Abstract:
A single facer for corrugated paperboard of the type using a very large diameter fluted bonding roll and a much smaller diameter fluted corrugating roll which engages the bonding roll to provide a corrugating nip. The small diameter corrugating roll is made to be resilient so that it is capable of inward deflection in the vicinity of the corrugating nip in order to cushion impact as the rolls interengage along the corrugating nip. This cushioning deflection absorbs vibrational movement due to chordal action of the interengaging flutes, and thereby reduces noise levels, roll wear and improves the quality and consistency of corrugation.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part application of U.S. Ser. No. 09/336,104, filed Jun. 18, 1999, now U.S. Pat. No. 6,170,549. 
    
    
     FIELD OF THE INVENTION 
     The invention pertains to an apparatus for forming a single face web of corrugated paperboard. More particularly, the invention relates to a corrugating roll assembly comprising a large diameter corrugating roll (i.e. a bonding roll) and a small diameter corrugating roll in which the small diameter roll is resilient so that it is capable of deflection in the vicinity of the corrugating nip in order to cushion impact as the rolls mesh along the corrugating nip. 
     BACKGROUND OF THE INVENTION 
     In the manufacture of corrugated paperboard, a single facer apparatus is used to corrugate the medium web, to apply glue to the flute tips on one face of the corrugated medium web, 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. For many years, conventional single facers have typically included a pair of fluted corrugating rolls and a pressure roll, which are aligned so that the axes of all three rolls are generally coplanar. The medium web is fed into a corrugating nip formed by the interengaging corrugating rolls. While the corrugated medium web is still on one of the corrugating rolls, adhesive is applied to the flute tips by a glue roll. The liner web is immediately thereafter brought into contact with the adhesive-coated flute tips. 
     In the past, the fluted corrugating rolls have typically been generally the same size as each other. More recently, a significantly improved single facer apparatus has been developed in which the corrugating rolls comprise a large diameter bonding roll and a substantially smaller diameter roll, with the ratio of diameters preferably being 3:1 or greater. One such apparatus is disclosed in U.S. Pat. No. 5,628,865, and improvements thereon are described in copending application Ser. No. 08/854,953, filed May 13, 1997 and Ser. No. 09/044,516, filed Mar. 19, 1998, and Ser. No. 09/244,904, filed Feb. 4, 1999, all of which disclosures are incorporated herein by reference. In accordance with these disclosures, the single facer typically includes a backing arrangement for the small diameter corrugating roll. One preferred backing arrangement includes a series of axially adjacent pairs of backing idler rollers, each pair having a backing pressure belt entrained therearound. Each of the pressure belts is positioned to bear directly against the fluted surface of the small diameter corrugating roll on the side of the small corrugating roll opposite the corrugating nip. Each pair of associated idler rolls and pressure belts is mounted on a linear actuator, and can thus engage the small diameter corrugating roll with a selectively adjustable force. The application of force against the small diameter corrugating roll, in turn, applies force along the corrugating nip between the small diameter roll and the large diameter roll. Typically, a force of approximately 100 lbs. per linear inch (e.g. 10,000 lbs. for a 100 inch roll) is desirable for properly fluting a medium web at typical line speeds. 
     The impact of the flutes on the small diameter corrugating roll against the flutes on the large diameter corrugating roll along the corrugating nip can cause undesirable vibrations that can detriment the quality of corrugation. More specifically, chordal action due to the interengagement of the rolls causes the small diameter roll to move up and down. The center axis of the large diameter roll is analytically stationary, and vibrational energy is transmitted primarily to the small diameter roll and to the belted backing arrangement. It has been found that excessive vibrations of the belted backing arrangements is sometimes evident under certain high-speed operating conditions, especially when the system is operated at or near the natural resonance frequency of the system. 
     SUMMARY OF THE INVENTION 
     The invention involves the use of a small diameter corrugating roll that is designed to cushion contact at the corrugating nip between the flutes on the small diameter corrugating roll and the flutes on the large diameter corrugating and bonding roll. The cushioning by the small diameter corrugating roll reduces the transmission of vibration impulses to the belted backing arrangement, and thus reduces undesired vibrational movement of the small diameter corrugating roll. Reduction of such vibrational movement, and primarily reduction of radial vibrational movement, improves the quality and consistency of the corrugation. It also reduces noise levels and roll wear rate. 
     In its preferred form, the small diameter corrugating roll is made to be resilient, e.g., constructed using an inner steel tube or carbon fiber tube having approximately a four inch outside diameter and a ⅛ inch wall thickness. Preferably, the small diameter corrugating roll is a composite roll in which the flutes are made of a sacrificial material such as reinforced phenolic resin as described in the above-incorporated copending U.S. patent application Ser. No. 09/244,904. Such flutes are preferably mounted on the outside surface of the resilient steel or carbon fiber tube with epoxy. 
