US3677481A

US3677481A - Method and apparatus for taking up fiber

Info

Publication number: US3677481A
Application number: US44821A
Authority: US
Inventors: David J Haley; Robert E Cunningham; Wilbur J Privott Jr
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1970-06-09
Filing date: 1970-06-09
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18
Also published as: DE2128504B2; NL7107761A; SE382925B; CA931721A; LU63303A1; FR2094140A1; GB1316063A; BE768240A; DE2128504A1; DE2128504C3; FR2094140B1; JPS541808B1

Abstract

An in-line take-up apparatus and process isolate the tensional forces needed in a fiber for good packaging about a wind-up member from the portion of a fiber having very low tensile strength which occurs immediately after extrusion.

Description

United'States Patent Haley et al. [451 July 18, 1972 METHOD AND APPARATUS FOR [56] References Cited TAKING UP FIBER UNITED STATES PATENTS [72] Inventors: David J, Haley, Durha R b rt E, C 2,030,189 2/1936 Taylor "18/8 B X i Wilbur prim, Jr both of 2,582,639 1/ 1952 Ljungberg. ....18/8 B UX l i n of NC. 3,367,399 2/1968 Easton 164/282 [73] Assignee: Monsanto Company, St. Louis, Mo. FOREIGN PATENTS OR APPLICATIONS [22] Filed: June 9, 1970 1,191,555 4/1965 Germany ..l8/8 B 383,564 l/l965 Switzerland ..65/1 1 W 21 App1.No.: 44,821

Primary Examiner-Stanley N. Gilreath Attorney-Vance A. Smith, Russell E. Weinkauf, John D. [52] US. Cl ..242/l8 R, 18/8 B, 18/12 TB, Upham and Neal E. Willis 65/11 W, 164/82, 164/282, 242/147 R, 264/176 F [51] Int. Cl ..B65h 54/00 57 T C [58] Field of Search..... ....242/18 R, 18 G, 147; 18/1 FZ,

18/8 B, 8 WB, 12 TB, 12 TF, 12 TM; 164/82, 282; 264/176 F; 65/11 R, 11 W An in-line take-up apparatus and process isolate the tensional forces needed in a fiber for good packaging about a wind-up member from the portion of a fiber having very low tensile strength which occurs immediately after extrusion.

17 Claims, 6 Drawing Figures Patented July 18, 1972 0 0 b DISTANCE FROM ORIFICE FIG.

INVENTQ S DAVID J. HALEY ROBERT E. CUNNINGHAM WILBUR J. PR] VOTT, JR. BY Iflf! A ORNE Y METHOD AND APPARATUS FOR TAKING UP FIBER CROSS-REFERENCES TO RELATED'APPLICATIONS This application is related to copending and commonly assigned applications Ser. No. 829,2l6, filed June 2, 1969; ofS. A. Dunn, L. F. Rakestraw, andR'. E. Cunningham; Ser. No. 863,311 filedOct. 2, 1969, of W. .l. Privott and R. E. Cun ningham; and Ser. No; 870,646 filed Oct; 27, 1969 of W. .l. Privott'and R. E. Cunningham:

FIELD OF THE INVENTION The'present inventionrelates to the take-up of continuous fiber and,-more particularly, tothe in-line take-up of continuous fiber extruded from a low viscosity melt.

BACKGROUND OF THE INVENTION Descriptionof the Prior Art It has long been known that liquid streams with low viscosities break up into discrete particles sometimes called drops shortly after issuance from an extrusion assembly. The high surface tension of the liquid relative to its viscosity causes the inherent cross-sectional non-uniformities existing side-by-side in the stream to become more pronounced until break-up occurs. Many materials of interest such as the metals, ceramics, and other inorganic materials-have low viscosities in the liquid phase. Until recently, it was generally consideredto be almost impossible to extrude these materials as amolten stream and solidify the stream into a continuous fiber prior to break-up due to the surface tension effect.

