US3067458A - Melt spinning apparatus and process - Google Patents

Description

Dec. 11, 1962 E. F. DAUCHERT MELT SPINNING APPARATUS AND PROCESS Filed April 7, 1959 2 Sheets-Sheet l INVENTOR EUGENE E DAUCHERT ATTORNEY Dec. 11, 1962 E, F. DAUCHERT 3,067,458

MELT SPINNING APPARATUS AND PROCESS Filed April 7, 1959 2 Sheets-Sheet 2 INVENTOR EUGENE F. DAUCfiERT BY jade 0.1%

ATTORNEY United States Fatent Pont de Nemours and Company, Wilmington, Del., a

corporation of Delaware Filed Apr. 7, 1959, Ser. No. 804,782 12 Claims. (Cl. 188) This invention relates to the quenching of extruded streams of molten organic filament-forming materials to produce solid filaments, which may then be collected in or converted to any desired form, such as yarns, tows, staple fibers, monofilaments, etc. More particularly, it relates to an improved process and apparatus for spinning such molten compositions in a uniform manner at a high rate of speed to obtain spun filaments having physical propertieswhich are uniform to a high degree.

As disclosed by W. W. Heckert in his US. Patent 2,273,105, the process of forming solid filaments from extruded molten compositions is facilitated by spinning the filaments into a moving current of gas to dissipate the heat from the filaments as rapidly as possible. Un fortunately, it has been found that when the molten filaments are quenched in this way, the spinning cells have a relatively low productivity limit, or limit to the rate at which yarn may be spun in the cell, at any given level of yarn uniformity. Non-uniformities arise from differential quenching conditions across the filament bundie such as differences in temperature, velocity of air, and other variable factors.

Perhaps the most serious difficulty exhibited by nonuniform filaments is differential behavior in accepting dyes, which leads to dyed products having streaks or flecks of a noticeably different shade of color than the predominant color of the product. Differential behavior with dyes seems to be associated with differences in orientation which may be observed in spun filaments subjected to differential quenching conditions. Among other properties which may be afiected are the uniformity of size (denier) of the filaments and their tenacity and break elongation.

In another apparatus for quenching molten filaments, as disclosed by D. F. Babcock in his US. Patent 2,252,- 684, the filaments are spun into a cylindrical tube, with cocurrent flow of the quenching air brought about by uniform radial introduction of the air into the filament bundle through a foraminous member at the top of the tube. Such an apparatus provides relatively uniform quenching conditions for the extruded filaments, especially at low spinning speeds. However, in practice, certain restrictions are encountered in the use of such apparatus. In order to spin large numbers of filaments effectively from each spinneret, which is highly desired in commercial practice, convergence of the filament bundle at a considerable distance from the spinneret is required.

In the process of quenching filaments with cocurrent air fiow through a cylindrical tube, however, convergence of the filament bundle at a point relatively close to the spinneret is necessary owing to the turbulence of the air a short distance below its point of introduction, as disclosed in U.S. 2,252,684. The problem of turbulence and the associated problem of avoiding non-uniformities become more severe as the spinning speed of the filaments is increased. Another restriction encountered from the practical viewpoint is that the cylindrical tube is bulky and not adapted for ready removal and replacement to make possible such routine tasks as wiping the spinneret face during spinning, or replacement of defective spinneret packs.

It is, therefore, an object of this invention to provide ice an improved process and apparatus for quenching extruded filaments of molten organic filament-forming compositions to form the corresponding solid filaments. Another object is to provide a process and apparatus for producing at high throughput spun structures which are highly uniform in their degree of orientation, dye receptivity, and other physical properties. A further object is to provide a quenching apparatus in which access to the spinneret during spinning is readily provided. Other objects will appear as the description of the invention proceeds.

These and other objects are achieved by means of the apparatus and process as set forth in the following description and claims.

Briefly described, the apparatus comprises a spinneret or other means for extruding molten organic filaments; a hollow cylindrical foraminous member positioned below the extruding means; a plenum chamber surrounding the foraminous member; an exit tube positioned below the foraminous member and having an open lower end; means positioned below the exit tube for forwarding solidified organic filaments; and, between the lower end of the exit tube and the means for forwarding the solidified filaments, means for directing a current of gas against the filaments in a direction substantially perpendicular to the filaments.

The invention also includes a novel process which comprises, in the process of extruding filaments of a molten organic filament-forming composition and quenching the filaments by continuously directing a current of cooling gas radially inward from all directions towards the filaments and thence cocurrently downward with said filaments, the improvement which comprises bracing the filaments by directing a second current of gas against the filaments in a direction substantially perpendicular to the filaments and below the point at which the filaments become completely solidified.

