US3342248A

US3342248A - Method of blowing aluminum

Info

Publication number: US3342248A
Application number: US381278A
Authority: US
Inventors: Laszlo J Bonis; August F Witt
Original assignee: Ilikon Corp
Current assignee: Ilikon Corp
Priority date: 1964-05-14
Filing date: 1964-05-14
Publication date: 1967-09-19
Anticipated expiration: 1984-09-19

Description

Sept. 19, 1967 J o s ET AL METHOD or" BLOWING ALUMINUM 4 Sheets-Sheet 5 Filed May 14, 1964 FIG. 8

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FIG. 9

FIG. 7

INVENTORS kfiikg a T' BY W/W VW ATTORNEYS Sept. 19, BQN|$ ET AL METHOD OF BLOWING ALUMINUM Filed May 14, 1964 4 Sheets-Sheet 4 FIG. IO

INVENTORS LASZLO J. BONIS AUGUST F. WITT n w WW ATTORNEYS United States Patent 3,342,248 METHOD OF BLOWING ALUMINUM Laszlo J. Bonis, Brookliue, and August F. Witt, Arlington, Mass., assignors to Ilikon Corporation, Natick, Mass, a corporation of Delaware Filed May 14, 1964, Ser. No. 381,278 33 Claims. (Cl. 164-55) This invention relates to an improved method of fabricating articles and is particularly directed to a novel method of blowing hollow articles directly from a fused or liquid material. This application is a continuation-inpart of our copending application, Ser. No. 274,381, filed on Apr. 15, 1963, now abandoned, which was a continuation-in-part of our application, Ser. No. 188,473, filed Apr. 18, 1962, now abandoned.

An object of our invention is to provide a novel method of blowing hollow articles, such as containers and the like, directly from a reservoir of material maintained in a liquid state.

Another object of this invention is to provide a method of blowing hollow, thin-walled articles directly into an open-ended die from a reservoir of molten material.

Another object of this invention is to provide a method of blowing a hollow article with a liner.

A further object of this invention is to provide a rapid, economical method of producing an article of manufacture directly from a liquid or semi-liquid material.

Yet another object of the invention is to provide a method of shaping a film of liquid or semiliquid material in a die and stabilizing the material in the die to produce a solid article of manufacture.

A more specific object of the invention is to provide a method of blowing aluminum directly into an open-ended die from a reservoir of molten aluminum to form hollow, thin-walled articles. l

Other objects of our invention will be apparent to those skilled in the art from the following description.

The objects of this invention are achieved by a method whereby a molten material or other material capable of being blown while in a fused or liquid state, is contained in a supply reservoir and an article is blown directly from the reservoir into a die suspended over the reservoir, by releasing a blowing fi-uid below the surface of the liquid material. The term blowing as used herein is used to indicate the action of the blOWing fluid, such as an expandable gas under pressure,.in forming a bubble beneath the surface of the liquid material in the reservoir and rising to carry into the open end of the die, and shape therein, a thin coherent shell of thematerial from the reservoir. The term blowing as used herein is not used in the sense of blowing to provide a foam or a multicellular structure.

In accordance with one aspect of this invention, a quantity of material, such as metal, is melted in a supply reservoir or vessel in which is disposed at blowpipe having an orifice directed upwardly toward and spaced -a predetermined distance below the surface of the molten metal. In this regard it should be noted that the term metal is used herein in its usual metallurgical sense, and not in the sense at one time common in the glassmaking art to mean molten glass. A hollow die, characterized by a die cavity internally formed to shape the desired article, is suspended over the vessel in registry with the orifice of the blowpipe.

A predetermined minimum volume or charge of pressurized gas is introduced into the blowpipe to form a bubble at the orifice. The pressure of the gas should be sufiicient to overcome the hydrostatic head of liquid on the reservoir above the blowpipe. Where a die is employed the gas pressure also should be sufficient to permit the bubble to enter the die cavity i.e. suflicient to overcome the overpressure within the die, and to expand upwardly into the desired contact with the internal walls of the die before solidification. The bubble expands and rises to carry into intimate conformity with the die a thin, coherent, film-like shell of metal directly from the molten supply. When the bubble has reached its desired limiting or constraining position in the die, it is stabilized into the desired form by solidification, chemical reaction, polymerzation, heating, cooling or the like. After the bubble has blown the article into the die, the latter is removed from its position above the surface of the melt'to permit extraction of the solidified article.

Referring to the drawings: FIGURE '1 is a diagrammatic representation of an apparatus used in practicing the method of our invention.

FIGURES 2 through 5 are diagrammatic representations of the use of our novel blowing method, in fabrieating a hollow sealed article.

' FIGURES 6 through 8 are diagrammatic representations of our novel method used in fabricating a hollow article with a liner.

FIGURE 9 is a cross-sectional view of the article formed by the method of FIGURES 6 through 8.

FIGURE 10 is a diagrammatic view of a modified form of the apparatus shown in FIGURE 1..

It is believed that the nature and types of articles which are capable of being fabricated by our method will be understood from a description of the method as practiced in forming hollow container bodies from aluminum alloy.

With reference to FIGURE 1, a quantity 10 of a suitable aluminum alloy is contained in a vessel 12 and mainmelt 10 with its open end facing and in registry with is'stretched and pressed against the walls the blowpipe orifice 18. As shown, the open end of the die may be immersed slightly below the melt surface for reasons to be explained hereinafter. The die is internally configurated with a cavity shaped to form a tubular container, and is closed at its upper end except for a vent hole-22 through which the air within the die cavity may be evacuated during the blowing of the container.

As best illustrated in FIGURE 2, a predetermined volume of gas released from its source through blowpipe 16 causes a bubble 24 of molten aluminum to rise from orifice 16 and expand upwardly through the melt 10, above the melt surface and into the cavity of the die 20. The bubble expands so that the film continually expands and of the die cavity to solidify and form a thin, coherent, stabilized shell 26 in the shape of the desired container, as seen in FIGURE 3. The die 20 is then removed, the gas within the die permitted to escape, and the solidified, thin-film article as used herein includes a thin film of liquid material inflated with a fluid such as gas.

A specific example of the practice of our method involved the use of a cylindrical cast iron die having a cavity shaped to form a container having a diameter of 1.5" and a length of 2.5. The material used was ASTM aluminum alloy 2024 and was maintained in a molten state at a temperature of about 1200 F.

