Note: Descriptions are shown in the official language in which they were submitted.
CA 02367586 2002-O1-14
3677-0012 US , _ 267544/GJL
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APPARATUS TO FACILITATE
OPENING OF MOLTEN METAL CASTING VESSELS
Field of the Invention.
The present .invention relates to molten metal casting
operations, and in particular to a system to facilitate self opening of a
vessel
discharge port in molten metal casting vessels.
Background of the Invention
Molten metal is often dispensed from a bottom discharge
pouring and holding reservoir, referred to as a tundish, into casting molds.
The tundish is usually kept. supplied with molten metal from a ladle. At the
bottom, the ladle usually has one or more discharge ports, or nozzles, each
having a pouring channel through which molten metal flows to the tundish
and then to the casting molds. The flow of molten metal through the
pouring channel is often controlled by a slide gate valve.
Before tapping a heat from a furnace into the ladle, it is a
common practice to close the slide gate valves and fill the pouring channel
in the nozzles and the well area with a granular material, such as sand, so
that the molten metal is not permitted to enter the pouring channel when
the heat is tapped and the ladle filled with molten metal from the furnace.
If molten metal were allowed to enter the pouring channel when the slide
gate valve is in the closed position, the molten metal would freeze in the
nozzle and obstruct the channel every time.
To begin pouring from the ladle, the slide gate valve is moved
to the open position, and the granular material flows out of the pouring
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channel, followed by the molten, metal. When this occurs without
intervention, it is referred to as a free open or self open. However, ladles
sometimes fail to self open because of chilling and/or crusting of a
combination of the sand, metal, and possibly slag that may have remained
in and around the well area prior to tapping the furnace into the Iadle. In
a high production facility, a very good free open rate might be 98-99% of
the time, a fair free open rate would be about 95-97% of the time, and a
poor rate would be 95% or less. It is extremely rare for the success rate to
be 100% for periods longer than several months.
When a ladle does not self open, there are two important
considerations. The ladle must be opened i.n a timely manner, usually
within ten-minutes or less, to continue the casting operation. In addition,
the ladle should be opened with the ladle shroud in place to avoid exposing
the molten metal to the atmosphere and/or pouring through the slag layer
for a prolonged period.
When a ladle fails to self open, a number of procedures may
be employed to open it. One technique is simply to manually strike the side
of the ladle with a hand-held hammer. A sophisticated mechanical vibrating
hammer is even more effective in opening stubborn ladles. Stroking the
slide gate open and closed several times occasionally is enough to open the
ladle.
If these expedients do not open the ladle, the most common
approach to opening the ladle is to first remove the ladle shroud, and then
insert an oxygen pipe into the metal pouring channel and lance through the
obstruction. Initially, when the molten metal flow begins, it cannot be
stopped for longer than a few seconds or it will freeze in the molten metal
channel. It is common to pour for five to ten minutes before the ladle is
completely shut off and the ladle shroud reattached. The event is commonly
called "open pouring" because the metal is exposed to the atmosphere and
the system is not closed. In addition, because the ladle shroud is not being
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used, the molten metal is being poured through the slag layer in the tundish,
v~hich introduces additional impurities into the finished product.
Another solution is to insert a telescoping lance into the ladle
shroud and blow oxygen through the lance. When oxygen is injected, the
telescoping lance will telescope into the metal pouring channel and
automatically burn through whatever material is preventing the ladle from
free opening. However, there are several problems associated with using a
telescoping lance. Telescoping lances are costly, and they can take more
time than desired. The reliability of telescoping lances is only 90 to 95%.
Finally, by definition; telescoping lances introduce some oxygen into the
metal; which is undesirable.
The present invention remedies the above problems through
an improved system for injecting gas into the ladle near the nozzle inlet to
aid in opening the vessel and facilitating the free flow of molten metal.
Summar3i of the Invention
In its broad aspect, the present invention is an apparatus to
facilitate the opening of molten metal casting vessels, and comprises a well
block within a discharge port of a casting vessel, the well block having a
central opening therethrough along a longitudinal axis thereof; at least one
nozzle insert within the central opening, the nozzle insert having a central
opening therethrough substantially coaxial with the central opening of the
well block through which molten metal may flow, an outer surface
complementary to and matingly engaging the central opening of the well
block; and at least one channel extending along the outer surface; a plenum
within the well block and substantially surrounding the central opening of
the well block and being in fluid flow communication with said channel; and
a fluid supply line in communication with the plenum for supplying a fluid
under pressure to the plenum and said channel. Fluid supplied to the
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plenum flows through the channel and upward and into the
interior of the vessel:
In another aspect, the invention is a discharge port for a
molten metal pouring and holding vessel, and comprises an opening in a
wall of the vessel and a well block located within the opening. The well
block has a central opening therethrough lined with a refractory insert, the
insert having a metal flow channel therethrough. The insert can be made
of a material different from the material of the well block for improving the
resistance of the insert to wear due to passage of molten metal
therethrough, the insert being removable and replaceable after being
subjected to a preselected amount of wear.
