Note: Descriptions are shown in the official language in which they were submitted.
~4578;2
1 The present invention relates to a continuous process
for making a solid or a liquid-solid metal composition containing
non-dendritic primary solids and to the processes for shaping
such compositions.
Prior to the prese~t invention, alloys have been pre-
pared containing non-dendritic primary solids by a batch method
as disclosed ln the applicant's U.S. Patent 3,948,650 which
issued April 6, 1976. As disclosed in that applicationt a metal
alloy composition is formed by heating an alloy to a temperature
10 at which most or all of it is in the liquid state and vigorously
agitating the alloy, usually while cooling the alloy, to convert
any solid particles therein to degenerate dendrites or nodules
having a generally spheroidal shape. The degree of agitation must
be sufficient to prevent the formation of interconnected dentritic
networks and to substantially eliminate or reduce dendritic
branches already formed within the alloy due to cooling. After
the primary solids have been formed, the liquid remaining in the
alloy composition can be allowed to cool to form a dendritic
solid surrounding the primary solids.
It has been found that the compositions formed by the
process of the invention described in the above patent provide
substantial advantages in casting methods as compared to
the prior existing casting methods in which a molten metal is
poured or forced into a mold. A number of problems exist when
casting molten alloy including the fact that when the liquid changes
to the solid state, metal shrinkage normally is encountered and
the cooling process is fairly long. Furthermore, a large number
of liquid alloys are highly errosive to dies and molds and the
high temperature of the liquids and their errosive characteristics
- 1 -
A`
.. . ... . . ~ ..
~45'~2
1 make difficult or impossible -the casting of such alloys as copper
or iron alloys. By casting a liquid-solid slurry containing the
non-dendritic primary solids, the severity of these problems is
substantially reduced or eliminated since the casting is contacted
with a metal composition having a relatively low -temperature there-
by reducing the errosive problem, cooling times and metal shrinkage.
The processes specifically described in the above- i
identified patent produce products which have substantial advantages
over the prior art. However, the processes specifically disclosed
in that application are batch-type processes and have some dlsadvan-
tages as compared to the continuous process disclosed specifically
herein. In these batch processes, the entire liquid-solid composi-
tion is subjected to vigorous agitation including a top surface of
the composition which is in direct contact with a gaseous surround-
ing atmosphere. Due to the vigorous agitation, there is some gas
entrainment into the composition being formed which i3 undesirable
since the entrapped gas may adversely affect articles which are
formed therefrom. In addition, the batch technique generally is
slow and temperature control generally is more difficult.
2~ SUMMARY OF THE INVENTION
The present invention provides a process for forming a
metal composition containing degenerate dendritic primary solid
particles homogeneously suspended in a secondary phase having a
lower melting point than the primary solids and having a different
: .
metal composition than the primary solids wherein both the secondary
phase and the solid particles are derived from the same alloy. The
present invention is based upon the discovery that these composi-
tions can be formed continuously or semi-continuously ~y vigorously
agitating a solid-liquid mixture J which mixture is separated from
any gaseous atmosphere ~y an alloy, in the molten state from which
the liquid-solid mixture is derived. It has been discovered that
:.
- 2 - ~
.
1~:D457~3~
1 by operating in this m~nner, the molten alloy can be directed con-
tinuously to an agitation zone which is maintained at a temperature
at which the alloy becomes partially solid without entrainment of
gas and in a manner such that control of the portion solid in the
agitation zone can be maintained easily. The liquid-primary solid
mixture then is passed from the agitation zone at about the same
rate as the liquid entering the agitation zone which can be con-
tinuous or semicontinuous. The mixture can be cast or passed
through a forming zone adjacent the agi~ation zone. The resultant
composition can exit from the forming zone either as 100 percent
solid or as a liquid-solid mixture. In either case, the composi-
tion comprises non-dendritic primary solids homogeneously dispersed
in a second phase, which second phase can either be solid or liquid.
