2906 Chapter 24 



24-1 DEFINITIONS OF STRUCTURAL FLAKEBOARDS^ 



Vajda (1978a) observed that structural-grade particleboards are called by 

 some sources particleboards, by others flakeboards, and by still others wafer- 

 board, or strandboard. All of these terms refer mainly to the types of particles 

 used to manufacture the panel product. His definitions of essential terms 

 follows: 



• Particles, the generic term for any kind of wood particles, may be of 

 random size or of specified length, width, and thickness; they may be 

 cut parallel to the grain or across the grain. Some sources include 

 mechanically pulped wood fibers within this generic term. 



• Flakes are particles cut parallel to the grain in the 0-90 mode (figs. 18- 

 1, 18-98 top, 18-104ABCD, and 18-264 through 18-269). 



• Wafers are large, square flakes, used in waferboard. (See wafers in 

 upper and lower left comers of fig. 18-274 A.) 



• Strands are flakes whose length is at least three or four times greater 

 than their width; this slendemess ratio promotes alignment in oriented- 

 strand boards. (See figs. 18-264 and 18-274B.) 



• Semi-flakes or chip flakes are cut from conventional pulp chips or 

 longer and narrower maxi-chips or fingerlings by a ring-type flaker 

 (figs. 18-270 and 18-271); resulting flakes have some cross grain. (See 

 ring-flaked wood in figures 18-274ABC.) 



• Random particles are produced on a hammermill or hog-type machine 

 (fig. 18-276 through 18-279) from shavings, sawdust, or other mill 

 residue. 



Vajda (1974) also noted that particleboards of various sorts have been manu- 

 factured in quantity in North America since 1940 and that some of the products 

 have been used in load-bearing applications; some examples follow: 



• Particleboard in mobile home decking (i.e., floor systems) 



• Hardboard in exterior siding 



• Particleboard in vertical siding and exterior sheathing 



• Hardboard (1/8- to 1/4-inch thick) in stressed-skin applications 



• Particleboard and hardboard in self-supporting, but non-critical, load- 

 bearing applications in furniture and as shelving. 



Until the advent of structural flakeboard however, none of these products 

 was accepted in building construction for general structural applications. This 

 lack of acceptance was due partly to insufficient strength retention on exposure 

 to weather or to fluctuations in temperature and humidity (in the case of particle- 

 board), and partly because of excessive weight and density (in the case of 

 hardboard). Additionally, ample supplies of lumber and plywood available at 

 reasonable prices satisfied the needs of the building industry. 



'See sections 24-19 and 24-20 (figures 24-50 through 24-54) for illustrations of composite panels. 



