Improved single facer with small intermediate corrugating roll

Abstract: The labyrinth path in the corrugating nip of a single facer is substantially reduced by utilizing a small diameter corrugating roll (12) captured between a larger diameter conventional corrugating (1) roll and a backing roll arrangement (12). The smaller diameter corrugating roll is captured to prevent bending thereof under corrugating loads. The corrugator may be operated at high speeds without the adverse increase in labyrinth path and web tension characteristic of a pair of large diameter corrugating rolls.

Description: The present invention pertains to an apparatus for forming a single face web of corrugated paperboard and, more particularly, to a corrugating roll assembly for a single facer. In the manufacture of corrugated paperboard, a single facer apparatus is used to corrugate the medium web, apply glue to the flute tips on one face thereof, and to bring a liner web into contact with the glued flute tips of the medium web with the application of sufficient heat and pressure to provide an initial bond. A conventional single facer typically includes a pair of fluted corrugating rolls and a pressure roll, which are aligned so the axes of all three rolls are generally coplanar. The medium web is fed between the inter-engaging corrugating rolls and the adhesive is applied to the flute tips by a glue roll while the medium is still on the corrugating roll which comprises the intermediate of the three roll arrangement. The liner web is immediately thereafter brought into contact with the adhesive-coated flute tips in the nip between the pressure roll and the corrugating roll. As corrugating nip roll pressures and corrugating speeds have increased, changes have been made in the construction of single facers to maintain the quality of the corrugated medium and to attempt to deal with the problems of high noise and vibration. For example, the load between corrugating rolls at the corrugating nip has required that one of the fluted corrugating rolls be made with a crowned surface to accommodate roll deflection under high nip loads. Deflection as a result of high loading is also believed to be one source of noise and vibration. In a conventional single facer construction, where the two corrugating rolls and the lower pressure roll are in general alignment (their axes lying generally coplanar), corrugating roll loads are transmitted to the pressure roll adding further to the problems associated with high loads and high speeds. This has resulted, in some cases, in manufacturing the pressure roll with a negative crown to match deflections in the corrugating roll which together form the nip for joining the two single face web components. One of the most serious problems in the operation of high speed single facers is the so-called "labyrinth" effect. In order to handle high loads and higher speeds, single facer manufacturers have gone to increasingly larger diameter, heavier and stronger corrugating rolls. As the medium web is drawn into the pressure nip, formed by the inter-engaging flutes on the two corrugating rolls, the medium web begins to be deformed, folded and gathered as it moves into the actual nip centerline where full engagement of the flutes occurs. Larger diameter corrugating rolls inherently create a more tortuous path for the web as the web begins to be wrapped partially around opposite alternating teeth or flutes of the mating corrugating rolls while moving into the fully nipped position. Each wrap of the web encompasses a slightly larger radius around the flute tip as it approaches the nip and each deformation or wrapping of the web on a flute tip adds a tension component to the overall web tension. As indicated, the additive labyrinth effect is increased as the corrugating roll diameters increase and it is not uncommon for the medium web to rupture or tear. One proposed solution to the labyrinth problem is disclosed in US Patent No. 3,990,935. The single facer construction disclosed in this patent proposes to maintain relatively small diameter corrugating rolls to minimise the labyrinth length and to provide internally pressurised flexure compensation for the inevitable bowing to which the rolls are subjected under high corrugating nip loads. Another proposed solution to the labyrinth effect is described in US Patent 4,531,996. In accordance with this patent, the upper corrugating roll contact with the lower corrugating roll is "dephased" by dividing the upper roll into axially adjacent segments each of which makes nip contact with the other corrugating roll at a different point. Alternately, the dephasing effect is provided by making the segments of the upper corrugating roll of different diameters. Both of the foregoing solutions require extremely complex roll