US3203680A - Crucible furnace - Google Patents

Description

ug- 31, 1965 M. H, BERNS 3,203,680

CRUGIBLE FURNACE Original Filed July 3, 1965 /Z/ VENTOR. W W;

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United States Patent 3,203,680 CRUCIBLE FURNA'CE Milton H. Berns, Hamburg, N.Y., assignor to Electro Refractories & Abrasives |Corporation, Buffalo, ',N.Y. Continuation of abandoned application Ser. No. 292,678, July '3, V1963. This application Oct. 6, 1964, Ser. No.

z claims. (ci. 263-11) This application is a continuation of my application Serial No. 292,678 of July 3, 1963, now abandoned.

The invention relates to Crucible furnaces having supports or so-called pedestal blocks for supporting Crucibles for melting non-ferrous metals in gas or oil iired combustion chambers. The customary practice has been to support crucibles for this purpose on solid blocks of material of a composition approximately that of the crucibles themselves although occasionally the bottoms have been sawed off of worn out and discarded crucibles and these have been packed with refractory cement, then inverted on the bottom of the combustion chamber, and crucibles for melting metal have been set thereon to support them, the complete bottom of the Crucible being fully supported on the pedestal.

As crucibles have been made larger in diameter, the wide area of contact between the base of the crucible and the top of the suporting block has become so great as to present access of heat to the central bottom area of the Crucible, resulting in slow heating and often in breakage of the crucible due to the sharp temperature gradient set up inwardly from the edge of the pedestal across the bottom of the crucible.

In order to remedy this condition it sometimes has been attempted to cut cross grooves perhaps an inch deep and an inch and a half wide across the upper face of the support block, intersecting at its center. Another approach has been to make the support block in vertical sections, either quarter circles or with sections of teardrop shape on which the crucible rests. None of these approaches has however been completely successful as the heat has not penetrated the grooves across the top of the pedestal effectively. The sectional blocks have not been much better in that respect and have also tended to become displaced and to fall over at inopportune times, making support of the crucible uneven and precarious as righting upset pieces in a hot blazing furnace is hazardous and irnpractical.

Aside from these troubles, however, the advantages of high production using crucibles of larger diameters has been so material that in recent years crucibles with base diameters of 15 and even 20 inches have been offered to the trade and have come into considerable use despite the aforementioned drawbacks, particularly in tilting furnaces where the crucible is not lifted out with tongs in order to pour the molten metal.

Accordingly one object of the present invention is to accelerate the melting of metal in crucibles of relatively large diameter.

Another object is to decrease the tendency of such crucibles to break due to uneven heating across the bottom thereof while metal is being melted in them.

Another is to provide a reliable and stable support under the Crucible while allowing free access of heat to the bottom of the crucible. I have found moreover that with supports of my design the eiciency of combustion in the furnace is increased, giving better oxidation of the fuel and greater metal output per unit of fuel consumed.

The principles of my invention may be more clearly understood by reference to the drawing in FIG. 1 which represents diagrammatically a vertical cross section of a furnace embodying my improvements having a combus- 323,68() Patented Aug. 31, 1965 l Ce tion chamber containing a Crucible resting upon one of my support blocks.

FIG. 2 is a perspective view of my support block.

In the drawing, 1 represents the outer refractory wall of a furnace surrounding the combustion chamber 2. This wall is customaritly made of silicon carbide or of iire clay with a silicon carbide lining, and in the present case would be tiltable to the right to pour metal, though for simplicity I have not indicated the tilting mechanism. Heat is applied by one or more burners 3 which supply gas or oil with air to burn the same in chamber 2 around the crucible.

The crucible 4 is Centrally disposed in chamber 2 with combustion space surrounding it on the sides and across the top where it is loosely covered by cover 5 with a vent 6 for escape of combustion gases. A lip or spout 7 integral with the crucible is shown on one side from which molten metal may be poured. A lateral support 8 is built out from wall 1 to support the crucible side while the assembly is tilted for pouring molten metal. This is indicated diagrammatically but the principle is well known in this art.

Under the crucible I provide my supporting member 9 which rests on the bottom of cumbustion chamber 2 and supports the crucible 4. The height of the support may vary as desired. For example, I have found that a cylindrical support of l5 inches outside diameter and 9 inches inside diameter and 7 inches high proved very satisfactory. The support should be approximately of the same outside diameter as that of the base of the crucible which it supports, although some leeway is permissible, that shown in FIG. l of the drawing being of slightly smaller diameter. It should be of such size as to support the crucible base near its periphery fairly fully although the support may have a horizontal cross section which is either circular as here indicated, or a geometric figure of four or more sides inscribed in a circle of the approximate diameter of the base of the crucible which it is to support.

The thickness of wall 1t) of support 9 should be suicient to support the weight of the crucible full of metal. For outside diameters of 15", I use wall support thickness of 21/2 or more and for 20" outside diameter I use supports 3 thick. I however keep the wall thickness small enough to make the internal diameter of the central cavity from 50 to 75% of the diameter of the base of the crucible which is to be supported on the pedestal.

Through the Wall 10 I provide openings 11, 12 and 13 connecting combustion chamber 2 with central cavity 14 of support 9. This cavity extends all the way from the bottom lining of the furnace up to the bottom of crucible 4. I providde any desired number of holes such as 11, 12, 13, of any desired shape leading through Wall 1t) and spaced evenly around support 9. These holes should be of such diameter as to permit llame from the combustion area 2 to travel freely through them into and through the central cavity 14 of support 9, restricting their spacing with respect to one another only sufficiently to make sure the solid portion of wall 10 between them is sufficient to impart wall strength enough to carry the crucible of molten metal without collapsing. I ind hole diameters of from 2 to 31/2 inches give good results, but do not limit my invention thereto. In general the distance between edges of adjacent holes should not be less than the thickness of Wall 10.

