Field of the Invention
[0001] The invention relates to continuous casting of metals, in particular aluminium.
Background of the Invention
[0002] It is known an invention "A method and apparatus for electromagnetic stirring of
molten metals at an advanced stage of solidification" (Patent
WO2009117803, publication date: 2009.10.01), wherein an apparatus comprises one or more multiphase inductors arranged along
a billet and providing the stirring of a liquid core about the axis of the billet
and, generating at least a first and a second rotating magnetic fields differing in
frequency about an axis of solidifying molten metal. The rotating magnetic fields
from different inductors superpose providing, in addition to the main stirring, an
increased turbulent motion that provides efficient heat and mass exchange at the border
of crystallization and obtaining equi-axial dendrites and a more uniform structure
over the cross-section of the cast product.
[0003] The main shortcoming of such method and apparatus as applied to aluminium slabs is
impossibility to generate stirring action coinciding in character with the directions
of flows in natural convection in a liquid core of an aluminium slab. According to
said method within the creation of rotating stirring in a billet about its axis it
is created a circular motion of metal which due to elongated profile of the slab results
substantially different conditions of cooling of wide and narrow sides. Besides, taking
into account that the depth of the liquid core D is comparable with the dimensions
of the cross sections A and B, a rotation along the whole height of the liquid core
will be created, resulting a flow similar to a funnel breaking the meniscus form,
and an intensive burling in the meniscus area.
[0004] It is known an invention "A method and apparatus for flow control in a crystallizer
for continuous casting of slabs" (Patent
RU 2325245, publication date: 27.05.2008), wherein the molten metal is fed into crystallizer through immersed pouring nozzle
provided with lateral outlet holes turned towards the smaller faces of the crystallizer.
Configuration of the molten metal in the crystallizer may be naturally set into single
loop, double loop or unstable loop modes. Sliding magnetic fields are generated along
the whole cast product to induce, or stabilize a permanent configuration of flow in
the double loop mode. Or the magnetic fields are induced only in case the configuration
of flows hasn't naturally set into the double loop mode. At that, the used inductors
generate electromagnetic field at a single frequency.
[0005] The principal shortcoming of such method and apparatus as applied to aluminium slabs
is non-optimal use of inductor that generates electromagnetic field at a single frequency
from the point of control of flows in liquid core making it impossible to flexibly
control the flow structure in the liquid core.
[0006] It is known an invention "A method of electromagnetic stirring for continuous casting
of metal products of elongated cross-section" (Patent
RU 2357833, publication date: 10.06.2009) wherein in order to promote liquid metal exchange at the solidification well between
the secondary cooling zone and the crystallizer, a longitudinal metal flow localized
in the central region of the cast product is forcibly created by two opposed collinear
currents providing four-foil liquid metal circulation in a form of two upper and two
lower flows forming the foils, wherein two upper ones reach in the crystallizer the
currents exiting through the outlet ports of the immersed pouring nozzle. The invention
makes it possible to provide general stirring of metal along the whole metallurgical
length providing thermal and chemical uniformity between the upper and lower parts
of the liquid well without detriment to positive effects characteristic to stirring
in a crystallizer and secondary cooling zone, without disturbing and even improving
the mode of local flow in the crystallizer.
[0007] The principal shortcomings of such method and apparatus as applied to aluminium slabs
are non-optimal use of inductor generating the electromagnetic field at a single frequency
from the point of control of flows in the liquid core, impossibility to flexibly control
the structure of flows in the liquid core. In addition to the shortcoming of limited
control over the structure and turbulization of flows, the alternating magnetic field
of a single frequency is commonly generated with a view to efficiently create main
streams in the liquid core and doesn't take into account a possibility of mechanical
resonance of liquid oscillations.
[0008] Said invention is the closest to the claimed one, i.e. is the prior art.
Description of the Invention
[0009] The object of the present invention is to provide flexible control over the rate
of stirring, the flow structure and turbulization capacity along the entire liquid
core of the crystallizing aluminium slab.
[0010] The steel continuous casting operations commonly use a practice of melted steel stirring
in the area of crystallizer of the apparatus for continuous steel casting and in the
area of liquid core of a steel ingot by a low-frequency electromagnetic field of alternating
current applied from outside. At present, according to patents
FR 03 12555 (
RU2357833) and
FR 02 12706 (
RU 2325245), for steel slabs casting it is used one or more pairs of inductors arranged in various
zones along the whole length of liquid core of a steel ingot with a length of up to
several meters, wherein each inductor may induce an alternating electromagnetic field
at different frequencies according to the desired action on the metal. That provides
levelling of chemical composition along the entire melted metal and increases heat
exchange in the area of crystallization providing more qualitative and uniform structure
of the produced ingot. To provide stability to the free surface of the melt commonly
called meniscus, inductors that generate permanent or alternating magnetic fields
in the area of pouring nozzle are used. However, in case of continuous steel casting
the depth of the liquid core D is much greater than the width of the ingot A and may
constitute more than 10 meters for the ingot with the section of 2000 mm x 600 mm.