The blowpipe orifice had a diameter of 11 millimeters, and the distance X of the orifice below the melt surface was approximately 15 millimeters. The blowing gas was a mixture of about 97 parts nitrogen and about 3 parts oxygen, by volume, and was released through the blowpipe in charges of predetermined volume corresponding to a source pressure of approximately 25 mm. Hg above atmospheric pressure and a time interval of about one second.

The open end of the die was immersed below the melt surface a distance Y (FIGURE 2) of about millimeters. At these conditions, hollow containers having the above length and diameter dimensions were blown successively with fairly uniform wall thickness of about .050".

The above-described method may be used to blow hollow articles from any liquid material which is capable of forming a continuous expandable bubble by the action of a blowing fluid released below the surface of the liquid material. The term liquid as used herein includes molten, fused, semiliquid, liquid dispersion, liquids or any fluidtype material capable of being blown into a bubble, and which materials are capable of being stabilized such as by solidification, fusion, polymerization, or the like. Suitable materials would include metals, metal alloys, and natural and synthetic organic materials such as plastics, resins, and monomeric and polymeric materials either in bulk, dispersion, or solution form. These materials may be blown from the bulk material in molten or syrup form, from an aqueous or organic solvent solution of the material, from latices, and from dispersions of the material in diluents, plasticizers, 'or other liquids. These materials may be stabilized after being blown or partially stabilized prior to or during the process of being blown. For example, stabilization may be affected by maintaining the die or other article forming means or the blowing gas or the material at a high or low controlled temperature or by polymerizing the material through employing a blowing fluid containing an accelerator, a curing agent or a polymerization catalyst or otherwise contacting the material being blown, the blown material or the internal walls of the die cavity with additives or catalysts suflicient to affect the desired stabilizing condition either alone or in combination with the employment of controlled temperatures of the die and blowing fluid.

Suitable specific materials would include, but not be limited to thermoplastic and thermosetting resins such as vinyl resins like polyvinyl chloride and copolymers of vinyl chloride and other vinyl halides with vinyl esters of short-chain fatty acids like vinyl acetate, and other ethylenically unsaturated modifying monomers or polymers. Hollow plastic articles may be blown from solvent hydrocarbon solutions of the resins or from dispersion of the resin particles in suitable plasticizers to form vinyl plastisols or solvent-plasticizer combinations to form vinyl organosols. For example, hollow vinyl articles may be formed by blowing a vinyl plastisol bubble into a die which is maintained at a temperature above the fusion temperature of the vinyl resin whereby stabilization is effected by the fusion and cooling of the blown vinyl film within the die.

Other materials include thermosetting resins such as phenol-aldehyde and resorcinol-aldehyde and other such resins prepared either under acid, alkaline or neutral conditions, either as two-step novolak or as one-step resol resins. For example, a resol-type, phenol-formaldehyde aqueous resin solution containing a smallamount of hexamethylene tetra-amine may be blown as a bubble into a die maintained at a temperature sufficiently high to induce the breakdown of the hexamethylene tetra-amine whereby sufficient methylene radicals are generated to effect stabilization of the blown phenol-formaldehyde resin by cross-linking to form the infusible, insoluble resin product. A two-step resin, that is, a resin containing less than a stoichimetric amount of formaldehyde sufficient to produce the insoluble resinous product, may also be blown from a phenol-formaldehyde solution by employing a blowing gas containing formaldehyde whereupon the formaldehyde in the blowing gas combined with the temperature of the die into which the phenol-formaldehyde resin is blown, is sufficient to effect stabilization of the resin by a cross-linking chemical reaction.

Other organic material prepared by polymerization or cross-linking reactions may be blown such as the polyether and polyester-type urethane prepolymers and polymers, as well as regular polyester resins, polyamides (nylon), epoxy resins, and the like. For example, these resins may be blown from a solution and stabilized by employing a polymerization catalyst or cross-linking agent in the blowing fluid or within the die prior to blowing the material. If desired, the material or one or more reactants may be blown into the die and stabilized subsequently by the introduction into the die of a necessary catalyst, stabilization additive or other reactant to complete the reaction to form the stabilized hollow plastic article.

Other suitable material includes natural and synthetic elastomers, such as natural rubber and the conjugated diene polymerizates such as styrene-butadiene copolymers, acrylonitrile-butadiene-styrene copolymers, butadieneacrylonitrile rubbers, polybutadiene, polyisoprene, butyl rubber, halogenated butyl rubber, ethylene-propoylene copolymers and other elastomeric-type materials including elastomeric urethanes. These materials may be stabilized by being vulcanized or cured in a conventional manner such as by employing curing agents and accelerators and a heated die. Curing may be effected partially in the reservoir or the curing agents and accelerators may be incorporated into the blowing fluid or onto the internal walls into which the material is blown and the die maintained at a temperature sufiicient to induce rapid curing or vulcanization. These materials may be employed in a latex or hydrocarbon solution form.

Thermoplastic resins may also be employed with our methods, these materials being characterized by being plastic or by assuming a molten form upon being heated.

Suitable specific materials may include polyolefin resins such as polyethylene and polypropylene, vinyl resins such as polyvinyl chloride and polyvinyl chloride-vinyl acetate copolymers, styrene polymers and copolymers such as polystyrene, styrene-butadiene copolymers, acrylic copolymers such as homo and copolymers containing a hydrocarbon ester or aminoester of an acrylic acid or a 'methaacrylic acid, protein resins, alkyd resins, cellulosic resins as well as other natural resins such as petroleum and polyterpene resins, and the like. These materials may be placed in condition for blowing by dissolving in a suitable solvent or blown in bulk from a molten solution provided the temperature is not sufliciently high to cause charring or degradation of the effective properties of the thermoplastic material. Additives such as plasticizers may be incorporated into the materials prior to being blown. The stabilization of these materials after being blown may be effected by blowing the material from a bulk solution into a chilled die whereupon the hot film thermoplastic resin is sufiiciently cooled upon contact with the internal walls of the die to effect stabilization into the desired hollow plastic article. Where the material is blown from a solvent solution, stabilization may be effected by the rapid removal of the solvent such as by using a vacuum or high and low temperatures of the die.