When the secondary phase is liquid, the compositions so-formed can
be allowed to cool or can be formed such as by casting. When the
final product is entirely solid, it can be formed at a later time
merely by heating it hack to the liquid-solid temperature range
wherein it may be thixotropic and rendered formable when subjected
to shear forcesO
DESCRIPTION OF SPECIFIC EMBODIMENTS
By the term "primary solid" as used herein is meant the
phase or phases solidified to form discrete degenerate dendrite
particles as the temperature of the melt is reduced below the
liquidus temperature of the alloy into the liquid-solid temperature
range prior to casting the liquid-solid slurry formed. By th~
term "secondary solid" as used herein is meant the phase or phases
that solidify from the liquid existing in the slurry at a lower
temperature than that at which the primary solid particles are
formed after agitation ceases. The primary solids obtained in the
compositions prepared by the process of this invention differ from
5782
1 normal dendrite struc-tures in that they comprise discrete particles
suspended in the remaining liquid matrix. Normally solidified
alloys, in absence of agitation, have branched dendrites separated
from each other in the early stages of solidification i.e. up to
lS to 20 wt. percent solid, and develop into an interconnected
network as the temperature is reduced and the weight fraction solid
increases. The structure of the compositions prepared by the pro-
cess of this invention on the other hand prevents formation of the
interconnected network by maintaining the discrete primary particles
separated from each other by the liquid matrix even up to solid
fractions of 60 to 65 wt. percent. The primary solids are degen-
erate dendrites in that they are characterized by having smoother
surfaces and less branched structures which approaches a spherical
configuration than normal dendrites and may have a quasi-dendritic
structure on their surfaces but not to such an extent that inter-
connection of the particles is effected to form a network dendritic
structure. The primary particles may or may not contain liquid
entrapped within the particles during particle solidification de-
pending upon severity of agitation and the period of time the par-
ticles are retained in the liquid-solid range. However, the wei~ht
fraction of entrapped liquid is less than that existing in a nor-
mally solidified alloy at the same temperature employed in present
processes to obtain the same weight fraction solid.
The secondary solid which is formed duxing solidification
from the liquid matrix subsequent to forming the primary solid con-
tains one or more phases of the type which sould be obtained during
solidification of a liquid alloy of identical composition by pre-
sently employed casting processes not employing vigorous agitation.
That is, the secondary solid can comprise dendrites, single or
multiphase compounds, solid solutions, or mixtures of dendrites,
compounds and/or solid solutions. -
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5'78Z
1 The siæe o the primary particles depends upon the alloy
or metal compositions employed, the temperature of the solid-liquid
mixture and the degree of agitation employed with larger particles
being formed at lower temperature and when using less severe agi-
tation. Thus, the size of the primary particles can range from
about 1 to about 10,000 microns. It is preferred that the com-
position contain between about 10 and 55 wt. percent primary par-
ticles since they have a viscosity which promotes ease of casting
or forming without causing heat damage to the forming or casting
apparatus.
As employed herein, t~e terms "agitation" or "vigorous
agitation" as applie~ to the process of this invention mean that
the liquid-solid composition is subjected to an agitation force
sufficient to prevent the formation of interconnected dendritic
networks and to substantially eliminate or reduce dendritic branches
already formed on the primary solid particles.
In accordance with this invention, a metal alloy is
rendered molten in a first zone which is in communication with an
agitation zone. The agitation zone is connected to the first zone
and is sealed to prevent entrainment of gas into the metal composi-
tion therein. The agitation zone is provided with means for cool-
ing the metal composition therein and for vigorously agitating
the metal composition therein. The degree of agitation in the
agitation zone must be sufficient to prevent the formation of
interconnected dendritic networks from the metal composition while -
it lS cooled. The particular means employed for providing the
degree of agitation is not critical so long as the interconnected
dendritic networks are not formed and the primary solids are formed
while the metal composition therein is cooled. The primary solids
content of the metal composition in the agitation zone can comprise
1~S'78Z
1 up to about 65 wt. percent of the liquid-solid metal composition.
