JP2024545647A - Plant and method for producing rolled products - Google Patents

Abstract

The method for producing a metal strip (P) in coil-to-coil, semi-endless or endless mode is performed in a rolling plant (10) comprising a continuous caster (11) configured to produce a slab, a furnace (16) configured to maintain said slab at a certain temperature and/or heat said slab to a certain temperature, at least one roughing stand (25) configured to reduce the thickness of said slab to obtain an intermediate rolled product, a plurality of finishing stands (31) configured to reduce the thickness of said intermediate rolled product to obtain said strip (P), and a rapid heating device (28) arranged between said at least one roughing stand (25) and said plurality of finishing stands (31) for heating said intermediate rolled product in each operating mode such that the temperature of said metal strip (P) associated with the outlet of the last finishing stand (31) is comprised between 830° C. and 860° C.

Description

The present invention relates to a method and plant for producing flat rolled products, such as, but not limited to, metal strip wound to form a roll or coil.

Rolling plants are known in which at least one rolling mill is arranged in line downstream of a continuous casting machine for producing thin slabs, a so-called "thin slab caster", for producing metal strip that is wound to form rolls or coils.

Examples of this type of rolling plant are described in the present applicant's WO 2011/141790 and WO 2021/140531 and consist of a caster with several roughing stands or machines arranged downstream of the caster and several finishing stands or machines, between which are interposed rapid heating devices, usually induction furnaces consisting of several inductor modules.

Downstream of the finishing stand is an exit table (also called a run-out table) with a cooling shower and finally two take-up reels that wind the strip to produce coils.

In order for the rolling in the finishing mill to be carried out in the austenitic range, i.e. without metallographic phase transformation, the strip must leave the last finishing stand of the mill at a temperature of about 850°C or higher.

Therefore, the rolling mass flow rate in the finishing stand must be set to obtain strip having said optimum temperature of at least about 850°C at the exit of the last stand of the rolling mill.

Mass flow rate is the product of strip thickness and velocity. In casting, mass flow rate is usually expressed in units of measurement mm*m/min, whereas in rolling, it is usually expressed in units of measurement mm*m/s.

WO 2011/141790 further teaches how to design and configure such a plant so that it can be operated in a "coil-to-coil" mode, a "semi-endless" mode, or an "endless" mode. In particular, the mode in which the rolling process is carried out is selected from the three modes based on the quality of steel being produced, the maximum casting speed possible for that quality of steel, the final thickness of the strip, and the production costs.

The characteristics of the three rolling modes mentioned above can be summarized as follows:

For the endless mode, the cast slabs are fed directly and continuously into the rolling mill, so the so-called rolling "mass flow" must be equal to the casting mass flow. During operation, there is no entry into the rolling stands, so the endless mode reduces the risk of roll wear and blockage and allows stationary rolling, making it ideal for the production of very thin thicknesses between 0.7 mm and 1.5 mm. Furthermore, in the endless mode, except for the first strip to be produced, the strip head is not transported between the last finishing stand and the take-up reel of the rolling mill. This contributes to increased process stability. However, the endless mode cannot be used for some steel grades that need to be cast at very low speeds. Furthermore, since in this mode the rolling mill must adapt to the casting mass flow, the temperature of the strip at the exit of the last finishing stand depends on the casting mass flow and the heat contribution from the rapid heating device.

For this reason, when the maximum casting mass flow rate is defined, the final temperature of the strip is controlled only by acting on the power supplied by the rapid heating device. Furthermore, in endless rolling, the final speed of the strip is related to the casting mass flow rate and the final thickness of the strip.

For the coil-to-coil and semi-endless modes, the casting and rolling mass flows are different, since there is no continuity between the casting and rolling mills, and each slab is formed at the outlet of the casting device by means of shearing with a pendulum shear. In the coil-to-coil mode, the weight of each individual slab corresponds to the weight of a single coil, while in the semi-endless mode, the weight of each superslab corresponds to the weight of a defined "n" number of coils, defined by a high-speed shear located before the take-up reel. In these modes, the full range of steels that can be cast with a thin slab caster can be produced. On the contrary, for each slab (or superslab) to be rolled, a rolling mill must be entered, which complicates the production of strips with a final thickness of less than 1.5 mm in the case of coil-to-coil mode, or less than 1.2 mm in the case of coil-to-coil mode, due to the difficulty of entering the final finishing stand, since the strip is very thin.

