US3596319A

US3596319A - Foam filament cutter

Info

Publication number: US3596319A
Application number: US746353A
Authority: US
Inventors: Winfield L Mckenica; Marvin Scher; James Gerald Smith
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1968-07-22
Filing date: 1968-07-22
Publication date: 1971-08-03
Anticipated expiration: 1988-08-03
Also published as: NL6911226A; DE1937215A1; GB1237360A

Abstract

Gas-inflated foamed filaments are cut to staple length immediately after spinning by a whirling knife cutter located well below the spinneret. A duct surrounds the filaments from spinneret to cutter and confines a sheath of gas flowing cocurrently with the filaments. Velocity of gas is low in upper part of duct, but greater than rate of filament extrusion in lower part. A second duct below the cutter prevents rapid deceleration and expansion of the gas so that fibers are conveyed away from the cutter. Cross sections of ducts are much larger than total cross section of filaments so contact of filaments with walls is avoided.

Description

United States Patent Inventors Winfield L. McKenica Primary Examiner-.l. Spencer Overholser Assistan! ExaminerMichael 0. Sutton All0rne \'Don M. Kerr ABSTRACT: Gas-inflated foamed filaments are cut to staple length immediately after spinning by a whirling knife cutter located well below the spinneret. A duct surrounds the filaments from spinneret to cutter and confines a sheath of gas flowing cocurrently with the filaments. Velocity of gas is low in upper part of duct, but greater than rate of filament extrusion in lower part. A second duct below the cutter prevents rapid deceleration and expansion of the gas so that fibers are conveyed away from the cutter. Cross sections of ducts are much larger than total cross section of filaments so contact of filaments with walls is avoided.

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JAIIES GERALD smm BY 21 m ATTORNEY PATENTEU ms 319?: 3,596,319

SHEET 2 BF 2 2 F I 6 I 3 u y a la 4 x 29 A 25 6 s5- 5 r-L 5:11 I

' INVENTORS IINFIELD L. "0 KENICA MARVIN SCHER JAIES GERALD SMITH ATTORNEY FOAM FILAMENT CUTTER BACKGROUND OF THE INVENTION This invention relates to a method and an apparatus for 5 One process for forming suitable foamed filaments is dis.- closed by Blades and White in US. Pat. No. 3,227,784, issued Jan. 4, 1966. Particularly useful foamed filaments are ultramicrocellular as disclosed by Blades and White in US. Pat. No. 3,227,664, issued Jan. 4, 1966. A preferred ultramicrocellular filament comprises polyethylene terephthalate as the polymer and is preferably obtained by extruding a solution of the polymer in methylene chloride, at elevated temperature and pressure, through at least one orifice into a region of reduced temperature and pressure where solvent vaporization and foam formation are substantially instantaneous. The linear rate of foam-filament formation ordinarily exceeds 500 yd./min./orifice (475 m./min./orifice) and frequently exceeds l,000 yd./min./orifice (914 m./min./orifice). Collecting these filaments into packages from which they can subsequently be backwound and cut into uniform staple is difficult not only because of the high linear rate of formation but also because of the bulkiness of low-density foam which severely limits the length of filament which can be collected in a single package of manageable size. It is commercially desirable to continuously cut into staple fibers the foamed filaments being obtained by extrusion.

Numerous methods and devices are known for converting customary textile fibers into staple. Ordinarily these involve at least one knife. Some use two touching or very closely spaced surfaces intermittently crossing one another in oppositely directed relative velocities to cut the fibers with a scissorlike action. Of this type is the well-known rotating drum into which a roving enters axially and is expelled centrifugally through an opening in its surface which intermittently crosses a fixed knife edge to cut the roving. Another type provides for mechanically supporting the filament or roving over a space intermittently crossed by a knife. In still another type, the filaments are forwarded by an air jet to an exit opening crossed intermittently by a knife. In still another type, the filaments are forwarded by an air jet to an exit opening crossed intermittently by a knife. None of these known devices avoid substantial contact of the advancing filament(s) with confiningwalls. Thevery low-density, high-volume, and high surface friction of suitable foamed filaments cause them to quickly plug any known device wherein substantial contact with confining surfaces is involved.

