US 3063099 A
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Nov. 13, 1962 G. H. TURNER ETAL METHOD FOR PRODUCING METAL SPHERES Filed Jan. 16, 1961 lnvenfors GORDON H. TURNER JOHN R. WELLINGTON CHARLES ASUTHERLAND ARNOLD G. WHITE QW Aiforriey United States Patent Ofiice 3,063,099 Patented Nov. 13., 1962 METHOD FOR PRODUCING METAL SPHERES Gordon Henry Turner, John Richard Wellington,
Charles Alexander Sutherland, and Arnold George White, all of Trail, British Columbia, Canada, as-
signors to The Consolidated Mining and smelting Company of Canada Limited, Montreal, Quebec, Canada,
a corporation of Canada Filed Jan. 16, 1961, Ser. No. 83,067 3 Claims. (Cl. 18-48) This invention relates to a method of producing metal spheres. It is particularly directed to providing a method for the manufacture of low melting temperature metals and alloys thereof, such as indium and alloys of indium, in the form of metal spheres.
It'is known that metal particles of random shape and sizes can be formed by spraying the metal of interest in molten state into the upper part of a spray tower; by sputtering when molten metal is dropped on a cooler surface; and by granulation when a stream of molten metal is poured into a bath of chilling liquid. These methods are satisfactory for the purposes for which they are intended, that is, for example, to produce metal particles suitable for grinding into powder form for use in powder metallurgy, and to produce metal shot, such as lead shot. However, these known methods have the disadvantage that they do not produce the particles of the metal or metals of interest in substantially uniform shape and size. Also, these known methods are not applicable in certain instances such as, for example, the formation of indium spheres.
We have found that low melting temperature metals and alloys can be produced in the form of spheres of substantially uniform shape and, if desired, of substantially uniform size by an inexpensive and easily conducted method. The method comprises, in general feeding metal in the form of solid or liquid particles into a column of liquid having a lower density than that of the metal. The upper part of the column of liquid is maintained at a temperature above the melting temperature of the metal of interest and the lower part is maintained at a temperature below the melting temperature of the metal. It is found that the metal particles fed into the upper part of the column form liquid globules of generally spherical shape and they settle downwardly towards and into the cooler lower part. As these globules settle through the cooler, lower part, they solidify and in solidifying they retain their spherical shape. The solid metal spheres settle to the base of the liquid column from which they can be removed, either intermittently or continuously, and after washing and drying, they are ready for use.
The operation of the method of this invention is described in detail hereinafter as applied to the production of spheres of indium and indium alloys and lead alloys. It will be understood, of course, that the method can be employed to produce metal spheres from other low melting temperature metals and alloys.
In practice, a liquid medium is selected with regard to its density, its boiling temperature and its inertness to the metal of interest. Its density must be less than that of the metal of interest and its boiling temperature must be safely above the melting temperature of the metal. The liquid medium also should be inert to the metal of interest to avoid the possibility of chemical reaction with the metal particles. The heated upper part of the column must be of a depth sufiicient to permit the metal particles fed thereinio to form molten spheres as they settle through it. The cooler lower part must be of depth sufiicient to permit the molten spheres to solidify as they settle to the base of the column.
The height and diameter of the column are determined with regard to the rate of production desired.
There are a number of suitable liquid media which can be employed in our process.
We have used glycerol in the manufacture of indium and indium alloy spheres and we have used a silicone oil such as Dow Corning 550 fluid in the manufacture of lead alloy spheres. Glycerol has a useful temperature range for the purpose of this invention of up to 200 C. and Silicone DC 550 has been found useful up to about 425 C.
Depending upon the form and the rate of feed of metal to the column, it may be necessary to heat the upper part and cool the lower part. For example, if the metal is fed as solid particles, it is necessary to supply heat to the upper part of the column. If the metal is added as molten globules, there may be sufiicient heat in the metal to maintain the desired temperature without heat from an extraneous source. In order to solidify the molten spheres, it may be necessary to cool the lower part of the column. Conventional heating and cooling coils can be employed to heat the upper part and cool the lower part of the column.
