US2017337A - Casting furnace - Google Patents

Description

Oct. 15, 1935. v BERRYMAN 2,017,337

CASTING FURNACE Filed July 2, 1932 2 Sheets-Sheet 1 INVENTORT ELME/P h. BERRYMA/V.

: i f w ATTORNEY Oct. 15, 1 935. E. H. BERRYMAN 2,017,337

I CASTING FURNACE 7 Filed 'July 2, 1932 2 Sheets-Sheet 2 V v I 2744/ 4? 4 //4// INVENTOR, ELMER If. BERRVMAN.

ATTORNEY Patented-Oct.1 5, 1935 UNITED STATES PATENT OFFICE 2,017,331 I css'mva memos I Elmer n. W, San Francisco, Calif.

Application July 2, 1932, Serial No. 620,616

3 Claims. (01. 22-691) This invention relates in general to casting furnaces and in particular to furnaces for making dental castings and the like. For purposes of illustration I shall describe its use in connection with dental castings, although itis to be noted that it can be used for manyother purposes, as, for example, baking materials such as porcelain, and in the manufacture of jewelry.

In dental operations the casting process comprises the following steps:-

1. Forming in wax or other plastic material a model or pattern of the object desired tobe reproduced by casting.

2. Attaching to the pattern a. sprue former to form a sprue for permitting the injection of the metal into the mold.

3. Enclosing. the pattern together with its attached sprue former in a mass of investment material, capable of setting in a short time and of withstanding heat without substantial change in dimensions.

4. Eliminating the wax from the investment by some form of applied heat, thus freeing the,

mold for the introduction of the metal through the sprue.

5. Fusing the metal in a crucible-like depres-.

sion in the investment which communicates with the interior moldby meansof the sprue.

6. Applying pressure to the molten metal to force it into all parts of the moldto insure the production of a sharp casting. The various methods of doing this include the-use of gravity, vibration, mechanicalr pressure, compressed air or gas, partial vacuum, centrifugal force and 3 steam. In the past there has been no provision made for maintaining the molten metal'at a uniform temperature during the time in which it was being injected through the sprue into the mold or investment, for invariably the source of heat was removed prior to forcing the metal into the mold. This has resulted in defective castings, for, on chilling, thefused metal becomes more or'le'ss sluggish and will not strictly conform to the mold. Care must also be taken not to run the temperature of the fused metal up too high,

for oxidation and volatiiization take place at elevated temperatures. This changes the composition of the metal and. renders it unfit for further use. Furthermore, in excessively superheating the gold or other casting material, the investment deteriorates,- resulting in rough surfaces in the mold, change in form of the latter, and in some cases intimate union of the investment with the casting.

In general it is the object of my invention to provide a furnace in which dental castings can be made under the influence of a differential pressure and without any substantial or detrimental change in the temperature of the fused 5 metal or other casting material until such inaterial has had ample time to strictly conform to the mold. V

Another object of the invention is to provide a furnace in which a casting material can be fused and made to conform to the desired mold while at all times in the presence of .a substantially inert, gas.

. A further object of the invention is the provision of a furnace which will permit observation at all times of what is taking place within it.

Still another object of myinvention is the provision of quickly attachable and detachable means for securing a dental casting ring to the floor or base of a furnace.

Another object of my invention is the provision of a furnace which can be operated under the influence of a vacuum either for melting and casting metals or forbaking porcelain or other materials.

- The invention possesses other features of advantage, some of which, with the foregoing, will be set forth at length-in the following description, where I shall outline in full that form of my invention which I have selected for illustra tionin the drawings accompanying and forming part of the present specification. In said drawings I have shown one form of my invention, but 4 it is to be understood that I do not limit myself to such form, since the invention asset forth in 3 Figure 3 is a horizontal section taken on they line 3-3 of Figure 2.

Figure 4 is a vertical section taken on the line 4-4 of Figure 1.

' Figure 5 is a horizontal section taken on the line 5-5 of Figure 2. Figure 6 is an elevation of one type of casting I ring which may be used in combination with my 5 furnace.

, Figure 'I isan elevation partly in section of a somewhat smaller type of casting ring.

