The corrugated fluting medium with one liner attached to it is called single face web and travels along the machine towards the double backer where the single face web meets the outer liner and forms a continuous web of single wall rigid corrugated board, which is then cut to length and width and stacked.
Details on the various operations
The splicers and reelstands
These are the machines which feed the paper rolls into the corrugator and enable rolls to be changed without interrupting the production of corrugated board.
The single facer
This machine transforms the paper into a series of connected arches called « flutes » thanks to the corrugating rolls (large cylinders with a corrugated profile). Changes in flute profile are accomplished by changing the corrugating rolls.
The glue unit and double backer
Here, the single face web is prepared for gluing to the outer liner. It is roughly the same process as the single facer unit with some variations of the pre-heating and gluing processes.
This glues the outer liner to the fluting to make single, double or triple wallboard. The single face web is pre-heated, starch is applied to the tips of the flutes, and the outer liner is then bonded to the single face web to form corrugated board.
This is a complex operation that requires great expertise in the pre-heating, moisture control and gluing processes in order to produce perfectly flat, stable sheets of board.
The bridge
This enables the double backer to run at different speeds from the single facer especially when reel or order changes take place. This is achieved by the single face web forming festoons that are controlled at the single facer station.
Bridge festoons
Example of festoons
The hot plate section
It is at this stage that the combination of the single face web and the outer liner is completed. The heating section ensures that the bond is strong by gelling the glue and removing moisture.
The rotary shear
After the board emerges from the double backer, it passes under a rotary shear that cuts across the whole width of the web when necessary. This is used to chop out damaged lengths of board or to effect a change over from one grade of board to another. The small amount of sheared board is ejected from the machine and collected for recycling.
The slitter / scorer
This operation slits and scores the continuous web of acceptable board in the machine direction. It is this operation which determines the style of the finished box.
The cut-off knives
These cut the board to the exact required lengths of corrugated sheet to be used in the making of corrugated packaging.
The stacker
Finally, corrugated sheets are automatically stacked, ready to be moved directly to the conversion machine or sent to another converting plant.
The Conversion process: the line convertor