In coil-to-coil and semi-endless modes, a rolling mass flow rate of typically 2.0-3.0 times the casting mass flow rate can be acted upon to obtain the correct final temperature of the rolled product. Thus, once the final thickness of the strip is determined, the mass flow rate of the rolling mill can be changed acting upon the rolling speed, so that the rapid heating device is usually left switched off.

In coil-to-coil and semi-endless modes, it is necessary to limit the maximum speed of the strip as it leaves the final finishing stand and heads towards the take-up reel, to prevent a dangerous lift of the strip head as it leaves the final finishing stand due to aerodynamic effects of speed.

The maximum speed of the strip head is typically limited to approximately 11 m/s to 12 m/s.

This speed limitation may prevent the optimum temperature of at least 850°C from being reached at the exit of the final finishing stand, especially for thin strip.

To overcome such cases, so-called "speeding up" of the rolling stands of the finishing mill is carried out after the head has entered the take-up reel in order to speed up the passage of the strip and reduce temperature losses, allowing the body and tail of the strip to exit the last rolling stand at a target temperature of at least about 850°C.

This "speeding up" means increasing the rotational speed of the rolls in the rolling mill stands, and thus the rolling speed of the strip after the head is wound onto the take-up reel, to a speed value that provides a rolling mass flow rate sufficient to obtain the optimum temperature at the exit of the final finishing stand.

This speed increase averages 40%-50% and can reach 80% in some cases.

Moreover, this speed increase means that the head of the strip is rolled at a first speed (e.g. 12 m/s) and the body and tail of the strip are rolled at a second speed (e.g. 18 m/s) that is faster than the first speed. Such variations in the rolling speed of a single strip create transients in the rolling process and hinder the control of both the geometric parameters of the strip, mainly the "crown", flatness and thickness, and the winding temperature of the reel.

Therefore, if the head is rolled at the set limit speed of about 12 m/s, and the mass flow rate required to obtain the optimum outlet temperature is high, the head will be produced at a temperature lower than the optimum temperature.

This causes undesirable phase changes in the steel and means that the mechanical and geometric properties of the metal strip are not uniform along the development of the length of the final coil.

In addition, to "speed up," large electric motors must also be installed in the stands and winding reels of the roughing mill and finishing mill.

These large electric motors are oversized to allow the plant to function in endless mode, resulting in low plant availability despite the high initial investment (CAPEX).

Furthermore, as the strip "speeds up", the tail of the strip exits faster than the head, and dynamic control of the cooling shower is required to ensure that the strip is wound onto the take-up reel at a fairly constant temperature over its entire length, around 550°C to 600°C. This also results in a significant increase in the run-off table, as longer cooling segments are required depending on the strip speed.

The first object of the present invention is therefore to provide a plant and to complete an improved method for producing flat-rolled products in which the "speed-up" of the rolling stands in a plant capable of operating in the three operating modes mentioned above can be avoided or at least significantly reduced, and in which the temperature of the strip at the exit of the final finishing stand of the rolling mill is always kept at an optimum value.

Another object of the present invention is to provide a plant for producing flat rolled products which is more compact and has lower construction costs compared to plants known from the prior art.

Another object of the present invention is to provide a plant and to complete a method for producing flat rolled products, which allows the rolling process to be carried out in coil-to-coil mode, semi-endless mode or endless mode, and which allows a consistently high utilization rate to be obtained.

Another object of the present invention is to provide a plant and complete a method capable of producing flat-rolled products that can improve the final quality of both the size and the mechanical properties of the produced strip.

Applicant has invented, tested and embodied the present invention to overcome the shortcomings of the current art and to obtain these and other objects and advantages.

The invention is set out and characterized in the independent claims. The dependent claims describe further features of the invention or variants of the main inventive idea.

