Note: Descriptions are shown in the official language in which they were submitted.
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Method and Rolling Installation for the Austenitic Rolling of
Thin Strips
The invention relates to a method for austenitic rolling of thin
strips in hot rolling mills, preferably in CSP hot rolling mills,
comprised of a multi-stand rolling mill, a runout roller table with
devices for cooling the rolled strip, and coilers arranged
downstream for coiling the strip.
Hot rolling mills for producing strips are nowadays usually
configured and operated such that the deformation in the individual
rolling stands is carried out under austenitic conditions.
Accordingly, it is ensured that the rolling temperature in the
individual roll stands is above the GOS line of the steel carbon
diagram. Only after the last rolling pass, cooling to the coiling
temperature is carried out in the cooling stretch resulting in
micro-structure conversion.
Depending on the level of the carbon contents of the strips, the
final rolling temperature is approximately 890 to 930 °C in the
above described method. Maintaining the final rolling temperature
is controlled by changing the final rolling speed which has an
effect on the natural cooling and on the heat supply by means of
the rolling process.
This can be applied without problems for strip thicknesses above a
minimum strip thickness which, depending on the rolling mill type,
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is within the magnitude of 1.3 mm. When dropping below this strip
thickness, the required rolling speed reaches values of more than
12 m/s which in the free runout on the runout roller table
downstream of the rolling mill can no longer be controlled because
the hot strip on the runout roller table at this high speed can no
longer be guided properly and, moreover, also cannot be
subsequently coiled.
Moreover, there is a thermal problem in that the rolling process is
characterized by non-constant strip temperatures (deviations across
the strip width and strip thickness, greater cooling of the pre-
strip end in comparison to the pre-strip head during rolling in the
finishing train).
Development tendencies are directed toward producing also strip
thicknesses below 1.3 mm. In this connection, it is attempted
inter alia to lower the final rolling temperature in order to reach
in this way controllable final rolling speeds.
In DE 195 38 341 Al a production device for manufacturing thin
strips up to 1 mm thickness is described wherein first an
austenitic rolling to 5 to 15 mm is carried out and, subsequently,
a ferritic rolling to a strip thickness of approximately 1 mm is
carried out at a temperature above 850 °C. For this purpose, the
first stand of the rolling mill is firstly configured as a
reversing stand which has arranged upstream and downstream thereof
at least one coiling furnace, respectively, wherein a controllable
cooling device is provided between the upstream coiling furnace and
the successive reserving stand.
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In the patent application (EP 97 120 406.0) it is suggested for the
purpose of equilibrating the strip temperature - so that hot strip
having thicknesses under 1 mm can be rolled - to arrange between
the reserving stand and the hot strip finishing train a
compensation furnace which ensures, by means of a number of
receiving spaces for strips capable of being heated for
compensation, a total heating time for each pre-strip with pre-
strip thickness which is a multiple of the rolling time in the hot
strip finishing train. This produces a pre-strip with a homogenous
temperature wherein the best possible preconditions for the rolling
of strips with minimal final strip thicknesses can be provided.
In an article ("Around-up of CSP thin slab", Steel Times-
incorporation Iron and Steel, GB, Fuel and Metallurgical journals
Ltd., London, Vol. 226, No. 5, 1 May 1998, pages 175, 176, 178) the
layout of a CSP hot rolling mill is described which is comprised of
two casting lines, a mufti-stand rolling mill and a cooling
stretch. The rolling mill has arranged downstream thereof a coiler
with two horizontal mandrels located on a vertical turntable. The
mandrel oriented toward the rolling mill is provided for coiling
the strip exiting the rolling mill. After initial coiling, the two
mandrels are pivoted by 180° . While the strip is finish-coiled onto
the mandrel facing the rolling mill to a coil, a free mandrel is
available for initial coiling of the successive strip - without any
loss of time.
In order to be able to roll on CSP hot rolling mills thin strips
under austenitic conditions, extremely high runout speeds (up to
approximately 20 m/s) are required. A safe transport of the rolled
strip on the runout roller table is, however, possible only at
maximally 12 m/s and up to a point where the strip end exiting the
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last rolling stand is engaged by the underfloor toiler and is then
coiled. Only thereafter the rolling mill can be accelerated to
higher runout speeds. For such a rolling strategy, different
rolling conditions and the great spacing between the last roll
stand and the underfloor toiler have the result that the rolled
leading end of the strip does not have the desired mechanical
material properties. They are reached only when already
approximately 130 m have been rolled so that the output of the mill
is thus reduced.
