US3812664A

US3812664A - Continuous crimping of yarns

Info

Publication number: US3812664A
Application number: US00275174A
Authority: US
Inventors: H Schippers
Original assignee: Barmag Barmer Maschinenfabrik AG
Current assignee: Oerlikon Barmag AG
Priority date: 1971-07-27
Filing date: 1972-07-26
Publication date: 1974-05-28
Anticipated expiration: 1991-05-28
Also published as: DE2137451A1; JPS4835153A; FR2147643A5; GB1384728A; CH565876A5; CH547364A; CH906372A4

Abstract

A process and apparatus for continuous crimping of thermoplastic heat-settable yarns by the pretwisting of separate yarns into a twisted strand which is then continuously pulled apart at one end while using the rotational movement thus imparted to the strand to feed the individual yarns into the other end of the strand under tension, the strand passing through a heat-setting zone to durably crimp the individual yarns before they reach the separation point where they are pulled apart, the invention being essentially characterized by the step or means of frictionally rotatably driving the strand in the vicinity of the point where the yarns are separated at a drive velocity greater than the peripheral rotational velocity of the strand itself. The process and apparatus are especially useful for very high speed continuous crimping in a twist-detwist manner with uniform results.

Description

United States Patent [191 Schippers m1 3 3,812,664 May 28, 1974 CONTINUOUS CRIMPTNG OF YARNS [75] Inventor: Heinz Schippers, Remscheid,

Germany [73] Assignee: Barmag Barmer Maschinent'abrik Aktiengosellschaft, Wuppertal, Germany 22 Filed: July 26, 1972 211 Appl. No.: 275,174

52 u.s.c|. 57/34 HS,S 7/77.4,57/157TS [51] Int. Cl D02g 1/02 [58] Field of Search... 57/34 R, 34 HS, 77.3-77.4 S;

57/l'57 R, 157 MS, 157 TS [56] References Cited UNITED STATES PATENTS 3,413,796 12/1968 Comer et al. 57/34 HS X 3,423,924 H1969 Comer et al. 57/34 HS X 3,643,4l2 2/1972 Maeda et al 57/34 HS Primqry Examiner-Donald E. Watkins Attorney, Agent. or Firm-Johnston, Keil, Thompson 7 & Shurtleff 5 7 1 ABSTRACT A process and apparatus for continuous crimping of thermoplastic heat-settable yarns by the pretwisting of separate yarns into a twisted strand which is then continuously pulled apart at one end while using the rotational movement thus imparted to the strand to feed 'the individual yarns into the other end of the strand under tension, the strand passing through a heatsetting zone to durably crimp the individual yarns before they reach the separation point where they are pulled apart, the invention being essentially characterized by the step or means of frictionally rotatably driving the strand in the vicinity of the point where the yarns are separated at a drive velocity greater than the peripheral rotational velocity of the strand itself. The process and apparatus are especially useful for very high speed continuous crimping in a twist-detwist manner with uniform results.

I 9 Claims, 14 Drawing Figures fATENTEDMAY 28 1914 sum 1 0r 2 FIG. 4b

FIG. 4a

mmrmm m4 3312.664 SHEET 2 OF 2 WNWQ 3:: In 3 1 CONTINUOUS CRIMPING OF YARNS referred to as the twist-detwist method, two or more separate threads or yarns are twisted or coiled with one another into a twisted strand, subjected to heatfixing or heat-setting and then separated again into individual crimped threads, each of which can be collected or wound up by itself.

For the initiation of such a separation twist procedure, the ends of two or more threads situated on separate feed bobbins or pirns are brought together and pretwisted with one another to form a twisted lengthor strand over a predetermined length. In such twisting, each individual thread or yarn can also be turned about its own axis so that there exists a true twist of two or more yarnsv lf the threads or yarns are wound about one another without the individual yarn being turned on its own axis, one speaks ofa cooling of the yarns.

ln this application, the term twisting" isused generically to include and have the same meaning as the term coiling. Also, the term yarn is used herein in its generic sense so as to apply to threads, tows and other filamentary forms of all typical thermopastic fibrous materials, especially the synthetic linear fiber-forming polymers such as the polyamides (nylon 6, nylon 66), polyesters (polyethylene .terephthalate), polyolefins (polypropylene) or the like.

