U.S. patent number 3,788,382 [Application Number 05/301,158] was granted by the patent office on 1974-01-29 for vacuum metal casting apparatus.
Invention is credited to Arnold Daniel, Joseph Burdette Richey, II.
United States Patent |
3,788,382 |
Daniel , et al. |
January 29, 1974 |
VACUUM METAL CASTING APPARATUS
Abstract
A metal casting apparatus especially adapted for the rapid
melting and casting of small charges of metal, utilizing a
metal-heating crucible in communication with a mold contained in a
heated enclosure. The metal charge within the crucible is rapidly
heated to melt the same to bring the molten metal to optimum
casting temperature, whereupon the molten metal in the crucible is
subjected to sufficient pressure differential to force the molten
metal through a small opening in the crucible into the mold.
Inventors: |
Daniel; Arnold (Cleveland
Heights, OH), Richey, II; Joseph Burdette (Cleveland
Heights, OH) |
Family
ID: |
26785824 |
Appl.
No.: |
05/301,158 |
Filed: |
October 26, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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92583 |
Nov 25, 1970 |
3712364 |
Jan 23, 1973 |
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Current U.S.
Class: |
164/151.4;
164/255; 164/155.6; 164/4.1; 164/250.1 |
Current CPC
Class: |
A61C
13/20 (20130101) |
Current International
Class: |
A61C
13/20 (20060101); B22d 027/16 () |
Field of
Search: |
;164/4,62,63,65,80,150,155,255,256 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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798,772 |
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Jul 1958 |
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GB |
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991,240 |
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May 1965 |
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GB |
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Primary Examiner: Annear; R. Spencer
Attorney, Agent or Firm: Donnelly, Maky, Renner &
Otto
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a division of our copending United States
application Ser. No. 92,583, filed Nov. 25, 1970, now U.S. Pat. No.
3,712,364, granted Jan. 23, 1973.
Claims
We, therefore, particularly point out and distinctly claim as our
invention:
1. Metal casting apparatus comprising an insulated enclosure, a
mold within said enclosure, heating means for heating the interior
of said enclosure to heat said mold to optimum casting temperature,
a metal-heating crucible above said mold having an opening in
communication with said mold within said enclosure, additional
heating means for rapidly heating a metal charge within said
crucible to melt the same and bring the molten metal to optimum
casting temperature within said crucible, said opening in said
crucible being too small to permit ready passage of such molten
metal therethrough, means for sensing the temperature of the molten
metal in said crucible, and means for subjecting such molten metal
in said crucible to sufficient pressure differential to force such
molten metal through said opening into said mold after the molten
metal has reached such optimum casting temperature.
2. The apparatus of claim 1 wherein said additional heating means
for rapidly heating the metal charge in said crucible comprises
electrical contact plates connected to said crucible for passage of
electric current through said crucible and through the metal charge
to cause resistance heating of the latter.
3. The apparatus of claim 1 wherein said crucible is vertically
split to provide split portions of electrically conductive
material, with insulating material separating said split portions,
and said additional heating means for rapidly heating the metal
charge in said crucible comprises means for passing an electric
heating current between said split portions through the metal
charge contained therein to melt such metal charge.
4. The apparatus of claim 3 further comprising means for pressing
such metal charge against said crucible split portions to enhance
passage of such electrical current through such metal charge
rapidly to heat the same.
5. The apparatus of claim 3 further comprising a holddown member
mounted to bear downwardly upon the metal charge in said crucible
to insure good electrical contact of such metal charge with both of
said crucible split portions to enhance passage of such electric
current through such metal charge rapidly to heat the same.
6. The apparatus of claim 5 wherein said hold-down member is also
electrically conductive and is connected to an electric current
source for passage of current between said hold-down member and
said crucible split portions through such metal charge.
7. The apparatus of claim 5 wherein said hold-down member is
resiliently mounted for downward pressure upon such metal charge,
and stop means are provided for limiting downward movement of said
hold-down member to prevent direct contact of said hold-down member
with said crucible split portions.
8. The apparatus of claim 1 wherein said mold is a suction mold,
and said means for applying such pressure differential to force
such molten metal through said opening in said crucible into said
mold comprises a suction pump for applying suction to said mold to
draw such molten metal from said crucible into said mold.
9. The apparatus of claim 8 further comprising clamping means for
clamping said mold in sealing engagement with the underside of said
crucible thereby to permit application of such suction to said
crucible through said mold.