The liquid-solid metal composition is removed from the agitation
zone through an outlet at about the same rate as the molten com-
position is passed into the agitation zone. The liquid-solid metal
composition can be cooled to form a solid which can be subsequently
reheated to a liquid-solid range for subsequent forming or casting
at any time or the liquid-solid composition can be cast upon re-
moval from the agitation zone. It is not critical to this inven-
tion that a particular mode of casting be employed. However, the
1Q continuous embodiment of the process of this invention affords
casting techniques not available in the prior art since the liquid- -
~solid mixtures continuously produced herewith have a degree of
structural strength which is not a characteristic of molten metal.
This degree of structural strength affords the use of unique
means for transporting and subsequently forming of the liquid-solid
mixtures. The casting techniques afforded by this invention will
be described below in greater detail. -;~
Any metal alloy system or pure metal regardless of its
chemical composition can be employed in the process of this inven-
tion. Even though pure metals and eutectics melt at a single tem-
perature, they can be employed since they can exist in liquid-
solid equilibrium at the melting point by controlling the net heat
input or output to the melt so that, at the melting point, the pure
metal or eutectic contains sufficient heat to fuse only a portion
of the metal or eutectic liquid. This occurs since complete re-
moval of heat of fusion in a slurry employed in the casting pro- ~-
cess of this invention cannot be obtained instantaneously due to
the size of the casting normally used and the desired composition
is obtained by equating the thermal energy supplied, for example
~0 by vigorous agitation and that removed by a cooler surrounding
.. . ..
~ (
:~(J14S71~2
1 environment. Representative suitable alloys include magnesium
alloys, 2inc alloys, aluminum alloys, copper alloys, iron alloys,
nickel alloys, cobalt alloys and lead alloys such as lead-tin
alloys, zinc-aluminum alloys, zinc-copper alloys, magnesium-
aluminum alloys, magnesium-aluminum-zinc alloys, magnesium-zinc
alloys, aluminum-copper alloys, aluminum-silicon alloys, aluminum-
copper-zinc-magnesium alloys, copper-tin bronzes, brass, aluminum
bronzes, steels, cast irons, tool steels, stainless steels, super-
alloys such as nickel-iron alloys, nickel-iron-cobalt-chromium
alloys, and cobalt-chromium alloys, or pure metals such as iron,
copper or aluminum.
This invention will now be discussed upon reference to
accompanying drawings, in which:
Fig. 1 is an elevational view of an apparatus having
three agitation zones useful for effecting the process of this
nvention.
Fig. 2 is an elevational view of an apparatus having one
agitation zone.
Fig. 3 is a cross-sectional view o~ the apparatus of
Fig. 2 taken along line 3-3.
Fig. 4 is a reproduction of a photomicrograph showing
the structure of a copper~lO percent tin-2 percent zlnc casting
made employing the teaching of this invention.
Fig. 5 is a reproduction of a photomicrograph showing
the structure of a tin-15 percent lead casting made employing the
teaching of this invention.
Fig. 6 is a reproduction of a photomicrograph showing ~;
the structure of a cast iron casting containing 2.48 percent
carbon and 3.12 percent silicon.
Fig. 7 is an elevational view showing a means for continu-
ously casting the li~uid-solid composition obtained by the process
of this invention.
-,
578Z
1 Fig. 8 is a schematic view of a means for casting discre-te
portions of the liquid-solid composition obtained by the process
of this invention.
Fig. 9 is a schematic view of an alternative means for
casting discrete portions of the liquid-solid composition obtained
by the process of this invention.
Referring to Figure 1, a metal alloy in the liquid state 1
is retained within container 2. The metal alloy l can be heated
conveniently to the liquidus state or maintained at or above the
liquidus temperature by means of induction heating coils 3 which
surround container 2. Container 2 is provided with three openings
4, 5 and 6 the size of which are regulated by baffles 7, 8 and 9.
