EP2595766B1

EP2595766B1 - Continuous casting and rolling method and line to make long rolled metal products

Info

Publication number: EP2595766B1
Application number: EP11760547.7A
Authority: EP
Inventors: Gianpietro Benedetti
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 2010-07-21
Filing date: 2011-07-20
Publication date: 2016-03-09
Anticipated expiration: 2031-07-20
Also published as: IT1402237B1; EP2595766A1; WO2012010956A1; ITUD20100147A1

Description

FIELD OF THE INVENTION

The present invention concerns a continuous casting and rolling method and plant, or line, in endless or semi-endless mode, to make high productivity long rolled metal products such as bars, rod, girders, rails or shapes in general.

BACKGROUND OF THE INVENTION

Plants known in the state of the art for the production of long rolled products provide a casting machine and a rolling train, which is disposed in line and downstream of the casting machine. It is also known that in solutions in which the casting axis defined by the casting machine and the rolling axis defined by the rolling train coincide, the plant can be configured and used in endless mode (that is, without a break in continuity), or in semi-endless mode (that is, starting from segments of the cast product sheared to size).
In these operating solutions, if the rolling train is stopped, either accidentally due to obstacles for example, or programmed so as to change channels or change production for example, it is necessary to stop the rolling process, which also entails interrupting the casting machine; moreover, in the event of an accidental stoppage of the rolling mill, it is necessary to scrap both at least part of the intermediate material between the casting and the point of stoppage, and also the material being processed from the tundish to the rolling train.
Consequently stopping the rolling train entails a reduction in productivity and the factor of use of the plant, an increase in management costs which are the principal cause of an increase in energy required.
Document WO 2006/092404 A1 describes a casting line connected to a rolling line to produce rolled products starting from a continuous casting of square billets. This document provides a temperature restoration system consisting of an inductor which cannot in any way carry out the function of a buffer in the event of a temporary stoppage of the line.
One purpose of the present invention is to make a high productivity casting and continuous rolling in line process which can work both in endless and semi-endless mode, and to perfect a relative production plant which allows to manage the stoppages of the rolling train, substantially without interrupting the casting and therefore without loss in production and without penalizing the steelworks upstream.
Another purpose of the invention is to reduce to a minimum or eliminate waste material in emergency situations or during the programmed stoppages and in any case to completely recover the product which in such situations is temporarily accumulated in an intermediate point along the production line.
A further purpose of the invention is to exploit to the full the enthalpy of the original liquid steel along the whole production line so as to obtain a considerable saving in energy and a reduction in working costs compared to conventional processes.
Further purposes of the present invention are:

to guarantee an increased yield, equal to the ratio between weight of the finished product and weight of the liquid steel to produce a ton;
to obtain a greater stability of the rolling train and an improved dimensional quality of the finished product;
to guarantee the possibility of changing production sizes and types without stopping the continuous casting, obtaining a higher factor of use for the plant.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea.
A casting and rolling plant for the production of long rolled products according to the present invention comprises a single continuous casting machine and a rolling train disposed downstream and in line with the casting machine. By disposed in line, we mean that a hypothetical casting axis of the casting machine substantially coincides with a hypothetical rolling axis of the rolled products, so that this configuration is suitable to obtain a continuous process of the endless type; in any case it is always possible to also make a continuous process of the semi-endless type.
In some forms of embodiment, the casting machine has a crystallizer suitable to cast liquid steel at high speed and high productivity (for example, but only indicatively, from 35 to 200 ton/h). By high speed casting we mean that the continuous casting machine can cast products, in relation to thickness, at a speed variable from about 3 to about 9 m/min.
Advantageously, the crystallizer produces a substantially rectangular section, hereafter defined in general as bloom, in which the ratio between long side and short side is comprised between 1.02 and 4, that is, just higher than the square section up to a rectangular section in which the long side is up to 4 times longer than the short side.
In the present invention the section of the cast product is not limited to the quadrangular with straight sides, parallel two by two, but also comprises sections with at least a curved, concave or convex side, advantageously but not necessarily two by two opposite and specular, or combinations of the said geometries.
Casting a rectangular section, given the same casting speed and thickness (or height) of the section, one obtains a greater quantity in tons of material in the unit of time, that is, an increase in the hourly productivity, for example higher than 120 t/h.
To give an example, the rectangular sections cast have sizes of about 100 mm x 140 mm, 130 mm x 180 mm,130 mm x 210 mm, 140 mm x 190 mm, 160 mm x 210 mm, 160 mm x 280 mm, 180 mm x 300 mm, 200 mm x 320 mm or intermediate sizes. In the production of average profiles bigger sections can also be used, for example about 300 mm x 400 mm and similar.
In general the cast section has a surface equal to that of a square with equivalent sides comprised between 100 to 300 mm.
The rolling train advantageously comprises from 3 to 4 rolling stands up to 15 or 18 rolling stands in relation to the type of final product to be obtained, to the thickness of the cast product, to the casting speed or other parameters.
According to the invention, the line provides an additional rolling unit, consisting of at least a stand, advantageously from 1 to 4 stands, in order to return the rectangle to a square, round or oval shape or in any case less wide, suitable for the rolling train.
The additional rolling unit, in a first solution, is placed immediately downstream of the casting machine, while in another solution it is placed immediately upstream of the rolling train. The positioning along the line of the additional rolling unit conditions, as will be explained hereinafter, both the lay-out configuration and the rolling process modes which are performed.
The casting and rolling line also comprises, downstream from the continuous casting, at least shears for shearing the blooms to size, into segments of desired length in semi-endless mode or in the event of an emergency in endless mode. By desired lengths of the segments we mean a value comprised between 12 and 80 meters.
Moreover, the shears can carry out the emergency scrapping of the material coming from casting.
According to the present invention, there is a maintenance and/or possible heating unit downstream of the casting machine, which comprises a tunnel furnace configured to act, as well as a heating and/or temperature maintenance chamber, also as a possible store for accumulating the blooms in the case of a temporary interruption of the rolling train, for example to allow programmed maintenance programs or channel changes or changes in production, or due to accidents.
In this way, the casting machine does not necessarily have to be stopped, but only slowed down, at least for a predetermined period of time, the so-called "buffer-time", because the product exiting therefrom, sequentially sheared into blooms of a predefined length, is accumulated inside the furnace and is maintained there at a working temperature, thus releasing it from the rolling train which is stopped. The blooms, accumulated and maintained at temperature, are then fed again toward the rolling train, once this is working again.
The maintenance and/or possible heating unit can also perform the function of restoring the temperature of the blooms in transit and/or stopped inside it.
The minimum length of the maintenance and/or possible heating unit is advantageously determined as a function of the buffer time, as a function of the casting speed, lower than the value of the normal speed in an emergency condition, and as a function of the rolling speed of the rolling line placed downstream.
In particular, if the additional rolling unit is placed immediately downstream of the casting machine, the maintenance and/or possible heating unit can provide to heat the blooms to suitable values for rolling, restoring the loss of temperature caused by the rolling step in the additional reduction unit.
On the other hand, if the additional rolling unit is placed upstream of the rolling train, and therefore downstream of the maintenance and/or possible heating unit, a rapid heating device can be provided, advantageously one or more inductor furnaces, downstream of the additional rolling unit and upstream of the rolling train, in this case too with the function of restoring the temperature of the blooms, bringing it to a suitable value for rolling, and therefore of recovering the loss of temperature due to the rolling pass in the additional reduction unit.
In another form of embodiment, the inductor furnace may be present, or also present, in an intermediate position between the stands of the rolling train, for example after the first stand and/or after the second stand up to the tenth if the number of stands is comprised between ten and eighteen.
The intermediate disposition of the inductor furnace between the stands of the rolling train allows to roll the product at a more balanced and uniform temperature along the rolling train, and therefore a reduction in power, less wear on the rolling channels etc.
In a further form of embodiment, that is, when products with small sections are rolled, for example round pieces with a diameter between about 5 mm and about 20 mm, the inductor furnace can be advantageously used in said positions in order to recover the considerable heat dispersions due substantially to the low rolling speeds which must be maintained, above all in the first rolling stands of the train.
In any case the inductor furnace allows, by its action, to obtain a more uniform heating of the blooms, in particular to also heat the edges, thus avoiding the formation of cracks in these zones during rolling.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein:

figs. 1-3 show three possible layouts of a rolling plant according to the present invention;
figs 4-7 show examples of some different sections that can be cast with the plant in fig. 1;
fig. 8 is a summary Table of a numerical example of sizing of a component of the plants in figs. 1-3;
fig. 9 is a graphic representation of the numerical example in fig. 8.