Brief Descriytion of the Drawings
For the purpose of illustrating the invention, there is shown in
the drawings a form which is presently preferred; it being understood,
however, that this invention is not limited to the precise arrangements and
instrumentalities shown.
Figure 1 illustrates, in cross-section, the elements of the
present invention, shown in context as installed in a pouring ladle having a
pouring nozzle controlled by a slide gate valve.
. Figure 2 is an exploded view of a lower nozzle., upper nozzle,
and ladle nozzle according to the present invention, shown apart from an
associated well block.
Figure 3 is a cross-sectional view of a modified nozzle well
block according to the present invention, taken along the lines 3-3 in Figure
1.
Figures 3A and 3B are partial sectional views of a portion of
the modified nozzle well block of Figure 3, shown at different stages of
fabrication.
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Figures 4 and 5 illustrate other styles of well blocks which can
be used with the present invention.
Figure 6 illustrates an alternative embodiment of the present
invention.
Description of the Invention
The description contained herein is intended to be illustrative
only and not limiting as to the scope of the present invention.
Referring now to the drawings, wherein like numerals indicate
like elements, there is shown in Figure 1 an apparatus 10 for facilitating the
opening of a molten metal casting ladle, in accordance with the present
invention. While the present invention described herein is described in
connection with a molten metal casting ladle, the invention is applicable
generally to other types of bottom pour vessels for use in molten metal
casting and smelting operations.
As shown in Figure 1, the nozzle arrangement 10 is shown in
the context of a molten metal holding and pouring box in the form of
pouring ladle 12 equipped with a vessel discharge port controlled by a
conventional slide gate valve 14 mounted to the exterior of the bottom
wa1116 of ladle 12. Slide gate valve 14 controls the flow of molten metal
through a pouring channel I8 therein and into a casting mold (not shown),
as will be understood by those skilled in the art. Slide gate valve 14 is
shown in the closed position in Figure 1. Slide gate valve 14 also has an
open position (not shown in the figures) in which the opening 20 in the
slide gate is aligned with the pouring channel 18.
The bottom of ladle 12 is lined with a refractory material 22
and includes a ladle level plate 24, preferably made of high temperature
steel. Ladle level plate 24 supports a well block 26, which has a central
opening through it. The central opening is tapered and increases in
diameter from top to bottom. Located within the central opening are, from
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bottom to top, a bottom nozzle insert 28, a center nozzle insert 30, and a
top nozzle insert 32. Each of the bottom nozzle insert 28, center nozzle
insert 30, and top nozzle insert 32 has a central opening of constant
diameter which together define pouring channel 18. The outer surfaces of
each of the bottom nozzle insert 28, center nozzle insert 30, and top nozzle
insert 32 is tapered to match the taper of the central opening through the
well block 26. If desired, mating surfaces of the bottom nozzle insert 28,
center nozzle insert 30, and top nozzle insert 32 may be provided with
complementary tongues 34 and grooves 36 to facilitate their alignment and.
fit.
Of course, although three separate nozzle inserts are
illustrated, the invention is not limited to a specific number of inserts. A
single insert, or any other number of inserts, can be used without departing
from the scope of the invention.
Well block 26 is provided with an annular groove 38 around
its inner surface, located adjacent the bottom of top nozzle insert 32.
Groove 38 is in fluid flow communication with a gas distribution line 40
which has a fitting 42 at one end. Gas distribution line 40 communicates,
in turn, to a gas feed line 44 which is connected to a source (not shown) of
gas under pressure. Preferably, fitting 42 includes a porous ceramic safety
disk between gas distribution line 40 and gas feed line 44, to reduce the risk
of runout of molten metal through gas distribution line 40 in the event of
damage to top nozzle insert 32 or well block 26.
Preferably, although not necessarily, groove 38 has a porous
ceramic ring 46 fitted therein. Porous ceramic ring 46 has an inner diameter
t
approximately equal to the outer diameter of top nozzle insert 32 at the
location where top nozzle insert 32 is adjacent groove 38. The inner
diameter of porous ceramic ring 46 may have a taper which is
complementary to and matches the taper of top nozzle insert 32. Porous
ceramic ring 46 has an outer diameter which is slightly less than the depth
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of groove 38, so that it does not completely fill groove 38 but leaves a
narrow annular plenum 48 between the vertical wall of groove 38 and
porous ceramic ring 46.
Pressurized gas from the source flows in the direction of the
arrow in Figure 1 through gas feed line 44 and gas distribution line 40 to
annular groove 38. The gas flows through annular plenum 48, and quickly
fills plenum 48. Once plenum 48 is filled with gas, the pressure of the gas
forces the gas to flow through the ceramic ring 46 (if present) to the outer
surface of top nozzle insert 32.
As best seen in Figure 2, the outer surface of top nozzle insert
32 has a grooved, or serrated, outer surface which defines a plurality of
channels 50 which extend axially from top to bottom. Channels 50 permit
gas forced through the ceramic ring 46 to flow axially along the outer
surface of top nozzle insert 32 and upward into the interior of the ladle 12.
