U.S. patent number 3,858,640 [Application Number 05/368,434] was granted by the patent office on 1975-01-07 for reinforced composite alloys, process and apparatus for the production thereof.
This patent grant is currently assigned to Societe Industrielle De Combustible Nucleaire. Invention is credited to Raymond Henri Sifferlen.
United States Patent |
3,858,640 |
Sifferlen |
January 7, 1975 |
REINFORCED COMPOSITE ALLOYS, PROCESS AND APPARATUS FOR THE
PRODUCTION THEREOF
Abstract
This invention relates to improved process and apparatus for
producing reinforced composite light alloys. The improved apparatus
comprises means for feeding a fluidized mixture of particulate
additions, carried by a neutral gas, to a crucible in which a basic
metal consisting preferably of nearly pure aluminium ingots is
molten. Means are provided for stirring the contents of the
crucible during the feeding of said mixture thereto, in order to
prevent the sedimentation or decantation of the dispersion formed
therein. Means are further provided for transferring the mixture of
basic metal and additions into another receptacle in which the
desorption and degasing of said mixture take place.
Inventors: |
Sifferlen; Raymond Henri
(Veurey-Voroize, FR) |
Assignee: |
Societe Industrielle De Combustible
Nucleaire (Annecy, FR)
|
Family
ID: |
9099962 |
Appl.
No.: |
05/368,434 |
Filed: |
June 8, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Jun 9, 1972 [FR] |
|
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72.20864 |
|
Current U.S.
Class: |
164/513; 148/437;
266/182; 266/234; 420/528; 420/590; 164/97; 164/259; 266/216;
266/235; 420/552 |
Current CPC
Class: |
C22C
1/02 (20130101); C22C 1/1036 (20130101); B22F
2999/00 (20130101); B22F 2999/00 (20130101); C22C
47/00 (20130101); B22F 2202/01 (20130101) |
Current International
Class: |
C22C
1/02 (20060101); C22C 1/10 (20060101); C22b
009/12 () |
Field of
Search: |
;164/48,51,61,66,68,97,250,251,256,258,259,266 ;266/34A,34T,34V
;148/2 ;75/135,138 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dost; Gerald A.
Attorney, Agent or Firm: Sughrue, Rothwell, Mion, Zinn &
Macpeak
Claims
What is claimed is:
1. Apparatus for preparing a reinforced composite alloy, which
comprises a crucible, means for supplying liquid basic metal to
said crucible at a constant temperature and at a substantially
constant level, means for causing rapid circulation of a gas, means
for introducing particulate additions into said gas, means for
imparting mechanical vibrations to said introducing means, means
for ensuring the rapid displacement of said additions and said gas,
means for simultaneously stirring said metal and introducing said
additions into said metal during stirring, said last-named means
being connected to said means for rapid displacement of said
additions and said gas, means for stirring the dispersion thus
obtained and preventing its sedimentation or decantation, and means
for transferring the stirred mixture of basic metal and additions
to another receptacle, said last-named means desorbing and degasing
said mixture.
2. Apparatus according to claim 1, comprising a container having a
funnel-shaped bottom, a vibrating table supporting said container,
means for feeding said particulate additions to said container, a
duct for directing said gas into said container, a plug valve body
mounted in said container to be vertically movable substantially at
the level of the tapered portion of said funnel-shaped bottom,
means for adjusting the vertical position of said plug valve body,
and a conduit comprising a first vertical section projecting in
said container and opening below said plug valve body, and a second
section emerging from said container, for transferring the
additions and gas into said crucible.
3. Apparatus according to claim 2, wherein said first conduit
section is an integral part of said plug valve body, so as to open
from its lower end.
4. Apparatus according to claim 1, comprising a hopper having a
bottom discharge pipe, a vibrating table supporting said hopper,
means for introducing particulate additions into said hopper, means
for controlling the cross-sectional passage area of the bottom
discharge pipe of said hopper, a chamber disposed beneath said
bottom discharge pipe of said hopper, so that said discharge pipe
opens into said chamber, a first conduit for feeding said gas into
said chamber, a second conduit opening at one end into said chamber
for transferring said additions and gas from said chamber into said
crucible.
5. Apparatus according to claim 1, comprising a crucible having a
vertical axis of symmetry, a screw-like stirring member disposed
within said crucible with its axis being in a substantially
parallel and spaced relationship to said crucible axis, and means
for rotatably driving said stirring member to create eddies in the
liquid metal contained in said crucible.
