US2125080A - Founding apparatus and method - Google Patents

Description

.Ey 26, w3- A. W. Mmmm 29mm@ FOUNDING APPARATUS AND METHOD Filed May 13, 1937 2 SheetsnSheet l INVENTOR, .Alberti W.' Merrick BY 7i My 26, E938. A. w. MERRHCIK FOUNDING APPARATUS AND METHOD Filed May 13, 1937 2 Sheets-Sheet 2 INVENTOR.

Alber! W Merrie/f Patented Julyv 26,` 1938 UNITED STATES PATENTv QFFICE FOUNDING APPARATUS AND METHOD Application May 13, 1937, Serial No. 142,354

16 Claims.

My present invention relates generally to. founding, and has particular reference to an improved founding apparatus and method.

It is a general object of my invention to provide a founding apparatus which is particularly useful for small-scale founding operations, and which is unusually efficient in permitting metals and alloys-including those which are extremely susceptible to oxidationto be melted in clean and oxide-free condition.

The present invention is of particular utility in the founding procedures involved in the manufacture of metal dentures and denture parts, or similar small castings, but it will be understood that certain phases of my invention are not necessarily restricted to any specific casting operation.

'I'he molds used in the manufacture of dentures and denture parts are relatively small, and the mold charges are correspondingly small, thus presenting certain problems which do not arise in connection with large-scale casting operations. One of the customary procedures is to place the small charge of metal in the sprue of the mold; reduce it to a molten state by a blow torch or the like; and then force the molten metal into the mold by rotating the mold and driving the charge into it by centrifugal force. Certain alloys commonly employed for dentures and the like require a more uniform heating than that which is capable of accomplishment by this relatively crude method; and certain alloys manifest their desirable qualities to a better extent if they are shielded from contact with the 5 atmosphere during the melting and casting procedures. Moreover, in working with relatively small mold charges, it is sometimes extremely diiiicult, by ordinary methods, to introduce minor ingredients where such ingredients are of low melting point and readily susceptible to oxidation.

In accordance with my present invention, I am enabled to provide an apparatus and a method which accomplishes a more efficient melting of the metal under non-oxidizing conditions; which permits an unusually accurate control of temperature; and which effects a more uniform heating of the molten charge. My present apparatus and method also permits minor ingredients, even of the readily oxidizable types, to be introduced into the melt in accurately controllable quantities. Of outstanding importance is the possibility, by my present invention, of introducing and driving the molten charge into the mold without undesirable contact with the atmosphere and at the most propitious moment so far as the temperature, uniformity, and cleanliness of the charge is concerned.

One of the features of my invention lies in the employment of a closed crucible which is 5 heated from the midportion thereof and adapted to be rocked around an axis which passes through the crucible. 'I'his subjects the metal charge, in the most efficient manner, to the action of the applied heat, and permits the charge to be gently 10 agitated so as to subject it to the heating action of successive portions of the crucible wall. Preferably, but not necessarily, the crucible has a spherical interior and is capable of rocking and rotation around one of its diameters as an axis. 15 This type of rocking furnace is not new, per se, but my present invention provides for certain improvements whereby the use of such a furnace, for small-scale work and in a complete founding operation, is made possible.

In accordance with my invention, a carbon monoxide or other non-oxidizing atmosphere-is maintained within the crucible during the melting procedure; and means are provided'l for feeding the molten charge directly into the sprue i a mold while maintainingv such atmosphere around the charge, the latter being finally impelled into the mold.

One way of carrying out the invention lies in providing a passage in the crucible from the interior to the exterior thereof; providing a means for removably securing a mold to the crucible with the sprue of the mold in registry with said passage; and causing the molten charge to be driven into the mold by a blast of gas pressure introduced into the crucible, and thence through the passage to the sprue, at the proper moment.

Another and preferred method of carrying out the present invention lies in the provision of an arrangement for rotating the crucible bodily around an axis that passes through the crucible at a speed which is sulciently great to impel the molten charge into the mold by centrifugal force. Such bodily rotation of the crucible is effected at the proper time, i. e., after the molten stantially along the line 2--2 of Figure 1,v showing a mold in association with the crucible;

Figure 3 is a view similar to Figure 2, showing the parts in the relationship they assume at the moment when the molten charge is fed directly to the sprue of the mold;

Figure 4 is a fragmentary elevational view taken substantially in the direction of Figure 1, showing a detail of the automatic furnace-rotating mechanism;

Figure 5 is a fragmentary view taken from the left of Figure 4;

Figure 6 is a view similar to Figure 3, illustrating a modification; and

Figure 7 is a fragmentary view similar to the midportion of Figure 1, illustrating a further modication.

