US 3896203 A
A method of forming filamentary material by rotating the outer circumferential edge of a disk-like heat-extracting member in contact with an unconfined drop of molten material. An apparatus for carrying out the method comprising a disk-like heat-extracting member having a V-shaped circumferential edge which contacts a drop of molten material produced by the local heating of an elongated solid member advanced toward the edge of the rotating member.
Claims available in
Description (OCR text may contain errors)
United States Patent Maringer et al.
CENTRIFUGAL METHOD OF FORMING FILAMENTS FROM AN UNCONFINED SOURCE OF MOLTEN MATERIAL Inventors: Robert E. Maringer, Worthington; Carroll E. Mobley, J12, Columbus, both of Ohio Battelle Development Corporation, Columbus, Ohio Filed: Apr. 23, 1973 Appl. No.: 353,692
US. Cl. 264/165; 164/87; 264/8; 264/332 Int. Cl. B29c 5/04; B22d 11/06 Field of Search 164/78, 87, 276', 264/8, 264/164, 165, 332
References Cited UNITED STATES PATENTS 12/1908 Strange et a1, 164/87 July 22, 1975 3,522,836 8/1970 King 164/87 3,710,842 1/1973 Mobley et a1 164/78 3,812,901 5/1974 Stewart et al 164/87 FOREIGN PATENTS OR APPLlCATlONS 7,315 8/1910 United Kingdom 264/8 24,320 10/1910 United Kingdom 164/276 Primary Examiner-41. Spencer Annear Attorney, Agent, or FirmStephen L. Peterson [5 ABSTRACT A method of forming filamentary material by rotating the outer circumferential edge of a disk-like heatextracting member in contact with an unconfined drop of molten material. An apparatus for carrying out the method comprising a disk-like heat-extracting member having a V-shaped circumferential edge which contacts a drop of molten material produced by the local heating of an elongated solid member advanced toward the edge of the rotating member.
13 Claims, 5 Drawing Figures CENTRIFUGAL METHOD OF FORMING FILAMENTS FROM AN UNCONFINED SOURCE OF MOLTEN MATERIAL BACKGROUND OF THE INVENTION The present invention relates to the art of making elongated filamentary articles by rotating a heatextracting member in contact with a source of molten material and solidifying a portion of the molten material as a filamentary product on the surface of the rotating member from where it spontaneously releases and is subsequently collected.
The prior art is replete with methods and apparatus disposed to produce filamentary material directly from a source of molten material. Most prior art methods are limited to metal products and use some type of forming orifice to control the size of the filament. Typical of such teachings is US. Pat. No. 2,825,108, Pond, where the molten material (a metal) is formed into a filamentary form by forcing it through an orifice so as to form a free standing stream of molten material subsequently solidified into filamentary form on a rotating heatextracting member. The rate of production is determined by the rate at which the molten material is expelled from the orifice and for continuous filament this rate must be at least roughly synchronous with the rate of movement of the heat-extracting member at the point of impingement. Techniques of this type are troubled by the relative complexity of process control and the inherent difficulty in passing molten material through small orifices. The orifices must be of an exotic material if the molten material has a relatively high melting point and the orifices have a tendency to erode or clog. A successful solution to the problem of forming orifices is taught in US. patent application Ser. No. 251 v9E5, Maringer et al. assigned to a common assignee. where a disk-like heat-extracting member forms the filamentary product by solidifying the product on the outer edge of the disk as it rotates in contact with the surface of a pool-like source of molten material. In this manner a filamentary product is formed without the use of a forming orifice. This teaching, however, is limited to the use of a pool-like source of molten material. Such a source of molten material necessitates the melting and holding of significant quantities of material. While the amount of heat needed to melt a given mass of a solid is the same regardless of its future disposition, the holding of quantities of molten material introduces several problems. The first is simply the energy required to maintain the molten material at high temperature. Second is the exposure of the molten material to the atmosphere. Without isolating the poollike source of molten material from the atmosphere, it is difficult to maintain constant chemical compositions in the molten material due to oxidation at the surface of the melt or the loss of volatile materials from the melt.
