US2919471A - Metal fabrication - Google Patents

Description

Jan. 5,' 1960 c. HECHINGER METAL FABRICATION Filed April 24, 1958 /l /l l l/l Unite States METAL FABRICATION Carl J. Hechnger, St. Louis, -Mo., assignor ta olin Mathieson Chemical CorporetionyEast Alton, Ill., a co'poration ot Virginia :Application -ril 2, 1953,`Sei-ial No. 732,'112 17 Claims. Cile-47.2

This inven'tion relates 'to pellets and more specifically to 'a method for 'treating'me'tal and making metal pellets, and is a continuation in-part of application Serial Number 5624 47, n'ow abandonei filed January 31, 1956. -I`n certain "fabricating Operations, particularly in the extrusion of me'talparts, slug's of metal 'are fed into a machine 'and fabrica'ted into useful articles. must beof 'substantially uniformweight, size, shape and composition. '-Iere'tofore `"such slugs have usually been either stamped "from 's`heets, 'cut 'from bars or 'individually cast n rnold's. Although *slugs formed in this manner are =`s`atisfactory, 'it is of course highly desrable 'that the 'cost *of pr'odci'ng the slugs `be 'reduced to the greatest degree possible. p

-I'n` the manufacture of'metal'pellets, such as lead pellets, it has "been the "general practice to *drop globu'les 'of molten metal through a cooling medium such as a 100 foot column of air a water spray, or steam, and to catch the solidified globules in water which may be provided with additives for cleaning the pellets or for applying a protective coating to the pellets. It is during this fall that the ?globule solidifies with the result 'that upon striking the water bath in the base of the tower the globule is substantially solid. When the 100 foot column of cooling gas or vapor is reduced and the iglobule strikes the water bath after a fall of only -a few feet the resultant pellets are not spheric'a'l, At best they have shrink holes and usually they splatter into irregular mass resembling popped popcorn. This method of fabricating pellets has given rise to the familiar tall and slender dropping tower having `aheight of 'about 100 to 150 feet through which the globules are dropped into a deep well. The dropping tower process is the most W-dely used 'method of fabricating pellets of lead for use in sporting ammunition. Unfortunately only a few metals such as lead can be satisfactorily fabricated into pellets by this method.

Other methods of forming pellets are known such as, dropping globules of molten metal through a relatively short column of air a'nd into various solutions such as a bath 'of water in which is dissolved soluble alcohol, ketones, aldehydes,`*esters of Organic acids or water solutions containing fluxes such as Zinc chloride or ammonium `chloriles Many metal pellets made by these methods tend todevelop gas pockets or splatter upon contact with the liquid bath. This is particularly true in the fabrication of aluminum, nickel or Copper pellets. Another previously known method of fabricating pellets comprehehds dropping molten metal into pulverized graphite. Whenthis method was tried it was found that the pellets would tend to flatten out, that the surface of the pellets was roug'h and contaminated by the graphite. The dropping of the globules of metal into water `and liquid $olutions,`sing1e`-phase, was proven unsatisfactory when These slugs e Pa tented .Jan. 5, 1960 ICC '2 the surface of the pellets was also found to be rough and the pellets misshapen. Still another previously ::nown method of fabricating pellets involves dropping molten metal into a liquid bath which is relatively cool in its lower regions and hot in its upper regions so tha t the pellet passed through the hottest portion of the bath and into the cool'er portion. The temperature 'differental of the quenching bath did not 'appear to have 'aii'y su'bstantial advantages.

It has also been proposed to formpellets by eliminatin'g any `free drop and passing molten metal globuls directly into a cooling bath of another molten metal having a melting point below the soldfication tempera ture of the molten globules and relying on the diference in density between the metals to cause the globules to pass through the cooling medium. None of these methods produce satisfactory pellets either because the size of the resultant pellets is too small or cannot be controlled 'accurately, or because the resultant pellets contain gas pockets 'or are in the form of a splattered .mass of metal resembling popped popcorn rather than substantially spherical pellets. y

Certain of the above described methods, particularly the dropping tower method, will produce pellets of sufficiently large size and consistent configuraton for use in some shot gun shells and similar applications. However, such a process does not lend itself'to the production of larger pellets and the dropping tower method hasthe obvous additional disadvantage of requiring a location where such a structure may be erected and these `s`tfuctures are expensive to build.

