Note: Descriptions are shown in the official language in which they were submitted.
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TUNDISH SLAG STOPPER WITH SEALING RIM
FIELD OF THE INVENTION
This invention is an improved tundish slag stopper
assembly which prevents slag from entering the stopper chamber
during movement of the plunger. The invention is particularly
useful where the stopper chamber serves the additional
function of an alloying chamber.
BACKGROUND OF THE INVENTION
Tundish slag stopper assemblies, including a slag
stopper chamber generally above and surrounding the tundish
drain and a piston driven stopper plunger penetrating the
stopper chamber directly above the drain, are used in some
tundishes for reducing slag and for stopping and starting the
flow of liquid metal through the tundish drain. By way of
background, a conventional tundish vessel 10, shown in FIG. 1,
includes a floor 20, a front wall 12, a back wall 14, two side
walls 16 and 18, an impact region 22, and a drain 24. An
impact pad 26 having a sinusoidal upper surface helps reduce
splashing and turbulence caused by pouring molten metal into
the impact region 22. An upright baffle 28 helps regulate the
flow of molten metal leaving the impact region 22 and
proceeding toward the drain 24.
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Referring to FIG. 2, the inside of the conventional
tundish vessel 10 is lined with a refractory liner 11 adjacent
to the outer steel shell 13. The drain 24 includes a drain
nozzle 23, a refractory drain block or block assembly 25 above
and surrounding the drain nozzle 23, and a layer of refractory
binder or cement 27 between the drain block 25 and the nozzle
23. Flow of molten metal through the drain nozzle 23 is
regulated using a stopper plunger 30. The stopper plunger 30,
also shown in FIG. 8, includes an elongated piston 32 which
can be raised and lowered by conventional techniques known in
the art, and a wider drain stopper 34 connected to the piston
32.
Above and surrounding the drain block 25, and
surrounding the stopper plunger 30, is a stopper chamber 40
used for keeping impurities known as "slag" from mixing with
the molten metal which exits the drain 24. The stopper
chamber 40, shown in FIGS. 2 and 6, includes a lower rim 42
surrounding the drain block 25, a center opening 44 for
receiving and slidably engaging the piston 32, and a slanted,
preferably conical or frustro-conical wall 46 between the rim
42 and the center opening 44. A plurality of smaller openings
48 for receiving molten metal are located in the slanted wall
46, preferably closer to the lower rim 42 than to the center
opening 44. Because slag tends to float toward the top of the
tundish, the amount of slag passing through the drain is
minimized by allowing molten metal to enter the chamber 40
only through openings 48 located very near to the floor 20 of
the tundish vessel.
The amount of space between the piston 32 and the
inner wall 45 of the central opening 44 is just enough to
permit the piston 32 to comfortably slide back and forth
through the opening 44. When the drain is closed, the piston
32 is in a fully extended position as shown in FIG. 2. When
the drain is open, the piston 32 has conventionally been in a
fully retracted position as shown in FIG. 3. In other words,
when the drain is open, the piston 32 has typically been
raised until the wider drain stopper 34 comes into contact
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with the narrow top region of the slanted wall 46 of the
chamber 40, as shown in FIG. 3.
In the conventional apparatus described above, some
contamination of the molten metal leaving the tundish drain
has resulted from the presence and operation of the stopper
plunger 30. First, the space between the plunger piston 32
and the inner wall 45 of the center opening, though small,
nevertheless permits some slag and lower purity molten metal
to pass through the center opening 44 and into the chamber 40
due to suction from the drain. Second, the movement of the
piston 32 between the fully retracted position shown in FIG. 3
and the fully extended position shown in FIG. 2 helps drag
some of the impurities through the center opening 44. Third,
wear and tear on the piston 30 and chamber 40 is facilitated
by extensive movement of the piston 30, causing refractory
contaminants to chip or erode away from these mechanical
components.
SUMMARY OF THE INVENTION
The present invention is an improved slag stopper
assembly which reduces the movement of the stopper plunger,
reduces the wear and tear incurred by the plunger piston and
the slag stopper chamber, reduces the amount of slag entering
the chamber during movement of the piston, and restricts slag
from entering the chamber through its center opening when the
piston is less than fully retracted. A rim having a diameter
wider than the diameter of the plunger piston is placed on the
piston above the drain stopper. When the piston is retracted,
the rim comes into contact with the slanted chamber wall
before the drain stopper contacts the chamber wall. This
causes the piston to stop in a position that is less than
fully retracted, but which is sufficiently retracted to permit
molten metal to flow freely through the drain.