     In operation, the resilient tube deflects inward as the flutes on the small diameter roll impact the flutes on the large diameter roll at the corrugating nip. This deflection occurs without causing substantial movement of the center axis of the tube for the small diameter roll. Preferably, the maximum inward deflection of the resilient tube is within the range of {fraction (2/1000)} to {fraction (5/1000)} of an inch for typical corrugating loading conditions. While this amount of deflection may seem relatively small, it significantly reduces the amplitude of vibrations transmitted to the belted backing arrangement. After the deflected region passes through the corrugating nip, it springs outward to its normal position. If the flutes are made of a sacrificial phenolic resin or other similar material, the flutes themselves assist in cushioning the impact, although deflection of the resilient tube accounts for a substantial portion of the cushioning. 
     It is preferred that the flutes on the small diameter corrugating roll have a different profile than the flutes on the large diameter corrugating roll such that there is a clearance between flute tips on the large diameter bonding roll and the gullets or roots of the flutes on the small diameter corrugating roll. In this manner, the medium web fed to the corrugating nip is pressured against the fluted profile of the large diameter corrugating roll as the medium web passes through the meshed flutes in the corrugating nip. Also, inasmuch as wear does not effect the radial distance of the gullets, this arrangement assures that the small diameter corrugating roll follows the bonding roll more consistently. 
     Another advantage of designing the small diameter corrugating roll with a relatively thin wall thickness is that the reduced weight of the small diameter roll has been found to significantly change the natural resonance frequency for the system. In fact, using a small diameter roll having a thin wall in accordance with the invention typically causes the natural resonance frequency to shift upward outside of practical operating speeds for producing corrugated paperboard. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of a single facer using a small diameter corrugating roll designed in accordance with the present invention. 
     FIG. 2 is a perspective view of a small diameter corrugating roll constructed for use in accordance with the invention. 
     FIG. 3 is a cross-sectional view of a small diameter corrugating roll in accordance with the prior art. 
     FIG. 4 is a cross-sectional view of a small diameter corrugating roll in accordance with an embodiment of the invention. 
     FIG. 4 a  is a view similar to FIG. 4 illustrating cushioning deflection (exaggerated) of a small diameter corrugating roll in accordance with the invention. 
     FIG. 5 is a detailed schematic view showing the meshing of flutes on a large diameter corrugating roll with flutes on a small diameter corrugating roll with a medium web therebetween as in accordance with the invention. 
     FIG. 6 is a cross-sectional view of a small diameter corrugating roll in accordance with a presently preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a single facer  10  includes a very large diameter upper corrugating roll  11  (i.e. a bonding roll  11 ) and a much smaller diameter lower corrugating roll  12 . The rolls  11 ,  12  are fluted and mounted for interengaging rotational movement on parallel axes, all in a manner well known in the art and which has been described in greater detail in the above-identified co-pending patent applications. A medium web  13 , which may be suitably pretreated by moistening and heating, is fed into a corrugating nip  14  formed by the interengaging corrugating rolls  11  and  12 . The corrugating medium web  13 , as it leaves the nip  14 , remains on the surface of the large diameter bonding roll  11 . At that point in the process, a glue roll  15  applies a liquid adhesive, typically starch, to the exposed flute tips of the corrugated medium web  13 . Immediately thereafter, a liner web  16  is brought into contact with the glued flute tips of the corrugated medium web by a liner delivery roll  17 . The resulting freshly glued single face web  18  continues around at least a portion of the outer circumference of the large diameter roll  11 . Inasmuch as the large diameter roll  11  also functions as a bonding roll, it is internally heated, for example with steam, to cause the starch adhesive to enter the so-called “green bond” stage. By assuring that green bond is reached while the single face web  18  is still on the bonding roll  11 , integrity of the glue lines is better assured and downstream handling, including back-wrapping, is not likely to disturb the bond. The circumferential residence of the single face web  18  on the bonding roll  11  may be varied by the use of a pivotable wrap arm  20  depending on many variable factors, such as paper weight, web speed, bonding roll temperature, and the like. The free end of wrap arm  20  includes an idler roller  21  that bears on the outer face of the liner web  16  to control the amount of wrap of the single face web  18  on the bonding roll  11 . 
     The large diameter corrugating and bonding roll  11  typically has a diameter in the range of 39 inches (about 1000 millimeters) and the much smaller diameter lower corrugating roll  12  typically has a diameter of about five inches (about 128 millimeters). The prior art identified herein above provides various backing arrangements for the small diameter roll  12 , one of which backing arrangements  23  is shown in the drawing. The backing arrangement  23  includes a series of axially adjacent pairs of backing idler rolls  24 , each of which pairs has a backing belt  25  entrained therearound. Each of the pressure belts  25  is positioned to bear directly against the fluted surface of the small diameter corrugating roll  12 . Each associated pair of idler rolls  24  and backing belt  25  is mounted on a linear actuator  26 . By operation of the linear actuator  26 , the pressure belts  25  are moved to engage the small diameter roll  12  with a selectively adjustable force. The entire backing arrangement  23  is described in more detail in copending application Ser. No. 09/044,516, identified above. 
