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United States Patent 3,646,745
Baldwin ,   et al. March 7, 1972

METHOD AND APPARATUS FOR MAKING STAPLE-FIBER YARNS

Abstract

A method and apparatus for making "cracker"-free staple fiber yarns from staple-fiber rovings provide one or two drafting stages for the roving and a final stage which is a substantially zero draft stage and which wholly supports the roving during its passage therethrough. The length of the final stage is less than the effective staple length of the fibers in the roving.


Inventors: Baldwin; Tony Lewis (Harrogate, EN), Burton; Roy Harold (Harrogate, EN)
Assignee: Imperial Chemical Idustries Limited (London, EN)
Appl. No.: 04/869,778
Filed: October 27, 1969


Foreign Application Priority Data

Nov 08, 1968 [GB] 53,061/68

Current U.S. Class: 57/315 ; 19/250; 19/258; 19/259
Current International Class: D01H 5/18 (20060101); D01H 5/26 (20060101); D01H 5/00 (20060101); D01h 005/22 (); D01h 005/26 ()
Field of Search: 57/36,51.2-51.6,156 19/236,244-251,258,259,260,266,261

References Cited

U.S. Patent Documents
2728112 December 1955 Berker
2930085 March 1960 Konig
3051997 September 1962 Vialle
3304584 February 1967 West et al.
3385045 May 1968 Slowiak
Foreign Patent Documents
900,793 Jan., 1954 DT
Primary Examiner: Petrakes; John

Claims



What we claim is:

1. A method of manufacturing a yarn from a roving composed of staple fibers, comprising passing the roving through at least one stage in which it is subjected to a drafting operation and twisting the drafted roving to form a yarn, wherein the insertion of the twist is held off bypassing the drafted roving through a further stage in which it is subjected to a substantially zero draft and is wholly supported during its travel therethrough.

2. A method according to claim 1, wherein the roving is passed through two successive drafting stages, it being subjected to a higher draft in one stage than in the other, prior to being passed through the further stage wherein it experiences substantially zero draft.

3. A method according to claim 2, wherein the draft ratio of the first drafting stage is lower than the draft ratio of the second drafting stage.

4. A method according to claim 1, wherein the roving from which the yarn is made is composed of synthetic, manmade, or natural staple fibers, or mixtures thereof.

5. A method according to claim 4, wherein synthetic fibers include those made from polyesters and polyamides; manmade fibers include cellulosic fibers; and natural fibers include wool and cotton fibers.

6. A method of making a staple-fiber yarn from a roving composed of cotton-type, staple fibers, wherein the roving is drafted during its passage through two successive stages, one stage having a higher draft ratio than the other stage, the drafted roving is passed through a further stage having a length not greater than the effective staple length of the fibers in the roving and wherein the drafted roving is subjected to a substantially zero draft, and the drafted roving is twisted and collected in the form of a yarn.

7. Apparatus for manufacturing a yarn from a roving composed of staple fibers comprising means forming at least one drafting stage for the roving, twisting means operable to insert twist in the drafted roving, and means arranged to hold off the insertion of the twist and being operable to subject the drafted roving to a substantially zero draft and to wholly support the drafted material during its travel from the or the final drafting stage to where the twist is inserted in the drafted roving by the twisting means.

8. Apparatus according to claim 7 comprising two drafting stages.

9. Apparatus according to claim 8, wherein the two drafting stages are formed by three sets of rolls, each set comprising a nip roll and a drive roll, and which sets are rotatable at different speeds defined by the draft ratios required for the two drafting stages.

10. Apparatus as in claim 8 wherein the two drafting stages are formed by three nip zones at least one of which is an apron system.

11. Apparatus according to claim 7, wherein the means for holding off the twist is a single roll positioned after the final drafting stage.

12. Apparatus according to claim 7, wherein the twisting means is a ring-and-traveller windup mechanism.

13. Apparatus as in claim 7 wherein the means for holding off the twist is a nip roll/drive roll set positioned after the final drafting stage.

14. Apparatus as in claim 7 wherein the means for holding off the twist is a pair of aprons positioned after the final drafting stage.

15. Apparatus for making staple-fiber yarns from rovings composed of cotton-type, staple fibers, which comprises means for supplying a roving, three sets of rolls, each set being composed of a nip roll and a drive roll therefor, which are arranged and adapted to operate at speeds in such a manner as to form two drafting stages, one having a higher draft ratio than the other, a fourth nip roll and a drive roll therefor arranged to form a third drafting stage with the third set of said three sets of rolls, which drafting stage has a length not greater than the effective staple length of the fibers in the roving, and being adapted to operate in such a manner that the fourth nip roll has a speed ratio of 1:1 with the third nip roll, and means for twisting and collecting the drafted roving as a yarn.

