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 of the corrugated medium web, and to bring a liner web into contact with the glued flue 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 the axes of all three rolls are generally co-planar. The medium web is fed into the nip formed by the interengaging corrugating rolls and the adhesive is applied to the flute tips by a glue roll while the corrugated medium is still on one of the corrugating rolls. 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 carrying the glued medium web.

More recently, a significantly improved single facer apparatus has been developed in which the fluted corrugating rolls comprise a large diameter roll and a substantially smaller diameter roll, with the ratio of diameters preferably being 3 to 1 or greater.

Once such apparatus is disclosed in U. S. Patent 5,628,865, and improvements thereon are described in co-pending application Serial Nos. 08/854,953, filed May 13,1997 and 09/044,516, filed March 19,1998, all of which disclosures are incorporated herein by reference.

Corrugating rolls are typically made of forged steel and, in those single facers using an interengaging roll pair comprising a large diameter roll and a substantially smaller diameter roll, some means of supporting the small diameter roll along substantially its full axial length must be used to maintain uniform nipping engagement between the corrugating rolls.

The above identified U. S. patent and patent applications describe various backing arrangement to hold nipping engagement and prevent deflection of the small diameter corrugating roll.

In accordance with one aspect of modem single facer development using large and small corrugating rolls, a very large diameter heated corrugating roll which may have a diameter of 39 inches (about 1000 mm) is used. The roll is provided with an internal construction to facilitate heating, as with steam, and such a roll is very expensive to manufacture. When the large and small corrugating roll pair are made of steel, wear is

distributed between the two rolls such that the small roll wears at N times the rate of the large roll, where N is the ratio of length to small roll diameters. The small roll, which is typically not heated, is substantially less costly to manufacture.

SUMMARY OF THE INVENTION In accordance with the present invention, the small diameter corrugating roll is made from a material having a significantly lower hardness than the material (such as steel) forming the large diameter roll. As a result, the wear imposed by engagement of the rolls is borne substantially exclusively by the small diameter roll. The small diameter roll may be made to be completely expendable or to be amenable to remanufacturing and reuse. The directly corresponding benefit, of course, is increased life of the larger and more expensive corrugating roll. Depending on the material used for the lower hardness small diameter roll, many other benefits may be realized, such as quieter operation, reduced vibration, substantially reduced weight, lower impact forces on the paper web being corrugated, resistance to starch glue build-up, the ability to run both corrugating rolls together without a paper web, extended life of components of the backing arrangement because of lower wear, elimination of expensive machining, and finishing operations, insulating effect helping to prevent heat loss from the large diameter heated roll, and a cushioning effect protecting the flutes of the large diameter steel roll against damage from a foreign object traveling through the nip.

In conjunction with a large diameter steel corrugating roll, the lower hardness small diameter corrugating roll may be made of relatively softer metals, such as aluminum, or from a wide range of suitable phenolic resins which may include fiber or fabric reinforcement.

Epoxy resins, rubber and thermoplastic materials may also be used.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side elevation of a single facer utilizing a low hardness, high wear small diameter corrugating roll of the present invention.

Fig. 2 is a perspective view of a small diameter corrugating roll utilizing a construction suitable for use in the single facer of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1, a single facer 10 includes a very large diameter upper corrugating roll 11 and a much smaller diameter lower corrugating roll 12. The rolls are fluted and mounted for interengaging rotational movement on parallel axes, all in a manner well known in the art and has described in greater detail in the above identified co-pending 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

corrugated medium web 13, as it leaves the nip 14, remains on the surface of the large diameter roll 11, and a glue roll 15 applies a liquid adhesive, typically starch, to the exposed flute tips of the corrugated medium. Immediately thereafter, a liner web 16 is brought into contact with the glued flute tips of the corrugated medium 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 corrugating roll 11. The large diameter roll 11 also functions as a bonding roll and is internally heated, as 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 bonds. Depending on many variable factors, such as paper weight, web speed, bonding roll temperature, and the like, the circumferential residence of the single face web 18 on the bonding roll 11 may be varied by use of a pivotal wrap arm 20.

The free end of the wrap arm 20 includes an idler roll 21 which bears on the outer face of the liner web 16 to control the amount of wrap of the single face web on the bonding roll.

The large diameter corrugating and bonding roll 11 may have a diameter of about 39 inches (about 1000 mm) and the much smaller diameter lower corrugating roll 12 a diameter of 6 inches (about 150 mm). If the small diameter corrugating roll 12 were rotationally supported only on bearings (not shown) at the opposite ends of its roll shaft 22, the roll would be subject to deflection by the load imposed on the bearings required to maintain the nip pressure. Thus, the prior art identified hereinabove 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 which the belt 25 may be made to engage the small diameter roll 12 with a selectively adjustable force. The entire backing arrangement 23 is described in greater detail in co-pending applications Serial No. 09/044,516, identified above.

