Abstract:
A system and methods for collecting and managing air discharged from a melt spinning apparatus. The air management system includes an outer housing defining a first interior space, an intake opening for receiving the discharged air into the first interior space, and an exhaust opening for discharging the air. Positioned within the first interior space is an inner housing defining a second interior space coupled in fluid communication with the exhaust opening and an opening fluidically coupling the first and second interior spaces. The air management system includes a flow control device inside the first interior space that controls the flow of air from the first interior space to the second interior space and an air-directing member outside of the first interior space near the intake opening that extends in a cross-machine direction for dividing the intake opening into two portions in a machine direction.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is related to U.S. application Ser. No. 09/750,820, filed Dec. 28, 2000 and now U.S. Pat. No. 6,499,980, which is expressly incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to apparatus and methods for manufacturing nonwoven webs and laminates from filaments of one or more thermoplastic polymers. 
     BACKGROUND OF THE INVENTION 
     Melt spinning technologies are routinely employed to fabricate nonwoven webs and multilayer laminates or composites, which are manufactured into various consumer and industrial products, such as cover stock materials for single-use or short-life absorbent products, disposable protective apparel, fluid filtration media, and durables including bedding and carpeting. Melt spinning technologies, including spunbonding processes and meltblowing processes, form nonwoven webs and composites from one or more layers of intertwined filaments or fibers, which are composed of one or more thermoplastic polymers. Fibers formed by spunbonding processes are generally coarser and stiffer than meltblown fibers and, as a result, spunbonded webs are generally stronger but less flexible than meltblown webs. 
     A meltblowing process generally involves extruding a row of fine diameter, semi-solid filaments of one or more thermoplastic polymers from a meltblowing die of a melt spinning apparatus and attenuating the extruded filaments while airborne with high velocity, heated process air immediately upon discharge from the melt spinning apparatus. The process air may be discharged as continuous, converging sheets or curtains on opposite sides of the discharged filaments or as individual streams or jets associated with the filament discharge outlets. The attenuated filaments are then quenched with a flow of a relatively cool process air and blown in a filament/air mixture for depositing in a forming zone to form a meltblown nonwoven web on a collector, such as a substrate, a belt or another suitable carrier, moving in a machine direction. 
     A spunbonding process generally involves extruding multiple rows of fine diameter, semi-solid filaments of one or more thermoplastic polymers from an extrusion die of a melt spinning apparatus, such as a spinneret or spinpack. A voluminous flow of relatively cool process air is directed at the stream of extruded filaments to quench the molten thermoplastic polymer. A high-velocity flow of relatively cool process air is then used to attenuate or draw the filaments to a specified diameter and to orient them on a molecular scale. The process air is heated significantly by thermal energy transferred from the immersed filaments. The attenuated filaments are propelled in a filament/air mixture toward a forming zone to form a nonwoven web or a layer of a laminate on a moving collector. 
     Spunbonding processes typically incorporate a filament drawing device that provides the high velocity flow of process air for attenuating the filaments. Hydrodynamic drag due to the high velocity air flow accelerates each filament to a linear velocity or spinning speed significantly greater than the speed of extrusion from the extrusion die and applies a tensile force that attenuates the filaments as they travel from the die to the inlet of the filament drawing device. Some additional attenuation occurs between the outlet of the filament drawing device and the collector as the filaments are entrained by the high velocity air exiting the filament drawing device. Conventional filament drawing devices accelerate the filaments to an average linear velocity less than 8000 meters per minute (m/min). 
     One deficiency of conventional filament drawing devices is that a large volume of high velocity process air is required for attenuating the filaments. In addition, the process air captures or entrains an excessive volume of secondary air from the ambient environment surrounding the airborne filament/air mixture. The volume of entrained secondary air is proportional to the volume and velocity of the process air exiting the filament drawing device. If left unmanaged, such large volumes of high velocity process and secondary air tend to disturb the filaments as they deposit on the collector, which degrades the physical properties of the spunbonded web. 
     As mentioned above, large volumes of process air are generated during both the meltblowing and spunbonding processes. Moreover, much of the process air is heated and is moving with high velocities, sometimes approaching sonic velocities. Without properly collecting and disposing of the process air and the entrained secondary air, large volumes of high-speed air would likely disturb personnel working around the manufacturing apparatus and other nearby equipment. Further, large volumes of heated process air would likely heat the surrounding area in which the nonwoven web or laminate is being fabricated. Consequently, attention must be paid to collecting and disposing of this process air and entrained secondary air when manufacturing nonwoven webs and laminates with melt spinning technologies. 
     Management of the process and secondary air is also important with regard to tailoring the characteristics of the filaments as deposited on the moving collector. The homogeneity of the distribution of deposited filaments across the width of the nonwoven web, or in the cross-machine direction, depends greatly on the uniformity of the air flow in the cross-machine direction around the filaments as they are deposited onto the collector belt. If distribution of air flow velocities in the cross-machine direction is not uniform, the filaments will not be deposited onto the collector uniformly, yielding a nonwoven web that is nonhomogeneous in the cross-machine direction. Thus, the variation of the air flow velocity in the cross-machine should be minimized in order to produce a nonwoven web having homogenous physical properties, such as density, basis weight, wettability, and fluid permeability, in the cross-machine direction. Moreover, large volumes of unmanaged air may also affect fiber formation upstream and downstream of the forming zone in the upstream and downstream fiber-making beams, respectively. Therefore, effective and efficient disposal of large volumes of air is necessary to avert irregularities in the physical properties of the nonwoven web. 
     Filaments deposited onto the collector have an average fiber orientation in the machine direction (MD) and an average fiber orientation in the orthogonal cross-machine direction (CD). The ratio of filament orientation, termed the MD/CD laydown ratio, indicates the isotropicity of the nonwoven web and strongly influences various properties of the nonwoven web, including the directionality of the tensile strength or flexibility of the web. Given a uniform distribution of air flow velocities in the cross-machine direction, the distribution of air flow velocities in the machine direction controls the MD/CD laydown ratio and, therefore, is an important consideration in the management of the large volumes of process and secondary air. 
     Various conventional air management systems have been used to collect and dispose of the flow of process and secondary air generated by melt spinning apparatus. Most conventional air management systems include an air moving device, such as a blower or vacuum pump, and a collecting duct having an intake opening positioned below the collector proximate to the forming zone for collecting the air and an exhaust opening coupled in fluid communication with the air moving device for disposing of the collected air. In some of these conventional systems, the negative pressure applied at the intake opening is controlled by one or more movable dampers positioned at the threshold of the intake opening. In other conventional air management systems, the collecting duct is subdivided into an array of smaller air passageways in which each individual air passageway includes an intake opening, an exhaust opening, and an air moving device coupled in fluid communication with the exhaust opening for drawing the collected air into the individual intake openings. Control of the negative air pressure applied at the intake opening is provided by multiple moveable dampers each associated with an exhaust opening of one of the air passageways. 
