KR20210102877A - A method for producing a metal strip and a production plant implementing the method - Google Patents

Abstract

Casting the cast product P through a casting machine 11 provided with a crystallizer 15a to obtain a slab B and a rolling station to obtain a metal strip N having a different strip thickness SN A method for producing a metal strip (N) comprising the step of hot rolling the slab (B) in (19). The casting machine 11 exerts an action of reducing the thickness of the cast product P that has exited the crystallizer 15a during casting.

Description

A method for producing a metal strip and a production plant implementing the method

The present invention relates to a method for producing a metal strip and to a production plant implementing said method.

In particular, the method according to the invention allows to define the mode for obtaining the metal strip and the constructive layout of the plant for producing the hot rolled metal strip.

In the iron and steel industry, plants for the production of metal strips are known, usually a mold configured to cast a slab, an extraction device provided to extract the slab from the mold and the overall thickness of the slab until a metal strip of the desired thickness is obtained. and a rolling line disposed downstream of the extraction device, configured to reduce

It is known to properly size the entire plant so as to satisfy the required parameters, at least in relation to the productivity of the plant and the thickness of the strip, depending on the thickness of the metal strip to be obtained and the overall productivity the plant should have.

In connection with these requirements, it is known to provide clients with "endless" type plants, semi-continuous type plants, such as "coil-to-coil" and/or "semi-endless" or "endless" and semi-continuous combined plants.

Endless type plants offer to supply the gripped cast product directly from the mold to the rolling line, without cutting the product being worked on except prior to final winding.

A semi-continuous type plant, downstream of a roughing stand or casting machine, allows the cast product to be cut to any size and, if necessary, to stop downstream rolling due to, for example, minor accidents or programmed roll changes, accumulation for the cast product. Provided to be placed in a heating and/or holding furnace that acts as a buffer.

When the cast product is cut to a length such that a single coil is obtained at the end of the rolling process, downstream of a casting machine or roughing stand, the process is called coil-to-coil. On the other hand, if the cast product is cut to a length so as to obtain a plurality of coils, usually two to five, at the end of the rolling process, downstream of the casting machine or roughing stand, the process is called semi-endless.

It is also known by suitable experience that semi-continuous type plants can be made to function in endless mode, so that the advantages of this approach can be obtained.

The selection of the type of plant to be employed and the number of components required, such as the choice of the number of rolling stands or how many roughing stands and how many finishing stands to employ, is usually made based on the experience of the person skilled in the art.

However, this sizing, i.e., the preparation of the strip production plant, does not allow an efficient compromise between the investment required in the construction of the plant, sometimes called Capex, and operating transformation coasts, also called Opex. Thus, a situation in which the investment incurred in the construction of the production plant is too high relative to the return, so that the production plant is oversized for the productivity of the client or, alternatively, the production plant is downsized, resulting in the production capacity required by the client. Circumstances exist that do not allow it to be reached.

Some known methods and plants for producing metal strips that address the above problem are described, for example, in WO 92/00815 A1, JP S62 248542 A and WO 02/40201 A2.

Accordingly, it is an object of the present invention to provide a production plant sized precisely according to the needs of clients working with the method of hot production of metal strip, for example steel, which can optimize the productivity of the strip production plant with the smallest possible number of stands. On the other hand, it is to maintain maximum casting speed for various types of steel.

It is also an object of the present invention to provide a plant for producing hot rolled metal strip which has a lower operating transformation cost (Opex) compared to a traditional plant for producing the same strip thickness and requires a limited investment (Capex). will be.

Another object of the present invention is to provide a plant for producing hot rolled metal strips capable of selectively changing the thickness of a cast slab with respect to the final thickness of the strip and complete the process.

It is also an object of the present invention to provide a method for producing metal strips which can be adapted to specific client requirements and allows obtaining very flexible plants.

It is also an object of the present invention to provide a plant for producing metal strips competitive in the market.

Applicants have developed, tested and practiced the present invention in order to overcome the shortcomings of the prior art and to obtain these and other objects and advantages.

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

According to the above object, the method for producing a metal strip according to the present invention comprises casting a cast product through a casting machine provided with a crystallizer to obtain a slab and in a rolling station to obtain a metal strip having a different strip thickness. It involves hot rolling the slab.

The casting machine acts to reduce the thickness of the cast product that exits the crystallizer during casting.

According to one aspect of the present invention, the method provides that the casting machine is optionally set up to apply another action to reduce the thickness of the cast product, in each case as the strip thickness changes.

In particular, the method produces a first strip having at least a first thickness, when the crystallisers are the same size, wherein the casting machine applies a first reduction ratio of the thickness of the cast product and a second step less than the first thickness a second step of producing a second strip having a thickness and wherein the casting machine applies a second rate of reduction in thickness of the cast article different from the first rate of reduction in thickness, wherein the rate of reduction in thickness of the cast article exits from the crystallizer is defined as the difference between the thickness of the slab exiting the casting machine, relative to the thickness of the cast product exiting the crystallizer.

This approach allows to adjust the thickness of the slab exiting the casting machine as a function of the final strip thickness in order to increase the quality of the produced strip and increase the efficiency of the strip production plant.

In particular, the present invention can, in some embodiments, reduce the number of rolling stands of a rolling station to at least one unit with the same productivity as known plants. This sets the economic and efficient advantage of the entire production plant.

The action of reducing the thickness induced in the produced strip in each case is split partly in the casting machine and partly in the rolling station, improving the efficiency and increasing the quality of the strip produced.

For the same productivity, if the number of rolling stands of the rolling station is substantially equal to that of the known plant, the present invention provides that not only at the rolling station as occurs in the prior art, but also part of the reduction in thickness is carried out directly by the casting machine Therefore, the number of rolling compressions can be reduced.

