Abstract:
A method and an apparatus for melt spinning and cooling a plurality of synthetic filaments, wherein the filaments are extruded in a first step in an annular arrangement by means of a spinneret ( 1 ). The filaments subsequently advance along an outflow quench diffuser ( 12 ) and undergo cooling by an airflow that radially emerges from the jacket of the outflow quench diffuser. The filaments undergo for purposes of being solidified and before being cooled by the diffuser jacket airflow, a precooling by an additional precooling airflow ( 7 ), which is generated by a cooling means ( 6 ) arranged between the spinneret ( 1 ) and the outflow quench diffuser ( 12 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is a continuation of international application PCT/EP2003/011807, filed 24 Oct., 2003, and which designates the U.S. The disclosure of the referenced application is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a method and apparatus for melt spinning and cooling a plurality of synthetic filaments to form a multifilament yarn, of the general type disclosed, for example, in DE 36 29 731 A1.  
         [0003]     In the production of staple fibers, the fibers are extruded in a first step as strandlike filaments from a polymer melt by means of a spinneret with a plurality of spin holes. Depending on the throughputs of the spin holes and the withdrawal speeds from the spinneret, one distinguishes between so-called short spinning processes and long spinning processes. In the case of short spinning processes, low withdrawal speeds and low spin hole throughputs are adjusted, so that a cooling of the freshly extruded filament strands is possible within a short distance. In such processes, however, one uses spinnerets which have a very large number of spin holes, so that a relatively dense sheet of filaments is produced and must be cooled. To this end, one employs, for example, cooling devices as are disclosed in U.S. Pat. No. 5,178,814. In these devices a cooling air stream is generated downstream of the spinneret, which is operative over a very short length and radially penetrates the filament sheet from the inside outward.  
         [0004]     In the so-called long spinning processes, however, one obtains a very much higher throughput through the spinneret and accordingly substantially higher withdrawal speeds. To cool the freshly extruded filaments in an optimal manner, a long and uniform quench zone is needed. To this end, so-called outflow quench diffusers have been found to be particularly effective, which form a radially emerging airflow over a uniform quench zone on their jacket. A method as well as an apparatus of this type are disclosed in DE 36 29 731 A1, which forms the basis of the invention.  
         [0005]     By the known method and the known apparatus, the filaments are extruded through annularly arranged spin holes in the spinneret. Arranged downstream of the spinneret is the outflow quench diffuser. The outflow quench diffuser has a porous jacket, which consists, for example, of a sintered material, so that the cooling air having entered the interior of the outflow quench diffuser via an air supply system radially emerges from the jacket of the outflow quench diffuser and cools as a diffuser jacket airflow the filament strands as they advance along the outflow quench diffuser. In the known apparatus, the outflow quench diffuser has at its free end a closable annular gap, which is opened for pivoting and moving the diffuser, so that the filament strands are prevented from gluing to the outflow quench diffuser while it is being moved to an operating position. As soon as the outflow quench diffuser has reached its operating position downstream of the spinneret, the annular gap will be closed. The filaments are exclusively cooled by the airflow from the diffuser jacket.  
         [0006]     In the known method and known apparatus, one has found in particular when melt spinning and cooling filaments with fine deniers, that outer lying filaments are often subjected to breaks. Since the use of the spin holes in the spinneret and thus that of the extruded filaments is greater in the case of fine deniers than in the case of coarse deniers, the airflow from the jacket of the outflow quench diffuser performs an inadequate cooling of all filaments.  
         [0007]     Likewise, the adjustment of an airflow profile on the diffuser, such as is disclosed in DE 37 08 168 A1, has been unable to solve the problem.  
         [0008]     It is therefore an object of the invention to further develop a method and an apparatus of the initially described type such that they permit a uniform cooling of a plurality of extruded filaments with relatively fine deniers, which advance in an annular arrangement.  
