Abstract:
A web stabilizer adapted to stabilize a web moving across a span between two components of a web machine or machines, the stabilizer including: a surface facing and adjacent the moving web, and at least one transition in the surface of the stabilizer, wherein the transition is a protrusion or recess in the surface between a leading edge of the stabilizer facing a direction of web travel and a trailing edge of the stabilizer.

Description:
CROSS RELATED APPLICATION 
       [0001]    This applications claims priority to U.S. Provisional Patent Application Ser. No. 61/157,446 filed Mar. 4, 2009, the entirety of which application is incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Webs of material (including but not limited to tissue paper, towel paper, other papers, board, plastics, and polymers) are transported through spans that typically have web stabilizers, such as shown in U.S. Pat. No. 4,321,107. The webs move at a relatively high speed through the spans and across the stabilizers. 
         [0003]    Stabilizers traditionally have a generally flat or planar surface against which the web moves as the web traverses a span. The stabilizer is positioned adjacent the web such that the web is a short distance from the flat surface of the web. The web moves at a high speed, such as 4,000 to 7,000 feet per minute (1,200 to 2,100 meters per minute). The movement of the web induces air flows on both the top and bottom sides of the web. The air flow tends to move at the same speed as the web. 
         [0004]    The web may flutter due to disturbances in the air flows on either or both sides of the web. Disturbances may be caused by the laminar air stream immediately adjacent the web, e.g. the air flow boundary layer, to separate from the web such that a disturbed airflow is adjacent the web. 
         [0005]    A web stabilizer having a surface immediately adjacent the web reduces the tendency of the web to flutter. U.S. Pat. Nos. 4,321,107 and 4,906,333 disclose examples of web stabilizers. As the web moves across the surface of the stabilizer, the stabilizer provides a physical barrier to web flutter in the direction the stabilizer and tends to smooth the air flow between the stabilizer and web. By smoothing the air flow, a laminar boundary layer air flow may be maintained adjacent the web, which reduces flutter of the web. 
         [0006]    A difficulty with conventional stabilizers is that the web tends to fall away from the surface of the stabilizer, especially if the surface is long in the direction of web travel and the web travels below the stabilizer. Bump bars have been added to the leading edges of stabilizers to reduce flutter. A bump bar is a pipe or bar (circular in cross-section) welded to the leading edge of the stabilizer and extending below (in the direction of the web) the stabilizer such that the web first moves over the bar before moving over the bottom surface of the stabilizer. 
         [0007]    Another approach to overcome the difficulty of web flutter below a stabilizer is to inject a high velocity air stream in the gap between the stabilizer surface and web, such as disclosed in U.S. Pat. No. 6,325,896. The high velocity air reduces the air pressure between the web and stabilizer. The reduced air pressure draws the web towards the stabilizer. However, injecting a high velocity air stream requires an air supply, air ducts and air jets or slots, which increase the cost to make and operate a stabilizer. Further, the air injection nozzles and slots are subject to clogging. 
         [0008]    Another approach is to shape the stabilizer as an airfoil such that a low pressure is formed between the stabilizer and the web, as disclosed in U.S. Pat. No. 6,325,896. However, an airfoil shaped stabilizer, that is long relative to the direction of web travel, has difficultly in reducing flutter in the downstream region of the stabilizer. There is a need for web stabilizers that suppress web flutter over long stabilizer surfaces, have low manufacturing and operating costs, and are not susceptible to clogging of air injection nozzles and slots. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0009]    A web stabilizer has been developed having one or more transitions in the surface facing the web. These transitions may be transverse to the direction of web travel, such as a ridge or step extending the width of a stabilizer or an array of recesses and protrusions on the surface of the stabilizer. Because of the transitions and the movement of the web, a low pressure region is formed immediately downstream of each transition in the direction of web travel. These low pressure regions create a pressure differential between opposite sides of the web that draw (bias) the web towards the surface of the stabilizer. 
         [0010]    The transitions in the surface of the web stabilizer create low pressure regions between the web and stabilizer, preferably without injection of high velocity air at the transitions. By arranging the transitions at various locations on the surface of the stabilizer, the low pressure regions formed by the transitions draw the web towards the stabilizer along the length of the stabilizer. The transitions on stabilizers with long surfaces above a web assist in reducing flutter in the web along the entire length of the stabilizer. 