A technique of preventing disruptions in stream continuity due to surface tension has beendeveloped and is discussed in detail in application Ser. No. 829,216. Generally, the molten stream is extruded into a gaseous atmosphere hereinafter called the stabilizing atmosphere which reacts and/or decomposes in the presence of the stream and formsa film about the periphery of the stream. The film has sufficient strength to prevent surface tension-induced disruptions from taking place in the molten portion of the stream while solidification is occurring. Thus, this technique provides a simple and quick method of producing fiber which before its adventwas accomplished via the slower and generally more complex drawing or glass sheathing techniques.

One troublesome problem which has proven to be difficult to solve is fiber take-up. Inthe continuous take-up of afiber, it is necessary to apply a certain amount of tension to the fiber. When tension is applied to the fiber attained via a film stabilizing process, it is transferred to'the film which has a very small tenacity, causing the stream to be disrupted.

Varied take-up procedures have herebefore been utilized. The simplest is called back-winding" which merely allows the fiber to accumulate before winding proceeds, Back-winding is not only time-consuming and tedious, but it oftenresults in kinks and tangles in the packaged fiber.

Another technique is described and claimed in application Ser. No. 870,646 wherein freely falling continuous fiber, especiall'y a fine diameter fiber, can be made to fioat down in a helical configuration by providing a sufficiently large upward acting aerodynamic drag force on the fiber. The helical configuration isolates the tensional force applied to the lower end of the filament from the fragile liquid portion of the stream.

This technique is not self-regulating, however, and necessitates continuous and close scrutiny since an increase in winding take-up speed (or decrease in melt extrusion velocity) results in the disappearance of the helical buffer and, ultimately, in stream disruption. Conversely, a large accumulation of fiber occurs when the take-up velocity is slower than the extrusion velocity, resulting in a situation analogous to backwinding.

Consequently, there is a definite need for a continuous and self-regulating technique and apparatus for in-line take-up of a continuous fiber where it is desired to isolate the tension required for winding from fragile portions of the fiber. It is a primary object of the present invention to provide for an apparatus and method which fulfills the stated need, particularly in cooperation with low viscosity spinning'processes and assemblies.

SUMMARY OF THE PRESENT INVENTION To a greatextent, the present invention involves the recognition of certain physical forces present in theinter-action of a moving fiber over curved surfaces and the manipulation thereof to accomplish the desired winding-up of the fiber withoutconcurrent occurrence of tensile breakage in the upstream fragile portions of the fiber. As stated previously, it is necessary for a fiber to be under a certain amount of tension for it to be wound-up properly. The problem heretofore has been that the upstream fragile portions of the fiber, as, for example, the liquid portion in an extruded metal stream, cannot withstand even the minimal amount of tensional force needed towindafiber. It may be shown that this minimal tensional force shouldbe pAu where p, A, and v are the density, crosssectional area, andfiber speed, respectively. This amount of tension merely counteracts the centrifugal force on the wire. Ordinarily, commercial uses and needs dictate that fiber must be wound under even greater tension for good packaging. Thus, in order to wind-up an extruded fiber having upstream fragile portions, it is necessary to isolate the tensional forces from the upstream fragile portions of the fiber.

One embodiment of the present invention accomplishes the desired isolation by providing a take-up apparatus which comprises a first tensioning means including a concave slide surface for intercepting a fiber moving at about a velocity v at a first point on the surface. The fiber is constrained to move along the concave surface due to centrifugal force. The major contribution to the tensional force induced into the fiber is due to the frictional interaction between the moving fiber and concave surface; It may be shown that the buildup of tension due to friction asymtopically approaches a value of pAv Thereare, however, other factors which contribute to the tension-in the fiber such as aerodynamic drag, friction effect due to the weight of the fiber, and the change in height of the concave surface. At apoint along the slide, the combined effects of the factors mentioned above induces a tensional force of about pAv into the fiber at which point the fiber forms an unsupported loop above the concave surface. That is, the fiber at the second point moves away from the concave surface and forms a loop unsupported by the surface.

