Processes 2021 , 9 , 274
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composed of a pulper, a refiner, and a chest. The pulper is the first equipment used in the pulping and papermaking stage. The paperboard is first mixed with water and then disintegrated by the pulper to obtain the pulp with a certain concentration. The obtained pulp is stored in the chest (there are usually multiple chests). However, the quality of the pulp disintegrated by the pulper cannot meet the requirements of papermaking. Therefore, it is necessary to further improve the quality of the pulp using the refiner. The pulp obtained by the refiner will be stored in other chests. The pulper and the refiner operate intermittently, which mainly depends on the liquid level of the chest. Afterwards, the pulp is sent to the forming sector through the approach flow system. The forming sector removes part of the water, and finally, the paper is formed. Next, the paper is further dehydrated by the press section. The dryness of the paper from the press section falls far short of the requirements. Paper is dried in the dryer section to make the dryness of the paper meet the requirements. The last step of the pulping and papermaking stage is the winding section. The paper is reeled by the reel cylinder, thus forming the parent roll. The parent roll will be further processed in the conversion stage.
Figure1. Production process of tissue paper mills.
In the conversion stage, a certain number of parent rolls are simultaneously rolled into reels using the winder, and the number of the parent rolls depends on the numbers of paper layers in the finished product. The reel paper is cut into small reels with a cutter. Finally, the small reels are packaged into the finished product by the packaging machine. Discrete production mainly occurs in the pulping process and the processing between the pulping and papermaking stage and the conversion stage. The processing is continuous in the papermaking or conversion stage. The interval time between two stages is uncertain. Different from other flow shops, only when enough parent rolls are produced in the papermaking stage can the conversion stage be started, rather than after finishing a roll of parent roll in the papermaking stage. The interval time between two stages is related to the product characteristics and the machine speed. Too long of an interval time
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