U.S. patent number 3,718,175 [Application Number 05/025,897] was granted by the patent office on 1973-02-27 for plant for continuous casting without deep casting stream penetration.
This patent grant is currently assigned to Vereinigte Osterreichische Eisen-und Stahlwerke Aktiengesellschaft. Invention is credited to Rudolf Rinesch.
United States Patent |
3,718,175 |
Rinesch |
February 27, 1973 |
PLANT FOR CONTINUOUS CASTING WITHOUT DEEP CASTING STREAM
PENETRATION
Abstract
The invention proposes a plant for continuously casting liquid
metals comprising a casting mould, a tundish arranged above the
casting mould, adapted to be gastightly sealed and evacuated, and
provided with a draining tube extending below the metal level in
the mould, a supply ladle for liquid metal, and pneumatic means for
conveying the metal from the supply ladle into the tundish, a
chamber which is connected with a pneumatic pressure conduit and
arranged below the tundish, into which chamber the supply ladle
charged with liquid metal is inserted, an ascending pipe line
starting from the bottom of the ladle, penetrating the lid of the
chamber and leading into the tundish, the length of said ascending
pipe line being dimensioned that the level difference between the
metal in the tundish and the metal in the supply ladle exceeds 1.4
m, i. e. the height of the ferrostatic column at atmospheric
pressure, and the length of the draining tube being dimensioned
that the level difference between the metal in the tundish and the
metal in the mould does not exceed 1.5 m. This plant is of great
advantage because by releasing the atmospheric ferrostatic pressure
the metal flows into the casting mould practically without exerting
any pressure so that the solidifying casting shell is prevented
from being damaged. The invention permits also of subjecting the
steel to a highly effective vacuum treatment.
Inventors: |
Rinesch; Rudolf (Linz,
OE) |
Assignee: |
Vereinigte Osterreichische
Eisen-und Stahlwerke Aktiengesellschaft (Linz,
OE)
|
Family
ID: |
25600229 |
Appl.
No.: |
05/025,897 |
Filed: |
April 6, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Apr 15, 1969 [OE] |
|
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A3607/69 |
Aug 14, 1969 [OE] |
|
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A7831/69 |
|
Current U.S.
Class: |
164/254; 164/415;
164/438; 164/420 |
Current CPC
Class: |
B22D
11/11 (20130101); B22D 11/113 (20130101) |
Current International
Class: |
B22D
11/113 (20060101); B22D 11/11 (20060101); B22d
011/10 () |
Field of
Search: |
;164/64,256-258,281,156,337,254,259 ;266/346,DIG.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
72,085 |
|
May 1947 |
|
NO |
|
879,153 |
|
Jun 1953 |
|
DT |
|
947,626 |
|
Jan 1964 |
|
GB |
|
1,372,527 |
|
Aug 1964 |
|
FR |
|
632,096 |
|
Jan 1962 |
|
IT |
|
Primary Examiner: Baldwin; Robert D.
Claims
What I claim is:
1. A plant for the continuous casting of metals comprising
a supply vessel for containment of a portion of molten metal,
a pressure chamber enclosing the supply vessel and adapted to be
gas-tightly sealed,
an ascending pipe in communication with the tundish and the supply
vessel and adapted to convey metal from the supply vessel into the
tundish,
a casting mold,
a draining tube connected to the tundish and adapted to convey
molten metal from the tundish into the casting mold,
means for supporting said supply vessel, and tundish and said
casting mold at respective heights such that during operation of
said plant, the level of molten metal in said tundish may be
maintained more than 1.4 m above the level of molten metal in said
supply vessel and above the level of molten metal in said mold by a
distance enabling gravity flow of metal from said tundish to said
mold and not exceeding 1.5 m, and
pressure means for conveying the metal from the supply vessel into
the tundish and then conveying the metal from the tundish into the
casting mold with a minimum of force on the metal in the casting
mold,
said pressure means comprising means for increasing the pressure in
the supply vessel above atmospheric pressure and means for lowering
the pressure in the tundish below atmospheric pressure.
