US3139654A - Mold assembly - Google Patents

Description

N. A. HARRIS MOLD ASSEMBLY July 7, 1964 2 Sheets-Sheet 1 Filed May 28, 1959 INVENTOR.

Norman A Harris .iai

Agent N. A. HARRIS MOLD ASSEMBLY July 7, 1964 2 Sheets-Sheet 2 Filed May 28, 1959 INVENTOR. Norman A. Harris Agent United States Patent 3,139,654 MOLD ASSEMBLY Norman A. Harris, Henderson, Nev., assignor to Titanium Metals Corporation of America, New York, N.Y., a corporation of Delaware Filed May 28, 1959, Ser. No. 816,415 7 Claims. (CI. 2261) This invention relates to a mold assembly particularly adapted for use in arc melting apparatus of the so-called fcold mold type.

In cold mold arc melting furnaces the mold itself is generally fabricated as a relatively thin walled copper vessel surrounded by a jacket through which is circulated a cooling fluid such as water. An arc is maintained between metal in the mold and an electrode, which may be consumable or non-consumable, and a solid ingot is formed in the mold by progressive solidification of transferred molten metal. Such apparatus is inherently dangerous because perforation of the mold wall by the are results in inflow of water onto hot and molten metal. A disastrous explosion can occur under such conditions. A serious need therefore exists for a safe crucible assembly for use in such apparatus.

It is therefore a principal object of this invention to provide an improved crucible assembly for use in arc melting apparatus of thecold mold type. object of this invention is to provide a safe crucible assembly for use in such apparatus. Another object of this invention is to provide a crucible assembly for are melting apparatus in which no cooling fluid is employed during melting. These and other objects of this invention will be apparent from the following description thereof and from the annexed drawings in which:

FIG. 1 shows a vertical sectional view of a crucible assembly embodying features of this invention,

FIG. 2 shows a section of the assembly of FIG. 1 taken along the line 2-2,

FIG. 3 shows a modified form of the apparatus of FIG. 1, and, 7

FIG. 4 shows a section of the assembly of FIG, 3 taken along the lines 44.

Referring now to FIGS. 1 and 2, the crucible assembly comprises an open top shellindicated generally at 10, formed of sidewall 12 and bottom 14. Extending outwardly from the top of sidewall 12 is flange 16 which provides means for attaching the assembly to electrode positioning or driving apparatus of which flange 18 is a part, attached to housing 20 which may enclose the teams (not shown) for positioning or driving an elec- A further trode 22. A resilient gasket member 24 may be interposed between flanges 16 and 18 and the attachment made temporarily firm by appropriate tightening of bolts 26. The electrode positioning and driving apparatus itself forms no part of this invention and it is referred to herein only for ready understanding of the attachment of the crucible assembly thereto.

Contact plate 23, preferably of copper, is disposed interiorly on the bottom 14 of shell 10, and securely attached and electrically connected thereto as by welding at 30. pin 32 is attached to or fabricated as a part of contact plate 28 for reasons which will be hereinafter explained in detail. Means for connection of an electrical current lead to bottom plate 14, exteriorly of shell 10, are provided as by terminal 34 which is secured in firm contact with an extending flange of plate 14 as by bolt 35. Preferably, but not essentially, the sidewall 12, flange 16, and bottom plate 14 are fabricated of alloy steel to provide necessary strength to these elements.

Free standing on contact plate 28 and spaced apart In a preferred embodiment an upstanding guide from the interior surface of sidewall 12, is a massive metal mold preferably fabricated of two sections as mold top 36 and mold bottom 37, these two sections being removably attached in rigid tight relationship by bolts 38. Cavity 40 extends into the mold through mold top 36 and terminates interiorly thereof at the top surface of mold bottom 37. The mold is fabricated of a common metal having high heat conductivity. Copper and aluminum are most suitable for this purpose being readily available at a reasonable price and having the required heat conductivity. Silver and certain other precious and rare metals have desirable thermal characteristics but are not suitable for use because of their cost and availability.

