US3715418A - Low viscosity melt spinning process - Google Patents

Low viscosity melt spinning process Download PDF

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Publication number
US3715418A
US3715418A US00863266A US3715418DA US3715418A US 3715418 A US3715418 A US 3715418A US 00863266 A US00863266 A US 00863266A US 3715418D A US3715418D A US 3715418DA US 3715418 A US3715418 A US 3715418A
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stream
melt
point
spinning
surface tension
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W Privott
R Cunningham
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Monsanto Co
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Monsanto Co
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/005—Continuous casting of metals, i.e. casting in indefinite lengths of wire
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/02—Manufacture of glass fibres or filaments by drawing or extruding, e.g. direct drawing of molten glass from nozzles; Cooling fins therefor
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S264/00—Plastic and nonmetallic article shaping or treating: processes
    • Y10S264/19—Inorganic fiber

Definitions

  • the present invention also relates generally to the formation of fibers from inorganic materials having a low melt viscosity surface tension ratio and, more particularly, the formation of fibers of varying lengths directly from a free falling stream which has the numerical relationship between its viscosity and surface tension as defined by the following expression melt viscosity melt surface tension wherein, the viscosity and surface tension are expressed in poises and dynes/cm., respectively.
  • the stabilized stream portion of the stream is highly susceptible to disruption by forces engendered by the impact or deceleration incident to supporting or taking up the streaming body after solidification.
  • the forces generated during such deceleration are normally of sufficient magnitude as to propagate upstream to weaker regions where stream deformation and disruption may occur.
  • a recognition of the nature of the deceleration forces has brought forth the realization that such streams conveyed under carefully controlled conditions may result in fibers of predetermined lengths.
  • a low stress spinning operation may be established wherein the fragile, low strength upper regions of a low viscosity stream, initially stabilized against disruption due to mass transfer within the liquid region, is effectively utilized for the formation of staple fiber of preselected lengths.
  • the location of the point D along the stream may readily be varied, both relatively and absolutely, by appropriate manipulation of one or more spinning conditions to thereby facilitate preferred operating conditions and results.
  • FIG. 1 is a diagramatic graph depicting the typical 1nterrelationship of fiber length to stream free-fall distance
  • FIG. 2 is a vertical, partially sectionalized view of a simplified apparatus which may be employed in the p tice of the instant process;
  • FIG. 3 is a schematic circuit diagram of conventional design which may be employed to electrically monitor and record stream continuity
  • FIGS. 4-7 are graphical presentations of pertinent data obtained in carrying out the reported examples which show the effect of variations in selected spinning parameters upon the interrelationship of fiber length with stream free-fall distance.
  • melts of materials having viscosity-surface tension ratios not greater than one have a tendency to break into shot prior to solidification when extruded as a stream.
  • inorganic materials having the above tendency are ceramics, metals and alloys thereof, metalloids, and intermetallic compounds.
  • a metallic melt has a viscosity-surface tension ratio on the order of 1X 10
  • the viscosities thereof are not greater than approximately poises.
  • materials such as glass, polymers, and materials of large molecular size have viscosity-surface tension ratios significantly greater than one and viscosities much greater than ten poises. Thus, the disruptive effect of surface tension is prevented by the viscous inertia of the molten material.
  • the problem initially encountered in the streaming of low viscosity-surface tension ratio melts is one of stabilizing the liquid region of the stream against a surface tension-driven mass transfer mechanism.
  • a surface tension-driven mass transfer mechanism As set forth in the hereinbefore referenced Alber patent and the copending application Ser. No. 829,216, and proceeding from a proper recognition of the c ntrolling mechanisms causing liquid jet breakup, it has recently been discovered that breakup of the jet, prior t0 solidification, may successfully be suppressed by the generation of a stabilizing film of minute thickness about the nascent, essentially inviscid stream prior to its disruption and pending solidification by normal heat transfer phenomena.
  • the liquid portion of such streams may be successfully film-stabilized by spinning into suitable atmosphere which, ether by reaction, decomposition, or deposition, result in the rapid formation of thin films about the nascent stream to thereby suppress the above referred disruptive forces pending solidification of the stream into wire-like form.
