Abstract:
A method and an apparatus for stuffer box crimping a multifilament yarn, wherein the yarn being processed is pneumatically advanced by means of a conveying fluid into a stuffer box chamber and compacted to a yarn plug, with the conveying fluid leaving the stuffer box chamber through openings and being removed by suction. To be able to influence the yarn plug formation mainly by the suction stream, the invention provides for constructing the source of vacuum as an injector, which connects to a source of pressure via a pressure connection and to a suction line via a suction connection that precedes in the direction of the flow. As a result, the suction stream of the conveying fluid is generated by a compressed air stream, with the compressed air stream and the suction stream being jointly discharged as a common airflow.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a method and apparatus for stuffer box crimping a multifilament yarn, of the general type disclosed in WO 03/004743 A1. 
   For stuffer box crimping a preferably freshly spun, synthetic multifilament yarn, a feed nozzle pneumatically advances the yarn into a stuffer box chamber. To this end, the feed nozzle comprises a yarn channel, into which a conveying medium is introduced under a high pressure. Together with the conveying medium, the multifilament yarn advances from the yarn channel of the feed nozzle into a stuffer box chamber directly downstream thereof. Inside the stuffer box chamber, a yarn plug is formed, so that the action of the conveying medium causes the fine filaments of the yarn to collect in loops and coils on the surface of the yarn plug. Preferably in its upper region, the stuffer box chamber comprises a gas permeable wall, so that the conveying fluid is able to leave the stuffer box chamber for being removed by suction. 
   To obtain an as uniform plug formation as possible and thus a crimp of the yarn that is as even as possible, it is necessary that in particular the conveying forces acting upon the yarn plug, as they develop, for example, because of the impact pressure effect of the conveying medium leaving the yarn channel of the feed nozzle, and the frictional forces acting upon the yarn plug, be at a defined ratio to each other. Thus, it is known to raise the conveying pressure of the feed nozzle for increasing the conveying speed. However, in this connection one must make sure that the conveying pressure does not result in blowing the yarn plug out of the stuffer box chamber, because the frictional forces between the yarn plug and the stuffer box chamber wall are unable to produce adequate retaining forces. 
   Basically, there exist two possibilities of forming inside the stuffer box chamber an as uniform plug as possible. In a first variant, the formation and advance of the yarn plug inside the stuffer box chamber is largely determined by friction. In this case, the frictional forces acting between the yarn plug and the stuffer box chamber wall are decisive for building up retaining forces, so that a defined force ratio is active between the conveying pressure of the conveying fluid and the retaining forces, and that thus a uniform advance of the yarn plug prevails within the stuffer box chamber. 
   In a second variant, a pair of feed rolls is arranged directly at the outlet end of the stuffer box chamber. These paired feed rolls remove the yarn plug from the stuffer box chamber. Thus, the speed of the yarn plug and yarn plug formation is largely determined by the speed of the feed rolls. 
   In both cases, it is common to remove conveying fluid emerging from the stuffer box chamber by additional suction. To this end, it is common to connect a source of vacuum to an expansion chamber, which substantially surrounds the walls of the stuffer box chamber. By adjusting a defined suction effect, a further parameter exists to influence the plug formation within the stuffer box chamber. However, the use of this additional controlled variable gives rise to the problem that an intensive suction causes volatile components, such as, for example, residues of a yarn lubricant that adhere to the yarn, to be carried along and to cause contaminations. Furthermore, a precise and reproducible adjustability of the suction effect is needed to be able to perform fine adjustments for forming and advancing the plug. 
   It is therefore an object of the invention to further develop a method and an apparatus of the initially described type for stuffer box crimping a multifilament yarn such that the plug formation in the stuffer box chamber can be influenced by a suction stream of the conveying fluid in a precise and reproducible manner. 
   A further object of the invention is to provide a reliable and rapid removal of the suction stream from the stuffer box chamber. 
   SUMMARY OF THE INVENTION 
   The invention distinguishes itself in that for stuffer box crimping a multifilament yarn only a single source of energy suffices to be able to influence with the greatest possible flexibility both the advance of the yarn and the plug formation of the yarn. To this end, the suction stream of the conveying fluid is generated by a compressed air stream of an injector, with the compressed air stream and the suction stream being jointly discharged as an airflow. With that, it is becomes possible to advance to a central collection point with a high energy and without risk of contamination in particular volatile components that are contained in the suction stream of the conveying fluid. 
   The injector action has in addition the advantage that the suction effect is exclusively determined by the supplied compressed air stream. To this end, the injector comprises a compressed air connection, through which the compressed air stream can be supplied by means of a connected source of pressure. Thus, for example, one common source of compressed air could supply both the feed nozzle for generating a conveying stream and the injector for generating a suction stream. 
   In a preferred embodiment, the injector connects at its outlet end to a filter device, so that the airflow is filtered before entering the surrounding environment. Also, in practice, one may use heated compressed air as the conveying fluid, so that the conveying fluid can be discharged into the surroundings after expanding. In this connection, the use of a filtering device is especially advantageous for keeping away from the surroundings all foreign components, in particular residues of a yarn lubricant that are carried along in the suction stream. 