Besides, while creating a stirring action in the liquid core of the steel ingot, they
generally try to create a rotational motion of the melted metal about the direction
of ingot extraction or in the plane being perpendicular to the direction of extraction
mainly due to the fact that the depth of the liquid core D exceeds the width of the
ingot A, and due to the radiussed form of the ingot, making it difficult to create
symmetric circulation of metal according to the double loop model.
[0011] While designing the inductors intended for the steel ingot liquid core stirring arranged
along the ingot, they proceed from the fact that the thickness of the skin of the
ingot on one end of the inductor Tb changes slightly and practically corresponds to
the thickness of the skin on the other end of the inductor Tt, i.e. Tb - Tb. Taking
that into account, for the liquid core stirring in a particular location they use
an inductor (mainly a linear induction machine) that generates travelling or rotating
field of a single frequency, and disregard the difference in magnetic field attenuation
due to different thickness of the ingot skin along the length of the inductor. To
determine the thickness of the layer from the wall of the ingot where the main effective
area of induced electromagnetic forces is concentrated, it is used a commonly used
term "electromagnetic field penetration depth» or "skin-layer" where 86 % of power
released in the melt is concentrated, which skin thickness in the simplest case for
pulsating field is determined as

where γ - is a specific conductivity (Ohm·m) )
-1; µ
a - is an absolute permeability, (Henry/m); ω - an angular frequency (rad/sec) being
related to the cyclic frequency f by the relation ω = 2·π·f.
[0012] However, in the casting of aluminium slabs of rectangular section in the direct chill
crystallizer by a method of semicontinuous casting, for example, with the use of vertical
molding machine by Wagstaff, the process conditions considerably differ from the steel
ingot casting. That is, for an aluminium slab having section A x B - 0,6 x 2,3 m,
the depth of the liquid core constitutes D - 1,2 m with the length of the slab L -
11 m, thus D is comparable with A, i.e. D - A. That is mainly conditioned by the fact
that aluminium possesses considerably greater heat conductivity as compared to iron.
Besides, the thickness of the aluminium slab skin considerably differs on the portions
at the outlet of the crystallizer - Tt and at the area of the bottom of the liquid
core - Tb. Thus for an aluminium slab having section of 2,3 m x 0,6 m, corresponding
Tt - 3 cm, Tb - 20 cm, and their relation Tb/Tt - 6,6. According to formulae (1),
the frequency f to which the depth of electromagnetic field penetration into the solid
aluminium corresponds, for aluminium thickness Tt - 3 constitutes f - 6 Hz, for aluminium
thickness Tb - 20 cm constitutes f - 0,17 Hz. Taking into account high electro-conductivity
of solid aluminium, it's obvious that the use of an inductor that generates electromagnetic
field at a single frequency is not optimal from the point of control over the flows
in the liquid core. Thus, in case of use of sliding electromagnetic field acting on
the entire liquid core along the length D under the condition that this field provides
effective stirring in the area of the bottom of the liquid core, the development of
excessive stirring in the area of meniscus is obvious, being a far undesirable phenomenon.
On the contrary, in case of applying a similar sliding magnetic field which value
doesn't create excessive stirring in the area of the meniscus, the efficiency of stirring
in the area of the bottom of the liquid core will be insufficient due to a high screening
effect of the solid skin of the billet having thickness Tb.
[0013] In addition to the shortcoming said afore, the use of alternating magnetic field
of a single frequency does not provide a possibility to flexibly control the structure
of flows in the liquid core. Of course, it is possible to control the direction of
rotation of vortices by reversing the direction of magnetic field motion, or shifting
the location of main vortices due to magnetic strength and its frequency, however,
in whole, at present there are no methods and apparatuses for slabs which make it
possible to organize flexible control over the structure of hydrodynamic fields such
that the sliding magnetic field of a single frequency acting along the entire area
of the liquid core D would create essentially different flows in the liquid core,
for example, would create a flow not only in the form of a single or double loop or
one vortex, but also a large array of highly perturbed flows with flexible control
over the number of vortices and the location thereof.
[0014] In addition to the shortcoming of limited control over the flow structure and turbulization,
an alternating magnetic field of a single frequency is usually created in order to
efficiently create main flows in the melt of the liquid core and doesn't take into
account a possibility of mechanical resonance of liquid oscillations. Nonetheless,
it is known that in case of application to a body or a liquid volume of forces at
the frequency of natural oscillation, then the oscillations in the body or in the
liquid volume greatly increase and the mechanical system becomes especially sensitive
to force application at such frequency. At that, the liquid volume under the force
acting with the resonance frequency is characterized not only by the fact that the
rate of flows in the liquid volume increases with the minimum energy consumption,
but also by the fact that the pulsation constituent of oscillation increases resulting
an increase of oscillations of turbulent fluctuations and as consequence an increase
of the share of turbulent motion.
