Patent Publication Number: US-2001000390-A1

Title: Method and apparatus for injecting steam at a single facer bonding nip

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     1. This application is a continuation of copending U.S. patent application Ser. No. 09/065,349, filed Apr. 23, 1998, which claims the benefit of U.S. Provisional Patent Application No. 60/044,104, filed Apr. 24, 1997.  
    
    
     
       BACKGROUND OF THE INVENTION  
       2. 1. Field of the Invention  
       3. The present invention relates to a method and apparatus for manufacturing corrugated paperboard, and more particularly, to a method and apparatus for injecting steam at the bonding nip of a single facer to accelerate the gelatinization of glue between a liner web and a medium web.  
       4. 2. Description of the Prior Art  
       5. The manufacturing of double face corrugated paperboard typically begins with an apparatus known as a single facer. A conventional single facer includes an upper corrugating roll and a lower corrugating roll wherein each roll has a plurality of longitudinally extending teeth. The corrugating rolls are rotatably mounted adjacent each other such that the teeth of each roll are in a meshing relationship. A medium paperboard web is fed into a corrugating nip defined by the upper and lower corrugating rolls wherein the medium web conforms to the contour of the meshing teeth to form flutes in the medium web. Prior to entering the corrugating nip, the medium web typically passes over a preheater for increasing the temperature of the web.  
       6. The preheater typically comprises a steam pressurized drum heater having an internal cavity supplied with steam from an external source. The medium web is wrapped around a portion of the outer circumference of the drum and heat from the surface of the drum is transferred to the moving medium web.  
       7. A gluing roll, arranged to turn in a bath of starch-based glue, is positioned downstream from the corrugating nip and applies glue to the tips of the medium web flutes. The glue applied to the flutes of the paperboard webs is typically a suspension of raw or uncooked starch in a suitable liquid carrier. In this state, the starch has little or no adhesive qualities. However, at a certain temperature, dependent upon the type of starch utilized and the kind and amount of additives dissolved in the carrier, the starch granules will absorb the available liquid of suspension and swell, causing gelatinization of the suspension. In this gelatinized state the starch has superior adhesion abilities and will form a good bond between many substrates, including paper. The temperature at which gelatinization occurs for any particular formulation of glue can be easily determined by heating the particular formulation and observing the changes that occur in its viscosity.  
       8. As glue is applied to the paperboard medium web, a paperboard liner web is simultaneously supplied to a preheater having a design similar to that of the medium web preheater. Both the liner web and medium web preheaters depend on conduction for heat transfer to the respective paperboard web. Conduction heat transfer is directly related to the surface area of the paperboard web contacting the preheater, the duration of such contact and the temperature gradient between the preheater and the web. In order to provide sufficient heat transfer, the web preheaters must therefore define a relatively large surface area and the processing speed of the single facer must be limited.  
       9. The large surface area required of prior art preheaters substantially increases the overall size of the single facer. In fact, such preheaters are often so large that the preheater must be placed exterior to, and many times behind, the corrugating apparatus. Further, frictional forces opposing the movement of the liner and medium webs are substantially increased the greater the wrap angle around the outer surface of the preheater. Such frictional forces generate tension within the webs, often resulting in web breakage. Prior art attempts to eliminate such problems generated by friction have resulted in complex mechanical arrangements including rotatable preheater drums and variable wrap mechanisms.  
       10. The conventional single facer further includes a pressure roll arranged adjacent the lower corrugating roll for bringing the liner web into engagement with the glued flute tips of the medium web. The pressure roll and corrugating roll define a pressure nip for applying a pressure to the corrugated medium web and the liner web, whereby an initial bond is formed therebetween. While both webs are typically preheated to a predetermined temperature, additional heat is transferred to the webs by the pressure roll and lower corrugating roll. This combination of heat and pressure gelatinizes the glue between the medium web and liner web thereby forming a single face web of corrugated paperboard.  
       11. The pressure roll and corrugating roll are typically heated by high pressure steam passing through an internal channel. The high pressure steam heats the cylindrical walls of the rolls such that heat is transferred to the webs through conduction. This conduction heat transfer from the rolls is directly related to the surface area of the paperboard web contacting the roll, the duration of such contact, and the temperature gradient between the roll and the web.  
       12. Effective bonding of the medium web and liner web further depends upon the pressing duration and pressing force exerted by the pressure roll to force the webs together in an intimate relationship until a secure bond is formed by the gelatinization of the glue. The pressing duration is directly related to the length of the pressing nip and processing speed of the single facer. If the nip length is decreased while maintaining a constant processing speed then the pressing force must be increased to provide effective bonding. However, if the pressing force is decreased and the processing speed held constant then effective bonding necessitates that the nip length be increased.  
       13. Traditional pressure rolls provide a small nip length for acting against the medium web and the liner web, thereby necessitating a high pressing force. Such a high pressing force between the pressure roll and lower corrugating roll typically results in linear press marks, corresponding to the pitch of the teeth of the lower corrugating roll, being formed laterally on the surface of the liner web. Further, such a high pressure may weaken the liner web. The single face web produced by the prior art single facers therefore often have an unattractive appearance or are rejected as being defective.  