After the fiber leaves the concave surface, it is necessary to increase the tensional force to a value above pAu to facilitate wind-up. This may be accomplished by positioning a convex surface spaced apart from the concave surface and above the point at which the fiber forms an unsupported loop. The convex surface is not effective to increase tension unless the tensional force is already above pAv because the centrifugal force of the fiber acts in adirection away from the convex surface, thus preventing a frictionally induced tensioning force from being generated. The gravitational force, however, acting downward on the fiber as it moves upward to the convex surface increases the tension in the fiber to a value slightly above pAv, allowing the convex surface to be effective in further increasing the tension in the-fiber.

At constant take-up speeds, the position of the unsupported loop with respect to the concave surface remains unchanged. When the take-up velocity increases the point at which the unsupported loop forrns tends tomove along the surface since pAu has increased in value. A variation in take-up speed (and therefore in the tensional forces required) is compensated for by the proper utilization of the concave surface. Thus, the continued presence of the unsupported loop indicates that the surface is frictionally inducing a tensional force sufficient to provide the minimum force necessary for wind-up.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features believed characteristic of the present invention are set forth in the appended claims. The invention with further objects and advantages thereof may be best understood by reference to the following description taken in connection with the accompanying drawings in which:

FlG. 1 is a graph depicting filament length as a function of the intercept distance measured from the point of issuance of the molten stream.

HO. 2 is a schematic of a take-up system in accordance with one embodiment of the present invention.

FIGS. 3, 4, 5 and 6 illustrate schematically various other embodiments of the present invention.

DESCRIPTION The following discussion describes the utilization of the present invention relative to a film stabilization technique in producing continuous fibers. After a reading of the invention as described, however, it will be realized that this invention may be employed wherever is in a weakened condition immediately after extrusion. Thus, the phrase "upstream fragile portions of a fiber" as used herein is meant to include both the liquid region of fibers being stabilized in accordance with a film stabilization technique and those other fibers which when extruded are not initially strong enough near the origin of extrusion to withstand the sum total of the tensional forces needed to wind a fiber about a rotating member and weight of the free length of fiber.

In the fabrication of continuous filamentary material via a stabilizing technique, it is extremely important to catch, intercept, or otherwise decelerate the falling stream at an appropriate position along its path. Premature deceleration may result in a non-fibrous mass of material since insufficient time has elapsed for the molten stream to solidify into filamentary form. The point which demarks the boundary between decelerating positions attaining non-fibrous mass as opposed to a fibrous mass is called D,,. Tardy deceleration results in the formation of staple since the weight of the stream creates a tensional force which exceeds the strength of the stabilizing film so that the stream breaks in the liquid portion near the orifice. The point above which the stream must be collected to prevent breaks due to its weight is called D,,.

The net tensional force is the resultant of the forces due to gravity and aerodynamic drag acting upon the stream. More explicitly, it may be shown that the maximum net tensional force F (max) acting on a stream of a length extending from the orifice to the point D,, is given very closely by F,(max)=(pAg-l.l3V)D (I) where p is the density of the stream, gms/cm;

A is the cross-sectional area of the stream, cm";

g is the gravitational constant, cmlsec is the viscosity of the gas, poises;

a V is the extrusion velocity of the stream, cm/sec;

D is the length of the stream from the orifice to D cm. and the vertical downward direction is taken as positive. Thus, from relationship (1) it is seen that it is necessary to decelerate the stream before the tensional forces reach F (max). In other words, the stream must be decelerated prior to reaching the point D,,.

Deceleration of the stream between points D,, and D,, does not assure continuity, however. Because of the physical characteristic of the stream immediately below D,,, the stream will break into staple upon deceleration. As seen in FIG. 1, the length of the staple increases from an intercept at D,, until the fiber becomes continuous at a point D,, w en D,, lies below D,,. Copending application Ser. No. 863,3l 1 discusses and claims the spinning conditions which may be varied to manipulate the points D,,, D,,, and D,, to ensure that the points are properly positioned along the stream.

