U.S. patent application number 11/294629 was filed with the patent office on 2006-06-08 for method and apparatus for melt flow control in continuous casting mold.
Invention is credited to Yogeshwar Sahai.
Application Number | 20060118272 11/294629 |
Document ID | / |
Family ID | 36169127 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060118272 |
Kind Code |
A1 |
Sahai; Yogeshwar |
June 8, 2006 |
Method and apparatus for melt flow control in continuous casting
mold
Abstract
A method and apparatus for continuous casting of metal. The flow
of molten metal is altered to eliminate or reduce the transfer of
entrained mold flux slag and non-metallic particles to the vicinity
of solidifying metal near the mold walls, thereby resulting in
significantly reduced sliver and related defects. Flow modifier
members are placed such that their larger surface is more aligned
with the larger dimension of the interior volume of the vessel in
which the member is placed. In a particular form, the members may
be shaped as rectangular plates and placed substantially parallel
to the longer interior wall of the vessel.
Inventors: |
Sahai; Yogeshwar; (Powell,
OH) |
Correspondence
Address: |
DINSMORE & SHOHL LLP;One Dayton Centre
Suite 1300
One South Main Street
Dayton
OH
45402-2023
US
|
Family ID: |
36169127 |
Appl. No.: |
11/294629 |
Filed: |
December 5, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60633241 |
Dec 3, 2004 |
|
|
|
Current U.S.
Class: |
164/488 |
Current CPC
Class: |
B22D 11/041 20130101;
B22D 11/10 20130101; B22D 11/103 20130101; B22D 41/50 20130101 |
Class at
Publication: |
164/488 |
International
Class: |
B22D 11/10 20060101
B22D011/10 |
Claims
1. A continuous casting system comprising: a mold vessel adapted to
receive a flow of molten metal therein, said vessel comprising a
plurality of inner surfaces such that an interior volume is defined
thereby, said interior volume comprising a width dimension and a
thickness dimension that generally corresponds to a respective
width and thickness of a slab of metal produced by said system; a
submerged entry nozzle arranged within said interior volume and
extending below a molten metal upper surface formed upon
introduction of said molten metal into said interior volume, said
submerged entry nozzle comprising at least one discharge port
adapted to dispense a mixture of gas and said molten metal into
said interior volume; and at least one flow modifier member
disposed in said interior volume, said at least one flow modifier
member having a height dimension, a width dimension and a thickness
dimension such that at least one major surface and at least one
minor surface is defined thereby, said at least one major surface
defining a larger surface area than said at least one minor
surface, said major surface angularly aligned closer to the wider
of said width and thickness dimensions of said interior volume.
2. The system of claim 1, wherein said major surface is angularly
aligned substantially parallel to the wider of said width and
thickness dimensions of said interior volume.
3. The system of claim 1, wherein said at least one flow modifier
member extends below said molten metal upper surface.
4. The system of claim 1, wherein said interior volume comprises a
rectangular shape.
5. The system of claim 4, wherein each of said at least one flow
modifier members is disposed between said submerged entry nozzle
and the narrower of said width and thickness dimensions of said
interior volume.
6. The system of claim 1, wherein said at least one flow modifier
member extends upwardly at least into a flux layer disposed
substantially on top of said molten metal upper surface.
7. The system of claim 1, wherein said height, width and thickness
dimensions of said at least one flow modifier member are such that
said at least one flow modifier member defines a plate.
8. The system of claim 7, wherein said plate is substantially
planar.
9. The system of claim 1, wherein said discharge port of said
submerged entry nozzle extends below said flow modifier member.
10. The system of claim 1, wherein said at least one discharge port
is adapted to dispense said mixture of gas and molten metal into
said interior volume at an angle relative to said interior volume
width and thickness dimensions.
11. The system of claim 1, wherein said at least one discharge port
is adapted to dispense said mixture of gas and molten metal
substantially parallel to said interior volume width dimension.
12. The system of claim 11, wherein said at least one flow modifier
member comprises a group of flow modifier members, said group
configured such that individual flow modifier members in said group
are spaced apart from one another substantially along a
through-the-thickness axis thereof such that at least a majority of
said mixture of gas and molten metal exiting said discharge port
flows substantially between said individual flow modifier members
in said group.
