Fiberboards 



2799 



FLOOR 

 LINE 



FAN 

 MOTORS 



CHAIN ^ j ff 



TIGHTENER D / D 



1 



■ZONE I — - — ^ZONE 2 



IWET SAW I JIPPL^I FEED _ 



Htable I Hois"rl section" 



-ENCLOSED DRYER 



CIRCULATING 

 ^ FANS 

 n / DRYER 



]fi / DRIVE 



— ZONE 3 



_ENCLOSED 

 DRYER 



H 



|cooling|_unloader.i dry ^ 

 Isection'^ I^table" 



Figure 23-39. — Gas-fired fiberboard dryer. (Drawing after Lyall 1969.) 



leaving the last zone the board passes through a cooling section. Dryer entrance 

 and exit are protected from leakage by seal sections in which unheated air is 

 circulated and a negative air pressure maintained equal to the slightly negative 

 dryer pressure. 



Heating and circulation. — The drying medium, air at temperatures above 

 the boiling point of water, can be heated by gas, oil, or steam, but is typically gas 

 heated. Gas- and oil-heated dryers operate at higher air temperatures, and cost 

 less to install, than steam-heated dryers. Maintenance costs and fire hazard for 

 dryers direct-fired with gas and oil may be higher than for steam dryers, howev- 

 er. Typically, gas burners capable of delivering 26 million Btu/hour are installed 

 in each zone, requiring about 4,000 cu ft of combustion air per minute. Heated 

 air and spent combustion gases are circulated in each zone by two fans located 

 above the dryer, driven on a common shaft by a 125-hp motor capable of 

 circulating about 165,000 cu ft of air per minute (Lyall 1969). 



Feeding and transporting. — The drying mats are transported by closely 

 spaced chain driven-rollers on eight separate decks. The speed of the rollers is 

 adjustable and is matched to the line speed so that there are no unnecessary gaps 

 between boards. Standard roller diameter is 3 inches with a roller spacing of 4 

 inches at the wet end and up to 2 feet at the dry end. A 250-foot, eight-deck dryer 

 contains approximately 8,100 rolls and 16,200 bearings. In order to keep all 

 eight decks completely loaded with a continuous supply of cut-to-length mats, a 