2. The plant set forth in claim 1, wherein the lower end of the
draining tube is broadened in downward direction to be
funnel-shaped.
3. The plant set forth in claim 1, wherein the lower end of the
draining tube and the mold are gas-tightly enclosed by a hood which
is connectable with a conduit for the supply of protective gas
selected from the group including argon, so that above the metal
surface in the mold a gas space subjected to slight overpressure
can be produced.
4. The plant set forth in claim 1, wherein the draining tube
comprises two parts which are releasably connected with each
other.
5. The plant set forth in claim 4, wherein the lower part of the
draining tube is made of a metal-ceramic material comprising
molybdenum and zircon oxide.
6. The plant set forth in claim 1, wherein the supply vessel is
provided with a slanting bottom and the top of the ascending pipe
is positioned slightly above the bottom of the supply vessel.
7. The plant set forth in claim 1, wherein the ascending pipe is
arranged eccentrically of the longitudinal axis of the supply
vessel.
8. The plant set forth in claim 1, wherein the pressure chamber and
the supply vessel are adapted to be movable.
9. The plant set forth in claim 1, wherein the ascending pipe
comprises an ascending tube which is connected to the top of the
pressure chamber and a supply tube which is connected to the bottom
of the tundish, the upper end of the ascending tube and the lower
end of the supply tube being releasably connected by means of a
slide valve connection.
10. The plant set forth in claim 1, wherein the tundish is designed
to be liftable, lowerable and rotatable.
11. The plant set forth in claim 9, wherein the tundish is provided
with a plurality of draining tubes, each of which is leading into
one casting mould, the bottom ends of each of said draining tubes
being situated somewhat below the connection level of the ascending
tube and the supply tube.
12. The plant set forth in claim 1, wherein the tundish is provided
with a slanting bottom, the top of the ascending pipe being
positioned above the top of the draining tube.
13. The plant set forth in claim 1, wherein the tundish is
positioned at an angle from the horizontal, and the top of the
ascending pipe is situated above the top of the draining tube.
14. The plant set forth in claim 1, wherein a refractory body
having a nozzle-like opening is provided in the tundish at the top
of the ascending pipe, said body being positioned to change the
direction of the metal which is upwardly conveyed through the
ascending pipe.
15. The plant set forth in claim 1, wherein the cross section of
the ascending pipe is greater in size than the cross section of the
draining tube.
Description
The invention relates to a plant for continuous casting of hot
liquid metals and to a continuous casting method in which this
plant is used.
In known continuous casting plants the casting stream falling
vertically into the casting mould penetrates deeply into the yet
liquid core of the bar, which may damage the solidifying casting
shell. When leaving the mould a damaged casting shell cannot resist
the pressure of the metal melt contained in the interior of the bar
and the liquid metal may break through so that the plant is damaged
and the cast product is wasted. The casting stream penetrating into
the liquid core of the bar does not permit casting of bars having
flat cross sections of any desired small thickness, because the
danger of damage to the casting shell increases greatly when the
thickness of the bar is reduced. It has been attempted to reduce
the kinetic energy of the metal falling into the mould, by using
draining pipes with a closed bottom and laterally arranged mouths.
However, such outlet tubes are difficult to manufacture, they are
rapidly worn and have not shown the desired effect in practice. The
invention is aimed at avoiding the deep penetration of the casting
stream.
Further it is a task of the invention to provide for a casting
plant, which may also be built into existing steel works in which
casting cranes are used having a relatively small lifting height.
Known casting plants are provided either with a straight mould, to
which a longer vertical bar guide is joined, or with a circularly
curved mould, to which a bar guide having the form of a quarter
circle is joined. In any case, particularly in vertical plants, the
construction height of the plant is considerable and the casting
ladle has to be liftable from the mill floor level to the area of
the mould. In steel works not designed to have a casting plant
built in the lifting height of the casting cranes frequently is
insufficient.
