Introduction to plywood.

Plywood is a three-layer or multi-layer board-like material that is made of wood sections that are peeled into veneers or sliced ​​into thin wood, and then glued with adhesives. Usually, odd-numbered veneers are used, and adjacent layers of veneers are used. The fiber directions are glued perpendicular to each other.

Plywood is one of the commonly used materials for furniture, and it is one of the three major boards of wood-based panels. It can also be used for aircraft, ships, trains, automobiles, buildings and packaging boxes. A group of veneers are usually assembled and glued together according to the direction of the wood grain of adjacent layers perpendicular to each other. Usually, the surface board and inner layer board are symmetrically arranged on both sides of the center layer or core. The slab made of the veneer after gluing is criss-crossed according to the direction of wood grain, and pressed under heating or non-heating conditions. The number of layers is generally an odd number, and a few have even numbers. The difference in physical and mechanical properties in the vertical and horizontal directions is small. The commonly used types of plywood are three-ply board, five-ply board and so on. Plywood can improve wood utilization and is a major way to save wood.

In order to improve the anisotropic properties of natural wood as much as possible, so that the properties of plywood are uniform and the shape is stable, the structure of general plywood must abide by two basic principles: one is symmetry; the other is that the fibers of adjacent layers of veneer are perpendicular to each other. The principle of symmetry is to require that the veneers on both sides of the symmetrical central plane of the plywood should be symmetrical to each other regardless of the nature of the wood, the thickness of the veneer, the number of layers, the direction of the fibers, and the moisture content. In the same plywood, veneers of a single species and thickness can be used, or veneers of different species and thickness can be used; however, any two layers of veneers that are symmetrical to each other on both sides of the symmetrical central plane must have the same species and thickness. The face and back panels are not allowed to be of the same tree species.

To make the structure of plywood meet the above two basic principles at the same time, its number of layers should be odd. Therefore, plywood is usually made into odd-numbered layers such as three layers, five layers, and seven layers. The names of each layer of plywood are: the surface veneer is called the surface board, the inner veneer is called the core board; the front board is called the panel, and the back board is called the back board; in the core board, the fiber direction is parallel to the board It is called long core board or medium board. When forming cavity deck slabs, the front and back panels must face tightly outward.