Fluid sprinkling – spraying – and diffusing – Rigid fluid confining distributor – Having interior filter or guide
Reexamination Certificate
2001-06-14
2002-10-15
Morris, Lesley D. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Rigid fluid confining distributor
Having interior filter or guide
C239S553000, C222S603000
Reexamination Certificate
active
06464154
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a casting or submerged entry nozzle and more particularly to a casting or submerged entry nozzle that improves the flow behavior associated with the introduction of liquid metal into a mold through a casting nozzle.
2. Description of the Related Art
In the continuous casting of steel (e.g. slabs) having, for example, thicknesses of 50 to 60 mm and widths of 975 to 1625 mm, there is often employed a casting or submerged entry nozzle. The casting nozzle contains liquid steel as it flows into a mold and introduces the liquid metal into the mold in a submerged manner.
The casting nozzle is commonly a pipe with a single entrance on one end and one or two exits located at or near the other end. The inner bore of the casting nozzle between the entrance region and the exit region is often simply a cylindrical axially symmetric pipe section.
The casting nozzle has typical outlet dimensions of 25 to 40 mm widths and 150 to 250 mm lengths. The exit region of the nozzle may simply be an open end of the pipe section. The nozzle may also incorporate two oppositely directed outlet ports in the sidewall of the nozzle where the end of the pipe is closed. The oppositely directed outlet ports deflect molten steel streams at apparent angles between 10-90° relative to the vertical. The nozzle entrance is connected to the source of a liquid metal. The source of liquid metal in the continuous casting process is called a tundish.
The purposes of using a casting nozzle are:
(1) to carry liquid metal from the tundish into the mold without exposing the liquid metal to air;
(2) to evenly distribute the liquid metal in the mold so that heat extraction and solidified shell formation are uniform; and
(3) to deliver the liquid metal to the mold in a quiescent and smooth manner, without excessive turbulence particularly at the meniscus, so as to allow good lubrication, and minimize the potential for surface defect formation.
The rate of flow of liquid metal from the tundish into the casting nozzle may be controlled in various ways. Two of the more common methods of controlling the flow rate are: (1) with a stopper rod, and (2) with a slide gate valve. In either instance, the nozzle must mate with the tundish stopper rod or tundish slide gate and the inner bore of the casting nozzle in the entrance region of the nozzle is generally cylindrical and may be radiused or tapered.
Heretofore, prior art casting nozzles accomplish the aforementioned first purpose if they are properly submerged within the liquid steel in the mold and maintain their physical integrity.
Prior art nozzles, however, do not entirely accomplish the aforementioned second and third purposes. For example,
FIGS. 19 and 20
illustrate a typical design of a two-ported prior art casting nozzle with a closed end. This nozzle attempts to divide the exit flow into two opposing outlet streams. The first problem with this type of nozzle is the acceleration of the flow within the bore and the formation of powerful outlets which do not fully utilize the available area of the exit ports. The second problem is jet oscillation and unstable mold flow patterns due to the sudden redirection of the flow in the lower region of the nozzle. These problems do not allow even flow distribution in the mold and cause excessive turbulence.
FIG. 20
illustrates an alternative design of a two-ported prior art casting nozzle with a pointed flow divider end. The pointed divider attempts to improve exit jet stability. However, this design experiences the same problems as those encountered with the design of FIG.
18
. In both cases, the inertial force of the liquid metal traveling along the bore towards the exit port region of the nozzle can be so great that it cannot be deflected to fill the exit ports without flow separation at the top of the ports. Thus, the exit jets are unstable, produce oscillation and are turbulent.
Moreover, the apparent deflection angles are not achieved. The actual deflection angles are appreciably less. Furthermore, the flow profiles in the outlet ports are highly non-uniform with low flow velocity at the upper portion of the ports and high flow velocity adjacent the lower portion of the ports. These nozzles produce a relatively large standing wave in the meniscus or surface of the molten steel, which is covered with a mold flux or mold powder for the purpose of lubrication. These nozzles further produce oscillation in the standing wave wherein the meniscus adjacent one mold end alternately rises and falls and the meniscus adjacent the other mold end alternately falls and rises. Prior art nozzles also generate intermittent surface vortices. All of these effects tend to cause entrainment of mold flux in the body of the steel slab, reducing its quality. Oscillation of the standing wave causes unsteady heat transfer through the mold at or near the meniscus. This effect deleteriously affects the uniformity of steel shell formation, mold powder lubrication, and causes stress in the mold copper. These effects become more and more severe as the casting rate increases; and consequently it becomes necessary to limit the casting rate to produce steel of a desired quality.
Referring now to
FIG. 17
, there is shown a nozzle
30
similar to that described in European Application 0403808. As is known to the art, molten steel flows from a tundish through a valve or stopper rod into a circular inlet pipe section
30
b
. Nozzle
30
comprises a circular-to-rectangular main transition
34
. The nozzle further includes a flat-plate flow divider
32
which directs the two streams at apparent plus and minus 90° angles relative to the vertical. However, in practice the deflection angles are only plus and minus 45°. Furthermore, the flow velocity in outlet ports
46
and
48
is not uniform. Adjacent the right diverging side wall
34
C of transition
34
the flow velocity from port
48
is relatively low as indicated by vector
627
. Maximum flow velocity from port
48
occurs very near flow divider
32
as indicated by vector
622
. Due to friction, the flow velocity adjacent divider
32
is slightly less, as indicated by vector
621
. The non-uniform flow from outlet port
48
results in turbulence. Furthermore, the flow from ports
46
and
48
exhibit a low frequency oscillation of plus and minus 20° with a period of from 20 to 60 seconds. At port
46
the maximum flow velocity is indicated by vector
602
which corresponds to vector
622
from port
48
. Vector
602
oscillates between two extremes, one of which is vector
602
a
, displaced by 65° from the vertical and the other of which is vector
602
b
, displaced by 25° from the vertical.
As shown in
FIG. 17
a
, the flows from ports
46
and
48
tend to remain 90° relative to one another so that when the output from port
46
is represented by vector
602
a
, which is deflected by 65° from the vertical, the output from port
48
is represented by vector
622
a
which is deflected by 25° from the vertical. At one extreme of oscillation shown in
FIG. 17
a
, the meniscus M
1
at the left-hand end of mold
54
is considerably raised while the meniscus M
2
at the right mold end is only slightly raised. The effect has been shown greatly exaggerated for purposes of clarity. Generally, the lowest level of the meniscus occurs adjacent nozzle
30
. At a casting rate of three tons per minute, the meniscus generally exhibits standing waves of 18 to 30 mm in height. At the extreme of oscillation shown, there is a clockwise circulation C
1
of large magnitude and low depth in the left mold end and a counter-clockwise circulation C
2
of lesser magnitude and greater depth in the right mold end.
As shown in
FIGS. 17
a
and
17
b
, adjacent nozzle
30
there is a mold bulge region B where the width of the mold is increased to accommodate the nozzle, which has typical refractory wall thicknesses of 19 mm. At the extreme of oscillation shown in
FIG. 17
a
, there is a large surface flow F
1
from left-to-right into the bulge region in fro
Dorricott James Derek
Heaslip Lawrence John
Morris Lesley D.
Nguyen Dinh Q.
Versuvius Crucible Company
Williams James R.
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