       SUMMARY OF THE INVENTION  
       [0009]     The invention has the advantage that cooling of the filament starts already directly after the filaments emerge from the spinneret. To this end, an additional cooling means generates between the spinneret and the outflow quench diffuser a precooling airflow that is directed toward the filaments for precooling. This results in a greater flexibility in the cooling of the filaments. In particular in the production of staple fibers, the intensive precooling of the filaments showed a possibility of producing especially fine deniers.  
         [0010]     It was also possible to improve the effect in that the method of the invention causes the precooling airflow and the diffuser jacket airflow to impact upon the filaments in the same direction, with the velocity of the precooling airflow being higher than the velocity of the diffuser jacket airflow. With that, it was possible to realize on the one hand a uniform spreading of the filament sheet. On the other hand, the intensive precooling airflow led to a uniform and thorough precooling of all filaments within the filament sheet. The subsequent further cooling of the filaments by the diffuser jacket airflow along the diffuser permits in particular a uniform solidification of the filaments even at higher withdrawal speeds.  
         [0011]     To obtain a uniform and intensive penetration of the filament sheet for evenly cooling also the filaments advancing in the outer region, an adjustment has turned out to be favorable, wherein the velocity of the precooling airflow upon its emergence is at least twice as high as the velocity of the diffuser jacket airflow, when it emerges.  
         [0012]     In this connection, a precooling airflow generated in particular by a ring slot nozzle has shown to be most effective. To this end, the ring slot nozzle comprises an annular nozzle opening arranged in spaced relationship with the filaments. With that, it was possible to achieve in particular a total displacement of the warm air that is entrained in the filament sheet, which improved in particular the further cooling of the filaments by the diffuser jacket air flow.  
         [0013]     To ensure that both the precooling and the further cooling of the filaments can occur with optimized airflows, an advantageous further development provides for adjusting the precooling airflow independently of the diffuser jacket airflow.  
         [0014]     To carry out the method, the apparatus of the invention includes an additional cooling means between the spinneret and the outflow quench diffuser, which is used to generate an additional precooling airflow for precooling the filaments.  
         [0015]     In this connection, the additional cooling means and the outflow quench diffuser may be jointly connected to an air supply device or be each supplied by separate air supply devices. To obtain a precooling airflow operating at a possibly higher velocity than the diffuser jacket airflow, the cooling means is preferably constructed as a ring slot nozzle, from which the precooling airflow emerges through a nozzle opening that is annularly arranged in spaced relationship with the filaments.  
         [0016]     In this process, it is possible to realize an intensive precooling of the extruded filaments in particular in that the spacing between the nozzle opening of the ring slot nozzle and the filaments is kept smaller than the spacing between the jacket of the outflow quench diffuser and the filaments.  
         [0017]     Furthermore, it is possible to influence the flow velocity of the precooling air in that the nozzle opening is adjustable in its clearance height.  
         [0018]     The additional cooling means may be rigidly connected directly downstream of the spinneret or directly to the outflow quench diffuser. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     In the following, the method of the invention is described in greater detail by means of several embodiments of the apparatus according to the invention with reference to attached drawings, in which:  
         [0020]      FIG. 1  is a schematic cross sectional view of a first embodiment of an apparatus which embodies the present invention;  
         [0021]      FIG. 2  is a schematic cross sectional view of a further embodiment of an apparatus according to the invention; and  
         [0022]      FIGS. 3 and 4  are schematic cross sectional views of further embodiments of an apparatus according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]      FIG. 1  schematically illustrates a cross sectional view of a first embodiment of the apparatus according to the invention. The apparatus comprises a spinneret  1 , which is arranged inside a heated spin beam  2 . The spinneret  1  is made annular, preferably circular or rectangular, and arranged on the underside of the spin beam  2 . The spinneret  1  connects via melt distribution lines  3  to a spin pump  4 . The spin pump  4  receives a polymer melt, for example, from an extruder via a melt supply line  5 . On its underside, the spinneret  1  comprises a plurality of spin holes (not shown), from each of which a filament is extruded in the form of a strand.  