6. Apparatus according to claim 5, further comprising means for
vertically moving said stirring member in said crucible between an
upper position, in which said crucible can be loaded with ingots of
solid metal, and a lower position, in which said stirring member is
restored when said solid ingots are melted.
7. Apparatus according to claim 1, further comprising an induction
heating coil disposed externally of, and surrounding, said
crucible, and means for energizing said coil with high-frequency
electric current, whereby a high-frequency field is generated in
the liquid metal contained in said crucible and said field generate
eddies in said liquid metal.
8. Apparatus according to claim 1, wherein an ultrasonic generator
is immersed in the liquid metal contained in said crucible.
9. Apparatus according to claim 1, wherein the means for ensuring
the rapid displacement of said additions and gas comprises at least
one electrode disposed upstream of said crucible so as to be swept
by said gas and said additions, further means being also provided
for applying a high potential difference between said electrode and
the metal contained in said crucible.
10. Apparatus according to claim 9, wherein said means for causing
the rapid displacement of said additions and gas comprises a
vertical duct opening into said crucible and having at least one
portion disposed above the free surface of the liquid metal
contained in said crucible, said electrode consisting of a metal
wire mounted in said portion of said vertical duct with its end
being located at a predetermined height above said free surface of
said liquid metal.
11. Apparatus according to claim 1 wherein said crucible has its
bottom provided with a runner, said apparatus further comprising
means for normally plugging said runner and a fluid-tight chamber
in which said crucible is enclosed together with an ingot-mould
having an open upper portion disposed within said chamber, below
the runner of said crucible, and an open lower portion disposed
externally of said chamber.
12. Apparatus according to claim 11, further comprising at least
one vacuum pump and conduit means for connecting said vacuum pump
to said fluid-tight chamber.
13. Apparatus according to claim 11, further comprising means for
filling said fluid-tight chamber with at least one inert gas under
a predetermined pressure.
14. Apparatus according to claim 1, further comprising means for
casting the mixture contained in said crucible under a vacuumized
atmosphere.
15. Apparatus according to claim 1, further comprising means for
casting the mixture contained in said crucible under an inert gas
atmosphere.
Description
BACKGROUND OF THE INVENTION
The present invention relates to reinforced composite alloys, and
also to a process for the formation of composite alloys, reinforced
by dispersed particles. It is also concerned with an apparatus for
carrying this process into effect.
SUMMARY OF THE INVENTION
A first object of this invention is a reinforced composite alloy
without residual porosity, having improved properties and
particularly a good ductility, consisting of a matrix of very pure
aluminium having dispersed therein 3 to 20 percent by weight of an
addition in grain form, said addition being insoluble in aluminium
both in the solid and liquid states, and said addition grains being
dispersed homogeneously throughout the aluminium matrix to which
they are bonded individually.
Another object of this invention is a process for preparing a
reinforced composite alloy consisting of fine particulate additions
incorporated in an aluminium matrix, said process comprising the
following steps:
A. FORMING A DISPERSION OF GRAINS OF A REFRACTORY MATERIAL USING A
FLUIDIZED SUSPENSION IN A STREAM OF PREHEATED GAS, WHICH IS NEUTRAL
WITH RESPECT TO THE ADDITION GRAINS AND TO THE ALUMINIUM;
B. DESORBING MOISTURE, OXYGEN AND NITROGEN FROM SAID GRAINS TO
SUPERFICIALLY ACTIVATE SAID GRAINS;
