Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND DEVICE FOR PRODUCING A METAL STRIP
BY CONTINUOUS CASTING
The invention concerns a method for producing a metal
strip by continuous casting, where a slab, namely, a thin
slab, is first cast in a casting machine and then deflected
from a vertical orientation to a horizontal orientation, and
where downstream of the casting machine in the direction of
conveyance of the slab, the slab is subjected to a milling
operation in a milling machine and at least one rolling
operation in at least one rolling train. The invention also
concerns a device for producing a metal strip by continuous
casting.
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
increasing in thin-slab installations.
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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.
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. The method that constitutes the
object of the invention and the corresponding device are thus
focused chiefly on the use of milling.
A method and a device of the aforementioned type with a
milling operation carried out downstream of a continuous
casting installation and a milling machine arranged downstream
of said continuous casting installation are already known from
CH 584 085 and DE 199 50 886 Al.
A similar device is also disclosed by DE 71 11 221 Ul.
This document discloses the processing of aluminum strip with
utilization of the casting heat, in which the machine is
connected with the casting installation.
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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 B1,
and EP 1 213 077 Bl. Similar or other solutions are disclosed
by EP 0 646 431 Al, US 3,702,329, EP 1 097 764 A2, and DE 1
508 952 Al.
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
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 lessen the output too much.
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The in-line milling machine is not usually 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.
It is desired that the prior-art technology be used even
more efficiently and thus cost-effectively. It is to be used
preferably but not exclusively for the fast and high-quality
production of thin slabs.
The method of production that constitutes the object of
the invention is aimed especially, but not exclusively, at the
production of tube-quality strip. This requires an absolutely
crack-free slab surface. In addition, a preliminary group of
rolling stands for forming the slab in a first rolling train
is necessary for metallurgical reasons.
Therefore, the objective of the invention is to refine a
method and a device of the aforementioned type in such a way
that it is possible to ensure that a high degree of economy
can be achieved and that, at the same time, an improved
production process and treatment process can take place. In
this regard, it is desired that optimization be achieved with
respect to the necessary introduction of heat into the cast
strand and into the production process and that a crack-free
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surface and the desired metallurgical and mechanical
properties be obtained at the same time.
With respect to the method, the solution to this problem
by the invention is characterized by the fact that the rolling
and milling operations are carried out directly after the
casting of the slab in the casting machine, where the rolling
operation is divided into at least two partial rolling
operations in at least a first rolling train and a second
rolling train, and where the milling operation in the milling
machine is carried out between the two rolling operations.
The slab is preferably heated, e.g., in a roller hearth
furnace, upstream and/or downstream of the first rolling train
and the milling machine.
In addition, the slab can be cleaned in a cleaning and/or
descaling unit upstream of the first rolling train.
In accordance with the invention, the device for
producing a metal strip by continuous casting with a casting
machine in which a slab, namely, a thin slab, is cast, where a
milling machine and at least one rolling train are installed
downstream of the casting machine in the direction of
conveyance of the slab, is characterized by the fact that a
first rolling train and a second rolling train are installed
directly downstream of the casting machine in the direction of
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conveyance, with the milling machine being installed between
the two rolling trains.
If the casting installation is a twin-strand CSP
installation, the milling machine and the first rolling train
are installed downstream of the furnace transverse conveyor,
so that they can process both strands.
A furnace is preferably installed between the first and
second rolling trains. In addition, a cleaning and/or
descaling unit can be installed before the first rolling
train. Another furnace can be installed upstream of the first
rolling train. Each rolling train can comprise at least one
rolling stand; in this regard, it is especially contemplated
that the first rolling train has one or two rolling stands,
which are realized as two-high or four-high stands.
Provision can also be made for the device to comprise
means for adjusting the contact setting of the milling cutters
of the milling machine as a function of the setting position,
the thickness position, and/or the amount of swivel of the
rolling stand or strong driver upstream of the milling
machine.
In one embodiment of the invention, the slab is milled in
the milling machine in such a way that the upper side and the
underside of the slab are milled in the same place in the
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direction of conveyance. Alternatively, however, it can also
be provided that the upper side of the slab and the underside
of the slab are milled in two successive places in the
direction of conveyance.
The pass carried out in the first rolling train can be a
skin pass, especially when the rolling train is a single-stand
rolling train. This provides the advantage that the milling
is carried out on a slab that has already been subjected to a
well-defined profiling and can thus be carried out more
effectively (the specific values for the rolling forces to be
set are determined as a function of the width of the slab).
Scratches of the bottom rolls, oscillation marks, and similar
surface defects can already be partially leveled by the
rolling process in the first rolling train, so that only a
relatively small milling offset must be removed in order
nevertheless to obtain a clean slab surface after the milling.
The proposal of the invention also eliminates any
transverse bending of the slab that may be present.
It is hoped that the relatively small amount of material
removed in the milling process will result in a straight slab
rather than strip turn-up.