     Controlling the distribution of air flow velocities proximate to the forming zone in both the cross-machine and machine directions simultaneously, however, has proven challenging for conventional air management systems. Conventional air management systems, such as those described above, are incapable of systematically controlling the directionality or symmetry of the air flow velocities in the machine direction while maintaining a relatively uniform distribution of air flow velocities in the cross-machine direction. In particular, movable dampers in such conventional systems either are incapable of varying the distribution of air flow velocities in the machine direction or cannot vary the distribution of air flow velocities in the machine direction without significantly reducing the uniformity of the air flow velocities in the cross-machine direction. As a result, conventional air management systems lack the ability to select the distribution of air flow velocities in the machine direction in order to effectively control the MD/CD laydown ratio. It follows those melt spinning processes using such conventional air management systems cannot control or otherwise tailor the properties of the nonwoven web in the machine direction. 
     What is needed, therefore, is an air management system for a melt spinning system that can manipulate the disposal of the process air so as to control the distribution of air flow velocities near the forming zone for the nonwoven web in the machine direction and maintain a uniform air flow in the cross-machine direction. Also needed is a melt spinning system capable of generating reduced volumes of process air and entrained secondary air for disposal. 
     SUMMARY OF INVENTION 
     The present invention provides a melt spinning system and, more particularly, a melt spinning and air management system that overcomes the drawbacks and disadvantages of prior melt spinning and air management systems. The air management system of the invention includes at least one air handler for collecting air discharged from a melt spinning apparatus. The air handler generally includes an outer housing having first walls defining a first interior space and an inner housing positioned within the first interior space and having second walls defining a second interior space. One of the first walls of the outer housing has an intake opening positioned below a collector for admitting the discharged air from a melt spinning assembly into the first interior space and another of the first walls of the outer housing has an exhaust opening for exhausting the discharged air. The second interior space is coupled in fluid communication with the exhaust opening and one of the second walls of the inner housing has an elongate slot with a major dimension in a cross-machine direction and coupling the first interior space in fluid communication with the second interior space. 
     In certain embodiments of the invention, an adjustable flow control device is positioned in the first interior space of the air management system. The flow control device is operative for controlling the flow of discharged air between the first interior space and the second interior space. 
     In other embodiments of the invention, an air-directing member is positioned outside of the first interior space of the air management system and proximate to the intake opening. The air-directing member extends in the cross-machine direction and divides the intake opening into first and second portions in the machine direction. 
     According to the principles of the invention, an apparatus is provided which includes a melt spinning apparatus and an air management system having three air handlers. The melt spinning apparatus is operative to extrude filaments of material and is positioned vertically above a collector. A first air handler of the air management system is positioned directly below the melt spinning apparatus in a forming zone. A second air handler is positioned upstream of the first air handler and the forming zone. A third air handler is positioned downstream of the first air handler and the forming zone. The second and third air handlers each include an air-directing member, as described above, and an adjustable flow control device, also as described above. 
     According to the principles of the present invention, an apparatus is provided that is configured to discharge filaments of material onto a moving collector. The apparatus includes a melt spinning apparatus operative for extruding filaments, a filament drawing device positioned between the melt spinning apparatus and the collector, and an air handler having an intake opening positioned proximate to the collector. The filament drawing device has an inlet for receiving the filaments from the melt spinning apparatus and an outlet for discharging the filaments toward the collector. The filament drawing device is operative for providing a flow of process air sufficient to attenuate the filaments of material. The flow of process air entrains secondary air from the ambient environment between the outlet and the collector. The intake opening of the air handler collects process air discharged from the filament drawing device and secondary air entrained by the process air. The apparatus further includes a forming chamber having a side wall at least partially surrounding the intake opening of the air handler and the outlet of the filament drawing device, an entrance opening upstream of the intake opening, and an exit opening downstream of the intake opening. The side wall defines a process space for the passage of the filaments of material from the outlet of the filament drawing device to the collector and partitions the process space from the surrounding ambient environment. The entrance and exit openings are dimensioned so that at least the collector can traverse the process space. The side wall of the forming chamber includes a perforated metering sheet configured to regulate the flow of air from the ambient environment into the process space. 
     The invention further provides a method for depositing a nonwoven web of filaments on a collector moving in a machine direction in which filaments of material are discharged from a melt spinning assembly discharging filaments of material from a melt spinning assembly and mixed with a flow of process air. The filaments of material are deposited on the collector and the process air is collected with an intake opening of an air management system having a substantially uniform collection of the discharge air in the cross-machine direction and a selectively variable ratio of air flow velocity in the machine direction to air flow velocity in the cross-machine direction. 
     Various additional advantages and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     DETAILED DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic plan view of a two-station production line incorporating the air management system of the invention; 
     FIG. 2 is a perspective view of the two-station production line of FIG. 1 with the collector belt removed for clarity; 
     FIG. 3 is a perspective view of the air management system of FIG. 1; 
     FIG. 4 is a partially disassembled perspective view of the forming zone air handler of FIG. 3; 
     FIG. 5 is a cross sectional view of the forming zone air handler in FIG. 4 taken generally along lines  5 - 5 ; 
     FIG. 6 is a plan view of the forming zone air handler bottom in FIG. 4 taken generally along lines  6 - 6 ; 
     FIG. 7 is a partially disassembled perspective view of one of the spillover air handlers of FIG. 3; 
     FIG. 8 is a view of the spunbonding station of FIG. 1; 
     FIG. 9 is a perspective view of the filament drawing device of FIG. 1; 
     FIG. 10 is a cross sectional view taken generally along line  10 - 10  of FIG. 9; and 
     FIG. 11 is a cross-sectional view of an alternative embodiment of the filament drawing device of FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to FIG. 1, a two-station melt spinning production line  10  is schematically illustrated. The production line  10  incorporates an air management system  12  at a spunbonding station  14  and a separate air management system  12  at a meltblowing station  16  downstream of station  14  in a machine direction, indicated on FIG. 1 by arrow  15 . 
     While the air management system  12  has been illustrated in conjunction with the two-station production line  10 , the air management system  12  is generally applicable to other production lines having a single station or a plurality of stations. In a single station production line, the nonwoven web can be manufactured using any one of a number of processes, such as a meltblowing process or a spunbonding process. In a multiple-station production line, a plurality of nonwoven webs can be manufactured to form a multilayer laminate or composite. Any combination of meltblowing and spunbonding processes may be used to manufacture the laminate. For instance, the laminate may include only nonwoven meltblown webs or only nonwoven spunbonded webs. However, the laminate may include any combination of meltblown webs and spunbonded webs, such as a spunbond/meltblown/spunbond (SMS) laminate. 
