Note: Descriptions are shown in the official language in which they were submitted.
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CONTINUOUS CASTlNG METHOD AND APPARATUS THEREFOR
5 The present invention relates to a continuous casting method and apparatus
therefore including a new tundish design for ensuring the continuous casting
method may be continued for long casting runs with minimised interruption.
ln td1e continuous casting of metals and in particular steel it is advantageous to
10 extend the length of the cast. This provides two main advantages. Firstly, itm~ximi~es the duration of the steady state conditions when the best product
quality is achieved and this in turn reduces the amount of scrap steel produced
typically from the begim1ing and end portions of a casting run which are not of
sufficiently quality and it also improves the overall quality of the finished
15 product. Secondly production levels are m~ximised and the existing plant and
equipment is able to be utilised to a greater extent which improves the return on
investment.
There is an additional advalltage in that the length of the cast can be optimised
20 with the duration of the available life from the wear components in the casting
process which can be changed at the end of each cast. Thus if the cast is long
enough the full life of the main wear components can be used which reduces
downtime and the cost of replacement of the wear parts.
25 Duril1g the casting process metal is poured thlough a tap hole in a vessel and
this vessel is typically in the form of a tundish. ln order to extend the desired
casting time it is necessary to replace the tundish a nurmber of times after each
time its life is expended. In particular for the casting of fenous metals such as
steel, the high temperature chemical aggression and physical erosion of the
30 refractory material of the tundish permits the tundish to run continuously for
only short periods before they have to be exchanged cleaned of slag and
relined. Thus it is necessary to changeover the tundish a number of times in
order to continuously cast the steel over a long period. Such tundish changes
are sometimes known as flying tundish changes.
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A known method of ch~n,Qing over tundishes and a tundish used is shown in
figures 1 to 3. ln figure 1 the first tundish is in the casting position over the
mould and the second tundish 2 is in a "waiting to cast" position to one side.
When it is time to change the first tundish 1, the first tundish 1 remains in the
5 casting position until all the metal in the first tundish 1 is poured into the mould
5. The tap hole is then closed and the first tundish 1 is moved sideways to a
parking position as shown in figure 2. Simultaneously the second tundish is
moved sideways from a pre-fill position into the casting position over the
mould 5. When it is in the desired casting position, as shown in figure 3, it is10 filled with metal and its tap hole is opened and casting can recommence.
This conventional tundisll changeover method is acceptable for standard
conventional continuous casting runs. In such runs a strand which is
essentially parallel is formed during the solidification process of the continuous
15 casting operation. With this process, because of the maximum length allowed
in the continuous casting machine for solidification and because the stral1d is
essentially parallel, there is enough flexibility to slow down the machine to
allow a shand stoppage. Typically such a conventional continuous casting
machine would have sufficient flexibility to allow a strand stoppage of up to
20 three minutes which allows the tundish change to takes place.
GB 1145860 discloses an apparatus and method for the continuous casting of
metal having tundishes which, as the time for changeover of the tundish
approaches, pour metal continuously into the mould. This is achieved by the
25 use of refractory chutes which, in this simultaneous pouring stage, transfers the
molten metal from the nozzle of the tundishes to the mould. Thus metal is
continuously poured whilst the tundish is changed over. The problem with this
method however is that the chutes get clogged up with molten metal l)ecause it
is difficult to m:~int:~in a sufficiently high temperature in the chute. Also
30 oxidation of the metal occurs in the chute which results in diminished ~luality
of the final product and loss of yield. The molten metal falls from the chute
into the mould through the opening 90.
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There are additional significant disadvantages with all the above conventional
methods. It is not possible to increase the casting speed significantly without
c~ . significant interruption problems. Additionally there are inlelluplion
problems with lower strand thicknesses. Additionally, and more recently
5 casting machines have been developed which are tapered such that the cast
section is gradually reduced after initial forming in the mould and before finalsolidification. These circumstances mean that it is not possible to slow down
or stop the casting process for a sufficient length of time to allow the
conventional flying tundish change method and therefore long runs are not
10 possible for these specific circumstances.