In the production of chips and grains of solid polymer, it is known to extrude a rod of polymer and to cut it with a flying knife close to the die outlet. Goins in US. Pat. No. 3,089,l94, issued May 14, I963, describes the comminuting ofa continuously formed strand of polymeric foam using a high-speed rotating knife preferably positioned within about 0.25 inch (6.35 mm.) ofthe outlet from which the foamed strand issues. In Goins case, however, there is no concern about the quality of the foam obtained as long as it is comminuted for further processing. Several severe disadvantages occur when Goins' technique is applied to the cutting of closed-cell, gas-inflated, foamed filaments. The rotating blade creates turbulence in the gaseous atmosphere which results l in cooling of the face of the extrusion die with consequent erratic changes in quality of the foam produced and (2 in gas currents which carry much of the staple through the plane of the blade two or more times thus forming a quantity of too short and nonuniform lengths.

Even more importantly, however, the shock of impact of the blade with the filament is transmitted back to the orifice where it causes a sharp permanent decrease in cross-sectional area of the filament, Le. a notch. At the notch the gas-retaining and tensile properties of the staple fiber are greatly reduced. When the spacing between the plane of rotation of the blade and the orifice is increased to overcome these difficulties, the very low density filaments are deflected sufficiently by the turbulence that some portions miss the blade completely to cause extra long lengths of staple to be cut. In the extreme, deflected filaments wrap around and jam the cutter.

BRIEF STATEMENT OF THE INVENTION According to this invention, a novel method for converting continuous filaments of a low-density polymeric foam into staple lengths is provided. The method comprises the steps: (I continuously extruding a foamable composition through at least one orifice of a die into a sheath of gaseous atmosphere to produce at least one continuous, foamed, polymeric filament; (2 continuously flowing the sheath about the filament generally along the extrusion direction from at least the region of the die to a position remote from the die; (3 increasing the velocity of the sheath along the extrusion direction from a velocity in the region of the die which is less than the linear rate of filament formation to a velocity at the remote position which at least exceeds the linear rate of filament formation whereby the filament is directed centrally within the sheath and is caused to move substantially parallel to the extrusion direction, the cross-sectional area of the sheath being at least 10 times greater than total cross-sectional area of the filament o r filaments at the remote position; (4 cutting the filament by impact with at least one blade rotated in the plane intersecting the extrusion path and positioned within about 0.5 inch (1.27 cm.) beyond the remote position, the point of impact cutting being sufficiently displaced from the axis of rotation of the blade that the blade velocity at that point greatly exceeds the linear rate of filament formation; and (5 conveying the staple fibers away from the plane of blade rotation along the extrusion direction within the continuing stream of gaseous atmosphere; whereby staple fibers are obtained.

As another element, this invention also includes an apparatus for implementing the above process. The apparatus comprises, in association with an extrusion die having at least one orifice: (a) a cutter composed of at least one blade mounted on a rotatable disc, the cutter being located at a point below and remote from the die and positioned such that the blade intersects the path of the filament; (b) means for rotating the disc; (c) means between the die and the cutter blade for forming and confining about the filament a sheath of gas flowing currently with the filament at a velocity exceeding the linear rate of filament formation in the vicinity of the cutter, but at a relatively low velocity near the die, the crosssectional area of the confining means at the end thereof nearest the cutter being at least 10 times greater than the total cross-sectional area of the orifice or orifices, and (d) a duct downstream of the cutter of cross-sectional area sufficiently large to permit deceleration of the gas but sufficiently small to cause the filaments to be carried out of the path of the cutter blade or blades.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagram of a vertical cross-sectional view of the apparatus of the present invention.

FIG. 2 is a similar diagram illustrating a second form of the apparatus of the present invention.

FIG. 3 is a similar diagram illustrating the preferred form of the apparatus of this invention wherein the gaseous atmosphere employed is isolated from the ambient atmosphere.

FIG. 4 shows in perspective view a single staple fiber cut according to this invention.

FIG. 5 similarly shows a single staple fiber cut according to a prior art method.

FIG. 6 is a diagram of a suitable rotating knife assembly as seen along its axis of rotation.