       14. In response to the above-noted problems, it has been proposed to replace the conventional pressure roll with an endless belt having a portion wrapped about the lower corrugating roll thereby forming an extended nip for pressing the liner web together with the medium web. More specifically, the endless belt is extended over a plurality of rolls to run freely in cooperation with the lower corrugating roll wherein the liner web and the corrugated medium web pass between the lower corrugating roll and the endless belt and are nipped therebetween.  
       15. A common problem associated with the prior art single facers employing such an endless belt is that the belt cannot provide sufficient pressing force given the available nip length to provide effective bonding of the liner web and the corrugated medium web. While the tension in the belt may be increased to thereby increase the pressing force, this tension is limited based upon the properties of the belt. Excessive tension in the belt may cause accelerated wear or tearing of the belt.  
       16. Accordingly, there is a need for a method and apparatus for providing an adequate bond between a medium web and a liner web to produce a single face web without damaging the liner web. Further, there is a need for such a method and apparatus for facilitating rapid gelatinization of the glue between the medium web and the liner web.  
       SUMMARY OF THE INVENTION  
       17. The present invention provides a method and apparatus for accelerating the gelatinization of a glue between paperboard webs by the application of a heated fluid to a bonding nip defined for pressing the webs into adhering contact.  
       18. The method of the present invention includes the steps of providing a corrugating nip and passing a paperboard medium web through the corrugating nip to form a plurality of flutes within the medium web. The method further includes the steps of applying glue to the plurality of flutes of the medium web and providing a bonding nip for pressing a paperboard liner web into adhering contact with the medium web. A heated surface is provided facing the bonding nip and is in thermal communication with at least one primary channel. High pressure steam is supplied to the at least one primary channel for heating the heated surface.  
       19. A plurality of fluid ports are provided in fluid communication with the heated surface and the bonding nip. At least one secondary channel is provided in spaced relation to the at least one primary channel wherein steam is supplied to the at least one secondary channel for release through the plurality of fluid ports toward the glue between the liner and the medium webs. The steam supplied to the at least one secondary channel preferably comprises a low pressure dry steam.  
       20. The apparatus of the present invention comprises a single facer including a forming corrugating roll for corrugating flutes on a paperboard medium web. A carrier corrugating roll is operably connected to the forming corrugating roll for carrying the medium web into contact with a paperboard liner web. A glue applicator cooperates with the carrier corrugating roll for applying glue to the flutes of the medium web. A bonding nip is defined by the carrier corrugating roll for pressing the liner web into adhering contact with the flutes of the medium web, thereby forming a single face web.  
       21. A steam supplying device is positioned adjacent the bonding nip and includes a plurality of fluid ports in fluid communication with the bonding nip for supplying a steam against at least one of the liner and medium webs. The steam supplying device further includes a body having a heated surface extending circumferentially from proximate a point of initial contact between the liner and medium webs to proximate a point of divergence of the single face web from the carrier corrugating roll. At least one primary channel extends between opposite ends of the body and is in thermal communication with the heated surface. A first inlet port is in fluid communication with the at least one primary channel for supplying a high pressure steam thereto for heating the heated surface.  
       22. A plurality of secondary channels extend parallel to the at least one primary channel and are in fluid communication with the plurality of fluid ports communicating with the bonding nip. A second inlet port is in fluid communication with the plurality of secondary channels for providing a low pressure steam to the secondary channels from an external steam source. The low pressure steam travels through the secondary channels and exits through the fluid ports. The steam is thereby released against one of the liner and medium webs at the bonding nip to facilitate rapid gelatinization of the glue and formation of the final bond between the webs.  
       23. Therefore, it is an object of the present invention to provide a method and apparatus for increasing the gelatinization and bonding rate of glue between paperboard webs.  
       24. It is a further object of the present invention to provide a method and apparatus of bonding paperboard webs with reduced pressing force applied to the webs.  
       25. It is another object of the present invention to provide a method and apparatus of bonding a medium web and a liner web so as to reduce marking and damage to the resulting single face web.  
       26. Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     27.FIG. 1 is a side schematic view of a single facer of the present invention;  
     28.FIG. 2 is a cross-sectional view taken along line  2 — 2  of FIG. 1;  
     29.FIG. 3 is a side elevational view of the pressure roll shown in FIG. 1, with a portion of the end face removed to reveal the primary channel;  
     30.FIG. 4 is a side schematic view of a further embodiment of the single facer of the present invention;  
     31.FIG. 5 is a top plan view of the shoe of FIG. 4, where the shoe is partially broken away to show the internal structure;  
     32.FIG. 6 is a cross-sectional view taken along the line  6 — 6  of FIG. 5;  
     33.FIG. 7 is a detail view of FIG. 4;  
     34.FIG. 8 is a side schematic view of a further embodiment of the single facer of the present invention;  
     35.FIG. 9 is a detail view of FIG. 8;  
     36.FIG. 10 is a side schematic view of a further embodiment of the single facer of the present invention;  
     37.FIG. 11 is a side schematic view of a further embodiment of the single facer of the present invention;  
     38.FIG. 12 is a cross-sectional view taken along line  12 — 12  in FIG. 11;  
     39.FIG. 13 is a side elevational view of the carrier corrugating roll shown in FIG. 11, with a portion of the end face removed to reveal the primary channel;  
     40.FIG. 14 is a side schematic view of a further embodiment of the single facer of the present invention; and  
     41.FIG. 15 is a detail view taken along line  15 — 15  in FIG. 14.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     42. Referring initially to FIGS. 1 and 2, a single facer  100  of the present invention is shown as including a first, or forming, corrugating roll  102  operably connected to a second, or carrier, corrugating roll  104 . Both corrugating rolls  102  and  104  include longitudinally extending teeth  106  formed on their respective circumferences. The corrugating rolls  102  and  104  are rotatably supported such that the teeth  106  of the carrier corrugating roll  104  are engagable with the teeth  106  of the forming corrugating roll  102  via a paperboard medium web  108 .  
