Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Process and Device for Feeding metal into a molten metal
bath
The invention relates to a process for feeding metal to a
molten metal bath, in particular for the purpose of melt-
in down solid metal such as for example scrap metal or granular dross, and relates also to a device for this.
With a view to protecting the environment, and in recogni-
lion of the limited availability of raw materials, in-
creasing efforts are being made to recycle raw materials.
10 This includes metal which appears in large amounts in in-
dustrial and household waste and applies in particular to
the recycling of used cans as metal cans are being employ-
Ed increasingly today as containers for drinks ox various
kinds.
15 One possibility for recycling is to introduce the scrap
metal into a molten metal bath in order to melt it down.
In that case it is particularly important for the solid
metal to be immersed as quickly as possible in a turbulent
metal stream in order to minimize oxidation of the metal
20 and to increase the efficiency of melting. Counterproduc-
live in this respect is that thin walled metal such as in
scrap cans is much less dense than the melt; as a result,
the scrap metal tends to remain on the melt surface for a
long time. This is unfavorable in view of the above men-
25 toned efforts to minimize metal oxidation and to increase melting efficiency.
On the other hand processes exist in which the melt is
made to rotate in a container so that a whirlpool is form-
Ed near the middle of the melt, and the metal to be melted
is introduced into the whirlpool. In practice it has been
found that the metal still tends to stay on the surface of
the melt, also in the whirlpool. Furthermore, the turbo-
fence produced at the surface of the melt and at the place
where the scrap is introduced into the container creates
an excessive amount of dross. Also, the heat transfer from
10 the melt to the metal is small and the resultant efficient
cry of melting is unsatisfactory.
The object of the present invention is therefore to devil-
ox a process and device of the above mentioned kind by
means of which metal which is to be melted sinks as fast
15 as possible below the surface of the melt and is therefore
excluded from contact with air as quickly as possible. The
process and the device are, furthermore, intended to be
usable in many different ways and in particular should
enable better mixing-in of alloying additions made to the
20 melt. Also, it should be possible to melt down granular
dross to achieve a high metal yield without the use of
salts.
This object is achieved by way of the invention in that at
least part of the melt is divided, and each part is made
25 rotate in a direction counter to that of the other part,
so that at least two rotating streams or "rolls" of molten
metal are produced, the middle axes of which are at an
angle to each other, and the metal to be melted is added
at that place where the two rotating "rolls" or streams of
I 2
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molten metal meet.
If the scrap, dross granules or alloying additions are fed
to the melt from above, then the stream of metal left of
the direction of metal flow is preferably set in motion
rotating clockwise, the stream on the right hand side of
the direction of flow in an anti clockwise rotation (Vega-
live kinetic moment opposed to positive kinetic moment).
As a result, at the place where the two whirling streams
of metal meet, a channel or furrow is formed into which
10 the scrap, dross or alloying additions that are to be
melted are sucked. Also the melt is repeatedly and thou
roughly mixed due to this movement; there is no stationary
melt surface and so no metal is held there floating on the
surface.
15 As soon as the two whirling melt streams meet, additional
turbulence is created - which also ensures intimate con-
tact between the melt and the metal to be melted down. At
the same time thorough mixing of the solid and liquid
phases making up the various parts of the melt is promote
20 Ed It must also be mentioned that the oxide skins are de-
stroked in the process. Both the heat transfer coefficient
an the melting rate are considerably increased. Briefly
after the whirling streams strike each other the component
of rotation is lost and the melt flows almost without any
25 agitation into the subsequent channel or a subsequent
dross treatment station.
In order to split the melt into two counter-rotating
streams or "rolls" two versions of the process according
4:2
to the invention can be employed. In both cases the said
rotating or whirling streams are produced via two pipe
lengths which are joined together in such a manner that
their central axes form an angle. The feeding of the metal
then takes place at the place where they are joined as it
is also there that the two whirling streams meet.
One case is such that the melt is made to flow approxima-
tell perpendicular to the central axes and approximately
tangentially into the cross section of the pair of pipe
10 sections. The other method makes use of electrodynamics
forces, in particular electromagnetic forces, to set the
melt into such a motion that it rotates about the central
axes. Both methods can also be used in combination.
A device of the kind described above ensures that a supply
15 channel or pipe for the melt is provided, connecting up to
a feeder station made up of at least two ridded pipe sea-
lions, the central axes of which form an angle such that
the feeder station has a Y shape. The melt streams in the
two pipe lengths can be made rotate about the middle axis
20 of the pipe length through which it passes. An opening for
feeding the metal to the unit is provided at the place
where the two pipe lengths meet.
One method for transferring the melt from the supply chant
not into the pipe sections is to divide the supply channel
25 into two branches which feed the melt approximately per-
pendicular to the central axes and approximately tangent
tidally to the cross section of the pipe length. As the
metal flows into the pipe length in this manner, it is dip
SLY
vented from its original direction of flow, follows thinner wall of the pipe and is thus made to adopt a rotate
in, whirling movement.