The nature of the invention will be more fully apparent from the accompanying drawings in which FIGURE 1 is a partially diagrammatic side view, with parts in section, showing a spinning cell employing apparatus for quenching constructed in accordance with the present invention;

FIGURE 2 is a top view in section, taken along the line 22 of the apparatus shown in FIGURE 1;

FIGURE 3 illustrates a damper which may be used to cortrzol the fiow of air in the apparatus of FIGURES 1 an FIGURE 4 is a sectional side view of another embodiment of a quenching apparatus constructed in accordance with the invention; and

FlGURE 5 is a top view in section, taken along the line 55 of the apparatus shown in FIGURE 4.

Referring now to FIGURES 1 and 2, reference numeral 1 designates a spinneret pack provided with a spinneret 2 through which a plurality of filaments 3 may be extruded. The freshly extruded molten filaments are passed down through a hollow quenching chamber generally designated by reference numeral 4 to guide 5, which comprises a part of a conventional forwarding system. The yarn also contacts finish applicator roll 6. The walls of the quenching chamber may be a cylindrical screen member 7 or other hollow cylindrical foraminous member mounted above exit tube 8, which in the embodiment of FIGURE 1 is a cylindrical tube. The exit tube and superposed foraminous member are mounted within generally cylindrical jacket 9, inwardly flanged at top and bottom. Plenum chamber 10, which comprises the generally annular space between the jacket 9 and the hollow quenching chamber 4, is maintained with air or other cooling gas under slight- 1y higher than atmospheric pressure, sufficient to cause 0 uniform radial flow of cooling gas into the quenching chamber through the foraminous member. Gas for the plenum chamber is supplied through inlet ll in jacket 9 communicating with opening 12 from supply chamber d3 in supporting structure Damper .15 at the outer end of opening 12 allows for control of gas flow. A current of gas is also maintained from supply chamber 13 through for-aminous member 16 at the back of the spinning chamber. The latter flow of gas does not function to quench the filaments, since the filaments are already solidified before leaving the tube 8, but rather functions as an tial control means to stabilize the filaments against turbulence and the erratic currents of air normally encountered during commercial spinning operations, such as drafts emanating from openings in the room, currents of air circulated for the purpose of warming or cooling the room, transitory drafts caused by the movements of personnel and equipment, etc. The direction of fiow of the cocurrent cooling gas and cross-current bracing gas are indicated in the figures by arrows.

As indicated in FIGURES l and 2, jacket 9 is advantageously provided with wheels 1'7 mounted upon brackets 18 and riding in rectangular grooves or tracks 19 in the supporting structure down the sides of the spinning cell.

By pulling out pin 2t} mounted in brackets 21, the entire quenching apparatus comprising jacket 9 and its attached parts is therefore adapted to be removed downwardly from the spinneret, affording ready access to the spinneret for performance of routine functions during the spinning operation.

As illustrated in FEGURE 3, damper 15 may comprise slotted upper disc 22 and slotted lower disc 23 (portions of which are seen beneath disc 22), one of which may be rotated with respect to the other so as to superimpose or partially superimpose slots 24 to allow passage of air. Arm 25, attached to the rotatable disc, is provided for ease in opening or closing the damper. In operation, the damper is closed when it is desired to stop the spinning operation and the quenching apparatus is then removed downwardly. The damper is kept closed while the quenching apparatus is in the down position and during resumption of spinning when the quenching apparatus is returned to the operating position. As soon as the apparatus is properly strung up in operating position, the damper is opened and normal collection of the spun filaments is resumed. By operating in this manner, exposure of the spinning filaments to turbulence of uncontrolled air flow is prevented when the quenching apparatu is out of operating position.

Turning now to FIGURES 4 and 5, in which another embodiment of the apparatus of the invention is shown, filaments 3 are extruded as before from spinneret pack 1 and spinneret 2 through hollow quenching chamber 4- to finish applicator roll 6 and guide 5, which comprises a part of a conventional forwarding system. bodiment of the invention the exit tube comprises a funnel 26 upon which is mounted hollow cylindrical foraminous member 7, which in this instance comprises hollow cylindrical screen 27 surrounded by perforated cylindrical plate 28. Jacket 29 surrounds the hollow cylindrical foraminous member, forming plenum chamber It}, but in this case does not extend downwards to surround the exit tube 26. Air or other cooling gas is supplied to the plenum chamber through inlet 11 in the jacket communicating with opening 12 from gas supply chamber 13. A current of gas is also passed from the supply chamber through foraminous member 16 perpendicular to the fila ment bundle as it issues from funnel 2a to stabilize the spinning filaments. The entire quenching apparatus com prising jacket 29 and its attached parts is adapted for downward removal from the spinneret on tracks or grooves 19 in the side of the spinning cell by means of wheels 17 mounted on brackets 18 affixed to the jacket, as shown in FIGURE 5. Pin 20 mounted in brackets 21 and sliding through hole St in supporting structure 14 In this ernr ill.

