US3768246A

US3768246A - Spun yarn and its doubled yarn and the process for manufacturing the same

Info

Publication number: US3768246A
Application number: US00888093A
Authority: US
Inventors: M Tabata; K Susami; H Edagawa
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 1966-12-20
Filing date: 1969-12-24
Publication date: 1973-10-30
Anticipated expiration: 1990-10-30
Also published as: CH480461A; US3501907A; FR1552320A; DE1710029A1; GB1212874A

Abstract

A method for producing spun yarn in an open-end spinning system having a rotary open-ended spinning chamber comprises feeding a bundle of fibers to the open-ended spinning chamber, rotating the open-ended spinning chamber at a peripheral surface speed V to successively accumulate superimposed layers of fibers upon the peripheral surface of the spinning chamber, withdrawing the accumulated fiber layers from the rotating open-ended spinning chamber in the form of spun yarn at a withdrawing speed W to self-double the spun yarn at a doubling number V/W, and selectively varying the speeds V and W to provide the spun yarn with a predetermined doubling number V/W during only a single passage through the open-end spinning system. The bundle of fibers is fed to the spinning chamber in a compressed air stream which transports the fibers in a mutually liberated condition to the open-ended spinning chamber.

Description

United States Patent Tabata et al.

[111 3,768,246 1 1 Oct. so, 1973 SPUN YARN AND ITS DOUBLED YARN AND THE PROCESS FOR MANUFACTURING THE SAME Inventors: Masaaki Tabata; Kozo Susami;

IIiroshi Edagawa, all of Otsu-shi, Japan Assignee: Toray Industries, Inc.

Filed: Dec. 24, 1969 Appl. No.: 888,093

Related US. Application Data Division of Ser. No. 691,056, Dec. 15, 1967, Pat. No. 3,501,907.

Foreign Application Priority Data Dec. 20, 1966 Japan 41/8298 July 12, 1967 Japan 42/44377 us. C1. 57/156, 57/5889 Int. Cl D0111 1/12 Field of Search 57/5889, 58.91,

References Cited UNITED STATES PATENTS 1/1930 Gross 57/5893 UX 1/1965 .luillard, 57/5889 3,399,523 9/1968 Ripka et a1 57/5889 UX FOREIGN PATENTS OR APPLICATIONS 489,538 12/1929 Germany 57/5891 825,776 12/1959 Great Britain 57/5889 Primary ExaminerWerner H. Schroeder Attorney-Robert E. Burns and Emmanuel J. Lobato [57] ABSTRACT A method for producing spun yarn in an open-end spinning system having a rotary open-ended spinning chamber comprises feeding a bundle of fibers to the open-ended spinning chamber, rotating the openended spinning chamber at a peripheral surface speed V to successively accumulate superimposed layers of fibers upon the peripheral surface of the spinning chamber, withdrawing the accumulated fiber layers 2 Claims, 12 Drawing Figures PAIENIEuucTaoms 13,768,246 SHEET 3 OF 4 MOMENT CURVATURE- RESIDUAL BREAKING STRENGTH in 'o s o I60 I50 "260' UNTWISTING RATE in%- PATENTEDnmsn ms 3,768,246

SHEET 4 OF 4 F/G. m F1678 FIG. 70

SPUN YARN AND ITS DOUBLED YARN AND THE PROCESS FOR MANUFACTURING THE SAME The present invention, is a divisional application of the U.S. Pat. application Ser. No. 691,056 filed on Dec.

15, now U.S. Pat. No. 3,501,907 by the same applicant of the presentinvention, and relates to a method for manufacturing an improved blended yarn having better doubling effect.

ln case of fiber blending in the conventional spinning system, a larger blending number'was required in order to obtain a blended yarn of a uniformly mixed composition. Such enlargement of the blending number usually entailed multiple staged fiber doubling operations resulting in an unfavourable increase in the production cost of the blended yarn obtained. 7

Such necessity for multiple staged fiberdoubling operations seemed to be mitigated to an appreciable extent by the employment of the recently developed open-end spinning system. However, the actual utilization ofthe conventional open-end spinning system in the fiber blending has proved the fact that there still remains a difficulty in the adjustment of the mechanical conditions in the system corresponding to the required degree of the doubling effect. In the conventional open-end spinning system, only a negative pressure within the rotor due to a high speed rotation of the rotor was utilized for sucking the material fibers into the system from the given supply source. Thus, the peripheral speed of the rotor, which is a function of the rotating speed of the rotor and the effective internal diameter of the rotor, should have been primarily determined in a close relation with the required negative pressure and there was no room for the adjustment thereof, from the view point of the resulting blending effect.

