Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF MAKING METAL STRIP AND PLANT FOR CARRYING OUT THE METHOD
The invention relates to a method of continuous and
discontinuous production of hot-rolled strips made of cast metal,
in particular steel.
The invention further relates to a plant for carrying out
the method.
In a known method of horizontal strip casting, it is
possible for melts of different types of steel to be cast with less
than 20 mm strip thickness close to their final dimensions. Using
this method, lightweight steels in particular with a high content
of C, Mn, Al, and Si may be produced.
A production method of the production of hot-rolled thin
flat products is known from EP 1 047 510 [US 6,527,882]. According
to this method, steel melts are cast close to their final
dimensions in a range of 5 mm to 18 mm strip thickness and cooled
in a controlled manner and in a protective gas atmosphere before
reaching a single-stand roughing train.
The blank hot strip is cooled, heated, or its temperature
is maintained in a controlled fashion in a unit provided downstream
of the roughing train, and the edges of the hot strip are reheated.
The single-stand roughing train is followed by a
multistand finishing train, a run-out roller table having a device
for cooling the hot strip, and coilers upstream and downstream for
winding the hot strip.
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The rolling temperature upstream of the multistand
finishing train may be controlledly set by the device for cooling,
heating, or maintaining the temperature of the hot strip, in the
austenite or ferrite range or in the transition range from
austenite to ferrite.
In addition, WO 2006/066551 [CA 02591060] discloses a
method of the production of hot strips of lightweight steel that
has particularly good cold deep drawability and has Fe Mn, Si, and
Al as its primary elements. The rough strip produced by casting
upstream passes through a device for homogenization in a protective
gas with optional maintenance of the temperature, cooling, or
heating. The rough strip is subsequently subjected to a hot-
rolling step having at least one pass with a total degree of
deformation of at least 50%. After the last pass, the hot strip is
cooled and wound up. The hot-rolling step occurs inline or
decoupled depending on the ratio of casting speed to rolling speed.
The homogenization zone is intended to equalize the
temperature over the surface of the hot strip and reduce tension
within the hot strip independently of whether the temperature level
is maintained, increased, or decreased.
The question of whether the rolling step should occur
inline or decoupled from the casting step essentially becomes a
function of the different speeds in the casting and rolling step,
with the recrystallization behavior of the workpiece having
significance as well.
In the casting step, a direct connection exists between
the material in the liquid phase in the pouring region of the melt
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and the later process steps of the hardened workpiece via the cast
strip.
The cast strip is guided to further processing along a
transport path. The subsequent method steps may be: straightening,
rolling, cutting, and winding (reeling, coiling). These and other
components of a casting system may lead to fluctuations in the
tension and mass flow in the cast strip. If these disruptions
continue in the direction of the liquid steel, casting disruptions
may occur as well as negative influences on the cast strip such as,
for example, fluctuations in thickness, overflows, edge
constrictions, and tears in the strip or the flow.
The object of the invention is to refine a method of the
production of hot strips by a strip caster and a strip caster
having a coiler or stacker in such a way that the method steps
following the casting step do not have any negative influence on
the quality and material properties of the cast strip being
produced and that the cast strip, after the casting step, may be
separated into pieces of predetermined size that can be transported
and/or stored such as, for example, stacked sheets or coils.
According to an aspect of the invention, the rough strip
produced by strip casting passes through a homogenization zone in a
protective gas atmosphere in order to homogenize its structural
composition in conjunction with maintaining the temperature of the
rough strip, reducing the temperature, or increasing the
temperature C, driver, looper,
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driver error]. Then the rough strip passes through a temperature
controller in order to maintain the temperature of the rough strip,
reduce the temperature, or increase the temperature of the rough
strip. Thereafter, the rough strip is subjected to a reduction in
thickness of less than 49% in a hot-rolling step having at least
one pass. Finally, the rough strip passes through a downstream
homogenization zone before it is separated as a hot strip from the
following rough strip.
