Note: Descriptions are shown in the official language in which they were submitted.
~1~4~t;9
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METAL CASTING APPARATU~
TECEINICAL FIELD OF THE INVENTION
The present invention relates generally to
metal casting apparatus, of the kind adapted for melt-
ing small charges of metal and cast.ing objects such as
dental inlays, jewelry, precious metal works, and pre-
cision machine parts. More particularly, the invention
relates to an improved metal casting apparatus for such
use, employing a metal-heating crucible in communication
with a mold via an opening through which molten metal
from the crucible is automatically let into the mold by
gravity, without the employment of any intermediate means
and/or process.
BACKGROUND OF THE INVENTION
An example of the general kind of apparatus
to which this invention relates is disclosed in U.S.
Patent No. 3 7 ~, 3~ . In the apparatus disclosed in
this patent, a metal is electrically heated in a crucible
to optimum cas-ting temperature. The temperature of the
molten metal is sensed and, in response to such sensing,
the molten metal is sucked under vacuum into a mold
through an opening provided in the bottom of the crucible,
with the vacuum being produced in the mold. In practice,
apparatus such as that shown in the noted patent tends
to have certain disadvantages, among which are the
following:
(a) The products made with such apparatus are
L5t~9
--2--
prone to having faults therein. The reasons for such
faults can be traced to a number of factors: (1) the
range of the optimum casting temperatures is unfavor-
ably limited; (2) the detector of the optimum tempera-
ture may fail to detect an average temperature of thewhole body of the molten metal, in which temperature can
differ from spot to spot, thereby resulting in an impro-
per detection of the temperature so that the molten metal
is sucked into the mold either too soon or too late; and
(3) there is inherent in the arrangement an unavoidable
time lag between the detection of the optimum temperature
and the initiation of the suction vacuum, during which
time lag the molten metal is in dangex either of exces-
sive heating or detrimental cooling. When excessively
heated, the metal is liable to form rough surfaces, blow-
holes and pinholes. When cooled below the optimum cast-
ing temperature the molten metal lacks its optimum fluid-
ity and, for this reason, can fail to reach deeply enough
into molding cavities. Accordingly, when the temperature
of the molten metal is not optimum, it sometimes happens
that a particular desired shape or surface condition
for an object cannot be achieved, and other related pro-
blems can be encountered.
(b) The melting temperature and the optimum
casting temperature are different, depending upon the
kind of metal. When using apparatus like that shown in
the patent, a complicated procedure is required for pre-
determining the optimum melting temperature.
(c) A temperature detector device and an elec-
tronic control device connected with the detector andarranged to operate a vacuum pump in response to the
detection of a specific temperature by the detector are
required in apparatus like that shown in the patent.
These devices require a high degree of reliability and,
with their inclusion, the apparatus as a whole becomes
both expensive and complicated.
(d) In apparatus like that shown in the patent,
the reliability of the temperature detector device and of
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the electronic control device must be maintained, requiring
a constantly ongoing, labor--consuming maintenance effort.
But even with such a maintenance effort, the life of these
devices tends to be short.
(e) In order to perform the resistance heating
of a metal in the apparatus of the patent, a vertically
split type of crucible is employed, with an insulating
plate interposed between its paired sides. In addition, a
backing means must be provided for securing the metal in
between the paired sides of the crucible. This arrange-
ment again requires expensive maintenance, and makes the
apparatus structurally complicated and costly.
