Note: Descriptions are shown in the official language in which they were submitted.
- 132~326
METHO~ OF PRODUCING A 5-l~L STRIP H~VIN~ A THICKNESS OF LESS
THAN 10 MM
The invention relates to a process for the production of a steel
strip having a thickness of less than 10 mm by the casting of a
steel strand in a cooled continuous ingot mould, whereafter the
not yet completely solidified steel strand ~ithdra~n from the
ingot mould is compressed up to the welding of the inner walls of
the already solidified strand shell.
In a prior art method of the kind specified ~"Patent Abstracts of
Japan", Vol. 8, No. 210 (M-328~ 1647, September 26 1984: Japanese
Patent Application A 5997747 (A1) the already solidified strand
shells of the not yet completely solidified steel strandwithdrawn
from the ingot mould are compressed until the thickness of
the strip is substantially equal to twice the thickness of the
already solidified strand shell. To ensùre reliable welding of ^~
the strand shells, according to this prior art method a pressure
can be exerted on the strand shells such that the strand emerging
from the pinch rolls is equal to the sum of the thicknesses of
the two strand shells.
: .
However, by this known step, which is applied in continuous
casting to obtain strands free from piping, only strips having a
thickness of 20 - 50 mm are achieved, For many uses such strips --
are too thick, since strips having a thickness of 20 - 50 mm
cannot be reduced to the required minimum thickness of about 2 mm
in conventional cold rolling mills.
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For the production of thin strips, the preliminary strip produced
in the conventional manner is cooled and, after complete
solidification, subdivided into pieces of suitable length or
wound into a coil. In preparation for the subsequent rolling out
into thin strips, the coil is subiected to a heating treatment in
an intermediate regenerative furnace and adiusted to a uniform
temperature. The strip is rolled out in a number of passes. It
is still very expensive to roll out thin strips, due to the need
for the intermediate regenerative furnace and the large number of
roll stands. A further disadvantage in such rolling out
following the heating of the strip is that its surface scales,
making satisfactory hot rolling difficult.
It is therefore an obiect of the invention to provide a method ~
and an installation by means of which high quality steel strips -
having a thickness of 1 - 10 mm can be produced in a very simple
manner.
This problem is solved in a method of the kind specified by the
feature that the thickness of the solidified strand shells is
reduced in the same operation as the compresoion of the cast -
strand with a degree of deformation of ~ 40~. Such a reduction
in thickness can be achieved with a roll stand, more particularly
a horizontal drive four-high stand, disposed at the ingot mould ~ -~
outlet.
By the method according to the invention it is possible to
produce in one operation from the not yet completely solidified
steel strand withdrawnfrom the ingot mould a thin strip which.
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132~326
immediately after suitable cooling, can be wound into coils or
further processed. The production of steel strips by the method
according to the invention is extremely inexpensive, since no
large energy-intensive installations are required with heatin~
furnaces and roll stands
According to the invention the different parameters in the
casting of the steel strand on the one hand and the reduction in
the thickness of the strand shells on the other are so harmonized
with one another that the steel strand can be compressed without
breaks and the strand shells can withstand considerable
deformation~ during reduction in thickness. It has been found to
be particularly advantageous if the casting speed and~or the
cooling intensity of the ingot mould is so controlled that on
withdraw~lfrom the ingot mould the steel strand has a shell
thickness of 5 - 10 mm. This ensures that the strand shell is
strong enough to withstand the forces occurring during
deformation without the formation of cracks.
It has been found to be convenient for a uniform deformation of ~ -
the cast strand and a satisfactory structural formation if after
the withdrawalof the cast strand from the continuous ingot mould
the solidified strand shells are compressed at the highest
possi~le temperatures. Satisfactory results are obtained if the
surface temperature of the cast strand is higher than 1100C,
preferably being 1200C to 1400C, more particularly 1300 C. It
has proved advantageous for the strand shell to have
perpendicularly to the strand surface a temperature gradient
which is determined ~y the strand surface temperature and a
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-- 132~326
temperature close to the solidus temperature in the interior of
the cast strand. Since all qualities of steel are highly
loadable at a temperature of more than 1200C, cracks in the
strand skin during deformation are prevented by the maintenance
of the aforementioned temperatures.
Also advantageously for the formation of a particularly
satisfactory structure of the rolled strip. the thickness of the
strand shells is reduced during the compression of the cast
strand with a degree of deformation of 50 - 80~. For many
applications and/or with certain steel qualities, it may be
advantageous to improve the surface texture by giving the strips
an additional rerolling with a degree of deformation lower than
5%. At the same time the strip can also be given a contour.
According to one feature of the invention, a first reduction in
the thickness of the cast strand is performed in the continuous --
ingot mould. To this end the strand shells forming on the wide
sides of the continuous ingot mould are moved together, at least
in the central zone, during the withdrawal of the cast strand by a
suitable construction of a~.funnel-shaped zone of the continuous
ingot mould. The cooling of the continuous ingot mould is so ~-~
adiusted that the strand shells start to be formed in the funnel-
shaped zone, so that a strand still having a molten core is -
formed at that place. It is important for the strand shell to be
formed only with a thickness at which such moving together is
still possible.
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; - 132~32~
21421-244
An embodiment of the invention in the form of an installation for
the production of a steel strip will now be described in greater
detail with reference to the accompanying diagrammatic drawings,
wherein:
Fig. 1 is a side elevation of an installation for the
performance of the method, and
Fig. 2 shows a detail, to an enlarged scale in comparison ~ -
with Fig. 1, the detail of the installation
illustrated in Fig. 1 in the zone between the
continuous casting ingot mould and the roll stand.
Molten steel flows out of a tundish 1 into an oscillating ingot
mould 2, consisting of a funnel-shaped upper part and a lower
part having parallel cooled walls, the distance of which
corresponds to the thickness of the strand to be cast. Due to
the funnel-shaped construction of the ingot mould, during the
withdrawal of the cast strand the solidifying strand shells are
moved together in the funnel-shaped zone, thus achieving a first
reduction in the thickness of the cast strand. ~isposed ~-
immediately at the ingot mould outlet is a roll stand 3 by which ~-
the solidified strand shells are pressed together, welded to one
another and reduced in thickness. The rol I stand is, for
example, a horizontal four-high stand whose driven working rolls
3a for the compression and reduction in thicXness of the strand
10 can be~adiusted by~means of hydraulic cylinders. Section-
determining supporting rolls should be associated with the narrow
sides In the zone of the working rolls 3a. The diameter d of
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` 132~326 21421-244
the working rolls 3a should be between 0.5 and 1 m. while the
distance D between the start of the zone of engagement and the
bottom edge of the ingot mould 2 should be smaller than 0.5 m.
These relations are shown in Fig. 2.
Disposed downstream of the roll stand 3 following a curved guide
4 there can be a roll stand 5 by which the fully solidified cast :~
strand is pressed with a small degree of deformation o~ aboùt 5%.
Disposed downstream of the roll stand 5 are a cooling system 6, ;
shears 7 and a reel 8 for the coiling of the strip 9. ~
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