In accordance with my invention, a crucible i0 is mounted for rotation about a horizontal axis. In the illustrated embodiment, I have shown the crucible with a` substantially spherical interior, mounted for rotation about a horizontal diameter. 'Ihe crucible proper is surrounded by a mass Il oi heat-insulating material, the latter being enclosed within a substantially cylindrical metal shell I2. At its ends, the shell I2 abuts against metal end walls i3 and i4, the latter being rigidly secured together by the tie rods I5. 'Ihe end walls i3 and i4 have .portions i6 and i1 which serve as journals mounted for rotation within suitable bearings i8. 'I'he latter may be supported in any suitable or desired manner upon rigid stanchions or pedestals lil or the like.

In accordance with my invention, a focal source of heat is arranged at a midportion of the crucible. Preferably, but not necessarily, the heating instrumentality projects into the crucible I0 along the axis of rotation. In all of the figures, except Figure 7, I have shown the preferred construction consisting of opposed carbon electrodes. These electrodes are designated by the reference numeral 20 in Figure 1. 'I'hey are not intended vto rotate, and they are, therefore, preferably mounted within insulating bushings 2| which are secured against rotation. For example, the bushings 2| may be securely engaged with the bearings II, either by a frictional drive ilt or by any other convenient method of assembly. f

'Ihe electrodes form the elements of a carbon arc, and suitable means (not shown) not only secures the electrodes against rotation, but permits the electrodes to be moved toward and. away from each other so as to produce the desired arc. The source of heat for the crucible is thus located at a midportion oi' the crucible, preferably at the approximate center of the crucible, and this is a highlydesirable condition. Extending from the interior of the crucible I0 to the exterior of the shell i2 (this entire unit being referred to hereinafter and in the appended claims as the crucible) is a passage 22 which is arranged substantially in a plane transverse to the axis of rotation. 'I'his passage is preferably tangential with respect to the interior of the crucible, and it terminates at its outer end in a plate 23 to which a mold 24 may be applied.

I have illustrated a denture mold 2l of typical character, the same being a substantially cylindrical body, with the mold cavity 25 and the gates or passages 26 converging toward a sprue 21.

Means are provided to secure the mold 24, removably, to the crucible itself, and I have illustratively shown one way of accomplishing this. A plate 28 is applied to the outer end of the mold 2l, and threaded bolts 23 extend between the* plates 23 and 2l so as to permit the tightening of wing nuts 3l to press the plates toward each other.

Before describing the founding procedure in its entirety, I will point out that the crucible is adapted to be rotated by means of a pulley 3| secured, as at 32, to one of the journal portions i1, a pulley belt 33 extending to a suitable driving source such as a motor 34 (Figure 4). The motor derives its power from an electric circuit which includes the connection plug 35, the main switch 3i, and the auxiliary switch 31. The latter switch is preferably provided with the switch buttons 3l and 39, the former serving to estab- 'lish the circuit, the latter serving to disconnect the circuit. y

In accordance with my invention, the switch 31 is preferably secured to the framework Il of the furnace, in a position which cooperates with a cam carried by the end wall i3 of the crucible. 'I'his cam is shaped substantially as shown in Figures 4 and 5, and is so positioned that when the crucible is rotated into a predetermined angular position, thc cam contacts with the button 38 and actuates the latter so as to establish the desired electric circuit.

In carrying out a founding procedure, the furnace is rst heated up by establishing the necessary connections to the electrodes and adjusting the latter so that a carbon arc is produced and maintained. At the proper time, the metal to be melted is fed into the crucible through the passage 22, the exact amount being dependent upon the ultimate casting to be made.

The crucible is then gently rocked to-and-fro and, if desired, depending upon conditions, this may be accomplished either by hand or otherwise. The operator might, for example, grasp the belt 33 and by moving the latter thus cause a gentle rocking of the crucible. Thisrocking is effected through approximately 180, the approximate extent being designated by the curved arrow Il in Figure 2. This rocking subjects the molten charge to a gentle agitation, and the charge is brought successively into contact with different portions of the crucible wall, thereby becoming uniformly heated and utilizing the heat of the crucible with maximum efficiency.

Either before, during, or after the melting procedure, the mold 2l is secured'to the crucible so that it assumes the relationship shown in Figure 2.