10. The apparatus of claim 1 wherein the surface tension of such
molten metal is sufficient to prevent passage of such molten metal
through said crucible opening under the influence of gravity, and
such pressure differential is effective to overcome such surface
tension when applied.
11. The apparatus of claim 1 further comprising separate
temperature sensing means for sensing the temperature of said mold
and the molten metal in said crucible, signal means connected with
said mold temperature sensing means for signalling that a
predetermined desired temperature has been achieved in said mold,
means for activating said additional heating means, and electrical
control means responsive to a signal from said molten metal
temperature sensing means that a predetermined desired temperature
has been achieved in such molten metal automatically operative
thereon to activate said means for subjecting such molten metal to
sufficient pressure differential to force such molten metal through
said crucible opening into said mold as aforesaid.
12. The apparatus of claim 1 wherein said insulated enclosure has
an upper wall with an opening therein for receipt of said crucible,
and means are provided for clamping said crucible in place within
said opening.
13. The apparatus of claim 12 further comprising a removable cover
enclosing said crucible, means for admitting an inert gas to said
cover, and a vent for said enclosure.
14. The apparatus of claim 12 further comprising a vertically
reciprocable support for said mold within said enclosure, and means
for reciprocating said support to clamp said mold against the
underside of said crucible with said opening in said crucible in
juxtaposition to a sprue inlet in said mold.
15. The apparatus of claim 14 wherein said means for subjecting
such molten metal to sufficient pressure differential to force such
molten metal through said crucible opening into said mold comprises
a vacuum pump, a suction passage through said support leading to
said mold for applying suction to said mold to draw such molten
metal from said cricible rapidly into said mold, and means for
connecting said suction pump to said suction passage.
16. The apparatus of claim 15 wherein said support has a platform
on the upper end thereof for supporting said mold thereon, and
there is a sealing ring interposed between said platform and mold
around the outer periphery of said mold which serves to space the
underside of said mold slightly from the upper surface of said
platform to permit suction to be applied to the entire undersurface
of said mold.
17. The apparatus of claim 15 further comprising a cover over said
mold, a sealing ring interposed between said cover and mold to
provide an air-tight seal therebetween, said cover having a central
aperture therein in alignment with said opening in said crucible
and a sprue inlet to said mold, and a sealing ring interposed
between said cover and the underside of said crucible providing an
air-tight seal between said crucible and cover around said central
aperture.
18. The apparatus of claim 1 wherein said temperature sensing means
electrically senses the temperature of the molten metal charge in
said crucible.
19. The apparatus of claim 1 wherein said temperature sensing means
comprises an infrared radiation detector which is focused upon the
metal charge in said crucible to sense the temperature of such
metal charge by response to the infrared radiation of the
metal.
20. The apparatus of claim 1 wherein said additional heating means
comprises means for passing an electric heating current through the
metal charge within said crucible to cause resistance heating of
the latter to melt such metal charge.
21. The apparatus of claim 20 wherein said mold is a suction mold,
and said means for applying such pressure differential to force
such molten metal through said opening in said crucible into said
mold comprises a suction pump for applying suction to said mold to
draw such molten metal from said crucible into said mold.
22. The apparatus of claim 20 wherein the surface tension of such
molten metal is sufficient to prevent passage of such molten metal
through said crucible opening under the influence of gravity, and
such pressure differential is effective to overcome such surface
tension when applied.
Description
BACKGROUND OF THE INVENTION
Investment casting procedures have long been employed in the
production of investment castings of precious metals for use in
jewelry, dental inlays and bridges, and the like. The present
system is particularly advantageous when very precise control of
the casting operation is required in order that the casting may be
of exact predetermined dimensions and alloy composition.
In the conventional production of dental alloy castings, an
investment mold is prepared about a wax model or pattern and the
mold is preheated to volatilize the wax and to bring the mold up to
the desired casting temperature. The achievement and maintenance of
such temperature during the casting operation is of considerable
importance inasmuch as both the mold and the casting tend to shrink
upon cooling and in order to obtain a finished casting of exact
predetermined dimensions it is essential that both the molten metal
and the mold be at proper temperatures when the molten metal is
introduced into such mold. In a typical operation, the mold has
thus been preheated and then transferred to a centrifugal casting
machine. The gold alloy charge is placed in the machine and heated
by means of an oxyacetylene torch to melt the charge, whereupon the
machine is activated and the molten metal forced into the mold
under the influence of centrifugal force. Under such circumstances,
it is obviously not possible to ensure that the mold is at the
precise optimum temperature at the moment the molten metal enters
the same and it is also not possible to ensure that the molten
charge itself is at an optimum temperature. Furthermore, the alloy
composition may be somewhat modified during the heating operation
and the charge may be contaminated by atmospheric gases and the
gases produced by employment of such torch. An appreciable excess
of the alloy must be provided requiring subsequent cutting and
grinding away of the metal sprue produced, and the entire operation
requires such a degree of skill and experience that many dental
offices prefer to send such work to specialist laboratories rather
than to perform the work themselves. This results in considerable
delay and increased expense, particularly when several castings
must be produced until one is achieved which is found to be
entirely satisfactory for the intended purpose.