     With continued reference to FIG. 1, the two-station production line  10  is shown fabricating a two-layer laminate  18  with a spunbonded web or layer  20  formed by spunbonding station  14  on a collector  32 , such as an endless moving perforated belt or conveyor, moving generally horizontally in the machine direction  15  and a meltblown web or layer  22  formed on top of web  20  by meltblowing station  16 . Additional meltblown or spunbonded webs may be added by additional stations downstream of meltblowing station  16 . The laminate  18  is consolidated downstream of the meltblowing station  16  by a conventional technique, such as calendering. It is understood that spunbonded web  20  may be deposited on an existing web (not shown), such as a spunbonded web, a bonded or unbonded carded web, a meltblown web, or a laminate composed of a combination of these types of webs, provided on collector  32  upstream of the spunbonding station  14  and moving downstream on collector  32  to stations  14 ,  16 . 
     The spunbonding station  14  includes a melt spinning assembly  24  with an extrusion die  25 . To form the spunbonded web  20 , the extrusion die  25  extrudes a downwardly-extending curtain of thermoplastic fibers or filaments  26  from multiple orifices (not shown) that generally span the width of the collector  32  in a cross-machine direction  17  substantially orthogonal to machine direction  15  and that delimit the width of the spunbonded web  20 . The airborne curtain of filaments  26  extruded from the extrusion die  25  passes through a monomer exhaust system  27  that evacuates any residual monomer gas from the extrusion process. The airborne curtain of filaments  26  next traverses a dual zone quenching system  28  that directs two individual flows of cool process air onto the curtain of filaments  26  for quenching the filaments  26  and initiating the solidification process. The process air from the quenching system  28  is typically supplied at a flow rate of about 500 SCFM/m to about 20,000 SCFM/m and has a temperature ranging from about 2° C. to about 20° C. 
     The airborne curtain of filaments  26  exits the quenching system  28  and is directed by suction, along with a large volume of secondary air from the surrounding environment, into an inlet  29  of a filament drawing device  30 . The filament drawing device  30  envelops the filaments  26  with a high velocity flow of process air directed generally parallel to the length of the filaments  26  for applying a biasing or tensile force in a direction substantially parallel to the length of the filaments  26 . The filaments  26  are extensible and the high velocity flow of process air in the filament drawing device  30  attenuates and molecularly orients the filaments  26 . The attenuated filaments  26  are entrained in the high velocity process air and secondary air when ejected from an outlet  34  of the filament drawing device  30 . The mixture of attenuated filaments  26  and high velocity air will be referred to hereinafter as a filament/air mixture  33 . The filament/air mixture  33  enters a forming chamber  31 , which is provided above the collector  32 , and the attenuated filaments  26  in the filament/air mixture  33  are propelled toward the collector  32 . The filament drawing device  30  may be mounted on a vertically movable fixture (not shown) for adjustment, as indicated generally by the arrow on FIG. 1, of the vertical spacing between the outlet  34  and the collector  32  among various vertical spacings. 
     The attenuated filaments  26  of the filament/air mixture  33  are deposited on the collector  32  in a random manner, generally assisted by the air management system  12 , which collects the high velocity process and secondary air generated by the spunbonding station  14 . The filament/air mixture  33  entrains additional secondary air from the environment surrounding the forming chamber, which is regulated as described below, in its airborne path between the outlet  34  and the collector  32 . 
     According to the present invention, the air management system  12  includes a pair of spill air control rollers  38 ,  40 , which have a spaced relationship in a direction parallel to the machine direction  15 . Defined in the machine direction  15  between spill air control rollers  38 ,  40  is a forming zone  35  flanked on the upstream side by a pre-forming zone  36  and on the downstream side by a post-forming zone  37 . The zones  35 ,  36 ,  37  extend lengthwise across the width of the air management system  12  in the cross-machine direction  17 . Most of the filaments  26  in the filament/air mixture  33  are deposited on the collector  32  in the forming zone  35 . The entraining process air of the filament/air mixture  33  passes through the spunbonded web  20  as it forms and thickens, the collector  32 , and any pre-existing substrate on collector  32  for collection by the forming zone  35 , pre-forming zone  36  and post-forming zone  37 . The collector  32  is perforated so that the process air from the filament/air mixture  33  flows through the collector  32  and into the air management system  12 . The process air at spunbonding station  14  is then evacuated by controlled vacuum or negative pressure supplied by the air management system  12 . The vacuum in pre-forming zone  36  is selectively controlled by a pair of spill air control valves  41 ,  42  (FIG. 8) and, similarly, the vacuum pressure in the post-forming zone  37  is selectively controlled by a pair of spill air control valves  43 ,  44  (FIG.  8 ). 
     The meltblowing station  16  includes a melt spinning assembly  45  with a meltblowing die  46 . To form the meltblown web  22 , the meltblowing die  46  extrudes a plurality of thermoplastic filaments or filaments  47  onto the collector  32 , which cover the spunbonded web  20  formed by the upstream spunbonding station  14 . Converging sheets or jets of hot process air, indicated by arrows  48 , from the meltblowing die  46  impinge upon the filaments  47  as they are extruded to stretch or draw the filaments  47 . The filaments  47  are then deposited in a random manner onto the spunbonded web  20  on the collector  32  to form the meltblown web  22 . The process air at meltblowing station  16  passes through the meltblown web  22  as it forms, the spunbonded web  20  and the collector  32  for evacuation by the air management system  12 . 
     Several cubic feet of process air per minute per inch of die length flow through each station  14 ,  16  during the manufacture of the spunbonded web  20  and the meltblown web  22 . The process air entrains secondary air from the surrounding environment along the airborne filament path from the extrusion die  25  to the collector  32 . The flow of process air and secondary air has a velocity represented by a vector quantity that may be resolved in three-dimensions as the resultant of a scalar component directed vertically toward the collector  32 , a scalar component in the machine direction  15 , and a scalar component in the cross-machine direction  17 . 
     The air management system  12  efficiently collects and disposes of the process air and any entrained secondary air from the stations  14 ,  16 . More importantly, the air management system  12  collects the process and secondary air such that the process air has a substantially uniform flow velocity in at least the cross-machine direction  17  as the process air passes through the collector  32 . Ideally, the filaments  26 ,  47  are deposited on the collector  32  in a random fashion to form the spunbonded and meltblown webs  20 ,  22 , which have homogeneous properties in at least the cross-machine direction  17 . If the air flow velocity through the collector  32  is nonuniform in the cross-machine direction  17 , the resultant webs  20 ,  22  will likely have non-homogeneous properties in the cross-machine direction  17 . Therefore, it is apparent that the variation in the magnitude of the component of air flow velocity in the cross-machine direction  17  must be minimized to produce a web  20 ,  22  having homogeneous properties in cross-machine direction  17 . 