DETAILED DESCRIPTION OF SOME PREFERENTIAL FORMS OF EMBODIMENT

With reference to the attached drawings, fig. 1 shows a first example of a layout 10 of a plant for the production of long rolled products according to the present invention.
The layout 10 in fig. 1 comprises, in its essential elements shown, a continuous casting machine 11 with a single line which uses a crystallizer, or other suitable device to cast blooms of various sizes and rectangular shape with straight, curved, concave or convex sides, or other shape. Some examples of sections that can be cast in the context of the present invention are shown in figs. 4-7, which respectively show a rectangular section with straight and parallel sides (fig. 4), a section with short sides with a convex curve and long, straight parallel sides (fig. 5), a section with short sides with a concave curve at the center and long, straight parallel sides (fig. 6), and a section with short sides with a concave curve and long, straight parallel sides (fig. 7).
The continuous casting machine 11 is disposed on a line coincident with the rolling line defined by a rolling train 16 placed downstream. In this way it is possible to realize an endless process, that is without a break in continuity. A semi-endless process can also be realized.
The continuous casting machine 11 has high productivity, being able to reach casting speeds comprised between 3 and 9 m/min, depending on the type of product (section, quality of steel, final product to be obtained etc.), and casting sections with one size predominant over the other, in a ratio preferably comprised between 1.02 and 4.
In particular, the casting machine 11 allows to obtain a variable productivity from 35 ton/h to 200 ton/h.
To give an example, the cast blooms have sizes of about 100 mm x 140 mm, 130 mm x 180 mm,130 x 210 mm, 140 mm x 190 mm, 160 mm x 210 mm, 160 mm x 280 mm, 180 mm x 300 mm, 200 mm x 320 mm or intermediate sizes. In the production of average profiles, bigger sections can also be used, for example about 300 mm x 400 mm and similar. In general, the cast section has a surface equal to that of a square with equivalent sides comprised between 100 and 300 mm.
Downstream of the continuous casting machine 11 there are shears 12 to shear to size, which can cut the blooms cast into segments of desired length, both for the semi-endless mode functioning of the plant 10, and for the endless mode functioning when the rolling train 16 is stopped. The shears 12 can also carry out the emergency scrapping of the material coming from casting.
There is also an additional reduction/roughing unit 13 present in the line, generally consisting of from 1 to 4 rolling stands, and, in this case, of 3 alternate vertical/horizontal/vertical rolling stands or in other forms of embodiment vertical-vertical-horizontal or other combinations. It is also possible to use a single vertical rolling stand.
The stands are used for bringing the rectangular cast section to a square, round, oval or in any case, less wide shape than the starting shape, in order to make it suitable for rolling in the rolling train 16 placed downstream. It is understood that the number of rolling stands can be selected between 1 and 4, depending on the overall design parameters of the line and the products to be continually cast.
The best positioning of the additional reduction/roughing unit 13 along the line comprised from end of casting to start of rolling train 16 is established in relation to the speed which can be obtained at the entrance to the first stand of the unit. For example, if the speed is comprised between 3 and 4.8 m/min (0.05 m/s and 0.08 m/s), the reduction/roughing unit 13 is positioned immediately downstream of the continuous casting machine 11 and upstream of the cutting to size shears 12 (fig. 1), while if the entrance speed to the stand is greater, for example comprised between 5 and 9 m/min, the additional reduction/roughing unit 13 is placed at the head of the rolling train 16 and downstream of the maintenance and/or possible heating furnace 14 (fig. 2), as will be shown hereafter.
Another parameter that can condition the choice of inserting the additional reduction/roughing unit 13 immediately downstream of the continuous casting machine 11 and upstream of the shears 12 is the energy factor.
Indeed, when the first section reduction is carried out immediately downstream of the continuous casting, immediately after the closing of the metallurgical cone, there is a reduction in energy consumption because the section reduction occurs on a product with a core which is still very hot, and therefore it is possible to use a lower force of compression and use smaller stands which require less power installed.
In three layouts 10, 110, 210 shown as examples in figs. 1-3, downstream of the continuous casting machine 11 a maintenance and/or possible heating tunnel furnace 14 of the horizontal type is disposed. More precisely the tunnel furnace 14 is disposed along the continuous casting line and along the rolling line which are defined respectively by the continuous casting machine 11 and the rolling train 16.
