Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
The present invention relates to a metal inlet in
continuous casters equipped with a stationary refractory pouring
body, or tundish, and a mold which in part surrounds the pouring
body and is provided with walls which are movable in the casting
direction.
Such prior art continuous casters can be operated
successfully, particularly when the metal inlet is closed -toward
the outside, since access of air to the molten liquid metal can
be prevented and the adjustment of the quantity of metal intro-
duced~ particularly at high casting speeds, can be mastered.
Difficulties arise in the region of the stationary pouring body
since that body must be sealed with respect to the mold wall.s
which move in the casting direction, so as to prevent the escape
of molten metal to the outside, and, for example, to insure
good bar qualities.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide
an inlet for the liquid metal which, with a relatively
simple structural design, provides sufficient tightness
in the -transition region between the pouring body and the
moving mold walls, the mold walls possibly being designed
in the form of bands.
It is another object of the present invention to
provide an inlet for use particularly with con-tinuous
casters which process metals such as aluminum, copper,
steel and zinc.
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It is a further object of the present in~ention to
assure operational safety in the region of the metal inlet,
especially at high casting temperatures and for materials having
high chemical aggressivity.
The engineering problem on which the present invention
is based is that the forces acting between metal melt and mold
material or casting body material require very small gap dimensions
to provide a purely mechanical seal and such dimensions cannot be
maintained over the necessary periods of several hours at the high
casting temperatures, particularly for copper and steel with their
high aggressivity towards refractory materials. Although the
molten metal entering the gap between the mold walls and the pour~
ing body could have a sealing effect once it is completely solidi-
fied, this solidification process is undesirable and disadvan-
tageous since the just solidified metal would be continuously
pulled out of the gap or scrape on the moving mold walls and thus
be damaged on its surface. This would result in destruction of the
just produced metal skin, a poor surface of the cast produced, and
possible damage to the continuous caster.
Accordingly, the present invention provides in an inlet
for molten metal in a continuous caster, which inlet comprises a
stationary refractory pouring body having an exit portion defining
a passage from which molten metal e~its, and a mold which partially
encloses said pouring body and is equipped with mold walls which
are movable in the casting direction, the improvement wherein a)
each said mold wall is spaced from said pouring body to define a
gap with said pouring body in the region of said exit portion; b)
each said mold wall is pro~ided, at the surface thereof facing said
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pouring body, with a coating selected to influence solidification
of the metal; and c~ said coating is selected and said mold walls
are arranged to move at such a speed during flow of molten metal
out o said pouring body via sa.id passage to cause the molten
metal to solidify at a location starting at said mold walls and to
create a region filled with molten metal and located within each
such gap and between said pouring body and said location of molten
metal solidiication.
The present invention is thus based on the concept that
a continuous casting process is possible under stationary con-
ditions only if no bridge of solidified metal is formed in the gap
between the facing surfaces of the mold walls and the pouring
body. It is therefore important to prevent solidification of the
metal at the pouring body, since otherwise the danger of hridge
formation to the mold would exist. In order for the beginning
solidification not to reach the pouring body~ i.e. to mai.ntain a
liquid region filled with liquid metal between the pouring body
and the mold walls, the mold walls are provided with a suitable
heat insulating coating and move relative to the pouring body at
such speed that only as much metal flows into the gap between the
walls and the pouring body as is consumed by solidification and
removed by the movement of the mold walls.
A two-phase region is thus always present between the
mold walls and at least the exit region of the pouring body. In
-this region the metal Elowing into the gap is just consumed by
solidification in the solidification region.
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Thus, the gap set between the pouring body and the
moving mold walls can be automatically sealed by solidifying
metal if the material properties and geometric relationship of
the components to be sealed against one another, and the velocity
of movement of the mold walls are precisely adjusted to one
another so that the quantity of metal flowing into the gap
corresponds to the quantity of solidified metal removed from
the gap by the mold walls.
Coating materials according to the present invention,
are, in particular, powders and alcoholic suspensions based
on glass, slag, graphite, or ceramic-graphite. The coating may
also be produced with the use of suitable salts, fats and oils.
In preferred embodiments of -the invention, the gap
is set in such a manner that its width is no greater than two
millimeters and is preferably no more than 1.5 or 1 millimeter.
With appropriate mutual matching of the material properties and
geometric relationships of the components to be sealed against
one another, and taking into consideration the metal being cast,
it is possible, however, to also set the gap larger than two
millimeters. The facing walls of the mold and of the pouring
body are therefore advantageously designed and arranged in such
a manner that at least in the exit region of -the pouring body,
they are parallel to one another.
