Abstract:
This disclosure is related to the manufacture of melt blown coreless tubular nonwovens. Such manufacture includes a melt blowing apparatus to deposit fibers onto a rotating mandrel for forming a tubular nonwoven; a puller device to withdraw the tubular nonwoven from the mandrel; and a cutting device to cut the tubular nonwoven into cartridges of a desired length. The puller device has a pair of drive axles mounted on a gap-setting device, such as a scissor jack or its equivalent. Each drive axle includes one or more driven multi-directional puller wheels, which is formed of or surrounded by non-driven rollers. When the rollers engage the rotating tubular nonwoven, the tubular nonwoven is pulled axially and steadily from the mandrel without affecting the rotational motion of the tubular nonwoven. As a result, the tubular nonwovens have consistent dimensions and quality without damage to the inner or outer surfaces of the tube.

Description:
TECHNICAL FIELD 
     The present disclosure relates to a system and apparatus for making coreless nonwoven tubes for uses in filtration, irrigation, drainage, and the like. More particularly, an apparatus for the manufacture of the nonwoven tubular products by a process commonly known as “melt blowing” includes an improved puller device. 
     BACKGROUND 
     The term “melt blown” refers to fibers or a mat formed by extruding a molten thermoplastic material (the “melt” or the “polymer melt”) through a plurality of fine orifices as molten filaments into converging flows of high-speed heated gas. This process is described more fully in U.S. Pat. No. 3,825,380; U.S. Pat. No. 3,849,241; and U.S. Pat. No. 4,889,476, all of which are incorporated by reference herein, as well as in numerous other publications. Generally speaking, the polymer is melted in an extruder and forced through a row of fine capillaries (also known as “orifices” or “nozzles” or “spinnerets”) to produce molten filaments. The orifices are drilled through the apex of a sharp angled metal structure called the “die tip.” Two adjacent parts known as “air plates” or “air blades” surround the die tip and define the gaps between them, which constitute the geometry of the “air knives”. 
     High pressure and temperature air or gas (known as the “primary air”) passes through the air knives. The pressure of the supplied primary air determines the blowing speed of the air knives. The air knives attenuate and agitate the molten filaments as they exit the orifices to reduce their diameters and to improve the molecular alignment of the polymer. By regulating the temperature and pressure of the primary air and those of the polymer melt, this arrangement is capable of producing fibers of different diameter sizes, from the sub-micron diameter range to macro fibers (with average diameters of greater than 40 microns). According to U.S. Pat. No. 3,825,380, the upper limit for the diameter of the melt blowing orifice is about 0.03 inches. Orifices of larger size may produce excessively large shots in the resulted nonwoven products. Melt-blown fibers are sufficiently continuous and self-bonding, when deposited onto a collecting surface. 
     One of the major uses of nonwoven fabrics or articles (often simply called “nonwovens”) is for gas and liquid filtration. Melt-blown (MB) nonwovens are particularly suitable for such uses, because their micro-sized fibers and pores can trap even microscopic particles while still allowing flow to pass through the article. Melt-blown nonwovens meet stringent filtration requirements better than other nonwovens can, including spun bonded, air-laid, wet-laid, carded, needle-punched, and spun-laced nonwovens, as well as most glass or wood fiber mats. 
     In filtration applications, both planar mats and cylindrical tubular filters are common. The latter functions especially well in situations with tight space, large flow volume, or high flow pressure. The early tubular filters were made by rolling up nonwoven sheets and then cutting into a desired length. This method has been found to have some significant drawbacks. 
     First, this manufacturing approach requires numerous steps and pieces of equipment, including cutting off and recycling the two ends of the rolled-up tube. These discrete steps cannot be integrated into a continuous process flow. Predictably, the equipment, material, and labor costs are high. Additionally, the layered filter tubes have lower material utilization efficiency than that of a one-piece nonwoven tube of the same weight. 
     Secondly, the resulting rolled-up filter has deficiencies. For example, the layered tube has poor rigidity, and often requires a hard inner core to help withstand flow pressure. Incorporating such a core requires additional equipment, material, and costs. Moreover, seams are required to secure the inner and outer edges to the tube body, which can be problematic for some applications. Also, variations in the nonwoven sheets (such as variations in weight, thickness, porosity, and the like) result in variations in the final tubular product. 