In the manufacture of my support blocks, l usually use the same compositions as are used for making crucibles, particularly Compositions bonded with carbon and high in graphite and in silicon carbide, such as those disclosed in Patents 1,356,939; 1,458,724; 1,438,726; 1,479,- 107 and 2,013,625. These have excellent strength and also have thermal emissivity in excess of at temperatures up to 2800 degrees F. These bodies are formed with pitch or tar and are readily molded in the plastic state as is well known in the art of Crucible manufacture. After they are made into rings or other hollow forms by means Well known in the art, the desired holes can be cut through them before tiring them, after which they are buried in a supporting sand or graphite and tired and glazed in the usual familiar manner.

While it would be within the scope of my invention to close off the bottom end of the central cavity 14, making it solid below the lateral holes 11, 12, 13, this in general requires additional material with no resulting benefit so I do not do so. The important thing is to make the upper portion tubular with free access of combustion gases to its interior and direct radiation of heat to the bottom of the Crucible.

When the Crucible to be heated is put in service, flames from combustion area 2 pass freely through the holes into the central cavity 14 of support 9. In so doing they heat the solid portions lt) of the support to incandescence and also themselves contact and directly heat the bottom of the Crucible above cavity 14. The radiant heat from the incandescent section 10 however is particularly effective in heating the exposed central portion of the bottom of the Crucible by radiation to it and it has been my experience that when a Crucible is thus supported and heated the time of melting of metal in the crucible is materially reduced and the difficulty otherwise experienced with crucibles cracking across their bottoms is completely eliminated.

lt will be understood that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to exnlain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

I claim:

1. A crucible furnace unit, comprising:

(a) a hollow refractory container having a bottom,

side walls and an opening at the top thereof, and hav- 4 ing a removable refractory cover over said opening; (b) said side wall having an inlet opening adjacent the bottom thereof for passage of the combustion gases to the inside of said refractory container;

(c) a burner outside said side wall adjacent said inlet opening;

5 (d) a hollow mounting piece of high thermal emissivity when heated disposed within said container and centrally positioned on said Container bottom, said mounting piece extending up to a point above said inlet opening;

(e) a Crucible within said container and Supported on said mounting piece in spaced relation with respect to said Container side walls to dene a combustion chamber about said Crucible;

(f) said mounting piece being open at the top thereof and having access openings which are substantially horizontally aligned with said wall inlet opening so that ilame from said burner will pass therethrough into said combustion chamber to envelop the Crucible side walls, said ame also passing through said mounting piece access openings to simultaneously contact substantially the entire outer surface of the bottom wall of said Crucible which is exposed within said mounting piece.

2. A Crucible furnace as set forth in Claim 1 wherein 25 the wall thickness of said mounting piece is approximately 1A of the overall width of said mounting piece.

References Cited by the Examiner UNITED STATES PATENTS 30 104,179 6/70 McManus 263-47 449,803 4/91 Nimmo 263.-.48 2,362,823 11/44 Hubbell zes-47x FOREIGN PATENTS 05 637,940 11/36 Germany.

14,924, 1907 Great Britain. 425,388 3/35 Great Britain.

O CHARLES SUKALO, Primary Examiner.

JOHN I. CAMBY, Examiner.

Claims (1)

1. A CRUCIBLE FURNACE UNIT, COMPRISING: (A) A HOLLOW REFRACTORY CONTAINER HAVING A BOTTOM, SIDE WALLS AND AN OPENING AT THE TOP THEREOF, AND HAVING A REMOVABLE REFRACTORY COVER OVER SAID OPENING; (B) SAID SIDE WALL HAVING AN INLET OPENING ADJACENT THE BOTTOM THEREOF FOR PASSAGE OF THE COMBUSTION GASES TO THE INSIDE OF SAID REFRACTORY CONTAINER; (C) A BURNER OUTSIDE SAID SIDE WALL ADJACENT SAID INLET OPENING; (D) A HOLLOW MOUNTING PIECE OF HIGH THERMAL EMISSIVITY WHEN HEATED DISPOSED WITHIN SAID CONTAINER AND CENTRALLY POSITIONED ON SAID CONTAINER BOTTOM, SAID MOUNTING PIECE EXTENDING UP TO A POINT ABOVE SAID INLET OPENING; (E) A CRUCIBLE WITHIN SAID CONTAINER AND SUPPORTED ON SAID MOUNTING PIECE IN SPACED RELATION WITH RESPECT TO SAID CONTAINER SIDE WALLS TO DEFINE A COMBUSTION CHAMBER ABOUT SAID CRUCIBLE; (F) SAID MOUNTING PIECE BEING OPEN AT THE TOP THEREOF AND HAVING ACCESS OPENINGS WHICH ARE SUBSTANTIALLY HORIZONTALLY ALIGNED WITH SAID WALL INLET OPENING SO THAT FLAME FROM SAID BURNER WILL PASS THERETHROUGH INTO SAID COMBUSTION CHAMBER TO ENVELOPE THE CRUCIBLE SIDE WALLS, SAID FLAME ALSO PASSING THROUGH SAID MOUNTING PIECE ACCESS OPENINGS TO SIMULTANEOUSLY CONTACT SUBSTANTIALLY THE ENTIRE OUTER SURFACE OF THE BOTTOM WALL OF SAID CRUCIBLE WHICH IS EXPOSED WITHIN SAID MOUNTING PIECE.

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