Paper Machine Press Section
A constant function of the forming section, the press section and the drying section of the machine is dehydration. The amount of interstitial space in the paper sheet decreases as the water in the sheet is extruded during the press process and some degree of fiber compression occurs where the fiber is in contact with the fiber and the applied pressure helps to distribute the moisture throughout the paper sheet.
Paper machine press section dewatering
The main factor to promote dehydration is through the sheet of water pressure difference, pressure nausea residence time and pressure uniformity, the nodular pressure and residence time product called press impulse; The main resistance is the flow resistance of the paper itself. Water temperature increased by 1 degree flow performance increased by 2.5%, during the press process will increase the temperature of paper from 20 degrees to 30 degrees, then out of the dryness of the press sheet increased by 2 to 3%.
Pressing dehydration divides into pressure control and flow control type two categories. Pressure control type is mainly in the low quantitative and high freeness of the paper, because the paper is very thin, paper structure does not significantly restrict the flow of water, dehydration mainly by the nip pressure of the fiber network layer mechanical compression and nip After the midpoint from the blanket to the wet sheet to determine the possibility of rewetting.
Flow control type is mainly in high-quantitative paper, this paper is quite thick, paper structure restricts the water from the paper outflow. Papers density, temperature and felt porosity have a significant impact on water resistance, this time in the nausea residence time has become a constraint. Respectively pressure-controlled dehydration and flow-controlled dehydration indicate the direction of efforts to improve the efficiency of the press.
There is also a critical point in pressing and dewatering, where it is uneconomical to compress or dewater beyond the critical point, or to over-compress the sheet, leaving the moisture in the sheet to be removed by evaporation. According to the type of slurry, squeezing the form and operating conditions are different from the critical point of 50 to 57%.