     43. The medium web  108  is supplied from a web feeding source (not shown), which is assumed to be on the right hand side of FIG. 1, to a corrugating nip  110  defined between the teeth  106  of the forming and carrier corrugating rolls  102  and  104  for forming predetermined flutes  112  within the medium web  108 . A glue applicator  114  is disposed diagonally below the carrier corrugating roll  104 . The glue applicator  114  is of conventional design and consists of a glue roll  116  rotatably supported to turn in a bath of glue  118  in response to rotation of the carrier corrugating roll  104 . The medium web  108  is glued at its flutes  112  by the glue applicator  114  and then carried upwardly along the circumference of the carrier corrugating roll  104  into contact with a liner web  120 . The medium web  108  may be held against the carrier corrugating roll  104  through either positive air pressure or a vacuum in a manner well known in the art.  
     44. The liner web  120  is fed from a web feeding source (not shown), which is assumed to be on the left hand side of FIG. 1, to a bonding nip  122  defined between the carrier corrugating roll  104  and a pressing device in the form of a pressure roll  124 . The bonding nip  122  presses the liner web  120  into adhering contact with the glued flutes  112  of the medium web  108 , thereby forming a single face web  126 . The pressure roll  124  is mounted for rotation such that the single face web  126  is conveyed upwardly along a circumference of the pressure roll  124  and then exits the single facer  100  for additional processing.  
     45. Referring to FIGS. 1-3, a steam supplying device  128  forms an integral part of the pressure roll  124  and includes a body  130  forming a plurality of radially extending fluid ports  132  in fluid communication with the bonding nip  122  for supplying a low pressure steam directly against the liner web  120 . The body  130  includes a cylindrical wall  134  having planar end faces  136  and  138  (FIG. 2). An axially extending primary channel  140  is defined by the cylindrical wall  134  and is in fluid communication with a first, or high pressure, inlet port  142 . The inlet port  142  is in fluid communication with an external high pressure steam source (not shown) and may be of conventional design. More particularly, a rotary steam joint of the type well known in the art may be utilized to define the high pressure steam inlet port  142  which is concentrically disposed around a high pressure steam condensate return port  144  (FIG. 1). Heat from the high pressure steam is conducted from the primary channel  140  through the cylindrical wall  134  to an outer peripheral surface  146  of the pressure roll  124 . The cylindrical wall  134  is preferably comprised of carbon steel, although other known materials having suitable heat transfer quality may be substituted therefore.  
     46. A plurality of axially extending secondary channels  148  are disposed within the cylindrical wall  134  in substantially parallel relation to the primary channel  140 . The secondary channels  148  are circumferentially spaced at equal distances from each other within the cylindrical wall  134 . Each secondary channel  148  includes a second, or low pressure, inlet port  150  at end face  136  of the cylindrical wall  134 . Each secondary channel  148  may also include an inlet port  152  at the second end face  138  of the cylindrical wall  134  to provide uniform steam distribution to the plurality of fluid ports  132  (FIG. 2). Alternatively, the secondary channels  148  may be sealed with plugs (not shown) proximate the second end face  138  of the pressure roll  124 .  
     47. Referring further to FIGS. 2 and 3, the plurality of fluid ports  132  are arranged in axially, or laterally, extending rows  154  wherein the fluid ports  132  of each row  154  are equally spaced from each other and intersect a single secondary channel  148 . Each row  154  of fluid ports  132  is circumferentially, or longitudinally, offset from each adjacent row  154  in a direction of travel of the paperboard webs  108  and  120 , as indicated by arrow  155  in FIGS. 1 and 3. The fluid ports  132  extend circumferentially a full 360 degrees around the pressure roll  124 . As is visible in FIG. 2, the plurality of fluid ports  132  provide communication between the secondary channels  148  and the heated outer surface  146  of the pressure roll  124 .  
     48. Referring further to FIGS. 2 and 3, a pair of arcuate sealing members  156  and  158  slidably and sealingly engage the first and second end faces  136  and  138  of the pressure roll  124  for providing selective communication with a predetermined number of active inlet ports, designated by reference numerals  150 ′ and  152 ′, respectively. It should be noted that secondary channels and fluid ports supplied with low pressure steam will likewise be designated by reference numerals  148 ′ and  132 ′, respectively. The arcuate sealing members  156 ,  158  each include a housing  160  defining an arcuate passageway  162  for communicating with the inlet ports  150 ′ and  152 ′. A seal  164  is mounted to the housing  160  for sealingly engaging each end face  136 ,  138  of the rotating cylindrical wall  134 . The seal  164  is preferably made of teflon, however, other similar materials having suitable wear-resistance and sealing properties may be substituted therefore. It may be readily appreciated that as the pressure roll  124  rotates, the inlet ports  150 ,  152  will also rotate relative to the arcuate passageway  162  of the sealing members  156 ,  158  such that the active inlet ports  150 ′,  152 ′ will be continually changing.  