Through this pretwisting of two or more individual yarns, there is provided the so-called twisted strand which has a length and a number of turns'per unit length as predetermined at the beginning of the separation twist process. The yarn ends which are separated and taken from this twisted strand may then be separately fed each to a winding or collection bobbin. The windings of the heat-fixed or heat-set yarns can also be formed on a single collection sleeve or tube. It is also an expedient and known practice to conduct the yarns after their separation from the twisted strand by means of yarn guides and/or draw-off rollers, godets, nip rolls or similar arrangements. After setting into operation the draw-off roller or winding bobbins, the yarns are drawn off from their feed bobbins into the twisted strand so as to be twisted with one another, subjected to a heat-fixing or heat-setting i.e., a heat treatment of the twisted strand and a subsequent cooling thereof, after which the individual yarn ends are again drawn apart under a certain tensional force and wound up or collected separately. In this separation-twist process, there is formed a so-called natural or floating separating point, i.e., the point at which the individual yarns in the twisted strand separate under the lateral or tensional forces acting to pull them apart.

Through the heat-setting of the twisted strand, each individual yarn undergoes a crimp formation. Crimping and qualityof the crimped threads or yarns produced in a typical separation twist process as well as the production speed are limited by the fact that the separation of two or more yarns from the twisted strand presents a number of difficulties. l

The separation of the yarns and the tension thereby exerted on the yarns exerts a torsional moment on the twisted strand. Excessively high tension on the yarns leads to a twisted strand which is too strongly twisted and forms knots or nodules. This can then lead to a breakage of one or more filaments of the yarns. Where the yarn tension is not constant, especially at the feed side, the so called floating separation point moves upward or downward in a vertical direction, i.e., substantially in the vertical direction usually occupied by the twisted strand. The length of the twisted strand thus changes so as to vary the turns per unit length in the strand and thereby the crimping number. It is also important that the yarns twisted together in the strand are drawn apart with equal or at least uniform tension. In the most exceptional case, the yarn drawn off with the highest tension remains uncrimped because it has remained untwisted, while the other yarn or yarns have been laid or coiled around it in windings. Unequal or variable yarn tensions lead to the result that the floating separation point migrates in the direction of the yarn drawn off with the greater force.

Many proposals'to solve such problems have been made to achieve some improvement. According to German Pat. Application No. 1,435,477, it is proposed that the draw-off tensionof each yarn after the separation point be regulated with the aid of a regulating element which is operated in dependency upon the lateral deviation of the floating separating point. According to US. Pats. No. 3,091,908 and No. 3,327,462, thetensions of the yarns running apart in different directions are controlled by means which reduce draw-off speed in response to yarn tension. It is further indicated that excessively great displacement of the separating point in a verticaldirection can be preventedby thread or yarn guide elements arranged laterally after the separating point (for example, note US. Pat. No. 3,327,462, column 4, lines 2 to 8) Simultaneously, however, these guide elements represent the extreme limit to which the separating point can stray laterally.

None of these prior measures eliminate the cause for the fluctuations of the thread tension. Accordingly,

such methods and apparatus can only provide a relative evening or smoothing out of the yarn tensions through regulating or stabilizing means, especially since the control of the yarn tensions is always subject to inertia and the yarn tensions change quite rapidly and under some circumstances in sudden and pronounced leaps. The remaining deviation of the separating point, even when relatively slight, still leads to an uneven crimping effect. Furthermore, the control of the yarn tensions, especially if it takes place through a necessary reduction of the draw-off speed, results in a simultaneous reduction of the production speed.