It is accordingly an object of the present invention to provide a
self-contained unit wherein the mold need not be removed from the
heat bath prior to or during performance of the casting
operation.
It is also an object to provide a metal casting system and
apparatus for performing the same of small size which may be
operated from the ordinary 110 volt AC source available in all
dental offices and which will incorporate a control system to
ensure the automatic production of high quality castings without
the requirement of any special skills on the part of the
operator.
A further object is to provide a metal casting system wherein both
the molten metal and the mold are brought to the optimum
temperatures and the casting operation is performed very rapidly in
a manner to keep the molten metal charge uncontaminated and to
maintain the proportions of any alloy elements unchanged.
Other objects of the invention will appear as the description
proceeds.
To the accomplishment of the foregoing and related ends, the
invention, then, comprises the features hereinafter fully
described, the following description and the annexed drawings
setting forth in detail certain illustrative embodiments of the
invention, these being indicative, however, of but a few of the
various ways in which the principles of the invention may be
employed.
DESCRIPTION OF THE DRAWING
In said annexed drawing
FIG. 1 is an isometric view of a novel metal casting apparatus,
including associated control means, for practicing the method of
the present invention;
FIG. 2 is an enlarged vertical longitudinal section taken on the
line 2--2 of FIG. 2, but omitting the control panel;
FIG. 3 is a wiring diagram illustrating suitable control means for
the operation of such apparatus;
FIG. 4 is an enlarged exploded isometric detail view of the melting
crucible assembly of such apparatus; and
FIG. 5 is a wiring diagram of an optional modification of the metal
heating means.
DESCRIPTION OF THE INVENTION
In accordance with the invention, investment casting apparatus is
provided comprising an insulated enclosure or muffle having heating
means for heating the interior thereof to a high temperature. A
metal heating crucible is mounted in the upper portion of such
enclosure and means is provided to support a mold directly beneath
such crucible in clamping engagement therewith so that molten metal
produced in the crucible may be directly discharged into the mold
therebeneath. Suction means is applied to the mold to assist in
drawing the molten metal charge from the crucible into the mold
cavity, and electrical control means ensure that the various
operations are carried out at the proper times and at the proper
temperatures. The melting crucible may be enclosed within an inert
atmosphere to avoid any possibility of contamination of the molten
charge.
Now referring more particularly to said drawing and especially
FIGS. 1 and 2 thereof, the embodiment of the invention there
illustrated comprises a furnace or oven 1 desirably supported on
legs such as 2 and having an outer sheet aluminum shell or casing
3. Such casing is lined with a thick wall of refractory insulating
material 4 which encloses a refractory ceramic inner liner 5.
Nichrome heating elements 6 are interposed between such outer liner
4 and inner liner 5 in order to raise the interior of the furnace
to a high temperature. The front of the furnace is closed by an
insulated hinged gate or door 7 normally held in closed position by
means of counterweight 8.
A control panel 9 is carried by brackets spacing the same from the
end of the furnace, and a removable hood 10 is mounted on the top
of the furnace. Such hood may be connected, if desired, to a source
of inert gas such as cylinder 11 by means of flexible tubing 12,
admission of such gas (e.g. helium, nitrogen, or argon) to the hood
being controlled by means of hand operated valve 13.