The flow of gas. serves to dislodge any solid debris or slag that can collect
around.the inlet to pouring channel 18, such as, for example, residual sand
left over from packing the slide gate valve prior to opening the nozzle. To
avoid undesired chemical and metallurgical reactions with the molten metal
in the ladle, the gas is preferably an inert gas such as argon. However, any
other gas can be used as appropriate for the desired effect. For purposes of
the present invention, it is the mechanical, rather than chemical or
metallurgical, interaction of the gas with the molten metal that agitates any
accumulated material located near the inlet to pouring channel 18. The
interaction of the gas with the material tends to break up slag, sand,
solidified metal, or the like, which may accumulate and prevent pouring
channel 18 from opening:
A preferred fabrication method is to hold the nozzle inserts,
including top nozzle insert 32, in place in well block 26 using a refractory
mortar 52. As illustrated in Figures 3, 3A, and 3B, a layer of mortar 52 is
applied to the outer surface of each nozzle insert, including top nozzle
insert
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32, which joins each insert to the inner surface of the central opening in
well
block 26. Mortar alone is usually sufficiently porous to permit gas to flaw ,
through it, so that gas from plenum 48 can flow through ceramic ring 46
and along channels 50 through mortar 52.
Alternatively, a layer of burnout material 54 may first be
placed over the outer surface of top nozzle insert 26, before the mortar 52
is applied. As those skilled in the art will understand, burnout material 54
is a non-refractory material which will burn at a temperature much lower
than the operating temperature of the ladle 12. Thus, as ladle 12 is heated,
burnout material 54 will burn and be consumed, leaving behind a space 56
between the top nozzle insert 32 and the layer of mortar 52. The space
permits higher gas flow rates than can be realized with porous mortar alone.
Although the invention has been illustrated and described with
reference to a well block having a continuously tapered central opening, the
invention is equally applicable to other styles of well block, as well. For
example, the invention can be used with a so-called canopy style well block
58, illustrated in Figure 4, and with a so-called stovepipe style well block
60,
illustrated in Figure 5. In each case, the well block is modified to include
groove 38, gas distribution line 40, and fitting 42. Also in each case, a top
nozzle insert with a serrated outer surface similar to top nozzle insert 32
illustrated in Figures 1 and 2, can be inserted into the central opening in
the
well block adjacent groove 38, to permit gas to be introduced as already
described in connection with the embodiment illustrated in Figure 1.
Likewise, a porous ceramic ring rnay be placed within groove 38, in the
same manner as illustrated in Figure 1.
The invention offers additional benefits. For example, top
nozzle insert 32 may be used even without a source of gas as a sacrificial
insert to protect the associated well block. As those skilled in the art will
understand, as a result of use the inserts and the well block will wear away
and will have to be replaced. It is widely known that well block
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performance, measured by the number of heats that can be poured before
the well block must be replaced, can be increased significantly (10% to
20%) by using a canopy style well black such as illustrated in Figure 4,
compared to a stove pipe style well block such as illustrated in Figure 5.
The major reason some casting operations do not use the
canopy design is that in those operations, the nozzle inserts are removed by
pushing a metal rod that is slightly smaller than the opening at the top of
the
well block but larger than the bore of the top nozzle insert into the well
block throat 62, forcing the inserts down and out of the well block. A few
casting operations use a canopy style well block where the opening at the
top is larger than necessary to accommodate this method of removal. In
many cases, the well block is damaged by the metal rod used to remove the
nozzle inserts when the steel rod is not inserted exactly into the center of
the
opening.
The configuration shown in Figure 6, without the gas feed
feature of the invention, lends itself to a unique well block design that
incorporates a removable and replaceable canopy. In Figure 6, top nozzle
insert 64, referred to in this instance as a canopy nozzle insert, does not
have a serrated outer surface but has a smooth one. The outer diameter of
canopy nozzle insert 64 is slightly smaller than the inner diameter of the
central opening in well block 60. Canopy nozzle insert 64 is joined to well
block 60 by mortar, in conventional fashion.
Canopy nozzle insert 64 is fabricated from a refractory
material, and can be the same material as, or a material different from, the
material of well block 60. For example, canopy nozzle insert 64 can be
fabricated from a better-wearing material, thus extending its service life.
After pouring enough heats to deplete the service life of the well block by
30% to 50%, canopy nozzle insert 64 can be replaced to restore the well
block to 80% to 90% of its original service life. Removal and replacement
of canopy nozzle insert 64 can be done many times, greatly extending the
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service life of the well block 60. As a result, the service life of the well
block
can be eliminated as a limiting factor in the service life of the ladle
refractory system.
The present invention may be embodied in other specific forms
without departing from the spirit or essential attributes thereof and, accord-
ingly, reference should be made to the appended claims, rather than to the
foregoing specification, as indicating the scope of the invention.