One object of the present invention is to overcome these drawbacks and serious disadvantages by providing a separation twist process and apparatus which, at the highest production speed, produces heat-set textured yarns of constant crimping. It is also an object to eliminate the danger of yarn or filament breakage as a consequence of the torsional moment being provided at the separating point and the yarn tensions required for this purpose.

Another object of the invention is to provide a separation twist apparatus whereby the floating separation point of the yarns being pulled apart is much less dependent upon variations in the feed and draw tensions of the individual yarn ends, the separation point still being stabilized in its position through improved twist or torque regulating means. Other objects and advantages of the invention will become more apparent upon consideration of the following detailed disclosure.

It has now been found, in accordance withthe invention, that a substantial improvement can be achieved in such a process for the continuous crimping of a thermoplastic heat-settable yarn 'wherein separate yarns are pretwisted together over a predetermined length to form a twisted strand which is heated and then cooled under tension in a heat-setting zone and wherein said yarns are continuously separated by being pulled apart at one end of said twisted strand while continuously feeding the separate yarns together into said twisted strand at the other end thereof, thereby imparting a rotational movement to said strand, the improvement residing in the step which comprises frictionally rotatably driving the twisted strand in the vicinity of the point where the yarns are separated at a drive velocity which is greater than the peripheral velocity of the rotational movement of the strand itself.

In order to keep the required surface or contact pressure between the friction drive and twisted strand as low as possible, it is further proposed to carry out the separation twist process of the invention such that the frictional drive velocity on the twistedstrand decreases toward the separating point of the two or more yarns.

An especially useful separation twist appatatus for carrying out the continuous heat-set crimping of a thermoplastic yarn is a combination which comprises, in addition to conventional heating and cooling means forming a heat-setting zone, yarn feed and withdrawal means to continuously transport a rotating twisted strand of individual yarns under tension through the heat-setting zone, this withdrawal means acting to pull apart and separate the individual yarns from each other at a point of separation of the twisted strand following the heat-setting zone, and a frictional torque assembly positioned along the twisted strand in the vicinity of the point of separation and acting to frictionally drive the twisted strand on itsouter periphery.

To provide a gradually reduced frictional drive velocity over a length of the twisted strand in its direction of longitudinal travel, the frictional torque assembly can be constructed with a conical configuration, e.g., either as conically formed drive rolls with the conical apexdirected toward the separating point of the yarns or else as a plurality of friction wheels which are arranged successively along the twisted strand and which become smaller in diameter toward the separating point of the individual crimped yarns.

In the process and apparatus of the invention, the rotatable friction drive of the torque assembly can be driven at such a speed and at such a Contact or bearing pressure on the twisted strand that the torsional moment introduced in this manner into the strand is smaller than the torsional moment of the twisted strand itself. In this case theindividual yarns are finally separated only by exertion of a positive separating pull or draw tension, so that a separating point is formed following the frictional torque assembly. In order to prevent any excessive lateral or vertical excursion of the separating point under these conditions, it is preferable separating point of the yarns lies between the output of the frictional torque assembly and the yarn guide means. 1

In a preferred embodiment, it is further proposed according to the invention that the frictional torque assembly be arranged in such a manner that the separating point of the yarns lies in the torque assembly itself, i.e., this assembly preferably including at least two frictional drive members arranged at the point of separation of the individual yarns to simultaneously act as yarn guide means in directing each of the separated yarns in a different path outwardly from the point of separation. In this case, the torsional moment exerted by the frictional drive means of the torque assembly on the twisted strand can be so great that the separation of the yarns occurs without exertion of an especially high pull force or draw tension on the separated yarns. It is also possible, however, for a smaller torsional moment to be provided by the frictional torque assembly, so that the threads must be separated under additional pull or draw tension. In every case in this preferred arrangement, an excursion of the separating point is virtually completely prevented and the position of this floating point of separation ishighly stabilized.

