US3655862A - Aspirator jet for drawing-off filaments - Google Patents

Abstract

In an aspirator jet for drawing-off thermoplastic filaments having a nozzle and a throat, the primary aspirating air is smoothly expanded to supersonic velocities through a throat into an outwardly diverging expansion chamber which is preferably dome-shaped. A guide tube for the filaments and secondary air extends centrally through the throat and through the expansion chamber to the draw-off tube, which has a constant diameter. The design is such that the aspirating air flows parallel to the filaments issuing from the guide tube and goes not impinge thereon as is the case with the jet designs of the prior art. This design permits draw-off of filaments at high speeds, in excess of 2,000 meters/min., with good separation and substantially complete parallelism between the filaments and without intermingling or twisting and interlocking of the filaments.

Description

April 1972 o. DORSCHNER T 3,655,862

ASPIRATOR JET FOR DRAWINGOFF FILAMENTS 2 Sheets-Sheet 1 Filed Aug. 15, 1969 April 11, 1972 o, DORSCHNER ETAL 3,655,862

ASPIRATOR JET FOR DRAWING-OFF FILAMENTS Filed Aug. 15, 1969 2 Sheets-Sheet 2 United States Patent ASPIRATOR JET FOR DRAWING-OFF FILAMENTS Oskar Dorschuer, Bad Hamburg, Franz Josef Carduck,

Bergen-Enkheim, Nordring, Christoph Storkebaum,

Egelsbach, and Claus Rother, Petterweil, Germany, as-

signors to Metallgesellschaft AG, Frankfurt am Main,

Germany Filed Aug. 15, 1969, Ser. No. 850,500 Claims priority, application Germany, Aug. 17, 1968, P 17 85 158.0 Int. Cl. B29c 17/02 U.S. Cl. 264-290 11 Claims ABSTRACT OF THE DISCLOSURE In an aspirator jet for drawing-01f thermoplastic filaments having a nozzle and a throat, the primary aspirating air is smoothly expanded to supersonic velocities through a throat into an outwardly diverging expansion chamber which is preferably dome-shaped. A guide tube for the filaments and secondary air extends centrally through the throat and through the expansion chamber to the draw-oil? tube, which has a constant diameter.

The design is such that the aspirating air flows parallel to the filaments issuing from the guide tube and does not impinge thereon as is the case with the jet designs of the prior art.

This design permits draw-01f of filaments at high speeds, in excess of 2,000 meters/min., with good separation and substantially complete parallelism between the filaments and without intermingling or twisting and interlocking of the filaments.

PRIOR ART In the production of non-woven webs, mats, layers and similar products from continuous filaments, the molten raw materials are extruded through spinning orifices and the spun yarn is generally drawn-0E by pneumatic jets and blown onto the lay-down surface. Such processes for the production of non-woven materials and the pneumatic jets used are described, for example, in British Pat. No. 932,482 and in US. Pat. No. 3,341,394. The use of pneumatic jets, usually referred to as aspirator jets or air jets, allows high draw-01f speeds. As a great number of filaments can be routed through one jet, the production speeds for the non-woven product are high which is very much desired from the aspect of low production costs. Compressed air is generally supplied to the jets to serve as the moving medium. To achieve high draw-off speeds in jets, the moving air is generally accelrated by expansion to supersonic velocity and directed at a small angle against the filaments running through the jet. This exerts a tension on the filaments which, with filaments of thermoplastic organic plastics, efiects drawing and orientation of the filaments. To achieve special effects, e.g. crimping of the filaments, hot air or steam instead of air can be used.

Several different designs of draw-ofi' jets are known. They all have in common a funned-shaped inlet port for the filament bundles which finishes up in a cylindrical or almost cylindrical filament guide channel. 'In this filament guide channel or at the end of it, the expanding or expanded aspirating gas is directed toroidally at an angle of about 5l5 against the filaments. When the aspirating gas is introduced around the end of the cylindrical filament inlet, the external wall at the lower end of the filament inlet pipe has been generally tapered downwardly to facilitate the tangential impingement of aspirating gas. Because of the friction efiect which the aspirating gas exerts on the filament bundle, the filament is 'ice drawn through the jet at a speed which is greater than the spinning speed.