     With reference to FIG. 2, transport structure  50  of the two-station production line  10  of FIG. 1 is shown. While the two-station production line  10  includes two air management systems  12 , the following description will focus on the air management system  12  associated with the spunbonding station  14 . Nonetheless, the description is understood to be equally applicable to the air management system  12  associated with the meltblowing station  16 . An air management system similar to air management system  12 , and upon which the principles of the present invention represent an improvement, is described in co-pending, commonly-owned U.S. patent application Ser. No. 09/750,820, entitled “Air Management System for the Manufacture of Nonwoven Webs and Laminates” and filed Dec. 28, 2000, which is expressly incorporated by reference herein in its entirety. 
     With further reference to FIGS. 2 and 3, air management system  12  includes three discrete air handlers  52 ,  54 ,  56  disposed directly below the collector  32 . Air handlers  52 ,  54 ,  56  include intake openings  58 ,  60 ,  62  and oppositely disposed exhaust openings  64 ,  66 ,  68 . Individual exhaust conduits  70 ,  72 ,  74  are connected respectively to exhaust openings  64 ,  66 ,  68 . Exhaust conduit  70 , which is representative of exhaust conduits  72 ,  74 , is comprised of a series of individual components including first elbows  76 , second elbows  78 , and elongated portion  80 . In operation, any suitable air moving device (not shown), such as a variable speed blower or fan, is connected by suitable ducts to elongated portion  80  to provide suction, vacuum or negative pressure for drawing the process air through the air management system  12 . 
     With continued reference to FIGS. 2 and 3, air handler  54  is located directly below the forming zone  35 . As such, air handler  54  collects and disposes of the largest portion of the process air used during the extrusion and filament-forming processes to form spunbonded web  20  and the secondary air entrained therewith. The pre-forming zone  36  of the upstream air handler  52  and the post-forming zone  37  of the downstream air handler  56  collect spillover air which air handler  54  does not collect. 
     With reference now to FIGS. 4-6, forming zone air handler  54  has an outer housing  94 , which includes intake opening  60  and oppositely disposed exhaust openings  66 . Intake opening  60  includes a perforated cover  96  with a series or grid of apertures through which the combined process and secondary air flows. Depending on the manufacturing parameters, air handler  54  may be operated without using the perforated cover  96  at all. Air handler  54  further includes an inner housing or box  98  which is suspended from the outer housing  94  by means of spacing members  100  which include a plurality of openings  101  therein. Two filter members  102 ,  104  are selectively removable from air handler  54  so that they may be periodically cleaned. The filter members  102 ,  104  slide along stationary rail members  106 ,  108 . Each of these filter members  102 ,  104  are perforated with a series of apertures through which the combined process and secondary air flows. 
     The inner box  98  has a bottom panel  110  that includes an opening, such as elongate slot  112 , with ends  114 ,  116  and a center portion  118 . As illustrated in FIG. 6, slot  112  has a length or major dimension extending across the inner box  98  in the cross-machine direction  17 . An inner periphery of the slot  112  has a minor dimension or width that is relatively narrow at ends  114 ,  116  and relatively wide at center portion  118 . The shape of slot  112  is symmetrical about a centerline  113  extending in the machine direction  15 . Specifically, the width of slot  112  in the machine direction  15  generally increases in a direction extending from either of ends  114 ,  116  toward the centerline  113 . The largest width of slot  112  occurs at the centerline  113 . The slot  112  could be formed collectively of one or more openings of various geometrical shapes, such as round, elongate, rectangular, etc., operative to reduce variations of air flow velocities in the cross-machine direction  17  at the intake opening  60 . 
     The shape of elongate slot  112  influences the air flow velocity in the cross-machine direction  17  at the intake opening  60 . If the shape of the slot  112  is not properly contoured, the air flow velocities at the intake opening  60  may vary greatly in the cross-machine direction  17 . The particular shape shown in FIG. 6 was determined through an iterative process using a computational fluid dynamics (CFD) model which incorporated the geometry of the air handler  54 . A series of slot shapes were evaluated at intake air flow velocities ranging between 500 to 2500 feet per minute. After the CFD model analyzed a particular slot shape, the distribution of air flow velocities in the cross-machine direction  17  was checked. Ultimately, the goal was to choose a shape for the slot  112  that provided a substantially uniform air flow velocity in the cross-machine direction  17  at intake opening  60 . Initially, a rectangular shape for slot  112  was evaluated, yielding a distribution of air flow velocities in the cross-machine direction  17  at the intake opening  60  that varied by as much as twenty percent. With the rectangular shape of slot  112 , the air flow velocities near the ends of the intake opening  60  were greater than the air flow velocities approaching the center of the intake opening  60 . To address this uneven air flow velocity distribution, the width in the machine direction  15  of each of ends  114 ,  116  is reduced relative to the width in the machine direction  15  of the center portion  118 . After approximately five iterations, the geometrical shape of slot  112  illustrated in FIG. 6 was selected as optimal. That slot shape yields a distribution of air flow velocities at the intake opening  60  that varies by about ±5.0% in the cross-machine direction  17 . Such a variation in the cross-machine air flow velocities produces an acceptably uniform air flow in the cross-machine direction  17  for providing adequate homogeneity in the distribution of deposited filaments across the width of the spunbonded web  20 . 
     With specific reference to FIG. 5, process and secondary air enters through perforated cover  96  and passes through porous filter members  102 ,  104 , as illustrated generally by arrows  120 . The process air passes through the gap between the inner box  98  and the outer housing  94  as illustrated by arrows  122 . The air then enters the interior of inner box  98  through slot  112  as illustrated by arrows  124 . Finally, the air exits the inner box  98  through exhaust opening  66  as illustrated by arrows  126  and then travels through exhaust conduit  72 . The openings  101  in spacing members  100  allow the air to move in the cross-machine direction  17  to minimize transverse pressure gradients that would otherwise be communicated to the intake opening  60 . 
     As illustrated in FIG. 3, the intake openings  58 ,  62  of air handlers  52 ,  56  are significantly wider in the machine direction  15  than intake opening  60  of air handler  54 . However, intake openings  58 ,  62  are divided in the machine direction  15  by the presence of spill air control rollers  38 ,  40 . As best shown in FIG. 8, the negative pressure area of the intake opening  58  is divided into two discrete zones, an upstream zone  57  upstream in the machine direction  15  from spill air control roller  38  and the pre-forming zone  36 . Similarly, the negative pressure area of intake opening  62  is divided into two discrete zones, a downstream zone  59  downstream in the machine direction  15  from the spill air control roller  40  and the post-forming zone  37 . 
