Plywood usually refers to plywood or plywood, which is formed by pressing two or more layers of veneer with the same thickness and glue at high temperature. Usually, odd-numbered boards are used and the fibers of adjacent boards are glued perpendicular to each other.
Principle of symmetry: The veneers on both sides of the symmetrical central plane, regardless of the thickness of the veneer, the number of layers, the manufacturing method, the fiber direction, and the moisture content of the veneer, should correspond to each other, that is, the principle of symmetry. The plywood center plane on both sides of the corresponding layer in different directions The stress is equal in size. Therefore, when the moisture content of the plywood changes, its structure is not chaotic, and there will be no defects such as deformation or cracking; otherwise, if the corresponding layers on both sides of the symmetrical central plane have some differences, the stress of the veneers on both sides of the symmetrical central plane will be made. Not equal, so that plywood deformation, cracking.
The principle of odd-numbered layers: Because the structure of plywood is that the fiber direction of the veneers of adjacent layers hangs each other, and must conform to the principle of symmetry, its total number of layers must be odd. Such as: three layers, five layers, seven layers and so on.
The maximum horizontal shear stress of the odd-numbered plywood is applied to the central slat to give it greater strength. The maximum horizontal shear stress of an even-numbered plywood is exerted on the adhesive layer rather than acting on the single-board, which easily damages the adhesive layer and reduces the strength of the plywood.