BRIEF SUMMARY OF THE INVENTION
In accordance with an aspect of the invention
there is provided a metal casting apparatus including a
casting furnace including an upper, first chamber, and a
lower, second chamber positioned beneath said first
chamber, said first and said second chambers being divided
by generally horizontal separating wall means; means
forming a vertically extending liquid passageway through
said separating wall means between said first chamber and
said second chamber; a crucible made of electrically
conductive material received within said first chamber and
supported on said separating wall means, said crucible
having a recess therein for receiving a body of casting
metal and supporting the lower end thereof, and an opening
therethrough extending from the bottom of said recess
downwardly to the bottom surface of said crucible, said
crucible opening being smaller in diameter than the lower
end of said body of casting metal and being dimensioned
such that when said body of casting metal has been
completely melted and placed in a molten state it will
flow freely therethrough by gravity without the employment
of any additional flow causing means; said crucible being
placed on said separating wall means with said crucible
1154S~9
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opening in communication with said liquid passageway, and
said crucible having open gas passage means therein
leading from the outer diameter thereof to a location on
the surface of said crucible opening beneath said crucible
recess to thereby freely communicate said first chamber
with both said crucible opening and said liquid passagway;
mold means received within said second chamber, and
includiny a mold cavity having an inlet; means supporting
said mold means within said second chamber, with said mold
inlet in communication with said passageway; electrode
- means mounted within said first chamber on the ceiling
thereof above said crucible, said electrode means being
vertically adjustable for adjusting the gap between said
electrode means and the upper end of a body of casting
metal received in said crucible recess; and power supply
means connected with said electrode means; said electrode
means and said power supply means being connected and
arranged to establish an electric arc between said
electrode means and the upper end of a body of casting
metal received in said crucible recess, effective to melt
said body of casting metal downwardly from the top to the
bottom thereof, the lower end of said body of casting
metal serving to block liquid flow through said crucible
opening until all of said body of said casting metal has
been placed in a molten state by said electric arc.
In the present invention, the metal casting
apparatus includes a metal-heating crucible which i5
located above a mold, there being a liquid passageway
located between the crucible and the mold. An electric
heating means is located above the metal-heating crucible,
so as to melt casting metal placed in the crucible from
the top of the casting metal to its bottom, the arrangement
being such that the casting metal is simply allowed to
drop by gravity through the passageway and into the mold
after it has become molten.
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Accordin~ to another aspect of the invention, the
use of the force of gravity to cause the molten material
metal to fall into the mold is supplemented by a gas
pressure differential produced between the heating section
and the molding section of the apparatus.
It is the principal object of the present
invention to provide a metal casting apparatus in which an
optimum casting temperature for the casting metal is
maintained until the molten metal enters the mold, thereby
assuring a precise molding of the desired object even when
fine, delicate shaping and a smooth surface are required.
Another object is to provide a metal casting
apparatus capable of trouble-free operation and easy
.~
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adjustment of the casting ternperature, even when differ-
ent cas~ing materials are used.
A further object is to provlde a metal casting
apparatus having a simplified construction, thereby
reducing the costs of production and maintenance.
Other objects and many of the attendant advan-
tages of the invention will become readily apparent from
the following detailed description of the preferred em-
bodiments, when taken together,with the accompanying
drawings.
BRIEF DESCRIPTION OF THE: DRAWINGS
_ . _ . _ _
FIG. 1 is a perspective view of a cabinet in
which is mounted a metal casting apparatus constructed
according to the present invention;
FIG. 2 is a perspective view on an enlarged
scale of the casting unit of the metal casting apparatus
of FIG. 1, shown with the door thereof open for viewing
the interior of the upper, heating chamber and the lower,
molding chamber;
FIG. 3 is a vertical, longitudinal sectional
view taken through the metal casting apparatus of FIG. 1,
with the control circuit and allied components thereof
being schematically shown;
FIG. 4 is an enlarged, exploded perspective
view showing the metal-heating crucible, a body of
casting metal, and the electrode of the metal casting
apparatus of FIG. l;
FIGS. 5a through 5d show in diagrammatic form
the manner in which a body of casting metal is melted
from the top to the bottom thereof within the metal-
heating crucible of the invention, with FIG. 5d showing
the molten casting metal passing downwardly out of the
crucible;
FIG. 6 is an enlarged, vertical sectional
view of the metal-heating crucible of FIG. 4, shown
with a body of irregular shaped casting material therein;
FIG. 7 is an enlarged, fragmentary front
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elevational view of the cam structure mounted on the
bottom of the metal casting apparatus, taken generally
at the arrow VII in FIG. 3;
FIG. 8 is an enlarged, fragmentary vertical
sectional view showing the arrangement for mounting the
metal-heating crucible in the casting unit of the inven-
tion, and is taken generally at the arrow VIII in FIG. 3;
FIG. 9 is a view similar to FIG. 8, but showing
the mold lowered so that it is not in contact with the
bottom of the crucible assembly;
FIG. 10 is an enlarged, fragmentary sectional
view taken generally along the line X-X in FIG. 3, show-
ing details of the mechanism for locking closed the door
of the casting unit;
FIG. 11 is a fragmentary, enlarged perspective
view further showing the arrangement of the mechanism -
for loc~ing the door of the casting unit in a closed
position, and is taken generally at the arrow XI in
FIG. 10;
FIG. 12 is a diagrammatic view showing how a
separate, shaping crucible is replaced for the metal-
heating crucible, for use in molding a body of casting
material into generally a mushroom shape;
FIG. 13 is an enlarged, half-perspective view
of the shaping crucible of FIG. 12;
FIG. 14 is a perspective view of a body of
casting materi.al which has been molded into a mushroom
shape, by use of the arrangement of FIG. 12i
FIG. 15 is an enlarged, half-perspective view
of a modified form of metal-heating crucible;
FIG. 16 is an enlarged, half-perspective view
of another modified form of metal-heati.ng crucible;
FIG. 17 is an enlarged, vertical sectional
view through a modified casting mold: and
FIG. 18 is a schematic view showing a modified
arrangement for the gas port of the molding chamber of
the casting unit, the gas port being indicated generally
at XVIII in FIG. 3.