A further aim of the invention consists in obtaining an effective
vacuum treatment of the steel in a plant for continuous casting;
such a vacuum treatment may bring about apart from lowering the
contents of hydrogen and non-metallic inclusions, also a reduction
of the oxygen content in the steel. This, as well as an even and
appropriate casting temperature is a prerequisite for the
production of excellent bars when rimming steels are cast according
to the continuous casting method. In a known plant liquid steel is
sucked by vacuum from a ladle into a tundish of relatively large
dimensions in which a bath of rather great depth is maintained.
Despite of the considerable expenditure of equipment, the degassing
effect is insufficient and the temperature of the metal in the
tundish falls rapidly. A further disadvantage rests in the small
level distance between the metal in the ladle and in the tundish,
which level difference at a vacuum of e.g. 0.5 Torr amounts to
maximally 1.4 m (ferrostatic pressure column). Therefore, ladles
having a capacity of 50 - 300 mt of steel and a vertical extension
of about 2.5 to 4 m and which are arranged at a lower level than
the tundish, cannot be degassed continuously.
When alloy steels are cast with a low casting temperature in known
continuous casting plants a metallurgical disadvantage resides in
that the metals or alloys added into the ladle or during tapping
are dissolved rather slowly so that the chemical composition of the
bar varies greatly over its entire length.
The invention meets the mentioned tasks by avoiding the
disadvantages referred to above; it starts from a plant for
continuously casting liquid metals comprising a casting mould, a
tundish arranged above the casting mould and adapted to be
gastightly sealed and evacuated, which tundish is provided with a
draining tube extending below the metal level in the mould, a
supply vessel for liquid metal, and pneumatic conveying devices
serving to convey the metal from the supply vessel into the
tundish; and is, according to its main feature, characterized in
that in a manner known per se a pressure chamber connected with a
pneumatic conduit is provided below the tundish, into which
pressure chamber a ladle charged with liquid metal may be inserted
and that an ascending pipe line starting from the bottom of the
ladle and penetrating the lid of the pressure chamber leads into
the tundish, the length of said ascending pipe line being such that
the level difference between the metal in the tundish and the metal
in the ladle is always greater than 1.4 m, i.e. the height of the
ferrostatic column at atmospheric pressure, and that the length of
the draining tube is such that the level difference between the
metal in the tundish and the metal in the mould is maximally 1.5 m
so that when a vacuum is created the ferrostatic pressure is
compensated and the metal flows into the mould practically without
exerting any pressure. Obviously, the level difference between the
metal in the tundish and the metal in the mould must not be smaller
than 1.4 m when the tundish is completely evacuated, because
otherwise the metal column in the draining tube would break. With a
completely evacuated tundish the level difference thus lies between
the mentioned limits of 1.5 and 1.4 m. When the tundish is not
completely evacuated the level difference should correspond to the
vacuum employed.
In the plant according to the invention the liquid metal does not
get into contact with atmospheric oxygen so that no undesired
oxidation may occur; thus the content of non-metallic inclusions is
reduced and flaws caused by such inclusions are thus avoided in
sheets produced from the cast bars.
A casting plant in which a ladle may be inserted into the pressure
chamber which is connected by means of an ascending pipe line with
a tundish, as is provided by the present invention, is known per
se. In the known plant, however, the tundish cannot be evacuated so
that neither the metal may be supplied into the mould without
exertion of pressure nor is it possible to provide for vacuum
treatment.
The lower part of the draining tube reaching into the casting mould
may broaden in downward direction to be funnel-shaped. By providing
for a continuous transition from a smaller to a larger cross
section within the funnel-shaped part of the draining tube the
speed with which the metal leaves the tundish is further reduced.
When slabs are cast the cross section of the funnel-shaped part may
also be oval.
Suitably the lower part of the draining tube and the casting mould
are gastightly enclosed by a hood which is connectable with a
conduit for the supply of a protective gas, e.g. argon, so that
above the metal level in the casting mould a gas space subjected to
slight overpressure can be produced. The drain suitably comprises
two parts which are releasably connected with each other by means
of connecting elements such as flanges and brackets. The lower part
of the drain may be made of metal-ceramic material containing
primarily molybdenum and zircon oxide.