  • the Rayleigh parameter (wherein V, p, D, and 'y are stream velocity, density, diameter, and surface tension respectively).
  • the Rayleigh parameter (abbreviated Ra) is the square root of the well known hydrodynamic expression known as the Weber number.
  • the Rayleigh parameter should lie in the range of 1 to 50, preferably 2 to 25. It has been discovered that, where the velocity of the stream for a given stream density, diameter, and surface tension does not satisfy this condition that elfective film stabilization cannot be established. For example, when molten material having a density of 4 gms./cm.
  • the optimum velocity within the Rayleigh parameter range of 1 to 50 may normally be determined experimentally.
  • actual propagation of surface tension breakup determines the lower limit of the Rayleigh parameter range, while either sinuous breakup or aerodynamic deceleration determine its upper limits.
  • the upper limit of the range is increased as the density of the melt relative to the spin atmosphere increases; i.e. the greater the density of the melt and/or the less the density of the spin atmosphere, the higher the Rayleigh parameter value (taken as a measure of extrusion velocity) at which successful spinning may be accomplished, though optimum performance may dictate a somewhat lower level.
  • a simplified spinning assembly as schematically depicted in FIG. 2, was employed.
  • an apparatus essentially comprises a melt crucible 10 which, in the case of the examples which follow, was fabricated from stainless steel.
  • the crucible is provided with an upper header plate 12 and a lower orifice plate 14, both of which are maintained in sealing engagement with crucible 10 to provide a gas-tight melt chamber 26.
  • the orifice plate 14 has seated centrally thereof a watch-sized jewel 18 formed of any suitable material chemically compatible with the melt being processed; the jewel is drilled to provide a suitable spinning orifice 20.
  • a ruby jewel having an orifice diameter of microns and a length/diameter ratio of unity was employed. Melting of the spin charge within chamber 16 was accomplished by means of electrical resistance heating elements 22 and the charge temperature was monitored by means of a thermocouple arrangement 24. Preferably, the spinning charge was melted under a vacuum prior to effecting extrusion under an inert gas pressure; this may readily be accomplished by the two-way valve and conduit arrangement indicated at 26, whereby chamber 16 may be alternately evacuated and pressurized to effect the desired extrusion rate.
  • a glass (Pyrex) spinning column 27 is arranged to receive the stream extruded through orifice 20.
  • the spin gas mixture is supplied through conduit 28 to be gently deployed throughout the spinning column by means of a gas distribution ring 30 provided with equi-spaced gas orifices 32.
  • the spinning column Prior to extrusion into the desired gas mixture, the spinning column is preferably swept out under vacuum, which may be provided by means of a valved connection 34.
  • the lower end of the spinning column may be temporarily sealed by means of any suitable plate arrangement, not shown.
  • the extruded stream was collected at selected distances down the column by means of a collection surface 36, which may take the form of a metal plate. As indicated by the twoway arrow heads, the collection surface 36 is adjustable in the vertical direction to establish the desired catch distance. Normally, the plate was maintained horizontal, but we have found that it may be inclined at widely varying angles without any substantial effect upon the fiber lengths obtained.
  • spinning assembly merely represents a typical apparatus which may be employed in the practice of the present invention, which latter is in no way limited to the details of the apparatus.
  • an induction-heated spinning assembly would be found preferable, if not essential.
  • freefall distance shall be taken to denote that vertical distance between the spinning orifice and the collection surface.
  • free-fall distance is not necessarily defined by the position of a solid collection surface such as depicted in FIG. 2. Such a surface is merely to be taken as symbolic of that point below the orifice at which a decelerating force is brought to bear upon the stream. Deceleration may arise by the sudden impact of the solidified stream upon a solid surface, or more gradually, by causing the solidified stream to pass through a significantly denser and/or counterflowing spin atmosphere; similarly, a more gradual stream deceleration may be achieved by the imposition of a suitable electrostatic field.
  • the chosen length of fiber may be found experimentally. That is, the collection surface may be moved up and down the stream until a level is reached wherein the resulting fiber is of the desired length. Interruption of the solidified stream so as to impart a deceleration thereto at a level intermediate D and D, generally results in the formation of continuous filament as described and claimed in the parent copending application Ser. No. 599,539.
  • the point D may be defined as a point along the stream at which the stream must be decelerated to avoid repeated tensile breaking. Interruption intermediate D, and D results in staple fiber the length of which we have found to be a function of the free-fall distance. This may be seen in FIG. 1.
