Note: Descriptions are shown in the official language in which they were submitted.
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BACKGRO~ND OF THE INVENTION
This invention relates to me-thods and apparatus for
feeding and continuously casting molten metal for continuously
easting metal strip, sheet, slab, pla-tes, bars, or ~illets
directly from molten me-tal introduced through a semi-sealing
nosepiece into the casting region of a moving mold between spaced
portions of two moving cooling surfaces which cool the metal
being cast.
The invention herein is described as embodied in the
structure and operation of casting machines in which the molten
metal is fed through a semi-sealing nosepiece into the moving
mold or casting region located bet~,~een opposed portions of two
moving water or liquid-cooled molds having surfaces defining the
mold region. The moving molds in the illustrative examples
shown are flexible bands or belts which act as cooling surfaces
and enelose or confine the molten metal introduced into the
moving mold between them, and they simultaneously move the molten
metal progressively toward solidification into forms or products,
sueh as strip, sheet, slab, plates, baxs~ or billets, hereinafter
ealled the "cast product" or "produet being cast". Continuous
casting maehines employing such flexible bands or belts, often
called twin-belt casters, have been pioneered and manufac-tured
for many years by the ~azelett Strip-Casting Corporation of
Mallets Bay, Vermont. If fu~ther information on various aspects
of such machines is desired, it can be obtained from the patents
assigned to that Company, the assignee of the present invention.
In the introduction, feedin~, or charqing of molten
metal into the moving mold of a substantially horizontal or down-
wardly inclined continuous casting rnachine, critical factors
for casting metal of acceptable quality and having appropriate
urface qualities and surface c" acteristics for commercial
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applications are the avoidance of rapid changes in the veloci-ty
of the mol-ten metal being introduced, and the avoidance of
turbulence in the molten metal, the limiting of exposure
of the me-tal to a reactive atmosphere or other reac-tive
agen-ts, and the provision of favorable interac-tion be-tween -the
moving mold surfaces and the metal being confined by these
surfaces.
Molten metal handling and distribution equipment,
which conveys the molten metal to be cast from -the melting or
holding furnace to the mold region of the casting machine, is
generally designed to avoid restrictions and to limit exposure
of the molten metal to an uncontrolled atmosphere~ usually
accomplished by under-pourin~ at each transfer. Thus, the molten
metal is not ~oured over an open lip, but instead is drawn well
below the surface in the vessel, so as to leave behind surface oxides
and most foreign matter. Such under-pouring technique further
transfers or introduces the molten metal into the next vessel
under the surface of the metal therein,in such a~ay as to minimize
agitation and to avoid contact with atmospheric or oxygen-bearing
agen-ts. These stric-tures and techniques apply generally -to the
handling of molten lead, zinc, aluminum, copper, iron and steel,
and to the alloys of these metals, as well as to other metals.
Failure to observe such strictures and techniques may result in
the uncontrolled formation of oxides, which ten~ to adversely
affect the metallurgical qualities of the metal being cast,
and which otherwise cause difficulty in the molten-metal feeding
equipment and in the mold. In cer-tain of -these metals, relative-
ly small percentages of oxygen are capable of causing such
difficulties. Hydrogen may also become dissolved within
the cast metal emanating fromthe dissociation of atmospheric water
~ 8~
vapor molecules resulting from contact with the hot molten metal or
from con-tact with hydrogen~bearing combustion gases. Such hydrogen
dissolved, even in small c~uantities, can cause un~esirable porosit~ .
Even nitrogen may be unwelcome, under some conditions.
Oxidation problems within launders, trouyhs, and
tundishes have been generally sol-ved by under-pouring, together
with the use of reducing atmospheres applied to the surface of the
molten me-tal. Such reducina atmospheres are obtained through
flames of burning oil or gas which are rendered deficient in the
oxygen supplied to -them. In the case of aluminum, a protective
oxide film will remain quietly upon the surface of an open vessel,
when designed so as to minimze agita-tion, and in this case reducinc
atmospheres are not required in the preliminary stages of aluminum
transfer with under-pouring.
~ ntrapment of oxides, or other impurities, is less
apt to occur in the conventional vertical continuous casting
processes, which use a riaid mold that is open at the top and
bottom. In those vertical casting processes the pouring into the
mold is generally accomplished by under-pouring, and at a relative
ly slow rate. Such oxides, and o-ther impurities as do form,
have time to float to the top, and thus -they are prone to remain
in the top oxide layer which forms there or to become frozen in -th
center or core region of the ingot of relatively large cross-
sectional area being cast. In this case of vertical casting of
large cross-sectional products, -the entrapped oxides or other
impurities are not li~ely to be detrimental to, nor render un-
acceptable, the products beina cast.
The situation is quite different and peculiar in
casting in substantially horiæon-tal or downwardly inclined
continuous casting machines. When the mold region is
elongated as in twin-belt casters, for example, the continuously
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moving mold surfaces are normally operated at relatively high
linear speeds. Here the problems of entrapment of oxides,
or other impurities, can be more serious ana can render the
product being cast unacceptable.
When casting relatively -thin sections
close to the horizontal, the technique
of under-pouring for the introduction of the molten metal
into the moving mold region of continuous casting machine is
usually not practical or feasible, as there is insufficient
vertical clearance between the mold surfaces. When casting such
relatively thin sections~ the molten metal is usually introduced
through a semi-sealing nosepiece. As a practical matter this
nosepiece mus-t be spaced slightly away from the moving mold
surEaces near the entrance to the mold region in order to
compensate for the inevitable variables and variations in the
entrance to the continuously moving mold. Such spacing from
the continuously moving mold surfaces is also needed to allow for
the dimensional tolerances involved in the forming and shaping
of the refractory material having suitable physical, chemical
and thermal properties for the demanding service of handling
molten metal. The refractories suitable for this demanding
purpose are difficult to shape and maintain within close and
consistent operating tolerances.
Thus, the fit between the nosepiece for feeding
molten metal and the continuously moving mold surfaces must be
relatively loose, with an initial gap of 0.010 inch (0.25 mm)
being customary for a new nosepiece. However, this gap, through
wear, will tend to widen, especially on the top of the nosepiece.
