Open-end rotor spinning arrangement

Details Open-end rotor spinning arrangement Open-end rotor spinning arrangement

2000-10-16

2001-08-07

Worrell, Danny (Department: 3741)

Textiles: spinning, twisting, and twining

Apparatus and processes

Open end spinning

Reexamination Certificate

active

06269623

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of German Patent Application DE P 19949533.5, filed Oct. 14, 1999, herein incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to open-end spinning arrangements. More particularly, the present invention relates to an open-end spinning arrangement basically having a rotatable spinning rotor, a fiber guide conduit with an exit mouth for delivery of spinning fibers into the spinning rotor, and a yarn withdrawal nozzle for withdrawing a yarn formed of the fibers from a transition zone within the spinning rotor and simultaneously for rollingly and slidingly deflecting the yarn over a yarn contact surface of the yarn withdrawal nozzle to impart a false twist thereto. In the present invention, the yarn withdrawal nozzle has a means for reducing the false twist within a zone extending over a circumferential portion of the yarn withdrawal nozzle, the false twist reducing means and the exit mouth of the fiber guide conduit being arranged relative to the direction of the rotor rotation such that actual twisting of the yarn is reduced thereat.
BACKGROUND OF THE INVENTION
When producing yarns in accordance with an open-end spinning process, the yarn is drawn out of the interior of the rotor via a withdrawal nozzle. A yarn tail turns because of the rotation of the rotor and provides the yarn with a real twist. Because of the rolling and sliding movement of the yarn over the surface of the withdrawal nozzle, a temporary twisting (i.e., a false twist) in the same direction is simultaneously generated. It is possible to improve the spinning stability during the open-end spinning process by an increase of the false twist. In accordance with the principle of the twisting compensation in the tensed yarn, both portions of the twist are propagated opposite to the yarn withdrawal direction in the yarn as far as the rotor groove and produce the transition zone thereat.
The length of the transition zone has an effect on the formation of wrap fibers, or so-called belly bands. Wrap fibers are individual fibers which have not been, or only incompletely have been, twisted into the yarn core, and which then are wound in alternating directions of rotation partially loosely, partially quite tightly, around the yarn periphery. Wrap fibers are increasingly formed by an increase in false twists, and the formation of such wrap fibers also takes place unevenly. The yarn structure suffers from this effect, and the range of application of open-end rotor yarns is limited.
It is known from German Patent Publication DE 39 34 166 A1 to affect the production of yarn in respect to spinning stability and hairiness by means of a suitable design of the withdrawal nozzle, and thereby to affect the formation of false twists. The yarn withdrawn from the rotor rolls over the surface of the orifice funnel of the yarn withdrawal conduit and receives a false twist in the process. This false twist formation is reduced respectively during and after passing notches in the yarn withdrawal nozzle, which essentially extend in the yarn withdrawal direction. In the deflecting area, the yarn is always at least partially in contact with the surface of the yarn withdrawal nozzle. Protrusions, which are arranged exactly in the center between two notches, are intended to have the effect of napping the yarn, while simultaneously providing good spinning stability. A regularly alternating contact of the yarn between the notch and the protrusion is intended to permit stable spinning on the one hand, and to cause a desired hairiness in yarn on the other hand. The yarn is plucked and thereby brought into a hairy state. Hairiness is partially caused in that outer fibers, which are not completely bound up in the yarn, are partially released from the yarn bundle and project outward. The notches or grooves cause the yarn to oscillate. The yarn oscillations are propagated as far as into the rotor groove and affect the spinning stability, the yarn structure and the yarn quality.
German Patent Publication DE 36 34 567 A1 discloses a device for drawing the yarn out of the yarn collector groove of the rotor of an open-end spinning arrangement. The surface of the yarn withdrawal nozzle, on which the yarn slidingly rolls, has sectors in the circumferential direction, in which the coefficient of friction is less than in the remaining sector or sectors. Because of the reduced friction, the yarn is given a lesser amount of false twist than outside of feeding fiber zone. Customarily, the fiber feeding zone is defined by the position of the fiber guide conduit and its orifice. The false twist is imparted to the yarn at the withdrawal nozzle. However, the wrap fibers, or so-called belly bands, are predominantly formed in the transition zone, i.e. in the rotor groove or in fiber feeding zone. The sector with the locally limited change of the coefficient of friction between the yarn and the withdrawal nozzle surface is positioned in respect to the location of fiber delivery in such a way that the reduction of false twist formation in the course of the passage of the yarn through fiber feeding zone takes place in the rotor groove.
The separation point of the yarn from the rotor groove is the location in which the yarn undergoes the greatest stress during withdrawal. The extent of yarn between the rotor groove and the deflecting zone caused by the withdrawal nozzle is subjected to greater twisting by the false twist than would result by the rotor rotation alone. The increased twisting imparted at the separation point results in an improvement of the spinning stability. Therefore the maintenance of a false twist formation is usually desired.
OBJECT AND SUMMARY OF THE INVENTION
An object of the invention is therefore to lower the probability of the formation of undesired wrap fibers or so-called belly bands. In accordance with the invention, this object is attained by an open-end rotor spinning arrangement wherein the yarn withdrawal nozzle of the spinning arrangement has a depression in the yarn contact surface of the yarn withdrawal nozzle which is abruptly offset in the circumferential direction of the yarn withdrawal nozzle and which has a depth and an extent in the circumferential direction of the yarn withdrawal nozzle such that the yarn essentially loses contact with the yarn contact surface of the yarn withdrawal nozzle over a deflection distance in the direction of the yarn withdrawal and over an angular extent in the circumferential direction of the yarn withdrawal nozzle of at least about 10 degrees.
This yarn withdrawal nozzle not only causes a controllable complete interruption of the false twist formation, but even a removal of the false twist present in the yarn tail. The yarn pulling force of the rotating yarn tail is diminished to approximately zero simultaneously with the drop of the false twist moment. As tests have shown, this removal of the false twist in the short period of time surprisingly has no adverse effects on the spinning stability.
The fibers collected in the rotor groove make a transition from an essentially untwisted condition in the fiber collection groove into a twisted condition in a zone prior to the point at which the fibers separate from the groove. This area within the rotor groove is called a transition zone. When the yarn, and therefore the transition zone, passes through the area of fiber feed into the rotor groove, and when the fibers are tied up in this zone, the probability of the formation of wrap fibers increases. By means of a yarn withdrawal nozzle in accordance with the invention, the transition zone can be shortened at the location of the fiber delivery to the rotor groove to such an extent that it becomes possible to considerably reduce the formation of wrap fibers or belly bands. The interruption of the contact of the yarn tail with the yarn withdrawal nozzle leads to a brief change, or reduction, of the twisting of the yarn tail and to a displacement of the force equilibrium between the yarn twist moment and section

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