KR102591941B1 - Method to produce a metal strip, and production plant implementing said 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 metal strips (N) with different strip thicknesses (SN). A method for producing a metal strip (N), comprising the step of hot rolling the slab (B) at (19). The casting machine 11 acts to reduce the thickness of the cast product P exiting the crystallizer 15a during casting.

Description

Method for producing a metal strip and a production plant implementing the method {METHOD TO PRODUCE A METAL STRIP, AND PRODUCTION PLANT IMPLEMENTING SAID METHOD}

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

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

In the iron and steel industry, plants for producing metal strips are known, usually consisting of a mold configured to cast a slab, an extraction device provided to extract the slab from the mould, and an extraction device provided for extracting 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 .

Depending on the thickness of the metal strip to be obtained and the overall productivity that the plant should have, it is known to appropriately size the entire plant so as to satisfy the required parameters, at least with regard to the productivity of the plant and the thickness of the strip.

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

Endless type plants provide for the feeding of gripped cast products directly from the mold to the rolling line, without cutting the product being worked on except before final winding.

Semi-continuous type plants are used downstream of the roughing stand or casting machine to ensure that the casted product is cut to size and, if necessary, to stop downstream rolling due to minor accidents or programmed roll changes, as well as accumulation for the cast product. Provided for placement in a heating and/or holding furnace to act as a buffer.

If the cast product is cut downstream of a casting machine or roughing stand to a length that yields a single 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 downstream of the casting machine or roughing stand to a length such that a plurality of coils, usually two to five, are obtained at the end of the rolling process, the process is called semi-endless.

It is also known, through appropriate experience, that semi-continuous type plants can be made to function in endless mode, so as to obtain the advantages of this solution.

The choice of the type of plant to be adopted and the number of components required, such as the number of rolling stands or how many roughing stands and how many finishing stands to be adopted, are usually decided based on the experience of the person skilled in the art.

However, this sizing, i.e. preparation of the strip production plant, does not allow reaching an efficient compromise between the investment required to build the plant, sometimes called Capex, and the operating transformation costs, sometimes called Opex. Therefore, there may be a situation where the investment incurred in the construction of the production plant is too high compared to the return, and the production plant is oversized to supply the client's productivity, or alternatively, the production plant is downsized, providing the production capacity required by the client. There are situations in which it is not permitted to reach .

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

Accordingly, the object of the present invention is to provide a production plant precisely sized according to the needs of a client working with a method of hot production of metal strip, e.g. steel, which is capable of optimizing the productivity of the strip production plant with the smallest possible number of stands. Meanwhile, it is to maintain maximum casting speed for various types of steel.

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

Another object of the present invention is to provide a plant and complete method for producing hot rolled metal strips in which the thickness of the cast slab can be selectively varied with respect to the final thickness of the strip.

Furthermore, the object of the invention is to provide a method for producing metal strips which can be adapted to specific client needs and which allows obtaining a highly flexible plant.

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

The applicant has developed, tested and implemented the present invention 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 dependent claims describe changes to the main inventive idea or other features of the invention.

In accordance with the above purpose, the method for producing metal strips according to the invention consists in casting the cast product through a casting machine provided with a crystallizer to obtain slabs and on a rolling station to obtain metal strips with different strip thicknesses. It involves hot rolling the slab.

During casting, the casting machine acts to reduce the thickness of the cast product as it exits the crystallizer.

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

In particular, the method produces a first strip having at least a first thickness when the size of the crystallizer is the same, wherein the casting machine applies a first thickness reduction rate to the cast product in a first step and a second strip less than the first thickness. A second step of producing a second strip having a thickness, wherein the casting machine applies a second thickness reduction ratio to the cast product that is different from the first thickness reduction ratio, wherein the thickness reduction ratio is different from the first thickness reduction ratio to the cast product exiting the crystallizer. Provides that it 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 adjusting the thickness of the slab exiting the casting machine as a function of the final strip thickness to increase the quality of the strip produced and increase the efficiency of the strip production plant.

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

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

For the same productivity, if the number of rolling stands in the rolling station is substantially the same as that of the known plants, the invention allows for the reduction of the thickness to be carried out directly by the casting machine, not only at the rolling station, as happens in the prior art. Therefore, the number of rolling compressions can be reduced.