serves to fix the quenching apparatus in its proper position. In the embodiment shown in FEGURES 4 and 5, insertion of the pin also serves to open damper 31 automatically when the apparatus is returned to operating position and strung up. The damper is mounted on pivot 32 with resilient means (not shown) to return the damper to closed position when the pin is pulled out, as indicated by the dotted lines in Fl'G-URE 5.

Radial introduction of the quenching gas uniformly from all directions followed by cocurrent flow of the gas with the filaments causes uniform and rapid solidification of the filaments within the quenching apparatus. In the optimum form of the apparatus, the he'ght of the hollow cylindrical foraminous member is of about the same order as its width, which in turn is determined by the diameter of the filament bundle. Usually the hollow cylindrical foraminous member is made slightly Wider than the diameter of the filament bundle as it is extruded from the spinneret; i.e., at least slightly larger than the outermost circle of spinneret orifices. Similarly, the height of the exit tube of the quenching apparatus is advantageously of about the same order as its Wid h, which should be the same as or slightly smaller than the Width of the hollow cylindrical foraminous member. More specifically, the height of the hollow cylindrical foiaminous member is usually in the range of about 0.25 to about 4 times its width and the height of the exit tube is usually in the range of about 0.25 to about 4 times the width of the tube. Of course, the foraminous member and exit tube are positioned in axial alignment with the path of the filaments between the spinneret and forwarding means. In the case of molten polyethylene terephthalate filaments extruded at a temperature of about 285 C., the optimum rate of air flow is usually in the range of about l-l0 cubic feet per minute per square inch of cross section of the exit tube, measured at the upper end of the exit tube or of the cross section of the filament bundle.

In accordance with the process of the present invention, it has been found to be very important in promoting the uniformity of the yarn product that the smooth, cocurrent fiow of air be maintained in contact with the filaments until they are fully solidified. A simple test for determining the point at which the filaments become fully solidified is to insert a ceramic pin or rod in the bundle of spinning filaments and pass it upwardly towards the spinneret until the point is reached at which the filaments pile up on the pin. When operating under the conditions described above, it is found that the filaments are fully solidified before leaving the exit tube. v

In quenching extruded molten filaments with a radially introduced cocurrent flow of cooling gas, the yarn product obtained is quite uniform in properties so long as the spinning filaments are maintained in a smooth, stable pattern. However, yarn uniformity is severely affected by interruption of the spinning pattern, i.e., movement of the filaments relative to each other. Such fluttering of the filaments, even though it may be caused by air turbulence below the point at which the filaments are completely solidified, results in interfilarnent fusion near the spinneret as well as difierential tension on the filaments in the bundle at the solidification point.

When attempts are made to spin using only the cocurrent flow of gas, the pattern of the spinning filaments is found to be quite sensitive to the influence of the variations in the movement of the air in the environment, including drafts caused by movements of operators attending to the spinning machine. Although extension of the exit tube provides protection against such extraneous air currents, the cocurrently flowing air itself becomes turbulent a short distance below its point of introduction when a long tube is used, as previously noted. However, by directing a second current of gas against the filaments below the point at which they become completely solidified, in accordance with the prescut invention, a stable pattern of spinning filaments is readily achieved.

The current of gas is preferably directed perpendicular to the filament bundle. The optimum rate of flow of the second current of gas to brace the filament bundle against extraneous currents of air is readily determined. At the lower limit, the rate of flow should be at least sufficient to maintain an observable bowing of the filament bundle in the direction away from the source of the gas; while at the upper limit, the rate of flow is considered excessive if the degree of bowing is such that the filament bundle is forced into contact with the exit tube of the quenching apparatus. The amount of air required to achieve the desired result is dependent, of course, upon such factors as the denier and number of filaments, the size of the filament bundle, the spinning speed, and the distance between the spinneret and the convergence point of the bundle.

