CORRUGATING PAPERBOARD This invention relates to improvements in machinery for forming of corrugated paperboard structures in which two fluted mediums bonded together at their flute tips to form the core of the corrugated paperboard structure. Australian Patent 567853 discloses an improved corrugated paperboard structure in which two layers of corrugated medium (flutes) are bonded together at or adjacent to the peaks of the flutes, and are sandwiched between two outer liners. The disclosures of Australian Patent 567833 are incorporated herein by reference. Patent Specification 567833 also discloses a method of forming the structural paper board in which two separate layers of corrugating medium are corrugated and then brought into flute tip to flute tip contact on synchronised corrugating rollers.

Australian Patents 609089 and 615053 disclosed improvements in this basic process by providing continuous support for the fluted mediums in the form of a carrier roll. The size of the carrier roll disclosed is about three times the diameter of the corrugating rolls. The difference in size between the carrier roll and the glue applicator roll (for bonding the liner) can lead to irregularities in glue application. Patent Application PCT AU 92/00439 discloses a means of reducing the length of the production line by utilising radiation curing of adhesive bonding between the liners and the fluted mediums.

An alternative form of support was disclosed in U.S. Patent 4935082 where a corrugated belt withdrew the bonded fluted mediums on a straight line from the point where the mediums are first bonded flute tip to flute tip.

A disadvantage of many of these earlier proposals is the available space for applying adhesive, liners and for allowing curing of adhesive while the fluted mediums are still supported.

Although U.S. Patent 4,935,082 discloses the use of a corrugated belt which increases the supported length of the fluted mediums the floor space occupied is quite large.

Endless belts have been proposed for use in various parts of a corrugating plant. Generally these have been smooth belts for supporting the lined face of a corrugated board through part of the corrugating apparatus as disclosed in AU patent application 89956/91, U.S.A. Patent 3,676,268, U.S.A. 4,278,486.

In U.S. Patent 3,700,518 (OHMORI) a method of forming a corrugated board having two intermediate fluted mediums bonded at their flute tips is proposed using endless belts to support to separately formed single faced boards prior to bonding the fluted mediums together. U.S. Patent 1,802,880 (CUMFER) discloses the use of two corrugated belts to corrugate two mediums which are then bonded to a liner interposed between them.

None of these prior art proposals, however, address the problem of bonding a liner to one side of a pair of fluted mediums bonded at their flute tips while continuously supporting them and doing this in a cost effective way with minimal floor space utilization.

It is an object of this invention to provide an effective arrangement for forming corrugated paperboard which has two fluted mediums bonded together at their flute tips. To this end the present invention provides apparatus for forming a corrugated board structure comprising two fluted mediums bonded together at their flute tips and at least one liner board bonded to one of said fluted mediums, wherein said apparatus comprises a) two synchronised corrugating stations arranged to corrugate and bring two fluted mediums into contact at their flute tips; b ) an adhesive applicator adapted to apply adhesive to at least one of said fluted mediums prior to the two mediums being brought into abutment at their flute tips; c) a transfer roll adjacent said synchronised corrugating rollers to provide continuous support for the bonded fluted mediums from the initial point of contact of the flute tips, said transfer roll having a diameter less than 2 times the diameter of any one of the corrugating rolls; and

d) a corrugated belt mounted on said transfer roll and adapted to support said bonded fluted mediums and convey them until a liner is bonded to at least one of said fluted mediums.

The provision of a corrugated belt to extend the support surface for the fluted mediums allows the reduction of the diameter of the transfer roll with a number of consequential advantages.

Preferably a second adhesive applicator is located adjacent the transfer roller to apply adhesive to said fluted mediums for bonding the first liner. The liner applicator rolls are positioned adjacent the corrugated belt downstream of such second adhesive applicator. Because the diameter of the transfer roll is smaller than in the apparatus proposed in the prior art, the difference in diameter of the transfer roll and the glue applicator roll is reduced and regular and even glue application is achieved.

In order to assist in maintaining tension of the fluted mediums and the liner and the corrugated belt, it is passed over a curved shoe. This curved shoe comprises a vacuum plate with a vacuum. The belt is perforated so that the applied vacuum holds the fluted mediums to it. An advantage of this arrangement compared to the previously proposed carrier roll arrangements is that the space occupied is reduced and consequently costs are reduced. It is easier using the extended curved surface of the corrugated belt to position ancillary equipment such as dryers and liner applicators in a more economical use of space.

Another advantage acquired by the use of a corrugated belt is that vacuum is easier and cheaper to provide in a belt configuration than in a large diameter carrier roll.

In order to achieve quick adhesive curing the high intensity energy applicators are designed so that these surfaces conform with that of the corrugated belt as it passes over the vacuum shoe subsequent to the liner being applied. A preferred embodiment of this invention is illustrated in the accompanying drawing which schematically represents the arrangement of this invention.

A first fluted medium 1 is corrugated on rolls 4 and 5 and the second fluted medium 2 is corrugated on rolls 6 and 7. The rolls 5 and 7 are synchronised to bring the flute tips of mediums 1 and 2 into contact for bonding. Adhesive is applied to medium 1 by adhesive application station 8. The bonded mediums are supported on roll 7 and then transferred to transfer roll 9 which supports the corrugated belt 10. The belt 10 is corrugated to support the flutes of the corrugated mediums. The belt 10 is perforated and composed of a material able to withstand high radiation levels in the infra-red region. The diameters of all rolls 4, 5, 6, 7 & 9 are substantially the same.

The corrugated belt 10 runs between transfer roll 9 and 11 and passes over a curved shoe 12 which incorporates a vacuum box to apply negative pressure through the perforations of the belt 10 to hold the bonded mediums 1 and 2 to the belt 10. Adjacent transfer roll 9 is the second adhesive unit 13 which applies liner adhesive to the outer medium 2 of the bonded pair 1 and 2. A liner 3 is passed over the S wrap rollers 14 and 15 and applied to medium 2 as it passes over the curved surface of the vacuum shoe 12.

A high energy source of radiant energy 16 is used to accelerate curing of the adhesive bond between liner 3 of medium 2. This occurs prior to the reaching roll 11. After passing roll 11 the liner and the two mediums are conveyed downstream for further processing.

From the above it can be seen that the configuration of this invention provides a cost effective solution to the problem of forming paperboard where there are two mediums bonded together at their flute tips.