16. Apparatus according to claim 15, wherein the third and fourth nip rolls are arranged to be driven by a common drive roll.
Description



The present invention concerns improvements in and relating to the production of yarns composed of staple fibers, wherein a roving of staple fibers is drafted and twisted to form such a yarn.

Staple-fiber yarns are generally produced on a drafting apparatus which usually consists of one or, more often, two drafting stages. In the later case the first stage through which the roving passes commonly has a lower draft ratio than the second stage.

A fault which can, and often does, arise during the production of yarns composed of staple fibers by methods involving drafting and twisting is commonly referred to as a "cracker," which term is used to describe a bundle of small fiber loops tightly bound together. The number of crackers which occurs in a yarn is variable and so is the length of each cracker formed. A cracker may vary in length, for example, from as little as 0.125 inch up to 2 inches.

A major factor contributing to the occurrence of crackers in a yarn composed of cotton-type, staple fibers, is thought to be the presence of overlength staple fibers in the roving from which the yarn is made. An "overlength" staple fiber is a fiber, present in the roving, having a length which is in excess of the effective staple length of the majority of the staple fibers in the roving. In other words, the majority of the staple fibers in a roving has the same length, i.e., the effective staple length, but the roving may also contain minority groups made up of fibers having lengths shorter than the effective staple length and fibers having lengths greater than the effective staple length. During drafting of a roving, the drafting conditions are chosen with the effective staple length in mind so that the majority of the staple fibers are efficiently processed. The smaller staple fibers pass through the drafting apparatus without difficulty but the longer staple fibers, i.e., the overlength fibers, give rise to crackers. The part played by the overlength fibers in the formation of crackers is considered to be as follows:

An overlength fiber present in a roving advances through the drafting apparatus at the speed imparted to it as it enters the, or the final, drafting stage even when its leading end emerges from that drafting stage, in those circumstances when the length of the overlength fiber is such that it spans that drafting stage. The normal staple fibers in the roving, however, have their speed increased as they pass through and emerge from the drafting stage. There is then a tendency for the normal staple fibers to catch on and be retarded by the overlength fiber, the result being the formation of a loop or loops of fibers due to the overfeed rate of the normal staple fibers. The high degree of twist being imparted to the drafted material by the windup mechanism rolls up the loop or loops and a cracker is formed. The formation of the cracker continues until the trailing end of the overlength fiber passes through the entrance to the drafting stage or the fiber breaks.

Overlength fibers occur in rovings composed of natural fibers because some fibers grow to longer lengths than others. In the case of manmade or synthetic fibers, overlength fibers may arise during the production of the staple fibers from a heavy denier tow of continuous filaments and may be due, for example, to differing tensions in the continuous filaments, or to nonparallelism of some of the continuous filaments as the tow passes through the cutter, or to malfunctioning of the cutter.

An object of the present invention is the provision of a method and apparatus for making staple-fiber yarns wherein, if overlength fibers are present in the rovings from which the yarns are made, the occurrence of cracker formation, if not eliminated, is at least greatly reduced.

According to the present invention, a method of manufacturing a yarn from a roving composed of staple fibers, comprises passing the roving through at least one stage in which it is subjected to a drafting operation and twisting the drafted roving to form a yarn, wherein the insertion of the twist is held off by passing the drafted roving through a further stage in which it is subjected to a substantially zero draft and is wholly supported during its travel therethrough.

The roving may be passed through two successive drafting stages, it being subjected to a higher draft in one stage than in the other, prior to being passed through the further stage wherein it experiences substantially zero draft. The draft ratio of the fist drafting stage is usually lower than the draft ratio of the second drafting stage.

By the expression "...... the insertion of the twist ..... is held off ....." is meant that the twist inserted in the drafted roving is prevented from running back to the exit of the, or the final, drafting stage by the further, substantially, zero draft, stage.

Also according to the present invention, apparatus for manufacturing a yarn from a roving composed of staple fibers comprises means forming at least one drafting stage for the roving, twisting means operable to insert twist in the drafted roving, and means arranged to hold off the insertion of the twist and being operable to subject the drafted roving to a substantially zero draft and to wholly support the drafted material during its travel from the or the final drafting stage to where the twist is inserted in the drafted roving by the twisting means.