This leads to energy savings by reducing the pressure of compression on the slab being rolled and to 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. Allowed.

Moreover, the invention can reduce maintenance intervention at least at the rolling station.

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.

The effect of the invention is to provide a production plant precisely sized according to the needs of a client working with a method of hot production of metal strip, such as steel, which can optimize the productivity of the strip production plant with the lowest possible number of stands, while The goal is to maintain maximum casting speed for various types of steel.

In addition, the effect of the present invention is to provide a plant for producing hot rolled metal strips that has a lower operating transformation cost (Opex) and requires limited investment (Capex) compared to traditional plants for producing the same strip thickness. will be.

Another effect of the present invention is to provide a plant and complete method for producing hot rolled metal strips in which the thickness of the cast slab can be selectively varied with respect to the final thickness of the strip.

Furthermore, the effect of the invention is to provide a method for producing metal strips which can be adapted to specific client needs and which allows to obtain a very flexible plant.

Additionally, the effect of the present invention is to provide a plant for producing metal strip that is competitive in the market.

1-9 represent part of a possible embodiment of a plant for producing metal strips implementing the method according to the invention.
Figure 10 plots some curves defined for the thickness (H) of the cast product exiting the crystallizer, showing the increasing rate of thickness reduction of the cast product applied by the casting machine as a function of the thickness of the strip.
Figure 11 shows a defined curve for the thickness (H) of the cast product exiting the crystallizer, showing the increasing rate of thickness reduction of the drawing unit as a function of the thickness of the strip.
Figure 12 shows criteria for selecting rolling mode.
Figure 13 diagrammatically illustrates different criteria for selecting a rolling mode versus the capacity and strip thickness of the plant layout to adopt one and/or the other of the rolling modes.
Figures 14 and 15 are graphs showing the relationship of nominal slab thickness to casting speed and plant productivity. These charts represent a casting operation of 7,200 hours/year.
Figure 16 is a graph showing the relationship between the ratio of thickness to the number of rolling stands required.
17-22 show two embodiments of implementation of the present disclosure.

To aid understanding, identical reference numbers are used, where possible, to indicate identical common elements in the drawings. It is understood that elements and features of one embodiment can be readily incorporated into another embodiment without further recitation.

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. For example, features shown or described as being part of one embodiment may be adopted or associated with another embodiment to provide another embodiment. It is understood that the present invention includes all such changes and modifications.

Embodiments of the invention relate to a method for producing a metal strip (N) in a production plant (10).

2-9 show a possible layout of a plant 10 for producing strip embodying the principles of the present invention.

In particular, reference is made to Figure 1, which shows a plurality of operational components interdisposed along a line of operation. These operational components shown in Figure 1 may be combined with each other to obtain one or more layouts for producing strips, shown in Figures 2-9. For this purpose, the alternative embodiment of the production plant 10 shown in Figures 2-9 refers to the components of the plant described with reference to Figure 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 the 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 the strip N. .

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

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

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

At 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 versions of the invention, the casting machine 11 may be provided with thickness reduction means arranged downstream of the crystallizer, which reduce the thickness of the cast product P exiting the crystallizer 15a. To apply the action, the strip thickness can be set selectively in each case as it changes.

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 arranged downstream of the mold 15 and is configured to effect a reduction in the thickness of the cast product P exiting the crystallizer 15a while its core remains liquid. It comprises a free rolling device 16 with rollers, hereinafter also referred to as roller units, which are liquid or partly liquid.

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

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

Regulating devices 17 of known types, such as hydraulic cylinders, move the rollers of the roller units 16 towards/away from each other and reduce the thickness of the cast product P exiting the crystallizer 15a. It is associated with a segment to perform.

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

The slab B pulled out of 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 compression carried out by the roller unit 16 allows the two half skins to be connected at the connection point, also called the "Kissing Point" (KP), where there is complete solidification of the cast product. KP is also seen as the terminal vertex of the liquid cone originating from the meniscus of liquid metal in crystallizer 15a.

According to one aspect of the invention, the position of the KP can be varied along the longitudinal stretch of the roller unit 16, depending on the intensity of the secondary cooling and the intensity of the liquid core thickness reduction obtained by adjusting the segments of the roller unit 16. intervene. The position of the 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 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 and 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 the roller unit 16 and may be configured to cool the outer surface of the slab and thereby determine further solidification. The cooling device may include nozzles to provide sprayed water or water mixed with air (“air mist”). The action of the cooling device also has an effect on the location of the KP.

