Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to continuous casting of steel with
emphasis on true continuity.
Generally speaking it is a known fact that for small cross sections
of the casting the throughput of steel is correspondingly small; the through-
put may be about 500 killograms per minute maximum. On the other hand, it
has to be observed that the temperature of the steel in the ladle drops
during the casting process so that the residence time of the steel is limited.
Therefore if relatively large quantities of molten steel are to be processed
in that manner and involving particularly castings of small cross sections,
it is necessary to cast a plurality of such small ingots simultaneously.
On the other hand it has to be observed that the number of castings cannot
be increased arbitrarily because the distance between the point of charging,
e.g., a tundish serving as a distributor for the steel, and the various
locations of discharge into the respective molds may well be different for
the different molds, for example, some molds are positioned relatively far
from the charge points of the tundish and the temperature drop may be
significant. One can, therefore, say that for a given casting machine there
is a limit in the number of castings that can be produced, and for small
cross sections the amount of steel processed in that manner is well below
the maximum throughput of the concurrently operating steel converter.
In order to obtain the maximum possible use of a given casting
machine a timing relation is necessary between the steel production and the
casting operation. Any interruptions in the casting process provide
detrimental feedback to the steel making process. From a different point
of view, it has to be observed that if one provides a maximum number of
cas*ings for a given throughput of steel then the resulting ingots and
billets may be larger than needed or than can be processed, for example,
within a particular time frame. This in turn will lead to a reduction
in equipment use, the equipment will run at less than maximum capacity.
3Q Another problem, of course, is that in between two melts or in between two
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sequences of continuous casting or both, the casting machine runs idle.Also, in most instances, the tundishes have to be changed from time to time.
All that amounts to an interruption in the production.
It is an object of the present invention to provide an improved
continuous casting machine and method operating independently from the
intermittency of steel production but permitting true, uninterrupted continu-
ous casting as a whole, and permitting repairs and replacement of critical
portions without shut down of the machine as a whole.
The invention provides method of continuous casting a plurality
of castings in parallel using a tundish comprising the steps of, extracting
a plurality of flows or steel from the tundish; individually controlling
the flows of steel; and heating the tundish to obtain heating of steel as
temporarily stored in the tundish.
From another aspect, the invention provides apparatus for continu-
ous casting a plurality of castings in parallel which includes a plurality
of molds for continuous casting, the improvement comprising a tundish
having a plurality of feeder channels for respectively feeding the molds of
the plurality; means for individually controlling the flow of steel in the
feeder channels; and means for heating the tundish to obtain heating of
steel as temporarily stored in the tundish.
In the preferred embodiment of the present invention a tundish
is heated, preferably using strategically distributed induction heaters,
and has a plurality of output channels or ducts each ending in preferably
rapid-exchange type casting heads for feeding individual molds. The
individual tundish outlet channels are separately and individually closeable
so that an individual casting head-mold configuration can be operatively
disconnected from the tundish without interrupting the casting process as a
whole.
The inventive machine therefore permits a proper adjustment between
steel production and the continuous casting proper whereby the heated tundish
operates as a temporary store, reservoir, or buffer which maintains the steel
at the necessary temperature even if the residence time for that steel is
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relatively long. As a practiced rule, it was found to have the amount of
steel stored in the tundish to be larger than the threefold amount that
leaves the tundish per minute.
It was found that the pouring period of the ladle is much better
utilized with such equipment and the steel has the same temperature in each
of the outlets irrespective of the distance of any of the outlets from the
charge point of the tundish. Therefore there is in particular no temperature
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differential among the several outlets and, most importantly, the temperature
of the steel pouring into the individual molds is no longer dependent upon
the residence time of the steel in the tundish even though the period of
time between the extraction of such steel from the steel making process
up to the time it is poured into the mold may vary greatly. Also, the
heated tundish buffers the intermittency of steel production and ladle
pouring.
While the specification concludes with claims particularly pointing
out and distinctly claiming the subject matter which is regarded as the in-
vention, it is believed that the invention, the objects and features of the
invention and further objects, features and advantages thereof will be
better understood from the following description taken in connection with
the accompanying drawings in which:
Figure 1 is a lateral, section view through equipment improved
in accordance with the present dimensions,
Figure 2 is a top view of the device as shown in Figure 1,
Figure 3 is a detail of the machine shown in Figure 1, in section
view but on an enlarged scale, and
Figure 4 shows a modification of the preferred embodiment of the
present invention also in section view, analogous to Figure 1.