It is therefore an objective of the invention to provide a tundish change methodand an apparatus therefore and tundish shape which enables long casting runs
for reduced strand thickness as well as for tapering of the castin~ machine. lt is
15 also an objective of the invention to provide a tundish change method and
tundish therefore which allows long casting runs to be continuous and
unilltellupted at increased speeds.
According to the invention there is provided a method of continuous casting of
20 metal, comprising pouring the molten metal from a tundish into a mould
thlougll a tap hole in a base wall of the tundish, and wherein first and second
tundishes each comprising a corresponding first and second tap hole and
associated first and second nozzle means, are used to enable the flow of molten
metal to be continuous or nearly continuous, such that when one of the first
25 tundish is required to be changed it is moved into a first tundish changeoverposition, and the second tundish is moved into a second tundish changeover
position, and wherein in the changeover position both the first and second
tundishes are in position over the mould so that metal may flow from both
tundishes simultaneously into the mould, characterised in that in the
30 chall~eover position tlle first and second nozzle meatls of the first ~nd second
tundishes are immersed in the molten metal in the mould.
ln the first stage of the preferred method of the invention a first tundish in the
casting position is positioned over the mould so that molten metal can flow
35 tllrougll tlle lap llole inlo ~lle moul~l. Tllc rlrst lu~ isll is lyl)ieally loealc(l 400
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mm above the mould and a pouring tube directs the flow of metal from the
tundish into the mould. A second tundish is in a position alongside the first
tundish in the plan view.
5 In the second stage of the method of the invention, which occurs when the level
of the molten metal in the first tundish has reached a pre-determined low level,the second tundish is lowered to the level of the fill position, which is in a
preferred embodiment approximately 400 mm above the mould. Then both the
first and second tundishes are positioned so that the tap hole of the second
10 tundish is also located over the mould. Although the first tap hole has been
moved sideways with the first tundish, it nevertheless is still in a position over
the mould and molten metal is still flowing into the mould from the first
tundish. The tap hole of the second tundish is then opened so that molten metal
flows from the second tundish into the mould. Preferably the flow from the
15 first and second tundishes will be regularised so that is does not exceed a
prescril~ed rate which is preferably the same rate as a single tap hole when fully
open. The flow rate is preferably regulated by tap hole valves which may l~e
controlled by suitable control systems. Preferably this stage is maintained until
the first tundish is emptied at which point the flow from its tap hole is zero and
20 the flow from the second tundish tap hole is correspondingly regulated to the required full flow.
Preferably the tap holes of the fist and second tundishes are arranged
symmetrically on either side of a centreline of the mould.
According to a subsequent third stage of the method of the invention, when the
first tundish is empty its tap hole is closed and it is raised above the level of the
fill position and moved to a park position. The second tundish is then able to
be moved sideways to a position where the tap hole of the second tundish is
30 positioned centrally in the mould. This is the pl~;relled position when the
whole of the flow is coming from a single tundish.
Accordillg to a fourth stage of the method of the invention, the first tundish is
located in the side ways to a parking position above the fill level which permits
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a third tundish to be moved into position ready for the cycle to be repeated
agam.
According to the invention there is also provided a continuous casting
5 apparatus for carrying out the method described above. The apparatus
comprises the two tundishes which are so shaped as to each have top sides
which when the tundishes are arranged so that the corresponding sides of each
tundishes are abutting, the tap holes of the corresponding tundishes are close to
each other. This enables pouring to occur simultaneously from both of the tap
10 holes into the mould for casting strands with a strand width which is at least as
wide as the distance between the respective tap holes.
According to the invention there is also provided a tundisll which comprises
sides two front sides, two long sides, two short sides and a rear side, a base
15 and an open or closed top. The tap hole is arranged at the top end of the
tundish in the base so that molten metal flows out downwaldly, into the paper
as shown, into the mould. The base comprises slightly angled surfaces, angled
towards the tap hole, to enable the molten metal to flow towards the tap hole.
The tundish is so arranged so that the tap hole is a close as possible to the front
20 sides so that the distance between the tap holes of corresponding tundishes
when in the position when both tundishes are pouring simultaneously, is
minimised. The front sides could be arranged to be non-symmetrical and at
any desired angle.