It is therefore an object of 'this invention to produce by a dropping process, metal pellets having a practicable size and consis'tency for use in subsequen't metal fbricating p ocsses. V

Another object of this inveition is to 'fabricat by a dropping process metal pellets of r'elativly large 'and consistent size.

Another object of this invention is to fabricate by a dropping method pellets having a g'en'etally spherical conguration.

Another object of this 'inventon'is to 'provide a 'n'ov'el method for s'ubdviding a 'mass of metal into sphercal pellets.

Another object 'of this invention is to provide pellets which are not unduly porous and which have a relativly smooth surface.

Another 'objectof this invention is to provideamethod of producing 'pellets i n `a "relatively limited space and with apparatus having a small if'itial cost.

Another object of the invention is to produce metal pellets more safely.

Additional objects and advantages will become apprent from the following description and drawings in which:

Figure 1 is a schematic sectional view illustrating ne method of obtaining the correct dropping temperature of the metal, and

Figure 2 is a schematic se'ctional view illustrating sa embodiment of a suitable pellet making appar'ati's in operation.

As used throughout 'this specification 'and claims the term pliable 'plastic defines a viscous semi-solid mass ot such a consstency that it is deformable under its own weight, but is not a free running mass as is the case 'n' liquids. This defined mass 's intermediate between 'a solid and a liquid, and will include some of 'the properties of, each, a liquid and a solid, -but n'ot all of'ethe'. Th"

pliable plastic condition.

meaning of the term semi-molten, hereinafter, is restricted to dene a two temperature zoned mass of metal consisting of a pliable plastic core within a liquid surface layer. The pliable plastic core of the metal, as dened above, is at a temperature below the liquefying temperature of the metal whereas the liquid surface layer of the two zone mass of metal is at a temperature at or above the liquefyng temperature of the metal. In addition the term liquid suspension hereinafter refers to a two-phase system consisting of a finely divided solid dispersed in liquid. The term pellets as used hereinafter defines a substantial ellipsoid or special shaped smooth mass of metal.

The invention comprehends a method of fabricating metal pellets which eliminates the need for tall dropping towers and which provides substantially spherical pellets of consistent composition, devoid of air pockets and having a relatively smooth and clean surface. The weight of the individual metal spheroids thus produced is highly consistent. The invention contemplates dropping globules of metal in the semi-molten stage from an orifice and permitting the globule to fall 12 inches or less and preferably about 2 to 4 inches through air or other gas and into liquid suspension.

Figure 1 shows one method of obtaining metal in the pliable plastic condition. A metal 2 is melted in a crucible 4 and then cooled to the pliable plastic condition by being stirred with rods 6 of the same metal until the molten metal no longer rapidly melts the rods. The pliable plastic metal 8 is then poured into a second crucible 10 which is heated to maintain the metal in the The heat input into the crucible is controlled to provide a thin liquid zone 16 along the walls of the crucible 10 to serve as a lubricant for the passage of the pliable plastic mass of metal through its passage in the crucible.

The second crucible has a discharge orifice 12 in its bottom wall. This pliable plastic mass of metal 8 will pass through the orifice 12 by gravity. By maintaining proper control of the temperature at the orifice 12 slightly above the melting point of the metal, the surface of the portion of the mass of pliable plastic metal in contact with the walls of the orifice, melts as indicated by 25, and acts as a lubricant for the remaining portion of the pliable plastic mass of metal to pass through the orifice as a semi-molten embryo globules 14.

It is necessary that the pliable plastic mass of metal pass from the crucible in a relatively short time to prevent the entire mass of semi-molten metal from being melted by the crucible or to prevent the temperature of the crucible from being lowered by the pliable plastic mass of metal to a point where it will no longer melt the contacting surface of the contained mass. The crucible temperature must be high enough to liquefy only the surface of the pliable plastic metal at the orifice but not so high that it will liquefy any appreciable amount of the mass contained in the crucible before the metal can pass through the orifice.

A suspension 18 is contained in a receptacle 28 with the top surface 22 of the suspension positioned about 12 inches or less below the bottom of the orifice 12. As the globules 14 of semi-molten metal emerge from the orifice and break off they fall through a resultant column of air or other gas and into the suspension '18 forming substantially spherical metal shot 24 having a substantially consistent composition throughout. Pellets produced by this method normally have a weight variation of only 10-15%.

