Effects of Veneer Preheating Temperature, Press and Assembly Time on Aspen LVL

Use of preheated veneers to reduce press time in the bonding of six-ply, 32-mm-thick aspen laminated veneer lumber (LVL) with phenol-formaldehyde adhesive is discussed. Preheating temperatures ranging from 80? to 120?C prior to glue application and pressing periods of 6 to 12 minutes per panel are examined and bond quality compared with panels made from nonheated veneers. Both conditions showed similar shear strength development with increasing glueline temperature while wood failure values for nonheated veneer panels were markedly lower than preheated veneer panels at glueline temperatures less than 110?C. Thus, wood failure gave a better indication of glue cure than did shear strength. Veneer preheating temperatures of 100? to 110?C appeared optimum for providing the greatest press time reductions–about 50 percent of nonheated condition–while still being sufficiently low to prevent dry-out with 30-minute assembly time. A useful relationship was developed between the product of veneer temperature times press time and wood failure or shear strength which could be used to predict the pressing time necessary to attain good bond quality.

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