FIG. 7 shows a preferred type of cross section of a cutting blade taken at 7-7 of FIG. 6 and enlarged.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method and a suitable apparatus for carrying out this invention are now discussed with reference to FIG. 1. A foamable composition comprising a synthetic thermoplastic polymer and a vaporizable or gas-forming expanding agent is continuously led to extrusion die l0,via suitable conduit 11 as indicated by arrow 12. Exit face 13 of extrusion die 10 is perforated to form a plurality of closed cell, foamed, gas-inflated filaments 14. A plenum I is provided into which a gaseous atmosphere is injected by suitable means, e'.g., blower l6; and plenum 15 preferably surrounds extrusion die in an area upstream of exit face 13. The gaseous atmosphere passes from plenum into funnel-shaped feed duct l7.-Preferably there is provided between plenum 15 and duct 17 a suitable means 18 for directing the gaseous atmosphere generally along the extrusion direction, such means being, for example, a series of screens or a honeycombed plate with openings axially parallel to the extrusion direction.' This gas-directing means is hereinafter denoted distributor l8.

Duct l7 confines the gaseous atmosphere-in the form of a sheath which surrounds and transports filaments 14 from extrusion die 10 to a remote location corresponding to outlet 19 of duct 17. In a plane parallel to, out of contact with, but within about 0.5 inch (1.27 cm.) downstream of the plane of outlet 19, at least one'blade 20 is rotated so that its velocity at the point of impact with filaments 14 is very much greater than the linear rate of filament formation. Periodic impact of each blade 20 with filaments 14 cuts them into staple fibers 21. The velocity of the gaseous sheath at and near outlet 19 and along the extrusion direction exceeds the linear rate of filament formation thereby serving to draw filaments 14 through duct 17, to generate pressure gradients across outlet 19. which centrally direct filaments l4 and substantially prevent their contact with confining walls, and to generally align each filament I4 with the extrusion direction just before contact with blade 20. This high velocity of gaseous sheath at outlet 19 results after passage through most of the converging duct 17. Between extrusion die 10 and this high velocity region there exists a region in the wider portions of duct l7 where the velocity of the gaseous sheath is less than the linear rate of filament formation, thus tending to oppose the motion of filaments ldthrough duct 17. By first passing the filaments through a lower velocity sheath of gases, enough resistance to filament passage occurs that the subsequent high velocity sheath holds the filaments straight and parallel near the cutter without causing elongation at the spinneret face. It is through that thisacceleration of the gaseous sheath probably helps to I prevent the transmission of cutting shock back to the spinneret face. However, placing the cutter remote from the spinneret also places more mass of filament between spinneret and cutter. The increased mass and distance probably account at least in part for the diminished transmission of cutting shock.

Each blade 20 is'suitably mounted to a supporting device, e.g., disc 22, which in turn is rotated either by direct or geared coupling with a motor 23. Speed-regulatable electric motors are preferred. FIG. 6 shows a view of a preferred knife assembly taken as indicated at 6-6 of FIG. 1. Blades 20, attached to disc 22, are rotated about axis 24 from which it is readily apparent that the point of impact cutting is radially displaced from axis' 24. Depending on the number of blades 20 attached to thedisc 22 and on their angular separations, it may be necessary to attach co'unterweights to disc 22 in order to achieve dynamic balance of the assembly. While equal angular spacings between blades 20 are usually employed to provide staple fibers 21 of one length, unequal spacings may be employed to obtain a predetermined mixture of staple lengths.

. Each blade 20 has cross-sectional dimensions in and normal to its plane of rotation only sufficient to provide the necessary strength. Sharp cutting edges are notrequired; and, indeed, lengths of rigid round wire can serve as blades 20. Preferred blades 20 are, however, sharpened as indicated by FIG. 7, taken at 7-7 of FIG. 6, where sharp. cutting edge 25 is shown.