With some jet designs the filaments may flutter, swing to and fro and intermingle (see British Pat. No. 1,088,931).

A properly produced non-woven web made in this manner contains parallel extending filaments which mutually cross each other at random intervals and which may overlap backwardly. To prevent converging or banding together of the filaments at high filament draw-off speeds, the filaments usually are electrostatically charged, e.g. by means of corona discharge devices or by the application of a tribe-electric charge. (See US. Pat. No. 3,341,394 and British Pat. No. 932,482.) The electrostatic repulsion between the like-changed filaments prevents a converging of the filaments. A disadvantage with these methods is that special devices for charging the filaments are required. In addition, it is necessary to bring the draw-off jets to the same potential as the filaments to prevent the filaments from sticking to the jet wall. The application of such processes using electrostatic charging of the filaments demands specific electric properties of the filament material which a number of major raw material, such as polypropylene and polyethylene terephthalate, do not possess. Such raw materials have to be treated in some manner to improve their electric properties to render them suitable for electrostatic charging. The introduction of sulfonated comonomers or inorganic salts for this purpose into the organic polymer structure, as has been done, complicates and further increases costs. Apart from electrostatic charging of the filaments, little is known as to how the undesired mutual interference of the filaments at high draw-oft speeds can be eliminated. Subsequent improvements of the original methods still use electrostatic charging of the filaments (see US. Pat. Nos. 3,293,718, 3,364,538, 3,314,122, and 3,368,934).

The same problem exists with flat or slotted jets. With flat 0r slotted jets the moving medium is directed at an angle through the two longitudinal sides of the rectangular filament opening (see US. Pat. No. 3,302,237). When intermingling of the filaments at high draw-off speeds is not desired, electrostatic charging cannot be dispensed with (see US. Pat. No. 3,364,538). Attempts have been made to eliminate intermingling of filaments by using adequate jet designs (see US. Pat. No. 3,286,896). To achieve this aim, the turbulence in the jet was reduced. On the other hand, a certain turbulence is needed in order to achieve the necessary tension on the filaments. To meet these requirements, a jet design was used in this patent wherein air was admitted at two points located below each other. However, this method did not render electrostatic charging of the filaments unnecessary.

It is further desirable that the jets draw-in through the filament inlet port a certain amount of secondary air so that in the event of filament breakage the filament can easily be reintroduced into the filament inlet port. High draw-off speeds with complete parallel arrangement of the filaments and without electrostatic charging and adequate aspiration of secondary air through the filament inlet port have so far been incompatible requirements.

THIS INVENTION The object of the present invention is to provide a jet for the draw-off of filaments which positively prevents mutual interference of the filaments, without the need for additional electrostatic charging of the filaments or the jet, even at high draw-off speeds above 2000 m./min. and where the aspirated secondary air at the end of the filament guide channel reaches at least sound velocity. The jet of this invention is in particular suitable for use in the production of non-woven products from deposited continuous filaments where the spinnable material is extruded through spinnerets, drawn-off and laid down on a moving receiving surface, such as web, mat or the like.

The invention relates to a jet for withdrawing a single filament or a plurality of filaments in which a tension is applied to the filaments by the aspirating medium expanding to supersonic velocity, with a narrowing inlet port for the filaments which finishes up in a guide channel extending through the smallest cross-section of the jet. This jet is characterized by the expansion chamber enlarging outwardly below the narrowest jet cross-section. The enlargement of the expansion chamber can be conical but a curved dome-shaped enlargement of the expansion chamber is preferred.

The aspirating gas is accelerated to sound velocity when it reaches the narrowest jet cross-section and in the expansion zone below it is expanded to Mach figures of up to 3.5 and higher either parallel to the direction of the filaments or away from the direction of the filaments depending upon the motive pressure and the ratio between exit cross-sectional area and inlet cross-sectional area of the expansion zone.

Compared to the conventional jet designs, the present invention deliberately avoids having the aspirating gas impinge the filaments at an angle. This is achieved by outwardly enlarging the expansion chamber below the narrowest jet cross-section or throat of the jet and by arranging the outer boundary of the guide channel such that it extends through the narrowest jet cross-section, cylindrically or by expanding it in the downstream direction.

