U.S. patent number 3,692,088 [Application Number 05/094,116] was granted by the patent office on 1972-09-19 for method and apparatus for investment casting.
Invention is credited to Frank M. Kulig.
United States Patent |
3,692,088 |
Kulig |
September 19, 1972 |
METHOD AND APPARATUS FOR INVESTMENT CASTING
Abstract
A casting machine adapted for the manufacture of precision
investment castings of the type used in dental applications has a
burner arm assembly including a torch and means adapted to
sealingly engage and pressurize a mold assembly. The mold assembly
is positioned on a support member and is heated by the burner
assembly, after which it is raised against the burner assembly.
Vacuum is drawn through the support member, and molten metal is
caused to flow from the crucible portion into the mold portion of
the mold assembly, and by also supplying gas under positive
pressure to the crucible portion to facilitate such flow. Control
means extinguish the burner assembly and operate the vacuum as well
as the produce movement of the support member.
Inventors: |
Kulig; Frank M. (Bloomfield,
CT) |
Family
ID: |
22243115 |
Appl.
No.: |
05/094,116 |
Filed: |
December 1, 1970 |
Current U.S.
Class: |
164/62;
164/DIG.4; 164/255 |
Current CPC
Class: |
B22D
17/14 (20130101); Y10S 164/04 (20130101) |
Current International
Class: |
B22d 027/14 ();
B22d 027/16 () |
Field of
Search: |
;164/62,63,65,255,DIG.4
;18/5.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Baldwin; Robert D.
Claims
I claim:
1. In a casting machine adapted for molding precision investment
castings in a mold assembly including a gas-permeable refactory
molding member having mold and crucible portions connected by at
least one passageway, the combination comprising:
a. a frame;
b. a support member having a mold assembly support portion
configured to carry and sealingly engage the end of the associated
mold assembly adjacent the mold portion thereof, said support
member having a conduit therein for drawing a vacuum through said
mold support portion and thereby the associated molding member;
c. transport means on said frame for selectively raising and
lowering said support member;
d. a heating member carried by said frame above said support
member, said heating member having a mold sealing portion
cooperatively dimensioned and configured to seal the end of the
associated mold assembly about the crucible portion thereof when it
is moved thereagainst by movement of said support member upon
operation of said transport means, said heating member having a gas
burner adjacent said sealing portion providing a flame and hot
gases for heating metal in the crucible portion of the associated
molding assembly, said heating member also having a conduit for
supplying a gas under pressure to the surface thereof inwardly of
said sealing portion; and
e. control means for extinguishing the flame of said burner, for
applying a vacuum through said conduit, for operating said conduit
to supply gas under pressure and for operating said transport means
to effect movement of the support member towards said heating
member, said control means extinguishing the flame of said burner
prior to completion of said movement of said transport means,
whereby metal in the crucible portion of the associated mold
assembly may be heated in the lowered position of the support
member which may be thereafter raised to bring the associated mold
assembly into engagement with said sealing portion of said heating
member to provide a sealed condition after extinction of the flame
of said gas burner in which sealed condition the applied vacuum and
gas under pressure cooperate to provide a pressure differential
which will draw molten metal from the crucible portion into the
mold portion of the associated mold assembly.
2. The casting machine of claim 1 wherein said heating member is
pivotally mounted on said frame for movement from a position in
substantially vertical axis alignment with said support member to a
second position wherein said burner is spaced farther from said
support member to permit facile and safe manipulation of the
associated mold assembly while the burner is ignited.
3. The casting machine of claim 1 wherein said control means
includes a timer and solenoid valves for sequentially extinguishing
said burner and raising said support member to bring said molding
member into sealing engagement with the heating member and through
the support member applying a vacuum to the molding member and
supplying a gas under pressure through said heating member to the
associated mold assembly.
4. The casting machine of claim 1 wherein said conduit for
supplying a gas under pressure contains selectively operable
pressure control means.
5. The casting machine of claim 1 wherein said heating member
includes conduit means for said combustible burner gases.
6. The casting machine of claim 5 wherein said conduits for the
combustible gases include selectively operable flow control
means.