     49. Referring now to FIG. 3, the arcuate sealing members  156 ,  158  each include a pair of ports  166  communicating with the passageway  162 . Both ports  166  are preferably connected to an external low pressure steam source (not shown) to provide an even steam distribution within the passageway  162 . However, it may be appreciated that given external piping arrangements, only one of the two ports  166  may be supplied with low pressure steam, while the other port  166  may be sealed with an end plug (not shown).  
     50. A plurality of anchors  168  are fixed by welding or similar means to the housing  160  to facilitate mounting of the arcuate sealing members  156 ,  158  to a frame (not shown) of the single facer  100 . A pair of mounting holes  170  are provided in each anchor  168  through which bolts may pass for securing the anchors and housing  162  the frame.  
     51. Next, the operation of the single facer  100  of FIGS. 1-3 will be described in greater detail. The medium web  108  is supplied to the corrugating nip  110  wherein the teeth  106  of the forming and carrier corrugating rolls  102  and  104  form flutes  112  within the medium web  108 . The medium web  108  is next carried along the outer circumference of the carrier corrugating roll  104  to the glue applicator  114  where glue  118  is applied to the exposed flutes  112  of the medium web  108 .  
     52. The carrier corrugating roll  104  then transports the medium web  108  to the bonding nip  122  formed between the rotating carrier corrugating roll  104  and the rotating pressure roll  124 . The medium and liner webs  108  and  120  are brought together within the bonding nip  122  proximate the first end  171  of each arcuate sealing member  156  and  158 . At the bonding nip  122 , the liner web  120  is pressed into adhering contact with the glued flutes  112  of the medium web  108  for forming an initial bond between the webs  108  and  120 .  
     53. High pressure steam is supplied to the primary channel  140  of the pressure roll  124  through the high pressure steam inlet port  142  from the external high pressure steam source. The high pressure steam heats the cylindrical wall  134  and the arcuate outer surface  146  such that contact between the liner web  120  and the outer surface  146  results in heat transfer to the glue between the webs  108  and  120 . It should be noted that the high pressure steam is preferably saturated steam at a pressure of 185 pounds per square inch gravity (psig) at a temperature of 375° F. While 185 psig is the optimum pressure for the high pressure steam supplied to the primary channel  140 , the high pressure steam may possess a pressure within a wide range about 185 psig, but preferably between 150 psig and 200 psig.  
     54. Low pressure steam at approximately 0.6 psig is supplied to the ports  166  of the arcuate sealing members  156  and  158  by the low pressure steam source. While 0.6 psig is the optimum pressure for the low pressure steam, it is envisioned that such pressure may be within a range between 0.5 psig and 10 psig. It is believed that 0.5 psig is the minimum pressure required for the low pressure steam to adequately penetrate the porous paperboard webs  108  and  120  and contact the glue  118 . It is further believed that 10 psig is the maximum pressure which may be applied to the bonding nip  122  without severely damaging the paperboard webs  108  and  120 . The low pressure steam travels through the passageway  162  of the housing  160  through the active inlet ports  150 ′ and  152 ′ of the active secondary channels  148 ′. The low pressure steam is then released through the outlet fluid ports  132 ′ to form a thin steam film  172  between the liner web  120  and the outer surface  146  of the pressure roll  124 . The steam exiting the fluid ports  132  passes through the liner web  120  to the glue  118  between the medium and liner webs  108  and  120 . The newly formed single face web  126  diverges from the pressure roll  124  proximate a second end  174  of each arcuate sealing member  156  and  158 .  
     55. From extensive experimentation it has been unexpectedly discovered that the low pressure steam film  172  significantly accelerates the gelatinization of the glue  118  between the paperboard web  108  and  120 . This method and apparatus dramatically increases the heat transfer to the glue  118  as compared to the prior art method and apparatus, which relies on the inherently poor thermal conduction between a heated surface and the paperboard webs  108  and  120 . The rapid glue gelatinization improves the initial bond formed between the medium web  108  and the liner web  120 , thereby permitting the formation of an adequate bond with less pressure applied at the bonding nip  122 . Further, the processing speed of the corrugating equipment may be increased as the paperboard does not require long heat transfer periods of time. Additionally, the steam film  172  facilitates the processing of multi-walled paperboard webs.  
     56. It is believed that the significant benefits resulting from the use of the low pressure steam at the bonding nip  122  result from a mass transfer process including the absorption and condensation of steam in the paperboard webs  108  and  120  and, in particular, on the glue  118  between the webs  108  and  120 . A large quantity of thermal energy is released upon the condensation of steam giving rise to the observed improvements in the gelatinization of the glue  118  between webs  108  and  120 .  