Generally, the cut staple 21 is carried away from blade 20 in the stream of gaseous atmosphere ejected from outlet 19, and this area is confined within a much larger duct 33 serving to enclose the knife assembly for safety and to lead the cut staple 21 to storage or further processing (not shown). At and past the plane of cutting, however, it is possible for rapidly expanding gases to convey some staple fibers 21 back through the plane of cutting. It is preferred, therefore, to provide a staple duct 32 within larger duct 33 and aligned with the axis of outlet 19. A slight outward taper of the walls of staple duct 32 aids in diminishing turbulence within it. Not only does the primary stream of gaseous atmosphere enter inlet 30 of staple duct 32 but also additional gaseous atmosphere is thereby aspirated into it as indicated by arrows 31. Therefore, staple fibers 21 are conveyed to a distance removed from the plane of cutting before substantial expansion and deceleration of the gaseous atmosphere. Its greatly lowered velocity below duct 32 is insufficient to convey staple fibers 21 up and through the plane of cutting along arrows 31.

FIG. 2, similar to FIG. 1 and with corresponding parts identically numbered, presents an alternative method for gasconveying filaments 14 to a cutting plane remote from extrusion die 10. Its significant difference is the provision of a sucker-jet 26 with outlet 19. If sucker-jet 26 is positioned close to extrusion die. 10, the disadvantages inherent to known prior art methods are encountered. Therefore, a perforated portion 28 of duct 17 extending from the extrusion die 10 to the sucker-jet 26 is provided. Blower-compressor l6 injects gaseous atmosphere through duct 27 to create a velocity of the gaseous sheath near outlet 19 which exceeds the linear rate of filament formation. Additional gaseous atmosphere is aspirated through perforated portion 28. This provides a lower velocity sheath of gaseous atmosphere in the vicinity of theextrusion die 10 and tends to prevent contact of filaments 14 with the walls of perforated portion 28. In this alternative operation, the necessary acceleration of the gaseous sheath occurs without the need for decreasing the cross-sectional area of the duct, but both mechanisms may be employed simultaneously.

In the production of the preferred ultramicrocellular staple fibers comprising polyethylene terephthalate,'it is desirable that the gaseous atmosphere contacting filaments l4 and staple 21 be composed substantially of methylene chloride vapor at or above its normal boiling temperature. For this as for many other foam-production systems, a closed spin-cell is required to isolate the gaseous atmosphere employed from the external ambient air atmosphere. FIG. 3 presents in vertical cross section the preferred apparatus according to this invention. Corresponding parts are labeled as in FIGS. 1 and 2. A closed spin-cell 40 has walls also enclosing the cutting apparatus. As before, a foamable composition flows via conduit 11 to extrusion die 10 within closed spin-cell 40. Plenum 15 surrounds conduit 11 and receives confined gaseous atmosphere via pipe 45. Duct 17 surrounds extruded filaments l4 and communicates with plenum 15 through distributor 18. Unlike duct 17 of FIG. 1, this duct accelerates gaseous atmosphere to remote outlet 19 with no abrupt angular changes in cross section, which is preferred since it reduces undesirable eddy currents. A smoothly curved shroud 29 surrounds extrusion die 10 both to promote smooth flow lines and to preventcooling of exit face 13 by the circulated atmosphere. Preferably a layer of thermal insulation 37 also surrounds conduit 11 in plenum l5. Thecutting assembly is as already described, but preferably remote means (not shown) are provided to selectively move this assembly from the cutting position shown to a position indicated by dashed outlines where blade 20 is withdrawn from the extrusion path. Alternatively, blade 20 can be spring-retracted into disc 22 so that it is operatively extended centrifugally only during rotation of disc 22. Access door 34 permits servicing the cutting assembly, and

access doors

35 and 36 provide for servicing die 10. Additional gaseous atmosphere is drawn along arrows 31 into opening 30, which is the open end of duct 32 through which staple 21 is conveyed to separator 39 where staple is removed via arrow 42 and gaseous atmosphere withdrawn by blower 16. The type of separator 39 used is not a part of this invention. For very high gas flows, centrifugal separators are preferred. Alternatively, separators 39 may be an expansion chamber as shown having internal walls 41 perforated to allow passage of gaseous atmosphere but not staple fibers.

Finally, gaseous atmosphere is recirculated by blower.l6 which communicates with separator 39 and forwards gas via pipe 44 to divide

pipes

45 and 46, the latter provided respectively with flow-

control valves

47 and 48 for regulatably dividing the circulated gas to plenum and to spin-cell 40 for intake along arrows 31. A heat exchanger 49 along pipe 44 is ordinarily required for maintaining the desired temperature of recirculated gaseous atmosphere. Liberal use of thermal insulation (not shown) along all exposed external walls is usually made.