[0015] However, in case of use of multi-frequency electromagnetic field it becomes possible
to organize efficient stirring in all liquid cores of all layers of the billet. A
major problem in the casting of oversized aluminium billets is the problem of difference
of the billet structure at the start portion and at the end portion of the billet,
arising mainly because of the conditions of crystallization at the beginning of the
casting process when the casting bottom is in the crystallizer and begins to move
downwards, and at the end of the casting process when the casting process is deemed
to be steady, are too much different.
[0016] Indeed, at the beginning of the casting process the thickness of the metal solid
skin on the billet side face is small and, the liquid core is separated from the casting
bottom by a short thickness of metal predetermining special thermal conditions of
crystallization at that stage where the heat removal through the casting bottom may
prevail or be comparable with the heat transfer through the billet side faces. On
the contrary, within further casting process the form of the liquid core elongates,
the thickness of solid aluminium between the liquid core and the casting bottom increases
resulting the prevalence of the heat removal through the billet side faces over the
heat removal through the billet bottom portion.
[0017] The object of the claimed technical solution is to provide a possibility to flexibly
control the rate of stirring, the flow structure and turbulization along the entire
volume of the liquid core of crystallizing aluminium slab.
[0018] The posed technical problem is solved by an apparatus for continuous or semicontinuous
casting of aluminium slabs comprising a crystallizer that is open at both ends in
the casting direction, means for feeding the melt into the crystallizer, at least
two electromagnetic inductors adapted to induce stirring motion in the crystallizer,
wherein said inductors are arranged symmetrically to each other relative to the vertical
plane of symmetry of the billet, wherein each inductor is adapted to generate at least
two electromagnetic fields travelling in opposite directions along the billet extraction
direction, the area of action of the fields covers the entire liquid core.
[0019] Besides, the inductor is adapted to generate at least a frequency of one of said
travelling electromagnetic fields that is close or coincides with the natural resonance
frequency of mechanical oscillations of the volume of the liquid core.
[0020] Besides, the inductor is adapted to create at least a travelling electromagnetic
field increasing over the depth of the liquid core D with distance from the crystallizer
to the bottom of the core, wherein the relation between the strength of electromagnetic
field in the areas of utmost upper and lower portions of the inductor exceeds 2.
[0021] Besides, the increase of the value of electromagnetic field along the inductor over
the depth of the liquid core D proceeds according to linear, power or exponential
dependencies.
[0022] Besides, the inductor is adapted to generate at least one electromagnetic field with
a frequency decreasing over the depth of the liquid core D with distance from the
crystallizer to the bottom of the core.
[0023] Besides, the frequency of the electromagnetic fields induced by inductors does not
exceed 6 Hz.
[0024] Besides, at least one inductor arranged within the space between at least two billets
is adapted to provide liquid core stirring in at least two slabs, between which it
is arranged.
[0025] Besides, at least one inductor arranged along the outer edge that covers at least
two billets is adapted to provide liquid core stirring in such billets.
[0026] Besides, the directions of motion of travelling electromagnetic fields induced by
one inductor coincide.
[0027] Besides, said inductors generate travelling electromagnetic fields being symmetric
relative to the billet axis.
[0028] The posed technical problem is solved by a method for continuous or semicontinuous
casting of aluminium alloys comprising exposure the liquid metal to electromagnetic
field via at least two electromagnetic inductors providing electromagnetic stirring
of the liquid core of the billet by at least two electromagnetic fields travelling
along the billet extraction direction, wherein each said electromagnetic field is
generated at different frequencies which directions of motion are opposite, and which
area of action on the liquid core covers the entire depth of the liquid core.
[0029] Besides, at least the frequency of one of said travelling electromagnetic fields
is selected to be close to or coinciding with the natural resonance frequency of mechanical
oscillations of the volume of the liquid core.
[0030] Besides, it is created a travelling electromagnetic field increasing over the depth
of the liquid core D with distance from the crystallizer to the bottom of the core,
wherein the relation between the value of electromagnetic field in the area of utmost
upper and lower portions exceeds 2.
[0031] Besides, the increase of the value of electromagnetic field along the inductor over
the depth of the liquid core D proceeds according to linear, power or exponential
relations.
[0032] Besides, the electromagnetic fields are selected with a frequency decreasing over
the depth of the liquid core D with distance from the crystallizer to the bottom of
the core.
[0033] Besides, the frequency of the electromagnetic fields generated by inductors is selected
as not exceeding 6 Hz.