Suitable means, such as lifting eyes 42, are attached to or made integral with mold top 36 for convenience when removing the mold from shell 10. In addition, in a preferred embodiment, the mold bottom 37 is provided with socket 44 with which guide pin 32 mates to insure accurate positioning of the mold within shell 10 to provide uniform spacing between it and sidewall 12, and also to provide accurate alignment of mold cavity 4i) with an electrode, such as 22, employed during melting.

In operation, the crucible assembly of this invention is employed as a part of arc melting apparatus which will include mechanism for driving or positioning an electrode. The electrode may be consumable or nonconsumable. Such mechanisms are well known in the art and will not herein be describedin detail. Since the melting operation will be carried out in an atmosphere of inert or other special gas, or under vacuum, the electrode driving mechanism will be enclosed, at least in part, in a suitable housing, the bottom portion thereof being represented in FIGS. 1 and 2 as wall 20 and attached flange 18. The mold and shell are assembled and attached to the driving mechanism and other auxiliaries by placing and tightening bolts 26 with gasket 24 interposed between flanges 18 and 16 to provide a gas tight seal.

Melting is then conducted according to known methods. If the electrode 22 is'consumable, the metal of which it is composed will be melted and transferred to form an ingot in cavity 40 in the mold, the melting are being maintained through electric power connected by suitable means (not shown) to electrode 22 and to the mold and metal therein through contact plate 28, bottom plate 14 and connected terminal 34. If the electrode is non-consumable, suitable feed means will be employed to supply metal to be melted in the arc zone and a similar ingot in the mold obtained. After melting is complete and the ingot has'solidified, the mold assembly is disconnected by removing bolts 26. The hot'mold and ingot is then lifted out of shell 10, conveniently by hoisting means engaging lifting eyes 42, and the ingot is removed from the mold by separating mold top 36 and mold bottom 3'7 by removing bolts 38. The ingot will slide freely out of the mold top 36 since the metal, which is liquified on melting, shrinks on solidification. The ingot may then be allowed to cool in air or may be quenched if desired. The mold is preferably cooled by immersion in a water bath, being again conveniently handled during this operation by a mechanical hoist engaging eyes 42. The cooled mold is dried, cleaned, and reassembled by bolting mold top 36 to mold bottom 37 and replacing in shell 10 standing on contact plate 28, and the assembly is then ready for use in a subsequent melting operation.

Referring now to FIGS. 3 and 4, a modified crucible assembly 30 is illustrated in which the open top shell 5%) is formed of side wall 52 with flange54 extending outwardly at its top with bolts 56 provided to attach the assembly to flange 58 of housing 60, which encloses or partially encloses positioning or driving mechanism for an electrode 62. The seal is maintained between fianges 58 and 54 by resilient gasket 64. The bottom of sidewall 5'2 is provided with outwardly extending flange 66 which is firmly attached as by bolts'ti5 to bottom plate 70 with gasket 72 interposed between flange 66 and bottom 7 0 to maintain a seal. Since operation contemplates detachment of the assembly from electrode driving mechanism by loosening of bolts so, that is, at the top of shell 50, the gasket 72 is preferably of copper or other metal since this will be a more or less permanent attachment. In addition the higher temperature in this area will generally require a heat resistant or metallic gasket since resilient material such as rubber will not be practicable.

Fixedly attached to bottom plate 70 as by welding at 74, to provide mechanical joining as well as good electrical connection, is contact plate 76 preferably fabricated of copper and having upstanding guide pin 78. Means are provided for connection of an electrical lead to bottom plate 7 0, exteriorly of shell 50 as by terminal 80 which is secured in firm contact with plate 70 by one of bolts 68. Preferably, but not essentially, the sidewall 52, flange 54, and bottom 70 are fabricated of steel to provide necessary strength to these elements.