In accordance with the above objectives, the present invention relates to a method for producing a metal strip having a final thickness comprised between 0.6 mm and 25 mm in a rolling plant configured to operate in any one of the operation modes selected from the group consisting of a coil-to-coil mode, a semi-endless mode and an endless mode, the rolling plant comprising: a continuous caster configured to produce at least a thin slab having an initial thickness comprised between 50 mm and 160 mm; a furnace configured to maintain the slab at a specific temperature and/or heat the slab to a specific temperature; at least one roughing stand configured to reduce the thickness of at least one of the slabs to produce an intermediate rolled product; a plurality of finishing stands configured to reduce the thickness of the intermediate rolled product to obtain the metal strip; and a rapid heating device consisting of selectively operable elements, arranged between the roughing stand and the plurality of finishing stands, configured to heat the intermediate rolled product.
According to one aspect of the invention, the rapid heating device is kept operated in the coil-to-coil mode or in the semi-endless mode to produce the metal strip having a final thickness of less than 4.0 mm, preferably less than 2.5 mm, and heats the intermediate rolled product such that the temperature of the metal strip associated with the outlet of the last finishing stand is comprised between 830°C and 860°C.

According to another aspect of the invention, when the operating mode is the coil-to-coil mode or the semi-endless mode, the rolling speed of the metal strip associated with the plurality of finishing stands at the exit of the last rolling stand is less than or equal to about 12 m/s.

According to another aspect of the invention, the rolling speed in the finishing stand is substantially constant.

According to another aspect of the invention: For the same final thickness, the rolling speed in the finishing stand (V _L ) is substantially the same for the coil-to-coil mode or the semi-endless mode.

According to another aspect of the invention, the rolling speed is adjusted to an optimized value associated with the speed that minimizes the operating cost of the plant, calculated as follows:
C _OPEX (V _L , SF) = C _HI (V _L , SF) + C _RI (V _L , SF)

where C _HI (V _L , SF) is the operating cost for the power supply of the rapid heating device and C _RI (V _L , SF) is the operating cost represented by the reduced quality of the strip due to not reaching the temperature comprised between about 830°C and about 860°C associated with the exit of the final finishing stand and the risk of blockage of the intermediate rolled product due to the increase in the rolling speed.

According to one aspect of the present invention, a rolling plant configured to operate in any one of the operation modes selected from the group consisting of coil-to-coil mode, semi-endless mode and endless mode to produce a metal strip having a final thickness comprised between 0.6 mm and 25 mm comprises a continuous caster configured to produce at least thin slabs having an initial thickness comprised between 50 mm and 160 mm, a first selectively actuable shears configured to cut the slabs produced by the continuous caster, a furnace configured to maintain the slabs at a specific temperature and/or heat the slabs to a specific temperature, at least one roughing stand configured to reduce the thickness of at least one of the slabs to produce an intermediate rolled product, a plurality of finishing stands configured to reduce the thickness of the intermediate rolled product to obtain the metal strip, a rapid heating device consisting of selectively actuable elements, arranged between the roughing stand and the plurality of finishing stands, configured to heat the intermediate rolled product, and a second selectively actuable shears configured to cut the metal strip based on a predefined length.
According to another aspect of the invention, the plant further comprises a management and control unit configured to command the functioning of at least said plurality of shears to define said operation mode and configured to maintain said rapid heating device always operated in coil-to-coil mode or in said semi-endless mode to produce said metal strip having said final thickness smaller than 4.0 mm, preferably smaller than 2.5 mm.

According to another aspect of the present invention, the management and control unit is further configured to set the rolling speed of the plurality of finishing stands to a value less than about 12 m/s corresponding to the finishing stands in the coil-to-coil mode or the semi-endless mode.
These and other aspects, features and advantages of the present invention are explained, by way of non-limiting example, in the following illustrative embodiments taken in conjunction with the accompanying drawings, in which:

1 is a schematic diagram of an embodiment of a plant for producing flat-rolled products according to the invention; FIG. 1 is a graph relating the final thickness of a flat rolled product to the required rolling speed for a given mass flow rate. 2 is a graph relating the operating costs in a plant according to the invention to the rolling speed, for a given final thickness of the strip produced, and for a coil produced; 1 is a graph relating optimum rolling speed to final thickness of flat rolled product according to the method of the present invention.