     Lastly, this method is not suitable for making tubular filters with density-gradient walls, which are more popular in the industry due to their better filtration efficiency and longer service life. 
     Therefore, the filtration industry has enthusiastically pursued methods and equipment for making one-piece melt-blown (MB) tubes that are coreless and seamless. In this approach, a tubular nonwoven system  1  includes a melt-blowing die  101  that blows molten fibers  103  directly onto a rotating mandrel roll  102  to form a porous tubular nonwoven  104 , as shown generically in  FIG. 1 . The distance between the die tip and the mandrel roll influences the tightness of the laid fibrous body. As the tube reaches the desired outer diameter, it is continuously withdrawn from the mandrel by a puller device  107  (as indicated by dashed lines, more details of which will be provided below). Downstream of the puller device  107 , a motor-driven cutting device  105  (e.g., a flying knife or saw) is used to cut the moving tube  104  into nonwoven cartridges  106  of a desired length. The results are better products with low capital, labor, and waste. 
     Examples of such efforts to produce tubular melt-blown nonwovens may be found in U.S. Pat. No. 4,112,159; U.S. Pat. No. 4,116,738; U.S. Pat. No. 4,847,125; U.S. Pat. No. 5,366,576; U.S. Pat. No. 5,409,642; U.S. Pat. No. 5,591,335l; U.S. Pat. No. 5,672,232; U.S. Pat. No. 6,391,200; and U.S. Pat. No. 6,736,274. Some of these exemplary devices use a single die, while others use multiple dies. 
     It is well understood that there are numerous, sometimes conflicting, requirements to develop a satisfactory means of pulling the rotating tube off the mandrel continuously and steadily. Some of these requirements include: 
     a. The puller device should be economical to build, easy and safe to use. 
     b. The position and movement of the puller device should permit the safe and free movement of the tube-cutting knife or saw. 
     c. The puller device should be able to operate over a broad range of speeds and inner and outer tube diameters with quick and simple adaptation only, because tubular products are routinely made in many diameters, lengths, and wall thicknesses. 
     d. All melt-blown devices have a fluctuating and generally declining output rate, due to the gradual clogging of the melt filter, contamination of the nozzle, and possible fluctuation in the voltage received by the device. Therefore, the puller device&#39;s speed should be self-correcting or at least easily adjustable to maintain product consistency. 
     e. Physical damage to the inside or outside of the tubular cartridges should be avoided to preserve their functionality. Crushing, cuts, tears, scratches, punctures, fluid channeling, or loose fibers adversely affect the performance of the tubular cartridges. Cuts to the inside wall may be particularly destructive, as they cause filtrate leakage. 
     f. The rate of fiber mass being removed from the mandrel must match the rate of fiber deposition onto the mandrel, so that the resulting tube will have consistent weight and diameter. Slippage among the mandrel, the tube, and the puller device cannot be tolerated. 
     g. When the puller device pulls the tube off the mandrel, it must not fight against the rotational motion of the tube (as imparted by the mandrel). Rotational speed change or slippage between the tube and the mandrel may lead to uneven weight and dimension in the tubular cartridges, and such quality issues are difficult to detect and correct during production. 
     h. The puller device should maintain a firm and constant grip on the rotating tube, even as the latter&#39;s surface often has varied and changing properties including tube diameter, coefficient of friction, hardness, material&#39;s oily content, average fiber diameter, fuzziness, moisture, spray coatings, out-of-roundness, compaction treatment on tube wall, and the like. With conventional puller devices, tightening the grip is the only method of accommodating differences in nonwoven properties, which may interfere with the tube&#39;s rotational motion. Rotational retardation or slip, detectable or not, violates requirements “f” and “g” above. 
     i. To meet so many requirements simultaneously, the puller device&#39;s operation and control should be able to utilize modern automation technology to reduce manual labor and avoid errors and inaccuracy. 
     Currently, there are several types of puller devices in commercial use, which are widely apart in concept and design but none of which can be considered as satisfactory. The existing types of puller devices include devices with a rotating screw inside the tubular nonwoven; devices with rotating screws on the outside of the tubular nonwoven; devices with multiple canted rolls; devices with gears and pulling arms; and devices with canted rolls with detents, each of which is discussed below. 