   To enable an adjustment of the suction stream, a regulating means is associated to the injector at its pressure connection, so that the supply of compressed air to the injector can be adjusted in quantity and/or pressure. 
   The method and the apparatus of the invention are thus particularly suited for the basic processes, wherein the yarn plug is exclusively influenced by friction inside the stuffer box chamber. 
   In the case that a driven pair of feed rolls is associated to the outlet end of the stuffer box chamber, it is possible to achieve a maximally possible flexibility in influencing the plug formation. In practical operation, however, a variant of the method has been found especially advantageous, wherein the plug formation initially occurs by an intensive suction stream at the beginning of the process. Upon expiration of a startup time, the supply of compressed air to the injector for generating the suction stream is adjusted to a minimum supply or totally shut down, so that the plug formation is exclusively influenced by the driven feed rolls at the outlet end of the stuffer box chamber. For carrying out this variant of the method, a regulating means may be associated with the injector and with a drive unit of the driven feed rolls. To this end, the regulating means of the injector and the drive unit of the feed rolls are connected to a controller. 
   In practice, it is common to arrange at the same time a plurality of feed nozzles and the stuffer box chambers in one mounting support. In this case, it is possible to discharge the conveying fluids of the individual stuffer box chambers advantageously by means of a common suction stream, so that the suction connection of the injector may advantageously be connected to a plurality of expansion chambers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the method and the apparatus of the invention are described in greater detail by means of several embodiments and with reference to the attached Figures, in which: 
       FIG. 1  is a schematic, longitudinally sectioned view of a first embodiment of the apparatus according to the invention for carrying out the method of the invention; and 
       FIG. 2  is a schematic cross sectional view of a further embodiment of the apparatus according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  schematically illustrates a longitudinally sectioned view of a first embodiment of the apparatus according to the invention for carrying out the method of the invention. The apparatus comprises a feed nozzle  1  and a crimping device  2  downstream thereof. The feed nozzle  1  includes a yarn channel  3 , which forms at its one end an inlet  4  and at its opposite end an outlet  5 . The feed nozzle  1  connects via a fluid inlet  8  to a source of pressure  11 . The fluid inlet  8  ends in a pressure chamber  7 , which connects via a plurality of air inlet passageways  6  to the yarn channel  3 . The air inlet passageways  6  terminate in the yarn channel  3  such that a conveying medium entering via the pressure chamber  7  through the air inlet passageways  6  flows into the yarn channel in the direction of the advancing yarn. 
   A supply line  33  arranged at the fluid inlet  8  is associated to a heating device  9  for heating the conveying fluid, as well as to a fluid regulating means  10  for regulating the conveying pressure and conveying quantity. 
   Arranged directly downstream of the feed nozzle  1  is a crimping device  2 . The crimping device  2  forms a stuffer box chamber  15 , which comprises an upper section with a gas permeable wall  14  and a lower section with a closed chamber wall  27 . In the present embodiment, the gas permeable chamber wall  14  is formed by a plurality of lamellae arranged in side-by-side relationship, which annularly extend at a small distance from one another. The lamellae of the gas permeable chamber  14  are held in an upper lamella holder  13 . 1  and in a lower lamella holder  13 . 2 . Both the chamber wall  14  and the holders  13 . 1  and  13 . 2  are arranged in a closed casing  12 . An annular space formed by the casing  12  outside of the gas permeable wall  14  forms an expansion chamber  16 . The expansion chamber  16  connects to a suction line  17 . The suction line  17  connects outside of the crimping device  2  to a suction connection  19  of an injector  18 . The injector  18  includes a pressure connection  20 , to which a regulating means  21  is associated. The pressure connection  20  connects via the regulating means  21  to the source of pressure  11 . 
   Inside the injector  18 , the suction lines  17  and the pressure connection  20  terminate in an acceleration zone  22  that is formed by a cross sectional contraction. The acceleration zone  22  connects to an airflow duct  23  and forms the outlet of the injector  18 . The airflow duct  23  ends in a filter device  24 . 
   The underside of the crimping device  2  includes a plug outlet  34  of the stuffer box chamber  15 . At a short distance downstream of the plug outlet  34 , a feed means  30  is arranged, which is formed in the present embodiment by two opposite rolls. The feed rolls are driven in opposite directions via a drive unit  31 . 
   The feed nozzle  1  and the crimping device  2  are controlled by a controller  32 . To this end, the controller  32  connects via a plurality of control lines to the fluid regulating means  10 , the suction regulating means  21 , the heating device  9 , and the drive unit  31 . 
   In the embodiment of the apparatus according to the invention for carrying out the method of the invention as shown in  FIG. 1 , a yarn path is shown for better illustrating the operation of the apparatus. In the apparatus, a conveying fluid made available by the source of pressure  11  is supplied to the feed nozzle  1  in a first step. The fluid regulating means  10  permits adjusting preferably a conveying pressure, under which the conveying medium is supplied to the fluid inlet  8  via supply line  33 . Before that, the conveying fluid is heated by the heating device  9 . From the fluid inlet  8 , the conveying fluid enters the pressure chamber  7 , and flows at a high velocity through the air inlet passageways  6  into the yarn channel  3 . The conveying fluid entrains a yarn  28  that has been inserted into the yarn channel  3 , and advances it into the adjacent stuffer box chamber  15  of the crimping device  2 . Inside the stuffer box chamber  15 , a yarn plug  29  is formed, so that that when impacting upon the yarn plug  29 , the yarn formed by a plurality of fine filaments collects in coils and loops on the surface of the yarn plug and compacts under the impact pressure of the conveying medium. 