Generally, it is well-known that twisting in the spinning operation is an inevitable operation for forming yarn made from a fleece comprising a plurality of fibers which are continuously gathered and aligned along their lengthwise direction to bestow the strength of the yarn. The twisting of yarn by the ring spinning frame, flyer spinning frame, are also well-known arts. These conventional twisting methods twist the yarn in the same way, that is, one end of the bundle of fibers if fixed while the other end of the bundle of fibers is turned continuously by the rotation of the package of twisted yarn.

Generally, if the fibers of the fiber strand before twisting can be maintained in the twisting operation and the relative positions of each fiber in the fiber strand do not change even after the twisting operation, the fibers are occupied in the respective layer of the configuration of yarn. Consequently, the projection length of the fiber toward the axis of the yarn varies in accordance with the layer wherein the fiber is occupied, in other words, the projection length of the fiber disposed in the outer layer of the yarn is shorter than that of the fiber disposed in the inner layer of the yarn. In fact, it cannot be considered that the fibers are stretched to form the above-mentioned configuration of yarn while the twisting operation is being performed.

of yarn, or vice versa. The above-mentioned phenomenon is generally called migration" in the field of textile technology. A yarn having the configuration of migration has such defects as the stiffness of the yarn increasing with the continuance of the twisting while the resilience of the yarn degrades with decrease of the twisting. Consequently, it is very difficult to produce spun yarn having a soft feeling of touch and sufficient resiliency by the conventional twisting methods.

A principal object of the present invention is to provide an improved blended yarn having an uniformly blended composition and an excellent bulkiness, and a method for producing the same.

Another object of the present invention is to obtain a fabric having superior handling quality provided by the improved blended yarn of the present invention.

In conformity with the above-described objects of the invention, the method of the present invention utilizes, basically, the art of open-end spinning, wherein a pneumatic flow ejection caused by compressed air on the supplied fiber bundle is employed for the purpose of fiber sucking and liberating. The mentioned liberating force on the supplied fibers becomes dependent upon the additional pneumatic force. So, it becomes possible to change the mentioned peripheral speed of the rotor from the view point of the blending effect with less regard to the sucking and liberating effect. Thus, the peripheral speed of the rotor can be changed freely in relation with the taking-up speed of the blended yarn and the required self-doubling number. As a result of such an adjustment of the mechanical condition of the rotor, the actual self-doubling effect acquired on said blended yarn becomes larger than the doubling effect obtained by a' conventional spinning system whose doubling number is equal to that defined by the mentioned relation.

Further features and advantages of the invention will be apparent from the ensuing description with reference to the accompanying drawings; wherein FIG. 1 is a skeleton sketch of an embodiment of the spinning device used for carrying out the method of the invention,

FIG. 2 is an explanatory drawing of the twisting mechanism of the spinning device shown in FIG. 1,

FIG. 3 is an enlarged side view of an embodiment of the spun yarn produced by the method of the invention,

FIG. 4A, 4B and 4C are explanatory drawings showing the shapes of the fibers in the conventional yarn and the yarns of the present invention, respectively,

FIG. 5 is an explanatory diagram showing the bending moment of a yarn,

FIG. 6 is a diagram showing a relation between the residual strength of a yarn and the rate of back twist for the conventional spun yarn and the yarn of the present invention,

FIGS. 7A, 7B and 7C are several embodiments of the spinning device for producing blended yarn having the fiber configuration shown in FIGS. 38 and 3C,

FIG. 8 is an enlarged cross sectional view of the blended yarn produced by the spinning device shown in FIG. 7B,

Recently, blending of several kind of fibers has been developed for manufacturing a blended spun yarn. One remarkable example is a blended yarn of acrylic fiber with another kind of fiber having of superior bulkiness. The high-bulky acrylic blended yarn has a large market in the field of knitted fabrics. The properties such as bulkiness of the blended yam mentioned above can be improved remarkably by applying the particular configuration of yarn of the present invention.