Agitation zones 10, 11 and 12 are located adjacent each opening
4, 5 and 6 respectively and are ioined to the bottom surface of
container 2 in a manner to prevent gas from becoming admixed with
the metal alloy within either container 2 or agitation zones 10,
11 and 12. Augers 16, 17 and 18 are provided within agitation
zones 10, 11 and 12 respectively and are mounted to rotatable
shats 20, 21 and 22 which are powered by any suitable means ~not
shown). Each of the agitation zones 10, 11 and 12 is provided
with induction heating coils 25, 26 and 27 and with a cooling
jacket 28, 29 and 32 in order to control the amount of heat and
the temperature of the metal alloy within the agitation zones 10,
11 and 12. Each cooling jacket is provided with a fluid inlet 30
and a fluid outlet 31. The distance between the inner surface 35
of agitation zone 12 and the outer surface 36 of auger 18 as well -
as the corresponding distances between surfaces 37 and 38 and sur
faces 39 and 40 are maintained sufficiently small so that high
shear forces can be applied to a liquid-solid mi~ture in the agita-
tion zones 10, 11 and 12 sufficient to prevent the formation of
interconnected dendritic networks while at the same time allowing
.
-- 8 --
L578;2
passage of the li~uid-solid mixture through the respective agita-
tion zones 10, 11 and 12. Since the induced rate of shear in the
liquid-solid mixture at a given rotational speed of the auger is
a function of both the radius of the agitation zone and the radius
of the auger, the clearance distance will vary with the size of
the auger and agitation zone. To induce the necessary shear rates,
increased clearances can be employed with larger augers and agi-
tation zones. The bottom surface of agitation zones 10, 11 or 12
are each provided with an opening 40, 41 or 42 respectively so
that the liquid-solid mixture in the agitation zones can be re-
moved conveniently by gravity or, if desired by establishing a
pressure differential between the upper surface of molten metal 1
and openings ~0, 41 and 42. The effective opening 40, 41 or 42
can be controlled easily by raising or lowering the shaft 20, 21
or 22 so that the bottom end of the auger 44, 45 or 46 can fit into
all or a portion of the respective openings 40, 41 or 42.
The operation of the apparatus shown in Figure 1 will be
described with respect to one auger shown therein. A metal alloy
is introduced into container 2 wholly molten, partially solid or
wholly solid. In any eventj the metal alloy is rendered molten
in container 2 by heat induction coils 3, if necessary. After the
molten alloy is formed, the baffles 7 are opened to admit the
molten alloy into agitation zone 10. The baffles 7 also minimize
migration of primary solids from the agitation zone 10 into the
container 2. Meanwhile, rotation of shaft 20 and auger 16 is
initiated, for example at a rotational speed between about 100
and about 1000 r.p.m. The heat in agitation zone 10 is removed
therefrom by heat exchange with a fluid, such as air or water,
that enters jacket 28 through inlet 30 and exits through outlet 31.
Heat induction coils 25 are provided for process control in the
'` -
~34~i782
1 event the metal composition in agitation zone 10 is cooled to a
fraction solid content above that desired, e.g. above about 65
weight percent. The molten metal 1 is passed continuously through
the opening 4 into the agitation zone 10 wherein the desired quan~
tity of heat content of the alloy is removed to render it partially
solid and partially liquid wherein the solid portion comprises
primary so~ids. The rate at which the liquid-solid mixture exits
agitation zone 10 depends upon the effective opening in hole ~0
controlled by the position of the end 44 of the auger 16. The
10 heat exchange within agitation zone 10 can be controlled easily
by controlling the flow rate and temperature of the cooling fluid
in jacket 28, controlling the power input in induction coils 3,
and the flow rate of metal through agitation zone 10 by controlling
the size of the opening 4 baffles 7 and the size of the opening
40 with the end 44 of auger 16. ThermGcouples (not shown) can be
provided along the length of agitation zone 10 and at the end
thereof in order to monitor the temperature of the liquid-solid
mixture within agitation zone 10. By operating in this manner,
the molten metal in zone 2 serves to seal the liquid-solid mixture
within zone 10 from the outside gaseous atmosphere thereby prevent-
ing undesirable random entrainment of gas within the liquid-solid
mixture in zone 10.
