US3685568A - Method of quenching metal filament in froth - Google Patents

Abstract

A process for directly producing metallic filaments and fibers from molten metal by extruding a stream of the molten metal into a froth quenchant. The froth serves to quickly solidify the molten metal stream without damaging inertial effects, thus making the process ideally suited for metals having a high latent heat of fusion and/or a high surface tension.

Description

United States Patent 1151 3,685,568 Pond, Sr. 1 51 Aug. 22, 1972 [54] METHOD OF QUENCHING METAL 2,976,590 3/l96l Pond ..l64l82 FILAMENT IN FROTH 3,2l6,076 l [/1965 Alber et al 164/82 X 3,347,959 10/1967 Engelke et a]. ..l64/82 X [72] a?" westmmste" 3,543,831 12/1970 Schile ..l64/86 x [73] Assignee: United States Steel Corporation P i Examiner R Spencer Anneal- 22 Filed: March 1 1971 Attorney-Forest C. Sexton [21] Appl. No.: 119,752 57 ABS A process for directly producing metallic filaments [52] US. Cl. ..l64/89, l64l82, 264/ 176 F and fibers from mom metal by extruding a stream of [5i] I ll. Cl. 11/12 v the molten metal into a froth quenchant The froh Fleld of Search 89, Serves to the molten stream without damaging inertial effects, thus making the [56] References cued process ideally suited for metals having a high latent UNITED STATES PATENTS heat of fusion and/or a high surface tension.

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Attorney BACKGROUND OF THE INVENTION It is well accepted that metallic filaments and fibers can be formed by nondrawing processes involving direct casting techniques. Direct casting renders a wirelike product without distortion of the metal grain form and therefore without substantial residual stresses. Although early processes for such direct casting involved the mere casting of molten metal into grooves, more recent advancements have resulted in improved processes which usually involve extrusion of a continuous stream of molten metal, and then solidification of the stream in flight while it is in the extruded filamentary form. solidification of the extruded form may be effected by passing the liquid stream through a cooling atmosphere, or by extruding the liquid stream onto a rotating or moving chill plate, the motion of which is sufficient to maintain the extruded molten metal in its filamentary form until solidified.

In my US. Pat. No. 2,879,566, I describe another process for direct casting of metal filaments wherein a continuous stream of molten metal is extruded into contact with an unconfined gaseous jet stream. The jet stream not only serves to quench the molten metal, but further serves to support the molten metal in its filamentary form.

The manufacture of fine wires or filaments by the above patented process finds a limitation when the latent heat of fusion of the metal is sufficiently high and/or the surface tension of the metal sufiiciently large to cause the extruded metal stream to be pinched off before solidification can occur. The result is that these metals, such as iron, steel, copper, nickel, beryllium and boron, for example, can be processed to produce only short or extremely short fibers. In order to produce a filament of appreciable length from these metals, it is apparent that solidification of the metal stream must be effected more quickly and closer to the extrusion nozzle than is possible in air or other gaseous coolants at ambient temperatures. Although water or other liquid quenchants would indeed solidify a metal filament very quickly as necessary, liquid quenchants are not suitable because of the excessive inertial effect the liquid would have on the metal filaments. That is to say, a rapidly moving molten metal stream disintegrates when it strikes a massive liquid surface.

SUMMARY OF THE INVENTION This invention is predicated upon my development of a new method for producing metallic filaments and fibers utilizing a froth quenchant. A froth provides a rapid quenching efiect similar to water due to its relatively high specific heat, heat conductivity and heat of vaporization but without the damaging inertial efl'ect due to the liquid mass. The method is therefore ideally suited to the manufacture of fibers and filaments of metals having a high latent heat of fusion and/or a high surface tension.

It is, therefore, an object of this invention to provide a new and improved method for the direct production of filaments and fibers of appreciable length from metals having a relatively high latent heat of fusion and/or a relatively high surface tension.

It is another object of this invention to provide a method for the direct production of metallic filaments and fibers by extruding a molten metal stream into a froth quenchant.

BRIEF DESCRIPTION OF THE DRAWING The attached FIGURE illustrated apparatus, shown in partial cross-section, as may be used in the practice of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The embodiment of the apparatus shown in the drawing essentially comprises means for injecting a molten metal stream into a vertically disposed froth column over a frothing solution such that the extruded molten filament will quickly solidify as it falls through the froth column prior to settling in the frothing solution. More specifically, the apparatus shown comprises an open tank 10 containing a frothing solution 12. The frothing solution 12 may be an aqueous soap solution or any similar solution, aqueous or nonaqueous, having a suitable surface tension as will form a reasonably stable froth having relatively high specific heat, heat conductivity and heat of vaporization values.

An elongated froth stand pipe 14, open at both ends, or any walled body defining a laterally confined space, is vertically disposed over the frothing solution 12 with the lower open end thereof immersed below the surface of solution 12. Any means, such as flange supports 16 secured radially to the outer walls of stand pipe 14, may be used to maintain stand pipe 14 in a vertical position over the frothing solution 12. At least one conduit 18 is provided through or under the wall of stand pipe 14 at a point below the surface of solution 12, to admit compressed air or gas thereto and thereby form a froth 20 which will raise in stand pipe 14 above the frothing solution 12.