This is to achieve energy savings by reducing the pressure of compaction on the slab being rolled, and to obtain a higher quality of the strip, for example because its profile and flatness are improved and the risk of scale applied to its surface is reduced. allow

Moreover, the present invention can reduce maintenance interventions, at least in the rolling station.

These and other features of the present invention will become apparent from the following description of some embodiments given by way of non-limiting example with reference to the accompanying drawings.

1-9 show some of possible embodiments of a plant for producing a metal strip embodying the method according to the invention.
Figure 10 plots some curves defined for the thickness (H) of the cast article exiting the crystallizer, showing the increase in the rate of reduction in thickness of the cast article applied by the casting machine as a function of the thickness of the strip.
11 shows a curve defined for the thickness H of the cast product exiting the crystallizer, which shows the increase in the rate of reduction in thickness of the drawing unit as a function of the thickness of the strip.
12 shows criteria for selecting a rolling mode.
13 diagrammatically illustrates another criterion for selecting a rolling mode with respect to the capacity and strip thickness of the plant layout for adopting either and/or the other of the rolling modes.
14 and 15 are graphs showing the relationship of the casting speed and the nominal slab thickness to the productivity of the plant. These charts represent a casting operation of 7,200 hours/year.
16 is a graph showing the correlation of the ratio of the thickness to the number of required rolling stands.
17-22 show two embodiments of implementations of the present disclosure.

To facilitate understanding, the same reference numbers have been used, where possible, to indicate like common elements in the drawings. It is understood that elements and features of one embodiment may be readily incorporated into other embodiments without further recitation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the invention are described in detail, one or more examples of which are shown in the accompanying drawings. Each example is provided as an illustration of the invention and should not be construed as a limitation thereof. For example, features shown or described as being part of one embodiment may be employed in or associated with another embodiment, providing another embodiment. It is understood that the present invention includes all such modifications and variations.

An embodiment of the invention relates to a method for producing a metal strip (N) in a production plant (10).

2-9 show possible layouts of a plant 10 for producing strips embodying the principles of the invention.

In particular, reference is made to FIG. 1 , which shows a plurality of actuating components interleaved along a line of work. These actuating components shown in Figure 1 can be combined with each other to obtain one or more layouts for producing a strip, shown in Figures 2-9. For this purpose, the modified embodiment of the production plant 10 shown in FIGS. 2-9 refers to the components of the plant described with reference to FIG. 1 .

The plant 10 for producing the strip N comprises at least one casting machine 11 in which the liquid metal is solidified and cast to obtain a slab B.

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

The casting machine 11 comprises at least one mold 15 provided with a crystallizer 15a in which the formation of the cast product P takes place, passing through the entire casting machine 11 .

The crystallizer 15a has at least two wide plates facing each other and spaced apart, at least in the terminal segment, by a predetermined value corresponding substantially to the thickness H of the cast product P exiting the crystallizer 15a. may include.

Moreover, the plate of the crystallizer 15a has a width which is determined with respect to the width of the strip N to be obtained.

At the exit from the crystallizer 15a, the cast product P has a solidified outer shell or skin, which allows it to contain liquid metal even outside the crystallizer 15a.

According to some schemes of the invention, the casting machine 11 may be provided with a thickness reducing means arranged downstream of the crystallizer, which reduces the thickness of the cast product P exiting from the crystallizer 15a. In order to exert the action, it can be optionally set, in each case, as the strip thickness varies.

The thickness reduction means may comprise, for example, a roller unit of the drawing type and/or a pre-rolling device with rollers, as described below.

According to some embodiments, the casting machine 11 is disposed downstream of the mold 15 and configured to perform a reduction in the thickness of the cast product P exiting the crystallizer 15a while its core is still liquid. or a pre-rolling device 16 having rollers, hereinafter also referred to as roller units, which are partially liquid.

According to some embodiments of the present invention, the roller unit 16 is provided with a plurality of rollers grouped into segments opposite to each other and aligned along the casting axis.

The rollers selectively move toward/away from each other to exert a selective action of reducing the thickness of the cast product.

A regulating device 17 of a known type, for example a hydraulic cylinder, moves the rollers of the roller unit 16 towards/away from each other and reduces the thickness of the cast product P exiting from the crystallizer 15a It is associated with a segment to perform

The overall reduction in thickness experienced inside the roller unit 16 by the cast product P exiting the crystallizer 15a is a liquid core reduction, and thus does not result in an increase in the length of the material.

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

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

The compaction performed by the roller unit 16 allows to join the two half skins at a connection point, also called the “Kissing Point” (KP), where there is complete solidification of the cast product. KP is also seen as the terminal apex of the liquid cone originating from the meniscus of the liquid metal in the crystallizer 15a.

According to one aspect of the present invention, the position of the KP can be varied along the longitudinal extension of the roller unit 16, depending on the strength of the liquid core thickness reduction obtained by adjusting the segments of the roller unit 16 and the secondary cooling strength. intervene 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 exiting from the roller unit 16 .

According to one aspect of the invention, the slab thickness SB1 is optionally set as a function of the final thickness of the strip N, in particular as a function of the product mix to be produced by the plant, as will be explained further below.

According to a possible solution, a known type of cooling device, also called secondary cooling, may be associated with a roller unit 16 and configured to cool the outer surface of the slab to achieve further solidification. The cooling device may include a nozzle for providing atomized water or water mixed with air (“air mist”). The action of the cooling device also has an effect on the position of the KP.