The present invention alleviates both oxidation and material evaporation problems since only a small portion of molten material is exposed to the atmosphere at any one time. Furthermore, since the molten material is localized it can be easily protected by a local inert gas shield.
A further advantage of the present invention is that the location of filament formation relative to the circumference of the rotating member is variable and can be manipulated to enable filament trajectories not possible where the configuration of filament formation in relation to the rotating member is dictated by the use of an open pool-like source of molten material.
The present invention produces a filamentary product without the use of a forming orifice or the need for a pool-like source of molten material thereby improving the prospects of making low-cost filamentary material directly from molten material.
The present invention finds significant utility in forming filamentary products from materials that are difficult to mechanically form. The advent of fiber reinforced composites has created a demand for filamentary material of refractory metals and alloys yet those materials are extremely difficult to mechanically form into filament. The present invention is known to be operable in forming such materials into both continuous and discontinuous filament in sizes down to l5 microns in effective diameter. With the present invention providing filamentary materials heretofore only available through expensive and difficult mechanical forming the potential usefulness of fiber reinforced materials is greatly enhanced.
SUMMARY OF THE lNVENTlON The present invention is a method of forming filamentary material directly from a source of molten material. The present invention is not confined to metallic fiber but will form filament from any material having properties in the molten state similar to those of metals. The source of molten material for the present invention is a portion of molten material adherent in a drop-like form to a solid with its shape determined by the surface tension of the molten material. The circumferential edge of a rotating disk-like heat-extracting member is brought into contact with the molten material and a filamentary product is formed adherent to the rotating member. Ultimately the filament spontaneously separates from the rotating member to be collected.
The crux of the present invention is the fact that the edge of the heat-extracting member having a significant velocity can contact a small unconfined portion of molten material and extract from it a solid formed into a filament without materially disturbing the stability of the drop-like form of the molten material. The present invention is capable of producing both continuous and controlled length discontinuous filament.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is the side view of a rotating heat-extracting member forming a filament from a drop of molten material pendant on a rod-like source of material.
FIG. 2 is the same embodiment as FIG. 1 turned so as to show the shape of the molten material in relation to the heat-extracting member.
FIG. 3 is an enlarged cross section of the embodiments of FIGS. 1 and 2 showing the molten material and the configuration of the circumferential edge of the rotating heat-extracting member.
FIG. 4 is an enlarged cross section of the present invention in which the pendant drop is produced by having a drop pendant from an orifice leading to a supply of molten material.
FIG. 5 is a side view of a prior art rotating member that produces controlled length discontinuous filament when used with the present invention.
DETAILED DESCRIPTION OF THE INVENTION One embodiment of the present invention is shown in the FIGS. 1 through 3 where a rotating disk-like heatextracting member 30 has a V-shaped edge 32 on a circumferential projection 31. The member 30 is rotated in a direction indicated by the arrow in FIG. I so as to contact a molten portion of the member 20. The member 20 is the material supply for the process with the portion 51 of the member 20 being melted by some means of local heating at 50. The local heating of the portion 50 creates a molten zone adherent to the member 20 but in contact with the moving edge 32. Surprisingly the surface tension of the material in the portion 51 is sufficient to maintain stability even with the edge 32 entering and inducing a shear flow within the liquid portion 51. For purposes of definition the unconfined molten material adherent to a solid member will be termed a pendant drop irrespective of the geometric configuration of the drop to the solid member or the force of gravity. By unconfined it is meant that the drop is not restrained by any member disposed to oppose the shear forces generated by the forming member passing through the drop. The drop may be supported against the effect of gravity by the presence of the solid member from which the drop is formed by local heating or the presence of an orifice may support the drop but no attempt is made to restrain the drop from the motion induced by the forming member. When the circumferential edge 32 passes through the pendant drop 51, a portion 10' of the molten material solidifies on the edge 32. Further rotation of the member 30 draws this (solidified) filamentary portion 10' out of the pendant drop 51. The filament 10', still adherent to the edge 32, ultimately spontaneously separates from the edge 32 at point 12 to become a collectable solid filament 10.
FIG. 4 shows the present invention in a different embodiment where the pendant drop 51 is not produced by the local heating of a solid but is instead produced by forming a pendant drop adherent to an orifice 40 leading to a supply of molten material 22. The pendant drop need to be spherical in cross section but may be elongated, formed by an elongated orifice so as to permit a plurality of edges to pass through the elongated pendant drop.
