Abstract
The authors review briefly the history of the cold pressing of plywood with various adhesives, and discuss the development and adoption of hot pressing with thermosetting synthetic-resin adhesives which are more water resistant than the adhesives developed for cold pressing. The various types of domestic and foreign hot presses and their characteristic features are described. It is shown that several factors in the behavior of wood under heat are common to all known types of resin adhesives; these are the speed of heat penetration through various thicknesses of veneer and the heat losses encountered in practicable bonding periods of time, both differentiated as to core thicknesses, moisture content, and temperature. Specific pressure and wood species are found to have little if any influence on these factors. Another factor is the effect of heat on the tensile strength of wood, which is shown to be relatively unchanged in practicable bonding periods. These phenomena are shown by tables and graphs and are fully described. Other factors individual to the adhesive used, and the characteristics of a resin film, are outlined in tables and are described. The authors predict that the rapidly growing adoption of hot pressing and resin adhesives is widening the plywood market.
