Fluid sprinkling – spraying – and diffusing – Processes – Of discharge modification of flow varying
Reexamination Certificate
2001-06-11
2003-11-25
Hwu, Davis (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Processes
Of discharge modification of flow varying
C239S088000, C239S533100, C239S597000, C239S589000
Reexamination Certificate
active
06651899
ABSTRACT:
BACKGROUND OF THE INVENTION
During processing, liquid metals, and in particular liquid steel, flow from one vessel, such as a tundish, into another vessel, such as a mold, under the influence of gravity. A nozzle may guide and contain the flowing stream of liquid metal during passage from one vessel to another.
Controlling the rate of flow of the liquid metal during processing is essential. To this end, a regulator or flow controller allowing adjustment of the rate of liquid metal flow is used. A common regulator is a stopper rod, although any type of flow regulator known to those skilled in the art can be used. Thus, a typical continuous steel casting process allows liquid metal to flow from a tundish into a mold, through a nozzle employing a stopper rod for flow regulation.
Referring to
FIG. 1
, in such a typical continuous steel casting process, a tundish
15
is positioned directly above a mold
20
with a nozzle
25
connected to the tundish
15
. A nozzle
25
provides a conduit through which liquid metal
10
flows from the tundish
15
to the mold
20
. A stopper rod
30
in the tundish
15
controls the rate of flow through the nozzle
25
.
FIG. 2
is a partial schematic view, drawn to an enlarged scale, of an entry portion and a lower portion
40
35
of a nozzle bore
45
of the nozzle
25
of FIG.
1
. In
FIG. 2
, the entry portion
35
extends between points
1
and
2
. The lower portion
40
extends between points
2
and
3
. The entry portion
35
of the nozzle bore
45
is in fluid communication with liquid metal
10
contained in the tundish
15
. The lower portion
40
of the nozzle bore
45
is partially submerged in liquid metal
10
in the mold
20
.
Returning back to
FIG. 1
, to regulate the liquid metal flow rate from the tundish
15
into the mold
20
, the stopper rod
30
is raised or lowered. For example, the flow of liquid metal
10
is stopped if the stopper rod
30
is lowered fully so that a nose
50
of the stopper rod
30
blocks the entry portion
35
of the nozzle bore
45
. As the stopper rod
30
is raised above the fully lowered position, liquid metal can flow through the nozzle
25
. The rate of flow through the nozzle
25
is controlled by adjustment of the position of the stopper rod
30
. As the stopper rod
30
is raised, the nose
50
of the stopper rod
30
is moved farther from the entry portion
35
of the nozzle bore
45
, which increases the open area between the stopper nose
50
and the nozzle
25
allowing a greater rate of flow.
FIG. 3
shows another liquid metal flow system from the tundish
15
to the mold
20
. This system has a control zone
55
located between the nose
50
of the stopper rod
30
and the entry portion
35
of the nozzle bore
45
. The control zone
55
is the narrowest part of the open channel between the stopper nose
50
and the entry portion
35
of the nozzle bore
45
. Liquid metal
10
in the tundish
15
has a static pressure caused by gravity. If the stopper rod
30
does not block the entry of liquid metal
10
into the bore
45
of the nozzle, the pressure of liquid metal
10
in the tundish
15
forces liquid metal
10
to flow out of tundish
15
and into nozzle
25
.
When the flow is less than the maximum, the characteristics of the open area of control zone
55
are primary factors in the regulation of the rate of flow into the nozzle
25
and subsequently into the mold
20
.
FIG. 4
graphically shows changes in the pressure of liquid metal
10
flowing out of the tundish
15
through the control zone
55
and into the nozzle
25
. As shown in
FIG. 3
, point
60
represents a general location within the liquid metal
10
contained in the tundish
15
upstream of the control zone
55
. Point
65
represents a general location within the open bore
45
of the nozzle
25
downstream of the control zone
55
. As shown in
FIG. 4
, the general trend in the pressure of liquid metal
10
between points
60
and
65
is a sharp drop in pressure across the control zone
55
. The pressure at
60
is generally higher than atmospheric pressure. The pressure at
65
is generally less than atmospheric pressure, resulting in a partial vacuum.
FIG. 5
illustrates a two-component nozzle, including an entry insert
70
and a main body
75
. The entry portion
35
of bore
45
extends from points
21
to
22
to
23
, and the lower portion
40
extends from points
23
to
24
.
FIG. 6
illustrates a liquid metal flow system, from tundish
15
to mold
20
and incorporates the nozzle of FIG.
5
.
FIG. 7
illustrates the pressure trend from point
60
to point
65
in the system of FIG.
6
. The pressure trend for the system of
FIG. 6
basically is the same as that for
FIG. 3
, including a sharp drop in pressure across control zone
55
.
In summary, the nozzles of
FIGS. 1
,
3
and
6
cause a sharp pressure drop across the respective control zones. This sharp pressure drop causes the flow regulation system to be overly sensitive. An overly sensitive flow regulation system tends to cause an operator to continually hunt, or move the regulator to achieve the correct position so as to adjust the size and/or geometry of the control zone for flow stabilization at a desired rate. Hunting for the proper flow regulation causes turbulence in the entry portion
35
and throughout the bore
45
of the nozzle
25
.
Turbulence caused by hunting and also by the partial vacuum/low pressure generated downstream of the control zone accelerate erosion around the control zone. For example, erosion of a nose
50
of a stopper rod
30
and an entry portion
35
of a nozzle bore
45
can occur. The highest rate of erosion generally occurs immediately downstream of the control zone
55
. Erosion in and about the control zone
55
exacerbates difficulties associated with liquid metal flow rate regulation. Undesirable changes in the critical geometry of the control zone
55
, as a result of erosion, lead to unpredictable flow rate variances, which ultimately can result in the complete failure of a flow regulation system.
Referring again to
FIG. 5
, for reducing erosion, hence improving flow regulation, in some nozzles the entry insert
70
is generally composed of an erosion-resistant refractory material. However, the addition of the entry insert
70
to the nozzle
40
does not affect the sharp pressure drop across control zone
55
, as shown in
FIGS. 4 and 7
. Thus, flow regulation for conventional nozzles remains overly sensitive to regulator movements, due to the size and shape of the control zone defined thereby, making flow rate stabilization difficult to achieve.
Accordingly, a need exists for a nozzle that minimizes the pressure differential across a nozzle control zone, reducing the corrosive effects thereof and stabilizing the size and shape of the control zone, thereby reducing hunting and increasing flow stability.
SUMMARY OF THE INVENTION
The present invention fulfills the above-described need by providing a nozzle with a minimal pressure differential across a nozzle control zone, reducing the corrosive effects thereof and stabilizing the size and shape of the control zone, thereby reducing hunting and increasing flow stability.
To this end, the present invention includes a nozzle for controlling a flow of liquid metal including an entry portion for receiving the liquid metal. A regulator such as a stopper rod is movable from an open position to a closed position with respect to the entry portion for respectively permitting and prohibiting flow through the nozzle. The entry portion and the regulator define a control zone therebetween. A pressure modulator, downstream of the control zone, is adapted to minimize a pressure differential across the control zone. The pressure modulator constricts flow downstream of the control zone.
The invention diminishes the sharp pressure drop across the control zone by modulating the pressure in the nozzle downstream of the control zone, reduces the turbulence of the flow immediately downstream of the control zone, and eliminates over-sensitivity of flow regulation. The nozzl
Dorricott James D.
Heaslip Lawrence J.
Xu Dong
Hwu Davis
Klemz Robert S.
Vesuvius Crucible Company
Williams James R.
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