According to some embodiments, the casting machine 11 comprises a drawing unit 18 arranged downstream of the roller unit 16 and configured to draw the slab B towards the rolling station 19 .

The drawing unit 18 includes a number of 1 to 6 pairs of drawing rollers.

Each pair of rollers is arranged on the opposite side of the slab B to be drawn.

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

By way of example only, each pair of rollers or at least one of them may be used to move the rollers towards/away from each other and also to define a predefined compressive action on the fully solidified slab B, as will be explained below. , with a moving device, for example a hydraulic cylinder of known type (not shown).

According to a possible solution, the drawing unit 18 may comprise a first drawing device 18a arranged immediately downstream of the roller unit 16 , ie in a vertical segment of the casting machine 11 . According to one possible solution, possibly combinable with the preceding solution, the drawing unit 18 may comprise a second drawing device 18b arranged immediately downstream of the curved segment of the casting machine 11 .

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

The presence of the second drawing device 18b is provided in the case of vertical and vertical curve casting.

The first drawing device 18a and/or the second drawing device 18b may comprise one to three pairs of a plurality of rollers.

As mentioned above, the rollers of the drawing unit 18 are configured to perform a slight liquid core thickness reduction to the slab B of thickness SB1 to perform actual rolling, although to a lesser extent, which determines the elongation of the material. . The weak but rolling of the drawing unit 18 causes a further decrease in the thickness of the slab B, which has a different thickness SB2 than SB1, so that the downstream rolling station 19 reaches a thinner thickness. allow to do Since the drawing unit 18 is placed at the end of the casting machine 11 , the thickness SB2 of the slab B exiting from the drawing unit 18 is equal to the thickness of the slab B exiting the casting machine 11 . corresponded

Together with the roller unit 16 and the crystallizer 15a, the drawing unit 18 forms an integral part of the casting machine 11, which by means of the rolling action performed by the rollers, the "Rolling Caster )" can be defined.

By the rolling caster is meant the casting machine 11, which can perform casting and rolling of the product, is partly liquid core and partly solid core.

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

According to an embodiment of the invention, the distribution of the thickness reduction of the casting machine 11 can advantageously be adjusted between the liquid core and the solid core, according to specific product requirements.

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

The roughing unit 12 may be provided with one or more roughing stands 20 .

According to another embodiment of the invention, the rolling station 19 comprises a finishing unit 13 configured to roll the slab B and bring it to its final size, ie to define a metal strip N.

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

The finishing unit 13 may comprise one or more finishing stands 21 , each configured to roll and define a strip thickness SN.

According to a possible solution, a cutting shear 26 is provided immediately downstream of the roughing unit 12 , which will be subjected to subsequent rolling to cut the roughed slab B and obtain strips N, in this field is configured to define a bar also called a transfer bar in

The plant 10 may comprise at least one induction heating device configured to heat the slab B, in this case one, two or three induction heating devices 22 , 23 , 24 .

According to one possible solution, the plant 10 is arranged downstream of the casting machine 11 , in this case upstream of the roughing unit 12 , and is configured to restore the temperature of the slab before introduction into the rolling station 19 . A heating device 22 is included.

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

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

According to another option, the plant 10 comprises a third induction heating device 34 arranged between the two of the finishing stands 21 and configured to restore the temperature of the bar during the finishing process.

According to another embodiment, the production plant 10 may comprise at least one heating and/or holding unit configured to heat or maintain the temperature of the bar segment, in this case two heating and/or holding units 32 , 33 . can

The heating and/or holding unit 32, 33 acts as an accumulation buffer for the bar in case the rolling process is interrupted due to an accident or programmed roll change, avoiding loss of material and energy; It may include, among other things, a heating and/or holding tunnel type furnace that avoids interruption of casting.

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

According to another implementation, the production plant 10 comprises a second heating and/or holding unit 33 arranged between the roughing unit 12 and the finishing unit 13 .

According to this embodiment, a production plant 10 is arranged between the casting machine 11 and the rolling station 19 and is configured to cut the slab B produced by the casting machine 11 into segments. It is advantageous to provide that (35) is provided. In case of an emergency or due to maintenance needs, for example due to roll changes at the rolling station 19 , the segments may be later stored and stored at any temperature inside the first heating and/or holding unit 32 .

According to some embodiments, the production plant 10 is disposed between the cutting shear 26 and the finishing unit 13 and winds the bar cut by the cutting shear 26 and previously wound into the finishing unit 13 to cut the cut. an intermediate winding/unwinding device 29 configured to feed the bar.

According to a possible embodiment, the plant 10 may comprise an intermediate winding/unwinding device 29 and a second heating and/or holding unit 33 arranged downstream with respect to the heating unit 32 .

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

According to some schemes, the intermediate winding/unwinding device 29 alternates between the function of winding the bar received from the roughing unit 12 and the function of unwinding the previously wound bar for supply to the finishing unit 13 . It includes a unit 30 and a second unit 31 .

In particular, while one of the two units 30 , 31 winds one bar, the other unit 31 , 30 unwinds the other roughed bar feeding downstream. This intermediate winding/unwinding device 29 also allows to define a temporary accumulation buffer for compensating for different working speeds of the casting machine 11 and the finishing unit 13 . In this way, the intermediate winding/unwinding device 29 does not require interruption of the casting process and thus without loss of production, and without adversely affecting the upstream steel mill, small maintenance or programmed roll changes or minor accidents/ Allows to absorb the shutdown time of the rolling mill for shut-off.

According to a possible solution, the intermediate winding/unwinding device 29 may include a heating device (not shown) for heating or maintaining the bar housed therein to a certain temperature.