Hood 10 is adapted to cover an opening in the upper side of the
furnace within which a metal heating crucible is received and
mounted. Such crucible is a vertically split graphite crucible
comprising half portions 14 and 15 (see also FIG. 4) separated by a
layer of inert refractory material such as asbestos 16 which may be
provided with a centrally disposed gap in the lower edge thereof to
serve as a sprue for the crucible; the two halves of the crucible
are thus electrically insulated from each other. In the preferred
embodiment illustrated in detail in FIG. 4 the sprue 17 is,
however, provided in one crucible half only, with the inner
surfaces of the other half and such asbestos divider being inclined
theretoward. Such sprue may, for example, be approximately 0.04 mm.
diameter. Accordingly, when the crucible blocks 14 and 15 are
assembled with the interposed insulating layer 16 they define a
crucible cavity the upper end of which projects above the upper
surface of furnace 1 and the lower end of which projects into the
interior of furnace 1. The graphite blocks 14 and 15 are
respectively backed by heavy sheet aliminum or copper contact
plates 19 and 20 to the upper edges of which electric power cables
21 and 22 are connected. Layers of electrical insulation 23 and 24
laterally enclose the crucible and contact plates so that the two
halves of the crucible are not only electrically isolated from each
other but also from the supporting upper furnace wall.
An optional, but ordinarily highly preferred device is also
provided within hood 10 to bear downwardly upon a metal charge to
be melted within the crucible and thereby ensure better contact
between the two half sections of such crucible and the charge which
bridges therebetween. Such device may comprise a bracket 25 mounted
on the upper surface of the furnace and carrying a vertically
disposed plunger 26 directly axially reciprocable above the sprue
of the graphite melting crucible.
A compression spring 27 serves normally to maintain such plunger in
depressed condition so that the graphite rod 28 coaxially secured
thereto may thus bear firmly downwardly upon the charge in the
crucible. Plunger 26 and rod 28 may be temporarily manually
elevated when it is desired to place a new charge within the
crucible by depressing lever handle 29.
A circular metal, e.g. stainless steel, jig or platform 30 is
supported within the furnace chamber or muffle 31 on the upper end
of vertically reciprocable metal tube 32. The upper end of such
tube opens to a centrally disposed orifice in the upper surface of
platform 30 and the lower end of such tube connects through an
elbow 33 of stainless steel tubing to vacuum hose 34. A manually
rotatable nut 35 is threaded on the lower projecting end portion of
metal tube 32 and held against axial movement by upper washer 36
interposed between such nut and the underside of the furnace and by
lower washer 37 interposed between such nut and the centrally
apertured spider 38 affixed to the underside of the furnace and
projecting downwardly therefrom. Accordingly, when nut 35 is thus
manually rotated, jig or platform 30 will be correspondingly
elevated or lowered within the furnace chamber.
The remaining elements of the assembly may best be understood from
the description of the operation of the metal casting system set
forth below.
OPERATION
The operation of this new metal casting system will first be
generally described, and then more specifically with reference to
the electric control system.
The usual wax pattern or model is prepared and embedded in a
suitable porous plaster mold 39 enclosed in the usual tubular metal
casting ring 40. Such mold may desirably initially be placed within
furnace chamber 31 laterally of platform 30 as shown at 40' for
preheating prior to performance of the casting operation. Such
preheating serves to volatilize and drive off the wax pattern, the
fumes being vented from chamber 31 through vents V, and to heat the
mold 39 to proper casting temperature. The door to the furnace will
then be opened and the operator will lift the mold onto platform 30
where it is supported on annular asbestos sealing ring 41 which
serves thus to space the underside of the mold slightly from the
upper surface of platform 30, thereby permitting suction
subsequently to be applied to the entire undersurface of the mold
through metal tube 32. In some cases, if the mold is not
sufficiently porous, it may be desirable to provide a very small
vent passage 42 leading from the mold cavity 43 to a layer of
porous asbestos 44 extending to the lower surface of mold 39 and
thereby permitting suction (e.g. 28-29 inches of mercury) to be
applied more directly to such mold cavity. The upper surface of the
mold is cratered at 45 to provide a funnel shaped cavity
terminating in a small sprue 46 leading to the mold cavity 43. A
centrally apertured sheet metal cover 47 fits over the top of the
mold and asbestos sealing ring 48, and a smaller asbestos sealing
ring 49 is interposed between such cover and the underside of the
crucible so that the sprue 17 of the crucible communicates directly
with a closed vacuum system.
A crucible assembly is clamped firmly in place by means of large
set screw 50 (which may be insulated from contact plate 19, or
which may merely be grounded by grounding of outer aluminum casing
3 of the furnace). The hand nut 35 will now be rotated to elevate
platform 30 to raise the mold and clamp cover 47 firmly against
sealing ring 49 interposed between the same and the underside of
the split crucible.
Cover 10 is now lifted, handle 29 is depressed to raise rod 28, and
the measured solid metal charge 51 is placed in the crucible.