Figure 8-is a wiring diagram illustrating how,

' by means of a suitable switch, a pair of heating elements such as shown in Figure 5 can be concylindrical metallic shell I, open at its lower endand closed at its up r end by a dome-shaped cover 2 secured there 0 by any suitable means as screws 3. The shell I is provided with a pair of rectangular, diametrically opposed lateral extensions 4 and 5 forming compartments 5 and 1 for housing the terminals of the heating elements to be described later. Plates 8 and 9, secured to the lateral extensions 4 and 5 by means of screws II, are used in conjunction with asbestos gaskets l2 and I3 to seal the compartments 6 and 1 from the exterior atmosphere. f

As shown in Figure 1 the shell I is provided on one'side with a vertically extending sleeve l4, tapped to accommodate set screws l5 and 16 by which it can be adjustably mounted on a post or cylinder -|1.. I Snugly fitted withinthe shell I is piece of refracto'rymaterial l8 having formed in its base a central chamber l9 and provided with-an upwardly extending bored neck 2|. Disposed over 7 this refractory material and surrounding the neck 2| is a layer of insulation 22 such as, for example, Diatex", a material composed essentially of diatomaceous earth. A disk of refractory material 23 provided with a central bore'24 is supported on the shoulder 25 formed in the upper end of the shell I, and serves to seal the refractory material 3 and the insulation 22 from the cover 2. Resting one. shoulder formed in thecentral bore 24 of the disk 23 and extending up into acentral tapped opening 28 provided in the cover 2, is a piece of tubing.21, and at each end of the tubing aretransparent mica or quartz disks 28 and 29.

This entire assembly, which may beltermed a 7 window, is clamped in position bymeans of the tubular nut 3| threaded in the tapped opening 25. It is to be noted that the tube 21 andnut ,3| are in line with-the bore in theneck 2| of the refractory material -l8, and that therefore an unobstructed view is provided from the upper side of the cover'2 to the interior of the furnace.

- Two diametrically opposed pairs of L shaped iron'conductors 32 pass through the refractory material l8, the insulation .22 and the refractory disk 23, and are threaded at each end to provide binding posts 33 and '34. Electric leads 95 and 38 are secured to the bindingposts 94 and pass through an air tight connection 31 sealed in the cover 2. securedto the binding posts 33 and depending therefrom are spring legves-38 provided at their lower ends with inwardly extending keepers 39. The leaves and keepers may be advantageously made of a high heat resisting steel such as Ascoloy. The inner ends of the keepers 39 are provided with conical sockets and extend into passageways-4| formedin the refractory 'material. By so orienting the heating elements the heat generated is un'iformlyfdissipated throughout the chamber I9, and furthermore,

they do not obstruct the line. of vision through the tube 21 to the chamber l8. As shown in Figure 5, the heating elements and ,43 may be I should be treated so as to form good conductors,

easily removed or replaced by merely unscrewing one or both of the plates 8' and 9.

Considerable care must be exercised in selecting a suitable material from which to make these heating elements, for they are required to oper- 5 ate at'rather elevated temperatures. An excellent material for this purposeis the composition known to the trade as Globar consisting mainly of silicon carbide. The ends of the elements while their central portions should have a suflicient resistance to furnish the required temperatures at the amperage and voltage for which the furnace is designed. One convenient method of concentrating-the heat generated to a limited 15 area is to decrease the diameter of the elements: midway between their ends as sliown in Figure 5. Platinum wire, which is often used for heating elements in muflles, has been found -to be altogether unsatisfactory for my purposes. 20

Secured within the lower flanged edge 44 of the shell I is an annular plate 45 made of any suitable refractory material and provided on its lower surface with a. pair of concentrically disposed beads 45, the purpose of which will be de- :5 scribed later. 4

The inner bore ofthe neck 2| is. connected with a source of pressure sucli'as a pressure tank 41by means of a pressure line 48 passing through the insulation22-and'the shell I. 30 Disposed below the-shell (see Figure. l) and directly in line therewith is a work supporting pinion 55, while the other end of the bracket carries a sleeve 58 mounted on the post or cylinder 5 I1, and is adjustably secured thereto by means of the set screw 6|. The pinion 59 may be rotated by means ,of a handle 92 and operates to elevate the pedestal 49 to any desired position where itcan-then be locked by means of a cam- 5 53. A pipe 54 connects the bore of the stem 52 with a two-way valve 65, which in turn com-' municates either with the atmosphere through a nipple 68, or with the vacuum cylinder |1 through a flexible-hose 51. The cylinder l1 may be placed 55 in communication with any suitable source of vacuum'by means of a. vacuum line 58 and 'is provided at its upper end with a vacuum gauge 59.