         [0024]     Arranged on the underside of the spin beam  2  is a cooling means in the form of an outflow quench system  6 . To this end, the outflow quench system  6  includes an annular air chamber  8  and an air-permeable wall  10  covering the air chamber  8  toward the outside. In its size, the quench system  6  is dimensioned such that there is a space between a sheet of filaments  18  extruded from the spinneret  1  and the air-permeable wall  10 . The quench system  6  connects to a first air supply  7 , which extends through the spin beam  2  and the spinneret  1 . The air supply  7  connects via air distribution lines  9  to the air chamber  8 .  
         [0025]     Arranged downstream of the quench system  6  and within the annular arrangement of downwardly advancing filaments is an outflow quench diffuser  12 , which lies at its upper end via a centering stop  11  against the quench system  6 . At its opposite end, the outflow quench diffuser  12  connects to a mounting device  13 . The outflow quench diffuser  12  comprises a porous jacket  15 , which may be made, for example, from a nonwoven material, foam, screen mesh, or a sintered material. The mounting device  13  connects to a second air supply  14 , with the interior of the outflow quench diffuser  12  communicating with the air supply  14  via the mounting device  13 . Preferably, the mounting device  13  is made movable for guiding it out of or into the threadline for servicing, or cleaning, or changing the outflow quench diffuser  12 .  
         [0026]     Downstream of the outflow quench diffuser  12 , the mounting device  13  comprises a yarn lubrication ring  17 , which is contacted by the sheet of filaments  18  for applying a lubricant to the filaments.  
         [0027]     With the use of the apparatus shown in  FIG. 1 , the spin pump  4  delivers in operation a polymer melt under pressure to the spinneret  1 . In this process, strandlike filaments emerge on the underside from the spin holes of the spinneret  1 , which form the sheet of filaments  18 . The sheet of filaments  18  is annularly advanced and jointly withdrawn from the spinneret  1  by a withdrawal mechanism (not shown).  
         [0028]     At a short distance downstream of the spinneret  1 , the cooling means that is constructed as an air quench system  6 , directs a precooling airflow  19  from the inside radially outward through the sheet of filaments  18 . The intensity of the precooling airflow  19  can be directly regulated via the air supply  7 . The precooling airflow  19  is adjusted such that each of the filaments advancing within the sheet undergoes a uniform cooling. In addition, the filament sheet is spread, so that the individual filaments in the filament sheet can be uniformly surrounded by the subsequent airflow from the diffuser jacket.  
         [0029]     For their solidification, the filaments undergo a further cooling by an airflow  16  from the jacket of the outflow quench diffuser  12 . With that, a uniform and adequate cooling of the filaments is also realized at high spinning speeds of more than 800 m/min. To obtain an intensive and uniform precooling of the filaments, the velocity of the precooling airflow is set higher than the velocity of the diffuser jacket airflow. To this end, the spacing between the air-permeable wall  10  and the sheet of filaments  18  is adjusted substantially smaller than the spacing between the diffuser jacket  15  and the sheet of filaments  18 .  
         [0030]      FIG. 2  illustrates a second embodiment of an apparatus configured to carry out the method of the invention. In this embodiment, the precooling airflow is generated by a cooling means that is constructed as a ring slot nozzle  20 . The precooling airflow emerging from a nozzle opening  21  produces a relatively strong quench flow for effecting a precooling in the sheet of filaments. In the following description of the embodiment with reference to  FIG. 2 , components of like function are indicated at identical numerals. In the embodiment of the apparatus according to the invention as shown in  FIG. 2 , an annular spinneret  1  connects via a melt distributor  30  to a spin pump  4 . The spin pump  4 , melt distributor  30 , and spinneret  1  are arranged in a heated spin beam  2 .  
