FRICTION OPEN-END SPINNING PROCESS AND DEVICE TO PRACTICALLY EMBODY IT

Abstract: Friction open-end spinning process, wherein the fibres of the feeding fibre sliver (3), once discretized, are sucked by a suction slot on a revolving twister element, provided with perforated surface (17), to feed the free of the yarn being formed, characterized in that the fibres are fed in direction parallel to the free end (29) of the yarn (23) be­ ing formed, are kept under an adjustable tension throughout the twisting operation, and are subjected to a progressively increasing twist, from the open end of the end of the yarn being formed onwards. The device embodying the above process substantially uses as the twister element a revolving flat disc (13) provid­ ed with perforations (17) arranged according to an annulus, which cooperates with a sucking slot (19), the edge of which, constituting the yarn formation line, is positioned ac­ cording to a chord of said disc.

Description: The present invention relates to a spinning process and device of the friction open-end type. From the present state of the art DE-A-2361313 and GB-A-9366281 processes and devices for open-end friction-spinning are known, in which the fibres of a feeding sliver, after being opened by a discretization unit, are conveyed onto a generally revolving or anyway moving twisting element, provided with a perforated surface and cooperating with a suction duct, which defines a slot positioned across the moving direction of the twisting element at the side thereof opposite the fibre feed side. The discretized fibres are fed to the free end of the yarn being formed, also thanks to the air jet induced in the said suction duct, exactly in correspondence of said suction slot, where they condense because of the effect of suction and, while being kept adhering to the twisting element by this suction, are conveyed by said element. As soon as they come in the proximity of the rear edge of the suction slot, and begin hence to be no longer influenced by said suction, they roll up around each other and gain twist. Summarizing, the fibres are condensed and twisted due to the effect of the forces caused by the suction and the motion of the twisting element. The yarn which is thereby formed is then extracted along the direction of the suction slot by draw-off rollers and is finally wound and collected on a package. Now, such spinning processes and devices of the prior art show drawbacks, which are reflected on the quality of yarn. In the process and device of DE-A-2 361 313, the fibres deposited on a perforated linearly movable conveyor are caused to be twisted along a yarn formation line extending transverse to the moving direction of the conveyor. They therefore undergo a force directed perpendicularly to the plane of the perforated conveyor surface (suction force) and a frictional force acting in the direction of movement of the conveyor and perpendicularly to the withdrawing direction of the formed yarn. This results in an unfavourable composition of forces for obtaining a satisfactory twist and a high yarn quality, and the obtained yarn is rather of poor strength. In the process and device of GB-A-936 628 the suction slot or slots are arranged so as to form an angle with respect to the travelling direction of the perforated twisting element, which may be a rectilinearly movable conveyor or a rotatable disc. The orientation of the suction slots is such that the frictional force originated by the motion of the perforated twisting element on the fibres results in a component extending in the direction of the yarn formation line favouring conveyance of the fibres from the open end towards the already twisted end of the yarn. Besides requiring proper withdrawing action in order to cause sufficient tensioning of the yarn for withdrawal, the conditions of open-end twisting are also unfavourable in this known process and device, owing to the component which tends to drag the fibres toward the twisted end of the yarn. In summary, in the known process and device the lack of a proper tension on the fibres not only limits the posibility of stretching and straightening of the same fibres, but also causes the twist structure to be not closed enough, so that the produced yarn results by nature swollen and with poor strength. In a case of a cylindrical twisting element, furthermore, as the twisting of the fibres is substantially depending on the dragging force applied by the motion of the twisting cylinder, which is constant along a generatrix of the cylinder, and hence along the whole length of the suction slot, so that the fibres undergo a twisting action inversely proportional to the radius or thickness of fibre agglomerate and hence to a twisting action practically null at the outlet from the slot, and gradually increasing towards the open end of the yarn, it derives that said end, by revolving at a high rpm value, results strongly centrifuged, which causes a loss of fibres, especially of short fibres, as well as a reduction in yarn evenness, and furthermore a high twist takes place in correspondence of said end. The purpose of the present invention is Precisely that of obviating said drawbacks and supplying hence a spinning process and device of the friction open-end type, which provides for the fibres to be kept under a proper tension during their twisting, as well as for the application of a twisting progressively increasing from the open end of yarn onwards, said open end thus being no longer undergoing a high centrifuging and twisting, which constitutes and optimum condition for obtaining a yarn having high characteristics of quality and strength. This purpose is achieved by the invention as claimed in main process claim 1 and main device claim 4. Preferred features of the invention are claimed in claims 2,3 and 5 to 11. The above said purpose is therefore substantially and simply achieved by the fact that the suction slot is positioned with the yarn formation line along a chord of the twisting element, which is constituted by a revolving disc provided with perforations according to an annulus pattern, the position relative to the rotational direction of the twisting element being such that the fibres become subjected to an axial force opposite to the draw-off direction. The