The periodic leakage of most molten metals around the sealing
surfaces of the nosepiece is inevitable if the operator of the
~L%~
movinq mold attempts to keep the mold region continuously filled
up against -the nosepiece with molten metal. In other words, it
is just usually not practicable to attempt to keep -the ~ol-ten
metal in -the mold region Eull up ayainst the nosepiece. Indeed,
a gap of about 0.020 inch (0.5mm) around the nosepiece will
generally leak any molten metal of low surface tension, and such
metal will readily,quickly solidify or freeze un-timely in-to "fins" ,
causing an undesirable jamming action against the nosepiece,
resulting in destruction of the nosepiece.
Consequently, it is usually necessary to avoid
filling the mold region so as to avoid back-up of the molten
metal up to the nosepiece. Such attemp-ted filling is somewhat
more tolerable with aluminum, because of its high surface tension
which tends to impede leakage through the gaps. Even wi-th alumunum,
however, a "head" of molten metal significantly higher than the
upper mold region is to be avoided, because the resultant pressur~
in the molten aluminum at the qaps near -the nosepiece will over-
come the surface tension and cause leakage. Therefore, even with
aluminum, the operator will often keep the level of molten metal
in the mold region no higher than the front lower edge of the
nosepiece, so that a considerable gas cavity will be present.
Actually, during the continuous casting, notably
of aluminum, with a closely fitting nosepiece, a small yas cavity
will persist despite a small head of metal pressure that is
slightly higher than any point in the mold reqion; tha~ is,
higher than the location of said residual gas cavity. It is our
belief that this phenomenon of an unintended residual gas cavity
results in part from the dynamics of the in-feed and from -the
drag of the moving mold surfaces upon the surface of the molten
metal, ausmented by surface tension.
Therefore, as a result of intentional opera-tion to
avoid any chance for leakage of the molten metal to occur out
throu~h the gaps adjacent to the nosepiece or even where not in-
tended, as a result of such dynamic drag phenornenon, there is
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usually a gas space or cavity within the mold region. This
cavity is located in the upper portion of the mold region
above the level of the molten metal and adjacent to the front
end of the nosepiece.
It will be appreciated that with the nosepiece sur-
faces positioned within approximately 0.020 of an inch (0.5 mm)
near the continuously moving mold surfaces, the operator is not
able to ascertain by visual observation the physical status ox
level of molten metal at any time in the mold region. Thus,
the operator cannot rely upon visual observation to control the
level of molten metal or to control the size of the ahove-
described cavity. Novel methods and apparatus for overcoming
the ~ifficulties relating to the operator's lack of visible
observation for pour level control are described and claimed
in U.S. Patent Nos. 3,~64,973 issued February 11, 1975 to Petry
and 3,921~697 issued November 25, 1975 to Petry. The methods
and apparatus of these patents have been successfully applied
to twin-belt casters, where they eliminate the need to see
physically the level of the molten metal. They have proven
practical for control of twin-belt casters in commercial produc-
tion. Thus, the use of a suitably fitting nosepiece becomes a
practical way to introduce metal into the casting region, while
maintaining a controlled cavity in the upper portion of the mold
region between the nosepiece and the molten metal.
Molten aluminum and alumin~um alloys in particular are
highly reactive. They can combine with other metals, gases and
refractories. For example, in a molten state during continuous
casting, aluminum alloys are susceptible to random reaction
with or are affected by atmospheric oxygen, water vapor, and
trace atmospheric gas pollutants. In the continuous casting
of aluminum alloys containing magnesium, random atmospheric
contact results in reactions which, in turn, cause oxide spots
or streaks on the cast surface, and will also reduce the
fluidity of such alloys in a molten state.
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:121P~3~a1Z
The difficulties of un~ontrolled oxida-tion and
reaction of -the molten metal are compounded in two ways when
relatively thin sections are being continuously cast. ~irst, -ther
is the cited problem of lack of clearance for means to underpour
the metal into the continuously rnoving mold region, but secondly,
the ratio of surface to volume is increased with such -thin sec-tion .
As oxidation is generally a surface or interface reaction, oxide
formation on such relatively thin continuously cast sections
constitutes a greater relative proportion of the product as con-
trasted wi-th thick sections. Also, with such thick sections, it
;s practical to scalp oxides from -the surface oE the cast product,
but not with the relatively thin sections.
While a portion of the above description has been
in terms of twin-belt casting machines, the same problems occur
with other types of continuous casting machines in casting relativ _
ly thin sections in a horizontal or downwardly inclined mode.
"r~elatively thin sections" as used herein is
intended to include the range from l/4 inch (6 mm) to 2 inches
(51 mm), the preferred range beina l/4 inch (6 mm) to 1-l/2 inches
~3~ mm).
SUM~RY O~ THE INVENTION
Among the objects of this invention are to
provide me-thods and apparatus for the in--feeding and settling of
molten metal and the continuous casting of metal products~of accept
able surface qualities and characteristics, and acceptable in-ternal
structure and qualities via continuous casting machines
employing a moving, horizontal or downwardly inclined mold region.
The molten metal is introduced into the upstream or entrance
end of the continuously moving mold region through a semi-
sealing nosepiece accura-tely matina or fitting with -the moving
mold surfaces and having clearance gaps from the moving
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mold surfaces of less than 0.050 of an inch (1.27 mm) while
inert gas is appliec to the moving mold surfaces and to the
entering metal for the protection or shrouding of -the molten
metal surface wi-thin the mold cavity from oxygen ana other
de-trimental a-tmospheric gases. An advantageous shrouding of in--
feeding molten metal, controlled cavity in the upper end of the mold
region an~ of the moving mold surEaces is accomplished by means of inert
gas injected into the mold through the semi-sealing nosepiece,
or directed at the mold cavity and passing through the clearance
gaps around the nosepiece. Such inert gas is further circulated
for cleansing the moving mold surfaces of undesired accompanying
or adhering gases associated with the mold surfaces as the mold
surfaces approach the nosepiece before enterina the mold region.
The invention in certain of its aspects,as embodied
in the illustrative methods and apparatus,comprises in-feeding
molten metal through at least one passage in a nosepiece of
refractory material inserted toward the upstream end of a conti-
nuously moving mold region and having clearance gaps of less than
O.050 of an inch (1.27 mm) from the continuously moving mold
surface, securing the nosepiece with rigid support structure
clamps above and below, supplying inert gas through at least one
passage in at least one of the said clamps, to quietly introduce
sai~ inert gas into at least one of the narrow clearance gaps
around the inserted nosepiece, for shrouding the entering molten
metal and the controlle~ cavity in the upper end of the moving
mold region.
