Note: Descriptions are shown in the official language in which they were submitted.
W ~ 2!09390 PCT/AU91/00536
- 2096750
CONTINUOUS CASTING OF MOLTEN METAL
The present invention relates to continuous
casting of molten metal and, in particular, to
continuous casting of molten steel.
In the continuous casting of molten steel the
molten steel is usually transferred from a.tundish to a
continuous casting mould. Usually, a tundish has an
outlet nozzle which is arranged to bridge a gap,
I W092/09390 PCT/AU9l/0053 ~
', 29,6~ S~
-- 2 --
typically 50 cm, between the lower wall of the tundish
and a continuous casting mould and to extend into the
mould and a valve mechanism to control the flow of
molten steel through the nozzle. In Europe, the
preferred valve mechanism is a stopper rod located in
the tundish, and in Australia and Japan the preferred
valve mechanism is a sliding gate valve located below
the tundish in the gap between the tundish and the
mould.
The nozzle tends to be susceptible to clogging,
usually due to a build up of alumina on the inner wall,
and it is necessary to regularly replace the nozzle
during continuous casting in order to prevent disruption
to continuous casting caused by clogging of the nozzle.
International Industrial Bngineering SPRL
("IIE") has developed technology for changing a nozzle
of a stopper rod controlled tundish without the
change-over step itself causing disruption to the
continuous casting. The basis of the technology is to
force the upper surface of the nozzle upwardly against
the lower surface of a tundish with sufficient force,
typically 3-4 tonnes, to form a fluid tight seal between
the surfaces and to slide the nozzle whilst in contact
with the lower surface of the tundish into and out of
register with the tundish opening. With such an
arrangement, a nozzle can be replaced by locating a
replacement nozzle ad~acent an existing nozzle, lowering
the stopper rod to stop the flow of molten metal through
the nozzle, sliding the replacement nozzle into the
operative position which simultaneously pushes the
existing nozzle out of the operative position, and
W ~ 2/09390 PCT/AU91/00536
2o967~o
-- 3
raising the stopper rod to allow molten steel to flow
through the nozzle. It has been found that the IIE
technology can effect nozzle change-over in 2-3 seconds.
For relatively slow continuous casting ~up to 1.0 m/min)
typically used in Europe a stopper rod provides adequate
flow control. However, the IIE technology is not
suitable for use with a sliding gate valve controlled
tundish which is required for high casting rates (above
1.0 m/min). In this regard, there are severe space
constraints caused by the tundish and the mould and
difficulties applying an upward force of 3-4 tonnes to
the nozzle to form a fluid type seal with the sliding
gate valve without adversely affecting the operation of
the sliding gate valve.
An object of the present invention is to provide
an apparatus for changing over the nozzle of a sliding
gate valve controlled tundish for use in continuous
casting of molten steel without adversely disrupting the
continuous casting.
According to the present invention there is
provided a tundish sliding gate valve and nazzle
change-over assembly for use in transferring molten
metal from a tundish to a continuous casting mould, the
assembly comprising:
~a) a sliding gate valve located below an outlet
in the tundish a~d operable to control the
flow of molten metal from the tundish to the
mould; and
(b) a change-over assembly for supporting a
tundish nozzle in an operative position with
W092/09390 PCT/AU91/00~3 ~
209~7~
-- 4
respect to the sliding gate valve to allow the
transfer of molten metal from the tundish
through the sliding gate valve and the nozzle
to the mould and for moving the nozzle into
and from the operative position, the
change-over assembly comprising a means to
bias together the sliding gate valve and the
nozzle to form a fluid tight seal therebetween
without *he biasing force provided by the
biasing means affecting the operation of the
sliding gate valve.
It is preferred that the change-over assembly
further comprises a means to slide the nozzle in contact
with the sliding gate valve to move the nozzle into the
operative position and subse~uently from the operative
position when nozzle replacement is necessary against the
resistance to sliding movement provided by the biasing
force of the biasing means.
It is preferred particularly that the sliding means
is arranged to simultaneously move a replacement nozzle
into the operative position as the nozzle is moved from
the operative position.
It is preferred that the sliding gate valve
comprises an upper and a lower plate fixed together and a
sliding plate located for sliding movement in a gap
between the plates, each plate having an opening
extending therethrough with the openings in the upper and
lower plates being aligned vertically.