  • the process embodying the present invention is based on our discovery that, in the case of streams issuing from low viscosity-surface tension ratio melts, there is a point D, above which such streams cannot undergo a given deceleration without disruption in the stream continuity.
  • spinning conditions such as, for example, spinning velocity, heat transfer, aud melt temperature may be varied so as to cause the point D, to move upward and downward as desired for a particular material.
  • FIG. 1 illustrates diagrammatically the relationship between the free-fall distance of the stream and fiber length. As seen therein, four distinct regions appear on this curve.
  • the stream For free-fall distances less than the distance D, (denoting the freeze point of the stream, as hereinbefore defined) the stream is still molten and any attempt to collect the stream at lesser distances results in but a molten, non-fibrous mass. For distances intermediate the points D and D fiber length is seen to increase approximately exponentially with increasing freefall distance. Although the stream is at least partially solid in this region, disruption thereof may be effected by deceleration due to impingement upon the collection surface. When the stream is allowed to fall through distances equal to or greater than D the tensile force due to the increased stream length (and, therefore, weight) is sufiicient to cause stream breaking. Thus, at collection points at or below D relatively uniform fiber lengths are obtained independently of the free-fall distance.
  • the relative and absolute positions of the points D D,. and D may be manipulated as desired by proper variations of the process variables.
  • D occurs upstream of D,. This may be caused by numerous combinations of factors affecting the tensional force upon the stream but is largely present when spinning high density melts, especially in the larger diameter range.
  • the force system acting upon the stream must be modified in light of the present teachings such as, for example, the use of counter-current gas flow so that the point D is caused to be shifted downstream relative to the point D when indefinite length production is desired.
  • An effective aid in determining stream continuity relative to free-fall distance may take the form of a very simple electrical continuity tester circuit, such as schematically diagrammed in FIG. 3. As there indicated, such a tester serves to electrically interconnect the collection surface with the melt crucible to thereby sense electrical continuity, or lack of it, because the collection surface and the spinning head where an electrically conductive melt is being processed. Similar determinations are, of course, made by directly measuring the fiber lengths obtained at varying free-fall distances, but use of the continuity tester allows one to monitor stream continuity continuously and to modify spinning conditions accordingly.
  • the fiber lengths obtained under various process conditions will vary in a characteristic manner with free-fall distance, as shown in FIG. 1.
  • Indications of the mechanism by which stream breakup occurs in the regions above point D are obtained by relating fiber length to free-fall distance to indicate where and when stream breakage occurred, while microscopic examination of the ends of broken lengths serve to indicate stream state at the position of break as well as the rapidity of the break.
  • FIG. 1 In the lower portion of FIG. 1 is shown a recording of the continuity tester for the typical graph appearing there-above. In relating this recording to the free-fall distance curve, it may be observed that the freeze point D of the stream is the point below which fibrous shaped, as opposed to a molten mass, may be collected.
  • the configuration of the ends of the staple vary according to the material employed, the temperature thereof, and the rapidity of the break. For example, if deceleration occurs when a melt material such as a lead-tin is very hot but solid, the fiber ends are relatively square due to the rapidity of the break.
  • the recorded continuity curve of FIG. 1 clearly illustrates that, for distances greater than D the stream undergoes breakage before impingement upon the collection surface. Because the force due to gravity has, beyond this point, become greater than the sum of stream strength and the upward drag force generated under the chosen spinning conditions, the stream is caused to break prior to contacting the collection surface; thus, the recording indicates a continuously open circuit.
  • the spinning conditions were as follows: extrusion pressure of p.s.i.g. argon at an extrusion temperature of 400 C.; a reactant/cooling gas mixture of 7 vol. percent oxygen/ 93 vol. percent helium at room temperature and atmospheric pressure; extrusion through a 100 micron diameter orifice formed in a watchsized ruby jewel, the orifice having an L/D ratio of unity; and a Pyrex spin column of 6 in. inside diameter and 300 cm., length.
  • the melt crucible was fabricated from stainless steel having an inside diameter of 1% in. and a depth of 6 in. Preferably, heating to the melt state was accomplished under a vacuum of below 100 microns of mercury. Also extrusion was commenced prior to introducing the spin gas into the spinning column.