The plant according to the invention may also include the features
that the ladle is provided with a slanting bottom and the ascending
pipe line starts from slightly above the lowest place of the ladle
bottom; further, that the ascending pipe line is arranged
eccentrically of the center axis of the ladle. Suitably, the
pressure chamber and the ladle are arranged on a traveling
vehicle.
The ascending pipe line may comprise an ascending tube which is
connected with the lid of the pressure chamber and a supply tube
which is inserted in the floor of the tundish, the upper end of the
ascending tube and the lower end of the supply tube being
releasably connected by means of a slide valve connection. In order
to have sufficient space available when the ascending tube and the
supply tube of the tundish are connected, the tundish is designed
to be liftable and lowerable. Furthermore, the tundish may also be
rotatable so as to provide for room whenever servicing work has to
be carried out.
According to a preferred embodiment the tundish is provided with
one or several draining tubes, each reaching into one casting
mould, the lower ends of said draining tubes being situated
somewhat below the connection level of the ascending tube and the
supply tube. Thus, when the ascending tube and the supply tube are
connected or disconnected, it is not necessary to lift the end of
the draining tube out of the metal sump in the mould, so that any
impurification of the steel in the mould owing to access of oxygen
is avoided.
Preferably the tundish is provided with a slanting floor or is
arranged to be slanting, the upper edge of the supply tube being
situated on a higher level than the upper edge of the draining
tube. With such an arrangement owing to the influence of the vacuum
in the tundish the steel running over the upper edge of the supply
tube is degassed in an explosion-like process in which the steel is
distributed into a plurality of droplets and owing to the thus
obtained large surface is subjected to a highly effective vacuum
treatment.
In the tundish, above the mouth of the supply tube a highly
refractory hollow body with a nozzle-like opening may be provided
for changing the direction of the metal stream which is conveyed in
upward direction through the pressure conduit.
The cross section of the ascending and supply tubes may further be
greater than the cross section of the draining tube. Thus it
becomes possible to quickly fill and drain the tundish.
The continuous casting plant according to the invention is
particularly suitable for a method of continuous casting in which a
plurality of ladles are cast successively without interruption.
According to the present invention it is proposed for such methods
to compensate temporarily the pneumatic pressure acting upon the
liquid metal in the ladle or to reduce said pressure to a degree
that metal flows back from the tundish into the supply ladle so as
to equalize differences in concentration and temperature of the
liquid metal. By employing this measure the bar obtains a highly
uniform chemical composition over its entire length because an
effective circulation of the stock of metal is achieved in the
ladle on account of considerable portions of the liquid metal
temporarily flowing back from the tundish into the ladle and the
eccentric arrangement of the ascending tube. Metallic additions,
e.g. manganese, introduced into the ladle prior to its being
filled, dissolve under the influence of the circulatory movement
and are evenly distributed. The temperature is qualized. Thereby, a
non-oxidizing atmosphere may be maintained in the tundish.
When employing the plant of the invention a highly effective method
for degassing the metal to be cast resides in that the tundish is
evacuated while the metal is conveyed from the ladle into the
tundish. The metal enters the evacuated tundish under the action of
the pneumatic conveying pressure and is distributed into a
plurality of droplets. Hence, the degassing effect is
excellent.
Also when it is not intended to subject the liquid metal to a
vacuum treatment the tundish may be kept under reduced pressure
during casting so as to reduce the kinetic energy of the metal
stream running from the tundish into the continuous casting mould
and deep penetration of the metal stream into the liquid sump is
avoided.
A non-oxidizing gas may be used for generating the pneumatic
pressure acting upon the surface of the metal in the ladle.
In order that these and further features of the plant according to
the invention and of the continuous casting method in which this
plant is used may be more fully understood, they will now be
carefully described with reference to the accompanying drawings, in
which FIG. 1 is a vertical sectional view of the entire plant, FIG.