In the upstream homogenization zone, an inert-gas
argon/CO2-nitrogen mixture is used. In the upstream homogenization
zone, the temperature is maintained in the region of 900 to 1000 C,
reduced by 200 C, and increased by 250 C.
In order for the workpiece to be able to be bent into a
coil, it must have a suitable structural composition that allows
deformation under tensile and compressive stress.
These structural properties may be attained by the one or
more rolling steps with one pass up to a degree of deformation of
49%.
This deformation step triggers a recrystallization of the
workpiece. In the subsequent downstream homogenization zone, the
thus treated hot strip undergoes recrystallization at least at its
edges while the temperature of the hot strip is maintained, if the
temperature is reduced, or if the temperature is increased.
In the downstream homogenization zone downstream of the upstream
roll stand, the workpiece is able to recrystallize and is therefore
able to withstand tensile and compressive stress. This method of
recrystallization is particularly suitable for
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lightweight steels that, among other things, may have a very wide
solidification range, i.e. a larger or smaller "temperature window"
from the beginning of the hardening of the melt to complete curing
and have zero solidity and ductility temperatures that depend on
the "window."
After the rough strip has passed through the downstream
homogenization zone, the hot strip is guided to a cutter with a
working speed synchronized to the roller or transport belt speed,
subdivided into pieces of rough strip of predetermined length, and
wound into a coil in a winding system.
However, the hot strip may also be cut directly after
leaving the downstream homogenization zone, the pieces of hot strip
of a particular length then being conveyed to a stacking system by
suitable conveyors and stacked there as plates.
In the embodiment of the method according to the
invention, the casting step is decoupled from the rolling step.
This has advantage that, on the one hand, the casting
speed may be selected as a function of the progression of the
solidification step and, on the other hand, the hot-rolling step is
able to occur at a defined hot-strip temperature until a
predetermined degree of deformation is attained.
In another embodiment of the method according to the
invention, after the upstream homogenization of the structural
composition, the transport speed of the rough strip is varied by a
mass-flow controller. This prevents disruptions from the following
process steps within the production method from negatively
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influencing the casting step and the cast strip and prevents
overflows, edge constrictions, and tears in the strip or the flow.
According to a general aspect of the present invention,
the plant for carrying out the method according to the invention
comprises a casting machine known per se and downstream of which an
upstream homogenization zone is provided in a protective-gas
atmosphere for influencing the structural composition of the cast
rough strip and where the temperature of the rough strip is
maintained, reduced, or increased.
An upstream temperature controller for maintaining,
reducing, or increasing the temperature of the rough strip is
provided downstream of the upstream homogenization zone.
Relative to the transport direction of the rough strip, a
downstream temperature controller is provided downstream of the
upstream temperature controller, with a mass-flow controller
integrated between an upstream and a downstream rough strip
conveyor; in the downstream temperature controller, the cast strip
is brought to a suitable rolling temperature, by maintaining,
reducing, or increasing the temperature of the cast strip.
An upstream roll stand is provided downstream of the
downstream temperature controller to subject the rough strip to a
reduction in thickness of less than 49% at the appropriate
temperature in at least one pass. In a downstream homogenization
zone provided downstream of the upstream roll stand, the rough
strip, now hot, is recrystallized at a temperature of 700 to 900 C,
particularly at the edges of the hot strip, such that the workpiece
is able to absorb tensile and compressive forces as well
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as plastic deformations that occur during winding or stacking
without damage to the structural composition.
Finally, downstream of the downstream homogenization zone
is a cutter operated at a working speed that is synchronized with
the transport speed of the hot-strip conveyor. In the cutter, the
hot-rolled hot strip continually approaching the device is wound
after being cutting and is stacked as plates.
In an additional embodiment of the plant according to the
invention, a mass-flow controller is provided downstream of the
upstream temperature controller and is embodied as a dancer roll or
a looper. The mass-flow controller, viewed in the transport
direction of the strip, is integrated between an upstream rough
strip conveyor and a downstream rough strip conveyor.