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DETAILED DESCRIPTION OF THE PREFERRFJD EMBODIMENTS
Referring now to FIGS. 1-3 of the drawings, a
cabinet A is shown within which is mounted the casting
apparatus of the invention, the apparatusincluding a
casting unit B having an upper, heating chamber 1 and
a lower, molding chamber 8. When the casting unit B is
in use, an electric arc 4 is produced in the heating
chamber 1 between an electrode 2 and a body of casting
metal 3 placed in a metal-heating crucible 5 disposed
within said chamber. As is best shown in FIGS. 5a through
5d, the body of casting material 3 is melted from its top
surface to the bottom thereof by the electric arc 4.
When the bottom portion of the body of casting
material 3 has been completely melted, the molten metal
3a will then drop through an opening 6 provided in the
bottom of the metal-heating crucible 5. This occurs be-
cause the bottom of the molten body of casting metal 3
has become fluid, and will thus no longer support the
casting metal. The molten metal 3a passes along a pour-
ing path 7 (FIG. 3), and pours into a mold 9 located inthe molding chamber 8 and positioned directly below the
metal-heating crucible 5 in communication therewith. The
mold 9 includes an inlet port 10, cavities 11 formed with-
in granular packing material 13, and a cylindrical frame
49 which embraces and confines the grains of the material
13. The reference number 14 indicates passageways pro-
vided among the packed grains of the granular material
13, through which a gas is passed, as will now be more
particularly described.
The metal heatin~ chamber 1 and the molding
chamber 8 are filled with an inert gas, such as argon,
for the period of time from the initiation of heating to
the completion of molding. The presence of the inert
gas during an operating cycle of the apparatus protects
the casting metal against oxidizing or nitrifying. In -
addition, the yas is used to supplement the gravity flow
of the molten metal.
The inert gas atmosphere is produced such that
a pressure differential of about 4 kg/cm2 exists between
the chambers 1 and 8, with the heating chamber 1 having
the higher pressure. Owing to the pressure differential,
the inert gas ls caused to flow from the heating chamber 1
to the molding chamber 8 via gas passageways 12, the pour-
ing path 7, the inlet port 10 of the mold 9, and the mold-
ing cavities 11. As described above, the interior of the
mold 9 is of a porous quality because of the passageways
14 formed between the grains of the packed granular
material 13, and the inert gas flows through the passage-
ways 14 about the grains, and then out of the bottom of
the mold 9 into the molding chamber 8. The urging of the
flowing inert gas stream assists the falling molten metal
in flowing into the mold 9, and reaching the depths of the
molding cavities 11.
In order to produce the inert gas atmosphere
just described, and referring now in particular to FIG.
3, the chambers 1 and 8 are first subjected to air evacu-
ation by means of a vacuum pump 17, which is operated by
pressing a button 15 under the control of a sequence con-
troller 16. The air in the heating chamber 1 is with-
drawn via pipes 18 and 19, connected with the chamber 1
and the vacuum pump 17, respectively, and connected with
each other by a three-way shuttle valve 20 and a coupler
33. Similarly, air is withdrawn from the molding chamber
8 through a pipe 22 and a strainer 23 connected therewith,
and which in turn are connected to the pipe 19.
