How are the plywood made?
Plywood usually refers to three plywood or multilayer board, that is, with the same thickness of two or more layers of wood veneer and glue high temperature suppression. Usually, the odd layer single plate is used, and the fiber direction of the adjacent layer single plate is perpendicular to each other.
Principle of odd number layer: because the structure of plywood is adjacent layer, the fiber direction of single board is perpendicular to each other, and must accord with symmetry principle, so its total layer number must be odd number. Such as: three laminates, five laminates, seven laminates and so on. When the odd ply plywood is bent, the maximum horizontal shear stress acts on the central veneer to make it have greater strength. Even when the plywood is bent, the maximum horizontal shear stress acts on the adhesive layer, not on the veneer. It can destroy the adhesive layer and reduce the strength of plywood.
Symmetry principle: single plate symmetrically on both sides of the central plane, regardless of species veneer thickness, layer, manufacturing method, water fiber direction and single board rate should correspond with each other, namely the principle of symmetry on both sides of the plywood central plane corresponding layers of equivalent stress in different directions. Therefore, when the change of veneer moisture content, its stable structure, no deformation, cracking and other defects; on the contrary, if the central symmetry plane on both sides of the corresponding layer has some differences, will make the central symmetry both sides of the plane board is not equal to the stress, deformation and cracking of plywood.