13. The system of claim 12, wherein said individual flow modifier
members within said group are substantially parallel to one
another.
14. A flow modifier member configured for use in a continuous
casting system, said flow modifier comprising at least one first
surface and at least one second surface, said at least one first
surface covering a larger surface area than said at least one
second surface, said flow modifier member configured such that upon
placement into a substantially rectangular casting vessel defining
a width dimension and a thickness dimension such that said with
dimension the is greater of the two, said at least one first
surface is angularly aligned closer to said width dimension while
said at least one second surface is angularly aligned closer to
said thickness dimension of said vessel.
15. The flow modifier member of claim 14, wherein said flow
modifier member comprises a refractory material.
16. The flow modifier member of claim 15, wherein said refractory
material is a ceramic.
17. The flow modifier member of claim 14, further comprising at
least one joiner disposed between adjacent ones of said flow
modifier members, said at least one joiner sized to block the
substantial entirety of space defined between said adjacent ones of
said flow modifier members.
18. A method for controlling the flow of molten metal in a
continuous casting system, said method comprising: configuring a
vessel to comprise a plurality of walls comprising a height
dimension, a width dimension and a thickness dimension to define an
interior volume thereby, said width dimension being greater than
said thickness dimension; introducing a mixture of molten metal and
gas into said interior volume such that a molten metal upper
surface is defined within said interior volume; and placing a flow
modifier member in a location within said interior volume between
where said mixture introduction occurs and said wall that defines
said thickness dimension, said flow modifier member comprising a
height dimension, a width dimension and a thickness dimension such
that at least one major surface and at least one minor surface is
defined thereby, said at least one major surface defining a larger
surface area than said at least one minor surface, said major
surface angularly aligned closer to said wall that defines said
width dimension such that the velocity of molten metal flowing
adjacent said molten metal upper surface is reduced.
19. The method of claim 18, wherein said mixture introduction
occurs through a submerged entry nozzle.
20. The method of claim 19, wherein said submerged entry nozzle is
angled relative to said interior volume such that said introduced
mixture exits said submerged entry nozzle at an angle relative to
both said width and thickness dimensions of said interior
volume.
21. The method of claim 20, wherein said flow modifier member
comprises a pair of flow modifier members, each arranged on
opposite sides of said submerged entry nozzle such that each is
disposed between said submerged entry nozzle and said walls of said
vessel that define said thickness dimension thereof.
22. The method of claim 18, wherein said flow modifier member
comprises a plurality of flow modifier members arranged in at least
one group such that individual flow modifier members within each
said at least one group are spaced apart from one another
substantially along a through-the-thickness axis thereof such that
at least a majority of said mixture of gas and molten metal exiting
said discharge port flows substantially between said individual
flow modifier members in said at least one group.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/633,241 filed Dec. 3, 2004.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to the field of
continuous casting of steel, and more particularly to a device and
method for flowing molten metal in continuous castings that
produces fewer defects in the cast product.
[0003] In continuous casting of steel (such as plain carbon steel),
molten metal is poured from a ladle or tundish into a water-cooled
copper mold vessel by using a submerged entry nozzle (SEN). In the
continuous casting process, steel begins to solidify as it comes in
contact with the walls of the copper mold, the slab descending down
the height of the vessel. The thickness of slabs produced in such a
mold typically is about 9 to 12 inches (.about.230 to 300 mm),
whereas in a thin slab caster the thickness is only about 2 to 4
inches (.about.50 to 100 mm), while the width is much larger,
typically 60 to 72 inches (1500 to 1830 mm) and even up to 100
inches (2540 mm). A layer of mold flux (typically a metal oxide) is
maintained at the free surface of the molten metal in the mold.
This flux serves a couple of purposes; first, it protects the hot
metal from atmospheric oxidation, and second provides a thin
lubricating layer between the descending slab and the mold walls to
inhibit bonding between the two.