FIG. 5 illustrates a rotating heat-extracting member 30 having, in this embodiment, semi-circular indentations 33 on the edge 32 of the rotating member. The indentations 33 on the edge attenuate the filament into discrete fibers 11 equal in length to the distance between the indentations. Surprisingly the passage of the edge 32 containing indentations therein through an unconfined drop 51 of molten material does not mate rially disturb the stability of the drop. For most embodiments of the invention utilizing the indented rotating member th edge 32 appears to protrude into the drop a distance of less than 10 mils. The use of high rotational speeds for the rotating member (and hence high linear velocities at the edge 32) are preferred for this embodiment and discontinuous fiber having: a length in the range of from 0.18 to 0.24 inches, an effective diameter in the range of from I to l0 mils has been most effectively produced at linear edge velocities in the range of from 5 to 60 feet/second. The invention is, of course, operable in this embodiment outside the aforementioned preferred range.
The source material must have certain properties so as to be operable with the heat-extracting member to form a filament. The molten material should have. at a temperature within 25 percent of its equilibrium melting point in K, the following properties: a surface tension in the range of from l0 to 2,500 dynes/cm, a viscosity in the range of from 10' to l poise and a reasonably discrete melting point (Le, a discontinuous temperature versus viscosity curve). The present invention is known to be operable with most metals as well as chemical compounds. and elements meeting the above criteria. In addition, the present invention is operable with metal alloys even where such alloys display a wide temperature range between the first solidification of any component within the alloy (the liquidus temperature) and the temperature at which the lowest melting point compositions solidify (the solidus temperature) yielding a completely solid material. For purposes of definition, such an alloy would be molten" only above the liquidus temperature even though there is some molten material present at a temperature between the liquidus and solidus temperatures.
Because of the limited exposure of the molten mate rial to the surrounding atmosphere and the ease in providing local gas shielding of the pendant drop, the oxidation characteristics of many metals and alloys do not limit their operability with the present invention as depicted in FIGS. 1 through 5. Materials known to be operable without the need for complete oxidation protection include the metals consisting essentially of iron, aluminum, copper, nickel, tin, and zinc. Where it is desired to totally isolate the process from the surrounding atmosphere, the entire apparatus may be confined within a gas tight sealed closure. The process could then be carried out in a vacuum or in inert gas. If the source material has a significant vapor pressure, the composition and pressure of the gas within the enclosure could be manipulated so as to reduce evaporation from the molten material. Such an enclosure would also facilitate the use of local heating means that are inoperable in the atmosphere (e.g., electron beam heating). Metals operable with means to reduce oxidation include those consisting essentially of chromium, titanium, columbium, tantalum, zirconium, magnesium, and molybdenum.
The means used to locally heat the material so as to form an adherent pendant drop is not critical to the invention. There are numerous means available in the art to locally heat a member and one skilled in the art can arrrive at an operable embodiment of the invention without the need for excessive experimentation. For example, an oxygen-acetylene torch may be used with many materials and is an acetylene rich flame is used would have the advantage of providing a shielding atmosphere to the pendant drop to reduce oxidation of the molten material. Various heating means may be used including resistance heating, induction heating, electron beam heating etc. The means used for local heating of a solid source would be determined by considering the melting point of the material to be melted, the mass of material to be molten at a given time and the rate at which the source material is to be heated to its melting point. If the heat supplied the source material is excessive, then the pendant drop may become too large to remain stable. If the heat is insufficient, then the rotating filament forming member will not have sufficient molten material to produce a filament of controlled dimension.
In the embodiment of FIG. 4 the means used to create the molten metal supply may be of any conventional type. Some means of heating the material at the orifice may be needed if the configuration of the molten supply is such that the orifice is at a significantly lower operating temperature than the remainder of the molten metal supply.
