2782 Chapter 23 



wet process and section 23-9 the dry process. Subsequent steps of board humidi- 

 fication and fabrication after pressing are similar for boards made by both 

 processes. 



Until mats emerge from wet forming and pressing the technology of manufac- 

 ture is almost identical in all wet lines. From that point on, however, processing 

 of the wet mat is distinctively different for each of the three principal wet-formed 

 products. The distinguishing feature in the insulation board line is the dryer and 

 lack of a hot press, in the SIS hardboard line the hot press and lack of a dryer, 

 and in the S2S line the dryer and hot press combination (fig. 23-28). 



HOTPRESS 



SIS HARDBOARD 



WET PRESS -4 — »— DRYER 



INSULATIONBOARD 



DRYER 



HOTPRESS 



S2S HARDBOARD 



Figure 23-28. — Schematic description of processing wet fiberboard mats into the three 

 principle wet-formed fiberboard products. (Drawing from Suchsland and Woodson 

 1985.) 



CONSISTENCY AND WATER CONSUMPTION 



Throughout initial stages of the wet process fibers are suspended in water, 

 most of which is removed at the forming machine. The furnish consistency 

 varies in these stages (fig. 23-25), and therefore water consumed or recirculated 

 varies proportionately. Water quantities pumped can be very large; e.g., a 

 reduction of consistency from 2 to 1 percent doubles the amount of water in the 

 pulp stock. 



Figure 23-29 schematically illustrates an SIS fiberboard process indicating 

 both furnish consistency and actual quantities of water and fiber based on daily 

 board production of 100 tons. The center part of the diagram shows the consis- 

 tency variation in percent. The incoming raw material has an assumed moisture 

 content of 100 percent (based on dry weight), which corresponds to a consisten- 

 cy of 50 percent. To produce 100 tons of board in 24 hours requires a constant 

 rate of dry fiber flow from one end of the process to the other of 0.069 ton/ 

 minute. 



At 100 percent moisture content (50 percent consistency) the raw material 

 introduces into the process 18 gallons of water per minute. As water is being 

 added and removed, the consistency of the furnish changes. The absolute quant- 

 ity of dry wood fiber passing through each step of the operation, however, 

 remains constant at 0.069 ton/minute. 



To reduce consistency from 50 to 12 percent requires addition of only 116 

 gallons/minute. To further reduce the consistency from 12 to 1 percent, how- 



