IL43798A - Method of producing continuous filament by solidification of molten material on a moving heat extracting member - Google Patents

Description

43798/2 IniB lain © pix'a ·>"ρ C»D*ST o^a^o -ηχΌ πυ·»ϊ? Din K'sion p"?n A method of producing continuous filament by solidification of molten material on a moving heat extracting member Battelle Development Corporation BACKGROUND OF THE INVENTION The present invention relates to the field of the art where a source of molten material is solidified on a moving heat-extracting member so as to form an elongated solid product on such a member.

The prior art pertinent to the present invention would include U.S. Patent App-H^ation-Seriei No . 2*&i-,*9&&- 3.838.1 where a method of producing filamentary materials is disclosed. In that reference there are no external forces applied to the filament as it spontaneously leaves the rotating heat-extracting member and as a consequence the point of filament release varies somewhat during the process. Similarly U.S.

Patent 2,825,108 discloses a method of making filament by impinging a stream of molten material onto a rapidly moving heat-extracting member. In both methods of filament production the variations of the adhesion to the rotating heat-extracting member made the release point unstable and as a consequence both such processes have shortcomings that the present invention alleviates.

Surprisingly when a tension force is applied to the filament and the filament is supported, the inherently variable adhesion is overcome and the release point stabilized without inducing breakage in the filament due to variations in tension. In addition, the applied force in the filament does not interrupt the solidification of the filament on the rotating heat-extracting member even though the tension force is applied very close to the point of filament solidification. This is especially significant when it is realized the present invention operates at high rotational speeds and produces a One embodiment of the present invention also reduces filament breakage by controlling the rate of heat removal from the filament subsequent to formation from the melt thereby reducing filament embrittlement caused by solid state trans-formations dependent on the rate of heat removal.

It is one object of the present invention to stabilize the release point of the filament from the rotating heat-extracting member. In doing so the present invention alleviates numerous shortcomings of the aforementioned prior art methods. The present invention is applicable to prior art forming techniques that rely on spontaneous release of the filamentary product from the rotating heat-extracting member.

When such release occurs, it is influenced by the speed of the rotating member and the trajectory of the released filament is a function of this speed. As a result the collection of the filament is difficult since the collecting means must be able to adapt to the different trajectories introduced when the rotating member changes speeds. The present invention makes the trajectory of the filament independent of the speed of rotation of the heat-extracting member, therefore, eliminating some collection problems.

In addition, the two noted prior art processes introduce small cross-section filaments into a gaseous atmosphere at high velocities. This results in the generation of aerodynamic forces on such filaments that tend to buckle the filament in mid-air. Where the object of the process is to produce continuous filament, this buckling and the resultant tangling of the filament prevent collection of the filament in a usable form and thereby limits its use. The present a filament by having the filament slide on a support between the release point and the tension exerting means and therefore the filament may be collected in an orderly manner that was impossible with the prior art methods.

The sliding contact of the filament in contact with the support has additional benefits. First it limits the access of the surrounding atmosphere to the surface of the filament which reduces oxidation of the filament. Second the support itself can be used to control the rate of heat removal from the filament by manipulating the thermal capacity of the support means. In this manner materials that undergo embrittling transformations dependent on the rate of heat removal could be collected where such an embrittlement would have ordinarily made such a filament virtually uncollectable.

The present invention not only improves the application of the prior art techniques of producing continuous filament but makes such techniques practical for the collection of continuous lengths of materials heretofore considered unmanageably brittle if produced directly from the molten material.

SUMMARY OF THE INVENTION The present invention is a method of stabilizing the release point of a filament producing method that solidifies a filamentary product on the surface of a rotating heat-extracting member relying on spontaneous release of the fiber from the surface of the rotating member. By the application of a tension force to the filament subsequent to its release from the rotating member while supporting the filament at a position lower than its free flight trajectory the operation of the the filament may also be used to control the rate of heat removal from the filament subsequent to its release from the rotating member by altering its thermal capacity.