[0004] Traditionally, the molten metal was the only thing
introduced into the mold through the SEN. In more recent
variations, argon gas has also been injected with molten metal, so
metal and gas exit the SEN ports. The presence of gas has been
found to be beneficial in that it prevents inclusions (such as
alumina) inherent in the metal from clogging up the SEN as it
passes through. Additionally, the gas helps push inclusions present
in the molten metal upward to a free molten metal surface.
Nevertheless, the presence of gas also changes the molten metal
flow in the mold, as part of the molten metal is carried in the
wake formed by the rising gas bubbles. Several fluid flow studies
of continuous casting molds have shown that the flow of molten
metal in a mold has a large influence on the surface and subsurface
quality of the resultant cast metal. Factors that influence molten
metal flow in the mold include casting rate, mold width and
thickness, SEN design parameters and submergence depth. Among the
SEN design parameters are SEN internal configuration, port size,
number and location of ports, port tilt angle and SEN rotation
angle. One way to deal with the differing flow patterns produced by
the introduction of gas has been to rotate the angle of the SEN
about a vertical axis such that the traditional flow of molten
metal could be made to contact the walls of the mold in different
locations. In such rotated SEN configurations, metal flow would not
be substantially parallel to the wider of the mold walls; this
asymmetric flow condition produces significantly different flow
patterns that if left unchecked have the ability to exacerbate
rather than correct slab contamination through flux slag
entrainment.
[0005] One especially troublesome flow pattern for the continuous
casting of steel under such asymmetric flow conditions involves the
tendency of the gas and molten metal that exits the SEN to contact
the wider walls of the mold, after which they ascend to the free
surface of metal. Once it reaches the free surface, it flows across
the thickness (i.e., the shorter dimension) of the mold at the
interface between the molten metal and the flux with a relatively
high velocity. This high velocity can cause shearing of the mold
flux and the non-metallic inclusions from the interface, which in
turn could be carried downward to the solidifying metal slab when
molten metal contacts the opposing wall.
[0006] Regardless of whether the SEN is in a rotated or non-rotated
configuration, it is important when operating a SEN to dispense
mixtures of molten metal and gas to avoid high surface flow
velocities and the resultant downward carrying of impurities along
the walls of the casting vessel. Accordingly, there exists a need
for a device and method of continuous casting that reduces
contamination of the slab being cast.
BRIEF SUMMARY OF THE INVENTION
[0007] These needs are met by the present invention, wherein a
continuous casting system and a method of operating the system that
incorporates the features discussed below are disclosed. By the
present invention, the flow of metal is altered in such a way so
that it reduces the transfer of the entrained mold flux slag and
non-metallic particles to the vicinity of solidifying metal near
the mold walls, thereby significantly reducing sliver and other
defects. Although described with respect to the field of steel
casting, it will be appreciated that similar advantages of cleaner
metal casting with reduced defects, along with other advantages,
may apply to other applications of the present invention. Such
advantages may become apparent to one of ordinary skill in the art
in light of the present disclosure or through practice of the
invention.
[0008] In accordance with a first aspect of the present invention,
the system includes a mold vessel configured to contain and
dispense a molten metal for casting. The vessel includes numerous
inner surfaces that define an interior volume between them, where
the interior volume includes height, width and thickness
dimensions, where at least the width and thickness dimensions
generally correspond to a respective width and thickness of a slab
of metal produced within the vessel. A SEN is situated within the
vessel, and is arranged within the interior volume and extends
below a molten metal upper surface formed upon introduction of the
molten metal into the interior volume. The SEN includes one or more
discharge ports adapted to dispense a mixture of gas and the molten
metal into the interior volume. One or more flow modifier members
are disposed between the walls of the vessel to control the flow of
molten metal. In contrast to conventional flow modifier members
(which have an elongate dimension aligned substantially parallel to
the narrower (i.e., thickness) dimension of the casting vessel), an
elongate dimension of the one or more flow modifier members is
aligned substantially parallel to the more broad widthwise
dimension, thereby inhibiting flow along the thickness dimension of
the vessel.
