Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR DELIVERING
METALLURGICALLY IMPROVED MOLTEN METAL
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for enhanced
metallurgical processing of molten metal compositions during transfer and
delivery
of molten metal.
BACKGROUND ART
In traditional metal alloy production, the ingredients for making a
predetermined composition of metal are introduced to a furnace such as a basic
oxygen furnace or an electric arc furnace, in which the constituents liquify
and mix
to form a molten metal pour. A layer of slag including impurities and
catalysts is
carried at the top of the molten metal layer. The molten metal is then
discharged to
a ladle for transport to an intermediate processing station or another
production
facility such as strand or sheet processing. At the production facility, the
metal is
discharged from the ladle to a vessel such as a tundish. While the processing
stations
may be provided with heat sources to maintain a liquid mixture once the pour
has
reached the processing destination, a substantial amount of heat was lost from
the
previously known open-topped ladles.
In order to address energy conservation concerns, it has been found
to be useful to enclose the ladles during the transporting of molten metal
from the
furnaces to the processing equipment and during processing. Moreover, another
recent innovation has been to enhance the metallurgical composition of the
pour by
adding metallurgical enhancements to the slag layer or the molten metal while
heat
energy is being maintained or adjusted in the ladle. Unfortunately, while
closure of
the ladle chamber permits metallurgical enhancement even during transport of
molten
metal from the furnace to a processing station or production facility, the
prolonged
period of the processing conditions, including heat and inaccessibility, does
not
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permit previously known pour control techniques to be employed with success in
these vessels.
For example, previously known techniques for controlling discharge
from the vessel wherein a refractory plug is positioned and lowered over the
nozzle
by mechanical arms, as in a stationary furnace, cannot be employed with the
closed
vessels. Moreover, previously known refractory bodies such as that taught in
U.S.
Patent No. 4,601,415 to Koffron cannot be introduced into a closed vessel when
the
level of molten metal in the vessel approaches the critical level at which a
vortex
forms over the discharge nozzle. Moreover, the previous refractory bodies
formed
with a specific gravity designed solely so that they are buoyantly supported
in the
melt may deteriorate rapidly under prolonged exposure to the ladle conditions
and
could not complete their intended function under prolonged contact with the
molten
metal and the slag layer interface.
DISCLOSURE OF THE INVENTION
The present invention overcomes the above-mentioned disadvantages
by providing a method and apparatus for extending processing of the molten
metal
and improving the amount of improved quality metal discharging from a vessel
after
enhanced processing. In general, the process of metallurgically improving
metal
pouring processes is combined together with enhanced delivery involving
closing the
metal pouring vessel with a cover, preferably after initiating intermediate
refining,
such as by introducing a balancing composition to achieve a target equilibrium
composition in the vessel. The method comprises introducing a specially
constructed
refractory body, and maintaining the metal pour, preferably with the balancing
composition, and a refractory body in the vessel, until discharge of molten
metal is
terminated. A prolonged period of refractory body maintenance is assisted by a
specially constructed vortex inhibitor in which a refractory composition body
shaped
to fit within a ladle has an adjusted specific gravity, the adjusted specific
gravity
having a reduced steel ballast to refractory material ratio less than the
ratio for a
specific gravity required to buoyantly support the body in the molten metal at
the
interface of slag and molten metal in the ladle. For preferred alignment at
the
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interface, the ratio is also preferably greater than the
ratio for a specific gravity required to support the body
entirely in the slag layer. Preferably, the refractory body
also includes a penetration inhibitor resisting
deterioration of the body throughout the residence time in
the metal.
As a result, the present invention provides a
refractory body that resists deterioration throughout the
prolonged exposure to the molten metal, to the slag and to
the retained heat. The present invention provides a
substantially more robust structure that maintains integrity
of the body so as to provide vortex reduction in pouring
operations previously inhospitable to the previously known
slag controlling or yield-improving technologies. In
addition, the covered ladle provides an improved transfer
mechanism and an enhanced metallurgy production system that
permit greater precision in the production of alloys,
improved production or utilization quantities of high
quality metals and greater energy efficiency than previously
known production systems.
