Note: Descriptions are shown in the official language in which they were submitted.
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Continuous Casting and Rolling System
Including Control System
This invention concerns a continuous casting and
rolling system for steel strips and a corresponding
control system.
Since the very first continuous casting and
rolling system as described in German patent 52,002, many
different designs of such casting and rolling systems
have been developed. What these developments have in
common is that so far they have been successful only for
low-alloy steel, when the casting system produces a
so-called thin slab at least 50 mm thick (German patent
3,712,537 A1), which is then fed to the first roller or
cast as strips in the case of stainless steel as
described in European patents 458,987 A1 and 481,481 A1.
The object of this invention is to provide a
continuous casting and rolling system and a control
system that will allow production of steel strips of any
grade within the processing tolerances, assuming the cast
strips are 5 to 20 mm thick.
This object is achieved with an optimized
design of individual parts of the system with respect to
their interaction to produce steel strips suitable for
further processing and by coordinating the operations.
Such coordination is preferably optimized by a
neuro-fuzzy system.
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1a
In accordance with this invention there is
provided a continuous casting and rolling system for steel
strips, comprising: a vertically working two-roll casting
device; a first device for adding molten steel to the
casting device; a second device for guiding a cast strip
produced by the casting device into a horizontal position; a
horizontally working rolling mill for working the cast
strip; a reel device receiving the strip worked in the
horizontally working rolling mill, each of the casting
device, the first device, the second device, the
horizontally working rolling mill and the reel device being
controlled by respective individual closed-loop control
systems; and a central control system connected to the first
device, the casting device, the second device, the rolling
mill and the reel device for an integrated adjustment of the
respective individual closed-loop control systems as a
function of mathematical models, wherein each of the first
device, the casting device, the second device, the rolling
mill and the reel device is an individual component of the
continuous casting and rolling system, and wherein the
central control system automatically controls the individual
components with respect to their interaction to produce a
strip which is suitable for further processing to allow for
an effects control procedure of one of the individual
components on downstream devices of the system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a control system in
accordance with the invention.
FIG. 2 is a block diagram of another control
system in accordance with the invention.
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1b
FIG. 3 is a block diagram of another control
system in accordance with the invention.
FIG. 4 is a block diagram of another control
system in accordance with the invention.
FIG. 5 is a schematic view of a rolling and
casting system in accordance with the invention.
FIG. 6 is a view of the casting rolls in
accordance with the invention.
FIG. 7 is an enlarged schematic view of the
casting roll mechanism.
Advantageous details concerning the individual
parts of the system and the control system are given in the
following description.
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Starting with a pouring stream discharged from
a tundish or a fore-hearth, a hot-rolled strip approx. 2
to 4 mm thick is to be produced by rolling directly from
the molten condition and subsequent forming. In
individual cases, a thickness of 1 mm should be feasible.
Continuous casting and rolling systems with the following
basic electrotechnical components, some of which are
already known, are used for this purpose.
Slide valve drive with regulation of the
pouring stream on the tundish or fore-hearth. The
pouring stream enters a precooling system, optionally an
inlet mold, where the casting level is set with an
accuracy of ~3 mm by means of a radiometric measurement
such as that performed with an instrument manufactured by
Dr. Berthold, for example. This setting does not depend
on the cross section of the distribution and/or
precooling system, which may be designed as a chamber or
may be open at the top.
Coolant regulation and optionally a stirring
device in the form of an electric coil are provided for
the distribution and precooling systems, which can
especially be designed as an inlet mold for thick cross
sections, but it may also be designed as a distributor
trough or as a box attachment with a cover. When
designed as an inlet mold, it is advantageous for the
design to be controllable, as described in German patent
4,030,683-A1.
The pair of casting rolls preferably have
coolant regulation and also power regulation and position
control and especially calculation of the instantaneous
form. The shape of the casting and rolls is based on the
requirements of the downstream rolling equipment, so as
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to yield a steel strip that conforms to the required
tolerance with a minimum of adjustment. A rectangular
outlet profile, especially with crowned edges, has proven
to be especially suitable.
Downstream from the casting rolls, there will
preferably be an electromagnetic strip control and
appropriate strip guidance devices that at least
partially replace the rolls customary in the past, which
can lead to surface defects, especially in continuous
operation, or promote the development of edge cracks. In
addition, inductive strip temperature distribution and
regulating equipment is also provided in this area, and a
pressurized water descaling system is also provided
directly upstream from the first forming roll.- The
casting rate is preferably set at approx. 6 to 10 m/min.