When the pressure values of the chambers 1 and
8 reach about 700 mml~g, a switch 2~ is automatically
operated and functions to shift the core 25 of the
shuttle valve 20 to the left in FIG. 3, against a spring
26. Thus, the connection between the pipes 18 and 19
is broken, causing air evacuation from the chamber 1 to
stop. An inert gas from a container 27 is then intro-
duced under pressure into the heating chamber 1, via aregulator 28 and a pipe 29 connected to the shuttle
valve 20, the shuttle valve 20, and the pipe 18. The
regulator 28 will normally be set at about 3 kg/cm2,
1i545f;9
thereby produciny an inert gas atmosphere of about the
same pressure value in t}le heating chamber 1.
Air evacuation from the molding chamber 8 is
continued until molding is finished, assuring mainte-
nance of a pressure differential between the chambers 1and 8. When the molding is finished, the sequence con-
troller 16 works to stop the operation of the vacuum
pump 17, and the core 25 of the three-way shuttle valve
20 is then returned to the right in FIG. 3 by means of
the spring 26. In this manner, both the air evacuation
of the molding chamber 8 and the introduction of the
inert gas into the heating chamber 1 are stopped. The
inert gas remaining in the chamber 1 is drained to the
atmosphere via the pipe 18, the shuttle valve 20, the
coupler 33, and a check valve 34. The inert gas is
partially withdrawn into the molding chamber 8 via the
pipes 19 and 22, whereby atmospheric pressure is restored
in both of the chambers 1 and 8. This completes a cycle
of the molding process, with respect to the inert gas.
Turning now to the entire molding apparatus
and process, reference is made in particular to FIGS. 2
and 3, wherein the casting unit B is shown to include a
casting furnace 35 made of aluminum or a zinc alloy. The
casting furnace 35 includes the upper, heating chamber 1
and the lower, molding chamber 8, which are separated by
a wall or partition 36 having a central opening 77 there-
through, within which is received a sleeve fixture 37
containing the pouring path 7. An electrical heating
unit.31 is mounted in the ceiling of the heating chamber
1, and includes the electrode 2, which is mounted to
extend through the ceiling of the chamber 1 and projects
downwardly toward the metal~heating crucible 5 mounted
on the sleeve fixture 37.
The electrode 2 is arranged to generate an
electric arc 4 between it and the body of casting metal --
3 placed in the crucible 5. To produce the arc 4, vol-
tage is impressed across the electrode 2 and the casting
furnace 35 from an electric power supply 32, which has
1~4`~ti9`
g
terminals 3~ and 40 thereon. The terminal 38 is con-
nected to the protruding tip of the electrode 2, and
the other terminal 40 is ~rounded to the cas-ting fur-
nace 35. Thus, the casting furnace 35, the sleeve
fixture 37, the crucible 5, and the body of cas-ting metal
3 as a whole constitute an electrical path from the ter-
minal 40 to the gap between the body of metal 3 and the
electrode 2.
The electrode 2 is carried by a holder 39,
which is secured in an airtight manner within an opening
provided in the ceiling of the heating chamber 1 by an
insulating fitting 41, and is preferably made of tungsten.
The distance between the electrode 2 and the body of
casting material 3 can be adjusted by means of an adjust-
ing screw 42. The electrode 2 is slidable within itsbore in the holder 39, but can be secured in a selected
position with the screw 42.
The construction of the preferred embodiment of
the metal-heating crucible 5 is shown in detail in FIGS.
4-6, wherein the body thereof is indicated generally at
42. The body 42 is made of copper or any other suitable
electrical conductor, and takes a cylindrical form. The
upper surface of the body 42 has an inverted, truncated
cone-shaped recess 43 centrally thereof for receiving
a body of casting metal 3, the recess terminating at its
lower end in a cylindrical intermediate bore 44a, the
sidewall of which extends paral]el with the longitudinal
axis thereof. An inwardly projecting, annular rim 45
is positioned beneath the intermediate bore 4~a, and
defines the opening 6 through which molten metal exits
~he crucible 5. The opening 6 has a sidewall which also
extends parallel with the longitudinal axis thereof, and
has a diameter predetermined such that it will allow the
molten casting metal to pass therethrough by gravity,
35 a~ainst its surface tension. ~-
The upper surface of the annular rim 45 has
the shape of an inverted, truncated cone, and extends
upwardly from the opening 6 to the lower end of the
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--10~
intermediate bore 44a. As shown in the drawings, the
slope of the rim upper surface 44 is about the same as
the slope of the recess 43, and preEerably the upper and
lower edges of the opening 6 are chamfered.