       FIGS. 2 and 3  illustrate a tubular nonwoven system  200  having a first type of puller device  2  (“Type A”), which includes a rotating screw  207  inside a tubular nonwoven  204 . Such a device is illustrated, for example, in U.S. Pat. No. 5,366,576; U.S. Pat. No. 5,409,642; and U.S. Pat. No. 5,672,232. 
     A rotatable mandrel  202  functions as a collector surface for a melt-blowing die  201 , which deposits molten fibers  203  onto the surface thereof. The rotatable mandrel  202  is driven at a first rotational speed Ω 1  by a first motor “M”. The first motor is connected to a first pulley  214  that is connected by a drive belt  213  to a second pulley  212 , which is attached to the mandrel  202 . 
     The rotatable screw  207  (having a slightly larger diameter than the outer diameter of the mandrel  202 ) is installed at the end of the mandrel  202 . A shaft  208 , which is positioned through the hollow mandrel  202 , drives the screw  207  at a second rotational speed Ω 2 . The shaft  208  is turned at speed Ω 2  by a third pulley  209 , which is connected by a drive belt  211  to a fourth pulley  210 . The fourth pulley  210  is operably connected to a second motor “M.” 
     When the rotational speed Ω 2  of the screw  207  is significantly (15% to 25%) faster than the rotational speed Ω 1  of the mandrel  202 , the screw thread cuts into the inner wall of the nonwoven tube  204  and pushes the tube  204  forward in an axial direction toward the cutting device  205 . The cutting device  205  cuts the nonwoven tube  204  into tubular cartridges  206  of a desired length. 
     Although its mechanical system is complex and expensive, Type A pullers with inside screws (e.g.,  2 ) are one of the most popular puller devices currently in use. One shortcoming associated with these types of puller devices  2  is that the rotating screw  207  cuts grooves into the inner wall of the nonwoven tube  204 , and the resulting grooves may function as a continuous flow channel for filtrate and contaminants to escape under pressure. This concern is more serious when the flow pressure is high, the filtration requirement is stringent, or the filtrate is of high value. 
     Another limitation of Type A puller devices is the necessity to replace the complete set of the mandrel and screw each time a product change demands a different inner diameter. Such a requirement increases equipment and operational costs. All other types (discussed below) require only the mandrel to be replaced. 
       FIGS. 4 and 5  illustrate a tubular nonwoven system  300  having a second type of puller device  3  (“Type B”), which includes rotating screws  307  on the outside of the tubular nonwoven  304 . Such a device is illustrated, for example, in U.S. Pat. No. 5,366,576 and U.S. Pat. No. 5,672,232. 
     A melt-blowing die  301  deposits molten fibers  303  onto a rotating mandrel  302  to form a continuous tubular nonwoven  304 . The puller device  3  includes multiple (usually three) screws  307  that are positioned around and against the outer surface of the tubular nonwoven  304 . An endless drive belt  309  engages the screws  307 , and a pulley wheel  308  is connected to a motor “M”. A drive belt tensioner  310  may be used to ensure the appropriate tension on the drive belt  309 . The puller device  3  advances the nonwoven tube  304  to a cutting device  305 , which cuts the tube into individual nonwoven cartridges  306  of a desired length. The surface speed of the screws  307  is faster than that of the nonwoven tube  304 , pushing it in an axial direction toward the cutting blade  305 . 
     The three puller screws  307  cut multiple grooves on the outer wall of the nonwoven cartridge  306 . Except for detracting from the appearance of the product, the screws  307  result in less harm than the cuts on the inner wall that are produced by the Type A puller (the inner screw type) discussed above. However, this system&#39;s hardware and operation are more complicated and difficult to use than Type A. 
       FIGS. 6 and 7  illustrate a tubular nonwoven system  400  having a third type of puller device  4  (“Type C”), which includes multiple canted rollers  407  that are driven and that are pressed against a newly formed tubular nonwoven  404 . Such a device is illustrated, for example, in U.S. Pat. No. 4,112,159; U.S. Pat. No. 4,116,738; and U.S. Pat. No. 5,591,335. 
