US3703753A

US3703753A - Method for producing a bulked yarn and apparatus therefor

Info

Publication number: US3703753A
Application number: US140393A
Authority: US
Inventors: Jack C Binford; Frederick A Ethridge; James R Talbot
Original assignee: Fiber Industries Inc
Current assignee: Celanese Corp
Priority date: 1971-05-05
Filing date: 1971-05-05
Publication date: 1972-11-28
Anticipated expiration: 1989-11-28

Abstract

A method for producing a yarn having latent bulking characteristics and the apparatus therefor is described. The yarn is composed of multifilament synthetic fibers which have been crimped and subjected to a constant tensioning process. The process involves subjecting a drawn yarn, preferably freshly drawn, to a crimping process which can be any of a number of crimping methods including stuffer box crimping, gear crimping, steam jet crimping and the like. The yarn emerges from the crimping step under a low, substantially uniform tension, is tensioned under a higher constant tension to at least partially extend the crimps, is entangled or twisted and then taken up on a package. The bulk characteristics of the yarn are preferably developed after incorporation into the end product such as a carpet by subjection to heat and moisture.

Description

United States Patent Binford et a1.

[ NIETHOD FOR PRODUCING A BULKED YARN AND APPARATUS THEREFOR [72] Inventors: Jack C. Binford; H'ederick A. Ethridge; James R. Talbot, all of Charlotte, NC.

[73] Assignee: Fiber Industries, Inc.

[*1 Notice: The portion of the term of this patent subsequent to April 11, 1989, has been disclaimed.

[22] Filed: May 5,1971

[21] Appl. No.: 140,393

Related US. Application Data [63] Continuation-in-part of Ser. No. 848,549, Aug.

8, 1969, Pat. No. 3,654,677.

[ *Nov. 28,1972

FOREIGN PATENTS OR APPLICATIONS 1,484,358 5/1967 France ....28/1 .3 1,064,765 4/ 1967 Great Britain ..28/72. 1 2

Primary Examiner-Louis K. Rimrodt Attomey-Thomas J. Morgan, Stephen D. Murphy and Louis Gubinsky ABSTRACT A method for producing a yarn having latent bulking characteristics and the apparatus therefor is described. The yarn is composed of multifilament synthetic fibers which have been crimped and subjected to a constant tensioning process. The process involves subjecting a drawn yarn, preferably freshly drawn, to a crimping process which can be any of a number of crimping methods including stufi'er box crimping, gear crimping, steam jet crimping and the like. The yarn emerges from the crimping step under a low, substantially uniform tension, is tensioned under a higher constant tension to at least partially extend the crimps, is entangled or twisted and then taken up on a package. The bulk characteristics of the yarn are preferably developed after incorporation into the end product such as a carpet by subjection to heat and moisture.

14 Claims, 6 Drawing Figures COMPACTING MEANS PACKAGING PATENTEDNM 28 m2 3. 703; 753

' SHEET 1 or 3 JAM R. TALBOT JAC BINFORD BY 7FREDBIC2A. ETH RIDGE PATENTED uuv 28 I972 v 3. 7 03. 7 5.3

SHEEIEUFS YARN DIRECTION FIG 2 FIG 3 F|G4 FIG 5 INVENI'OR JACK c. BlNFORD FREDRICK A. ETHRIDGE JAMES R. TALBOT BY QM? ATTORNEY INVENTOR. JAMES R. TALBOT BY FREDRICK A. ETHRIDGE JACK C. BINFORD METHOD FOR PRODUCING A BULKED YARN AND APPARATUS THEREFOR This application is a continuation-in-part of copending, commonly-assigned application Ser. No. 848,549, filed Aug. 8, 1969, now US. Pat. No. 3,654,677, issued Apr. ll, 1972.

BACKGROUND OF THE INVENTION This invention relates to production of a crimped yarn which has latent bulking characteristics and more particularly to the production of a crimped yarn under conditions which lead to improved uniformity of bulking characteristics and of dyeability in the end product. In particular, the invention is directed to carpet yarns, and more particularly, nylon carpet yarns, although other yarns and other uses are also contemplated as will be evident from the descriptions set forth herein.