The present invention would contemplate the application of a tension force to a filament subsequent to its release from a rotating heat-extracting member and the supporting of such a filament on a member below the free flight trajectory of such a filament leaving the rotation member without the applied tension. The magnitude to the tension is less than other forces causing the release of the filament from the rotating member and is sufficient only to overcome variations in the adhesion of the filament to the rotating member with the filament spontaneously releasing from the rotating member with or without the application of the tension force.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partial cross section of the invention as it is used with one particular filament forming method showing the relationship between the process of filament formation and the application of an aligned force through the filament.

Figure 2 is a cross section of the circumferential edge of the rotating member of Figure 1.

Figure 3 is a partial cross section of the invention as it is used with a second filament forming method showing the relationship of the free flight trajectory to the path of the filament utilizing the present invention.

Figure 4 is one embodiment of a means used to generate the tension force in the filament.

DETAILED DESCRIPTION OF THE INVENTION solidifying molten material in filament form on a rotating heat-extracting member where the filament is spontaneously released from the rotating member. The small tension and bending forces applied even to materials exhibiting little measurable ductility do not promote breakage and product continuity is significantly easier with the present invention than with the cited prior art techniques involving spontaneous filament release. The application of a directed tension force stabilizes the process of filament formation by inducing a constant release point of the filament from the heat-extracting member. The present invention is operable with extremely brittle materials in some embodiments and facilitates a constant release point without inducing filament breakage.

Figure 1 shows a cross-sectional view of one embodiment of the present invention. The rotating disk-like member 30 is in contact on its circumferential edge 32 with the surface 15 of a pool of molten material 10. The final filament 20 is shown as being solidified on the circumferential edge 32 as 20' and then leaving contact with the edge 32 at the release point 21. The release point 21 is determined in part by the configuration of the guide member 50 and the force F applied through the filament 20. The force F has two operative components, F^, is the tension component of the force F at the point 51 where the filament 20 begins contact with the member 50 and F the 3 n component normal to F^, at point 51 keeping the filament in contact with the member 50.

While the application of a tension force F creates both FmT and 'Fn the two forces have two separate functions.

FT as applied through the filament determines the location of point that yields an improvement in operation over the prior art. The normal force Fn as applied to the member 50 through the filament 20 keeps the filament 20 in contact with the member 50. This contact maintains the geometric relationship of the tension force FT that maintains the stability of the release point 21.

The contact of the filament 20 with a support member 50 between the release of filament and the means used to apply the force F is a necessary element of the present invention. The application of a tension force in the filament with the support produces an improvement in filament continuity.

In addition to the improvement in filament continuity provided by the present invention, the member 50 can be utilized to provide other improvement to the process.

Where the filament is prone to oxidation after formation, the contact with the support member 50 shields one side of the filament from the gaseous atmosphere while reducing the access of the gas to the other side by preventing unimpeded gas flow over the filament.

The member 50 may also be used as a means to control the rate of heat removal from the filament subsequent to formation. Where the filament material undergoes a heat rate dependent solid state transformation (as for example the martensitic reaction of carbon steel) the member 50 may be heated so as to reduce the heat removal rate from the filament and thereby reduce the quenching effect of the atmosphere surrounding the filament subsequent to its formation from the melt.. In addition, the thermal capacity of the support member 50 may be used to control the rate of heat removal from the filament. If it is desired to accelerate the rate of heat removal capacity. Such a member could be a mass of material having a high intrinsic heat capacity or a solid material artificially cooled. Where it is desired to retard the rate of heat removal from the filament, the support member would be heated thereby lowering its capacity to remove heat from the filament in contact with it. It should be understood that the term "thermal capacity" does not correspond to a specific material property such as heat capacity or thermal conductivity but is simply descriptive of the capacity of the support to alter the temperature of the filament in contact with it by the transport of heat.

