The invention relates to open end spinning of textile yarns at a high rate of production and improved quality whereby the staple fibres are transported as individual fibres in an air stream from a fibre opening device to a fibre assembly zone where the fibres are joined to the freely rotating tail of the forming yarn, and thereafter the fibre assembly twisted to form yarn.

Previously the development of friction spinning for general use in the production of textile yarns has been retarded by the perceived need to form the fibre assembly and insert the twist simultaneously in the same operational phase. This concept of friction spinning typically produces a structure of spirally oriented fibres rather than straightened and parallelised fibres. Also substantial slippage occurs between the fibre assembly and the friction surfaces, as a result of the wide gap between the friction surfaces that is necessary in order to accommodate the dual functions of fibre assembly and twisting. The spirality of the fibre assembly and the lack of positive control of the application of twist to the fibre assembly results in a weak yarn with variable twist rates.

Similar difficulties have also occurred with yarn produced in other friction spinning systems, even when the phases of fibre assembly and twisting have been separated, as in such systems provision has not been made to ensure that the rotation of the forming yarn is maintained in an open-end condition to the tip of the tail and that such rotation is in substantial synchronisation with the twist inserted by the friction surfaces. The same problems of weak yarn and variable twist beset known vortex spinning systems.

These problems are exhibited in the process described in the German Patent Application No. DE 3348045.0 which endeavoured to spin fibres ducted into a wide funnel shaped air chamber fitted with a series of pressured air jets to produce a vortex air flow increasing in circumferential velocity towards the narrow end of the funnel, where an air exhaust tube, serving also as a spinning tube, is connected to a suction source. Fibres carried by the outflowing air-stream, are picked up by the tail of the forming yarn in the exhaust tube, but the fibres are necessarily coiled in structure around the forming yarn as the

vorticular speed increases towards the exhaust tube. The forming yarn, with the coiled fibres, is withdrawn from the exhaust tube through the funnelled vortex to a withdrawal tube axially aligned with the exhaust tube. A supplementary twisting unit is located in the withdrawal tube. It is not feasible in such a system to add twist to that which is inserted vorticularly at the open end of the tail. Neither is it possible to synchronise the rotation of the open-end tail with the supplementary twisting unit. False twist therefore results from the supplementary twisting. Accordingly, true twist in the finished yarn will depend on the variable level of twist inserted at the yarn tail and so the yarn will be weak. Further the incidence of true twist insertion cannot be accumulated by increasing the rotational speed of the twisting unit above that inserted at the tail. The result is high production rates of high quality yarn is not achieved.

The present application presents solutions to the previous difficulties and constraints encountered in the known practice of open end spinning systems, including known friction spinning systems.

It is the object of the present invention to provide a method of establishing a fibre assembly for forming yarn by the open-end friction spinning technique, that overcomes or reduces the above discussed problems, and enables high production rates with satisfactory degrees of twist insertion and a high quality.

With this object in view there is provided a method of fibre assembly for open-end spinning of yarn by a twisting unit, comprising delivering air entrained fibres into a defined assembly zone, maintaining a circumferential air flow around the air entrained fibres in the assembly zone, said circumferential air flow being of a pressure to radially compress the fibre assembly in the assembly zone, and being in the required direction of twist of the finished yarn as governed by the twisting unit, and withdrawing air from said assembly zone in the axial direction of entry of the fibres, and withdrawing the assembly of fibres formed in the assembly zone in the opposite axial direction to pass to the twisting unit.

Conveniently, the assembly zone is formed by an internal cylindrical surface and the air flow enters the assembly zone in a direction substantially tangential to said cylindrical surface. The fibre laden air entering the assembly zone axially is encircled and radially squeezed by the circumferentially moving air, so the air-borne fibres, and the tail of the forming yarn that extends into the assembly zone, are substantially free of contact with the circumferential surface forming the assembly zone, and which is stationary. Thus a continuous laying up of fibres and withdrawal of the fibre assembly is possible with the forming yarn having a true open end. The pressure of the encircling air compresses the fibre laden airstream to thereby promote the attachment of the fibres to the tail of the forming yarn and prevent fibres flying to waste, while simultaneously assisting the rotation of the tail of the forming yarn as an \'open-end\'. The air which conveys the fibres to the assembly zone stripped of fibres that have adhered to the open ended rotating tail, proceeds to the remote end of the assembly zone to a suction source, together with the pressured air. The outflowing airstream, being in the opposite direction to the withdrawal of the fibre assembly, applies a beneficial axial tension to the fibre assembly to keep the fibres straight and thereby aiding the tensile strength of the yarn. The fibres are initially prepared in a conventional fibre opening device, such as a beater, and are then carried in an airstream, such as through a duct, to the fibre assembly area.