         [0031]     Arranged downstream of the spinneret  1  is an additional cooling means in the form of the ring slot nozzle  20 . The ring slot nozzle  20  is rigidly connected to the outflow quench diffuser  12 . To this end, the outflow quench diffuser  12  comprises at its free end a head plate  25 . The ring slot nozzle  20  is constructed in the shape of a collar at the free end of the outflow quench diffuser  12  and rigidly connected to the head plate  25 . The circumferentially annular nozzle opening  21  of the ring slot nozzle  20  is formed between a perforated plate  23  and a cover plate  24 , which are secured to each other via a sealing ring  22 . The clearance height of the nozzle opening  21  is determined by the thickness of the sealing ring  22 . With that, it is possible to adjust any desired clearance height of the opening  21  of ring slot nozzle  20  by exchanging or varying the sealing ring  22 . The nozzle opening  21  connects via passageways in the perforated plate  23  and head plate  25  to the interior of the outflow quench diffuser  12 . Thus, the ring slot nozzle  20  and the outflow quench diffuser  12  are supplied via a common air supply  14 . The ring slot nozzle  20  and the outflow quench diffuser  12  are secured by means of a mounting device  13  with a centering stop  11  to the underside of the spin beam  2 .  
         [0032]     The outflow quench diffuser  12  of  FIG. 2  is constructed for axial displacement relative to the mounting device  13 , with axially operative biasing means  27  holding the outflow quench diffuser  12  in an operating position. An axially displaceable outflow quench diffuser of this type is disclosed in EP 1 231 302 A1, so that this prior art publication is herewith incorporated by reference. In this arrangement, the outflow quench diffuser  12  is held at its lower end in a connecting element  26 , which extends for displacement in a centering opening  28  of the mounting device  13 . In the present embodiment, the biasing means  27  is a compression spring, which facilitates an axial displacement of the outflow quench diffuser for exchanging it.  
         [0033]     The further construction of the apparatus of  FIG. 2  is identical with that of the apparatus of  FIG. 1 , so that the foregoing embodiment is herewith incorporated by reference.  
         [0034]     For cooling the filaments, the outflow quench diffuser  12  receives a cooling airflow via the air supply  14  and mounting device  13 . In this process, a portion of the cooling airflow enters the ring slot nozzle  20  directly at the free end via passageways in the head plate  25 . A relatively strong precooling airflow then emerges from the nozzle opening  21  at a short distance from the sheet of filaments  18  and penetrates the sheet of filaments  18 . At the same time, a radially directed airflow emerges from the porous jacket  15  of the outflow quench diffuser  12 .  
         [0035]     In tests, it was found that with the use of a common air supply, the precooling airflow had an exit velocity of about 10 m/sec., whereas the exit velocity of the diffuser jacket airflow was about 3 m/sec. This made it possible to produce stable fibers, which had a final denier of 0.6 dtex. With a standard design of the outflow quench diffuser without additional cooling means and under the same air supply conditions, it was possible to produce only fibers with a final denier of more than 0.9 dtex. It was not possible to reliably produce finer deniers because of frequently occurring filament breaks. Only with the method of the invention was it possible to accomplish that fibers of fine deniers can be reliably produced without occurrence of filament breaks. It was also possible to further optimize precooling of the filaments by varying the clearance height of the nozzle opening  21  of ring slot nozzle  20 . In this instance, the clearance height ranged from 0.1 to 0.9 mm.  
         [0036]      FIG. 3  illustrates a further embodiment of an apparatus according to the invention for carrying out the method of the invention. The embodiment of  FIG. 3  is largely identical with the foregoing embodiment of  FIG. 2 . In this respect, the foregoing description is herewith incorporated by reference and only differences will be pointed out.  
         [0037]     In the embodiment illustrated in  FIG. 3 , the additional cooling means is likewise constructed as a ring slot nozzle  20  that extends at the free end of the outflow quench diffuser  12  in the shape of a collar. The construction of the ring slot nozzle  20  is identical with the embodiment of  FIG. 2 .  
