Abstract:
A chill roll for a web printing press includes a cylindrical drum. A porous layer is provided at a circumference of the drum and configured to provide a pathway for air from a first location between the chill roll and a web passing over the chill roll and a second location having a lower air pressure. Air between the chill roll and the web is thereby removed, providing improved heat transfer from the web to the chill roll.

Description:
BACKGROUND  
         [0001]    The present invention relates generally to chill rolls for web offset printing presses, and in particular to a chill roll having a porous surface.  
           [0002]    In web offset printing presses, ink is applied to an elongated web of paper or other material as the web is moved lengthwise through the printing press. The freshly printed web is moved through a drier, which elevates the temperature of the web. The web is then moved through a chill roll assembly in order to cool the heated web and to set the ink. A chill roll assembly typically included a succession of rolls which are cooled by water or other coolant flowing through the interior of the rolls.  
           [0003]    A chill roll assembly is described in the “Handbook of Printmedia,” Helmut Kipphan, Springer-Verlag Berlin Heidelberg 2001, Germany, pp. 269-70.  
           [0004]    Various devices have been used to improved the heat transfer between the web and the chilled rolls. Many of these devices are aimed at reducing or eliminating the thin layer of air which typically forms between the moving web and the rotating roll due to entrainment or other processes. The thin layer of air typically may have a thickness of about 0.1 mm to about 0.13 mm. This thin layer of air acts as an insulator and may markedly degrade the heat transfer between the web and the chill roll.  
           [0005]    Prior attempts at reducing or eliminating this air layer are described in the following patents: 1) U.S. Pat. No. 4,476,636 describes rolls which are rotated opposite the direction of web travel to “scrub” the web of the air layer; 2) U.S. Pat. No. 5,036,600 describes an arrangement with chill rolls in a closely spaced relationship whereby the web path around the rolls acts to scrub off the air layer; 3) U.S. Pat. Nos. 4,369,584 and 5,416,984 describe using jets of air impinging upon the surface of the web to force it closer to the roll surface; 4) U.S. Pat. Nos. 5,111,595 and 5,571,564 describe additional “nip rolls” designed to force out the air layer and put the web and chill roll into intimate contact; and 5) U.S. Pat. No. 5,275,103 describes using attractive electrostatic charges placed on the web and chill roll to reduce the gap between them.  
           [0006]    These prior attempts at removing the air layer have proven not fully satisfactory for various reasons. Scrubbing methods cannot totally eliminate the entrainment of air between the web and the chill roll. Air jets typically cannot overcome the high pressures between the web and chill roll associated with high speed operation. Nip rolls introduce unwanted complexity as the nip roll itself must now be cooled, and care must be taken so that the nip roll does not mar the web or the printed ink films. Likewise, electrostatic methods add complexity and are not fully effective.  
           [0007]    U.S. Pat. No. 4,688,784 describes a sheet-supporting transfer drum (see FIG. 9, reference numeral 16) with a perforated surface and which is connected to a suction device so that air is blown out of or sucked into the transfer drum through the perforations and a sheet to be transferred properly contacts the cylinder guiding surface (see column 7, lines 21-31 and 59-68). U.S. Pat. No. 3,542,358 describes a sheet-folding device including a sheet drum with an outer peripheral wall made at least partly of an air permeable material. Such a material may be a sintered material or a porous plastic (see column 1, lines 72-74). Neither of these patent documents describe a chill roll with which the air layer between the web and the chill roll may be reduced or eliminated.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a chill roll for a web printing press. The chill roll includes a cylindrical drum and a porous layer disposed at a circumference of the drum. The porous layer is configured to provide a pathway for air from a first location between the chill roll and a web passing over the chill roll and a second location having a lower air pressure.  
           [0009]    The porous layer may be attached to a circumferential surface of the drum.  
           [0010]    The porous layer may integral with a circumferential surface of the drum.  
           [0011]    The porous layer may form a circumferential surface of the drum.  
           [0012]    The pathway may be configured to enable the air to move in a radial direction. Moreover, the pathway may be further configured to enable the air to move in at least one of a lateral and a circumferential direction.  
           [0013]    The porous layer may include a matrix of material.  
           [0014]    The porous layer may include a fibrous material.  
           [0015]    The porous layer may include a foamed material.  
           [0016]    The porous layer may define at least one of a hole, a slot and a tube so as to provide the pathway.  
           [0017]    The porous layer may include a material having a high thermal conductivity.  
           [0018]    The porous layer may include at least one of steel, aluminum and copper.  
           [0019]    The porous layer may have a thickness of from about 1 mm to about 2.5 mm.  
           [0020]    The second location may be at a lateral edge of the drum.  
           [0021]    The air may be entrained at the first location.  
           [0022]    The pathway may be configured to enable the air to move from the first location so as to improve a heat transfer between the web and the chill roll.  
           [0023]    The drum may define a coolant inlet and a coolant outlet configured for circulating a coolant through an interior space defined by the drum.  