     As indicated in the background discussion above, the large diameter roll  11  has substantially more mass than the small diameter corrugating roll  12 , and therefore remains relatively stable as it rotates even at high speeds. On the other hand, due to chordal action at the nip  14 , substantial up and down movement can occur in the small diameter corrugating roll  12  and the backing arrangement  23 . Under extreme conditions, such vibrations (especially in the radial direction) can cause the small diameter corrugating roll  12  to bounce at the corrugating nip  14 , and in any case cause increased noise levels and increased wear rates. The vibration problem is exacerbated if the line speed matches the natural frequency of the system. For example, in early designs of systems having a small corrugating roll, the small diameter corrugating roll was typically made of solid steel. Due to the weight of solid small diameter corrugating rolls  12 , the natural resonance frequency of such systems occurred at a line speed of approximately 300 feet per minute, which is within the typical operating range of single facers  10 . 
     In accordance with copending patent application Ser. No. 09/244,904, it has been found to be advantageous to construct the flutes on the small diameter corrugating roll  12  from a fiber reinforced phenolic resin mounted upon an inner cylindrical tube. Such a composite roll  12  is shown in FIG.  2 . The composite roll  12  in FIG. 2 is illustrative of the prior art roll shown in the above referenced copending patent application, and is also illustrative of a small diameter corrugating roll  12  constructed in accordance with a preferred embodiment of the invention. Referring to FIG. 2, the small diameter corrugating roll  12  is machined with a conventional hobbing machine to cut the flutes  28  therein. Stub ends with shafts  27  are mounted to the roll  12 . 
     FIG. 3 is a cross-section illustrating the composite construction of the prior art small diameter roll  112 . The prior art roll  112  has a relatively rigid, solid steel tube  130  and a phenolic resin-impregnated sacrificial layer  132  adhered to the tubular shaft  130 . The outer diameter of roll  112  shown in FIG. 3 is typically about five inches as measured from diametrically opposed flute tips. The outside diameter of the steel shaft  130  is typically about 3⅛ inches and the thickness of the wall of the steel tube  130  is typically be about ½ of an inch. It is preferred that the sacrificial fluted layer  132  include a cotton canvas as a reinforcing fabric for the phenolic resin, although other reinforcing fibers are also believed to be suitable. In addition, it may be possible to use other resins for the sacrificial layer  132 . As mentioned, the sacrificial layer  132  is preferably attached using epoxy. The construction of the prior art roll  112  shown in FIG. 3 is explained in detail in copending patent application Ser. No. 09/244,904, as well as various advantages of using the sacrificial layer  132 . 
     The use of a sacrificial phenolic fluted layer  132  in itself results in quieter operation, as well as longer wear life for the large diameter bonding roll  11 . The extended wear lift for the bonding roll  11  is particularly desirable because the large diameter bonding roll  11  is much more expensive than the small corrugating roll  12 . When the small diameter phenolic roll  112  wears to a point where it can no longer be effective, the roll  112  may be discarded, or preferably, it may be rehobbed to reform the flute pattern and used again. 
     FIG. 4 shows a small diameter corrugating roll  12  constructed in accordance with the preferred embodiment of the invention. More specifically, the roll  12  includes a thin wall steel tube  30  or a thin wall carbon fiber tube  30 . Preferably, the outside diameter of the steel or carbon fiber tube  30  is about four inches, and the inside diameter of the steel tube  30  is about 3.75 inches. Therefore, the steel or carbon fiber tube  30  has a wall thickness of about ⅛ of an inch, thus rendering the tube  30  somewhat flexible and resilient. The fluted sacrificial layer  32  (preferably reinforced phenolic resin as described above) is mounted to the outside surface of the steel or carbon fiber tube  30  in order to form a composite structure for the small diameter corrugating roll  12 . 
     For the relatively rigid small diameter corrugating roll  112  shown in prior art FIG. 3, the roll  112  moves up and down due to interaction between the flutes of the large diameter roll  11  and the flutes of the small diameter roll  112 . As mentioned, this motion is well known in the industry and is called “chordal action”. Analysis has shown that the amplitude of vertical motion of a rigid, small diameter corrugating roll  112  as shown in FIG. 3 is typically within the range of {fraction (2/1000)} of an inch to {fraction (3/1000)} of an inch at normal operating loads and speeds. At high line speeds, vertical motion creates a dynamic force that is transmitted both to the bonding roll  11  and to the supporting belt  25 . As a result, noise level and roll surface wear are relatively high, even when using a sacrificial layer  132  construction. In addition, bouncing can actually occur, especially at speeds at or near the natural resonance frequency. 