7. The casting machine of claim 5 including a housing about at
least a portion of said frame with fittings thereon for external
connection to sources of combustible gases and vacuum, said
fittings being in fluid communication with said conduits for said
combustible gases and vacuum.
8. The casting machine of claim 7 wherein said housing is provided
with fittings for external connection to a source of gas under
pressure, said fitting being in fluid communication with a conduit
for supplying a gas under pressure to the surface of said heating
member inwardly of the sealing portion thereof and wherein said
control means operates said conduit to supply gas under pressure to
provide a positive pressure in the crucible portion of the
associated mold assembly.
9. The casting machine of claim 6 wherein said burner is configured
and dimensioned to provide a flame substantially blanketing the
crucible portion of the associated assembly whereby selective
operation of said flow control means for said burner gas conduits
may produce a reducing flame blanketing the crucible portion.
10. The casting machine of claim 1 wherein said transport means
includes a fixed cylinder on said frame and a piston in said
cylinder and carrying said support member.
11. The casting machine of claim 10 wherein fluid conduits are
provided to said cylinder on opposite sides of said piston and said
piston is movable in both directions within said cylinder by fluid
supplied through said conduits in response to operation of said
control means, said piston having a rod element extending from the
upper face thereof to carry said support member.
12. The casting machine of claim 1 wherein said heating member and
said support member each have a face with a recess therein
dimensioned and configured to receive one end of the associated
molding assembly, at least one of said members having sealing means
in said recess for sealing engagement with the molding
assembly.
13. The casting machine of claim 1 wherein said support member
includes a removable support element having a recess in its upper
surface to seat the associated mold assembly and a conduit
therethrough opening in said recess for application of vacuum to
the bottom surface of the mold assembly.
14. The casting machine of claim 13 wherein said mold support
element has a filter element in said recess overlying said
conduit.
15. In a method for investment casting, the steps comprising:
a. making a mold assembly having a refractory molding member with
mold and crucible portions interconnected by at least one
passageway, the passageway at said crucible portion being of small
dimension for bridging by molten metal at ambient pressure;
b. placing said mold assembly on a mold support with said crucible
portion disposed below a heating member having a gas burner;
c. placing metal within said crucible portion;
d. heating said metal in said mold assembly by a flame from said
gas burner to effect melting thereof, the flame and combustion
gases of said burner blanketing said metal to eliminate
substantially any oxidation thereof;
e. discontinuing said flame of said gas burner and moving said mold
support and mold assembly upwardly against said heating member into
sealing engagement therewith; and
f. applying a vacuum to said mold portion through said mold support
and supplying a gas under pressure through said heating member to
said crucible portion to provide positive pressure on the surface
of said molten metal in said crucible portion and a vacuum in said
mold portion to cause metal from said crucible portion to flow into
said mold support.
16. The method of claim 15 wherein said flame is discontinued
before said movement of said mold assembly upwardly.
Description
BACKGROUND OF THE INVENTION
Investment casting is widely used in the dental, jewelry, and other
fields for casting metal elements used in the production of various
types of members with sharp, thin edges or where high fidelity
reproductions are required. The method generally used in making the
mold employs a prepared cluster of the pattern(s) and one or more
sprues, and may include one or more intermediate runners, from the
sprue to the pattern(s) in some techniques. This cluster is
positioned in a metal casting ring which is filled with a
refractory investment material, and the casting ring is placed in a
furnace and fired to drive off completely the organic material used
to provide the pattern and sprues and to bond the refractory
material into a porous mold. It is the practice to form the mold
cavity in a completely enclosed relation within the investment
mold, with only the very small sprue leading to a cavity or recess
in the one surface of the mold material which serves as a crucible
portion in which the alloy is melted.
In order to force the molten metal through the gate and sprue
leading from the crucible portion in the investment mold, positive
pressure has been applied to the molten metal in the crucible
portion by means of previously compressed gas or an air compressor.