Briefly, however, the location of the point D,, depends primarily on the stream velocity and the coefficient of heat transfer away from the stream. The location of the point D,, is a function of the stream diameter, density, stabilizing film strength, gas density, and gas viscosity. The stream diameter and density are variables generally preset by the type, size, and quantity of fiber desired. Gas density and viscosity are variables generally utilized in optimizing conditions already set. Because the small tensile strength possessed by the liquid portion of the stream is primarily due to the film strength, it follows that the film strength is the most significant variable in determining D,,. Introduction of the stabilizing gas as close to the extrusion origin as the stream flow patterns permit is desirable since this ensures that the film forms early in the stream existence and, along with the gas concentration, determines to a large extent the strength of the film. A film of sufficient strength allows the stream to attain a length which extends beyond D,, i.e., D,, lies below D,,. Increasing the aerodynamic drag between the fiber and surrounding gaseous atmosphere also causes the distance to D,, to increase. To determine whether conditions are properly set so that D,, lies beneath D,,, a flat surface may be inserted into and moved along the path of the stream. When D,, lies below D,,, continuous fibers are formed as the surface enters the region intermediate the two points.

The primary problem involved in the in-line take-up of fibrous materials produced from low viscosity melts by a stabilization technique is the relatively large tensional forces needed in the fibrous materials for take-up as opposed to the ordinarily much smaller strength of the stabilizing film which holds the liquid portion of the stream together. It may be shown that the minimum tensional force which must be supplied to a fiber to allow take-up by a rotating member such as a bobbin is:

F, p141! 2) where p is the density of the fibrous material;

A is the cross-sectional area of the fiber;

v is the take-up speed of the fiber.

The maximum force AF that can be applied to the filament at distance AD above the point D, is given by AF=(pAgl.l3;.tV)AD (3) where AD must necessarily be less than the distance between points D,, and D,,. Unfortunately, the tensile force of equation (2) is ordinarily greater than the force that can be applied at maximum AD. Generally, the tensile force needed for wind-up is several times greater than the tensile strength of the stabilizing film.

it is now evident from the above discussion that in-line takeup of a fiber having fragile upstream portions may be accomplished only if the tensional force created by the rotary motion of the winding element is isolated from the fragile portion of filamentary material. This may be accomplished by imposing a force in a direction along the axis of the fiber below the fragile upstream portions which force has a magnitude sufficient to maintain the tensional force about equal to that required to wind the fiber about a bobbin. This relationship may be shown 1) (4) where F,, is the net tensional force acting upon the fragile portion of the fiber and F, is the force imposed along the axis of the fiber.

FIG. 2 illustrates a tensioning device 10 which is utilized in providing the amount of tensional force needed for take-up to fibers having upstream portions of low tensile strengths. As depicted therein, side supports 11 support a multiple curved surface having a descending first concave region 13 and an ascending second concave region 14 which flexes into a convex region IS. A rotating member 16 for take-up of a fiber is positioned adjacent tensioning device 10.

The first concave region is positioned to intercept a fiber 17 extruded from crucible 18 which fiber for purposes of illustration is formed via a film stabilizing technique. Thus, the point of interception 19 may be further defined as lying between points D, and D along the fiber path. The operating effect of device is to provide the tensional force to the fiber yet ism late the same force from the liquid upstream portion. Due to its centrifugal force, fiber 17 is constrained to slide across the

concave regions

13, 14 of the multiple curved surface. The interaction between fiber 17 and the surface causes a frictional force, the force F, in equation (4), to continually build up, and with contributions from aerodynamic drag, gravity, and friction due to the weight of the fiber, the tension reaches a value of about pAv". Atthis point, fiber 17 has sufiicient tension to form an unsupported loop 20. Convex region is positioned above the point at which the fiber forms the loop thus the fiber moves both up and over convex region 15 enroute to rotating member 16.

The tension build up in a fiber due solely to the frictional interaction of the fiber moving against a concave surface because of its centrifugal force may be represented by dT pAu T where [L is the coefficient of friction between the fiber and concave surface;

r is the radius of curvature of the concave surface;

x is the distance along the surface, cm;

Tis the tensional force on the fiber, dynes;

p is the fiber density, gms/cm;

A is the fiber cross-sectional area, cm

v is the fiber velocity, cm/sec.