constructions. Alternately, one of the larger diameter corrugating rolls may be eliminated and other means used to stabilise a small diameter intermediate corrugating roll to provide the required nip force and prevent deflection of the small roll. SUMMARY OF THE INVENTION In accordance with the present invention there is provided a single facer apparatus for producing a single face corrugated web, including first and second fluted corrugating rolls rotatable on parallel spaced roll axes with flutes adapted to interengage to form a corrugating nip for a paper web, means rotatably mounting said corrugating rolls to impose a corrugating nip force normal to the roll axes generally in the plane common thereto, said first corrugating roll having a diameter sufficiently smaller than the diameter of said second corrugating roll to provide a reduction in the labyrinth paper path sufficient to prevent rupture of the paper web, and the apparatus having means for independently applying a plurality of axially spaced radial forces to said small diameter roll along substantially the full axial length thereof, the resultant of said radial forces creating a nip force acting through said corrugating nip in a plane generally common to the axes of said corrugating rolls, said radial forces restraining said small diameter roll against deflection. Preferably said means for independently applying a plurality of axially spaced radial forces to said small diameter roll comprises a plurality of backing roll means in operative rotatable engagement with said small diameter corrugating roll for applying a backing force to said small diameter roll sufficient to provide said nip force and to restrain the small diameter roll against deflection, said roll means each being independently supported to impose the backing force along substantially the full axial length of said small diameter corrugating roll. Desirably said backing roll means comprises a plurality of pairs of backing rolls positioned along the length of said small diameter corrugating roll, the rolls of each pair positioned on opposite sides of the plane common to the corrugating roll axes, and means providing common support for each roll pair. Conveniently an actuator is operatively connected to each roll pair support means to impose a variable backing force thereon. Preferably there is means for individually operating each actuator to vary the force applied to said small diameter roll. Preferably said small diameter roll has a diameter not greater than about one third the diameter of said large diameter roll. A significant reduction in the labyrinth path of the web is effected by maintaining the ratio of the diameters of the first and second corrugating rolls, which together form the nip, not less than about 3:1. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic side elevation of a single facer in accordance with one example of the present invention; Figure 2 is a schematic representation of the labyrinth path in corrugating rolls of the present invention; Figure 3 is a schematic representation of the labyrinth path in the corrugating rolls of the present invention; and, Figure 4 is a generally top plan view, taken on line 4-4 of Figure 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the single facer apparatus shown in Figure 1, a conventional first large diameter corrugation roll 11 meshes with a second, smaller diameter corrugating roll 12. Each of the rolls 11, 12 is provided with a conventional fluted peripheral surface with the flutes of each roll being of the same size, shape and pitch. In accordance with standards in the corrugated paperboard industry, flute configurations vary in terms of pitch dimension (number of flutes per foot) and flute depth (crown to root dimension). In the US, the configurations range from A-flute having 33 to 35 flutes per foot and a flute depth of 4.7 mm (.185 inch) to E-flute having 90 to 96 flutes per foot and a flute depth of 1.1 mm (.045 inch). A corresponding pitch dimension range from A-flute to E-flute is about 8 mm (1/3 inch) to about 3 mm (1/8 inch). For many years, single facers have been made with a single pair of same diameter corrugating rolls which were counterrotated to create a corrugating nip therebetween. In the present invention a paper medium web 13 is fed directly into the corrugating nip 16 defined by the rolls 11, 12 and corrugated in the usual matter. Referring also to Figures 2 and 3, there is shown schematically the generation of the so-called labyrinth path which the medium web 13 follows as it is pulled into the corrugating nip. Each of the Figures 2 and 3 illustrations utilises inter-engaging corrugating rolls having flutes of the same pitch and shape, the only differences being in the diameter of one corrugating roll in each pair. Figure 2 shows the medium web moving