As indicated in the background discussion above, in prior art constructions both corrugating rolls 11 and 12 are typically made of steel. The fluted cylindrical surfaces must be carefully machined and the overall construction of the rolls, particularly the very large diameter roll 11 which is also typically made to be internally steam heated, is costly. In accordance with the present invention, the small diameter corrugating roll 12 is made from a material other than steel and having a significantly lower hardness than steel. Many advantages may be realized

from such a construction, as listed briefly above. One particularly good material for use in the construction of small roll 12 has been found to be a phenolic resin and, in particular, a fiber reinforced phenolic resin.

In accordance with a presently preferred method of manufacture and referring to Fig. 2, a fiber-reinforced phenolic resin tube is machined, with a conventional hobbing machine, to cut the flutes therein. The cylindrical tube may be formed in accordance with prior art methods, such as winding a phenolic resin-impregnated fabric on a mandrel. The resulting phenolic tube is mounted on a suitable shaft 27 and machined in a conventional gear hob to form the flutes 28. The shaft 27 may be solid, but a hollow tubular shaft, as shown in Fig. 2, has been found to be suitable.

One suitable construction for the phenolic roll has incorporated a cotton canvas as the reinforcing fabric. However, glass and other reinforcing fibers are also believed to be suitable. Other materials in addition to thermosetting plastics may also be utilized. For example, the small diameter roll 27 may be made of aluminum and, otherwise, machined to form the flutes in the same manner as the phenolic roll or a conventional steel roll.

Other materials which may be utilized in the manufacture of small diameter roll which provide a construction with substantially higher wear rate than the large diameter steel roll include thermoplastics, epoxies and rubber. These materials may also be fiber filled or fabric reinforced as with the preferred phenolic material. A solid aluminum roll may be hopped to form the flutes in a conventional manner. Rolls made of all of the non-metal materials may be supported on steel or aluminum shafts. Further, composite rolls of non-metallic materials, such rolls having a nylon or Kevlar casing may be utilized. The non-metallic rolls may also be formed by a protrusion process with the roll body formed directly on a metal shaft. The flutes may also be formed in the protrusion process, preferably in a rough preliminary shape and subsequently finished in a gear hob to final tolerance.

The use of the fiber-reinforced phenolic roll has resulted in a number of significant benefits over prior art constructions using two steel rolls. When running, the single facer 10 with a large diameter steel roll 11 and a small diameter phenolic roll 12 is much quieter. The phenolic material has a higher natural frequency than steel. As a result, resonance and other vibration related problems are found to occur only at high machine speeds above the desired operating range, e. g. above 1300 fpm web speed (about 7m/sec.).

The large diameter and much more expensive roll 11 will enjoy an increase in wear life because of the relative softness and significantly lower hardness of the small diameter lower corrugating roll 12. A phenolic resin roll, an aluminum roll, as well as rolls of other

suitable lower hardness materials are all substantially lighter than steel. A reinforced phenolic material, for example, is about three times lighter than steel. A direct advantage of the lower density material is that the inherently lower mass of the small diameter corrugating roll results in less acceleration force imposed on the paper medium in the nip 14 caused by the inherent and unavoidable vibration of the small roll in operation.

When the small diameter phenolic roll 12 wears as a result of use to the point where it is no longer effective, the roll may be discarded or, preferably, it may be rehobbed to reform the flute pattern and used again. The worn flutes may be simply shaved off to provide a new cylindrical roll surface which is then hobbed to form a new flute pattern. It is believed that a roll may be rehobbed as many as three times before the diameter is reduced to a point where it may no longer be used. It has also been found that the typical starch-based adhesives used in the manufacture of corrugated paperboard do not stick aggressively to the preferred phenolic material. Some prior art single facers using two steel rolls require special roll heating to prevent excessive starch build-up.

In conventional single facers, it has been found to be detrimental and to result in high wear when the corrugating rolls are run together without a paper medium web also being run. Nevertheless, running a single facer without web is sometimes unavoidable. The single facer of the present invention may be a run without any risk of damage to the large diameter steel roll 11. Similarly, the backing arrangement 23, using a series of backing belts 25, enjoys a substantially longer wear life because the small diameter roll 12 does not have to be heated and its lower hardness reduces belt wear.

The manufacturing time and cost of the phenolic roll are substantially reduced.

The machining time is much shorter because of the lower hardness material as compared to steel. In addition, the typical hardening and plating operations required for steel rolls are eliminated.

Because phenolic materials are insulating, the small diameter corrugating roll 12 will not pull heat from the preheated medium web 13 during the fluting process. The substantially softer phenolic material protects the costly large diameter steel roll 11 from damage if a hard foreign object inadvertently travels through the corrugating nip 14. Any resultant damage to the small diameter phenolic roll 12 would be minimized and, in any event, not require costly repair or replacement. Finally, although the small diameter phenolic corrugating roll 12 has substantially less strength than a comparable steel roll, particularly in resistence to bending, the full length axial back-up provided by the backing arrangement 23 obviates any serious problems.