As can be seen from equation (5), the value of Tapproaches pAv as a limit. Thus, for values of T near Av the concave surface is ineffective to cause significant increases in tension. It may-further be shown that aerodynamic drag and gravity are the most significant factors in increasing the tension in the fiber during the last 10 percent or so of travel along concave surface where T is near pAv Because as explained below, it is highly desirable to attain an unsupported loop in the fiber, it is preferable in many instances to enhance the effect of gravity by utilizing a concave surface with an ascent or up-slope portion (such as region 14 in FIG. 2) immediately following the descent portion. Relationship (5) also illustrates the importance of the radius of curvature of the curved surface. The smaller the radius, i.e., the more pronounced the curvature, the shorter is the length of surface necessary to approach pAv all other factors being constant.

As stated before, a convex surface is ineffective to increase the tensional force in a fiber unless the fiber already possesses a force greater than pAv The force of gravity acting upon the fiber as it moves up to the convex surface increases the tensional force to a value slightly greater than pAv The convex surface then via frictional interaction with the fiber further increases the tensional force to a value preselected for good packaging about a bobbin. Although the stiffness of the wire does contribute to tensioning, the effect thereof is small and is neglected for purposes of this disclosure.

As can now be appreciated from the preceding discussion, the optimum shape of the slide is determined by the relative importance of l. tension build up due to the moving fiber being constrained against the concave portion by centrifugal force,

2. tension build up due to aerodynamic drag;

3. tension build up due to friction caused by the force of gravity,

4. tension build up due to movement with or against gravity. Thus, it follows that the shape depends upon the weight of the fiber, coefficient of friction, and fiber velocity.

The presence of unsupported loop not only indicates that a tensional force of about pAv has been induced into fiber 17, but also indicates that self-regulation is present. When the take-up speed of fiber 17 and/or extrusion velocity is changed, the unsupported loop generally forms at a different position along the slide. This is because the tensional force relationships are changed.

The extent of self-regulation is limited primarily by the possible differential between the extrusion speed and take-up speed, the take-up speed being a value as large or larger than the extrusion speed. It has further been found that the take-up speed can exceed the extrusion speed by as much as 20 percent, i.e., V 1.20 V, where V is the extrusion speed and V is the take-up speed. The efi'ect of a take-up velocity greater than an extrusion velocity is to attenuate the molten stream to a smaller diameter which under many circumstances is highly desirable.

The angle of interception a, i.e., the angle between concave region 13 and fiber 17, as seen in FIG. 2 should have a value such that the forces generated in striking concave surface region 13 are absorbed in bending the fiber to follow the slide contour rather than creating tensional forces. It may be shown that the force on the fiber at impact is pAv cos a where T is the force in the wire before impact in dynes, and T is the force in the wire after impact in dynes. At very small values for a, the exact point of contact with the slide would vary considerably for small lateral displacements. At large values of a, the bending moment of the fiber causes the tensional force in the falling fiber to exceed the maximum tensional force F, (max) of equation (1). Thus, it has been found that the intercept angle a should have a value with optimum results occurring between 20 and 45.

It should now be apparent to those skilled in the art that the frictional characteristics between the fiber and surface may be varied as desired, for example,,through the use of magnets (for fibers of magnetic materials), oil, or air currents. In FIG. 2, magnets 21 (shown in dotted outline) are appropriately positioned to enhance friction between the concave surface and, for example, steel fibers.

In certain instances when either or both the coefficient of friction of the multiple curved surface of FIG. 2 and the fiber are small and/or the take-up speed is large, the distance from the interception point to the unsupported loop may become large enough to require an extremely long concave region. When space is limited, long friction surface lengths become highly inconvenient or impractical. Reference is made to the embodiment illustrated in FIG. 3 which is specifically structured to minimize the amount of space required to tension a fiber. Tensioning device 30 comprises a plurality of concave friction surfaces 31 arranged so as to have the bottom portion or base of each surface positioned adjacent to and in a noncontacting relationship with the top portion of a concave surface therebeneath. The base of the bottom surface 31 is positioned. adjacent to a convex surface 33. A rotating take-up means such as bobbin 34 is positioned adjacent surface 33.