According to some embodiments, the casting machine 11 includes 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 pairs of drawing rollers, from 1 to 6.

Each pair of rollers is disposed on opposite sides 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 through it.

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

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 a possible solution, possibly in combination 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 provides for vertical and vertically curved casting.

The first drawing device 18a and/or the second drawing device 18b may comprise a number of pairs of rollers, from 1 to 3.

As mentioned above, the rollers of the drawing unit 18 are configured to carry out actual rolling, albeit to a slight extent, in the slab B of thickness SB1, which results in a slight liquid core thickness reduction, thus determining the extension of the material. . The rolling, albeit mild, of the drawing unit 18 causes a further reduction in the thickness of the slab B, which has a different thickness SB2 less than SB1, so that the rolling station 19 arranged downstream reaches a thinner thickness. Allow to do so. Since the drawing unit 18 is disposed at the end of the casting machine 11, the thickness SB2 of the slab B exiting the drawing unit 18 is equal to the thickness of the slab B exiting the casting machine 11. corresponds to

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, is called a “Rolling Caster”. )".

By a rolling caster, casting and rolling of products can be carried out, meaning a casting machine 11 with a partly liquid core and partly a solid core.

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

According to one 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, depending on the 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 final size, i.e. define the 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 of which is configured to roll and define the strip thickness SN.

According to a possible option, a cutting shear 26 is provided immediately downstream of the roughing unit 12, which cuts the roughened slab B and undergoes subsequent rolling to obtain strips N. It is configured to define a bar, also called a transfer bar.

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 option, the plant 10 is arranged downstream of the casting machine 11 , in this case upstream of the roughing unit 12 and is configured to recover the temperature of the slab before introduction into the rolling station 19 . It includes a heating device (22).

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

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

According to another alternative, the plant 10 comprises a third induction heating device 34 arranged between two of the finishing stands 21 and configured to recover 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 maintaining unit, in this case two heating and/or maintaining units 32, 33, configured to heat or maintain the temperature of the bar segments. You can.

The heating and/or holding units 32, 33 act 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 a heating and/or holding tunnel type furnace to, among other things, avoid 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 includes a second heating and/or holding unit 33 arranged between the roughing unit 12 and the finishing unit 13 .

According to this embodiment, the production plant 10 is arranged between the casting machine 11 and the rolling station 19 and is equipped with a shear 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 emergency or due to maintenance needs, for example due to roll changes at the rolling station 19 , the segments can later be 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 is previously wound by the finishing unit 13 to produce the cut bar. and 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 the international application WO-A-2011/080300 in the name of the present applicant.

According to some options, the intermediate winding/unwinding device 29 is a first device whose function alternates between winding the bar received from the roughing unit 12 and 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 is winding one bar, the other unit 31, 30 is unwinding the other roughed bar feeding downstream. This intermediate winding/unwinding device 29 also allows defining a temporary accumulation buffer to compensate for the different working speeds of the casting machine 11 and the finishing unit 13. In this way, the intermediate winding/unwinding device 29 requires little maintenance or programmed roll changes or minor accidents/changes without the need to stop the casting process and thus without loss of production and without disadvantage to the upstream steel mill. Allows to absorb shutdown time of rolling mill for blocking.

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

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

According to another option, 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. Allow collection.

According to another implementation 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 member 25 suitable for winding the strip N into a coil.

According to some embodiments, the plant 10 is disposed upstream of the final winding unit 14 and includes a cutting device ( 27). The cutting device 27 may be arranged between the cooling unit 24 and the final winding unit 14.

Referring to Figure 2, this includes a casting machine (11), a sear (35), a first induction heating device (22) and/or a first heating and/or holding unit (32) as defined above, arranged in sequence; An alternative embodiment of a production plant comprising a finishing unit 13, a cooling unit 24 and a final winding unit 14 is shown.