As can be seen, a wide variety of materials may be successfully employed in our novel process provided the material is capable of being blown into a bubble and stabilized. Additives, such as curing agents, accelerators, fillers, carbon black, plasticizers, stabilizers, antioxidants, lubricants, greases, oils, solvents, colorants, dies, fibers, chemical blowing agents, metal salts, catalysts, clays, metal powder and the like, may be incorporated into the materials to be blown, introduced with the blowing fluids, or introduced into the die either before or after forming the hollow article. Additionally, where desired hollow articles containing a combination of properties may be obtained by the formation of multilayers of different materials within the same die by a series of sequential blowing steps employing the same die where venting means are provided after the formation of each blown layer. Particularly advantageous may be the method of employing a reservoir containing a monomer or monomer-polymer syrup with an additive amount of a polymerization catalyst and blowing the material into a die which die is maintained at a temperature suflicient to induce polymerization. Based on the foregoing discussion the die or other means to form the expanding bubble into the desired articles should preferably be capable of having a controlled temperature.

Metals and metal alloys appear especially suited for blowing by this method because of their ability to quickly stabilize and form a thin coherent bubble film. Aluminum alloys in which additive elements such as Group VI elements like sulphur, oxygen, selenium, or other elements or combinations thereof are present in the base metal, may be blown. Usually, these additives are present in the alloy ingot or are added to the base metal in the melt; however, additives may be incorporated into the blowing fluid and thus added to the base metal during the blowing step. For example, a sulphur-containing gas such as sulphur dioxide or hydrogen sulfide may be used as the blowing fluid to obtain desired properties.

Aluminum alloys appear especially convenient for use in this method because of their high strength-to-weight ratio, reasonable melting point, and their ability to stabilize rapidly due to a desirable range of constitutional supercooling (i.e. solid plus liquid phase region). Aluminum alloys are noted for their ability to oxidize almost instantaneously upon contact with an oxidizing gas such as oxygen. It is believed this contributes to the ability to rapidly stabilize in the form of a continuous, relatively thin, strong, coherent, filmlike layer in that as the bubble forms, a thin layer of aluminum oxide is created on the surface of the bubble exposed to the oxygen. This oxide film forms on the interior of the bubble due to the presence of oxygen in the blowing gas. A like oxide film may form on the exterior of the bubble as it rises above the surface of the melt in those instances where oygen-containing atmosphere, such as air, is present in and around the die. The term film-like particularly characterizes the surface film formed, which may be a mono or polymolecular layer, such as a monomolecular layer of an oxide of aluminum.

Among the aluminum alloys which have produced satisfactory results are ASTM 3003, 2024, 2025, 4043, B195, B750, A356, C612F and aluminum-silicon binary alloys are preferred where it is desired to obtain a ductile, grainoriented product having a relatively smooth finish, such as a can for packaging comestibles. ASTM 2024 being a relatively low-grade commercial alloy, its use will result in savings in the cost of manufacture as compared to the use of specially compounded alloys.

Other metals which have oxide-forming and rapid stabilization characteristics similar to that of aluminum alloy may be used with this method. Many metal alloys are capable at their relatively high melting temperatures and above of rapidly forming filmlike surface layers such as of oxide, sulfides, selenides and combinations thereof and the like. For example, the metal alloys and metals which appear particularly suitable include those which are oxidizable such as aluminum alloys and whichare subject to almost instantaneous oxidation or reaction in a molten or semi-molten condition with the atmosphere or blowing gas. In some cases it is desirable to blow the bubble into a nonoxidizing atmosphere or an inert atmosphere, even though the metals are capable of being oxidized. For example, metals which oxidize in an undesirable manner, such as copper which may form an unsightly green oxide, or magnesium which in many forms is too reactive to be blown into an oxygen atmosphere or metals which form very brittle oxides, such as stainless steel and the like, may be blown into an inert or nonoxidizing gaseous atmosphere with an inert gas such as argon, nitrogen and the like, or at least a gas containing a considerably reduced amount of oxygen concentration in the gas.

A wide variety of metals and metal alloys can be blown by this process. Those metals or metal alloys like aluminum and aluminum aloy on being blown, form a discernible oxide skin; however, other non or less oxidizable metals may also "be successfully blown into hollow articles. Some metals which by their inherent nature will not form thin film-like oxide layers may also be successfully blown with this process. For example, those metals which ordin-arily have the ability to stabilize. rapidly, but in which an oxide film is undesirable or which does not form filmlike oxide layers on being blown, may be used. These metals include, but are not limited to: lead, tin, cadmium, nickel cobalt, zinc, iron, silver, gold, bismuth, platinum, palladium and the like, as well as their alloys such as brass, bronze, Woods metal and the like. Metals which are embrittled by oxidation or the reactions such as cast iron may be successfully blown in an inert or non oxidizing atmosphere. Some metals inherently brittle may require a controlled rate of solidification in the die. The metal bubble upon expanding and contacting the internal wall of the die forms a cooled and solidified film-like layer.

A number of variables in the method above described will have an effect on the final article porduced. It is apparent that one of these is the temperature of the melt. When the melt is maintained at a temperature just above the solidus point, the viscosity of the metal will be greaterthan when a higher temperature is utilized. Thus, when the bubble is formed in the higher viscosity material,

there will be a tendency for a greater amount of material to form around the bubble, thereby resulting in a greater amount of material being blown into the die. Conversely, a higher temperature with attendant lower viscosity will result in less material being blown into the die by the bubble. Thus, it will be seen that melt temperature is one factor that can be controlled tovary the wall thickness of the resulting article.

The temperature of the'die or any portion thereof may be varied as desired to aid in controlling the thickness of the hollow article and in promoting stabilization of the bubble. In particular, the die may be maintained at a lower temperature than the temperature of the melt to effect a rapid stabilization by solidification and cooling of the molten metal or plastic material. Conversely, the die or portions thereof may be maintainedat a higher temheated to produce the desired uniformity or nonuniformity in the hollow article so-formed or all or a portion 'ofthe die may be fabricated of nonheat conductive or less heat conductive material than other portions. Likewise, thematerial of which the die is constructed and internal surface of the die may be so selected to promote adesired surface finish or heat transfer characteristics. For example, where a simple die is used as shown in FIGURES 1 through 9,'the contact of the die with the melt would normally cause a heating of the die to some equilibrium temperature. However, thetemperature at the top of the die generally will be less than that at the bottom of the die wherein it contacts the melt. Where desired, this difference in nonuniformity of die temperature may be further increased in order to obtain progressive stabilization from the one part to the other part of the die after the blown material has contacted the die surface. If desired, the die may be maintained at a uniform temperature in order to control the wall thickness of the hollow article. Progressive stabilization sometimes is desirable so that the die may be readily removed from the melt while the lower material is still in a rather molten condition.