The fibre assembly can be withdrawn axially into a friction spinning device such as that disclosed in Australian Patent 501999 or U.S. Patent 4091605, the disclosure in each of which is incorporated herein by reference.

Normally the axis of the fibre assembly zone would be disposed at right angles to the plane of rotation of the friction twisting members and thus, on a space consideration basis, a duct delivering the air entrained fibres can be located at right angles to the passage defining the assembly zone, or less favourably, rearwardly inclined at an acute angle. In these configurations, the air stream and the fibres are subject to a sudden major change in direction in

order to enter the fibre assembly zone. This has an adverse influence on the air and fibre flow causing turbulence and affecting the nature of the fibre assembly structure. It is not possible to align the fibre feed duct more directly with the assembly zone passage so that the flow would not be severely interrupted from a regular course, because of the constructional and design constraints imposed by the nature, the action, and the location of the rotating friction surfaces.

Furthermore good operation of an open-end system demands that the rotation of the fibre assembly be unimpeded, the tail short, and the fibre assembly zone close to the entrance of the fibre assembly between the rotation friction surfaces. Otherwise unfavourable whipping of the fibre assembly occurs and the steady rotation of a centralised fibre assembly, as required to be imparted by the action of the friction surfaces, is negated.

In accordance with another aspect of the present invention there is provided in a method of open-end spinning yarn from fibres including the steps of entraining the fibres in an air stream, delivering the entrained fibres to a fibre assembly zone, attaching the fibres in said assembly zone to a revolving fibre assembly tail, withdrawing the tail with the fibres attached thereto from the assembly zone in a direction opposite to the air flow in the fibre assembly zone, and passing the fibre assembly between two rotating friction surfaces of revolution and in contact with each thereof to impart twist to form a yam, characterised in that said fibre assembly zone is located within a duct having an axis aligned to pass between said friction surfaces and inclined to the plane of rotation thereof, said fibres being delivered into said fibre assembly duct at a location between the assembly zone and the rotating surfaces and at an angle not less than about 90° to the axis of the fibre assembly duct downstream of the junction with the fibre assembly duct.

Conveniently the fibres are conveyed to the fibre assembly duct along a path substantially parallel to the common plane of rotation of the respective members upon which the friction surfaces are formed. Preferably the friction surfaces are each equally and oppositely inclined to the axis of rotation, and arranged to define therebetween a gap through which the assembly of fibre

is drawn, in contact with each friction surface, after leaving the assembly zone. The members on which the friction surfaces are provided rotate in opposite directions at the same peripheral speed so the "nip area", through which the assembly of fibres passes, retains a fixed position in axial alignment with the fibre assembly duct axis.

In previously proposed open end friction spinning apparatus, wherein the fibre assembly is drawn through a gap between two rotating friction surfaces, there existed two opposing friction forces. One friction force is in the circumferential direction to effect the rolling or twisting of the fibres to form the yarn, while the other friction force is in the axial direction arising from the fibre assembly being drawn through the gap between the friction surfaces. The axial friction force produces a tension in the twisted fibre assembly that can result in yarn breakage that reduces reliability and production rates. __ These problems can be significantly reduced by using tapered friction surfaces to define the gap through which the fibre assembly is drawn, and arranging the fibre assembly to enter the gap at the smaller diameter ends of the tapered surfaces and exit from the larger diameter ends.