Single-part or multi-part line inductors are used to
regulate the edge temperature, and plate inductors that
can be switched on and off individually are provided to
make the temperature uniform, if necessary. These
measures even make it possible to adjust the inlet
temperature of the cast strip into the first roll stand
with a given temperature profile over the width. Like
the casting temperature, the inlet temperature of the
strip into the forming rolls is adjusted essentially
according to the alloy, in other words, the grade of
steel, and the final dimensions to be achieved in
rolling, namely the degree of forming by the rolls.
Simple two-high or four-high stands having at
least a roll gap adjustment and a roll bending device are
provided. If possible, the nominal profile and cross
section, which is also influenced by the reel tension,
are adjusted here on the basis of the strip profile
actually cast.
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A heat treatment zone containing inductive
equipment and optionally also cooling systems may be
provided downstream from the last roll stand when the
system includes one to three roll stands, depending on
the degree of forming needed to achieve the final cross
section. Cycle annealing, for example, is used here to
influence the grain. In addition, a temperature holding
zone may be provided upstream from the reel. This yields
a controlled heat treatment starting from the rolling
heat.
Downstream from the rolls, there are preferably
thickness and profile measurement devices to monitor the
roll settings, roll bending and the pull-out force from
the rolls to produce a strip that conforms to the
required tolerances. The profile entering the rolls is
advantageously determined by computation, and the
computations can be verified through measurements. The
computations may be based on the alloy solidification
data, the calculated instantaneous form of the casting
rolls and optionally also the strip temperature profile
across the width.
The inductive equipment and the casting
equipment (including cooling? are preferably controlled
and regulated by an automation system based on Siemens
"SIMATIC S5" whereas the casting rolls, the forming rolls
and the reel preferably have a control and regulation
system based on Siemens*"Symadin D." The automation
equipment is preferably linked by a bus system and
connected to a control unit. The finished rolled strip
has profile deviations below the cold roll inlet
tolerance of approx. max. ~0.025 mm for a 4 mm strip.
The individual automation and measurement
*Trade-mark
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devices are organized especially in automation groups
based on the technology and they are linked together by a
feed-forward-feedback control system. In an especially
preferred embodiment, the control system has an empirical
5 value matrix with an influence logic circuit in the basic
form of a self-optimizing neural network with fuzzy input
data and automatically generated expert knowledge. This
yields a higher-level control system that can link
together individual units with a relatively simple design
in an inexpensive embodiment to produce a_crack-free
strip with tolerances within the control limits of a
downstream cold-rolling mill and in doing so
automatically brings together the empirical results
regarding how the individual units will perform with
different input values and procedures.
In additional special embodiments of this
invention, the tundish or fore-hearth output control into
a pouring spout and channel, etc., is regulated by means
of slides with an electric drive as a function of the
inlet casting level and given requirements, such as the
thickness of the strip. The inlet casting level or the
level above the casting rolls can be determined not only
by radiometric measurements but also by optical
measurements or float measurements.
If coolant regulation of the inlet area is
needed, it is based on wall thermocouples or the data
from the tundish outlet control in conjunction with a
measurement of the output flow rate. Here again, a
matrix of empirical values is used, taking into account
the alloy influences, for example.
The casting rolls have speed and torque
control, and the instantaneous forming energy required is
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determined in a very advantageous manner by cyclic
release of the speed and torque control. The greater the
forming energy required instantaneously, the higher will
be the combining~zone of the two solidification shells
formed on the casting rolls above the connecting plane of
the casting roll center lines and vice versa. The
forming energy required instantaneously is thus a good
control parameter. This makes it possible to avoid a
breakthrough to the discharge side to great advantage as
l0 well as an excessively high position of the
solidification shell combining zone. Misalignment of the
combining zone toward one side can be compensated by
selective cooling. German patent 4,021,197 A1 discloses
details regarding unilateral misalignment of the
combining zone. Such misalignment of the combining zone
can be detected, fox example, on the basis of the
discharge temperature profile. The casting rolls are
controlled with reference to their axial position
(spacing, offset). Their actual shape and position can
be determined by means of continuous IR-laser
measurements, for example, and corrected if necessary.
The amount of coolant is adjusted in particular according
to information on the inlet area and the speed of the
casting roll. Minor corrections in crowning are possible
by means of electric devices such as induction heating.