Numerous methods have been proposed for the production of crimped yarns. Many of these processes provide useful yarns which can be used in many applications without difficulty. However, in the production of carpet yarns and certain fabric yarns wherein a great number of yarn ends or yarn packages go into a single strip of carpet or fabric, the uniformity'from package to package and within a single yarn from inside to outside of the package must be extremely good in order to provide a yarn which is useful'for the piece dyeing of the end product. Yarns which do not have the required uniformity have to be package dyed and the yarn shades matched to obtain the desired uniformity or space dyed prior to producing the end product. Because it is more preferred in most instances ,to produce the end product, such as a carpet, and then dye the end product in its entirety, yarns which do not have the required degree of uniformity are considered to be of reduced value.

It is therefore an object of the present invention to provide a method for reducing, and in many instances eliminating, yarn imperfections by reducing yarn tension variations to a minimum. It is another object of the present invention to provide a method for closely controlling the process history of the yarn from the drawing step through the crimping and final packaging of the yarn, thereby controlling the tensions applied to the yarn in a manner whereby tension fluctuations are maintained at an absolute minimum. It is a further object of the present invention to provide an apparatus for the application of tensions to the yarn and a total process apparatus for applying and controlling the history of yarn tensions from the drawing step through the packaging of the crimped yarn. These and other objects will become apparent to those skilled in the art from the description which follows.

THE INVENTION In accordance with the invention, a process is provided for producing a crimped yarn having latent bulk in g characteristics comprising feeding a drawn, pretensioned, multifilament yarn to a crimping zone, crimping said yarn, exiting crimped yarn from said crimping zone under a low, substantially constant tension and at a substantially uniform speed, cooling said yarn, where desired, regulating the tension on said yarn to a substantially constant tension between 0.003 to 1.0 grams per denier to at least partially reduce the amplitude of said crimps and compacting said yarn to facilitate further processing.

In accordance with a further aspect of the invention, an apparatus is provided for treating said yarn comprising yarn drawing means, yarn crimping means, yarn tensioning means and yarn compacting means, said means being consecutively, operatively connected, said yarn drawing means comprising a feed roll and a draw roll having a draw pin positioned therebetween to draw yarn, said crimping means being positioned in relationship to said drawing means for the receipt with a minimum delay of freshly drawn yarn, said yarn tensioning means being positioned for the receipt of freshly crimped yarn from said crimping means and for the application of constant tension to said yarn. Where desired, further yarn tensioning means comprising a braked wheel and a withdrawal roll having thereinbetween a tension leveler wherein the yarn is passed from said braked wheel across said tension leveler through said withdrawal roll to said compacting means may be consecutively employed.

DETAILS OF THE INVENTION The invention will be described more clearly by reference to the drawings wherein:

FIG. 1 is a schematic flow sheet representing a preferred embodiment of the present invention;

FIG. 2 is an enlarged sectional view of a preferred pretensioning jet illustrated in FIG. 1;

FIG. 3 is a sectional view along line 33 of FIG. 2 further illustrating a preferred tensioning jet;

FIG. 4 shows two traces indicating the recorded tensions (4a) and bulking force value (4b) of running yarn in accordance with the present constant tensioning process; and

FIG. 5 shows two traces of recorded tensions (5a) and bulking force values (5b) of yarns in accordance with the prior art constant elongation stretch method.

FIG. 6 is a longitudinal cross section of fluid jet crimper usable with the invention.

Referring to FIG. 1, yarn 10 is drawn from one or more packages 12 to produce the yarn of the desired total denier by nip rolls 14. Yarn 10 then proceeds to feed roll 16 and across draw pin 18 to draw roll 20. Draw roll 20 operates at a higher linear speed than roll 16, thereby effecting a drawing of the yarn at pin 18 in the desired draw ratio. Such ratio is determined by the relative roll speeds which are selected in accordance with the particular yarns being treated and the particular properties desired in the drawn yarn. Normally the draw ratio is between about 2:1 to 6: l while for nylon 6,6, a draw ratio of about 2.0: l to 4.5: l is preferred.