[0009] Optionally, the major surface is angularly aligned
substantially parallel to the wider of the width and thickness
dimensions of the interior volume. In a preferred option, the
interior volume of the vessel is rectangular shaped. Additionally,
the one or more flow modifier members extend below the molten metal
upper surface. Moreover, each of the flow modifier members can be
disposed between the submerged entry nozzle and the narrower of the
width and thickness dimensions of the interior volume. The flow
modifier member (or members) preferably extends upwardly at least
into a flux layer that is situated substantially on top of the
molten metal upper surface. In another option, the height, width
and thickness dimensions of the flow modifier member(s) are such
that they define a plate, where in a particular form, the plate is
substantially planar. In a particular form, the discharge port of
the submerged entry nozzle extends below the flow modifier member.
In another, the discharge port is adapted to dispense the mixture
of gas and molten metal into the interior volume at an angle
relative to both the width and thickness dimensions of the vessel's
interior volume. In an alternate variation, the discharge port (or
ports) is adapted to dispense the mixture of gas and molten metal
substantially parallel to the interior volume width dimension. More
particularly, there are a group of flow modifier members. The group
is configured such that individual flow modifier members in the
group are spaced apart from one another substantially along a
through-the-thickness axis of the members. In such a configuration,
at least a majority of the mixture of gas and molten metal exiting
the discharge port flows substantially between the individual flow
modifier members in the group. More preferably, the individual flow
modifier members within the group are substantially parallel to one
another.
[0010] According to another aspect of the invention, a flow
modifier member configured for use in a continuous casting system,
the flow modifier comprising at least one first surface and at
least one second surface, the at least one first surface covering a
larger surface area than the at least one second surface, the flow
modifier member configured such that upon placement into a
substantially rectangular casting vessel defining a width dimension
and a thickness dimension such that the with dimension the is
greater of the two, the at least one first surface is angularly
aligned closer to the width dimension while the at least one second
surface is angularly aligned closer to the thickness dimension of
the vessel. Optionally, the flow modifier member is made from a
refractory material, such as a ceramic. In another option, at least
one joiner disposed between adjacent ones of the flow modifier
members, the at least one joiner sized to block the substantial
entirety of space defined between the adjacent ones of the flow
modifier members.
[0011] According to yet another aspect of the invention, a method
for controlling the flow of molten metal in a continuous casting
system is disclosed. The method includes configuring a vessel to
comprise a plurality of walls to produce an interior volume of the
vessel in which casting of the molten metal takes place. The walls
have height, width and thickness dimensions, where the width
dimension is of greater size than the thickness dimension.
Additionally, the method includes introducing a mixture of molten
metal and gas into the interior volume such that a molten metal
upper surface is defined by the top of the quantity of molten metal
within the vessel's interior volume. Another part of the method
includes placing a flow modifier member such as those previously
described in a location within the interior volume between where
the mixture introduction occurs and the wall that defines the
thickness dimension of the interior volume. The orientation of the
flow modifier member is such that a major surface (i.e., a larger
surface) is angularly aligned closer to the wall that defines the
vessel's width dimension. In this way, the velocity of molten metal
flowing adjacent the molten metal upper surface is reduced.
