Apparatus for producing corrugated board

Abstract

 Apparatus (1) for bonding together plies (5, 6) of corrugated board (4) during manufacture thereof has an upstream heating section (2) and a downstream traction section (3). The upstream section (2) has means (8) (e.g. steam chests) for heating the board (4) during its passage through the upstream section (2). The downstream section (3) has first and second endless belts (12, 13) which do not extend into the heating section (2). The belts (12, 13) have facing runs between which the board (4) may be held and the downstream section (3) has means (12a, 13a) (e.g. air plenums) for pressing the facing runs of the first and second belts (12, 13) towards each other to hold the board therebetween.

Description

[0001] The present invention relates to apparatus for producing corrugated paperboard, corrugated board and like materials, such materials being referred to herein generically as corrugated board for simplicity.

[0002] Various constructions of corrugated board are known and widely used in the packaging industry. For example one form of board, known as single wall board, comprises a corrugated fluting medium bonded between two liner webs. Another product, known as double wall board, comprises a central liner web, two outer liner webs and corrugated fluting medium bonded between the inner and outer webs.

[0003] In a first stage of corrugated board production, a liner web is bonded to one side of a fluting medium. The exposed corrugated tips of the composite material are then coated with an adhesive and at least one run of the thus treated material (depending on whether single wall, double wall, or other type of corrugated board is required) is supplied together with a'liner web to apparatus for bonding together the plies of the board in a "double-backing" operation.

[0004] The apparatus for performing this double backing operation is known as a "double backer" and comprises an upstream heating and pressing section for drying or curving the adhesive and bonding the plies firmly together, and a downstream traction section serving to draw the board through the apparatus. During its residence in the traction section the board is cooled and may subsequently be cut, and/or slotted and/or printed as required.

[0005] A conventional double backer has an upper endless belt running the full length of the apparatus through the heating and traction sections. This upper endless belt is usually of a textile material and is expensive. The heating section has heating means, usually a heated surface (e.g. provided by heated platters hotplates or steam chests) arranged such that the board will locate between the surface and a run of the first belt. The downstream or traction section has a lower second endless belt arranged such that the board will locate between the first and second belts in this section.

[0006] In the heating section pressure is applied to the back of the first belt, e.g. by rollers or one or more plenum chambers, so that the belt presses the board against the heated surface as the board is advanced through the section. Thus the adhesive is dried or cured and the plies bonded together. The use of a woven textile belt as the upper endless belt ensures that moisture generated in the heating and pressing section is absorbed.

[0007] In the traction section of a conventional double backer pressure is applied to the reverse side of the first and second belts by variable weight rollers so that they grip the board and draw it through the apparatus.

[0008] According to the invention there is provided apparatus for bonding together plies of corrugated board during manufacture thereof, the apparatus comprising an upstream heating section and a downstream traction section, said upstream section having means for heating the board during its passage through the upstream section, and said downstream section having first and second endless belts which do not extend into said heating section and which have facing runs between which the board may be held, and means for pressing the said runs of said first and second belts towards each other to hold the board therebetween.

[0009] The means for pressing the facing runs of the first and second endless belt towards each other may be rollers or, more preferably, pressure chambers for applying gaseous pressure to at least one of said belts to press them towards eachother so as to hold the board therebetween.

[0010] The means for applying gaseous pressure to the runs of the first and second belts preferably comprise at least one plenum chamber at each of the reverse sides of the opposed belt runs, the chambers being associated with means for supplying air under pressure thereto. The air pressure acting on the reverse sides of the belts is effective to press the belts towards each other to hold the board therebetween. Preferably the plenum chamber acting on the lower belt run has a perforated plate (e.g. steel) on which the bottom belt will float.

[0011] In the case where plenum chambers are used for applying pressure to the reverse sides of the first and second belts, it is preferred that these belts be made of a non-porous material (e.g. conventional belting of rubber or PVC) so that the gaseous pressure is used efficiently to press the belts againa:the board.

[0012] The use of gaseous pressure and, particularly when supplied by air plenums, in the traction sections has the advantage that a uniform pressing of the belts is obtained so that the board is not crushed, as is often the case when rollers are used in the traction section.

[0013] Alternatively, plenum chambers may be used for applying pressure to one of the first or second belts and conventional means (e.g. rollers) may be used for applying pressure to the other belt.

[0014] Preferably the heating and pressing section (the upstream section) comprises a/third endless belt (separate from the aforementioned first and second belts) and means are provided for pressing a run of said third endless belt against the board in the upstream section. Such means may be weighted rollers or, more preferably, one or more pressure chambers for applying gaseous pressure to the reverse side of the third belt. The pressure chambers preferably extend across the width of the first belt. The pressure chambers may be used in conjunction with weighted rollers.

[0015] Preferably also the means for heating the board in the heating and pressing section is a heated surface (e.g. provided by heated platters, hotplates or steam chests) against which the board is pressed (e.g. by the aforementioned third belt) in the heating and pressing section.

[0016] The use of belts in the traction section which do not extend into the heating and pressing section has the advantage in that the material of these belts may be chosen simply for the properties that the belts are required to have in the traction section. This is particularly important in the case where the heating and pressing section includes a separate endless belt as will be appreciated from the following discussion. Different conditions prevail in the heating and traction sections since in the former section there is a large amount of moisture (originating mainly from the adhesive) generated by the heating and pressing of the board, whereas there is no such moisture generation in traction section.