A rim may alternatively be placed on the slanted
wall of the chamber to contact the drain stopper and limit the
retractive movement of the piston. Alternatively, rims may be
placed on both the piston and the chamber wall, which contact
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each other and limit the retractive movement of the piston.
Any arrangement of rims is permissible as long as the result
is to limit the retractive movement of the piston to a lesser
extent than would occur if no rims were present.
With the foregoing in mind, it is a feature and
advantage of the invention to provide a slag stopper assembly
which reduces the retractive movement of the plunger piston,
thereby reducing wear and tear on the plunger piston and slag
stopper chamber.
It is also a feature and advantage of the invention
to provide a slag stopper assembly which further reduces the
amount of slag in the molten metal which exits the drain due
to movement of the plunger piston.
It is also a feature and advantage of the invention
to provide a slag stopper assembly which seals off the upper
part of the slag stopper chamber, including its center
opening, when the tundish drain is open.
It is also a feature and advantage of the invention
to provide a tundish vessel which incorporates the improved
slag stopper assembly of the invention.
The foregoing and other features and advantages of
the invention will become further apparent from the following
detailed description of the presently preferred embodiments,
read in conjunction with the accompanying drawings. The
detailed description and drawings are merely illustrative of
the invention rather than limiting, with the scope of the
invention defined by the appended claims and equivalents
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top plan view of a conventional tundish
vessel, without a slag stopper assembly above the drain.
FIG. 2 is a front sectional view showing the drain
region of the tundish vessel, further including a conventional
slag stopper assembly with the plunger piston in the extended
(drain closed) position.
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FIG. 3 corresponds to FIG. 2 except that the plunger
piston is in the fully retracted (drain open) position.
FIG. 4 corresponds to FIG. 2 except that the plunger
piston has been modified to include a sealing rim above the
drain stopper, in accordance with the invention.
FIG. 5 corresponds to FIG. 2 except that both the
slanted wall of the chamber and the plunger piston have been
modified to include sealing rims which engage each other when
the plunger piston is partially retracted.
FIG. 6 is a bottom view of a conventional slag
stopper chamber as shown in FIG. 2.
FIG. 7 is a bottom view of a slag stopper chamber
including a sealing rim, as shown in FIG. 5.
FIG. 8 is a front view of a conventional plunger
piston as shown in FIG. 2.
FIG. 9 is a front view of a plunger piston including
a sealing rim, as shown in FIG. 4.
FIG. 10 is a front view of a plunger piston
including a sealing rim, as shown in FIG. 5.
FIG. 11 is a side sectional view of a tundish vessel
of the invention in which the slag stopper chamber is also
used for alloying, and the plunger piston is designed to
accommodate an alloying wire feed.
FIG. 12 is an exploded lower sectional view of the
plunger piston shown in FIG. 11.
FIG. 13 is an exploded side sectional view of the
plunger piston shown in FIG. 11.
DETAILED DESCRIPTION OF THE
PRESENTLY PREFERRED EMBODIMENTS
Referring to FIG. 4, a tundish vessel is shown
which, for the most part, is as described above with respect
to FIGS. 1 and 2. A slag stopper assembly includes a slag
stopper chamber 40 whose lower lip 42 rests on the floor 20 of
the tundish 10 and surrounds the block portion 25 of the drain
24. The chamber 40 has a frustro-conical configuration and
further includes, as shown in FIG. 6, a central opening 44, a
slanted wall 46 between the central opening 44 and the lower
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lip 42, and a plurality of openings 48 near the bottom of the
slanted wall 46 for receiving molten metal from the tundish
vessel at large.
Extending through the center opening 44 of the
chamber 40 is the stopper plunger 30 including the elongated
plunger piston 32 and the drain stopper 34 having a diameter
wider than the diameter of the plunger piston 32, and
connected to the lower end of the plunger piston 32. As
shown, the drain stopper 34 has a slanted and pointed lower
end 35 which is adapted to engage and seal the opening in the
drain nozzle 23 so as to terminate the flow of molten metal
passing through the drain 24. As shown, the plunger piston 32
is in the extended (drain closing) position.
