Note: Descriptions are shown in the official language in which they were submitted.
I
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LLEC°I'RO~IAG~TIC STIRRIl~~ DE'~J~ICE ICI Ald IING~"1.° ~1IU~
The present invention relates to an electromag-
netic stirring device in an ingot mould of a continuous
casting installation comprising a vertical mould, which
receives molten metal, and an electromagnetic inductor
for producing a gyratory movement of the molten metal in
the mould about the axis thereof.
A device of this kind is known from the document
EP-A-0,093,06. Essentially two different casting methods
are employed depending on the quality and the nature of
the cast products. The open or free-stream casting method
consists simply in allowing the liquid metal to flow into
the mould through a nozzle calibrated to give a more or
less constant flow rate. The steel meniscus .level i;n the
ingot mould is controlled by altering the withdrawal
speed as a function of the withdrawal and in accordance
with the reading of level-measuring equipment based on a
radioactive principle. This .method is essentially used
for casting steel billets of average quality, since the
casting is carried out in contact with air.
To improve the quality of the steel, a casting
method protected from air is used, .namely .casting with
submerged nozzles and powders. According to this method,
the liquid steel is introduced into the mould through a .
nozzle which is immersed in the liquid metal present in
the mould. Contact with air and oxygen is presented by a
layer of powder which covers the surface of the metal at
the casting meniscus.
In this case, the casting is performed at a
constant withdrawal speed. The steel level in the ingot
mould is controlled by a stopper or a distributing slide
valve.
In both casting methods, it is also known to
improve the quality of the steel-by means of electromag-
netic stirring, which, however, has to be adapted to the
chosen casting method and to the intended qualities of
the steel. Thus, for example, in the case of the casting
of billets by the free-stream method, the main object
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sought by the application of electromagnetic stirring in
the ingot mould consists in improving the surface condi-
tion of the billets by eliminating pinholes and slag
incrustations. To achieve this, the rotational speed of
the steel in the ingot mould at the meniscus level must
be very high, hence the importance of the location of the
inductor relative to the meniscus in respect of the
surface condition of the billets.
In contrast, in the case of the casting of blooms
i
using a submerged nozzle and casting powder, it is
advantageous to reduce the rotational speed at the
meniscus level in order to prevent as fax as possible the
casting powder from being carried away and to reduce wear
v on the nozzle, by retaining as high a stirring intensity
Z5 as possible below the meniscus. In other words, in free
stream casting it is preferable for the inductor to be
located in the upper region of the mould, whereas in
submerged-nozzle casting it is preferable for the induc
tor to be disposed at a lower level. This is the reason
why, in order to benefit fully from the advantages
offered by electromagnetic stirring in the ingot mould,
it is preferable to have available two different instal-
lotions in order to implement each of the two. casting
methods.
The object of the present invention is to provide
a new electromagnetic stirring device in an ingot mould
which permits implementation of the two casting methods
in the same installation.
To achieve this objective, the present invention
proposes an electromagnetic stirring device of the kind
described in the preamble, which is essentially charac
terised in that the inductor is disposed outside the
mould and is vertically displaceable relative thereto..
According to an advantageous embodiment, the
mould is surrounded by a first coaxial tube made of steel
which, in turn, is disposed inside a second coaxial tube
around which the inductor is mounted, whilst the annular
spaces betweenythe two tubes and between the mould and
the first tube are traversed by a cooling liquid.
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The device may be equipped with a detector for
detecting the steel level in the mould, consisting of a
cylindrical radiation source mounted inside the second
tube and associated with a scintillometer mounted an the
opposite side of the said second tube.
The radiation source is preferably located inside
a protective cylindrical jacket made of lead, provided
with a radial slot and movable about the axis of the said
source between an angular position in which the slot is
directed to=,~ards the mould and an i..noperative angular
position in which the slat is directed towards a cylind-
rical block made of lead which extends along the said
jacket.
Theingot mould, which consists of the mould, the
inductor and the two tubes, can be integral with a set of
underlying rollers and dismountable as a unit therewith.
Other features and characteristics will a>merge
from the xietailed description of an advantageous embodi
ment given below, by way of illustration, with reference
to the accompanying drawings in which:
figure 1 shows diagrammatically a vertical
section ,of a device according to the present invention
illustrating the: inductor in the position for free-stream
ca-st~:ng;
~5 Figure 2 shows a similar view to that of
figure 1, t~hP inductor being in the position for submerged-
nozzle casting, and
i~igure 3 shows diagrammatically a horizontal
section through the mould and the radiation source.