C. INTRODUCING SAID DISPERSION INTO THE MOLTEN ALUMINIUM WITH
ENERGETIC STIRRING, AT A TEMPERATURE SELECTED IN THE RANGE FROM
850.degree. TO 1,300.degree. C; and
D. DEGASING THE HOMOGENEOUS COMPOSITE PRODUCT.
Still another object of this invention is a process for preparing a
reinforced composite alloy consisting of fine particulate additions
in an aluminium matrix, said process comprising the following
steps:
A. FORMING A DISPERSION OF GRAINS OF A REFRACTORY MATERIAL USING A
FLUIDIZED SUSPENSION IN A STREAM OF PREHEATED GAS, WHICH IS NEUTRAL
WITH RESPECT TO THE ADDITION GRAINS AND TO THE ALUMINIUM;
B. DESORBING MOISTURE, OXYGEN AND NITROGEN FROM SAID GRAINS TO
SUPERFICIALLY ACTIVATE SAID GRAINS;
C. INTRODUCING SAID DISPERSION INTO THE MOLTEN ALUMINIUM WITH
ENERGETIC STIRRING, AT A TEMPERATURE SELECTED IN THE RANGE FROM
850.degree. TO 1,300.degree. C;
d. degasing the homogeneous composite product;
E. CASTING THE COMPOSITE PRODUCT;
F. SUBJECTING THE SOLIDIFIED COMPOSITE PRODUCT TO AT LEAST ONE
HOT-ROLLING STEP; AND
G. SUBJECTING THE ROLLED COMPOSITE PRODUCT TO AT LEAST ONE
ANNEALING STEP.
A still further object of this invention is an apparatus for
preparing a reinforced composite alloy, which comprises a crucible,
means for supplying liquid basic metal to said crucible at a
constant temperature and at a substantially constant level, means
for causing rapid circulation of a gas, means for introducing
particulate additions into said gas, means for imparting mechanical
vibrations to said introducing means, means for ensuring the rapid
displacement of said additions and said gas, means for
simultaneously stirring said metal and introducing said additions
into said metal during stirring, said last-named means being
connected to said means for rapid displacement of said additions
and said gas, means for stirring the dispersion thus obtained and
preventing its sedimentation or decantation, and means for
transferring the stirred mixture of basic metal and additions to
another receptacle, said last-named means desorbing and degasing
said mixture.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Various embodiments of the apparatus for forming the composite
alloys according to the invention are hereinafter described by
reference to the accompanying drawings in which:
FIGS. 1 and 2 illustrate diagrammatically in fragmentary sections
two embodiments of means for introducing the additions into the
gas;
FIGS. 3 and 4 illustrate diagrammatically in fragmentary section
two embodiments of means for introducing the stream of additions
and gas into the molten metal contained in a crucible, for stirring
the mixture in said crucible, and for casting the same from the
crucible into at least one ingot mould.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The apparatus illustrated in FIG. 1 comprises a container or vessel
1 having a funnel-shaped bottom 2; this container 1 is supported by
a vibrating table 4 through vertical columns 3. A conduit 5
provided with a control valve 6 is adapted to supply neutral gas
such as air or argon to the lower portion 2a of the funnel-shaped
bottom 2 of container 1 through a perforated plate or grid 2d. At
its upper portion the container 1 comprises means for supplying the
particulate additions thereto; in the specific form of embodiment
contemplated these means comprise a hopper 7 connected to the top
of container 1 via a vertical duct 8 in which two sliding-plate
shutter valves 9a, 9b forming a lock chamber between them are
mounted. A conduit 10 provided with a control valve 11 is provided
for directing neutral gas, such as air or argon, on the one hand,
into the lock chamber formed between said shutter valves 9a and 9b
via a branch line 12, comprising a control valve 13, and, on the
other hand, into the container 1, at mid-height thereof, through
another branch line 14 equipped with a control valve 15. A valve
member 16 is supported by a vertical rod 17 within the container 1,
above said tapered portion 2c of its funnel-shaped bottom 2; said
rod 17 extends through the top wall of the container provided to
this end with a suitable rod packing 18 in which it is slidably
fitted, the outer end of said rod being drivingly connected to a
mechanism 19 adapted to produce the vertical movement of said rod
for adjusting the position of said valve member 16 in relation to
said tapered portion 2c of the bottom of container 1. A pipe line
20 equipped with a valve 21 extends coaxially through said rod 17
and valve member 16 so as to open under the latter into the
straight lower portion 2b of the funnel-shaped bottom 2 of
container 1.
The vibrating table 4 is adapted to impart to the above-described
assembly vertical vibrations of an amplitude of, say 1 to 3 mm, at
a frequency in the range of 25 to 50 Hz. The conduits 5 and 10 may
be connected to a common source of neutral gas, such as air.
Automatic means known per se and therefore not described in detail
herein may be provided for controlling the shutter valves 9a, 9b,
valves 6, 11, 13, 15, 21, and also the mechanism 19, for example as
a function of a predetermined program.