Some metals and/or metal alloys, such as indium and alloys of indium, tend to resist forming into spherical shape during their passage through the heated part of the column. It may be that this resistance is caused by the formation of a film, such as an oxide film, on the surface of the liquid globule. We have found that this resistance can be overcome by adding to the liquid medium a minor amount of a solvent for the film. A
finite amount, ranging from about 0.1 to about 0.5 percent, by weight, of an inorganic acid such as hydrochloric acid is suitable as a solvent for films which form on the surfaces of such metals and alloys.
It is found that provided there is no agglomeration or coalescing of molten spheres through contact during their passage through the heated part of the column, the size of the resulting sphere is in direct proportion to the weight of the metal in the original solid particle. Thus, spheres of substantially uniform size can be obtained by feeding into the column individual metal particles of substantially uniform weight and feeding the particles into the column in a manner such that there is minimum contact between the individual metal spheres during their passage through the upper part of the column. Thus, when a product of substantially uniform size is desired, the metal should be added to the column as solid particles of substantially uniform weight. However, molten metal, or a metal alloy, can be sprayed into the heated upper part of the column and substantially uniformly shaped solid metal spheres will be collected in the base of the column but the spheres will be of random sizes. It is very diflicult, if not impossible, to spray molten particles of substantially uniform weight and also to prevent contact of sprayed molten particles as they settle through the upper part of the column. However, the solid metal spheres produced by spraying molten metal into the upper part of the column can be segregated into desired sizes by conventional screening or centrifuging procedures.
The following example illustrates the operation of the process to produce indium metal spheres of predetermined size, in this instance mils in diameter. Discs of indium metal of a diameter of about 15 mils were punched from a sheet of indium metal which previously had been rolled to a thickness of 10 mils. These discs were fed into the upper part of a column of glycerol, about 3 feet high and about 3 inches in diameter. Indium has a melting temperature of about 155 C. The upper part of the column was maintained at a temperature of from about 170 C. to about 200 C. and the lower half was maintained at about room temperature, about C. A finite amount of hydrochloric acid, equivalent to about 0.25% by weight of the glycerol in the upper heated part of the column, was added to the top of the column of glycerol. The indium discs melted and assumed a spherical shape during their passage through the heated part of the column and solidified in the form of spheres during their passage through the cooled, lower part of the column. The metal spheres which collected at the bottom of the column were removed and washed successively with water, alcohol and acetone and were then dried.
The spheres produced in the above operation were substantially circular in shape and were 15.0 mils in diameter within 10.1 mil.
It is found that the size of the metal spheres can be varied by varying the weight of the original solid particles of metal. In the above example, the original indium particles are in the form of discs but other shapes can be used.
In a further example of the operation of the method of this invention, molten indium was sprayed into the top of a column of glycerol, the upper part of which was maintained at a temperature above the melting point of indium and the lower part was matained below the melting point of indium. The product from this spraying modification was in the form of substantially circular spheres but the spheres were of random sizes. Metal 'spheres of desired sizes were segregated from the product by screening.
In the above examples glycerol constituted the liquid medium in which the spheres were formed. Glycerol has been used as the liquid medium in the production of spheres from indium and indium alloys such as gertitanium-indium, gallium-indium and tin-indium alloys having melting points below 200 C. Silicone oil has been used for the production of spheres from antimoniallead and cadmium-lead alloys having melting points below 400 C.
An apparatus suitable for conducting the method of this invention is illustrated partly schematically and partly in section in the accompanying drawing. Discs 10 of uniform diameter and of substantially uniform thickness are punched by a conventional punching device 2, illustrated schematically, from a strip 1 of substantially uniform thickness of a relatively low melting temperature metal or metal alloy, such as indium or an indium alloy. The discs can be, for example, of a diameter of 15 mils (0.015 inch) and a thickness of 10 mils (0.01 inch). The punching device 2 is of a conventional design and can be manually or automatically operated. It can be located in any convenient position, such as above a feeding device 3 which receives the punched discs and advances them to the open upper end of the column 4.