Referring to Figures 2 and 3, an alternative apparatus
design is shown. Molten metal 50 is maintained in the heated
zone 51 having an opening 52 in the bottom surface thereof. A
rotatable shaft 53 extends through heated zone 51 and into an
agitation zone 54 wherein an auger 55 is located. The auger 55
has splines 56 extending the length of the auger 55 through the
agitation zone 54. The agitation zone 54 is surrounded by a cool-
ing jacket 58 having an inlet 59 and an outlet 60. In addition,
~ 10 --
l~LS7~32
1 the agitation zone 54 is surrounded b~ heat induction coils 61 sothat the cooling jacket in combination with the induction coils
61 serve to regulate the heat outflow from the metal alloy composi-
tion within agitation zone 54. As best shown in Fig. 3, typical
useful sizes of the mixing apparatus comprises an agitation zone
with a diameter of 1 1/4 inches, an auger having a diameter of 1
to 1 1/8 inches and grooves between the splines o~ 1/16 inch. It
is to be understood that these dimensions are only exemplary and
that larger or smaller sizes can be employed so long as a high
shear rate on the metal can be maintained. The size of opening
52 can be regulated by moving the rotating shaft 53 and auger 55
vertically to open or close opening 52 with baffle 63 located on
shaft 53. The heating zone 51 is surrounded by heat induction
coils 64 to provide heat to the metal composition 50 therein. The
agitation zone 54 is provided with an outlet 66 for removal of the
liquid-solid composition containing the primary solid therefrom
for subsequent forming.
Figure 4 is a reproduction of a photomicrograph taken
at 50 times magnification of an oil-quenched copper-10 percent
tin-2 percent zinc alloy 5copper alloy 905). This alloy was formed
with the apparatus shown in Figures 2 and 3 but with only one auger.
The temperature in heating zone 51 was maintained above the liquidus
temperature of the alloy, i.e. 999C. The conditions of tempera-
ture and heat in the agitation zone 54 were maintained so
that the liquid-primary solid mixture contained about 45
weight percent primary solids. The sample was taken at about
925C. The speroidal primary solid metal formations 70 and den-
dritic secondary solids 71 show an overall metal formation quite
different from the normal dendritic network observed upon cooling
this alloy without agitation. The black portion 72 of the primary
-- 11 --
~S7132
1 solids 70 comprise liquid which was entrapped within the primary
solids during their formation.
Figure 5 is a photomicrograph taken at 100 times magni-
fication of a casting made of ten-fifteen percent lead which was
agitated in the apparatus of Figure 1 but employing only one auger
so that the liquid-primary solid mixture contained about 55 weight
percent primary solids. The sample was taken at about 191C. As
can be readily observed, the non-dendritic primary solids 73 are
surrounded by a secondary solid portion 74 which is dendritic in
nature.
Figure 6 is a reproduction of a photomicrograph taken
at 100 times magnification of cast iron containing 2.48 percent
carbon and 3.12 percent silicon. The alloy was formed with the
apparatus shown in Figures 2 and 3. The condition of temperature
and heat were maintained so that the liquid-primary solid mixture
contained about 35 weight percent primary solids. The sample was
taken at about 1280C. The speroidal primary solid metal forma-
tions 75 are surrounded by dendritic secondary solids 71a. The ~-
black portion 72a of the primary solids 75 is entrapped graphite
which precipitated during cooling while the darker grey portion
73a comprises liquid which was entrapped within the primary solids
during their formation.