After the charge has been melted to the satisfactory extent, the crucible is swung gently into the position of Figure 3, at which time the charge flows through the passage 22 into the sprue of the mold. As soon as this has been accomplished, the crucible is set into rapid rotation by connecting the circuit of the motor 3l, and thereupon the molten charge is driven into the mold by the centrifugal force that is engendered.

In order that the rapid rotation of the crucible may be initiated at exactly the right time, with a minimum of manipulations on the part of the operator, the cam 40 is so positioned with respect to the switch 3l that as the crucible reachesqthe position of Figure 3, the switch 31 is automatically closed; whereupon the crucible automatically starts to rotate at the desired relatively rapid `rate.

After the casting has been completed, which may be a matter of about ten seconds or so, the main switch 36 of the motor is manipulated to disconnect the circuit, and the crucible thereupon usual-way..

r electrodes are used. a .carbon monoxide atmos-'f phere is vautomaticallydeveloped and maintained v'ithin the crucible notwithstanding the, relatively small communicatiomthrpugh thepassage 22, :with the external air. The molten charge is M thusconstantly Ashielded from any oxidizing in; uence, and there is no opportunity for cooling v impeiledintothe molditself. A

or` for oxidationv between, the time that the charge is properly melted .and `the time when it is introducedinto the sprue of vthemold and then If desired, itwill be understood that any other neutral non-oxidizing atmosphere may be maintained within thecrucible, although vthe carbon monoxide atmosphere is .preferablebecause of its t automatic production by the carbon electrodes.

kThe process may be slightly modified, as shown vin Figure-6, yby replacing the rapid rotation of the .crucible `by the4 action of gas pressure. In the apparatus illustrated. in Figure 6, the reference numerals correspond to -those heretofore employed, and it will K- be understood that the crucible is capable `of rocking, as before. In this construction, however, al tube orconduit 42 extends intov .communication with the interior of the crucible,. ata point preferably alongside of the passage. 22. vAfter lthe metal has been suitably melted, and after the `crucible has been rocked into` a` position which introduces the molten charge into ythe sprue21', a vblast. of gas under pressure is fed ,throughthe tube 42, and this gas pressureforcibly `impels the molten charge from the sprue 2V into the moldcavity.

The gas that isemployed is preferably of carbon monoxide .or similar; neutral non-oxidizing `which the gas, is fed.. A, valve 45 i's mounted in the conduit 44, and the opening and closing of the valve 45v is controlled by, a handle or rod 46 which `maybe pushedin or out, relative to the valve. By mountingacam4'l on the crucible,

in the. properpOsition, itispossible to effect a .movement ofthe rod 4 6 to openlthevalve 45 at exactly the right time. "I he cam .4] is preferably so arrangedlthat it wilistart to operate upon the` rod ,4 6 just`- before themoldreaches the bottomiposition shown infFigure 6.] At ythis time,

the mo1ten; charge lis already in the sprue of the mold, and the subsequent introduction 4of the `gas forcibly v.ix'rip`e`l`sthfe molten Vcharge into lthe `mold,whilel the latter is in,the;position of Figure 6, Preferabiy, the r`end ofthev conduit 42 is provided witha cap 4BV havinga transparent portion through which the interiorofthe crucible may be viewed, during ,themelting procedure. If desired, ingredients of -the.harge may be intro- Y duced through lthe conduity -42l by removing the cap 48.

. In' Figure? Ifjhave illustratedainotliiledconfA struction in which the heating instrumentality is' in theform cfa relatively high-resistancelelei ment 48 ,supported between two `elec'ztrodes Sil. The .portion4 4,. m'ay o'r may not"beirintegrally formed with' respect ,t9/the lfitlodesliiy For example, if,l the 'electrodes 50 and the 'portion' '49 were integral, .they Imay be composed Lof silicon carbide or the'flilce, l and the portion maybe oi' Vreduced cross-sectional area.'` Alternatively, theele'ctrodesl 5D might'bec'ompo'sed of graphite or the like, and the portionl 49 may be a separate block or element held in positionbetweenfthe two electrodes; and in4 such an event theblcck 49 is of suitable high-resistance material. The result in either case is to produce a focal `Source of heat at the center` of the crucible,;the heat emanating from this source in Ath'e direction of the arrows of Figure '7.

