Fourdrinier wire section

Fourdrinier wire section, the most common forming principle in the past and which has been continuously improved since its early invention, is a horizontal forming wire supported by different kinds of dewatering elements. 

The majority of paper machines worldwide produce graphic paper grades on fourdrinier wire sections or on hybrid formers. These kinds of conventional forming section usually satisfy the quaHty requirements. Their disadvantages are the limitation in machine speed of about 1200 m min and for some paper grades the nonsymmetry in the web z-direction. 

At the end of the Fourdrinier wire a couch roll removes more water from the web before it is transferred to the press section. At this point the moisture content of the web is about 80% water (20% consistency, 200g/L). The white water from the Fourdrinier is continuously recycled 1000 kg of stock at 0.5% consistency is reduced to a 25 kg mat (5 kg fibre, 20 kg water) by the time it leaves the wire and 975 kg of white water is recycled to the make-up chest and thence back to the headbox. A 500 tonne a day papermachine recycles some 100 000 m of water a day. 

Table roUs (Fig. 6.39), used in the fourdrinier section for drainage and to generate turbulence. Pressure is developed in the upstream wedge between the wire and roU, and a vacuum is induced in the downstream nip. With increasing machine speeds the pressure and vacuum pulses increase over-proportionally and thus hmit the application of table rolls to machine speeds of about 500 m min. ... 

The Fourdrinier former is likely the most widely used forming method employed in modem papermaking. It has proven uniquely versatile in the variety of paper grades it can produce. Wire speeds up to 5000 feet per minute are possible with some lightweight grades. The following description follows the pulp flow fi-om the headbox to the couch roll just prior to the press section. A Fourdrinier wet end is shown in Figure 3. 

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