Abstract:
An air handler for collecting air discharged from a melt spinning apparatus. The air handler includes an outer housing having walls defining a first interior space. One of the walls has an intake opening for receiving the discharge air. Another wall has an exhaust opening for discharging the air. The intake opening is in fluid communication with the first interior space. An inner housing is positioned within the first interior space and has walls defining a second interior space. At least one of the walls of the inner housing has an opening. The first interior space communicates with the second interior space through the opening. The second interior space is in fluid communication with the exhaust opening.

Description:
This application is a divisional of application Ser. No. 09/750,820, filed Dec. 28, 2000, now issued as U.S. Pat. No. 6,499,982, the disclosure of which is fully incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to apparatus and methods for managing air flow during the manufacture of nonwoven webs and laminates. 
     BACKGROUND OF THE INVENTION 
     Meltblowing and spunbond processes are commonly employed to manufacture nonwoven webs and laminates. With meltblowing, a molten thermoplastic is extruded from a die tip to form a row of filaments or fibers. Converging sheets or jets of hot air impinge upon the fibers as they are extruded from the die tip to stretch or draw the fibers, thereby reducing the diameter of the fibers. The fibers are then deposited in a random manner onto a moving collector belt to form a nonwoven web. 
     With spunbond processes, continuous fibers are extruded through a spinneret. Air is directed at the extruded fibers to separate and orient them. The fibers are collected onto a moving collector belt. At a downstream location, the fibers are consolidated by passing the layer of fibers through compacting roller, for instance. The spunbond process frequently utilizes quenching air to cool the extruded before they contact the collector belt. 
     Large volumes of air are used during both the meltblown and spunbond process. Moreover, much of the air is heated and moving at very high velocities, sometimes approaching the speed of sound. Without properly collecting and disposing of the process air, the air would likely disturb personnel working around the manufacturing apparatus and other nearby equipment. Further, the heated air would likely heat the surrounding area in which the nonwoven is being produced. Consequently, attention must be paid to collecting and disposing of this process air. 
     Managing the process air is also important to producing a homogeneous nonwoven web across the width of the web. The homogeniety of the final nonwoven web depends greatly on the air flow around the fibers as they are deposited onto the collector belt. For instance, if the air flow velocity is not uniform in the cross-machine direction, the fibers will not be deposited onto the collector belt uniformly, yielding a non-homogeneous nonwoven web. 
     Various air management systems have been used to collect and dispose of the process air. One particular air management system uses a collecting duct situated below a perforated collector belt to collect and dispose of the process air. An air moving device, such as a fan or vacuum pump, is connected to the collecting duct to actively draw the air into the collecting duct. The collecting duct is comprised of a plurality of a smaller air passageways arranged side-by-side in a rectangular grid. The grid includes a central row of air passageways extending across the machine width and upstream and downstream air passageways flanking either side of the central row. The central row of air passageways is disposed directly below the extrusion die in what is commonly referred to as the forming zone. Each air passageway includes an inlet and an outlet with a 90 degree elbow in between. An air moving device is operatively connected to each outlet to draw the process air into the individual inlets. 
     As mentioned above, the air flow velocity of the process air around the collector belt should be uniform, especially in the machine direction at the forming zone, to form a homogeneous nonwoven web. Achieving a uniform air flow velocity, however, has proven challenging. In the collecting duct described above, moveable dampers are associated with each outlet of the air passageways. To achieve uniform air flow velocity with this collecting duct, an technician must manually manipulate each damper until the air flow velocity is sufficiently uniform. In some instances, the technician may be unable to achieve a uniform air flow velocity no matter how much time and effort is spent adjusting the dampers. Moreover, the dampers must be readjusted each time a different fiber material or process air flow rate is used. Thus, the operator must readjust the dampers virtually every time the process is started or an operating condition is changed. The readjustment process takes a great deal of time and may ultimately yield a nonuniform air flow velocity regardless of how the moveable dampers are adjusted. 
     What is needed, therefore, is an air management system that can collect and dispose of the process air so as to produce a uniform air flow velocity at the collector belt, especially around the forming zone. The air management system should be designed such that dampers and other manual controls are not necessary, even over a wide range of process air flow rates. 
     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 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. In accordance with a general objective of the invention, the air handler produces a uniform air flow velocity in at least the cross-machine direction as the air enters the air handler. This is accomplished without the typical adjustable baffles and dampers required in the past. The air handler generally includes an outer housing having walls defining a first interior space. One of the walls has an intake opening for receiving the discharge air from the melt spinning apparatus. Another wall has an exhaust opening for discharging the air collected by the air handler. The intake opening is in fluid communication with the first interior space. An inner housing is positioned within the first interior space and has walls defining a second interior space. At least one of the walls of the inner housing has an opening. The first interior space communicates with the second interior space through the opening. The second interior space is in fluid communication with the exhaust opening. 