It must be made clear that the expressions and terminology used in this specification, as well as the figures of the accompanying drawings, which are similarly described, have the sole function of better illustrating and explaining the invention, and that their function is to provide a non-limiting example, since the scope of the invention is defined by the claims.

For ease of understanding, the same reference numbers have been used wherever possible to identify identical common elements in the drawings. It will be understood that elements and features of one embodiment may be suitably combined or incorporated into other embodiments without further description.

With reference to FIG. 1, this shows a plant 10 according to the invention for rolling flat-rolled products, such as metal strip P, having a final thickness SF of, for example, 0.6 mm to 25 mm.

The plant 10 is configured to carry out the rolling process in an operating mode selected from "coil-to-coil", "semi-endless" and "endless" and comprises a continuous caster 11 having a die 12 for producing the preferred cast product, i.e., a slab having a thickness between 50 mm and 160 mm.

The plant 10 comprises a first waterscaling device 14 and a first cutting device, in this case a pendulum shear 15, which in a coil-to-coil operating mode cuts slab segments of a length to obtain rolls or coils of a desired weight, for example 25 tonnes. On the other hand, in a semi-endless operating mode, the pendulum shear 15 cuts slab segments (super slabs) having a weight of 2 to 5 times more than the slabs in the coil-to-coil mode. In steady state conditions in the endless operating mode, the pendulum shear 15 does not cut any of the slabs coming out of the mould 12.

Downstream of the pendulum shear 15 is a tunnel furnace 16 into which the slabs or slab segments are introduced to restore or maintain their temperature.

In the example shown here, the tunnel furnace 16 comprises a penultimate module 17 of the lateral type with a shuttle function that allows the use of a second casting line parallel to a first casting line sharing the same rolling mill. This module 17 can also be used to temporarily accommodate multiple slab segments, for example in case of blocking and/or replacement of the rolling cylinders.

Furthermore, the tunnel furnace 16 is equipped with a final module 18 that can alternatively have a parking function in case the line is interrupted for the same reasons as above.

Downstream of the tunnel furnace 16 are arranged, in order, an oxy-cutting device 19, a second water-scaling device 20, a vertical or edging stand 21, and a third water-scaling device 23, which are of a known type and will not be described in detail.

The plant 10 also includes a rolling mill having at least one roughing stand 25 for reducing the thickness of the slab to produce an intermediate rolled product, and a number of finishing stands 31 for further reducing the thickness of the intermediate rolled product to produce metal strip P.

In the exemplary solution shown, downstream of one or more roughing stands 25, crop shears 26 are arranged to trim the head and tail of the intermediate rolled product to facilitate its entry into the finishing stand 31.

The plant 10 also includes a rapid heating device 28 arranged between the roughing stand 25 and the finishing stand 31 and comprising, for example, an induction furnace consisting of selectively operable elements.

Furthermore, preferably, this rapid heating device 28 is positioned downstream of the crop shears 26.

Downstream of the rapid heating device 28, a fourth water scaling device 29 and a number of finishing stands 31 are arranged in sequence.

The fourth water scaling device 29 has the function of cleaning the scaling formed on the surface of the intermediate rolled product at the outlet of the rapid heating device 28 during use.

Downstream of the finishing stand 31, a cooling device for cooling the strip P is arranged, which includes a number of showers 34, at the outlet of which is arranged in turn a final cutting device, in this case a flying shear 35, and two winding reels 36, 38.

The flying shears 35 are used only in the "semi-endless" and "endless" operating modes to cut the strip P at predetermined lengths to obtain the desired final weight of the coil.

According to one aspect of the present invention, the rapid heating device 28 is configured to selectively and adjustably heat the intermediate rolled product in coil-to-coil, semi-endless, and endless modes.

The temperature to which the intermediate rolled product is heated is selected as a function of at least the starting slab thickness and the final thickness SF of the strip P, among other parameters, to reach the optimum value for rolling and to ensure that the strip P has an optimum temperature of about 830°C to about 860°C, preferably about 850°C, at the exit of the final finishing stand 31.

This makes it possible to reduce the value of the rolling mass flow MF _L required in coil-to-coil or semi-endless operating mode in order to obtain said optimum temperature at the exit of the last finishing stand 31 .