     57. In the following description of alternative embodiments of the present invention, it is to be understood that like reference numerals refer to like components. Additionally, the formation of flutes  112  in the medium web  108  is identical to that disclosed with respect to the embodiment of FIG. 1. However, it should be understood that the precise method or apparatus for flute  112  formation in no way limits the scope of the present invention and that other methods and forms of apparatus for such formation may be readily substituted therefore.  
     58. Turning now to FIG. 4, an alternative embodiment of the single facer  200  of the present invention is illustrated. The pressing device comprises a pressure belt  202  is wrapped around a plurality of rotatably mounted belt rolls  204 ,  206 ,  208  for guiding the belt  202  in motion. The pressure belt  202  cooperates with the carrier corrugating roll  104  to form an extended bonding nip  210  for pressing the liner web  120  into adhering contact with the glued flute tips  112  of the medium web  108 .  
     59. The steam supplying device  128  as illustrated in FIG. 4 comprises a shoe  212  mounted within the inner run of the belt  202 . The shoe  212  includes an arcuate heated surface  216  extending circumferentially from a first side edge  232  proximate a point of initial contact between the webs  108  and  120  to a second side edge  234  proximate a point of divergence of the single face web  126  from the carrier corrugating roll  104 . The heated surface  216  includes a plurality of fluid ports  218  in communication with the bonding nip  210  and facing the inner surface  222  of the belt  202  and the teeth  106  of the carrier corrugating  104 .  
     60. With reference now to FIGS. 5-7, the shoe  212  will be described in greater detail. The shoe  212  is defined by a body  214  defining the arcuate heated surface  216  and a plurality of fluid ports  218 . The body  214  is preferably comprised of a carbon steel, although other known materials having suitable heat transfer qualities are also possible. It should be noted that the shoe  212  is arcuately formed by rolling the body  214  into the requisite curvature. The body  214  forms a plurality of primary channels  226  extending between opposite end faces  228  and  230  in a direction substantially perpendicular to the direction of web movement  155  and parallel to side edges  232  and  234 .  
     61. A plurality of secondary channels  236  extend in substantially parallel relation to the primary channels between opposite end faces  228  and  230  of the shoe  212 . It should be noted that the channels  226  and  236  are preferably cylindrical in nature and formed by drilling through the body  214  from one end  228 ,  230  to the other end  230 ,  228 , thereby defining walls  238  between adjacent channels.  
     62. Adjacent primary channels  226  are interconnected proximate alternating end faces  228 ,  230  of the shoe  212  to form a continuous serpentine path therethrough. In order to interconnect adjacent channels, slots  240  are provided at the end faces  228 ,  230 . While the primary channels, secondary channels, walls and slots are referred to generally by reference numerals  226 ,  236 ,  238  and  240  respectively, a particular item will be referred to by the reference numeral in combination with a lower case letter, as more clearly shown in FIGS. 6 and 7.  
     63. Referring further to FIG. 5, slot  240   a  is included at end  228  of the body  214  to interconnect the first two primary channels  226   a  and  226   b.  At the opposite end  230 , slot  240   b  interconnects the second and third primary channels  226   b  and  226   c.  Each pair of adjacent primary channels  226  are interconnected at alternate ends to form a serpentine path through the body  214 .  
     64. With further reference to FIGS. 5 and 6, the body  214  further includes a first, or high pressure, steam inlet port  242  preferably located proximate the end face  230  and side  232  for intersecting the primary channel  226   a  opposite the slot  240   a  interconnecting the primary channel  226   a  with primary channel  226   b.  The high pressure steam inlet port  242  is connected to an external high pressure steam source (not shown) for supplying a second, or high pressure, steam to the serpentine path formed by the primary channels  226 . The body  214  further includes a first, or high pressure, condensate return port  244  communicating with primary channel  226   f  proximate side  234  and extending through end  230 . As may be appreciated, high pressure steam applied through inlet port  242  travels through the serpentine path defined by the primary channels  226  and exits through return port  244 .  
     65. In the preferred embodiment of the invention, the slots  240  are formed by milling a portion of the walls  238  between two adjacent primary channels  226  at the appropriate ends  228 ,  230 . To seal the interconnection between the alternate primary channels  226 , end plugs or plates  246  are placed within the slots  240 , only partially filling the void created by the slots  240 , and are preferably welded to the end faces  228 ,  230  of the body  214 . End plugs or plates  247  are similarly welded to the body  214  for sealing opposing ends of the secondary channels  236 . Each secondary channel  236  is sealed from the other channels  226  and  236  within the body  214 .  
     66. The plurality of secondary channels  236  extend parallel to the primary channels  226  between end faces  228  and  230 , and are preferably located intermediate adjacent primary channels  226 . The secondary channels  236  extend laterally or perpendicular to the direction of travel  155  of the paperboard webs  108 ,  120 , and are circumferentially, or longitudinally, offset from the primary channels  226 . Each secondary channel  236  intersects a plurality of the fluid ports  218  thereby forming a laterally extending row  248  of fluid ports  218 . As may be readily seen in FIG. 5, the rows  248  of fluid ports are longitudinally spaced in the direction of web travel  155 .  
