Fiberboards 



2795 



SUCTION BOXES 



FOURDRINIER WIRE 



^TOP WIRE 



COUCH I _L 

 ROLL- ^' 



\- FOURDRINIER WIRE 



Figure 23-36. — Wet-press sections of Fourdrinier machines. (Top) Insulation board ma- 

 chine. All rolls are 30 inches in diameter; rolls 1 , 2, 3, and 4 are suction rolls; rolls 5, 6, 

 and 7 are perforated shell rolls; roll 8 is rubber covered with no perforations. (Bottom) 

 Hardboard machine. Rolls 1, 2, 3, and 6 are 24 inches in diameter, rubber covered, 

 and not perforated; rolls 4 and 5 are also 24 inches in diameter, but are perforated. 

 (Drawings from Suchsland and Woodson 1985.) 



Figure 23-36 diagrams wet-press sections of insulation board and hardboard 

 machines. The numbered rolls are the press rolls, the main elements in such wet 

 presses. Between each pair of press rolls starting from the infeed end, the gap 

 between the Fourdrinier wire and the top wire is reduced by forcing the top rolls 

 down against adjustable stops by means of hydraulic cylinders. This reduces the 

 air volume in the mat until the mat is saturated with water at a density of 62.5 

 pounds/cu ft. At this point hydraulic pressure inside of the mat builds and forces 

 water to flow from the mat. The water flow can be approximated by the follow- 

 ing equation: 



Press loading x temperature 



Water removal = 



xK 



(23-1) 

 Feed rate x weight per 1 ,000 sq ft of dry sheet 



K is a constant reflecting permeability of the pulp. Total press loading (nip 

 pressure) is the sum of internal hydraulic pressure and resistive pressure of the 

 mat (fig. 23-37 top). According to equation 23-1 , water flow could be increased 