Yarn 10 proceeds from the drawing means through the crimping means which can be any of a number of well known crimping means including a hot plasticizing fluid, for example steam, jet bulking means such as is shown by FIG. 6 and stuffer box crimping means. A further method of crimping which can be used is by means of intermeshing geared wheels which crimp the yamjthereinbetween as is well known in the art.

One preferred method of crimping is by crimping wherein the yarn is tensioned off of the draw roll 20 by bulking jet 24, passing therethrough. The bulking jet is supplied with a heated, yarn plasticizing fluid, thereby producing and setting the crimps into the yarn. Crimped yarn 10 is preferably extruded from jet 24 or otherwise extracted under a low tension of 0 to 0.05 grams per denier and passed through quenching and pretensioning means 26 which causes a constant tension increase on the yarn to about 0.003 to 0.2 grams per denier, preferably 0.01 to 0.2 grams per denier, by impeding yarn travel and enables the yarn to make low slippage contact with the takeout roll 34 and, where desired, braked roll 28. Braking action in roll 28 restrains the rotation thereof relative to withdrawal roll 34 and provides a further increase in yarn tension to the desired 0.03 to 1.0 grams per denier level which is below the drawing force of the yarn. In certain embodiments of the invention the yarn passes directly to roll 34 from pretension 26, pretension 26 providing the increase in tension to a constant value level of about 0.01 to 0.2 grams per denier. Alternative pretension means 26 can include nip rolls or other holding means which impede the forward motion of the yarn sufficiently to engage the yarn against braked roll 28 and/or roll 34. Thus, yarn 10 can travel from braked roll 28 across idler roll 30 and tension leveler 32 to withdrawal roll 34.

A particularly significant aspect of the present invention resides in the maintenance of a substantially constant pretension, draw tension, crimp amplitude reduction tension and windup tension which is not allowed to vary significantly. In this manner, there is precise overfeed control (yarn mass per unit length) at a time when the freshly bulked yarn is sensitive to tension variation, especially at low tension levels, which leads to crimp variability.

When tension leveler 32 is employed, it is preferably a spring loaded movably mounted means which varies the distance between braked roll 28 and withdrawal roll 34. Suitable tension leveler means include spring loaded dancer arms, reciprocal spring mounted rollers or the like means, eg tension controlled roll speeds, for leveling out an applied tension.

From withdrawal roll 34, the yarn proceeds through compacting means 36 coupled with a preferred relaxation of the yarn in the range of (stretch) to 10, preferably 0.05 to 5 percent. The compacting means utilized include conventional twisting take-ups or twist substitutes including air entanglement or the application of an adhesive material. From the compacting means 36, yarn can be passed through feed rolls 38 to packaging 40 or directly to the end use.

Referring more particularly to one specific embodiment of the present invention, it is often preferred to control tension of yarn between draw roll and the crimping means, for example with a steam jet crimper the yarn should be pulled off of the draw roll into the texturing zone. Such tension control has been found to facilitate processing for the development of crimp which produces a particularly desirable bloom in the end product.

The crimping means utilized can extrude the crimped fibers but preferably in the case of steam jet crimping the crimped fibers are withdrawn under substantially zero tension or a very low tension, e.g. 0 to 0.05 grams per denier and more preferably 0 to 0.01 grams per denier. It has been found that the application in any greater amount of tension, such as would be required to actually pull the yarn from the crimping means, introduces variations into the yarn which subsequently show up in the bulking properties of the yarn and/or the dyeability thereof as streaks, worms" or other undesirable imperfections. This is believed to occur because of the periodic or sporadic requirement of increased tensions to extract such yams.

Normally, yarn coming from the crimping zone is in a heated condition either because of the application of heat in the setting of the yarn or the heat of friction developed in the crimping process or other added heat. Thus, yarn temperatures up to about the melting point of the yarn for example, temperatures of about 40 to 250 C., are preferably developed in the texturing apparatus, depending on the particular texturing process. The higher temperatures are normally used with steam jet crimping and the lower temperatures with stuffer box and gear crimping means. As such, it is preferred to quench the yarn within or as it comes out of the crimping means.