Within the operable range of heat input to the source material the size of the filamentary product may be controlled by the amount of molten material available to the edge of the rotating member. By limiting the volume of the molten source material and rotating the heat-extracting member at high rates of speed filamentary products of very small cross section can be produced. Since the cross section of the filamentary product is normally non-circular the size of the filament is defined in terms of its effective diameter. The effective diameter ofa filament having an irregular cross section is equal to the diameter of a filament having a circular cross section and equal in cross-sectional area to the cross section of the non-circular filament. The present invention is known to be capable of producing filament having an effective diameter in the range of from 0.0004 to 0.030 in.
The present invention can produce both continuous and discontinuous filament. FIG. 5 illustrates an embodiment disposed to produce discontinuous fiber of controlled length. The edge of the rotating heatextracting member is indented at the interval desired to be the filament length. The shape of the indentations is not known to be critical and a semi-circular indentation of a depth greater than the thickness of the filament will produce controlled length discontinuous filament.
FIGS. 1 through 4 show three embodiments of the present invention. The circumferential edge of the rotating heat-extracting member in those embodiments has a V-shape so as to limit the area of the circumferen tial edge in contact with the pendant drop. The area may also be limited by using an edge having a circular cross section if the radius of that cross section is less than 0.5 inch. A dimensionally inferior product will result from rotating a member in contact with the pendant drop without limiting the area in contact with the molten material. Such a process would not produce a dimensionally consistent product as does the present invention since such a surface generates larger shear forces within the pendant drop that degrade its stability. To produce dimensionally consistent filamentary material the pendant drop should be as stable as possible during the process. The stability of the pendant drop as utilized in the present invention is due to the fact the edge of the rotating member passed through the pendant drop is extremely narrow in relation to the width of the drop. This minimizes the disturbance of the drops surface which through surface tension is responsible for the stability of the drop form.
The Vshaped member depicted in the figures is a preferred embodiment of the invention and such an embodiment would have a radius of curvature at the tip of the V in the range of from 0.0005 to 0.10 inch. Such a member will produce dimensionally consistent filament having a cross-sectional area of less than 0.003 square inches.
The diameter of the rotating heat-extracting member is not critical to the invention but a preferred embodiment would have a diameter in the range of from I to 30 inches. The heat-extracting member need not be of any special material but must simply have the capacity to remove heat from the molten material at a rate so as 5 to solidify the material in the form of a filament on the circumferential edge. The heat-extracting member should have either a high intrinsic heat capacity or have good thermal conductivity so as to extract heat from the molten material. Even materials not having either a high heat capacity or thermal conductivity can he used if they are subjected to some means of internal cooling. The present invention is known to be operable with heat-extracting members composed of the metals copper, aluminum, nickel, molybdenum, and iron. There is no indication a metal member is needed and a nonmetal (as for example, graphite) may be used as the material for the heat-extracting member. The member may also be composed of several different materials so as to combine the properties of each to optimize the performance of the rotating heat-extracting member.
The geometric configuration of the various elements of the embodiment shown in the figures is not the only operable configuration. However. with the pendant drop being unconfined, the force of gravity must always be considered. The shape of the pendant drop is determined by gravity, the surface tension of the molten material and the viscous drag induced by the contact of the rotating member. Where the pendant drop is contacting the rotating member in the upper l80 of its eir cumferenec, the drop is also supported to some degree by the edge of the wheel and the stability of the pen dant drop in that preferred embodiment is improved over other configurations.
While the term pendant drop is used throughout the specification and the term is clearly applicable for the embodiments having the drop on the upper 180 of the forming member it should be understood that the invention is also operable with what is termed a sessile drop. Looking at FIG. 1 if the location of the drop were l80 from its indicated location (i.e., if the member were inverted and contacted the member 30 at its lower extremity) the drop would properly be called a sessile drop. The invention is operable in both configu rations and the drop is referred to as a pendant drop in this specification.
The ultimate size of the filamentary product is deter mined by the amount of molten material available at the circumferential edge of the heat-extracting memher, the shape of the edge introduced to the pendant drop, the viscosity of the molten material and the speed at which the edge is passed through the pendant drop. The invention is known to be operable where the linear velocity of the circumferential edge is in the range of from 3 to 100 feet per second. The upper limit does not appear to be a limitation of the invention but merely the effect equipment limitations made apparent by the high rotational speeds required to generate that linear rate of the edge of the rotating member.