[0012] Optionally, the mixture introduction occurs through a
submerged entry nozzle such as that previously discussed. More
particularly, the submerged entry nozzle can be angled about its
vertical axis relative to the interior volume. In this way, the
introduced mixture exits the discharge port of the nozzle at an
angle relative to both the width and thickness dimensions of the
interior volume, thereby producing an asymmetric flow pattern when
viewed from above. In another particular form, the flow modifier
member is made up of a pair of flow modifier members, each arranged
on opposite sides of the submerged entry nozzle such that each is
disposed between the submerged entry nozzle and the narrower walls
of the vessel that define the vessel thickness dimension. In
another option, the flow modifier member is made up of numerous
flow modifier members arranged in one or more groups. Thus, that
individual flow modifier members within each group are spaced apart
from one another substantially along a through-the-thickness axis
of the members. In this way, at least a majority of the mixture of
gas and molten metal exiting the discharge port flows substantially
between the individual flow modifier members in each group.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 shows a front section elevation view of a
conventional continuous casting system, including a general melt
flow pattern without gas injection in a continuous casting
mold;
[0014] FIG. 2 shows a front section elevation view of a
conventional continuous casting system showing a general melt flow
pattern with relatively low volume of gas injection in a continuous
casting mold;
[0015] FIG. 3 shows the continuous casting system of FIG. 2 with
higher volume of gas injection;
[0016] FIG. 4 shows the continuous casting system of FIG. 2 with a
still higher volume of gas injection;
[0017] FIG. 5A shows a SEN with rotated orientation relative to the
narrow and broad walls of a conventional casting vessel;
[0018] FIG. 5B shows a SEN with a non-rotated orientation relative
to the narrow and broad walls of a conventional casting vessel;
[0019] FIGS. 6A and 6B show respectively a perspective and plan
view of a conventional continuous casting system, including flow of
injected gas and liquid metal in a mold with rotated SEN;
[0020] FIG. 7 shows a side (i.e., through the thickness) section
elevation view of a conventional continuous casting system,
including showing a general melt flow pattern of injected gas and
associated metal in the conventional continuous casting system
FIGS. 6A and 6B;
[0021] FIG. 8 shows a perspective view of a continuous casting
system including a pair of surface flow modifier members in
accordance with an embodiment of the present invention to reduce
the problems associated with the system of FIGS. 6A, 6B and 7;
[0022] FIGS. 9A through 9C show respectively a plan and front and
side elevation views of the system of FIG. 8;
[0023] FIG. 10 shows how a general melt flow pattern of injected
gas and associated metal is changed by the surface flow modifier
members of FIG. 8;
[0024] FIGS. 11A through 11C show a front sectioned elevation view
of the SEN having respectively a downward, horizontal and upward
discharge ports;
[0025] FIGS. 12A and 12B show respectively a perspective and plan
view of a conventional continuous casting system, including flow of
injected gas and liquid metal in a mold with a non-rotated SEN;
[0026] FIG. 13 shows a side sectioned elevation view of a
continuous casting system of FIGS. 12A and 12B, showing a general
melt flow pattern of injected gas and associated metal;
[0027] FIG. 14 shows a perspective view of a continuous casting
system including groups of cooperating surface flow modifier
members in accordance with an alternate embodiment of the present
invention to reduce the problems associated with the system of
FIGS. 12A, 12B and 13;
[0028] FIGS. 15A through 15C show respectively a plan and front and
side elevation views of the system of FIG. 12;
[0029] FIG. 16 shows how a general melt flow pattern of injected
gas and associated metal is changed by the surface flow modifier
members of FIG. 14;
[0030] FIG. 17 shows a variation on the embodiment of FIG. 14,
where the groups of cooperating flow modifiers are replaced with
substantially non-planar members; and
[0031] FIGS. 18A through 18C show respectively a plan and front and
side elevation views of the system of FIG. 17.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Referring first to FIG. 1, an elevation view of a
conventional continuous casting system showing a general flow
pattern in vessel (also referred to as a mold or mold vessel) 1 is
shown. Molten metal 2 emerges from discharge ports 3A in SEN 3 and
enters the vessel 1, flowing generally along flow lines 4A, 4B and
4C (collectively referred to as flow lines 4). Molten metal 2 then
emerges from the vessel 1 as a partially solidified slab 5 in the
shape of the vessel 1, which is typically rectangular with a
thickness dimension T, height (or length) dimension H and a width
dimension W (not presently shown). As the molten metal 2 progresses
through the vessel 1, a layer of solidified steel 6 is formed
against the interior surfaces 8 of the vessel 1, resulting in the
formation of a shell over the freshly cast slab 5. One or more flow
modifier members (not presently shown) may be located on either
side of the SEN 3, and have traditionally been used to prevent or
minimize downward liquid metal flow near the mold walls. This in
turn reduces the likelihood of entrapment of the liquid flux or
non-metallic inclusion (i.e., that which is carried with the liquid
metal from metal/flux interface) in the solidifying metal shell.