The column 4 is open ended andd efined by a circular vertical wall 5, such as glass. A flask 6 is removably positioned below the open bottom end. A rubber sleeve 7 connects the upper end of the flask 6 to the open lower end of the wall 5 in liquid tight engagement. A conventional pinch cock type valve 8 is provided in the rubber s eeve.
Conventional heating coils 11 are provided around the upper part of the column 4, such as electric resistance coils. Conventional cooling coils 12 are provided around the lower part of the column, such as water cooling coils provided with water inlet and outlet connections 13 and 14 respectively.
The column 4 is filled with a liquid medium, such as glycerol, which has a boiling point safely above the melting point of the metal or metal alloy discs 10. The uper part of the column is heated to above the melting point of the discs 10 by the heating coils 11 and the lower part is maintained below the melting temperature of the discs.
Relatively low melting temperature metal or metal alloy discs of substantially uniform diameter and thickness are fed into the heated upper part of the column 4 wherein they melt and form molten metal spheres 100. As the spheres settle into the cooler, lower part of the column, they olidify as substantially circular solid spheres 1011 which are collected in the flask 6. When the flask is filled with these solid spheres to the desired extent, the pinch cock 8 is closed, the flask removed, emptied, and thereafter replaced.
it will be understood, of course, that other types of conventional or unconventional apparatus can be employed in the operation of this method and it can be conducted on a continuous, semi-continuous or batch basis.
The method of this invention possesses a number of important advantages. It is easily and inexpensively conducted to produce metal particles in substantially spherical form. If desired, the spheres can be produced of substantially uniform size. The method is of particular advantage in instances in which uniformity in size and shape of the product is important, such as in the production of indium and indium alloy spheres used in the manufacture of transistors and the like.
It will be understood, of course, that further modifications can be made in the preferred embodiment of the invention described herein without departing from the scope of the invention as defined by the appended claims.
What we claim as new and desire to protect by Letters Patent of the United States is:
1. The method of producing spheres of a metal selected from the group consisting of indium and its alloys which comprises feeding non-spherical particles of the metal into the upper part of a column of liquid which is maintained at a temperature above the melting temperature of the metal whereby the metal particles form molten metal spheres as they settle through the upper part of the column towards and to the lower part thereof, maintaining the lower part of the column of liquid at a temperature below the melting temperature of said metal whereby the molten metal spheres are cooled and solidified during their settling to the bottom of the column, and collecting solid metal spheres from the bottom of the colume; said liquid having a boiling point higher than the melting point of the metal, being inert to and of lower density than the metal and containing a finite amount of hydrochloric acid the amount of said acid not substantially exceeding that required to remove films which form on the surfaces of metal particles fed into said column which would interfere with the conversion of the metal particles to spheres.
2. A method according to claim 1 wherein the nonspherical particles which are fed to the column are in the solid state.
3. The method of producing spheres of a metal selected from the group consisting of indium and its alloys which comprises feeding non-spherical particles of the metal into the upper part of a column of glycerol which contains from about 0.1% to about 0.5%, by weight, hydrochloric acid and which is maintained at a temperature above the melting temperature of the metal whereby the metal particles form molten metal spheres as they settle through the upper part of the column towards and to the lower part thereof, maintaining the lower part of the column of glycerol at a temperature below the melting temperature of said metal whereby the molten metal spheres are cooled and solidified during settling to the bottom of the column, and collecting solid metal spheres from the bottom of the column.
References Cited in the file of this patent UNITED STATES PATENTS 83,152 Glasgow et a]. Oct. 20, 1868 6 Linebarger Oct. 11, Linebarger June 10, Vogt Apr. 21, Stulzman Nov. 6, Stammer et a1. Nov. 6, Hechinger Jan. 5, Rowan Sept. 20,