The invention in other of its aspects as embodied in
the illustrative methoas and apparatus comprises in-feeding molter
~etal through at least one passage in a nosepiece of refractory
material inserted toward the entrance of the continuously moving
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mold region and mating ~ith the continuously moving mold surfaces
with clearance gaps therefroln of less than 0.050 of an inch
(1.27 mm), introducing the molten metal -to be cast -throuyh a-t
least one passage in at least one part of the inserted nosepiece;
simultaneously injecting inert gas directly through at least one
additional passage in at least one part of said nosepiece for
introducing the inert gas directly into the controlled cavity
in the entrance end of the mold region for enhancing the
qualities and characteristics of the metal product being conti-
nuously cast.
The invention in additional aspects comprises -those
features or aspects described in the above two paragraphs
including feeding inert gas through at least one passage in at
least one of the nosepiece support structures while simultaneously
also feeding inert gas throuah at least one passage in the nose-
piece itself.
In another of its aspects, the invention comprises
placing a shield member or structural member relatively near
to at ].east one of the moving mold surfaces where it is travel-
llng toward ~he entrance to the moving mold region and applying
inert gas to the channel thus defined close to this moving mold
surface for causing the moving mold surface to become bathed in
the inert gas for carrying or propelling the inert gas through
the clearance gap by the nosepiece and into the entrance to the
moving mold region.
In additional as ects, -the present invention
comprises placing a shield member or structural member relatively
near to a-t least one of the moving mold surfaces w~ere it is travel-
ling toward the entrance to the movina mold region for casting a
relatively thin metal section and applying inert gas to the cha~e
thus defined close to this moving mold surface for cleansing the mold
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surface for removing therefrom atmospheric gases and/or contami-
nating pollution gases and/or water vapor which may be carried
by or adherent to the moving mold surface for enhancing the
qualities and characteris-tics of the con-tinuously cast me-tal
product of relatively thin section being cast.
Among other aspects of the present invention are
feeding of inert gas through passageways and/or chambers asso
ciated with support structure for the metal feeding nosepiece
for applying this gas forwardl~ against the moving mold surfaces
as they are travelling in converging relationship toward the
entrance of the moving mold for casting a relatively thin metal
section. Moreover, such passageways and/or chambers may include
outlets directed laterally toward the respective moving edge
dams employed in the twin-belt casters for bathing, enveloping
and cleansing -these moving edge dams with inert gas as they are
approaching the moving mold.
Among the many advantages provided by the illus-
trative methods and apparatus described herein in certain aspects
are those resultin~ from the fact that inert gas can be intro-
duced directly into any cavity existing in the upstream portion
of a moving mold casting a relatively thin metal section in
generally horizontal or downwardly inclined orientation for
establishing an inert gas pressure in such cavity slightly
exceeding atmospheric pressure for shrouding the cavity itself anc
for causing the inert gas to flow outwardly in back-flushing,
cleansing, bathing relationship through clearance gaps between the ~ving
mold surfaces and the inserted metal-feeding nosepiece. Moreover,
the inert gas is in-troduced through at least one passage in -the
refractory material of the nosepiece itself while molten metal
is in-feedinq through at least one other passa~e in the nosepiece.
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The outlet of the gas passage may be elevated above the
centerline of the nosepiece for assuring that the inert gas
is entering any cavity in the upstream portion o-f the moving
mold above the level of the molten metal therein.
Among the many advantages provided by the illustra~
tive methods and apparatus described herein in certain aspects
are those resulting from the fact that the inert gas can be
introduced indirectly into any cavity e~isting in the upstream
portion of a moving mold casting a relatively thin metal sec-
tion in generally horizontal or downwardly inclined orienta-
tion by applying the inert gas to at leas~ one of the moving
mold surfaces while said surface is travelling toward the
entrance to the moving mold. The inert gas is introduced
gently through passages and/or chambers in the support structure
for the refractory nosepiece feeding the molten metal, and at
least one shield member may be conformed in configuration
relatively near to the moving mold surface for achieving
effective application of the inert gas to the moving mold sur-
face for achieving effective application of the inert gas to
the moving mold surface and for cau~ing a diffusing~ enveloping,
cleansing action of the inert gas a~ainst the moving mold
surface~
A further aspect of the present invention in those
installations wherein inert gas is indirectly introduced into
the mold through clearance gaps around the nosepiece will now
be described. This aspect is the simultaneous, advantageous
use of two kinds, two densities, of inert gas at the same time.
Specifically, an inert gas which is heavier than air is applied
above the nosepiece; such gas will tend to lie down upon the
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nosepiece and its upper s~lpport s-tructure rather than to dis-
sipate. At the same time, an inert gas which is lighter than
air may be applied below the nosepiece; such gas will tend to
rise and to lie up against the bottom of the nosepiece and its
lower support structure rather than to dissipate. As an
illustration, a suitable heavier-than-air gas for top use is
argon, which is about 35 percent heavier than air. A suitable
lighter-than-air gas for bottom use is nitrogen, which is
about 3 percent lighter than air.
BRIEF DESCRIPTION`OF THE DRAWINGS
The invention, together with further objects, aspects,
advantages and features thereof, will be more clearly understood
from a consideration of the following description taken in
conjunction with the accompanying drawings, in which like elementc
will bear the same reference designations throughout the various
Figures. Qpen arrows drawn therein indicate the direction of
movement of the metal being fed into the moving mold and being
cast therein in a direction from upstream to downstream, the metal
.
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being fed into the upstream end of the continuously moving mold.
The drawings are not necessarily to scale, emphasis instead
being placed upon illustrating the principles of the invention.
FIGURE 1 is a perspective view of the input or
upstream end of a continuous casting machine embodying the
present invention, as seen looking toward the machine from a
position upstream of, and outboard beyond the outboard side of,
the two belt carriages.
FIG. 2 is an elevational view, partly broken away
and in section, of a casting machine embodying th~ present
invention as seen looking toward the outboard side of the two
belt carriages, showing the casting region downwardly inclined
at a predetermined angle of inclination.
FIG. 3 is a sectional elevational view of the up-
stream or feeding end of this machine, shown enlarged, equipped
with a semi-sealing nosepiece for casting a relatively thin metal
section while applying inert gas, the configura-tion shown being
especially suitable for metals of the lower range of melting
points.