Preferably, the gap between the pouring body and the
moving mold walls is set to a value between 0.5 and 1 millimeter,
with the mold walls moving at a rate of between 10 and 20 meters
per mirlute. Sucn an embodiment is par-ticularly suitable for the
casting of steel.
Due to the high thermal stresses on the mold walls,
warping of the walls, which changes their distance from the pour-
ing body, poses a particular problem. In order to keep this
distance, i.e. the gap width, as constant as possible at the
desired ~alue, it is advisable to provide guide rails which
support the mold walls under a slight tension. The guide rails
which are advantageously made of -the same material as the pouring
body, particularly in the exit region, may be fixed to the pouring
body, but are advisably movable therein in a manner such that
either a desired distance between mold and pouring body remains
in effect during the casting process or the distance between the
mold and the pouring body can be varied to the desired extent.
The guide rails may be arranged to be movable in the
pouring body, particularly with the use of spring elements. In
a particularly preferred embodiment of the present invention, the
position of the guide rails may be externally varied with respect
to the mold walls. For this purpose, the guide rails may be
made adjustable in height within the pouring body particularly
by means of adjustment wedges or s milar remotely controllable
lifting devices.
Advisably the guide rails are made relatively narrow on
their side which faces the mold walls. Their width transverse
to the longitudinal direction of the pouring body is preferably
no more than five millimeters.
It has also been found to be advantageous to arrange
the guide rails in such a manner that -their greatest distance
from one another in the direction transverse to the longitudinal
direction of the pouring body is -two hundred millimeters. In
order to prevent bridge formation between -the mold walls and
the pouring body, the guide rails should approach the exit edge
of the pouring body no closer than thirty millimeters and prefer-
ably no closer than fifty millimeters.
In a particularly preferred embodiment of the
present invention, the exit portion of the pouring body is
equipped with a bore which widens in the cas-tlng direction in the
manner of a funnel. Advantageous:Ly, the bore walls have convex
curvature, but under certain circumstances, they can also be
linear or can have a concave curvature. The curvature of the
exit portion, which is adjusted to the specific casting conditions,
permits the optimum attainment of high mechanical stability of
the spout region of the pouring body, sufficiently high heat
capacity and heat dissipation to the outside, i.e. in the direction
toward the mold, and substantial calming of the turbulent flow.
The exit portion and the remaining, or main, portion of
the pouring body are preferably made of refractory materials
having different thermal conductvities. Advantageously, the
exit portion and remaining portion of the pouring body will be
connected together in such a manner that thermally caused changes
in the dimensions of each portion may take place. In particular,
these two regions of the pouring body may be fastened together
by means of plug-in connec-tions. This connection between the
exit portion and the remaining portion is par-ticularly advantageous
if the exit region is made of a material having good thermal
conductivity, and the conductivity of -the exit portion is higher
than tha-t of the remaining region.
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Suitable materials for construction of the exit
portion arel in particular, Si3N4, BN and cermet. The remaining
portion oE the pouring body may be constructed particularly of
refractory ceramics containiny a large amount of alumina, such
as sillimanite rock.
To prevent the molten metal from penetrating too far
into the gap between the mold and the pouring body, the gap is
advantageously filled with an inert gas, in the exit region of
the pouring body. The pressure of this inert gas is selected to
lie slightly below that of the metallostatic pressure of the
melt in exit region. Since the inert gas pressure is always
less than the metallostatic pressure of the melt, the inert gas
cannot enter the liquid metal and the cast bar.
In one embodiment of the invention employing an inert
gas seal! the pouring body, in its outer side facing the mold
walls is provided with an annular channel which is connected
outside of the mold to an inert gas source and which, on the
side facing away from the exit region, is sealed against the mold
walls.
~0 It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
but are not restrictive of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
. .
Figure 1 is a longitudinal, partial sectional,
schematic elevational view of one-halE of a metal inlet according
to the invention, in -the exit region of the pouring body.
Figure 2 is a partial sec-tional view, to a smaller
scale than that of Fi~ure 1, of a pouring body equipped with a
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plurali-ty of juxtaposed gulde rails, the sectional view being
transverse -to the longitudinal direction of the pouring body.