As a result of this conformation, and the fact that the members upon which the friction surfaces are formed are driven at identical rotational speeds in opposite directions, the surface speeds of the friction surfaces graduate from slower to faster over the length of the gap from the entry end to the exit end. Because the tapered surfaces, interact frictionally on either side of the forming yarn, the axial friction between the fibre assembly and the friction surfaces is used advantageously to augment and facilitate the withdrawal of the fibre assembly by the propulsive screwing effect induced by the matching increase of surface velocities from the smaller to the larger end of the tapered friction surfaces.

One practical arrangement of the invention will now be described with reference to the accompanying drawings. In the drawings:

Figure 1 is a diagrammatic representation of the method of

spinning fibres into yarn;

Figure 2 is an axial sectional view of the fibre assembly unit and friction twister and

Figure 3 is a sectional view along line 3-3 in Figure 2. Referring now to Figure 1 , a sliver 1 of fibres is fed into a suitable beater 2 where the fibres are individually separated from the sliver and launched into an airstream. Various conventional types of beaters are known that may be used for this purpose. The rate of feed of the sliver is controllable, in the known manner, according to the specific requirement of the fibres, to match the required count of yarn being produced, and the offtake rate of the spun yarn.

The fibres from the beater 2 are carried in an airstream through the duct 3 and delivered to the fibre assembly unit 4. The fibre assembly unit is one major aspect of the present invention and will be described in greater detail hereinafter. Air is withdrawn from the assembly unit via the duct 5 by the suction source 7. The assembly of fibres issuing from the unit 4 is passed to the friction twister unit 8 and the finished twisted fibre yarn is withdrawn from the twister unit 8 by the withdrawal rollers 11 and thereafter passed to the yarn reception spool 12.

Referring now to Figure 2, the separate fibres entrained in the air are carried by the duct 3 from the beater as shown in Figure 1 into the fibre assembly unit 4, comprising the tubular member 17, defining the central fibre assembly zone 16 of cylindrical form open at each end 20 and 21. The open end 20 communicates with the suction device 7 as seen in Figure 1 , and the open end 21 communicates with the fibre supply duct 3, that delivers the fibres from the beater to the assembly zone.

The shield 18, located in the area of the junction of the duct 3 and tubular member 17, is contoured to provide a smooth transition surface to change the direction of flow of the fibres from the duct 3 into the tubular member 17. Also the shield 18 prevents the incoming fibres from impinging upon and becoming prematurely attached to the fibre assembly moving from the assembly zone 16 to the twisting device 8 as will be discussed further hereinafter.

The duct 3 is tapered so as to accelerate the air and fibres to achieve a straightening of the fibres from the disorientation condition that can exist on exiting from the beater. As a result, the fibres finally delivered into the assembly zone 16 are substantially straight and extend in a direction substantially parallel to the direction of the air flow. Also the fibres are spatially distributed at the larger entry end of the duct 3 and as the fibres and air flow accelerates towards the smaller delivery end, due to the reducing cross sectional area of the duct 3, straightening of the fibre occurs. At the same time the fibres are progressively condensed laterally. The resulting straightening, parallelising and layering of the fibres, and the protection of the fibre stream by a boundary layer of air, results in the mass of fibres assuming a rounded form similar to a hollow disconnected warp as they enter the assembly zone 16.

The continuous cavity 25 is provided about the exterior of the tubular member 17 at the fibre assembly zone 16 (not shown) which is in communication via the passage 26 with a source of compressed air. The cavity 25 is in communication with the fibre assembly zone 16 through ports or slots 28 (see insert \'A\' Figure 2) passing through the wall of the tubular member 17 in a tangential relation to the internal wall of the tubular member 17. At least two such ports or slots 28 are provided in diametrically opposite locations and in a common transverse plane to the axis of the assembly zone 16.

A rotational air flow is created in the fibre assembly zone 16, by the disposition of the slots 28 and promotes the rotation of the assembly of fibres within the assembly zone 16 about the axis thereof. The tangential aspect of the ports or slots 28 is selected so that the direction of rotation imparted by the air to the fibre assembly is the same as the direction of twist as inserted by the twisting unit 8. In addition to creating the above referred to rotational air flow in the assembly zone 16, the air entering through the ports or slots 28 is of a pressure sufficient to effect a compressive compacting of the fibres in a generally inward direction away from the wall of the tubular member 17 and towards the axis of the assembly zone 16.