2, simply as a non-limiting example, the final thickness SF of the strip P is shown on the horizontal axis and the rolling speed in a coil-to-coil or semi-endless mode of operation is shown on the vertical axis. Curve A represents the trend of the rolling mass flow rate MF _{L required in a coil-to-coil or semi-endless mode as a function of the final thickness SF without the heat input of the rapid heating device 28, while curve B represents the trend of the rolling mass flow rate MF L required} in a coil-to-coil or semi-endless mode as a function of the final thickness SF with the heat input of the rapid heating device 28 as a function of the final thickness SF.

The reduction of the rolling mass flow rate MF _L in the coil-to-coil or semi-endless operating mode reduces the maximum rolling speed required from the plant 10 as a whole in order to obtain a strip P with an optimum rolling end temperature. This reduces the overall costs (CAPEX) of the plant 10, since so-called "speeding up" during rolling in the coil-to-coil or semi-endless mode can be avoided or at least significantly reduced, and the rolling stands 25, 31 and the take-up reels 36, 38 can be equipped with electric motors of smaller size than in known plants.

The plant 10 also comprises a management and control unit 40 of the electronic programmable type connected to the roughing stand 25 and the finishing stand 31 and configured to set the rolling speed _VL at which they operate.

In particular, the management and control unit 40 is configured to limit the rolling speed to a maximum value of approximately 12 m/s in coil-to-coil and semi-endless operating modes.

Furthermore, the management and control unit 40 is also connected to the pendulum shears 15 and the flying shears 35 and is configured to manage their operation in order to define and select the operating mode of the plant 10.

In particular, the management control unit 40 is configured to drive the pendulum shears 15 when it is necessary to cut the slab at the outlet from the continuous casting machine 11.

Furthermore, the management control unit 40 is configured to drive the flying shears 35 when it is necessary to cut the strip P before it reaches one of the take-up reels 36, 38.

For example, in a coil-to-coil operating mode, the management control unit 40 activates the pendulum shears 15 to produce a slab having a weight corresponding to the weight of the coil being produced, and keeps the flying shears 35 stationary.

Alternatively, in a semi-endless operating mode, the management and control unit 40 operates the pendulum shears 15 to produce a slab having a weight corresponding to the weight of "n" coils, and operates the flying shears 35 to cut the strip P at a predetermined length corresponding to a single coil.

Alternatively, in an endless mode of operation, the management and control unit 40 keeps the pendulum shears 15 inactive and activates the flying shears 35 to cut the strip P to a predetermined length corresponding to a single coil.

The management and control unit 40 is also configured to keep the rapid heating device 28 operating in coil-to-coil or semi-endless mode at all times to produce strip having a final thickness SF of less than about 4.0 mm, preferably less than 2.5 mm, and to regulate the heat output delivered, and thus the heating of the intermediate rolled product, for example by activating one or more selectively operable elements that constitute the intermediate rolled product.

It must be clarified that in this specification and in the appended claims, the expression "always active" means that the rapid heating device 28 is active when at least a portion of the intermediate rolled product being rolled passes through the rapid heating device 28, whereas between the passage of one intermediate rolled product and the passage of the next intermediate rolled product, it is inactive and may be deactivated.

Preferably, the rapid heating device 28 operates throughout the entire passage of the intermediate rolled product through the rapid heating device 28.

In particular, the management and control unit 40 is configured to keep in an active state, in each operating mode, at least one of the selectively operable elements constituting the rapid heating device 28, in order to obtain a strip P at a temperature comprised between about 830°C and about 860°C, preferably about 850°C, associated with the outlet of the final finishing stand 31.

The present invention also relates to a method for producing a strip P having a final thickness SF of less than about 4.0 mm, preferably less than about 2.5 mm, by maintaining the rapid heating device 28 in operation, even when rolling is performed in coil-to-coil or semi-endless mode.

In so doing, for the same final thickness SF, the heat input imparted to the intermediate rolled product by the rapid heating device 28 reduces the rolling mass flow rate MF _L required in coil-to-coil or semi-endless operating mode, while at the same time the target temperature of the strip P reaches a temperature comprised between about 830° C. and about 860° C., preferably about 850° C., corresponding to the exit from the final finishing stand 31.