Based on this prior art, it is an object of the invention to
provide a method which can control the higher final rolling speed
or runout speed resulting in the production of thin strips below
1.2 mm with simple means such that for known methods and rolling
mills the resulting disadvantages, such as, for example, an
unfavorable removal or a high apparatus expenditure, in combination
with additional operating costs, can be substantially prevented by
additional heating or cooling.
This object is solved by a hot rolling mill, preferably a CSP hot
rolling mill, by the characterizing features of claim 1.
Advantageous embodiments of the invention are defined in the
dependent claims.
For rolling of extremely thin strips, according to the invention a
toiler, for example, a rotor toiler, is pivoted into the rolling
train behind the last rolling stand and before the runout roller
table. The first strip is then coiled at its high runout speed
onto the first mandrel of the rotor toiler to a first coil, then
the mandrels of the rotor toiler are pivoted by 180° . While the
first strip is now uncoiledw by the slower transport speed
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(maximally 12.5 m/s) and transported via the runout roller table to
the underfloor coiler, the following strip is coiled at its high
runout speed as a second coil onto the second mandrel of the rotor
coiler. Subsequently, the mandrels of the rotor coiler are again
pivoted by 180° and the next strip can now be coiled. In this way,
the coiling and uncoiling can be performed continuously.
Because the strip is coiled directly after exiting from the last
roll stand at its high final rolling speed or runout speed, but is
then instantly uncoiled - at a substantially slower transport speed
- the rolling mill is decoupled from the runout roller table so
that high final rolling or runout speeds and low transport speeds
are possible simultaneously, and disadvantages and problems are no
longer caused by a too high runout speed even when the runout speed
is > 12.5 m/s.and is, for example, 20 m/s and the transport speed
at < 12.5 m/s is substantially slower.
There is no effect on the slab or coil sequence by means of the
measure of coiling and uncoiling because, according to the
invention, the coiling of the subsequent strip is carried out
already during uncoiling. Since the coiling as a result of the
higher speed is completed faster than the simultaneous uncoiling of
the preceding strip, the rotor coiler is pivoted by 180° only
subsequent to the uncoiling process being completed. Therefore,
the wound coil is subjected to a small pause which advantageously
results in a temperature compensation of different strip areas. A
further advantage of the invention resides in that after completion
of coiling and uncoiling, the ends of the strip are switched with
one another and the original strip end is now guided first onto the
runout roller table for cooling.
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A rolling mill for performing the method according to the invention
comprises a coiler, for example, a rotor coiler, which is arranged
so as to be moveable into the rolling train behind the last roll
stand and before the runout roller table, which comprises two
coiling mandrels displaced relative to one another by 180°, and
which is configured to be pivotable with its mandrels by 180°.
Further advantages, details, and features of the invention are
explained in more detail in the following with the aid of an
embodiment illustrated in the schematic drawing figures.
It is shown in:
Fig. 1 a detail of a conventional rolling mill with rotor coiler
according to the invention;
Fig. 2 a diagram of the different strip speeds;
Fig. 3 a plan view onto a detail of the rolling mill according
to Fig. 1,
Fig. 4 a plan view onto a detail of a rolling mill with a
further embodiment of the invention.
Fig. 1 shows a continuous casting device 1 (this is a two-strand
device) which has arranged downstream thereof a cutting device 2,
a compensation furnace 3, a further cutting device 4 as well as a
multi-high rolling mill 5. Behind the rolling mill 5 there is a
runout roller table 10 with devices 6 for cooling, and finally a
deflection roll 9 with a successive underfloor coiler 7 for coiling
the finished strip.
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According to the invention, a rotor coiler 8 with two coiling
mandrels 8', 8 " is moved into this conventional hot strip rolling
mill directly behind the last roll stand of the rolling mill 5.