The plunger piston 32 can be retracted from the
drain by a conventional piston drive assembly (not shown)
familiar to persons skilled in the art. In order to limit the
amount of retraction, in accordance with the invention, the
plunger piston 32 also includes a sealing rim 37 extending
around the perimeter of the piston 32 (FIG. 9), at a distance
above the drain stopper 34. The sealing rim 37 is adapted to
engage the inner surface of the slanted wall 46 when the
piston 32 is retracted, preferably allowing just enough
retraction to facilitate the free flow of molten metal through
the drain 24.
The sealing rim 37 not only limits the movement of
the piston 32 but also isolates and seals the center opening
45 in the chamber 40 from suction pressure occurring when the
drain is open. Depending somewhat on the configuration of the
piston 32 and of the chamber 40, the sealing rim 37 should
generally be placed so that the maximum retractive movement of
the piston 32 is at least 25 percent less than the maximum
retractive movement if no sealing rim were present.
Preferably, the sealing rim should be positioned so that the
maximum retractive movement of the piston 32 is at least 50
percent less than if no sealing rim were present.
The same objectives of limiting the movement of the
piston 32 and isolating the center opening 45 from suction,
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can alternatively be accomplished by placing an appropriate
sealing rim on the inner surface of the slanted wall 46 of the
chamber 40 (FIG. 7), or by placing cooperating sealing rims on
both the piston 32 and the slanted wall 46 (FIG. 5).
Referring to FIGS. 5, 7 and 10, the slanted wall 46 of the
chamber 40 further includes a sealing rim 49 extending around
the inner perimeter of the slanted wall 46. The plunger
piston 42 also includes a sealing rim 39 located just above
the drain stopper 34. The sealing rim 39 and sealing rim 49
are configured and adapted to engage each other in a sealing
relationship when the piston 32 is retracted just enough to
permit molten metal to flow freely and unobstructed through
the drain 24.
All of the key components of the slag stopper
assembly 30, including the plunger piston 32, the drain
stopper 34, the rims 37 or 42 and 49, and the chamber 40, can
be constructed from a high strength, high temperature
resistant, erosion resistant refractory material. Examples of
refractory materials include, but are not limited to,
aluminas, alumina-silica combinations, refractory clays, and
mixtures thereof. The rim or rims may be constructed from the
same refractory materials used to make the conventional slag
stopper assemblies not having rims. r
Applicant has previously developed an invention
wherein a chamber similar to the slag stopper chamber above
the drain described above, has been converted into an alloying
chamber for mixing an alloy feed wire with a base molten steel
to form a steel alloy. The invention of the present
application can also be adapted to practice the previously
developed invention. Referring to FIG. 11, the tundish 10 is
used in combination with a ladle 60 that feeds a base molten
metal 52 (e.g. steel) into the tundish at a continuous rate.
The ladle 60 has a spout 62 which empties above the impact
region 22 of the tundish 10. When the tundish 10 and ladle 60
are at steady state, the level of liquid metal in the tundish
is roughly defined by a
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line 54. At this liquid level, the flow rate of finished
metal leaving the tundish through the drain 24 is about the
same as the overall flow rate of metal entering the tundish.
The base steel is processed in the tundish 10, i.e.,
its flow is regulated by the baffle 28 having openings 29 such
that alumina inclusions and other impurities rise to the top
and the purified base steel approaches the alloying chamber
40, which is above and surrounding the drain 24. The alloying
chamber 40 makes it possible to combine the base steel with
alloying ingredients to form a steel alloy just before the
steel leaves the tundish.
The base steel enters the alloy chamber 40 through
the openings 48. Simultaneously, an alloy ingredient wire 68
is fed from a wire feeder 66 located above the tundish 10,
through a feed pipe 74 which doubles as the stopper plunger 30
hereinbefore described. The feed pipe 44 extends vertically
from above the tundish 10 to the interior of the chamber 40.
The wire feeder 66 can be any conventional automated wire
feeder known in the art, for example, an automated spool. The
details of the wire feeder 66 are not important. However, it
is important that the wire feeder 66 be able to feed the wire
68 continuously and at a steady predetermined rate, and that
the predetermined rate be adjustable to permit the manufacture
of different alloys having different compositions.
The composition of the alloy ingredient wire 68
varies with the specific alloy being produced, and should
contain the alloy ingredients in the exact ratios that are to
be added to the base steel. For example, if tin is the only
alloy being added to the base steel, then the alloy ingredient
wire may include tin and no other alloy ingredients.
Alternatively, if cobalt, titanium and nickel are to be added
to the base steel, in equal amounts, then the alloy ingredient
wire should include equal amounts of cobalt, titanium and
nickel. Alternatively, a plurality of alloy ingredient wires
68 may be fed simultaneously to the allow chamber 40, with one
wire supplying the cobalt, one wire supplying the titanium,
and one wire supply the nickel.