[0034] Besides, the directions of motion of travelling electromagnetic fields induced by
one inductor are selected as coinciding.
[0035] Besides, said travelling electromagnetic fields are symmetric relative to the vertical
axis of the billet.
Brief Description of the Drawings
[0036]
Fig. 1 - schematically shows the arrangement of inductors relative to the billet in
section. It also shows the increase of the value of magnetic field of the sources
from s1 to sN with distance from top to down, and the main dimensions are given.
Fig. 2 - shows the arrangement of inductors in three-dimensional space and the main
dimensions defining the section are given.
Fig. 3 - shows the action of the inductor arranged in the casting bottom on the liquid
core within the casting process at the initial stage of a billet shaping. The travelling
electromagnetic field is generated by serial connection of the magnetic field sources
s1 ... sn. It also shows zonal connection of side inductors, beginning from zone 1
to zone N, with increase of the billet.
Fig. 4 - shows the main flows arising upon the action of the travelling electromagnetic
fields induced by the inductor arranged in the casting bottom, wherein: Fig. 4A) shows
the character of flows arising in case of two counter travelling fields; Fig. 4B)
shows the character of flows arising in case of two reversed fields; Fig 4C shows
the character of flows in case of only one travelling field which penetration depth
provides the coverage of layers of the liquid only in the proximity of the casting
bottom; Fig. 4D shows the character of flows in case of only one travelling field
which penetration depth provides the coverage of the layers of the liquid in the major
portion of the liquid volume.
Fig. 5 - shows as an example a scheme of an installation of two tree-phase linear
induction machines symmetrically arranged about the axis of the billet.
Fig. 6 - shows the principle of creation of rotative moment and as consequence a vortex
in the melt in case of imposition of two travelling electromagnetic fields at different
frequencies, wherein Fig. 6A) shows the creation of vortex E in case of imposition
of counter travelling fields; Fig. 6B) shows the creation of vortex E in case of imposition
of consonant travelling fields, one of which produces greater power in the melt in
absolute magnitude than the other one.
Fig. 7 shows as an example a possible scheme of arrangement of inductors relative
to several billets casted simultaneously.
Fig. 8 - schematically shows the arrangement of integrated forces F1 and F2 in the liquid core that generate at different frequencies the travelling electromagnetic
fields Field_1 and Field_2 respectively.
Fig. 9 - schematically shows the controlled splitting of the main four-loop flow into
several loops, wherein: Fig. 9A) shows vertical splitting of the loops; Fig. 9B) shows
horizontal splitting of the loops.
Preferred Embodiment of the Invention
[0037] An apparatus for continuous and semicontinuous casting of aluminium alloys (Fig.
1) comprises a crystallizer 1 that is open at both ends in the direction of casting,
means 6 for feeding the melt into the crystallizer, at least two electromagnetic inductors
3, 4 adapted to induce stirring motion in the melt, wherein said inductors 3, 4 are
arranged mainly symmetric to each other relative to the vertical plane of symmetry
of the billet, the installation is equipped with a device to adjust the position of
inductors 3, 4 that makes it possible to move and position the inductors relative
to the billet and crystallizer in any direction, each inductor 3 and 4 is adapted
to generate at least two electromagnetic fields travelling in opposite directions
along the billet extraction direction, the area of action of the fields covers the
entire liquid core, the casting bottom 5, the billet 7, the casting table 2.
[0038] Besides, the inductor 3, 4 is adapted to generate at least a frequency of one of
said travelling electromagnetic fields that is close to or coinciding with the natural
resonance frequency of mechanical oscillations of the liquid core volume.
[0039] Besides, the inductor 3, 4 is adapted to generate at least a travelling electromagnetic
field increasing over the depth of the liquid core B with distance from the crystallizer
to the bottom of the core, wherein the relation between the value of electromagnetic
field in the areas of utmost upper and lower portions of the inductor exceeds 2.
[0040] Besides, the increase of the value of electromagnetic field along the inductor 3,
4 over the depth of the liquid core D proceeds according to linear, power or exponential
dependencies.
[0041] Besides, the inductor 3, 4 is adapted to generate at least one electromagnetic field
with a frequency decreasing over the depth of the liquid core D with distance from
the crystallizer to the bottom of the core.
[0042] Besides, the frequency of the electromagnetic fields generated by the inductors 3,
4 does not exceed 6.
[0043] Besides, at least one inductor arranged within the space between at least two billets
is adapted to provide liquid core stirring in at least two billets between which it
is arranged.
[0044] Besides, at least one inductor 3, 4 arranged along the outer edge that covers at
least two billets is adapted to provide liquid core stirring in such billets.
[0045] Besides, the directions of motion of travelling electromagnetic fields induced by
one inductor 3 or 4 coincide.
[0046] Besides, said inductors generate travelling electromagnetic fields being symmetric
relative to the axis of the billet 7.