2 is a top view of a tundish with four draining tubes, FIG. 3 is a
vertical sectional view of a tundish with two draining tubes, and
FIG. 4 is a vertical sectional view of a tundish with one draining
tube. FIGS. 5, 6, 7 are vertical sectional views showing preferred
embodiments of tundishes. FIG. 8 shows a plant in which a draining
tube broadening to be funnel-shaped is used, equally in a vertical
sectional view.
In FIG. 1 numeral 1 denotes a ladle having a slanting bottom 2 and
being filled with liquid steel 3 upon which a thin slag layer 4 is
floating. This supply ladle 1 is inserted in a pressure chamber 5
comprising the bottom part 6 and the lid part 7 which is provided
with a refractory insulation 8. The bottom part 6 and the lid part
7 are connected with each other by means of a flange connection 9
which may easily be opened. A duct 10 leads into the pressure
chamber 5 through which compressed air or preferably a
non-oxidizing gas, such as argon, may be introduced under pressure.
A refractory ascending tube 12 is built into the lid 7 in a manner
that its lower end comes to stand slightly above the lowest point
of the ladle floor 2 when the lid 7 is placed onto the bottom part
6. The pressure chamber 5 is arranged on a vehicle 11 so that it
may travel together with the casting ladle 1 on the floor level 36,
beneath the pouring platform 35, to the continuous casting
plant.
The tundish 13 which is designed in two parts, is arranged on the
pouring platform 35. Preferably the tundish has a circular cross
section; its dimensions are designed as small as possible in order
to reduce the temperature loss of the steel. The tundish 13
comprises a closed sheet casing 14, 15. The bottom part is lined
with highly refractory material 17, while the upper part may be
made of refractory insulating material 16. The tundish 13 is
arranged at an acute angle to the pouring platform 35. At the
lowest point a supply tube 18 with a conical end piece 19 is
vertically inserted into the bottom of the tundish. The supply tube
18 has the same diameter as the ascending tube 12. The tundish 13
is liftable and lowerable by means of a hydraulically operated
cylinder 29. It may be lifted in vertical direction approximately
up to the position 13' shown in dotted lines, which the tundish
occupies prior to operation. The cylinder 29 is arranged on the
pouring platform 35 to be rotatable. This revolving bearing is
denoted by numeral 30 and serves to enable swinging of the tundish
13 so that re-lining is facilitated and the continuous casting
mould 31 can be removed. The supply tube 18 of the tundish 13 is
connected to a slide valve which may be designed as a rotary slide
valve 25. The slide valve 25 is provided with a guide 26 into which
the supply tube 18 engages from above and the ascending pipe 12
engages from below so that a form locking connection is achieved.
The guide 26 is water cooled so as to prevent any breakthrough of
the liquid steel in the area of the connection in case of leakages.
Water supply and draining tubes are indicated with numerals 27 and
28, respectively.
The tundish 13 may be provided with a refractory stopper 21, which
is operated by a pneumatic cylinder 22. This stopper serves to
close the draining tube 20 or to regulate the outflowing amount of
liquid steel. At the site where the stopper rod passes through the
upper wall of the tundish it is surrounded by a casing 23 which
provides a gastight sealing.
In working position the draining tube 20 immerses below the metal
level 32 in the continuous casting mould 31. The cast bar 33 is
withdrawn from the mould vertically downwardly and is gradually
deflected. The guide rollers for the bar 33 are indicated by
numeral 34.
Before casting is started, a non-oxidizing gas, preferably argon,
is blown into the tundish 13 through the opening 24 of the tundish
13, and its interior, the ascending and supply tubes 12, 18 and the
draining tube 20 are flushed and filled with the protective gas
respectively so that the liquid steel cannot be oxidized when it
enters and flows through the tundish. It is also possible to
connect the opening 24 to a vacuum pump not shown in the
drawing.