   The impact pressure acting upon the yarn plug  29  is increased by a vacuum, which the injector  18  generates in the expansion chamber  16 . To this end, the injector receives from the source of pressure  11 , via the suction regulating means  21 , a second fluid stream, which is supplied to the injector  18  via the pressure connection  20 . The resultant vacuum forming at the suction connection  19  of the injector  18  generates a suction stream that is discharged from the expansion chamber  16  via the suction line  17 . At the outlet end of the injector  18 , the suction stream and the compressed air stream are jointly supplied via the airflow duct  23  to the filter device  24 . In the filter device  24 , the suction stream is freed from entrained and carried along foreign particles, which largely result from volatile components of the yarn  28 . The injector  18  determines on the one hand the impact pressure of the conveying medium, which influences the formation of the yarn plug, and ensures on the other hand a fast and contamination free discharge of the suction stream from the crimping device  2 . 
   At the outlet end of the crimping device  2 , the feed means  30  continuously removes the yarn plug  29  from the stuffer box chamber  15 . In this process, the speed of the yarn plug  29  is adjusted such that the height of the yarn plug  29  inside the stuffer box chamber  15  remains substantially unchanged. 
   Normally, after cooling, the yarn plug is disentangled by withdrawing the yarn at a higher speed. The crimped yarn forming in this process is subsequently wound to a package after possibly undergoing an aftertreatment. 
   With the use of the embodiment shown in  FIG. 1 , a variant of the method for crimping a yarn has been found especially advantageous, wherein at the beginning of a process a high vacuum is adjusted in the expansion chamber  16  by the injector  18 . In so doing, great retaining forces form on the yarn or the yarn plug over the entire length of the gas permeable wall  14 . A yarn advancing through the yarn channel  3  into the stuffer box chamber  5  automatically forms a yarn plug. After the formation of the yarn plug is completed, the injector action is reduced or stopped via the suction regulating means  21 . The formation of the yarn plug  29  within the stuffer box chamber  15  can then be largely controlled by the feed means  30  at the outlet end of the crimping device  2 . 
   It is accordingly possible to intervene in the plug formation by changing the conveying pressure of the feed nozzle  1  via the fluid regulating means  10 , by the vacuum for the suction via the suction regulating means  21 , or by varying the circumferential speed of the feed means  30  via the drive unit  31 . 
     FIG. 2  schematically illustrates a cross sectional view of a further embodiment of the apparatus according to the invention for carrying out the method of the invention. The embodiment comprises two crimping devices  2  arranged in parallel and side-by-side relationship in a mounting support  35 . The crimping devices  2  and the mounting support  35  are made bipartite and can be jointly moved relative to one another about a pivot axle  36 . The crimping device  2  is shown at the height of the gas permeable wall  14 . Located in the center of the crimping device  2  is the stuffer box chamber  15 . The stuffer box chamber  15  connects via openings in the gas permeable wall  14  to an expansion chamber  16  surrounding the gas permeable wall  14 . The expansion chamber  16  of each of the crimping devices  2  connects to a suction line  17 . The suction line  17  connects with an opposite end to a suction connection  19  of an injector  18 . The injector  18  comprises a pressure connection  20 , which is formed in the present embodiment by a plurality of inlet channels. Associated to the pressure connection  20  is a suction regulating means  21 . An airflow duct  23  connects the injector  18  to a filter device  24 . 
   In the embodiment shown in  FIG. 2 , the crimping devices are constructed identical with the foregoing embodiment of  FIG. 1 , so that the foregoing description may herewith be incorporated by reference. Unlike the foregoing embodiment of  FIG. 1 , in the embodiment of  FIG. 2  two feed nozzles and crimping devices arranged parallel in side-by-side relationship are operated in parallel, so as to crimp two parallel advancing yarns at the same time. In this case, it is possible and advantageous to arrange also more than two crimping devices in side-by-side relationship on a common mounting support. 
   To generate a suction stream, each of the crimping devices connects to a common suction line  17 . The suction line  17  connects to the injector  18 , so that a vacuum generated by the injector is operative in the same way in the two expansion chambers of the crimping devices  2 . The function for building up the vacuum as well as for discharging the suction stream is identical with the foregoing embodiment of  FIG. 1 , so that the foregoing description may herewith be incorporated by reference. 
   The method and the apparatus of the invention are thus especially suited for influencing a plug formation with the greatest possible flexibility. With that, it is possible to treat yarns of a relatively large denier range. The great flexibility thus permits producing individual crimps depending on the type and quality of the yarn. The use of an injector for removing the conveying medium by suction provides a process reliable and excellently reproducible adjustability, which additionally permits discharging the suction stream in a safe way.