Referring to Figure 3, this means that in addition to the components provided in the production plant 10 of Figure 2, the rolling station 19 includes a roughing unit 12, a second induction heating device 23, a second heating and/or maintenance unit. Another alternative 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 Figure 4, this includes a casting machine 11 as previously defined, a roughing unit 12, a cutting shear 26, a second induction heating device 23, and an intermediate winding/unwinding device ( 29), shows a variant embodiment of the production plant 10 comprising a cutting member 28, a finishing unit 13, a cooling unit 24 and a final winding unit 14.

Referring to Figure 5, the production plant 10 includes a casting machine 11 as previously defined, arranged in sequence, a rolling station 19 provided with a roughing unit 12, a cutting shear 26, and a second induction heating. It includes 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 configured to operate in coil to coil mode.

Referring to Figure 6, the production plant 10 is arranged in sequence, a casting machine 11 as defined above, a rolling station 19 provided with a sear 35, a second induction heating device 23, a second It includes 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 operate in coil-to-coil or semi-endless mode.

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

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

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

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

Referring to Figure 9, the production plant 10 is arranged in sequence, a casting machine 11 as defined above, a rolling station 19 provided with a sear 35, a first induction heating device 22, a first A 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 includes 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 operate in coil-to-coil, semi-endless or endless mode.

The embodiment of plant 10 described with reference to FIGS. 2-9 provides a configuration of production plant layouts that the end user can select in an optimized manner as a function of productivity, product mix, and type of steel, also referred to as “steel grade,” to be produced. Defines examples of families.

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

According to one aspect of the invention, the casting machine 11 acts to reduce the thickness of the cast product P exiting the crystallizer 15a during casting.

According to another aspect of the invention, for each thickness size of strip (N) produced, the casting machine (11) applies a different action to reduce the thickness of the cast product (P) exiting the crystallizer (15a). It is optionally set to do so.

In particular, 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. provided.

This solution is intended to reduce the compressive action that must be exerted on the rolling station 19, to reduce the rolling power required, to reduce the wear to which the rolling rolls are subjected, and in some cases to reduce the wear experienced by rolling rolls with respect to known plants with the same overall productivity. Allow the number of stands to be reduced to at least one.

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

According to one approach, 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 invention, the applicant has determined that the casting machine 11 can be selectively set to have the effect of reducing the thickness of the cast product P, defined by the formula below:

K: variable parameter from 0.8 to 1.1

A: coefficient equal to approximately 4689

H: Thickness of the cast product (P) exiting the crystallizer (15a), i.e. the thickness of the crystallizer (15a)

a: coefficient equal to -0.37

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

The TAU A derived from the formula is a percentage value and, by way of example only, may typically have a value between 2% and 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, as previously defined, allows optimizing the settings of the casting machine 11 as a function of the thickness of the crystallizer 15a and the strip thickness SN to be obtained for efficient functioning of the entire production plant.

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

i) represents the thickness reduction ratio (TAU1) of the roller unit, which acts to reduce the thickness of the cast product (P) by the roller unit 16 and liquid core pre-rolling;

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

Thickness reduction by drawing unit 18 may be optional.

The thickness reduction ratio (TAU A) is thus given as a 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 from the crystallizer (15a) and the thickness (H) of the cast product (P) exiting from the crystallizer (15a). It is defined by the difference between the associated slab thickness SB1 exiting the roller unit 16.

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

According to a possible solution of the present invention, the applicant has established that the drawing unit 18 can be selectively set to have the effect of reducing the thickness SB1 of the solid core cast product P, defined by the formula below: decided.

Q: variable parameter from 0.8 to 1.1

B: first coefficient equal to 10928

H: Thickness of cast product (P) exiting crystallizer (15a) as previously defined

b: second coefficient equal to -1.659

SN: Thickness of strip

C: third coefficient equal to 10648

c: fourth coefficient equal to -1.596

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

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

Figure 11 shows some examples of curves plotted against the thickness (H) of the cast product (P) exiting the crystallizer, showing the increase in TAU2 as a function of 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. , is 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 is related to the thickness of the slab B upstream of the finishing unit 21 and the resulting strip thickness SN, which is related to 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 is related to the slab thickness SB2 exiting the casting machine 11 and the slab thickness SB2 supplied by the casting machine 11, resulting in the strip N ) is defined as the difference between the thicknesses. The overall reduction ratio (TAUB) of the rolling station 19 can also be defined as a combination of the reduction ratios (TAU3, 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 includes supply by a client of design data, which includes at least

- e.g. annual productivity (PR) of the production plant 10;

- the range of the average width (LN) and thickness (RS) of the strip that the production plant 10 must produce;

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

- the type of product that can be cast by the casting machine, i.e. steel grade as above;

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

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

Providing a range of thicknesses (RS) serves to determine the maximum (SMAX) and minimum thickness (SMIN) of the strip that can be obtained.