At least the lower portion of the body of cast-
ing metal 3 will have a cylindrical shape, and a diameter
less than the diameter of the intermediate bore 44a, but
greater than that of the opening 6. Thus, the lower end
of the body 3 will rest centra~ly on the upper rim sur-
face 43. The truncated cone configuration for the upper
rim surface 43 assures that contact with the lower cylin-
drical end of the body 3 is minimal, which is advanta-
geous in enabling the molten metal to flow smoothly with
a minimum heat insulating effect; otherwise, the molten
metal would readily become solid due to cooling, thereby
causing clogging of the opening 6. The under surface 43a
of the rim 43 is a truncated cone in shape, and the lower
end thereof terminates in an enlarged cylindrical bore 43b.
When the body of casting metal 3 is placed in
the crucible 5 with its lower edge resting on the sloping
upper rim surface 43, communication between the crucible
5 and the mold 9 through the opening 6 is completely
blocked, as is illustrated in FIG. 3 and FIG. 5a. When
the castiny furnace 35 is placed in operation and the
electric arc 4 is formed, the casting metal 3 will be
melted from the top down, as shown in FIGS. 5a through
5d. Owing to the conductive nature of the crucible body
42, the heat will be evenly transmitted, thereby avoiding
a spot-by-spot melting of the casting metal. Because of
the top-to-bottom melting process, the lower end of the
body of casting metal will remain as a plug in the opening
6 until all of the metal has become molten and has reached
the desired state of fluidity, related to a specific melt-
ing temperature. Thereafter, the molten metal will drop
through the opening 6, as is shown in FIG. 5d.
The body of casting metal 3 can be cylindrical
and well formed, as shown in FIGS. 4 and 5a. However, in
some instances it is desirable to use at least some
llS~5~ig
shapeless casting ma-terial, such as a cas-ting waste.
This ls accommodated by the metal-heating cruc;ble 5,
as is shown in FIG. 6.
When using shapeless material, a circular plate
3b of the same material is first placed in the intermedi-
ate bore 44a, to rest on the upper rim surface 43. Then,
the shapeless casting metal 3c is placed on the plate 3b,
the intermediate bore 44a serving with the inclined re-
cess 43 to center and position the casting metal 3c.
Thereafter, melting of the metal proceeds as before, with
the plate 3b retaining the metal until it is all molten
and in a proper state.
The bottom face of the crucible body 42 is pro-
vided with grooves which form the gas passageways 12, and
establish communication between the heating chamber l and
the inlet 10 of the mold 9. As shown in the drawings, the
groove passa~eways 12 are arrayed in a cross-shape; how-
ever, other arrangements are possible. The groove
passageways 12 function to pass inert gas from the heat-
ing chamber 1 to the molding chamber 8, after the formerhas been filled with the gas and a pressure dlfferential
between the chambers 1 and 8 has been established, as has
been described earlier. The inert gas, such as argon,
performs the dual functions of helping to accelerate the
falling molten metal, and preventing such from oxidizing
or nitrifying.
The crucible body 42 is provided with a detach-
able handle 47 (FIG. 6), which is insertable into a blind
hole 48 provided therein. When the crucible 5 is in
operation, the handle 47 is removed. The handle 47 can
be inserted into the hole ~ when it is desired to move
the crucible 5, and thereafter the crucible can be lifted
by the handle.
Turning now to the mold 9, the casing 49 thereof
will usually be made of iron in the form of a cylinder. -
The granular packing material 13 is placed therein in the
usual manner and forms the cavities 11. The passageways
14 will be located between the grains of the material 13
1154~tie3 . ......
-12-
and the mold includes an inlet port 10. Between the open-
ing 6 of the crucible 5 and the mold inlet port 10, there
is formed the pouring path 7.
Air is withdrawn from and inert gas is admitted
into the upper, heating chamber 1 through a port 50
located adjacent to the ceiling thereof, and which is con-
nected to the pipe 18. Similarly, the lower, molding
chamber 8 has a port 51, located near its ceiling and con-
nected with the pipe 22. The ~anner by which the chambers
1 and 8 are evacuated of air - a pressure differential is
formed therebetween, and an inert gas is introduced into
the heating chamber 1 and flows into the lower chamber 8
- has already been described.