The reduction of the rolling mass flow rate MF _L required in coil-to-coil or semi-endless operating mode allows rolling to be carried out at a lower rolling speed V _L , preferably below 12 m/s, while at the same time reaching an optimum temperature of about 850° C. at the exit of the final finishing stand 31 and preventing or at least reducing the so-called “speed-up” of the head of the strip P.

More specifically, in coil-to-coil mode, the method according to the invention allows, thanks to the operation of the rapid heating device 28, to reach the optimum rolling end temperature of about 850 ° C instantly for the head of the strip P without speeding up, and limits the speeding up to values of about 15% to 25% for values of the final thickness SF greater than about 2.0 mm, preferably greater than about 1.5 mm, and for values of the final thickness comprised between 0.6 mm and 1.5 mm. Such a modest speeding up is advantageously applied in order to constantly maintain the optimum rolling end temperature of about 850 ° C constant, while at the same time reducing the required heat input from the heating device 28.

Furthermore, due to the increase in temperature of the intermediate rolled product achieved thanks to the rapid heating device 28, a large reduction in thickness in the finishing stand 31 can be realized, thus making it possible to produce strip P with a thickness even smaller than 1.2 mm in coil-to-coil mode or semi-endless mode.

This has the advantage that it extends the range of thin walls that can be achieved in coil-to-coil or semi-endless mode for steels that cannot be cast in endless mode, i.e. harder steels such as HSLA type steels.

The reduction in rolling speed, on the one hand, facilitates the entry of the intermediate rolled product into the finishing stand 31, and on the other hand, facilitates the transfer of the strip P to the take-up reels 36, 38.

Furthermore, for the same final thickness SF, the rolling speed in the finishing stand 31 is substantially the same for each of the operating modes.

In coil-to-coil or semi-endless mode, the absence or at least reduction of the rolling speed makes it possible both to keep the temperature of the strip P constant between the head and the tail and to select the most appropriate temperature control (e.g. thermomechanical treatment) as a function of the steel grade and the end use of the strip P.

Another advantage lies in the fact that carrying out rolling at a substantially constant rolling speed in coil-to-coil or semi-endless mode allows a high degree of control over both the final shape of the strip P, e.g. its crown and flatness, both of which are advantageously uniform over the entire length of the coil, and also allows a high degree of control over the mechanical properties of the strip P over the entire length of the coil, which are advantageously constant and uniform over the entire length of the coil.

This last advantage is particularly important for the high-quality production of steels that cannot be cast in endless mode, i.e. harder steels, such as HSLA type steels.

Finally, the reduction in rolling speed allows the number of showers 34 present in the cooling system to be reduced, thus shortening its length by approximately 20% to 30% compared to prior art plants.

According to another aspect of the invention, when rolling occurs in coil-to-coil mode or semi-endless mode, the method also provides for setting the rolling speed to an optimum value V _L-OPT .
In the example shown here, the optimum rolling speed V _L-OPT is the rolling speed that minimizes the following function after the final thickness SF is set:
C _OPEX (V _L , SF) = C _HI (V _L , SF) + C _RI (V _L , SF)

where C _HI (V _L , SF) is the operating cost for the power supply of the rapid heating device 28 and C _RI (V _L , SF) is the operating cost related to the rolling speed V _L and represented by the resulting increase in the risk of blockage due to the increase in the rolling speed and the resulting decrease in the quality of the strip P if the optimum rolling end temperature is not reached.

3 shows a graph with the rolling speed _VL on the horizontal axis and the value of the function C _OPEX (V _L , SF) on the vertical axis, corresponding to a particular final thickness SF of strip P, e.g., 1.2 mm. In particular, curve C represents the function C _HI (V _L , SF), curve D represents the function C _RI (V _L , SF) and curve E represents the function C _OPEX (V _L , SF).

It is clear that corresponding to a velocity V _L-OPT , the function C _OPEX (V _L , SF) reaches a minimum value (approximately 10 m/s in this case).