     67. As may be seen in FIGS. 4-6, the channels  226  and  236  may be substantially equally spaced between an upper surface  249  of the body  214  and the lower arcuate heated surface  216 . Alternatively, the secondary channels  236  may be positioned closer to either surface  216  and  249  than the adjacent primary channels  226 . For example, if the primary channels  226  are positioned closer to the heated surface  216  than the secondary channels  236 , it may be appreciated that the primary channels  226  may be spaced closer to each other thereby increasing the number of primary channels  226  within the body. Of course, the larger the number of primary channels  226 , the greater the potential for heat transfer to the heated surface  216  of the shoe  212 . Therefore, the particular placement of the primary and secondary channels  226  and  236  relative to each other may be varied greatly depending upon operating conditions and properties of the paperboard webs  108  and  120  and glue  118 .  
     68. Referring further to FIGS. 4-6, the shoe  212  further includes an arcuate manifold  250  centrally located between end faces  228  and  230  and fixed to the upper surface  249  of the body  214 . The manifold  250  includes arcuate side plate  252  and  254  secured to an arcuate top plate  256  for defining an internal passageway  258 . The ends of the passageway  258  are sealed by end plates  260  and  262 . As illustrated in FIG. 5, a plurality of ports  264  are provided through the upper surface  249  of the body  214  for providing communication between each secondary channel  236  and the passageway  258  defined by the manifold  250 . An inlet port  266  is provided within the arcuate top plate  256  of the manifold  250  for providing fluid communication between the passageway  258  and an external low pressure steam source (not shown). The inlet port  266  is preferably centrally positioned between end plates  260  and  262 . Low pressure steam supplied to the inlet port  266  is distributed through ports  264  to the plurality of secondary channels  236  and is then released through a plurality of fluid ports  218  into the bonding nip  210  for acting upon the paperboard webs  108  and  120  therein.  
     69. The low pressure steam supplied to the secondary channels  236  is preferably superheated by heat transfer from the primary channels  226 . Additionally the belt  202  comprises a porous material such that the steam exiting the fluid ports  218  passes through the belt  202  and into direct contact with the liner web  120 . As described above with reference to the embodiment of FIG. 1, the injection of steam against the glue  118  between the medium web and the liner facilitates rapid glue gelatinization and bond formation. To facilitate mounting within the single facer  200 , the shoe  212  may include a plurality of mounting plates  267  fixed to the body  214 .  
     70. In operation, the medium web  108  is supplied to the corrugating nip  110  and glue  118  is applied to its exposed flutes  112  in the manner described above with reference to FIG. 1. The medium and liner webs  108  and  120  are then supplied to the bonding nip  210  defined by the pressure belt  202  and carrier corrugating roll  104  such that the webs  108  and  120  are pressed together in adhering contact.  
     71. Simultaneously, high pressure steam is supplied to the high pressure steam inlet port  242  for supplying the primary channels  226  with high pressure steam for heating the arcuate heated surface  216  of the shoe  212 . Turning now to FIG. 7, low pressure steam is supplied to the manifold  250  through inlet port  266  from a low pressure steam source. The low pressure steam passes through ports  264  into the plurality of independently sealed secondary channels  236 . The low pressure steam exits through the plurality of fluid ports  218  into the bonding nip  210  for forming a thin steam film  268  between the arcuate heated surface  216  and the belt  202  which lubricates the surface  216  from frictional contact. The low pressure steam passes through the porous pressure belt  202  and contacts the liner web  120 . Given the porosity of paperboard, a portion of the steam passes through the liner web  120  and condenses proximate the glue  118  defined between the liner and medium webs  120  and  108 . As described above with respect to the FIG. 1 embodiment, upon condensation, the steam releases a large amount of thermal energy which facilitates rapid gelatinization of the glue and formation of a final bond between the webs  108  and  120 .  
     72. Turning now to FIGS. 8 and 9, a further embodiment of the single facer  300  of the present invention is illustrated. The single facer  300  is similar to that disclosed in FIGS. 4-7, the major difference being the removal of the pressure belt  202  cooperating with the carrier corrugating roll  104 . A bonding nip  302  is instead formed by the arcuate heated surface  216  of the shoe  212  cooperating with the carrier corrugating roll  104 . In other words, the shoe  212  itself forms the pressing device. The shoe  212  may be resiliently mounted for applying an adjustable pressure within the pressure nip  302 . More particularly, the shoe  212  may be spring biased for pressing the liner web  120  into adhering contact with the glued flutes  112  of the medium web  108 .  
     73. The liner web  120  is guided through the pressure nip  302  by a pair of idler guiding rolls  304  and  306  positioned in spaced relation to each other proximate opposite sides of the carrier corrugating roll  104 . Guiding roll  304  guides the liner web  120  into initial contact with the medium web  108  at a point proximate the first side edge  232  of the shoe  212 . Guiding roll  306  guides the newly formed single face web  124  away from the single facer  300  such that the single face web  124  diverges from the carrier corrugating roll  104  proximate the second side edge  234  of the shoe  212 . Either one of the idler rolls  304  and  306  may be configured to cooperate with the carrier corrugating roll  104  to form an auxiliary nip for pressing the liner web  120  and the medium web  108  against the carrier corrugating roll  104 .  
     74. The remaining structure of the shoe  212  is substantially identical to that described above with respect to the embodiment of FIGS. 4-7.  
