Note: Descriptions are shown in the official language in which they were submitted.
~2~7~ 20365-2319
The present invention relates to method and apparatus for
transporting liquid metal, and more particularly refers to a new and improved
system employing electromagnetic pumps for removing and transporting molten
metal from vessels, especially liquid aluminum in foundries.
Description of the Prior Art
Electromagnetic pumps are known. They utilize the motor principle
that a conductor in a magnetic field, carrying a current which flows at an
angle to the direction of the field has a force exerted on it. In all
electromagnetic pumps the fluid is the conductor.
German U.S. 29 24 116 and German Published Non-Prosecuted Application
DEMOS 31 41 774 and a paper by R. Hans at the German Foundry Convention in
Koblenz on June 15 and 16, 1982, entitled "New Electromagnetic Pumps for
Aluminum Casting", discloses different types of pumps for transporting liquid
metal. They are described on the one hand, as a canal pump and on the other
hand, as an immersion pump for transporting aluminum. An example of the canal
pump described in German U.S. 29 24 116 is a tube having a prismatic cross
section, a plurality of comb-like slotted magnet cores grouped about the
periphery of the tube and extending parallel to the flow direction of the
liquid metal, electromagnetic coils respectively connected to one of the phases
of a polyphase alternating current and mounted respectively on teeth of the
plurality of comb-like magnet cores, nix of the coils of which n equals an
optional whole number and x er~luals the number of a-c phases being mounted on
each of the magnet cores, the magnet cores being disposed in planes extending
at an angle other than 90 to the
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surface of the tube. Similarly, an example of an induction immersion pump
described in German Application No. DE 31 41 774 comprises a temperature-
resistant housing extended above and below a given liquid level, a channel
disposed in said housing at least partially below said given liquid level,
said channel having a substantially rectangular cross section with wide and
narrow outer surfaces, a comb-shaped coil core being disposed in said housing
and having teeth pointing toward said channel, copper induction coils
disposed on said coil core at said wide outer surface of said channel, and at
least one feed line and at listen discharge line for inert gas disposed in
lo said housing above said given liquid level.
While the canal pump can handle larger outputs, it has the
disadvantage that it is not self-priming and therefore must first be filled
With liquid metal at the start of the casting process. Although the immersion
pump is self-priming, it cannot provide as high an output as a canal pump
because of temperature problems.
Summary of the Invention
An object of the present invention is to provide a system for
transporting liquid metal which combines the advantageous properties of both
pumps and therefore results in a self-priming pumping device with high output.
With the foregoing and other objects in view, there is provided
in accordance with the invention a system for transporting molten metal
comprising a vessel, a body of molten metal in the vessel, an electromagnetic
immersion pump capable of self-priming with an inlet side and a discharge side
immersed in the body of liquid metal, a transport canal having one end
connected to the discharge side of the electromagnetic immersion pump and the
other end of the transport canal extending outside the body of liquid metal, an
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electromagnetic canal pump incapable of self-priming with an inlet side and
a discharge side disposed outside the body of liquid metal, said other end of
the transport canal connected to the inlet side of the electromagnetic canal
pump, and a discharge tube connected to the discharge side of the electron
magnetic canal for discharge of the liquid metal.
Other features which are considered as characteristic for the
invention are set forth in the appended claims.
Although the invention is illustrated and described herein as
embodied in a method and apparatus for transporting liquid metal, it is
nevertheless not intended to be limited to the details shown, since various
modifications may be made therein without departing from the spirit of the
invention and within the scope and range of equivalents of the claims.
Brief Description of the Drawing
The invention, however, together with additional objects and
advantages thereof will be best understood from the following description when
read in connection with the accompanying drawing which diagrammatically
illustrates a system for transporting molten metal in which a vessel containing
molten metal has immersed therein a self-priming electromagnetic immersion
pump from which extends a transport canal which latter is connected to an
electromagnetic canal pump incapable of self-priming.
Detailed Description of the Invention
In accordance with the invention for transporting liquid metal,
an electromagnetic immersion pump and an electromagnetic canal pump, as are
known per so, are arranged in tandem. This has, first, the advantage that the
canal pump can be flooded by the immersion pump, eliminating the need for
expensive priming devices of the mechanical type, which have heretofore been
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necessary for canal pumps. In this manner, some problems which heretofore had
to be considered due to temperature shocks in priming the canal pumps can now
be avoided.