For a-further detailed description of the invention, reference is made to the particular embodiments described by way of example hereinafter in conjunction with the accompanying drawingswherein:

FIG. 1 is a schematic representation of the process and conventional apparatus for continuous crimping by separation twisting;

FIGS. 2a and 2b illustrate twisted and coiled yarns respectively;

FIG. 3a is an enlarged view of yarn segments at the separation point as taken from FIG. 1

FIG. 3b shows the same yarn segments as FIG. 3a but with reduced tension or pull force on theyarns being separated; I

FIG. 30 shows the same yarn segments as FIG. 30 but with increasing tension or pull force on the yarns being separated;

FIGS. 4a and 4b illustrate portions taken from FIG. 1 with unequal yarn tension in the yarns being separated;

FIGS. 5 through 9 illustrate a number of different embodiments of the combination for separating twisting apparatus according to the invention; and

FIG. 10 illustrates a preferred overlapping arrangement of three friction wheels as torque drive means in a false-twist assembly of the invention.

In FIG. 1, from the run-off or feed bobbins 1 and I there are drawn two yarns Y and Y which are conducted over a delivery system such as the feed roller pairs 2 and 2 and then drawn through converging paths into a twisted strand 3 which has been initially produced with a predetermined length and degree of twist of the yarns according to the required crimp. In

= a heat-setting zone 6, by means of a heating device 7 and any suitable cooling device 8, the twist of the yarns is fixed. At the separating point 5, the textured yarns 4 and 4' are pulled apart in diverging paths by means of the draw-off rollers 9 and 9' and wound onto the takeup reels or bobbins l0 and 10. This conventional process can also be carried out with more than two yarns although, to be sure, the crimping is less. The delivery or feed rolls 2 and 2' can also be omitted or preferably replaced or supplemented by thread or yarn brakes.

Such braking means on the yarn feed make it possible for the yarn to run into the twisted strand 3 at the necessary high yarn tension required to exert on the strand the rotation or torsional moment for twisting. Also, as is known, tension on the twisted strand 3 is desirable in maintaining the necessary contact with the heating means 7 which can best be in the form of a conventional heating plate or the like, e.g., one which is slightly curved and pressed slightly outwardly against the travelling twisted strand.

It is of particular advantage that the feed and withdrawal means according to the invention can be of any usual construction and need not be specially designed for stabilizing the yarn separation point, i.e., with the rather complicated mechanisms now required for this process. At the same time, the present invention does not exclude such additional stabilizing means which may offer some additonal benefit in adjusting or maintaining the separation point.

The present invention is particularly concerned with the use of a rotating or torque drive means applied to the twisted strand at the separating point 5, as described more fully below, so that the zone immediately following the cooling means 8 is significant, especially that zone in the vicinity of the separating point represented by the segments enclosed by A, B and C.

The yarns can be twisted or coiled with one another in the twisted strand 3. As represented in FIG. 2a, the individual yarns Y and Y during their twisting are each turned simultaneously about the other and also about their own axis. Thus, a displacement of the real or imaginary filaments al, a2 and bl, b2 of the yarn takes place relative to the yarn axis. In the so-called coiling," as represented in FIG. 2b, in contrast, the individual imaginary or real filaments of the yarn retain their position parallel to the yarn axis, i.e., the yarns are not turned or twisted about their own axis.

The heating device 7 can be operated according to any desired system, e.g., by convection, radiation or heat conduction, and can be of any conventional construction. Special cooling means 8 can be arranged for the cooling zone such as, for example, a blower or fan using cooled air or even air at room temperature with a sufficiently long cooling zone. The yarn path of the strand 3 in the cooling zone 8 can even be so long that special cooling apparatus is unnecessary, the cooling being accomplished simply by running the strand 3 is a normal atmosphere, i.e., at prevailing room conditions.

