Corrugated board production
Corrugated Board is manufactured from a number of specially conditioned layers of recycled and/or virgin papers, called Fluting Medium and Linerboard. Reels of Fluting Medium and Linerboard are fed into a machine called a Corrugator. The Fluting Medium paper is conditioned with heat and steam and fed between large corrugating rolls that give the paper its fluted shape. Starch is applied to the tips of the flutes on one side and the inner liner is glued to the fluting. 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 corrugated board. A number of layers of single faced web may be built up to produce double and triple wall corrugated board. The corrugated board is slit into the required widths and cut into sheets which are then stacked or palletised. The final stage of the process consists of printing and then slotting, folding and gluing the corrugated board to manufacture a corrugated box.
Fig. 1d Corrugated board production
Various structures of corrugated fibreboard are illustrated below (after ISO 4046):
Most boxes are printed in one or more colours to identify the product they are going to contain, the product manufacturer, the box manufacturer and other information regarding the distributed goods. Different converting operations are carried out according to the customer’s specification and according to the type of packaging. The two main categories are the regular slotted box and the die-cut box. The latter concerns packaging that requires a very precise cutting and which can have a complex design.
Regular slotted boxes are usually produced with an in-line flexographic Printer/Slotter/ Folder/Gluer which, in one operation, prints, cuts, folds and glues the board into its final shape.
The die-cut boxes are manufactured on a die-cutter (rotary or flatbed) which cuts and creases the board.
After converting, the corrugated packaging is put on a pallet and delivered to the customer.
Figure 1e shows an example of a box blank and Figure 1f shows the result when this blank is erected as a converted box
The corrugated board composition of the corrugated box depends on the function that it has to fulfil.
The consumption of liner and fluting can be calculated from the dimensions of the box, grammage of the liners and fluting, what kind of flute i.e. wave type used and weight of the sheet before die cutting. Different wave types lead to different heights of the corrugated layer and to different paper consumption (due to the take-up factor). In Table 1 indicative figures are given for different flute types, as an example.
|Flute||Flute height* mm||Number of flutes per m length of the corrugated board||Take-up factor||Glue consumption g/m2, glue layer|
The take-up factor governs the amount of fluting material required to manufacture the corrugated board. It allows for the fact that, when laid out flat before converting, the area of fluting material required to manufacture a defined area of corrugated board is greater than the surface of the converted board itself.
For example, a typical take-up factor for C-flute is 1.43, meaning that 1.43m2 of fluting (measured flat) is required to manufacture 1m2 of converted corrugated board, as shown in the example below:
Figure 1g illustrating the take-up factor
|Example:||FEFCO Code 0201|
|Box weight:||650 g|
|Dimensions :||575 x 385 x 225 mm (L x B x H)
corrugated board C flute
|Facings:||Kraftliner 175 g/ m2, Testliner 175 g/ m2|
|Medium:||Recycled Fluting 140 g/ m2|
|The composition of the corrugated board is then:|
|Recycled Fluting||1,43 x 140 = 200|
|Glue||2 x 5 = 10|
The corrugated board manufacturer can give the weight of the sheet before die-cutting. For a standard type construction the weight can also be calculated using the International Fibre Board Case Code published by FEFCO. In this code the form of the box blank is shown and by using the box dimensions it is possible to calculate the total length and width of the blank. Adding a 20 mm broad strip to the edges of the blank gives a fair estimate of the sheet area before die-cutting.
In the example L tot = 1,95 m and W tot = 0,61 m. The dimensions of the sheet are:
Asheet = (1,95 + 0,04) x (0,61 + 0,04) = 1,2935 m2
and the weight:
Msheet = 1,2935 x 560 = 724 g
Assuming 3% as corrugator trimmings (i.e. hcorrugator = 0,97, a common value for modern corrugators), the consumption of liner and fluting can be calculated as follows:
|Kraftliner||175 * 1,2935/0,97 =||233|
|Recycled Fluting||200 * 1,2935/0,97 =||267|
|Testliner||175 * 1,2935/0,97 =||233|
|Glue||10 * 1,2935/0,97 =||13|
Total (shavings) = 746 - 650 = 96 g/box = 12,9% of the input.
Please note that this is only an example of a particular box of a certain standard type construction.
Corrugated board boxes are far from standardised. They show a huge variation in composition, design and appearance. Boxes are tailor made to fit the box user’s needs and requirements which are determined by the product to be packed. The percentage of trimmings/shavings vary according to the design of the packaging.
Since standard boxes do not exist, the database is set up in a flexible way giving the user the possibility to make calculations for any composition needed and using project specific assumptions on transport distance, waste management scenarios etc.