Referring to Figure 7, a convenient means for continuously
casting the liquid-solid compositions formed by the process of
this invention is shown, The process shown in this figure pro-
vides substantial advantage over continuous casting processes of
the prior art which continuously cast molten metal alloys. Due to
the heat of fusion in the molten metals and their higher temperature -
~than the liquid-primary solid compositions, they must be rendered
solid by heat extraction therefrom at a lower rate than with the
- 12 -
. . ..
78~2
1 liquid-primary solid compositions. If the heat is extracted too
quickly from the molten metals, undesirable cracking of the cast
product is observed frequently. This results in an undesirably
lower throughput rate of metal in the continuous casting apparatus.
In addition, undesirable long range segregation (macrosegregation
of the alloy constituents) is obtained when continuously casting
molten metals. In contrast, when continuously casting the liquid-
primary solid compositions of the present process, there is far
less heat of fusion available therein which must be removed and
therefore much faster throughput rates can be attained without metal
cracking. Furthermore, due to the presence of the primary solids,
long range segregation is minimized or eliminated. The liquid-
solid mixture 76 exiting from the agitation zone l0 is directed
to a cooling zone formed by generally cylindrical cooling jacket
77 provided with a cooling fluid inlet 78 and a cooling fluid
outlet 79. The agitation zone l0 is constructed and operated in
the manner described abo~e such as described with reference to
Fig. l or Figs. 2 and 3. The final rod-shaped or cylindrical-
shaped solid product 80 containing the primary solids homogeneously
dispersed therein is formed by initially providing a plate along
the bottom surface of the jacket 77, as indicated by the dotted
line 81 in order to initially form a solid within the jacket 77.
After the solid is formed, the plate is removed and the solid 80
allowed to move by gravity out of the casing 77. Once this process
has been initiated, and interfaced between the solid 80 and the
liquid-solid mixture 8~ as indicated by line 83 is formed. Subse-
quent to formation within the casing 77, the solid 80 is directly
subjected to a spray of cooling liquid as indicated by the arrow 84.
Referring to Figure 8, an alternative means for collecting
and subsequently forming e.g. casting, the products formed by
- 13 -
~4S713Z
1 the process of this invention is shown schematically. This process
can be used on a batchwise or a continuous basis to form discrete
portion of the liquid-primary solid mixture. At or near the exit
40 of the agitation zone, a holding chamber 90 provided with a
heating means such as induction heated coils 91 is provided. The
agitation zone is constructed and operated in the manner described
above such as described with reference to Fig. l or Figs. 2 and 3.
Within the holding chamber 90, a generally cylindrical sleeve 92
formed from a heat resistant material is placed to retain a dis-
crete portion of the liquid-primary solid mixture. A discrete
portion of the liquid~solid mixture exiting from opening ~0 is
directed into sleeve 92 as composition 93. In order to maintain
the desired fraction solid in the alloy 93, the heating coils 91
are activated in order to maintain the desired temperature. Once
the desired amount of metal 93 has been metered into the sleeve 92,
it can be formed or cast in any manner desired. Thus, this
apparatus provides a convenient means for metering a desired -
amount of metal which is easily transportable to a subsequent
process. For example when, it is desired to form or cast the
composition 93, the sleeve 92 and the holding chamber 90 are
rotated 90 so that the sleeve 92 can be removed from holding `
chamber 90 easily while retaining the composition 93 therein.
Because of the mechanical characteristics of the liquid-primary
solid mixtures formed by the process of this invention, the use
of a sleeve 92 eliminates the need for a shot sleeve normally
employed in casting and therefore eliminates the problems
associated with shot sleeves which result from the need to avoid
undue temperature gradients in the metal contained in the shot
sleeve. The liquid-primary solid mixture is suficiently mechani-
cally stable so that when sleeve 92 is removed from holding chamber
- 14 -
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1C~4S7~3~
1 90, the liquid-primary solid mixture is removed therewith
without substantial leakage. Furthermore, when sleeve 92 is
placed in a horizontal position so that the open ends thereof
are unsupported, the liquid-primary solid mixture will not leak
therefrom. The sleeve 92 and compQsition 93 are then located
between a mold 95 and a pneumatically actuated piston 96 housed
within a piston guide 97. The piston 96 can be pneumatically
actuated at the desired time, for example by means of air cylinder
98. When actuated, the piston 96 forces the composition 93
within the interior 99 of mold 95 to form the desired product.