Normally, a molten metal upper (i.e., free) surface 10 will bear an
oxidation-preventing flux layer (for example, based on a metal
oxide), while the flow modifier members will extend into one or
both of the flux layer and the molten metal. In one form, the flux
is placed in powder form onto the molten metal upper surface 10;
the heat from the molten metal then striates the flux into a
powdered top layer and a liquid lower layer such that an interface
between the top of the molten metal and the bottom of the liquid
flux is formed (all shown and described later). The downward
movement of the metal through the vessel 1 is facilitated by a
layer of flux 9 that is situated on top of the molten metal upper
surface 10 that extends between the interior surfaces 8 and the
layer of solidified steel 6.
[0033] The molten metal 2, with no gas injection, exits SEN 3 at an
angle relative to the horizontal and impinges on the narrower wall
1A of vessel 1 that corresponds to the thickness dimension of the
formed slab. This flow impingement results in the formation of
upper and lower recirculating flow lines 4A, 4B. The upper
recirculation flow lines 4A cause a standing wave at the molten
metal upper surface 10. The height of the wave typically oscillates
with time. The oscillating standing wave and associated turbulence
at the molten metal upper surface 10 is considered to be one of the
reasons for most of the defects in cast slabs made by this
process.
[0034] Referring next to FIGS. 2 through 4, the introduction of a
metal and gas mixture into the vessel 1 through SEN 3 is shown. As
mentioned above, the nature of the surface standing wave and
turbulence changes with different levels of gas injection. FIG. 2
shows that at relatively small gas flow ratio, the upper
recirculation flow lines 4A still remain counter-clockwise on the
right side of the vessel 1, while the height of the surface
standing wave is reduced as some molten metal 2 is carried to the
upper surface 10 by gas bubbles 11. FIGS. 3 and 4 show altered
upper recirculation lines 4A with increasing gas flow ratios, where
at large gas flow ratios (FIG. 4), upper recirculation lines 4A are
completely reversed and one large loop forms on each side of the
vessel 1. While the increased gas flow is desirable for reducing
standing waves and for conveying some of the inclusions upward and
away from the solidifying slab 5, it can be detrimental in that it
allows relatively high velocity molten metal on the upper surface
10 to capture and drag flux or other surface contaminants downward
near the solidifying slab 5.
[0035] Referring next to FIGS. 5A and 5B, the difference in molten
metal flow exiting the SEN 3 can be seen for non-rotated (FIG. 5A)
and rotated (FIG. 5B) conditions. In the non-rotated embodiment of
FIG. 5A, the flow of the molten metal is generally parallel to the
widthwise dimension of the vessel 1, while in the rotated
embodiment of FIG. 5B, SEN 3 is rotated about its longitudinal
(vertical) axis such that the flow is angled relative to a central
axis A by an angle .theta. and produces an asymmetric (when viewed
from above) profile.
[0036] Referring next to FIGS. 6A, 6B and 7, the gas/liquid jet
exiting from the rotated SEN 3 of FIG. 5B would contact the more
broad wall 1B of the vessel 1 and rise to the molten metal surface
of metal. Referring with particularity to FIGS. 6A and 6B, the
width, thickness and height dimensions W, T and H of the vessel 1
define an interior volume V into which molten metal 2 is placed and
slab 5 (not presently shown) is formed. In particular, the flow F
of the gas and molten metal mixture is divided into numerous
regions, including F1 through F4. In the first region F1, gas and
liquid flow F that exits the discharge port 3A of SEN 3 first
contacts the more broad (i.e., wider) wall 1B of vessel 1. In the
second region F2, the buoyancy of the gas 11 causes the mixture to
travel upward to the surface 10. In the third region F3, the flow
F, upon reaching the surface 10, travels horizontally across the
surface and toward the opposing wall 1B. Depending on the velocity
of this horizontal flow F3, the flux layers 12A, 12B can shear,
which causes a disruption of inclusions or other contaminants that
have settled on the surface 10. Upon reaching region F4, the flow F
can capture and drag these contaminants downward into the shell 6
and the as yet unsolidified molten metal 2, where they can corrupt
the formed slab 5 (not presently shown). A side view (i.e., looking
along the widthwise dimension of the vessel 1) of regions F2, F3
and F4 of the flow F is shown in FIG. 7 with the relative position
of the molten metal upper surface 10 and flux 12, where the latter
is made up of a powdered flux layer 12A and a liquid flux layer
12B. FIG. 7 further indicates that with the relatively small
thickness dimension T (and concomitant inability to allow for
geometric spreading of the flow) of vessel 1, the velocity of the
liquid metal increases along the interface 14 of the molten metal 2
and liquid flux 12B. These high velocities can cause shearing of
the flux 12 and any non-metallic inclusions present on the
interface 14.
