Note: Descriptions are shown in the official language in which they were submitted.
CA 02651766 2008-11-07
DEVICE AND METHOD FOR PRODUCING A METAL STRIP
BY CONTINUOUS CASTING
The invention concerns a device for producing a metal
strip by continuous casting with a casting machine in which a
slab, preferably a thin slab, is cast, where at least one
milling machine is installed downstream of the casting machine
in the direction of conveyance of the slab, at least one
surface of which and preferably two opposite surfaces of which
can be milled down in the one or more milling machines. The
invention also concerns a method for producing a metal strip.
In the continuous casting of slabs in a continuous
casting installation, surface defects can develop, for
example, oscillation marks, casting flux defects, or
longitudinal and transverse surface cracks. These occur in
both conventional and thin-slab casting machines. Therefore,
the conventional slabs are subjected to flame descaling in
some cases, depending on the intended use of the finished
strip. Many slabs are subjected to flame descaling as a
general rule at the customer's request. In this connection,
the requirements on surface quality have been continuously
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increasing in thin-slab installations.
Flame descaling, grinding, and milling are available
methods of surface treatment.
Flame descaling has the disadvantage that the material
that has been flashed off cannot be melted down again without
processing due to the high oxygen content. In the case of
grinding, slivers of metal become mixed with the grinding
wheel dust, so that the abraded material must be disposed of.
Both methods are difficult to adapt to the given conveyance
speed.
Therefore, surface treatment by milling must be considered.
The hot millings are collected during the milling operation.
They can then be briquetted and melted down again without
processing and without any problems and thus returned to the
production process. Furthermore, the miller speed can be
easily adjusted to the conveyance speed (casting speed,
feeding speed into the finishing train). The device of the
aforesaid type that constitutes the object of the invention is
thus aimed at the use of milling.
A device of the aforementioned type with a milling
machine arranged downstream of a continuous casting
installation is already known from CH 584 085 and DE 199 50
886 Al.
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A similar device is also disclosed by DE 71 11 221 Ui.
This document discloses the processing of aluminum strip with
utilization of the casting heat, in which the machine is
connected with the casting installation.
In-line removal of material from the surface of a thin
slab (flame descaling, milling, etc.) shortly before a rolling
train on the upper side and underside or on only one side has
also already been proposed. EP 1 093 866 A2 is cited in this
connection.
DE 197 17 200 Al discloses another embodiment of a
surface milling machine. This document describes, among other
things, the adjustability of the milling contour of the
milling device, which is installed downstream of the
continuous casting installation or upstream of a rolling
train.
Another embodiment and arrangement of an in-line milling
machine in a conventional hot strip mill for treating a near-
net strip are proposed by EP 0 790 093 Bl, EP 1 213 076 Bl,
and EP 1 213 077 B1.
In the surface treatment of thin slabs in a so-called CSP
plant, about 0.1-2.5 mm should be removed from the surface on
one or both sides of the hot slab in the processing line ("in
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line"), depending on the surface defects that are detected. A
thin slab that is as thick as possible is advisable (H = 60-
120 mm) so as not to diminish the output too much.
The in-line milling machine is not generally used for all
products of a rolling program but rather only for those that
have relatively high surface requirements. This is
advantageous from the standpoint of output, reduces milling
machine wear, and therefore is useful.
The in-line milling machine requires building space. The
slab temperature loss in the vicinity of the machine is an
interfering factor. This applies to installations after the
casting machine, since the casting speed (mass flow) is
usually low. However, even before the finishing train, the
temperature loss is disadvantageous, because, especially in
the case of relatively thin strip, a high final rolling
temperature, combined with acceptable strip runout speed from
the finishing train, is sought.
Therefore, the objective of the present invention is to
improve a device and a method for producing a metal strip by
continuous casting with the use of a milling machine in such a
way that optimum slab machining is possible, even with
different process-engineering requirements. In particular,
temperature losses during slab processing and machining are to
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be kept small.
The solution to this problem by the invention is
characterized by the fact that at least one milling cutter of
the milling machine and preferably the whole milling machine
is arranged in a way that allows it to be moved in a direction
transverse to the direction of conveyance of the slab.
This makes it possible to optimize the thermal balance of
the installation, as will be shown in detail below.