Another factor that will have an effect on the final blown article is the distance X between the blowpipe orifice and the surface of the melt. It has been found that the orifice must be maintained at a certain minimum distance below the surface of the melt in order for proper formation of the bubble to occur. If this distance is less than the minimum, the bubble will not fully form and an inadequate amount of material will be carried into the die, thus resulting in an incompletely formed article, such as the formation of a thin-film article containing holes in the film. When the depth of the blowpipe orifice below the surface of the melt is too great, the diameter of the bubble expanding as it moves upwardly through the melt, at the surface of the melt will be greater than the diameter of the cavity of the die and will thus not enter the die cavity or not enter properly, resulting in a poorly formed blown article. As the depth of the blowpipe orifice is increased there is the additional possibility of multiple bubble formation. The blowpipe orifice depth also influences the film thickness of the top portion of the article formed and the total amount of material carried into the mold. If the blowpipe orifice is too low the expanding bubble of gas carries increasing quantities of material on top of the bubble audit the orifice goes even lower, then mutiple bubble formation results.

The volume of the gas introduced into the blowpipe is varied depending upon the size of the article to be blown. In other words, the larger the article, the greater the volume of gas.

, Further, when blowing large objects or ones having an irregular or nonsymmetrical shape, it may be found advantageous to induce a partial vacuum, for example, on the order of to 20 mm. of mercury, to a section or sections of the die into which it may be difiicult to blow the metal because of the final size or shape of the blown article. This partial vacuum, which may be induced through the air vent 22, will tend to draw the bubble into the die and assist in the full formation of the desired blown article. The creation of a vacuum within the die may be properly timed with the introduction of the bubble into the die. Creation of a continuous vacuum may tend to raise the level of the material into the open end of the die. Elongated hollow articles such as tubes and tubular containers may be fabricated by a die which contains a movable fitted piston or cap member. The piston is moved upwardly or away from the bubble as the bubble rises within the die thereby drawing the bubble into the desired form.

The ability and rate of expansion of the bubble into and within the die cavity depends in part upon the overpressure of the atmosphere within the die cavity. Where there are means for rapidly expelling the atmospheric pressure within the die cavity as the bubble expands upwardly therein such as by the employment of large vents, little if any overpressure develops and the bubble easily enters, rises and forms the desired article in the die. Where small vents are provided the rate at which the rising molten bubble is permitted to rise and expand within the die is decreased and the bubble may solidify prematurely within the die. If the overpressure is too high the bubble will have difliculty in entering the open end of the die. This results in an undesired and improperly formed hollow article. It is, therefore, desirable that means 8 be provided for a fairly rapid expelling of the gaseous atmosphere from the die cavity and at least a suflicient rate to prevent premature stabilization of the bubble.

One method of producing hollow objects is to provide a double open-ended die with one end of the die immersed in the melt and the other end of the die open so that as the bubble expands in the die cavity, no overpressure or little overpressure is created therein. The top lid of the die is then put on just before the bubble reaches the open end of the die, so that the article may be formed. This method restrains the bubble to the desired diameter and reduces problems associated with overpressure within the die cavity. The bubble material should be formed by the introduction of a gas at a minimum gas volume at a predetermined pressure and a predetermined time flow rate sufficient to have the bubble overcome the hydrostatic head and the die overpressure whereby the bubble will expand and fill the entire die cavity.

Numerous other factors, such as the diameter of the blowpipe orifice, bubble volume, blowing fluid, and melt material are variables effecting the ultimate article to be formed.

Various articles have been blown from ASTM 2024 aluminum with a variety of blowing gases. Such mono and polyatomic gases as nitrogen, argon, helium, oxygen, air, and mixtures of these gases have been used. When it is desired that an oxide film be formed during the blowing of aluminum, the quantity of oxygen necessary in the blowing gas is relatively small. It should be noted, however, that the preferred oxygen content be from approximately 1 to 3 parts to parts of the remainder of the gas. It will be understood that our method is not limited to true gases where the oxygen is in the form of 0 but also includes the use of fluids such as gaseous carbon dioxide, which, upon heating in contact with molten aluminum, will liberate sufficient O to create the oxide film.

Many blowing fluids can be employed in this invention. These include those relatively inert fluids which may be used with those blowing materials where the article to be 'blown does not have an oxide film, or other gases which react with the material to form desirable materials and impart desired properties to the article. Other fluids include those which react with the blowing material to form a filmlike oxide layer, as is the case with aluminum and oxygen as above described.

In the practice of this invention, the molten materials are essentially stabilized by the transformation of a liquid phase to a solid phase. However, where desired, stability may be fully obtained or at least aided by chemical reaction of the blowing fluid with the molten material as previously described. The selection of the particular fluid depends upon the material to be blown and the article desired, whether the stabilization be accomplished by phase transformation or by chemical reaction.

Suitable gaseous fluids that may be employed in this method include water vapor, helium, hydrogen, carbon dioxide, carbon monoxide, hydrocarbon gases such as methane, ethane, butane, nitrogen and nitrogen-containing gases such as oxides of nitrogen, sulphur-containing gases such as sulphur dioxide and hydrogen sulfide, halohydrocarbons such as fluoro and chloro methane and ethane, halogens, rare earth halides, argon and other gases.

Suitable liquids that may be utilized as the blowing fluid include silicone fluids and polysilicones which remain stable at temperatures of the molten material, or liquids which decompose to form blowing gases or reactive elements.

Fluidized solids also may be used as the blowing medium. These include gases containing finely divided 7 metal, metal oxide, or other additive or alloying elements in the fluid stream.

In order to insure the proper formation of the blown article, it is desirable that the interior surfaces of the die be dry. If, for example, water should be present on the inside surfaces of the die as the aluminum bubble is blown, the hot material will vaporize the water, thus deforming the bubble and producing an uneven surface on the article.