A particularly desirable manner of quenching the yarn while at the same time applying the initial pretensioning to the yarn is accomplished by the apparatus illustrated in FIG. 2 and FIG. 3. Because the yarn exiting from the crimping area preferably is under a very low tension, a pretension is preferably applied so as to aid in the further processing of the yams in the subsequent tensioning step. As such, quenching jet 42 is preferably utilized. Quenching jet 42 utilizes two opposed sidewalls 44 having in each wall a plenum chamber 46 for the distribution of pressurized gas to exit ports 48. Exit ports 48 preferably are slots or a plurality of holes or a combination thereof, which are preferably positioned in a parallel relationship with respect to each other. Exit ports 48 are aimed at the opposing wall of the quench jet in an angled relationship to sidewall 44 and the line of yarn travel. As yarn is passed through the gaseous jet stream, the gas impinges against the yarn, thereby inhibiting the forward motion of the yarn and creating a tension on the yarn exiting from the jet area. To establish the desired tension, it is preferred to have the jets aimed at an angle of a of about 5 to with respect to sidewall 44 or running line of the yarn, and more preferably 5 to 45, thereby exerting the desired back pressure and pretensioning of the yarn as the yarn passes therethrough. Thus, the quenching jet accomplishes both the cooling of the yarn and the pretensioning thereof in an amount of 0.003 to about 0.8 grams per denier and more preferably 0.003 to 0.2 most preferably about 0.01 to 0.2 grams per denier. Because of the desire to cool the yarn, any non-reactive gas can be used, with air being preferred. Special cooling of the air is normally not required. Thus, ambient gas temperatures are generally quite suitable.

While the exit ports can be so arranged to induce a twisting action in the yarn, it is preferred that the exit ports are positioned to avoid a twisting efiect. The amount of tension applied to the yarn in the pretensioning is controlled by controlling the gas pressure, the angle at which the gas impinges against the yarn, the gas flow rate, the positioning of the sidewalls, and the like. Further, it is desirable to effect at least some entanglement of the yarn so as to aid in the further processing of the yarn by containing broken or projected filaments. The described apparatus readily accomplishes this, particularly at the preferred gas impingement angles and back pressure producing velocities.

The particular gas used in the quenching jet is preferably air, but can be any cooling gas such as nitrogen, various inert gases and the like as is well known to those skilled in the art. The gas pressure utilized is dependent upon the number of exit ports used, the shape thereof, the cross-sectional area and the desired degree of pretensioning. Thus, it is preferred to adjust the air pressure in accordance with the desired pretensioning.

When employed, brake wheel 28 can be a number of different known equivalent braking devices such as frictionally impeded channeled wheels, a magnetic particle clutch, fluid clutches, eddy current braking and the like.

Between ejector jet 26 and withdrawal roll 34, a substantial constant tension is applied to the moving yarn. This tension is below the tension required to draw the yarn, but is sufficient to partially remove the crimps in the yarn by reducing their amplitude without permanently removing the crimp. Such tensioning takes the crimps out of registry with each other and induces a latent effect to the crimp which enables easier fabrication of the end product with the yarn as well as improving the development of 'bulkiness in the end product. Thus, the amount of tension applied is in the range of about 0.003 to 1.0 grams per denier and more preferably about 0.01 to 0.2 grams per denier.

FIG. 4 represents (a) a tension trace showing the substantially constant tension applied by the present method in the area between idler roll 30 and tension leveler 32 and (b) the uniform bulk of such a yarn. FIG. 5 represents a (a) tension trace showing the fluctuations in tension as occur in the prior art constant elongation stretching process and (b) the non-uniformities in bulk thereby introduced.

