Fiberboards 



2767 



/EXHAUST 

 ^X CYCLONE 



463 FEEDER ~~ 



451 ROTARY 

 VALVE 



STEAM 

 HEADER 



Figure 23-20. — Bauer 418 pressurized refining system. (Drawing courtesy of The Bauer 

 Bros. Co.] 



for the 36-inch unit and 400 tons per day for the 42-inch unit. Pulps are similar to 

 defibrator pulps, and are suitable for both wet- and dry-formed hardboard and 

 for medium-density fiberboard. 



The Bauer 418 pressurized refiner (figs. 23-20 and 23-21) was an important 

 element in the development of dry-formed medium-density fiberboard during 

 the 1960's. It is a double-disk mill (both disks revolve, counter-rotating), and 

 produces a fluffy, bulky pulp which requires considerable compression — a pre- 

 requisite for the favorable gluing conditions — when densified to medium board 

 densities. Such fiber is too fluffy to make good wet-formed fiberboard. 



All three of the machines just described are currently being used to manufac- 

 ture pulp for dry-process board of medium and high density. In such pulps 

 freeness can be disregarded, but low fines content, controlled particle-size 

 distribution, and low bulk density (below 2 pounds per cubic foot) are of primary 

 importance. 



Pulp consistency, plate design, and refiner selection. — Pulp consistency, 

 the percent dry weight of fibers in the pulp slurry of fiber and water, interacts 

 with degree of refiner-plate wear to affect pulp freeness. Mihelich et al. (1972) 

 found that with new plates, increasing consistency (measured at refiner dis- 