In most operations an air atmosphere above the melt will permit. satisfactory operation of the blowing process. However, where the molten metal is one that is readily oxidized by air, a dross will form on the surface of the melt and tend to interfere with the efiicient operation of the blowing process in that the dross could be carried into the die with the bubble. To obviate this problem, a controlled atmosphere of nitrogen or other non-oxidizing gas may be maintained about the bath and/ or within the die. Alternately, a mechanical skimming operation may be employed to remove the objectionable dross from the melt surface prior to each blowing cycle.

It is also within the scope of our invention that a thin layer of less dense, nonsoluble, nonoxidizable material, such as molten glass be employed above the molten metal alloy surface in the reservoir to prevent or reduce oxidation of the lower metal being blown. In this embodiment a thin layer of A" to /2" of molten glass may be used whereupon blowing the bubble of metal alloy, a bubble containing a thin outer layer of glass and a thin inner layer of aluminum is formed and carried into the die cavity to form a metal-lined glass article. The upper layer of the reservoir may be any inorganic or organic material either capable of being blown or which serves as a protective layer and parts when a bubble is blown.

From the foregoing description it will be apparent that this invention will provide a relatively thin-walled, hollow article in a manner which achieves economy and simplicity of operation. Additionally, the article offers distinct advantages over articles of similar types fabricated by conven tional casting and cold forming operations. This method may be employed to form numerous articles having any desired regular or irregular shape, such as containers, hubcaps, light sockets, trays, etc.

In another form of the invention, specifically illustrated in FIGURES 2 through 5, sealed hollow articles may be produced. More particularly, the method may be used to provide, for example, a cylindrical hollow article closed at both ends. In this case the bubble 24 is blown inthe manner as describedabove (FIGURES 2 and 3). After the thinshell 26 is blown into intimate contact with the die cavity, an imperforate plate 28 is placed under the open end of the die 20. The plate should cover the entire open end of the die. The die and plate are then removed from the melt, whereby the plate traps a layer 30 in the lower open end of the die. The thickness of this lower layer substantially corresponds to the distance the die is immersed in the melt, when the plate closes the die. It will be understood that when desired the die may be lifted partially out of the melt to an immersed depth Z (FIG- URE 3) before the plate is placed under the open end of the die, in order to provide a thinner layer 30. Upon cooling, this layer forms an integral end wall for the article. The blowpipe 16 is preferably moved out of a blowing position an amount sufficient to enable plate 28 against the open end of the die 20.

If a thicker end wall 30 is desired, the distance Z may be varied acocrdingly. The blowing fluid, used to blow the article 26 is entrapped within the article. It is readily apparent that the melt surface below the trapped bubble within the die 20 will be slightly lower than the surrounding melt surface as shown in FIGURE 3. This factor must be considered in selecting the immersion depth Z to accomplish the desired thickness of the end wall 30. If desired, the entrapped blowing fluid may be exhausted from the die 20 prior to placing plate 28 beneath the die, by first raising the die out of the melt and then lowering it again to the predetermined distance Z.

After the die 20 and plate 28 are removed from the melt 10, the end wall layer 30 solidifies integrally with the shell 26 to form a sealedhollow article (FIGURE 5).

placement of the In still anotherform of the invention, lined articles may be blown. FIGURES 6 through .9 illustrate this aspect in the formation of a glass-lined metal container. A quantity of molten glass 34 is first placed on the orifice 18 of the blowpipe 16 by suitable means. A predetermined volume of blowing fluid released through the blowpipe 16 causes a glass bubble 38 to rise from the orifice 18 and expand upwardly. As the glass bubble 38 rises, a thin layer 40 of material from the melt 10 will adhere to the exterior surface of the bubble and be carried with the expanding bubble into intimate conformity with the die cavity walls.

FIGURE 8 shows the formation of a blown glass-lined container 42 which conforms to the inner shape of the die 20. As shown, the die has been raised up out of the melt, resulting in the glass being pulled into a very thin bubble 44 and outwardly expanded by the pressure of the blowing fluid. On solidification of the enclosed article 42, the thin walled glass bubble 44 is broken, and the edges of the article 42 at the open end of the die 20 smoothed by a torch or other conventional finishing means. The article is then removed from the die providing the finished glass lined container 42 shown in FIGURE 9. It is contemplated that such container 42 or other preformed hollow articles may be subsequently lined with an inner layer of another material by employing the container as a die, with orwithout a supporting die fixture, for a subsequent blowing operation.

As described, the lining material blown may be glass, having a softening point below the temperature. of the melt or otherwise capable of being placed in a sufiicient softened state to be blown. Any material such as plastics, metal alloys, vitreous amorphous materials and the like, besides glass, which are compatible and capable of withstanding the temperature of the melt material, may be used as the inner liner of articles prepared in the foregoing manner. The wall thickness of the liner material and, to some extent that of the outer shell, may be controlled by the quantity of material used, its nature and the blowing pressures employed. The glass-metal layers formed by this method have a very high bond strength.

As indicated in FIGURE 1, the open end of the die 20 is immersed slightly below the surface of the melt. This is to ensure that the bubble, as it rises, will properly enter the die to completely form the desired article. In other words, the immersed end of the die guides the bubbles into thedie for proper formation. On the other hand, depending on operating conditions and the nature of the material of the melt, it may be desirable that the open end ofthe die not be immersed directly. in the melt, but be positioned in approximate contact with the melt surface.

FIGURE 10 shows a modification of the die shown in FIGURE 1. In this embodiment the die 20 comprises in addition a lower sleeve member 52 immersed in the melt to the desired depth Y, the upper end of which sleeve member 52 extends above the melt surface and tightly abuts or telescopes without the open end of the 'die 20. The die 20 is sli-dably, but tightly, mounted in the lower sleeve member 52. The sleeve member 52 may be in a fixed location at the desired depth of Y or preferably it is mounted for periodic immersion in the melt between blowing cycles. In this embodiment the upper member of the die 20 need only be brought into a position wherein its lower open end fits within or abuts the lower sleeve member 52. With this arrangement the die 20 need not 20 to insure the proper entry of the blown bubble of material into the die 20. After the buble has been blown into the die 20, the upper die 20 can then be withdrawn from the lower sleeve member 52 by a vertical upward movement so that the blown hollow article formed therein may be removed. The sleeve member 52 being a separate member is periodically immersed in the melt between blowing cycles to remove any solidified metal that may collect thereon. Thus, when the die 20 is remove-d from contact with the sleeve member 52 so that the blown article may be recovered, the lower sleeve member 52 is completely immersed in the melt and returned to its original position so that when the die 20 is returned to its abutting position with the sleeve member 52, the die 20 is ready for the next blowing cycle.