Referring now to FIGS. 8 and 9, the details of
the sleeve fixture 37 for mounting the metal-heating
crucible 5 are shown. The sleeve 37 includes an upper
part 74 and a lower part 75, held in connected relation-
ship by a screw thimble 76. The upper and lower parts
74 and 75 have aligned, vertical bores therethrough, which
together define the flow path 7 from the crucible opening
6 to the mold inlet 10.
The opening 77 in the separating wall 36 has a
relatively large diameter, and includes an annular pro-
jection 78 positioned between the upper and lower ends
thereof. The upper part 74 of the sleeve fixture 37 has
a flange 74a thereon, and is adapted to be received in
the opening 77 so that the flange 74a comes to rest on
the annular projection 78. The upper part 74 carries an
O-ring 79 in a groove thereon, positioned to engage the
cylindrical wall formed by the annular projection 78 when
the flange 74a is seated on the projection.
The lower end portion of the upper part 74 of
the sleeve fixture 37 is cylindrical, and is threaded
for receiving the screw thimble 76. The screw thimble
76 is tightened until the annular projection -/8 is clamped
between it and the flange 74a, whereby the sleeve assembly
is ~irmly secured to the separating wall 36. The O-ring
79 assures a gas-tight relationship, and such is preferably
~ . /
l:~S~S~9
-13-
made of heat-proof material.
The screw thimble 76 includes an inwardly
directed flange 80 having a rounded upper surface which
accommodates a like rounded surface on the lower part 75,
and the bottom face of the upper part 74 has a concave
surface 81 while the top face of the lower part 75 is
formed as a mating convex surface 82. An O-ring 83 is
carried in a groove 84 on the convex surface 82, to form
a gas-tight seal. Like the O-ring 79, the O-ring 83 is
preferably made of heat-proof material. The bottom face
52 of the lower part 75 is made flat, so as to receive
the top end face of the mold 9 in a tight fit, with a
gasket 53 clamped therebetween. By pressing the mold 9
upwardly against the gasket 52 as shown in FIG. 8, with
the opening 6, the pouring path 7 and the inlet port 10
all in alignment, molten metal from the cruclble 5 can
pass together with inert gas from the grooves 12 into the
mold 9. Because the lower part 75 is mounted for univer-
sal movement, misalignments can be accommodated.
The mold 9 is moved into and out of engagement
with the sleeve fixture 37 by a pusher device 54, which
includes a base 55 mounted on the upper end of a rod 56,
the rod bein~ slidably received within a bore 62 pro-
vided in a bracket 61 secured to the bottom wall of the
casting furnace 35. An O-ring 64 is carried in a groove
provided on the rod 56, to provide a seal between the
rod and its bore 62, and the joint between the bracket
61 and the bottom wall of -the furnace 35 is sealed by
another O-ring 64a.
The base 55 o~ FIG. 3 includes a lower part
69 and an upper part 70, which are detachably doweled
together by a projection 71 and a socket 72. Each of
the base parts 69 and 70 has grooves 73 in the upper
surface thereof, so as to facilitate a smooth flow of
gas through a mold 9 resting thereon. The use of a
two-part base 55 provides flexibility to accommodate
~5~j9 ~ j
-14-
molds 9 of different heights. When a relatively short
mold 9 is being used, as in FIG. 3, the upper part 70
is employed. If a substan-tially taller mold than that
shown in FIG. 3 is used, then the upper part 70 can be
removed, and the taller mold can rest only on the upper
surface of the lower base part 70. The presence of the
grooves 73 on the upper surface of both of the base
parts 70 and 69 assures good gas flow, regardless of
which supports the mold.
The rod 56 is moved vertically within the
bracket 61 by a cam 57, which is arranged to be engaged
by a cam follower 65 connected with the bottom of the
rod 56. The cam 57 is mounted on one end of a cam shaft
58 received in a transverse bore 63 provided in the
bracket 61, the other end of the cam shaft 58 carrying
a handle 59. ~ bracket arm 68 projects from the bottom
of the bracket 61, and anchors the lower end of a spring
60. The upper end of the spring 60 is connected with a
bolt 67 projecting from the cam follower 65, and the
spring 60 functions to urge the rod 56 downwardly and
to keep the cam follower 65 in engagement with the cam
57. The rear face of the cam follower 65 is flat and
slides on a flat surface 66 formed on the bracket 61
to prevent turning of the rod 56 and any consequent
misalignment between the cam fo]lower 65 and the cam 57.