         [0011]    Various transition shapes and arrangements of transitions on the stabilizer, such as disclosed herein, are in accordance with the invention. The shapes of transitions include: steps, ridges and grooves extending the width of the surface of a stabilizer and transverse to the direction of web travel; air passages extending from the surface of the stabilizer and facing the web to an exhaust port discharging air to atmospheric pressure or to a suction device such as a dust collector, where the passages are preferably tilted away from the direction of web travel; and arrays of protrusions and recesses on the surface of the stabilizer, wherein the protrusions and recesses are preferably widest in a direction transverse to the direction of web travel. 
         [0012]    Further, the surface of the stabilizer between the transitions may be linear, curved, undulating or otherwise shaped. The various shapes and arrangements of transitions on the surface of the stabilizer between the transitions promote a low pressure zone between the stabilizer surface and the web and reduce web flutter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1A  is a diagram of a web moving across a stabilizer having a step transition. 
           [0014]      FIG. 1B  is a diagram of a web moving across a stabilizer having a surface with a step transition. 
           [0015]      FIG. 2  is a schematic side cross-sectional view of a web stabilizer having a surface with step (square) transitions and planar surface regions between the transitions, where the planar surface regions are substantially parallel to each other and to the direction of web travel. 
           [0016]      FIG. 3  is a schematic side and cross-sectional view of a web stabilizer having a surface with step (concave or fillet) transitions and planar surface regions between the transitions, where the planar surface regions are substantially parallel to each other and to the direction of web travel. 
           [0017]      FIG. 4  is a schematic side and cross-sectional view of a web stabilizer having a surface with step (square) transitions and planar surface regions between the transitions, where the planar surface regions are substantially parallel to each other and are inclined with respect to the direction of web travel. 
           [0018]      FIG. 5  is a schematic side and cross-sectional view of a web stabilizer having a surface with step (square) transitions extending the width of the stabilizer and the stabilizer has concave surface regions between the transitions. 
           [0019]      FIG. 6  is a schematic side and cross-sectional view of a web stabilizer having a planar surface which is generally parallel to the direction of web travel, the surface has grooves or concave transitions extending the width of the surface at intervals along the length of the surface. 
           [0020]      FIG. 7  is a schematic and side cross-sectional view of a web stabilizer having a planar surface which is generally parallel to the direction of web travel, the surface has slots or passages preferably extending traverse to the direction of web travel, where the slots or passages allow air from between the web and stabilizer surface to exhaust and thereby form low pressure regions at the inlet to slots and passages on the surfaces. 
           [0021]      FIG. 8  is a schematic and side cross-sectional view of a web stabilizer having a surface with an array of recesses and protrusions. 
           [0022]      FIG. 9  is a schematic plan view of the surface of the stabilizer shown in  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIGS. 1A and 1B  show a portion of a tissue machine  10  in which a web  12  moves across a span  13  between components  11 , e.g., a calendar and a roller, of the machine. A stationary stabilizer  1  is fixed immediately above the web and in the span such that the web moves across a lower surface  14  that is generally parallel to the web. 
         [0024]    The lower surface  14  of the stabilizer has a bump bar transition  16  extending across the width (W) of the stabilizer. The bump bar  16  forms a step in the lower surface  14 . As the web  12  moves (direction of travel  19 ) over the bump bar, the web is drawn up to the rearward area  17  of the lower surface. The web is pulled up because a low pressure region is formed immediately downstream of the bump bar  16  in the gap between the lower surface and the web. Because the web is pulled up to the lower surface  14 , the tendency of the web to flutter is reduced. 
         [0025]    The transitions  16  may be arranged at various locations along the length of the lower surface of the stabilizer. For example, transitions may be arranged at intervals of one third the length of the lower surface. Preferably, a least one transition  16  is at the upstream half or third of the length of the lower surface  14  of the stabilizer in the direction  19  of web travel and another transition is at the downstream half or third of the length of the lower surface of the stabilizer. Transitions at the downstream half or third of the stabilizer assist in reducing flutter in the web as the web moves past the stabilizer. 
