US 2553016 A
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Patented May 15, 1951 UNM'EQ S'H'A'EES ATE QFFHCE No Drawing. Application December 26, 1947, Serial No. 794,087
4 Claims. (Cl. 148-31) This invention relates to a product of manufacture comprising a foam-like metal, and is a continuation in part of my copending application for patent, Serial No. 486,209, filed May 8, 1943, for Process for Making Foamlike Mass of Metal which has issued to United States Letters Patent No. 2,434,775, dated January 20, 1948.
One of the objects of the invention is a foamlike mass of metal that is relatively light in proportion to the volumetric mass of metal, and which metal is structurally resistant to shock and strain to a greater degree than a solid body of metal of the same kind, and which possesses greater resiliency to impact than in a solid metal, and also greater resistance.
Another object of the invention is the provision of a foamlike mass of metal having an increased resistance to bending and buckling over such resistance by the solid metal from which it is formed. The binding and buckling strength is greatly increased as a consequence of the increased thickness, and this reduces the weight of material required for a given strength without sacrifice of any desirable resiliency.
A still further object of the invention is a foamlike mass of metal having an increased resistance to the passage of heat and sound over the solid metal or one that is porous.
An added object is the provision of a relatively strong foamlike metal product that oiiers increased resistance to the passage of bullets or projectiles over solid or porous metal and that also has a substantial cushioning eilect for explosions and shocks.
The metal of the present invention may be cast, fashioned, processed, out to the desired shape, such as blocks, sheets, plates, tubing, or in whatever form is desired. This metal has dispersed substantially throughout its body. a multitude of completely enclosed spaces or voids. The size and. uniformity of size of spaces or voids may vary in accordance with the requirements of the usage to which the product is to be placed. The shape of the spaces is usually generally spherical or ellipsoidal but this may be varied in accordance with the requirements of usage to which the product is to be placed. Where the walls of the cells are round, as is the case where they are generally spherical or ellipsoidal, they produce a body that is highly resistant to stresses and bending.
The size of the individual spaces or voids vfor small bodies varies from about one one-hundredth of an inch in diameter to about one tenth of an inch. A given body may have the spaces or voids of substantially uniform size or there may be a variation in size according to the intended use of the product. For a large body thickness the space or void diameters may be increased, but usually the space of the void diameters is not over one tenth of the body thickness. In general, the over-all volume of the foamlike mass of metal is large in comparison with the volume of the metal before conversion into the foamlike state. In other words, a given weight of foamlike metal has a much greater volume, and consequently a much lower overall specific gravity, than the metal from which it is produced.
In general, the process of making the metal comprises heating the desired metal, mixture of metals, compounds, alloys, or other minerals, etc. to a temperature between the melting point thereof at atmospheric pressure and a temperature sufiicient to produce a vapor pressure of volatile material in the mixture, and under conditions where the volatile portion or portions are held in the molten mass against escape therefrom. The molten mass is then released into a lower pressure space resulting in the formation of a froth or mass of metallic, gas filled bubbles, which. after cooling will constitute the foamlike mass of metal.
As examples of mixtures that are suitable for forming the foamlike mass of metal, one or more of the following combinations may be used:
Iron, aluminum, zinc Iron, magnesium, zinc Aluminum, magnesium, iron, mercury Magnesium, mercury Aluminum, mercury Chromium, cadmium Gold, mercury In carrying out this process, any conventional apparatus may be employed capable of withstanding the necessary heat and pressure, it being understood that the volatile portion of the material treated is prevented from escape so as to produce the desired vapor pressure.
As a concrete example, assuming aluminum and mercury are used, these may be mixed in the proportion of parts of aluminum to 10 parts of mercury, and are melted in a closed chamber or under conditions preventing escape of the mercury vapor. The proportions are, of course, greatly dependent upon the capacity of the enclosure and the desired vapor pressure, that is, the less vapor pressure space the less mercury is required, and the greater the space the more is needed.
