2698 Chapter 22 



rybark oak, and water oak, when dry, have modulus of elasticity greater than 2 

 million psi; black tupelo and hackberry average only about 1.2 million psi. 



Techniques for applying glue to laminae with roll spreaders are simple and 

 well developed. For structural laminated beams, glue is usually spread on both 

 mating surfaces because of the long assembly periods required for layup. Appli- 

 cation of glue to both mating surfaces permits longer assembly times — both 

 open and closed, but particularly closed — than application of glue to only one 

 surface. 



As an alternative to the roll-spreading technique, Hann et al. (1971) reported 

 that a phenol-resorcinol glue of high viscosity could be advantageously extruded 

 in a ribbon pattern on oak laminae. Advantages for the ribbon spread — which is 

 accomplished by pumping glue through orifices as the lumber passes below — 

 include cleanliness of operation, accurate control of spread rate, little waste of 

 glue, and little solvent evaporation; by this system glue is spread only on one 

 surface. 



Following glue appliction and beam layup, pressure is uniformly applied for a 

 time which varies with both press temperature and glue. Most heavy laminated 

 beams and arches are pressed several hours (or overnight) in massive clamps 

 temporarily arranged to manufacture only a few of each structure. For 1- and 2- 

 inch oak lumber, experience indicates that a specific pressure of about 150 to 

 250 psi is required (Freas and Selbo 1954). 



Descriptions of presses utilizing the stored-heat principle to laminate small 

 beams and decking have been provided by Marra (1956), Malarkey (1963), 

 Hann et al. (1971), FPL Press-Lam Research Team (1972), and Jokerst (1972). 



Mann (1954), Syme (1960), and Anonymous (1962) reviewed fast-cycling 

 batch equipment designed to edge-glue and laminate with radio frequency heat- 

 ing, and Carruthers (1965) described a continuous laminating machine for 

 beams that uses radio frequency energy to cure the gluelines. Miller and Cole 

 (1957), Clark (1959), Carruthers (1963), and Miller and George (1965) have 

 reviewed gluing problems associated with the use of radio frequency energy to 

 cure gluelines. 



The following paragraphs present data that are specific to lamination of oak — 

 the species group of major importance among the hardwoods that grow on 

 southern pine sites, and briefly discuss strength of beams laminated from mill- 

 run oak and the possibilities of manufacturing two-ply lumber for furniture 

 dimension stock and for highway sound barriers. 



Flat-grain white oak versus vertical-grain for lamination. — Selbo (1960) 

 fabricated laminated white oak beams consisting of 13 laminations of Va- by 9- 

 y4-inch boards bonded with phenol-formaldehyde adhesive. Some beams had all 

 vertical-grain boards; in others, vertical-grain and flat grain were alternated. 

 Both were subjected to 4 to 5 years of salt-water soaking and weathering 

 exposure. Selbo concluded that adequate and durable glue bonds can be obtained 

 in both types of construction, but vertical-grain oak laminations have a tendency 

 to develop-cleavage parallel to the glue lines when subjected to severe expo- 

 sures, and therefore may be less desirable than flat-grain oak for use in exterior 

 service. 