         [0038]     Inside the outflow quench diffuser  12 , an air supply line  29  extends, which connects with its one end to the passageways in the head plate  25 . With its other end, the air supply line  29  connects to the air supply  7 . Thus, the ring slot nozzle  20  can be separately supplied with a cooling airflow independently of the cooling air supply to the outflow quench diffuser  12 . The outflow quench diffuser  12  connects to the air supply  14  via the mounting device  13 . With that, it is possible to adjust the precooling airflow and the diffuser jacket airflow independently of each other for cooling the filaments. In addition, it would also be possible to use different cooling media or different compositions of the cooling air for causing the filaments to solidify.  
         [0039]     A further embodiment of the apparatus according to the invention is schematically illustrated in  FIG. 4 . The embodiment differs essentially in that an outflow quench diffuser  12  is mounted to the underside of a spin beam  2 , as is disclosed, for example, in EP 1 247 883 A1. As regards the construction and operation of an apparatus of this type, the contents of the cited publication are herewith expressly incorporated by reference. In the following description of the embodiment with reference to  FIG. 4 , components of like function are provided with the same numerals as in the foregoing embodiments.  
         [0040]     In the embodiment of the apparatus according to the invention as shown in  FIG. 4 , an annular spinneret  1  connects via melt distribution lines  31  to a spin pump  4 . The spin pump  4  is driven by a drive shaft  33 . The spin pump  4 , distribution lines  31 , and spinneret  1  are arranged in a heated spin beam  2 . Arranged downstream of the spinneret  1  is a ring slot nozzle  20  as an additional cooling means. On its underside, the ring slot nozzle  20  is rigidly connected to an outflow quench diffuser  12 . The ring slot nozzle  20  and the outflow quench diffuser  12  connect with their end facing the spin beam  2  to an air supply system. A first air supply  7  is formed by an inner air supply line  29 , which extends through the spin beam  2  and projects into the outflow quench diffuser  12 . The inner air supply line  29  is enclosed by an outer air supply line  32 , which connects to the ring slot nozzle  20 , and is used to provide a second air supply  14  to the ring slot nozzle  20 .  
         [0041]     The ring slot nozzle  20  is formed by a perforated plate  23  and by a head plate  25  arranged below the perforated plate. The perforated plate  23  comprises an inlet, which is connected to the nozzle opening  21  between the perforated plate  23  and the head plate  25 . Subjacent to the head plate  25  is the outflow quench diffuser  12 .  
         [0042]     Downstream of the outflow quench diffuser  12  is a lubrication device in the form of lubrication ring  17 , which surrounds a sheet of filaments  18  that is extruded through the spinneret  1 . The sheet of filaments  18  advances along an inner contact surface of the lubrication ring  17 .  
         [0043]     In the embodiment shown in  FIG. 4 , the filaments of the sheet of filaments  18  that have been freshly extruded by the spinneret  1  are initially cooled after emerging from the spinneret  1  by a precooling airflow  19 , which is generated by the ring slot nozzle  20 . After an intensive precooling, the sheet of filaments  18  undergoes a further cooling by the diffuser jacket airflow  16 , which is generated by the jacket  15  of the outflow quench diffuser  12 . As has been previously described, the clearance height of the opening  21  of ring slot nozzle  20  can be varied to be able to adjust the intensity of the precooling of the sheet of filaments  18  to defined conditions.  
         [0044]     The apparatus illustrated in the embodiments of  FIGS. 1-4  are exemplary in their construction and can be selectively combined. Thus, for example, it would be possible to arrange a cooling means in the form of a ring slot nozzle directly downstream of the spin beam as shown in  FIG. 1 . However, it is also possible to construct the cooling means with a plurality of annular nozzle openings, which are successively arranged at short distances from one another. Important for the invention is that it makes it possible to generate at a short distance downstream of the spinneret an intensive precooling airflow for precooling the filaments, and that a longer lasting, further cooling of the filaments follows by means of an outflow quench diffuser.