The aspirating gas expansion chamber is bounded at its inlet by the throat, i.e., the narrowest cross-section of the jet. The outlet of the expansion chamber ends at or prior to the orifice plane of the end of the filament guide channel. The outward enlargement of the expansion chamber can be realized in different ways. A tapered enlargement can be used with round jets and a rectilinear or an almost rectilinear enlargement can be adopted for slotted jets. To provide for parallel flow and smooth expanson of the aspirating gas, a dome-shaped enlargement is preferable. The transition from the throat of the jet opening to the draw-oft conduit consists of a wall which has preferably a curvilinear section. A tangent of the section, measured against the vertical, has an angle of 8 to 20, preferably 10 to To ensure that the secondary air drawn in through the guide channel has at least sound velocity at the end of the guide channel and to eliminate intermingling of the filaments passing through the jet, the ratio between exit cross-section and inlet cross-section of the expansion zone desirably does not exceed 10:1. A ratio of between 7:1 and 3:1 is preferred.

Air is preferably used as the aspirating gas in the jet of this invention. The air can be cold or warm. However, steam or any other suitable medium can also be used. The gas is supplied to the jet at pressures higher than those used with conventional pneumatic filament draw-01f jets. The inlet pressure of the gas is preferably between 10 and 50 atmospheres gauge. It is so chosen that at a predetermined ratio between exit cross-section and inlet cross-section of the expansion zone the secondary air drawn in through the inlet port reaches at least sound velocity by the time it reaches the end of the guide channel. The lower end of the guide channel is preferably bevelled from the inside to the outside, or outwardly tapered.

At a ratio between exit cross-section and inlet crosssection of the expansion zone of, say, 4.9: 1 and a pressure of the primary air of 22 atmospheres gauge, a static head of 0.5 atmospheres absolute is achieved in the orifice plane of the end of the guide channel so that the secondary air drawn in through the inlet port just reaches sound velocity. The Mach number of the expanded primary air stream is 3.15.

With an area ratio of 6:1 and with the same pressure of the primary air of 22 atmospheres gauge, the static head in the orifice plane of the guide channel is reduced to 0.37 atmospheres absolute. The velocity of the expanded moving stream reaches a Mach number of 3.36. The aspirated secondary air reaches a Mach number of 1.3.

The outer boundary or surface of the guide channel can have a constant diameter end to end, although it is preferred in some cases to have the guide channel expand at its lower end as this contributes to the separation of the filaments.

The guide tube can be arranged to be adjustable with respect to the expansion chamber whereby the ratio between exit cross-section and inlet cross-section of the expansion zone can be varied. The inlet cross-section or throat is the area between outer boundary of the guide channel and narrowest part of the jet. The exit cross-section is the area between the lower end of the guide channel and the boundary of the expansion chamber or draw-off channel. With round jets, both areas are circular. With constant motive pressure, it is generally not necessary to vary the set area ratio during operation. The jets are preferably so designed that during normal operating conditions the lower end of the filament guide channel terminates about 1 to 2 mm. below the transition point of the enlargement of expansion chamber and the beginning of the draw-off channel.

To prevent intermingling of the filaments, the filament draw-off channel should have a uniform cross-section from end to end and its length should not exceed 150 times its diameter. The length of the filament draw-off channel is generally at least 20 times, preferably 30 to times its diameter. In the case of slotted jets, the width of the rectangular filament draw-off channel is substituted for the diameter.

The length of the guide channel, which extends through the narrowest jet cross-section and in whose orifice plane the expansion zone finishes, should be 10 to 40 times, preferably 15 to 30 times its diameter (with round jets) and its width (with slotted jets) respectively.

The conical inlet port of the jet for the filaments and for the secondary air should be so arranged that the angle between inlet port wall and the vertical is between 5 and 15. The angle is normally so chosen that it lies between 7 and 11.

In the case of round jets, the aspirating gas is first passed through one horizontal or two oppositely arranged horizontal boreholes into an annular hold-back or plenum chamber. The inner boundary of the hold-back chamber is formed by a baffle, the upper end of which is located so high that the admitted moving medium cannot pass direct into the funnel-shaped jet opening. The hold-back chamber checks the incoming stream and reverses it upwardly at low velocity before it enters the funnel-shaped jet opening and reaches sound velocity in the narrowest cross-section of the jet.

