Abstract:
A method for producing a filament yarn with alternating S- and Z-twists. The yarn is moved between two twisting stops and submitted alternatively to S- and Z-twisting by at least one false twisting unit. The twists are fixed in a fixing unit situated downstream from the false twisting unit. The twisting stop downstream of the fixing unit is moved synchronously with the yarn and held in a yarn engagement position to stop the twisting until at least the twisting inversion points is fixed in the yarn. At least one other twisting stop oriented at a distance from the above mentioned moving twisting stop is engaged with the yarn in a way to stop the twisting and is moved along with the yarn before said yarn is submitted to an opposite twisting by the false twisting unit.

Description:
FIELD OF THE INVENTION 
     The invention relates to a method for producing a filament yarn with alternating S- and Z-twists, in which at least one yarn is moved between two spaced apart twisting stops arranged at a distance from each other, and the yarn receives thereby through at least one false twisting unit of the clamping type arranged between the twisting stops alternately S- and Z-twists which are fixed by means of a fixing unit which is interconnected downstream of the false twisting unit in yarn advancing direction. 
     BACKGROUND OF THE INVENTION 
     In such a method known from the DE 39 31 110 C2, the twisting stops are formed by two stationarily arranged delivery mechanisms, of which one is arranged upstream of the false twisting unit or units, and the other one downstream of the fixing unit, which is designed either as a heating device or as an air-circulating device. The alternating formation of the S- and Z-twists is carried out in a predetermined cycle by switching on and off the clamping action of the false twisting unit. Since, however, the second twisting stop is arranged downstream of the fixing unit in yarn advancing direction, the S- and Z-twists earlier applied to the yarn are, depending on the twisting direction, partially again untwisted and partially yet more tightly twisted in the yarn section extending downstream of the false twisting unit. Thus it is not possible in this manner to produce a yarn which has reproducible alternately defined S- and Z-twists. Furthermore nontwisted sections with a lesser S- or Z-twist are each created between the sections with S-twist and the sections with Z-twist. 
     SUMMARY OF THE INVENTION 
     The basic purpose of the invention is therefore to provide a method for producing a filament yarn with alternating S- and Z-twists, with which in a simple, economical and reproducible manner a filament yarn can be produced which has defined S- and Z-twists per unit of length and therebetween as much as possible no nontwisted or little twisted sections. 
     This is attained according to the invention by the twisting stop provided in yarn advancing direction downstream of the false twisting unit being moved synchronously with the yarn and being held in an engagement with the yarn stopping the twisting until at least the twisting inversion point in the yarn is fixed, and by at least one further twisting stop, following the aforementioned moved twisting stop at a distance, entering into an engagement with the yarn stopping the twisting, and advancing together with same before the yarn is twisted in an opposite direction by the false twisting unit. 