Critical velocities and dimensions cannot be absolutely specified since they vary over broad limits to accommodate different systems. Sufficient guidelines are established to enable one skilled in the art to apply this invention to the preparation of staple fibers from any continuously extruded, foamed, polymeric filaments. Specific limits are given for the preparation of ultramicrocellular polyethylene terephthalate staple (hereinafter designated PET staple).

As hereinbefore discussed, the plane of rotation of blade must be remote from extrusion die 10. FIG. 4 shows a single staple fiber cut according to this invention. HO. 5 correspondingly shows a single staple fiber out according to a prior art method wherein the plane of cutting is within about 0.5 inch (1.27 cm.) of the exit face 13 of die 10. Closed-cell foams are more turgid and readily cut when fully gas-inflated. This distance should, therefore, be great enough to allow for full expansion and, in the case of foam which collapses after full expansion, short enough to allow cutting before collapse commences. For PET staple, this distance is preferably from about 7 to about 36 inches (about 18 to about 90 cm. The plane of rotation of blade 20 should be out of contact with but within about 0.5 inch 1.27 cm.) ofthe plane of outlet 19.

Generally, critical dimensions and velocities are selected to be nearly the minimum ones since the expense of operation increases with increasing gas flow. As discussed hereinabove, total gas flow should be great enough that at outlet 19 filaments 14 are forwarded by the sheath of gaseous atmosphere, are rendered substantially parallel to the extrusion direction, and are directed centrally within the sheath of gaseous atmosphere, thus substantially avoiding contacts with confining walls. The total cross-sectional area of filaments 14 passing through outlet 19 should not exceed about 10 percent of the area of outlet 19 and is preferably less than about 5 percent. Gas-velocities through outlet 19 can be characteristic of either laminar or turbulent flow as computed using the well-known Renynolds Number.

As hereinabove described, staple fibers 21 preferably enter opening 30 of a second duct 32. Since impact cutting displaces staple fibers 21 slightly, they can get caught on the edges of opening 30 if it is not sufficiently large. Moreover, the sheath of gaseous atmosphere passing from outlet 19 to opening 30 tends to expand a bit so that some hits the edges of opening 30 and creates excessive turbulence if opening 30 is too small. Thus, opening 30 should always be at least as large and of generally the same geometric shape as outlet 19. For circular or oval shapes, the radial dimensions of opening 30 should be no larger than about 4 times those of outlet 19, preferably about 2 times larger. When a large number, e.g., more than 20, of filaments 14 are being fed through this apparatus, it is frequently desirable that

openings

19 and 30 be slot-shaped, forming an are so that filaments l4 distributed along the arc are all cut at substantially the same point on knife 20, Le, at

the same radial displacement from its axis of rotation. In this case, the width of the slot forming opening 30 is larger than that of outlet 19 by the above factors, and the absolute increase in length of arc of the slot is substantially identical to the absolute increase in slot width.

The linear velocity of each blade 20 at its point of contact with a filament 14 should be much greater than the linear rate of filament formation, i.e., preferably at least about 4 times greater. Again, however, the required velocity is dependent on the composition of filaments 14 being cut. For PET staple this velocity is preferably from 1 1,000 to 30,000 ft./min. (3,330 to 9,100 m./min.) and more preferably between about 15,000 and 25,000 ft./min. (4,600 to 7,600 m./min.). For a given rotational velocity of blades 20, radial displacement of the point of impact from the axis of rotation (24 of FIG. 6) is adjusted to provide the required linear velocity. Also, as is wellunderstood, the number of blades 20 fastened to disc 22, as well as their velocity, can be varied to yield the required length of staple 21. With reference to H0. 6, it is sometimes preferable to fasten blades 20 to disc 22 so that they form acute angles with respect to radii of disc 22. Preferably the tip of each blade 20 is tipped backward in the plane of rotation, with respect to the direction of rotation as indicated by the arrow of FIG. 6.