According to another variant of the invention, the plant 10 is arranged between the roughing unit 12 and the finishing unit 13 and fed by the roughing unit 12 , in this case by an intermediate winding/unwinding device 29 . and a cutting member 28 configured to cut a head end or a tail end of a bar to be fed to the finishing unit 13 .

According to another method, a cooling unit 24 is provided between the rolling station 19 and the final winding unit 14 to cool the strip N exiting the rolling station 19 and the final winding unit 14 . allowed to be collected in

According to another embodiment of the invention, the plant 10 comprises a final winding unit 14 of the strip N.

The final winding unit 14 may comprise a winding element 25 suitable for winding the strip N into a coil.

According to some embodiments, the plant 10 is arranged upstream of the final winding unit 14 and a cutting device configured to cut the strip N to a size when a predetermined weight of the coil of the strip N is reached. 27). The cutting device 27 can be arranged between the cooling unit 24 and the final winding unit 14 .

Referring to FIG. 2 , it comprises a casting machine 11 as defined above, a shear 35 , a first induction heating device 22 and/or a first heating and/or holding unit 32 , arranged in sequence, A modified embodiment of a production plant comprising a finishing unit 13 , a cooling unit 24 and a final winding unit 14 is shown.

Referring to FIG. 3 , it is shown that in addition to the components provided in the production plant 10 of FIG. 2 , the rolling station 19 includes a roughing unit 12 , a second induction heating device 23 , a second heating and/or maintenance Another variant embodiment of the production plant 10 is shown which provides for comprising a unit 33 and a cutting member 28 disposed upstream of the finishing unit 13 .

Referring to Fig. 4, it is a casting machine 11 as defined above, a roughing unit 12, a cutting shear 26, a second induction heating device 23, an intermediate winding/unwinding device ( 29 ), a modified embodiment of the production plant 10 comprising a cutting element 28 , a finishing unit 13 , a cooling unit 24 and a final winding unit 14 is shown.

Referring to FIG. 5 , the production plant 10 comprises a casting machine 11 as defined above, arranged in sequence, a rolling station 19 provided with a roughing unit 12 , a cutting shear 26 , a second induction heating a device 23 , a second heating and/or holding unit 33 , a finishing unit 13 , a cooling unit 24 and a final winding unit 14 .

The production plant 10 described with reference to FIGS. 2-5 may optionally be set to work in a coil to coil mode.

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

The production plant 10 described with reference to FIG. 6 may be configured to work in a coil-to-coil or semi-endless mode.

Referring to FIG. 7 , the production plant 10 comprises a casting machine 11 as defined above, arranged in sequence, a rolling station 19 provided with a roughing unit 12 , a cutting shear 26 , a second induction heating a third induction heating device 34 disposed between the device 23 , the finishing unit 13 , the finishing stand 21 , a cooling unit 24 , a cutting device 27 and a final winding unit 14 . .

The production plant 10 described with reference to FIG. 7 may be configured to work in an endless mode.

Referring to FIG. 8 , the production plant 10 comprises a casting machine 11 as defined above, arranged in sequence, a rolling station 19 provided with a roughing unit 12 , a cutting shear 26 , a second induction heating A third induction heating device 34 disposed between the device 23 , the intermediate winding/unwinding device 29 , the cutting member 28 , the finishing unit 13 , the finishing stand 21 , the cooling unit 24 ) , a cutting device 27 and a final winding unit 14 .

The production plant 10 described with reference to FIG. 8 may be configured to work in coil-to-coil or endless mode.

Referring to FIG. 9 , the production plant 10 comprises a casting machine 11 as defined above, a rolling station 19 provided with a shear 35 , a first induction heating device 22 , a first, arranged in sequence. Third induction heating disposed between the heating and/or holding unit 32 , the roughing unit 12 , the cutting shear 26 , the second induction heating device 23 , the finishing unit 13 , and the finishing stand 21 . It comprises a device 34 , a cooling unit 24 , a cutting device 27 and a final winding unit 14 .

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

The embodiment of the plant 10 described with reference to FIGS. 2-9 is an example of a production plant layout that the end user can select in an optimized manner as a function of productivity, product mix, type of steel, also referred to as "steel grade" to be produced. Define examples of families.

According to one aspect of the present invention, a method for producing a metal strip (N) comprises casting a cast product (P) through a casting machine (11) to at least obtain a slab (B) and a metal strip (N) Hot rolling the slab B in a rolling station 19 to obtain

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

According to another aspect of the present invention, for each thickness size of the strip N produced, the casting machine 11 has a different action to reduce the thickness of the cast product P exiting from the crystallizer 15a. is optionally set to

In particular, such that the thickness of the slab B produced by the casting machine 11 is adjusted in each case as a function of at least the final thickness of the strip N to be obtained, and possibly the various products or product mixes to be obtained. is provided

This approach reduces the compressive action that has to be applied to the rolling station 19, reduces the required rolling power, reduces the wear on the rolling rolls, and in some cases for known plants with the same overall productivity. Allow to reduce the number of stands to at least one.

By way of example only, given the same size of the crystallizer 15a, the method produces a first strip having a first strip thickness SN', wherein the casting machine 11 is removed from the crystallizer 15a. A first step of applying a first thickness reduction ratio TAU A' of the outgoing cast product P and producing a second strip having a second strip thickness SN" less than the first thickness, the casting machine 11 ) is the second thickness reduction ratio TAU A" of the cast product P exiting from the crystallizer 15a, and the first thickness reduction ratio TAU A' is the second thickness reduction ratio TAU A" ) and may be provided to include a different second step.

According to one scheme, the first thickness reduction ratio TAU A' is smaller than the second thickness reduction ratio TAU A".