Generally one of the features required in the blended yarn is uniform condition of the blending fibers. In case of knitting yarn such as a high-bulky acrylic yarn, some desirable mechanical properties such as soft feeling of touch and sufficient resiliency of the blended yarn are always required. As the spun yarn of the invention has a particular configuration without migration, the above-mentioned preferable mechanical properties can be acquired by the configuration of the yarn of the invention. Further, a very superior blending effect, which was not obtained by the conventional spinning method,

can be obtained by the self-doubling effect of the rotating rotor of the spinning device shown in FIG. 1.

To obtain soft feeling of touch and superior resiliency of a yarn, the yarn must have a novel configuration without migration. Such yarn can be manufactured by the spinning device shown in FIG. 1. The twisting mechanism of the spinning device shown in FIG. 1 differs completely from that of the conventional twisting mechanism. That is, one end of the bundle of fibers is turned while the other end of the bundle of fibers receives no restriction during the twisting operation. A detailed illustration of the above-mentioned twisting mechanism and its operation are as follows:

A bundle of fibers l is supplied successively from a draft device comprising a trumpet 2, a pair of back rollers 3, 3', a pair of middle rollers 4, 4', and a pair of front rollers 5, 5', and the supplied bundle of fibers is sucked into a guide inlet of a supply device 8 wherein the sucking force is caused by compressed air supplied from a compressed air supply source. Fibers 6 sucked into the supply device 8 are individually separated from the composite bundle 1 by the air force just after leaving the nip point of the front rollers 5, 5', and are fed to a rotor in a liberated condition through the delivery pipe 9 of the supply device 8 by the air stream feeding means. The outlet of the delivery pipe 9 points toward the inside peripheral wall of the rotor 10 as shown in FIG. 2. The rotor 10 is formed in a pot-like shape and is supported by a vertical cylindrical axis 13 rotatably supported by a machine frame 11 through a bearing 12 and is rotated at a high rotating speed by a driving belt 16. The fibers liberated from the bundle l are ejected and deposited successively, adhering to the inside wall of the rotor 10 caused by the centrifugal force and air stream, and rotated by the rotor 10 at a high rotating speed. The liberated fibers thus deposited upon the inside wall of the rotor 10 are collected for rebundling and twisting into a form of a complete spinning yarn l5 and taken up by a pair of take-up rollers 19 disposed downstream of the outlet of the cylindrical axis 13.

In the above-mentioned twisting mechanism, the liberated fibers l adhere to the inside wall of the rotor 10 by the centrifugal force and are successively accumulated, whereby a self-doubling effect is imparted to the rebundled fibers released from the inside wall of the rotor 10. The expression self-doubling effect" is explained as follows. Generally, in the spinning operation, uneveness in the thickness of the products such as a sliver or roving is decreased by so-called doubling of a plurality of the products during the drafting operation. This effect is called a doubling effect. However, in the present case, only the liberated fibers successively fed from the delivery pipe 9 are doubled by their accumulation upon the inside wall of the rotor 10 in the form of mutually superimposed successive layers. In other words, the supplied bundle of fibers l is liberated into numerous individual fibers and doubled successively by the above-mentioned manner. Consequently, unevenness in the thickness of the supplied bundle of fibers 1 can be reduced remarkably. The abovementioned effect is hereinafter called a self-doubling effect. The fiber bundle released from the inside wall of the rotor 10 is positively turned at the position where the bundle of fibers is released from the inside wall of the rotor 10 while each fiber of the fiber bundle does not receive restriction to change in the relative aligned position of fibers because the fiber bundle is accumulated upon the inside wall of the rotor 10 by the centrifugal force due to the high speed rotation of the rotor 10.