Proceeding now to the detailed description of the drawings Figures
1 and 2 show a tundish 1 with plural outlet channels or feed ducts, each
duct or channel being covered by a cover 5. The tundish itself is covered
by a top 3. Each of the outlet channels 4 is constructed as an upwardly
sloping conveyor and steel is moved up against gravity by electromagnetism.
Turning the energization off amounts to a shu~ down of steel flow ir. the
respective duct; the top of the conveyor will always be above the steel
level in the tundish.
The ducts are releasably connected to tundish 1 and each is provided
3~ with a casting head 6 being of the rapid exchange variety. A plurality of
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molds 6a are respectively disposed un~er the casting heads 6 and serve as
outlets to feed the respective mold 6a.
The tundish 1 is, in addition, provided with a plurality of in-
ductive heaters 2 which are more or less irregularly arranged along the
bottom of vessel 1. The inductive heaters are in particular removably
connected to tundish 1. The molten material, i.e., steel is fed by means
of a siphon 16 into the tundish, and the arrangement of inductive heaters
ensures a uniform heating of the molten steel in the tundish so that
particularly the steel flows into the channels and into the molds at the
same temperature.
The Figure 3 shows an individual casting head of the quick 7
change variety on an enlarged scale. The head 6 has a slide path or sliding
guide 7 which is part of a slide lock having also a seal 8. This particular
locking and connection mechanism is located away from the mold to facilitate
rapid exchange of the casting head. The slide guide 7 and the seal 8 could
have horizontal disposition instead of the vertical one illustrated.
The head 6 itself is comprised of a trough or channel shaped body
9 having a connection 10 at its inlet side for communicating with the top
of the conveyor. Each head 6 has an opening 11 in which is inserted an
immersion type feed pipe 12 which dips into the mold. The head 6 is addi-
tionally provided with a lid or cover 13 having a closeable opening 14 being
located opposite the outlet 11.
Figure 4 illustrates a mechanical slide lock and gate 15 for the
molten material in a duct 41 leading from the tundish to the rapid change
casting head 6'. The duct 41 can also be separated from this head as well
as from the tundish. The steel flows in the ducts or channels 41 by the
force of gravity.
The machine as illustrated works as follows. Molten steel flows
from the ladle through this externally disposed and exchangeable siphon 16
into the heated tundish 1. The particular steel may be metallurgically and/or
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thermally treated in the tundish and from there the steel flows through
electromagnetical (Figure 1) or gravity ~Figure 4) conveyor channels towards
individual exchangeable casting heads.
In the preferred embodiment illustrated in Figures 1, etc., the
tundish is constructed as an induction channel furnace of elongated configur-
ation, basically being arranged in parallel to the row of molds 6a. The
several inductor heaters 2 are independently controllable to obtain a
constant temperature of the passing steel, being temporarily stored into
the tundish whereby particularly a constant distribution of the temperature
over the length of the tundish is obtained. Accordingly, the various
castings as produced by the several molds are produced with steel having the
same temperature. In particular the temperature of the steel as it pours
into the mold being the farthest from the siphon is not, or only very insig-
nificantly, different from the temperature of the steel flowing out of the
casting head being positioned the closest to the siphon 16. Any temperature
difference is really only the result of differences in operation of the
controlled induction heaters, and has very little relation to the length
of the flow path of the steel from the siphon to the respective casting
heads and mold. It can also be seen that the tundish 1 can be made quite
long and the number of molds being fed can be selected accordingly.
The fact that the tundish works as a heated, temporary store and
reservoir permits an entension of the period of casting because any loss in
temperature, e.g. in the ladle is readily compensated. The tundish serves
also as a bufer to take up the difference in the timing of the steel-making
process on one hand and the casting machine and its operation on the other
hand. The storage capacity of the tundish should be about three times the
rate of outflow per minute through all of the channels and molds. In other
words, the heated, temporary storing of the molten steel permits a relative
shortening of the ladle pouring period in relation to the total period of
casting. In general, the period between extracting the molten steel from the
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steel-making facility and actual charging of the molds can be varied.
Utilizing the maximum permissible residence time of the steel in the ladle
permits a further extension of the casting period as a whole, and it is
for this reason that the tundish buffers the intermittency of steel-
making to arrive at a truly continuous casting.
The particular casting and distributor channels 4 are conventionally
used for the separation of slag from the steel. It will also ~e observed
that the machine of Figure 1 exhibits a comparatively small almost ~eglible
ferrostatic pressure at the outlet of the casting head which in turn means
that the falling stream of poured steel penetrates very little into the
casting ingot being formed in the molds 6a. The equipment is provided for
automatically interrupting the flow of steel in the case of any interference
and disturbance in the respective conveyor channels so that followup
interference as it is conventional in stopper control equipment will not be
observed here. Either the electromagnetic conveyor is turned off, or the
slides ~15) are closed.