The apparatus illustrated in FIG. 1 operates as follows: valve 9a
is opened first, thus filling the lock chamber formed in the
vertical duct 8 between this valve 9a and the underlying valve 9b;
then, valves 11 and 13 are opened together with valve 9b, and the
neutral gas, which may possibly be fed under a more or less high
pressure, facilitates the fall of the particulate additions
contained in said lock chamber into the container 1. When the valve
member 16 engages the tapered portion 2c of the bottom 2 of
container 1, the particulate additions accumulate in the upper
portion of said container 1, and the latter is filled up to a
sufficient level, as shown in FIG. 1. The position of valve member
16 is then adjusted in relation to the tapered valve 2c of said
bottom 2, so that a flow channel or passage 22 of suitable width is
formed therebetween, and the valves 15, 6 and 21 are eventually
opened; thus, the neutral gas entering the intermediate portion of
container 1 via branch line 14 tends to facilitate the flow of
particulate additions through said annular passage 22 towards the
straight section 2b of bottom 2 of container 1, with an output
depending particularly on the width of said annular passage 22, and
therefore on the position in which said valve member 16 was
adjusted in relation to the tapered wall 2c; the particulate
additions received in said straight section 2b are stopped therein
by the perforated grid 2d and picked up therefrom by the stream of
neutral gas under pressure fed through conduit 5 to the lower
portion 2a of said bottom 2, and the thus formed fluidized bed
rises in the lower portion of pipe line 20 and is directed thereby
into the crucible (this pipe line 20 corresponding therefore to the
lines 29 illustrated in FIGS. 2, 3, 4 and 5 of U.S. Pat. No.
3,728,108, assigned to the assignee of the present application).
The fluidization of the particulate additions by the neutral gas is
promoted on the one hand by the vibration imparted by the table 4
to the container 1 and to the various members supported thereby,
and on the other hand by the action of the compressed neutral gas
fed through said branch lines 12 and 14. In the specific
arrangement illustrated in FIG. 1, the control valve 6 of conduit 5
may be kept constantly open during the operation of the apparatus,
so as to deliver a constant flow of neutral gas into the lower
portion 2a of the bottom 2 of container 1 of which the intermediate
portion is then recharged periodically via the lock chamber formed
in duct 8, as already explained hereinabove. The action exerted by
the vibrating table 4 is particularly advantageous in the case of
pulverulent additions, notably very finely powdered products having
a granulometry of less than one micron.
In FIG. 2, the same reference numerals designate homologue elements
of FIG. 1. Thus, the apparatus illustrated comprises a hopper 1
provided with a funnel-shaped bottom having a tapered portion 2c
and a straight section 2b constituting a lower discharge pipe for
the hopper 1; this discharge pipe 2b projects somewhat into the
upper portion of a chamber 23 separate from said hopper 1, and the
bottom of this chamber is supplied with neutral gas such as air or
argon through a conduit 5 provided with a control valve 6 and
opening into this chamber 23 beneath a perforated plate or grid 2d;
a pipe line 20 provided with a control valve 21 is connected to the
upper portion of chamber 23 for discharging the fluidized bed
consisting of said additions and said gas. The hopper 1 is
supported by a vibrating table 4 by means of columns 3; its upper
portion is connected to a vertical duct 8 leading from a loading
hopper (not shown); this duct 8 is provided with a pair of parallel
spaced sliding-plate shutter valves 9a, 9b forming therebetween a
lock chamber; the reference numeral 16 designates a valve member
carried by a rod 17 slidably mounted for vertical movement and
constituting an efficient means for controlling the input
cross-sectional passage area between the lower or discharge section
2b of hopper 1 and said valve member 16.
The hopper 1 may be filled with the assistance of the lock chamber
formed between said valves 9a and 9b in duct 8, as already
explained hereinabove with reference to FIG. 1; when a sufficient
level is attained by the particulate additions in hopper 1, as
shown for example in FIG. 2, the passage leading from the hopper 1
to the discharge pipe 2b is cleared by moving the valve member 16
away from the tapered bottom 2c, i.e., by pulling the sliding rod
17 upwards, in order to fill up completely the independent chamber
23; then both valves 6 and 21 are opened in order to fluidize the
particulate additions filling said chamber 23 by means of the
neutral gas fed through duct 5, and discharge the fluidized bed
thus formed through the discharge line 20. The filling of the
aforesaid bottom chamber 23 is also facilitated by the vibration
imparted by the table 4 to this chamber. This apparatus may operate
continuously, the valves 6 and 21 remaining constantly open, and
the chamber 23 can be filled again by lifting the valve member 16
when the amount of particulate additions contained in this chamber
23 tends to become insufficient.