1n the following examples, all parts and percentages are by weight unless indicated otherwise.

EXAMPLE I Apparatus substantially as shown in FIG. 1 is used to cut continuously extruded, ultramicrocellular, polyethylene terephthalate filaments into 4 to 6 inch (10 to 15 cm. long staple fibers. The uniform composition extruded through 4 or 12 orifices is 65 percent polyethylene terephthalate and 35 percent methylene chloride. The dried polymer used in making this composition is characterized by a relative viscosity (RV) of about 58 (RV is the solution-to-solvent ratio of absolute viscosities at 25 C. when the solvent is 70 parts of 2, 4, 6-trichlorophenol in parts of phenol, and the solution is 8.7 percent polymer). The composition about 220 C. and under about 700 p.s.i.g, (about 49.2 kg./cm. gauge) pressure passes through orifices 0.012 inch (0.30 mm.) in diameter and 0.006 inch (0.15 mm.) long into a sheath of ambient air injected by blower l6. Filaments l4 and staple fibers 21 so formed are 0.070: 0.005 inch (1.78:0.13 mm.) in diameter at a density of 002010.004 gm./cc. in their solidified, fully inflated state.

Details of several separate runs are given in Table 1. in each case feed duct 17 is funnel-shaped with a maximum inside diameter at the level of extrusion die 10 of 13.25 inches (33.65 cm.). The conical section is 8.125 inches (20.64 cm.) long and tapers to the specified inside diameter of a 6 inch (15.24 cm) long cylindrical section. The plane of rotation of the cutter assembly is positioned at or less than 0.5 inch (1.27 cm.) below the plane of outlet 19. The cutter assembly has a single 3.75 inch (9.55 cm.) long blade 20 extending from a disc so that its point ofimpact cutting is about 7.75 inch (19.8 cm.) from the axis of rotation corresponding to a linear velocity at the point of impact-cutting of 16,200 ft./min. (4,950 m./min.). Rotational velocity of blade 20 is at least 4,000 rpm. Staple duct 32 has an inlet opening 30 at about 0.5 inch 1.27 cm.) below the cutting plane and with an inside diameter given in Table 1. Its length is about 2.67 times and its outlet diameter about 1.42 times the inlet diameter. The linear rate of filament formation is of the order of 25 ft./sec. (7.62 m./sec.).

Table 1 indicates for several runs the number of filaments being formed, the inside diameter of outlet 19 (feed duct), the inside diameter of opening 30 (staple duct), and the approximate minimum velocity of air near outlet 19 of duct 17 to avoid its becoming plugged.

As can be seen from Table 1, the air velocity required to avoid plugging is independent of the diameter of staple duct TABLE -I.MINIMUM AIR VELOCITIES FOR STAPLE CUTTING Outlet diameter Inlet diameter Air velocity at I I of feed duct of staple duet feed-duct outlet 1 O. filaments Inches Cm Inches Cm Ftjsvc. M./see. 1. n 2. 54 3. 0 7. 62 203 an. 4 1. 0 2. 54 4. 11. 43 293 80. 4 1. 5 3. 81 3. 0 7. 62 154 46. 0 1.5 3. 81 4.5 11. 43 154 46.11 1. 5 3. 81 (i. 0 15. 24 154 46. .1 1.5 3. 81 4.5 11.43 154 46. ll 2. 33 5. E12 3. 0 T. 02 73. 5 22. 4 2. 33 5. .12 4. 5 11. 43 73. 5 2'1. 4 .2. 33 5. [l2 ti. (1 15. 24 73. 5 .22. 4