In this connection, the direction transverse to the
direction of conveyance is preferably horizontally oriented.
At least one thermally insulating cover element can be
provided and is arranged in a way that allows it to be moved
in the direction transverse to the direction of conveyance.
The thermally insulating material is preferably refractory.
For example, a relatively thick sheet or plate of nonmetallic
refractory material may be adequate for the purpose.
In this regard, it can also be provided that the one or
more cover elements are designed to be heated. In this case,
therefore, the cover part acts as a furnace.
A furnace can be installed upstream of the milling
machine in the direction of conveyance. One milling cutter
each can be arranged on the upper side and the underside of
the slab for machining its surface. In this regard, it is
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preferably provided that the two milling cutters are arranged
some distance from each other in the direction of conveyance.
In addition, it has been found to be effective if each milling
cutter cooperates with a support roll arranged on the other
side of the slab.
A furnace can be installed between the two milling
cutters that machine the upper and lower surfaces of the slab.
A descaling system can be installed downstream of the
milling machine in the direction of conveyance. In this
connection, it can be provided that a furnace is arranged
between the milling machine and the descaling system.
In an alternative embodiment of the invention, a
descaling system is arranged adjacent to the milling machine
at the same level with respect to the direction of conveyance,
and moving means can be used to move the milling machine and
the descaling system selectively in or out of the processing
line in the direction transverse to the direction of
conveyance.
A rolling train is usually installed downstream of the
milling machine in the direction of conveyance.
The milling machine can be divided into two partial
machines that are spaced some distance apart and mill
different sides of the slab.
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Furthermore, it is advantageous if the milling machine or
parts of it are integrated in a descaling system, which allows
compact construction.
The method for producing a metal strip by continuous
casting is characterized by the fact that a simulation model
running in a machine control unit uses determined or
predetermined surface properties of the slab to decide whether
or not the milling machine is to be used before a rolling
operation on the slab. The simulation model is preferably a
process model or a so-called level-3 system, which in itself
is already known from the prior art.
An optimum production process can be automatically
provided in this way. Specifically, where surface-critical
products are concerned, a milling operation is carried out
before the rolling operation, whereas when standard products
are involved, rolling is carried out without preliminary
surface machining by milling.
The proposed solution makes it possible to keep
temperature losses low during slab processing and machining
and to achieve an acceptable finishing train run-in
temperature. This results in qualitatively improved
production of slabs, especially thin slabs.
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The milling machine moved out of the processing line can
generally be replaced by another functional unit, by which is
preferably meant a descaling unit. However, it is also
possible, for example, to move part of a furnace into the
processing line in place of the milling machine. Naturally,
as explained earlier, it is also possible to move only an
insulating element into the processing line in place of the
milling machine or milling cutter to prevent cooling of the
strip.
In addition, the proposed procedure makes it possible to
achieve -- preferably automatically -- a method of operation
that is optimally adapted to the given practical application.
At the same time, an acceptable finishing train run-in
temperature is obtained.
Specific embodiments of the invention are illustrated in
the drawings.
-- Figure la is a schematic side view of a device for
producing a metal strip by continuous casting, in which a
milling machine can be used.
-- Figure lb is a top view of the device that corresponds
to Figure la.
-- Figure 2a is a side view of an alternative to the
device of Figure la for producing a metal strip.
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- Figure 2b is a top view of the device that corresponds
to Figure 2a.
-- Figure 3 is a schematic view of a milling machine
similar to that of Figure 1 but enlarged and with the
insulating elements shown.
-- Figure 4 is a side view of another alternative to the
device of Figure la, where the milling units are arranged in
different locations from each other and mill different sides
of the slab.
-- Figure 5 is a side view of an alternative device to
that of Figure 4.
-- Figure 6 is a side view of another alternative to the
device of Figure la with a furnace between the milling machine
and the rolling train.
Figures la and lb illustrate a device for producing a
metal strip 1 by continuous casting. The metal strip 1 or the
corresponding slab 3 is continuously cast by well-known means
in a casting machine 2. The slab 3 is preferably a thin slab.
Immediately downstream of the casting machine 2, the slab 3 is
subjected to a slab cleaning in a cleaning installation 15. A
surface inspection is then performed by means of a surface
measuring device 16. The slab 3 then enters a furnace 8 for
the purpose of holding it at a desired process temperature.