This action of the pressurised air establishes in addition to forming a condensed fibre assembly also provides a fibre free clearance between the fibre assembly and the internal surface of the tubular member 17 so that the fibre assembly can freely rotate as an open end. Thus true open end conditions are established for the tail of the forming yarn and the fibres being applied thereto.

It is also to be appreciated that the suction device 7 withdraws air from the assembly zone 16 towards the open end 20 of the tubular member 17, and thus an axial tension is maintained on the fibre during the assembly of the fibres. This beneficially assists in maintaining the fibres straight during the fibre assembly process.

The condensed fibre assembly is withdrawn from the end 21 of the tubular member 17 through the axially aligned open end 29 of the shield 18 to enter the friction spinning or twisting device 8 such as that described in my prior U.S. Patent No. 4091605 and Australian Patent No. 501999, previously incorporated into this specification. The shield 18 is important in guiding the incoming fibres from the duct 3 to change direction to enter axially into the assembly zone 16 without impinging on the condensed fibre assembly being withdrawn to enter the twisting device.

Referring now to the preferred form of twisting device 8, as shown in detail in Figure 2, it comprises a stationary support base 50 forming part of the basic structure 35 and rotatably supports the outer friction ring 51 and inner friction ring 52. The outer friction ring 51 rotates about the axis 53 and the inner friction ring 52 about the axis 54, eccentric to the axis 53.

The outer ring 51 has an internal frustro conical surface 55 concentric with the axis 53 and the inner ring 52 has an external frustro conical surface 56 coaxial with the axis 54. The angles of the respective cones are equal and the respective axes are arranged so that at one location a narrow gap therebetween is provided as indicated at 58. The assembly of fibres from the fibre assembly zone 16 is passed through this gap 61 to have twist applied thereto as referred to further hereinafter.

The inner frusto conical surface 55 of the outer ring 51 is of a

friction material, such as rubber, and the outer surface 56 of the inner ring 52 is of the same or similar friction material. The inner and outer surfaces 55 and 56 are arranged to be in frictional driving contact at 60 as seen in Figure 3. The inner ring 52 is coupled by the co-axial shaft 59 to the drive pulley 58 and the pulley can be coupled to a suitable drive motor such as an electric motor (not shown). This drive arrangement results the rings 51 and 52 rotating both so the conical surfaces move at the same peripheral speed in opposite directions.

The fibre assembly passes between the inner and outer rings at 58 in frictional contact with the respective frictional surface whereby the fibre assembly is rolled on the axis thereof to apply true twist to the fibre assembly. Also because of the surfaces moving at the same peripheral speed, albeit in the opposite directions, the assembly of fibres will remain in a secure and constant location between the two surfaces.

It will be understood that other drive constructions can be used to drive the inner and outer ring to achieve the same peripheral speed of the respective inner and outer rings to retain the gap 61 in the fixed location relative to the fibre assembly issuing from the assembly zone 16.

As seen in Figure 2, the location of the gap 61 is in alignment with the end 21 of the tubular member 17 and the guide tube 29, through which the fibre assembly is withdrawn from the assembly zone 16. It is also seen that the plane in which the rings 51 and 52 rotate is inclined with respect to the axis of the tubular member 17 and thereby allows the duct 3, that delivers the fibres into the tubular member 17, to be similarly inclined thereto. This provides for a smoother transition of the direction of travel of the fibres as they enter the tubular member 17 to pass to the assembly zone 16, and also shortens the distance between the assembly zone 16 and entrance to the gap 61 between the rotating friction surfaces 55, 56.

Also as previously referred to, as the friction surfaces 55 and 56 are each inclined to their respective parallel axes of rotation, and as the fibre assembly enters the gap 61 at the smaller diameter end thereof, the fibre assembly is subjected to an increase in peripheral velocity of the friction

surfaces as it passes from the small diameter entry end to the larger diameter exit of the gap 61.

This aids in promoting the forward passage of the fibre assembly through the gap 61 and so reduces the tension required to be applied to the fibre assembly by the withdrawal rollers 11 to pull the yarn through the twisting device 8.