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

According to a possible solution of the present invention, the applicant has determined that the casting machine 11 can be selectively set to exert the action of reducing the thickness of the cast product P, defined by the equation below.

K: variable parameter from 0.8 to 1.1

A: a coefficient equal to about 4689

H: the thickness of the cast product P exiting from the crystallizer 15a, that is, the thickness of the crystallizer 15a

a: coefficient equal to -0.37

SN: thickness of strip (N) to be obtained at the end of rolling

The TAU A derived from the formula is a percentage value and may be, by way of example only, usually a value of 2% to 75%.

Figure 10 shows some examples of curves defined for the thickness H of the cast product P, showing the increase in TAU A as a function of the strip thickness SN.

This formula allows to optimize the setting of the casting machine 11 as a function of the thickness of the crystallizer 15a and the strip thickness SN to be obtained for the efficient functioning of the overall production plant, as defined above.

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

i) representing the thickness reduction ratio (TAU1) of the roller unit, the action of reducing the thickness of the roller unit 16 and the product P cast by the liquid core pre-rolling;

ii) It represents the thickness reduction ratio TAU2 of the drawing unit, and is configured to apply an action of reducing the thickness of the cast product P by the action of the drawing unit 18 .

The thickness reduction by the drawing unit 18 may be optional.

The thickness reduction ratio (TAU A) is thus given by the combination of the reductions (TAU1, TAU2).

The thickness reduction ratio (TAU1) of the roller unit is the thickness (H) of the cast product (P) exiting the crystallizer (15a) and the thickness (H) of the cast product (P) exiting the crystalizer (15a) and It is defined by the difference between the relevant, slab thickness SB1 exiting from the roller unit 16 .

The thickness reduction ratio of the drawing unit TAU2 is related to the slab thickness SB1 exiting the roller unit 16 and the slab thickness SB1 exiting the roller unit 16, the slab thickness exiting the drawing unit 18 (SB2) is defined as the difference between

According to a possible solution of the present invention, the applicant has found that the drawing unit 18 can be selectively set to exert the action of reducing the thickness SB1 of the solid core cast product P, defined by the equation decided

Q: variable parameter from 0.8 to 1.1

B: first coefficient equal to 10928

H: the thickness of the cast product P exiting from the crystallizer 15a as defined above

b: second coefficient equal to -1.659

SN: thickness of strip

C: third coefficient such as 10648

c: fourth coefficient equal to -1.596

According to a possible approach, a solid core reduction in the thickness of the cast product P is applied for a strip thickness SN from 0.6 mm to 3.5 mm. In practice, for these sizes of strip thickness SN, the action of liquid core reduction is relatively high, from the start, for maximally reducing the starting slab, and therefore the action of liquid core reduction and the thickness of the solids applied to the drawing unit 18 . It is advantageous to combine the additional action of core reduction.

Furthermore, the action of solid core rolling exerted by the drawing unit 18 allows to increase the production of the strip, which is particularly advantageous for thin strip thicknesses.

11 shows some examples of curves defined for the thickness H of the cast product P exiting the crystallizer, showing the increase in TAU2 as a function of the strip thickness SN.

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

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

The overall reduction ratio of the rolling station 19 is defined as TAUB, and the obtained strip N is related to the slab thickness SB2 exiting from the casting machine 11 and the slab thickness SB2 supplied by the casting machine 11 . ) is defined as the difference between the thicknesses of The overall reduction ratio TAUB of the rolling station 19 can also be defined as the combination of the reduction ratios TAU3 and TAU4 of the roughing unit 12 and the finishing unit 13 .

According to another aspect of the invention, a method for producing a metal strip comprises supply by a client of design data, which at least

- eg annual productivity (PR) of the production plant 10 ;

- the range of the average width (LN) and thickness (RS) of the strip to be produced by the production plant 10 ;

- individual distribution of productivity as a function of the thickness of the strip N produced;

- the type of product that can be cast with the casting machine, ie the steel grade as above;

- Includes individual distribution of productivity as a function of the type of castable product.

The above set of parameters defines the so-called "product mix" of the plant, ie the various products that the production plant 10 has to produce, which are sized to achieve the purposes of the present invention.

Providing a range of thickness (RS) provides for defining the maximum thickness (SMAX) and minimum thickness (SMIN) of the strip that can be obtained.

In some embodiments of the present invention, the rolling method provides for determining the optimal type of rolling mode of the slab B for the product mix required by the client.

The rolling mode of the slab B is selected from endless, semi-endless and coil-to-coil rolling mode.

12 shows a graph showing the criteria for selecting one of the above rolling modes, at least for strip thickness (SN) and steel grade.

In general, in order to achieve a production plant 10 which allows to work in several modes of operation, the rolling mode to be implemented in each case depends on the economic assessment (energy consumption and yield of the product) and the required quality (of the strips) for the final product. Based on mechanical properties and size tolerances), it is defined by optimizing the operating conditions of the plant.

By way of example only, if there are mainly thin thicknesses, without special types of steel in the product mix, such as peritectic steels that are difficult to cast and require low casting speeds, then the endless type of rolling mode is chosen, thus FIGS. 7, 8 , one of the plant layouts shown in Fig. 9 can be selected.

In the product mix, there is mainly a thin thickness, but also when there is a need to cast a special type of steel, coil-to-coil and semi-endless rolling modes are generally selected, so that one of the plant layouts shown in Figs. can The coil-to-coil and semi-endless modes allow casting special steels at low speeds, as the casting process is not constrained by the rolling process. The semi-endless mode is preferred for thin and ultra-thin strip (N) thicknesses of, for example, 0.8 mm to 1.4 mm. The coil-to-coil mode is instead preferred for strip thicknesses greater than 1.4 mm.

