Paper processes - Paper machines

The paper machine itself will be used, from a raw material (or pulp) prepared for this purpose (cf. ), to produce a continuous sheet of paper or cardboard, of a given width and corresponding to well-defined specifications (grammage, thickness, given physical and optical properties). Modern machines currently reach speeds of 1,800 m/min (newsprint), and even 2,200 m/min for special machines used for sanitary and household papers. Some machine manufacturers are looking to increase speeds up to 2,500 m/min, and several pilot paper machines are already running in excess of 2,000 m/min for light grades (newsprint). Machine widths can reach 10 m, but an increase in width is unlikely in the short term.

The paper machine consists of three main parts (figure 1 ):

• the wet section, comprising the headbox and the production table. This is where the sheet is formed and drained, first by gravity and then by vacuum;

• the press section, where the sheet is mechanically dewatered as much as possible;

• drying, where the remaining water is thermally eliminated (evaporation).

On leaving the dryer, the sheet, at a moisture content of between 4 and 9% (by mass), is stored in reels using a rewinder. Before this final stage, which represents the end of the paper machine, the sheet can undergo a number of additional in-line treatments: coating, coating, smoothing, calendering, etc. All these operations generally add value to the paper. All these operations, which generally add value to the paper, can of course be carried out off-machine, on special installations: coaters, calenders, supercalenders.

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