generally tangentially into the corrugating nip between two equal and relatively large diameter corrugating rolls 10, 11. As the diameter of a corrugating roll increases, its arc or pitch circle naturally tends to straighten or flatten. As the medium web 13 is drawn into the nip 14, it begins to be gathered and folded by contact with the flutes of both rolls upstream of the nip. Thus, before the web reaches its final corrugated flute shape at the centerline of the nip 14, it has already been subjected, in the illustrated embodiment, to some degree of folding or wrapping around three flute tips in addition to the fully inter engaged flute tip pair at the nip. This is what is referred to in the industry as the labyrinth path. The wrapping of the web around each flute tip creates added tension in the web and these tension forces are additive. The forces are calculated in accordance with the function e µ β, where µ is the coefficient of friction and β is the angle of wrap around the arcuate flute tip in radians. As corrugating roll diameters have increased to match corrugator speeds and nip loadings, the labyrinth paths have increased to the point where excess tension in the web often results in rupture of the medium web at the nip. In accordance with the present invention, the use of a small diameter corrugating roll 12 meshing with large diameter corrugating roll 11 has the effect of considerably reducing the labyrinth path length and the corresponding build up of additive web tension. As shown in Figure 3, the length of the labyrinth path into the corrugating nip 16, formed by interengagement of the first, large diameter corrugating roll 11 and the smaller diameter second corrugating roll 12, is substantially reduced in length. As may be seen, the medium web 13 is partially wrapped on only two flute tips (in addition to the fully engaged pair at the nip 16) resulting in a labyrinth length significantly shorter than the length of the labyrinth in the Figure 2 illustration. It is also believed that as the number of reverse bends imparted to the medium web as it travels through the serpentine labyrinth path increases with corrugating roll diameter increase, the problem of increasing tensile force on the web is compounded. By maintaining the relatively large diameter of the first corrugating roll 11, high corrugating speeds and the resistance of the roll to deflection may be retained. To minimise the risk of deflection of the smaller diameter roll 12, the roll 12 is supported by a backing assembly 30 to apply radial forces to the roll 12. The assembly 30 provides support for the roll 12 to resist deflection as the material web 13 is corrugated in the nip 16 of the rolls 11, 12 in use and so provides the necessary corrugating nip force. The preferred assembly 30 includes backing rolls, and the backing roll arrangement 30 is positioned and operated to provide a downward force against the small corrugating roll 12, the resultant of which force acts through the corrugating nip generally in the plane common to the axes of both corrugating rolls 11 and 12. The backing roll arrangement 30 applies a force along the full axial length of the small diameter corrugating roll 12 to provide a uniform nipping pressure or force and a uniform backing force which restrains the small corrugating roll against deflection normal to its axis. The backing roll arrangement 30 includes a series of pairs of idler rolls 31, with each pair attached to a mounting bracket 32 such that the rolls are mounted on opposite sides of the common plane through the corrugating roll axes. The idler rolls 31 are positioned to bear directly on the outside of the fluted small diameter corrugating roll 12. The opposite axial ends of the small corrugating roll 12 are supported on the ends of a pair of pivot arms 34, the opposite ends of which are pivotally attached to the machine frame 35. Each idler roll pair includes a pneumatic cylinder 33 operatively attached to the mounting bracket 32 to impose a selectively variable force on the idler rolls and thus on the small corrugating roll 12. The idler rolls 31 may comprise a hard rubber or rubber-like material to help reduce noise and vibration. The cylindrical outside surfaces of the idler rolls 31 may be smooth, as indicated, or may be provided with flutes to match the flute pattern of the corrugating roll 12 engaged by the idler rolls. In another embodiment, the small diameter corrugating roll 12 could be provided with a series of axially spaced annular grooves which interrupt the flute pattern and in which grooves narrow idler rolls (similar to roll pairs 31) are positioned to operate and provide the desired backing force. It is possible, if desired, to substantially increase the diameter of the corrugating roll 11 to, for example, about 60 cm (24 