In operation, the upper surface 31 functions to intercept fiber 35 which in turn remains in contact with concave surfaces 31 until it reaches bottom surface 31. At a portion along bottom surface 31, the tensional force induced into fiber 35 reaches the magnitude necessary for the formation of an unsupported loop. As in the embodiment of FIG. 2, the additional tensional force is provided by the frictional interaction of the moving fiber with the convex surface 33. Convex surface 33 is spaced above the base of bottom surface 31. The properly tensioned fiber is then wound around rotation bobbin 34 Still another embodiment is illustrated by FIG. 4 in which the fiber 40 is constrained to pass over two

concave surfaces

41 and 42, one positioned over the other. The tensional force in the fiber reaches about a value pAv at a point somewhere along surface 42. As in the embodiments of FIGS. 2 and 3 the tension force may further be increased by causing the fiber to move upward against the force of gravity and/or passing it over a convex surface, 43 to a rotating take-up bobbin 44.

Surface depicted in FIG. illustrates that, while fiber 50 must move in a concave path, the surface itself need not be completely concave but only present the general appearance of concavity. Fiber 50 touches only the peaks 52 of surface 51 as it moves thereacross. As before, a convex surface 53 may be used to increase the tension beyond Av prior to take-up on bobbin 54.

FIG. 6 illustrates a limiting case of the embodiment of FIG. 3 through which fiber 60 is constrained by gravity and the position of plates 6], to move against plates 61. That is, the centrifugal forces experienced by fiber 60 is always in a direction toward plates 61. The tensional force is thereby increased to a value of about pAv. Reaching this tensional value, fiber 60 forms an unsupported loop. Additional plates cannot further increase the tensional forces, thus making it necessary to increase the tensional force through other means such as convex surface 62, for example, to facilitate take-up about rotating bobbin 63.

To better illustrate the present invention, reference is now made to the following example.

EXAMPLE A tensioning device similar to that depicted in FIG. 2 was utilized to collect and take-up continuous aluminum fiber. The multiple curved surface was fabricated from 0.037 inch thick sheet steel against which an aluminum wire has a coefficient of friction of approximately 0.7. The radius of curvature of the surface varied from about 7 feet in the descending portion to about 2 feet in the ascending portion adjacent to the convex surface. The radius of curvature of the convex surface was approximately 10 inches. The diameter of the extrusion orifice was about 7.2 mils. The density of the molten aluminum utilized for fabricating the metal fiber was approximately 2.3 gms/cm.

In operation, the initial extrusion velocity of the aluminum stream at the orifice was 690 ft/minute. Oxygen present in the atmosphere under approximately room temperature and pressure conditions was utilized to stabilize the molten stream. When spinning a metal wire of this diameter comprised essentially of aluminum at this velocity, the concentration of oxygen in air is sufficient to ensure that D,, lies below D,,. This was determined by moving an intercepting surface along the stream until continuous fibers were formed. Using the descending portion of the concave surface, the stream was intercepted slightly below the D point at about 10 feet below the orifice at an angle of about 30. As the fiber moved down the surface, the lead end was manually picked up and passed over the convex surface region into a self-feeding winder mechanism. The latter was essentially a rotating bobbin and a transverse feed device to ensure proper positioning on the bobbin.

The unsupported loop was observed to form at about 6.5 feet from the interception point along the ascending portion. Attenuation of the fiber was mainly attributed to the net tension force formed on the fiber since the fiber velocity at interception was essentially the same as the take-up speed, i.e., about 700 ft/minute.

Table I indicates that with increasing take-up speeds the cross-sectional diameter of the fiber decreases.

TABLE I Take-Up Speed, ft/min. Fiber Diameter, mils 700 (350 cm/sec) 7.1 (.0l8 cm) 725 (362 cm/sec) 6.96 (.0l76 cm) 750 (375 cm/sec) 6.8 (.0173 cm) 775 (387 cm/sec) 6.7 (.0l7 cm) 800 (400 cm/sec) 6.6 (.Ol67 cm) 825 (4l2 cm/sec) 6.5 (.0164 cm) The smaller diameter at a take-up speed of 700 ft/min. reflects the attenuation due primarily to the weight of the fiber extending from the orifice to the interception point, i.e., gravity attenuation. The important feature illustrated by Table I is that small but significant changes in take-up speeds and/or extrusion velocities are not detrimental to continuous fiber formation and take-up.