In operation, the handle 59 is first turned
to lower the base 55, after which the mold 9 is placed
on the base 55. Then, the handle 59 is turned in the
opposite direction to raise the rod 56 and the base 55,
whereby the top of the mold 9 is placed in engagement
with the bottom face of the sleeve fixture 37.
Turning now to other structural features of
the casting furnace 35, the sleeve fixture 37 is cooled
by passing cooling fluid through a cooling jacket bore
85 provided in the separating wall 36, as shown in FIGS._
8 and 9. The front of the furnace 35 is provided with
a flat face 86, provided with upper and lower openings
87 and 88 that give free accessto the upper, heating
1~54St;~
-15-
chamber 1 and the lower, molding chamber 8, respectively.
A door 89 is mounted by hinges 91 to mate in an airtight
manner with the face 86, seals being formed by sealing
rings 101 and 102 carried in grooves 103 and 104, res-
pectively, provided on the mating face of the door 89.A window 105 in the door 89 permits viewing of the
interior of the heating chamber 1.
A latching arrangement is provided to ensure
that the door 89 can be locked in its closed, airtight
position, and such is illustrated in detail in FIGS.
10 and 11. The latch arrangement includes a rotary
shaft 93 mounted within a bore 96 passing through the
door, the outer end of the shaft 93 carrying a handle
92. The shaft 93 has an arcuate groove 97 therein which
receives the tip of a stop screw 98 carried by the door
89, the groove 97 extending for about 90. The groove -
97 and the stopscrew 98 function to limit rotation of
the shaft 93, and are arranged so that the handle 92
is movable between horizontal and vertical positions.
The inner end of the shaft 93 carries a pair
of pawls 94, arranged symmetrically with respect to the
axis of the shaft. The front face 86 of the furnace 35
has a mating apperture 99 therein, shaped to receive
the pawls 94. The upper and lower rims 95 of the aper-
ture 99 are recessed, and are adapted to receive slant
cam faces 100 provided on the pawls 94. The arrangement
is such that when the handle 92 is at one extreme of its
movement, as determined by the groove 97 and the stop
screw 98, the pawls 94 and their cam faces 100 can enter
the aperture 99. Rotation of the shaft 96 through 90
will then cause the cam faces 100 to securely clamp the
door 89 against the face 86, in a wedging action that
will assure airtightness. The recesses 95 are adapted
to initially receive the slant cam faces 100 of the pawls
94, and to then receive the pawls wholly therein during -_
rotation of the shaft 96 from its open position to its
closed and latching position.
Referring to the drawings, when the handle 92
l5~S~
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is in its horizontal position as shown in FIG. 11, the
door 89 can be freely opened about the hinges 91. After
the door 89 has been closed, the handle 92 is rotated in
a counterclockwise position until it is vertical, which
causes the pair of pawls 94 to come into engagement with
the recesses 95. Thereafter, when the door is to be
opened the lever 92 is slowly moved back toward its hori-
zontal position. In so returning the handle, after
rotational movement of about 45, a small gap will be
opened between the face 86 and the door 89,and the
seals carried thereon. However, the pawls 94 will still
remain engaged in their recesses 95 at this stase of
opening, thereby preventing the door 89 from opening
explosively under a relatively high pressure that may
be present in the chambers 1 and 8~ but allowing such
pressure to escape to the atmosphere. After any pres-
sure that is present in the chambers 1 and 8 has been
allowed to bleed off, the handle 92 can be fully moved
to its horizontal, open position, and the door 89
safely opened.
Referring now to FIGS. 12 and 13, a modified
crucible is shown at 106, which is especially useful
for shaping a body of casting metal for use in the
casting furnace 35. ~he shaping crucible 106 is simply
substituted for the crucible 5, and is used to melt
casting material odds and ends 107 into a convenient
shape to form a slug for latter casting use. The odds
and ends of casting material 107 are melted in the cast-
ing furnace 35 by an electric arc 4, in the same manner
as described earlier, to form the slug. This can save
on production cost, and leads to the saving of material.