The apparatus preferably comprises two drafting stages formed by three sets of rolls, each set being formed of a nip roll and a drive roll, and which sets are rotatable at different speeds defined by the draft ratios required for the two drafting stages. In alternative embodiments of the apparatus, apron systems may be utilized in place of some or all of the sets of rolls. By an "apron" is meant a roller-driven, endless belt.

The twisting means may be, for example, in the form of a ring-and-traveller windup mechanism or one of other well-known windup mechanisms which twist and collect the twisted drafted material, or yarn.

Preferably, the means for holding off the twist is a single roll, or a nip roll/drive roll set, or a pair of aprons, positioned after the, or the final, drafting stage.

The rovings used to make the yarns according to the invention may be synthetic, manmade, or natural staple fibers, or mixtures thereof. Examples of synthetic fibers are those made from polyesters and polyamides; examples of manmade fibers are cellulosic fibers; and examples of natural fibers are wool and cotton fibers.

The present invention is particularly applicable to the manufacture of staple-fiber yarns composed of "cotton-type" staple fibers. By a "cotton-type" staple fiber is meant a fiber of the natural product or a synthetic staple fiber having a length which is substantially the same as that of the natural product.

Accordingly, therefore, the present invention provides a method of making a staple-fiber yarn from a roving composed of cotton-type, staple fibers, wherein the roving is drafted during its passage through two successive stages, one stage having a higher draft ratio than the other stage, the drafted roving is passed through a further stage having a length not greater than the effective staple length of the fibers in the roving and wherein the drafted roving is subjected to a substantially zero draft, and the drafted roving is twisted and collected in the form of a yarn.

Typically the first drafting stage has a draft ratio of the order 1.5:1 and the second drafting stage has a draft ratio of the order 22:1.

The invention further provides a drafting apparatus for making staple-fiber yarns from rovings composed of cotton-type, staple fibers, which comprises means for supplying a roving, three sets of rolls, each set being composed of a nip roll and a drive roll therefor, which are arranged and adapted to operate at speeds in such a manner as to form two drafting stages, one having a higher draft ratio than the other, a fourth nip roll and a drive roll therefor arranged to form a third drafting stage with the third set of said three sets of rolls, which drafting stage has a length not greater than the effective staple length of the fibers in the roving, and being adapted to operate in such a manner that the fourth nip roll has a speed ratio of 1:1 with the third nip roll, and means for twisting and collecting the drafted roving as a yarn.

In a preferred embodiment of the apparatus of the invention, the third and fourth nip rolls are arranged to be driven by a common drive roll.

The present invention not only provides for the manufacture of substantially cracker-free yarns from poor quality rovings, but enables rovings composed of deliberately blended staple fibers of differing lengths, which rovings would normally be extremely difficult to process into substantially cracker-free yarns.

The invention will now be further described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 illustrates diagrammatically in side elevation one embodiment of an apparatus according to the present invention;

FIG. 2 is a similar illustration of a second embodiment of the apparatus, and

FIG. 3 is a similar illustration of a third embodiment of the apparatus.

FIG. 4 is a similar illustration of a fourth embodiment of the apparatus.

In the drawings, like parts have been given the same reference numerals.

Referring to FIG. 1, one embodiment of an apparatus according to the invention comprises three sets of rolls forming two drafting stages. The first set comprises a nip roll 1 and a drive roll 2, the second set comprises a nip roll 3 and a drive roll 4, and the third set comprises a nip roll 5 and a drive roll 6. The speed ratio of the first and second sets of rolls is less than that of the second and third sets of rolls so that the second drafting stage has a higher draft ratio than the first drafting stage.

The nip rolls 1, 3 and 5 are adjustably mounted on springs (not shown) whereby the nip pressures may be varied. A further nip roll 7 is also mounted so as to be driven by the drive roll 6. Means are provided (not shown) for adjusting the pressure exerted by the nip roll 7 on the drive roll 6.

The apparatus is also provided with a ring-and-traveller windup mechanism 16.

In operation, a roving 8 composed of staple fibers is fed through the apparatus and is subjected to two drafting stages, one being between the sets of rolls 1,2 and 3,4 and the other between the sets 3,4 and 5,6. The drafted roving issues from the nip between the nip roll 5 and the drive roll 6, i.e., the exit from the second drafting stage, and is supported by the surface of the roll 6 until it passes through the nip between the nip roll 7 and the drive roll 6. The rolls 5, 6 and 7 are rotating at the same speed so that the further stage between the nips of rolls 5, 6 and 6, 7 has a substantially zero draft. The length of the further stage is chosen to be not greater than the effective staple length of the fibers in the roving 8.

