Paper Manufacture

Publisher Summary Paper consists of a web of pulp fibers, usually formed from an aqueous slurry on a wire or screen, and held together by hydrogen bonding. The same basic steps are involved for either hand- or machine-made paper. The steps are: forming (applying the pulp slurry to a screen), draining (allowing water to drain by means of a force such as gravity or a pressure difference developed by a water column), pressing (further dewatering by squeezing water from the sheet), and drying (air drying or drying of the sheet over a hot surface). The paper machine is a device for continuously forming, dewatering, pressing, and drying a web of paper fibers. The most common type of wet end machine was the fourdrinier, where a dilute suspension of fibers is applied to an endless wire screen or plastic fabric. Water is removed by gravity, or the ΔP developed by table rolls, foils or suction equipment, and the drilled couch. The web at this point is 18-23% consistency. More water is squeezed out in the press section to a consistency of 35-55%. Finally the sheet is with steam heating in the dryer section. Modem paper machines can be quite expensive, costing up to several hundred million dollars each.