In one broad aspect, there is provided a vortex
inhibitor for extended processing of molten metal during
delivery by a ladle having an opening and a closeable cover
over said opening and a discharge nozzle in said ladle, the
inhibitor comprising: a refractory body shaped to fit
within said ladle opening; said refractory body having an
adjusted specific gravity, said adjusted specific gravity
defined by having a reduced steel ballast to refractory
material ratio less than required for a specific gravity
required to buoyantly support the body in said molten metal
in said ladle; and said refractory body having a penetration
inhibitor resisting deterioration of said body by slag and
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molten metal, and said refractory body includes intermixed
steel ballast and refractory material.
In another broad aspect, there is provided a method
for improving metal pouring processes with a metal pouring
vessel containing molten metal and a discharge opening in
said vessel comprising: introducing a refractory body having
an adjusted specific gravity, said refractory body including
intermixed steel ballast and refractory material, and said
adjusted specific gravity defined by a reduced steel ballast
to refractory material ratio less than required for a
specific gravity required to buoyantly support said body in
the molten metal wherein said adjusted specific gravity
is 2.7-4.5; closing the metal pouring vessel with a cover;
maintaining said refractory body enclosed in said vessel
until discharge of said molten metal is terminated.
BRIEF DESCRIPTION OF DRAWING
FIGURE 1 is a partly diagrammatic view of a metal
production processing facility including a sectional
representation of a transfer vessel employed in the system;
FIGURE 2 is an enlarged sectional elevation of a
ladle bottom with a gate valve nozzle arrangement for
discharging molten metal; and
FIGURE 3 is an enlarged sectional elevation from
the perspective of line 3-3 in Figure 2.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIbMENT
Referring to Figure 1, a metal production system 10
is shown comprising a formation facility 12, a transfer
mechanism 14 and a processing facility 16. The formation
facility 12 may include a basic oxygen furnace, an electric
arc
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furnace or other alloy melting facility, at which the basic raw materials for
metal
production are introduced to a furnace and heated to melt and intermix the raw
materials for production of a particularly desired composition of metal.
Although
the quality and particular composition of the metal formed at the furnace 13
is
consistent with the original raw materials introduced to the furnace,
impurities in
each of the ingredients may cause variations between the desired metal
composition
and the requirements of metal to be used in a processing facility 16. The
processing
facility 16 may be a bulk production facility, for example, a strand-making
facility
including a tundish that receives molten metal for delivery as a strand, or a
sheet or
other shaped commodity of molten metal that hardens for subsequent reheating,
shaping, forming or processing operations. Nevertheless, the complexity, size
and
functional differences between the equipment 12 and 16 renders it necessary to
use
a transfer mechanism 14 by which the molten metal is unloaded from the
formation
facility 12 and delivered to an intermediate processing station 15 or to the
processing
facility 16 or between the station and the facility.
The invention is also well adapted for systems 10 in which an
intermediate processing station 15, such as a secondary refining facility, may
be
included between the production facility 12 and the processing facility 16. In
general, the furnace produces steel to a target chemistry and temperature
range. That
steel is then poured into a ladle and transported to a ladle refining furnace,
stirring
station, or degassing station - each can be described as an intermediate
processing
station - useful in adjusting the chemistry of the metal. The chemistry and
temperature are then adjusted to a far more exact, narrow range based upon the
desired grade that is being produced, which is generally driven by customer
orders.
Accordingly, when preferred, every heat (pour) discharged from the furnace may
be
basically to the same chemistry range. Then all chemical adjustments for the
various
grades to be produced are made at the ladle refining furnace. As an example,
adding
such material as Ca, Mn, Al, MgO, Si and Calcium Carbide; bubbling Argon
through the steel; and re-heating it with electrodes or other re-heating
processes may
be used to improve content compliance with specifications. Preferably, the
intermediate processing occurs before introduction of a refractory body when
the
body is not restrained in position over a discharge nozzle by extrinsic means.
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In general, the transfer mechanism 14 includes a displacer 18 for
transferring a molten metal load. In the preferred embodiment, the displacer
18
includes a ladle 22 carried by a crane 20 or other conveyance, and can include
as
well a crane 24 for a lid 90 for the ladle 22. In general, the crane 20
delivers the
ladle to the formation facility 12 so that the open top 26 of the ladle 22
receives
discharge from a nozzle or other discharge opening of a furnace 13 at the
facility 12.
Likewise, the ladle includes a discharge nozzle 28 that enables the contents
to be
discharged to a tundish or other receiving vessel at the processing facility
16.
Preferably, the nozzle 28 includes a gate valve 30. The gate valve 30 is
responsive
to a control 32.