As is best shown in FIG. 13, the shaping cru-
cible 106 includes a body 108 made of an electrical con-
ductor, such as copper or carbon, and has a short, cylin-
drical shape. The top surface of the crucible 106 has ~-
an inverted, truncated cone-shaped recess 109 therein,
terminating at its lower end in a cylindrical recess
110. The body 108 is provided with a handle 111, which
llS~Ssi~ . -
. .
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is removably receivable in a bore llZ in the body.
Referring now to FIG. 14, there ls shown a
mushroom-shaped slug or body of casting material 3d, such
as will typically be formed from scrap material 107 with
use of the shaping crucible 106. When forming such a
slug 3d within the casting furnace 35, it has been found
that the impurities in the material will tend to gather
at the top 116 of the mushroom. When this occurs, the
impurities can then be removed simply by abrading the
location 116 with a grinder or similar tool. Thereafter,
the mushroom-shaped slug or body 3d is placed in the melt-
ing crucible 5, and is processed in the casting furnace
35 in the manner described above.
The shaping crucible 109 will form the mush-
room-shaped slug or body 3d with a cylindrical trunk
portion 113, an inverted, truncated cone portion 114, -
and a rounded head 115. The cylindrical recess 110 has
a diameter smaller than the intermediate portion 44a of
the melting crucible 5, so that the trunk portion 113
of the body will rest in line contact on the surface 44.
This assures even transmission of heat in the body of
casting material 3d, and a smooth flow of molten metal
with the minimum possibility of cooling.
Certain additional modifications of the inven-
tion can also be made, as follows:
(1) The melting crucible 5 can be made ofcarbon, which sublimates at 3727C. This point of sub-
blimation stands higher than the -temperature of the
electric arc, thereby keeping the crucible 5 safe from
sublimation due to the arc heating.
(2) As illustrated in FIG. 15, the inside
surface 43' of a crucible 5' can be wholly or partially
coated with a thermal insulating substance 117, thereby
avoiding possible damage to the crucible caused by the
3~ electric arc or a heated metal. In addition, the coated
surface 43' can conserve heat for a relatively long time,
thereby preventing the molten metal from cooling rapidly.
(3) As illustrated in FIG. 16, the inside
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surface of the recess 43" of a melting crucible 5" can
be provided with a plurality of radial grooves 118 for
insulating heat to the body of the crucible, wherein
the width and depth of the grooves 118 are determined
such that the surface tension of the molten metal is
adequate to prevent the molten metal from entering the
grooves. Thus, the molten metal is protected against
its rapid cooling in the recess ~3", but can still flow
through the opening 6".
(4) The slant surface 44 of the recess 43
in the melting crucible 5 can be provided with one or
more steps, or can be convexed or concaved, if so
desired.
~S) The slant surface 44 in the recess 43 of
the melting crucible 5 can be made rectangular, or of
any other polygonal shape, such as pentagonal, hexagonal,
in accordance with the sectional shape of the body of
casting metal.
(6) When the mold cavities 11' of a mold 9'
are delicate and complicated, as illustrated in FIG.
17 for example, thereby increasing the difficulty in
obtaining deep penetration of molten metal therein, the
iniet port 10' can be initially covered with a tray 119
of air impenetrable quality, so as to initially block
the gas stream from entering the cavities 11'. Thus,
gas pressure will then accumulate on the tray 119, while
the space thereunder remains at a low pressure. ~t this
stage the molten metal is poured into the inlet port 10',
and the tray 119 is readily meltecl away to enable the
molten metal to pass through the inlet port 10' under
a relatively large pressure gap. In this way, the flow
of the molten metal accelerates and penetrates more
deeply into the fine cavities 11'.
(7) The extra shaping crucible 106 illustrated
in FIGS. 12 and 13 can replace the mold 9 or 9' for mold-
ing a body of casting metal of irregular shapes to the
desirable form illustrated in FIG. 14.
(8) Referring to FIG. 18, a gas pressure
--19--
regulator 120 can be provided at the outlet of the gas
drain port 51, so as to control the internal pressure oE
the molding chamber 8, whereby such internal pressure is
not reduced to become negative but, rather, is kept
positive. This eliminates the possibility of pinholes
and blowholes forming in the cast product. In this case,
it is required that the internal gas pressure in the
heating chamber 1 be kept relatively high.
Other modifications and variations of the pre-
ferred embodiments can also be made without departing
from the spirit of the present invention.