The position of the separating point 5 depends on the torsional moment under which the twisted strand 3 has been placed by the pretwist and by the tension with which the yarns 4 and 4' are drawn off. The angle under which the threads are drawn off is equal to the pitch angle 11 at which the threads are twisted with one another in the zone of the separating point 5 as illustrated for example in FIG. 3a. In FIG. 3b there is represented the manner in which the separating point strays upwardly in the case of a reduced torsional moment with increasing pitch angle 11 of the twisted strand 3. FIG. illustrates how the separating point strays downwardly with increasing torsional moment and a decreasing pitch angle 11.

FIGS. 4a and 4b indicate the lateral excursion of the separating point 5 in the case of unequal tension in the two yarns 4 and 4'. In the extreme case, the yarns in the twisted strand 3 are not twisted together but instead the yarn 4 in FIG. 4a or yarn 4' in FIG, 4b is coiled in a helical winding or spirals around the yarn under such a strong tension that it remains practically linear, e.g., as suggested by 4' in FIG. 4b. This technique is sometimes adopted where one yarn is replaced by a continuous loop thread or wire but still remains difficult to control except by carefully regulating the unbalanced tensions.

Both the vertical and also the lateral excursion of the separating point, which proceed very rapidly and can be brought about through an unevenness inone or both yarns, e.g., by nodules or the like in the twisted strand, lead to non-uniform crimping and under some circumstances to yarn or filament breakage.

In the embodiment of the present invention which is represented in FIG. 5, the twisted strand 3 is driven on its periphery by means of the frictional torque assembly 12 which consists of two friction wheels 13 and 13'. It will be understood that these wheels or any other torque drive means of the invention always rotate and, namely, in the same direction according to the rotation in which the twisted strand turns naturally as the yarns are withdrawn at 4 and 4. Otherwise, the construction of the apparatus and the sequence of process steps corresponds to that shown in FIG. 1. In other words, the torque drive means such as

wheels

13 and 13 should be positively driven preferably at the same rate, by any suitable motor or drive linkage such as the variable speed motors M, so that the drive velocity proceeds in the same direction at tangential contact points with the strand 3 but with a greater velocity than that of the peripheral or circumferential speed of 'the strand itself.

The frictional torque assembly can be of any convenient type of construction. It can consist, for example, of one or several coaxially arranged wheels of the same diameter. It can also be constructed as a rotatably mounted sleeve which drives the twisted strand on the inner periphery of the sleeve. There can also be provided three frictional drive wheels or three groups of drive wheels which rotate on three axles arranged in a triangle, the wheels overlapping in such a way that the thread can be conducted through between them in axial direction and substantially in a straight line while being in frictional contact with the circumference of each wheel (cf. FIG. 10).

This complementary rotation or torque being applied to the twisted strand is used to resolve or even substantially cancel the normal. rotation or torsional moment produced by the draw means 9 and 9'. The amount of torque applied by the assembly 12 is thereby positively used to control the torsional moment placed on the strand 3, the amount of tension in the yarns 4 and 4' and also the position of the separating point 5.

In the example shown in FIG. 5, the rotation of the twisted strand 3 is in part resolved by the

frictional drive wheels

13 and 13. The pitch angle 11 of the twisted strand before the frictional torque assembly 12 is smaller than the pitch angle 11' following the torque assembly.

In FIGS. 6, 7 and 8, the twisted strand 3 is driven on its periphery with a drive velocity which decreases toward the separating point 5. In FIG. 6, this is accomplished by the conical frictional drive rolls l4 and 14'. In FIG. 7, four coaxially arranged friction wheels 15 become smaller in diameter toward the separating point 5 to provide a similar conical configuration in stages, the yarn guides 17 cooperating to lay the twisted strand 3 against the circumference of each friction wheel 15. Still another embodiment is shown in FIG. 8 and includes a rotating conical sleeve 16, which drives the strand 3 at the input and output edges of the sleeve inner periphery which can be suitably rounded or beaded as shown. This sleeve can be gear or belt driven when mounted rotatably as indicated. Otherwise, the construction of the separation twist apparatus and the course of the process according to FIGS. 6, 7 and 8 corresponds to that of FIGS. 1 and 5. 7

in FIGS. 6 and 8 there is additionally provided the yarn guide 18. This fixed guide 18, is arranged in such a way that the separating point lies between the output of the torque or false twist assembly 'l2 and the guide l8. The spacing between the two is relatively small and the yarn guide 18 is narrow in diameter (having been greatly exaggerated in the drawing). This assures that the separating point of the yarns can stray only slightly in the case of uneven yarn tension in one or both yarns. 1