[0047] Fig. 2 - shows additional inductors 8, 9.
Implementation Example of the Method
[0048] According to Fig. 1 and Fig. 2, the molten metal is fed into the zone of liquid melt
in at least one crystallizer 1 that is open at both ends in the direction of casting
via at least one means 6 immersed into the melt, or at least one jet of metal. Within
the process of casting bottom 5 immersion and molten metal cooling by heat transfer
through the walls of the crystallizer, side faces of the billet 7 and the material
of the casting bottom, the crystallization of the billet occurs with its shaping and
formation of its liquid core. The casting bottom 5 is equipped with at least one source
of pulsating and travelling magnetic field disposed within or directly below it (not
shown) providing the liquid core stirring at the initial stage of casting and billet
shaping. The casting bottom 5 is arranged and secured to a platform that moves downwards
under the action of lowerator, for example hydraulic cylinder, or is put in downward
motion under the action of electromagnetic forces, for example, under the action of
travelling electromagnetic field. At least one pair of inductors of alternating magnetic
field 3 and 4 (8 and 9) is arranged on the opposite sides of the casted billet 7,
that are arranged mainly symmetrically relative to the vertical plane of symmetry
on the opposite sides of the billet and stir the liquid core according to the trajectories
10 (Fig. 2). In the context of the present invention, the inductors of alternating
electromagnetic field 3 and 4 and the inductor arranged in the casting bottom 5, are
an array of elementary sources of alternating magnetic field and functionally may
be implemented as linear induction machines or as an array of travelling or rotating
permanent magnets.
[0049] According to Fig. 4, within the billet casting process, at the beginning of the process,
they use an alternating field generated by the inductor arranged in the casting bottom
or under the casting bottom 5. Such alternating field provides efficient metal stirring
in the liquid core being formed at the initial stage of casting.
[0050] At that, due to use of varying order of connection of the sources of alternating
electromagnetic field in the inductor - S1, S2...Sn, the desired travelling and pulsating
magnetic fields are created.
[0051] According to Fig. 4, the most obvious hydrodynamic flows created in case of use of
the combination of oppositely directed fields are:
- A scheme of natural circulation of 4 main vortices - I, II, III, IV (Fig. 3). These
flows are similar to the steady flows at natural convection and are created by at
least two counter travelling electromagnetic fields - Field_1 and Field_2.
- A scheme of abnormal circulation of 4 main vortices - I, II, III, IV (Fig. 3B). These
flows are similar to the steady flows at natural convection but are opposite in direction
and are created by at least two counter travelling electromagnetic fields - Field_1
and Field_2.
- A scheme of asymmetric circulation of 3 main vortices - I, II, III (Fig. 3C). This
flow structure is created by a relatively weak travelling electromagnetic field Field_1,
that directly acts on the layers of the melt in the vicinity of the bottom of the
liquid core.
- A scheme of asymmetric circulation of 1 main vortex - I (Fig. 4D). This flow structure
is created by a relatively intensive travelling electromagnetic field Field_1 that
directly acts on the layers of the melt occupying no less than a half of the height
of the liquid core from below.
[0052] As the billet forms, at least one pair of inductors 3 and 4 creating alternating
travelling (sliding) magnetic field along the direction of the billet extraction is
connected. The magnetic field generated by the inductors acts on the liquid core along
the entire height D. At that, according to Fig. 3, the inductors 3 and 4 may be connected
by zones - zone 1, zone 2 ...zone N, or may be implemented as segments and be connected
as the casting advances and the liquid core increases.
[0053] In the result of action of the alternating electromagnetic field the vortex currents
arise and consequently the field of Ampere forces, that puts in motion the molten
metal.
[0054] The electromagnetic field generated by each inductor possesses the following characteristics
(features) that are implemented simultaneously or separately:
- 1. The magnetic induction of magnetic field increases over the depth of the liquid
core D with distance from the crystallizer to the bottom of the core. The dependence
of the growth of the magnetic induction on the distance may be proportional, power
or exponential;
- 2. At least one frequency is present in the composition of the field;
- 3. At least one natural resonance frequency of oscillations of the billet liquid core,
or the one close to it is present in the composition of the field;
- 4. At least one natural resonance frequency of oscillations inherent to the border
of crystallization, or the one close to it is present in the composition of the field;
- 5. At least one natural resonance frequency of oscillations inherent to a solid billet,
or the one close to it is present in the composition of the field;
- 6. The frequency of oscillations of electromagnetic field decreases over the depth
of the liquid core D with distance from the crystallizer to the bottom of the core.
The dependence of the growth of the magnetic induction on the distance may be linear,
power or exponential.