It is important to realize that the tundish is covered and contains
a significant amount of steel. Due to the heating the upflow of non-metallic
inclusions is enhanced, which in turn means a further increase in the
quality of the castings. The particular tundish permits in addition metallur-
gic treatment of the steel such as alloying de-sulphurization, etc. The
treatment of course, must be controlled in dependence upon the rate of flow
of the steel as it passes from the siphon to the various outlets.
A particularly advantageous side effect here is the thermally induced
flow of the molten steel in the tundish on account of the operation of the
induction heaters. This convection or convective flow can be used for
treating the steel in the tundish. Moreover, one obtains a rapid homogeniza-
tion and a rapid uniformity in temperature. Since each mold is fed individu-
ally and since the flow of steel can be metered individually as to each mold
and casting head one can also provide for individual metallurgic treatment,
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for example, in the respective channel 4. In other words, it is not required
that all of the castings result in the same kind of ingot. From an overall
point of view, it will readily be appreciated that the inventive method and
equipment amounts to a significant expansion of continuous casting as a
technique and a particular machine permits optimized matching of the through-
put in the steel-making process to the casting process under the inherent
constraints which such a casting process poses particularly when the cross
sections of the ingots are to be rather small.
The particular opening 14 in head 6 is provided for the purposes
of control and supervision of the respective casting head so that the wear
and tear of the head can readily be observed and monitored. If an exchange
is needed, the flow of steel to this particular casting head is stopped
without however, interrupting the operation of the other heads and molds
and the particular head is being exchanged by a new one.
The utilization of electromagnetically operated conveyor channels
for the steel replaces stopper control and permits individual shut down of
the channels, e.g., for purposes of replacement or repairs of the casting
heads, molds, etc., without interrupting the casting as a whole. Each channel,
head and mold constituting a casting branch can individually be halted and
started up again. Conventional equipment required simultaneous starting
and stopping. This was particularly critical when "freezing" of any stopper
had to be avoided, and was complicated and required extensive use of personnel.
The fact that the connection and joining to the respective channel is located
fairly remote from the respective mold facilitates the rapid exchange. Due
to individual channel shut down a head can be exchanged regardless whether
or not steel just pours into the tundish. Extensive personnel is not needed
because the heads will be exchanged one at a time, so will be any maintenance
of any channel.
For purposes of head exchange, the head is lifted, i.e., slid up,
in the centering connection 7 so that the casting pipe 12 is lifted out of the
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mold, and the head is then removed as is convenient for such an operation.
If the casting head is not provided with an immersion pipe, the head may
be slid off laterally using suitable lifters.
As stated such an exchange of the several casting heads will be
carried out independently so that the machine as a whole can continue to
runJ and casting in the branch which was interrupted for any reason can be
resumed immediately following, e.g. J the exchangeJ replacement, repair,
etc. It can thus be seen that the entire casting machine operates on a
continuous basis and intermittency is introduced only in one particular
mold at a time, while casting continues in the other molds. It can also ~ -
be seen that the periodic exchange and renewal of equipment before excessive
wear has begun to pose problems with regard to the quality of the casting
are possible without any interruption in the overall operation. It should
be noted, that this independence of the individual branches is independent
also from the sequence of tundish charging.
The particular device illustrated could be modified, in that the
feeder path from the heated tundish to the individual molds is carried out on
the basis of gravity (Figure 4) whereby the flow is in effect driven by the
ferrostatic pressure in the tundish. In this case, of course the steel will
2~ not be metered in the channel, but passes from the tundish through fireproof
pipes 41 or ducts, which are also releasably connected to the bottom of the
tundish and have an~outlet that can be opened and closed through a slide
lock and of course, they are also connected to rapid exchange types of
casting head being of the variety outlined above. The steel flow is metered
preferably through metering equipment in such a head and may include a
stopper 62 or the like in order to control the flow of steel into the mold
without being dependent upon the possibly varying ferrostatic pressure in the
tundish system.
Finally it should be mentioned that the invention arose of course,
in an environment and from a problem inherent in the requirement of having
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to process particular amounts of steel within certain periods of time while
casting machines have certain constraints as to throughput, particularly
if the ingots are perhaps small in cross section. That problem is solved
and particularly the casting can be matched to the steel production. Moreover,
the casting of billets of small cross sections can be carried out more
economically. ~owever, the particular mode of heating the tundish is
applicable also to casting machines having but a few or a single casting
outlet.
The invention is not limited to the embodiments described above
but all changes and modifications thereof not constituting departures from
the spirit and scope of the invention are intended to be included.
