US3692088A

US3692088A - Method and apparatus for investment casting

Info

Publication number: US3692088A
Application number: US94116A
Authority: US
Inventors: Frank M Kulig
Original assignee: Ney J M Co
Current assignee: Ney J M Co
Priority date: 1970-12-01
Filing date: 1970-12-01
Publication date: 1972-09-19
Anticipated expiration: 1989-09-19

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.

Description

[ 51 Sept. 19, 1972 United States Patent Kulig [54] METHOD AND APPARATUS FOR Primary Examiner-Robert D. Baldwin INVESTMENT CASTING Attorney-Peter L. Costas [57] ABSTRACT A casting machine adapted for the manufacture of [72] Inventor:

[73] Assignee: The J. M. Ney Company, Bloomfield Conn 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 221 Filed: Dec. 1,1970

21 Appl.No.: 94,116

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 x l mw l md 42 62 1 ,2 54 a 5 5 0M M23 1 s 2 22 6B% 4 mm 6 ml 1 "r mmm L m C d sum UIF .11] 2 00 555 [ll [56] References Cited UNITED STATES PATENTS operate the vacuum as well as the produce movement of the support member.

1,469,282 10/1923 St0rz.....................l64/DIG.4 1,644,543 10/1927 Richmond .................l64/255 16 Claims, 3 Drawing Figures ACCUMULATOR PATENTEDSEPIS I972 3.692.088

sum 3 or 3 By K /QZQW METHOD AND APPARATUS FOR INVESTMENT CASTING 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 l 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 materialused to provide the pattern and sprues and to bond the refractory material into a porous mold. It is the practice to form themold cavity in a completely enclosed relation within the investment mold, with only the very small sprueleading 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 castingsin 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 theend 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 as sociated molding member. Transport means on the frame selectively raises and lowers the support member relative to a heating @member carried by the frame 0 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 operationof the transport means. The heating member has a gas burner adjacent the sealing .duit 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, andto facilitate flow of molten metal from the crucible portion into the mold portion of theassociated 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 saidburner and raising the support member to bringthe 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 combustiongases 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 7 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 framegenerally 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 l6 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 4060 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 anaperture 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 actuatedburner 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 havinga float (not shown) which is buoyed upwardly in a tapered tube (not shown) against the force of gravity by the moving gas. The gas supply86 in the preferred embodiment is external to the machine and may be a city gas line having aminimum 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 oxygensupply 92. The valve83 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 83are independent although the solenoid actuation and pneumatic operation are accomplished concurrently by the same mechanism. The flowmeter 89 is similar to the flowmeter84, 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. Aminimum 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 regulator61 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, normallyclosed 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 ac cumulator43 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 accumulator43 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 ap paratus 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 portsSlb and 510 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 th switches valves and control mechanisms shown in FIGS. l-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 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 ll 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 circuitryof 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. 1

The energization of the solenoid 83a of the pilot ac tuated 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 may be extinguishes by depressing the Torch Off button 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 l74a 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 1720 each take 30 seconds per revolution. Contacts 172a are closed between the 2 and 360 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. a

With the initiation of the timer cycle, contacts l72b also close from the 2 to 360 positions and, upon subsequent momentary closure of the contacts of the Cast Start switch 158 the relay coil 174a is energized which causes contacts 174!) to close and supply power through the timer contacts 172b to the solenoid 510 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 l74a 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 and 360 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 1720 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 1580 located within the Cast Start button 158 and also to the solenoid 42a of the valve 42 which thereupon opens to connect the accumulator 43and vacuum pump 44through aperture 34 of the piston 26 to the casting ring 23. The closing of the limit switch 176 also armsthe contacts l72c 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 isapplied 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 apparatuslends itself to utilization with different sizes of castingrings 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 madewith 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 r 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 usedin 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 citygasand oxygen, acetylene and oxygen, or othervarious mixtures of combustible gases. To further reducethe 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' moltenmetal in the crucible portion to furtherlimit 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 .simpleand easy to operatecasting machine capable of producinghigh quality castings in a minimum amount of time. Themechanism provides a rmeans for casting which minimizes the problems and dangers of handling hot metal and insures the quality of .the resulting castings by minimizing oxidation thereof.

lclaim: 1. [n 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;

. 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

. 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 thesupportmember 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 r the lowered position of the supportmember which may bethereafter 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 port-ion intothe 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 as- 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.

Claims

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.

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.

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.