     In contrast, a small diameter corrugating roll  12  constructed in accordance with the invention absorbs vertical vibration due to chordal action by providing for cushioning deflection within the inner tube  30 . FIG. 4 a  illustrates this cushioning deflection in an exaggerated manner. In FIG. 4 a , the portion  34  of the small diameter corrugating roll  12  engaging with the flutes on the large diameter roll  11  (not shown in FIG. 4 a ) are deflected inward in the direction of arrow  36  in order to cushion impact at the corrugating nip  14 . Finite element analysis has shown that the maximum amount of deflection (arrow  36 ) is in the range of {fraction (2/1000)} of an inch to {fraction (5/1000)} of an inch in the vicinity of the corrugating nip  14  when the roll  12  is subject to a backing force of 100 lbs. per inch. For a composite phenolic/carbon fiber roll  12  having the previously disclosed dimensions and loading, the typical deflection is approximately {fraction (3/1000)} of an inch. For a steel tube  30 , the deflection is slightly less. Although the portion  34  of the small diameter corrugating roll  12  deflects inward, the center axis  38  of the roll  12  remains relatively stable. Also, the portion  40  of the roll  12  in contact with the backing belt  25  remains round because the deflected portion  34  returns to its normal position after it passes the corrugating nip  14 . It has been found that using a lower corrugating roll  12  as constructed in accordance with the invention to have a resilient and relatively flexible inner tube  30  further reduces noise level and roll wear. In addition, a small diameter corrugated roll  12  constructed in accordance with the preferred embodiment of the invention has less mass than conventional solid steel rolls, as well as the prior art composite roll  112  shown in FIG.  3 . Because of the lighter mass, the resonance frequency of the system occurs at a higher line speed that is well above normal operating speeds for single facers. 
     FIG. 5 is a detailed view illustrating the medium web  13  entering the corrugating nip  14  between flutes  28  on the small diameter corrugating roll  12  and the flutes  29  on the large diameter roll  11  (i.e. the bonding roll  11 ). In FIG. 5, the bonding roll  11  is rotating in the direction of arrow  42  and the small diameter corrugating roll is rotating in the same direction as depicted by arrow  44 . The medium web  13  enters the corrugating nip from the left side of FIG.  5 . The profile of the flutes  28  on the small diameter corrugating roll  12  are different than the profiles of the flutes  29  on the large diameter corrugating roll  11 . More specifically, the gullets or roots  46  of the flutes  28  on the small diameter corrugating roll  12  are deeper than the flute gullets  48  for the large diameter bonding roll  11 . With this configuration, only the tips  50  of the flutes  28  on the small diameter corrugating roll  12  contact the flute gullets  48  on the bonding roll  11 . This means that there is a clearance  52  between flute tips  54  on the bonding roll  11  and the flute gullets  46  on the small diameter corrugating roll  12  (e.g., preferably {fraction (10/1000)} to {fraction (20/1000)} of an inch). Also, inasmuch as the radial distance from the flute gullets  48  on the bonding roll  11  to the center axis for the bonding roll  11  is constant and the only point of contact between the bonding roll  11  and the corrugating roll  12  is at the flute gullets  48  for the bonding roll  11 , the speed of the small diameter corrugating roll  12  will more consistently follow the bonding roll  11 . 
     Extensive testing of small diameter corrugating rolls made in according with the previously described embodiments has shown that a sacrificial fluted layer (e.g.  32  or  132 ) exhibits unsatisfactory wear characteristics and a short wear life under certain conditions of use. To solve this problem and referring to FIG. 6, a resilient thin walled corrugating roll  212  was formed from a unitary thin walled steel tube. Specifically, a steel tube of about 5¾ inch diameter (about 145 mm) and a wall thickness of 0.5 inch (about 13 mm) was used. Flutes  228  were cut in the OD of the tube using conventional hobbing techniques. After cutting the flutes, the minimum remaining wall thickness of the tube  232  was about 0.25 inch (about 6.5 mm). The flutes were then plated with a wear coating of nickel with a thickness of about 0.003 inch (about 0.08 mm). 
     The unitary steel roll  212  was found to exhibit substantially better flute wear life and yet provide the same beneficial cushioning deflection exhibited by the previously described rolls. As an additional benefit of the unitary construction of the roll  212 , the natural frequency as compared to the rolls  12  and  112  is increased. As a result, harmonic vibrations are not as significant a problem with this embodiment. 
     Various alternatives and other embodiments are contemplated as being within the scope of the following claims which particularly point out and distinctly claim the subject matter regarded as the invention. For example, it is not necessary for the small diameter corrugating roll  12  to have a composite construction to implement the primary features of the invention.