SUMMARY Although the prior art has employed chutes and the like to collect various materials, no one heretofore has been successful in the in-line take-up of extruded fibers with fragile upstream portions. Applicants, however, recognizing that prior attempts to take-up such fibers have failed because of tensioninduced breakage in the upstream portions, have not only isolated the needed take-up tension from the upstream portion but have provided a self-regulating take-up apparatus and method which is independent of variations in the extrusion and take-up speed of the fiber.

From the foregoing discussion, it is now apparent that the present invention involves the concept of positioning concave and/or fiat surfaces so as to constrain a moving fiber to move against the surfaces. The total length of the surface or surfaces is sufficient to cause a frictional interaction between the fiber and surface or surfaces which creates a tensional force to develop in the fiber which increases in value toward a limiting value of .411". Other important contributions to increasing the tension in the fiber to the desired value of pAu are drag, gravity, and fiber weight. At a value of about pAv the fiber forms an unsupported loop. Because the take-up of a fiber requires a value of somewhat more than pAv", it is necessary to further increase the tension in the fiber. This may be accomplished in various ways, the use of which ordinarily depends upon the magnitude of tensional force increase needed. One way is to pass the fiber over a convex surface positioned at a selected distance above the point at which the unsupported loop forms. The force of gravity increases the tensional force to a value which constrains the fiber to move against the convex surface. The frictional interaction between the fiber and convex surface further increases the tensional force.

Although it is preferred to use a second tensioning means, such as a convex surface prior to wind-up, under special conditions the take-up means may be used as a second tensioning means by winding the fiber directly after the unsupported loop is formed, utilizing only the effect of gravity to increase the tension above pAv It should be apparent that while applicants have described the present invention in connection with vertical extruding assemblies it is also adaptable for use with non-vertical spinning assemblies as well.

It is now apparent that the various embodiments of the present invention attain the objects and advantages as described. Thus, the invention having been set forth with respect to certain embodiments and examples thereof, those skilled in the art will become readily aware of the many modifications and changes obtainable in light of the descriptive matter contained herein. Accordingly, the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the present invention.

What is claimed is:

1. Apparatus for taking up a continuous fiber moving at a velocity v comprising a. a source for a continuous fiber having a low tensile strength in the upstream region.

b. first tensioning means including at least one surface situated beneath said fiber source for intercepting said fiber so as to constrain said fiber to move along said surface until a tensional force of about pAv is induced into said fiber, p and A being, respectively, the density and crosssectional area of said fiber, at which position along said surface the fiber forms an unsupported loop, and

c. means for increasing the tensional force on the fiber to a value about pAv including at least one convex surface engaging said unsupported loop and means for taking up said fiber under a tension greater than pAv 2. The apparatus of claim 1 in which the take-up means is a rotating bobbin spaced above the point at which the tension in the fiber is about pAv a vertical distance sufficient to increase the tension in the fiber to a value above pAu prior to winding about the bobbin.

3. The apparatus of claim 1 in which the first tensioning means is essentially a concave surface.

4. The apparatus of claim 3 in which the concave surface intercepts the fiber at an angle of between to 90.

5. The apparatus of claim 4 in which the intercept angle is between 20 to 45.

6. The apparatus of claim 1 in which the first tensioning means includes a plurality of surfaces positioned to constrain a moving fiber to a path which causes the fiber to have centrifugal forces in directions toward the surfaces.

7. The apparatus of claim 6 in which the surfaces are essentially Hat.

8. The apparatus of claim 7 in which the surfaces are essentially concave.

9. The apparatus of claim 8 in which the concave surfaces are arranged in descending order with the bottom portion of each surface positioned adjacent to a top portion of the concave surface therebeneath so as to present a substantially downward path to the fiber moving across the surfaces.