The discharge of the cast strip is regulated by
taking into account the low maximum tensile stress on the
outlet side of the casting rolls. This regulation can be
regarded either in conjunction with the regulation of the
roll stands or as regulation of a separate roll stand
with electromagnetic regulation of tension. Regulation
is optimally based on a constant maximum melt flow,
depending on the maximum cooling power, with adjustment
of the roll speed to the speed of the casting roll.
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Downstream from the outlet from the casting
rolls, there is preferably a device for monitoring the
temperature and shape of the edge of the strip. The
shape and temperature of the edge of the strip can be
controlled by regulating the cooling and adjusting the
side elements on the casting rolls. The side elements of
the casting rolls are preferably arranged on the
circumference of the casting rolls and they preferably
work in conjunction with inductive heating or a cooling
system and a position control system based on a matrix of
empirical values, for example.
The surfaces of the casting rolls preferably
have a structural pattern, where a fishbone or zigzag
pattern is especially advantageous. Structural
depressions can be cleaned by spraying with water in
combination with a brush system, for example, where it is
advantageous to monitor the cleaning with a laser, which
may optionally also make any corrections required.
For satisfactory separation of the strip from
the casting rolls, it is advantageous to provide an
electromagnetic strip vibrating system, for example,
which is supplemented as needed by a platform and casting
roll vibrating system which may also be electromagnetic.
An imaging and pattern recognition unit, such as a system
using infrared cameras to monitor the surface quality of
the strip is preferably provided between the casting
rolls and the first forming stand. Assuming that visible
scale cracks exceeding a maximum length and likewise
scale cracks at the edges on both sides are a sign of
surface cracks (deviation from a normal crack pattern),
the behavior of the electromagnetic equipment is
influenced accordingly, and optionally a repair of the
cracks may be performed by partial inductive heating.
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Defects are corrected through controlled electric
measures, supported by position control and/or heating
and cooling regulation of the edge forming control
elements in the case of edge cracks. This results in
entry of the strip which is free of macroscopically
visible cracks into the first forming stand, where
microcracks and intercrystalline separations are
unavoidably welded. Upstream from the roll stands there
may optionally be a profile and thickness measuring
device which especially performs a trend analysis of the
profile and thickness. This information is used
especially for the neuro-fuzzy system with its if-then
rules, but it can also be analyzed by differentiation in
the conventional way. The same thing is also true of the
other trends that are considered.
Downstream from the rolls there is preferably
an inductive heat treatment with a given temperature
profile, such as a cycle annealing treatment at
temperatures around 720'C and/or subsequent holding at
500'C to 550'C in the case of alloyed steel.
The downstream reel has a tension control to
achieve the predetermined final thickness of the strip on
the last roll stand while maintaining a minimum and
maximum tension.
The higher-level control system which
essentially also functions on the basis of mathematical
models with adaptation on a neuro-fuzzy basis (mostly
with training of the network) serves especially to
coordinate the profile produced in the casting roll and
the condition of the strip with the downstream units.
This makes it possible to operate the casting rolls as
well as the forming rolls to advantage without expensive
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displacement equipment (forming rolls) or equipment to
change the crowning (casting rolls). Using this matrix
of empirical values, an optimum reaction to the
prevailing conditions can be achieved relatively rapidly
for the different feed conditions to the casting rolls
whose behavior in operation can be determined by
simulation and/or experimentation as part of the startup
operation and for the feed conditions to the roll stand.
Depending on the alloy and the inlet conditions,
especially the inlet temperature, strips that conform to
the required tolerances can be produced with very simple
equipment after a relatively short time, taking into
account the available cooling power. As a rule,
estimated values for the fuzzy set parameters that are
improved with the help of the self-learning neural
network are sufficient for the matrix of empirical
values. The respective fuzzy rules for processing the
fuzzy sets are verified as part of trial operation after
prior simulation of effect (especially with regard to
critical states) and also become part of the empirical
value matrix, where the neural network changes the
weighing of the fuzzy rules in accordance with
requirements.
Under the central control system with an
especially advantageous neural network with a fuzzy
structure and a matrix of empirical values for
preliminary control or direct control, arranged control
structures, some of them according to this invention, are
derived from captioned Figures 1 to 4. The principles of
some important fuzzy rules are apparent from the
accompanying table and some important design details
according to this invention as well as a survey of the
control system according to this invention are shown in
Figures 5 to 7.
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A continuous variable casting system with an
automatic control is shown in FIGS. 5, 6 and 7. The casting
system is capable of forming extremely thin hot-rolled
strips of steel, of varying alloys and grades. The
5 automated control of the system utilizes a central control
unit 11, 12 and a plurality of local control units 14, 15,
16, 17, 18, which are interconnected via a bus interface.