The generating angle of the funnel-shaped jet opening, i.e. the angle between jet opening wall and the vertical can vary between 20 and 50. It normally ranges between 25 and 40. The hold-back chamber and the shape and size of the jet opening have to be suitably adapted to each other so that the velocity of the incoming medium stream is between A and A; Mach, preferably between /5 and Mach at the beginning of the jet opening. After passing through the narrowest jet cross-section the medium stream is expanded to supersonic velocity in the outwardly enlarging expansion chamber. After expansion, a negative pressure of about 0.1 to 0.5 atmospheres absolute is established in the orifice plane of the guide channel. In the design of the jet of this invention, expansion takes place at a minimum of pressure drop. The secondary air drawn in through the guide channel reaches at least sound velocity at the guide channel outlet. The strong aspiration of atmospheric air facilitates considerably the threading of filaments through the inlet opening of the jet.

The drawings:

FIG. 1 is an elevational view in section of a. round jet of this invention;

FIG. 2 is an elevational view in section of a portion of a jet of this invention;

FIG. 3 is an elevational view in section of a portion of an alternative design; and

FIG. 4 is an elevational view of a slotted jet embodying the teachings of this invention.

In FIGS. 1-3, the same members are used to identify like parts.

DESCRIPTION The round jet of this invention illustrated in FIG. 1 consists of lower part 1 and upper part 2 bolted to the lower part. Upper part 2 accommodates conical inlet funnel 3 for filaments and secondary air, the inner wall of which finishes up downwardly in guide tube 4. At point 5, upper part 2 and lower part 1 are provided with fine thread, and at point 6 both parts are ground. The ground portions and the threads are so arranged that the two parts fit properly. Conical inlet opening 3 has a generating angle a (see FIG. 1) of to 15, preferably 7 to 11". This, in conjunction with the maintenance of the other critical dimensions of the jet of this invention, aids in the separating of the filaments before, in and after the jet.

Inlet funnel 3 finishes up downwardly in guide tube 4 and upwardly with a relatively small radius of curvature at opening 8. The height of inlet funnel 3, i.e. the distance between the transition of the inlet funnel to opening 8 and the transition of the inlet funnel to guide tube 4 must not exceed 40 times the inside diameter of guide tube 4. A height of the inlet funnel of to 20 times the inside diameter of tube 4 is preferred. The external wall of guide tube 4 finishes upwardly in a rounded corner 9 and lower horizontal boundary surface 10 of upper part 2.

Lower part 1 has a central borehole, the inner wall of which is ground in its upper portion and provided with fine thread in its lower portion so that the upper part 2 can be screwed to the lower part. Horizontal borehole 11 extends through lower part 1 for the supply of the primary aspirating air and ends in annular holdback chamber 12. To eliminate torsional force on the air, which would cause curling of the individual filaments, it is preferable to provide two boreholes 11 displaced relatively to each other at an angle of 180 for the supply of the air to hold-back chamber 12 vertically to the direction of the filaments. The hold-back chamber is bounded inwardly by vertical bafiie walls 13, which end upwardly in a circular corner 14 connecting with funnel-shaped jet opening 15. Jet opening 15 tapers in the form of a funnel up to the narrowest point or throat 16. Below the narrowest point 16 the jet enlarges outwardly and ends in cylindrical draw-01f tube 18. In the jet presented in FIG. 1, the expansion chamber conically enlarges outwardly. The conical boundary wall of expansion chamber 17 commences tangentially from the circular edge at the narrowest point 16. The angle 5 between the tangent and the vertical is 8 to 20", preferably 10 to 15.

The outer wall of guide tube 4 forms with the narrowest point 16 an annular throat up to which the aspirating gas is accelerated to sound velocity and passes downwards into expansion chamber 17. Rounded-01f portion 9 and lower surface 10 of the upper part form the upper boundary of hold-back chamber 12. Rounded-off portion 9 favors turbulent-free reversing of the moving medium into the jet funnel 15. The generating angle (see FIG. 1) of jet funnel 15 should be between 20 and 50.

The length of guide tube 4 below the narrowest point 1.6 can be varied by screwing upper part 1 more or less deep into lower part 2. Unduly deep screwing of upper part 1 into lower part 2 is prevented by annnular supporting surface 7 which contacts an appropriate boundary surface of the upper part.