     Thus the invention is based on the thinking to grasp the yarn directly behind the false twisting unit by twisting stops successive in timely and spacial intervals, and to then advance the twisting stops synchronously together with the yarn. A twisting stop has the purpose to prevent a continuation of a twist applied to the yarn into a yarn section lying upstream of or downstream of the twisting stop. Clamping devices are primarily used as twisting stops in the present case, however, a twisting stop can also be designed as a guide edge or through clamping in a delivery mechanism. Yarn sections are in the inventive method each temporarily “fixed” between two spaced twisting stops which follow each other until the final fixation by means of the fixing unit takes place. The yarn sections extending fixed between two twisting stops have either a S- or Z-twist with a specific twist, whereby the term “twist” means according to DIN 60900, Part 2, the number of twists of a single yarn per/m. The specific twist of a section of yarn clamped between two adjacent twisting stops is not influenced or changed by the twists applied to the following yarn sections because the false wire is constructed always only up to the twisting stop closest to the false twisting unit. In this manner also nontwisted sections between the yarn sections with S- or Z-twist are avoided. The inventive method can be continuously carried out and enables the production of a filament yarn with alternating S- and Z-twists. The filament yarn can be produced out of a yarn component, namely a bunch of filaments, and is fixed during the production process following the false twisting unit, which is done by thermofixation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be discussed hereinafter in greater detail in connection with the exemplary embodiments illustrated in the drawing, in which: 
     FIG. 1 schematically illustrates the structure of the finished filament yarn, 
     FIG. 2 schematically illustrates the operating sequence for the method, 
     FIG. 3 illustrates the relationship between the minimal distance of the movable twisting stops from the false twisting unit under the theoretical twist distribution, 
     FIGS. 4 a  to  4   c  illustrate the operating principle of two series-connected false twisting units in a first embodiment, 
     FIGS. 4 d  to  4   f  illustrate the operating principle of a second embodiment, 
     FIGS. 5 to  7  schematically illustrate various movable twisting stop devices, 
     FIG. 8 is a view in direction VIII of FIG.  7 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 schematically illustrates the structure of the finished filament yarn. Same has alternating yarn sections  1   a  with S-twists and yarn sections  1   b  with Z-twists. The twisting inversion points  2 , the expansion of which in longitudinal direction of the yarn can be kept very small with the inventive method, each lie between two yarn sections  1   a,    1   b  with opposite twists. The lengths of the yarn sections  1   a  ,  1   b  can vary. Smooth and textured multi-filament yarns, preferably in a titer range of between 17 and 330 dtex, are supposed to be utilized as feed materials. FIG. 2 schematically illustrates the operating sequence for the method. The yarn  1 ′ is moved from A to B in a yarn advancing direction C by means of the delivery mechanism  6 , and leaves the delivery mechanism  6  as a finished filament yarn  1  with alternating S- and Z-twists, as it is illustrated in FIG. 1. A first twisting stop  7  is arranged stationarily and can advantageously be designed as a delivery mechanism or as a yarn tensioning device. A false twisting unit  8  is arranged at a distance L 0  downstream of the stationary twisting stop  7 , with which false twisting unit it is possible to subject the yarn  1 ′ successively to alternating S-twists and Z-twists. The detailed design of such false twisting units  8  will be discussed later on in connection with FIGS. 4 a  to  4   f . A twisting stop device  9  with several twisting stops  3  movable in the yarn advancing direction C is provided behind the false twisting unit  8 . Each twisting stop  3  is formed by two cooperating clamping jaws  3   a ,  3   b , whereby these clamping jaws  3   a ,  3   b  are supposed to have an as small as possible expansion in the yarn advancing direction C, and are therefore advantageously designed like a blade. It is thus possible to reduce the length expansion of the twisting inversion point  2  to a minimum so that in the finished textile surface these inversion points  2  do not appear as areas of error. The clamping jaws  3   a,    3   b  are arranged on continuously driven belts  10   a ,  10   b , with which they each can be returned to the false twisting unit  8 . Furthermore the clamping jaws  3   a ,  3   b  can in this manner be turned on and off. In the area lying between the belts  10   a  and  10   b , opposing pairs of clamping jaws  3   a ,  3   b  are pressed against one another with the inter positioning of the yarn  1 ′ to form then a twisting stop  3  movable in the yarn advancing direction C. The movable twisting stops  3  are spaced apart at a distance L 2 . The twisting stops  3  are moved through a fixing unit  11 , which consists of a heating zone  4  and a downstream oriented cooling zone  5 . The spaced apart distance L 2  of the twisting stop  3  is thereby less than the length L 3  of the fixing unit  11 . It is assured in this manner that the twists alternately oppositely applied to the yarn  1 ′ and temporarily fixed between two twisting stops  3  are thermally fixed when the finished filament yarn  1  leaves the fixing unit  11 . 