suction slot extends hence from the rim of the disc up to the proximity of the revolution centre of said disc, and is limited to a portion of perforated annulus of the same disc. By this arrangement, indeed, the dragging speed of the fibres in the individual points of the slot is no longer constant, but it varies with the distance of said point from the revolution centre and it hence increases linearly from the centre to the rim of the disc, and moreover each dragging speed can be resolved into one component axial to, and into one component perpendicular to the yarn. Now, the axial components of the speeds, all of which have the same intensity, which is equal to the product of the angular velocity of the twisting element by the distance of the yarn formation line of the suction slot from the disc diameter, parallel to the same slot, is directed opposite to the yarn draw-off direction, which means that the fibres of yarn being formed are tensioned with a consequent better straightening of the fibres and better closure of the twist and hence with a yarn having higher strength and quality being obtained. On the other hand, from the above the possibility results of an easy and fast adjustment as desired of the said tensioning of the fibres, by simply varying the intensity of the axial components of the speeds, and, after all, with the disc velocity being the same, by varying the above said distance between the slot and the disc diameter parallel to the slot: to increase the tension applied to the fibres, increasing the said distance by properly adjusting the position of the slot relative to said diameter shall be enough. The perpendicular components of the speeds, which are the generators of the fibre twist, are instead not constant along the yarn formation line, but they vary linearly like the dragging speed, and hence, the shorter such distance, the smaller said perpendicular components, which precisely allows the centrifuging of the open end of yarn to be limited, and a tension gradually increasing from said end to the point of complete yarn formation to be conferred. The invention is now better clarified with reference to the attached drawings, which illustrate a preferred form of practical embodiment supplied to purely exemplifying but not limitative purpose, in that technical and structural variants can be supplied at any time within the scope of the present invention. So, for example, the revolving twisting element, instead of being a flat disc, can be a hollow conical disc, with its point being directed towards the discretization unit or to the opposite direction, or it can have the shape of a small cylinder mounted on outer supporting bearings, wherein the perforated surface is provided in the flat basis of the cylinder. In this latter case, the central revolution axle is eliminated, so that it is possible to provide the perforations on its whole surface, and not only on an annulus area, thereby the advantage being obtained that it becomes possible to increase the length of the suction slot up to come to the centre of the cylinder, wherein the perpendicular component of the speed acting on the yarn end gets to zero, and hence to reduce, as desired, the twisting effect on the open end of the yarn being formed. On the other hand, the perforated base of the small cylinder, besides being flat, can also be either concave or convex. Finally, a differentiated pattern of perforations of the surface of the twisting element, i.e., with a hole-to-solid percentage variable along the yarn formation line, or a differentiated surface treatment or finishing (roughness) allowing a variable friction coefficient between yarn and twisting element to be attained, can be other elements onto which one can act to the purpose of achieving such values of axial tension and fibre twisting as to ensure the accomplishing of a yarn endowed with optimum quality characteristics. In the drawings: Fig. 1 shows in partial perspective view a device for friction open-end spinning according to the invention; Fig. 2 shows a plan sectional view of the device of Fig. 1; Fig. 3 shows a partial front view taken along the path AA of Fig. 2, showing the twisting element of the device of Fig. 1; Fig. 4 shows the vectorial representation of the speeds along the yarn formation line of the device of Fig. 1; Figs. 5 to 9 show lateral sectional views of variants, they too according to the invention, for the twisting element. Referring to the Figures, 1 generally indicates a feed unit, per se well known in the open-end spinning art, comprising a condenser 2, the task of which is that of condensing or compacting a fibre sliver 3 being fed to the device, to cause it to assume a flat shape of rectangular cross section, suitable to be pinched between a pressure plate 4, onto which a spring 5 reacts, and a feeding roller 6, driven by an electrical motor 7. The plate 4 applies to sliver 3 a determined pressure strength, and owing to the friction existing between the sliver 3 and the roller 6, this latter performs a driving action on sliver 3, which is thus fed to a discretization unit 8, provided with teeth and pins and driven by an electrical motor 9, so that sliver 3 is opened into descrete fibres. The discretized fibres 10, also thanks to a stream of intaken air induced in a fibre feed channel 11 by the suction (arrow 12) created by a vacuum source not shown in the figures, are conveyed onto a twisting element 13, constituted by a revolving disc, the shaft 14 of which, rotatably supported by bearings 15 (see Fig. 2) is made revolve according to the direction of the arrow 16 (counterclockwise in the figures) by means not shown. Said twisting disc 13 is provided with perforations 17 arranged along an annulus, and opposite the feed channel 11 the disc 13 cooperates with a duct 18 provided with a rectangular suction slot 19, the rear edge of which, constituting the yarn formation line 20, is positioned generally along a chord of disc 13 (see specifically Fig. 4), and extends from the disc rim up to the proximity of the centre 21 of this latter (see fig. 3). The discretized fibres 10 are conveyed in the feed channel 11 onto said disc 13 in a direction having a componant parallel to said slot 19, and hence parallel to the yarn formation line 20 and to the end 