     Because of the substantial similarity of air handlers  52  and  56 , the following description of air handler  52  applies equally to air handler  56 . With reference to FIGS. 7 and 8, air handler  52  has an outer housing  136  which includes intake opening  58  and exhaust openings  64 . Intake opening  58  includes a perforated cover  135  with a series of fine apertures through which the process air and entrained secondary air flows. Depending on the manufacturing parameters, perforated cover  135  may be eliminated from air handler  52 . 
     Air handler  52  further includes an inner housing or box  138  that is suspended from the outer housing  136  by multiple latticed dividers  140  having a spaced-apart relationship in the cross-machine direction  17 . A flow chamber  141  (FIG. 8) is created in the substantially open volume between the intake opening  58  (FIG. 7) and an upper wall  143  of the inner box  138 . Spaced-apart vertical air plenums  137 ,  139  (FIG. 8) are created by respective spaced-apart gaps in the machine direction  15  between the inner box  138  and the outer housing  136 . Air plenum  137  has an air inlet port  128  coupled in fluid communication with flow chamber  141 , and air plenum  139  has an air inlet port  130  coupled in fluid communication with flow chamber  141 . Each of the latticed dividers  140  includes a plurality of openings  142  that couple the various portions of the flow chamber  141  partitioned by dividers  140 . The latticed dividers  140  participate in equalizing the flow of process and secondary air from the intake opening  58  to plenums  137 ,  139  and operate to disrupt turbulent flow. Air plenum  137  includes latticed dividers  132  and air plenum  139  includes latticed dividers  134  in which dividers  132 ,  134  have a similar function as latticed dividers  140 . 
     With continued reference to FIGS. 7 and 8, the inner box  138  includes a bottom panel  144  spaced vertically from the outer housing  136  to define a horizontal air plenum  145  (FIG. 8) having opposite open ends respectively coupled in fluid communication with air plenums  137 ,  139 . The bottom panel  144  includes an aperture or slot  146  that is configured similarly to slot  112  and that couples the air plenum  145  in fluid communication with the interior of inner box  138 . Slot  146  is operative to direct air arriving via plenums  137 ,  139 ,  145  into the interior of inner box  138 . An inner periphery of slot  146  includes ends  148 ,  149  and center portion  150 . Like slot  112 , the width at center portion  150  of slot  146  is greater than the width at ends  148 ,  149 . Air is exhausted from the interior of the inner box  138  via exhaust openings  64  (FIGS.  1  and  3 ). It is appreciated that air handler  52  is representative of air handler  56  so that like features are labeled with like reference numerals in FIG.  8 . 
     With reference to FIG. 8, spill air control roller  38  extends in the cross-machine direction  17  across the length of the intake opening  58  and is mounted for free rotation on a shaft  151 , which is supported at opposite ends by the forming chamber  31 . The spill air control roller  38  is journalled on bearings (not shown) to the shaft  151  and is suspended above the collector  32  with which roller  38  has a rolling engagement. The spill air control roller  38  has a length in the cross-machine direction  17  across the length of the intake opening  58  substantially equal to the width of the collector  32  and to the width of the spunbonded web  20 . 
     A smooth-surface anvil or support roller  152  is located below the collector  32  and extends in the cross-machine direction  17  across the length of the intake opening  58 . The support roller  152  is positioned vertically relative to the spill air control roller  38  by a distance sufficient to provide an entrance opening  131  for collector  32  and any substrate residing thereupon. The rollers  38 ,  152  frictionally engage collector  32  and rotate in opposite directions as collector  32  is conveyed into the forming chamber  31  of spunbonding station  14 . This spatial relationship between the collector  32 , the spill air control roller  38 , and the support roller  152  significantly reduces the aspiration of secondary air from the surrounding environment of forming chamber  31  that might otherwise disturb fiber laydown on the collector  32  inside the forming chamber  31  while allowing entry of the collector  32  and any substrate residing thereupon into the process space  171 . 
     The spill air control roller  38  is formed of an unperforated sheet of metal and is shaped geometrically as a right circular cylinder having a smooth, cylindrical peripheral surface. Each opposite transverse end of the spill air control roller  38  may be closed with a circular disk of sheet metal (not shown) each having a central aperture through which shaft  151  protrudes for mounting to the forming chamber  31 . 
     Similarly, spill air control roller  40  is mounted for free rotation to the forming chamber  31  by a shaft  153  and an anvil or support roller  154  that operates in conjunction with spill air control roller  40  to define post-forming zone  37  by dividing intake opening  62  of air handler  56 . Collector  32  and spunbonded substrate  20  formed by spunbonding station  14  exit the forming chamber  31  by passing through an exit opening  133  provided between roller  40  and roller  154 . Spill air control roller  40  has similar attributes as spill air control roller  38  and hence the above description of control roller  38  applies equally to control roller  40 . It is apparent that the spill air control rollers  38 ,  40  and support rollers  152 ,  154  provide guide surfaces spaced in the machine direction  15  which guide the filament/air mixture  33  (FIG. 1) to target zones  35 ,  36 ,  37 . 
     With reference to FIG.  8  and continuing to describe spillover air handler  52  with the understanding that the description is equally applicable to air handler  56 , spill air control valve  41  is positioned in flow chamber  141  proximate to air inlet port  128  of vertical air plenum  139  and spill air control valve  42  is positioned in flow chamber  141  proximate to air inlet port  130  of vertical air plenum  137 . Spill air control valves  41  and  42  are selected from any of numerous mechanical devices by which the flow of air may be regulated by a movable part that partially obstructs one or more ports or passageways. 
     Spill air control valves  41  and  42  are illustrated in FIG. 8 as having a butterfly valve structure, although the present invention is not so limited. Spill air control valve  41  comprises a shutter  156 , which may be rectangular, extending in the cross-machine direction  17  and a rotatable shaft  157  to which shutter  156  is diametrically attached. Spill air control valve  41  regulates the flow of process air into air inlet port  128  of vertical air plenum  139 . Specifically, the shaft  157  is rotatable about an axis of rotation extending in the cross-machine direction  17  along its length so that shutter  156  can regulate the flow of process air into vertical air plenum  139 . The rotational orientation of shutter  156  at least partially determines the flow resistance of process air being evacuated through intake opening  58  upstream of spill air control roller  38  and into vertical air plenum  139 . 