In FIG. 9, which otherwise corresponds to FIG. 5, the twisted strand 3 is driven at such a high velocity or with such slight slippage, that the twisting (Verdrehung) is already cancelled in the frictional torque assembly 12.

There, the separated threads 4 and 4' are drawn off in such a direction that the

rounded edges

19 and 19 of the friction wheels 13 and 13' serve as the yarn guides. An excursion or straying of the separating point 5 is virtually impossible in this embodiment and the device is especially distinguished in that it is surprisingly selfregulating.

For the apparatus constructed and operated accord- 7 ing to FIG. 9, it is particularly advantageous to provide a frictional torque assembly 12 constructed as shown in FIG. 10.. The three

friction wheels

20, 20' and 20" have their axes arranged in atriangle in such a way that the wheels overlap and the twisted strand 3 can be threadedthrough and between these wheels very nearly in a straight line and in contact with the outer circumference of each of the wheels.

A special advantage of the invention resides in the fact that it becomes possible to eliminate the causes of thread tension fluctuations and the consequential displacement of the separating point, fluctuations in the crimpingand filament or yarn breakages, while hitherto it was only possible to keep the efi'ects of yarn tension fluctuations within limits, e.g., by more or less stabilizing the yarn separation point. The invention permits a much stronger twisting of the yarns in the twisted strand and thereby a stronger crimping with increased production speed and output of a very uniformly textured yarn.

The invention is hereby claimed as follows:

I. In a separation twist process for the continuous crimping of a thermoplastic heat-settable yarn wherein separate yarns are pretwisted together over a predeter mined length to form a true twisted strand which is heated and then cooled under tension in a heat-setting zone and wherein said yarns are continuously separated by being pulled aprat at one end of said twisted strand while continuously feeding the separate yarns together into said twisted strand at the other end thereof, thereby imparting a rotational movement to said strand, the improvement which comprises: frictionally rotatably driving the twisted strand in the vicinity of the point where the yarns are separated at a drive velocity which is greater than the peripheral velocity of the re tational movement of the strand itself and with said drive velocity on said twisted strand being decreased toward the point where the yarns are separated.

2. A process as claimed in claim I wherein the yarns being separated are pulled outwardly over a fixed guide surface and the point of separation is maintained between said guide surface and the preceeding frictional drive contact on the twisted yarn.

3. A process as claimed in claim I wherein the point where the yarns are separated is maintained at about the last point of frictional drive contact on the twisted yarn.

4. A separation-twist apparatus for the continuous heat-set crimping of a thermoplastic yarn which comprises:

yarn feed and withdrawal means to continuously transport a rotating twisted strand of individual yarns under tension through a heat-setting zone, said withdrawal means acting to pull apart and separate the individual yarns from each other at a point of separation of the twisted strand following said heat-setting zone; and

a frictional torque assembly positioned along the twisted strand in the vicinity of said point of separation, said assembly including drive means arranged to frictionally rotate said twisted strand at tangential contact points along its outer periphery with successively reduced drive velocities toward the point where the yarns are separated.

5. Apparatus as claimed in claim 4 wherein said frictional torque assembly has a conical configuration with reference to its surfaces which are in driving contact with the twisted strand, the conical apex being directed toward said point of separation of the individual yarns.

6. Apparatus as claimed in claim 4 wherein said torque assembly includes a plurality of frictional drive wheels arranged successively along the twisted strand with their diameters becoming smaller toward said point of separation of the individual yarns.