Handle 29 is thereupon released so that rod 28 may firmly press
such charge downwardly against the respective crucible half
sections. Heating current may now be directed to the crucible
sections through leads 21, 22 for a sufficient period of time (e.g.
10 seconds) to melt the metal charge. The plunger assembly 26, 27,
28 will ordinarily be so dimensioned and proportioned that, even
when the crucible is completely empty, the lower end of rod 28 will
not extend entirely to the bottom of the crucible, it being desired
only that the lower end of such rod should bear upon the solid
metal charge with sufficient force to ensure adequate electrical
contact between such charge and the respective crucible sections.
When the charge has melted and been brought to optimum temperature
(as determined by thermocouple or infrared detector sensing means
described in more detail in connection with the discussion of the
wiring diagram, below) suction is applied to tubing 34 and
therefore through elbow 33, tubular support 32, porous mold 39,
mold cavity 43, and sprue 46 to the crucible sprue to overcome the
surface tension of the molten metal and rapidly draw the latter
downwardly into the mold cavity. Platform 30 may thereupon be
lowered, door 7 opened and the mold removed from chamber 31.
Alternatively, if it is desired to cool the mold more slowly in
order better to control the solidification phenomena which affect
the grain structure of the casting, the mold may be left within
such chamber for an extended period of time while the chamber is
very gradually cooled.
It will be apparent from the foregoing that the molten metal may
thus be very rapidly drawn into the mold cavity immediately upon
attainment of optimum temperature and with minimal opportunity to
absorb any impurities. As above explained, an inert gas may be
admitted to cover or hood 10 from cylinder 11 prior to performance
of the melting operation and, if desired, such inert gas may even
be admitted under sufficient pressure substantially to purge the
hood and crucible prior to elevation of the mold into clamping
relationship with the underside of the crucible. The inert gas
pressure within the hood may thereupon assist in ejecting the
molten metal from the crucible into the evacuated mold cavity if
the hood is tightly clamped down and the crucible is adequately
sealed at the top of the furnace.
Now referring more particularly to FIG. 3 of the drawing, the
operation of the metal casting system of this invention will be
described in greater detail, with particular reference to the
electrical control system. After the investment rings 40 and 40'
with their enclosed molds have been placed within furnace chamber
31, and door 7 closed, line switch 52 will be manually closed to
admit 100 volt AC heating current from main line 53, 54 to lines
55, 56 connected with the nichrome heating elements 6 in furnace 1.
Line 56 is connected through a standard temperature control unit 57
which may be preset to disconnect such line when a desired
temperature has been attained within the furnace. Temperature
sensing means in the form of the thermocouple 58 may be provided in
the furnace and connected with such temperature control unit 57 to
activate the latter. A neon pilot light 59 signals that power is
on.
Hand screw 35 is rotated to elevate platform 30 to clamp the mold
in place beneath the split crucible, and the metal charge 51 is
placed within such crucible and downwardly biased rod 28 is caused
to press thereon. Hood 10 is closed, clamped, and inert gas is
admitted thereto if desired.
When thermocouple 58 signals that the predetermined temperature has
been attained in furnace chamber 31, the temperature control unit
57 automatically cuts off or limits further power to the nichrome
heating elements 6 to maintain the constant preset temperature.
After sufficient time is allowed for the mold to reach optimum
temperature, the operator may thereupon initiate the melting cycle
by depressing the reset switch 60 on crucible temperature
controller 61. This energizes the coil of contactor 62 which in
turn applies line voltage to the primary of transformer 63, causing
very high current to flow through the secondary of such
transformer, the two graphite mold sections 14 and 15, and the
metal charge 51 bridging the latter. When the predetermined melting
optimum temperature of the molten metal produced has been sensed
and signaled by thermocouple 64 embedded in the crucible but
electrically insulated therefrom or by infrared detector D located
above the crucible, the temperature control unit 61 deenergizes the
coil of contactor 62 and energizes the coil of time delay relay 65
which in turn energizes the coil of normally closed solenoid valve
66 to open the latter and connect suction line 34 to vacuum for a
length of time determined by the time delay relay. This immediately
operates as above described to draw the molten metal through the
crucible sprue into the evacuated mold cavity 43. After a preset
time determined by time-delay relay 65, valve 66 automatically
recloses, cutting off the vacuum connection to the mold.
During application of the vacuum, the pressure differential is
effective to overcome the surface tension of the molten metal and
force the latter through the small crucible sprue.