Any liquid suspension which will withstand the temperature of the globules and has sufficent cooling capacity will produce satisfactory pellets. However, even suspcnsions which will decompose at the temperature of the globules will usually produce a few units of satisfactory pellets. For example, when aluminum in the semi-molten stage is dropped into a starch suspension i '4 water a few satisfactory pellets were obtained but as additional globules were dropped into the suspension the starch scorched. The resultant pellets ceased to be spherical and assumed a solidified conguration which resembled popped popcorn.

Various additives may be included in the suspension. For example, with colloidal graphite suspensions stablizers such as ammonium hydroxide are generally required and with many suspensions it is desirable that soluble oils or salts be added to prevent the dispersed particles in the suspension from adhering to the newly formed shot. For example, the addition of 1% to 5% soluble oil or 10% common table salt added to a colloidal graphite suspension produced cleaner shot but had no other pronounced eifect on the shot.

There is a definite relationship between the size of the orifice 12 and the consistency or fiuidty of the suspension 18 for each different metal or alloy 8 being treated. The relationship adheres substantially to the rule that as the size of the orifice increases the consistency or fiuidty of the suspension must be decreased. Of course, as the size of the orifice increases the size of the resultant pellets also increases and optimum ranges exist for each different combinaton of metal or alloy, oriced size and the consistency or fiuidty of the suspension.

For example, the following table lists for different metals 8, the size of pellets 24 produced for various diameters of the orifice 12 as well as the pcrcentage of colloidal graphite in the water suspension 18. The globules were dropped through a 2 to 4 inch column of air. It should be noted that smaller pellets can be produced when the semi-molten globule of metal is dropped from an orifice smaller than /g" if a sufciently high hydrostatic head is applied to force the pliable plastic metal through the orifice. The pellets are substantially spher ical but may flatten slightly depending on the precise percentage of dispersed matter in suspension. In the event that the pellets are not absolutely spherical the following table indicates the largest diameter.

Perecnt by Weight colloidal Graphite in Water Pellet Diameter (inches) Pellet Weight a s) orifice Diameter (inches) Metal Alumlnum Nickel Copper In addition to the above listed metals a 5 to 30 mix brass, phosphorous and silicon bronzes and cupro nickel have been satisfactorily formed into pellets by this process. Lead pellets formed by dropping in a foot high dropping tower have a diameter ranging from about 0.005 inch to 0.180 inch. substantially spherical pellets of aluminum and silicon bronze larger than Vz inch have been readily formed by the instant process.

In making pellets of commercially pure aluminum (1100 or 2S alloy), which contains a minimum of 99.0% chemically pure aluminum, the aluminum is melted and then cooled to the pliable plastic condition at a temperature range between 643 C. and 657 C. and preferably 650 C. i 2 C., as prevously described. The pliable plastic mass of aluminum is then transferred to a second crucible preheated to between 675-750 C. and having an /8 inch orifice in its bottom wall. The aluminum passes through the orifice as above described, and drops through air a distance between 2 to 4 inches into a water suspension of the type indicated in the following table.

The following table indicates the preferred percentage of material Suspended in water. These pcrcentages may a agasmallameunrde "nding on the grain size of the Suspended material.

Various materials well known in the art may be added to the suspension to increase the suspendability of the disi persed matter.

Any suitable colloidal graphite may be used such as that available under the trade name Superflake manufactured by superior Graphite Co., Chicago, Illinois, or Prodag" manufactured by Acheson Colloids Co., Port Huron, Michigan. It has been found that a suspension of colloidal graphite produces satisfactory resultswhen held between temperatures of 35-100 F. and preferably between 38-80 F. The temperature of the suspension must be high enough to prevent the liquid from freezin g but low enough so that the globules of semimoltel metal will solidfy very rapidly. Also, colloidal graphite is generally provided with a stabilizer such as ammonium hydroxide and when using this material it is necessary that the bath temperature be kept below about 100 F. so that the stabilizer will not be driven out of the suspension. The following suspensions in water:

I 43-45% starch, stearic acid and 2% caustic solution, or 1% agar agar each produced a few satisfactory pellets but subsequent pellets were of nondescript configuration because the starch was scorched, and the stearic acid and agar agar was melted by the temperature of the globules. Accordingly, any particulate solid inert at the temperatures to which the bath is subjected is suitable as a material to be dispersed in a liquid in forming the suspension so long as the particles are sufficiently small i and present in the correct amount.

