Mechanics of paper pressing

造纸机由三个主要部件组成：成形部、压榨部和干燥部。离开成形部的湿纸垫具有约15%的稠度（稠度是纸的干重与湿重的比率），并且在压榨部中稠度增加到约50%。压榨部脱水通过在高压下将由纸和干压榨毡组成的夹层结合在一起而发生，所述干压榨毡是柔性多孔介质。在所施加的压力的作用下，水从纸中挤出并被困在压榨毡中。纸张压榨是重要的，因为压榨部的脱水效率比干燥部高几个数量级。通过湿纸的机械压榨提取的每公斤水在干燥部节省约2兆焦耳的能量。压榨也会影响成品纸的机械性能，因为压榨会增加纸张密度并增加纤维间的粘合强度。在本研究中，我们将研究两个不同方面的纸张压榨-压榨毛毯磨合和回湿。压榨毛毯磨合是指新压榨毛毯安装后的几天时间，在此期间毛毯的吸水特性缓慢增加，接近其稳定状态。回湿是指当所施加的压力减小时，已经从纸挤压到毛毡中的水可能返回到纸中的可能性。我们的研究将包括压榨的实验研究和造纸压榨机械模型的开发。

Papermachines are comprised of three major components: the forming section, the press section, and the dryer section. The wet mat of paper leaving the forming section has a consistency of around 15% (consistency is the ratio of dry weight to wet weight of the paper), and in the press section the consistency is increased to about 50%. The press section dewatering occur by bringing together at high pressure a sandwich comprised of the paper and a dry press felt, which is a flexible porous medium. Under the action of the applied pressure water is squeezed from the paper and becomes trapped in the press felt. Paper pressing is important because water extraction in the press section is orders of magnitude more efficient than in the dryer section. Each kilogram of water extracted through mechanical pressing of wet paper saves about 2 megajoules of energy in the dryer section. Pressing can also affect the mechanical properties of the finished paper, as pressing increases the sheet density and increases the inter-fiber bond strength.****In this research we will study two different aspects of paper pressing -- press felt break-in and rewetting. Press felt break-in is the period of a few days after the installation of a new press felt during which the water absorption characteristics of the felt slowly increase to approach their steady state. Rewetting refers to the possibility that water that has been squeezed from the paper into the felt may return to the paper as the applied pressure is reduced. Our research will include both experimental studies of pressing and the development of a mechanistic model of paper pressing.********