     A melt-blowing die  401  deposits molten fibers  403  onto a rotating mandrel  402  to form the continuous tubular nonwoven  404 . The rotatable mandrel  402  is driven at a first rotational speed Ω 1  by a first motor “M”. The puller device  4  includes multiple (usually three) canted rollers  407  that are positioned around and against the outer surface of the tube  404 . The canted rollers  407  are driven by a second motor (not shown) at a second rotational speed Ω 2 . The nonwoven tube  404  is cut by a cutting device  405  into nonwoven cartridges  406  of a desired length. 
     By adjusting the angles between the axis of the mandrel and those of the canted rollers and by adjusting the speed differential between the surfaces of the tubular nonwoven and the canted rollers, an axial force component is produced that nudges the tube forward and off the mandrel, while the mandrel, the nonwoven tube, and the rollers are in rotational motion. It has been found that simultaneous adjustment of the angles, rotational speed, and compressive force of the rollers  407  is difficult to achieve and is impractical to automate by modern technology. As a result, although nonwoven manufacturers have used Type C puller devices commercially for the longest time, these manufacturers have found it hard to consistently obtain high product quality; and the off-quality ratio is high. 
       FIG. 8  illustrates a tubular nonwoven system  500  having a fourth type of puller device  5  (“Type D”), which includes gears  505  with puller arms  506 . Such a device is illustrated, for example, in U.S. Pat. No. 4,847,125. 
     In this system  500 , a melt-blowing die  501  deposits molten fibers  503  onto a rotating mandrel  502  to form a continuous tubular nonwoven  504 . The rotatable mandrel  502  is driven by a first motor “M”. When the nonwoven tube  504  reaches a desired diameter on the mandrel  502 , a puller device engages the nonwoven tube. 
     The puller device  5  includes two gears  505 , which are attached to puller arms  506  and which are positioned around and against the outer surface of the tube  504 . The gears  505  are rotatable, but not motor-driven. The puller arms  506  pull the nonwoven tube  504  from the mandrel  502  in an axial direction  507 , so that the nonwoven tube  504  may be subsequently cut by a cutting device (not shown) into nonwoven cartridges of a desired length. 
     The Type D puller device is complicated to operate and, thus, has limited practical utility. Because the puller device itself is located in an area previously used for the cutting device, this system is incapable of working in continuous production. 
       FIGS. 9 through 11  illustrate a tubular nonwoven system  600  having a fifth type of puller device  6  (“Type E”), which includes a large canted wheel  607  with detents that engage the outer surface of a tubular nonwoven  604 . Such a device is illustrated, for example, in U.S. Pat. No. 6,736,274. 
     As with the previous melt-blowing systems, a melt-blowing die  601  deposits molten fibers  603  onto a rotating mandrel  602  to form a continuous nonwoven tube  604 . The rotatable mandrel  602  is driven by a first motor “M”. The canted wheel  607 , which is driven by a second motor “M”, includes multiple sharp detents on its outer periphery. The detents penetrate into the nonwoven tube  604  to pull the tube  604  from the mandrel  602  to a cutting device  605 . The nonwoven tube  604  is cut by the cutting device  605  into nonwoven cartridges  606  of a desired length. 
     When the detents pierce the outer surface of the nonwoven tube  604 , they pull the tube  604  in the direction of the rotational motion of the canted wheel  607 . As a result, the detents leave permanent holes  608  in the outer surface of the nonwoven tube  604 , which can impact the functionality of the nonwoven cartridge  606 . Additionally, the pulling force of the canted wheel  607  may unwittingly cause rotational slippage between the nonwoven tube  604  and the mandrel  602 . 
     Like the Type C puller device, the Type E puller device requires simultaneous adjustments to the speed, the slant angle, and the compression force of the canted wheel  607 . Such multiple adjustments are difficult and imprecise. For this reason and because of the detent damage to the resulting product, these Type E systems have limited commercial applicability. 
     With these conventional puller devices, it has been observed that the forces of pull are imprecise and insufficient. When the puller devices engage the rotating nonwoven tube, they resist the tube&#39;s rotational motion with an undesirable and immeasurable torque, which often leads to inconsistency in product quality. 
     By using the performance criteria (a to i) listed above, the relative merits of each of the said types (A to E) are estimated below in TABLE 1. The requirements are rated on a scale of 1 to 10, where 1 is the least satisfactory and 10 is the most satisfactory. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Performance characteristics of prior puller systems 
               
             
          
           
               
                   
                 Manufacturing Requirements (rated on scale of 1-10) 
               
               
                   
                 1 = least satisfactory, 10 = most satisfactory 
               
             
          
           
               
                 Puller Type 
                 a 
                 b 
                 c 
                 d 
                 e 
                 f 
                 g 
                 h 
                 i 
               
               
                   
               
               
                 A (inner screw) 
                 3 
                 10 
                 3 
                 4 
                 2 
                 6 
                 4 
                 5 
                 8 
               
               
                 B (outer screws) 
                 4 
                 10 
                 4 
                 4 
                 3 
                 6 
                 4 
                 5 
                 7 
               
               
                 C (canted rollers) 
                 2 
                 10 
                 4 
                 3 
                 5 
                 4 
                 4 
                 3 
                 3 
               
               
                 D (gears and arms) 
                 5 
                  1 
                 5 
                 4 
                 3 
                 6 
                 7 
                 5 
                 3 
               
               
                 E (canted roll with  
                 5 
                 10 
                 6 
                 4 
                 1 
                 8 
                 3 
                 8 
                 5 
               
               
                 detents) 
               
               
                   
               
             
          
         
       
     
     As observed, none of the puller types scores highly in all requirements. From this background, it is clear that there remains a need for a better puller device and method. 
     SUMMARY 
     This disclosure is related to the manufacture of melt blown coreless tubular nonwovens. Such manufacture includes a melt blowing apparatus to deposit fibers onto a rotating mandrel for forming a tubular nonwoven; a puller device to steadily withdraw the tubular nonwoven from the mandrel; and a cutting device to cut the tubular nonwoven into cartridges of a desired length. The puller device has a pair of drive axles mounted on a gap-setting device, such as a scissor jack or its equivalent. Each drive axle includes one or more driven multi-directional puller wheels, which is formed of or surrounded by non-driven rollers. When the rollers engage the rotating tubular nonwoven, the tubular nonwoven is pulled axially and steadily from the mandrel without affecting the rotational motion of the tubular nonwoven. As a result, the tubular nonwovens have consistent dimensions and quality without damage to the inner or outer surfaces of the tube. Furthermore, the disclosed puller device is suitable to employ modern sensors and controllers to make processing more accurate and automatic. Other benefits include low cost, easy operation and maintenance, quick adaptation for product change, and reduced rejects. 
     According to one aspect, a system for producing tubular nonwovens is provided, the system comprising: a melt-blowing die for producing molten fibers; a rotating mandrel having a surface onto which the molten fibers are deposited to produce a continuous tubular nonwoven; a puller device downstream of the melt-blowing die, the puller device having a plurality of multi-directional rollers engaged with an outer surface of the tubular nonwoven, each of the multi-directional rollers being independently rotatable; and a cutting device for cutting the tubular nonwoven into a nonwoven cartridge. 
     In another aspect, a system for producing coreless nonwoven cartridges comprises: at least one melt-blowing die for producing molten fibers; a rotating mandrel having a surface onto which the molten fibers are deposited to produce a continuous tubular nonwoven; a puller device downstream of the melt-blowing die, the puller device having a plurality of multi-directional rollers engaged with an outer surface of the tubular nonwoven, each of the multi-directional rollers being operably connected to a hub and being independently rotatable; a radially adjustable gap-setting device to position the rollers against the tubular nonwoven; and a cutting device for cutting the tubular nonwoven into a nonwoven cartridge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present products and methods, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  is a side view of a conventional system for producing a coreless melt-blown tubular cartridge; 
         FIG. 2  is a side view of a conventional tubular nonwoven system having a traditional puller device (referred to herein as “Type A”), which uses an inside screw to advance the formed tube; 
         FIG. 3  is a detailed side view of the Type A puller device of  FIG. 2 ; 
         FIG. 4  is a side view of a conventional tubular nonwoven system having a traditional puller device (referred to herein as “Type B”), which uses three outside screws to advance the tube; 
         FIG. 5  is a cross-sectional view of the Type B puller device of  FIG. 4 ; 
         FIG. 6  is a side view of a conventional tubular nonwoven system having a traditional puller device (referred to herein as “Type C”), which uses three canted rollers to advance the tube; 
         FIG. 7  is a cross-sectional view of the Type C puller device of  FIG. 6 ; 
         FIG. 8  is a side view of a conventional tubular nonwoven system having a traditional puller device (referred to herein as “Type D”), which uses gears and attached arms to advance the tube; 
         FIG. 9  is a side view of a conventional tubular nonwoven system having a traditional puller device (referred to herein as “Type E”), which uses a large canted roll with detents to advance the tube; 
         FIG. 10  is a cross-sectional view of the Type E puller device of  FIG. 9 ; 
         FIG. 11  is a side view of a nonwoven cartridge produced by the apparatus of  FIGS. 9 and 10 , which illustrates damage on the cartridge surface caused by the detents; 
         FIG. 12  is a side view of a tubular nonwoven system with a puller device of the present disclosure (referred to herein as “Type F”), using adjustable puller arms with multi-directional wheels; 
         FIG. 13  is a cross-sectional view of the Type F puller device of  FIG. 12 ; 
         FIG. 14  is a perspective view of the multi-directional wheel, used in the Type F puller device of  FIG. 12 ; 
         FIG. 15  is a cross-sectional view of the multi-directional wheel of  FIG. 14 ; 
         FIG. 16  is a plan view of an alternate design of the multi-directional wheel of  FIG. 14 ; 
         FIG. 17  is a cross-sectional view of the alternate multi-directional wheel of  FIG. 16 ; and 
         FIG. 18  is a perspective view of the alternate multi-directional wheel of  FIGS. 16 and 17 . 
     
    
    
     For convenience, their elements and reference numbers are listed in TABLE 2 below. 
     
       
         
               
             
               
               
               
               
             
               
             
               
               
               
               
             
               
             
               
               
               
               
             
               
             
               
               
               
               
             
               
             
               
               
               
               
             
               
             
               
               
               
               
             
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Component List for Figures 
               
               
                   
               
             
             
               
                 FIG. 1 
               
             
          
           
               
                 1 
                 tubular nonwoven system 
                 104 
                 tubular nonwoven 
               
               
                 101 
                 melt-blowing die 
                 105 
                 cutting device 
               
               
                 102 
                 rotating mandrel 
                 106 
                 nonwoven cartridge 
               
               
                 103 
                 molten fibers 
                 107 
                 puller device 
               
             
          
           
               
                 FIGS. 2 and 3 (Type A puller device) 
               
             
          
           
               
                 2 
                 puller device of Type A 
                 207 
                 screw 
               
               
                 200 
                 tubular nonwoven system 
                 208 
                 rotatable shaft 
               
               
                 201 
                 melt-blowing die 
                 209 
                 pulley 
               
               
                 202 
                 rotating mandrel 
                 210 
                 pulley 
               
               
                 203 
                 molten fibers 
                 211 
                 drive belt 
               
               
                 204 
                 tubular nonwoven 
                 212 
                 pulley 
               
               
                 205 
                 cutting device 
                 213 
                 drive belt 
               
               
                 206 
                 nonwoven cartridge 
                 214 
                 pulley 
               
             
          
           
               
                 FIGS. 4 and 5 (Type B puller device) 
               
             
          
           
               
                 3 
                 puller device of Type B 
                 305 
                 cutting device 
               
               
                 300 
                 tubular nonwoven system 
                 306 
                 nonwoven cartridge 
               
               
                 301 
                 melt-blowing die 
                 307 
                 rotating screws 
               
               
                 302 
                 rotating mandrel 
                 308 
                 pulley 
               
               
                 303 
                 molten fibers 
                 309 
                 drive belt 
               
               
                 304 
                 tubular nonwoven 
                 310 
                 drive belt tensioner 
               
             
          
           
               
                 FIGS. 6 and 7 (Type C puller device) 
               
             
          
           
               
                 4 
                 puller device of Type C 
                 404 
                 tubular nonwoven 
               
               
                 400 
                 tubular nonwoven system 
                 405 
                 cutting device 
               
               
                 401 
                 melt-blowing die 
                 406 
                 nonwoven cartridge 
               
               
                 402 
                 rotating mandrel 
                 407 
                 canted rollers 
               
               
                 403 
                 molten fibers 
                   
                   
               
             
          
           
               
                 FIG. 8 (Type D puller device) 
               
             
          
           
               
                 5 
                 puller device of Type D 
                 504 
                 tubular nonwoven 
               
               
                 500 
                 tubular nonwoven system 
                 505 
                 gears 
               
               
                 501 
                 melt-blowing die 
                 506 
                 puller arms 
               
               
                 502 
                 rotating mandrel 
                 507 
                 direction of pulling force 
               
               
                 503 
                 molten fibers 
                   
                   
               
             
          
           
               
                 FIGS. 9, 10, 11 (Type E puller device) 
               
             
          
           
               
                 6 
                 puller device of Type E 
                 604 
                 tubular nonwoven 
               
               
                 600 
                 tubular nonwoven system 
                 605 
                 cutting device 
               
               
                 601 
                 melt-blowing die 
                 606 
                 nonwoven cartridge 
               
               
                 602 
                 rotating mandrel 
                 607 
                 canted roll with detents 
               
               
                 603 
                 molten fibers 
                 608 
                 perforations caused by detents 
               
             
          
           
               
                 FIGS. 12 through 18 (Type F puller device of present disclosure) 
               
             
          
           
               
                 7 
                 puller device of Type F 
                 708 
                 multi-directional wheel 
               
               
                 700 
                 tubular nonwoven system 
                 709 
                 roller in wheel 708 
               
               
                 701 
                 melt-blowing die 
                 710 
                 axle of wheel 708 
               
               
                 702 
                 rotating mandrel 
                 711 
                 hub of wheel 708 
               
               
                 703 
                 molten fibers 
                 712 
                 alternate multi-directional wheel 
               
               
                 704 
                 tubular nonwoven 
                 713 
                 roller in wheel 712 
               
               
                 705 
                 cutting device 
                 714 
                 anchor for roller 713 
               
               
                 706 
                 nonwoven cartridge 
                 715 
                 puller arm 
               
               
                 707 
                 gap-setting device (e.g.,  
                   
                   
               
               
                   
                 scissor jack) 
                   
                   
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the inventive products and methods, one or more examples of which are illustrated in the drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. As used herein, the terms “first,” “second,” and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. 
     Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to one of ordinary skill in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as fall within the scope of the appended claims and their equivalents. 
     This disclosure is directed to a system for the continuous production of the coreless melt blown (MB) tubular cartridges, which are suitable for use as filter media. 
     Equipment and processes for making coreless nonwoven tubes are described in the Background section of the present disclosure and in the patents referenced herein. The conventional types of puller devices (Types A to E), along with their advantages and disadvantages (Table 1), are also discussed in the Background section with reference to  FIGS. 2 to 11 . 
     The performance of the puller device impacts process efficiency and product quality in many ways. Its performance should at least meet these requirements: (1) the puller device should grip the rotating tubular nonwoven firmly without slippage; (2) through the grip, a firm force of pull in an axial direction should be applied to the tubular nonwoven; (3) neither the grip or the force of pull should interfere with the rotation of the tubular nonwoven; (4) the forces of grip and of pull should be separately measurable and controllable; and (5) these forces should not cause damage or lasting deformation to the inner and outer peripheries of the resulting product. Only the presently disclosed puller devices are capable of meeting all these requirements, while none of the state-of-the-art types (types A through E) have such capability. 
     Other benefits of the disclosure include simplicity of equipment and operation, low cost, easy-to-apply automation, less waste, and better product quality. 
       FIGS. 12 and 13  illustrate a system  700  for the production of coreless nonwoven cartridges, according to a first aspect of the present disclosure. A melt-blowing die  701  deposits molten fibers  703  onto a mandrel  702 , which is rotated by a motor “M”. As the fibers  703  are deposited onto the rotating mandrel  702 , a tubular nonwoven  704  is created. The tubular nonwoven is drawn downstream from the melt-blowing die  701  by a puller device  7  and is cut into individual nonwoven cartridges  706  by a cutting device  705 . 
     The puller device  7  of the present disclosure, which is located downstream from the melt-blowing die  701 , includes two puller arms  715  for gripping and pulling the nonwoven tube  704 . Each arm  715  has two multi-directional puller wheels  708  mounted on an axle  710 , which is operably connected to a drive motor “M”. The arms  715  are mounted in parallel on a gap-setting device  707  (such as a scissor jack or equivalent structure), so that the distance between the arms  715  can be varied to accommodate tubular nonwovens  704  of different diameters. The gap-setting device  707  can also control the grip force applied on the tube  704 . 
     Independently, the speed control of the wheels  708  determines the speed of pull and the resulting outer diameter of the nonwoven tube  704 . When the manufacturer desires to produce a nonwoven tube  704  with a small outer diameter, the pull speed of the wheels  708  may be set to a relatively fast speed. Conversely, when the manufacturer desires to produce a nonwoven tube  704  with a larger outer diameter, the pull speed of the wheels  708  is slowed. To accommodate different outer diameters, the drive motor on the gap-setting device  707  may be adjusted to maintain the appropriate contact between the nonwoven tube  704  and the wheels  708 . 
     The wheels  708  do not impede the rotational motion of the nonwoven tube  704 , even when the wheels  708  are pressed tightly against the nonwoven tube  704 , nor do the wheels  708  damage the exterior surface of the nonwoven tube  704 . Even though a single multi-directional wheel  708  on each puller arm  715  may be able to engage and pull the nonwoven tube  704 , two wheels  708  on each arm  715  (as shown in  FIG. 13 ) may afford a safer accommodation for the rotating tube  704 . 
       FIG. 14  illustrates the puller wheels  708  on one of the puller arms  715 . The puller wheels  708  include four rollers  709 , each of which is shaped as a prolate spheroid that rotates about its own major (longitudinal) axis. The structural details of the wheel  708  and the rollers  709  are shown in  FIG. 15 . 
     As shown in  FIG. 15 , the drive axle  710  of the puller arm wheels  708  is surrounded by a multi-spoke hub  711 . The hub  711  and the axle  710  may be secured by a key or tab. Each roller  709  rotates around a rod (shown in dashed lines) that is positioned through a pair of adjacent spokes in the hub  711 . Since each roller  709  has its own axis of rotation (i.e., about the rod), each roller  709  can rotate independently of the other rollers  709 , while the collective profile of the rollers  709  produces a wheel or circular shape conducive for engaging the tubular nonwoven  704 . The rollers  709  may be made of, or covered with, a semi-hard material to avoid slippages and scratches on the tubular nonwoven  704 . Providing grooves in the roller surface (as shown in  FIG. 14 ) or roughing up the surface of the roller can also improve traction. 
       FIGS. 16 ,  17 , and  18  illustrate alternate multi-directional wheel assemblies  712  that can be used as the puller assembly  7  in the present melt-blowing system. The puller device with these multi-directional wheel assemblies  712  performs as well as the puller wheel  708  (shown in  FIGS. 14 and 15 ). In this puller device, each of the two multi-directional wheel assemblies has a center axle  712  surrounded by a plurality of passive rollers  713 , each of which has a cylindrical shape. The passive rollers  713  are arranged in two parallel, axially separated planes. Each center axle  712  is driven by a motor “M”. Each of the plurality of rollers  713  is mounted on two roller anchors  714 . Each roller  713  can rotate separately from the other rollers  713  as a result of its contact with the tubular nonwoven  704  (in other words, the rollers  713  themselves are not driven). 
     The tubular nonwoven  704  has four points of contact with the respective rollers  713 , two of which are associated with an upper multi-directional wheel assembly and a two of which are associated with a lower multi-directional wheel assembly. The multiple points of contact help to ensure the uniform and symmetrical shape of the nonwoven cartridge  704 . As the center axle  712  of each wheel assembly is driven by the motor, the contact between the rollers  713  and the nonwoven tube  704  pulls the tubular nonwoven  704  in an axial direction toward a cutting blade (not shown). The rotation of the rollers  713  is counter to the rotation of the tubular nonwoven  704 , as shown in  FIGS. 17 and 18 , and is designed to absorb the rotational movement of the tubular nonwoven  704 . 
     Puller wheels  708  and  712  are design examples used for teaching the essence of present disclosure and should not be construed as limiting the invention. The gap-setting device  707  is also exemplary and not intended to limit the invention to a particular structure. From the teachings of this disclosure, those with ordinary skill in the art may well identify additional configurations or modifications for wheels  708  and  712  and the gap-setting device  707 . Such extensions are intended to fall within the spirit of the present invention and its claims. 
     Finally, modern sensors and controllers can be employed with reasonable simplicity to make the present puller assembly  7  more dependable and self-controllable. For instance, non-contact sensors can measure the outer diameter and the axial speed of the tubular nonwoven. A piezoelectric sensor (not shown) can measure the compression force between the puller wheel and the tubular nonwoven. Alternately or additionally, an optical sensor may be used. Alarms and E-stops may be employed to reduce labor and waste. A process controller (PC) may use these signals to operate the puller device on a “cruise-control” mode. 
     The present puller devices are simple and economical. Further, they meet all the performance requirements (a to i) described in the Background section. TABLE 3 shows a comparison of the present puller device (Type F) with the prior-art types of puller devices (Types A to E, as described above). Again, the requirements are rated on a scale of 1 to 10, where 1 is the least satisfactory and 10 is the most satisfactory. 
     
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Performance characteristics of prior puller systems 
               
               
                 compared to the present puller device 
               
             
          
           
               
                   
                 Manufacturing Requirements (rated on scale of 1-10) 
               
               
                   
                 1 = least satisfactory, 10 = most satisfactory 
               
             
          
           
               
                 Puller Type 
                 a 
                 b 
                 c 
                 d 
                 e 
                 f 
                 g 
                 h 
                 i 
               
               
                   
               
               
                 A (inner screw) 
                 3 
                 10 
                 3 
                 4 
                 2 
                 6 
                 4 
                 5 
                  8 
               
               
                 B (outer screws) 
                 4 
                 10 
                 4 
                 4 
                 3 
                 6 
                 4 
                 5 
                  7 
               
               
                 C (canted rollers) 
                 2 
                 10 
                 4 
                 3 
                 5 
                 4 
                 4 
                 3 
                  3 
               
               
                 D (gears and arms) 
                 5 
                  1 
                 5 
                 4 
                 3 
                 6 
                 7 
                 5 
                  3 
               
               
                 E (canted roll with detents) 
                 5 
                 10 
                 6 
                 4 
                 1 
                 8 
                 3 
                 8 
                  5 
               
               
                 F (present device with 
                 8 
                 10 
                 8 
                 9 
                 8 
                 9 
                 8 
                 9 
                 10 
               
               
                 multi-directional rollers) 
               
               
                   
               
             
          
         
       
     
     Specifically, the present puller devices facilitate the production of nonwoven cartridges of uniform dimension and without damage to the inner or outer surfaces of the cartridge. In addition, the present puller devices permit manufacturers to rapidly change the outer diameter of the nonwoven tube without replacing the mandrel or making cumbersome adjustments to the puller device. For these reasons, the present puller devices as described herein are believed to be advancements over the state of the art. 
     While the present embodiments are illustrated as being produced with a single melt-blowing apparatus, it should be understood that multiple melt-blowing apparatuses may be used in the production of a multi-layered product and that the layers of the product may be of different polymer types or sizes. Such systems are described in co-pending and concurrently filed U.S. patent application Ser. No. 14/614,277, entitled “Heterogeneous Melt-Blown Nonwovens and Die Tips Used in Production Thereof,” the disclosure of which is hereby incorporated by reference. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other variations that occur to those skilled in the art. Such other variations are intended to fall within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.