The term die as used herein refers broadly to any means of forming the upwardly rising, expanding bubble of material and includes in particular the die 20, as well as the die containing an abutting and retractable or immersible sleeve member 52. It is recognized that the bubble of material may be captured and formed into the desired article by other means such as by the use of free forming techniques employing fluid streams, such as air streams, or other forces to restrain and mold the liquefied metal bubble into the desired form prior to stabilization thereof. The die serves as a limiting or restraining means to capture the bubble.

It has been found that the blowing process of this invention can be applied to metals other than aluminum. Examples of metals blown include but are not limited to: Woods metal (M.P. 73 C.), lead (M.P. 327 C.), tin (M.P. 232 C.), cartridge brass (M.P. 1030 C.), zinc (M.P. 419 C.), and copper (M.P. 1083 C.). Small cylinders were successfully blown from each metal. Copper oxidized rapidly, but the rate was not so rapid that an impervious crust formed on the surface of the bath. Right cylinders of copper were somewhat lacey in the thin sections at the rim of the cylinder due to oxidation.

In all cases, a 3" diameter by 6" deep alundum crucible was used as the container. The metal was heated to melting by resistance wires around the crucible. Normal fireback insulation surrounded the crucible.

The blowpipe tube was of Vycor glass tubing 9 mm. ID by 11 mm. OD. A gas diffuser of 1" diameter containing 20-30 mil holes was affixed to the end of the tube with sodium silicate. The blow gas used was 97% nitrogen and 3% oxygen. The blowpipe was inserted beneath the molten metal so that the top of the gas diffuser was 1% beneath the molten metal surface. The molten metal was maintained at 60 F. above its melting point. The total gas overpressure ranged from 100-250 mm. above atmospheric, depending on the metal. In the case of Woods metal and tin it was 100 mm. above atmospheric, with cartridge brass and copper it was 250 mm. above atmospheric. Blow times were 0.4 second in all cases.

The mold was of gray cast iron. The ID of the die was 1%", wall thickness was A". The free length of the die was 3". The bottom of the die was open, the top was fitted with a flat insert closure held by screws so that there was a clearance of 0.010" between the periphery of the insert and inner wall of the die.

The blowing procedure was similar to that described with aluminum. The open end of the die was inserted into the liquid to a depth of 1", the vertical axis of the die having been aligned with the center of the gas diffuser beforehand. Immediately after the die was inserted a gas bubble was injected. Then the die was raised and the blown cylinder removed.

With the use of a protective nonoxidizing or inert atmosphere about a bath of cast iron (M.P. 1230 C.), cast iron may be blown, while a protective atmosphere would also reduce the oxidation of blown copper.

One of the distinguishing features of blown aluminum in contrast to cast aluminum is the tendency toward crystal orientation in the blown aluminum. The degree to which this tendency exists depends on the particular alloy and the particular blowing conditions. The reasons for the preferential crystal growth are not fully understood; however, examples can be given to demonstrate the preferential growth.

A hypothesis of the microscopic mechanism of the blowing process may be set forth. At the instant a gas bubble is inserted beneath the molten aluminum, nucleation starts because of the temperature difference between the gas and the melt or because of the formation of an unstable chemical intermediate which nucleates crystallization. At this stage, nuclei are probably not oriented due to agitation within the melt, at the surface of the rising bubble. As the bubble rises into the die, the mass of melt decreases and the bubble walls contact the relatively cooler die Walls. The bubble walls become pinned to the die walls and nuclei present initiate growth into the still semimolten mass of the bubble walls. The semimolten bubble walls are simultaneously stretched and nucleated as the bubble rises to fill the die. The crystals growing from the nuclei propagate in the easiest growth direction under the stretching force. These steps take place rapidly in time because of the heat sink represented by the die walls. The maximum time within which oriented crystal growth can occur is set by the temperature difference between the die walls and the semiliquid bubble walls and the difierence between the liquidus and solidus curves of the particular alloy. This latter statement is based on the simplifying assumption that the die walls are essentially an isothermal heat sink during the instant of solidification. This is known not to be exactly true, because a thermal gradient is generated across the thin film air interface between the aluminum bubble walls and the inner die walls and between the die walls and the bulk die material. The composition of the nuclei is dependent on the temperature at which nucleation is initiated.

It can be seen that the extent to which preferred orientation of the growing crystals occurs is in some varying de gree dependent on the specific alloy, the temperature of the molten metal bath, the speed of injection of th gas bubble, the gas temperature, the depth of the blowpipe beneath the surface, the die wall temperature and the thermal conductivity of the die material. The hypothesis postulates nucleating sites formed within the semimolten mass of the aluminum bubble walls immediately before and during entrance into the die. These nuclei are pinned on entering the die and under the stretching force while in the mold propagate crystal growth in the easy direction, into the bubble walls. The process may be simply due to crystallites forming at the interface between the cooler injected gas and the melt, or the nucleating sites may be due to contact with the cooler die walls.

Below are experimental data demonstrating preferred crystal growth in two alloys of aluminum blown as taught in this patent application. A side wall taken from a blown container or can was flattened, polished and mounted in the usual technique for X-ray diffraction. The blown samples were compared with a similarly flattened sample prepared from a rapidly chilled, thick casting of the same molten metal. The X-ray tube utilized had a copper metal target.

The four strongest diffraction lines were compared in' each case. The preferential orientation is evidently such that the 111 planes lie parallel to the sample plane.

One alloy examined was essentially a binary mixture of 8% silicon in aluminum. The other blown sample was made from commercial 2025 alloy. Two orientations (A.

and B) of the 8% silicon sample (at right angles to each other) were examined. One orientation of 2025 alloy was investigated. The relative intensities of the four strongest lines are shown normalized to the intensity of reflection of the 111 plane at a value of 100.