The strip coming from the roll stand, when exiting the rolling
mill, is then guided about the first deflection roll 9' into this
underfloor rotor coiler 8 and coiled onto the mandrel 8' as a
coiled strip 11. The strip is uncoiled as a feed strip 12 from the
second mandrel 8 ", which is displaced relative to the first
mandrel 8' by 180°, and guided across the second deflection roll
9" back into the rolling train onto the runout roller table 10.
The two coiling mandrels 8', 8 " of the underfloor rotor coiler 8
can be driven independently from one another so that different
coiling and uncoiling speeds according to the invention can be
realized.
Fig. 2 shows schematically, matching Fig. l, the speeds of the
strip present within the hot strip rolling mill. At the speed Vslab
or vs the thin slabs are cast and then moved into the compensation
furnace 3 and into the rolling mill 5. This is followed by the
runout speed vrolling or yr with which the finish-rolled thin strip 11
is coiled onto the underfloor rotor coiler 8. From this rotor
coiler 8 the preceding strip is then uncoiled as a feed strip 12 at
the speed Vtransport or vt to the underfloor coiler 7 via the runout
roller table 10.
In Fig. 3 a detail of Fig. 1 is illustrated in a schematic plan
view. The strip which exits the rolling stand 5 at the coiling
speed yr is coiled - as the coiled strip 11 - onto the mandrel 8'
of the rotor coiler 8. At the same time, the feed strip 12 is then
uncoiled at the transport speed vt from the second mandrel 8 " of
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the rotor coiler 8 arranged in the transport direction behind the
mandrel 8'.
As soon as the feed strip 12 has completely been removed from the
mandrel 8 " - as a result of the higher coiling speed yr the coiled
strip 11 has already been completely coiled - a pivoting of the
mandrels 8' and 8" about the pivot point 15 by 180° takes place so
that the two mandrels 8', 8 " switch their positions. The feeding
mandrel 8 " which is now empty is then positioned in the position
of the previous coiling mandrel 8' and the full coiling mandrel 8'
is in the position of the previous feeding mandrel 8 " .
In order to be able to carry out during this position change the
coiling onto and uncoiling from onto the mandrels 8' and 8 ", the
two mandrels 8' and 8 " are displaced relative to one another by
180° so that each mandrel 8', 8 ", after the position change, is in
the same alignment as the previous mandrel.
Pivoting of the mandrels 8, 8 " for a position change can be
carried out in any direction according to the arrows 14 but also in
only one direction, for example, only in the clockwise direction.
In order to be able to dispense with the use of the measures of the
invention for the rolling of thicker strips at the lower runout
speed yr and to supply the strip directly to the cooling action,
the coiler 8 is arranged to be laterally pivotable into and out of
the rolling train according to the direction of arrow 13. Pivoting
into and out of the rolling train is also possible from below -
this is not illustrated in the drawing figures.
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In Fig. 4, a further possible embodiment of the invention is
illustrated in a plan view. In this embodiment of Fig. 4 the two
mandrels 8', 8 " are not successively arranged in the transport
direction, as in Fig. 3, but adjacently. The position change is
carried out by rotation of the two mandrels 8', 8 " by 180° in the
direction of arrow 14 but now about the pivot point 16 arranged
laterally adjacent to the coiled strip 11 and the feed strip 12.
In the following table the resulting cycle times for manufacturing
a thin strip are illustrated for one embodiment.
slab casting rolling to 0.8 mm, uncoiling/cooling
50 x 50 mm coiling
vs = 5 . 5 m/mi n yr = 2 0 m/ s vt = 12 . 5 m/ s
9 min/slab coiling 2.6 min pivoting - 0.3 min
(2-strand device) pause 1.6 min uncoiling = 4.2 min
pivoting 0.3 min
slab sequence coil sequence coil sequence
- 4.5 min - 4.5 min - 4.5 min
The table shows that with the measure of the invention only a time
shift corresponding to a slab sequence will result with which the
rolled strip is supplied to the cooling devise.
The invention is not limited to the illustrated and described
embodiment but can also be adjusted according to the available
conditions in accordance with the configuration of a hot rolling
mill that is already present or is to be configured when in this
context the basic principle of the invention is observed according
to which the thin strip is coiled directly after rolling at its
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high runout speed and then it is uncoiled at a correspondingly
reduced speed.