As mentioned above, the liberated fibers supplied from the pipe 9 to the inside wall of the rotor 10 are accumulated ina uniform condition of alignment while being provided with a self-doubling effect. Now, supposing that the inside radius of the rotor is R in meter, number of revolution of the rotor is M rpm, the surface speed of the inside wall of the rotor 10 is V meter per min., releasing speed of the bundle of fibers from the inside wall of the rotor 10 is W meter per min., an arbitrary point on the inside wall of the rotor is designated as point P, and the bundle of fibers is released from the inside wall of the rotor 10 at the position designated by point P at the time function I T, the releasing point on the inside wall of the rotor 10 travels along the inside wall of the rotor 10 at a speed of W meter per min. while releasing the bundle of fibers continuously from the inside wall of the rotor 10, and the releasing point returns to the original point P at the time t T 2'rrR/W min., that is, after a passage of 21rR/W min. While the releasing point of the bundle of fibers travels as mentioned above, the rotor 10 rotates M X 27rR/W V/W turns. As the liberated fibers are continuously blown to the inside wall of the rotor 10 while the releasing point is traveling along the inside wall of the rotor, it can be considered that the liberated fibers are blown V/ W times upon the position designated by the takingoff point P until the releasing point returns to the original point P. Now, supposing that the average number of fibers contained in the cross-section of the supplied roving is N, that the draft ratio of the draft element is D and that the surface speed of the front roller is U meter per min., the supplied roving is drafted at V/U times while passing through the draft zone formed between the nip point of the rollers 5, 5' and the inside wall of the rotor 10. Consequently, the bundle of fibers, wherein the average number of fibers n in the crosssection is considered as NU/DV, adheres upon the inside wall of the rotor at every revolution of the rotor 10. Thus, the bundles of fibers, wherein the average number of fibers in its cross-section is n, are doubled by V/ W. In other words, the drafted roving in the liberated condition is self-doubled by V/ W, that is, the produced spun yarn has a doubling number equal to V/W. The above-mentioned doubling operation is performed at any position in the inside wall of the rotor. The fibers accumulated on the inside wall of the rotor 10 only maintain their relative positions along the thickness direction within the bundle of fibers chiefly by the centrifugal force. Further, the releasing points of the bundle of fibers from the inside wall of the rotor 10 are not fixed at one releasing point P resulting in no disturbance of the mentioned relative positions. Consequently, no migration takes place during the twisting operation in the above-mentioned embodiment of the invention, and a spun yarn having uniform thickness due to the self-doubling effect of the rotor rotation can be manufactured.

When releasing the bundle of fibers continuously from the inside wall of the rotor 10, it is necessary to keep the force restricting the free turning of the bundle of fibers at the-releasing point on the'inside wall of the rotor 10 at a suitable magnitude. The force restricting the free turning of the bundle of fibers is mainly the frictional force between the bundle of fibers and the inside wall of the rotor 10. The above-mentioned frictional force may be defined by the product of centrifugal force working on the bundle of fibers by the coefficient of friction between the bundle of fibers and the inside wall of the rotor 10. According to our experimental tests, when the diameter of the largest portion of the rotor 10 is 50 mm, the rotating speed of the rotor 10 is 30,000 r.p.m., the preferable coefficient of friction between the bundle of fibers and the inside wall of the rotor 10 is in a range from 0.2 to 0.7. The abovementioned coefficient of friction was measured by the well-known Roder method at a linear speed of 50 meters per minute. The metallic inside wall of the rotor having a roughened plated surface is suitable for obtaining the above-mentioned preferable condition.

Someembodiments of the manufacturing method of the blended spun yarn according to the present invention are shown in FIGS. 7A, 7B and 7C. These manufacturing methods are characterized by the process comprising liberating a plurality of bundles of fibers of different kinds in a fluid stream, carrying the liberated fibers to the inside wall of a rotor through a delivery pipe or pipes, accumulating the supplied liberated fibers upon the inside wall of the rotor continuously by centrifugal force and the air stream, releasing the accumulated bundle of blended fibers from the inside wall of the rotor while twisting, taking up the twisted bundle of blended fibers through an aperture disposed to the central bottom of the rotor and onto a package. In the above-mentioned explanation, the term different kinds of fibers means fibers different in staple form" or fibers having different fineness or cut length, or different mechanical properties or different colors."

