2754 



Chapter 23 



MILLYARD 



WOODROOM 



MASONITE 

 GUN 



PRESSURIZED 



DISK 



REFINER 



ATMOSPHERIC 



DISK 



REFINER 



INSULA! I ONBOARD | 



» |sis hardboardI 



Figure 23-8. — Schematic summary of pulping, forming, and drying processes yielding 

 the five major fiberboard products. (Drawing from Suchsland and Woodson 1985.) 



Figure 23-8 summarizes the range of fiberboard processes and products. A 

 plant could produce any or all of the products shown; most, however, produce 

 only one or two because each product requires specific pulp characteristics, 

 generally different from requirements for other fiberboard products. Pulp free- 

 ness is one of the most important pulp characteristics. 



PULP FREENESS 



In wet fiberboard processes water must be removed after its service as a 

 conveying and distributing medium in sheet formation. Much of this water 

 drains by gravity through the fourdrinier screen while the mat is being formed; 

 what remains must be converted to steam in subsequent drying or hot pressing. A 

 pulp that drains quickly is a free pulp or a fast pulp; one that drains water slowly 

 is less free or a slow pulp. Fast pulps allow faster line speeds and therefore 

 greater plant productivity. Slow pulps provide more intimate fiber-to-fiber con- 

 tact and stronger bonds. Two types of freeness testers are in wide use in North 

 America: 