Moreover, in the invention, upstream of the roll stand is
a downstream temperature controller in which the rough strip is
brought to a suitable rolling temperature so that the rough strip
may be subjected to a hot-rolling step having at least one pass,
and the rough strip, as a hot strip, then has a degree of
deformation less than 49%.
Finally, according to the invention a coiler or stacker
in which the hot strip is wound into a coil or deposited as
individual plates is provided downstream of the cutter.
Additional features and advantages of the invention may
be found in the following description and in the illustrated
embodiment shown in the drawing, in which:
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FIG. 1 is a schematic view of the plant for carrying out
the method according to the invention for strip casting close to
the final dimensions, having a winder and/or stacker.
The single FIG. 1 is schematic view of a plant according
to the invention for carrying out the method according to the
invention. The plant has a casting machine 1 in the form of a
horizontal strip caster for carrying out the casting method or
casting step and having a conveyor in the form of an endless
conveyor belt 2 and two deflection rollers 3, 3'. The casting
machine 1 is moreover provided with a side wall 4 that prevents the
poured melt 5 from flowing down to the right and left sides of the
conveyor 2. The melt 5 is fed to the casting machine 1 from a
ladle 6 and flows through an outlet opening 7 ing the base of the
ladle 6 into a feed tank 8. This feed tank 8 is formed as an
overflow tank.
Devices for intensive cooling of the bottom of the
support reach of the conveyor 2 and the complete housing
surrounding the casting machine 1 and containing the corresponding
protective gas atmosphere are not shown in greater detail.
After the melt 5 has been poured onto the moving conveyor
2, intensive cooling results in solidification and the formation of
a cast or rough strip 9 that is completely solidified to a large
extent by the time it reaches the downstream end of the conveyor 2.
In order to equalize temperature and reduce tension, a
homogenizing zone 10 follows the casting machine 1. The
homogenizing zone is formed by a heat-insulated enclosure 11 and a
roller conveyor. This upstream homogenizing zone may be used to
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maintain the temperature of the cast rough strip 9, further cool
it, or, alternately, to heat it somewhat. In particular, provision
is made in this upstream homogenization zone 10 for the cast or
rough strip 9 to be subjected to an upstream step for homogenizing
its structure, by maintaining a temperature at approximately 900 to
1000 C, by reducing the temperature by approximately 200 C, or,
alternately, by increasing the temperature by approximately 250 C,
in a protective gas atmosphere composed of an inert-gas mixture of
argon-0O2-nitrogen.
Subsequently, the cast rough strip 9 passes through an
upstream temperature controller 12 and is then conducted to a
downstream temperature controller 15 by an upstream rough-strip
conveyor 14 and a downstream rough-strip conveyor 14' by a mass-
flow controller 13 provided between the upstream rough strip
conveyor 14 and the downstream rough strip conveyor 14' and
comprised of a dancer roll or a looper. In this downstream
temperature controller 15, the cast rough strip 9 is brought to the
rolling temperature before it is then subjected to a hot-rolling
step in a following upstream roll stand 16, with at least one pass
being conducted until the cast rough strip 9 has a degree of
deformation of less than 49% of the total deformation. In this
upstream temperature controller 15, the cast rough strip 9 is
maintained at a temperature of approximately 880 to 940 C, its
temperature is reduced by approximately 50 C, or, alternately, its
temperature is increased by approximately 50 C. After passing
through the upstream roll stand 16, the cast rough strip 9 is
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subsequently conveyed to a downstream homogenization zone
17 in which the cast rough strip 9 is subjected to a downstream
homogenization step, in particular for recrystallization of the
structural composition. This occurs in that the temperature of the
cast rough strip 9 in the downstream homogenization zone 17 is
maintained at a temperature of approximately 700 to 900 C, its
temperature is reduced by approximately 100 C, or its temperature
is increased by approximately 50 C. Downstream of the downstream
homogenization zone 17, the cast rough strip 9 then passes through
a subdividing unit 18 in the form of a cutter that is synchronized
with the transport or belt speed, and is then conveyed as pieces of
fully rolled hot strip that have been separated from the cast rough
strip 9 to a coiler 19 or a stacker 20.
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