Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to equipment for the electromagne-
tic stirring of the liquid core in a steel strand in a continuous
casting installation, wherein a support guide and at least one
stirring means, which sets up -turbulent flow in the liquid core
by means of electromagnetic travelling fields, are arranged along
the path of movement of the strand; the invention also concerns
a process which uses this equipment.
~ or the purpose of improving the internal condition of
the cast strand, it is known to impart circulatory movement to
the liquid core of the strand with the aid of electromagnetic
stirring means and travelling fields. In this way, core segrega-
- tion can be reduced and at the same time at least some increase
in the globulitic solidification zone can be achieved instead of
transcrystalline solidification.
A stirring system is known in which a stirring means is
arranged at each side of the strand. The stirring means is arranged
between- two large guide rollers and their support members, and
extends almost to the surface of the strand. In order to bridge
the large support distance between the guide rollers, small support
rollers are provided near each side of the stirring means, which
~20 rollers are backed by the support members of the large rollers.
A plurality of these small support rollers are arranged along the
width of the strand. The small distance between the stirring means
and the surface of the strand calls for less power and therefore
smaIler stirring means. The support distance Eor the strand be-
tween these small support rollers is, however, always too large
- because of the stirring means extending between them, so that harm~
ful bulging of the strand cannot be avoided.
In a further known apparatus for electromagnetically
stirring the liquid core, rollers are provided as guide elements
along a support and guide track, a stirring means also being pro-
vided outside said track~ When large widths of slab are to be
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produced, the guide rollers, made of non-magnetic material, have
a large diame-ter and the support distances between them is great;
the use of such rollers can lead to harmful bulging in strands for
producing slabs. secause of the rollers arranged between the
stirring means and the surface of the strand, a correspondingly
large gap is created between the stirring means and the surface
of the strand, and this leads to power losses. In order to
achieve an effective stirring action in the strand, the stirring
means has to be selected to suit size and power. Furthermore,
the literature concerned gives no solution to the problem as to
how, in the castingof slabs having large differences in width,
a stirring action, best suited to the size of product and pro-
viding a corresponding improvement in quality~ can be achieved
in the strand.
The object of the present invention is to elimi-
nate the above-men-tioned disadvantages and to provide a strand-
guide frame, having electromagnetic stirring equipment, for a
continuous casting installation that is able to produce, in an
economical manner, high-quality slabs having large differences
in width. Furthermore, the invention is intended to provide
procedural measures which enable an optimum stirring action to
be achieved in strand, so as to improve its quality.
Accordingly the present invention provides
equipment for theelectromagnetic stirring of the liquid core in
a steel strand in a continuous casting installation, wherein a
support guide and at least one stirring means, which sets up
turbulent flow in the liquid core by means of magnetic travelling
fields, are arranged along the path of movement of the strand,
characterized in that sup~ort columns are arranged between, on the
one hand, the support guide elements mounted at least three
points along their width, and, on the other hand, a cross-beam
carrying the support and guide elements and a-t least a part of
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the stirring means is secured outs,ide the s.upport and guide
system and between the support and gui.de elements and the cross-
beam, as well as between the support columns of the support and
guide elements.
The apparatus in accordance with the invention
permits the construction of a support and guide frame comprising
electromagnetic stirring mean,s for continuous-casting instal-. _
lations, o~ -
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a very economical basis as regards both capital and operating costs.
The use of a plurality of backing means over the width of the 5Up-
port and guide systems enables the thickness of the guide elements,
i.e. the diameter of the rollers to be correspondingly reduced.
With the arrangement of the stirring means between the guide ele-
ments and the cross-beam, i.e. with the backing for the guide ele-
ments, the stirring means can be fitted at a small distance from
the surface of the strand. This permits -the use of stirring means
which are o~ lower capacity and are therefore smaller, and this,
on the one hand, is more economical and, on the other, provides
a saving in energy costs. Furthermore, the support and guide
system designed in accordance with the invention permits smaller
roller spacings, so that harmful bulging and cracks in the crust
of the strand as well as break-outs can be prevented, even in the
case of large slab widths. A further advantage is that the arran-
gement of a plurality of stirring means or stirring elements along
the wide side of the support and guide system, makes it possible,
with the aid of suitable control- devices, for the travelling fields
to be selectively brought into operation, i.e. enables one of the
two possible travelling field directions to be selected as required,
so that the travelling fields can be selected to suit slabs of
differing widths. Thus, optimum turbulent flow in the liquid core
of the strand can be set up to provide a correspondingly advanta-
geous structure.
Use can be made of support and guide systems in the form
of plates or grids, as well as support rollers. Depending upon the
position of the stirring means in relation to the bath level, the
above-mentioned support and guide means can be used with varying
degrees of advantage. In the zone close to the mould, it is pre-
ferred to use a supp~rt and guide system in the form of a slidingguide such as a plate or grid.
An advantageous form of the invention is obtained if the
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support and guide system is divided up into segments or sections
and the stirring means can be removed jointly with a s~gment.
