Note: Descriptions are shown in the official language in which they were submitted.
~4336
The invention relates to a stirring process and device for
improving the quality of a continuously cast metal.
With the standards of quality for metals, steel in partieular,
becomi~g more and more severe, it is neeessary, in order to avoid
.r~5 downgrading of quality or rejects, to obtain a greater and greater
consistency of quality in production. This is in partieular the
purpose, in production with eontinuous easting, of the devices for
:~stirring the metal during casting, i.e. in the ingot mould and
during solidifieation at levels situated below the ingot mould
10 where a still liquid zone frequently called "liquid well" is to be
found in the middle of the cooling ingot. Such stirring, on the one
hand, reduees the length of the crystals during solidification and,
on the other hand, distributes the impurities whieh have not risen
to the surfaee on top of the ingot mou~d.
~A 15 Eleetromagnetie devices are known for stirring billets or
blooms operating by the action of a rotary magnetic field passing
through the billet during solidification, the magnetic field being
.~ created by inductor eoils disposed in -the ingot mould or therebelow.
Sueh a deviee is deseri~bed for example in tne Freneh patent applieation
of the applicant Published under the number 2355392 or in US patent
3153820.
.
Stirring deviees are also known for the eontinnous easting
of ~labs.
One of these deviees deseribed in the Freneh patent n
2 231 454 of the applieant comprises an inductor disposed inside a
-~ guide roll for the slab below the ingot mould, and creating there-
about a creeping field so as to create lateral movement of the still
~ liquid part situated behind the eooled skin.
-- A device is also known for stirring slabs in a continuous
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-'30 easting ingot mould described in the French patent of the applieant
published under the n 2 393 632 and which comprises an inductanee
situated in the ingot mould and ereating a creeping fild either in
the lateral direetion to ereate horizontal movement of the liquid
~metal during easting, or in the vertieal direetion to create a
rising or descending movement of the liquid metal.
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~1~4336
The processes described above all have the disadvantage,
because they are fed with AC current and because the magnetic field
created must pass through a considerable air space, of requiring
a considerable magnetizing power for a reduced active power required.
The result is considerable losses in the copper, low yield
and considerable equipment for the energy supply.
The invention aims at providing a process and device for
improving the quality o-f continuously cast metal which have, for
the same efYects as described above, a distinctly improved yield
and an increased stirring movement.
The process is characterized in that an inductor is rotated
producing a fixed magnetic field with respect to the inductor about
an axis parallelto at least one of the surfaces of the cast product.
Depending on the case, the relative movement will be a
rotational movement about an axis perpendicular to the casting
axis or an axis parallel thereto.
Devices corresponding to this process will comprise then
means for producing a constant magnetic field consisting of
permanent magnets or electromagnets, the magnetizing power being
then supplied in the second case by a DC current as in a synchronous
machine rotor.
Furthermore, means for rotating these devices are provided
so as to create the relative move~ent of the magnets and thus cause
eddy currents in the liquid metal and the production of forces for
circulating the liquid metal.
The accompanying figures, relating to two variations of the
device for implementing the process, will help in understanding the
invention, in which :
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Fig. 1 shows in a diametrical section a stirring device for
`~ the continuous casting of billets ox blooms.
',t;~ Figs. 2, 3 and 4 show a stirring device for the continuous
casting of slabs.
Fig. 2 shows a slab during continuous casting.
Fig. 3 shows schematically the stirring principle.
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. Fig. 4 gives the detail of a stirring roll.
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In ~ig~ 1 there is shown at 1 a billet cooling under the
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ingot mould, the still li~uid metaL being shown at 2. A stirring
~device 3 is placed around the billet It comprises an inductor 4
having a cylindrical yoke 5 in which are fixed two inductor poles
- 5 6 made from a magnetically hard matçrial so as to create a uniform
-~; field passing through the cylindrical space occupied partially bythe billet. So as to facilitate the construction, these poles may
be made by stacking relatively thin elements 7 disposed along
;~ generatrices and bonded together.
A material particularly well adapted to forming such a
stack is magnetic rubber which can be disposed in a uniform layer
either pre-magnetized or magnetizable after placing, ~or example
by disposing inside the cylindrical space available~an alternator
rotor in which will be fed a suitable excitation current.
, .. .
~` 15 Ioke 5 is disposed in two mounting elements 8 and 9 and the
whole of inductor 4 is placed in a steel casing 10 which has a lower
disc-shaped part 11 and a lateral cylindrical part 12 so that inductor
4 may rotate inside casing 10.
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~ For this purpose, rollers 13a and 13b are provided rotating
.,
about pins connected to mounting elements 8 and 9 and travelling
in races 14 and 15 integral with casing 10.
Mounting 8 has a toothed wheel 16 by means of which the
inductor ~ driven byelectric motor 17 and gear 18.
A cover 19 made from ordinary steel serves as a mngnetic
shield for the leakage flux in the same way as wall 11.