It will be seen from the foregoing that a method of discharging
molten metal from the crucible has been provided wherein the outlet
or sprue leading therefrom is of sufficiently small size that the
surface tension of the molten metal normally serves to prevent
discharge therethrough by gravity, the suction which is then
applied at the proper moment affording a pressure differential
sufficient to overcome such effect of surface tension and cause the
molten metal to flow through the sprue. The crucible should, of
course, be of material not wettable by such molten metal.
The investment may be prepared in generally well-known manner for
the production of cast dental inlays, onlays, crowns, bridges, and
frameworks for removable appliances, utilizing dental casting gold
alloys in accordance with American Dental Association specification
No. 5 (Federation Dentaire Internationale Specification No. 7 for
Dental Casting Gold Alloy) Approved April, 1965; Effective April 1,
1966.
The wax pattern is prepared and a 12 gauge (Brown & Sharpe)
sprue pin is inserted in the bulkiest part of the pattern and a
conical sprue former is affixed to the other end of such pin.
Normally, the extent of such pin from the pattern to the sprue
former should not exceed three-eighth inch. The assembly is
carefully washed and allowed to dry.
A cylindrical brass or stainless steel casting ring is lined with a
circularized strip of asbestos, the ends of which overlap slightly.
Such ring may be 1 1/2 inch in length and 1 1/4 inch in diameter,
for example, and the asbestos liner should be about one-eighth inch
shorter than the ring, at each end.
The investment plaster (usually a gypsum composition) such as Kerr
Luster Cast or Cristobolite is mixed with water (e.g. 30 to 34
parts of water to 100 grams of powder), the plaster being sifted
into the water, until a creamy consistency is obtained. The pattern
is painted with the mixture, usually after first lightly painting
it with a wetting agent, and inverted and placed within the ring
which is then filled with the same mix.
After being allowed to set for about one hour, the burnout
operation may be commenced. The sprue former and sprue pin are
removed and the casting ring and investment may now be placed in
the furnace with the sprue hole in the down position. When the mold
has gradually been brought to approximately 500.degree.F it is
turned with the sprue upward and brought to casting temperature
(1,292.degree. F in reference to Cristobolite). It should desirably
be allowed to heat soak for about 20 minutes at this temperature
prior to casting.
The crucible is charged with ingots of gold alloy (about 2 to 4
pennyweight for inlays and crowns, and about 20 to 30 pennyweight
for large partial framework castings) and brought to fusion
temperature, this ordinarily being nearer the upper (liquidus) than
the lower (solidus) limit of the melting range.
The mold is clamped and the vacuum applied as described above. The
vacuum should be high, e.g. 28-29 inches of mercury, if possible,
(12-13 psi) and the diameter of the crucible sprue opening may be
16 gauge (Brown & Sharpe) or less to prevent premature
dribbling.
Now referring more specifically to FIG. 5 of the drawing, the
optional form of hold-down there illustrated may comprise a
graphite electrode 67 corresponding to rod 28 in function but also
being electrically connected to transformer 63. It must accordingly
be electrically insulated as at 68 in its support, and a portion of
the heating current will flow between the electrode and the
crucible sections.
The temperature sensing thermocouple 64 (FIGS. 3 and 4) may have
its leads extending through an elongated ceramic insulating member
69 inserted in one of the graphite crucible blocks with the
thermocouple itself embedded in refractory ceramic insulating
cement adjacent the metal fusing zone. Insulating pads 70 and 71
may be provided on the crucible projections such as 72 and 73 to
ensure that the crucible is insulated from the furnace under the
upward pressure of threaded tube 32 and also to provide a gas tight
seal around the crucible.
The infrared radiation detector D referred to above as a preferred
alternative to thermocouple 64 is a commercially available unit
semi-diagrammatically shown in FIG. 2 as mounted in an extension of
bracket 25. Such detector (preferably the silicon type) is clamped
at an angle to focus upon the charge 51 in the bottom of the
crucible and thereby is enabled to sense the temperature of such
charge by response to the infrared radiation of the metal (infrared
radiation pyrometry). The leads from detector D thus connect with
temperature controller 61 instead of the leads shown coming from
thermocouple 64 in FIG. 3.
The apparatus and method of the present invention accordingly
provide a metal casting system adapted to ensure the integrity of
the resulting casting as to composition, physicals, and dimensions
to a degree not heretofore readily attainable. Such apparatus is
not unduly expensive, and the mode of operation is such that it may
be carried out without the benefit of exceptional skill and
training.
* * * * *