It is to be understood that the invention is not to be limited to the specific suspensions enumerated in the description of the invention nor is the invention to be limited to the particular method of obtaining metal in the pliable plastic stage, and the semi-molten globules as herein described and as set forth in appended claims. Although several specific embodiments, materials and details have been set forth in the foregoing description it will be understood that various changes may be made without departing from the spirit and scope of this invention and that this invention is therefore not to be limited to such specific embodiments, materials or details except as set forth'in the appendent claims.

I claim:

1. The process of fabricating metal pellets which comprises maintaning a mass of metal in a pliable plastic state, separating a portion of the metal from said mass in a quantity suflicient to form a globule of said metal, heating the said separating portion of metal to an extent sufl'icient to liquefy the surface thereo f and forma liquid layer on the core of the separated globule but insufficient to affect the physical state of the core within the globule, and cooling said globule by dropping it into a liquid suspension said liquid suspension being stable at the temperature of the globule upon entry thereinto, and said coolingbeing sufficent to cause solidification of said globule.

6 2. *The method of 'forming metal pellets comprising providing -a mass of metal in a p'lasti'c, pliable state, separatin g andsimultaneously heating a portion 'of-said metal to anextent suicient to form globules of said metal conssting of a pliable plastic core of metal within a completely liquefied surface layer, and'cool ing said globules by dropping them into a liquid suspension which is stable at the temperature of the globules upon entry into 'the suspension, said cooling being suificientto cause 'solidification of said globules. i

3. In a process of fabricating metal shot by passing the metal through an orifice to form a globule and cooling the metal by dropping it through a fluid bath, the improvement comprising passing said metal through said orifice while said metal is in a pliable plastic condition, completely liquefying the surface of a portion of said metal to form a globule and cooling said globule by pass ing it through a liquid suspension which is stable at the temperature of the said globule upon entry into the suspension, said cooling being suficient to cause solidification of said globules.

4. The process of forming metal pellets comprising passing metal in a pliable plastic condition through an orifice completely liquefying the surface of a portion of said metal in its passage through said orifice to form globules and cooling said globules by dropping them into a liquid suspension which is stable at the temperature of the globule upon entry into the suspension, said cooling being sufiicient to cause solidification of said globules.

5. The method of forming metal pellets comprising forming globules of metal with the 'metal temperature being in the range wherein the globule consists of a core in a pliable plastic condition within a completely liquefied surface layer and cooling said globules by dropping them into a suspension which is stable with the temperature of the globules upon entry into the suspension, said cooling being sufiicient to completely solidify said globules.

6. The method of forming metal pellets comprising forming globules of metal at a temperature wherein the core of the said globule is in a pliable plastic condition, and said core is within a completely liquefied surface layer and cooling said globules by dropping them into a suspension which is stable at the temperature of the globule upon entry into the suspension, said cooling being suflicient to cause solidification of said globules.

7. The method of forming a metal pellet comprising melting a mass of metal to form molten metal, cooling the molten metal to below the melting point wherein said metal is in a pliable plastic condition, liquefying the surface of a portion of said metal to form a globule and solidifying said globule by dropping it into a liquid suspension which is stable at the temperature of the globule upon entry into the suspension.

8. The method of claim 7 wherein said molten metal is cooled by stirring the molten metal with a solid mass of metal until the molten metal no longer rapidly melts the solid mass.

9. The method of claim 8 wherein the solid mass of metal is of the same composition as the molten metal.

10. The method of claim 7 wherein the metal is melted and cooled in a first crucible and wherein the cooled metal v is then poured into a second crucible at a temperature slightly above the melting point of the metal.

11. The method of claim 10 wherein the metal in a pliable plastic condition is passed through an orifice in said second crucible wherein the surface of a portion of said metal is completely liquefied to form a globule and said globule is dropped into said suspension.

12. The method of claim 11 wherein upon emerging from said orifice the said globule of metal drops a maximum distance of about 12 inches before entering said suspension.

13. The method of forming metal pellets comprising passing fiowable metal in a pliable plastic condition ,th'ough 'an orce, lquefyng 'the surface of a portion of said metal in said orifice to form a globule, and cooling said globule by droppng it into a liquid suspension ..which is stable at the temperature of the globule upon entry into the suspension, said cooling being suflcent to solidify said globule.

14. The method of claim 13 wherein the metal is .aluminum. 15. The method of claim 13 wherein the metal is nickel. 16.'The method of claim 13 wherein the metal is Copper.

17. The method of claim 1 3 wheren the. suspension comprises a dispersion of collodal graphte. e

References Cited in'the file of this patent UNITED STATES PATENTS North July 5,1195$

Images