Abstract:
An oscillating hauloff for blown film has a bearing structure positioned along the vertical process centerline. The bearing structure is separated into upper and lower sections to maintain a clear and open pathway for the web to pass across the process centerline. Passing the web across the process centerline allows the web to change directions before passing over a second turning bar, thus canceling any web wandering introduced by a first turning bar.

Description:
BACKGROUND  
       [0001]     This application relates to an oscillating hauloff device for removing blown film from an extruding apparatus.  
         [0002]     An oscillating hauloff receives film from an extruding apparatus and oscillates as the film is received to even out locations where there are variations in the thickness of the film. An oscillating hauloff thus has an oscillating portion for receiving the film, and a stationary portion for receiving the film from the oscillating portion and for providing the film to other equipment, such as a winder.  
         [0003]     When blown film is extruded, it is typically is in the form of a bubble. The hauloff has nip rolls that force together the sides of the bubble. As the bubble passes through the nip rolls, there are variations in the thickness of the film. If the film were wound directly onto a roll, thicker areas of the film could increasingly cause some parts of the wound roll to build up faster than others, thus creating hills and valleys in the roll.  
         [0004]     Problems can occur when an uneven roll is unwound and provided to converting equipment, such as printing presses, laminators, or bag machines. Uneven rolls considerably reduce the speed of such equipment and also reduce the quality of finished products. The unevenness causes slack in some areas of the film and tightness in other areas, thereby causing creases. On a printing press, ink might not transfer to film inside a crease, so product quality is degraded. Manufacturing processes often have to use spreader rolls or some other means to try to eliminate these creases, but these additional processing steps complicate and slow down the process. Bag machines have several nip rolls for drawing the film into a sealing and/or punching area. When film is drawn through the nip rolls, slack areas cause further creases. If a crease is located where a seal is placed, that seal will be defective.  
         [0005]     In general, the better the quality of the roll, the faster one can run downstream equipment and the greater the probability of producing a better quality product.  
         [0006]     Several attempts to improve quality have been made using a horizontal oscillating hauloff design. In such a design, the cross direction of the film always lies in a horizontal plane as it passes through and is provided out from the oscillating portion of the hauloff. Examples of such a horizontal design are found in U.S. Pat. Nos. 5,360,328 and 4,634,358, each of which is incorporated herein by reference for all purposes. Early horizontal devices could have stability problems and side-to-side swaying because a single, vertical, small diameter shaft was used for support. Current systems typically employ either single or multiple large diameter thrust bearings which eliminate stability problems and also address problems associated with weight restrictions on suspended nips and prevent collapsing that can occur when using a small shaft.  
         [0007]     Another problem in earlier devices was uncontrolled wandering of the film. In typical horizontal designs, there are two turning bars that constantly change angles with respect to the film and work together to allow for a total oscillation of 360°. As with any turning bar, frictional forces cause a slight shift in axial position as the film passes around its diameter, thereby causing the film to wander back and forth with the oscillating motion and wrinkles can form in the film. As a result, although normal variations in the thickness are spread evenly over the surface of the wound roll, wrinkles and creases due to wandering are also wound into the finished roll.  
         [0008]     Current horizontal systems address this problem by either actively guiding with the second turning bar or by passively self-canceling the wandering effects by opposing the two turning bars. Unfortunately, active guiding of turning bars disrupts the natural geometry required for wrinkle free operation and can actually induce winkles. The preferred passive “anti-web wandering” horizontal designs require the film to pass through the center of oscillation between the two turning bars to allow the film to approach the second turning bar from the opposite side. To keep the center free of obstruction, multiple fully encompassing rings are used to support the turning bars and idler rolls from the outside as described in U.S. Pat. No. 5,360,328. Recent price increases in raw material steel have made these systems very costly. Other known horizontal designs employ a single, less expensive thrust bearing ring design and require a centralized gearing and support assembly for the turning bars and idlers that prevents passage of the web over center and thus is not used with known passive anti-web wandering technology.  
         [0009]     Another design that solves the variable nature of this frictional wandering problem on turning bars is a vertical oscillating hauloff. Examples of such a system are found in U.S. Pat. Nos. 5,727,723 and 4,676,728, each of which is incorporated by reference. In such systems, the oscillating portion turns the film so that it lies on edge in a vertical plane as it is provided from the oscillating portion. A stationary portion then turns the film so that it is provided from the hauloff in a horizontal plane. Typical current vertical oscillating hauloff systems thus employ two turning bars to randomize thickness bands, with the turning bars held at a constant angle to the film thus eliminating changes in frictional effects due to angular shifts in the turning bars common to horizontal designs. The film is first turned on edge and then is sequentially wrapped around several vertically mounted idler rollers (idlers). Once wrapped around the idlers, the unit reverses direction and unwinds the film. This approach is less complex and less expensive than the horizontal design.  
         [0010]     The vertical design has other issues. Because the system accumulates and de-accumulates film (i.e., the path length increases and decreases) as the unit rotationally oscillates and the film goes around multiple vertical idlers, the overall speed of the film speed exiting the hauloff slows because some of the speed is taken up by the accumulation, and thus the line speed decreases. When the oscillating portion changes direction, line speed increases. Depending on how fast the oscillating portion is rotating, this change in direction can cause sizable variation in line speeds leading to tension variations, thus causing significant film web wandering, and thereby degrading the quality of the roll of film. This variable web speed problem has been addressed by more recent vertical designs that incorporate film accumulators as provided in U.S. Pat. No. 5,727,723, but such systems are more complex and expensive.  
         [0011]     An additional problem with vertical designs occurs during accumulation and de-accumulation. Vertical designs sequentially wrap and un-wrap film around each vertical idler roll. The resistance to the turning of each idler roll creates drag on the film and thus further affects the tension. In this portion of the hauloff where the film travels on end, gravity moves the film as the tension varies, thereby causing tracking problems and wrinkles and hence poorer roll quality or lost trim. If the tension drops too low, wrap-ups can occur in the hauloff causing the extrusion line to shut down. This problem does not occur in horizontal designs since the film is never turned on end.  
       SUMMARY  
       [0012]     The systems described here use a horizontal design oscillating hauloff that incorporates passive self canceling web wander technology in a simple, low cost design, without fully encompassing rings. These systems are comparable to the cost of a vertical design, but without inherent vertical design line speed related tension variations or gravitational web issues. Once the web is flattened, the flattened film passes through the oscillating hauloff in a horizontal orientation rather than a vertical one. Thus, axes along the width of the flattened film are maintained parallel to horizontal as the flattened film travels through the device.  
         [0013]     The described systems include an open frame, split support horizontal design oscillating hauloff which implements passive anti-web wander without fully encompassing support rings for oscillating film from an extruding apparatus. The film is provided in a horizontal plane, passing the web between idler rolls across the center of oscillation between turning bars in a manner that the web approaches a second turning bar from an opposite direction from the direction in which the web approaches the first turning bar. This arrangement of idler rolls and turning bars passively cancels the wandering effect of the web as it passes through the oscillating hauloff due to the natural shift in film position equally, but in opposite canceling directions on each of the two turning bars due to friction between the film and each of the two bars without the use of external fully encompassing support rings.  
         [0014]     Further, the systems described here are arranged to properly maintain well understood idler and turning bar geometry providing a constant total web path length throughout the oscillating motion, keeping line speed constant and remaining free of gravitation related web conveying issues.  
         [0015]     Other features and advantages will become apparent from the following detailed description, the drawings, and the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a schematic cross section view of an extrusion line and an oscillating hauloff according to one embodiment.  
         [0017]      FIG. 2  is a schematic cross section view of the oscillating hauloff of  FIG. 1 .  
         [0018]      FIG. 3  is a cross section view of a lower geared bearing assembly of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0019]     Referring to  FIG. 1 , plastic resin is provided from resin feeding bin  2  into an extruder  4  where the resin is melted and conveyed. Extruder  4  provides a plastic melt to the bottom of a blown film die  6 ; the plastic melt exits out of die  6  as an annular plastic melt concentric with a process centerline  8 . The melt passes through a cooling ring  10  and forms a continuous cylindrical bubble  12 . Bubble  12  is converted from a cylindrical shape to a flat sheet of film as it passes through collapsing shields  14 ,  16 . The film then passes between motorized nip rolls  20 ,  22 , which continually draw the film upwardly.  
         [0020]     Collapsing shields  14 ,  16  and nip rolls  20 ,  22  are attached to an oscillating portion  24  of a hauloff. As shown in more detail in  FIG. 2  and discussed below, oscillating portion  24  oscillates through typically 360° of rotation about a central unit axis parallel to (and often the same as) centerline  8  while receiving the film and maintaining the film&#39;s cross direction substantially in the horizontal plane. The film exits the unit as film  50  over a fixed exit idler roll  51 . Fixed exit idler roll  51  maintains a fixed angular position about the process centerline  8 . Film  50  is conveyed to a winder  52  where it is wound up on a roll  54 .  
         [0021]     Referring now to  FIG. 2  which shows the hauloff in more detail, film  50  passes out from between motorized nip rolls  20  and  22  and is conveyed around nip idler roll  26  and then horizontally inwardly to a first turning bar  28  where it wraps 180 degrees and is conveyed horizontally outwardly and around a first intermediate idler roll  30 . Film  50  then passes with its cross direction substantially horizontal and through process centerline  8  to wrap around a second intermediate idler roll  32  where it horizontally approaches and wraps around a second turning bar  34  from a direction opposite to the approach to first turning bar  28 , thus creating an equal and opposite self canceling effect on web wander caused by the geometry and properties of turning bars  28  and  34  as film  50  passes around them. This effect is known, as shown for example, in U.S. Pat. No. 5,360,328. Film  50  is then conveyed horizontally out of the oscillating unit.  
         [0022]     First turning bar  28  and second central idler roll  32  are supported by a lower geared bearing assembly  36  which acts to maintain the angular position of first turning bar  28  mid-way between the angular positions of nip idler roll  26  and first intermediate idler roll  30 . This mid-way angular position ensures the film  50  enters and exits the first turning bar at approximately equal and opposite angles. Collapsing shields  14 ,  16 , motorized nip rolls  20 ,  22 , nip idler roll  26  and lower geared bearing assembly  36  all rotate together as a unit and are attached to a rotating ring  46  which rotates ±180° about the central vertical process centerline  8  on top of a fixed ring  42  with interspersed ball bearings  44 . A motorized drive  48  acts to position rotating ring  46  directly.  
         [0023]     To maintain a clear path between first and second intermediate idler rolls  30  and  32  as the path of film  50  crosses the process centerline  8 , second turning bar  34  and first intermediate idler roll  30  are separately supported from above by an upper geared bearing assembly  38  which acts to maintain the angular position of second turning bar  34  mid-way between the angular positions of second intermediate idler roll  32  and the fixed angle of exiting film  50 . This mid-way angular position ensures the film  50  enters and exits the second turning bar at approximately equal and opposite angles. Upper geared bearing assembly  38  is mounted to fixed frame  40  which may be connected to another fixed structure or directly to fixed ring  42  as shown.  
         [0024]     Although numerous methods can be employed to properly position components, web  50  should enter and exit turning bars  28  and  34  at substantially equal and opposite angles. Web  50  should approach and exit all idler rolls  26 ,  30  and  32  perpendicular to their respective faces or wrinkles may result. In one embodiment, lower geared bearing assembly  36  and upper geared bearing assembly  38  perform this function and operate similarly as depicted in  FIG. 3  in order to gain economic advantage due to common design. For clarity, similar cross-hatching across multiple components depicts those components that turn together as a unit.  
         [0025]     As shown in  FIG. 3 , upper and lower support plates  62  and  60  are rigidly connected and directly support bearing halves  72   b  and  78   a.  Mating bearing halves  72   a  and  78   b  hold intermediate idler pivot shaft  70  in place while allowing shaft  70  to rotate centrally about the common process centerline  8  shown in  FIGS. 1 and 2 . Intermediate idler support frame  86 , drive gear  80  and bearing halves  74   a  and  76   b  are rigidly connected to intermediate idler pivot shaft  70 . Mating bearing halves  74   b  and  76   a  hold turning bar support frame  84  and turning bar drive gear  82  in place while allowing them to rotate centrally about the common process centerline  8  independent of intermediate idler pivot shaft  70 .  
         [0026]     Positioning gears  64  and  66  rotate together about a positioning gear axis  68  that is fixed to upper and lower support plates  62  and  60 , and offset from process centerline  8 . Positioning gear  64  engages central idler drive gear  80 , which may be the same size. Positioning gear  66  is ½ the size of and engages turning bar drive gear  82 . This gear ratio causes turning bar support frame  84  to rotate at ½ the rate of the rotation of intermediate idler support frame  86  relative to upper and lower support plates  62  and  60 . This gear and bearing arrangement ensures accurate positioning of turning bar support frame  84  at an angular position located ½ way between that of upper and lower support plates  62  and  60  and intermediate idler support frame  86 .  
         [0027]     Referring to  FIG. 2 , one method to position intermediate idler rolls  30  and  32  is to utilize an upper geared bearing assembly drive  39  and idler end connecting bars  31  (only the rear bar is shown on  FIG. 2 ). Idler end connecting bars  31  rigidly interconnect first and second intermediate idler rolls  30  and  32  and are located outside the edges of film  50  so they do not interfere with the passage of film  50 . Thus, the upper geared bearing assembly drive  39  rotation applied to upper gear bearing assembly  38  is translated through connecting bars  31  to lower geared bearing assembly  36 . The upper geared bearing assembly drive  39  rotates the intermediate idler rolls  30  and  32  about the vertical process centerline  8  at a rate that is half of the rotation rate of the rotating ring  46 .  
         [0028]     Idler end connecting bars  31  are not required. If connecting bars  31  are not employed, then upper and lower geared bearing assemblies  38  and  36  could be separately driven by drive connections to motorized drive  48  to maintain first and second intermediate idler rolls  30  and  32  substantially parallel to one another. The upper and lower geared bearing assemblies  36  and  38  may also be driven by drive systems independent from each other as well as independent from motorized drive  48 . In either embodiment, intermediate idler rolls  30  and  32  are rotated at a rate that is half the rotation rate of the rotating ring  46 .  
         [0029]     Referring again to  FIG. 1 , in some cases, bubble  12  is oriented to extrude vertically downward or sideways. In these cases, simple modifications to fixed and rotating rings  42  and  46  appropriate to the direction of gravity can be made to orient the machine in any direction. The terms “upper” and “lower” are thus used as relative terms and not in an absolute sense.  
         [0030]     The present invention has been described in connection with certain structural embodiments and it will be understood that various modifications can be made to the above-described embodiments without departing from the spirit and scope of the invention as defined in the appended claims.