Free standing on contact plate 76 and spaced apart from the interior surface of side wall 52, is massive metal mold 32 in the form of a thick walled tube provided with lifting eyes 83, and having a central bore 84 to provide a mold cavity. Preferably, plug 86 is loosely fitted into the bottom of bore or cavity 84 to form a supplementary bottom to the mold and is fabricated with socket 88 adapted to mate with pin 78, thereby providing a central guide to insure proper spacing between mold 82 and sidewall 52, and also to provide accurate alignment of bore 84 with an electrode such as 62 employed during melting.

Operation of the modified device shown in FIGS. 3 and 4 is initially similar to that described for the embodiment of FIGS. 1 and 2. The mold and shell are assembled and are attached to driving mechanisms and other auxiliaries by placing and tightening bolts 56 with gasket 64 interposed between flanges 54 and 58 to provide a gas tight seal.

Melting is then conducted as previously described with a solid ingot being formed in bore 84 on top of plug 86. After melting is complete and the ingot has solidified the mold assembly is disconnected by removing bolts 56. The hot mold 82 is then lifted out of the shell 50 conveniently by hoisting means engaging lifting eyes 83, and the ingot, which shrinks on cooling, is left free standing on plug 86. The ingot is then lifted out of shell 50, conveniently with the use of cable loop or sling. Plug 86 is then removed and cooled together with mold 82, preferably by immersion in a water bath. The ingot may be allowed to cool in air or may be quenched if desired. The mold and plug are then dried, cleaned, and reassembled in place in shell 50 and the assembly is then ready for use in a subsequent melting operation.

It is a unique feature of this modification of this invention that the bottom of the mold cavity is formed by a loose plug 86 and yet the metal during melting is completely and efficiently contained in the mold. The heat sink capacity of the mold freezes the metal being melted so that no leakage occurs between the edges of plug 86 and the adjacent mold sidewall. This organization provides an extremely convenient assembly from which the ingot may be readily removed without complicated handling since the mold side and bottom elements are already separate. These elements may be readily cleaned and reassembled without setting and tightening bolts or other fastening means. Through its relationship with guide pin 78, the plug 86 maintains mold 82 in proper spaced relationship with sidewall 52.

The mold assembly of this invention is useful for melting refractory, or other metals which are, or can be melted in cold mold type are furnaces including among others, titanium, copper, aluminum, zirconium, molybdenum, tantalum, steel thorium, and uranium. The weight of the mass of high heat conductivity metal constituting the mold is critical and must be sufiicientto absorb enough heat to produce a solid ingot of metal melted therein. The mass of mold metal must be sufficient to act as a heat sink, that is, to absorb the necessary amount of heat so that contained metal will be solid, without its own temperature becoming raised above the point at which undesirable fusion of the mold to the ingot might occur.

The weight of mold metal necessary will depend to a large extent on the particular metal being melted since the thermal characteristics of metals vary widely. The weight of the metal mass should not, however, be less than about 2,000 pounds per cubic foot of mold cavity volume to insure that the mold itself does not get too hot. A greater weight of mold metal may, and most generally will, be employed, particularly when melting metals whose thermal characteristics require greater heat sink capacity. It will also be obvious to those skilled in the art that an amount of metal which does not completely fill the mold cavity will generally be melted thus providing a safety factor in excess mold metal weight in the mold. The following table shows examples of approximate heat sink requirements of certain metals which may be melted in apparatus according to this invention, without considering unused space in the mold cavity.

It will be noted in Table 1 above that the mold weight requirement for aluminum is somewhat less than that for copper. This is because the heat capacity of aluminum is about four times that of copper, but the thermal conductivity is only about one half.

As an example of the weight of copper required for practical operation, a mold of 250 pounds of copper having a mold cavity volume of 0.0756 cubic foot was successfully employed to melt titanium. The titanium ingots produced, which were planned to leave a necessary and desirable unused space at the top of the mold cavity, weighed 13.5 pounds each. The Weight of copper per cubic foot of total mold cavity can be calculated for this embodiment as 3,300 pounds, and the weight per cubic foot of cavity filled by the titanium ingot (corresponding to Table 1 above) was about 5,400 pounds. A crucible of aluminum having a 4 inch diameter by 8 inch length mold cavity and used to melt the 9 pound ingots of titanium, weighed pounds.