[0037] Referring next to FIGS. 8 through 11C, an embodiment of the
present invention is shown where the SEN 3 is rotated such that the
discharge of the gas and molten metal mixture from the discharge
ports 3A is angled relative to the narrow and broad walls 1A and 1B
of the vessel 1. In the present embodiment, the mixture exits as
flow F through the discharge ports 3A (only one of which is shown)
at an angle relative to the central axis A. Referring with
particularity to FIG. 8, the unique orientation of the flow
modifier members 15 reduces the tendency of the flow of molten
metal 2 to shear the flux 12 at the interface 14, instead causing
the horizontal flow region F3 to form a predominantly
circumferential flowpath along the molten metal upper surface 10.
This eliminates or significantly reduces downward flow region F4 of
the mixture, as well as any entrained inclusions or other
contaminants from the flux 12, thereby reducing the likelihood of
introducing such into the molten metal 2 and solidifying metal slab
5 (not presently shown) at the vessel walls 1A, 1B. Three views of
the placement and orientation of flow modifier members 15 in a
vessel 1 are shown in FIGS. 9A through 9C. As before, the width,
thickness and height dimensions W, T and H define an interior
volume V of the vessel 1. The narrow walls 1A are formed by a plane
made up of the height and thickness dimensions H, T, while the more
broad walls 1B are formed by a plane made up of the height and
width dimensions H, W. In addition, the plates 15 extend both above
the molten metal upper surface 10, as well as below the surface
such that they project into the layer of molten metal 2. As shown,
the lower edge of the plates 15 do not project below the bottom of
SEN 3, although a configuration where the lower edges do extend
below the discharge ports of SEN 3 is within the scope of the
present invention. Referring with particularity to FIG. 10, a side
view of the flow of metal through vessel 1 with flow modifier
members 15 is shown. Downward flow near the wall is significantly
reduced or eliminated as a result of the placement of the flow
modifier members 15. As can be seen with particularity in FIGS. 11A
through 11C, the tilt angle of the discharge ports 3A can be
horizontal, downwards or upwards, for example, up to approximately
twenty degrees in either direction. Such can be used to control the
amount of first region F1 flow in vessel 1.
[0038] As shown, the flow modifier members 15 are
rectangular-shaped plates, although it will be appreciated that any
shape capable of causing significant changes in molten metal flow
could be adopted. In addition, the plates 15 are generally
positioned centrally within the vessel 1 and parallel to the longer
wall dimensions 1B and are oriented in-line with respect to each
other on opposite sides of the SEN 3 on the central axis A
extending through the center of the SEN 3. As shown with
particularity in FIG. 10, in a variation of the embodiment depicted
in FIG. 8, the plates 15 may also be positioned parallel to the
longer walls 1B but off-set of the central axis A. In yet another
variation (not shown), the plates 15 may be positioned at an angle
relative to the central axis A. For example, the plates 15 can be
angled up to approximately forty degrees relative to the central
axis A and still maintain a significant flow modification function.
The plates 15 are generally positioned such that they are placed
centrally of the space between the SEN 3 and the narrow walls 1A of
vessel 1, but they may be located closer or farther from the SEN 3.
The size of plate 15 would depend upon the width W of vessel 1 and
volume of injected gas. Preferably, each plate 15 is sized to cover
most of the width of gas and molten metal mixture that is rising up
to the molten metal upper surface 10.