7. Apparatus as claimed in claim 4 including yarntransport a rotating twisted strand of individual yarns under tension through a heat-setting zone, said withdrawal means acting to pull apart and separate the individual yarns from each other at a point of separation of the twisted strand following said heat-setting zone; and

a frictional torque assembly positioned along the twisted strand in the vicinity of said point of separation and acting to frictionally drive said twisted strand on its outer periphery, said frictional torque assembly including a set of at least two frictional drive members arranged at said point of separation of the individual yarns to simultaneously rotate the yarn and act as yarn guide means in directing each of the separated yarns in a different path outwardly from the point of separation.

9. Apparatus as claimed in claim 8 wherein said frictional torque assembly includes three frictional drive wheels arranged at said point of separation in overlapping relationship for tangential contact with the periphery of said twisted strand at about equal intervals around the strand circumference.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 1 661; Dated May 98 107A Invent r( Heinz Schippers It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

First page, left-hand column, ninth line, insert 30 Foreign Application Priority Data July 27, 1971 Germany P 21 37 451.6

Column 5, line &7, "is should read in Column 7, line 60, "aprat" should read apart Signed. and Scaled this A I test:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ofla tents and Trademarks

Claims

1. In a separation twist process for the continuous crimping of a thermoplastic heat-settable yarn wherein separate yarns are pretwisted together over a predetermined length to form a true twisted strand which is heated and then cooled under tension in a heat-setting zone and wherein said yarns are continuously separated by being pulled aprat at one end of said twisted strand while continuously feeding the separate yarns together into said twisted strand at the other end thereof, thereby imparting a rotational movement to said strand, the improvement which comprises: frictionally rotatably driving the twisted strand in the vicinity of the point where the yarns are separated at a drive velocity which is greater than the peripheral velocity of the rotational movement of the strand itself and with said drive velocity on said twisted strand being decreased toward the point where the yarns are separated.

2. A process as claimed in claim 1 wherein the yarns being separated are pulled outwardly over a fixed guide surface and the point of separation is maintained between said guide surface and the preceeding frictional drive contact on the twisted yarn.

3. A process as claimed in claim 1 wherein the point where the yarns are separated is maintained at about the last point of frictional drive contact on the twisted yarn.

4. A separation-twist apparatus for the continuous heat-set crimping of a thermoplastic yarn which comprises: yarn feed and withdrawal means to continuously transport a rotating twisted strand of individual yarns under tension through a heat-setting zone, said withdrawal means acting to pull apart and separate the individual yarns from each other at a point of separation of the twisted strand following said heat-setting zone; and a frictional torque assembly positioned along the twisted strand in the vicinity of said point of separation, said assembly including drive means arranged to frictionally rotate said twisted strand at tangential contact points along its outer periphery with successively reduced drive velocities toward the point where the yarns are separated.

5. Apparatus as claiied in claim 4 wherein said frictional torque assembly has a conical configuration with reference to its surfaces which are in driving contact with the twisted strand, the conical apex being directed toward said point of separation of the individual yarns.

7. Apparatus as claimed in claim 4 including yarn guide means immediately following the frictional torque assembly and positioned to receive and direct each of the separated yarns in a different path outwardly from said point of separation.

8. A separation-twist apparatus for the continuous heat-set crimping of a thermoplastic yarn which comprises: yarn feed and withdrawal means to continuously transport a rotating twisted strand of individual yarns under tension through a heat-setting zone, said withdrawal means acting to pull apart and separate the individual yarns from each other at a point of separation of the twisted strand following said heat-setting zone; and a frictional torque assembly positioned along the twisted strand in the vicinity of said point of separation and acting to frictionally drive said twisted strand on its outer periphery, said frictional torque assembly including a set of at least two frictional drive members arranged at said point of separation of the individual yarns to simultaneously rotate the yarn and act as yarn guide means in directing each of the separated yarns in a different path outwardly from the point of separation.