It will be apparent that the crucible assembly of this invention is more useful for melting relatively small ingots. Although theoretically there is no limit to the size of the mold, it will be appreciated that the weight of mold metal needed to produce very large size ingots will necessarily be correspondingly great. The cost and difficulty in handling an extremely heavy crucible may be limiting factors.

As explained hereinbefore the mold acts as a heat sink and the mold assembly operates Without other than incidental cooling during melting. Some heat will be transferred from the mold to the shell sidewall by radiation, and by convection if gas is employed as furnace atmosphere, and some by conduction through the contact plate to the shell bottom. Such heat will, of course, be in part transferred to the ambient atmosphere but the bulk of the heat will be retained in the metal mass constituting the mold. This will raise the temperature of the mold as melting progresses but not to the point'as explained above, where it will affect its structural integrity.

The free standing mold, which provides a path for heat conduction only at the bottom of the assembly, is

vacuum due to the spaced apart relation of the assembly shell side and the mold.

The mold assembly of this invention is completely free of explosion hazards associated with water cooled molds heretofore employed. The heavy metal mold will generally be much too thick to be perforated by a wandering arc and even if this could or should occur, no cooling fluid is employed which could contact molten or hot metal in the mold. The organization described is simple yet efficient to provide proper and useful heat retention in the mold metal mass. At the same time the weight of the mold can serve another useful purpose in promoting excellent electrical contact between the mold bottom and the contact plate attached to the bottom of the shell interior. Thus,-the mold may be readily removed and replaced in the shell, as described, and proper and adequate electrical contact maintained between it and the shell bottom without the necessity of attachments, or other conventional connector means.

This application is a continuation-in-part of my copending application Serial No. 777,274, filed December 1, 1958, and now abandoned.

I claim:

1. In an arc melting furnace of the cold mold type, a mold assembly comprising; a shell having a sidewall and a bottom, means for attaching said shell to electrode positioning apparatus, a massive mold of common metal having high heat conductivityfreely standing on said bottom interiorly of said shell and spaced apart from the interior surface of said sidewall, said mold having a cavity extending thereinto from its top, the mass of metal constituting said mold being sufficient to act as a heat sink during melting of metal in said cavity in said mold without other than incidental cooling, and means for providing connection of an electric current lead to said bottom of said shell.

2. In an arc melting furnace of the cold mold type, a mold assembly comprising; a shell having a sidewall and said mold having a cavity extending thereinto from its top, the mass of metal constituting said mold weighing not less than 2,000 pounds per cubic foot of volume of said cavity and capable of acting as a heat sink during melting of metal in the cavity in said mold without other than incidental cooling, and the weight of said mold promoting eflicient electrical contact between said contact plate and said mold resting thereon.

4. In an arc melting furnace of the cold mold type, a mold assembly comprising; a shell having a sidewall and a bottom, means for attaching said shell to electrode positioning apparatus, a copper contact plate disposed interiorly on the bottom of said shell and electrically connected thereto, means for connecting an electric current lead to said bottom exteriorly of said shell, a massive mold of common metal having high heat conductivity freely standing on said contact plate, and guide pin and socket means maintaining said mold spaced apart from the interior surface of said sidewall of said shell, said mold having a cavity extending thereinto from its top, the mass of metal constituting said mold being sufficient to be capable of acting as a heat sink during melting of metal in the cavity in said mold without other than incidental cooling, and the weight of said mold promoting efiicient electrical contact between said contact plate and said mold resting thereon.

