ROTARY TWISTER ELEMENT FOR FRICTIONAL OPEN-END SPINNING

Abstract: Rotary twister element suitable to keep under ten­ sion the fibres during the twisting operation in a fric­ tional open-end spinning process, constituted by a solid, hollow, reduced-thickness element (5) with perforated skirt (4), which is internally provided with a suction duct (7) defining a longitudinal slot (6), the edge of which, which constitutes the thread formation line, is suitably inclined relative­ ly to the generatrix of the same solid, hollow element, as a function of the direction of rotation of the solid element, and of the direction of thread extraction. Also a screen (21) is provided for the air dragged by the rotation of the solid element, which may have a cylindrical shape, a cone frustum shape, or the shape of any other revolu­ tion solid.

Description: The present invention relates to a rotary twisting device for frictional open-end spinning, according to the preamble of claim 1. A device of this type is known from BE-A-828 502. In such a device fibres fed to the rotary external surface of a cylindrical rotary element are caused by the suction of the slot, which extends along the generatrix of the rotary element, to become twisted into a thread along the thread formation line, the thread being withdrawn in a direction parallel to the generatrix. In this device the conditions for twisting are rather unstable and only thread with relatively small strength characteristics can be obtained. Another twisting device of the type for friction open-end spinning is known from GB-A-936 628 and JP-A-51 015 043, and comprises a movable perforated plane conveyor at one side of which the fibres to be twisted into the thread are fed and at the opposite side whereof a stationary elongated suction slot is arranged, which extends in a direction inclined to the travelling direction of the conveyor. The direction of the inclination is such that the movement of the conveyor creates on the fibres during twisting a force component directed in the direction of withdrawal of the formed thread. This requires a take-up speed for the thread that is fast enough to tension the thread being withdrawn from the twisting device. Such a device, therefore, allows thread to be obtained at high speed, but the quality and particularly the strength characteristics of the thread are generally not satisfactory because of the action of said component directed in the withdrawal direction, which while favouring high thread production rate does not allow strong interconnection of the individual fibres to provide a thread having high quality and strength. The purpose of the present invention is to provide a rotary twisting device which, by keeping under a proper adjustable tension the fibres during the twisting, and hence drafting and straightening them, allows a thread having high characteristics of quality and strength to be obtained. This purpose is achieved according to the present invention by a device as claimed in claim 1. In such a device, in fact, the speed of fibre dragging in the individual points of the slot, deriving from the rotation of the rotary element, to which the fibres are kept adherent by the suction, has a twisting component having a direction perpendicular to the longitudinal edge of the slot, and an axial component in the direction of the slot edge, which axial component is directed in the opposite direction relatively to the thread withdrawal direction, that means that the fibres of the thread being formed are subjected to an axial force and are kept under tension while being twisted and this results in a high quality and strength of the thread formed. It should be observed then that the thread tensioning can be easily and rapidly adjusted, as desired, by simply varying the inclination degree of the longitudinal slot edge, and therefore, definitely, by varying the inclination of the open end of the suction duct: a greater inclination shall cause, evidently, a higher tensioning. The invention is now clarified in greater detail by referring to the hereto attached drawings, which illustrate a preferred form of practical embodiment, given to purely exemplifying and not limitative purposes, in that in any case, technical and structural variants may be supplied within the scope of the invention. So, for example, the hollow rotary element may have a hollow cylindrical shape, a hollow cone-frustum shape, or the shape of any other hollow revolution solid. In said drawings: Fig. 1 shows, in a perspective fragmentary scrap view, a device for frictional open-end spinning, according to the invention; Fig. 2 shows a sectional plan view of the device of Fig. 1; Fig. 3 shows a longitudinal view taken along A-A path of Fig. 2; Fig. 4 shows a front fragmentary view taken along B-B path of Fig. 3. Referring to the Figures, with 1 a feed unit is generally shown, per se well known in the art of open-end spinning, which has the task of separating from one another and rendering parallel to one another the fibres of a fibre web 2 being fed and to deliver them, through a channel 3 (see specifically Fig. 2), onto a perforated skirt 4 of a rotary twisting element constituted by a hollow, reduced-thickness element such as a cylinder 5. At a longitudinal area or slot 6 adjacent the skirt 4 (see specifically Fig. 3), a suction is applied by a stationary suction duct 7, connected to a suction source not shown in the figures, which duct enters inside the perforated cylinder 5 and is kept fastened by a support 8. Said perforated cylinder 5 is rotatably supported, cantilevered, by a structure 9, through bearings 10 (see specifically Fig. 2) and is driven in rotary motion according to the direction of arrow 11 by a transmission belt 12 engaged on a pulley 13 integral with a shaft 14. The feed of fibres to the open end 15 of the thread 16 being formed , which is withdrawn in the direction of arrow 17 by means of withdrawing rollers 18, is performed, through the channel 3, in a direction generally parallel to the longitudinal edge 19 of the slot 6, constituting the thread formation line, and in the opposite direction relatively to the thread withdrawel direction 17, as it can be clearly seen in Fig. 2. On the other side, the suction slot 6 and consequently its longitudinal edge 19 is positioned inclined relatively to the generatrix of the cylinder or, which is the same, relatively to the cylinder axis 20. By considering the direction 11 of cylinder rotation and the direction 17 of thread withdrawal, the slot 6 and, in particular, the longitudinal edge 19, which constitutes the thread formation line, is be inclined as shown in Fig. 3, so that the speed of fibre dragging in the individual points, e.g., in a point P (see Figure 3), of the line 19 of thread open end formation, is resolved in an twisting component v t perpendicular to the thread formation line and in an axial component v a directed in the opposite direction relatively to the direction 17 of thread withdrawal and providing an axial force on the fibres causing proper tensioning thereof while being twisted. Finally, a shield 21 is positioned close to or in contact with the cylinder 5 externally thereto (see Fig. 4) and upstream the slot 6 relatively to the direction 11 of rotation of the same cylinder, to stop the air dragged by the rotation of the cylinder and prevent it from having the possibility of disturbing the open end 15 of the thread being formed.

Claims: Rotary twisting device for frictional open-end spinning, comprising a hollow rotary element (5) having a reduced thickness and a perforated skirt (4), and a stationary suction duct (7) having an elongated suction slot (6) in the interior of the rotary element (5) adjacent the skirt (4), a longitudinal edge (19) of said slot (6) defining a thread formation line, characterized in that said edge (19) is inclined relatively to the generatrix of the rotary element (5) and the inclination relative to the rotational direction of the rotary element (5) and to the thread withdrawal direction (17) is such as to submit the fibres (2) along said thread formation line to an axial force opposing the thread withdrawal. Rotary twisting device as claimed in claim 1, characterized in that a feed channel (3) for the fibres (2) extends in a direction generally parallel to said edge (19), whereby the feeding direction of the fibres (2) is generally opposite to the thread withdrawal direction (17). Rotary twisting device as claimed in claim 1 or 2, characterized in that a stationary air stopping shield (21) is positioned close to or in contact with said rotary element (5) externally thereto and upstream said slot (6) relatively to the rotational direction of said rotary element (5).

Inventors: BOTTOS, ROBERTO, FERRO, FRANCESCO, GREGO, FRANCESCO, NERLI, GIOVANNI
Applicants: SAVIO S.P.A.
Application year: 1987
Main classification: D01H4
IPC codes: D01H4