Figure 2 shows a cross-sectional view of the circumferential edge of the rotating member 30 disposed to produce a filamentary product operable with the present invention. The embodiment shown in Figure 2 is from the prior art (U.S. Patent Application 251,985) and consists of a dislc-like member 30 having a V-shaped peripheral edge. The legs of the V 31 are angularly disposed on angle Θ with the tip of the V 32 (see Figure 1) having a radius of curvature in the plane of the drawing in Figure 2 of r. The V-shaped circumferential edge 32 is at a distance R from the axis of rotation of the member 30 below the surface 15 of the melt 10.

A preferred embodiment of the present invention comprises the embodiments of Figures 1 and 2 to produce continuous filamentary material when the member 30 is of the dimensions in the ranges : Radius (R) from 2 to 10 inches Thickness (T) from 0.05 to 2 inches Θ from 60 to 120 degrees ferential edge and would have a depth of insertion (d) into the melt 10 less than 60 mils below the surface 15. The upper bound of the preferred rotational speed appears to be the result of equipment limitations imposed by the high rotational speeds rather than an inherent limitation of the invention. It is within the skill of persons in the art of equipment design to devise rotating members capable of greater circumferential speeds than is the upper bound of the preferred embodiment.

The present invention is also operable with other means of producing filamentary material by solidifying molten material in the form of a filament on a rotating heat-extracting member. Figure 3 depicts the present invention as used with a variant of the teachings of U.S. Patent 2,825,108, Pond. The rotating heat-extracting member 30' is a cylindrical disk-like member having a smooth outer radial surface 33. A closed container 40, with a source of gas pressure 43, is used to heat a volume of molten material 10 by heating element 42 adjacent the container walls. An orifice 41 in the container 40 forms the molten material 10 into a continuous filamentary shape 22 upon the application of the gas pressure. When the ejection velocity of the molten material from the orifice is substantially close to the linear velocity of the outer radial surface 33 of the rotating member 30' , a continuous product 20 is formed. Similar to the embodiment shown in Figure 1 the adhesion of the filament 20 to the surface 33 is variable and as a result the release point 21' is variable. As shown in Figure 3 the trajectory of the filament 20 without the application of the force F is indicated by the path 70. The application of the force F lowers the path of the filament 20 below its equilibrium free flight trajectory 70 into sliding contact with the sup ort member 50. to those embodiments. The invention is applicable to any filament producing method where a continuous solid filament is produced by the solidification of molten material on the surface of a moving heat-extracting member where such filament is spontaneously released from the surface without the necessity of external forces to break the adhesion of the filament to the surface.

By filamentary product, we mean that the product should have an effective diameter less than about 60 mils. An effective diameter is a way of defining the size of a filament having a cross section that may be non-circular. A filament having an effective diameter of 60 mils has a cross-sectional area equal to a circular filament 60 mils in diameter. Therefore the present invention is operable with filament having large width-to-thickness ratios commonly termed ribbon fiber.

The present invention is not inherently limited as to the speed at which the member 30 is rotated (which of course controls the linear product rate of filament) as long as the means used to generate the tension force F can do so at the operating speed. At normal production speeds we have found that a synchronous carousel arrangement as depicted in Figure 4 is one operable embodiment that generates a self-regulating tension force of the required magnitude.

The member 60 rotates, on a horizontal plane where the filament 20 naturally exits the support 50. The member 60 is rotated at a continuous speed having a vertical containment 61 at its outer radius. The self-regulating force is generated by having this outer radius rotating at a linear velocity in excess of the rate at which the filament 20 is supplied. The embodiment is known to be operable where the linear velocity at the vertical containment is 100 percent greater than the input velocity of the filament. Upon initiation of the process the filament 20 travels by its free flight trajectory to impinge on the horizontal surface 65. This surface is relatively flat and the filament 20 will continue to travel on the surface 65 until it strikes the vertical containment 61. The rotation of the member 60 carries the filament around the circumference but in doing so places some portion of the filament 20 on a radius of the surface 65 where the linear velocity of the filament equals that of the surface 65 at impingement so as there is no relative motion between the filament 20 and the surface 65.