The drafted roving issuing from the rolls 6 and 7 is twisted into a yarn and is collected by the ring-and-traveller windup mechanism. The twist inserted in the drafted roving runs along the drafted roving in a direction opposite to the latter's movement. The twist, is, however, held off from reaching the exit of the second drafting stage by the nip roll 7 and the drive roll 6 of the further, zero draft, stage.

In the second embodiment illustrated in FIG. 2, the nip roll 7 is replaced by a fourth set of rolls, comprising a nip roll 9 and a drive roll 10 which is arranged to be driven at the same speed as the rolls 5, 6. The distance between the nips of rolls 5, 6 and 9, 10 is chosen to be less than the effective staple length of the fibers in the roving 8, so that the majority of the fibers in the roving will at some instant during the travel of the roving 8 bridge the gap between the rolls 5, 6 and 9, 10. By this mechanism, the roving 8 is wholly supported during its travel through the further zero draft stage. Again, the twist inserted in the drafted roving was held off by the rolls 9, 10 from running back to the exit (i.e., the nip of the rolls 5,6) of the second drafting stage.

In the third embodiment illustrated in FIG. 3, a twin-apron system is used. The uppermost apron comprises a roll 12 and a guide 11 about which a belt 13 is fitted, and the lowermost apron comprises a roll 12a and a guide 11a about which a belt 13a is fitted. The roll 12a is a drive roll which drives the belt 13a. The roll 12 is an idler roll which is driven by friction contact with the roll 12a. The belt 13 is driven by the roll 12.

The speed of rotation of the drive roll 12a is synchronized with that of the drive roll 6 to provide a further zone having a substantially zero draft.

The distance between the nip of the rolls 5, 6 and the nip of the belts 13, 13a adjacent the guides 11, 11a is less than the effective staple length of the fibers in the roving 8, so that at any instant the gap between the nips is bridged by the majority of the staple fibers and the drafted roving can be considered to be wholly supported during its passage between the nips. The drafted roving is carried through the remainder of the stage between the belts 13, 13a.

The twist inserted in the drafted roving is held off from the exit (i.e., the nip of the rolls 5, 6) of the second drafting stage by the nip between the belts 13, 13a adjacent the rolls 12, 12a.

The fourth embodiment illustrated in FIG. 4 is a modification of the apparatus shown in FIG. 1. The rolls 3,4 are provided with endless belts 15, 15a and guides 14, 14a, respectively, to form a twin-apron system in the second drafting stage.

The following examples illustrate further the method according to the present invention.

EXAMPLE 1

a. A roving was prepared by plying 2.times.2.4 (246 tex) hank rovings of 100 percent Sudan Cotton staple fibers, the fiber lengths ranging from 0.38 inch to 1.63 inch.

The roving was processed using an apparatus as illustrated in FIG. 1 of the accompanying drawings but with the roll 7 removed. The first drafting stage (x) had a draft ratio of about 1.5:1 and the second drafting stage (y) had a draft ratio of about 15.3:1, giving a total draft of about 23.

The first drafting stage (x) was set at 2 inches and the second drafting stage (y) was varied from a setting at which no crackers were formed in the drafted roving to a setting in which processing became inoperable due to the continuous formation of crackers.

b. A similar roving was processed under the same conditions, but according to the invention, using the apparatus of FIG. 1 with the roll 7.

The results obtained are given in Table 1. --------------------------------------------------------------------------- TABLE I

Setting of Second The number of crackers and t heir Drafting Stage lengths in. per yd. of roving __________________________________________________________________________ (inches) Example 1(a) Example 1(b) __________________________________________________________________________ 1.38 Nil Nil 1.31 2.times.0.13; 2.times.0.25; 1.times.0.38 Nil 1.25 11.times.0.13; 3.times.0.25; 2.times.0.50 Nil 3.times.1.00; 3.times.1.50; 1.times.2.00 1.19 Inoperable due to continuous Nil cracker formation __________________________________________________________________________

EXAMPLE 2

a. A roving was prepared from 100 percent wool fibers (64s Quality Bradford Tops), the fiber lengths ranging from 1.00 inch to 6.25 inches.