FIG. ~ is a perspective view, shown enlarged,
of one of a pair of structural support clamps for the refractory
nosepiece, the clamp is arranged for the distribution of inert
gas, by applying said inert gas at one of the clearance ~aps at
close range.
FIG . 5 is a perspective view of a refractory metal-
feeding nosepiece, or one section of a wide nosepiece, this con-
figuration being especially suitable for in-feeding molten metals
in the lower range of melting points.
FIG. 6 is a perspective view of a nosepiece as
illustrated in FIG. 5 which has a passage therein for the
introduction of inert gas directly into the cavity in the
entrance portion of the moving mold.
FIG. 7 is a plan view of a tundish especially
suitable for in-feeding molten metals of higher melting point.
FIG. 8 is a sectioned elevational view of the tun-
dish of FIG. 7 in relation to the upstream or feeding end of
a continuous casting machine for casting a relatively thin
metal section while applying inert gas.
FIG. 9 is a sectioned elevational view generally
similar to FIG. 3. FIG. 9 shows a gas-sealing-shroud funnel
~d gas-shield-channel assembled together with a metal-feeding
assembly for continuously casting higher-melting-point metal,
while applying inert gas with "open pool" metal in-feed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An illustrative exa~nple of a continuous metal casting
machine in which the present invention may be used to advantage
is shown in FIGS. 1 and ~. In this casting machine, molten
metal 1 is supplied through in-feed apparatus which may be a
pouring box, ladle or launder 2, and flow~ down through a
pouring spout 3 in under-pouring relationship into a tundish
4, which is lined with a suitable refractory material 31. For
clarity of illustration, the tundish is shown slightly with-
drawn in FIG. 1 from the entrance to the moving mold. The
rate of flcw from the launder which i5 shown at 2 to the tundish
4 is controlled by a tapered stopper (not shown), mounted on
the lower end of a control rod 5. From the tundish 4, the
molten metal 1 is fed through a nozzle or nosepiece 7 of
refractory material, or through tubes 21
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(FIG. 7) into the entrance E of the moving mold or casting
region C. This entrance E is at the upstream end of the
casting region C, which is formed between spaced and substant-
ially parallel surfaces of upper and lower endless flexible
casting belts 9 and 10, respectively. The casting belts are
normally made of low-carbon, cold-rolled strip steel of uniform
properties, and welded by TIG welding. They are normally grit-
blasted for roughening the surface which will face the molten
metal, followed by roller-levelling and coating.
The casting belts 9 and 10 are supported on and
driven by respective upper and lower carriages, generally
indicated at U and L. Both carriages are mounted on a machine
frame 11. Each carriage includes two main rolls or pulleys
which directly suppor~, drive and steer the castin~ belts. These
pulleys include upper and lower input or upstream pulleys 12 and
13, and upper and lower output or downstream pulleys 14 and 15,
respectively.
The casting belts 9 and 10 are guided by multiple
finned backup rollers 16 (FIG. 2), so that the opposed belt
casting surfaces are maintained in a preselec~ed relation~hip
throughout the length of the casting region C. These finned
backup rollers 16 may be of the type shown and described in U.S.
Patent No. 3,167,830 issued February 2, 1965 to R. W. Hazelett
et al.
A flexible, endless, side metal-retaining dam 17,
sometimes called a moving edge dam, is disposed on each side of
the casting region and for con~ining the molten metal. The side
dams 17 (only one is seen in FIG. 2) are guided at the input or
upstream end of the casting machine by guide members 35, shown
in part, which are mounted on the lower carriage L, for example,
such as are shown in said U.S. patent, or in U.S. Patent No.
4,150,711 issued April 24, 1979 to R. W. Hazelett et al.
During the casting operation, the two casting belts
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9 and 10 are driven at the same linear speed by a driving
mechanism 18 which, for example, is such as described in s~id
Patent No. 3,167,830. As shown in FIG. 2, the upper and lower
carriages U and L are downwardly inclined in the downstream
direction, so that the moving mold casting region C between
the casting belts is inclined at an angle A with respect to the
horizontal. This downward inclina~ion A facilitates flow of
molten metal into the entrance E of the casting re~ion C. This
inclination angle A is usually less than 20, and it can be
adjusted by a jack mechanism 50. The presently preferred
inclination for aluminum and its alloys is in the range from
6 to 9.
Intense heat flux is withdrawn through each casting
bell: by means of a high-velocity moving layer of liquid coolant,
applied from nozzle headers 6 and travelling along the reverse,
cooled surfaces of the upper and lower belts 9 and 10, respect-
ively. The liquid coolant is applied at high velocity, and
the fast-flowing layer may be maintained in a manner as shown
in said Patent No. 3,167,830 and in U.S. Patent No. 3,041,686
issued July 3, 1~62 to R. W. Haæelett et al. The presently
preferred coolant is water with rust inhibitors at a temperature
in the range from 70Q F (21 C) to 90 F t32 C).
After the cast product P has solidified at least on
all of its external surfaces, and has been fed out of the casting
machine, it is conveyed and guided away by a roller conveyor
(not shown).
For in-feeding metals of low melting point, for
example, lead, zinc, or aluminum, the nosepiece may be made
of marinite or other suitable refractory material. This nose-
piece 7 is made of one integral piece of refractory meterialas shown in FIGS. 5 and 6. Alternatively, this nosepiece 7
may be assembled from a plurality of integral pieces of
- refractory material.
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The term "nosepiece" as used throughout may refer
to a single integral member or to an assembly of a plurality
of integral pieces.
In order to support this refractory nosepiece 7,
there are rigid upper and lower support structures 25 and 26, res-
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pectively, positioned above and below the nosepiece 7 in the
manner ~f clampc wl:h the nosepiece sandwiched between these
clamping structures 25 and 26.
As shown in FIGS. 5 and 6, the refractory nosepiece
7 includes at least one metal feeding passage 20. In this
example, there are two such passages 20 shown extending in
parallel relationship in the downstream direction longitud-
inally through the nosepiece 7 with a central barrier wall 40
between them. These metal feeding passages 20 have a rec-
tangular cross section. They are relatively wide with shallow
vertical dimension as is appropriate for casting relatively
thin metal sections. In order to distribute the in-feeding
molten metal smoothly and quietly, without undue turbulence,
into the moving mold C (FIGS. 2 and 3) the downstream ends of
these metal feeding passages 20 are shown flared out gradually
laterally in the downstream direction as indicated at 41
(FIGS. 5 and 6~.