5. Inan arc melting furnace of the cold mold type, a mold assembly comprising; a shell having a sidewall and a bottom, means for attaching said shell to electrode positioning apparatus, a copper contact plate disposed interiorly on the bottom of said shell and electrically connected thereto, means for connecting an electric current a bottom, means for attaching said shell to electrode positioning apparatus, a copper contact plate disposed interiorly on the bottom of said shell and electrically connected thereto, means for connecting an electric current lead to said bottom exteriorly of said shell, and a massive mold of common metal having high heat conductivity freely standing on said contact plate and spaced apart from the interior surface of said sidewall of said shell, said mold having a cavity extending thereinto from its top, the mass of metal constituting said mold being suflicient to be capable of acting as a heat sink during melting of metal in the cavity in said mold without other than incidental cooling, and the weight of said mold promoting efficient electrical contact between said contact plate and said mold resting thereon.

3. In an arc melting furnace of the cold mold type, a mold assembly comprising; a shell having a sidewall and a bottom, means for attaching said shell to electrode positioning apparatus, a coppercontact plate disposed interiorly on the bottom of said shell and electrically connected thereto, means for connecting an electric current lead to said bottom exteriorly of said shell, and a massive mold of common metal having high heat conductivity freely standing on said contact plate and spaced apart from the interior surface of said sidewall of said shell,

lead to said bottom exteriorly of said shell, a massive mold of common metal having high heat conductivity freely standing on said contact plate, and an upstanding guide pin on said contact plate mating with a socket in the bottom of said mold to maintain said mold spaced apart from the interior surface of said sidewall of said shell, said mold having a cavity extending thereinto from its top, the mass of metal constituting said mold being sufficient to be capable of acting as a heat sink during melting of metal in the cavityin said mold without other than incidental cooling, and the weight of said mold promoting efiicient electrical contact between said contact plate and said mold resting thereon.

6. In an arc melting furnace of the cold mold type, a mold assembly comprising; a shell having a sidewall and a bottom, means for attaching said shell to electrode positioning apparatus, a massive mold of common metal having high heat conductivity freely standing on said bottom interiorly of said shell and spaced apart from the interior surface of said sidewall, said mold having a f of said shell.

7. In an arc melting furnace of the cold mold type, a mold assembly comprising; a shell having a sidewall and a bottom, means for attaching said shell to electrode positioning apparatus, a massive mold of common metal having high heat conductivity freely standing on said bottom interiorly of said shell and spaced apart from the interior surface of said sidewall, said mold being in the form of a thick walled tube with the bore of said tube forming acavity in said mold, the mass of metal constituting said mold being sufiicient to act as a heat sink during melting of metal in said cavity in said mold without other than incidental cooling, and means for providof said shell.

(References 011 following page) References Cited in the file of this patent UNITED STATES PATENTS Armstrong Mar. 4, 1941 Perry Nov. 1, 1927 5 Walker June 5, 1945 55 Herres et a1. Feb. 13, 1951 Findlay June 7, 1955 Laird et a1 Aug. 28, 1956 Garrny July 23, 1957 Beall et a1 Mar. 4, 1958 Gorga Apr. 28, 1959

Claims (1)

1. IN AN ARC MELTING FURNACE OF THE COLD MOLD TYPE, A MOLD ASSEMBLY COMPRISING; A SHELL HAVING A SIDEWALL AND A BOTTOM, MEANS FOR ATTACHING SAID SHELL TO ELECTRODE POSITIONING APPARATUS, A MASSIVE MOLD OF COMMON METAL HAVING HIGH HEAT CONDUCTIVITY FREELY STANDING ON SAID BOTTOM INTERIORLY OF SAID SHELL AND SPACED APART FROM THE INTERIOR SURFACE OF SAID SIDEWALL, SAID MOLD HAVING A CAVITY EXTENDING THEREINTO FROM ITS TOP, THE MASS OF METAL CONSITUTING SAID MOLD BEING SUFFICIENT TO ACT AS A HEAT SINK DURING MELTING OF METAL IN SAID CAVITY IN SAID MOLD WITHOUT OTHER THAN INCIDENTAL COOLING, AND MEANS FOR

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