It would at first appear that the pumping output of two series-
connected pumps would be determined more by the output of the weaker pump, but
surprisingly this is not the case with electromagnetic pumps. Since there are
no built-in components in the transport canal and the pumping is accomplished
only by magnetic traveling fields, an immersion pump can very well be made
with a low output but with a relatively large canal cross section. The reason
for this is that the output of the immersion pump is limited not so much by the
possible canal cross sections but rather by the maximum possible heat of
dissipation in the coils and in the core. An immersion pump can therefore be
constructed which has a canal cross section which corresponds approximately to
that of a canal pump. yule such an enlargement of the canal of the
immersion pump which exceeds the optimum size reduces the output of the former
and increases the dissipation loss in the coils and in the core, the pump can
nevertheless pump liquid metal without overheating for a short time. This
short time is adequate however, to flood the canal pump. Upon flooding the
canal pump, the immersion pump can then be switched off while the canal pump
thereupon takes over the entire output. The pump canal of the immersion pump
then serves only as a pump line.
In an embodiment, the output of the canal pump is considerably
large, 10-50% or more, than that of the immersion pump. This combination of
the use of the two pumps, which are of course more expensive than a simple
immersion pump, has distinct advantages. Actually only the output of the
canal pump now determine the properties during continuous operation, while
the immersion pump is used only for flooding the canal pump incapable of self-
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priming.
In a further embodiment of the invention the immersion pump is
designed only for short-time operation and in particular, to no longer use
any cooling and expensive, efficiency-increasing devices which are normally
associated with the immersion pump. Many of the problems which must be taken
into consideration in connection with immersion pumps, occur only as a
result of continuous use of the immersion pumps. For example, in extended
operation of an immersion pump, the coils and the core become considerably
hotter than the pumped liquid metal, causing problems with the Curie point of
the magnetic materials to arise and oxidation problems with copper coils.
In short-time operation of immersion pumps such difficulties are negligible,
consequently various measures for intermittently operated immersion pumps can
be dispensed with, such as flushing with inert or cooling gas and the use of
expensive materials with a particularly high Curie point.
In a method for transporting liquid metal, the self-priming
immersion pump is operated only a* the start of the pumping, until the canal
pump, not self-priming, is flooded, and the pumping is then continued
exclusively with the canal pump. This method avoids the heretofore customary
mechanical flooding of tile canal pump from a pouring vessel with the problems
of the temperature shock and other disadvantages. The use of this
combination eliminates the need for the supply vessel for liquid metal to be
accessible for ladling devices.
In a further embodiment the output is controlled in operation
exclusively by the canal pump in known manner. After the canal pump is
flooded, the immersion pump gem therefore be switched off entirely, whereby
the temperature of the entire system of the immersion pump corresponds
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approximately to the malting temperature of the metal. The control of the
output, for instance, for precisely apportioning the pumped liquid metal, is
accomplished only by the canal pump, so that the proposed system is not any
more difficult to 1l2ndle titan the known individual systems.
The proposed arrangement is particularly well suited for foundries
in Lucia large outputs are required. In addition, the use of immersion
pumps in combination with a canal pump may also be employed for liquid metals
which have a haggler melting temperature than aluminum since the problems of
the immersion pump occur mainly in long-time power operation. An immersion
pump itch is suitable in continuous operation for aluminum can also be used
for a short time for metals with very much higher melting points.
An embodiment example of the invention is shown schematically in
the drawing:
Vessel 1 contains a liquid metal melt 2, in which an electron
magnetic immersion pump 3 is immersed. As indicated by arrows, the liquid
metal is conducted through the immersion pump and via a transport canal 4 to a
canal pump 5, from which it is then conducted to a discharge tube 6. The
start of the pumping can be accomplished by the immersion pump I. From the
time at which the canal pump 5 is flooded, the pumping is done by the canal
pup alone. Flooding the canal pump from the outside, which has been
necessary heretofore is now unnecessary.
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