Classification of Paper Machines
According to the different network structure of paper machine, paper machine can be divided into long net type, round net type, clamp net type, overlay net type and with finishing roll type.
Paper machine can be regarded as a kind of linkage consisting of several equipments. Usually it can be divided into wet part and cadre part. The wet part includes the pulp conveying equipment, the net part and the press part: the cadres include the drying part, the calender and the paper reel machine.
After pulping, sizing, filling and purification, pulps with suitable properties for papermaking enter the pulp conveying equipment of papermaking machine at the concentration of 0.3% - 1.3%. Then, after the pulp distributor and headbox convection pulp distribution and leveling, the paper uniformly and steadily flows to the mesh of the forming network. After the pulp flow is connected to the net near the center line of the chest roll, it gradually filters and dehydrates to form a continuous wet sheet of paper. The net case is usually equipped with forming-dewatering elements such as case roll, vacuum suction tank and volt roll. When the wet sheet is dehydrated to a certain degree of dryness (usually about 20%), it can be peeled off the mesh and sent to the press to continue dehydration.
The press section of paper machine is composed of several groups of roller press. Wet paper sheets are dehydrated by mechanical extrusion between the rollers, dragged by a press blanket support. In order to maintain the good dehydration performance of the press blanket, the press upper roller is equipped with a blanket washing device. After pressing, the dryness of wet paper sheet can generally reach about 40%.
Wet paper sheets are further dehydrated on paper machines, usually by heating, evaporation and drying. The drying section of a paper machine is usually composed of many drying cylinders heated internally by steam. Dry blankets (or canvas, dry nets) are coated on the drying cylinder. The purpose is to press the sheet onto the surface of the cylinder to improve the heat transfer efficiency and the surface quality of the sheet.
After drying, a calender consisting of 6-8 rolls is usually used to improve the surface quality of paper sheet.