The particular yarn treated by the present process can be any of the synthetic continuous filament yarn including nylon, polyester, acrylic, modacrylic, polypropylene, polyvinyl chloride, polyvinylidene chlorides, Darvan, Spandex, and the like, as are well known in the art. The particular fiber denier can be any fiber denier within the range of about 0.5 to 200 denier per filament but particularly those in the textile range of about 0.5 to 10 denier per filament and those in the industrial and carpet yarn range of about 8 to 30 denier per filament. Accordingly, the total yarn denier can vary substantially depending upon the particular use to which the processed yarn is to be put. Carpet yarn total deniers are in the range of about 700 .to about 5,000, more preferably about 800 to 4,000 total denier. Textile yarns may conveniently have lower total denier ranges such as from about 40 to 800. Of course, greater and lesser total denier yarns can be readily processed, but the best applications are effected in the production of carpet yarns which are particularly sensitive to texturing and tension variations.

The invention will be described more particularly with reference to the following examples which illustrate certain preferred embodiments of the present invention.

EXAMPLE I Nylon 6,6, polyhexamethylene adipamide, fiber, was processed in accordance with the present invention and particularly in accordance to the schematic shown in therein. Undrawn yam was fed to a drawing means comprising a pin and draw roll wherein it was drawn at the rate of 1,620 feet per minute at a total draw ratio of 3.82. The freshly drawn yarn was directly fed to a stufier box crimper in place of bulking jet 24 at a feed input of 1,613 feet per minute to the crimper rolls. The stuffer box crimper utilized was that described in copending commonly assigned application Ser. No. 848,495, filed Aug. 8, 1969.

A crimped yarn of generally saw-tooth crimps at a temperature of about 80 C. exited under substantially zero tension from the stuffer box and was passed through the quenching jet of FIG. 2 and FIG. 3 which was operated at an air pressure of 30 pounds per square inch gauge. The angle of impingement of the gas jet stream against the yarnformed an angle of 30 degrees between the yarn and the axes of the jet exit port. This pressure and angle of impingement applied a tension of 50 to grams of tension to the yarn, which tension equaled about 0.019 to 0.029 grams per denier. The pretensioned yarn from the quench jet engaged a magnetically braked particle clutch and traveled across a spring loaded dancer arm to a withdrawal roll which applied a 400 gram tension to the running yarn between the clutch roll and the stretch roll. This tension equaled about 0.154 grams per denier. The consistency of the tension is illustrated in F IG. 4.

From withdrawal rolls 34, the yarn was relaxed 5 percent of the tensioned length and passed through a yarn entangling jet. The yarn was then wound on a package as a 2600/ 136 nylon 66 carpet yarn. This yarn had a skein length of about 14% inches and about 15 to 19 crimps per inch. The skein length was measured using a 22 wrap skein, the wrap circumference being 1 meter and subsequently submerging the skein in 60 C. water with a 15 gram load on the bottom of the loop for 3 minutes prior to determining the length.

The yarn produced in accordance with this method was made into a continuous filament carpet and piece dyed. Examination of the piece dyed product indicated that it was substantially free of bulk and dye variations. This is indicative of package to package uniformity of the yarn as well as within package uniformity.

The yarn produced could be varied in the number of crimps per inch and the skein length of the resulting yarn. Using a stuffer box crimper, a generally saw tooth crimp of primary and secondary crimp amplitudes is produced in the yarn. The number of crimps per inch can be adjusted between about 3 to 30 crimps per inch or more while about 5 to 20 crimps per inch is generally most preferred. Also, the skein length of the crimped yarn can be varied from about 10 inches to about 19 inches as may be desired in the particular end use by changes in the crimping temperature, the after tension and the like adjustments. The preferred range for carpet yarns of this type is a skein length of about I l to 17 inches.

In the same manner, other crimping processes such as gear crimping or steam jet bulking are substituted for stuffer box crimping whereby similar results are ob-' tained. The particular type of crimp is varied with the particular crimping method utilized.

While the invention has been described more particularly with respect to nylon, correspondingly good results are obtained with the other enumerated synthetic continuous filaments. Also, filaments of greater and lesser total denier and denier per filaments can be processed accordingly with correspondingly good results.

For example, in another preferred embodiment of the invention the bulking jet of FIG. 6 is employed to steam jet bulk a suitable feed yarn.

