3030 Chapter 24 



PHENOLIC-BONDED COMPOSITE PANELS WITH SOUTHERN PINE 

 VENEER FACES AND CORES OF SOUTHERN HARDWOOD FLAKES^^ 



Hse (1976) fabricated 72 1/2-inch-thick composite panels measuring 19 by 20 

 inches according to the following experimental design (fig. 24-50): 



Number of face veneers (rotary-peeled southern pine) 



Single veneer on each face 



Two veneers, cross-laminated on each face 

 Veneer thickness 



1/10-inch 



1/16-inch 



1/24-inch 

 Arrangement of hardwood core flakes (50 percent southern red oak, 25 percent hickory, 25 



percent sweetgum) 



Homogeneous, random orientation 



Homogeneous, oriented in direction perpendicular to the grain of veneer in immediate 

 contact 



Three-layer, cross oriented 

 Replications of panels: 4 



Thus the panels were variously constructed with two or four veneers and one 

 core layer (which might be random or oriented), or three oriented core layers 

 (fig. 24-50). Face veneers were rotary-peeled from heated loblolly pine bolts, 

 clear of defects, and dried to an average moisture content of 4 percent. Core 

 flakes, which were also rotary peeled veneer, were 0.015 inch thick, 3 inches 

 long, and 3/8-inch wide; they were dried to the moisture content of 3 percent. 



Resin application and panel preparation. — Liquid phenolic resin was 

 sprayed on veneers to achieve 5 lb of resin solids per 1 ,000 sq ft of single 

 glueline. Core flakes were weighed to yield a core density of about 43.7 Ib/cu ft 

 (basis of ovendry weight and volume at 5 percent moisture content) and liquid 

 phenolic resin was spray-applied to achieve resin solids content equal to 3- 

 percent ovendry weight of the flakes. The flakes, after blending, were felted 

 onto a face veneer in a forming box. All cores were prepared as a mixture of 50 

 percent southern red oak, 25 percent hickory, and 25 percent sweetgum. The 

 core mat with face veneer on both sides was hot pressed at 335°F at sufficient 

 pressure (about 400 psi) to close to stops in approximately 45 seconds. Closed 

 press time was 5 minutes. All boards were then conditioned at 50 percent RH 

 and 80°F, yielding average panel moisture content of about 4.8 percent. 



Test procedure. — To evaluate dimensional stability, 3- by 9-inch specimens 

 were given a VPS treatment, i.e., they were soaked in water under vacuum (30 

 inches of Hg) for 30 minutes and then under 65 psi pressure (at room tempera- 

 ture) for 24 hours. Other specimens of the same size were soaked in boiling 

 water for 5 hours. 



Standard mechanical tests were performed and MOR and MOE computed on 

 the assumption that the cross section of the composite panel was homogeneous. 



This subsection is condensed from Hse (1976). 



