Strand Movement During Oriented Strand Composite Mat Formation

Abstract

The properties of strand-based wood composites are known to be strongly influenced by strand orientation and horizontal density variation. While the influence of these geometrical factors on performance has been extensively investigated for more than 20 years, little research has been reported on how the strands move during the forming process to become oriented and located. Better knowledge of strand movement will allow for understanding of and improvement in mat formation through rational modification of equipment settings and ultimately design concepts. An industrial forming line was used to quantify the effect of strand length on strand movement from the bunker through the picker rolls, dissolving rolls, and orienting heads. Initial locations of dyed strands in the forming bin bunker were predetermined. After processing through the forming head, the location and orientation of individual strands were optically measured before and after the orienting deck. Nine-inch strands were found to have a more variable flow rate through the picker rolls relative to 4-inch strands. Substantial strand mixing and horizontal travel across the width of the forming head occurs prior to the orientation deck. This indicates that modifications in the strand chute will influence the cross-direction movement uniformity and final product density variation more than orienting deck modifications. As expected, longer strands were shown to project significantly farther along the orienting deck as well as to provide better alignment. A particle screen analysis showed that the doffing and dissolving rolls generated 70 percent of the unders (smallest screen fraction) in the forming process.