Thus, the optimum rolling speed V _L-OPT is comprised between the rolling speed V LE (e.g., about 6 m/s) that can be achieved using the rapid heating device 28 at maximum power (i.e., operating all selectively operable elements at the limit of the maximum allowable temperature at the exit from the rapid heating device 28) and _{the rolling speed V LC (} e.g., about 14 m/s) that can be achieved without using the rapid heating device 28, and reaches the optimum rolling finish temperature for the strip P at both speeds V _LE and V _LC .

As can be seen, below V _LE the cost C _RI (V _L , SF) increases because, despite the rapid heating device 28 being at maximum power, the strip P is produced at a lower than optimal finish rolling temperature and is therefore of lower quality.

Furthermore, below V _LE , the cost C _HI (V _L , SF) also increases because the strip advances slower and therefore the consumption per tonne produced (kWh/ton) of the rapid heating device 28 increases for the same power supplied.

On the other hand, above V _LC , the cost C _HI (V _L , SF) is zero since the rapid heating device 28 is inactive, but the cost C _RI (V _L , SF) increases exponentially due to the increasingly high risk of blockage.

4 also illustrates, by way of non-limiting example, the relationship between the final thickness SF of the strip P in coil-to-coil or semi-endless mode and the optimum rolling speed V _L-OPT , in particular the values of the optimum rolling speed V _L-OPT are plotted on the vertical axis and the values of the final thickness SF are plotted on the horizontal axis.

In particular, curve F represents the value of the rolling speed required in coil-to-coil or semi-endless rolling mode to obtain a strip P having a temperature of about 850° C., corresponding to the final finishing stand 31 without heating. It should be noted that a rolling speed higher than about 14 m/s, i.e. higher than the speed V _LC of the graph of FIG. 3, corresponds to a strip P having a final thickness SF of less than about 1.2 mm.

Furthermore, curve G represents the value of the optimum rolling speed V L-OPT required in coil-to-coil or semi-endless rolling mode to obtain a strip P with a final thickness SF comprised between about 0.6 mm and about 2.5 mm, and with a temperature of about 850° C., due to the heat input of the rapid heating device 28, corresponding to the last finishing stand 31. It should be noted that in these cases the optimum rolling speed V _{L-OPT is} always lower than the maximum value of 12 m/s, so as not to cause the head of the strip P to rise due to aerodynamic effects.

It is further evident that for a strip P having a final thickness SF of less than about 2.5 mm, the optimum rolling speed V _L-OPT with the heat input of the rapid heating device 28 is always lower than the rolling speed required without the use of the rapid heating device 28.

Furthermore, as shown by curve H, in order to always keep the optimum rolling end temperature of about 850°C constant while at the same time reducing the energy consumption required for the rapid heating device 28, a moderate speed-up limited to a value of about 15% to 25% can be preferably carried out for strips P having a final thickness SF comprised between about 0.6 mm and about 1.4 mm.

For a strip P having a final thickness SF greater than 2.5 mm, the optimum rolling speed V _L-OPT corresponds to the rolling speed required in coil-to-coil rolling mode or semi-endless rolling mode to obtain a strip P having a temperature of about 850° C., corresponding to the final finishing stand 31, without the heat input of the rapid heating device 28.

This allows one to identify an optimum rolling speed V _L-OPT at which a strip P having a particular final thickness SF can be rolled in coil-to-coil and/or semi-endless mode while minimizing operating costs.

It will be apparent that modifications and/or additions may be made to the method and plant 10 for producing flat rolled products described hereinabove without departing from the field and scope of the invention as defined by the claims.

It is also clear that although the invention has been described with reference to some specific examples, a person skilled in the art can certainly realise many other equivalent forms of a method and a plant 10 for producing flat-rolled products having the features set out in the claims and therefore all falling within the field of protection defined by the claims.

In the following claims, references in parentheses have the sole purpose of improving readability and must not be considered as limiting factors with regard to the field of protection defined by the same claims.