In some instances, a vacuum has been applied to the pattern side of
the mold to evacuate the air from the mold cavities, and it may be
sufficient to cause the molten metal to flow from the crucible
portion throughout the pattern portion in order to secure finer
detail in the finished product. The heating of the metal has
customarily been accomplished by a separate burner or other heating
means, oftentimes disposed at a distance from the point at which
the vacuum or pressure is applied. This results in problems of
handling the hot metal in the mold or the hot mold itself, in
increasing the time required to case the material and in various
other difficulties. The time delays and heating methods associated
with the prior art also increase the likelihood of oxidation of the
metal being cast, particularly of metal alloys containing readily
oxidizable elements.
Accordingly, it is an object of the invention to provide a casting
machine which is simple and easy to operate but which produces high
quality castings in a minimum amount of time.
It is another object to provide such a casting machine which
minimizes the problems associated with handling hot molds or
separate crucibles.
It is still another object to provide such a casting machine which
minimizes the likelihood of oxidation of the metals being cast.
A further object is to provide a method for casting dental alloys
into investment molds, which is facile, relatively safe and
relatively highly efficient.
SUMMARY OF THE INVENTION
It has been found that the foregoing and related objects can be
readily attained in a casting machine adapted for molding precision
investment castings in a mold assembly including a gas-permeable
refactory molding member having mold and crucible portions
connected by at least one passageway, the combination having a
frame and a support member having a mold assembly support portion
configured to carry and sealingly engage the end of the associated
mold assembly adjacent the mold portion thereof, the support member
has a conduit therein for drawing a vacuum through the mold support
portion and thereby the associated molding member. Transport means
on the frame selectively raises and lowers the support member
relative to a heating member carried by the frame above the support
member. The heating member has a mold sealing portion cooperatively
dimensioned and configured to seal the end of the associated mold
assembly about the crucible portion thereof when it is moved
thereagainst by movement of the support member upon operation of
the transport means. The heating member has a gas burner adjacent
the sealing portion providing a flame and hot gases for heating
metal in the crucible portion of the associated molding assembly,
and a conduit for supplying a gas under pressure to the surface
thereof inwardly of the sealing portion. There is also provided
control means for extinguishing the flame of the burner for
operating the conduit to supply gas under pressure, for operating
the transport means to effect movement of the support member and
for applying a vacuum through the conduit. The control means
extinguishes the flame of the burner prior to completion of
movement of the transport means, whereby metal in the crucible
portion of the associated mold assembly may be heated in the
lowered position of the support member which may thereafter be
raised to bring the associated mold assembly into engagement with
the sealing portion of the heating member to provide a sealed
condition after extinction of the flame of the gas burner in which
sealed condition gas under pressure and a vacuum may be applied to
evacuate air from the mold portion, and to facilitate flow of
molten metal from the crucible portion into the mold portion of the
associated mold assembly.
In its preferred aspect the casting machine heating member is
pivotally mounted on the frame for movement from a position in
substantially vertical axis alignment with the support member to a
second position wherein the burner is spaced farther from said
support member to permit facile and safe manipulation of the
associated mold assembly while the burner is ignited. The control
means includes a timer and solenoid valves for sequentially
extinguishing said burner and raising the support member to bring
the molding member into sealing engagement with the heating member
and through the support member applying a vacuum to the molding
member and also for supplying a gas under pressure through the
heating member to the associated mold assembly.
In its usual aspect, the conduit for supplying a gas under pressure
each contain selectively operable pressure control means and the
heating member includes conduit means for the combustible burner
gases having selectively operable flow control means. A housing
about at least a portion of the frame is provided with fittings
thereon for external connection to sources of combustible gases and
vacuum and they are in fluid communication with the conduits for
the combustible gases and vacuum. The housing is provided with
fittings for external connection to a source of gas under pressure
and the fitting are in fluid communication with a conduit for
supplying a gas under pressure to the surface of the heating member
inwardly of the sealing portion thereof and wherein the control
means operates the conduit to supply gas under pressure to provide
a positive pressure in the crucible portion of the associated mold
assembly. The burner is configured and dimensioned to provide a
flame substantially blanketing the crucible portion of the
associated assembly whereby selective operation of said flow
control means for said burner gas conduits may produce a reducing
flame blanketing the crucible portion. The transport means includes
a fixed cylinder on the frame and a piston in the cylinder carrying
said support member.