Such segments may be removed and fitted with the aid oE known
segment-change equipment, Eor example, or they may be lifted out
by means of a hoist, so that in the event of trouble the installa-
tion is stopped for only short periods.
In the zones where fairly high ferrostatic pressure oc-
curs in the liquid core, i~t is expedient for the guide elements
to take the form of guide rollers which are mounted atat least three
points, the support columns carrying the mountings for the rollers.
If the space and metallurgical conditions associated
with the installation permit it, the parts of the stirring means
are so arranged that turbulent flow is set up in the strand trans-
versely of its longitudinal direction. In a further possible
arrangement, the stirring means may be rotatable so as to enable
travelling fields to be introduced into the liquid core of the
strand in any required direction.
An optimum combination involving number and size of
mountings per roller, an advantageous roller diameter and a wide
choice of the control variants of the travelling fields as well
as the individual travelling-field strengths can be obtained if
use is made of rollers which are mounted at four points and if
two stirring means are arranged between the support columns for
the median portion of the rollers, and a stirring means is arranged
between the support columns for each of the two roller end portions.
A separate cross-beam can be provided for each roller
divided into several portions. For reasons of cost it is often
advantageous for the cross-beam to carry the support columns of
several rollers, for example, of one segment.
Apart from the advantages as regards apparatus, the
invention also provides considerable advantages affecting the pro-
cess when the apparatus is used. It is possible, for example,
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to set up unidirectional thrust forces with the aid of the
stirring means acting on a strand~ This mode of operation results
in thorough mixing of the steel and an advantageous equalization
of temperature between the liquid core in the zone below the stir-
ring means and the zone of the level of the bath.
If permitted by the width of the strand, it may be
advantageous if the stirring means set up turbulent flow which,
on one side of the centre axis of a broad side of the strand guide
means, proceeds in the direction in which the strand is e~tracted,
and on the other side of the central axis, in the direction oppo-
site to that in which the strand is extracted. In this way it is
possible, using a relatively small thrust force, -to produce a
closed flow circuit in a rapid manner. This enables the existing
travelllng field capacity to be efficiently exploited. An advan-
tageous stirring effe~t can be achieved if thrust forces of like
magnitude are set up by adjacent stirring means, and the turbulent
flow mutually influence each other.
A further advantageous adaptation to suit different
casting parameters is achieved if at least one of the adjacently
disposed stirring means is caused to set up, in the strand, thrust
forces acting on the molten metal, by means of a different elec-
trical loading or a different arrangement of the coils, the tur-
bulent flows then mutually influencing each other. In addition,
the phases can be-diffently loaded in at least one of the stirring
means. If, for example, only one stirring means is arranged trans-
versely of the longitudinal direction of the strand, it is pre-
ferred, in accordance with the invention, to vary the electrical
loads of the phases of the stirring means so as to set up diffe-
rently acting thrust forces within the travelling field. In
these arrangements, an improved metallurgical structure can be
achieved, and in particular white bands can be weakened or elimi-
- nated, and the negative segregation associated therewith is reduced.
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Embodiments will now be described by reference to the
drawings, in which:
Fig. 1 illustrates, diagrammatically, part of a conti~
nuous casting installàtion,
Fig. 2 is a cross-section through a segment with support
rollers and stirring means,
Fig. 3 is a cross-section through a segment with a
cooling plate and stirring means,
Fig. 4 is a cross-section through a segment with support
rollers and parts of the stirring means, and
Fig. 5 shows a cross-section through a segment with a
cooling grid and parts of the stirring means.
Referring to Fig. 1, an open-ended mould of a vertical
installation is followed by a strand-guide track consisting of
support and guide elements 3 which are secured in replaceable
segments 9. The support and guide system may also be of arcuate
form. Spray nozzles 4 indicate the secondary cooling equipment.
The segments 9 have support and guide elements in the form of
rollers 6, which guide a strand 8 and provide backing against the
ferrostatic pressure of the liquid core, which pressure acts on~
the shell of the strand. Arranged outside the rollers 6-is a ~
means 5 for electromagnetically stirring the liquid core 7 in the
partially solidified strand. The rollers ~ made of non-magnetic
material, preferably stainless steel, are fitted ln the zone of the
travelling field between the stirring means 5 and the surface of
the strand.
Referring to Fig. 2, the segment 9 of the support and
guide system is provided, at one side of the path of the strand,
~with- support and guide elements in the form of rollers 10, divided
at several points, and on the other side of the path of the strand,
- ~ with continuous rollers 11. The rollers 10, which are mounted~
~ at four points along the width oE the segment 9, are backed by
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a cross-beam 14 by way oE support and yuide roller bearings 12
and support columns 13, 13'. This cross-beam 14 provides the
actual backing for the rollers 10, and between ~hese and the
backing 14, as well as between the support frames 13, 13' are ar-
ranged four stirring means 15. The stirring means 15 can be con-
stituted by a multi-phase connected st:irring means or by only a
part of such a means. The segment parts oE the two guide paths
are clamped against stops 13 by hydraulic cylinders 17. Such
strand-guide segments, provided with at least one pair of rollers,
are readily removable from, and replaceable in, the strand guide
by means of known segment-changing equipment. Such a segment may
however, also comprise a plurality of pairs of rollers, and it
can be removed from, and introduced into, the strand-guide track
with the aid of a carriage.
