The formation of a sheet of paper

Additives
The additives are put in the mixture at the first stage of the actual converting process and consists in mixing the cellulose pulp raw materials as well as possible with the other non fibrous natural materials.
At this stage the mixture is diluted considerably, for technological reasons, to about 0.5% fibre.
This operation, which involves huge quantities of water, is done by using recycled water from other stages in the process and from the flotation plant. This allows a considerable water saving due to the fact that this recycled water has a high content of suspended fibres and other matter which reduces the pollution of the tributaries, the consumption of raw materials and the natural resources. Following the addition of the chemicals such as artificial starch “drive substances”, which are needed so as to obtain the desired physical characteristics for the paper, as far as resistance, softness, whiteness, printability etc. are concerned. The suspension is stored in the two 60 m3 containers which feed the round the clock machine where the sheet of paper is made.

Selector
In this stage the remaining impurities are removed so as to obtain the best possible purity in the finished paper.
The selector is a perforated basket which lets the diluted mixture through and any particles which are larger than 0.2mm stay in the basket and are then sent to the vibrating sieve, which collects the fibres from the impurities which will be disposed of.

Distribution of the paste mixture
In this stage the remaining impurities are removed so as to obtain the best possible purity in the finished paper.
The selector is a perforated basket which lets the diluted mixture through and any particles which are larger than 0.2mm stay in the basket and are then sent to the vibrating sieve, which collects the fibres from the impurities which will be disposed of.

Distribution of the paste mixture
At this point the sheet of paper is made (which is the finished product of this process) from the fibres, which has been refined, mixed, purified and diluted. In this stage the fibre mixture, which has been obtained from the above mentioned processes, is taken to the round the clock machine and the fibre suspension is transformed into a continual sheet form.

During this stage the suspension cycle has already been prepared so as to generate paper with the desired chemical and physical requirements. The mixture has also been mixed, the additives added and diluted to a concentration that can be around 0.2 – 0.5%.
This level of dilution is indispensable for the felting process, which is when the pulp fibres are welded to give cohesion and resistance.

The paste mixture and the water are distributed by the head box in a thin sheet which is 3m wide, with uniform characteristics.
The formation web, which is a never ending strip which wraps around 8 cylinders which make it rotate continuously, has the fundamental role of the mixture loose a large quantity of water which also favours the fibres in the pulp to join together.

The first stage of the formation of the sheet of paper takes place in the wet area of the round the clock machine. This is made up of:

Head box: this first element of the round the clock machine which is just before the formation web and the pressers section. It distributes the flow of mixture from the fan pump into a slow flow which is the same width as the round the clock machine thanks to the adjustable slit on the flat board.
Flat board: it has to support the fibre felt, the so called “formation web”, where the mixture starts to dehydrate and will then be completed in the drying section: there are four drains in the flat board:
by gravity directly under the rim;
naturally on fixed or movable foil doctors;
by means of a extractor fans linked to a vacuum system;
on the intake cylinder at the head of the flat board;
Pick-up cylinder: this transports the sheet from the flat board to the pressers section (pairs of cylinders covered in different strength materials) where the drying is continued by mean of uniform compression along the contact line with the two cylinders.

Drying
So that the sheet detaches from the web, it still has a high quantity of water in it.
The level of wetness can vary according to the type of mixture and the grammage, but it is normally about 60 to 80%. At this stage the sheet is delivered by the felt and is passed through the “pressers section”, in a section that is steam heated, commonly known as the “drying unit”, which has the job of dehydrating the sheet down to about a 5% water content.
The drying unit is made up of a series of steam heated drying cylinders which complete the drying to the technical specifications of the end product;
When the sheet leaved the drying unit it is immediately wrapped around a core which supports the paper.
This is how a reel of paper is formed. A reel weighs about 800 or 900 kilos.