The control 32 may include a sensor at the nozzle for detecting when
the flow through the nozzle is throttled, i.e., reduced in volume by a vortex
inhibitor
or other plug, to terminate discharge of metal from the ladle, preferably
before slag
floating on top of the molten metal mixes with the molten metal layer.
Nevertheless,
when the vortex inhibitor body is used, the transition from metal to slag is
nearly
instantaneous because the body has nearly eliininated metal-slag mixing by
eliminating the vortex. The transition happens very quickly and is more nearly
discrete. The discharge is usually to be terminated when slag is observed by
workers
or otherwise automatically sensed, although terminating in response to when
throttling is observed may not maximize yield. The throttling effect, or the
transition
from metal to slag flow, can be observed by workers or otherwise automatically
sensed. In addition, the response of the control 32 may be manually or
automatically
initiated in response to the detection of the throttling or the detection of
slag content.
As best shown in Figure 2, the response of terminating flow may be
handled by hydraulic-mechanical mechanisms responsive to the detection of
throttling. For example, a hydraulic cylinder 40 whose piston 42 is coupled
with a
guide piece 44 engages a slide case 46. The slide case 46 includes a recess
carrying
a slide plate 48 made of refractory. The slide plate 48 slides adjacent to a
bottom
plate 50, also made of refractory and carried in the brick setting metal 52.
The brick
setting metal 52 includes four side supports for the plate and an adjustment
mechanism with a set bolt 54 to adjust the position of the bottom plate 50
with
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respect to the nozzle inserts when the brick setting metal is mounted to the
ladle, so
that the bottom plate opening 56 is aligned with the opening 58 in a nozzle
insert 60.
A bottom plate supporter 62 is mounted or welded to the ladle shell and is
engaged
with slide plate housing 64 bolted to the bottom plate supporter 62.
Opening 66 in the slide plate 48 is displaced by the slide case in
response to operation of the hydraulic cylinder 40 in a well known manner. In
addition, the slide case is supported in a clamp 68 by a clamp arm 76 (Fig. 3)
for
retaining a chute nozzle 70 within a chute nozzle case. Chute nozzle 70 also
includes
an opening 74 which may be aligned with the openings 66 in the slide plate 48,
56
in the bottom plate 50, and the nozzle opening 58 in the insert nozzle 60. The
chute
nozzle case 72 is slid into and rotated into position with bayonet locks into
the slide
case 46. A clamp arm 76 includes an over center toggle which moves in response
to a clamp lever 80 to retain the chute nozzle 70 in alignment with the insert
nozzle,
60 and the gate valve opened by displacement of the slide plate 48 with
respect to the
bottom plate 50. A coil spring 82 mounted on a least thermally influenced
position
of the gate supports facial load on the sliding brick 48.
The open top 26 of the ladle is closed by a lid or cover 90 which may
be made of a refractory material or a refractory coated shell. The cover 90 is
carried
and positioned by a crane 24. The cover 90 maybe positioned or it may be
hinged
to the vessel to enclose the internal chamber 23 of the ladle between the
closed
nozzle 28 and the open top 26. Such covers have previously been known for use
in
retaining heat within the chamber 23. Moreover, in view of the heat retained
in the
ladle, enhanced metallurgy adjustments could be made to the contents of the
ladle
during the transport time. In particular, before the cover 90 is positioned on
the
open top 26 of a ladle 22, additional alloys constituents and catalysts can be
introduced to the chamber 23 so that the contents can be refined. In
particular, the
molten metal composition in the chamber 23 may be maintained within a desired
alloy or combination range while the slag layer continues to provide catalysts
that
remove impurities from the molten metal and avoids reintroduction of
impurities to
the molten metal content.
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Preferably, adjustments are not made during the transport time, but
rather while the ladle is at the intermediate processing station 15 or
secondary
refining facility. The ladle is not released from the intermediate processing
station
15 or secondary refining facility for transport to the production facility
until the steel
chemistry and temperature have reached a narrow target range. Preferably, the
refractory body is inserted into the ladle after all adjustments have been
made at the
intermediate processing station 15 or secondary refining facility. Preferably,
the
intermediate processing occurs before the cover 90 is put on top and more
preferably, before the introduction of the refractory body, either at the
refini.ng
facility, during transport to the production facility or at the production
facility.