Referring to FIG. 7A, a single roving 31 of a blend of two different fibers is supplied to the draft element, while in FIG. 73 two rovings 31 and 3f of different fibers are supplied to the draft elementin a doubled condition and the liberated different fibers in the double rovings are carried to the inside surface of the rotating rotor 40 through a single delivery pipe 39. On the other hand, in the embodiment shown in FIG. 7C, two rovings 31 and 31' of different fibers are supplied to the respective draft elements separately, and the respective liberated fibers are supplied to the inside surface of the same rotor 40 through the

respective delivery pipes

39 and 39 independently. By the above-mentioned function of the rotor 40, the self-doubling effect can be obtained in the three cases mentioned above. Consequently, a very uniform blending effect can be obtained. That is, as already illustrated in the explanation of the function of the rotor shown in FIG. 2, supposing the average number of fibers contained in the respective rovings are N and N, the bundle of fibers comprising a plurality of fibers, whose number n or n in its cross-section is calculated as n NU/DV or n N'U/DV, are doubled and adhered upon the inside wall of the roller 40. The number of the above-mentioned doubling can be calculated as V/W. Consequently, the bundle of fibers released from the inside wall of the rotor '40 contains two kind of fibers comprising a plurality of fibers represented by the following equation (N N')/D U/W and a perfect blending condition similar to the doubling of V/ W bundles of fibers can be expected. Further, by the twising of the abovementioned system, the blended yarn has novel configuration without migration. Consequently, the blended yarn having superior mechanical properties such as a soft hand feeling, high bulkiness and strong resiliency can be obtained. The mechanisms of the spinning deas that shown in FIG. 1, in which the spinning material is supplied to the back rollers 35, 35' and drafted by the draft zone comprising the back rollers 35 and 35', middle rollers 36 and 36', apron 36" and

front rollers

37 and 37. The drafted bundle of fibers is sucked into the delivery pipe 39 or 39', and carried to the rotating rotor 40 in a liberated condition by the air stream, and the accumulated bundle of fibers is released from the inside wall of the rotor 40 and advanced to the outside of the rotor through a bottom aperture formed through the central hollow shaft 40' of the rotor 40 during the twisting operation and the manufactured blended yarn 44 is taken up onto a package.

The above-mentioned features of the yarn manufactured by the method of the invention will be more clearly understood from the following examples.

EXAMPLE I Fiber used 1.5 den. X 38 mm polyester staple fiber Total draft l8 Yarn count 26' (English system) Delivery speed of the front roller (U) meter/min Rotating speed of the rotor 32,000 r.p.m.

Peripheral speed of the inside wall of the rotor (V) 3,000 meter/min Radius of the rotor 50 mm Taking-up speed of the yarn (W) 50 meter/min Compressed air pressure 0.25 kg/cm Referring to FIG. 8, it was noticed that the fibers contained in the yarn were blended in the cross-section of the yarn. I

It is one of the outstanding features of the invention that a blended yarn having satisfactory blending of fibers can be easily manufactured by the method of the invention in spite of the'very short-cut spinning system whose blending effect is superior to that in the conventional spinning system whosedoubling number corresponds to V/W.

In the above illustration, some embodiments for blending two kind of fibers are explained and the blending principle of the present invention may be applicable to the blending of more than two kinds of fibers.

Further, the blending principle of the present invention may be applied to the so-called direct spinning system, wherein two kind of tows are supplied to the draftcut device of the respective direct spinning equipments separately, next the bundles of fibers produced by the draft-cut device are supplied to a pair of front rollers like those shown in FIGS. 7A to 7C separately or in a doubled condition, then fed to the twisting device in the same way as shown in FIGS. 7A to 7C.

