 (seventh column) and the finishing unit 13 (ninth column), and how these operations are distributed according to the final strip thickness to be obtained.

On the other hand, fig. 19 and 22 graphically show the relationship between the hourly productivity (hourly productivity) distribution of the plant and the strip thickness to be obtained, in the case of known conventional casting and in the case of casting with variable thickness reduction according to the invention.

In particular, in fig. 19 and 22, it should be noted that in the case of known conventional casting, the hourly productivity is maintained constant for any strip thickness to be obtained, whereas in the case of said casting according to the invention, the hourly productivity is varied with respect to said strip thickness to be obtained.

As can be seen from the analysis of fig. 19 and 22, the present invention has lower productivity compared to conventional solutions for low strip thickness values and higher productivity compared to conventional solutions for high strip thickness values. However, in general, in the case of conventional casting and casting according to the invention, the annual productivity of the plant is equal, and in the solution according to the invention the above-mentioned advantages can be obtained compared with the known solutions.

With reference to the first case shown in fig. 17 to 19, we will now describe a mode of selecting the type of plant and the number of rolling stands of the rolling station 19.

In particular, according to the range of variable strip thickness between 1.2 and 8 mm and the diagram of fig. 12, it is advantageous to employ an apparatus layout that enables a roll-to-roll rolling mode.

Then, a casting speed set at about 5.5 m/min was provided, corresponding to a nominal slab thickness SBN of about 45 mm for an average strip width LN of 1300 mm and a production rate of 1.1 metric ton/year, as shown in fig. 14.

From the SBN value, the thickness H of the cast product P can be determined, which is 10 to 15 mm greater than the nominal slab SBN, which in this case is equal to 55 mm, as shown in the table in fig. 17.

The nominal slab SBN is then provided to determine the thickness reduction to be applied by the rolling station 19.

When working with minimum thickness, the slab thickness SB2 entering the rolling station 19 is 24 mm.

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

Referring to fig. 16, it can be observed that this thickness ratio corresponds to a number of racks equal to 5.

On the other hand, with reference to conventional casting, 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. Referring to fig. 16, the number of frames corresponds to this thickness ratio when it is equal to 6. From this example it can be observed how the number of rolling stands can be reduced by one unit with respect to the traditional production mode, with the same annual productivity of the plant.

With reference to the second case illustrated in fig. 20 to 22, we will now describe another mode of selection of the type of equipment and the number of rolling stands of said rolling station 19.

In particular, according to the variable strip thickness range between 0.8 mm and 3.0 mm and the diagram of fig. 12, it is advantageous to employ an equipment layout that enables endless rolling modes.

A casting speed of about 6.0 m/min, an average width LN of 1400 mm and a production rate of 1.4 metric tons/year were then set, corresponding to a scale plate blank thickness of about 50 mm, as can be seen from the diagram of fig. 15.

From this SBN value, the thickness H of the cast product P can be determined, which is 10 to 15 mm greater than the nominal slab SBN, which in this case is equal to 65 mm, as shown in the table in fig. 20.

When working with minimum thickness, the slab thickness SB2 entering the rolling station 19 is 34 mm.

The thickness ratio RSP of the rolling station 19 is thus 34/0.8=42.5.

Referring to fig. 16, it can be observed that this thickness ratio corresponds to a number of racks equal to 6.

On the other hand, with reference to conventional casting, 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. Referring to fig. 16, the number of frames corresponds to this thickness ratio when it is equal to 7. From this example it can be observed how the number of rolling stands can be reduced by one unit with respect to the traditional production mode, with the same annual productivity of the plant.

Clearly, modifications and/or additions of parts may be made to the method of producing a metal strip and to the production plant implementing the method, without departing from the field and 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 of skill in the art shall certainly be able to achieve many other equivalent forms of process for producing metal strip, and apparatus for carrying out the process as set forth above, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