When operation is started, excess pressure is generated in the
pressure chamber 5 by introducing compressed air or nitrogen via
the conduit 10; this excess pressure acts upon the slag 4, and the
steel 3 is thus conveyed into the ascending pipe 12 and into the
tundish 13, at first to the level 37. Then, by releasing the
pressure in the pressure chamber 5 the steel may be caused to flow
back into the casting ladle 1 so that the steel is effectively
mixed in the ladle and differences in concentration and temperature
of the steel are eliminated. This process may be carried out prior
or during casting and, if desired, repeatedly. During normal
operation the liquid steel gains approximately the level as
indicated at 38 in the tundish and flows continuously through the
draining tube 20 into the casting mould 31. When the casting ladle
1 is drained completely except for a small remainder, the slide
valve 25 is closed, after the steel in the tundish 13 has been
permitted to gain the level 39. In order to be able to move the
ladle away and to replace it by another one the pressure in the
pressure chamber 5 is released and the tundish 13 is lifted some
centimeters by means of the hydraulic cylinder 29 so that the
supply tube 18 which is closed by means of the slide valve gets out
of engagement with the ascending tube 12, while the bottom edge of
the outflow 20 is still below the metal surface level 32. The
vehicle 11 with the pressure chamber 5 and the emptied ladle 1 is
removed and a second vehicle, carrying a second pressure chamber
with a filled ladle is brought to replace it. The tundish 13 is
lowered again and the connection with the ascending pipe line is
reestablished. After pressure gas has been introduced into the
pressure chamber, the slide valve 25 may be opened again so that
the steel may flow into the tundish 13, in which the metal level
has meanwhile fallen from level 39 to level 38. The amount of
liquid metal stored in the tundish 13 has to be calculated on the
period during which the ladles are exchanged. In this manner it is
possible to cast liquid steel continuously and to keep the
construction height of the entire plant very small as may be
derived from FIG. 1. If the ladle 1 is arranged on a vehicle 11 it
is possible to use a ladle without a stopper which greatly
increases operation safety.
FIG. 2 shows a tundish 40 with four drains 20', 20", 20'", 20""
situated above the moulds for four bars 33', 33", 33'", 33""; FIG.
3 shows a tundish 41 with two outflows 20', 20" and the respective
stoppers 21', 21". The mouth of the supply tube 18' is arranged to
be lower than the upper openings of the draining tubes. In the
embodiment according to FIG. 4 a recess 45 is provided in a tundish
42 which comprises an upper part 43 and a bottom part 44; this tank
serves for the formation of a sump for the liquid metal which has
been lifted to the level 37' through the supply tube 18'. In
operation the metal reaches level 38' and, prior to the exchange of
the ladles, level 39'. The capacity difference between level 39'
and 38' is based on the period necessary for the exchange of
vessels. The outflow 20' may also be provided with a stopper.
Neither the vacuum pump nor the conduit for joining this pump to
the tundish are shown in FIGS. 2 to 4.
In FIGS. 5, 6 and 7 preferred embodiments of tundishes 46, 58, 60
are shown which are used when the steel is to be degassed. In these
embodiments the upper edge of the supply tube 18' is situated at
the same height as the level 51 of the liquid metal in the tundish
(FIG. 5) or above this level (FIG. 6). The tundish 46, 58, 60 may
be connected to a vacuum conduit 49 which is arranged off the axis
of the supply tube 18'.
Before the tundish 46 is evacuated the outflow 20' is closed with a
pot-like cover 53 which is pressed onto an element 52 by means of
fixing brackets 54 (FIG. 5). An appropriate vacuum sealing 55
provides for a gastight closure. The cover 53 may be made of steel
e.g. As soon as a certain amount of steel is present in the tundish
46, the floor 56 of the cover 53 will melt through and the metal
stream 57 may flow into the casting mould 31 which instance
signifies the beginning of casting.