EXA M PLE 11 A sucker-jet as described by Walton in U.S. Pat. No. 1,871,100 is used substantially as shown in FIG. 2 to forward a single ultramicrocellular filament of polyethylene terephthalate to a staple-cutting zone. Conditions and apparatus for forming the filament continuously are as described in example 1. Between the sucker-jet 26 and exit face 13 of extrusion die is placed a perforated cylinder 28 which is 4.22 inches (10.75 cm.) long and 1.25 inches (3.18 cm.) in inside diameter. It is constructed of l7-gauge sheet metal with 0.09375 inch (0.2381 cm.) diameter holes uniformly spaced over its area such that it is 40 percent open. The entrance of the sucker-jet smoothly tapers to an inside diameter of 1.0 inch (2.54 cm.). It is 4.15 inches (10.57 cm.) long overall and has top and bottom sections which, when assembled with suitable shims, provide a narrow, downward-directed, circumferential slot which, on a cross section of the jet, is inclined at 15 to the vertical. Precise dimensions of the slot are unknown, but the sucker-jet as assembled passes 6 ftflmin. (0.168 m./min.) of air from a source of compressed air at 30 p.s.i.g. (2.1 kgJcmFgauge). A 1.5 inch (3.8 cm.) long soft plastic bushing with 1.032 inch (2.61 cm.) inside diameter is positioned against and axially aligned with the outlet of the sucker-jet to protect the rotating blade in case of accidental contact. The cutter assembly is similar to that of example 1, the plane of rotation being 0.5 inch (1.27 cm.) or less below the outlet of the plastic bushing and the blade rotated at at least 4,000 rpm. With this arrangement, the overall distance from exit face 13 ofdie 10 to the cutting plane is 9.78 inches (24.8 cm.). No staple duct 32 is employed. Staple fibers 21 are conveyed away from the cutting zone by the air jet, and allowed to fall into a large container.

Uniform lengths of staple fibers 21 are obtained over a range of pressures for compressed air input to the sucker-jet of from about to 40 p.s.i.g. (1.4 to 2.8 kg./cm. gauge). Characteristic of this operating range is a slight but detectable slack in the filament as seen through the perforations in cylinder 28. At lower pressures, the sucker-jet plugs. At higher pressures. elongation occurs at the die face. with resultant poor foam formation.

EXAMPLE 111 20 continuous filaments, formed as described in Example 1, are cut to staple as described in connection with FIG. 3. Feed duct 17 conveys the filaments to a cutting plane located about inches (76.2 cm.) below exit face 13 of die 10 and at 0.5 inch (1.27 cm.) or less below outlet 19 of feed duct 17. The inlet diameter of duct 17 is 15 inches (38.1 cm.); it tapers smoothly over about 10.0 inches (25.4 cm.) of length to an inside diameter of 2.0 inches (5.08 cm.); and it terminates in a cylindrical section 8.0 inches (20.3 cm.) long and 2.0 inches (5.08 cm.) in inside diameter. A single blade is rotated in the cutting plane at about 5,000 rpm. with about 8 inch (20.3

cm.) radius of rotation measured from axis 24 to the center of outlet 19 to provide a cutting velocity of 20,900 ft./min.

(6,420 m./min.). The sharpened cutting edge of the blade extends completely across outlet 19. Staple fibers 21 are conveyed via conduit 32 with a 4.0 inch 10.16 cm.) inside diameter.

As described in connection with FIG. 3, this is a closed system isolate from the ambient atmosphere. The gaseous atmosphere is the vapor of methylene chloride at or slightly above 41 C. The staple fibers are separated from the vapor by a suitable separator 39, and the vapor is recirculated by blower 16 through a heater 49 to the closed spin cell. Rate of vapor circulation is about 300 ftF/min. (8.5 m. /min.), and it is about equally divided by

valves

47 and 48 for input via plenum l5 and via opening 30 as indicated by arrows 31.

In the foregoing examples, cutting under steady state conditions is described. Sometimes special procedures are employed in starting the systems. If foam production begins after the cutting apparatus is assembled, it is often necessary to augment gas flow through feed duct 17 to assure that filaments reach the high-velocity zone near outlet 19 before duct 17 plugs. This may be accomplished by, for example, increasing gas flow into plenum l5 temporarily or by injecting additional gas into the duct through auxiliary jets in the walls. Another technique is to assemble the cutting apparatus around continuously formed filaments. Other approaches to starting-up these systems will be obvious to those skilled in the art.

While it has been shown that the method and apparatus of this invention are particularly adaptable to the formation of staple from ultramicrocellular filaments comprising polyethylene terephthalate, it is generally applicable to any foamed fiber continuously formed by extrusion. High volume of production is characteristic of these systems, and by avoiding substantial contact of the filaments with confining walls, pluggage is prevented. Likewise, it is possible to gather the fibers into parallel array within a sheath of high-velocity gaseous atmosphere to assure uniform staple lengths without transmitting undesirable effects back to the extrusion orifices.