As seen in FIG. 3, the upper and lower suppcrting
structures 25 and 26 for clamping the refractory n~epiece 7
between them are generally similar in construction, except
that the lower one is inverted in configuration. These sup-
porting structures 25 and 26 are rigid, for example, being
made of steel.
In FIG. 4 is shown enlarged the upper support clamp
structure 25. This structure incll~des a rlgid base plate 28
whcse clamping surface 42 includes shallow transversely
extending lands 43 and grooves 44 for securing a firm clamping
engagement with the refractory nosepiece 7. There is an
upstanding rigid rear flange or wall 45 attached to the base
plate 28, for example, by welding at 46 and 47. The assembly
of this base plate 28 and rear ~all 45 is stiffened by a
diagonal plate 33 welded at 48 and 49, respectively, to the
base plate and rear wall. As
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seen in FIG. 3, the slope of this diagonal plate 33 generally
conforms to -the configuration of the nearby upper casting belt 9
where this helt is curved and travelling (arrow 51) around -the
upper input pulley roll 12. In other words, this diagonal
plate 33 is sloped to be qenerally parallel to an imaginary plane
tangent to the nearest region of the cylindrically curved belt 9.
There is a triangular side wall 53 (FIG. 4) secured
in gas-~ight relationship to the baseplate, rear wall and diagonal
plate 33 and a correspondin~ triangular side wall ~not seen)
at the other side of the support clamp structure 25 thereby
forming a "lean-to" plenum chamber 54. A portion of the struc-
ture 25 is shown cut away to reveal clearly this lean-to chamber
54, and there is a similar "lean-to" plenum cha~ber 54 in the
lower clamp structure 26. Sockets or mounting holes 55 are
provided in this clamp structure 25 for attachment to mounting
brackets 56 (FIG. 3) which are mounted on upstream end portions
57 of the main frame members of the lower carriage L. The
tundish 4 is shown supported by a bar 58 extending from the
bracket 56, and other support mounting means 65 for the tundish
may be provided.
In order to conform with the nearby curved
moving mold surface 9, the forward (downstream~ edge or lip of
the hase plate 2~ is chamfered at 59 at a slope less steep
than the diagonal plate 33. As seen in FIG. 3, this sloped lip
59 is generally parallel with an imaginary plane tangent to
the nearby curved moving mold surface 9. -
FIG. 3 shows the molten metal e~itina at 60 from
the passage 20 in the nosepiece 7 and entering the entrance
region E of the moving mold casting region C. A resultant gas
space or cavity 8 thereby exists in the entrance region E above
the level of the molten metal in the moving mold region C
adjacent to the downstream end of the nosepiece 7.
In order to introduce inert gas directly under
pressure into this cavity 8 for controlling the gas content
therein, the nosepiece 7 is provided with at least one longi-
tudinally extending gas ~eed passage 19 (FIG. 6) running along
side of the metal feeding passa~es 20 This gas feed passage 19
is located in the center portion 40 of the refractory material
in the nosepiece. This gas feed passage 19 is located at a
level above the centerline of the nosepiece 7 and its outlet 61
is near the upper edge o~ the downstream end or terminus 62 of
the nosepiece. ~he way in which the inert gas is fed down into
the vertical inlet port 63 connecting with the gas feed passage
19 will be explained later~
By virtue of having this gas feed outlet 61 at this
elevated location on the nozzle terminus 62, the gas flow is
generally above the level of the molten metal exiting 60 ~FIG. 3)
from the in-feed passages 20. Thus the i.nert gas enters directly
into the cavity 8 for maintaining this cavity charged with iner-t
gas at a pressure slightly above atmospheric pressure. Even if
the level of the molten metal in the entrance region E is
temporarily inadvertently allowed to rise up sli~htly above -the
level shown in FIG. 3, the elevated position of the gas feed out-
let 61 will usually place it above the metal, so that it wi.ll
usually remain unblocked by the molten metal in the entrance E and ..
therefore, be in continuous communication with the controlled
qas cavity 8. The gas feed outlet 61 is shown connected with a
horizontally extending transverse narrow groove or slot 61-1
~Z~ 2
cut into the terminus 62 of the refractory nosepiece 7 for aiding
in distributing the inert gas directly into the controlled gas
cavity 8 a-t low velocity with minimum resultina aaitation or
turbulence of the molten metal. The cavity 8 thus rernains con-
trolled by continuous in-feed of inert gas through one or more
passages 19 at a pressure slightly above atmospheric pressure.
Invasion into the cavity 8 of undesirable gases, particularly
oxygen and water vapor (and also atmospheric polluting gases,
such as sulphur aioxide and carbonic acid gas) is prevented by
this inert gas being continuously charged into this cavity. The
inert gas shrouds this cavity 8 and purges and -thereafter excludec
the undesirable gases from the entrance region E.
A constant flow of inert gas is maintained through
the gas feed passage 19 during casting, maintaining the cavity 8
full o~ inert gas slightly above atmospheric pressure. As
discussed in the introduction, there are slight clearance gaps
above and below at 22 (FIG. 3) between the downstream end of the
nosepiece 7 and the upper and lower mold surfaces 9 and 10 which
are continuously moving as indicated by the arrows 51 and 52. In
this casting machine these moving mold surfaces 9 and 10 are
formed by the casting belts. Some of this constant flow of
inert gas exits in the upstream direction through -the aforemen-
tioned narrow clearance gaps at 22. These clearance gaps 22 are
less than 0.050 of an inch ~1.27 mm) and are usually in the
range of 0.010 of an inch (0.25 mm) to 0.020 of an inch
~0.5 mm). The inert aas exiting through these clearance gaps
22 around the nosepiece 7 advantaqeously scours, cleans,
and displaces atmospheric gases, including water vapor, off from
the incoming mold surfaces 9 and 10 and flushes the gases away
from ~he entrance region E.