25 One side may be more acute angle to make that side closer to the tap hole.
Preferably the top sides are symmetrical and forming an apex of 90 degrees.
There now follows a more detailed description of a specific embodiment of the
method and apparatus according to the invention with the help of the attached
30 drawings in which:
Fig. 1 is a plan view of a first stage the existing tundish change method,
Fig. 2 is a plan view of a second stage of the existing tundish change
35 method,
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Fig. 3 is a plan view of a third stage of the existing tundish change
method,
5 Fig. 4 is a plan view of the apparatus of the embodiment of the
invention in a first stage of the method of the invention,
Fig. 5 is a plan view of the apparatus of the embodiment of the
invention in a second stage of the method of the invention,
Fig. 6 is a plan view of the apparatus of the eml~odiment of the
invention in a third stage of the method of the invention,
Fig. 7 is a plan view of the ~pal~lus of the eml)odiment of the
15 invention in a fourth stage of the method of the invention,
- Fig. 8 is an enlarged plan view of the apparatus of the embodiment of the invention,
20 Fig. 9 is an enlarged plan view of the tundish of the apparatus of the
embodiment of the invention, and
Fig. 10 is an elevation of the casting apparatus of the present invention.
Figures 1 to 3 showing a conventional method of tundish changeover as
described above. When the first tundish 1 is expended the tap hole 3 is closed
and the first tundish 1 is moved to the left to a parking position.
Simultaneously the second tundish 2 is moved into the moulding position and
30 its tap l~olc 4 is opcllcd ~l~d thc flow of moltell met~l into the mollld re-commences. It is clear to see that with this method the flow of molten metal
into the mould is actually stopped for the period of time it takes to cany out
these steps from the closing of the tap hole 3 to the opening of the tay hole 4.
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Referring now to figures 4 to 7, the apparatus accordin~ to the embodiment of
the invention is shown as well as four stages of lhe mefllod of tlle illventioIl. In
figure 4 a first tundish 11 is shown in the casting position and is positioned
over the mould 15 so that molten metal can flow through the tap hole 13 into
5 the mould 15. The first tundish 11 is typically located 400 mm above the
mould and a pouring tube, or nozzle means, directs flow to the mould. In this
casting position the first tundish is arranged so that the pouring tube is arranged
centrally in the mould and is immersed in the molten metal. The tap hole 13 is
fully open. A second tundish 12 is in a position alongside the first tundish 11
10 in the plan view. This position is called a pre-casting position.
Referring now to figure 5 a second stage in the method of the invention is
shown which occurs when the level of the molten metal in the first tundish 11
has reached a pre-determined low level. The second tundish 12 is then
15 positioned at a mould filling pOSitiOll, which is approximately 400 mm al)ove the mould. Additionally both the first and second tundishes are moved
sideways to corresponding changeover position, in which the tap hole 14 of the
second tundish 12 is also positioned over the mould 15. Although the first tap
hole 13 has been moved sideways with the first tundish 11, it nevertheless is
20 still also in a position over the mould 15 and molten metal is still flowing into
the mould from the first tundish 11. The tap hole 14 of the second tundish 12
is then opened so that molten metal flows from the second tundish into the
mould 15. At this point molten metal is flowing from both the first and second
tundishes into the mould. The flow will be regularised so that is does not
25 exceed a prescribed rate which is preferably the same rate as a single tap hole
when fully open. So the flow rate will be made up of a portion of the flow rate
from tap hole 13 and a portion of the flow rate from tap hole 14. This could be
for example half of the normal flow rate from each of the tap holes 13, 14. The
flow rate is regulated by tap hole valves which are known in the alt and which
30 may be controlled by suitable control systems, which would also be apparent to
the person skilled in the art, so that the desired flow from any one tap hole and
hence the total flow can be controlled. This stage is m:lint:lined until the first
tundish 11 is emptied at which point the flow from tap hole 13 is zero and the
flow from tap hole 14 is correspondingly increased to full flow, i.e. it is opened
35 complelely. Tlle flow ol' llle mollell mclal illlo llle moul(l llas lllcrel'olc l)ccll
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maintained at a constant flow rate and there has been no interruption, or
essentially no interruptioll, in the flow rate during the changeover of the
tundishes.