     75. In operation the idler guiding rolls  304  and  306  guide the liner web  120  around a portion of the circumference of the carrier corrugating roll  104  while the shoe  212  presses the liner web  120  into adhering contact with the medium web  108 . A high pressure steam is supplied to the primary channels  226  and low pressure steam is supplied to secondary channels  236  in the manner described above with respect to the embodiment of FIGS. 4-7. The low pressure steam exits through the plurality of the fluid ports  218  to form a thin steam film  268  between the liner web  120  and the arcuate heated surface  216 . The steam film  218  lubricates the surface  216  to prevent frictional contact between the moving liner web  120  and surface  216 . A portion of the steam passes through the porous liner web  120  to the glue  118  between the medium web  108  and liner web  120  where it transfers heat for facilitating gelatinization of the glue  118 .  
     76. Turning now to FIG. 10, an alternative embodiment of the single facer  400  of the present invention includes three corrugating rolls  402 ,  404  and  406  operably connected for combined rotation. A corrugating nip  110  is defined between the small diameter forming corrugating roll  402  and the small diameter intermediate corrugating roll  404  for forming flutes  112  within the medium web  108 . Both corrugating rolls  402  and  404  have small outer diameters of approximately 16 inches each. As with the previous embodiments, the corrugating rolls  402 ,  404  and  406  all have a plurality of laterally extending teeth  106  which mesh with an adjacent corrugating roll  402 ,  404  and  406 . The medium web  108  is held on the intermediate corrugating roll  404  until it meshes with the large diameter carrier corrugating roll  406 . The medium web  108  is then transferred to the carrier corrugating roll  406  where glue  118  is applied to its exposed flute tips  112 . The carrier corrugating roll  406  then transports the medium web  108  into adhering contact with the liner web  120  at an extended bonding nip  408 .  
     77. The bonding nip  408  is formed by the liner web  120  which is tightly drawn over the large corrugating roll  406  by being partially wrapped around a pair of rotatably mounted guiding idler rolls  410  and  412 . In other words, the liner web  120  cooperating with the rolls  410  and  412  define the pressing device. As illustrated in FIG. 10, the extended bonding nip  408  provided by this arrangement facilitates extended pressing duration for finalizing the bond between the medium and liner webs  108  and  120 . The bonding nip  498  extends circumferentially around the large diameter carrier corrugating roll  406  in an arc of approximately 180°. The carrier corrugating roll has a large outer diameter of approximately 48 inches for providing a longer bonding nip  408  than would be provided by a liner web  120  similarly wrapped around a smaller outer diameter carrier corrugating roll. It should be further noted that in order to avoid high paper tensions during the corrugation process, it is necessary that the flutes  112  be formed by the small diameter forming corrugating roll  402 , rather than by the large carrier corrugating roll  406  cooperating with a corrugating roll having a substantially equivalent large outer diameter. It may be appreciated that the corrugating nip  110  could be defined between corrugating rolls  404  and  406  such that corrugating roll  402  is eliminated.  
     78. A steam supplying device  128  comprising a shoe  414  is provided immediately adjacent the bonding nip  408 . The shoe  414  includes a body  416  having an arcuate heated surface  418  circumferentially extending substantially the full distance of the bonding nip  408 . More particularly, the body has a first side edge  420  proximate a point of initial contact between the liner and medium webs  120  and  108  and a second side edge  422  proximate a point of divergence from the newly formed single faced web  126  from the carrier corrugating roll  406 .  
     79. Since the bonding nip  408  of the single facer  400  of FIG. 10 has a circumferential distance greater than that of the bonding nip  302  as illustrated in FIG. 8, the shoe  212  of the embodiment of FIGS. 4-7 has been circumferentially extended to form an arc of approximately 180° thereby defining shoe  414  of FIG. 10. The remaining details of shoe  414  are substantially identical to those as disclosed above with respect to shoe  212  of FIGS. 4-7.  
     80. It may be appreciated that the single arcuate shoe  414  could be substituted with a plurality of individual arcuate shoes which collectively define the arcuate heated surface  418  and plurality of fluid ports  218 . With such an arrangement, each individual arcuate shoe could be resiliently mounted, or spring biased, so that the shoes could provide additional pressure acting against the medium and liner webs  108  and  120  for facilitating bonding therebetween.  
     81. Turning now to FIGS. 11 and 12, the single facer  500  is a variation of single facer  400  as disclosed in FIG. 10. However, the steam supplying device of FIG. 11 forms an integral part of a carrier corrugating roll  504 . More particularly, the steam supplying device  128  comprises a body  506  having a cylindrical wall  508  extending between end faces  510  and  512 . The cylindrical wall  508  forms a primary channel  514  extending between end faces  510  and  512 . A first, or high pressure, steam inlet port  516  is provided at one of the end faces  510  and  512  of the cylindrical wall  508  for supplying high pressure steam to the primary channel  514 . A first, or high pressure, steam condensate return port  518  is concentrically disposed within the inlet port  516 . The ports  516  and  518  may be defined by a conventional rotary steam joint as described above with respect to the embodiment of FIG. 1. High pressure steam supplied to the primary channel  514  conducts thermal energy to the cylindrical wall  508 , thereby heating an outer surface  520  of the carrier corrugating roll  504  as defined by the teeth  106 .  