The above-~escribed close-f~owl~ng, disp]acing,
enveloping, cleansing action on -the moving mold surfaces i~
enhanced and extended over a wide are of the moving mold
surfaces 9 and 10 as they converge 51, 52 toward thP entrance
region E by forming a narrow channel 66 for confining the
exiting inert gas close to these moving mold surfaces 9 and
lO by means of curved shield members 34 (FIG. 3) positioned
between the diagonal plates 33 and the moving mold surfaces.
The shield members 34 are cylindrically curve~ for nesting
close to the respective curved moving mold surfaces 9 and lO,
being spaced less than l/4 inch (6 mm) and preferably at close
proximity within 1/8 inch (3 mm) from these moving surfaces.
The forward ~downstream) edge of the curved shield member 34
is welded along the crest 6~ (F'C.. 4) of the base plate 28
near the upstream border of the chamfered lip 59. The inert
gas exits at 36 (FIG. 3) from the narrow channel 66 between
the shield 34 and the closely proximate moving mold ~urface
9 or lO after flowing through this naxrow channel in a
direction counter to the motion 51 or 52 of the moving mold
surface in close-flowing, displacing, cleansing relationship
therewith.
The use of the shield members 34 advantageously
reduces the consumption of inert gas and also increases the
time duration of exposure of the moving mold surfaces 9, lO
to the inert gas for displacing, cleansing of atmospheric
gases therefrom.
If desired to increase further the impedance against
invasion or intrusion of atmospheric gas into the entrance
region E, a loose, flexible packing material 23 may be placed
in this narrow channel 66. A suitable loose, flexible packing,
for example, is fiberglass insulation or l'Kaowool" ceramic
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~ . . ~
--~ ~2Q8~LZ
insulation, obtainable from Babcock & Wilcox. This loose packing
may be allowed only lightly to contact the moving mold surfaces
9, 10. It may be placed in the channel 66 and/or ad~acent to the
forward edge of the sloping li.p 59 against the nosepiece 7, as
shown at 23. This loose packing 23 may be used only with the
"direct" in-feeding of inert gas into the cavi-ty 8 through
passages 19 (FIG. 6) in the nosepiece 7.
There is evidence that some atmospheric oxygen and
other atmospheric gases, such as water vapor, are adsorbed upon
the moving mold surfaces 9, lO and/or upon -their coatings, for
example, such coatings as described and claimed in U.S~ Patent
No. 3,871,905. Again, with the use of moving mold surfaces 9,
lO, which have been roughened, as by grit-blasting, atmospheric
oxygen and other gases tend to be entrained inthe resulting
minute dimples. Also~ in addition to adsorption, rough coatings
OII the moving mold surfaces 9, lO can entrain atmospheric gases.
The adsorbed andlor entrained atmospheric gases would be carried
or conveyed continuously into the moving mold with consequent
adverse effects upon the metal produc~ P being cast, except for
the advantageous scouring, diffusing, and displacing action upon
the movingNDld sur:Faces 9 t 10 caused to occur by t.he inert gas
as described above.
In addition to exiting in a diffusing, scourinq
action on the moving mold surfaces 9 and lO, some of the~inert
gas exits from the pressuri2ed controlled gas cavity 8 by flowing
out laterally to each side past the respective moving edge dams
17, thereby scouring and displacing atmospheric gases off from
these edge dams and excluding such gases from invasion into
the entrance region 8.
~ 34~
This inert gas is often nitrogen, but it may be
argon, carbon dioxide, or other gas which is appropriately
inert and non-reactive in relation to the par~icular metal or
alloy 1 being cast. The inert gas which can be used to advantage
when casting aluminum and aluminum alloys is pre~purified
nitrogen that has been water-pumped, i.e., pumped wi-th water
sealing in the compressors and known as "dry" ni-trogen, as dis-
tinct from oil-pumped nitrogen. This "dry-pumped" nitrogen lS
ordinarily sold to welders as shielding gas. A typical specifica-
tion (for such nitrogen shielding gas) calls for less than two
parts per million of oxygen, and less than six parts per million
of water.
This in-feeding of inert gas through one or more
passages 19 in the refractory nosepiece 7 with outlet 61
communicating directly into the controlled gas cavity 8 is called
the "direct"injection of inert gas. A further advantageous
effect of this direct charging of the cavity 8 with the inert
gas is to dilute and expel away from the entrance region E any
oxygen, water vapor or other deleterious or contaminant gases
which may be evolved or given off by the mold and nozzle com-
ponents in the presence of tremendous heat release occurring from
the entering flow 6~ of the molten metal.
In order to properly control and exclude trouble-
some atmospheric gases more is required than the direct injection
of inert gas into the cavity 8 ~ se; that is, the moving mold
surfaces 9, 1~ should also be enveloped and cleansed by upstream
flowing gas channeled 66 in close proximity to the moving mold
surfaces by the curved shields 34 as described above.
:~Z~8~
In addition to this direct injection, or as an
a7ternative thereto, an advantageous "indirect" in-feeding
of the inert gas may also be employed. Inviting attention to
FIG. 4, it is seen that the inert gas G enters a suppl~ port
68 in the triangular end wall 53 for feeding the inert gas G
into the lean-to plenum supply chamber 54. This supply port
68 is threaded for a connection fitting to a gas feed pipeline
or flexible conduit (not shown~. From this chamber 54 the
gas G flows as indicated by arrows t.hrough a plurality of
vertical passages 27-1. into respective long kored passages
27-2 extending horizontally downstream in the base plate 28
connecting to a transversely bored header passage 27~3
connecting with multiple small orifices 24 in the chamfered
lip 59 of the base plate 28. The upstream end of each
longitudinally drilled passage 27-2 j-, closed by a plug 67.
Each end of the transversely dri.lled header passage 27-3 is
closed by ~. plug 67.
If it is desir~d that some of this iner~ gas G in
the header passage 27-3 be applied laterally to the edge dams,
then an orifice 24-2 is drilled in eaoh of the latter two
plugs 67. For casting up to approxi.mately 1 inch (25 mm)
thic:k, it is usually not nece.ssary to provide lateral flow
orifices 24-2. Up to that thickness, sufficient pressure can
usually be maintained in the controlled gas cavity 8 to move
the inert gas out laterally agains' the moving edge dams 17
and upstream along the vertical. side surfaces 69 of the base
28 at a suficient flow rate and volume that atmospheric gases
cannot intrude into the mold entrance region E.