At atmospheric pressure, the aluminum should melt at about 658 C. and as the boiling point of mercury is about 357 C. it will be seen that a vapor pressure due to the volatilizing of the mercury may be increased to the point where the mercury in the mixture is stabilized or is not vaporized unless there is a reduction in pressure. When this condition is reached and the pressure is released, which may be by withdrawing the molten mass from the high pressure chamber to a low pressure space, there will be a volatilizing of the mercury in the mass causing it to become foamy or foam like. Upon cooling an expanded foam like sponge metal will result.
Where iron, aluminum and zinc are used, the relative proportions of aluminum to iron may be from about 1% iron to 99% aluminum by weight, or from 99% to 1% aluminum, and from 1% to 20% of zinc relative to the entire mass will supply the desired amount of zinc for supplying the vapor. A higher temperature will normally result in less zinc being required.
In most instances in compositions of different metals their melting points will vary from that of the respective metals, hence exact melting point temperatures cannot be given.
In zinc alloys, the zinc in the alloy will be sufficient to produce the necessary gas, and where mercury is used, from 1% to by weight of the entire mass is generally adequate, and where no amalgam is formed, there will be some free mercury in the cells in the foam like metal, but the empty spaces will nevertheless be formed.
Iron alone with 1% to 20% zinc, or magnesium and iron with 1% to 20% magnesium, or magnesium and zinc may be used to form the metal.
As an example of mineral and a metal, gold and mercuric oxide melted together in a confined space will produce foamlike metal.
The pressure produced will vary in proportion to temperature, composition and solubility, but as a general principle in all instances the heatin is to the point where vapor pressure of volatile material or materials is above the pressure of the space into which the molten material is to be released, or a relatively rapid lowering of pressure in the space in which the material is melted is the equivalent if the molten material is not drawn from the space in which it is melted.
The above principle being understood, it is, of course, obvious that the invention is not restricted to exact metals disclosed, but to any metallic mixture, compound, alloy, etc. in which a metal or mineral is incorporated therein that has a relatively lower boiling point than the main body of the mass so as to produce the vapor pressure in the molten mass sufiicient to create the conditions in which a reduction of the vapor pressure or release from pressure of the molten mass will result in subsequent volatilizing of the said metal or mineral in the mass to produce the cellular structure when the mass is cooled in the low pressure space or area.
While earlier herein the statement was made that the cells in the foam like metal were not intercommunicating, this statement is to be taken generally, since some intercommunication between certain cells cannot be avoided.
1. A product of manufacture comprising a foam-like mass of metal formed with completely metal enclosed voids substantially uniformly distributed throughout said mass, the voids being of substantially spherical shape and of a size of less than ten percent of the thickness of the mass, and the metal enclosing the voids being thin relative to the diameter of the voids.
2. A product of manufacture comprising a foam-like metallic body having numerous metal enclosed imperforate walled cells substantially uniformly distributed throughout said body, said cells being voids of partial vacuum and being of substantially spherical shape and of a size of less than ten percent of the thickness of the body, and the metal enclosing the voids being thin relative to the diameter of the voids.
3. A product of manufacture comprising a foam-like body of a plurality of metals having numerous metal enclosed imperforate walled cells substantially uniformly distributed throughout said body, said cells containing a gas of one of said metals that is inert to chemical interaction, said cells being of substantially spherical shape and of a size of less than ten percent of the thickness of the body, and the metal enclosing the voids being thin relative to the diameter of the voids.
4. A product of manufacture comprising a foam-like mass of metal formed with completely metal enclosed voids substantially uniformly distributed throughout said mass, said mass having a low overall specific gravity as compared with the specific gravity of the metal from which said mass is formed, the voids being of substantially spherical shape and of a size of less than ten percent of the thickness of the mass, and the metal enclosing the voids being thin relative to the diameter of the voids.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,086,437 Rowe July 6, 1937 2,215,723 Jones Sept. 24, 1940 2,375,506 Turck May 8, 1945 2,398,703 Gardner Apr. 16, 1946 OTHER REFERENCES Metals and Alloys, February 1932, page 29.
Metals Handbook, 1948, published by American Society for Metals, Cleveland, Ohio, page 10.
Wulff: Powder Metallurgy, 1942, page 2. Published by American Society for Metals, Cleveland, Ohio.