With such an arrangement, it is preferred that the
assembly further comprises a means to bias the upper and
~ 2/09390 PCT/AU91/00536
2~967~o
-- 5
lower plates against the sliding plate to form fluid
tight seals between the upper plate and the sliding plate
and between the lower plate and the sliding plate.
.~
It is preferred particularly that the sliding gate
valve further comprises a means to slide the sliding
plate in the gap to move the opening in the sliding plate
progressively into and from alignment with the opening in
the upper and lower plates thereb~ to progressively open
and close the flow of molten metal from the tundish to
the mould.
It is preferred that the biasing force is at least 3
tonnes.
It is preferred that the biasing means is connected
to the lower plate so that the biasing force is isolated
from the upper plate and the sliding plate and therefore
does not affect the operation of the sliding gate valve.
It is preferred that the biasing means comprises a
plurality of spring assemblies arranged in two parallel
lines to define a path for moving the nozzle into and
from the operative position, each spring assembly
comprising a vertically extending spring means connected
to the lower plate and an arm connected to the spring
means to extend inwardly of the path to contact a
downwardly facing surface of the nozzle so that the
spring means causes the arm to apply an upwardly directed
biasing force against the nozzle.
It is particularly preferred that the spring means
comprises a compression spring and the arm is pivotally
connected to the lower plate at a point intermediate the
W092/09390 PCT/AU91/0053 ~
209~7~
ends of the arm so that the downwardly directed force of
the compression spring translates to the upwardly
directed biasing force applied by the arm against the
nozzle.
According to the present invention there is also
provided a continuous casing apparatus for molten metal,
comprising:
(a) a continuous casting mould;
~b) a tundish for retaining a supply of molten
metal for continuous casting;
~c) a nozzle for transfèrring molten metal from
the tundish to the mould; and
(d) the tundish sliding gate valve and nozzle
change-over assembly described in the
preceding paragraphs.
The present invention is described further by way of
example with reference to the accompanying drawings in
which:
Figure 1 is a vertical cross-section through a
preferred embodiment of a tundish sliding gate valve and
nozzle change-over assembly formed in accordance with the
present invention;
Figure 2 is a plan view along the line A-A in figure
l;
W~2/09390 PCT/AU91/00~36
20967~0
Figure 3 is a cross-section along the line C-C in
figure 2.
With reference to Figure 1, a preferred embodiment
of a tundish sliding gate valve and nozzle change-over
assembly (the "assembly") in accordance with the present
invention is located in a gap G, typically 50 cm, between
a lower surface S of a tundish 3 and the upper part of a
continuous slab casting mould 5 and supports a nozzle 7
to extend into the mould 5.
The assembly comprises a sliding gate valve,
generally identified in figures 1 and 3 by the numeral 9.
The sliding gate valve 9 comprises an upper plate 11
and a lower plate 13 which are fixed with respect to each
other and a sliding plate 15 located for sliding movement
in a gap between the upper and lower plates. Each of the
upper, lower and sliding plates 11, 13, 15 has an opening
therethrough, with the openings in the upper and lower
plates 11, 13 being aligned vertically. In the
arrangement shown in the figures, the opening in the
sliding plate 15 is aligned with the openings in the
upper and lower plates 11, 13 so that molten steel can
flow from ~he tundish 3 through the nozzle ~ into the
mould 5. The sliding gate valve 9 further comprises
means (not shown) to slide the sliding plate 15 in the
gap between the upper and lower plates 11, 13 to move the
opening in the sliding plate 15 progressively into and
from alignment with the openings in the upper and lower
plates 11, 13 thereby to progressively open and close the
flow of molten metal from the tundish 3 to the mould 5.
With reference to ~igures 2 and 3, the sliding gate
valve 9 is connected by means of tension springs 17 to a
W092/09390 PCT/AU~1~00~3 ~
20967~ 8 - i
~uick nozzle change device frame 20 which in turn is
bolted to the tundish 3. The springs 17 are connected at
one end to the quick nozzle change device frame 20 and
are operatively connected at the other end to the lower
plate 13 and thereby bias the sliding gate valve 9
upwardly so that the upper surface 19 of the upper plate
11 contacts shoulders 20a of the quick nozzle change
device frame 20 and the lower plate 13 is forced against
the sliding plate 15 and the sliding plate 15 is forced
against the upper plate 11. In this regard, the spring
pressure is selected so that a fluid tight seal is formed
between the lower surface of the upper plate 11 and the
upper surface of the sliding plate lS and between the
lower surface of the sliding plate lS and the upper
surface of the lower plate 13. It can readily be
appreciated that the use of tension springs 17 is
illustrative of one means to bias together upper, lower
and sliding plates 11, 13, 15.