The annular opening between the outer wall of guide tube 4 and narrowest point 16 is the smallest jet crosssection and at the same time is the inlet cross-section of expansion chamber 17. In the jet illustrated in FIG.1, guide tube 4 has uniform cylindrical outside diameter from top to bottom. The lower end of the inner part of guide tube 4 is enlarged outwardly like a funnel, ending in the orifice plane of the guide tube 19.

The annular area between the end of guide tube 4 and the beginning of draw-off tube 18 (i.e., the end of expansion chamber 17) forms the exit cross-section of the expansion zone. The end of the guide tube is located somewhat below the beginning of draw-off tube 18. Draw-oif tube 18 is uniformly cylindrical from top to bottom.

FIG. 2 shows an elevational view of the expansion chamber of another design. The outside of guide tube 4 is uniformly cylindrical from top to bottom. The inner part of guide tube 4 tapers towards lower end 19 outwardly like a funnel. Below the narrowest jet cross-section 16, expansion chamber 17 enlarges curvilinearly (in cross-section). The circular connecting edge 16 between jet funnel 15 and expansion chamber 17 extends downwardly. A tangent thereto forms, with the vertical, the angle )9.

FIG. 3 shows an elevational view of the expansion chamber of another jet of this invention. As before, the lower inner end of guide tube 4 is enlarged outwardly. The outer lower end 20 of guide tube 4 also is outwardly enlarged and in the elevation it forms with the vertical the angle 8.

FIG. 4 shows an elevational view of a rectangular or slotted jet of this invention. Inset 32 accommodates inlet port 33 for the filaments and secondary air, which continues downwards into guide channel 34 whose lower inner (49) and lower outer (50) boundary is enlarged outwardly. Attached to the two longitudinal members 31 with boreholes 41 for the aspirating gas are connecting members 35 and 36. Members 35 and 36 are so shaped that after connection of the two longitudinal members by transverse members 31, members 35 and 36 form in conjunction with inset 32 the jet. The bafiles in the plenum chambers 42 are marked 42 with 43 and end in transition edges 44. The circular edges at the narrowest jet portion or throat are marked 46 and the longitudinal boundaries of the draw-off channel 48. Several inlet ports 41, which are equally distributed over the length of the jet, end in the two hold-back chambers 42. The inlets to the throat are marked 45, the expansion chambers 47 and the circular transition of bafiles 43 to the inlet ports 44.

The critical dimensions have to be chosen the same as for the circular jets of this invention except that the width of the rectangular cross-section is to be substituted for the diameter.

EXAMPLE 1 A jet of this invention according to FIG. 1 has the following characteristic dimensions:

Cross-sectional area of the expansion zone (17) inlet (or throat)2 mm.

Cross-sectional area of expansion zone exit10 mm.

Ratio between exit cross-sectional area and inlet crosssectional area of expansion zone-5:1

Diameter of draw-off tube 184.35 mm.

Length of draw-off tube 18250 mm.

Length of guide tube 430 mm.

Outside diameter of guide tube 42.5 mm.

Inside diameter of guide tube 4-2. mm.

Generating angle a of inlet funnel 3-8 Generating angle '7 of jet funnel 1530 Radium in the narrowest cross-section at point 16-2 mm.

The jet was operated on cold air. The motive pressure was 22 atmospheres gauge and air consumption was 30 standard cubic meters per hour. The jet was arranged below a melt extruder from which the filaments were spun. The filament draw-01f speed was 3,400 m./min. The filaments had a denier of 3 den. and were blown onto a constantly moving lay-down receiver to form a web of irregularly crossing bundles of parallel filaments. Converging of filaments, twisting, interlacing and intermingling of the filaments did not occur. Special electrostatic charging of the filaments was not applied.

EXAMPLE 2 In the same round nozzle described in Example 1, 150' freshly spun filaments from polypropylene were drawnolf with equally good success and deposited to form a web. The filaments had a denier of 4.8 den. The drawoff speed was 2,100 m./min. The other operating conditions were the same as in Example 1.

EXAMPLE 3 A jet according to FIG. 3 had the following dimensions:

Diameter of narrowest cross-section (at 16) 3 mm.