Fluid conduits will normally be provided to the cylinder on
opposite sides of the piston and the piston is movable in both
directions within said cylinder by fluid supplied through the
conduits in response to operation of the control means. The piston
has a rod element extending from the upper face thereof to carry
the support member. The heating member and the support member each
have a face with a recess therein dimensioned and configured to
receive one end of the associated molding assembly, at least one of
the members having sealing means in the recess for sealing
engagement with the molding assembly. The support member includes a
removable support element having a recess in its upper surface to
seat the associated mold assembly and a conduit therethrough
opening in the recess for application of vacuum to the bottom
surface of the mold assembly.
The method for investment casting in accordance with the invention
includes making a mold assembly having a refractory molding member
with mold and crucible portions interconnected by at least one
passageway, the passageway at the crucible portion being of small
dimension for bridging by molten metal at ambient pressure, placing
the mold assembly on a mold support with the crucible portion
disposed below a heating member having a gas burner, placing metal
within the crucible portion, heating the metal in said mold
assembly by a flame from said gas burner to effect melting thereof,
the flame and combustion gases of the burner blanketing the metal
to eliminate substantially any oxidation thereof, discontinuing the
flame of the gas burner and moving the mold support and mold
assembly upwardly against the heating member into sealing
engagement therewith, and applying a vacuum to said mold portion
through the mold support to draw air from the mold portion and
supplying gas under pressure through the heating member to provide
positive pressure on the surface of the molten metal in the
crucible portion and a vacuum in the mold portion to cause flow of
metal from the crucible portion into the mold portion.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a casting machine embodying the
present invention;
FIG. 2 is a partially diagrammatical, fragmentary side elevational
view in section of the casting machine of FIG. 1 with portions of
the assembly shown in phantom line for clarity of illustration of
internal construction and showing a mold assembly mounted
thereon;
FIG. 3 is a schematic circuit diagram showing the electrical
control connection for the casting machine.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Turning first in detail to FIG. 1 of the appended drawings, therein
illustrated is a casting machine embodying the present invention
and having a base housing generally designated by the numeral 2 in
which is disposed a support member assembly generally designated by
the numeral 4. The housing 2 generally encloses the base portion 14
of the frame generally designated by the numeral 12 with the
upright portion 13 thereof extending upwardly therefrom.
Pivotably supported on the upright portion 13 is the blowhead arm
assembly generally designated by the numeral 16 and having a cover
member 8 thereabout. The housing 2 has a multiplicity of controls
and indicators in the face 9 thereof, which elements will be
discussed in detail hereinafter. On other faces which are not seen
in FIG. 1 are various fittings (not shown) for connection to
sources of vacuum, air under pressure, fuel gas, oxygen and
electricity, as will be discussed in detail hereinafter.
Turning now in detail to FIG. 2 of the attached drawings, it can be
seen that the base portion 14 has a circular aperture 15 extending
through the upper surface thereof and that the mold support
assembly 4 registers therewith. The support assembly 4 includes a
casting ring locator 24 of generally cylindrical configuration
which has an aperture 21 extending therethrough with enlarged
diameter portions at either end thereof. The enlarged diameter
portion at the lower end thereof receives the upper end of the head
17 on the piston rod 26, and an annular sealing member 33 is
provided between the adjacent faces thereof.
The upper end portion of the aperture 21 has a series of four steps
of diminishing diameter inwardly from the upper face of the locator
24. Seated on the shoulder 27 defined by the second step from the
small diameter portion of the aperture 21 is a porous filter member
29 of generally circular configuration, the increased diameter
portion therebelow permitting air flow over the bulk of the area
thereof. Seated on the shoulder 25 defined by the outermost step is
a casting ring 23 of generally cylindrical configuration which
provides the outer shell for the mold assembly when the refractory
mold material is formed into a molding member therewithin.
