Abstract:
The coating of the pressure roller ( 3 ) of a drawing roller frame for spinning frames comprises an outer layer and an inner layer fixed to the core of the pressure roller. The outer layer is thinner and harder than the inner layer and is embodied as an endless belt ( 1 ) which loosely surrounds the inner layer such that the belt can be displaced in relation to the inner layer. In order to improve the running of the belt, the belt is guided over a deflector rail ( 2 ), the cross-sectional area (u) of the rail being wider than the average staple length of the fibre material (F) drawn on the drawing roller frame. Furthermore, the belt is designed in such a way that it comprises a double thread interlining, one thread interlining being wound counter to the second thread interlining such that the threads of one thread interlining cross the threads of the second thread interlining.

Description:
FIELD OF THE INVENTION 
     The invention relates to a roller drawing apparatus for spinning machines in which the covering for the pressure roller at the output of a drafting field consists of an outer layer and of an inner layer fastened on the core of the pressure roller. The outer layer is thinner and harder than the inner layer, which outer layer loosely surrounds the inner layer so that the outer layer can move relative to the inner layer. 
     BACKGROUND 
     A roller drawing apparatus is described in DE 102 60 025.2. Since the apron covering on the withdrawal cylinder has a running speed approximately 40 times greater than is the case in customary drafting aprons, it is very important that the apron covering is well guided and causes as little friction as possible on the deflection rail. The tensioning force required for the guidance of the apron covering is therefore very low and is advantageously only produced in that the apron covering tends to assume an approximately circular form in the circumferential direction in the unloaded state (DE 103 48 452 A1). Conditioned by this low tension with which the apron covering glides over the deflection roller, fibers collect on the deflection roller during a rather long operation of this apparatus. As a consequence, laps form around the deflection rail that hinder the easy gliding over the deflection rail and generate a higher and higher tension that finally leads to breaking of the deflection rail. 
     Furthermore, the running properties of the apron covering over the deflection rail are adversely affected in that the yarn insert applied to hinder longitudinal expansion is customarily produced by winding a yarn onto the first inner layer, that is then covered with another layer. As a result, it occurs again and again that, at the high running speed, the apron covering behaves asymmetrically corresponding to the winding and has the tendency to run off to one side. This can be counteracted by positioning edges on the deflection rail. However, the borders of the apron covering are stressed and worn down by running against the edge. 
     SUMMARY 
     The present invention addresses the problem of avoiding the described disadvantages and of avoiding adverse effects during the gliding of the very rapidly running apron covering over the deflection rail. Additional objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     It surprisingly turned out that given sufficiently large dimensioning of the circumference of the cross section of the deflection rail, the lap problems of prior art systems can be avoided. The circumference of the cross section of the deflection rail is preferably greater than the length of the longest fiber of the fiber material processed on the drafting apparatus. A running of the rapidly running apron covering against limiting edges is avoided by the curvature of the apron gliding surface of the deflection rail transversely to the running direction of the apron. The limitation by edges can even be entirely eliminated, especially if the covering constructed as an endless apron is provided with a double yarn insert, which yarn inserts are wound in opposing directions. The opposing winding of the yarn inserts eliminates the asymmetric behavior of the apron covering at high running speeds. In addition, the advantage results that when using a rigid holder, the apron covering can still be readily replaced. The rigid holder for the apron covering is preferably mounted on the pressure roller shaft in a freely rotatable manner and is supported via stops on the upper roller carrying arm of the drafting apparatus. In this manner, an especially simple and operationally reliable guidance of the apron covering is achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details of the invention are described using the drawings. 
         FIG. 1  shows a cross section through the drafting apparatus. 
         FIGS. 2 to 4  show different cross-sectional profiles of the deflection rail. 
         FIG. 5  shows a one-piece design of the deflection rail with the holder. 
         FIG. 6  shows a replaceable deflection rail with holder. 
         FIG. 7  shows the apron covering with opposingly wound yarn inserts. 
         FIG. 8  shows another embodiment of the apron covering holder in a top view. 
         FIG. 9  shows the apron covering holder of  FIG. 8  in the insertion state and in section. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each embodiment is presented by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment may be used with another embodiment to yield still a further embodiment. It is intended that the invention include these and other modifications and variations of the embodiments described herein. 
