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Chapter 23 



CHIP 

 FEED 



Figure 23-21. — Section through pressurized doubie-disk refiner showing stock flow. 

 (Drawing courtesy The Bauer Bros. Co.) 



charge) from 5 to 20 percent caused a slight increase in freeness, but as consis- 

 tency was increased above 30 percent resulting pulp became slower (less free). 

 Worn plates produce a much freer pulp at low consistencies, but at higher 

 consistencies produce slower pulps than new plates. Thus pulp consistency can 

 be varied to compensate for the effect of plate wear on pulp freeness (Mihelich et 

 al. 1972). 



In most wet process atmospheric refiners water is added to the chip feed to 

 reduce consistency to about 12 to 14 percent dry wood content. More water is 

 added to the refined fibers after they leave the refiner disks in order to make the 

 furnish pumpable (1- to 2-percent consistency). 



High consistency refining refers to refining without addition of water. Vacu- 

 um is applied to remove the furnish from the refiner case. The resulting pulp is 

 finer and freer. This allows higher machine speeds, and, since the mat is fluffier, 