Another version of transferring the melt is such that the
supply channel connects up to the junction point of the
two lengths of pipe which are enclosed by two sleeves. As
a result of back pressure on the melt, the pipe lengths at-
so become filled with melt. The sleeves then generate
electromagnetic forces which act on the melt and cause it
10 to rotate. As a result one obtains two standing, rotating
streams or "rolls" of molten metal; the scrap added is wet
even better due to the direct impingement by the incoming
metal from the supply pipe, and is pushed forwards by the
two whirling streams of metal.
15 One of the most important advantages of this device is
that the melting takes place in the absence of air. Cons-
quaintly, the metal loss is reduced because of the Damon-
wished degree of oxidation and dross formation. The high
relative speed of movement between the solid and liquid
20 phases ensures that maximum heat transfer is achieved with
this device i.e. the rate of melting is substantially it-
creased. The very small dimension of feeder station ensure
that the heat losses are small. Also, because of the skimp-
Lucite of the device the investment costs and maintenance
25 costs are insignificant. The device permits conventional
scrap metal or other waste to be melted down, and allows
alloying elements or other melt treatment substances to be
added in any desired form. This applies in particular to
the addition of dross granules from treated dross; these
can be melted down without loss of metal and without any
accompanying addition of fluxing agents such as salt.
Further advantages, features and details of the invention
are revealed in the following description of preferred ox-
amplified embodiments and with the help of the drawings
viz .,
Fig 1 A perspective view of a partly sectioned unit formulating metal.
Fig 2 A perspective view of a further exemplified embo-
dominate as in fig 1.
A unit for melting metal, for example can scrap, is such that molten metal 1 is taken from a furnace - not shown
here - and conducted via supply channel 2 to a feeder stay
lion R for the metal which is to be melted. From there the
15 molten metal 1 then flows back into the furnace, or for
example a dross treatment station, via channel 3.
The feeder station R according to jig 1 comprises essenti-
ally two pipe lengths 4 and 5 arranged in a Y shape; con-
netting up to pipes 4 and 5, approximately perpendicular
20 to their central axes A and B, are branches 6 and 7 no-
spectively of supply pipe 2. The pipe lengths 4 and 5 meet
at an opening 9 which serves as a charging point 8 for the
metal which is to be melted down; from that point the
pipes 4 and 5 continue as one in the form of a pipe 10
25 which joins up with channel I The central axes A and B
run at an angle w to each other. At the end away from the
charging point 8 the pipe lengths 4 and 5 are closed off
- by lids 11.
Situated above the charging point 8 or opening 9 is a silo
12 from which metal that is to be melted - not shown here
- is introduced by means of screw conveyor 14 to the melt
1 through the opening 9.
The melt 1 enters pipes 4 and 5 via supply pipe 2. As it
enters approximately perpendicular and tangential to these
pipe lengths 4 and 5 via branches 6 and 7 rest. of pipe 2,
10 the melt is forced into a circular motion inside the pipes
4 and 5 around the central axes A and B.
The direction of flow of the melt 1 into pipes 4 and 5 is
such that the melt rotates in the clockwise direction x in
pipe and in the anti clockwise direction y in pipe 5.
15 Both streams or "rolls" of melt meet in the region of the
opening 9 below the silo 12. Arrows 15 indicate the con-
tinted path of the melt 1. If metal from the silo 12 is
now added, it inters the furrow formed by the melt streams
- for simplicity indicated here by arrows 15 - is "sucked"
20 in by the melt and completely wet by it. As they meet the
"rolls" of molten metal destroy each other - which pro-
motes further thorough mixing of the metal additions and
the molten melt 1. In pipe 10 the rotational movement of
the melt is eliminated and the melt flows on quietly into
25 a dross treatment station or the like - not shown here.
In the version according to fig 1 the feeder station R,
likewise comprises two closed pipe lengths 4 and 5, the
I
central axes A and B of which run at an angle w Jo each
other and meet at a point where there is an opening 9 next
to a charging inlet 8 for the metal which is to be melted
down. Here the melt is introduced to the feeder station I,
via pipe 22 which runs in the direction of flow of the
melt z and meets the feeder station R, directly at the
join 23 of both pipe lengths 4 and 5 below the charging
inlet 8.
Provided on pipe lengths 4 and 5 are sleeves 24 and 25
10 rest. which act as stators and induce a rotary field in
the melt, and this such that the melt in pipe 4 rotates in
the clockwise direction x while the melt in pipe 5 rotates
in the opposite direction. The rotation of the melt can
also be achieved for example by providing pipes 4 and 5
15 with the rotors of a motor - not shown here.
As a result again two counter flowing streams or "rolls" of
melt are achieved and with that the above described gape-
city for taking in metal which is to be melted. The
sleeves 24 and 25 can according to the invention also be
20 employed to assist in the formation of the "rolls" of melt
in accordance with the version of the feeder station R in
fig 1.