     The drafting apparatus in  FIG. 1  shows the customary construction of a double apron drafting system with lower cylinders  31 ,  61  and  71  by means of which apparatus fiber structure F is drawn to a yarn F′. The middle pressure roller  6  is looped around by a drafting apron  60  that is guided and tensioned by apron cage  63 . Lower cylinder  61  is looped around by a drafting apron  62  that runs over the deflection rail  64  and is pressed against upper apron  60 . Compressors  8  and  9  are provided in front of and in the drafting field for the compression of the fiber structure. 
     The delivery cylinder pair consists of the lower cylinder  31  and the pressure roller  3 , that is looped around by an apron covering  1  that runs over deflection rail  2 . Since pressure roller  3  has a speed approximately 40 or 60 times greater than pressure rollers  6  and  7 , cover apron  1  must run very rapidly. The deflection rail  2  is therefore provided with a smooth, low-fiction apron sliding surface  27  and covering  1 , designed as an apron, of pressure roller  3  is tensioned only slightly. The intrinsic tension of apron covering  1  that would result in a circular form of the apron  1  in the free non-tension state, is sufficient for this. Apron covering  1  is stretched by the arrangement of deflection rail  2 . The tension produced as a result is already sufficient for the unobjectionable running of apron covering  1 . 
     A clearer (i.e. cleaning) roller  5  is arranged in a customary manner above pressure roller  3  and of apron covering  1  in order to keep apron covering  1  free of fibers. However, during rather long running times of the drafting device, fibers accumulate on the inside of apron covering  1  between apron covering  1  and apron sliding surface  27  of deflection rail  2 , which fibers are not eliminated by or cannot be prevented by the clearer roller. These fibers become firmly fixed so that a greater and greater accumulation of fibers develops on gliding surface  27  of deflection rail  2 , and the tension of apron covering  1  increases in an inadmissible manner. The tension can even become so great that not only is apron covering  1  considerably braked and the course is thus adversely affected, but also deflection rail  2  breaks. 
     The accumulation of fibers between apron covering  1  and apron sliding surface  27  of deflection rail  2  is counteracted by the shaping of deflection rail  2 , especially of the cross-sectional circumference U. It turned out here that the size of the circumference U is important, and in any case should be greater than the average staple length of the fiber material drawn on the drafting apparatus. Good results were achieved, for example, with a cross-sectional circumference U of deflection rail  2  of at least 1.5 times the average fiber length. Since it is obviously important that the start and the end of a fiber can not close themselves to a ring around circumference U of deflection rail  2 , the cross-sectional circumference U of deflection rail  2  should preferably be slightly longer than the longest fiber of the fiber material drawn on the roller drafting apparatus. 
     Even the cross-sectional form plays a certain part here. It can be circular in accordance with  FIG. 2 . However, it turned out that cross-sectional forms like the ones shown in  FIG. 1  or in  FIGS. 3 and 4  avoid the accumulation of fibers under apron covering  1  the best. However, it is still important that the cross-sectional circumference U is sufficiently large that the fibers cannot form a ring around deflection rail  2 .  FIG. 3  shows, for example, a cross section in which apron sliding surface  27  has the form of a circular arc whereas the flanks are flattened. In deflection rail  2  according to  FIG. 1 , the cross section of deflection rail  2  is rectangular; however, the small sides are rounded off in an arched form so that apron sliding surface  27  is rounded off. In the embodiment according to  FIG. 4 , apron sliding surface  27  of deflection rail  22  is also rounded off; however, the sides are maintained straight. This cross-sectional form is particularly resistant to pressure loads and offers a smaller apron sliding surface  27  so that less friction is exerted on apron covering  1 . As can be gathered from  FIG. 1 , a clearer roller  5  is advantageously arranged above pressure cylinder  3  in order to keep apron covering  1  free of fibers on its outside. 
       FIG. 5  shows the holder  4  with two deflection rails  23  arranged as a pair. Holder  4  has cheeks  41  with which it rests on shaft  65  of pressure roller  3 . Cheeks  41  are designed in one piece with the two deflection rails  23 . Deflection rails  23  comprise cylindrical apron sliding surfaces  27  with lateral edges  24  that prevent a running off of apron covering  1 . As a result of the one-piece design of holder  4  with deflection rails  23 , this part can be especially advantageously produced and mounted as only one part. 