When the steel enters into the evacuated tundish 46, 58, 60 the
steel is atomized in an explosion-like process into a plurality of
droplets; thus its surface is extremely widened and the steel is
rapidly and effectively degassed and there is no necessity of
providing for a large surface 51 of the metal sump. In the drawing
the metal droplets are diagrammatically shown and indicated by
numeral 50. The lining is indicated with numeral 48; a perforated
brick 47 serves for inserting a supply tube 18' having a conical
shoulder 19' so that it may be exchanged from the outside (FIG. 5).
The effect of the vacuum on the liquid steel can be improved if a
highly refractory hollow body 61 with a nozzle-like bore is built
in above the inlet tube 18' (FIG. 7). The hollow body 61 is
arranged in a manner that the axis of its bore is slanted in
relation to the axis of the supply tube 18' so that the metal
droplets 50 cover as long a distance as possible in the tundish 60
before they impinge upon the metal sump.
The tundishes 42, 58, 60 may, of course, be also provided with
stoppers which may be built in and operated similarly as described
in relation with FIG. 1. The amount of metal flowing into the
casting mould may be regulated by changing the metal level in the
tundish or by actuating the stopper.
According to a preferred embodiment the tundishes are evacuated
also during casting in order to reduce or compensate the kinetic
energy of the metal stream entering the mould 31. When the height
difference h (FIG. 7) between the melt level 32 in the mould 31 and
the melt level 51 in the tundish 60 amounts to about 1.4 m and when
a vacuum of about 0.5 Torr is employed the steel flows into the
mould 31 practically without pressure because the ferrostatic
pressure has been compensated. Thus a deep penetration of the steel
into the liquid core 62 and damaging of the already solidified
marginal layer 63 of the bar 33 is prevented. It is possible to use
casting tubes 20' without bottoms, the manufacture of which is
cheap and simple.
Also when tundishes according to FIGS. 5, 6 and 7 are used a
portion of the liquid metal may be permitted to flow back from the
tundish 46, 58, 60 into the ladle 1, in order to achieve an
equalization of concentration or temperature. However, it is a
precondition that the level 51 of the liquid metal be sufficiently
high above the opening of the draining tube 20' so as to avoid an
interruption of casting. The metal present in the ascending tube 12
and in the supply tube 18' flows back when the pressure chamber 5
is relieved of pressure and the tundish 46, 58, 60 of the
vacuum.
In order to guarantee that portions of metal will quickly flow back
into the ladle 1 and that the tundishes 13, 40, 41, 46, 58, 60 are
filled quickly, the cross section of the ascending tubes 12 and
supply tubes 18, 18' are designed considerably larger than the
cross section of the draining tube or tubes 20, 20'.
FIG. 8 shows a plant in which a draining tube 20 comprising two
parts 20 a and 20 b is used. The end of this tube is broadening to
be funnel-shaped. The bottom part 20 a of the drain and the mould
31 are gastightly enclosed by a hood 65 which is connected to a
conduit 66 for the supply of argon. Thus a gas space 67 may be
produced above the level 32 of the metal in the mould, which gas
space is subjected to a slight over-pressure. The lower part 20 a
of the draining tube 20 is made of a metal-ceramic material
containing primarily molybdenum and zircon oxide and is releasably
connected with the upper part 20 b by means of flanges 68, 69 and
brackets 70.
The invention may advantageously also be used in vertical
continuous casting plants, whose pouring platform is situated e.g.
20 m above mill floor; in such vertical plants it is not only
difficult but also very dangerous to lift the filled, heavy ladles
to the necessary height. However, when employing the invention, the
ladle may be arranged at any distance below the pouring platform
even in vertical plants, so that the platform need not carry too
heavy loads and may be built as a lighter construction. As a rule
compressed air of 4 to 5 at. gauge will always be available in a
steel mill so that the liquid steel may be conveyed over a height
difference of about 5.6 to 7 m. If, in addition to compressed air,
also a vacuum is used in the tundish, a height of 7 to 8.4 m may be
overcome. Thus all types of plants may benefit from the advantage
that the heavy casting ladle may be arranged at any low position
desired, and only in individual cases it will be necessary to
increase the pressure of the compressed air in the pressure
chamber, which, however, may easily be carried out.
* * * * *