         [0026]      FIG. 2  shows a stabilizer  21  having a lower surface  14  with substantially parallel surfaces  2 ,  3  and  4  that are generally planar and arranged sequentially along the direction  19  of web travel. The surfaces  2 ,  3 , and  4  may be substantially parallel with each other and to the direction of web travel. The surfaces  2 ,  3  and  4  may extend the width of the web and lower surface of the stabilizer. 
         [0027]    Separating each of the parallel surfaces  2 ,  3  and  4 , are substantially square step transitions  5  that preferably extend the width of the stabilizer and are transverse to the direction of web travel  19 . These square transitions  5  form a step having right angled corners between surfaces  2  and  3  and between surfaces  3  and  4 . The step may have a height dimension in a range of, for example, 0.25 inches to 0.75 inches (6.3 to 19 millimeters—mm). The step may also be shorter than this range and have a height, for example, of 0.06 inches (1.5 mm). The step may also be greater than this range and a height, for example, of 1.5 inch (38 mm). 
         [0028]    The height of the step transition  5  may be determined to avoid interfering with, e.g., tearing, the web and to form a low pressure region immediately downstream of the step and between the surface of the stabilizer and the web. The transitions  5  may extend substantially the full width of the stabilizer or the width of the web. 
         [0029]    The transition  5  may be substantially perpendicular to the direction of web travel. Alternatively, the transitions may be oblique to the direction of web travel, such as at an angle of 75 degrees to 89 degrees to the direction of web travel. Further the transition may not form a straight line and have portions that are perpendicular to the web travel and other portions that are canted with respect to the direction of web travel. 
         [0030]    The transition may be formed by making corners or sloped surfaces in the lower surface of the stabilizer, by overlapping plates on the lower surface where the plates are separated by a narrow gap, or by some other irregular shape on the lower surface of the stabilizer. 
         [0031]    The square transitions  5  may be formed of one or more bars or other machined pieces that are fixed, e.g., welded or fastened, to the lower surface of the stabilizer. The square transitions  5  may form structural supports for panels forming the surfaces  2 ,  3  and  4 . The joints between the square transitions  5  and panels forming the surfaces  2 ,  3  and  4  may be sealed to avoid air entering or escaping from or to an interior portion of the stabilizer. Alternatively, the joints may not be sealed such that the air pressure in the region immediately downstream of each transition equalizes with an air pressure, e.g., ambient atmospheric pressure, inside the body of the stabilizer. 
         [0032]      FIG. 3  shows a stabilizer  23  with substantially parallel planar regions  2 ,  3  and  4  on a lower surface  14  of the stabilizer. Similar to the stabilizer  21  shown in  FIG. 2 , the planar regions  2 ,  3 , and  4  are separated by transitions that extend the width of the stabilizer and are generally transverse to the direction  19  of web travel. The transitions  16  form steps between the regions  2  and  3  and between regions  3  and  4 . 
         [0033]    The transitions  15  are concave or filleted step or otherwise curved steps at the joints between the surfaces  2 ,  3  and  4 . The transitions  24  may be formed from one or more pieces, e.g., bars, machined to form a concave, filleted or curved shape  25 . The pieces of the transition  24  are manufactured and assembled, e.g., welded or fastened, to the stabilizer and may provide structural support for the panels forming the regions  2 ,  3 , and  4 . The concave or filleted shape  25  of the transition  24  reduces the open corner volume at the transition as compared to the square transition shown in  FIG. 2  and thereby minimizes dust and contamination build-up in the transition corner volume immediately downstream and adjacent to the curved shape  24  of the transition. 
         [0034]      FIG. 4  shows a stabilizer  30  with substantially flat lower surfaces  31 ,  32  and  33  and a square step transition  34  between these surfaces. The lower surfaces may not be parallel to the web direction and may be parallel to each other. The lower surfaces  31 ,  32  and  33  may be inclined with respect to the web direction at an angle of 2 to 10 degrees such that the surfaces slope towards the web in the direction  19  of web travel. The transitions  34  may be substantially the full width of the stabilizer  30  and substantially perpendicular to the direction of web travel. 