13 graphically illustrates other criteria for selecting a rolling mode with respect to the strip thickness and capacity of the plant layout selected for adopting any and/or other of the above rolling modes.

By way of example only, with reference to FIG. 13 , if the constructive layout of FIGS. 2-5 is chosen, it is provided to make plant operation in coil-to-coil mode for a strip thickness of about 1.2 mm to 12 mm, while FIG. 9 When the constructive layout of It is provided to make the plant work in coil-to-mode for strip thickness.

According to another approach, the production method provides for setting the casting speed VC selected from values between 4.5 m/min and 6 m/min.

In particular, for types of difficult-to-cast steels, such as API, sack and Corten steel, advantageously lower casting speeds are set, such as 4.5 m/min to 5 m/min. For steels that are easy to cast, such as Low Carbon, Medium Carbon, HSLA, DP, CP, HC, MnB steels, higher casting speeds are set, for example 5 m/min to 6 m/min .

Likewise, the choice of casting speed VC can also be defined for the selected rolling mode, i.e. a relatively low casting speed for the coil-to-coil and semi-endless modes, and a higher casting speed for the endless mode.

The production method provides for setting the nominal slab thickness (SBN) values that allow the productivity (PR) to be reached for the casting speed (VC) and the average strip width (LN).

Nominal slab thickness (SBN) is also a constant thickness of equivalent slab corresponding to the average (average) of (variable) slab thicknesses after metered liquid core reduction in terms of individual hourly production, for the same overall production for that given product mix. can be interpreted as

According to a possible solution, the nominal slab thickness (SBN) is determined by the following equation.

SBN=PR/runtime/(VC*LN*PS)

Operating time here, and in the description and claims below, refers to the sum of the operating hours, ie when the plant is in operation, in calendar years, and production interruptions due to maintenance, accidents, etc.

PS is usually the specific weight of the steel, which can be about 7.8 kg/dm3.

Referring to FIGS. 14 and 15 , graphs showing the relationship of the nominal slab thickness (SBN) to the annual output (PR) of the plant and the casting speed (VC) are shown.

In particular, FIG. 14 shows a slab width of about 1300 mm, while FIG. 15 shows a slab width of about 1400 mm.

According to a possible implementation of the invention, the method determines the thickness of the cast product P exiting the crystallizer 15a, ie the distance between the outlet section of the latter and the corresponding plate of the crystallizer 15a. includes determining This thickness H of the cast product P is adopted for the overall product mix defined by the client.

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

The method is applied by the rolling station 19 and when a strip N of minimum thickness SMIN is machined, the value of the slab thickness SB2 entering the rolling station 19 and the obtainable strip N ) is provided to determine the ratio of thicknesses (RSP) calculated as the ratio between the minimum thicknesses (SMIN).

The value of the slab thickness SB2 entering the rolling station 19 when a strip N of minimum thickness SMIN is machined is the casting from the thickness H of the cast product P exiting from the crystallizer 15a. Calculated minus the maximum thickness reduction imparted by the machine. According to a possible solution, this maximum thickness reduction induced by the casting machine 11 is at least 31 mm or more.

The method also provides for setting the number of rolling stands of the rolling station 19 to the ratio of thickness.

For ratios of thickness from 4 to 12, four rolling stands are provided.

For ratios of thickness from 12 to 21, five stands are provided.

For thickness ratios of 21 to 52, six rolling stands are provided.

For thickness ratios of 52 to 110, seven rolling stands are provided.

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

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

Next, the method relates to a casting machine 11 carried out with a roller unit 16 and a drawing unit 18 for the final thickness of the strip N, for the slab B exiting from the crystallizer 15a Provides to set the mode for dispensing liquid core reduction and solid core reduction of

This mode for distributing the reduction in the thickness of the cast product P can be determined by the equations TAU A, TAU2 defined above.

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

According to a possible solution, the roller unit 16 can perform a maximum liquid core reduction (RCLMAX) of about 25 mm. According to a possible solution, the roller unit 16 can perform a minimum liquid core reduction RCLMIN of about 5 mm. This reduction allows to give a better quality to the cast metal product (P).

According to one aspect of the invention, the drawing unit 18 is capable of carrying out a maximum solid core reduction of at least 7 mm, while the minimum reduction is zero.

In particular, each individual pair of rollers of the drawing unit 18 can achieve a compression of 0.5 mm to 1.5 mm, if desired.

According to a possible implementation of the method, when the coil-to-coil production mode is set and the use of the winding/unwinding device 29 is provided, the number of roughing stands 20 is a bar having a thickness of 8 mm to 25 mm at the entrance. It is arranged to feed to the winding/unwinding device 29 . Bar thicknesses of less than 8 mm entail problems moving and introducing into the winding/unwinding device, while bar thicknesses greater than 25 mm cause operational and/or sizing disturbances with possible occurrence of surface defects in the bar.

According to another possible implementation of the method, when the coil-to-coil type production mode is set and the use of the heating unit 33 is provided, the number of roughing stands 20 is supplied to the heating unit with a bar having a thickness of 30 mm or more at the inlet. determined to do A size smaller than these thickness values requires the use of a very long heating unit, is difficult to manage, and is uneconomical.

According to a possible solution, the number of finishing stands 21 is provided to be at least two.

Yes

17-22, two examples of implementations of the present disclosure are described.

Specifically, referring to FIGS. 17-19 , the average width (LN) of the strip of about 1300 mm, the range of thickness (RS) of about 1.2 mm to 8 mm, and the production (PR) of about 1.1 Mton/year are required A first case is shown.