The central control unit 11, 12 utilizes an empirical data
matrix and a neural network based fuzzy logic system, and
10 provides control parameters for all system functions based
on sensor data (provided by the local control units 14, 15,
16, 17, 18). The neuro-fuzzy system used by the central
control unit 11, 12 can utilize if-then rules or other
conventional differentiation methods. The central control
unit 11, 12 generally provides an inexpensive and quick
adjustment of system parameters to enable changes in output
profile without significant delay.
A liquid-type metal can be poured or discharged
from a tundish or fore-hearth 1 into an inlet mold 2. The
regulation of the flow of the liquid-type metal is
controlled from the central control unit 11, 12 using
various flow control mechanisms such as a slide valve in the
pouring spout or channel. A hot molten metal accumulates
and is maintained at proper levels in a pool in the inlet
mold 2 on the top side of the crevice formed by a proximity
of casting rolls 3. The inlet mold 2 may also consist of a
distributor trough or other molten metal pooling devices.
The level of the pool may be monitored by a radiometric
measurement device, an optical measurement device or a float
measurement device. The measurements provided by any of
these devices are fed back to the central control unit 11,
12 through the local casting sensor control unit 14, from
which varying control of the tundish or fore-hearth 1 can be
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administered. The molten metal pool may also be monitored
via temperature measurement devices 24 (shown in FIG. 6).
Such temperature measurement devices 24 may utilize a
plurality of tube clad thermocouples or ultrasonic
oscillators to determine the temperature gradient of the
molten pool. An initial cooling mechanism 28 (shown in
FIG. 7) may be fixed centrally within the molten pool to
cool the metal to a temperature at which solid formation may
begin. The initial cooling mechanism 28 is hollow and has
continuous orifices 30 extending laterally. A coolant may
be pumped through these continuous orifices 30 at a
predetermined rate as controlled by the central control
unit 11, 12 through the local casting sensor control
unit 14. The rate of the coolant flow depends on the
measurements taken by the temperature measurement
devices 24. Consistent pool temperatures may also be
obtained by a circulation of the molten metal in the pool by
a stirring devices, i.e., an electronic coil. A precise
control of the temperature gradients throughout the pool
properly cools the molten metal at the casting rolls 3 to
enable a formation of solidification shells 31.
The casting rolls 3 provide a primary control for
setting the thickness of the metal to be formed. The
casting rolls 3 are preferably surfaced with a structural
pattern (e.g., a zig-zag, a fishbone design etc.). The
casting rolls 3 have an axial freedom of motion as indicated
by directional arrows 29. A substantially precise control
of the distance between centers of the two casting rolls 3
allows extremely thin (e.g., as small as 1 mm) strips to be
formed. The position of the casting rolls can be constantly
monitored by one or more lasers 19, with precise location
data being fed back to the central control unit 11, 12.
Several mechanisms for maintaining proper formation of the
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solidifying metal are provided adjacent to casting rolls 3.
A rectangular form of the required output strip 32 is
obtained by casting space side borders 23, a height and
position adjusting equipment 27, an electric arrangement 21
for correctional form, and roll form, and other form
influencing devices 26 (e. g., an induced hydraulic
adjustment cylinders, etc.). The casting rolls 3 also have
edge heating devices 22 to ensure that a proper crowned edge
can be formed on the output strip 32.
The casting rolls 3 rotate at a particular rate of
speed M, and a rate of torque n that is controlled by the
central control unit 11, 12 via the local casting sensor
control unit 14. These rates M, n, combined with the
regulation of the temperature of the molten metal pool in
the inlet mold 2, may generally affect the formation of the
solidification shell 31. By maintaining cool outer skin
temperatures on the solidification shells 31, a prompt
separation of the strip of steel from the casting rolls 3
occurs. The maintenance of the proper outer skin
temperature on the solidification shell 31 may be further
enhanced by selectively cooling the casting rolls 3 by a
coolant flowing through orifices 20 which extends laterally
through the casting rolls 3. A vibratory pumping of the
coolant through the casting roll orifices 20 (which is
controlled by the central control unit 11, 12 via the local
casting sensor control unit 14) makes the separation between
the casting rolls 3 and the solidification shells 31 easier.