     82. A plurality of axially extending secondary channels  522  are formed within the cylindrical wall  508  in substantially parallel relationship to each other and to the primary channel  514 . Each secondary channel  522  is in fluid communication with a plurality of fluid ports  524  arranged in laterally extending rows  526 , i.e. perpendicular to the direction of web travel  155 . The rows  526  of fluid ports  524  are circumferentially, or longitudinally, offset in the direction of web travel  155  in equally spaced relationship around the entire perimeter of the carrier corrugating roll  504 .  
     83. A pair of arcuate sealing members  528  and  530  sealingly and slidably engage the opposing end faces  510  and  512  of the cylindrical wall  508 . More particularly, each arcuate sealing member  510  and  512  includes an arcuate housing  532  defining an arcuate passageway  534 . A seal  536 , preferably teflon, sealingly and slidably engages one of the end faces  510  and  512  of the cylindrical wall  508 . A pair of inlet ports  538  are provided within the housing  532  for connection to an external low pressure steam source (not shown) for providing low pressure steam to the internal passageway  534 . The number and location of inlet ports  538  may be varied depending upon the arrangement necessary for connecting to external steam piping. The remaining details of the arcuate sealing members  528  and  530  are substantially identical to those described above with respect to arcuate sealing members  156  and  158  of FIGS. 1-3.  
     84. In operation, the flute tips  112  of the medium web  108  are brought into contact with the liner web  120  proximate a first end  540  of each arcuate sealing member  528  and  530 . The liner web  120  is wrapped around the pair of idler rolls  410  and  412  disposed on opposite sides of the carrier corrugating roll  504  such that the liner web  120  is in tension. Tension within the liner web  120  forces the liner web  120  against the carrier corrugating roll  504  such that the medium web  108  and liner web  120  are pressed together in adhering contact. Simultaneously, high pressure steam is supplied from an external source to the primary channel  514  for heating the outer surface  520  of the carrier corrugating roll  504  through the cylindrical wall  508 . Heat is thereafter transferred from the arcuate outer surface  520  of the carrier corrugating roll  504  to the medium web  108 .  
     85. Low pressure steam is supplied to the internal passageways  534  of the arcuate sealing members  528  and  530  through one or more of the inlet ports  538 . The low pressure steam travels through the plurality of secondary channels  522  and is released through the plurality of fluid ports  524  against the medium web  108  within the bonding nip  408 . A thin steam film  540  is produced between the medium web  108  and the outer surface  520  of the carrier corrugating roll  504 . A portion of the low pressure steam passes through the relatively porous paperboard medium web  108  to the glue  118  between the medium and liner webs  108  and  120 . As detailed above, the steam releases thermal energy to the glue to assist in its rapid gelatinization. The newly formed single face web  126  diverges from the carrier corrugating roll  504  proximate the second end  542  of the arcuate sealing member.  
     86. Referring now to FIG. 14, a further embodiment of the single facer  600  of the present invention is illustrated as comprising a carrier corrugating roll  602  of similar design to the carrier corrugating roll  504  as disclosed above with respect to FIG. 11. However, corrugating roll  602  is of smaller outer diameter and has longitudinally extending teeth  106  which directly mesh with respective teeth  106  of the forming corrugating roll  102  to define a corrugating nip  110 . Furthermore, the guiding idler rolls  410  and  412  do not provide for as great of a wrap of the liner web  120  around the outer periphery of the carrier corrugating roll  602 . As such, the bonding nip  604  defined between the corner roll  602  and the liner web  120  does not extend the same circumferential distance as that in the FIG. 11 embodiment. Arcuate sealing member  606  likewise has a smaller circumferential distance in the direction of paperboard travel  155 . However, the remaining details of the single facer  600  of FIG. 14 are substantially identical to that as disclosed above with respect to the single facer  500  of FIG. 11.  
     87. Turning now to FIGS. 14 and 15, the operation of single facer  600  will be described in greater detail. The medium web  108  is supplied to corrugating nip  110  where flutes  112  are formed therein. The medium web  108  is next transferred along the circumference of the carrier corrugating roll  602  to a gluing station  114  where glue  118  is applied to the exposed flutes  112 . The medium web  108  is then transported upwardly along the outer circumference of the carrier corrugating roll  602  into contact with a liner web  120  where tension within the liner web  120  from being wrapped around the guiding idler rolls  410  and  412  causes the liner web  120  to press into adhering contact with the glued flutes  112  of the medium web  108 .  
     88. High pressure steam is supplied to the primary channel  514  of the carrier corrugating roll  602  for heating the outer surface  520  of the cylindrical wall  508 . Heat is transferred from the outer surface  520  of the carrier corrugating roll  602  through the medium web  108  to assist in the gelatinization of the glue  118 . Low pressure steam, as represented by arrows  608 , is supplied to the passageway  534  formed within the housing  532  of the arcuate sealing member  606  and through the plurality of secondary channels  522 . The steam is released through the plurality of fluid ports  524  where a portion of the steam passes through the porous paperboard medium web  108  to the glue  118  between the liner and medium webs  120  and  108 . As described above in greater detail, the steam supplies thermal energy to the glue  118  for assisting in the rapid gelatinization thereof.  
     89. While the methods herein described, and the forms of apparatus for carrying this method into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims.