(For beginner) Plywood knowledge& Manufacturing Experience Part 48: Final plywood thickness and the hot pressing Compression ratio
Final plywood thickness in Various Hot-Pressing Cycles ,The present 5-8 per cent compression of plywood veneers during hot pressing could result in considerable say-ings, as veneers thinner than now customary could be used.
Possibility that compression in hot pressing could be reduced byadjusting the pressure had been indicated by research.
Several major factors involved in com-pression of veneer during hot pressing were studied, including tempera-ture (100, 120, 140, 150), pressure (100, 140, 180, ZZO,and 260 psi) and time (5 and 65 minutes).
The core veneer’s properties such as surface roughness can be improved, and the properties of plywood were also improved when the core veneers were pre-pressed. Linear relationship between the compression ratio and surface roughness was found. The tensile strength of veneer was not significantly influenced by the pre-pressing factors. The pre-pressing temperature has the largest effect on shear strength of plywood.
Via many Testing results revealed that the greatest influence on properties of core veneer is the pre-pressing temperature followed by the pre-pressing pressure and pre-pressing time.
The final thickness are also influnced by th epressing pressure and time .
Determine effect of 6 different pressure cycles on compression during hot pressing. Determine differences in compression due to 3 different glues. Determine recovery from compression resulting from rehumidification of plywood after pressing. Determine quality of glue bonds by various test methods. Determine possible differences between gluing hard- arid soft-grained veneer when hot-pressed with 1 type of interior glue.
From research on compression of veneers showed thickness should be measured at all four corners to average out differences caused by localized variations present in the veneers. Initial thickness. Shortly before hot pressing, groups of 10 as-semblies were removed from storage. Initial thickness of each 11-ply panel was determined by the following procedure: The empty press was closed, but without pressure. . The press was closed, and without applied pressure, all 4 dial gauges were read.