  • EXAMPLE I This example illustrates the effect of a variation in the reactant gas concentration upon the fiber length obtainable at given free-fall distances.
  • a helium/oxygen spin gas mixture was supplied to the spin column through the gas distribution ring 32 positioned approximately 50 cm. below the orifice, in a manner to effect a gentle gas motion in the vicinity of the orifice.
  • the helium flow rate which functions as a coolant gas, was maintained constant at 2.5 c.f.m. to maintain a relatively constant heat transfer rate, the oxygen flow rate being varied to obtain the desired volume percent oxygen in the mixture.
  • Oxygen functions as the reactant gas in forming an oxide stabilizing film about the lead/tin melt as it is given issue as a free stream through the orifice.
  • the variation in fiber length with free-fall distance was determined at oxygen concentrations of 2, 7 and 15 volume percent, the resultant data being presented in the graph of FIG. 4.
  • an oxygen concentration of 2% is virtually the minimum level at which indefinite length filaments can be obtained. That is, at a free-fall distance, as measured downstream from the orifice, of approximately 95 cm., substantially continuous lengths are obtainable, whereas a small decrease in free-fall distance (i.e.
  • EXAMPLE II This example illustrates the effect of coolant gas properties, particularly as regards viscosity, density and coefficient of heat transfer, upon the variation in fiber length with free-fall distance.
  • two series of runs were conducted employing spin gas mixtures of 3.3 c.f.m. helium/0.3 c.f.m. oxygen and 1.7 c.f.m. nitrogen/0.3 c.f.m. oxygen.
  • the molecular weight of the coolant gas affects the stabilizing film formation through its mass transfer effects on the rate of diffusion of the reactant gas to the stream surface; the freeze point and temperature history of the stream through its heat transfer effects; finally, the force system on the stream through its momentum transfer or viscous drag effect.
  • Nitrogen is not as an effective heat transfer agent as helium; it provides a greater viscous drag; finally, it retards the diffusion of oxygen to the stream surface necessary to form the stabilizing film.
  • EXAMPLE III This example illustrates the effect of spinning velocity upon the interrelationship between fiber length and freefall distance.
  • the rate at which the melt is extruded through an orifice determines the free, unbroken jet length of the stream in the absence of a reactant gas, as well as affecting the viscous drag force and heat transfer of the stabilized stream through its influence upon the relative velocity of the stream with respect to the spinning atmosphere.
  • These factors combine to provide the net result set out in the graph of FIG. 6 when following the procedure and conditions set out in Example I (using a reactant gas of approximately 7% oxygen/93% helium supplied at a rate at approximately 3 c.f.m., extrusion being carried out at a temperature of approximately 400 C.).
  • freeze points D and impact break points D are also seen to shift downstream with increasing spinning velocity due to the fact that mass flow rates increase faster than heat transfer rates, while the downstream migration of the tensile, break point D is greater than that of the impact break point D,, resulting in the observed increased in the freefall distance range over which continuous lengths may be collected.
  • EXAMPLE IV It is the purpose of this example to demonstrate the effect of spinning temperature upon the variation in fiber length with free-fall distance.
  • the temperature at which a low viscosity melt is extruded directly affects the heat transfer requirements necessary to solidify the stream and indirectly affects the rate of formation of the stabilizing film through the temperature-dependence of the filmforming reaction.
  • two series of runs were conducted at extrusion temperatures of 300 and 400 C. and an extrusion pressure of 42 p.s.i.g. the results obtained being graphically set forth in FIG. 7.
  • the decrease in heat transfer requirements at the lower temperatures are clearly reflected in the significantly decreased distances to the freeze point D and impact break point D3, due to a more rapid increase in stream strength.
  • the position of the tensile break point D relative to the orifice is determined by the balance between the force of gravity, on the one hand, and stream strength and viscous drag force, on the other hand.
  • the tensile breaking point D is shifted a finite distance downstream.
  • the force system imposed upon the stream must be modified by reducing the viscous drag force to a level at which the propagation velocity of drag-sustained deviations is less than the stream velocity.
  • the tensile break point D occupies a position of finite distance from the orifice and, when this distance is greater than the distance of the impact break point D deceleration of the stream at a point below D but above D results in .fiber of desired length.
  • a method for spinning staple fibers from inorganic melts having a viscosity-surface tension ratio of where ,u is the melt viscosity measured in poise and 'y is the melt surface tension measured in dynes centimeter comprising the steps of:

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US00863266A 1969-10-02 1969-10-02 Low viscosity melt spinning process Expired - Lifetime US3715418A (en)

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4188177A (en) * 1977-02-07 1980-02-12 Texas Instruments Incorporated System for fabrication of semiconductor bodies
US4236882A (en) * 1974-06-24 1980-12-02 Sandco Ltd. Apparatus for producing drops or portions of liquid and viscous materials and for producing pellets therefrom
USRE31473E (en) * 1977-02-07 1983-12-27 Texas Instruments Incorporated System for fabrication of semiconductor bodies
US4495691A (en) * 1981-03-31 1985-01-29 Tsuyoshi Masumoto Process for the production of fine amorphous metallic wires
US6585151B1 (en) 2000-05-23 2003-07-01 The Regents Of The University Of Michigan Method for producing microporous objects with fiber, wire or foil core and microporous cellular objects
US20220234937A1 (en) * 2021-01-22 2022-07-28 Macleon, LLC System and method of refining optical fiber

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2018491C1 (ru) * 1992-03-12 1994-08-30 Виктор Федорович КИБОЛ Способ получения базальтового волокна

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1219418A (en) * 1966-12-06 1971-01-13 Monsanto Co The manufacture of fibres, filaments and films form molten materials

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4236882A (en) * 1974-06-24 1980-12-02 Sandco Ltd. Apparatus for producing drops or portions of liquid and viscous materials and for producing pellets therefrom
US4188177A (en) * 1977-02-07 1980-02-12 Texas Instruments Incorporated System for fabrication of semiconductor bodies
USRE31473E (en) * 1977-02-07 1983-12-27 Texas Instruments Incorporated System for fabrication of semiconductor bodies
US4495691A (en) * 1981-03-31 1985-01-29 Tsuyoshi Masumoto Process for the production of fine amorphous metallic wires
US6585151B1 (en) 2000-05-23 2003-07-01 The Regents Of The University Of Michigan Method for producing microporous objects with fiber, wire or foil core and microporous cellular objects
US20220234937A1 (en) * 2021-01-22 2022-07-28 Macleon, LLC System and method of refining optical fiber
US12353037B2 (en) * 2021-01-22 2025-07-08 Macleon, LLC System and method of refining optical fiber

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FR2064103A1 (enrdf_load_stackoverflow) 1971-07-16
CA962022A (en) 1975-02-04
FR2064103B1 (enrdf_load_stackoverflow) 1973-12-21
DE2048347A1 (enrdf_load_stackoverflow) 1971-04-22

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