     In order for the method to operate as effectively as possible, the twisting stops  3  should engage the yarn  1 ′ to stop the twisting as close as possible to the false twisting unit  8 , and should then be advanced synchronously with the yarn  1 ′. With each new engagement of the yarn by a twisting stop it is possible to change the direction of the twist applications through the false twisting unit  8 . Yarn sections  1   a  with S-twist and yarn sections  1   b  with Z-twist are alternately temporarily “fixed” between two twisting stop devices, and the yarn  1 ′ is moved in a twisted state initially through the heating zone  4  and then through the cooling zone  5 . Only after the yarn has been cooled off to below a specified temperature, the clamping is cancelled during an exit from the cooling zone  5 . Because of the varying distance L 0  between the stationary twisting stop  7  and the false twisting unit  8  on the one hand and the distance L 1  between the false twisting unit  8  and the movable twisting stop  3  closest to it on the other hand, varying twist heights are created, namely twists per unit of length, in front of and after the false twisting unit  8 . However, only the portion of the twists which lie between the false twisting unit  8  and the nearest moved twisting stop is fixed in the production process. The yarn is theoretically only tightly untwisted and tightly twisted in the area between the twisting stop  7  and the false twisting unit  8 . The false twist is thus divided into two opposite true twists, of which in each case only the twist downstream of the false twisting unit is fixed. In order for this twist to no longer be influenced by the following reversal of the twisting direction, this twisting direction is supposed to be reversed only when the following twisting stop engages the yarn  1 ′. The respective next twisting stop is hereby supposed to be guided close to the false twisting unit  8  in order to keep the distance L 1  as small as possible. Namely, the yarn section in the area L 1  must during a reversal of the twisting direction be first again untwisted and twisted in the opposite direction. The shorter the distance at the start of the reversal of the twisting direction, the more effectively operates the method. 
     This can be recognized by looking at FIG. 3, which shows the theoretical influence of the distances L 0  and L 1  on the twist height upstream of and downstream of the false twisting unit  8 . The times for the engagements of the movable twisting stops are indicated by the reference  3 ′. FIG. 3 illustrates that a large relationship of L 0 /L 1  has a positive effect, and that the minimal distance L 1  between the respective twisting stop  3  which engage the yarn  1  and the twisting unit  8  should be as small as possible. 
     The changing twisting direction of the yarn can be realized both by one false twisting unit with changing twisting direction and also by two false twisting units which are constantly driven in opposite twisting directions, and which can be alternately interconnected. The use of two false twisting units, which are driven in different twisting directions and the active surfaces of which are interconnected, is advantageous. The masses, which are to be accelerated, are in this manner kept very small since the respective interconnection can occur through a movement of the yarn or through a deflection of the active areas. 
     False twisting units  8 ,  8 ′ or  8   a,    8 ′ a  of the clamping type are illustrated in FIGS. 4 a  to  4   f.  In the exemplary embodiment illustrated in FIGS. 4 a  to  4   c,  each of the false twisting units  8 ,  8   a  has two crossing, continuous belts  12 ,  12 ′, at the crossing point of which the yarn  1 ′ can be clamped in order to create the twists. The belts  12  of the first false twisting unit  8  are, for example, driven in such a manner that they can give the yarn downstream, namely in yarn advancing direction downstream of the false twisting unit a S-twist, whereas the belts  12 ′ of the second false twisting unit  8 ′ can give the yarn downstream of the false twisting unit  8 ′ a Z-twist. Each of the two false twisting units  8 ,  8 ′ has furthermore two pressure rollers  13 ,  13 ′, respectively, with the help of which the active areas  12   a,    12 ′ a  of the belts  12 ,  12 ′, respectively, which are usually spaced from the yarn  1 ′, can be alternately moved into operating position, as this is illustrated in FIGS. 4 b  and  4   c . The belts  12 ,  12 ′ of the two respective false twisting units  8 ,  8 ′ are continuously driven in the twisting directions indicated by arrows. When according to FIG. 4 b  the pressure rollers  13  press the active areas  12   a  against the yarn  1 ′, the yarn receives S-twists downstream when the second false twisting unit  8 ′ becomes inactive. In order to give the yarn Z-twists downstream, the pressure rollers  13  of the first false twisting unit  8  are according to FIG. 4 c  moved away from one another and the pressure rollers  13 ′ of the second false twisting unit  8 ′ press the active areas  12 ′ a  against the yarn  1 ′. By deflecting the active areas  12   a,    12 ′ a  of the belts  12 ,  12 ′ perpendicular to their direction of movement, very quick switching operations can be realized since, due to the geometry, only very small forces must be applied and only short paths of movement must be covered. The false twisting unit, which is not in the operating position, does not hinder the expansion of the twists in the yarn  1 ′ since their active areas  12   a  or  12   a  ′ are each spaced from the yarn  1 ′. 
