Structural Flakeboards and Composites 



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2991 



30 40 50 60 70 

 RELATIVE HUMIDITY (•/•) 



T 



80 90 SOAK 



30 40 50 60 70 

 RELATIVE HUMIDITY (•/•) 



80 90 SOAK 



Figure 24-42. — (Top) Relationship between relative humidity and thickness swell in 1/2- 

 inch-thick, phenolic-bonded, three-layer flakeboard made of randomly placed, 3- 

 inch-long, shaping-lathe flakes of mixed southern woods fabricated as described in 

 discussion related to figure 24-38, when pressed to a density of 44-48 pounds/cu ft, 

 based on ovendry volume and weight; the lower curve depicts data as RH is increased 

 from ovendry to 30, 50, 75, and 95 percent; the upper curves depict return to ovendry 

 and ovendry to soak. (Bottom) Linear expansion in such flakeboard from 50 percent 

 RH to ovendry, then during two cycles of ovendry-water soak-ovendry. (Drawings 

 from Study File FS-SO-3201-15, U.S. Department of Agriculture, Forest Service, 

 Southern Forest Experiment Station, Pineville, La.) 



linear expansion was attributed to partial restraint offered by the framing to 

 which the decking was nailed. 



Section 24-2 noted that unrestrained linear expansion of CDX plywood be- 

 tween 30- and 90-percent relative humidity is about 0. 10 percent along the major 

 axis and 0.14 percent across the major axis. For 2-MW waferboard and 2-MF 

 flakeboard, the National Particleboard Association (1980) specifies that linear 

 expansion between 50- and 90-percent relative humidity shall be less than 0.20 