The proposal of the invention can also be used to
advantage for spraying the head of the slab before milling in
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order to facilitate its threading into the milling machine.
The speeds of rotation of the rolls in the rolling stand
can also be different on the upper side and underside of the
slab.
The overall result is qualitatively improved production
of slabs, especially thin slabs.
Specific embodiments of the invention are illustrated in
the drawings. Figures 1 to 4 are schematic side views of a
device for producing a metal strip by continuous casting, in
which a casting machine is followed especially by rolling
trains and a milling machine.
Figure 1 shows a device for producing a metal strip 1 by
continuous casting. The metal strip 1 and the corresponding
slab 3 are continuously cast by well-known means in a casting
machine 2. The slab 3 is preferably a thin slab. In the
strand guide (casting segments), the cast strand is deflected
or bent by well-known means from a vertical orientation (V) to
a horizontal orientation (H). After it has been deflected
into the horizontal orientation (H), the slab 3 can be cleaned
by cleaning means 10, and then a profile measurement or
surface inspection can be performed by measuring means 11.
The condition of the surface of the slab and its geometric
formation can be determined in this way.
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These units are followed in the direction of conveyance F
first by a furnace 9 and then a transverse conveyor 12. After
the profile measurement 13, surface machining in a milling
machine 4 is carried out immediately downstream of the heated
transverse conveyor 12 at high slab temperature and thus low
stress. In the milling machine 4, the upper and lower
surfaces of the slab 3 are milled down.
The upper side and the underside of the slab 3 are milled
down in two successive places -- with respect to the direction
of conveyance F -- with two plain milling cutters 14 being
used. The slab 3 is supported by corresponding support rolls
15 during this milling operation.
It is especially advantageous that the conveyance speed
through the milling machine 4 can be determined independently
of the casting speed (in the casting machine 2) and
independently of the second rolling train 6 (finish rolling).
The milling machine 4 upstream of the rolling train 5
determines the conveyance speed of the slab 3. The first
rolling train 5 adjusts itself to this speed.
The milling operation is followed by a slab descaling
unit 8, whose use is optional. This is followed in direction
of conveyance F by the rolling train 5, which in the case
illustrated in Figure 1 comprises two rolling stands. The two
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rolling stands can carry out a high degree of deformation.
The temperature loss by the milling process and the
rolling process in the first rolling train can be largely
compensated by the second furnace 7 that follows the first
rolling train, so that the subsequent deformation in the
second rolling train 6 can advantageously take place at
sufficiently high temperatures in the rolling train 6. The
second furnace 7 can also be realized as an unheated roller
table enclosure, which reduces the temperature loss of the
deformed slab 3. The furnace 7 is followed by a descaling
system 16 and the aforementioned rolling train 6.
The rolling train 6 can comprise at least one stand
(including a reversing stand). As a rule, however, the
rolling train 6 comprises 4 to 7 rolling stands. The further
processing downstream of the rolling train 6 by cooling and
coiling of the metal strip 1 or the stacking of thicker metal
plates is not explained in detail here.
Figure 2 shows another embodiment of the invention. As
in the embodiment of Figure 1, the slab 3 is cast in a casting
machine 2 and heated in a furnace 9 and a transverse conveyor
12. A cleaning and descaling unit 8, in which the prepared
slab 3 is cleaned and descaled, is positioned downstream of
the transverse conveyor 12. The slab then enters a first
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rolling train 5. In the present case, it is equipped with one
rolling stand, which can be realized as a two-high or four-
high rolling stand. In the first rolling train 5, a skin pass
is carried out for the purpose of removing geometric
variations on the surface of the slab. In addition, a
systematic thickness reduction can already be undertaken in
the first rolling train 5. The slab 3 then passes from there
to the milling machine 4.
In this connection, the first rolling train 5 upstream of
the milling machine 4 can also be designed as a strong driver
to ensure reliable conveyance of the slab 3 through the
milling machine 4. As in the embodiment illustrated in Figure
1, after the milling machine 4, the slab is subjected to
further processing in a second furnace 7, a descaling unit 16,
and a rolling train 6 to obtain a finished product 1.
Figure 3 shows yet another embodiment of the invention.
The arrangement and function of this embodiment are similar to
those of the installation according to Figure 2. The only
difference is that here a first rolling operation 5 and a
surface machining operation by milling in the milling machine
are carried out downstream of the furnace, which consists of
the first furnace section 9, the transverse conveyor 12, and
the second furnace section 7. In this application, reheating
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of the slab 3 upstream of the second rolling train 6 is
dispensed with.
In the installation variant according to Figure 4, the
installation consists of two rolling trains. After the
casting in the casting installation 2 and heating in the first
furnace 9 and in the transverse conveyor 12, a first rolling
process 5 takes place. After reheating of the deformed slab 3
in the second furnace 7, the surface machining is carried out
just before the finishing train.