     Each of the two false twisting units  8   a,    8 ′ a  consist in the exemplary embodiment illustrated in FIGS. 4 d  to  4   f  of two continuously driven disks  14 ,  14 ′, the axial faces of which form the active areas  15 ,  15 ′, between which the yarn  1 ′ can be clamped. This is accomplished by the two disks  14  or  14 ′ axially approaching one another. Thus it is possible, for example according to FIG. 4 a,  to give the yarn  1 ′ downstream, namely in yarn advancing direction C the yarn section extending downstream of the false twisting unit  8   a,  Z-twists when the active areas  15  of the disks  14  are pressed against the yarn  1 ′ and the active areas  15 ′ of the second false twisting unit  8   a  ′ are spaced from the yarn  1 ′ and are thus inactive. The active areas  15 ′ are in the position of the false twisting units illustrated in FIG. 4 f  pressed against the yarn  1 ′ and the yarn thus receives downstream S-twists and the first false twisting unit  8   a  is inactive. 
     Various twisting stop devices are illustrated in FIGS. 5 to  7 . The twisting stop device  9  illustrated in FIG. 5 corresponds essentially to the exemplary embodiment illustrated in FIG. 2 so that an explanation reference can be made to the description of FIG.  2 . The evenly driven continuous driving means  10   a ,  10   b , can, for example, be belts or chains. 
     Several rigid clamping elements  17  are, in the twisting stop device  9 ′ illustrated in FIG. 6, arranged spaced from one another on the continuous driving means  16 . A movable clamping element  18 , which is pivotal about an axis  19 , is associated with each rigid clamping element  17 . When the movable clamping element  18  is pressed against the rigid clamping element  17 , clamping occurs. A control cam  20  can be used to control the movable clamping element  18 . The heating zone is identified by the referenced numeral  4 . 
     Several support arms  21  are provided, in the twisting stop device  9 ″ illustrated in FIG. 7, spaced from one another on a continuous driving means  16 , which support arms each carry one rigid clamping jaw  22  on their free end. Each support arm  21  is associated with a movable slide member  23  having a clamping jaw  23   a.  The slide members  23  can be moved relative to the support arms  21  in their longitudinal direction by operation of a control cam  20  or the like, and the movable clamping jaws  23   a  can thus each be moved into a clamping position or an opening position. Each clamping jaw pair  22 ,  23   a  forms one twisting stop. 
     In the exemplary embodiment illustrated in FIGS. 7 and 8, the clamping jaws  22  are arranged on relatively thin support arms  21  and at a greater distance from the driving means  16 . When the clamping jaws  22 ,  23   a  are in a clamping position and thus in an engagement to stop twisting, they can elastically yield in yarn-advancing direction C and can thus compensate for changes in the length of the yarn, which changes can be created by twisting and shrinkage. 
     When the fixing unit  11  consists of a heating zone  4  and a cooling zone  5  connected thereafter, each yarn section  1   a  ,  1   b  including the inversion points  2  lying therebetween is fixed. If necessary, it is, however, also possible to fix only the inversion points  2 , which can, for example, be accomplished by heated clamping jaws.