       FIG. 6  shows an embodiment similar to that of  FIG. 5  but here the deflection rails  200  are screwed into the cheeks  41  of holder by a threading and can be replaced without replacing holder  4 . In this manner, an adaptation to different spindle pitches is readily possible. Furthermore, deflection rails  200  are provided with a slightly curved apron sliding surface  203 . Apron covering  1  is held in the middle of sliding surface  203  by this curvature transversely to the direction of travel of the apron, which prevents it from running against sleeve  204 . An edge can be eliminated on the free side of deflection rail  200 , which simplifies the removal of apron covering  1 . 
       FIG. 8  shows another embodiment of a holder  40  for apron covering  1 . In accordance with the customary design of pressure roller  3 , deflection rails  25  are formed in pairs on cheeks  42  of holder  40  so that they form one part with holder  40 . Cheeks  42  comprise recesses  44  with which holder  40  rests and is supported on shaft  65  of pressure roller  3 . A side edge  26  is formed on each free end of deflection rails  25  which edge extends only over apron sliding surface  203  of deflection rail  25 . 
       FIG. 9  shows holder  40  in insertion position with the view onto holder  40  corresponding to section AA of  FIG. 8 . The shaft  65  of pressure roller  3  is held in a customary manner in a spring clamp (not shown in more detail) in the upper roller carrying arm  51 . Holder  40  grips with cheeks  42  by means of recesses  44  over pressure roller axis  65 , around which it can freely pivot. Holder  40  is pivoted counterclockwise during operation in accordance with the torque exerted via pressure roller  3  and apron covering  1  so that it is supported via stops  43  onto upper roller carrier arm  51  and is fixed in this position. This should advantageously take place at an angle α of approximately 30°. This fastening is extremely simple and ensures an assembly and disassembly of the entire holder  40  together with apron  1  without special fastening means. Coating aprons  1  can be easily stripped off pressure roller  3  laterally off deflection rail  25  via the edge  26 . Nevertheless, a reliable holding and guidance of apron covering  1  is ensured even at high turning speeds of pressure roller  3 . 
     As is described in DE 102 60 025.2, apron covering  1  is stiffened by a yarn insert in the direction of travel of apron covering  1  and is therefore largely non-elastic in this direction. The yarn insert is wound in a spiral during the production of apron covering  1  onto the running layer of apron coating  1 . During the cutting of apron covering  1  projecting fringes are produced by the yarn insert on the edges. This is disadvantageous because these fringes result in accumulations of fibers. Apron borders  13  ( FIG. 7 ) should be completely smooth so that no fibers are caught on them and entrained. Such a fringe-free cutting is achieved by cutting with a laser. 
     As a result of the yarn insert applied in spiral form, apron covering  1  exhibits an asymmetric behavior and runs on the one side against edge  24 . As a consequence, the smoothly cut borders  13  are roughened and a fringe formation with the above-described negative effects reoccur. The application of a yarn insert  11  in Z form and a yarn insert  12  in S form results in a crossing of the yarns in the spiral winding. Moreover, this counteracts the asymmetric behavior. Apron covering  10  runs uniformly, so that no damage occurs due to running on borders  13 . Edges  24  can even be omitted if apron sliding surface  203  of deflection rail  200  has a slight curvature transversely to the direction of travel of the apron. Apron covering  10  is constantly held and guided as a result in the middle of sliding surface  203 . The omission of outer edges  24  also has the advantage that apron covering  10  can be more readily replaced, even if deflection rail  200  is rigidly arranged. In the embodiment according to  FIG. 6  apron covering  10  can simply be pushed off the deflection rail  200  laterally. A raising over an edge is not required. 
     All these described measures bring about an easy and trouble-free course of apron covering  1  or  10 . Since this apron covering  1  or  10  runs at a very high speed, slight disturbances work themselves out to a large extent. The described measures can avoid disturbances in a simple manner and achieve an unobjectionable course of covering  1  even at high turning speeds of pressure roller  3 . 
     It should be appreciated by those skilled in the art that modifications and variations can be made to the embodiments described herein without departing from the scope of the appended claims.