In every case, the relative intensity of the 111' line in the blown can is stronger than the 111 line in a randomly oriented sample. The ratio of the intensity of the 111 line to the sum of the other lines supports this View. No estimate of the absolute amount of preferred orientation can be made because of the lack of calibration against single crystal material. However, tendency toward preferred orientation is significant. Inblown aluminum tested to date, the ratio of the principal diffraction line 111 to the sum of theother lines 200, 220 and 311 will be greater than 1.0.

The objects set forth above, among those made apparent from the preceding description, are attained in the method of this invention and'changes may be made in carrying out the method without departing from the scope ofthe invention." It is intended that all the matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense. 1

It is also to be understood that the language in the following claims is intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having thus described our invention, we claim:

' 1. A method of manufacturing a hollow article from a bulk quantity of liquid material which method comprises:

immersing the open end of a die a controlled depth into the liquid material and thereby enclosing a portion of the exposed surface of the liquid material and leaving a die cavity above said enclosed surface; conducting a predetermined volume of a fluid under pressure to a position in registry-with the open end of the die and at a controlled depth beneath the surface of the liquid material; V f t T forming at said position a bubble of said fluid and causing said bubble to rise to said enclosed surface and to form a thin coherent film shell of said bath material at andextending above said enclosed, surface, and causing the bubble to expand so that its film wall continually expands and is stretched and is pressed into'contact with the internal surfaces of the' die cavity;

stabilizingthe bubble material in the die; and

I recovering the stabilized hollow article from thefldie.

2. The method as described in claim 1 wherein a liquid material is a molten metal alloy capable of forming an oxide film'when contacted in the molten state by oxygen and wherein the fluid 'under pressure is a gas containing oxygen, in a controlled proportion;

3." The method as described in claim 1 wherein the material is stabilized by controlling the temperature of the die into which the bubble is blown.

4. The method as described in claim 1 whereinthe fluid under pressure is a gas, the liquid material is a molten metal, and the bubble is formed by introducing thepr'edetermined volume of the gas into the one end of a blow pipe wherein the other end of the blow pipe has an orifice disposed in registry with the open endof the die" and at a controlled depth material.

5. A method as described in claim 1 wherein the fluid under pressure is a gas containing a controlled amount of oxygen and the liquid material is a molten aluminum alloy and wherein the aluminum is stabilized by solidification of the bubble in the die.

6. A method ofcontinuously manufacturing a plurality of hollow articles from a bulk quantity of a liquid material and an open end die characterized by an internal die cavity and including a detachable open end lower sleeve member which method includes:

immersing the open end of the sleeve member of the die a controlled depth into the liquid material and thereby enclosing a portion of the exposed surface of the liquid material and leaving a die cavity above said enclosed surface;

conducting a predetermined volume of a gas under pressure, to a position in registry with the open end of the sleevemember and at a controlled depth beneath the surface of the liquid material;

beneath the surface of the liquid formin gand introducing a bubble of said material into the immersed open end of the sleeve member and die, said bubble being expanded by said gas under pressure. so that its film wall continually expands and is stretched and is pressed into contact with the internal surfaces of the die cavity; stabilizing the bubble material in the die cavity; separating the die from the sleeve member;

' recovering the hollow article formed from the separated die;

repositioning the die in mating contact with sleeve memblowing a bubble of the molten metal expanding above the surface of the bath from a controlled depth beneath the surface of the molten metal employing a predetermined volumeof gas under pressure to form the bubble;

forming the molten bubble so blown into a hollow article of the desired shape; and

solidifying the. formed bubble.

9. A method as described in claim 8 wherein the molten metal is selected from a group of metals consisting of aluminum, tin, lead, zinc, copper and alloys thereof.

'10. A method as described in claim 8 wherein the molten metal is capable of forming a thin oxidized surface and the gasunder pressure employed to blow the bubble is a gas with a controlled proportion of oxygen.

11. A method as described in claim 10 wherein the molten bubble is formed into a desired hollow metal article by introducing the bubble into the open end of a die immersed a predetermined distance into the molten metal which die is maintained at a temperature less than that of the molten metal.

12. A method of fabricating a hollow article which method comprises:

heating a quantity of molten material to a controlled temperature to provide a bath of fused material;

immersing the open end of a die a controlled depth into the said bath and thereby enclosing a portion of the exposed surface of the liquid material and leaving a die cavity above said enclosed surface, said die having an inner surface which defines the outer shape of the hollow article;

providing a blow pipe adapted to be connected at its one end with a source of fluid under pressure and having an orifice at its other end disposed in registry with the open end of the die and at a controlled depth beneath the surface of the bath;

blowing a bubble of said material into the open end of the die and into intimate contact with the inner surface of the die by connecting the one end of the blow pipe with a source of fluid under pressure to form at said orifice a bubble of said material and cause it to rise to said enclosed surface and to form a thin coherent film shell of said bath material at and extending above said enclosed surface, and thereby cause the bubble to expand so that its film wall continually expands and is stretched and is pressed into contact with the internal surfaces of the die cavity;

solidifying the blown article;

removing the open end of the die from the bath; and

recovering the article formed.

13. The method of claim 12 which includes controlling the temperature of the material in the bath to vary the wall thickness of the article formed.

14. The method of claim 12 which includes controlling the temperature of the die to stabilize the bubble blown into the die.

15. The method of claim 12 which includes controlling the overpressure developed within the die to permit the bubble to contact the internal walls of the die prior to solidification.

16. The method of claim 12 wherein said fluid under pressure used to blow the bubble is a gas containing a controlled proportion of oxygen and said material is a metal alloy capable of forming an oxide layer when formed with the blowing gas.

17. The method of claim 12 which includes controlling the pressure and amount of the fluid used to blow the bubble to vary the size of bubble.

18. The method of claim 12 which includes developing :an under pressure less than the blowing pressure within the interior of the die when the bubble is introduced into the die.

19. The method of claim 12 which includes controlling the orifice of the blow pipe to vary the diameter of the bubble blown.

20. The method of claim 12 which includes control- Hing the depth of the orifice of the blow pipe below the :surface of the bath of the material to vary the wall thick- :ness of the article.

21. The method of claim 12 wherein said material is :an aluminum alloy and the fluid under pressure is a gas containing about 1 to 3 parts per hundred of oxygen.