On the other hand, referring to FIGS. 20-22 , the average width (LN) of the strip of about 1400 mm, the range of thickness (RS) of about 0.8 mm to 3 mm, and the production (PR) of about 1.4 Mton/year are required. Two cases are shown.

Referring to the tables shown in FIGS. 17 and 20 , at least in the last four columns to the right, one can see a comparison of the distribution of production to the production mix in the case of a conventional casting and in the case of a casting with a reduction in thickness according to the present disclosure.

The production mix and annual productivity values (see the seventh and twelfth columns of the table) are parameters requested by the client and set according to how the client needs to use the plant.

Also, referring to the tables shown in FIGS. 17 and 20 , in the sixth column, the slab thickness SB2 escaping from the casting machine 11 is not a constant value as the thickness of the strip changes, and decreases as the thickness of the strap decreases. It can be seen that the value of On the other hand, in the prior art or in the known art, the slab thickness (SBN) exiting the casting machine is always the same as the thickness of the strip changes, as shown in the second column from the left. This is also shown graphically in FIGS. 18 and 21 .

This change in the thickness of the slab with respect to the thickness of the final strip is obtained by the fact that the casting machine 11 imparts to the cast product a liquid core reduction (RCL) of the thickness shown in the third column of the table in Figs. lose

The table also lists the thickness reductions carried out with the drawing unit 18 (fifth column), the roughing unit 12 (the seventh column) and the finishing unit (the ninth column) and the final strip thickness at which these actions will be obtained. It shows how it is distributed.

On the other hand, FIGS. 19 and 22 graphically show the distribution of productivity per hour of the plant as a function of the strip thickness to be obtained, for known conventional castings and for castings with variable thickness reduction according to the invention.

In particular, it can be seen that in the case of the conventional casting known in FIGS. 19 and 22, the annual productivity remains unchanged with respect to the strip thickness to be obtained, while in the case of the casting according to the present invention, the annual productivity varies with the strip thickness to be obtained. have.

From the analysis of Figures 19 and 22, it can be seen that for low strip thickness values, the present invention allows lower productivity compared to the conventional solution, while for high strip thickness values, the present invention provides higher productivity than the conventional solution. can However, overall, in the case of the conventional casting and the casting according to the present invention, the annual productivity of the plant is the same, and the above advantages can be obtained in the method according to the present invention compared to the known method.

A mode for selecting the number of rolling stands of the rolling station 19 and the type of plant will be described with reference to the first case shown in FIGS. 17-19 .

In particular, based on the range of the variable strip thickness of 1.2 mm to 8 mm, and for the graph of FIG. 12 , it is advantageous to adopt a plant layout capable of implementing a coil-to-coil type rolling mode.

It is provided to set a casting speed of about 5.5 m/min, which, for an average strip thickness (LN) of 1300 mm and a productivity of 1.1 Mton/year, as can be diagrammatically derived from FIG. 14 , is about 45 mm corresponds to the nominal slab thickness (SBN) of

Based on this SBN value, as shown in the table of Fig. 17, the thickness (H) of the cast product (P), which is 10 mm to 15 mm larger than the nominal slab (SBN) value, in this case equal to 55 mm, can be determined

This serves to determine the thickness reduction to be imparted by the rolling station 19 .

The slab thickness SB2 entering the rolling station 19 when the minimum thickness is machined is 24 mm.

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

Referring to FIG. 16 , it can be seen that a number of stands such as 5 correspond to this thickness ratio.

On the other hand, referring to the conventional casting, the ratio of the conventional thickness is given by the ratio between the minimum thickness of the strip (SMIN) and the nominal slab thickness (SBN), in this case 45/1.2=37.5. Referring to FIG. 16 , a number of stands such as 6 correspond to this thickness ratio. From this example, it can be seen how the number of rolling stands can be reduced to one unit, for the conventional production mode, for the annual productivity of the same plant.

Another mode for selecting the number of rolling stands of the rolling stand 19 and the type of plant will be described with reference to the second case shown in FIGS. 20-22 .

In particular, based on the range of the variable strip thickness from 0.8 mm to 3.0, and for the graph of FIG. 12 , it is advantageous to adopt a plant layout capable of implementing an endless rolling mode.

It is provided to set a casting speed of about 6.0 m/min, which for an average width (LN) of 1400 mm and a productivity of 1.4 Mton/year, as can be diagrammatically derived from FIG. 15 , of about 50 mm Corresponds to the nominal slab thickness (SBN).

Based on this SBN value, as shown in the table of Fig. 20, the thickness (H) of the cast product (P), which is 10 mm to 15 mm larger than the nominal slab (SBN) value, in this case, a value equal to 65 mm can be determined

This serves to determine the percentage of the thickness to be imparted by the rolling station 19 .

The slab thickness SB2 entering the rolling station 19 when the minimum thickness is machined is 34 mm.

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

Referring to FIG. 16 , it can be seen that a number of stands such as 6 correspond to this thickness ratio.

On the other hand, referring to the conventional casting, the ratio of the conventional thickness is given by the ratio between the minimum thickness of the strip (SMIN) and the nominal slab thickness (SBN), in this case 50/0.8=62.5. Referring to FIG. 16 , a number of stands such as 7 correspond to this thickness ratio. From this example, it can be seen how the number of rolling stands can be reduced to one unit, compared with the conventional production mode, for the annual productivity of the same plant.

Partial changes and/or additions may be made to the method for producing a metal strip as described and to the production plant implementing the method without departing from the field and scope of the present invention.

Although the present invention has been described with reference to some specific examples, a person skilled in the art will implement the method and method for producing a metal strip as described, having the features set out in the claims and falling within the defined protection scope. Many other equivalent types of production plants can be achieved.