[0055] Said characteristics of the electromagnetic field may be implemented by the following
acceptable technical solutions:
- 1. Use of two- or multiphase induction machine which windings are coupled to two-or
multiphase single-frequency power source such that the alternating electromagnetic
field generated at one end of the machine is less than the one generated at the other
end and, the generated field increases from one end of the machine to the other one.
For example, Fig. 5 shows the simplest three-phase inductors 1 and 2, each of which
is capable to create electromagnetic field increasing from the upper edge to the lower
one in the case the inductor is coupled to asymmetric three-phase voltage or current
system. At that the upper coil 3 through which the lowest current flows, generates
the lowest magnetic flow as compared to the middle coil 4, where the current is higher
than in the coil 3, but lower than in the coil 5, where the highest current flows
and that generates the highest magnetic flow.
- 2. Use of two- or multiphase linear induction machine, which windings are coupled
to two- or multiphase multi-frequency power source, such that the father from the
crystallizer downwards along the billet the coil is, the lower is the frequency of
current or voltage pulsation therein.
- 3. Use of two- or multiphase linear induction machine, deliberately designed as asymmetric,
such that when the coils are coupled to two- or multiphase single-frequency power
source an electromagnetic field increasing from one edge to the other one is generated
along the machine. The simplest example of such deliberately asymmetric inductor is
an inductor wherein the father from the crystallizer downwards along the billet the
coil is, the higher is the number of windings or the pole pitch.
- 4. Rotating the permanent magnets arranged in a row along the billet. At that, the
value of the magnetic field of permanent magnets increases from the crystallizer with
distance from the crystallizer to the bottom of the core. At the same time or separately,
the frequency of rotation of permanent magnets may decrease from the crystallizer
with distance from the crystallizer to the bottom of the core.
[0056] The creation of and control over vortex structure of flows due to use of at least
two travelling fields are possible with the use of two principles stated below.
[0057] The first principle - a principle of opposite fields, uses the imposition of at least
two counter travelling electromagnetic fields generated by one inductor at different
frequency providing arising of vortical hydrodynamic flows. Due to different frequency
of each field, the depth of penetration of each field differs making it possible to
obtain resulting force for each field being arranged at different distance from the
crystallization border, but at the same time at the same horizontal level of the liquid
core.
[0058] Thus, it is possible to obtain at least one pair of forces from at least two multi-frequency
fields making it possible to create a vortex motion in the melt.
[0059] Said principle may be explained in more details in the following way.
[0060] According to Fig. 6, the travelling high frequency electromagnetic field sliding
(moving) to the bottom of the billet creates in the horizontal layer of the liquid
core t the Ampere force distribution at section ab. In whole, the distribution of
forces at that section may be approximated by force F
1 applied in the center of gravity of a figure created by the field of forces at section
ab.
[0061] In turn, the low-frequency travelling electromagnetic field being opposite to the
high-frequency one creates in the layer 1 the Ampere force distribution at section
cd. In whole, the distribution of forces at that section may be approximated by force
F
2 applied in the center of gravity of a figure created by the field of forces at section
cd.
[0062] In the result of interaction of a pair of forces F
1 and F
2 a hydrodynamic vortex E is created (Fig. 6A).
[0063] The second principle - a principle of coinciding fields uses the imposition of at
least two travelling coinciding in the direction of motion electromagnetic fields
generated by one inductor at different frequency, providing creation of vortical hydrodynamic
flows.
[0064] According to Fig. 6B, as opposed to the method mentioned above, the resulting forces
are codirectional, but differ by the value providing creation of a pair of forces
and rotative moment that creates hydrodynamic vortex E (Fig. 6.B).
[0065] For the majority of casted aluminium rectangular billets the configuration of melted
metal flows in the liquid core at natural convection is commonly set into the single
loop mode or double loop mode with two main vortices I and II (Fig. 1) in the vertical
plane of the billet symmetry that form the main single loop and two secondary upper
vortices - III and IV (Fig. 1) which in combination with the single loop create the
melt circulation according to the double loop scheme. Depending on the depth of immersion
of the means for metal pouring and its delivery rate it is possible to set the metal
circulation mode both while in the double loop mode as well as in the single loop
mode.
[0066] However, despite different number of vortices in both circulation schemes two lower
vortices that create the single loop play the primary role.
[0067] Due to imposition of at least two mutually opposing travelling fields Field_1 and
Field_2 generated by one inductor at different frequencies (Fig. 8), different forces
F
1 and F
2 are created in different vertical layers that create rotative moment and provide
vertical splitting of at least two main vortices I and II (Fig. 1) and increase of
the number of vortices throughout the billet width. At that, a flow structure similar
to the one shown at Fig. 9A is created. In case of increase of the number of multi-frequency
travelling fields, the number of vortices increases respectively. The increase of
pulsating constituent of the Ampere force acting in perpendicular to the billet axis
results horizontal splitting of vortices and increase of the number of vortices over
the depth of the liquid core as shown at Fig. 9B. Such action may be created by the
inductor in different manner, for example by generating a standing wave along the
height of the core D, or by creating local zones throughout the height D, where the
normal component of Lorentz force generated in the melt and directed to the billet
axis considerably exceeds the tangential component resulting vortex splitting in that
zone. The creation of said zones is implemented by the sources that generate pulsating
electromagnetic field and which are arranged in the inductor in the place of arrangement
of such zones. Such sources of pulsating field may be separate windings connected
when appropriate.