Under certain circumstances, flame heating may be resorted to, providing a focal point of heat at the midportion of the crucible. Another possibility lies in. employing carbon-arc electrodes which are introduced into the crucible, side by side, `or at an angle to each other, or in any con-l venient and suitable manner. These electrodes may be completely dissociated from the crucible structure andmounting, and may be introduced linto the crucible through `the passage 22 or through any other suitableopening.

'I'he present furnace and the present mode of procedure are unusually eilicient. So lfar yas I am aware, no small-scale apparatus has ever be`- fore been successfully constructed which permits such accurate and uniform heating and the production of such clean and oxide-free charges. Merely by way of example, I will point out that the lpresent invention has been successfully employed with a variety of alloys having iron, nickel, or cobalt bases, and including as ingredients such readily oxidizable metals as chromium, tungsten, molybdenum, vanadium, aluminum, and beryllium. l

Since these ,ingredientsl are introduced in relatively small lumps itis inevitable that a certain amount ofsurface oxideis introduced into the crucible along with the charges. controlling the temperature,l this oxide `may be By carefully cobalt alloy, for example, the actual melting point cf the alloy (about 2400"v F.) is lower than the temperature at which the oxide isV reduced. The interior of, the c rucible may, however, be continuously inspected, and the heating may be caused to continue until the oxideis alleliminated. At such time', the molten charge presents a clean surface to View, and by the use 'of'an' optical pyrometer the temperature of thecharge can be accurately determined atany instant. `fI'ne non-.oxidizing latmosphere that is maintained around the charge during the4 melting procedure eliminates thel necessityv for any'V fiux, or slag blanket, and the molten charge is thus inthe purest and cleanest condition and at an accuratey ly observable temperaturewhen it is introduced into the sprueof the mold and `then immediately impelled intothe mold itself,

The present furnace permits me also to introi duce relatively small quantities'cf .minor ingred'ia charge that is melted in the open air is an extremely dilcult procedure, because of the low melting point and the susceptibility to oxidation. By means of the present invention, an accurately measured quantity of any such ingredient may be added to the molten charge without difficulty.

'Ihe present furnace and process are also of particular value in the melting and casting of the precious metal alloys,} especially where the resistor type of heating element is employed, because of the uniformity and accurate control of the heating, and the complete absence of contamination from products of combustion. Also, the agitation of the alloys by rocking the present furnace avoids segregation of the lighter ingredi-` ents, which is an 'undesirable phenomenon which commonly takes place.

In general, it will be understood that changes in the details, herein described and illustrated for thepurpose of explaining the nature of my invention, may be made by those skilled in the art without departing from the spirit and scope of the invention/ as expressed in the appended claims. It is, therefore, intended that these details be interpreted as illustrative, and not in a limiting sense.

Having thus described my invention, and Yillustrated its use, what I claim as new and desire to secure by Letters Patent is:

l. In a founding apparatus, a closed crucible mounted for rotation about a horizontal axis passing through the crucible, the cross-sectional conguration of the interior of the crucible, transverse to the axis of rotation, being substantially circular, said crucible having a tangential passage extending from the interior to the exterior thereof, carbon-arc electrodes extending into the crucible along the axis of rotation, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, and means for rotating said crucible at a speed sufficient to impel said molten charge into said mold by centrifugal force.

2. In a founding apparatus, a crucible having a substantially spherical interior, means for mounting said crucible for rotation about a horizontal diameter, said crucible having a tangential passage extending from the interior to the exterior thereof, said passage lying substantially .in a plane transverseA to the rotation axis, non-rotatable carbon-arc electrodes extending into the crucible along the axis of rotation so as to generate heat at substantially the center of said spherical interior, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, and means for rotating said crucible at a speed sufiicient to impel said molten charge into said mold by centrifugal force.

3. In a founding apparatus, a crucible having a substantially spherical interior, means for mounting said crucible for rotation about a horizontal diameter, said crucible having a tangential passage extending from the interior to the exterior thereof, said passage lying substantially in a plane transverse to the rotation axis, heating means extending into the crucible along the axis of rotation and adapted to generate a focal source of heat at substantially the center of said spherical interior, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, and means for rotating a, 125,0so

said crucible at a speed sufficient to impel said molten charge into said mold by centrifugal force.

4. In a founding apparatus, a crucible mounted for rotation about a horizontal axis, said crucible having a passage extending from the interior to the exterior thereof, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, a driving means for rotating said crucible at a speed suilicient to impel said molten charge into said mold by centrifugal force, and means automatically operable when the crucible is swung into a predetermined position for controlling the operation of said driving means.`

5. In a founding apparatus, a crucible mounted for rotation about a horizontal axis, said crucible having a passage extending from the interior to the exterior thereof, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, a driving means for rotating said crucible at a speed sufficient to impel said molten charge into said mold by centrifugal force, and means automatically operable when the crucible is swung into the spruefeeding position for initiating the operation of said driving means.

