Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CONTINUOUS PRODUCTION OF METAL STRIP
The present invention relates to a method of and an
apparatus for the continuous production of a metal strip of
substantially final dimensions, in which molten metal is
cast and solldified on an endless, advancing cooling strip.
In a method of the above-mentioned type, the main problem
is to supply the molten metal as uniformly as possible to
the advancing cooling strip and indeed the supply should be
as free from turbulence as possible and the molten metal
should reach substantially the same speed as the cooling
strip.
In one prior method of the above-mentioned type
(substantially as disclosed in German Patent Specification
3,810,302), the outflow of the molten metal is regulated by
the gas pressure in the distributer, the distributer being
connected to a partial-vacuum chamber. Relatively thick
wall thicknesses are required for the distributer. The wall
thickness of the distributer bottom essentially determines
the metallostatic pressure which builds up at the height of
the casting opening of the duct extending through the
distributer wall. This pressure is, when the outflow is
unrestricted, greater than necessary for the supply of the
molten metal. With the assistance of the partial vacuum,
the effective metallostatic height can, it is true, be
reduced below the distributer wall strength, but for copper
alloys containing zinc, due to the high zinc vapour
pressure, partial pressure in the distributer must be
avoided. A method utilizing partial pressure is therefore
excluded from the beginning.
It is an object of the present invention to enable the
outflow speed of the molten metal to be regulated, while
avoiding the use of a partial pressure, so that the metal
flow is as laminar as possible and the speeds of the molten
metal and of the cooling strip substantially coincide.
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According to the present invention, there is provided a
method for the continuous production of metal strips of
substantially final dimensions, comprising the steps of
casting molten metal on an endless, advancing cooling strip
and solidifying the metal on the cooling strip, the method
including causing the molten metal to flow from a
distributer through a duct connected to the distributer,
the duct having substantially rectangular cross-section
with a small cross-sectional height in relation to its
cross-sectional width, the duct being inclined in the
direction of flow of the molten metal and opening into a
casting opening above the cooling strip, and regulating the
speed of the outflowing molten metal by retarding the
molten metal flowing in the duct by an electromotive force
opposed to the gravitational force.
There is thus provided a method whi_h regulates the speed
of delivery of the molten metal in a simple manner without
utilizing mechanically moved components.
An inclined duct is in fact already known from the above-
mentioned German Patent 3 810,302. However, an association
between the inclination of the duct and the regulation of
the casting speed is not apparent.
The retardation of the molten metal in a narrow, vertical
duct is known, for example, from European Published
Specification 0.374.260. The duct itself, however, ends in
a mould, opposed wide sides of which are formed by endless
strips running from above to below and narrow sides of
which are formed by movable side edges. Such a mould is not
suitable for applying the melt to a horizontally extending,
moving eooling strip. The braking effect on the molten
metal in the duet is produeed by two so-ealled "linear
induetion motors" lying opposite the wide sides of the
mould. At page 20, lines 10 - 15 of European Published
Speeifieation 0.374.260, however, it is stated that
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complete retardation of the molten metal cannot be achieved
due to the high metallostatic pressure. The inventor named
in this prior publication has not realized that the strong
throttling necessary for the casting of metal strips,
particularly of substantially final dimensions, i.e. of
particularly thin metal strips, is not possible because by
his vertical arrangement of the electromagnetic throttle,
he must accept the following disadvantages: If the
electromagnetic throttle is too weak, it can in fact be
extended in the direction of the throughflow, i.e.
vertically downwardly in the arrangement according to the
European Patent Specification. The possibility of
increasing the throttling force is in fact thereby
obtained, since more coils can be provided. However, this
overlooks the fact that the elongation of the duct in the
vertical direction causes an increase in the metallostatic
pressure, so that even a multiple increase of the
throttling can not make complete retardation possible.
By the inclination of the duct according to the invention,
as opposed to the vertical arrangement according to the
state of the art, it has become possible, while the
metallostatic pressure otherwise remains the same, to
increase the length of the throttle in the duct so that a
complete retardation is possible.
Advantageously, a range of 10 to 500 is selected for the
angle of inclination ~ of the duct.
In order to achieve a complete braking effect, the molten
metal is, according to one particular embodiment of the
invention, retarded over the entire length of the duct.
For space reasons in particular, it is recommended that the
electromagnetic field producing the electromotive force is
applied from above the duct.
