Structural Flakeboards and Composites 



2955 



Fuei supply t 



Gear-drive r,„ 



' KKV-combustion chamber 

 ) Comt)«stior> air fan 

 Arduct 



Balancing dampers 

 Primary air 

 Setondaryair 

 Air inlet nozzles 

 Konus-Heater 

 Hearing stirface 

 Thermal oil supply 

 i Therrnaic 

 *■ Sight giass 



' Clear. ....^. ^ 



Flue gas breeching 

 i» Balancing dampers 

 ' Dust separate 

 '''• lndiK,ad draft fan 

 « Flue gas Ii 



Figure 24-25. — This system to heat thermal oil for a multiple-opening hot press can be 

 specified to burn either dry or wet bark and wood comminuted to particle size smaller 

 than a 1-inch cube. (Drawing from Konus-Systems, Inc.) 



Structural flakeboard is used primarily for floor decking and sheathing. For 

 use as roof sheathing the panels may be pressed with a screen caul on one side to 

 afford more secure footing to workmen. 



The curing time of phenol-formaldehyde resins used in flakeboard fabrication 

 decreases rapidly with increasing temperature; rapid temperature transfer to the 

 center of the panel is therefore the key to short press time. With low moisture 

 content in the mat, heat transfer occurs primarily by conduction, and short press 

 time requires high platen temperature. Although heat conductivity of wood 

 increases with increased moisture content, evaporation of water throughout 

 moist mats retards temperature transfer, and longer press times are required to 

 reduce moisture enough for adequate internal bond strength development. Mat 

 moisture contents of 9 to 11 percent are probably optimum. 



The density profile of a hot-pressed flakeboard varies according to distribu- 

 tion of moisture in the mat. Boards pressed from mats of uniform moisture 

 content show lower density near the surface, an increase to maximum density 

 within 3/32-inch of the surface, and a decline to lowest density at mid-thickness 

 (fig. 24-28). If moisture content in the core of the mat is decreased to 5 percent 

 moisture content and in face layers is increased to 15 percent, the contrast 

 between density of face and core layers will be increased. 



