The Fourdrinier machine and the CYLINDER MACHINE comprise the machines normally employed in the manufacture of all grades of paper and board. The Fourdrinier machine may be considered in four sections: wet end, press section, drier section, and calender section. (The supercalender is not a part of the papermaking machine, and, in fact, not all Fourdriniers have a calender section.) In the wet end, the pulp or stock, at a consistency or concentration of 0.2 to 1.0%, depending upon the grade and weight of the paper being manufactured, flows from a headbox through a slice onto a moving endless belt of wire cloth, theFOURDRINIER WIRE .
The wire runs over a breast roll, which is under or adjacent to the headbox, over a series of tubes or table rolls (or, more recently, drainage blades) which maintain the working surface of the wire in a plane and aid in water removal. The tubes or rolls create a vacuum on the downstream side of the NIP .
Similarly, the drainage blades create a vacuum on the downstream side where the wire leaves the blade surface, but also perform the function of a doctor blade on the upstream side. The wire then passes over a series of suction boxes, over the bottom couch roll (or suction couch roll), which drives the wire, and then down and back over various guide rolls and a stretch roll to the breast roll.
The press section usually consists of two or more presses, whose function is to remove still more water from the web mechanically and to equalize the surface characteristics of the felt and wire sides. The wet web of paper is transferred from the wire to the felt at the couch roll, and is carried through the presses on the felts, the texture and character of which vary according to the grade of paper being made.
The drier section consists of two or more tiers of driers, which are steam-heated cylinders. The web is held firmly against them by means of fabric drier felts. As the web passes from one drier to another, first the felt side and then the wire side are pressed against the heated surface of the drier. The web enters the drier train having a water content of approximately 65%, the bulk of which is evaporated in this section. Moisture removal may be further assisted by hot air blowing onto the sheets and in between the driers to effect removal of water vapor. Within the drier section and at a point at least half way along the drying curve, there is sometimes a breaker stack for use in imparting finish, as well as to facilitate drying. The stack generally consists of a pair of chilled iron and/or rubber-surfaced rolls. There may also be a size press located within the drier section, at a point where the moisture content of the paper has been reduced to approximately 5%.
The calendar section consists of from one to three calender stacks with a reel device for winding the paper onto a reel as it leaves the machine. The calender finishes the paper, i.e., smooths it and imparts the desired finish, thickness, or gloss. Water, starch, wax emulsions, etc., may also be used to obtain additional finishes. The reel winds the finished paper, which may or may not undergo further processing.
The wire, press section, drier section or sections, the calender stacks, and the reel are so driven that proper tension is maintained in the web of paper despite its elongation or shrinkage during passage through the machine. The overall speed of Fourdrinier machines is determined by the grade and weight of the paper being manufactured. (17 , 60 , 62 , 72 , 80 , 98 , 140 )
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