The roving was processed on an apparatus according to FIG. 1, but which was modified by the removal of the rolls 3, 4 to provide a single drafting stage which was arranged to have a draft ratio of 23:1. The roll 7 was also removed. The setting of the single drafting stage was varied from a setting at which no crackers were formed in the drafted roving to a setting in which processing became inoperable due to the continuous formation of crackers.

b. A similar roving was processed under the same conditions, but according to the invention, using the apparatus employed in Example 2(a) but with the roll 7. The results obtained are given in Table II.

EXAMPLE 3

a. A roving was prepared from 3 denier, 100 percent nylon, variable length staple fibers -- produced from a tow processed on a Pacific converter cutter, giving fiber lengths, which varied from 2.75 inches to 9 inches. --------------------------------------------------------------------------- TABLE

II Setting of The number of crackers and t heir Drafting Stage lengths in. per yd. of roving __________________________________________________________________________ (inches) Example 2(a) Example 2(b) __________________________________________________________________________ 5.5 Nil Nil __________________________________________________________________________ 4.5 6.times.0.13; 7.times.0.25; 5.times.0.3; 2.times.0.75; 2.times.1.5; 4.times.2.0; Nil 1.times.3.0 __________________________________________________________________________ 4.0 Inoperable due to continuous Nil cracker formation __________________________________________________________________________ 3.5 ditto Nil __________________________________________________________________________ 3.0 ditto Nil __________________________________________________________________________

Using the apparatus as in Example 2(a), with the single stage draft ratio of 23:1 the roving was processed and the setting of the drafting stage was varied from 6 inches to 8.5 inches. The fault rate in the drafted roving or yarn was noted and is given in Table III.

b. A similar roving was processed according to Example 3(a) but with the roll 7 being fitted to the apparatus. The results obtained are given in Table III. --------------------------------------------------------------------------- TABLE III

Setting of The number of crackers and t heir Drafting Stage lengths in. per yd. of roving __________________________________________________________________________ (inches) Example 3(a) Example 3(b) __________________________________________________________________________ 6.0 Inoperable 4.times.(0.13 to 0.25) __________________________________________________________________________ 6.5 Almost continuous crackers varying 1.0 to 20.0 inches Nil long __________________________________________________________________________ 7.5 23.times.(0.13 to 3.0) Nil __________________________________________________________________________ 8.0 15.times.(0.13 to 1.5) Nil __________________________________________________________________________ 8.5 4.times.(0.13 to 0.75) Nil __________________________________________________________________________

EXAMPLE 4

a. A 1.5 (394 tex) hank roving composed of 100 percent "Courtelle" (R.T.M.) acrylic fibers of 3 d.p.f. and having fiber lengths ranging from 2.2 inches to 2.8 inches, was processed using an apparatus as illustrated in FIG. I of the accompanying drawings but with the roll 7 removed.

The draft ratios in the drafting stages (x) and (y) were chosen to give a total draft of 23.

The first drafting stage (x) was set at 3 inches and the second drafting stage (y) was varied from a setting of 2.63 inches (i.e., greater than the effective staple fiber length) to 2.25 inches (i.e., less than the effective staple fiber length).

b. A similar roving was processed according to Example 4(a) but with the roll 7 fitted to the apparatus.

The results obtained from Examples 4(a) and 4(b) are given in Table IV. --------------------------------------------------------------------------- TABLE IV

Setting of Second The number of crackers and t heir Drafting Stage lengths in. per yd. of roving __________________________________________________________________________ (inches) Example 4(a) Example 4(b) __________________________________________________________________________ 2.63 2.times.0.13; 3.times.0.50; 1.times.0.75; Nil 2.times.1.0; 1.times.2.0 __________________________________________________________________________ 2.5 2.times.0.13; 2.times.0.25; 1.times.0.50; 1.times.0.75; 2.times.1.0; 3.times.1.5; Nil 1.times.2.0; 1.times.3.0 __________________________________________________________________________ 2.38 4.times.0.13; 6.times.0.25; 2.times.0.75; Nil 2.times.1.0; 1.times.1.5; 1.times.3.0; 1.times.4.0 __________________________________________________________________________ 2.25 Very many of all lengths up to Nil 14 inches __________________________________________________________________________

EXAMPLE 5

a. A roving weighing 45 drams/40 yards (2178 tex) was prepared from 3 d.p.f., 100 percent TERYLENE (R.T.M.) polyester staple fibers, which fibers varied in length from 2 inches to 7.75 inches. This roving was processed on the apparatus described in Example 2(a), the setting of the single drafting stage being varied from 5 inches to 7 inches.

b. A similar roving was processed according to Example 5(a) and 5(b) are given in Table V. --------------------------------------------------------------------------- TABLE V