[0068] The created horizontal and vertical splitting of the main vortices may be intermittent,
but may be permanent. According to Fig. 7, in order to use the space in the installation
for continuous casting to the maximum extent possible the inductors may be arranged
according to the following configurations:
- 1. At least one inductor 4 arranged within the space between at least two billets
7 provides liquid core stirring in at least two billets between which it is arranged.
- 2. At least one inductor 9 arranged along the outer edge covering at least two billets
provides liquid core stirring in such billets.
[0069] The suggested apparatus has the following advantages over the known ones:
- stirring the melt throughout the entire volume of the liquid core by symmetrical flow
structure relative to the vertical plane of the billet symmetry providing symmetric
conditions of crystallization and lack of mechanical deformations of the billet caused
by asymmetry of temperature-induced stresses in the billet;
- a possibility to create circulating flows in the liquid core being different in the
number of loops and structure by multi-frequency electromagnetic field and use of
resonance frequencies, making it possible to flexibly control the stirring motion
in the liquid core.
- simple design solution providing the possibility of liquid core stirring at various
thicknesses of the billets by increasing or decreasing the distance between the inductors
arranged at both sides of the plane of the billet symmetry.
- decrease of stirring power consumption due to use of resonance frequencies.
Industrial Applicability
[0070] A method for continuous and semicontinuous casting of aluminium alloys and an apparatus
for implementation of such method may be used to improve the functional specifications
of obtained aluminium billet and to accelerate the process of solidification of the
melt by intensive stirring of the melt throughout the entire volume of the liquid
core and continuous and semicontinuous casting of aluminium alloys.
1. An apparatus for continuous or semicontinuous casting of aluminium alloys comprising
a crystallizer that is open at both ends in casting direction, means for feeding the
melt into the crystallizer, at least two electromagnetic inductors adapted to induce
stirring motion in the melt, wherein said inductors are mainly arranged symmetrically
to each other relative to the vertical plane of symmetry of the billet, characterized by each inductor is adapted to create at least two electromagnetic fields of different
frequencies travelling in opposite directions along the direction of billet extraction,
and the area of action of the fields covers the entire liquid core.
2. The apparatus of Claim 1 characterized by the inductor adapted to generate at least a frequency of one of said travelling electromagnetic
fields being close to or coinciding with the natural resonance frequency of mechanical
oscillations of the liquid core volume.
3. The apparatus of Claim 1 characterized by the inductor is adapted to create at least a travelling electromagnetic field with
a magnetic induction increasing over the depth of the liquid core D with distance
from the crystallizer to the bottom of the core, wherein the relation between the
value of the magnetic induction of magnetic field in the areas of utmost upper and
lower portions of the inductor exceeds 2.
4. The apparatus of Claim 3 characterized by the increase of the value of the magnetic induction of electromagnetic field along
the inductor over the depth of the liquid core D proceeds according to linear, power
or exponential dependency.
5. The apparatus of Claim 1 characterized by the inductor is adapted with a possibility of generation of at least electromagnetic
field with a frequency decreasing over the depth of the liquid core D with distance
from the crystallizer to the bottom of the core.
6. The apparatus of Claim 1, wherein the frequency of the electromagnetic fields generated
by the inductors does not exceed 6 Hz.
7. The apparatus of Claim 1, wherein at least one inductor arranged within the space
between at least two billets is adapted to provide stirring of the liquid core in
at least two billets between which it is arranged.
8. The apparatus of Claim 1 wherein at least one inductor arranged along the outer edge
covering at least two billets is adapted to provide stirring of the liquid core in
such billets.
9. The apparatus of Claim 1, wherein the directions of motion of travelling electromagnetic
fields induced by one inductor coincide.
10. The apparatus of Claim 1 characterized by said inductors generating travelling electromagnetic fields that are advantageously
symmetric relative to the billet axis.
11. A method for continuous or semicontinuous casting of metals comprising exposure molten
metal to electromagnetic field via at least two electromagnetic inductors that provide
electromagnetic stirring of the liquid billet core by at least two electromagnetic
fields travelling along the direction of the billet extraction, wherein each of said
fields is generated at different frequencies which motion directions are opposite
and which area of action on the liquid core covers the entire depth of the liquid
core.
