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 in the Single Facer. 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. Various structures of corrugated fibreboard are (ISO 4046):
The final stage of the process consists of printing and then slotting, folding and gluing the corrugated board to manufacture a corrugated box.
Most boxes are also printed in one or more colours to identify the product they are going to contain, the product manufacturer, the box manufacturer and also bar codes providing other information regarding the distributed goods. Different 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.
Most of the regular slotted boxes are 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 the result as converted box
- B= breadth of the box
- L=length of the box
- H= height of the box
A corrugated box is composed of layers of paper: liner (linerboard) and fluting (corrugating medium). The four major paper grades used for the production of corrugated board boxes are Kraftliner, Testliner, Semichemical Fluting and Wellenstoff (recycled fibre based fluting) for which the data are found in the database.
The 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. In table 1 indicative figures are given for different flute types.
|Flute||Height of the corrugated member* mm||Flutes/m length of the corrugated board web||Take-up factor||Glue consumption g/m2, glue layer|
The take-up factor gives the amount of fluting per m2 of corrugated board: i.e. for a C-flute the amount of fluting in the corrugated board will be about 1,43 m2/ m2 corrugated board.
|Example:||FEFCO Code 0201|
|Box weight:||650 g|
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:||Wellenstoff 140 g/ m2|
|The composition of the corrugated board is then:|
|Wellenstoff||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|
|Wellenstoff||200 * 1,2935/0,97 =||267|
|Testliner||175 * 1,2935/0,97 =||233|
|Glue||10 * 1,2935/0,97 =||13|
Total losses (=shavings) = 746 - 650 = 96 g/box = 12,9% of the input.
For the example FEFCO Code 0201 there would be [(1,95*0,61)-(1,99*0,65)]*560 =58,24g losses from the 20 mm edges and (746-746/0,97)=22,4 g losses from the corrugator trimmings, in total 80,6/746 g = 10,8% losses before die-cutting and 12,9%-10,8%= 2,1% from die-cutting.
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.
Typical conversion losses for the sold corrugated product are about 10% and additional losses to the converted box are 7%. This is an estimate as these shavings are collected together on site and are 100% recycled.
A “blank” before corrugating and conversion would be length 2.00 m by width 0.7 m and hence an area of 1.4 m2.
With a grammage of 560 g/m2 the weight of the “blank” would be 560*1.4 = 784 g.
With the typical conversion losses, the “blank” for conversion would weigh 706 g and the converted box 650 g.
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 he/she wants and using his/her own assumptions on transport distance, waste management scenarios etc.