As can be seen, the piston rod 26 extends through the piston 28 and
outwardly of both ends of the cylinder 30, the upper end portion
having the head 17 mounted thereon. The piston 28 is movable
upwardly and downwardly within the cylinder 30 by fluid under
pressure introduced through the fittings 45, 46 and acting on
either of the faces 36, 38 thereof. End caps 32 on the cylinder
have fittings 45, 46 thereon and the upper end cap 32 of the
cylinder 30 has a radially outwardly extending flange by which it
is mounted on the botton surface of the top wall of the base
portion 14 by fasteners (not shown). The piston rod 26 has a
coaxial aperture 34 extending therethrough and registering with the
aperture 21 of the casting ring locator 24, and its lower end is
provided with a fitting 47 for connection to a vacuum source as
will be described in detail hereinafter.
The blowhead arm assembly 16 is pivotally mounted on the upright
portion 13 of the frame 12 by means of the pivot pin 20 which
extends through the rigid arm 18, and it may be pivoted upwardly
from the operating position shown in FIGS. 1 and 2 to a second
position (not shown), conveniently at an angle of about
40.degree.-60.degree. to the horizontal. A spring loaded detent pin
assembly (not shown) between the arm 18 and upright portion 13
locks the blowhead arm assembly 16 in one or both pivoted
positions. Adjacent its free end, the arm 18 has an aperture 97
therein overlying the support member assembly 4 in generally
vertical coaxial alignment, and in that aperture 97 is mounted the
heating and pressurizing assembly generally designated by the
numeral 22 and conveniently referred to as the blowhead
assembly.
As seen in FIG. 2, the blowhead assembly 22 includes a generally
cylindrical bushing 99 seated within the aperture 97 and having a
radially outwardly extending flange 100 at its outer end which
seats against the upper surface of the arm 18. The coaxial aperture
103 therethrough is of enlarged diameter at the lower end thereof
and the length of the body portion of the bushing exceeds the
thickness of the arm 18 so as to project therebelow. On the portion
of the bushing 99 projecting below the arm 18 is mounted a
generally cylindrical closure element 102 which is mounted thereon
by threaded fasteners (not shown), and the closure element 102 has
an aperture 105 therein coaxial with and of the same diameter as
the enlarged portion of the aperture 103 in the bushing 99. In
turn, a retaining ring 104 is threadably carried by the closure
element 102 and has a radially inwardly extending lip 107 at its
lower end which serves to support and retain an annular sealing
gasket 106 of heat resistant material such as silicon carbide
material and which will provide sealing engagement with the casting
ring 23 when it is moved thereagainst.
Threadably seated in the upper end of the bushing 99 is an
elongated tubular member 68 which in turn is secured at its upper
end within the coupling 77, which has a fitting 66 thereon
communicating with the aperture extending therethrough. The
coupling 77 also supports coaxially within the aperture of the
tubular member 68 the elongated tubular body portion 81 of the
burner member generally designated by the numeral 80, and the
external diameter thereof is less than that of the aperture of the
tubular member 68 so as to provide an annular spacing therebetween.
At its lower end, the burner 80 has a flared nozzle 81 which is
disposed within the enlarged portion of the aperture 103 in the
bushing 99 and in the aperture 105 of the closure element 102 but
inwardly of the plane of the lower end of the retaining ring 104.
The tubular member 68 is secured in position within the bushing 99
by the jam nut 70 and a seal is effected therewith by the pressure
of the nut 70 acting upon the washer and annular seal assembly 71.
The abutting faces of the lower end of the coupling 77 and the jam
nut 70 are in turn sealed by the seal element 82.
The blowhead assembly 22 includes a number of fittings for supply
of gases thereto including the combustible gas fitting 72 and the
oxygen fitting 74, located on the upper end of the burner 80 and
coupled to the tubes or conduits 76 and 78, respectively. The
fitting 66 is in communication with the annular spacing between the
body portion 85 of the burner 80 and the tubular member 68 and is
coupled to the tube or conduit 67. The tube 76 is serially
connected to needle valve 88, a solenoid pilot actuated burner gas
valve 83, a flowmeter 85 and a combustible gas supply 86.