5 Referring now to figure 6, the first tundishes 11 is moved upwardly above the
fill level out of the paper in figure 6 to permit the second tundish 12 to move to
a position where the tap hole 14 of the second tundish 12 is positioned
centrally in the mould 15. This is the preferred position when the whole of the
flow is coming from a single tundish.
Referring now to figure 7, the first tundish 11 is then moved side ways (to the
left in figure 7) to a parking position so that a third tundish can be moved into
position ready for the cycle to be repeated again.
15 Referring now to figure 8 an enlarged view of the continuous casting apparatus
of the invention is shown in the changeover position when both tundishes are
pouring molten metal, into tlle mould just before one of them is emptied and
moved out of position. It can l~e seen from the figure that the apparatus
comprises the two tundishes 11, 12 which are so shaped as to each have top
20 sides 16, 17 which when the tundishes are arranged so that the corresponding
sides of each tundishes are abutting, the tap holes 13, 14 of the corresl)ondingtundishes are close to each other. It will be appreciated that when the tundishes
are compared to the tundishes of the prior art it can l)e seen that the distancebetween the corresponding tap holes of the prior art tundishes is much greater.
25 This enables pouring to occur simultaneously from both of the tap holes into
the mould 15 for casting strands with a strand width which is at least as wide as
the distance between the respective tap holes 13, 14.
Referring to figure 9 an enlarged view of a single tundish of the invention is
30 shown which comprises sides two front sides 16, 17, two long sides 18, 19 twoshort sides 21, 22 and a rear side 23. The tap hole is arranged at the top end of
the tundish 11 in the base so that molten metal flows out downwardly, into the
paper as shown, into the mould. The l~ase 24 comprises surfaces which are
angled towards the tap hole. The tundish is so arranged so that the tap hole 13
35 is a close as possil)le lo lhe liont sides 16, 17 so lhal lile (lislallcc ~elweell llle
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tap holes 13, 14 of corresponding tundishes when in the position in figure 8, isminimi.~ed. lt will be appreciated that within the scope of the invention the top
sides could l)e arranged to be non-symmettical and at any desired aulgle. One
side could for instance be made at and significantly more acute angle to make
S that side closer to the tap hole 13 so that when it is abutted against a
corresponding side of a second tundish the distance between the conesponding
tap holes is reduced. The embodiment shown however, with the top sides
symmetrical and forming an apex of 90 degrees, has the advantage that the
tundishes can be used from either side which simplifies the changeover
10 operation and reduces the required inventory of spare tundishes. lt will be
appreciated that the apex could be at an alternative desired angle.
In order that even narrower strands of mould can be accommodated using thc
present invention to avoid any interruptions to the flow, it is possible to provide
15 an angled pouring tube which directs the flow of molten metal from the tap
hole inwardly into the narrow mould. Thus moulds for strands which are
narrower than the distance between the tap holes of corresponding tundishes
can be used.
20 Referring now to fig. 10 a side elevation of the apparatus, is shown to show the
complete operation of the casting appatatus and method of the invention. The
tundishes 11, 12 are charged from a ladle 8 as shown schematically in fig. 10.
In the 11, 12 have corresponding pouring tul)es 9, 10 which are immersed in
the molten metal in the mould 15. The tundishes are shown in fig. 10 in their
25 corresponding changeover positions with both tundishes 11, 12 discharging
metal and both pouring tubes 9, 10 immersed in the molten metal in the mould
15. When the first tundish 11 is empty it is closed and moved upwards in
figure 10 and then sideways out of the page in fig. 10 to a parking position
allowing the second tundish to adopt a central poring pOSitiOII over the mould
30 and a new tundish to ready to be moved into the moulding positions when the
second tundish is nearly empty. So in the same way as with the second tundish
the new tundish adopts a changeover position when the second tundish is
nearly empty with both tundishes pouring, followed by a central pouring
position when the second tundish has moved off to its parking position.
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After exiting the mould 15 the molten metal enters a series of casting rolls
forming a strand support 32 during which the metal solidifies completely and
then enters the subsequent operational steps 33 as a fully cast strand or slab.