The extrusion equipment, such as a thermally insulated vessel 22 having an extrusion nozzle 24, is positioned above the upper open end of stand pipe 14 with the extrusion nozzle 24 aiming downward at approximately the axis of stand pipe 14. Vessel 22 should be thermally insulated and may also be provided with a suitable heating means such as an induction coil (not shown) to maintain the metal therein in molten form.

To produce metallic filaments with the above described apparatus, tank 10 must be filled with a frothing solution 12, as described, to a level that will submerge the lower end of stand pipe 14 and the outlet of conduit 18. Compressed air, or other suitable gas, is admitted through conduit 18 at a rate sufficient to maintain an upwardly moving column of froth 20 within stand pipe 14. The filament forming metal, in molten state, is extruded from vessel 22 through nozzle 24 by any conventional extrusion technique. The extruded molten metal stream or streams, indicated by lines 26, falls downward due to gravitational pull, and momentum countercurrently through the upward moving froth column 20 where they quickly solidify during the fall due to direct contact with the froth 20. The filaments are then collected at the bottom of tank 10, in solution 12, and are thereby further cooled to the solution temperature.

The froth column 20, being a mixture of liquid and gas, will cool the molten metal stream much more quickly than will pure gaseous quenchants since thin films of liquid, i.e., bubble surfaces, are repeatedly deposited on the stream surface as the stream falls therethrough. The liquid film, of course, provides a greater cooling effect than would pure gas because of its heat of vaporization and higher specific heat and heat conductivity. It is apparent that the amount of liquid involved in heat transfer is not great and would perhaps be quite insignificant in quenching hot metal pieces of substantial volume. In this application, however, the molten metal stream is quite thin, providing a substantial surface area to volume ratio, so that the small amount of liquid film quenchant involved is quite effective in quickly quenching the stream' without damaging inertial effects.

As indicated above, this invention is particularly directed towards the use of those metals which have a high latent heat of fusion and/or a high surface tension, so that the metal can be quickly solidified before it is pinched off at the nozzle in extremely short fibers. To this end, therefore, the spacing between the froth 20 and nozzle 24 should be as close as possible without actual contact. It is most essential that the froth should not impinge on the nozzle as direct contact will either cause the nozzle orifice to be plugged due to premature metal solidification or cause the nozzle to crack due to thermal shock. For this reason, it is preferable to space the nozzle 20 somewhat above the terminus of stand pipe 14, and then controlling the air flow rate through conduit 18 to assure that the froth 20 crests as close as possible to the nozzle without contact therewith. Nozzle to froth spacings of 2 to 3 inches are usually satisfactory.

The distance of travel of the molten stream through the froth column 20 must be sufiicient to ensure that the stream is solidified before it falls into the solution 12. This will vary depending upon stream diameter, velocity and temperature, as well as the rate at which the froth is rising. As a practical matter, a 48-inch froth column proved satisfactory for most applications.

For most applications, control and maximization of froth formation rate is most essential for optimum production. Whenever suitable fibers are not being formed, an increase in froth fonnation rate will frequently solve the problem. For example, if the punch off" distance is decreasing due to a decreasing nozzle orifice diameter, an increase in froth formation rate will shorten the spacing between nozzle and froth to compensate therefor. On the other hand, when the metal is not solidifying fast enough due to thicker filaments caused by an increasing nozzle orifice diameter, an increase in froth formation rate may be necessary to remove the greater heat of fusion. An increase in metal stream velocity may necessitate an increase in froth formation rate to remove the heat faster.

To give one specific example of the above process in more detail, cast iron filaments having a diameter of 0.010 inch have been produced with apparatus substantially as shown utilizing a simple soap solution and compressed air to produce bubbles approximately three-fourths inch in diameter. The stand pipe was 3 inches in diameter and provided a froth column apfiff'fififlilil2hifl$ffi3 2*fll'33f2lll froth movement was varied from 0.2 to 0.8 gallons of water per minute, and the molten iron was extruded at 2,240F and at a rate of approximately 20 ft./sec. The resulting 0.010 inch iron filaments measured from 56 to 4 inches in length.

Although the above described embodiment is rather specific, it should be apparent that other embodiments and modifications could readily be utilized without departing from the basic concept of the invention. For example, the invention is said to be primarily directed to the production of filaments from metals having high surface tensions or high latent heats of fusion. Although this process does solve particular problems in processing such metals, many other metals not falling into this category could as easily be handled by this process. Although the apparatus and process described above is ideal for single stream laboratory production, commercial operations could easily incorporate many advantageous modifications, such as extruding a plurality of streams simultaneously. A larger solution tank 10 could then be utilized to eliminate the need for stand pipe 14, the walls of the larger tank serving to confine the froth as a large mass. In addition, a more intricate built-in frothing system could be devised to replace the single conduit 18, and a wide variety of frothing solutions, both aqueous and organic, could be used.

Iclaim:

l. The method of producing metallic filaments and fibers from molten metal comprising extruding a stream of molten metal directly into a froth mass of predetermined configuration such that the metal stream will solidify into a metallic filament while falling through said froth mass.

2. The method of claim 1 in which said froth is continuously formed over a frothing solution by bubbling compressed gas into said solution.

3. The method of claim 2 in which said continuously formed froth is caused to rise within a stand pipe counter to the molten metal filaments falling therethrough.

Claims (2)

1. 2. The method of claim 1 in which said froth is continuously formed over a frothing solution by bubbling compressed gas into said solution.
2. 3. The method of claim 2 in which said continuously formed froth is caused to rise within a stand pipe counter to the molten metal filaments falling therethrough.

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