In some embodiments of the invention, the rolling method provides for determining the optimal type of rolling mode of 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 modes.

Figure 12 presents 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 that allows to work with several operating modes, the rolling mode to be implemented in each case depends on the economic evaluation (energy consumption and output of the product) and the required quality for the final product (of the strips). is defined by optimizing the operating conditions of the plant, based on mechanical properties and size tolerances.

Just as an example, if the product mix is predominantly thin, without special types of steel, such as peritectic steels, which are difficult to cast and require low casting speeds, then the endless type in rolling mode is chosen, thus Figures 7, 8 , one of the plant layouts shown in 9 can be selected.

If, in the product mix, thin thicknesses are predominant, but there is also a need to cast special types of steel, coil-to-coil and semi-endless rolling modes are usually selected, and therefore one of the plant layouts shown in Figures 6 and 9 may be selected. You can. Coil-to-coil and semi-endless modes allow casting special steels at lower speeds, since the casting process is not constrained by the rolling process. Semi-endless mode is preferred for thin and ultra-thin strip (N) thicknesses, for example between 0.8 mm and 1.4 mm. Coil to coil mode is instead preferred for strip thicknesses greater than 1.4 mm.

Figure 13 graphically illustrates different criteria for selecting a rolling mode against the capacity and strip thickness of the plant layout selected to adopt one and/or the other of the above rolling modes.

By way of example only, with reference to Figure 13, it is provided that if the constructive layout of Figures 2-5 is selected, the plant operates in coil-to-coil mode for strip thicknesses of approximately 1.2 mm to 12 mm, while Figure 9 Once the constructive layout of is selected, it can be used in endless mode for strip thicknesses of about 0.6 mm to about 1 mm, in semi-endless mode for strip thicknesses of about 1 mm to about 2 mm, and for strip thicknesses of about 2 mm to about 12 mm. Provision is made to make the plant work in coil-to-mode for strip thickness.

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

In particular, for types of steel that are difficult to cast, such as API, peritoneal and Corten steels, advantageously lower casting speeds are established, 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. relatively low casting speeds for coil-to-coil and semi-endless modes, and higher casting speeds for endless mode.

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

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

According to a possible solution, the nominal slab thickness (SBN) is determined by the formula below:

SBN=PR/Operating Time/(VC*LN*PS)

Operating time refers here and in the description and claims below to the functional time, i.e., when the plant is in operation, in calendar years, plus production interruptions due to maintenance, accidents, etc.

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

14 and 15, graphs are shown that relate the nominal slab thickness (SBN) to the plant's annual production (PR) and casting speed (VC).

In particular, Figure 14 shows a slab width of approximately 1300 mm, while Figure 15 shows a slab width of approximately 1400 mm.

According to a possible implementation of the invention, the method determines the thickness of the cast product P exiting the crystallizer 15a, i.e. the distance between the exit 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 entire product mix as defined by the client.

In a possible implementation of the invention, the thickness H of the cast product P exiting 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 processed, the value of the slab thickness SB2 entering the rolling station 19 and the obtainable strip N ) provides to determine the ratio of thicknesses (RSP), which is calculated as the ratio between the minimum thickness (SMIN) of

When a strip (N) of minimum thickness (SMIN) is processed, the value of the slab thickness (SB2) entering the rolling station (19) is calculated from the thickness (H) of the cast product (P) exiting the crystallizer (15a). It is calculated by subtracting the maximum thickness reduction imparted by the machine. According to a possible option, this maximum thickness reduction induced by the casting machine 11 is at least 31 mm or more.

Additionally, the method provides for determining the number of rolling stands of the rolling station 19 with respect to the ratio of their thicknesses.

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

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

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

For thickness ratios from 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 Figure 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 is carried out with a roller unit 16 and a drawing unit 18 on the slab B exiting the crystallizer 15a to the final thickness of the strip N. Provides for setting modes for dispensing liquid core reduction and solid core reduction.