22 of the yarn 23 being formed, and, once arrived onto the disc, they get condensed under the effect of suction through the slot 19. As furthermore the suction keeps them adhering against the disc, they are dragged by this latter until they arrive in the proximity of said rear edge of suction slot 19 where influence of said suction ceases and they roll up on themselves and gain twist. The yarn 23 which in this way is formed is then extracted along the direction of the suction slot 19 and the yarn formation line 20 and according to the direction of arrow 24, by draw-off rollers 25 and 26, rotatably mounted on a support 27, with one of the two rollers being driven by a motor, and is wound and collected on a package not shown in the figures. As it can be clearly seen in Fig. 4, due to the particular position of the yarn formation line 20 along a chord of the twisting disc 13, the dragging speed v of the fibres in the individual points, for example P i , of the yarn formation line 20 varies with the distance r of the point in question from the revolution centre 21 of disc 13, according to the law v = w.r wherein w is the angular velocity of the same disc and hence increases linearly from the centre towards the edge of the disc. On the other hand, each dragging speed can be resolved, relatively to yarn, into a component axial to the yarn v a , and a component perpendicular to the yarn v n . The axial component v a of the dragging speeds has a value in each point of the line 20 which is constant, and of intensity equal to w.d, wherein d means the distance of the yarn formation line 20 from the axial line 28 of disc 13 which is parallel to said line 20, and, as it can be seen in Fig. 4, by properly positioning the slot 19 relative to the revolving disc (arrow 16), it is obtained that said axial component results directed in the direction opposite to the yarn withdrawing direction 24, and is hence able to tension the fibres during their twisting. The perpendicular components v n of the dragging speeds, which are the cause of the fibre twisting, result, on the contrary, variable like said latter speeds, they thus reaching their minimum value at the open end 29 (see Fig. 3) of the end of the yarn 23 being formed, as it must actually be, because in that point few fibres are present, and the yarn firmness is poor. Figures 5 and 6 illustrate variants of twisting elements constituted by a protruding-point hollow conical disc 30 and by a reentering-point hollow conical disc 31, provided with perforations 17. Figures 7 to 9 illustrate a further variant of twisting element, constituted by a small cylinder 32 mounted on outer bearings 33 and provided with perforations 17 in its base surface 34, which can be either flat (Fig. 7), concave (Fig. 8) or convex (Fig. 9).

Claims: A spinning process of the friction open-end type, comprising opening the fibres of a sliver (3), feeding with the opened fibres an end (22) of a yarn (23) to be formed while subjecting the fibres to a suction and keeping the fibres adherent to a revolving twisting element (13) having a perforated surface so that said end is twisted into the yarn (23) by the action of auction through, and rotation of, said surface, drawing-off the so-formed yarn (23) from the twisting element (13) along the direction of the yarn formation line (20) and winding up and collecting the drawn yarn (23) on a package, said fibres being subjected to a twisting action increasing from the open end (22) of the yarn (23) onwards, characterized in that along the yarn formation line (20) the fibres under twisting are subjected to an axial force opposite to the draw-off direction. A spinning process according to claim 1, characterized in that said axial force is substantially constant along the whole yarn formation line (20). A spinning process according to claim 1 or 2, characterized in that the opened fibres are fed to the twisting element (13) in a direction having a component parallel to the yarn formation line (20). A spinning device for implementing the process according to one of the preceding claims, comprising a unit for opening the fibres of a sliver (3), a revolving twisting element (13) in the form of a disc having a perforated surface, a suction slot (19) cooperating with the twisting element (13) in a position opposite to a yarn feed channel (11) and defining a yarn formation line (20), draw-off rollers (25, 26) for extracting the formed yarn (23), and means for winding up and collecting the formed yarn (23) on a package, the yarn formation line (20) extending along the direction (24) of extraction of the yarn (23) by said draw-off rollers (25,26), characterized in that the yarn formation line (20) extends generally along a portion of a chord of said disc substantially from the rim of the disc up to the proximity of the revolution centre (21) thereof, and in that the position of the yarn formation line (20) relative to the rotational direction (16) of the disc is such that rotation generates on the fibres an axial force opposite to the draw-off direction (24). A spinning device according to claim 4, characterized in that the feed channel (11) extends in a direction having a component parallel to the yarn formation line (20). A spinning device according to claim 4 or 5, characterized in that said suction slot (19) is adjustable in position relative to the disc along the surface thereof. A spinning device according to claim 4, characterized in that said disc is a conical disc (30 resp.31). A spinning device according to claim 4, characterized in that said disc is formed by a base (34) of a revolving cylinder (32). A spinning device according to claim 8, characterized in that said base (34) has a convex or concave shape. A spinning device according to claim 4, characterized in that the perforated surface of the twisting element (13) has a differentiated perforation pattern along the yarn formation line (20). A spinning device according to claim 4, characterized in that the perforated surface of the twisting element (13) has a roughness variable along the yarn formation line (20).

Inventors: BOTTOS, ROBERTO, FERRO, FRANCESCO, GREGO, FRANCESCO, NERLI, GIOVANNI, NESTI, SOLITARIO
Applicants: SAVIO S.P.A.
Application year: 1986
Main classification: D01H4
IPC codes: D01H4, D01H7