Preferably the valve 83 is a solenoid pilot actuated device
connected with tube 54 which supplies pneumatic pressure for
operation thereof. The flowmeter 85 is a variable area fluid flow
measuring device having a float (not shown) which is buoyed
upwardly in a tapered tube (not shown) against the force of gravity
by the moving gas. The gas supply 86 in the preferred embodiment is
external to the machine and may be a city gas line having a minimum
pressure of 6 inches of water.
The tube 78 connected to the blowhead assembly 22 fitting 74 is
serially connected to the valve 83, the needle valve 87, a
flowmeter 89 and an oxygen supply 92. The valve 83 which controls
the combustible gas supply to the burner 80 has separate fluid
ports for the oxygen. The flow paths of the combustible gas and the
oxygen in the valve 83 are independent although the solenoid
actuation and pneumatic operation are accomplished concurrently by
the same mechanism. The flowmeter 89 is similar to the flowmeter
84, and the oxygen supply 92 is external to the casting machine and
ordinarily would be a pressurized bottle although a piped utility
source may be utilized if available. A minimum oxygen pressure
supply of 10 psi is preferred.
The blowhead fitting 66 is connected through its tube or conduit 67
to the solenoid valve 64, gauge 62 and constant outlet pressure
regulator 61 to the air pressure line or conduit 54 which is
branched to provide air pressure to several elements of the
apparatus. As can be seen, the conduit 54 has a constant outlet
pressure regulator 58 before coupling to a source of pressurized
air 60. Preferably the gauge 62 is calibrated from 0 to 30 psi and
the valve 64 is a two-way solenoid actuated, normally closed
valve.
Turning now to the fittings of the piston assembly 28, and 30, the
fitting 47 at the lower extremity of piston rod 26 is coupled to
flexible tubing and is thereby connected through the gauge 41,
solenoid valve 42 and accumulator 43 to the vacuum pump 44.
Accordingly, a vacuum may be applied to the bottom surface of
casting ring 23 during and after upward movement of the piston rod
26. The gauge 41 preferably has vacuum graduations from 0 to 30
inches of mercury. The accumulator 43 preferably has a volume of
0.1 cubic feet to insure optimum operation and the solenoid valve
42 is a normally closed solenoid actuated valve. The vacuum pump 44
is preferably mounted externally of the apparatus with suitable
electrical and pneumatic connections thereto. Connected to the
fittings 45, 46 on the cylinder 30 are upper and lower air supply
tubes 48, 50 which are connected to a four-way solenoid actuated
valve 51. The valve 51 has a supply port 51a and two cylinder ports
51b and 51c which are respectively normally open and normally
closed. Two additional venting ports (not shown) are provided for
dumping pressure from either cylinder port 51b , 51c when the
supply therefor is closed. The air supply line 54 is connected to a
gauge 56, a constant output pressure regulator 58 and an air supply
60 which in the preferred embodiment is a laboratory air
system.
Turning now in detail to the interrelationship of the switches
valves and control mechanisms shown in FIGS. 1-3, the flowmeters
85,89 respectively measure the flow passed by needle valves 87, 88
whose handles 88a and 87a extend through the face 9 of the housing
2. An "Emergency Stop" button 138 and a "Power On" button 140 are
also provided. The pressure gauges 56, 62 and vacuum gauge 41
previously described are also mounted on the face 9. The vacuum
switch 150 is coupled with a vacuum pump light 152 indicating the
pump 44 is being supplied electrical power. Also provided on the
face 9 of the housing 2 are vacuum test switch 154, torch start
switch 156, cast start switch 158, and torch off switch 160.
During the initial operation of the casting machine, the blowhead
arm assembly 16 is pivotally moved about its pivot pin 20 to the
oblique position wherein it is approximately at 45.degree. with
respect to the horizontal in which position it is held by a detent
or locking pin (not shown).
The "power on" pushbutton 140 is depressed to energize the
circuitry of the casting machine by closing the single throw double
pole contact thereof which applies 115 volt electrical power to the
primary winding of a step down transformer 161 which supplies
reduced voltage, preferably about 14 volts, to the various control
circuitry of the casting machine. The secondary of the transformer
161 has connected across it a light bulb 140a which is mounted
within the "power on" pushbutton 140 and indicates when the
contacts of the switch 140 are closed.