The furnace tunnel 14 can act as a heating element, for example, in cases where the reduction/roughing unit 13 is placed immediately downstream of the continuous casting machine 11, in order to bring the temperature of the bloom to a value suitable for the subsequent rolling, or to restore the loss of temperature deriving from the passage through the reduction/roughing unit 13 when this is located between the continuous casting machine 11 and the shears 12.
The furnace tunnel 14 can also carry out the function of maintenance chamber, maintaining the temperature of the blooms, between entrance and exit, between about 900°C and about 1,100°C, for example when the reduction/roughing unit 13 is not provided immediately downstream of the continuous casting machine 11, but upstream of the rolling train 16.
The furnace tunnel 14 can also act as a store to accumulate the blooms, in particular in the event of an interruption in the functioning of the rolling train 16 because of accidents or programmed roll change or change in production.
The length of the tunnel furnace 14 is determined depending on the accumulation time of the blooms, or buffer time, which is required so that the stoppage of the continuous casting machine 11 is not necessary.
In particular, in an emergency condition, the continuous casting machine is made to work at a reduced casting speed compared with normal working speed. The time needed to fill the tunnel furnace in this emergency condition, or with a reduced casting speed, is the buffer time.
More particularly, to determined the minimum length of the tunnel furnace 14 the following equation is used: $LFT = BT / (1 / VE - 1 / VL)$
in which VL is the rolling speed of the rolling line (in m/min) when the rolling line is working under normal conditions, VE is the reduced casting speed compared with the normal working speed VL (in m/min) in an emergency condition, BT is buffer time (in minutes), that is, the maximum time in which the continuous casting machine 11 in a condition of reduced casting time VE fills the tunnel furnace 14 because of a stoppage of the rolling train 16, and LFT is thus the minimum length of the tunnel furnace (in meters).
To give an example, in figs. 8 and 9 a table and a graph are respectively shown in which the minimum lengths of the tunnel furnace 14 are shown for some casting speeds VE and for a rolling speed VL equal to 6m/min, depending on the three examples (10 min, 20 min and 30 min) of buffer time which may be required in situations relating to a casting and rolling cycle.
With reference to fig. 2, between the reducing/roughing unit 13 and the rolling train 16 an inductor furnace 15 is provided having the function of bringing the temperature of the blooms exiting from the unit 13 to suitable values for rolling.
For example, when the blooms exit from the reducing/roughing unit 13 at a temperature comprised between about 920 and about 950°C, then the inductor furnace 15 provides to restore the temperature to a value higher than about 1,000°C, whereas when the blooms exit from the unit 13 at a temperature comprised between about 1,050 and about 1,080°C, then it is not necessary to provide the functioning of the inductor furnace 15 at exit from the tunnel furnace 14, which can be kept switched off.
The number of rolling stands 17 used in the rolling train 16 is variable from 3-4 to 15-18 and more, depending on the type of final product to be obtained, on the thickness of the product cast, on the casting speed and on other parameters.
In another form of embodiment (fig. 3), the inductor furnace 15 is installed in an intermediate position between the rolling stands 17 of the rolling train 16, in this case after the fourth rolling stand, event if, in other forms of embodiment, it is possible to provide that it is disposed, for example, after the first and/or after the second rolling stand 17 as far as the tenth, when there are 15 or 18 rolling stands.
The intermediate disposition, between the stands of the rolling train 16, of the inductor furnace 15 allows to roll at more balanced and uniform temperatures along the rolling train 16 and therefore with less power, less wear on the rolling channels etc.
In one form of embodiment, that is, when products with small sections are rolled, for example round pieces with diameters comprised between about 5 mm and about 20 mm, the inductor furnace 15 can be advantageously used in the aforesaid positions in order to recover the considerable heat dispersions substantially due to the low rolling speeds which must be maintained above all in the first rolling stands of the train.
There are cropping shears 18 present upstream of the rolling train 16 (fig. 1), hydraulic shears for example, which as well as cropping the head end of the bloom before it enters the rolling train 16 and/or the additional reduction unit 13, can also carry out emergency scrapping.
Other known components in the state of the art, such as descalers, gauges etc. not shown, are normally present along the lay-out 10, 110, 210, present in the attached drawings.