     Similarly, spill air control valve  42  includes a shutter  158  extending in the cross-machine direction  17  and a rotatable shaft  159  to which shutter  158  is diametrically attached. Spill air control valve  42  regulates the flow of process air into air inlet port  130  of vertical air plenum  137 . Specifically, the shaft  159  is rotatable about an axis of rotation extending along its length so that shutter  158  can regulate the flow of process air into vertical air plenum  137 . The rotational orientation of shutter  158  at least partially determines the flow resistance (i.e., air volume and velocity) of process air being evacuated through intake opening  58  downstream of control roller  38  in pre-forming zone  36  and into vertical air plenum  137 . Regulation of the flow resistance with spill air control valves  41 ,  42  regulates the negative air pressure or vacuum applied in pre-forming zone  36 . The spill air control valves  41 ,  42  further regulate the negative air pressure or vacuum applied upstream of the spill air control roller  38  in upstream zone  57  for holding any material on the collector  32  in intimate contact therewith. 
     With continued reference to FIG. 8, spill air control valves  43 ,  44  of air handler  56  have a similar construction to spill air control valves  41 ,  42  and function similarly for selectively regulating the negative air pressure in the post-forming zone  37  and upstream of spill air control roller  40  in downstream zone  59 . The application of negative air pressure upstream of spill air control roller  40  in post-forming zone  37  is particularly important for controlling the accumulation of freshly-deposited filaments  26  on the outer peripheral surface of the roller  40 . 
     Spill air control valves  41 - 44  may be manually adjusted or mechanically coupled with actuators (not shown) for varying the flow of process air into plenums  137 ,  139 . Sensing devices (not shown), such as vacuum gauges or flow meters, may be provided in air handler  52  for monitoring the relative vacuum pressures or air flows in vertical air plenums  137 ,  139 . A control system (not shown) may be provided for receiving feedback from the sensing devices and controlling the actuators for varying the orientations of spill air control valves  41 - 44 . 
     The collection efficiency for the filaments  26  on collector  32  is a function of several characteristics of the filament/air mixture  33 , including the temperatures of the air and filaments  26 , the air velocity, and the air volume. The spill air control valves  41 - 44  may be adjusted to match the vacuum pressures in at least zones  35 ,  36 ,  37  for optimizing the collection efficiency. The vacuum pressures will differ in each of zones  35 ,  36  and  37  due to differing pressure drops across the thickness of the overlying material, including the collector  32 , any substrate thereupon and the spunbonded web  20 . Although the vacuum pressures must be sufficient for evacuating the process air, the vacuum pressures must not be so great as to compress the spunbonded web  20  as it is formed on collector  32 . The spill air control valves  41 - 44  are configured and/or dimensioned such that the distributions of air flow velocities in the cross-machine direction  17  are not significantly effected by their presence adjacent the vertical air plenums  137 ,  139 . 
     As mentioned above, the flow path of process and entrained secondary air through air handler  52  is similar to the flow path of process and entrained secondary air in air handler  56 . With reference to FIGS. 7 and 8 and as described with regard to air handler  52 , process and secondary air enters flow chamber  141  through intake opening  58  and perforated cover  135 , as illustrated by arrows  160 , and passes through the vertical air plenums  137 ,  139 , as illustrated by arrows  161 . The vacuum pressure controlling the individual flows of air into vertical air plenums  137 ,  139  is selected by orienting spill air control valves  42 ,  41  to vary the flow resistance to plenums  137 ,  139 , respectively. The air then enters the interior of inner box  138  through slot  146 , as illustrated by arrow  162 . Finally, the air exits the inner box  138  through exhaust opening  64  as illustrated by arrow  163  and then travels through exhaust conduit  70 . The openings  142  in latticed dividers  140  allow the air to move in the cross-machine direction  17  to minimize transverse pressure gradients. 
     With reference to FIG. 8, the forming chamber  31  constitutes a semi-open structure having a support housing  164  formed of one or more thin, unperforated metal sheets and a perforated metering sheet  166 . Metering sheet  166  generally surrounds a process space  171  created between the outlet  34  of the filament drawing device  30  and an inlet  165  to the forming chamber  31 . The inlet  165  is located between the outlet of the filament drawing device  30  and the collector  32  so that the filament/air mixture  33  can enter the process space. Top seals  167 ,  169  are each attached at one end to support housing  164  and have a second end respectively positioned above one of spill air control rollers  38 ,  40  for forming substantially air-tight, rolling engagements with respective upper portions thereof. 
     Generally, the metering sheet  166  is any structure operative to regulate the fluid communication between the surrounding ambient environment and the process space  171  inside the forming chamber  31  between the filament drawing device  30  and collector  32 . To that end, penetrating through the thickness of the metering sheet  166  is a plurality of holes or pores  168  arranged with a spaced-apart relationship in a random pattern or in a grid, array, matrix or other ordered arrangement. Typically, the pores  168  are symmetrically arranged for providing a symmetrical aspiration of secondary air in the machine direction  15  and in the cross-machine direction  17  from the ambient environment surrounding the forming chamber  31 . The pores  168  typically have a circular cross-sectional profile but may be, for example, polygonal, elliptical or slotted. The pores  168  may have a single, uniform cross-sectional area or may have various cross-sectional areas distributed to produce a desired flow of secondary air into the space between the filament drawing device  30  and the forming chamber  31 . For a circular cross-sectional profile, the average diameter of the pores  168  is less than about 500 microns and, typically, ranges between about 50 microns to about 250 microns. The pattern of pores  168  may be determined by, for example, a fluid dynamics calculation or may be randomly arranged to provide the desired flow characteristics. The metering sheet  166  may be, for example, a screen or sieve, a drilled, stamped or otherwise produced apertured thin metal plate, or a gas permeable mesh having interconnected gas passageways extending through its thickness. 
     The metering sheet  166  is characterized by the porosity or the ratio of the total cross-sectional area of the pores  168  to the ratio of the remaining unperforated part of the sheet  166 . The pores  168  of the metering sheet  166  provide significant regulation of the flow of secondary air from the surrounding ambient environment induced by aspiration through the sheet  166  and captured by the filament/air mixture  33 . The porosity of the metering sheet  166  is characterized by, among other parameters, the number of pores  168 , the pattern of the pores  168 , the geometrical shape of each pore  168 , and the average pore diameter. Typically, the ratio of the total cross-sectional area of the pores  168  to the ratio of the remaining unperforated part of the sheet  166  ranges from about 10% to about 80%. 
     In one embodiment and as illustrated in FIG. 8, the metering sheet  166  is a thin mesh screen or apertured shear foil that has a limited degree of flexibility. For example, the metering sheet  166  may be a thin foil ranging in thickness from about 10 microns to about 250 microns that is etched chemically to provide pores  168 . The flexibility of the metering sheet  166  accommodates the vertical movement of the filament drawing device  30  relative to the collector  32  and, to that end, metering sheet  166  is bent into an arcuate shape 
     The filament/air mixture  33  and the secondary air entrained therein collectively travel toward the collector  32  and the air is exhausted by the air management system  12 . The metering sheet  166  significantly reduces the entrainment of secondary air by the flow of filament/air mixture  33  toward collector  32  by restricting the air flow of secondary air from the ambient environment into space between the filament drawing device  30  and the forming chamber  31 , which reduces the total volume of air that the air management system  12  must exhaust from zones  35 ,  36 ,  37 . 
