Turbid water runs slowly across the wooden frame, which is spanned by a sieve. The frame is kept perfectly vertical by the papermaker. He waits until all that remains on the fine sieve is a wet layer of the material that was floating in the mash. In a further stage, the coucher was handed the frame by the papermaker, and very carefully rolled out its contents onto a felt cloth. A further employee in the workshop then had to remove the paper created by the pressing process from the felt.
That was the highly complex method used for paper production in the old days. In a series of difficult work steps, each gram of paper had to be arduously squeezed out. These days this work is done by machines. The principle of papermaking today is still the same as ever. First the fibers are suspended in water until an even emulsion is created. Then the fibers are separated again from the water using sieves, creating a fibrous web. The moisture is then removed again by means of mechanical and thermal processes.
Formerly, the main material used in production was "rag paper" - a fiber material consisting primarily of reject textiles such as cotton, hemp and linen - but today it is cellulose derived either from wood or from recycled paper. This forms the basic raw material for today's papermaking.
Now – an indispensable mass product
In this modern age, paper consumption is extremely high. The average annual demand in Germany is roughly 230 kilograms of paper per capita.
The following calculation reveals the importance of paper as a mass product:
- Distance from earth to moon = 384,400 km
- 1 DIN A4 sheet of paper = 5 g
- 1,000 DIN A4 sheets of paper = 5 kg (this is equal to a height of 11 cm)
- Annual consumption per capita x total population of Germany = distance
- 230 kg / 5 kg x 11 cm x 80 million = 404,800 km
If this amount of paper were placed in a pile, its height would reach from the earth to the moon - and even beyond!
To cover this immense demand, sophisticated high-tech production plants produce 1500-1700 metres of paper every minute. Ever increasing demand and ever higher requirements are forcing producers to steadily improve quality as well as productivity, so that today, paper machines up to 250 metres long and 11 metres high and with web widths of up to 10 metres are no longer a rarity.
Paper production takes place in eight stages:
- Material extraction
- Material preparation
- Forming section
- Pressing section
- Drying section
- Surface finishing
In the material extraction phase wood, the raw material, is initially separated into ultra-small sections, either mechanically or via the addition of chemicals. Recycled paper, if used, also has to be prepared, i.e. chopped and cleaned. In the next phase, the material preparation, the ingredients are mixed with water to form a paste. After this the mass is homogenised and the fibers spliced. The fiber mixture is then distributed evenly across the entire width of a long, constantly revolving sieve, whereby the water simultaneously flows away or is removed by suction.
The fibers form a so-called fibrous web. The evenness of the deposition determines the quality of the paper later on, and depends among other things on the running speed of the sieve and the fiber-forming technology. The fibrous web from the forming section still contains a large amount of water, which is squeezed out in the pressing section by means of large felt cylinders pressing against each other. After this, in the drying section, the paper web is guided through large furnaces and dried to the predetermined residual dampness. At the end of the process, depending on the application, the paper surface is finished, smoothed and cut to size.
Almost all paper types are produced according to this basic method. The variety of different paper types and their differing qualities derive from the selection, coordination and processing of the raw materials.
By the way, more detailed information on paper-machine felts and the respective solutions from Groz-Beckert provided by the article "Paper Production", which you can also find in this online newsletter.