     In one aspect of the invention, the opening between the first interior space and the second interior space is an elongate slot and preferably includes a center portion having a wider dimension than the end portions thereof. The intake opening is positioned at the top of the outer housing, and the slot in the inner housing is disposed proximate to the bottom of the outer housing. The outer housing can further include a filter member for filtering particulates from the air discharged by the melt spinning apparatus. 
     The invention further provides an air management system including three air handlers. One air handler is positioned directly below the melt spinning apparatus in a forming zone. Another air handler is positioned upstream of the forming zone, and the other air handler is positioned downstream of the forming zone. The widths of the intake opening of the upstream and downstream air handlers in the machine direction are respectively greater than the width of the intake opening of the air handler positioned below the forming zone. The upstream and downstream air handlers collect air which spills over, i.e., not collected, from the air handler below the forming zone. 
     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 along lines  5 — 5 ; 
         FIG. 6  is a plan view of the forming zone air handler bottom in  FIG. 4  taken 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 perspective view of another embodiment of the air management system of the invention; and 
         FIG. 9  is cross sectional perspective view of the air management system in  FIG. 8  taken along lines  9 — 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , a two-station production line  10  is schematically illustrated. The production line  10  incorporates an air management system  12  of the invention at both an upstream station  14  and a downstream station  16 . 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 process, such as a meltblowing process or a spunbond process. In a multiple-station production line, a plurality of nonwoven webs can be manufactured to form a multiply laminate. 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 spunbond webs. However, the laminate may include any combination of meltblown webs and spunbond webs. 
     The two-station production line  10  in  FIG. 1  is shown forming a two-ply laminate  18  with a meltblown layer or web  20  on the bottom and a spunbond layer or web  22  on the top. The two-ply laminate  18  is consolidated downstream using compacting rolls, for example. The upstream station  14  includes a melt spinning assembly  24  with a meltblowing die  26  and the downstream station  16  includes a melt spinning assembly  28  with a spunbond die  30 . 
     To form the meltblown web  20 , the meltblowing die  26  extrudes a plurality of thermoplastic filaments or fibers  32  onto a collector such as a belt  34 . It will be appreciated that the collector  34  may be any other substrate, such as a substrate used as a component in the manufacture of a product. Converging sheets or jets of hot air, indicated by arrows  36 , from the meltblowing die  26  impinge upon the fibers  32  as they are extruded to stretch or draw the fibers  32 . The fibers  32  are then deposited in a random manner onto the collector moving belt  34  from right to left to form the meltblown web  20 . The collector belt  34  is perforated to permit the air to flow through the collector belt  34  and into the air management system  12 . 
     Similarly, to form the spunbond web  22 , the spunbond die  30  extrudes a plurality of thermoplastic filaments or fibers  38  onto the meltblown web  20  being transported by the moving collector belt  34 . Hot air, indicated by arrows  40 , from the spunbond die  30  impinges upon the fibers  38  to impart rotation to the fibers  38 . Additionally, air ducts  42  direct quenching air onto the extruded fibers  38  to cool the fibers  38  before they reach the meltblown web  20 . As with the upstream station  14 , the air at downstream station  16  passes through the nonwoven web  20  and the collector belt  34  and into the air management system  12 . 
     Several cubic feet of air per minute per inch of die length flow through each station  14 ,  16  during the manufacture of the meltblown and spunbond webs  20 ,  22 . The air management system  12  of the invention efficiency collects and disposes of the air from through the stations  14 ,  16 . More importantly and as will be discussed in greater detail below, the air management system  12  collects the air such that the air has a substantially uniform flow velocity at least in the cross-machine direction as the air passes through the collector belt  34 . Ideally, the fibers  32 ,  38  are deposited on the collector belt  34  in a random fashion to form the meltblown and spunbond webs  20 ,  22  which are homogeneous. If the air flow velocity through the collector belt  34  is nonuniform, the resultant web will likely not be homogeneous. 
     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 upstream station  14 . Nevertheless, the description will be equally applicable to the air management system associated with downstream station  16 . 
     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 belt  34 . 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 . With specific reference to  FIG. 3 , exhaust conduit  70 , which is representative of exhaust conduits  72 ,  74 , is comprised of a series of individual components: first elbows  76 , second elbows  78 , elongated portion  80 , down portion  82 , and third elbow  84 . A series of parallel guide vanes  86  extend through down portion  82  and third elbow  84 . In operation, a variable speed fan (not shown) or any other suitable air moving device is connected to third elbow  84  to draw the 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, i.e., the location where the fibers contact the collector belt  34 . As such, air handler  54  collects and disposes of the largest portion of air used during the extrusion process. Upstream air handler  56  and downstream air handler  52  collect spill over air which air handle  54  does not collect. 
     With reference now to  FIGS. 4–6 , forming zone air handler  54  includes 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 of apertures through which the air flows. Depending of 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 air flows. 