A many alterations and alternatives are apparent without departing from the teachings of this invention, it is not intended to be limited to the foregoing except as specified in the appended claims. 1

lclaim:

1. Apparatus for cutting closed-cell, gas-inflated, foamed filaments (14) into staple length fibers as they are continuously formed by extrusion through orifices in an extrusion die (10), the apparatus comprising a. a cutter composed of at least one blade (20) mounted on a rotatable disc (22), the cutter being located at a point below and remote from the die and positioned such that the blade intersects the path of the filaments;

. means for rotating the disc;

0. a funnel-shaped duct (17) between the die and the cutter blade for forming and confining about the filament a sheath of gas flowing cocurrently with the filament at a velocity exceeding the linear rate of filament formation in the vicinity of the cutter, but at a relatively low velocity near the die, the larger end of the duct being located .about the die, the smaller end of the duct being located immediately above the cutter blade and having a crosssectional area at least 10 times greater than the total cross-sectional area of the orifices;

d. a plenum (15) located about the die and communicating with the funnel-shaped duct in the space between the duct and the die:

e. a blower (16) for introducing a stream of gas to the plenum and thence to the duct, said blower being connected to said plenum; and

f. a staple-receiving duct (32) downstream of the cutter of cross-sectional area sufficiently large to permit deceleration of the gas but sufficiently small to cause the filaments to be carried out of the path of the cutter.

2. Apparatus for claim 1 wherein said duct is partially perforated, the perforated section (28) being in the upper portion of the duct, there being a peripheral opening in the lower portion of the duct, a blower (16) for introducing a gas through the peripheral opening in the duct in a direction generally parallel to the direction of filament extrusion being operably associated with said apparatus.

3. Apparatus of claim 1, wherein the plenum and the funnelshaped duct are separated by an annular element (18) having a multitude of channels between major surfaces, the axes of which are generally parallel to the filament extrusion direction.

4. Apparatus of claim 3 including means operably connected to the terminal end of the staple-receiving duct and the intake side of the blower (16) for receiving and separating the gas and the staple fibers and recirculating the gas back to the plenum.

5. Apparatus of claim 4 wherein the die, cutter and at least the ends of the ducts adjacent the cutter are enclosed in a housing in order to prevent escape of gas and permit cutting in an atmosphere of the extrusion solvent.

6. Apparatus of claim 5 wherein interior surfaces of the funnel-shaped duct are smoothly curved in order to minimize turbulence of the gas stream.

7. Apparatus of claim 5 wherein a heat exchanger (49) is provided on the exit side of the blower to maintain the temperature of the recycled gas.

Claims

1. Apparatus for cutting closed-cell, gas-inflated, foamed filaments (14) into staple length fibers as they are continuously formed by extrusion through orifices in an extrusion die (10), the apparatus comprising a. a cutter composed of at least one blade (20) mounted on a rotatable disc (22), the cutter being located at a point below and remote from the die and positioned such that the blade intersects the path of the filaments; b. means for rotating the disc; c. a funnel-shaped duct (17) between the die and the cutter blade for forming and confining about the filament a sheath of gas flowing cocurrently with the filament at a velocity exceeding the linear rate of filament formation in the vicinity of the cutter, but at a relatively low velocity near the die, the larger end of the duct being located about the die, the smaller end of the duct being located immediately above the cutter blade and having a cross-sectional area at least 10 times greater than the total cross-sectional area of the orifices; d. a plenum (15) located about the die and communicating with the funnel-shaped duct in the space between the duct and the die: e. a blower (16) for introducing a stream of gas to the plenum and thence to the duct, said blower being connected to said plenum; and f. a staple-receiving duct (32) downstream of the cutter of cross-sectional area sufficiently large to permit deceleration of the gas but sufficiently small to cause the filaments to be carried out of the path of the cutter.

3. Apparatus of claim 1, wherein the plenum and the funnel-shaped duct are separated by an annular element (18) having a multitude of channels between major surfaces, the axes of which are generally parallel to the filament extrusion direction.