FIG. 3 illustrates a chamber 24 closed in a fluid-tight manner and
supported for example by a platform 25; a crucible 26 is supported
by a stand 27 laid on the bottom or floor of chamber 24. According
to this invention, the walls of curcible 26 consist of insulating
material or of conducting material such as graphite. In the form of
the embodiment illustrated in FIG. 3 the side wall of crucible 26
is surrounded externally by an induction heating coil 28, and its
bottom comprises a runner 29 normally plugged by a stopper-rod 30
extending through the upper detachable lid or cover 26a of crucible
26; in the exemplary form of embodiment illustrated, the
stopper-rod 30 is supported at its upper end, above the cover 26a
of crucible 26, by a pivotally mounted arm 31 carried by one wall
of chamber 24, and remote control means are provided for lifting
the stopper-rod 30 and thus opening the runner 29; in the example
illustrated these remote control means are shown diagrammatically
as consisting of a crank 32 extending through the wall of chamber
24 and adapted rotatably to drive a cam 33 for lifting the pivoted
arm 31. A pipe line 20 extends through the wall of chamber 24 and
also through the cover 26a of crucible 26 for feeding the fluidized
addition bed into this crucible. A vertical shaft 34 extends
through the upper wall or roof of chamber 24 and through the cover
26a of crucible 26, and carries at its lower end, i.e., within the
crucible 26, a helical stirring member in the form of a worm or
screw. The upper portion of shaft 34 extending through a sealed
bearing 36 carried by the top wall of chamber 24 is coupled to the
lower end of the vertical aligned shaft 37 of an electric motor,
for example a d.c. motor, 38, suspended in turn from a gantry 39
supported by said chamber 24, by means of a cable 40 and a
pulley-block 41; in the normal operative position the motor 38 is
supported by a platform 38a also carried by said gantry 39 and the
stirring member 35 lies inside the crucible 26; on the other hand,
it is possible, by actuating said pulley-block 41, to lift the
assembly comprising said motor 38, shaft 34 and stirring member 35
until said motor is in its uppermost position 38a shown in dash
lines, in which said stirring member 35 lies outside and above the
crucible 26. In the form of embodiment illustrated an annular
cooling chamber 42 is formed in the outer periphery of the vertical
shaft 34, and supplied with cooling fluid such as water via a
rolling-contact bearing 43, provided with suitable sealing means,
and a pair of conduits 44a and 44b. The lateral wall of chamber 24
also receives therethrough a conduit 45 connected to a suitable
source of vacuum (not shown) such as a vacuum pump device, and
another conduit 46 connected to a source of neutral gas, such as
argon, under suitable pressure; other ducts 47a and 47b extend
through the side wall of chamber 24 and permit of supplying both
high-frequency current and cooling water to the coil 28 of crucible
26 by means of suitable high-frequency seals 48. An ingot mould 49
is supported beneath the chamber 24 and platform 25 (through
adequate means, not shown) so that its upper open portion 49a lies
just beneath the runner 29 of the bottom of crucible 26; in the
form of embodiment illustrated the wall of this ingot mould
comprises a water jacket 49b in which suitable conduits 50a and 50b
produce a circulation of water or other cooling fluid.
The apparatus illustrated in FIG. 3 operates as follows: with the
stopper-rod 30 plugging the runner 29 of crucible 26 and the
stirring member 35 extracted from this crucible, the latter is
filled with ingots of solid basic metal which are melted by
energizing the coil 28; then, by actuating the pulley-block 41, the
stirring member 35 is lowered inside the crucible 26 and the motor
38 is also energized so as to drive said stirring member 35 at a
rotational speed sufficient to produce eddies in the liquid metal
filling the crucible 26; at the same time, a valve 21 inserted in
pipe line 20 is opened for feeding fluidized addition bed into the
crucible 26, and valve 51 inserted in line 45, or alternatively
valve 52 inserted in line 46, according as the subsequent casting
is to take place in vacuo or in argon atmosphere is also opened.