In the claims below, the sole purpose of the signs in parentheses is to aid in reading and should not be considered as a limiting element with respect to the scope of protection claimed in a particular claim.

Claims (12)

casting the cast product P through a casting machine 11 provided with a crystallizer 15a to obtain a slab B; and
hot rolling said slab (B) in a rolling station (19) to obtain metal strips (N) having different strip thicknesses (SN),
The casting machine (11) is a method for producing a metal strip (N) which, during casting, exerts an action to reduce the thickness of the cast product (P) which has exited the crystallizer (15a),
The casting machine 11 has another action of reducing the thickness of the cast product P, namely producing a first strip having at least a first thickness SN', given the same size of the crystallizer 15a. as the strip thickness SN is changed, optionally set,
The casting machine 11 produces a second strip having a first thickness reduction ratio TAU A' of the cast product P and a second thickness SN" which is at least less than the first thickness SN'. A second step of
The casting machine 11 applies a second thickness reduction ratio TAU A" of the cast product P which is different from the first thickness reduction ratio TAU A', said thickness reduction ratio exiting from the crystallizer 15a between the thickness H of the exiting cast product P and the thickness of the slab exiting from the casting machine 11 SB2 in relation to the thickness H of the casting product P exiting from the crystallizer 15a. A method characterized in that it is defined as the difference. According to claim 1,
The method according to claim 1 , wherein the first thickness reduction ratio (TAU A′) is less than the second thickness reduction ratio (TAU A″). 3. The method of claim 1 or 2,
Method, characterized in that the casting machine (11) is selectively configured to exert the action of reducing the thickness of the cast product (P) exiting the crystallizer (15a), defined by the equation below.

K: variable parameter from 0.8 to 1.1
A: a coefficient equal to about 4689
H: the thickness of the cast product P exiting from the crystallizer 15a
a: coefficient equal to -0.37
SN: the thickness of the strip to be obtained at the end of rolling 4. The method according to any one of claims 1 to 3,
The casting machine (11) comprises a pre-rolling device (16) having a liquid core and a roller applying the action of reducing the thickness of the cast product (P) which has escaped from the crystallizer (15a) by pre-rolling. How to. 5. The method of claim 4,
The pre-rolling device 16 with rollers is provided with a plurality of opposing rollers through which the cast product P passes,
The method according to claim 1 , wherein the rollers are selectively moved towards/away from each other to exert a selective action of reducing the liquid core in the thickness of the cast product (P). 6. The method according to claim 4 or 5,
The casting machine 11 is a drawing unit 18 that applies an action of reducing the thickness of the cast product P, which has escaped from the pre-rolling device 16 having the roller, by rolling the core core of the cast product P. ), comprising a method. 7. The method of claim 6,
A method, characterized in that the drawing unit (18) is selectively set to exert the action of reducing the thickness of the solid core cast product (P), defined by the equation below.

Q: variable parameter from 0.8 to 1.1
B: first coefficient equal to 10928
H: the thickness of the cast product P exiting from the crystallizer 15a
b: second coefficient equal to -1.659
SN: thickness of strip
C: third coefficient such as 10648
c: fourth coefficient equal to -1.596 8. The method of claim 6 or 7,
A method wherein a reduction in the thickness of the solid core cast article (P) is applied for a strip thickness (SN) of 0.6 mm to 3.5 mm. 9. The method according to any one of claims 1 to 8,
A method comprising determining a thickness (H) of the cast article exiting a crystallizer (15a) that is 10 mm to 15 mm greater than a nominal slab thickness (SBN) defined by the equation below.
SBN = PR/runtime/(VC*LN*PS)
PR: Plant productivity
VC: Casting speed selected from 4.5 m/min to 6 m/min
LN: average width of the strip
PS: specific weight of steel 10. The method according to any one of claims 1 to 9,
When a strip N of minimum thickness SMIN is machined, calculated as the ratio between the value of the slab thickness SB2 entering the rolling station 19 and the value of the minimum thickness SMIN of the strip N , determining the thickness ratio RSP applied by the rolling station 19 . 11. The method of claim 10,
counting the number of rolling stands of the rolling station (19),
For a thickness ratio of 4 to 12, four rolling stands are provided,
For a thickness ratio of 12 to 21, five rolling stands are provided,
For a thickness ratio of 21 to 52, six rolling stands are provided,
Method, characterized in that for a thickness ratio of 52 to 110, seven rolling stands are provided. a casting machine 11 provided with a crystallizer 15a configured to cast a cast product P and obtain a slab B; and
a rolling station (19) of said slab (B) for obtaining metal strips (N) with different strip thicknesses (SN);
The casting machine (11) is a plant for producing a metal strip (N), configured to exert an action of reducing the thickness of the cast product (P) which has escaped from the crystallizer (15a) during casting,
The casting machine 11 produces a first strip having at least a first thickness SN′, for the same size of the crystallizer 15a , so as to exert another action of reducing the thickness of the cast product P. is optionally configured, as the strip thickness SN changes, to apply the first step of:
The casting machine 11 produces a second strip having a first thickness reduction ratio TAU A' of the cast product P and a second thickness SN" which is at least less than the first thickness SN'. A second step of
The casting machine 11 applies a second thickness reduction ratio TAU A" of the cast product P which is different from the first thickness reduction ratio TAU A', said thickness reduction ratio exiting from the crystallizer 15a between the thickness H of the exiting cast product P and the thickness of the slab exiting from the casting machine 11 SB2 in relation to the thickness H of the casting product P exiting from the crystallizer 15a. A plant, characterized in that it is defined by the difference.

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