This radius is termed the equilibrium collection radius 62 on the turntable-like surface 65. In this manner the filament is free to determine a radius on the surface 65 without the need for precisely matched speeds of the collector to the filament producing means or mechanical guidance of the filament to the equilibrium collection radius 62. When the filament 20 is collected at such a radius, there is a force transmitted to the filament 20 that draws the filament into contact with the support member 50 and stabilizes the release point of the filament from the rotating heat-extracting member.

The only requirement of the tension applying means is that it produce a limited and relatively constant pulling force F of a specific magnitude. The exact tension required to utilize the benefits of the invention qualitatively depends upon the system used, the radius of the member 30, the size and composition of the filament, and the placement and shape of the support 50.

Quantitatively the magnitude of the force as applied at the release point (F„,) must conform to several relationships.

The force that holds the filament to the surface of the rotating member is composed of a minimum force of adhesion Fft plus Δ the deviation of the adhesion force above the value of Fft. It is the effect of the deviation Δ that makes the release point vary in relation to the position on the rotating member. When the system is in equilibrium there are three major forces that operate to break the adhesion of the filament from the forming surface of the rotating heat-extracting member. These three major forces have components generating a shear force parallel to the forming surface and a normal component to that surface. Both shear and normal forces operate to release the filament from the forming surface, however, the normal forces also operate to move the filament away from the forming surface. The first major force is centrifugal force (Fc) which is normal to the forming surface. The magnitude of Fc is dependent on the mass of the filament and the diameter and speed of the rotating member. The second force is then a predominantly shear force created by the differential thermal contraction (F^) between the filament an(3 tne forming surface upon cooling. This force is parallel to the forming surface and is determined by the difference between the thermal contraction of the materials comprising the filament and the material comprising the forming surface at their respective operating temperatures. The third major force is the tension force (FT) exerted on the filament. Such a force would, depending on the geometric relation of the tension to the release point, have both normal (FTn) and shear (FTs) components. Furthermore the production of continuous filament inherently generates a small force (F ) as evidenced by the fact that the free flight trajectory of discontinuous filament is somewhat different than that of continuous filament. The inherent force is believed to have a negligible shear component and is comprised mainly of a force normal to the forming surface. This force is generated by the weight of the continuous filament not adherent to the forming surface nor supported by the member 50.

In summary, the forces operating to determine the release point are: FA = minimum force of adhesion of the filament to the forming surface A = the deviation of the adhesion force above the value of F¾ Fc = the force normal to the forming surface generated by centrifugal force on the filament F^ = the force parallel to the forming surface generated by differential thermal contraction FT = the induced tension in the filament having both normal and shear components FTn = the component of the tension force FT normal to the forming surface FTs = the component of the tension force F,p parallel to the forming surface F^ = the inherent force generated when the product is continuous, normal to the forming surface It is the object of the present invention to use FTn to override the effect of Δ so as to stabilize the point of release of the filament from the forming surface. The release of the filament from the forming surface is spontaneous with or without the application of FT and therefore F. + A Δ < F + F , + F c a w This simply means that where no external tension FT is applied, centrifugal force, differential thermal contraction, and the small inherent tension force are sufficient to induce filament release. The problem is that the varying adhesion force Fft + Δ makes the release point vary thereby inducing instability to both filament production and collection.

When the external tension force FT is applied the shear component FTjg acts in conjunction with the other shear force F^ on the forming surface. As the tension force F^, is increased, the release point will move toward a position on the forming surface minimizing the normal component FTn and unless the geometry is correct, the equilibrium position may be a point prior to filament formation or at a point where the filament has insufficient strength to withstand the tension. In a geometric configuration where F^, is applied through the filament so FT is a tangent to forming surface at the release point, a significant tension may be exerted without moving the release point since there is no normal force (FTn) to induce movement of the release point and the shear force does not initiate separation of the filament from the forming surface. By contrast when the normal component FTn is significant, the effect of Δ is minimized and the release point is stabilized without the need of exerting a large tension force FT through the filament.