10. A tensioning device for use in the wind-up of a continuous fiber having an upstream portion of low tensile strength comprising a. a support;

b. a multiple curved upper surface supported by said support, said multiple curved surface having 1. a concave region with a descending first portion thereof for intercepting a downwardly moving continuous fiber at a preselected point along said surface and an ascending second portion wherein the length of said concave region from said preselected point, the coefficient of friction between said surface and the fiber moving thereacross, and the height of the ascending portion are sufficient to cause the fiber to form an unsupported loop, and

2. a convex region above said ascending second portion for imparting frictionally-induced tensional force to a fiber moving thereacross.

11. A method for taking-up an extruded continuous fiber having a low tensile strength in the upstream region comprismg a. constraining the fiber to move in a curved path with at least one surface member so as to induce a tensional force sufficient to cause the fiber to form an unsupported loop and b. winding the fiber about a rotating member.

12. The method of claim 11 in which the rotating member is spaced above the point at which the unsupported loop is formed a distance sufficient to cause an increase in the tensional force of the fiber.

13. The method of claim 11 in which the unsupported loop is terminated by passing the fiber over a convex surface positioned above the point at which the unsupported loop is formed.

14. A process for taking-up an extruded continuous fiber having a low tensile strength in the upstream region thereof comprising extruding the fiber against a concave surface at a velocity V passing the fiber across the concave surface until the fiber forms an unsupported loop, terminating the unsup-' ported loop on a convex surface and passing the fiber across the convex surface, and winding the fiber about a rotating member. 4

15. The process of claim 14 wherein the angle between the concave surface and the extruded fiber is between about 0to 16. The process of claim 14 wherein the angle is between about 20 to 45.

17. The process of claim 14 in which the fiber is extruded as a molten stream and subsequently stabilized pending solidification wherein the fiber is wound around the rotating members at a velocity V lying between V and V

Claims

1. Apparatus for taking up a continuous fiber moving at a velocity upsilon comprising a. a source for a continuous fiber having a low tensile strength in the upstream region. b. first tensioning means including at least one surface situated beneath said fiber source for intercepting said fiber so as to constrain said fiber to move along said surface until a tensional force of about Rho A2 is induced into said fiber, Rho and A being, respectively, the density and crosssectional area of said fiber, at which position along said surface the fiber forms an unsupported loop, and c. means for increasing the tensional force on the fiber to a value about Rho A2 including at least one convex surface engaging said unsupported loop and means for taking up said fiber under a tension greater than Rho A2.

2. The apparatus of claim 1 in which the take-up means is a rotating bobbin spaced above the point at which the tension in the fiber is about Rho A2 a vertical distance sufficient to increase the tension in the fiber to a value above Rho A2 prior to winding about the bobbin.

4. The apparatus of claim 3 in which the concave surface intercepts the fiber at an angle of between 0* to 90*.

5. The apparatus of claim 4 in which the intercept angle is between 20* to 45*.

7. The apparatus of claim 6 in which the surfaces are essentially flat.

8. The apparatus of claim 7 in which the surfaces are essentially concave.

10. A tensioning device for use in the wind-up of a continuous fiber having an upstream portion of low tensile strength comprising a. a support; b. a multiple curved upper surface supported by said support, said multiple curved surface having

11. A method for taking-up an extruded continuous fiber having a low tensile strength in the upstream region comprising a. constraining the fiber to move in a curved path with at least one surface member so as to induce a tensional force sufficient to cause the fiber to form an unsupported loop and b. winding the fiber about a rotating member.

14. A process for taking-up an extruded continuous fiber having a low tensile strength in the upstream region thereof comprising extruding the fiber against a concave surface at a velocity V1, passing the fiber across the concave surface until the fiber forms an unsupported loop, terminating the unsupported loop on a convex surface and passing the fiber across the convex surface, and winding the fiber about a rotating member.

15. The process of claim 14 wherein the angle between the concave surface and the extruded fiber is between about 0*to 90*.

16. The process of claim 14 wherein the angle is between about 20* to 45*.

17. The process of claim 14 in which the fiber is extruded as a molten stream and subsequently stabilized pending solidification wherein the fiber is wound around the rotating members at a velocity V2 lying between V1 and 1.20V1.