In FIG. 6, jet 100 comprises a T-piece 111, the double limb 112 of which communicates at each end with the atmosphere, while the third limb 113 is connected to a steam header (not shown) for the supply of steam to the unit. Within the double limb 112 is slipped cylin drical member 115 which is circumferentially grooved about one-quarter and three-quarters way along its length for the reception of rings 1 16 of suitable packing material adapted to make a tight joint against the wall of the double limb. Into one end of the cylindrical member is slipped a tubular yarn inlet member 1 17, the tip 118 of which is of double-conical form, having conical angles of 47 near the tip and 33 a short distance behind the tip. The inlet has an entry bore 119 of oneeighth inch which tapers to one thirty-second inch at the tip. At the other end of the cylindrical member 115 is inserted a venturi tube 120 having an inlet cone 121 of 40 angle, a throat diameter 122 of one-sixteenth inch, and an outlet cone 123 of 10 angle, the tip 118 of the inlet jet entering into the inlet cone 121 of the venturi. Both the inlet jet 117 and the venturi tube 120 are externally flanged to engage against the end of the cylindrical member 115 and are held in place by two

collars

124, 125 internally flanged to engage over the external flanges of the inlet 117 and venturi 120 respectively, and internally screw-threaded to screw over the cylindrical member 115. The inner edges of the

collars

124, 125 engage the packing rings 116 and compress them against the wall of the double limb 112 of the T-piece 111, so holding the whole assembly in place. Mid-way along its length the cylindrical member 115 is bored with diametrically opposite holes 126 for the admission of steam entering from the steam main through the third limb 113 of the T-piece 111. A gauge collar 27 may be provided surrounding the middle portion of the cylindrical member 115. Yarn passage 131 in tip 118 is arranged in concentric relationship with steam flow through cone 121 into throat 122.

Considering the operation of a jet crimper as disclosed in FIG. 6 in greater detail, hot fluid which will generally be either wet steam, dry steam or air, (although other setting fluids may be employed) is supplied to the jet at a temperature of over about 300F, preferably about 600 to 800F, under a pressure of at least about 30 pounds per square inch gauge (psig), preferably about 80 to 250 psig, most preferably about I to 170 psig. Yarn residence time through the jet is about 0.l to seconds.

Based on speed control immediately before and after the jet crimper (draw roll 170 and take-out roll 130 in FIG. 6 Pretensioner 1 10 is similar to pretensioner 26 of FIG. 1), the yarn is overfed about to 60 percent, preferably about to 40 percent through the jet crimper. Yarn linear shrinkage is regulated between about 5 to 50 percent, preferably about 10 to 30 percent, so that about 10 to 55 percent, preferably about 10 to 20 percent crimp or bulk at the withdrawal roll is produced based on overfeed minus linear shrinkage at the take-out roll.

EXAIVIPLE II Freshly drawn nylon 6,6 yarn (550 denier/34 filament drawn yarn) having less than 1 turn per inch producer twist is fed at about 2,000 feet per minute and at a 30 percent overfeed based on the peripheral surface speeds of rolls 170 and through the jet of FIG. 6. Superheated steam at about psig is supplied at about 800F to the jet. About 20 percent yarn linear shrinkage occurs, giving about 10 percent bulk in the process. The individual filaments of the yarn are crimped while being whipped about in the turbulent hot fluid and are set in a presistent, random, three dimensional, sinuous, curvilinear, extensible crimp, substantially free of ring-like loops and substantially free of twist reversals.

EXAMPLE III Example II is substantially repeated using the overall apparatus of FIG. 1 and a modified jet of FIG. 6. A 2250/34 undrawn nylon 6,6 yarn having less than 1 turn per inch producer twist is pretensioned, drawn about 4 to 1 and then fed into the jet of FIG. 6 at about 30 percent overfeed relative to roll 34 (Brake 28 and leveler 32 are not employed). Quench jet 26, operated at about 22 psig applied about a 25 gram constant tension to the yarns. A confining chamber, such as a stuffer box crimper, is attached to the bottom of the bulking jet (the jet being positioned so that the yarn entrance is at the top of the jet) and the yarn and steam pass directly thereto from the bulking jet exit. The yarn lays down in the confining chamber in the form of a plug with the hot fluid exiting in radial and axial directions. Yarn residence time can be 0.1 to 10 seconds using the apparatus of this example.