A pressure-reducing valve H is connected in the pressure line 48 between a reduced pressure 60 gauge 12 and a full pressure gauge 13, and the upper end of the pressure tank 41 is provided with i a master valve 14. The post or cylinder l1 and the pressure tank 41.are both mounted on a base .15, which may be provided with any'suitable 5 means for securing itlto a bench or table 15.

In Figure 6 there is shown a cylindrical casting ring 11 for making. large castings. The upper ends of this ring is provided with a neck 15 adapted to pass through the annular plate 45 7 and to permit, the beads 46 formed on the plate '45 toengage the asbestos gasket .19 carried on the upperface of the ring 11. It is to be noted that the engagement of the beads 46 with the gasket 19 seals the casting ring 11 to the plate 45.

2,017,337 The lower periphery of the ring 11 is supported upon the pedestal 49 and, as a. consequence, travels with it.

Asmaller casting ring 8| is shown Figure 7 ring is forced into engagement with an asbestos gasket 83 carried by the pedestal 49 thereby sealing the ring to the pedestal The pedestal 49 is then sealed to the under face of the plate 45 by elevating the pedestal until the asbestos gasket 84 carried on the upper face of the pedestalis pressed against the beads 48 of the plate 45.

As shown in Figure 7 the ring 8| contains an investment 85 which has formed therein the mold or impression 86, the sprue 81 and the cruciblelike' depression 88. It should be borne in mind inngiving consideration to the operation of the furnace above described that the investment is sumciently porous to permit the passage ofg as therethrough.

The wiring diagram shown in Figure 8 discloses a means whereby the heating elements 42 and'43 ay be used either in parallel or inseries and is t ought to be self-explanatory. When the switch 85 occupies the position asshown infull lines the heating elements are placed in series, whilein the alternative position of the switch they are placed in parallel. The switch 89 may be of any well known type andcan'be conveniently located on the sleeve I 4. 1

- When used as a dental casting furnace, an investment is first made in a ring such as shown in either Figures 6 or '7, the impression 86 and-sprue 81 being formed by applying heatv to the investment, which thereby eliminates the wax pattern and sprue forme r. --The investment material chosen is sucfr that its coeificient of expansion, taken in connection with the 'coeiflcient of ex-. pansion of the gold or other casting material used, substantially compensates for the slight shrinkage-of the gold upon cooling. This enables an inlay to be made having the identical dimensions of the wax impression. If a ring, such as shown in Figure '1, is used it is inserted within the collar 53 and locked therein by means of the bayonet and slot connection above described. As a rule, it is-desirable to pre-heat the furnace before inserting the investment. After the casting ring is locked in position, the pedestal 41 is elevated by meanspf the rack and pinion 55 and 56 until an efiective seal is-made between the beads 46 and the gasket '84. However, sometime before the furnace is closed and sealed in. this manner, a small piece of gold or other castingf material is placed in the crucible-shaped depression 88 formed 'in-the upper part of the investment. The

, window formed in the upper part of the furnace permits the operations within the furnace to be I watched at all times, and therefore there is no need of providing the furnace ,with an expensive thermopile to'indicate when the fusion point of the casting metal has been reached, It is of course to be understood that if for any reason it is desired to use a thermopile one can readily be installed without in any way changing the scope of my invention; The fusion of the casting metal can be conducted either in a vacuum or in the presence of a rarifl'ed atmosphere, which is naturally present due to the fact that the furnace has been pre-heated and is maintained at elevated temperatures, or in thepresence of an inert gas, such asnitrogen.

- mospheric pressure and the under side of the The furnace can be placed under super-atmcs-. pheric pressure by putting it in communication with the pressure tank 41 By connecting the line 48 with'the vacuum cylinder l1, instead of with thepressure tank 41, thegfurnace can be'placed under sub-atmospheric pressure. The molten metal is forced through the sprue into the mold or impression by creating a diflerential pressure between the exterior and'interior of the investment. This differential pressure may be obtained by maintaining the interior of the furnace at atmospheric pressure and the under side of the investment at sub-atmospheric pressure; by maintaining the interior of the furnace at super-atinvestment at atmospheric pressure, or by maintaining the interior of the furnace at super-atmospheric pressure and the under side of the Melting and casting under a vacuum has some decided advantages in dental work, for, in the first place, oxidation of the metal and its con- 30 sequent change in composition is prevented; and, in the second place, the resulting castings are free of occluded gases, and as a result are more dense and conform more strictly to their patterns;

The melting operation can. be carried on in a on-oxidizing atmosphere and under super-atmospheric pressure by filling the tank 41 with an inert gas sucl i as nitrogen, displacing the air con-- tained within the furnace by suitably adjusting the various valves and then closing all of the valves except those on the pressure line 48. When the casting metal has become molten it can be forced into the mold by simply opening the valve 55 to atmosphere.