The application of the normal tension force FTn is not required to remove the filament from the forming surface and such release is spontaneous with or without the applied normal tension force. Fm Tn does minimize the effect of Δ and promotes stability of the release point. It follows then that : While the absolute magnitudes of the forces are not known, the relative magnitudes can define the invention and one skilled in the art can use the teachings of this disclosure and create an operable embodiment of the invention without undue experimentation.

It should be understood that FA and Δ could be broken down into their normal and shear components, however, it is sufficient to describe those forces in general since the shear components do not change the point of filament release but merely reduce the adhesive bond so the normal forces can more readily affect the separation of the filament from the forming surface.

The member 50 determines the path of the filament 20 and therefore the direction of the tension force FT. The presence of the support 50 is critical to the present invention and the application of a tension force without a support member does not stabilize the release point of the filament. While there is no indication that the following configuration is the only operable embodiment of the invention, we have had particular success where the support member is below the free flight trajectory of the released filament and the tension force is applied so as to lower the path of the filament onto the support above its free flight path, however, care must be taken to prevent the position of the support to generate a large normal force at the release point so as to move the release point too far toward the area of filament formation.

The embodiment illustrated . in Figure 3 is confined to I metallic filament and the embodiment illustrated in Figures 1 and 2 is confined to materials having the following properties at a temperature within 25 percent of their melting points in °K: a viscosity in the range of from 10 to 1 poise, a surface tension in the range of from 10 to 2000 dynes/cm, a reasonably discrete melting point, and at least momentary compatibility with a solid material having sufficient thermal capacity to initiate solidification. For the purpose of definition a reasonably discrete melting point is in general where a material exhibits a discontinuous increase in viscosity upon removal of heat from the material while in a molten state.

The present invention is not limited to specific materials found to be critical in the embodiments of the filament forming methods. The present invention is operable on any filamentary material formed by solidification on a moving heat-extracting member.

The present invention has been shown to operate in the following examples.

Example 1 The carousel arrangement of Figure 4 was used to put a tension on a continuous aluminum fiber produced by rotating a brass heat-extracting member of the general configuration of the prior art embodiment of Figure 2 in contact with the surface of the molten aluminum. The aluminum was commercially pure (1100) aluminum at a temperature of approximately 1400°P. The rotating member had a V-shaped circumferential edge and a diameter of approximately 8 inches. The circumferential edge was in contact with the surface of the molten aluminum at a linear rate of approximately 15 feet per second. After release from the rotating member, the filament was supported below its free flight trajectory on a sheet metal support. The filament was directed by the support onto a turntable rotating so as to yield a radius having a velocity approximating that of the filament. The fila-ment was collected on an equilibrium radius lowering the filament onto the support member and continuous aluminum filament having an effective diameter of 21 mils was produced for 30 minutes of operation.

Example 2 The same tension-inducing embodiment used in the previous example was used to produce continuous austenitic manganese (Hadfield) steel filament having a typical analysis of 11-13% n, 1.0-1.3% C, 0.7-0.3% Si, balance Fe. A nickel rotating heat-extracting member was used having the V-shaped circumferential edge of Figure 2. The wheel was 8 inches in diameter and was water cooled at a flow rate of 80 gallons per hour. The forming surface had a peripheral speed of 5 feet per second. Lengths of steel fiber up to 900 feet long were produced having an effective diameter of about 18 mils. The melt temperature during filament formation was approximately 2800°F.

Example 3 Again the horizontal turntable embodiment was utilized to provide tension to continuous filament. The filament produced was white cast iron of a composition approximating 4.0% C, 0.8% Si, 0.7% Mn with the balance essentially Fe. The final filament had little measurable ductility and was extremely brittle. A copper wheel formed the filament by contacting its V-shaped circumferential edge moving at approximately 7 feet per second to the surface of the molten iron at 2670°F. The tension drew the filament down from its free flight trajectory into sliding contact with a support member and lengths of brittle cast iron fiber 50 feet long were collected on the tension inducing turntable. The filament had an effective diameter of 12 mils.