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

According to another possible option, the casting machine 11 reduces the thickness of the cast product (P) equal to 5 mm for a strip thickness equal to the maximum thickness (SMAX) and for a 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 achieve a maximum liquid core reduction (RCLMAX) of about 25 mm. According to a possible solution, the roller unit 16 can achieve a minimum liquid core reduction (RCLMIN) of about 5 mm. This reduction allows giving better quality to the cast metal product (P).

According to one approach of the invention, the drawing unit 18 is capable of performing 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, if necessary, achieve a compression of 0.5 mm to 1.5 mm.

According to a possible implementation of the method, if the coil-to-coil production mode is set up and the use of the winding/unwinding device 29 is provided, the number of roughing stands 20 is such that the bars have a thickness of 8 mm to 25 mm at the entrance. It is arranged to feed to the winding/unwinding device (29). Bar thicknesses less than 8 mm entail problems in transport and introduction into the winding/unwinding device, while bar thicknesses greater than 25 mm cause operational and/or sizing difficulties due to the possible occurrence of surface defects in the bar.

According to another possible implementation of the method, if 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 such that a bar with a thickness of more than 30 mm at the inlet is supplied to the heating unit. It is decided to do so. Sizes smaller than these thickness values require the use of very long heating units, are difficult to maintain, and are uneconomical.

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

yes

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

Specifically, with reference to Figures 17-19, an average strip width (LN) of approximately 1300 mm, a thickness (RS) ranging from approximately 1.2 mm to 8 mm, and a production (PR) of approximately 1.1 Mton/year are required. The first case is shown.

On the other hand, referring to Figures 20-22, the average strip width (LN) of about 1400 mm, a thickness (RS) ranging from about 0.8 mm to 3 mm, and a production (PR) of about 1.4 Mton/year are required. 2 cases are shown.

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

The production mix and annual productivity values (see columns 7 and 12 of the table) are parameters required 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, the slab thickness (SB2) exiting the casting machine 11 in the sixth column is not a constant value as the thickness of the strip changes, but decreases as the thickness of the strap decreases. You can see that the value is: On the other hand, in conventional or known techniques, the slab thickness exiting the casting machine (SBN) 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 Figures 18 and 21.

This change in the thickness of the slab relative 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 indicated in the third column of the table in Figs. Lose.

The table also shows the thickness reduction carried out by the drawing unit 18 (fifth column), the roughing unit 12 (seventh column) and the finishing unit (ninth column) and the final strip thickness to be obtained by these actions. Indicates how it is distributed.

On the other hand, Figures 19, 22 plot the distribution of the hourly productivity 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 from Figures 19 and 22 that for the known conventional casting the annual productivity remains unchanged with respect to the strip thickness to be obtained, while for the casting according to the invention the annual productivity varies with the strip thickness to be obtained. there is.

From the analysis of Figures 19 and 22, it can be seen that for low strip thickness values, the invention allows lower productivity compared to the conventional approach, while for high strip thickness values, the invention provides higher productivity than the conventional approach. You can. However, overall, in the case of conventional casting and 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.

17-19, the mode for selecting the number of rolling stands of the rolling station 19 and the type of plant will be described.

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

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

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

This provides for determining 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 rolling station 19 is thus 24/1.2=20 overall.

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

Meanwhile, referring to conventional casting, the ratio of 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 Figure 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.

With reference to the second case shown in FIGS. 20-22, different modes for selecting the number of rolling stands and type of plant of the rolling stand 19 will be described.

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

This provides for setting a casting speed of approximately 6.0 m/min, which, for a mean width (LN) of 1400 mm and a productivity of 1.4 Mton/year, as can be derived graphically from Figure 15, of approximately 50 mm. Corresponds to the nominal slab thickness (SBN).

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

This provides for determining the ratio of 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 thickness ratio (SRP) of the rolling station 19 is thus 34/0.8=42.5 overall.

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

Meanwhile, referring to conventional casting, the ratio of 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 Figure 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 to conventional production modes, for the same plant's annual productivity.

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 invention.