Angle B9 Angle 6-3 Inside diameter of guide tube 4, prior to taper2.0 mm.

Outside diameter of guide 4, prior to taper2.5 mm.

Ratio between exit cross-sectional area and inlet crosssectional area of expansion zone-5.7:1

Air at 28 atmospheres gauge was used as motive air. Air consumption was M standard-cubic meters per hour. 26 filaments of nylon-6 with a denier of 9 den. were drawn-off at a speed of 3,000 m./ min.

The jets of this invention can be used for drawingoif all materials which form filaments. Such materials include mainly polyolefins, polyamides, and polyesters.

What is claimed is:

1. An aspirator jet for drawing-off thermoplastic filaments comprising:

(a) a nozzle having a throat with a funnel-shaped inlet and a smoothly expanding outlet;

(b) an inlet conduit for admitting primary aspirating gas under pressure to said funnel-shaped inlet;

(c) a centrally located guide conduit extending through said funnel-shaped inlet, said throat, and said expanding outlet and terminating at or after the end of said expanding outlet,

(i) said guide conduit having at its upper end an outwardly tapered inlet port opening to the at mosphere,

(ii) the lower portion of said guide conduit extending through said throat and said expanding outlet having a uniform outside diameter and forming with said expanding outlet an expansion chamber for primary aspirating gas passing through said throat which chamber enlarges downwardly in cross-section from said throat; and

(d) a draw-ofi? conduit having a uniform cross-section from end to end coupled with said expanding outlet and continuing downstream therefrom.

2. Aspirator jet of claim 1 wherein the ratio of the open cross-sectional area of the end of said expansion chamber to the open cross-sectional area of said throat is in the range of 7:1 to 3:1.

3. Aspirator jet of claim 1 wherein said expansion chamber has a curved dome-shape.

4. Aspirator jet of claim 1 wherein said guide conduit has a length in the range of 10 to 40 times its smallest inside width and said draw-off conduit has a length in the range of 20 to times its width.

5. Aspirator jet of claim 4 wherein said expansion chamber has a dome shape and wherein the terminal end of said guide conduit downstream of said throat internally expands outwardly.

6. The aspirator jet of claim 1 wherein the external terminal end of said guide conduit expands outwardly downstream of said thorat.

7. Aspirator jet of claim 1 wherein a tangent to the surface at the beginning of said expansion chamber forms an angle in the range 20 to 50, and wherein the walls of said funnel-shaped inlet port to said throat forms an angle in the range of 5 to 15 to the center line.

8. Process for drawing off a plurality of filaments without intermingling or twisting the filaments which comprises:

(a) aspirating a primary flow of gas to sound velocity in an aspirating zone;

(b) smoothly expanding said aspirated primary gas to supersonic velocity in an expansion zone;

(c) thereafter passing said expanded primary gas into a draw-off zone having a uniform cross-section from end to end;

((1) conveying a plurality of filaments in a secondary flow of gas through said aspirating and expansion zones; and

(e) introducing said filaments and said secondary flow of gas centrally into said draw-off zone at a point where said expanded primary gas enters said drawolf zone or downstream therefrom, said expanded primary gas entering said draw-off zone in a direction parallel to the flow of said filaments and applying drawing tension to said filaments without impinging thereon.

9. Process of claim 8 wherein the expanded primary gas entering said draw-off zone brings said secondary gas to a supersonic velocity.

10. Process of claim 8 wherein the inlet pressure of said primary gas to said aspirating zone is between 10 and 50 atmospheres gauge.

11. Process of claim 8 wherein the inlet pressure of said primary gas to said aspirating zone is between 22 to 50 atmospheres gauge.

References Cited UNITED STATES PATENTS 2,971,243 2/ 1961 Burns 22697 2,971,267 2/ 1961 Berlyn 22697 2,971,683 2/1961 Paulsen 22697 3,559,860 2/ 1971 East 22697 2,411,660 11/1946 Manning 154-101 2,437,263 3/ 1948 Manning 188 2,622,961 12/ 1952 Finlayson et al. 28--1.4 3,341,394 9/1967 Kinney 161-72 JAY H. WOO, Primary Examiner U.S. Cl. X.R.

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