A microscopic test on the spun yarn shown in FIG. 3 proved the lesser extent or absence of fiber migration in the configuration of the yarn. The twist configuration of the yarn shown in FIG. 3 is characterized by a plurality of outer-to-inner continuously, concentrically and spirally layered twisted fibers. There is no definite boundary between the layers and the fibers in the inner layers are provided with a smaller number of spiral coils and smaller coil diameters while fibers in the outer layers are provided with a larger number of spiral coils and larger coil diameters. Fibers of a particular layer are provided with lengthwise uniform coil diameters.

Configuration models of the twisted fibers contained in the conventional yarn and in yarns manufactured by the method of the invention are illustrated in FIGS. 4A, 4B and 4C, wherein fibers in the outer layers are designated with letters a, c and e while fibers in the inner layers are designated with letters b, d andf.

Provided that the number of fibers in the yarn crosssection are equal and respective yarns are subjected to bending deformations under the same loading conditions, the bending deformation of the fibers in the outer layers is larger than that in the inner layers, that is, the outer is the layer, the larger is the contribution of fibers in the layer to the stress of the yarn. On the other hand, it might be well understood that the smaller the coil pitch the larger the coil number and the lesser the resilience is to the bending deformation. In other words, fibers in the outer layer have a weaker resistance to bending while fibers in the inner layer have a stronger resistance.

Consequently, it is clearly understood that the yarn having a twist configuration composed of fibers such as a and b shown in FIG. 4A has a stronger resistance to the bending deformation than the yarn having a twist configuration composed of fibers such as c and d, e and f shown in FIGS. 48 and 4C, respectively. Concerning the torsional deformation, the yarn of the invention is easier to twist than the conventional yarn by the same reason as mentioned above. Therefore, the yarn of the invention shown in FIGS. 43 and 4C is softer than the conventional yarn shown in FIG. 4A.

In the yarn of the present invention, the interference of the fibers in the inner layer to the fibers in the outer layer is very small. In other words, the fibers in the inner layer and the outer layer of the yarn can be deformed independently from each other. Consequently, the frictional resistance between the fibers in the inner layer and the outer layer can be considered as being very small.

On' the other hand, it is well-known that the friction between the individual fibers dominates the resiliency of the yarn in a small range of the deformation. Consequently, it can be considered that the yarn of the invention has superior resiliency.

EXAMPLE 2 A small amount of fibers dyed in black color was blended when spinning a yarn of polyester staple fiber and the yarn manufactured on the system shown in FIG. 1.

The rotation speed of the rotor 10 was 31,000 rpm. and the above-mentioned coefficient of friction measured by the Rc'ider method was 0.46.

The yarn produced was mounted with a tricrosylphosphate liquid, then the yarn was observed with a microscope by inserting a sensitive filter (530 my.) to a polarized light microscope with crossed-nicol. It was found from this test that there was no migration.

EXAMPLE 3 A spun yarn of polypropylene was manufactured in the same spinning condition. The mechanical properties of the yarn are shown in Table 1 together with the mechanical properties of the conventional yarn manufactured by the ring spinning system for the purpose of comparison.

TABLE I kind of yarn Yarn of the Conventional invention yarn Yarn count in English system 21 20.8 Number of twist tums/inch 16.3 16.0 Breaking strength in g. 860 996 Breaking elongation in 20.6 21.5 Bending stiffness CD 0.16 0.21 F 7.1 10.5 F/CD 44 5O I nitted cloth CD 0.18 0.24 F 11.4 18.1 F/CD 63.5 75.4 Bulkiness in cm lg. 73 65 coefficient of compressibility 35.9 39.6

In the Table 1, the bending stiffness of the yarn and its knitted cloth were measured in the following manner.

The hysteresis curve of the bending stiffness of the test piece in a sheet form with respect to the bending curvature of the test piece was recorded. One example of the above-mentioned hysteresis curve is shown in FIG. 5, wherein the average inclination of the curve between the points A and B is represented by CD. It is considered that the test piece is easier to bend, if the value of CT) is larger.

Further, the distance between points A and B is represented by F which is considered as a frictional force at the time of the bending deformation of the test piece in a sheet form. Then the value of F/C D is calculated, and it is considered that the resilience of the test piece in a sheet form is larger if the value of F/CD is smaller.