Figures 1 and 2 show an ingot mould i4 contained
in a metallic housing 12. The ingot mould 10 comprises
essentially a vertical tubular mould I4 containing liquid
metal 16, which is poured from a tundish (not shown). The
molten metal 16 solidifies progressively in this mould
and the metal blank is withdrawn therefrom, passing
through a set 18 of underlying rollers for guiding and
shaping the metal blanks. According to a preferred
embodiment of the invention, the set of rollers 18 is
integral with the ingot mould l0 and can be dismounted as
_ ~ _ ~~Q~~~~~
a unit therewith.
The mould 14, which generally co:~sists of a
copper tube, is surrounded by a coaxial steel tube 20
which forms with the mould an annular cylindrical space
22 in which a liquid for cooling the mould 14 circulates.
Another cylindrical space 24 is delimited :around the tube
20 by a second tube 26. This space 24 is closed towards
the bottom by an annular plate 28 fixed to the tyro tubes
20 and 26.
The Gaoling water enters the circuit at 30 and
then the annular interstice 22 between the mould 14 and
the tube 20. This space is very narrow ::o ensure rapid
circulation and efficient cooling in the ~~uld 14. The
cooling water thus rises alang the mould, flows over the
top of the tube 20 and fills the annular apace 24. The
cooling water leaves this space 24 by flowing over into
a vertical pipe (not shown) arranged along the inner wall
of 'the tube 26 and then through an outlet:.pipe.
Located around the outer tube .26 is an electro
magnetic inductor 32, known per se, fox ~o~~fectinc~ the
electromagnetic stirring of the metal 16 i°n :the mould 14.
The electromagnetic device 32 can consist of one or more
inductors.
In accordance with the present .,invention, the
inductor 32 is not fixed but can be displaced vertically
between a raised position according to .Figure 1 for free
stream casting and a lower~pos.ition according to Figure
2 for submerged-nozzle casting. The means for displacing
the inductor 32 can consist of any suitable means known
per se, for example three vertical threaded rods which
support the inductor 32 and which can be rotated syn-
chronously by a suitable motor.
According to a simple and efficient embodiment,
the inductor 32 slides vertically in a plurality of, for
example three, guide rods 50, the vertical movement being
effected by means of a crane (not shown). In the example
shown, the rods 50 are designed to position the inductor
32 in three different vertical positions defined by three
upper radial perforations 52 and two lower notches 54.
.~ ~t~40~~~.~
When the inductor 32 is raised into the position
according to Figure 1, it can be held there by manually
engaging a claw (not shown) in 'the upper notch 54 and
locked with the aid of a key (not shown) engaged through
5 the upper perforation.
2n the lower position, the inductor 32 rests on
the bottom of the ingot mould 10 and e:an be keyed by the
lower perforation 52. Although the embodiment illustrated
permits a third intermediate position (not shown), it is,
of course, possible to provide only two positions or to
provide more positions.
The inductor 32 can also comprise a separate
cooling circuit, which is indicated by the arrows 34 and
36 for the admission and the outlet of cooling water.
I5 Another feature of the present invention is the
monitoring of the meniscus level of the liquid metal in
the mould I4. This monitoring is carried out with the aid
of a radiation source 38, for example using cobalt, which
is arranged in the upper region of the annular space 24
and is associated with a scintillome~ter 40 disposed on
the opposite side of the mould I4. To reduce the risks of
exposure of personnel, this radiation source 38 is
located inside a protective cylindrical jacket 42, as
shown in greater detail and enlarged in Figure 3. This
protective jacket 42, which can, for example, be made of
lead, has a vertical slot 44 for the passage of .the
radiation. This protective jacket 42 can be rotated about
a vertical axis between an operative position shown in
Figure 3, in which the slot 44 is directed towards the
mould 14, and an inoperative position (not shown), in
which the slot 44 is directed against a vertical absorp-
tion block 46. By virtue of this arrangement, it is
possible for an operator to carry out work on the mould
14 without being exposed to the radiation from the source 38,
this radiation being absorbed by the protective block 46.
The actual measurement of the level will not be
explained in greater detail in view of the fact that the
use of a radiation source for measuring a level is known
par se.