When the necessary amount of additions have been introduced into
the crucible 26 through line 20 and these additions have been
stirred sufficiently in the liquid metal filling the crucible, by
virtue of the turbulence created on the one hand by the helical
stirring member 35 and, on the other hand, by the electromagnetic
field generated in the liquid metal by the inductor 28, the crank
32 is actuated to lift the stopper-rod 30 and open the runner or
casting orifice 29, thus filling the mould 49 in vacuo or in an
argon atmosphere, as already explained in the foregoing; when the
casting or filling of mould 49 is completed, the runner 29 is
closed again by actuating the crank 32 to the proper extent, and
after cooling the cast ingot is stripped so that another ingot can
be cast. Of course, the ingot-mould 49 illustrated may also be a
detachable one so that another empty mould can be substituted
therefor without waiting until the metal has cooled to a suitable
"handling" temperature.
Many changes and modifications may be brought to the apparatus
illustrated in FIG. 3 without departing from the basic principles
of the present invention; some of these changes and modifications
will readily occur to those conversant with the art. Thus, the
helical stirring member 35 may be dispensed with, or replaced with
or completed by a stirrer or agitator coupled directly to the
rotor, immersed in the liquid metal filling the crucible 26, of an
electric motor having its stator disposed externally of said
crucible 26, so that the stator field can induce a positive torque
in said rotor; an ultrasonic emitter 53 may be immersed in the
liquid metal filling the crucible 26 to produce or at least
promoting the stirring effect in the additions mixed with the
liquid metal. The frequency of the electric current energizing the
heating coil 28 of crucible 26, the residual pressure maintained in
chamber 24 by the pumping means connected to conduit 45, as well as
the pressure and nature of the gas to be supplied to said chamber
24 via conduit 46, are matters of choice.
In FIG. 3, a further improvement is illustrated which is
particularly advantageous for utilizing particulate additions in
the form of grains having an average size of less than 1 micron,
inasmuch as it is capable of preventing the agglomeration or
packing of these very fine powders into balls or cakes, thus
promoting their subsequent perfectly homogeneous dispersion through
the mass of molten metal filling the crucible 26. This improvement
consists essentially, in the embodiment illustrated in FIG. 3, in
utilizing a filamentary electrode 54 projecting through an
insulating plug 55 into a suitable section of the pipe line 20
directing the fluidized bed into the crucible 26; within said pipe
line 20 the electrode 54 is so disposed as to be somewhat spaced
and therefore not in electric contact with the walls of said line
20, so that its end lies at a predetermined height above the liquid
contained in said crucible 26. The portion of the filamentary
electrode 54 which is disposed externally of the pipe line 20 is
connected on the other hand to one terminal of a high-voltage d.c.
generator (having an output of 50,000 to 100,000 V), the other
terminal of this generator (not shown) being electrically connected
to the metal contained in said crucible 26, notably through the
metallic elements of the apparatus and the ground (alternatively,
the other terminal of said generator may be connected to an
electrode immersed in the molten metal). Thus, a strong electric
current voltage gradient is produced between the end of the
filamentary electrode 54 located adjacent the flow of fluidized
bed, on the one hand, and the free surface of the molten metal
contained in said crucible 26, on the other hand, in order to
electrify the particles in said fluidized bed; as all these
particles receive charges of the same polarity, they are less prone
to agglomerate into balls or cakes than neutral particles of the
same granulometry (less than one micron), thus promoting their
homogeneous dispersion throughout the molten metal.
In FIG. 4 a modified embodiment of the structure illustrated in
FIG. 3 is shown; the elements found in both embodiments of FIGS. 3
and 4 are designated by the same reference numerals. Whereas in the
apparatus of FIG. 3 the fluidized bed is fed to the crucible 26 via
a pipe line 20, from a separate fluidizing device, for example one
of the type shown in FIGS. 1 and 2, in the embodiment illustrated
in FIG. 4 this fluidizing device designated in general by the
reference numeral 56 is mounted directly above the chamber 24
receiving the crucible 26. This device comprises essentially a
container 57 having a funnel-shaped bottom 57a into which opens the
upper end of a substantially vertical pipe line 20 of refractory
material, which extends through the upper wall of chamber 24 and
also through the detachable cover 26a of crucible 26, into which
opens the lower end of said pipe line 20; argon is fed into the
upper portion of container 56 via a branch line 58 of conduit 46
which is controlled by a valve 59; the cover 57b of container 57
receives therethrough a vertical rod 60 (the corresponding passage
opening being sealed by a suitable packing), the lower end of said
rod 60 constituting a plug or valve member co-acting with the
tapered lower portion of the funnel-shaped bottom 57a of container
57; the position of this plug or valve member 60 in relation to the
tapered bottom 57a may be adjusted by moving said rod 60
vertically, and to this end this rod may comprise a screw-threaded
portion 60a at its upper end for engagement in a tapped bearing
rigid with the cover 57b. The columns 3 supporting said container
57 are carried by vibrating tables 4.