As a result of the closing of the open top 26 and the nozzle 28 of the
ladle 22, the chamber 23 is inaccessible to additional enhancements, such as
the use
of a vortex inhibitor to control the intermixture of the slag layer with the
molten
metal layer when discharge of the metal is desired. Moreover, upon reaching
the
destination vessel 17 of processing facility 16 by crane 2 4, the
cover 90 may not be opened until the pouring of nlolten metal has been
substantially
or entirely completed. In some plants, the cover is removed .from the ladle
when the
ladle is almost empty. This maybe done when the discharging ladle is nearly
empty,
and the next full ladle is brought to the continuous caster uncovered.
As a result, the introduction of a vortex inhibitor to a ladle that is to
be covered represents a substantially different time period during which the
refractory body is subjected to contact with the molten metal and the slag
layer than
in previously known uses. As a result, unlike previously known vortex
inhibitors,
the specific gravity and refractoriness of the refractory body is adjusted to
provide
proper results at the pouring step which occurs substantially after filling,
and after
an extended time of enclosed transport. Preferably, the pour occurs after
intermediate processing. Although the pouring step can range from 35-180
minutes
in duration, the refractory body must provide proper results during the last
portion,
for example, 10 nv.nutes, of the pouring step.
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In one example, while refractory bodies with specific gravity ranges
of 4.8 to 5.2 were commonly used to maintain separation between the slag layer
and
the molten metal layer in furnaces during a period of about two to ten minutes
for
inhibiting formation of a vortex at the critical heiglit level of molten metal
in the
furnace until the throttling or other termination point used to terminate the
flow from
the discharged nozzle, such bodies were ineffective in the closed ladle
environment.
As a result, several changes were made to contribute to longevity of the
vortex
inhibitors in a ladle environment. In particular, alumina (A1203) was changed
to a
high temperature range and increased in proportion to the remaining
constituents
from about 45 % by weight to about 70 % by weight. In addition, the
constituents
were mixed with high temperature cement, such as 1% to 2% by weight of a, for
example, calcium aluminate cement or equivalent high strength or low water
cement.
Moreover, the ratio of steel ballast to refractory material was reduced
to give a specific gravity, preferably of about 3.7, but preferably within the
range of
substantially 2.7-4.5. In addition, a non-wetting agent preferably in the form
of a
particulate carbonaceous material was introduced to the refractory mixture to
reduce
the amount the body would be penetrated by molten metal or slag and
deteriorated,
eroded, corroded, broken down, or dissolved by the slag or the molten metal,
during
the extended steel and slag contact periods. Nevertheless, other mineral-based
compounds, but preferably silicates, borosilicates and other glass could be
added as
penetration inhibitors.
Typically, more expensive refractory materials such as MgO may be
used, but may be avoided where expenses are to be limited. In any event, the
refractory body includes a mixture of steel ballast and refractory material
and has an
adjusted specific gravity from previously known refractory body inhibitors.
Adjustment may include changes due to desired target chemistry of the metal,
for
example, stainless steel fibers, silicon carbide, magnesite refractories,
chrome
refractories, zircon refractories, zirconia refractories, tabular alumina
refractories
or mallite refractories may be included. Adjustment may also be determined by
bulk
density specifications and life expectancy in molten steel. Preferred ranges
of steel
ballast with a per cubic foot weight of 300-400#, preferably in a range of 30%
to
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80 % by weight, and 30 % to 80 % by weight refractory material of the types
disclosed
above. A binder of high temperature cement, at least capable of withstanding
1000 F, but preferably capable of withstanding 2400 F to 3300 F without
substantial deterioration may be included, preferably 2%-12 % by weight.
The reduced steel ballast to refractory material ratio has a specific
gravity less than that required to buoyantly support the body in the molten
metal at
the slag layer interface in the ladle, but preferably greater than that
required to
buoyantly support the body in the slag layer. As a result, the specific
gravity and
refractoriness (ability to withstand or survive in a liquid metal environment)
adjustments have resulted in refractory bodies that are still maintained in
workable
shape to perform vortex inhibition and throttling functions even after the end
of a
prolonged time exposure to the enclosed environment of a ladle transferring
molten
metal from a furnace to a receptacle vessel. The change in the specific
gravity of
the body may also ensure that the body is not sucked to the discharge nozzle
too
early.
While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and describe
all
possible forms of the invention. Rather, the words used in the specification
are
words of description rather than limitation, and it is understood that various
changes
may be made without departing from the spirit and scope of the invention.
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