Claims

Method to make long metal rolled products in a line comprising at least a continuous casting machine (11), a maintenance and/or possible heating tunnel furnace (14) and a rolling train (16), comprising the following steps:
- high productivity continuous casting made by a single continuous casting machine (11), defining a casting axis, of a rectangular section product with a ratio between the long side and the short side comprised between 1.02 and 4;

- first reduction of section in an additional reduction/roughing unit (13) disposed upstream of the rolling train (16), having the function of bringing the rectangular section of the product at entrance to a square, round, oval or in any case less wide shape at exit;

- second reduction of section in a rolling train (16) defining a rolling axis substantially coinciding with the casting axis,
wherein said continuous casting machine (11) operates at a casting speed comprised between 3 and 9 m/min and with an hourly productivity comprised between 35 t/h and 200 t/h, and wherein the minimum length LFT of said tunnel furnace (14) is determined as an inverse function of the difference between the rolling speed VL and the programmed casting speed VE reduced with respect to the normal operating speed in an emergency situation, as a direct function of the product of the rolling speed VL and the programmed casting speed VE and as a direct function of the desired accumulation time BT in the event of a stoppage of the rolling train (16) according to the following formula: LFT = BT/(1/VE - 1/VL).
Method as in claim 1, characterized in that said first reduction of section in the reduction/roughing unit (13) is carried out immediately downstream of the continuous casting (11).
Method as in claim 1, characterized in that said first reduction of section in the reduction/roughing unit (13) is carried out downstream of the maintenance and/or possible heating tunnel furnace (14) and upstream of the rolling train (16).
Method as in claim 2, characterized in that it provides a step of heating the cast product, carried out in said maintenance and/or possible heating tunnel furnace (14), so as to restore at least part of the temperature loss due to the passage of the product in the reduction/roughing unit (13).
Method as in claim 3, characterized in that it provides a step of heating the cast product, carried out in a rapid heating unit such as an inductor furnace (15), disposed between the reduction/roughing unit (13) and the rolling train (16), so as to restore at least part of the temperature loss due to the passage of the product in the reduction/roughing unit (13).
Method as in claim 1 or 2 or 3, characterized in that it provides a step of heating the cast product, carried out in a rapid heating unit such as an inductor furnace (15), disposed in an intermediate position between the stands (17) of the rolling train (16), wherein the number of stands (17) of the rolling train (16) is comprised between three and eighteen, and wherein said inductor furnace (15) is disposed, depending on said number of stands (17), after the first and/or after one of the passes from the second to the tenth, through said stands (17), so as to roll with more balanced temperatures and/or to roll round sections of a diameter from about 5mm to about 20mm.
Method as in any claim hereinbefore, characterized in that it also comprises at least a selective shearing step in which the cast product is sheared to size in order to define segments of product to be accumulated and maintained at temperature inside the maintenance and/or possible heating tunnel furnace (14), in case of emergency stops or operating stops of the rolling train (16).
Method as in any claim hereinbefore, characterized in that the section of the cast product has a surface equal to that of a square with equivalent sides from 100 to 300 mm.
Casting and rolling line to make long rolled metal products, comprising at least a continuous casting machine (11), a maintenance and/or possible heating tunnel furnace (14) and a rolling train (16), wherein:
- the continuous casting machine (11) has a single line defining a casting axis, and is able to cast a product of rectangular section or equivalent with a ratio between the long side and the short side comprised between 1.02 and 4;

- the rolling train (16) defines a rolling axis substantially coinciding with the casting axis;
there is an additional reduction/ roughing unit (13) comprising from 1 to 4 rolling stands, configured to bring the rectangular section of the product at entrance to a square, round, oval or in any case less wide shape at exit, wherein the minimum length LFT of said tunnel furnace (14) is an inverse function of the difference between the rolling speed VL and the programmed casting speed VE reduced with respect to the normal operating speed in an emergency situation, a direct function of the product of the rolling speed VL and the programmed casting speed VE and a direct function of the desired accumulation time BT in the event of a stoppage of the rolling train (16) according to the following formula: LFT = BT/(1/VE - 1/VL).
Casting and rolling line as in claim 9, characterized in that said reduction/roughing unit (13) is located immediately downstream of the continuous casting machine (11).
Casting and rolling line as in claim 9, characterized in that said reduction/roughing unit (13) is located downstream of said maintenance and/or possible heating tunnel furnace (14), there being at least a rapid heating unit (15) present between said reduction/roughing unit (13) and said rolling train (16) in order to restore at least part of the temperature loss due to the passage of the long product in the reduction/roughing unit (13).