Fiberboards 



2817 



PRESS TIME 



Figure 23-52. — Pressing to stops. Press time and mat thickness related to platen pres- 

 sure on the board. (Drawing from Suchsland and Woodson 1985.) 



23-9 DRY-PROCESS FIBERBOARD MANUFACTURING 



OVERVIEW 



Dry-process boards (see fig. 23-1 for classification) are defined as those 

 formed by using air as a distributing medium, regardless of the moisture content 

 of the furnish. Any board process using a fiber furnish and air forming is thus a 

 dry fiberboard process. The semi-dry process differs from all other dry proc- 

 esses in that its mat moisture content is too high to allow the pressing of S2S 

 board. The high moisture content may be due to using green or cooked chips 

 without drying after refining (some drying always occurs as a result of the 

 temperature increase of the furnish during the pulping process), or it may be due 

 to addition of water to the board surface prior to pressing for improving surface 

 quality. In either case, screens are required and the boards have the same 

 screenback characteristics as wet-formed SIS boards. The process is "dry" 

 however, by our definition, because air is used for transporting the fibers and for 

 forming the mat. The first dry-process board plant in the United States was a 

 semi-dry plant (Anacortes, Wash.). It is today the only semi-dry plant in oper- 

 ation in the United States. 