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The feed pipe 74 protects the alloy ingredient wire
68 from exposure to the molten base steel while the wire 68 is
travelling between the wire feeder 66 and the alloying chamber
40. As shown in FIGS. 12 and 13, the feed pipe 74 includes an
outer wall 76 of high temperature-resistant refractory
material and an inner mesh or cage portion 78 of permanently
mounted wire or screen material. The inner mesh or cage
portion 78 defines a feed path 79 through which the alloy
ingredient wire 68 may travel, and prevents the wire 68 from
straying or touching the outer wall 76. The inner mesh or
cage portion 78 and outer wall 76 also define a space 77
therebetween, through which an inert cooling fluid, for
example, argon gas, may be injected.
As stated above, the feed pipe 74 also doubles as a
stopper plunger 30. As shown in FIG. 13, the feed pipe 74 is
formed as a part of the retractable plunger piston 32.
Attached to the lower end of the plunger piston 32 is a drain
stopper 34 having a diameter wider than the diameter of the
piston 32, and having a pointed lower end 35 adapted for
sealing off the tundish drain. A sealing rim 37 having a
diameter under than the diameter of the piston 32 is
positioned on the piston 32 at a distance above the drain
stopper 34. As explained above, the sealing rim 37 limits the
movement of the piston 32 when the piston is retracted to open
the drain.
Above the sealing rim 37, the feed pipe 74 follows a
substantially vertical path through the center of the piston
32. In the vicinity of the sealing rim 37, the feed pipe 74
begins to angle toward the side of the piston 32, and opens
into the alloy chamber 40 at a location 35 in the side of the
piston 32. As shown, the opening 35 is below the sealing rim
37 and above the drain stopper 34. The opening 35 need only
be larger than the diameter of the alloy wire 68. Preferably,
the inert cooling fluid enters the space 77 at the top of the
feed pipe 74 and exits through the opening 35, at a sufficient
velocity to both cool the wire 68 and prevent molten steel
from entering the feed pipe 74 through the opening 35.
-- 10 --
When the alloy ingredient wire 68 leaves the feed
pipe 74 and enters the alloy chamber 40, the wire 68 melts and
mixes with the base steel in the alloy chamber to form a
finished steel alloy. The feeding speed of the alloy
ingredient wire is calculated as an appropriate weight
percentage of the steady state flow rate of the molten base
steel 52 entering and passing through the tundish 10 and into
the alloy chamber 40, to give a steel alloy having the desired
composition.
\
Inside the alloying chamber 40, mixing of the base
steel and alloy ingredients can be enhanced by bubbling argon
gas or another suitable inert gas up through the drain nozzle
24 and into the alloying chamber 40, using techniques well
known in the art. In other words, it is a standard practice
in the art to bubble an inert gas up through the tundish
drain, to further homogenize the molten metal and to cause any
remaining inclusions to rise away from the drain. These same
inert gas bubbling techniques can also be employed to
facilitate mixing in the alloying chamber 40. Referring to
FIG. 11, argon gas may be injected using the inert gas purging
nozzle 25 located just below the drain 24.
Other mixing techniques can also be employed to
facilitate homogenization of the alloy ingredients with the
base steel in the alloying chamber 40. For example, as shown
in FIG. 11, an electromagnetic stirrer 27 may be located
beneath the drain 24. The swirling action of molten metal
caused by the electromagnetic stirrer carries up through the
drain 24 and into the alloying chamber 40.
When switching production from one alloy to another,
it is entirely unnecessary to disturb the steady state flow of
base steel from the ladle and through the tundish, or to lower
the level of liquid metal in the tundish. Instead, it is only
necessary to change the type of alloying wire or wires
originating from the one or more wire feeders 68. The time
required to achieve steady state production of a new alloy is
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substantially reduced compared to prior art techniques,
because the volume inside the alloying chamber is much less
than the overall volume of the tundish. Accordingly, the
amount of steel lost during transition is greatly reduced, and
it becomes economically feasible for the steel producer to
manufacture small order quantities of steel alloys.
While the embodiments of the invention disclosed
herein are presently considered to be preferred, various
improvements and modifications can be made without departing
from the spirit and scope of the invention. The scope of the
invention is indicated in the appended claims, and all changes
that fall within the meaning and range of equivalents are
intended to be embraced therein.