Figure 4 thus shows another variant of a device for
producing a metal strip 1 by continuous casting. The metal
strip 1 or the corresponding slab 3 is again continuously cast
by well-known means in a casting machine 2. After the slab 3
has been deflected into the horizontal orientation (H), the
slab can be cleaned by cleaning means 10, and this can be
followed by profile measurement or surface inspection by
measuring means 11. The condition of the surface of the slab
and its geometric formation can again be determined in this
way.
These units are followed in the direction of conveyance F
first by a furnace 9 and then a transverse conveyor 12.
A cleaning and descaling unit 8, in which the prepared
slab 3 is cleaned and descaled, is positioned downstream of
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the transverse conveyor 12. The slab then enters a first
rolling train 5. In the present case, it is equipped with one
rolling stand, which can be realized as a two-high or four-
high rolling stand. In the first rolling train 5, a skin pass
is carried out for the purpose of removing geometric
variations on the surface of the slab. In addition, a
systematic thickness reduction can already be undertaken in
the first rolling train 5.
After the first rolling train 5, the slab 3 enters a
holding furnace 7 and from there a milling machine 4.
Measuring means 13 for profile measurement are installed
between the holding furnace 7 and the milling machine 4.
The upper and lower surfaces of the slab 3 are milled
down in the milling machine 4.
The upper side and the underside of the slab 3 are milled
down in two successive places -- with respect to the direction
of conveyance F -- with two plain milling cutters 14 being
used. The slab 3 is supported by corresponding support rolls
15 during this milling operation.
Downstream of the milling machine 4, a second rolling
train 6 is installed, which can have several rolling stands.
In the second rolling train 6, the slab 3 is brought to the
final form of the metal strip 1.
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The essential aspect is that the rolling and milling
operations are carried out directly following (i.e., by the
in-line process) the casting of the slab 3 in the casting
machine 2, with the rolling operations being divided into at
least two partial rolling operations in at least a first
rolling train 5 and a second rolling train 6, and with the
milling of the slab 3 in the milling machine 4 being carried
out between the two rolling operations.
A deformation of the slab 3 is thus carried out before
the milling.
The first rolling train 5 can thus be arranged upstream
or downstream of the second furnace 7. The surface machining
can also be carried out upstream or downstream of the furnace
7.
To summarize, the proposal can be formulated as follows:
The surface machining is carried out immediately before
the first forming step or, alternatively, between two forming
steps (groups of rolling stands). According to the
illustration in Figure 1, the milling machine 4 and the
rolling train 5 are positioned immediately upstream of the
second furnace 7 to ensure good surface quality of the slab as
it enters the finishing train 6, in which the remainder of the
deformation to the desired final thickness takes place. The
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rolling stand 5 can also be arranged downstream of the holding
furnace 7. It is also possible for the surface machining to
be carried out directly between the rolling train 5 and the
holding furnace 7, so that reheating can be carried out after
preliminary deformation and surface machining.
In the illustrated embodiments, the upper side and the
underside of the slab are each assigned a plain milling
cutter. When a large amount of material must be milled from
each side or when very hard materials are to be milled, it is
possible to arrange two milling units one after the other on
both the upper side and the underside.
Alternatively to the use of plain milling cutters, it is
possible to use other types of milling cutters in the intended
places, such as face milling cutters, or even grinding tools
or other surface-removing tools (e.g., for flame descaling of
the surfaces). As an alternative to the use of plain milling
cutters or face milling cutters, it is thus possible to use
other types of material-removing tools.
Especially the following can be provided as cutting
materials for the cutting tips of the milling cutters: HSS;
uncoated or preferably coated cemented carbide alloys;
polycrystalline cutting materials. As a rule, commercially
available indexable cutter inserts can be used.
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The milling machine can consist of two or more milling
units, which can be arranged one after the other, for each
side of the slab.
The milling machine can set the conveyance speed upstream
of the first rolling stand, independently of the casting
machine and the second rolling train.
The furnace downstream of the milling machine serves
primarily to compensate the temperature loss in the area of
the milling machine and the first rolling train.
Systematic tapering of the head of the slab is preferably
carried out with the first rolling train.
To achieve optimum adaptation of the milling machine to
the input conditions (especially to the slab thickness and
slab thickness taper), not only the measurement of the slab
geometry can be used but also the setting position of the
rolling stand or strong driver upstream of the milling
machine. That is, the thickness position and the amount of
swivel of the rolling stand or driver are used for adjusting
the milling cutters, especially the plain milling cutter
setting positions. If, for example, a tilted position is
detected, it can be decided to adjust to this and to mill down
the slab uniformly over the width or to mill out the slab
taper.
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List of Reference Symbols
1 metal strip
2 casting machine
3 slab
4 milling machine
first rolling train
6 second rolling train
7 second furnace / roller table enclosure
8 cleaning and/or descaling unit
9 first furnace
cleaning means
11 measuring means
12 transverse conveyor
13 measuring means
14 milling cutter
support roll
16 descaling sprayer
F direction of conveyance
V vertical orientation
H horizontal orientation
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