In the following claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Claims

1. Method for producing a metal strip (N), in particular steel, in a production plant configured to operate in a roll-to-roll and/or semi-endless rolling mode and/or endless rolling mode, wherein a casting speed (V) is defined by a casting machine (11) equipped with a crystallizer (15 a) _c ) To cast a slab (B), and to hot-roll said slab (B) in a rolling station (19) to obtain metal strips (N) having different strip thicknesses (SN), said rolling station (19) comprisingComprising a plurality of rolling stands, wherein during casting, the casting machine (11) exerts a first action of hydraulic core pressure on the thickness of the slab (B) leaving the crystallizer (15 a) through a pre-rolling device (16) with a plurality of rolls, and a second action of solid core pressure on the thickness of the slab (B) through a stretching unit (18) located downstream of the pre-rolling device (16), characterized in that: with the strip thickness (SN) being different, the casting machine (11) is selectively set to apply different actions to reduce the thickness of the slab (B), wherein the first action of the liquid core reduction of the thickness is between 5 and 25 mm, the second action of the solid core reduction of the thickness is at most 7 mm and is applied to a strip thickness (SN) between 0.6 mm and 3.5 mm, wherein the total thickness of the slab (B) exiting the casting machine is reduced by between 2% and 75%, and the rolling mode of the slab (B) is selected according to the strip thickness (SN) and the various types of steel produced, so as to optimize the productivity of the production plant with the smallest possible number of rolling stands while maintaining the maximum casting speed (V) associated with the various types of steel produced _c )。

2. The method of claim 1, wherein: the casting machine (11) comprises the pre-rolling device (16) with a plurality of rolls, the pre-rolling device (16) exerting a reduction in thickness on a cast product (P) exiting from the crystallizer (15 a) by means of a pre-rolling with a liquid core.

3. A method according to claim 1 or 2, characterized in that: the pre-rolling device (16) with a plurality of rolls has a plurality of opposing rolls between which the cast product (P) passes and which selectively move toward or away from each other to exert a selective hydraulic core reduction on the thickness of the cast product (P).

4. The method of claim 2, wherein: the casting machine (11) comprises the stretching unit (18), by solid-core rolling of the cast product (P), the stretching unit (18) exerting a reduced thickness effect on the cast product (P) leaving the pre-rolling device (16) with the plurality of rolls.

5. The method of claim 2, wherein: the method comprises determining the thickness (H) of the cast product (P) leaving the crystallizer (15 a), said thickness being a number from 10 to 15 mm greater than the thickness (SBN) of a nominal slab, said nominal slab thickness (SBN) being defined by the formula sbn=pr/operating time/(VC LN PS), where PR is the productivity of the production plant, VC is a casting speed selected between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific gravity of the steel.

6. The method of claim 1, wherein: the method comprises determining a thickness Ratio (RSP) applied by the rolling station (19), said thickness ratio being calculated as the ratio between the value of the thickness (SB 2) of the slab entering the rolling station (19) and the value of the minimum thickness (SMIN) of the metal strip (N) when machining the minimum thickness (SMIN) of the metal strip (N).

7. The method of claim 6, wherein: the method comprises the following steps: -determining the number of rolling stands of the rolling station (19), wherein:

providing four rolling stands when the thickness ratio is between 4 and 12;

providing five rolling stands when the thickness ratio is between 12 and 21;

providing six rolling stands when the thickness ratio is between 21 and 52;

8. An apparatus for producing a metal strip (N), characterized in that: the apparatus is configured to operate in a roll-to-roll and/or semi-endless rolling mode and/or endless rolling mode, the apparatus comprising: a casting processMachine (11) with a crystallizer (15 a), said casting machine (11) being configured to cast at a defined casting speed (V _c ) -casting a slab (B), and-a rolling station (19) for hot rolling said slab (B) to obtain metal strips (N) having different strip thicknesses (SN), said rolling station (19) comprising a plurality of rolling stands, wherein during casting said casting machine (11) exerts a first action of hydraulic core pressure on the thickness of said slab (B) leaving said crystallizer (15 a) through a pre-rolling device (16) having a plurality of rolls, and a second action of solid core pressure on the thickness of said slab (B) through a stretching unit (18) located downstream of said pre-rolling device (16), characterized in that: with the strip thickness (SN) being different, the casting machine (11) is selectively set to apply different actions to reduce the thickness of the slab (B), wherein the first action of the liquid core reduction of the thickness is between 5 and 25 mm, the second action of the solid core reduction of the thickness is at most 7 mm and is applied to a strip thickness (SN) between 0.6 mm and 3.5 mm, wherein the total thickness of the slab (B) exiting the casting machine is reduced by between 2% and 75%, and the rolling mode of the slab (B) is selected according to the strip thickness (SN) and the various types of steel produced, so as to optimize the productivity of the apparatus with the smallest possible number of rolling stands while maintaining the maximum casting speed (V) associated with the various types of steel produced _c )。