22. The method of claim 12 which includes controlling the depth of the open end of the die to vary the overpressure within the die.

23. A method of fabricating a hollow sealed article which comprises:

forming a hollow article in accordance with the method of claim 12 and prior to removing the open end of the die from the bath placing an imperforate plate member in sealing engagement with the open end of th molt. I9 pr d .2 sealed lid of controlled thickness;

removing the sealed die from contact with the bath;

and recovering from the die a hollow sealed article. 24. A method of fabricating a hollow metal article which method comprises:

melting a quantity of a metal to a controlled temperature to form a bath of molten metal alloy;

immersing the open end of a die to a controlled depth in the bath and thereby enclosing a portion of the exposed surface of the molten metal and leaving a die cavity above said enclosed surface; disposing a blow pipe having at its one end an orifice disposed at a controlled depth beneath the surface of the bath; and in registry with the open end of the die;

blowing a bubble of said metal alloy above the surface of the bath and-into the open end of the die by introducing a predetermined volume of gas under pressure into the other end of said blow pipe to form the bubble and cause it to rise to said enclosed surface and to form a thin coherent film shell of said metal at and extending above said enclosed surface, and causing the bubble to expand so that its film wall continually expands and is stretched and is pressed into contact with the internal surfaces of the die cavity; and solidifying the blown article formed within the die.

25. The method of claim 24 wherein said gas under pressure comprises a gas capable of setting free a controlled amount of oxygen when in contact with the molten alloy.

26. The method of claim 24 wherein the metal is an aluminum alloy and the gas contains from about 1 to 3 parts per hundred of oxygen.

27. A method of fabricating a hollow aluminum article comprising:

melting a quantity of an aluminum alloy;

immersing a die having an open end a predetermined distance into the molten aluminum alloy and thereby enclosing a portion of the exposed surface of the liquid alloy and leaving a die cavity above said enclosed surface;

disposing the orifice of a blow pipe in a registry with the open end of the die and a predetermined distance below the surface of the molten aluminum alloy;

and I blowing a bubble of the molten aluminum alloy into the die using to blow the bubble an atmosphere containing free oxygen passed through the blow pipe to cause the bubble of alloy to rise to said enclosed surface and to form a thin coherent film shell of said bath material at and extending above said enclosed surface, and causing the bubble to expand so that its film wall continually expands and is stretched and is pressed into contact with the internal surfaces of the die cavity.

28. The method of claim 27 wherein the atmosphere used to blow the bubble comprises oxygen and an inert gas.

29. A method of fabricating a hollow metal article from a fused bath of a metal'which method comprises:

suspending the open end of a die slightly above the surface of the molten metal and in a position to cap ture within the die a bubble of molten metal from the surface of the metal; 7 providing a blow pipe adapted to be connected at its one end with a source of gas under pressure and having an orifice at its other end disposed in registrywith the open end of the die and at a controlled depth beneath the surface of the bath;

blowing a hollow bubble of the molten metal containing gas into the open end of the die by connecting the one end of the blow pipe with a source of gas under pressure;

solidifying the blown article in the die; and

recovering the article formed.

30. The method of claim 29 wherein the gas contains a controlled proportion of oxygen.

31. The method of claim 29 which includes inducing at least a partial vacuum within the cavity of the die to aid in capturing the bubble within the suspended die.

32. The method of manufacturing a hollow metal article from a bulk quantity of molten metal which method comprises:

suspending the open end of a die above the surface of the molten metal;

forming a hollow gas-containing bubble of the metal and introducing said bubble into the suspended open end of the die and into contact with the internal surfaces of the die by introducing a predetermined volume of gas under pressure into the metal through a blow pipe havig an orifice disposed in registry with the open end of the die and at a controlled depth below the surface of the molten metal;

stabilizing the bubble material in the die; and

recovering the stabilized hollow metal article from the die.

33. A method of manufacturing a hollow aluminum article from a bulk quantity of molten aluminum alloy which method comprises:

suspending the open end of a die above the surface of the molten alloy;

conducting a predetermined volume of gas under pressure and containing a controlled amount of oxygen to a position in registry with the open end of the die and at a controlled depth beneath the surface of the molten alloy;

forming and introducing a hollow bubble of the molten alloy and containing said gas into the suspended open end of the die and into contact with the internal surfaces of the die; solidifying the bubble in the die; and recovering the solidified aluminum article from the die.

References Cited UNITED STATES PATENTS 12,086 12/1854 Tiebe et al. 22-200 26,913 1/1860 Leonard 29-183 272,044 2/ 1883 Harker 22-200 397,641 2/ 18.89 Halford et a1. 22-202 740,874 10/1903 Krause 22-202 788,142 4/1905 Pease -192 788,144 4/1905 Pease 65-192 852,396 4/1907 Pease 65-192 X 901,361 10/1908 McCarty 22-209 1,435,292 11/1922 Grey 22-209 1,699,592 1/1929 Kadow.

1,725,144 8/1929 Kadow 22-209 X 2,002,875 5/1935 Woods 65-88 2,005,175 6/1935 Adams 29-183 2,019,046 10/ 1935 Delpech 49-31 2,174,930 10/ 1939 Soubier 65-263 X 2,209,877 7/ 1940 Ferngren 18-58 2,751,289 6/1956 Elliott -20 3,013,311 12/1961 Meissner 18-57 3,184,296 5/ 1965 Schaich 65-73 FOREIGN PATENTS 803,122 3/ 1951 Germany. 193,945 2/ 1923 Great Britain.

I. SPENCER OVERHOLSER, Primary Examiner. V. K. RISING, Assistant Examiner.

Claims

8. A METHOD OF FABRICATING A HOLLOW METAL ARTICLE FROM A LIQUID BATH OF A MOLTEN METAL WHICH METHOD COMPRISES: BLOWING A BUBBLE OF THE MOLTEN METAL EXPANDING ABOVE THE SURFACE OF THE BATH FROM A CONTROLLED DEPTH BENEATH THE SURFACE OF THE MOLTEN METAL EMPLOYING A PREDETERMINED VOLUME OF GAS UNDER PRESSURE TO FORM THE BUBBLE; FORMING THE MOLTEN BUBBLE SO BLOWN INTO A HOLLOW ARTICLE OF THE DESIRED SHAPE; AND SOLIDIFYING THE FORMED BUBBLE.