Inert. gas issuing through the orifices 24 in the
sloping lip surface 59 is advantageously applied to the moving
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~LZ~ 2
mold surfaces 9 and 10 at close range for gently, noiselessly,
covering, blanketing, enveloping and cleansing them. If the
direct in-feed gas passages 19 are omitted from the nosepiece
7, as shown in FIG. 5, then the motion 51, 52 (FIG. 3) of the
mold surface S, 10 carries and propels some of this inert gas
into the cavity 8. An advantageous arrangement is to drill
the orifices 24 in a horizontal row spaced one inch apart
(25 rr~) in a center-to-center distance and each having a
relatively small diameter, for example, of 0.062 of an inch
(1.6 mm). In continuous casting of aluminum and aluminum
alloy.s using the "indirect" in-feeding of "dry-pumped"
nitrogen âS ~he inert gas G through passaes 27-1, 27-2,
27~3 ard orifices 24, the flow rate that has ke~n success-
fully used is 10 cubic feet (0.28 cubic meter) per hour for a
cast width of 14 inches (355 mm), and a cast thickness up to
1 inch (25 mm). This ten cubic feet per hour i5 the volume
of inert gas at atmospheric pressure and at room temperature.
The correspcr.ding calculated velocity of noi~eless ejection of
inert gas from the orifices 24 is approximately 5 feet per
second (1.5 meters ~er second). The corresponding pressure
above atmospheric pressure in the lean-to plenum supply chamber
54 is, we believe~ below 0.01 pounds per square inch (under
0.07 kilopascals). Given the proportions of the orifices 24,
we have tne theory that this low flow falls within the region
of fluid flow parameters in which laminar flow prevails, as
opposed to turbulent flow. Laminar flow is by definition
non-turbulent flow, which non-turbulence is a necessity for
avoidin~ the entrainment of air. Th~ turbulence and disturb-
ance noise associated with too high a flow rate will entrain
air; such air entrainment being undesirable. ~egardless of
whether our theory that laminar flow is prevailins is correct
or not~ the employment of this inve~btion, as described, will
achieve the advantageous results descriked in continuously
- 25 -
8~Z
casting .~lwii.num and aluminum allcy~ and wiil be beneficial
in continuously casting other metals in a substantially
hoxlzontal. or downwardly inclined continuous machine ~rhere
oxid2tion or contamination of the cast product by atmospheric
gases is a problen;.
In order to reduce the possibility of turbulence
as the inert gas issues through the orifices 24 for reducing
any tendency to entrain air, these orifices can be terminated
in a transverse slot or groove 24-l milled into the sloping
surface 59.
As the inert gas is expelled from the multiple
orifices 24, it slows down and thus evidently creates a
continuous zone or "ridge" of minute pressure in the cusp
region between the moving mold surface 9 or lO, the sloping
lip 59 and the forward (downstream) end of the nosepiece.
This slowing do~n and creating of the pressure ridge is aided
and abetted by culminating the orifices 24 in the transverse -
slot or groove ~4-l. Some of the gas from this pressure ridge
flows through the cLearance gap 22 into the controlled gas
cavity 8. The remainder of the inert gas from this pressure
ridge ~lows upstream; that is, flows out through the channel
66 in the close-flowing, displacing, cleansing actlon, as
described above, exiting at 36.
This 'tindirect" method of applying the inert gas
quietly; that is, noiselessly with no audible disturbance
into the entrance E to the moving mold, by forming the
pressure ridge in the cusp region near the nosepiece, as
described above, is the preferred method for producing
aluminum cast product P and aluminum alloy cast
- 26 -
~z~ z
product P and especially for producing aluminum alloy cast
produc-ts P containing magnesium, even relatively high percen-tages
of magnesium, that are at-tractively free from undesirable and
troublesome surface oxide and have acceptable quali-ties and
characteristics on the surfaces and also in the interior.
The simultaneous use of both the "direct" and "in-
direct" methods of introducing the inert qas can be used to
advantage. For example, when the molten metal in the entrance E
to the moving mold can be anticipated to rise to a level su~fi-
cient to cover at least the lower clearance gap 22 (FIG. 3 or 8)
at the nosepiece, then this lower clearance gap 22 is appropriate-
ly shrouded and controlled by the "indirect" introduction of
inert gas through the lower lean-to plenum chamber 54 and communi-
cating gas~feed passages in the lower clamp struc-ture 26. Such
gas-feed passages in the lower clamp structure 26 are similar to
those shown in FIG. 4 in the upper clamp structure 25. Thus, the
lower clearance gap 22 (FIG. 3 or 8) is being shrouded and con-
trolled by the "indlrect" method, while -the upper clearance
gap 22 is simultaneously being controlled and shrouded by the
"direct" injected inert gas thereafter ~lowing upstream out of
the cavity 8 through the upper clearance gap 22 (FIG. 3 or 8) and
upstream through the upper close-flowing channel 66.
With reference to FIGS. 6 and 4, the inert gas is
fed into the inlet port 63 leading to the passage 19 by drilling
a passage 70 leadin~ from the slightly ~ressurized plenum chambex 5~
through the base plate 28 and through one of the lands ~3 in
alignment with and in communication with the inlet port 63.
If desired to augment the quiet, unturbulent flow of
the inert shrouding gas in the vicinity of the nosepiece clamp
support structures 25 and 25, additional outlet orifices 72 may
be drilled through the diagonal plate 33 into the pressurized
lean-to plenum chamber 54.
. .. . . . _ .. ~ . . .. .
_ . __ _ _ _ _ . _ _ . .
When casting metals of high melting temperature,
for example, copper, iron and steel, the moving mold surfaces
9 and 10~are covered with appropriate coating, for example,
coatings of silicone oil type or an alkyl oil type, such as
UCON LB-300X obtainable from Union Carbide Corporation, which may
be used with or without admixtures of graphite. With metals
of such high melting temperature, it is usually advantageous
to use a nosepiece 7 with a plurality of parallel,reinsertable
pouring nozzles or tubes 21 in conjunction with a tundish 4 as
shown in FIGS. 7, 8 and 9. These reins~rtable tubes 21 are
inserted into the nosepiece 7 to communicate with the molten
metal in the tundish 4, as seen most clearly in FIG. 9. These
tubes 21 are made of high temperature resistant refractory
material, for example, fused silicon dioxide (quartz3, titanium
dioxide, aluminum oxide, or high temperature refractory nitride
materials, all of which are-commercially available in the ~orm
of tubes. The tubes 21 are embedded in parallel holes in the
accurately machined nosepiece 7.