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The furnace is followed by a transverse conveyor 17.
As can be seen in Figure lb, two strands are cast
simultaneously, i.e., two parallel cast strands are provided.
Downstream of the furnace 8 and the transverse conveyor
17, the slab 3 enters a milling machine 4. In the present
case, two milling cutters 5 and 6 are installed in the milling
machine 4 some distance apart in the direction of conveyance F
for milling the lower surface and the upper surface,
respectively, of the slab 3. The corresponding opposite
surfaces of the slab 3, i.e., the upper side and the underside
of the slab, respectively, are supported by support rolls 9.
A descaling system 11 for removing scale from the surface
of the strip is located downstream of the milling machine 4.
Finally, downstream of the descaling system 11, the metal
strip 1 enters a rolling train, which in the case illustrated
here comprises rolling stands 13 and 14.
A collecting tank 18, in which material that has been
removed by milling is collected, is located under the milling
machine 4.
An essential aspect of the invention is that at least one
of the milling cutters 5 or 6 of the milling machine 4 but
preferably the whole milling machine 4 is arranged in a way
that allows it to be moved in a direction Q transverse to the
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direction of conveyance F of the slab 3.
As is best seen in Figure lb, the milling machine 4 can
thus be positioned in a first position (illustrated with solid
lines), in which it is moved into the processing line and can
mill the slab 3. However, it can also be positioned in a
second position (illustrated with broken lines), in which it
is not used.
To prevent heat losses from occurring in this case, it is
provided that, at the same time the milling machine 4 is moved
out of the processing line, a cover element 7 is moved into
the processing line (see Figure ib). The cover element 7 is
designed to be thermally insulating and thus prevents the slab
from cooling too strongly. The cover element 7 can also be
constructed as part of a furnace, i.e., it can be heated.
To change from the milling operation to the nonmilling
operation and vice versa, the unit consisting of the milling
machine 4 and cover element 7 can thus be moved simultaneously
in the direction Q transverse to the direction of conveyance
F.
The drawings in Figures 2a and 2b show an alternative
solution. In this case, it is provided that an alternative
selection can be made between a milling operation and a
descaling operation. For this purpose, at least an upper
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descaling unit 11' is provided, which is taken out of action
when the milling machine 4 is moved into position in the
processing line. In the same way, when the milling machine 4
is taken out of action by moving it in direction Q, the
descaling unit il' is moved into the processing line.
The complete descaling system 11 can thus be swiveled or
pushed out of the processing line and replaced by the milling
machine 4 and vice versa. In a preferred embodiment of the
invention, the descaling system 11 and the milling machine 4
are arranged one above the other, and, as necessary, the
desired unit is raised or moved into the pass line (processing
line).
Figure 3 shows a detailed but only schematically
illustrated view of how the system can be constructed. The
drawing shows two housings 19, in each of which a milling
cutter 5 or 6 and a corresponding support roll 9 are installed
for milling the upper and lower surface of a slab 3 that is
passing through in the direction of conveyance F. While cover
elements 7' with good thermal insulation properties can be
permanently installed next to the housings 19, it is provided
that, on the one hand, the elements 9 and 6 (support roll and
milling cutter) located above the slab 3 and, on the other
hand, the cover elements 7 can be positioned selectively and
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alternatively. Accordingly, if the upper support roll 9 and
the milling cutter 6 are in operation, the cover elements 7
are not in the position shown in the drawing. Similarly, if
the support elements 7 are positioned as shown in the drawing,
then the upper support roll 9 and the milling cutter 6 are
taken out of position.
The same is true of the underside of the slab. In this
case, the support roll 9 and the milling cutter 5 can be
replaced by the cover elements 7 and roller table rollers 22.
Figure 4 shows another alternative to the embodiments of
the invention according to Figure 1 and Figure 2. In this
embodiment, the milling machine 4 is divided into two partial
milling machines 4' and 411. In the first milling machine 4'
in the direction of conveyance F, the upper side of the slab 3
is milled, while in the milling machine 411, the underside of
the slab 3 is milled. A furnace 10 is installed between the
two milling machines 4', 411.