12. The method of Claim 11 wherein at least a frequency of one of said travelling electromagnetic
fields is selected to be close to or coinciding with the natural resonance frequency
of mechanical oscillations of the volume of the liquid core.
13. The method of Claim 11 characterized by an electromagnetic field is generated which magnetic induction increases over the
liquid core D with distance from the crystallizer to the bottom of the core, wherein
the relation between the value of the magnetic induction of electromagnetic field
in the area of utmost upper and lower portions of the inductor exceeds 2.
14. The method of Claim 13 characterized by the increase of the value of the magnetic induction of electromagnetic field along
the inductor over the depth of the liquid core D proceeds according to linear, power
or exponential dependency.
15. The method of Claim 11 characterized by electromagnetic fields are selected with a frequency decreasing over the depth of
the core D with distance from the crystallizer to the bottom of the core.
16. The method of Claim 11 wherein the frequency of electromagnetic fields generated by
inductors is selected as not exceeding 6 Hz.
17. The method of Claim 11 wherein the directions of the motion of the travelling electromagnetic
fields induced by one inductor are selected as coinciding.
18. The method of Claim 11 characterized by said travelling electromagnetic fields being advantageously symmetric relative to
the vertical axis of the billet.
Amended claims under Art. 19.1 PCT
1. An apparatus for continuous or semicontinuous casting of aluminum alloys comprising
a crystallizer that is open at both ends in casting direction, means for feeding the
melt into the crystallizer, at least two electromagnetic inductors adapted to induce
stirring motion in the melt, wherein said inductors are mainly arranged symmetrically
to each other relative to the vertical plane of symmetry of the billet, characterized by each inductor is adapted to create at least two electromagnetic fields of different
frequencies travelling in opposite directions along the direction of billet extraction,
and the area of action of the fields covers the entire liquid core, wherein the inductor
is adapted to create at least a travelling electromagnetic field with a magnetic induction
increasing over the depth of the liquid core D with distance from the crystallizer
to the bottom of the core, wherein the relation between the value of the magnetic
induction of magnetic field in the areas of utmost upper and lower portions of the
inductor exceeds 2, or the increase of the value of the magnetic induction of electromagnetic
field along the inductor over the depth of the liquid core D proceeds according to
linear, power or exponential dependency, or with a possibility of generation of at
least electromagnetic field with a frequency decreasing over the depth of the liquid
core D with distance from the crystallizer to the bottom of the core.
2. The apparatus of Claim 1 characterized by the inductor adapted to generate at least a frequency of one of said travelling electromagnetic
fields being close to or coinciding with the natural resonance frequency of mechanical
oscillations of the liquid core volume.
6. The apparatus of Claim 1, wherein the frequency of the electromagnetic fields generated
by the inductors does not exceed 6 Hz.
7. The apparatus of Claim 1, wherein at least one inductor arranged within the space
between at least two billets is adapted to provide stirring of the liquid core in
at least two billets between which it is arranged.
8. The apparatus of Claim 1 wherein at least one inductor arranged along the outer edge
covering at least two billets is adapted to provide stirring of the liquid core in
such billets.
9. The apparatus of Claim 1, wherein the directions of motion of travelling electromagnetic
fields induced by one inductor coincide.
10. The apparatus of Claim 1 characterized by said inductors generating travelling electromagnetic fields that are advantageously
symmetric relative to the billet axis.
11. A method for continuous or semicontinuous casting of metals comprising exposure molten
metal to electromagnetic field via at least two electromagnetic inductors that provide
electromagnetic stirring of the liquid billet core by at least two electromagnetic
fields travelling along the direction of the billet extraction, wherein each of said
fields is generated at different frequencies which motion directions are opposite
and which area of action on the liquid core covers the entire depth of the liquid
core, wherein an electromagnetic field is generated which magnetic induction increases
over the liquid core D with distance from the crystallizer to the bottom of the core,
wherein the relation between the value of the magnetic induction of electromagnetic
field in the area of utmost upper and lower portions of the inductor exceeds 2, or
the increase of the value of the magnetic induction of electromagnetic field along
the inductor over the depth of the liquid core D proceeds according to linear, power
or exponential dependency, or electromagnetic fields are selected with a frequency
decreasing over the depth of the core D with distance from the crystallizer to the
bottom of the core.
12. The method of Claim 11 wherein at least a frequency of one of said travelling electromagnetic
fields is selected to be close to or coinciding with the natural resonance frequency
of mechanical oscillations of the volume of the liquid core.
16. The method of Claim 11 wherein the frequency of electromagnetic fields generated
by inductors is selected as not exceeding 6 Hz.
17. The method of Claim 11 wherein the directions of the motion of the travelling electromagnetic
fields induced by one inductor are selected as coinciding.
18. The method of Claim 11 characterized by said travelling electromagnetic fields being advantageously symmetric relative to
the vertical axis of the billet.