Example 4 As in the previous examples the horizontal turntable was used to induce tension in the filamentary product. The filament produced was a plain carbon mild steel (Type 1005) containing approximately 0.05% carbon, 0.2% n with the balance essentially iron. An aluminum disk with a V-shaped periferal edge was used to form the filament by contacting its acute angle with the surface of molten steel at 7 feet per second.

The steel was at a temperature of approximately 2900°F. The filament was in sliding contact with a support below its free flight trajectory and continuous filament was collected on the turntable. The filament had an effective diameter of 25 mils.

While the invention is disclosed in terms of specific embodiments and examples, the scope of the invention is not limited thereto. The invention is known to be operable with additional metal alloys than those set out in the examples as for example the alloys of: copper, zinc, tin, nickel, and cobalt. The present invention was reduced to practice in numerous trials and the invention is operable as defined by the appended claims and any unsuccessful trials were not felt to be limitations to the

Claims (12)

1. In a method of forming filamentary material where said material solidifies in filament form adherent to a rotating heat-extracting member the improvement of: stabilizing the release point of said filament from said rotating heat-extracting member by the application of a tension to said filament with said force drawing said filament into sliding contact with a support member positioned between said release point and the location of the tension exerting means.

2. The method of Claim 1 wherein said release point is stabilized by the forces on said filament at its release point conform to the following relations F, + + F , + F + Pm A Δ < F c d w T F = F + F T Tn TS Δ<<ΡΤη where (in units of force) F,. = the minimum force of adhesion of said filament A to said member A = the deviation of the adhesion force above the value F¾ Fc = the centrifugal force exerted on said filament while adherent to said member F^ = the shear force exerted by differential thermal contraction at the interface of said filament and said member at the release point Fw = the inherent normal force due to the unsupported weight of the continuous filament FT = the tension force exerted on said filament FTn = the component of F^, normal to the forming surface ' FTs = the component of F^, parallel to the forming surface. j

3. The method of Claim 2 where said support member is below the free flight trajectory of the released Ifilament.

4. The method of Claim 1 where said filament is formed by forcing molten material through an orifice in the form of a free-standing stream of molten material and impinging said stream on the polished outer radial surface of a cylindrical rotating heat-extracting member before surface tension effects degrade said stream into a nonfilamentary form.

5. The method of Claim 1 where said filament is formed by rotating the V-shaped outer radial surface of a disk-like heat-extracting member in contact with the surface of a pool of molten material at a rotational speed yielding a linear velocity at the circumference of said rotating member in excess of 3 ft/sec.

6. The method of Claim 1 where the rate of heat removal from said filament subsequent to release from said rotating heat-extracting member is controlled by the thermal capacity of said support member. "\

7. The method of Claim 6 where the rate of heat removal is lowered by providing a support with low thermal capacity.

8. The method of Claim 6 where the rate of heat removal 1 is accelerated by providing a support with high thermal capacity.

9. The method of Claim 1 where said tension is exerted by directing said filament by means of said support member to the surface of a rotating horizontal turntable with said filament free to determine an equilibrium collection radius.

10. The method of Claim 1 where said material has, at a temperature within 25 percent of its equilibrium melting point . . . . -3 xn °K, a viscosity m the range from 10 to 1 poise,, a surface tension in the range of from 10 to 2000 dynes/cm, and a reasonably discrete melting point.

11. The method of Claim 1 where said material is a metal selected from the group consisting of the alloys of: iron, aluminum, copper, zinc, tin, nickel, and cobalt.

12. The method of Claim 1 where said material is a metal alloy selected from the group consisting of: 1100 aluminum, white cast, iron, austenitic manganese steel, plain carbon mild steel . For the Applicants Dr-r Yitzhak Hess