In addition, a profile measurement station 20 is provided
upstream of the first milling machine 4'.
In the embodiment illustrated in Figure 5, descaling
nozzle spray bars 21 are integrated in the second milling
machine 4" to save space by combining descaling and milling.
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Figure 6 shows another alternative embodiment of the
invention, in which a furnace 12 is installed between the
milling machine 4 and the descaling system 11. This makes it
possible, after the milling operation, to hold the slab 3 at a
desired optimum process temperature or to bring the slab 3 to
this temperature.
The proposed in-line milling machine 4, 41, 4" can thus
be adapted to the specific application and is intended to
achieve optimum temperature management at high temperature for
the subsequent rolling process or to keep temperature losses
low. To this end, the milling machine 4, 4', 4" is pushed
into the pass line or transport line only as needed, depending
on the application, or is arranged in such a way that
temperature losses are minimized. In this regard, Figures 1
and 2, which were explained above, show the advantageous
arrangement of milling machine, furnace, and descaling sprayer
upstream of a finishing train and the possible means of
adjustment. In Figure 1, as explained above, in a twin-strand
CSP installation, the downstream part of the furnace or roller
table enclosure is designed in a way that allows it to be
moved transversely, so that a furnace segment or the in-line
milling machine can be positioned in the pass line.
Alternatively, transverse displacement of the descaling
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sprayer or lifting out of the complete descaling sprayer and
thus replacement by the in-line milling machine is also
possible. In addition, the upper descaling nozzle spray bar
can be swung upward, as indicated in Figure 2b. The
arrangement of the in-line milling machine just upstream of
the finishing train has the advantage that renewed descaling
can be dispensed with, or the amount of pressure and water can
be reduced, or a complete spray bar can be shut down, because
the surface is cleaned by the milling machine. Moreover,
temperature losses are minimized in this way. Envelopment
with inert gas between the milling machine and rolling train
installed here is also conceivable.
As an alternative to transverse movement of the complete
milling machine, furnace segment, or descaling sprayer, the
area of the milling machine can be constructed with a passive
roller table cover (insulation) in order to reduce the
temperature losses in the area of the milling machine, as
shown in Figure 3. To this end, when the milling machine is
not active, only the plain milling cutters and possible
support rolls are moved out of the line, and the roller table
enclosure is swung or pushed into this area.
To minimize the temperature losses upstream of the
finishing train, it is advantageous to divide the surface
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machining of the upper and lower surfaces of the slab into two
machining locations (see Figures 4 and 5). It is advisable to
machine the upper side of the slab downstream of the
transverse conveyor 17 (in the middle of the furnace zone) and
the underside of the slab downstream of the furnace 10, so
that the milling zone upstream of the rolling train is kept as
small as possible.
Alternatively, the milling unit on the underside can be
integrated in the descaling sprayer, as illustrated in Figure
5. A milling machine on the underside of the slab downstream
of the furnace removes not only the casting defects but also
any damage to the surface of the slab that was caused by the
furnace rollers.
The possibilities mentioned above can be used alone or in
combination.
The surface machining on both sides or only on the upper
side upstream of the furnace (directly downstream of the
casting machine) would also be conceivable, but in a twin-
strand installation, it is twice as complicated.
Another arrangement of the milling machine 4 that is
favorable with respect to temperature management is one in
which the whole milling machine 4 (milling from above and from
below) is placed downstream of the transverse conveyor 17 (in
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the middle of the furnace zone), as Figure 6 shows. This is
an advantageous way for temperature losses that occur in the
vicinity of the milling machine 4 to be compensated in the
downstream section of the furnace. Instead of a conventional
gas-heated furnace, inductive heating can be used downstream
of the milling machine.
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List of Reference Symbols
1 metal strip
2 casting machine
3 slab
4 milling machine
4T milling machine
411 milling machine
milling cutter
6 milling cutter
7 cover element
7' cover element
8 furnace
9 support roll
furnace
11 descaling system
ll' descaling unit (descaling nozzle spray bar)
12 furnace
13 rolling stand
14 rolling stand
cleaning installation
16 surface measuring
17 transverse conveyor
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18 collecting tank
19 housing
20 profile measurement station
21 descaling nozzle spray bar
22 roller table roller
F direction of conveyance
Q transverse direction
19