[0039] Experiments conducted by the inventor have shown that the
design of the plates 15 is independent, to some extent, of the
width W of the vessel 1, gas flow rate and metal casting rate. Thus
during a normal casting operation, any fluctuations in the gas and
liquid metal flow rates should not have any effect on the plate 15
operation in controlling the metal flow. FIG. 8 shows that the
predominant vertical metal flow of FIG. 2 is transformed by the
presence of plates to a large horizontal metal flow at the surface
10. In addition to reducing surface flow velocity, this is also
good for uniform distribution of mold flux powder placed on the
surface 10. The flow instabilities, which are inherent in any
normal mold flow operation and are mainly responsible for the
casting defects, seem to have significantly reduced with the
installation of plates 15.
[0040] Referring next to FIGS. 12A through 16, a non-rotated SEN 3
and another embodiment of the invention useable with such a SEN 3
configuration is shown. Referring with particularity to FIGS. 12A,
12B and 13, which are a variation of the device shown in FIGS. 6A,
6B and 7, the flow F of the gas and molten metal mixture exiting
SEN 3 is shown. The particular flow regions F1 through F4 differ.
For example, in the present embodiment, the first region F1
transitions to the second region F2 without hitting the broad walls
1B. Thus, by the time the horizontal flow region F3 commences on
the surface 10, it can extend in both directions along the
thickness dimension T of vessel 1, after which it drops downward as
shown by the fourth region F4. Referring with particularity to FIG.
14, in situations where there is little or no rotation of the SEN 3
about its vertical axis, two plates 15 may be grouped together to
be used on either side of the SEN 3. In this embodiment, the plates
15 in each group 15A and 15B are typically arranged parallel to
both each other as well as to the longer walls 1B of the mold.
Moreover, they are in-line with each other along central axis A.
Although not shown, it will be appreciated that the plates 15 may
be positioned at an angle with each other. In the variant shown in
the figures, the plates 15 are spaced apart by a distance which is
approximately the same as the cross-sectional dimension of the SEN
3. As with the embodiment described in FIGS. 8 and 9, it is
possible for the plates 15 in each group 15A, 15B to be positioned
parallel to the broad walls 1B but off-set of the central axis A.
Alternatively, the plates 15 may be positioned at an angle (not
shown) to the central axis A, for example up to approximately forty
degrees. The plates 15 are generally positioned such that they are
placed centrally of the space between the SEN 3 and the narrow
walls 1A, but may also be located closer or farther from the SEN 3,
depending on the need. FIGS. 15A through 15C show three views of
the system configuration shown in FIG. 14. Because the SEN 3 is not
rotated, most of the gas exiting its discharge ports 3A may be
contained between the plates 15 of each group 15A, 15B. This
arrangement reduces the downward flow F4 near the broad walls 1B of
the vessel 1, as shown in FIG. 16, as the flow F of the gas and
molten metal mixture is carried to the surface 10 in between plates
15, thereby keeping it substantially within the middle of the mold
rather than near the broad walls 1B.
[0041] Referring with particularity to FIGS. 17 and 18, yet another
embodiment of the design of the system with flow modifier members
15 is shown. Here, each group 15A, 15B of plates are joined
together by joiner 16 at one end near the narrow wall 1A of the
mold. This is schematically shown in a three-dimensional
representation in FIG. 17 and two-dimensional views in FIG. 18. As
with the previous embodiments, the orientation options of the
plates 15 can also be varied, depending on the need. As with the
embodiment of FIG. 12, the present embodiment is particularly
well-suited to systems where the SEN 3 is in a non-rotated
position, so that most of the gas and molten metal mixture exiting
the SEN 3 may be contained between the two plates 15 of each group
15A, 15B. This design would be preferred when the gas volume is
high enough to cause a single loop flow shown in FIG. 4. This flow
modifier would also prevent flow of liquid metal near the mold
narrow wall.
[0042] Having described the invention in detail and by reference to
preferred embodiments thereof, it will be apparent that
modifications and variations are possible without departing from
the scope of the invention defined in the appended claims. More
specifically, although some aspects of the present invention are
identified herein as preferred or particularly advantageous, it is
contemplated that the present invention is not necessarily limited
to these preferred aspects of the invention.
* * * * *