     The inner box  98  has a bottom panel  110  that includes an opening such as slot  112  with ends  114 ,  116  and a center portion  118 . As illustrated in  FIG. 6 , slot  112  extends substantially across the width, i.e., the cross-machine direction, of the inner box  98 . The slot  112  is narrow at ends  114 ,  116  and widens at center portion  118 . The slot  112  could be formed from one or more openings of various shapes, such round, elongate, rectangular, etc. 
     The shape of slot  112  influences the air flow velocity in the cross machine direction 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. 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 air flow velocity profile in the cross machine direction was checked. Ultimately, the goal was to choose a shape for the slot  112  which provided a substantially uniform air flow velocity in the cross machine direction at intake opening  60 . Initially, a rectangular slot  112  was evaluated, yielding air flow velocities in the cross machine direction at the intake opening  60  which varied by as much as twenty percent. With the rectangular 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 profile, the width of ends  114 ,  116  was reduced relative to the width of the center portion  118 . After approximately five iterations, the shape of slot  118  is  FIG. 6  was chosen. That slot shape yields air flow velocities in the cross machine direction at the intake opening  60  which varied by ±0.5%. 
     With specific reference to  FIG. 5 , air enters through perforated cover  96  and passes through perforated filter members  102 ,  104  as illustrated by arrows  120 . The 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 to minimize transverse pressure gradients. 
     Generally, air handlers  52 ,  56  have a similar construction and air flow path as air handler  54 . However, as  FIG. 3  illustrates, air handlers  52 ,  56  have much wider, i.e, in the machine direction, intake openings  58 ,  62  than intake opening  60  of air handler  54 . The width of the these intake openings  58 ,  62  may vary depending on the particular manufacturing parameters. The following discussion of air handler  52  is equally applicable to air handler  56 . Thus, with specific reference to  FIG. 7 , air handler  52  includes an outer housing  136  which includes intake opening  58  and exhaust openings  64 . Intake opening  58  includes a perforated cover  137  with a series of apertures through which the air flows. Depending on the manufacturing parameters, air handler  52  may be operated without using perforated cover  137  at all. Air handler  52  further includes an inner housing or box  138  which is suspended from the outer housing  136  by means of spacing members  140  which include a plurality of openings  142  therein. Unlike air handler  54 , air handlers  52 ,  56  do not include filter members  102 ,  104 . 
     The inner box  138  includes a bottom panel  144  with a slot  146  which is configured similarly to slot  112 . Slot  146  includes ends  148 ,  150  and center portion  152 . Like slot  112 , the width at center portion  152  is greater than the width at ends  148 ,  150 . 
     As mentioned above, the air flow path through air handler  52  is similar to the air flow path in air handler  54 . Specifically, air enters through perforated cover  137  as illustrated by arrows  154  and passes through the gap between the inner box  138  and the outer housing  136  as illustrated by arrows  156 . The air then enters the interior of inner box  138  through slot  146  as illustrated by arrow  158 . Finally, the air exits the inner box  138  through exhaust opening  64  as illustrated by arrow  160  and then travels through exhaust conduit  70 . The openings  142  in spacing members  140  allow the air to move in the cross-machine direction to minimize transverse pressure gradients. 
     Another embodiment of the air management system of the invention is shown generally as  170  in  FIGS. 8 and 9 . As described above, air management system  12  includes three separate and discrete air handlers  52 ,  54 ,  56 . In contrast, air management system  170  includes air handlers  172 ,  174 ,  176  which share common walls to form a unitary device. Air handler  174  is placed under the forming zone of the production line to collect the majority of the process air and air handlers  172 ,  176  collect spill over air which air handler  174  does not collect. Each air handler  172 ,  174 ,  176  includes an intake opening  178 ,  180 ,  182  over which a single perforated cover  184  is placed. A plurality of individual perforated covers may be used in place of the single perforated cover  184 . Each air handler  172 ,  174 ,  176  further includes exhaust openings  186 ,  188 ,  190  oppositely disposed on either end of the respective air handlers  172 ,  174 ,  176 . Separate exhaust conduits (not shown) similar to exhaust conduits  70 ,  72 ,  74  connect to exhaust openings  186 ,  188 ,  190  to pull the air out of the air handlers  172 ,  174 ,  176 . Air handler  174  may include a filter member having a perforated surface through which the incoming air flows. 
     Air handlers  172 ,  174 ,  176  include inner boxes  192 ,  194 ,  196  and sidewalls  198 ,  200 ,  202 ,  204 . Spacing members  206 ,  208 ,  210  hold inner boxes  192 ,  194 ,  196  away from sidewalls  198 ,  200 ,  202 ,  204 . Inner boxes  192 ,  194 ,  196  include bottom panels  212 ,  214 ,  216  having slots  218 ,  220 ,  222 . The air flow path through air handlers  172 ,  174 ,  176  is similar to the air flow path in air handlers  52 ,  54 ,  56 . The air flow path through air handler  174  is represented by arrows  224 . 
     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 applicants 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.