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

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

Claims (8)

A method for producing a metal strip (N) in a production plant configured to operate in coil-to-coil and/or semi-endless rolling mode and/or endless rolling mode, comprising:
The slab B is cast at a defined casting speed Vc via a casting machine 11 provided with a crystallizer 15a, and the slab B is hot rolled on a rolling station 19 comprising a plurality of rolling stands. Rolled to obtain metal strips (N) with different strip thicknesses (SN), the casting machine (11) produces a slab (B) that exits the crystallizer (15a) through a free rolling device (16) with rollers during casting. ) and a second effect of reducing the thickness of the solid core of the slab (B) through a drawing unit (18) arranged downstream of the free rolling device (16),
The casting machine 11 is selectively set as the strip thickness SN changes in order to apply different actions to reduce the thickness of the slab B, the first action of reducing the thickness of the liquid core being from 5 to 25 mm. This second action of reduction of the solid core in thickness is up to 7 mm and applies for strip thicknesses SN of 0.6 mm to 3.5 mm, and the overall thickness reduction of the slab B exiting the casting machine is from 2% to 2%. 75%,
A method in which the rolling mode of the slab (B) is selected according to predetermined criteria related to the strip thickness (SN) and the various types of steel produced. 2. The casting machine (11) according to claim 1, wherein the casting machine (11) comprises a free-rolling device (16) having a liquid core and rollers which have the effect of reducing the thickness of the cast product (P) exiting the crystallizer (15a) by free-rolling. A method comprising: 3. The device according to claim 1 or 2, wherein the free rolling device (16) with rollers is provided with a plurality of opposing rollers between which the cast product (P) passes, the rollers moving towards/away from each other. A method characterized in that the liquid core is selectively moved away and exerts the selective action of reducing the thickness of the cast product (P). 3. The casting machine (11) according to claim 1 or 2, wherein the casting machine (11) is configured to roll the cast product (P) out of the free rolling device (16) with rollers by rolling the solid core of the cast product (P). A method characterized by comprising a drawing unit (18) which exerts a thickness reducing action. 3. Determining the thickness (H) of the cast product exiting the crystallizer (15a) according to claim 1 or 2, which is 10 mm to 15 mm greater than the nominal slab thickness (SBN) defined by the formula below: A method comprising:
SBN = PR/operating time/(VC*LN*PS)
PR: Plant productivity
VC: Selected casting speed between 4.5 m/min and 6 m/min
LN: average width of the strip
PS: Specific weight of steel 3. The method according to claim 1 or 2, wherein when a strip N of minimum thickness SMIN is processed, the value of the slab thickness SB2 entering the rolling station 19 and the minimum thickness of the strip N ( Characterized in that it comprises determining the thickness ratio (RSP) applied by the rolling station (19), calculated as the ratio between the values \u200b\u200bof SMIN). 7. The method of claim 6, comprising determining the number of rolling stands of the rolling station (19),
For thickness ratios from 4 to 12, four rolling stands are provided,
For thickness ratios from 12 to 21, five rolling stands are provided,
For thickness ratios from 21 to 52, six rolling stands are provided,
Characterized in that for a thickness ratio of 52 to 110, seven rolling stands are provided. A plant for producing metal strip (N), configured to work in coil-to-coil and/or semi-endless rolling mode and/or endless rolling mode, comprising:
A casting machine (11) provided with a crystallizer (15a) for casting a slab (B) at a defined casting speed (Vc) and a rolling station (19) for hot rolling the slab (B), the rolling station (19) comprises a number of rolling stands to obtain metal strips (N) with different strip thicknesses (SN), the casting machine (11) having a crystallizer during casting via a pre-rolling device (16) with rollers. The first effect of a liquid core reduction in the thickness of the slab B exiting from 15a and a solid core reduction in the thickness of the slab B via a drawing unit 18 arranged downstream of the free rolling device 16. Apply the second action of
The casting machine 11 is selectively set as the strip thickness SN changes in order to apply different actions to reduce the thickness of the slab B, the first action of reducing the thickness of the liquid core being from 5 to 25 mm. This second action of solid core reduction in thickness is up to 7 mm and applies for strip thicknesses SN of 0.6 mm to 3.5 mm, and the overall thickness reduction of the slab B exiting the casting machine is from 2% to 2%. 75%,
The plant where the rolling mode of the slab (B) is selected according to predetermined criteria related to the strip thickness (SN) and the various types of steel produced.