The stirrlng means 15 set up turbulent flow in the slab
20 in the longitudinal direction of the strand, and for a large
slab 20, all four stirring means 15, and for a smaller slab 20'
shown in broken lines, only the two median stirring means 15 are
brought into operation. The roller 10, mounted at four points~
permits two stirring means to be arranged between the support
columns 13' for the median portion of the roller, and enables a
stirring means 15 to be arranged between the support columns 13',
13 of each oE the-two end parts of the roller. The cross-beam 14
can carry the support columns 13, 13' for a plurality of rollers.
The distance between, and the thrust force oE, adjacent
stirring means can be so selected that the turbulent flows set
up by each stirring means mutually influence each other if the
adjacent stirring means have thrust Eorces of like magnitude.
Referring to Fig. 3, the segments 9 with guide elements
22 takes the form of a support and cooling plate. This sliding
guide element 22 is mounted at three points over the width of the
segment 9, and support columns 23 are provided between the sliding
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guide 22 and a cross-beam 24. If a slab is to be cast~ then, as
shown in this Figure, the two stirring means 25 can set up travel-
ling fields effective in different directions. On one side of the
central axis 26 of the broad side of the segment 9, for example,
turbulent 10w can be set up in the strand 28 in the direction in
which said strand is extracted, and on the other side of the axis
26 in the opposite direction. However, the two stirring means 25
are also able to set up unidirectional thrust forces acting in
the direction opposite that in which the strand is extracted.
Fig. 4 shows the segment 9 similar to that of Fig. 2.
The support and guide elements are in the form of rollers 30 which
are mounted at five points on a cross-beam 32 by means of support
columns 31. The four parts of the stirring means that are desi-
ganted by the numeral 34 set up turbulent flow transversely of
the longitudinal direction of the strand. In this example, the
parts 34 of the stirring means may also act as units having at
least two phases, or as single phase stirring parts in conjunction
with adjacent stirring elements. For the wide slab 20, all four
stirring parts are brought into operation, and for the small slab
20', only the two median parts.
Fig. 5 illustrates a further example of a segment 9
having a support and guide element 40 in the form of a cooling
grid. The cooling grids are equipped with the usual spray nozzles
41. the cooling grid lS mounted on the cross-beam 44 by means
of support columns 43. Stirring parts 45, 45', arranged between
the cooling grid 40 and the cross-beam 44 as well as between the
supporting columns 43, set up a travelling field transversely of
the longitudinal direction of the strand. The direction of the
travelling field is indicated by arrows 46, the length of the
arrow in each case representing a measure of the differing thrust
force within the travelling field. This differing thrust force
can be produced by different electrical loading of the phases.
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The median stirring means 45' may consist of a two-phase unit,
and the stirring means 45 may each consist of a single phase
stirring element, the stirring means 45' and the two stirring ele-
ments 45 co-operating to form a single unit in the case of wide
slabs.
As a variant, it may also be advantageous if the three
parts 45, 45' of the stirring means have at least two phases.
Instead of the differing electrical loading of the phases of the
stirring means or parts thereof that are adjacent each other,
transversely of the longitudinal direction of the strand, a dif-
fering electrical loading can also be provided by stirring means
adjacent each other in the longitudinal direction of the strand.
In this arrangement, differing thrust forces, acting on the molten
metal, are set up, and~the resultant turbulent flows still mutually
influence each other. Instead of the differing electrical loading,
a differing form of the coils may be provided. A further possible
variant consists in differently loading the phases at least in one
of two adjacent stirring means.
- The stirring means 5, 15, 25, 34 and 45, shown in the
2b drawings, can be switched on and off as required by means of suit-
able control devices. In addition, one of the two possible tra-
velling field directions can be established as required. The
magnitude of the thrust force can also be adjusted for each stir-
ring means. The various dispositions and control arrangements
that have been described permit a large number of individual adap-
~ tations to suit the metallurgical requirements or the needs de-
- pendent upon product size in contin,uous casting.
It is within the framework of the- teachings of the inven-
tion to employ, instead of the support columns 13, 23, 31, 43,
also support carriers extending in the direction of travel of the
strand over a number of roll bearings. When using the afore-
mentioned support carriers the traverses 14, 24, 32, 44, illustrated
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by way of example in the embodiments herein disclosed, can be
arranged at greater distances from one another and can be struc-
tured as transverse carriers or supports. With this a~rangement
the accessibility to the electromagnetic stirrers is insured.
Therefore, in the context of the disclosure and claims the expres-
sion "support columns" is to be understood as employed in its
broader sense as covering the just-mentioned modification and
equivalents thereof.
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