6. In a founding apparatus, a crucible mounted for rotation about a horizontal axis, said crucible having a passage extending from the interior to the exterior thereof, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be f K directly into said sprue, a driving means for rotating said crucible at a speed sufficient to impel said molten charge into said mold by centrifugal force, an electric switch for controlling the operation of said driving means, .and a cam carried by the crucible and automatically controlling the operation of said switch when the crucible is swung into a predetermined position.

'7. In a founding apparatus, a crucible mounted for rotation about a horizontal axis, said crucible having a passage extending from the interior to the exterior thereof, a mold, means for removably securing said mold to the crucible with the sprue in. registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, a driving means for rotating said crucible at a speed sufficient to impel said molten charge into said mold by centrifugal force, an electric switch for initiating the operation of said driving means, and a cam carried by the crucible and adapted automatically to actuate said switch 'when the crucible is swung into sprue-feeding position.

8. In a founding apparatus, a closed crucible mounted for rocking about a horizontal: axis passing through the crucible, said crucible having a passage extending from the interior to the exterior thereof, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, means for introducing a gas under pressure into the 'crucible for impelling the charge into the mold, and means automati- `cally operable when the crucible is rocked into a predetermined position for controllingi. the operation of said gas-introducing means.

9. The herein-described founding procedure which consists in melting a charge of metal and feeding the molten charge to the sprue of a mold while continuously maintaining a non-oxidizing atmosphere around the charge, and finally subjecting the mold to a rotation suciently fast to impel the charge into the mold by centrifugal force.

10. The herein-described founding procedure which consists in melting a charge of metal in a closed crucible heated from the approximate center thereof, rocking the crucible around an axis passing through the crucible so as to agitate the molten charge and subject it to the 'heating action of successive portions of the crucible wall, maintaining a non-oxidizing atmosphere in said crucible, feeding the molten charge to the sprue of a mold while maintaining said atmosphere around the charge, and finally impelling said charge into the mold.

1l. In a founding apparatus, a substantially enclosed crucible, said crucible having a passage extending from the interior to the exterior thereof, a focal source of heat within the crucible for melting a charge of metal within the crucible, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, and means for impelling said molten charge into said mold.

12. In va founding apparatus, a crucible mounted for rotation about a horizontal axis passing through the crucible, the cross-sectional configuration of the interior of the crucible, transverse to the axis of rotation, being substantially circular, said crucible having a passage extending from the interior to the exterior thereof, heating means extending into the crucible and adapted to generate a focal source of heat at substantially the center of said crucible, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, and means for rotating said crucible at a speed suiiicient to impel said molten charge into said mold by centrifugal force.

13. In a founding apparatus, a closed crucible mounted for rocking about a horizontal axis passing through the crucible, said crucible having a passage extending from the interior to the exterior thereof, heating means extending into the crucible and adapted to generate a focal source of heat at substantially the center of said crucible, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, and means for introducing a gas under pressure into the crucible for impelling the charge into the mold.

14. In a founding apparatus, a closed crucible mounted for rotation about a horizontal axis passing through the crucible, said crucible having a passage extending from the interior to the exterior thereof, heating means extending into the crucible along the axis of rotation and adapted to generate a focal source of heat at the approximate center of the crucible, a mold, means for removably securing said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, and means for rotating said crucible at a speed sufiicient t impel said molten charge into said mold by centrifugal force.

15. In a founding apparatus, a closed crucible mounted for rotation about a horizontal axis passing through the crucible, said crucible having a passage extending from the interior to the exterior thereof, heating means extending into the crucible along the axis of rotation and adapted to generate a focal source of heat at the approximate center of the crucible, said heating means comprising a high-resistance element, a mold, means for removably seeming said mold to the crucible with the sprue in registry with the outer end of said passage, whereby a charge of molten metal may be fed directly into said sprue, and means for rotating said crucible at a speed sufficient to impel said molten charge into said mold by centrifugal force.

16. In a founding apparatus, a closed crucible mounted for rotation about a horizontal axis passing through the crucible, said crucible having a passage extending from the interior to the4 exterior thereof, heating means extending into the crucible along the axis of rotation and adapt-

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