Vacuum pump 44 is started by closing toggle switch 150 which also
connects power to the vacuum pump light 152. In the normal casting
sequence, the torch start switch 156 (a normally open momentary two
pole switch) is closed which energizes light 156a mounted within
the pushbutton 156, the solenoid 83a of burner gas valve 83, and
the holding coil 170a of a relay which is shown schematically only.
The contacts 170b thereof lock in the power to the light 156a and
solenoid 83a after the momentary operation of the "Torch Start"
switch 156.
The energization of the solenoid 83a of the pilot actuated valve 83
allows the servo air pressure in conduit 54 to open the valve 83,
thus allowing the flow of burner gases to the burner 80. The gases,
which in the preferred embodiment are city gas and oxygen, are
manually ignited and the flow of each is adjusted with handles 82a
and 87a to move needle valves 88 and 87 and thus vary the flow as
indicated by the flowmeters 85 and 89. The proportional rate of
flow of the two gases is important since a reducing flame is
desirably produced. More specifically, the use of a relatively
limited amount of oxygen results in a desirably volume of carbon
monoxide as a combustion product which blankets the metal in the
casting ring 23 and limits the oxidation of the metal being melted
and thereby aids in the production of a high quality casting.
With the blowhead arm assembly 16 still in the tilted position, a
casting ring 23 containing a molding member (not shown) of
refractory material providing mold and crucible portions and the
metal (not shown) to be cast is positioned on the casting ring
locator 24 on the shoulder 25 thereof. The blowhead arm assembly 16
is then pivoted to the horizontal position so that the flame from
the burner 80 impinges upon the metal to be melted which is within
the crucible portion of the mold assembly. It should be understood
that the piston 28 is in the lowered position at this time in the
cycle and, accordingly, the upper surface of the casting ring 23
and the blowhead arm assembly 16 are vertically spaced apart.
Heating is continued to melt the metal and produce any desired
degree of superheat. Should it be necessary to terminate the
procedure at this point, the burner 80 may be extinguishes by
depressing the "Torch Off" button 160 which interrupts power to the
solenoid coil 83a of the burner gas valve 83, and light 156a. The
deenergization of the solenoid coil 83a causes the closure of
burner gas valve 83 which stops the flow of burner gases to the
burner 80.
During normal operation, after the metal has been sufficiently
heated, the "Cast Start" pushbutton 158 will be depressed which
will have the same effect of terminating flow of gases to the
burner as obtained by depressing the "Torch Off" pushbutton 160.
However, additional contacts in the switch 158 also causes power to
flow to the motor of the timer 172 having three cam operated pairs
of contacts 172a, 172b, and 172c and the coil 174a of a relay shown
only schematically. The three cam operated pairs of contacts above
mentioned connect power in fixed sequential relationship to the
motor of the timer 172, cylinder solenoid valve 51 and the solenoid
valve 64 which directs pressure to the blowhead assembly 22 to
apply positive pressure on the molten metal in the mold assembly.
The three timer cams (not shown) corresponding to the three pairs
of contacts 172a, 172b, and 172c each take 30 seconds per
revolution. Contacts 172a are closed between the 2.degree. and
360.degree. cam positions and, as can best be seen in FIG. 3, the
momentary closure of "Cast Start" switch 158 starts the motor of
the timer 172 which continues to operate once started because of
power supplied by contacts 172a for the remainder of the 30 second
cycle time.
With the initiation of the timer cycle, contacts 172b also close
from the 2.degree. to 360.degree. positions and, upon subsequent
momentary closure of the contacts of the "Cast Start" switch 158
the relay coil 174a is energized which causes contacts 174b to
close and supply power through the timer contacts 172b to the
solenoid 51c of cylinder solenoid valve 51. Upon energization of
the solenoid 51d, the face 38 of the piston 28 is pressurized and
the opposite side of the cylinder 30 is vented to atmosphere so
that the piston 28 and piston rod 26 are driven upwardly.