Claims (7)

1. A method for producing a metal strip (P) having a final thickness (SF) comprised between 0.6 mm and 25 mm in a rolling plant (10) adapted to operate in any one of the operation modes selected from the group comprising a coil-to-coil mode, a semi-endless mode and an endless mode, comprising the steps of:
The rolling plant (10) comprises at least a continuous caster (11) adapted to produce thin slabs with an initial thickness comprised between 50 mm and 160 mm;
a furnace (16) configured to maintain said slab at a particular temperature and/or heat said slab to a particular temperature;
at least one roughing stand (25) configured to reduce the thickness of at least one said slab to produce an intermediate rolled product;
a plurality of finishing stands (31) configured to reduce the thickness of said intermediate rolled product to obtain said metal strip (P);
a rapid heating device (28) comprised of selectively operable elements and disposed between said roughing stand (25) and said plurality of finishing stands (31), said rapid heating device (28) configured to heat said intermediate rolled product;
Equipped with
1. A method of rolling, comprising the steps of: producing said metal strip (P) in a rolling plant (10) in which the rapid heating device (28) is kept operated in the coil-to-coil mode or in the semi-endless mode so as to produce said metal strip (P) having said final thickness (SF) smaller than 4.0 mm, preferably smaller than 2.5 mm, and heating said intermediate rolled product such that the temperature of said metal strip (P) associated with the outlet of the last finishing stand (31) is comprised between 830° C. and 860° C. the operating mode is the coil-to-coil mode or the semi-endless mode,
2. The rolling method according to claim 1, characterized in that the rolling speed ( _VL ) of the intermediate rolled product associated with the plurality of finishing stands (31) is less than or equal to about 12 m/s. 3. The rolling method according to claim 1 or 2, characterized in that the rolling speed (V _L ) is a constant value. The rolling method according to any one of claims 1 to 3, characterized in that for the same final thickness (SF), the rolling speed ( _VL ) is substantially the same for the coil-to-coil mode or the semi-endless mode. the rolling speed is adjusted to an optimization value (V _L-OPT ) associated with the speed that minimizes the operating cost (C _OPEX ) of the plant (10);
The operating cost (C _OPEX ) of the plant (10) is formed by the following formula:
C _OPEX (V _L , SF) = C _HI (V _L , SF) + C _RI (V _L , SF)
5. The rolling method according to claim 2, wherein C _HI (V _L , SF) is the operating cost for the power supply of the rapid heating device (28) and C _RI (V _L , SF) is the operating cost represented by the reduced quality of the strip (P) and the risk of blockage of the intermediate rolled product due to not reaching the temperature comprised between about 830°C and about 860°C associated with the exit of the final finishing stand (31). 1. A rolling plant (10) configured to operate a metal strip (P) having a final thickness (SF) comprised between 0.6 mm and 25 mm in any one of the operation modes selected from the group consisting of a coil-to-coil mode, a semi-endless mode and an endless mode,
The rolling plant (10) comprises at least a continuous caster (11) adapted to produce thin slabs with an initial thickness comprised between 50 mm and 160 mm;
a first selectively operable shear (15) configured to cut the slabs produced by the continuous caster (11);
a furnace (16) configured to maintain said slab at a particular temperature and/or heat said slab to a particular temperature;
at least one roughing stand (25) configured to reduce the thickness of at least one said slab to produce an intermediate rolled product;
a plurality of finishing stands (31) configured to reduce the thickness of said intermediate rolled product to obtain said metal strip (P);
a rapid heating device (28) comprised of selectively operable elements and disposed between said roughing stand (25) and said plurality of finishing stands (31), said rapid heating device (28) configured to heat said intermediate rolled product;
a second selectively actuatable shear (35) configured to cut said metal strip (P) based on a predefined length;
a management and control unit (40) configured to command the functioning of the first selectively actuatable shears (15) and the second selectively actuatable shears (35) to define said operating mode;
Equipped with
1. The rolling plant (10), wherein the management and control unit (40) is further configured to maintain the rapid heating device (28) operating in the coil-to-coil mode or in the semi-endless mode to produce the metal strip (P) having the final thickness (SF) of less than 4.0 mm, preferably less than 2.5 mm. 7. The rolling plant (10) according to claim 6, characterized in that the management and control unit (40) is further configured for setting the rolling speed (V _L ) of the plurality of finishing stands (31) to a value less than about 12 m/s in the coil-to-coil mode or in the semi-endless mode.

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