[0017] The invention thus allows the selection of different belt materials for the heating and traction section. The belt of the heating section may be of a porous material (e.g. textile material selected for its moisture absorbing characteristics whereas the belts of the traction section which are not required to be moisture absorbent may be selected for their frictional characteristics to improve the traction on the belt. Additionally, where the plenum chambers are used for pressing the first and second belts of the traction section, these belts may be of non-porous material as mentioned above. Such non-porous belts are generally significantly cheaper than the porous woven textile belts and which have hitherto been used as a common belt in the upstream and downstream sections. The invention thus allows belts of optimum properties to be used for heating, and traction sections, whereas this was obviously not possible with the common belt in the prior art apparatus. Additionally, the invention may significantly reduce the cost of the belting for a "double backer" apparatus.

[0018] One embodiment of the invention will be described by way of example only with reference to the accompanying drawing showing apparatus for bonding together plies of corrugated board and embodying both the first and second aspects of the invention.

[0019] The illustrated apparatus 1 comprises an upstream hot pressing section 2 and a downstream traction section 3. The apparatus is shown for the production of single wall corrugated board 4 from a liner web 5 and a combined web 6 constituted by a corrugated fluting medium bonded to a line web.

[0020] Heating section 2 comprises an upper porous endless belt 7 of suitable absorbent material (e.g. textile material) and having a run 7a which is closely spaced above a heating surface provided by the upper faces of a plurality of steam chests 8 in a box structure 9. At the upstream end of heating section 2 are four rollers 10 the effective weight of which can be varied for pressing onto the reverse side of belt run 7a whereas downstream of the rollers there are a plurality of plenum chambers 11. Each chamber 11 is of a width substantially equal to that of belt 7 and is supplied with air by fans (not shown). These fans may be belt driven and take their inlet air from beneath the steam chests 8 thus supplying warm air into the plenums to heat the belt run 7a to increase the dissipation of moisture. The fans may be associated with means for adjusting the air supplied thereby lowering or raising the pressure in the plenums to take account of varying conditions and board grades.

[0021] The traction section 3 comprises upper and lower endless belts 12 and 13 respectively each of which are of a non-porous material, e.g. rubber or PVC. Means (not shown) are provided to ensure that belts 7, 12 and 13 are driven in synchronism. The belts 12 and 13 are arranged with opposing belt runs 12a and 13a respectively between which the board 4 is held, and upper and lower plenum chambers 14 and 15 respectively are provided on the reverse sides of belt runs 12 and 13a. Each chamber 14 and 15 extends across the width of the belts 12 and 13 with chamber 14 being open to the reverse side of belt run 12a and chamber 15 having a perforated steel plate (not shown) on which belt run 13a will float. Chambers 14 and 15 are associated with suitable fan arrangements (not shown).

[0022] To overcome any possibility of glue or debris from the belt 13 encrusting the perforated plate the plenum chamber 15 may be fitted with a pneumatic cylinder (not shown) at each corner and operated by a simple on/off actuator which allows the plenum 16 to be lowered and cleaned as necessary.

[0023] The traction section 3 operates by virtue of the plenum chambers 14 and 15 urging the belts 12 and 13 towards each other to grip the board 4 which is thus drawn through the apparatus on movement of the belts 12 and 13. The use of the plenum chambers 14 and 15 ensures than even pressure is applied to the belt thus avoiding board crushing such as can be caused by weighted rollers.

[0024] It will te appreciated that the rollers 10 may be omitted and replaced by the plenum chambers 11. Alternatively a small air pressure chamber (not shown) may be provided upstream of rollers 10 to provide an initial squeezing together of the plys 5 and 6 to enhance bonding. As a further alternative the plenum chamber 14 may be replaced by rollers.

[0025] It will also be appreciated that suitably located temperature sensors may be provided, e.g. immediately downstream of the hot pressing section 2, for monitoring the temperature of the board 4. Such sensors may control air pressure supply to one or more plenums 11 and/or steam supply to the chests 8, there being factors which influence board temperature. Consequently, if the sensed board temperature is outside predetermined limits the air pressure and/or steam supply may be adjusted accordingly.

Claims

1. Apparatus for bonding together plies of corrugated board during manufacture thereof, the apparatus comprising an upstream heating section and a downstream traction section, said upstream section having means for heating the board during its passage through the upstream section, and said downstream section having first and second endless belts which do not extend into said heating section and which have facing runs between which the board may be held, and means for pressing the said runs of said first and second belts towards each other to hold the board therebetween.

2. Apparatus as claimed in claim 1 wherein the means for pressing the facing runs of the first and second endless belts towards each other comprise pressure chambers for applying gaseous pressure to at least one of said belts.

3. Apparatus as claimed in claim 2 wherein pressure chambers are provided for applying gaseous pressure to both of said first and second belts.

4. Apparatus as claimed in any one of claims 1 to 3 wherein the first and second belts are of a non-porous material.

5. Apparatus as claimed in any one of claims 1 to 3 wherein the heating and pressing section comprises a third endless belt and means for pressing a run of said third belt against the board in the upstream section.

6. Apparatus as claimed in claim 5 wherein the third belt is of a porous material.

7. Apparatus as claimed in claim 5 or 6 wherein said means for pressing a run of said third belt against the board comprises at least one pressure chamber.

8. Apparatus as claimed in any one of claims 5 to 7 wherein the heating and pressing section has a heated surface against which the board is pressed by the third belt.

Drawing