Figure 3 is a longitudinal sectional, schematic
view of a metal inlet according to the invention, whose pouring
body is equipped with an inert gas channel in its exit region.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The metal inlet according to the invention, as shown
in Figure 1, includes, as its essential components, band-shaped
mold walls 2 which are movable in the direction of arrow 1, and
a stationary pouring body 3 which includes an exit portion 4 and
a remaining portion 5. The portion 4 is constructecl of a
material having good thermal conductivity and region 5 is con~
structed of a material having poor thermal conductivity. Portion
4 presents outer faces 4' and an exit edge 4". Each face 4'
and each outer face 5' of main portion 5 are spaced from the
associated mold wall 2 to define a gap 9.
The molten metal to be cast is introduced in the
direction of arrow 6 through a bore 7 in pouring body 3 between
moving mold walls 2. A region of solidification 8 begins at
mold walls 2. When viewed in the casting direction, according
to arrow 6, bore 7 having a longitudinal axis 7' widens in the
exit portion 4 in the manner of a funnel which has an outer
face 4' and an exit edge 4".
To seal gap ~ between each mold wall 2 and outer
faces 4' and 5' of portions 4 and 5, respectively, of
pouring body 3, the distance between each wall 2 and body 3
is always maintained at about 0.7 millimeters. Moreover, mold
walls 2, which move at a rate of about 17 meters per minute, are
coated in such a manner that the onset of solidlfication shown
in solidification region 8 does not reach the pourlng body 3
or its exit portion ~. Rather, a gap-like liquid region 8' filled
with molten metal remains between the walls and the pouring
body. The maintenance of this liquid region 8' has the result
that no bridge of solidifying metal forms in the gap 9 between
the walls 2 and pouriny body 3. The operating conditions existing
during the casting process, specifically gap width, coating of the
mold walls and rate of movement of the mold walls, are selected
such that exactly the same quantity of liquid me-tal always flows
to the left through gap-like liquid region 8' as is removed after
solidification at the mold walls 2 by their movement to the right
in the direction of arrow 1.
In order to assure that the gap width always remains
at the desired value amount, pouring body 3 is equipped at its
side facing mold walls 2 i.e. in the region of outer faces 4' and
5', with guide rails 10, whown in Figure 2, against which the
mold walls 2 are supported under a slight amount of tension. The
width _ of these guide rails is preferably no more than Eive
millimeters and the distance a between the rails, transverse to
the longitudinal direction of pouring body 3 is no more than two
hundred millimeters.
According to a modification oE the embodiment shown in
Figure 2, in order to be able to vary the yuiding effect of
guide rails 10, if required, the guide rails may be adjus-tably
held in pouring body 3. It is also possible to arrange guide
rails 10 to be movable within pouring body 3 through the
intermediary oE spring elements.
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The center plane of pouring hody 3 transverse to longi-
tudinal axis ~' is identified as 7" in Figure 2.
Advisably, guide rails 10 - when viewed in -the direction
of the longitudinal axis 7' (or in the direction of the arrows 1
and 6~ - will lie as close as possible -to exit edge 4" of exit
position 4. However, the distance of the rails from -this exi-t
edge must be selected in such a way that the rails will in any
case lie outside of solidification region 8 - which extends into
gap 9 - as indicated in Figure 1. Therefore, the dis-tance c in
Figure 1 of the leading edges of suide rails 10 from exit edge
4" is therefore no less than 30 millimeters.
In the embodiment shown in Figure 3, exi-t portion 4
of pouring body 3 is equipped with an annular channel 11 through
which inert gas is introduced into the gap between walls 2 and
exit position 4. This annular channel 11 is connected by conduit
12 to an inert gas source which is not shown.
The pressure of the inert gas is here selected to always
lie slightly below the value of the metallostatic pressure in
the melt in the region cf exit edge 4" of exit portion 4. The
presence of the inert gas a-t this pressure prevents excessive
penetration of the melt into the gap between walls 2 and exit
portion 4 without the danger of inclusion of inert gas in the
cast bar.
On the rear side of the annular channel facing away
from exit edge 4", -the channel is closed off by a seal 13 which
simultaneously con-tac-ts -the mold walls 2 and -the pouring body 3
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While the described embodiment incorporates band-shaped
mold walls, the presen-t invention is not limited thereto,
but can be used in conjunction with differently designed mold
walls.
It will be understood that the above description of
the present invention is susceptible to vari.ous modifications,
changes and adaptions, and the sa:me are intended to be comprehended
within the meaning and range of equivalents of the appended
claims.