MODE OF OPERATION OF THE INVENTION The present invention was utilized in the following illustrative examples:
EXAMPLE I A drop of liquid tin was formed on the end of a solid bar of tin by locally heating the end with a propane torch. The drop was adherent to the l inch by V4 inch cross section of the bar and was manually brought into contact with the circumferential edge of a rotating heat-extracting member. The rotating member was a water cooled copper disk /2 inch thick, 8 inches in diameter having a V-shaped peripheral edge. The angle between the faces of the V was 90 and the radius of curvature at the circumferential edge of the V was approximately 0.005 inch. Upon contacting the drop to the upper portion of the rotating member semicontinuous tin fibers were formed and spontaneously released from the forming edge. The heat-extracting member was rotated at various speeds in the range of from 100 to l .500 rpm (yelding linear velocities at the circumferential edge of from 3.9 to 59 feet/second). The cross-sectional area of the fiber generally decreased with increasing rotational speed of the heatextracting member.
EXAMPLE 11 The same heat-extracting member as was used in Example l was rotated at 250 rpm (9.8 feet/second at the circumferential edge) in contact with a drop of molten A1 formed by locally melting the end on an alumina rod with an oxyacethylene torch. Short lengths of A1 0 fiber approximately 1 inch long were produced.
EXAMPLE Ill The same heat-extracting member as used in the previous examples was rotated at 1,500 rpm (59 feet/second at the circumferential edge) in contact with a drop of molten 304 stainless steel (18.020.0 chromium, 8.0-1 1.0 nickel, 2.0 oxjacetylene maximum of manganese and 0.08 maximum carbon, all in weight percentages with the balance iron). The drop was formed by locally melting the end of a 3/16 inch diameter rod using an acetylene-rich oyacetylene torch. The flame of the torch was intentionally acetylene rich so as to provide an oxygen deficient gas surrounding the molten drop. There was no protective atmosphere other than the oxygen deficient flame and the melting was carried out in air. Fiber lengths in excess of 10 feet were produced with a cross-sectional area of 8 X 10 square inches and an approximate effective diameter of 3.1 X 10 inches.
EXAMPLE IV The same heat-extracting member as used in the pre vious examples was rotated at speeds in the range of from 500 to 1,500 rpm in contact with a drop of a heatresistant alloy N- l 55 (.15 carbon, 1.50 manganese, .50 silicon, 21.0 chromium, 20.0 nickel, 3.0 cobalt, 2.5 tungsten, 1.0 columbium. in nominal weight percent with the balance iron). The drop was formed adherent to a solid rod of the alloy by locally melting the end of the rod with an acetylene rich oxyacetylene flame. Fibers having lengths of several feet, cross'sectional areas of approximately 1.5 X 10 square inches and effective diameters ofapproximately 4.3 X inches were produced.
EXAMPLE V A cold rolled steel heat-extracting member of the same general shape as that used in the previous examples was used to produce pure chromium fiber. The heat-extracting member was water cooled and had a radius at its circumferential edge of 0.005 inch. The heat-extracting member was rotated at speeds in the range of from 200 to 1,500 rpm in contact with a drop of molten chromium produced by locally heating the end of a commercially pure chromium rod with an oxyacetylene torch. Fiber having lengths up to several inches, effective diameters of approximately 3 X 10' inches and cross-sectional areas of approximately 7 X 10 square inches were produced.
EXAMPLE VI A cold rolled steel heat-extracting member of the same general dimensions as those used in the previous examples was used to produce controlled length discontinuous fiber. The circumferential edge of the member (having a radius of 0.005 inch) included semicircular indentations approximately 0.010 inch deep and spaced approximately 0.25 inch along the circumference. The indentations were disposed to attenuate the filament into fibers of a length equal to that of the distance between indentations (.20 inch). The top of the water cooled heat-extracting member was brought into contact with a drop of molten 304 stainless steel adherent to the lower extremity of a vertically suspended solid rod of the same material. The drop was produced by locally heating the stainless steel rod with an oxyacetylene torch. The heat-extracting member was rotated at a speed in the range of from 200 to 1,000 rpm and discontinuous fiber approximately 0.20 inch in length and 5 X 10 square inches in cross-sectional area were produced.