In the arrangement illustrated in FIG. 4 the stirring device
comprises essentially a screw or fan 35a having a shaft 34
extending freely but in a fluid-tight manner through the cover 26a
of crucible 26, said shaft 34 being disposed vertically and
eccentrically in relation to said crucible 26. This eccentric
mounting of the shaft of said helical stirring member in relation
to the crucible 26 (which is also visible in FIG. 3, where it is
more enhanced than in FIG. 4) should be inasmuch enhanced as said
crucible 26 has a more symmetric configuration, for example a
circular cross-sectional shape, in order to avoid the creation, in
the molten metal contained in said crucible 26, of streamlines
following horizontal paths or lying in horizontal planes, since
this would cause the addition particles to follow plane, parallel
paths; in contrast thereto, the eccentric position of the helical
stirring member produces in the molten metal streamlines following
non-horizontal paths, thus ensuring the circulation of addition
particles depthwise in the molten metal.
Now various examples of practical applications of a process for
producing composite alloys by means of the apparatus illustrated in
FIG. 4 and described hereinabove will be described.
EXAMPLE 1
Referring to FIG. 3, after removing the cover 26a of crucible 26
and the helical stirring member 34, 35a by actuating the
pulley-block 41, aluminium ingots of the A5 grade (99.5 percent
pure A1) are introduced into the crucible 26 while keeping the
stirring member in its upper position so that its screw end lies in
the upper portion of the crucible, above the level of the ingots
introduced into it. By using means not shown in FIG. 4, aluminium
powder of grade .alpha. and of well-defined grain or particle size
(the granulometry of this powder being selected within the range of
0.1 to 10 .mu., and preferably less than 1 .mu.) is introduced into
container 57. Then valve 51 is opened to create a sufficient vacuum
in chamber 24 and the coil 28 of crucible 26 is supplied with
high-frequency electric current and cooling water for heating the
crucible together with its contents, in vacuo, to a temperature of
about 600.degree. C, thus degasing the crucible and its load.
Thereafter, valve 51 is closed and valve 52 is opened to fill the
chamber 24 with argon, and the supply of coil 28 is adjusted to
gradually heat the aluminium ingots contained in said crucible 26
firstly to their melting temperature and then to a suitable
processing temperature selected to be preferably of the order of
1,250.degree. to 1,300.degree. C). When the aluminium has molten
sufficiently the screw 35a of the stirring member is lowered into
the molten metal by actuating the pulley-block 41, and this screw
35a is driven, by energizing its motor 38, at a speed of 500 to 900
r.p.m. When the molten metal has attained the selected temperature
in the manner set forth hereinabove, the screw-rod 60 of device 56
is rotated in order to raise slightly its lower end above the
tapered bottom 57a of container 57, and valve 59 is turned on so
that pressurized argon will flow from top to bottom through the
container 57 and eventually escape via pipe line 20 while carrying
along the fluidized bed of alumina particles. If these particles
are less than 1 micron in size, a 50,000 to 100,000-Volt direct
current is fed to the filamentary electrode 54 in order to
electrify them and thus prevent the accumulation of cakes or balls
while promoting their homogeneous dispersion in the metal melt, in
which they are stirred by the screw stirrer 35a. Suitable means
well known to those conversant with the art and therefore not
described herein are provided for measuring the throughput of
alumina particles carried along by the argon stream through pipe
line 20, and discontinuing the supply of such particles to the
metal bath by actuating the valve rod 60 in the opposite or closing
direction when the proportion (by weight) of the particles thus
dispersed in the metal bath has reached a predetermined value
selected to be perferably within the range of 3 to 10 percent by
weight. Therefore, the time necessary for achieving the operation
is variable, and of the order of 5 to 45 minutes. The actuation of
the screw stirring member 35 a is continued thereafter, until a
perfectly homogeneous dispersion is obtained. Then the runner 29 is
opened by actuating the crank 32 and thus an ingot consisting for
example of a cylindrical bar approximately 500 mm long and having a
diameter of 60 mm is cast in an argon atmosphere into the ingot
mould 49.