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For preheating the duct, the side walls, comprising a
conductive material, are heated by the electromotive filed
which produces the electromagnetic braking force.
Additional conductive sheet material can be fed into the
duct and heated by the effect of the electromotive force.
The present invention further provides apparatus for the
continuous casting of metal strip, comprising a distributer
for the molten metal, a duct of substantially rectangular
cross-section connected to the distributer and having a
casting opening, the duct being downwardly inclined in the
direction of flow of the molten metal, a cooling strip
located below the casting opening and a linear induction
motor located above the duct and connected as an
electromagnetic brake for retarding the flow of the molten
metal down the duct.
The linear induction motor preferably extends over the
length of the duct.
For concentrating the electromotive field, a magnetic short
circuit beneath the duct may be provided.
For preheating of the duct, side walls of the duct may
comprise a conductive material, top and bottom walls
comprising a non-conductive material.
An embodiment of `the invention is described in greater
detail with reference to the accompanying drawings, in
which:
Fig. 1 shows a vertical section through a casting device
embodying the invention;
Fig. 2 shows detail A of Fig. 1 in an enlarged scale; and
Fig. 3 shows the cross-section of the duct through which
the molten metal flows.
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Fig. 1 shows a casting device for the continuous production
of a metal strip 1 of substantiall~ final dimensions,
comprising an endless cooling strip 2, which runs around
feed rollers 3 and 4, a distributer S for the molten metal
6 and an adjoinlng duct 7 extending downwardl~ in the
direction of flow of the molten metal at an angle of
inclination ~. A supply container 8 is connected before the
distributer 5.
The molten metal 6 flows downwardly from the duct 7 onto
the cooling strip 2 and is thus cast on the cooling strip
2, which is travelling in the direction of the arrow, and
solidifies on the cooling strip 2.
The duct 7 has a rectangular cross-section, with side walls
9, 10 and top and bottom walls 11, 12. A casting opening
7', into which the duct 7 opens, thus comprises a narrow
gap, the length of which is as wide as or narrower than the
width of the metal strip 1 which is to be cast (Cf. Fig.
3).
Above the duct 7, over the length thereof, there is
arranged a diagrammatically illustrated linear induction
motor 13, which is connected as an electromagnetic brake,
so that the molten metal 6 flowing in the duct 7 is
retarded by an electromagnetic force counteracting the
gravitational force. The flow of the molten metal 6 in the
duct 7 can be regulated so that the speeds of the molten
metal 6 and of the cooling strip 2 substantially coincide.
From Fig. 2, it can be seen that a magnetic short circuit
14 is arranged below the duct 7 for concentrating the
electromagnetic field. A cooling passage 15 is also shown.
Between each of the side walls 11, 12 of the duct 7, and
the induction motor 13 and the magnetic short circuit 14,
respectively, there is provided an insulation 16.
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For preheating the duct 7, the side walls 9, 10 comprise a
conductive material (for example graphite). The top and
bottom walls 11, 12 of the duct 7 advantageously comprise
a non~conductive material (for example silicon carbide
SiC). For preheating, additional conductive sheet material
17 (for example graphite) can be supplied into the duct 7,
and is heated under the effect of the electromotive force.
Example
The above-described casting device is suitable for example
for the continuous production of brass strip (CuZnO3) of
dimensions 5 mm x 400 mm.
For that purpose the molten brass 6, heated to about 1050C
is firstly supplied by the supply container 8 to the
distributer 5 and then flows from the distributer 5 through
the rectangular duct 7, which has an angle of inclination
~ = 45, and the cross-sectional dimensions 5 mm x 380 mm,
to the feed strip 2. The strip 2 is endless and is guided
over rollers 3, 4 which have a diameter of 1.2 m. A steel
band 2 with a thickness of 1 mm, a length between the
crowns of the rollers 3, 4 of 3600 mm and a width of 850 mm
is employed. The width of the casting strip 1 is determined
by lateral edges (not shown) advancing therewith.-
The molten metal 6 is indirectly cooled by water throughthe underside of the feed strip 2.
The speed of delivery is 20 m/min. By the utilization of
the linear motor 13 arranged above the duct 7, a thoroughly
laminar discharge of the molten metal 6 onto the strip 2 is
obtained. The speed of the molten metal 6 is substantially
the same as that of the feed strip 2.
As product, brass strips 1 with a satisfactory surface
quality and a with low-segregation and close grained
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structure are obtained.