The control of this cooling procedure provides three
separate zones of cooling: two edge zones I, III, and a
central zone II. The cooling of the casting rolls 3 by this
procedure may be accomplished independently for each casting
roll 3. With proper cooling settings, the metal strip 32 is
tangentially formed with respect to the casting rolls 3.
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The strip 32 passes through a vibration mechanism 36, which
further ensures a proper separation of the solidification
shells 31 from the casting rolls 3. A plurality of
vibration sensors can be utilized to provide a complete
control of the vibration mechanism 36 via the central
control unit 11, 12 and the local casting sensor control
unit 14.
After the metal strip 32 passes through the
vibration mechanism 36, this strip 32 is monitored for its
temperature and profile. Temperature distribution
sensors 3a monitor the skin temperature of the metal
strip 32. The temperature is fed back to the central
control unit 11, 12 through the local casting sensor control
unit 14, and then utilized to further adjust the cooling
parameters applied at the inlet mold 2 and the casting
rolls 3. The metal strip 32 is further measured by using a
profile measurement device 34. The strip profile and
thickness measurements can be taken by a plurality of
sensors (e. g., laser measurement devices). The values thus
obtained can be fed back to the central control unit 11, 12
via the local casting sensor control unit 14 to be used for
varying any of the parameters (e. g., spacing of the casting
rolls 3, a molten metal temperature profile, etc.).
Position sensors 35 can be utilized in conjunction with an
electromagnetic tension and guidance control arrangement 33
to provide a consistent feed of the metal strip 32 into the
remainder of the system. As the metal strip 32 moves
forward past the casting rolls 3 and various sensors, it is
placed into a horizontal position and prepared for the
forming rolls 7. An electronic inductive and vibration
control equipment arrangement 4 is utilized to maintain the
strip moving along the desired cornering path, preferably
free of defects that may be caused by any conventional
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device which is used to provide guidance and physical
contact with the metal strip 32.
Prior to entering forming rolls 7, a plurality of
line or plate inductors 5 are provided to establish a
uniformity in the temperature of the strip and to maintain a
desired initial temperature. The inductors are controlled
by the central control unit 11, 12 via the local casting
sensor control unit 14. As the metal strip 32 continues to
extend, an image and pattern recognition unit 6 may be
utilized to determine whether any cracks in the surface of
the strip have formed. For example, infrared cameras may be
used as the image and pattern recognition unit 6. The
information generated by this image and pattern recognition
unit 6 may be provided to the central control unit 11, 12
via the local image sensor control unit 15. In response,
the central control unit 11, 12 may adjust the parameters of
the casting temperature or apply different parameters to the
line or plate inductors 5. The metal strip 32 may also pass
through a descaling portion 7a, where a water spray applied
thereon. Thereafter (i.e., after the descaling phase), the
profile of the metal strip 32 can be checked before the
metal strip 32 enters into the first forming roll 7. A
strip profile and measurement device 7b (which is similar to
the profiling equipment 34 used as the metal strip 32 is
discharged from the casting rolls 3) can also be utilized.
The obtained measurements can be fed to the central control
unit 11, 12 via the local reel control unit 18, and they can
be utilized to vary the rate of speed M' and rate of torque
n', which are applied to a reel 9.
The metal strip 32 may pass through more than one
forming roll 7. These forming rolls 7 may consist of two-
high or four-high roll stands, which have a minimum roll gap
adjustment and may include a roll bending device. In
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addition, the metal strip 32 does not have to pass through
any forming rolls 7. The forming rolls 7 are controlled by
the central control unit 11, 12 via the local forming roll
control unit 16. At the discharge of the forming rolls 7,
5 an output strip profile and measurement device 7c is
utilized to verify that the strip and edge profiles of the
strip 32 are properly formed. A feedback to the central
control unit 11, 12 is provided through the local reel
control unit 18. Then, the metal strip 32 passes through a
10 heat treatment arrangement 8, which may include inductive
heating elements or cooling elements for providing a
temperature profile which depends on the grade and alloy of
steel to be rolled. The heat treatment is controlled from
the central control unit 11, 12 via the local heat treatment
15 control unit 17. At the output of the heat treatment
arrangement 8, the metal strip 32 may be rolled in a reel 9
at a rate of speed M' and a rate of torque n'. The reel 9
is controlled by the central control unit 11, 12 via the
local reel control unit 18.
The reel 9 (e. g., a finished reel) of the hot-
rolled steel may be transferred to a cold-rolling stand 10,
where a cold rolling of the steel may occur (via a direction
of the central control 11, 12 through an interface 13).