The assembly comprising inductor 4 and casing 10 is capped
with a water jacket 20, made from stainless steel for example,
comprising a vertical double-walled tube 20a and a double-walled
~r disc 20b, so as to protect the inductor from the radiation of the
billet and the projections of metal coming from the ingot mou~d.
This jacket will have a stream of water passing therethrough.
The operation is the following : rotation of inductor 4 under
the action of motor 7, causes rotation of the magnetic field
~- created which passes through the billet~ so that the eddy currents
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O generated therein cause by action on this field an energetic
rotational movement of the still liquid part 2.
Instead of poles made ~rom hard magnetic material~ they
:,.
could of course be made from magnetically soft steel surrounded by
an inductor winding through which passes a DC current. Sliding
electric contacts may be provided in this case between the windings
-~ which are placed in a system which rotates and the fixed part where
~ the electric current is fed.
,. ,u .
A device with permanent magnets such as described above
lends itself remarkably well to installation at the level of an
ingot mould. In this case, the rotating assembly will be placed
preferably in an annular enclosure which surrounds the ingot mould
and if necessary is filled with water. Only the drive shaft of the
motor gear will pass sealingly therethrough.
` 15 With respect to the solutions with a fixed electromagnetic`~J inductor supplied with AC current, the system proposed has, on the~ one hand, the advantage of greater simplicity and, on the other hand,
~~ allows fields of greater strength to be produced and not requiring
. .
any reactive power other than that required by the motor which will
only supply the power required for stirring, mechanical losses and
~i losses by eddy currents in the solidified part of the billet and
in the fixed parts (screens and water jacket).
As a variation, the diametrically opposed inductor poles 4
may be given a helical form so that the electric currents generated
in the billet by rotation of the inductors are inclined with respect
to the casting axis and generate forces which have a component
parallel to the casting axis, either in the rising direction or
:~ in the descending direction, so as to create helicai stirring, which,
as explained in French patent application n~ 78 15304 of the applicant
provides an improvement in the quality of the metal greater than that
given by simple rotary stirring.
In Fig. 2 which shows schematically a slab 21 during continuous
casting in the part situated below the ingot mould, as well as the
pairs of rolls 22 for guiding this slab, there are shown certain
pairs of rolls such as 221, 222, 223, 224 which have the particularity
of being provided at each end with cylindrical permanent magnet
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-~1 1144336
inductors 23 and 24 on each side of the slab and magnetized
transversely in an homogeneous way so that the lines of force of the
magnetic ~ield are perpenaicular to a diametrical plane.
~7
-l The magnetic axes of the permanent cylindrical magnets 23
j- 5 and 24 are orientated with respect to each other as shown in ~ig. 3
and rotate at the same speed, different from that of the guide rolls
and their arrangement inside the guide roll will be described further
-`1 on.
. .
~ With reference to Fig. 3 which gives schematically the
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`!., 10 orientation of the magnetic axes of magnets 24 situated on one side
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of the slab and designated by 241A, 241b, 242a, 242b, 243a, 243b,
244~ and 244b, the straight arrows passing through the centre of the
rolls indicate at a given moment the direction of magnetization and
the curved arrows situated in the circles representing the magnets
give the direction of rotation imparted to these magnets. It can be
seen that all the magnets 241a, 242a, 243a, 244a rotate in one direction
~ and that the magnets 241b etc.... which are opposite thereto rotate in
- the other direction.
It can be seen furthermore that from a magnet 241 to a
magnet 242 the directions of the magnetic axes are staggered by a
,,,~ .
-~, quarter of a revolution in the direction of rotation of the
corresponding magnets going from left to right.
By causing the magnets previously orientated as shown in
''e ` Fig. 3 to rotate in synchronism, there is created a creeping field
and the liquid metal situated in the middle part of the slab is
driven in the direction of arrow F (Figs. 2 and 3). If the same
arrangement is made on the other side of the slab with inductors
23 but by causing them to rotate in the opposite direction, the
liquid metal will flow in the direction of arrow F', so that there
will be created stirring by closed circuit circulation along
contours such as C.
Fig. 4 gives the detail of a stirring roll such as 22 in the
vicinity of one of its ends which contains a cylindrical magnet 24.
Hollow guide roll 22 rotates in bearings 25 situated at both its
ends. It is made in three parts, a central part 22a and two end
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" plugs 22b. The central partl i sl~u3a~eÇ so as to receive at each of
its ends the cylindrical magnets 24 situated inside a cylindrical
~ sleeve 26 made from a non-magnetic steel. The magnets are rotated
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by a shaft 27 rotating in roller bearings 29 and 30 housed in parts
22a and 22b. A flow of cooling air is provided between shaft 29 and
~j
plug 22b, and countersinking 32 and 33 allows the air to reach the
annular cylindrical space 34 situated between sleeve 26 and guide
roll 22 and to leave therefrom to go to the other end thereof
through a central channel 28. Arrows 35 and 38 show the flow of
10 cooling air.
The magnet may be formed by a stack of ferrite rings in
sleeve 26. It may also be formed from a ferrite powder mixed with
thermo-setting resin then injected and hardened.
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