It is noted that in the preferred embodiment shown
in the figures there is a gap G1, between the upper
surface 19 of the upper plate 11 and the lower surface S
of the tundish 3 when the upper surface 19 is biased
upwardly against the shoulders 20a and that in use
refractory material is packed into the gap G1.
The assembly further comprises a change-over
assembly for supporting the nozzle 7 in the operative
position shown in the figures to allow the transfer of
molten metal from the tundish 3 to the mould S and for
moving the nozzle 7 into and from the operative position.
The change-over assembly comprises two parallel
lines of spring assemblies, generally identified by the
W ~ 2/09390 PCT/AU91/00~36
20967~
numeral 22 in Figure 3, which define a path of movement
of the nozzle 7 into and from the operative position.
The spring assemblies 22 comprise compression springs 21
which, as can best be seen in Figure 3, are operatively
connected at one end to the lower plate 13 of the sliding
gate valve 9 and arms 23 which are operatively connected
to the other end of the compression springs 21 and are
arranged so that the free ends 24 of the arms 23 contact
a downwardly facing surface 26 of the nozzle 7 to apply
an upward force in the direction of the arrows Z in
Figure 3 in response to the biasing force of the springs
21. In this regard, the change-over assembly further
comprises pivot points 25 operatively coupled to each arm
23 so that the downward force of the compression springs
21 in the direction of the arrows D in Figure 3 causes
the arms 23 to pivot about the pivot points 25 with the
result that an upward force is applied to the nozzle 7 in
the direction of the arrows Z in Figure 3. It can
readily be appreciated that the effect of the arrangement
is to bias together the lower surface of the lower plate
13 and the upper surface of the nozzle 7 as indicated by
the numeral 27 in Figure 3. In this regard, the spring
pressure is selected so that a fluid tight seal is formed
between the surfaces at 27. It can readily be
appreciated that the arrangement of the compression
springs 21, the arms 23 and the pivot points 25 is
illustrative of one means to bias together the lower
surface of the lower plate 13 and the upper surface of
the nozzle 7.
Significantly, it is noted that the connection of
the compression springs 21 to the lower plate 13 of the
sliding gate valve 9 and the positioning of the arms 23
to force the nozzle 7 upwardly in response to the action
W092/09390 PCTtA~191/00~3 ~
2~9~7~0
.,
-- 10 --
of the compression springs 21 is such that the upward
force is isolated from the other components of the
sliding gate valve 9 and therefore does not affect the
operation of the sliding gate valve 9. In this regard,
it is noted that, typically, upward forces in the order
of 3-4 tonnes are required and if such forces were
transferred to the sliding gate valve 9 the efficient
operation of the sliding gate valve 9 would be seriously
disrupted.
The change-over assembly further comprises means
~not shown) to slide the upper surface of the nozzle 7 in
contact with the lower surface of the lower plate 13 of
the sliding gate valve 9 to move the nozzle 7 initially
into the operative position and subsequently from the
operative position when nozzle replacement is necessary
against the resistance to sliding movement provided by
the biasing force of the biasing means. Whilst not shown
in the figures, in the preferred embodiment, the assembly
comprises guides to locate a réplacement nozzIe adjacent
the existing nozzle 7 and a series of rams to move the
replacement and existing nozzles to effect nozzle
replacement.
The nozzle change-over may be effected by closing
the sliding gate valve 9 prior to actuating the rams. In
such situations, it is preferable to slow the casting
rate (typically to 0.6 m~min) to minimise the reduction
in the level of molten steel in the mould S.
Alternatively, the nozzle change-over may be effected
with the sliding gate valve 9 in the operative position
shown in the figures.
~ 92/09390 PCT/AU91/00536
~96~
-- 11
Many modificat.ions may be made to the preferred
embodiment described above without departing from the
spirit and scope of the present invention.