Owing to the stability of the filament bundles in the spinning cell of the present invention, higher productivities and greater uniformity of product are achieved than are attained with spinning cells employing cocurrent quenching gas without cross-flow gas to brace the filament bundle after quenching. Surprisingly, the productivity of the spinning cells of the present invention is also greatly improved as contrasted with spinning cells in which the filaments are quenched with cross-flow cooling gas only.

In a preferred apparatus embodiment of this invention, the exit tube is a funnel having its large opening adjacent to the hollow cylindrical forarninous member. In optimum form, the funnel is constructed such that the area of the lower end of the funnel is approximately half of the area at the upper end of the funnel, which in turn is approximately the same diameter as the diameter of the hollow cylindrical forarninous member. The funnel may have straight sloping sides, although in its preferred form the sides of the funnel are curved for constant rate of air acceleration in accordance with the equation where D is the diameter of the nozzle at any distance X from the entrance, and X and K are constants. The values of the constants for a funnel of selected height and diameter are readily determined by solving simultaneous equations in X and K obtained by substituting the appropriate values in the formula for the entrance and exit ends of the funnel.

It is also preferred that the hole pattern in the spinneret or other extruding means he radially symmetrical, such that the orifices are placed .on concentric circles, the holes being equally spaced in each circle. The individual holes may be of circular or non-circular cross section, in accordance with the desired filament cross section. The rate of extrusion and winding or otherwise forwarding the filaments may be similarly adjusted to vary the filament size in accordance with the requirements dictated by the end use of the filaments, whether textile or otherwise.

For practicability in routine spinning operations, it is highly preferred that the quenching apparatus be removably mounted. As shown in the figures, this may be accomplished conveniently by providing the apparatus with wheels riding in grooves or tracks down the sides of the spinning cell. Removable mounting of the apparatus may also be accomplished in other Ways, such as by mounting the apparatus for horizontal removal on bars or tracks to the front or side of the spinning position, by mounting the apparatus for pivotal displacement, or by other equivalent means.

The invention will be further illustrated by the following examples, which, however, are not intended to be limitative.

Example 1 Polyethylene terephathalate having an intrinsic viscosity of 0.6 is extruded at 290 C. from a conventional meltspinning apparatus through a spinneret containing 450 holes, each 0.009 inch in diameter, arranged in 8 equally spaced concentric circles, the diameter of the outermost circle being about 4 inches. The filaments are passed through quenching apparatus in which a funnel is used as the exist tube as illustrated in FEGURE 4 and packaged using conventional windup apparatus at 1600 yards per minute. The forarninous member comprises a cylindrical assembly of 5 layers of mesh screen, 7 inches high and 6 inches in inside diameter, positioned inside a hollow cylindrical perforated plate containing 1.6% free area. The funnel is 6 inches in height and has a diameter of 6 inches at its entrance at top and a diameter of 4 inches at bottom, with curved sides for constant rate of air acceleration. Cooling air is supplied to the chamber surrounding the foraminous member at 75 cubic feet per minute, and a cross current of air amounting to 75 cubic feet per minute is also supplied below the funnel. It is observed that the pattern of filaments during spinning is very stable, despite the occurrence of strong air drafts in the room as observed by releasing smoke in the vicinity of the apparatus. The yarn has a denier per filament as spun of 4.7. After warp-drawing at 3.13X, the yarn has a denier per filament of 1.5, a tenacity of 3.8 g.p.d., and an elongation of 33%. The yarn is found to be substantially free of segments of undrawn filament.

Example 2 In another experiment, the apparatus of Example 1 is modified by removing the quenching apparatus containing the cylindrical foraminous member and the funnel exit tube, and the screen for supplying cross-flow air is extended upward at the rear of the spinning chamber substantially to the top of the gas supply chamber. Using the same spinneret, polyethylene terephthalate having an intrinsic viscosity of 0.6 is spun and wound up as 4.7 d.p.f. yarn at 1600 yards per minute as in Example 1. However, despite variation of the volume of quenching air through the range 75 to 300 cubic feet per minute, the yarn product is unacceptable owing to the high incidence of interfilament fusing. When the yarn is drawn, an unacceptable level of segments of undrawn filament resulting from the sections of fused filaments is observed.

Similar results are achieved by repeating the experiment with a 450-hole spinneret having the same area, but in which the orifices are arranged in linear rows rather than circles. in order to obtain an acceptable yarn product, it is found necessary to employ a spinneret having only 360 holes.