~Z~8~2
A plurality of parallel in-feed gas passages 63 and
19 analogous to the arrangement shown in FIG. 6 are drilled in
the nosepiece 7 for the injection of inert gas G directly into
the controlled gas cavity 8 (FIG. 8). This inert gas comes from
the pressurized lean-to plenum chamber 54 (see also FIG. 4)
through appropriately located supply passages 70 communica-ting
with the respective vertical passages 63. The clearance gaps
adjacent to the downstream end of the nosepiece 7 are shown at
22.
In order to isolate the controlled gas cavity
8 from atmospheric gases and provide further impedance to in-
trusion of such gases, a loose flexible packing seal 23, as
described above, is placed above and below the nosepiece 7
adjacent to the downstream edge of the lip 59 (FIG. 4) of the
baseplate 28 of the support clamp structures 25, 26. This pack-
ing 23 may be allowed to contact the moving mold surfaces 9 and
10.
In addition to the in-feed gas passages 19, inert
gas may be fed into the narrow channels between -the diagonal
plates 33 ~FIG. 8) and the moving mold surfaces 9, 10 by
employing outlet orifices 72 (FIG. 4) in these diagonal plates~
Although FIG. 8 does not show the curved shie]d members 34
(FIGS. 3 and 9?, it is to be understood that such shields may be
employed with the multi-tube 21 metal feed shown in FIGS. 7 and
8. Also, indirect feeding of inert gas through passages 27-1,
27-2, 27-3, 24 an2 21-1 in the clamp structures 25 and 26 may be
employed.
The methods of feeding the molten metal into the
entrance E of the moving casting mold C, as shown in FIGS. 2, 3
and 8 are called "closed pool" feeding because the cavity 8 is
~Z~1~4~Z
essentially closed by the small clearance gaps 22 adjacent to
the downstream end of the nosepiece 7~ as described above.
An alternative method of feeding the molten metal,
called "open-pool" feeding is shown in FIG. 9. While open-pool
feeding involves no closely fitting nosepiece 7, its use is at
times appropriate, particularly when casting thicker metal
sections above 1-1/2 inches (38 mm) in thickness. The inert gas
is supt~lied through the supply ports 68 into "lean-to" chambers
54' of funnel-like configuration. These lean-to funnel chambers
54' are defined by the curved shield 34, the base plate 28 and
rear wall 45 of the supporting clamp structure 25 or 26 and by a
~ - - ` . .
shield-supporting wall plate 74 welded between the rear wall 45
and the shield 34. The inert gas flows downstream from the
funnel chamber 54' through the exit 38 ad~acent to the downstream
edge of the curved shield 34.
Some of this inert gas flows in shrouding relation-
ship into the entrance region E of the moving casting mold C.
Some of this inert gas returns upstream throuah the narrow
channels 66 in cleansing relationship wit~ the moving
mold surfaces and then exitin~ from these channels at 36.
Although metal feeding through multiple reinsertable
tubes 21 of high temperature refractory material (FIGS. 7, 8, 9)
is described as being used for meta~s or alloys having high
temperature melting points, such multi-tube feeding may also be
used for low temperature melting point metals and alloys, if
desired.
The results with any of the above-described methoc,s
and apparatus will be improved in the twin-belt casters by the
concurrent use of belt preheating as described and claimed in
U.S. Patents, Nos. 3,937,270 and 4,002,197 and/or by preheating
z
the belts with steam closely ahead of the entrance E to the
moving mold C, as described and claimed in copending applica-
tion, Serial No. 199,619, filed October 22, 1980, and assigned
to the assignee of the present invention.
The present invention improves the surface qualities
and charac-texistics of continuously cast metal product P of
relatively thin section when cast in approximately horizontal
or downwardly inclined orientation mode, particularly of
aluminum and its alloys, including high magnesium alloys
thereof, and also provides improvement in the internal qualities
and characteristics of such continuously cast metal products.
This invention also improves the qualities of thicker con-
tinuously cast metal product P when cast in the horizontal
mode or downwardly inclined mode.
As used herein, the term "downwardly inclined"
means at an angle less than 45 with respect to the horizontal
and usually less than approximately 20.
Examples of aluminum alloys which can be continu-
ously cast with advantage using the present invention are:
;2 ,~ EXAMPLE 1:
v
AA 1100 at casting speeds up to 1,400 pounds per
hour per inch of width of the moving mold.
EXA~5PLE 2:
AA 3003 at casting speeds up to 1,400 pounds per
hour per inch of width of- the moving mold.
EXAMPLE 3:
AA 3105 at casting speeds up to at least 1,000
pounds per hour per inch of width of the moving mold.
EXAL~qPLE 4:
AA 7072 at castlng speeds up to at least 1,000
pounds per hour per inch of width o~ the moving mold.
- 31 ~
`'~.
EXAMPLE 5~ 8~
Alloys containin~ up to 2.8% Magnesium by weight at
casting speeds up to 1,150 pouncls per hour per inch of width of
the moving mold.
EXA~PLE 6:
Hard alloys containing up to 3.0% of Magnesium by
weight at casting speeds up to at least 1,000 pounds per hour
per inch of width of the moving mold.
EXAMPLE 7:
Alloys containing up to 1.8% Magnesium at casting
speeds up to at least 1,175 pounds per hour per inch of width
of the moving mold.
EXAMPLE 8:
Alloys similar to AA 3105, except containing 0.8%
Manganese and 0.3% Magnesium by weight, at castin~ speeds up
to at least 1,000 pounds per hour per inch of width of the
moving mol~.
EXAMPLE 9:
Alloys containing 1.8% Magnesium, 0.3% Silicon,
0.3% Iron, and 0.52~ Manganese by weight at casting speeds up
to at least 1 J 000 pounds per hour per inch of width of the
moving mold.
Although specific presently preferred embodiments
of the invention have been disclosed herein in detail, it is
to be understood that these examples of the invention ha~e been
described for purposes of illustration. This disclosure is not
to be construed as limiting the scope of the invention, since
the described methods and a~paratus may be changea in details
by those skilled in the art in order to adapt the apparatus -
and methods of applying inert gas to particular casting machines
without deparling from the scope of the following claims.