The ingot is then stripped and cut into plates about 12-mm thick
which are subsequently hot-rolled (at about 400.degree. C) to
improve the homogeneous dispersion of the alumina powder in the
aluminium matrix. This rolling operation comprises for instance a
series of passes each producing a thickness reduction of about 0.6
mm, and annealing treatments at about 400.degree. C are applied to
the product between these passes; thus, the end product is a
composite-structure sheet about 4-mm thick which is eventually
annealed at about 350.degree. C during 5 hours.
If a substantial departure from the above-defined processing steps
and conditions is made, the following consequence will be observed:
if the temperature of the metal bath receiving the fluidized bed is
kept within lower limits of, say, 1,100.degree. to 1,250.degree. C,
the liquid composite product thus obtained consists of a
high-viscosity magma that cannot flow to form a casting; on the
other hand, if the temperature of the metal bath exceeds
1,300.degree. C, the particles accumulate into cakes by sintering,
and between 1,350.degree. and 1,400.degree. C gaseous Al.sub.2 0 is
released, in the form of bubbles carrying along the particles
towards the free surface of the metal bath while developing
blisters in the cooled ingot. Satisfactory products may still be
obtained by utilizing alumina having a granulometry of less than
0.3 .mu., and even as low as 0.02 .mu., provided that the
accumulation of agglomerated particles is prevented by the
fluidized bed electrification, as described hereinabove.
The rolled product of which the manufacturing process has been
described hereinabove is characterized by mechanical properties far
better than those of the pure aluminium constituting its matrix;
its elastic limit is higher (the difference is about 70 percent)
and its tensile strength or breaking load about 5 to 15 percent
better than that of A5-grade aluminium; at temperatures of the
order of 200 to 300.degree. C the elastic limit and breaking load
of the rolled product according to this invention remain higher by
about 40 to 80 percent and 15 to 50 percent, respectively, than
those of said A5-grade aluminium. In an extrusion test carried out
at a temperature of 200.degree. C, a test bar made from a rolled
product according to this invention displayed after 10 hours a
breaking stress improved by 15 to 35 percent over that of A5-grade
aluminium under the same testing conditions.
EXAMPLE 2
The manufacturing process described in Example 1 is repeated,
except that cubic zircon stabilized by the addition of 5 percent of
lime and in the form of grains having a granulometry of 1 to 10
.mu. is substituted for alumina powder; the percentage by weight of
the powder thus dispersed in the metal bath is limited to a
well-defined value selected preferably in the range of 10 to 20
percent by weight. In this case, the total time for introducing
this powder into the metal bath and stirring this bath is limited,
preferably, to a value of 10 to 15 minutes. Then, the metal bath is
kept at a temperature preferably within the range of 850.degree. to
890.degree. C. Above 900.degree. C, upon solidification, the
ZrAl.sub.3 compound develops and blisters due to gaseous release
appear in the ingot. The dispersion of the addition particles in
the aluminium matrix can be further improved by means of a rolling
operation. The rolled product thus obtained has an elastic limit
and a breaking load exceeding by 40 to 75 percent and 15 to 35
percent, respectively, those of A5-grade aluminium; at 200.degree.
C its elastic limit and breaking load exceed by by 80 to 170
percent and 35 to 100 percent respectively those of A5-grade
aluminium. A test bar made from a rolled product of this character
and submitted to an extrusion test at 200.degree. C has a breaking
stress (after 100 hours) exceeding by 80 percent that of A5-grade
aluminium under the same testing conditions.
EXAMPLE 3
The same manufacturing procedure is adhered to by utilizing a
TiB.sub.2 ot TiN powder in particles of a few microns or preferably
less than one micron; this powder is fed to the metal bath in a
well-defined proportion ranging preferably from 10 to 20 percent;
the metal bath is then held at a temperature approximating
900.degree. C. Below this temperature, for instance at 700.degree.
C, the particles tend to accumulate into cakes and balls. The
particle dispersion in the cast ingot is sufficiently homogeneous
to permit of dispensing with a subsequent rolling operation. The
product thus obtained has an elastic limit and a breaking load
greater by 100 percent and 25 percent, respectively, than those of
A5-grade aluminium. The modulus of elasticity of the end product
has a value comparable to that of high-grade aluminium alloys. When
tested by extrusion at 200.degree. C, a test bar made of said
product has a breaking stress (after 100 hours) greater by about 50
percent than that of A5-grade aluminium. This product is further
characterized by a high ductility and therefore by a very low
fragility.
* * * * *