Restrictors (not shown) in the cylinder limit the flow thereinto so
that the total upward stroke of the piston 28 takes about one half
second. The cylinder solenoid 51d will move to the lowered position
in the event the "Emergency Stop" button 128 is depressed which
interrupts power to the cylinder valve solenoid 51 a as well as to
the relay solenoid 174a which opens the "lock in" circuitry for
valve 51. The contacts 172c are also operated by a cam which closes
the contact between angular positions of 12.degree. and 360.degree.
or after about one second after actuation of the "Cast Start"
switch 138 until the remainder of the thirty second cycle is
complete. The function of the contacts 172c will be explained in
more detail hereinafter.
The movement of the piston 28 to the elevated position wherein the
casting ring 23 is brought into sealing engagement with the
blowhead assembly 22 closes a normally open limit switch 176 which
completes the power circuit to a light 158a located within the
"Cast Start" button 158 and also to the solenoid 42a of the valve
42 which thereupon opens to connect the accumulator 43 and vacuum
pump 44 through aperture 34 of the piston 26 to the casting ring
23. The closing of the limit switch 176 also arms the contacts 172c
which under the action of their cam will close about one half
second after the limit switch 176 closes. This switching sequence
insures that, in rapid succession, the burner 80 is extinguished,
the piston 28 is moved to its elevated position, the vacuum is
applied to the base of the casting ring 23 and then the positive
pressure is applied to the top of the casting ring 23.
A vacuum test button 154 is provided with contacts that apply power
only to the solenoid valve 42 for the purpose of checking the fluid
seal between the casting ring 23 and the casting ring locator
24.
As will be readily appreciated, the apparatus lends itself to
utilization with different sizes of casting rings or molding
members, conveniently by provision of a plurality of different
sizes of casting ring locators adapted to seat firmly the base of
the casting ring and to permit the drawing of a vacuum
therethrough. In the illustrated embodiment, the casting ring
locator merely sits upon the head of the piston rod and may be
readily removed to provide the desired interchangeability.
Although only the casting ring has been illustrated, it will be
appreciated that it is conventional to provide the investment
molding member therewithin by firing a refractory material
containing the pattern of the desired casting and the necessary
distribution elements from the crucible portion so as to volatilize
or burn off the organic material used therefor. It will be
appreciated that the casting ring provides a facile means for
supporting the investment molding member, for limiting air flow
radially outwardly and inwardly and for providing sealing surfaces
to facilitate the application of vacuum and pressure thereto.
However, other types of investment mold members may be employed in
which the permeability is blocked along the sides thereof, in which
case the sealing engagement may be made with the surfaces of the
upper and lower ends thereof.
Various means may be used to provide varying degrees of automation
for the casting machine of the present invention. For example, the
blowhead arm assembly may be pivoted by means of various servo
mechanisms; alternatively, a locking pin may be operated by a
pneumatic cylinder. The electrical circuitry may also be varied
widely as by the use of triacs and other solid state devices to
replace the relays presently employed. The transformer used in the
present embodiment may also be eliminated by the use of line
voltage to directly operate the various solenoid valves. The
materials used in the construction of the casting machine are
generally not critical except that those elements exposed to the
burner and its gases should be fabricated of materials resistant to
elevated temperatures.
The burner gases may be city gas and oxygen, acetylene and oxygen,
or other various mixtures of combustible gases. To further reduce
the oxidation of the metal being cast, it is possible to provide a
shield of inert gas about the burner by introducing inert gas
through the positive pressure line. Although the present invention
has been illustrated with respect to a jet-type burner, the burner
may be of a ring-type to produce a circular flame to surround the
molten metal in the crucible portion to further limit penetration
of air or oxygen although customarily the flame sufficiently
envelopes the crucible portion so that this is not necessary.
Thus it may be seen from the foregoing detailed specification and
drawings that the present invention provides a highly simple and
easy to operate casting machine capable of producing high quality
castings in a minimum amount of time. The mechanism provides a
means for casting which minimizes the problems and dangers of
handling hot metal and insures the quality of the resulting
castings by minimizing oxidation thereof.
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