inches). Correspondingly, the smaller corrugating roll 12 may have a diameter as small as about 15 cm (6 inches), but may have a diameter of about 20 cm (8 inches) or larger. It is believed that a ratio of diameters of corrugating roll 11 to corrugating roll 12 of at least about 3:1 is desirable. Variation in flute type may have some effect on the ratio, but the benefits of labyrinth path length reduction provided by the subject invention are applicable to all flute types. The remaining construction of the single facer utilising the subject invention may be generally conventional. Thus, one or both of the corrugating rolls 11 and 12 may be internally heated with steam, as through connections in their respective axial supporting shafts, all in a manner well known in the art. Preferably, both the smaller corrugating roll 12 and the larger corrugating roll 11 are provided with conventional vacuum systems by which vacuum is applied, via suitable networks of axial and radial vacuum passages 21 and 22, to the corrugated medium 23 wrapped thereon to help maintain its shape and position. The glue roll 24 of a conventional glue applicator makes rotating contact with the flute tips of the corrugated medium 23 on the lower corrugating roll 11. A liner web 26 is carried around a portion of a pressure roll 25 where it is brought into contact with the glued flute tips of the corrugated medium 23 in the pressure nip 27 formed by the pressure roll 25 and the corrugating roll 11. The pressure roll 25 may be of a conventional construction and positioned with its axis generally in the same plane as the axes of the corrugating rolls 11, 12. Alternately, other pressure roll constructions may also be used, including a low pressure nip roll with supplemental curing of the resultant single face web 28 such as in downstream web heating device 30, as disclosed in US Patent No. 4,500,900 entitled "Vacuum Assisted Web Drying System", issued February 11, 1997.

Claims: A single facer apparatus for producing a single face corrugated web (28), including first and second fluted corrugating rolls (12, 11) rotatable on parallel spaced roll axes with flutes adapted to interengage to form a corrugating nip for a paper web, means rotatably mounting said corrugating rolls (12, 11) to impose a corrugating nip force normal to the roll axes generally in the plane common thereto, said first corrugating roll (12) having a diameter sufficiently smaller than the diameter of said second corrugating roll (11) to provide a reduction in the labyrinth paper path sufficient to prevent rupture of the paper web (23), and the apparatus being characterised by means (31, 32, 33) for independently applying a plurality of axially spaced radial forces to said small diameter roll (12) along substantially the full axial length thereof, the resultant of said radial forces creating a nip force acting through said corrugating nip in a plane generally common to the axes of said corrugating rolls (11, 12), said radial forces restraining said small diameter roll (12) against deflection. A single facer apparatus as claimed in claim 1 characterised in that said means for independently applying a plurality of axially spaced radial forces to said small diameter roll (12) comprises a plurality of backing roll means (31, 32, 33) in operative rotatable engagement with said small diameter corrugating roll (12) for applying a backing force to said small diameter roll (12) sufficient to provide said nip force and to restrain the small diameter roll against deflection, said roll means each being independently supported to impose the backing force along substantially the full axial length of said small diameter corrugating roll (12). A single facer apparatus as claimed in Claim 2, characterised in that said backing roll means comprises: a plurality of pairs of backing rolls (31) positioned along the length of said small diameter corrugating roll (12), the rolls (31) of each pair positioned on opposite sides of the plane common to the corrugating roll axes; and, means (32) providing common support for each roll pair (31). A single facer apparatus as claimed in Claim 2 or Claim 3, characterised by an actuator (33) operatively connected to each roll pair support means (32) to impose a variable backing force thereon. A single facer apparatus as claimed in Claim 4 characterised by means for individually operating each actuator (33) to vary the force applied to said small diameter roll. A single facer apparatus as claimed in any one of the preceding claims characterised in that said small diameter roll (12) has a diameter not greater than about one third the diameter of said large diameter roll (11).

Inventors: MARSCHKE CARL R, MARSCHKE, CARL R.
Applicants: MARQUIP LLC, MARQUIP, LLC
Application year: 1998
Main classification: B31F1
IPC codes: B31F1