         [0035]      FIG. 5  shows a stabilizer  40  having a lower surface with concave surface regions  25 ,  26  and  43 , separated by step transitions  44 . The concave surface regions may or may not be parallel with the direction of web travel. The transitions  44  may be substantially the full width of the stabilizer  40  or the web, and substantially perpendicular to the direction  19  of web travel. The transitions  44  may be formed in the same manner as the transitions shown in  FIGS. 2 to 4 . The concave surface regions  41 ,  42  and  43  may be panels bowed to form a concave shape and supported at the transitions  44  and by the internal supports  45  in the stabilizer, such as internal ribs and support grids. These internal supports may also be included in the other stabilizers disclosed herein. Further, the surface regions  41 ,  42  and  43  may have convex surfaces rather than the concave surfaces shown in  FIG. 5 . 
         [0036]      FIG. 6  a stabilizer  46  with a lower surface formed of parallel surfaces  47  separated by substantially concave transitions  48 , e.g., grooves. The surfaces  47  are substantially parallel with the web direction. The transitions  48  may extend substantially the full width of the stabilizer and be substantially perpendicular to the direction of web travel. The surfaces  47  may be substantially planar with each other and interrupted by the recessed transition slots  48 . The transition slots  48  may be one or more pieces, e.g., bars, machined to have grooves forming the transition slots. The pieces are mounted in the stabilizer and may provide structural support for the panels forming the surfaces  47 . 
         [0037]      FIG. 7  shows a stabilizer  50  having a lower surface that may be formed of substantially parallel lower surface sections  51 ,  52  and  53  separated by slots, other air passages or open areas  54 . The surface(s)  51 ,  52  and  53  may be in a plane substantially parallel with the web direction and may be parallel to each other. 
         [0038]    The slots, air passage or open areas (collectively transitions)  54  may extend the width of the stabilizer (or the width of the web) and be generally perpendicular (or oblique) to the direction of web travel. The transitions  54  may be formed by one or more pieces, e.g., bars, machined to an appropriate shape and assembled, e.g., welded or fastened, in the stabilizer to form the slots, passage or open areas. 
         [0039]    The transitions  54  have air inlets adjacent the lower surface sections  51 ,  52  and  53 . The transitions  54  have outlets  55  that exhaust air from a surface of the stabilizer distant from the lower surfaces  51 ,  52  and  53  or to an internal air duct in the stabilizer. The outlets  55  may exhaust to the atmosphere at an ambient air pressure or to another device, such as a dust collection system  56 , e.g., a vacuum, that applies suction to the outlets  55  and transitions  54  to draw air from the inlets to the transitions. The ducts of the transitions  54  may be inclined, e.g., at an angle of 30 to 55 degrees with respect to the lower surfaces  51 ,  52  and  53  and sloped such that the inlet is upstream of the outlet  36  in the direction of web travel. The transitions  54  allow a portion of the air moving with the web and between the web and the lower surfaces  51 ,  52  and  53  to flow into the transitions and thereby create a low pressure region between the web and the lower surfaces. 
         [0040]      FIGS. 8 and 9  show a stabilizer  60  with a lower surface  62  that may be in a plane substantially parallel to the web. The lower surface may have convex or concave regions, and step transitions as shown in  FIGS. 2 to 7 . 
         [0041]    The lower surface  62  includes an array of transitions  64  which may be undulating regions in which the surface gradually rises and falls from the web. For example, the transitions may include recesses or protrusions  64  that have a width dimension perpendicular to the direction of web travel that is substantially greater than a length dimension. For example, a transition  64  may be a generally rectangular bump on the lower surface  62  having a width of between 50 mm to 500 mm, a length (parallel to web travel) of 20 mm to 200 mm and a height of 5 to 20 mm. These transitions  64  may have a sloped leading edge facing the direction  19  of web travel and a sharp cornered, e.g., 90 degree corners, trailing edge to form air disturbances and low pressures immediately downstream of the transitions. 
         [0042]    The transitions  64  may be arranged in an array such that the transitions are arranged in rows parallel to the direction of web travel and the transitions are staggered from row to row as shown in  FIG. 9 . 
         [0043]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.