In one embodiment, a plurality of holding chambers 90 and associ-
ated sleeve 32 can be located below the agitation zone exit ~6
on a support table (not shown) and they can be progressively
indexed below the exit 66 for filling and processed for subsequent
casting of the metal therein.
Referring to Figure 9, an alternative means for casting
the compositions formed by the process of this invention is shown -;
schematically. This particular means can be employed batchwise or
on a continuous basis to form discrete portions of liquid-primary
solid mixtures formed by the process of this invention. As shown
in Figure 9, as liquid-primary solid mixture 100 is exited from
the opening 54 of the agitation zone (not shown). Portions of
the liquid-solid mixture 101 would then break off on the main
portion 100 by virtue of the gravitational forces thereon and
allowed to fall between the die halves 102 and 103. When portion
101 is located between die halves 102 and 103, the die halves
102 and 103 are closed on the composition 101 by actuating the
pistons 104 and 105 pneumatically. The pistons 104 and 105 can be
actuated by any suitable electronic means such as a photosensitive
detector through which the portion 101 passes prior to being posi~
tioned between the die halves 102 and 103. After the composition
-- 15 --
.,
S7~2
lOl has been formed by cooling, the die halves 102 and 103 are
pulled apart and the desired product ormed from composition 101
is removed therefrom. A plurality of die halves similar to 102
and 103 can be passed under opening 54 continuously to capture
subsequéntly formed discrete compositions 101 and to cast them
in the manner described.
The liquid-solid mixture can, when the desired ratio of
liquid-solid has been reached, be cooled rapidly to form a solid
slug for easy storage. Later, the slug can be raised to the tem-
perature of the liquid-solid mixture, for the particular ratio of
interest, and then cast, as before, using usual techniques. A
slug prepared according to the procedure just outlined may possess
thixotropic properties depending upon the reheating temperature
and the time it is maintained as a liquid-solid either before the
slug is fully frozen or after the frozen slug is reheated. In-
creased time that the slug is maintained as a liquid-solid pro-
motes thixotropic increased behavior of the slug. ~t can, thus,
be fed into a modified die casting machine or other apparatus in
apparently solid form. However, shear resulting when this
apparently solid slug is forced into a die cavity causes the slug
to transform to a material whose properties are more nearly that
of a liquid.
Liquid-solid mixtures were prepared employing apparatus
like that shown in Fig. 2 and at speeds of about 500 RPM for the
auger. TemperaLure control at the exit 66 or agitation zone 54
was monitored by using a thermocouple. The temperature of the
liquid-solid at fifty percent solid for various alloys is given
below:
Sn - 10% Pb --- 210C
Sn - 15% Pb --- 195C
- 16 -
'
~4~7aZ
1 Al - 30% Sn --- 586C
~ 1 ~4.5% Cu --- 633C
Variations greater or less than the fifty percent primary solid-
liquid mixture will result from changes in the temperature values
given.
Casting of the partially solidified metal slurry or
mixture herein disclosed can be effected by pouring, injection
or other means; and the process disclosed is useful for die
casting, permanent mold casting, continuous casting, closed die
tO forging, hot pressing, vacuum forming (of that material~ and
others. The special properties of these slurries suggest that
modifications of existing casting processes might usefully be
employed. By way of illustration, the effective viscosity of the
slurries can be controlled by controlling fraction of primary
solid; the high viscosities possible when the instant teachings
are employed, result in less metal spraying and air entrapment
in die casting and permits higher metal entrance velocities in
this casting process. Furthermore, more uniform strength and more
dense castings result from the present method.
17 -