     With reference to FIGS. 1 and 8 and as described above, the filament drawing device  30  of the spunbonding station  14  attracts filaments  26  exiting the quenching system  28  with suction into inlet  29 , attenuates and molecularly orients the filaments  26  with a high velocity flow of process air directed parallel to the direction of motion of the filaments  26 , and discharges the attenuated filaments  26  from outlet  34  as a component of filament/air mixture  33 . The filament/air mixture  33  consists of attenuated filaments  26  entrained in high velocity process air and transported toward the collector  32 , where the filaments  26  are collected to form spunbonded web  20  and the process air is exhausted by the air management system  12 . The filament/air mixture  33  captures secondary air from the surrounding environment in flight or transit from the outlet  34  to the collector  32 . 
     With reference to FIGS. 9 and 10, one embodiment of the filament drawing device  30  includes a first process air manifold  170  and a second process air manifold  172  movably attached to the process air manifold  170  by a bracket  174 . Each of the process air manifolds  170  and  172  includes a cylindrical flow chamber  176  that extends in the cross-machine direction  17  between a flanged inlet fitting  178  at one end and a flanged exhaust fitting  180  at an opposite end. A flow of temperature-controlled process air is established in each flow chamber  176  between the inlet and exhaust fittings  178 ,  180 . To that end, a pressurized process air supply  182  is coupled in fluid communication with inlet fitting  178  by an air supply conduit  183 . A portion of the process air is directed in the filament drawing device  30  so as to attenuate the filaments  26 , as will be described below. Residual process air is exhausted from each flow chamber  176  to a waste gas sink  184  via an air exhaust conduit  185  connected to exhaust fitting  180 . Typically, the process air supply  182  provides process air at a pressure of about 5 pounds per square inch (psi) to about 100 psi, typically within the range of about 30 psi to about 60 psi, and at a temperature of about 60° F. to about 85° F. 
     The process air manifolds  170 ,  172  are separated by a flow passageway or slot  186 , best shown in FIG. 10, that extends axially or vertically from inlet  29  to outlet  34  and through which the filaments  26  pass in transit from inlet  29  to outlet  34 . The inlet  29  to the filament drawing device  30  has a width in the machine direction  15  that does not limit the suction generated within device  30 . The portion of the flow passageway  186  proximate the inlet  29  has a conical or flared throat  188  with a cross-sectional area that tapers to a uniform width channel  190 . The flared throat  188  includes a first segment  191  inclined inwardly relative to a vertical axis  192  with a first taper angle α and a second segment  193  inclined inwardly relative to the vertical axis  192  with a second taper angle β, wherein the first taper angle α is greater than the second taper angle β. The flared throat  188  and the channel  190  are in fluid continuity without obstruction or occlusion to the passage of the filaments  26 . 
     The length of the flow passageway  186  in the cross-machine direction  17  is approximately equal to the desired transverse dimension or width of the spunbonded web  20  (FIG. 1) in the cross-machine direction  17 . Typical lengths for the flow passageway  186  range from about 1.2 meters to about 5.2 meters for forming spunbonded webs  20  of similar dimensions in the cross-machine direction  17 . Typically, the marginal 0.1 meter portions of the spunbonded web  20  are excised and discarded after deposition. The separation between the process air manifolds  170 ,  172  in the machine direction  15  determines the width of the channel  190  of flow passageway  186 . 
     With continued reference to FIGS. 9-10, process air manifold  170  is movable relative to the process air manifold  172  in the machine direction  15  for varying the width of the channel  190  of flow passageway  186 . To that end, process air manifold  170  is movable mounted to the bracket  174  and a pair of electro-pneumatic cylinders  194 ,  195  are provided that are operative for providing motive power to move process air manifold  170  relative to process air manifold  172 . The electro-pneumatic cylinders  194 ,  195  may vary the width of the channel  190 , which alters the properties of the filaments  26  and filament/air mixture  33 . In preparation for operation, the width of channel  190  may be varied from about 0.1 mm to about 6 mm and, for most applications, is adjusted so that the separation between the process air manifolds  170 ,  172  is between about 0.2 mm and about 2 mm. Process air manifold  170  may also be moved a greater distance from process air manifold  172 , such as about 10 cm to about 15 cm, to enhance the access to the flow passageway  186  for maintenance events such as removing resin residues and other debris that accumulate during use. 
     Each of the process air manifolds  170 ,  172  includes a connecting plenum  196  defined by confronting side walls  197 ,  198 . The connecting plenum  196  couples the flow passageway  186  in fluid communication with each flow chamber  176  so that process air flows from each of the flow chambers  176  into the channel  190  of the flow passageway  186 . Specifically, each connecting plenum  196  has is coupled in fluid communication with one of the flow chambers  176  by a plurality of spaced-apart feed holes  200 . The feed holes  200  are arranged in a row or other pattern that extends in the cross-machine direction  17  for substantially the entire length of each process air manifold  170 ,  172 . For example, feed holes  200  having a diameter of about 4 mm may be spaced apart such that adjacent pairs of feed holes  200  have a center-to-center spacing of approximately 4.75 mm. 
     Air flow in each connecting plenum  196  is constricted by a pair of dams or bosses  202 ,  204  that extend in the cross-machine direction  17 . The bosses  202 ,  204  project inwardly from side walls  197 ,  198 , respectively, of the connecting plenum  196 . Bosses  202 ,  204  are aligned in opposite directions relative to the axis  192  and present a tortuous pathway that significantly reduces the wake turbulence of the process air flowing in each connecting plenum  196 . The reduction in the wake turbulence promotes a uniform flow of process air for uniformly and consistently applying the drawing force to the filaments  26 , which results in a uniform and predictable attenuation of the filaments  26 . 
     With continued reference to FIGS. 9 and 10, the side walls  197 ,  198  of the connecting plenum  196  curve and narrow to converge at an elongate discharge slit  206  that provides fluid communication between each connecting plenum  196  and the flow passageway  186 . The discharge slit  206  extends in the cross-machine direction  17  for substantially the entire length of each of the process air manifolds  170 ,  172 . Process air is ejected from the discharge slit  206  and enters the channel  190  of flow passageway  186  as an air sheet. Each discharge slit  206  is oriented such that the air sheet is directed downwardly toward the collector  32  and downwardly with respect to the filaments  26  traveling through the channel  190 . Specifically, the sheet of process air exiting from the discharge slit  206  is inclined with respect to the axis  192  with an inclination angle between about 5° and about 25° and typically, about 15°. 