Setting of The number of crackers and t heir Drafting Stage lengths in. per yd. of roving __________________________________________________________________________ (inches) Example 5(a) Example 5(b) __________________________________________________________________________ 5 1.times.0.75; 2.times.2.20; 1.times.4.5 Nil 1.times.11.5; 1.times.17.5 __________________________________________________________________________ 6 1.times.0.5; 3.times.1.5; 1.times.2.5; Nil 1.times.3.0 __________________________________________________________________________ 7 1.times.0.13; 1.times.0.25; 2.times.0.5 Nil __________________________________________________________________________

EXAMPLE 6

a. A roving weighing 45 drams/40 yards (2178 tex) was prepared from a blend of 55 percent by weight of 3 d.p.f. TERYLENE (R.T.M.) polyester staple fibers and 45 percent by weight of wool fibers. The fibers in the blended roving had lengths which varied between 1.25 inches and 6.5 inches.

This roving was processed on the apparatus described in Example 2(a), the setting of the single drafting stage being varied from 4.5 inches to 6.5 inches.

b. A similar roving was processed according to Example 6(a) but with the roll 7 fitted to the apparatus.

The results obtained from Examples 6(a) and 6(b) are given in Table VI. --------------------------------------------------------------------------- TABLE VI

Setting of The number of crackers and t heir Drafting Stage lengths in. per yd. of roving __________________________________________________________________________ (inches) Example 6(a) Example 6(b) __________________________________________________________________________ 4.5 1.times.0.5; 1.times.2.0; 1.times.4.0; 2.times.4.5; Nil 2.times.6.0; 1.times.10.0; 1.times.12.0; 1.times.15.0 5.5 1.times.0.13; 4.times.0.5; 2.times.0.25; 2.times.0.75 ; Nil 5.times.1.0; 3.times.1.5; 1.times.2.0; 3.times.3.0 6.5 1.times.0.13; 3.times.0.5; 3.times.0.75; 1.times.2.0 Nil __________________________________________________________________________

EXAMPLES 7 TO 10

These examples illustrate the manufacture of staple-fiber yarns from 0.75 hank (788 tex) rovings composed of various blends of different lengths of TERYLENE (R.T.M.) polyester, cotton-type, staple fibers. The apparatus used is that shown in FIG. 4 of the drawings for Examples 7(a) to 10(a), and without the roll 7 for Examples 7(b) to 10(b). The drafting stages were set at 2.0 inches (first stage) and 1.7 inches (second) stage which are conventional settings for spinning rovings composed of 1.5 inch staple fibers. The total draft used was 16. ##SPC1##

EXAMPLE 11

Using the apparatus (a) as shown in FIG. 4, and (b) without the roll 7, TERYLENE polyester/cotton blend rovings (0.75 hank .tbd. 788 tex) containing "overlength" fibers were made into yarns. The drafting stage settings were those used in examples 7 to 10, and the total draft ratio was 32. The composition of each roving was 67% 2 d.p.f. .times. 11/2 inch TERYLENE polyester staple fibers, 33% Aloala cotton staple fibers, and 2% (based on the weight of the TERYLENE polyester/cotton fibers) of 2 d.p.f. .times. 2 inch TERYLENE polyester, "overlength" staple fibers.

The results were that the yarn produced using the apparatus described in (a) above contained no crackers while the yarn produced using the apparatus described in (b) above contained occasional crackers.

In each of the Examples 1 to 11 the drafted roving was twisted and collected as a yarn using a ring-and-traveller windup mechanism. The spindle speed of the windup mechanism and the weight of the traveller used for each example were as follows: ---------------------------------------------------------------------------

Example No. Spindle Speed (r.p.m.) Traveller Weight (g.) __________________________________________________________________________ 1 1,750 0.048 2 1,500 0.172 3 1,500 0.172 4 1,750 0.048 5 900 0.338 6 1,500 0.048 7 6,000 0.018 8 6,000 0.018 9 6,000 0.018 10 6,000 0.018 11 6,000 0.078 __________________________________________________________________________

Also, in each example, the distance between the nips of the rolls 5, 6 and the rolls 7, 6 was set at 0.75 inches.

For the production of a high-quality yarn it is desirable to adjust the apparatus of the invention so that the drafted roving issuing from the exit of the final stage on its way to the windup mechanism does not contact a curved surface of a roll or belt. This ensures that the twist inserted in the drafted roving runs back to the exit of the final stage without running over a surface and hence the likelihood of faults occurring due to twist irregularities is minimized.

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