Example 3 The apparatus of Example 1 is modified by blocking off the cross-flow current of bracing air and operating solely with the cocurrent fiow of quenching air. The pattern of the spinning filaments is observed to be highly erratic owing to the occurrence of air drafts in the room, as observed by releasing smoke in the vicinity of the apparatus. The yarn product is uancceptable owing to the high incidence of fused filaments which result in an unacceptable level of undrawn filament segments in the drawn yarn.

When the cross-flow current of bracing air is allowed to flow at the rate of 25 cubic feet per minute, improved stability of the pattern of spinning filaments is observed. However, this rate of flow is found to be insufficient to maintain at all times an observable bowing of the filament bundle in the direction away from the source of the gas, owing to the occurrence of air drafts in the room, and the incidence of fused filaments in the product is still unacceptably high. The incidence of fused filaments is reduced to a very low level by returning to the 75 cubic feet per minute rate of cross-flow bracing air as described in Example 1, at which rate it is observed that the bowing of the filament bundle is maintained despite the occurrence of erratic currents of air in the room.

Example 4 Polyethylene terephthalate havingan intrinsic viscosity of 0.6 is extruded at 2' -6 C. from a conv melt-spinning apparatus through a spinneret cont 7G3 holes, each 0.009 inch in diameter, arranged in 8 equally spaced concentric circles. The filaments are passed through quenching apparatus of the type illustrated in FEGURE l and packaged using conventional windup apparatus at 1600 yards per minute. The foraminous member comprises a cylindrical assembly of 5 layers of 100 mesh screen, 10.4 inches high and 7 inches inside diameter, positioned inside a hollow cylindrical perforated plate containing 3.8% free area. Cool is supplied to the chamber surrounding the forammous member at 190 cubic feet per minute, and a cross current of air amounting to 75 cubic feet per minute is also supplied below the tunnel. it is observed that the pattern of filaments during s; inning is very stable. The yarn has a denier as spun of 4.7. A 'ter warp-drawing at 313x, the yarn is fond to be highly uniform and substantiaily free of seg vnts of undrawn fiiarents.

The present invention otters many advar es among which may be mentioned the production of exceptionally uniform d er filaments at good rates or" speed. The uniformity is of such a high degree that subsequent dyeing is level and the dyed yarn is free of streaks or flecks due to varying shades of color. The tenacity and break elongation of the filaments produced accordin; to the present invention, as well the denier. are likewise uniform. These results appear to be attributable to the combination of radial and back quenching herein described. Similar results are not obtained when these are used singly.

It will be apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore it is not intended to be limited except as indicated in the appended claims.

I claim:

1. An apparatus for producing uniform synthetic organic filaments which comprises a spinrierct; means for passing a molten organic fiim-torrn' composition therethrough; a holiow cylindrical foran ous member positioned immediately below the spinneret; a plenum chamber surrounding the foraminous member; an exit tube positioned below the for-aininous member provided with an open lower end; means positioned below the exit tube for forwarding solidified filaments; and, between the lower end of the exit tube and the means for forwarding the all 2. The apparatus of claim 1 in which the height of the said foraminous member is from about 4 to 4 times its Width.

3. The apparatus of claim 1 in which the height of the said foraminous member is of about the same order as its width.

4. The apparatus of claim 1 in which the diameter of said for-arninous member is slightly greater than the the diameter of the filament bundle as it is extruded from the spinneret.

5. The apparatus of claim 1 in which the height of the said exit tube is from about A; to 4 times the Width of the tube.

6. The apparatus of claim 1 in whiz. the of the said exit tube is about the same order as its width and is slightly smaller than the width of the said forarninous member.

7. The apparatus of claim 1 in which the exit tube is in the shape or" a funnel having its large opening adjacent to and of substantially the same size as the said iorarninous member.

8. The apparatus of claim 7 in which the area of the lower end of the funnel is approximately /2 the area of the upper end of the funnel.

9. The method of spinning filaments from a molten organic film-forming composition which comprises passing the same through a spinneret; quenching the filaments as they leave the said spinneret by continuously directing a current of cooling radially inward from all directions towards the filaments and thence cocurrently downward with the filaments; and simultaneously directing a horizontal second current of gas against the filaments as they travel vertically downward at a point below that at which the filaments become completely solidified.

10. The process of. claim 9 in which the radial air flow is in the range of about 1 to 10 cubic feet per minute per square inch of cross section of the filament bunrile.

1L The process of claim 9 in which the rate of flow of the second current of gas is suficient to maintain an observable bowing of the filament bundle.

12. The process of claim 9 in which the molten composition contains polyethylene terep thalate.

References Cited in the file of this patent UNITED STATES PATENTS ectin g a current of gas

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