EXAMPLE VII A copper heat-extracting member having dimensions similar to the member used in Example 1 through [V was used to form filament of commercially pure titanium. The filaments were formed in a bell jar vacuum system at a pressure of approximately 10" mm of mercury. A vertically suspended .25 inch diameter rod of titanium was locally melted at its lower extremity by an electron beam. The molten drop of titanium was contacted by the circumferential edge of the heatextracting member rotating at 350 rpm (linear velocity at the edge was 13.7 feet/second) without the use of internal water cooling. Titanium fiber in lengths ranging from one to several feet were produced. The crosssectional area of the fiber ranged from 5.5 X 10" to 1.2 X 10 square inches.
EXAMPLE VIII The same system as was used in Example Vll was used with two different heat-extracting members to produce commercially pure columbium (niobium) filament. The rotating heat-extracting members were of the same dimensions as that of Example Vll one being copper and the other molybdenum. The columbium rod was melted in the same manner as the titanium rod of the previous example. Approximately the same rotational speeds were used in two separate runs. With the copper heat-extracting member filament having a cross-sectional area of 8 X 10 square inches was produced. The molybdenum member produced filament having an area of 2 X 10 square inches. Both heatextracting members produced filament of lengths up to 1 foot.
The present invention has been disclosed by way of general discussion and specific examples. While the general discussion of the invention sets out the operable range of the invention the specific examples may not in all cases be the preferred embodiments. The speeifie examples illustrate embodiments of the invention known to be operable and are merely to indicate to one skilled in the art how the invention can be utilized. One skilled in the art may devise operating parameters within these general teachings with some beneficial result. however. the scope of this invention is defined solely by the appended claims.
1. A method of making filamentary material comprising the steps of:
a. heating a solid material so as to form an adherent pendant drop;
b. rotating a heat-extracting member at a rate so as to yield a velocity on its circumferential edge in excess of 3 feet per second;
c. limiting the area on said edge by constructing said member with at least one circumferential projection; and
d. contacting the surface of said pendant drop of molten material with said edge.
2. The method of claim 1 where said molten material has at a temperature within 25 percent of its equilibrium melting point in degrees Kelvin; a surface tension in the range of to 2,500 dynes per centimeter, a viscosity in the range of If) to l poise and a reasonably discrete melting point.
3. The method of claim 2 where said material is a metal.
4. The method of claim 3 wherein said metal is an alloy having a base metal selected from the group consisting of: iron. aluminum, copper, and nickel.
5. The method of claim 3 wherein said molten metal is protected from oxidation and where said metal is an alloy having a base metal selected from the group consisting of: chromium, titanium. columbium, tantalum. zirconium, molybdenum and magnesium.
6. The method of claim 5 wherein the means of protecting said molten metal comprises an evacuated enclosure surrounding the molten metal and the rotating heat-extracting member.
7. The method of claim 2 wherein said molten material is an inorganic compound.
8. The method of claim 7 wherein said inorganic compound is Algoa.
9. The method of claim 2 wherein said drop is formed by melting one end of a rod of solid material.
I0. The method of claim 9 wherein said drop is positioned adjacent the upper l of a cylindrical rotating heat-extracting member.
11. The method of claim 1 wherein said projections are V-shaped and have a radus of curvature at the tip of said V in the range of from 0.0005 inch to 0. l 0 inch and said filament has a cross-sectional area less than 3 X l0 square inches.
12. The method of claim 11 where said V-shaped projections include a plurality of indentations disposed to attenuate said filament into discontinuous fiber having a length approximating the circumferential distance along the tip of said V-shaped projection between said indentations.
13. A method of making filamentary material comprising the steps of:
a. providing a pendant drop of molten material protruding from an orifice; said drop having a shape determined by the surface tension of said molten material;
b. rotating a disk-like heat extracting member having at least one tapered circumferential projection at a rate so as to yield a velocity on its circumferential edge in excess of 3 feet per second;
c. contacting the surface of said pendant drop of mol ten material with said projection; and
d. withdrawing a solidifying filament from the drop on said projection while maintaining the form and stability of the pendant drop and without confining said drop.