The above-mentioned method of estimation was confirmed by repeated experimental test. Further, the results obtained by the present method exhibited the socalled functional feeling or handling quality of the test piece of the cloth. Thirty pieces of yarn aligned in a parallel condition with 20 mm width were prepared for the test. The test pieces of knitted cloth were cut in a width of 20 mm and the distance between the grips was 4 mm. The mechanical properties of the yarn shown in the Table l prove the yarn of the present invention has superior resiliency and soft feeling of touch.

ln Table l, the bulkiness of the test piece was measured with the conventional instrument for measuring thickness of the test piece continuously under a changing load. The original thickness of the test piece was measured under a load of 2 g/cm for calculating the specific volume of the test piece. Results in Table I show the yarn of the invention is bulkier than the conventional yarn.

As already explained, the yarn of the present invention has a novel internal configuration wherein there is no migration and each fiber contained in the yarn is provided with a plurality of spiral coils with almost uniform diameter with respect to the yarn axis. Consequently, when the yarn of the present invention is untwisted the yarn can maintain its internal configuration while, in case of the conventional yarn, the yarn loses its twisted configuration by untwisting and then loses its strength, thereof. To make clear the difference of the effect of untwisting of the yarns of the present invention and the conventional yarn, the relation between the residual strength of yarn and the rate of back twist of both yarns are shown in FIG. 6, wherein the curve a represents the case of the conventional yarn while the curve b represents the case of the yarn of the present invention.

As is clearly shown in the diagram, the residual strength of the yarn at the rate of back twist of 100 percent is still more than zero and the residual strength of the yarn at the rate of back twist of 75 percent is more than 30 percent of the original strength. As indicated by the experimental test, it is impossible to impart to the spun yarn of the invention'a no twist configuration. Consequently, it is clearly understood that the spiral configuration of fibers in the outer layers and inner layers of the yarn is not the same. In the above-mentioned illustration, the residual strength of the yarn and the rate of the back twist are defined as follows:

Residual strength Breaking strength of the back twisted yarn Original breaking strength of the yarn Number of turns for back twisting Original number of twist What is claimed is:

1. A method for producing spun yarn on an open-end spinning machine having an open-ended spinning chamber comprising: providing a bundle of fibers to be spun into yarn; transporting said bundle of fibers in an air stream to an inner peripheral surface portion of an open-ended spinning chamber while individually separating the fibers; rotating said open-ended spinning chamber at a peripheral surface speed V to accumulate longitudinally successive, superimposed layers of separated fibers upon the inner peripheral surface portion of said open-ended spinning chamber; longitudinally withdrawing the accumulated fiber layers from the rotating open-ended spinning chamber in the form of spun yarn at a withdrawing speed W to effect selfdoubling of the spun yarn at a doubling number V/ W; and selectively varying the peripheral surface speed V and the withdrawing speed W to provide the spun yarn with a predetermined doubling number V/W during only a single passage through the open-end spinning machine.

2. A method according to claim 1; wherein said pro viding step comprising providing a bundle of fibers composed of at least two different kinds of fibers.

Claims

1. A method for producing spun yarn on an open-end spinning machine having an open-ended spinning chamber comprising: providing a bundle of fibers to be spun into yarn; transporting said bundle of fibers in an air stream to an inner peripheral surface portion of an open-ended spinning chamber while individually separating the fibers; rotating said open-ended spinning chamber at a peripheral surface speed V to accumulate longItudinally successive, superimposed layers of separated fibers upon the inner peripheral surface portion of said openended spinning chamber; longitudinally withdrawing the accumulated fiber layers from the rotating open-ended spinning chamber in the form of spun yarn at a withdrawing speed W to effect self-doubling of the spun yarn at a doubling number V/W; and selectively varying the peripheral surface speed V and the withdrawing speed W to provide the spun yarn with a predetermined doubling number V/W during only a single passage through the open-end spinning machine.

2. A method according to claim 1; wherein said providing step comprising providing a bundle of fibers composed of at least two different kinds of fibers.