Mechanics of paper pressing

纸机由三个主要部分组成：成型部分、压紧部分和干燥部分。离开成型段的湿垫纸的稠度在15%左右（稠度是纸的干重与湿重之比），在压榨段的稠度提高到50%左右。在高压下，将由纸张和干燥的压毡（一种柔性多孔介质）组成的三明治组合在一起，从而实现压榨段脱水。在施加压力的作用下，水被从纸中挤出并被困在压毡中。压纸是重要的，因为水提取在压榨部分是数量级比在干燥部分更有效。通过机械压榨湿纸提取的每公斤水在干燥机部分节省约2兆焦耳的能量。压印也会影响成品纸的机械性能，因为压印增加了纸张密度，增加了纤维间的结合强度。在本研究中，我们将研究压纸的两个不同方面——压毡磨损和再润湿。压毡磨合期是指在安装新压毡后的几天内，毡的吸水特性逐渐增加，接近其稳定状态。再润湿是指当施加的压力减小时，从纸上挤到毛毡上的水可能会重新回到纸上。我们的研究将包括压纸的实验研究和压纸机理模型的发展。

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.