Various modifications of the invention will appear obvious to those skilled in the art.

As used herein constant tension means that there is not greater than :5 percent variability from the average tension value expressed in grams when taking five tension measurements on a running yarn between the pretensioning means (for example ejector het 26) and the take out roll (for example withdrawal roll 34) using a Rothschild tensionometer set for I second damping.

We claim:

1. A process for producing a crimped yarn which comprises feeding a multifilament yarn to a stream of superheated steam being jetted into a jet device so that the individual filaments of the yarn in said jet device are whipped in a turbulent stream of said superheated steam to impart a persistent, random three-dimensional, curvilinear crimp to said filaments; exiting said crimped yarn from said jet device; cooling said yarn and tensioning said yarn at a first low, substantially constant tension prior to further processing and/or packaging, said yarn being overfed about 15 to 60 percent through said jet device, said overfeed being determined between a first yarn forwarding speed controllable device, feeding said yarn into said jet device and a second yarn forwarding speed controllable device at the downstream end of said tension zone.

2. The process of claim 1 wherein said first low tension is in the range of about 0.003 to 0.2 grams per demer.

3. The process of claim 2 wherein said first low tension is in the range of about 0.01 to 0.2 gram per denier.

4. The process of claim 2 wherein said yarn is compacted after tensioning.

5. The process of claim 1 wherein said first low tension is applied by a tension jet impinging pressurized gas against said yarn.

6. The. process of claim 5 wherein said tension jet quenches the yarn.

7. The process of claim 1 wherein after first tensioning the tension on said yarn is increased in a tension zone to a second substantially constant tension between about 0.03 and 1.0 grams per denier to at least partially reduce the amplitude of said crimps.

v 8. The process of claim 7 wherein said first tensioning includes a pretensioning to about 0.003 to 0.08 grams per denier said second tensioning increases yarn tension to about 0.001 to 0.5 grams per denier.

9. The process of claim 1 wherein the speed of the yarn is not additionally controlled between said first and second devices.

10. The process of claim 1 wherein the yarn mass per unit length of yarn remains constant between said first tensioning and said second tensioning.

11. The process of claim 1 wherein said yarn'is formed of a polyamide.

'12. The process of claim 1 wherein said yarn exits from said jet device into a yarn confining chamber prior to constant tensioning.

13. The process of claim 1 wherein said yarn is formed of a polyester.

14. The process of claim 1 wherein said yarn is

Claims

1. A process for producing a crimped yarn which comprises feeding a multifilament yarn to a stream of superheated steam being jetted into a jet device so that the individual filaments of the yarn in said jet device are whipped in a turbulent stream of said superheated steam to impart a persistent, random threedimensional, curvilinear crimp to said filaments; exiting said crimped yarn from said jet device; cooling said yarn and tensioning said yarn at a first low, substantially constant tension prior to further processing and/or packaging, said yarn being overfed about 15 to 60 percent through said jet device, said overfeed being determined between a first yarn forwarding speed controllable device, feeding said yarn into said jet device and a second yarn forwarding speed controllable device at the downstream end of said tension zone.

2. The process of claim 1 wherein said first low tension is in the range of about 0.003 to 0.2 grams per denier.

4. The process of claim 2 wherein said yarn is compacted after tensioning.

6. The process of claim 5 wherein said tension jet quenches the yarn.

8. The process of claim 7 wherein said first tensioning includes a pretensioning to about 0.003 to 0.08 grams per denier said second tensioning increases yarn tension to about 0.001 to 0.5 grams per denier.

11. The process of claim 1 wherein said yarn is formed of a polyamide.

12. The process of claim 1 wherein said yarn exits from said jet device into a yarn confining chamber prior to constant tensioning.

13. The process of claim 1 wherein said yarn is formed of a polyester.

14. The process of claim 1 wherein said yarn is overfed 20 to 40 percent through said jet device.