           [0024]    The present invention also provides a printing press. The printing press includes a cylindrical chill roll having a porous layer disposed at a circumference of the chill roll and configured to provide a pathway for air from a first location between the chill roll and a web passing over the chill roll and a second location having a lower air pressure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0025]    The present invention is elaborated upon below based on exemplary embodiments with reference to the accompanying drawing.  
         [0026]    [0026]FIG. 1 shows a perspective view of a chill roll according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0027]    Referring to FIG. 1, a perspective view of a chill roll  10  according to an embodiment of the present invention is shown. Chill roll  10  includes cylindrical drum  12  having cylindrical surface  14  and disk-shaped lateral end surfaces  16  and  18  which together enclose an interior space  15 . Porous layer  20  is disposed on cylindrical surface  14  and includes outer surface  21 . Porous layer  20  rotates with cylindrical drum  12  as cylindrical drum  12  rotates about axis  40  defined by the drum. Opening  17  is provided in end surface  16  for coolant outlet pipe  32  and opening  19  is provided in end surface  16  for coolant inlet pipe  30 . Coolant circulating system  34  is provided for circulating coolant through coolant inlet pipe  30 , through interior space  15 , and out coolant outlet pipe  32  to transfer heat from web  8  passing over chill roll  10 .  
         [0028]    Web  8  contacts or at least nearly contacts chill roll  10 , and specifically surface  21  of porous layer  20 , at area  6 .  
         [0029]    Radial direction  42 , longitudinal direction  44  and circumferential direction  46  may be defined relative to cylindrical drum  12  and porous layer  20 . Radial direction  42  points radially toward axis  40 . Longitudinal, or lateral, direction  44  is parallel to axis  40 . Circumferential direction  46  lies generally orthogonal to radial direction  42  and longitudinal direction  44  so as to be parallel to a tangent of surface  21  of cylindrical drum  12  or of surface  21  of porous layer  20 .  
         [0030]    Cylindrical drum  12  may be made of a metal, plastic, composite or any other suitable material. The construction of cylindrical drum  12  may be of any suitable configuration for a chill roll as would be known to those of skill in the art.  
         [0031]    Coolant circulation system  34  may include one or more pumps and heat exchangers for moving a coolant through interior space  15  of cylindrical drum  12  and transferring heat from the coolant so as to cool chill roll  10 . The construction of such a system would be known to those of skill in the art.  
         [0032]    Porous layer  20  has one or more passageways  22  providing a pathway for air tending to be entrained and/or trapped at area  6  to move to areas of lower pressure. Porous layer  20  preferably is thereby maintained in contact with web  8  so that heat is conducted from the web to the coolant flowing through interior space  15  of cylindrical drum  12 .  
         [0033]    Passageways  22  may be pores, spaces, voids, holes, tubes or slots, or the like, or any combination thereof. Porous layer  20  may be a matrix or mesh of any suitable material having such passageways  22 . Porous layer  20  may, for example, have the structure of a metallic filter. Alternatively, porous layer  20  may be made of a “foamed” metal or other foamed material. In other embodiments of the present invention, porous layer  20  may be made from a solid material in which radial or interconnected radial and longitudinal holes, tubes or slots, or the like have been formed so create passageways  22 . Porous layer  20  may include any suitable combination of individual or interconnected passageways. Porous layer  20  may be made of a matrix of high thermal conductivity material, such as steel, aluminum or copper, for example. Porous layer  20  may have, for example, a thickness of from about 1 mm to about 2.5 mm. In other embodiments of the present invention, porous layer  20  may have a greater or a lesser thickness outside this range.  
         [0034]    In some embodiments of the present invention porous layer  20  may be a layer, for example in the form of a sleeve, added over the outer surface of an otherwise conventional chill roll. In other embodiments of the present invention porous layer  20  may be formed integrally with surface  14  of cylindrical drum  12  during manufacture of the chill roll. In yet other embodiments of the present invention, porous layer  20  may form surface  14  itself. Any of various suitable manufacturing methods may be using to form a chill roll having porous layer  20  according to the present invention.  
         [0035]    Passageways  22  preferably provide a pathway for air to move from area  6  in radial direction  42  and at least laterally in longitudinal direction  44  and/or circumferentially in circumferential direction  46  and/or in directions opposite to directions  44  and/or  46 . In this way, higher pressure air at area  6  may move to lower air pressure areas, near lateral end surfaces  16  and  18 , for example. In certain embodiments of the present invention, passageways  22  may lead from surface  21  of porous layer  20  to lower pressure areas in interior space  15  of cylindrical drum  12 .  
         [0036]    By providing a path for higher pressure air to move from area  6  to an area of lower pressure, the present invention may reduce or eliminate an air layer between web  8  and chill roll  10 . Heat transfer from web  8  to chill roll  10  may thereby be improved.  
         [0037]    It will of course be understood that the present invention has been described above only by way of example and that modifications of details can be made within the scope of the invention.