Principle of Symmetry in Composition of Wood-based Panel Plywood

Principle of Symmetry in Composition of Wood-based Panel Plywood

The mechanical properties and physical properties of wood (bamboo) along and across grain directions differ greatly. In order to improve this property, give full play to its advantages, and keep the shape and size of finished products stable, the following three principles should be followed in billet forming.

The tree species, thickness, manufacturing method, texture direction and moisture content of the unit in the corresponding layer on both sides of the symmetrical central plane of the wood-based panels should be the same (Fig. 1-3).

For example, when the moisture content of wood-based panels changes uniformly, the wood (bamboo) will be deformed (hygroscopic expansion, desorption and drying shrinkage). The stress caused by the deformation can be calculated by the following formula:

_=epsilon.E

In formula: _-stress (MPa);

E-strain .

Structure Indication of Wood-based Panel

Figure 1-3 Structure of Wood-based Panels

L-material original length or width or thickness (m);

Elongation of AL-Material due to Variation of Water Content

Or contraction (m);

Modulus of Elasticity of E-Wood (Bamboo) Wood (Same Wood Species, Fiber)

Direction, water content, etc. (MPa).

For example, the thickness of the corresponding veneer (unit) layer in plywood is only different from that of S1 > S2. When the plywood absorbs moisture, the deformation force P1 = _. S1. L. W and P2 = _. S2. L. W will occur, so P1 > P2 (Fig. 1-4). In this case, the internal stress in the plywood will occur, and the three-plywood will have upward bending deformation, cracking (glue) and other defects.

Figure 1-4 Deformation Force of Plywood

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