The window permits the operations within the furnace to be watched at all times, and enables the operator to determine when the metal has become molten and is ready for casting. The casting operation can be effected in any of the ways aboge' described without decreasing .the b,

casting and maintaining the temperature'within thefurnace above the fusing point of the metal.

The operationof the furnace under a vacuum has been found to be advantageous for baking porcelain, the resulting product being denser and more elastic than porcelain baked in the brdinary way. Porcelain baked in my furnace under the influence of a vacuum has agglazed appearance, while porcelain baked. under identical conditions, with the exception that the process is carried on under atmospheric pressure, has 9. porous appearance and is farmore brittle.

When the casting or baking operation is complete, the, pedestal canbe lowered bymeans of the rack' and pinion and the material removed either as a finished product orfor further treatment.

It will be seenfrom the above description that which can be oper'ated'under the influence of 7 any type of differential pressure. The provision of a window permits the operations within the furnace to be under observation at all times, and the bayonet and slot connection between the casting rings and the furnace pedestal affords a ,meansfor making a quick and effective seal between these two members. This latter feature is of considerable importance for it materially cuts down the time of operation. The heating "elements are effectively located with respect to.

' said work supporting means; and means for sealing the .work supporting means against the open side of the chamber to form a substantially hermetic furnace.

2. A casting furnace comprising a chamber of refractory material having an open side; a heating element supported within the chamber; work supporting means adapted to be brought into registration with the open side of said chamber;

' a casting ring adapted to be sealed against said worksupporting means by a bayonet and slot connection; and means for sealing the work supporting means against the open side of said chamber. 1

3.A furnace'comprising a metallicshell provided with lateral compartments; a chamber of refractory material accommodated within said shell and having an opening in its lower side; a heating element located within said chamber and having-its terminals disposed adjacent said lat-' eral compartments; means for sealing said lateral compartments; work supporting means adapted to be brought into registration with the open side of said chamber; and means for sealing said work supporting means against the open side of said chamber. 4. A furnace comprising a chamber of refractor'y 'material'having an open side; a heating element located within said chamber and having. its terminals engaged in keepers secured adjacent the outer surface of said chamber; a shell surrounding said chamber and provided with openings adjacent said keepers; closures for sealing said openings; work supporting means adaptedto be brought into registration with the open side of said chamber and means for sealing said work supporting means against the open side of said chamber. I

5. A furnace comprising a metallic shell pro- 5 vided with lateral compartments; a chamber of refractory material accommodated within 'said shell and having an open side; keepers secured to the outer surface of said chamber and adja- .cent said lateral compartments; a pair of spaced m side of said chamber; and a window in line with said work supporting means through which the operations within the chamber may be observed. 20

6. A furnace comprising a chamber of refractory material provided with an opening in its lower side; a pair of spaced heatingelenients symmetrically supported within said chamber with respect to said opening; a pedestal assou ciated with said chamber and adapted to be sealed against its lower open side; a socket formed I ln-said pedestal and provided with bayonet slots; a casting ring seated in said socket and provided with bayonet pins adapted to be engaged in said a bayonet slots; a conduit communicating with said pedestal and means for creating a differential pressure between said chamber and said conduit.

'7. An air-tight furnace of the character 'described comprising a chamber of refractory ma- 3; terial having an opening in one side; aheating element disposed within said chamber; a cover detachabiy sealed against said opening and itself provided with an opening for establishing communication between the interior and exterior 40 of the furnace and means for securing a casting ring to the interior face of said cover in registration with the opening therein. I 8. A casting furnace comprising: an air-tight chamber of refractory material having an open side; a heating element supported within the chamber and across its ppenside;- work supporting means adapted to be brought into registra- 1 tion with 'the open side of the chamber; andv means for sealing said work supporting means 0 against the open side of the chamber to form a hermetic v furnace.

ELMER. H. BERRYMAN.

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