Fiberboards 



SEPARATOR ASSEMBLY 



2841 



AIR ENTERING THROUGH 

 A WFFUSER 



FEEDER SECTION FORMER SECTION 



Figure 23-70.— Rando-Wood former. (Drawing after Wood 1976.) 



air without condensing them. They are then fluffed by a pair of spike rolls and 

 deposited on a moving-floor apron, where a stripping roll equalizes the flow 

 before they enter the forming section of the machine. Here air is removed 

 through perforations of the lower condenser and the fibers are deposited and 

 packed into the wedge-shaped entry to the gap between the upper and lower 

 condensers, simultaneously forming the entire cross section of the mat, with 

 finer furnish fractions concentrated on both surfaces. 



Another vacuum former is offered by the Swedish company Motala-Defibra- 

 tor under the name "Pendistor" (fig. 23-71), with air impulses replacing the 

 slower swing spout. It is said to produce superior uniformity in mats up to 9 feet 

 wide. The thick mats (9 to 24 inches) are precompressed by continuous band 

 presses (fig. 23-71 bottom) to a thickness of 3 to 6 inches. Mat trim waste and 

 entire mats rejected because of excessive weight variation are returned to the 

 forming station for reuse. Acceptable mats are transferred to the press loader 

 either with or without cauls. 



Pressing. — In the manufacture of thin boards, press cycles are largely de- 

 signed to achieve desired total densification of the mat and efficient water and 

 gas release; development of any particular density profile is secondary. For thick 

 medium-density fiberboards and particleboards, however, density profile can be 

 of primary importance; and press cycles are designed to manipulate this profile. 

 In figure 23-72 two boards of equal average density differ in its distribution. 

 Board A with high face density would have high modulus of elasticity and 

 strength in bending, but low internal bond strength (tensile strength perpendicu- 

 lar to the board surface). Board B would have greater internal bond strength but 