     In use and with reference to FIGS. 9 and 10, process gas flowing in each flow chamber  176  enters the respective connecting plenum  196  through the feed holes  200  and is accelerated to a high speed in the connecting plenum  196  before entering the channel  190  through the discharge slit  206  as a homogeneous air sheet of substantially uniform velocity directed substantially axially toward the outlet  34 . As the filaments  26  pass through flow passageway  186 , the converging air sheets ejected from the discharge slit  206  of each of the process air manifolds  170 ,  172  imparts drag forces to the filaments  26  and attenuates, stretches or otherwise draws down the filaments  26  to a reduced diameter. The air sheets entering the channel  190  of flow passageway  186  create a suction at the inlet  29  that supplies the tensile force operative for attenuating the fibers  26  and that aspirates secondary air from the ambient environment into the inlet  29 . The filament drawing force increases as the air velocity of each air sheet increases. The reduction of the filament diameter is also a function of distance from filament drawing device  30  to the extrusion die  25 . 
     The process air manifolds  170 ,  172  are preferably formed of any material that is dimensionally and thermally stable under the operating conditions of the filament drawing device  30  so that dimensional tolerances are unchanging during operation. Stainless steels suitable for forming the process air manifolds  170 ,  172  include a Carpenter Custom type 450 stainless steel alloy and a type 630 precipitation-hardened 17Cr-4Ni stainless steel alloy each available commercially from Carpenter Technology Corp. (Reading, Pa.). 
     The filament drawing device  30  of the present invention operates at a lesser pressure than conventional filament drawing devices while providing a comparable or improved fiber attenuation. Although the pressure of the process air is reduced, the filament drawing device  30  is highly efficient and the velocity of the filaments  26  in the filament/air mixture  33  is adequate to ensure high-quality fiber laydown for forming spunbonded web  20 . In particular, the filament drawing device  30  provides spinning speeds, as represented by the linear velocities for filaments  26 , that range from 8,000 m/min up to about 12,000 m/min. The reduction in the pressure of high-velocity process air exiting the outlet  34  also reduces the entrained volume of secondary air from the ambient environment between the outlet  34  of the filament drawing device  30  and the collector  32 . According to principles of the present invention, filament drawing device  30  enhances the spinning speed while simultaneously reducing the volume of secondary and process air that the air management system  12  must manage and, in doing so, enhances the characteristics of the spunbonded web  20  formed on collector  32 . 
     With reference to FIG. 11 in which like reference numerals refer to like features in FIGS. 9 and 10, an alternative embodiment of the filament drawing device  210  includes a single process air manifold  212  similar to the process air manifolds  170 ,  172  of filament drawing device  30 , and a flow diverter  214  that replaces process air manifold  170 . The flow diverter  214  includes a solid interior that lacks flow passageways for process air. In certain embodiments, the flow diverter  214  may be formed by blanking or otherwise disabling the inlet  178  and the outlet  180  of one of process air manifold  170  (FIGS. 9 and 10) so that the flow chamber  176  is inoperable. 
     The air management system  12  permits a significant degree of control over the properties of the spunbonded web  20  formed by spunbonding station  14 . Generally, the properties of spunbonded web  20  are a complex function of parameters including the temperature of the filaments  26 , the temperature of the process air in the quenching system  28 , the temperature of the process air in the filament drawing device  30 , and the velocity and volume of the process air at the collector  32 . Typically, the spunbonded web  20  has a filament size greater than about 1 denier and a web weight ranging from about 4 g/m 2  to about 500 g/m 2 . 
     Adjustment of the relative positions of the spill air control valves  41 - 44  of air management system  12 , in conjunction with the guide paths for the high velocity process and secondary air provided by the spill air control rollers  38 ,  40 , permits the air flow velocity in the machine direction  15  to be selectively controlled or regulated. The ability to regulate the air flow velocity in the machine direction  15  allows the ratio of the average fiber orientation in the machine direction  15  to the average fiber orientation in the cross-machine direction  17 , referred to hereinafter as the MD/CD laydown ratio, to be tailored. Specifically, adjustment of the positions of the spill air control valves  41 - 44  alters the flow resistance in the vertical air plenums  137 ,  139  and, thereby, permits the MD/CD laydown ratio to be adjusted from a value of 1:1, connoting isotropic or symmetrical fiber laydown of spunbonded web  20 , to values as large as 5:1, which connotes a highly asymmetrical or anisotropic fiber laydown to form spunbonded web  20 . 
     The resin used to fabricate the spunbonded web  20  formed by spunbonding station  14  can be any of the commercially available spunbond grades of a wide range of thermoplastic polymeric materials including without limitation polyolefins, polyamides, polyesters, polyamides, polyvinyl acetate, polyvinyl chloride, polyvinyl alcohol, cellulose acetate, and the like. Polypropylene, because of its availability and low relative cost, is a common thermoplastic resin used to form spunbonded web  20 . The filaments  26  used in making spunbonded web  20  may have any suitable morphology and may include hollow or solid, straight or crimped, single component, bi-component or multi-component fibers or filaments, and blends or mixes of such fibers and/or filaments, as are well known in the art. To produce bi-component and multi-component filaments and/or fibers, for example, the melt spinning assembly  24  and the extrusion die  25  are adapted to extrude multiple types of thermoplastic resins. An exemplary melt spinning assembly  24  and extrusion die  25  having a spin pack capable of extruding multi-component filaments to form multi-component spunbonded webs  20  is described in commonly-assigned, U.S. patent application Ser. No. 09/702,385, now U.S. Pat. No. 6,478,563, entitled “Apparatus for Extruding Multi-Component Liquid Filaments” and filed Oct. 31, 2000. 
     In certain embodiments of the present invention, it is understood that the filament drawing device  30  of spunbonding station  14  may have a conventional construction and that the properties of spunbonded web  20  fabricated by spunbonding station  14  incorporating a conventional filament drawing device will benefit from the presence of air management system  12 . Specifically, the MD/CD laydown ratio may be controlled, as described above, independently of the construction of the filament drawing device  30 . The filament drawing device  30  of the present invention, shown in FIGS. 9-11, enhances the filament linear velocity so that the filaments  26  are attenuated to a greater extent possible with the attenuation achievable with conventional filament drawing devices. In particular, conjunctive use of the air management system  12  and filament drawing device  30  of the present invention provides the optimal degree of control over the properties of spunbonded web  20 . 
     While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in considerable detail in order to describe the best mode of practicing the invention, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications within the spirit and scope of the invention will readily appear to those skilled in the art.