Plywood can be divided into ordinary plywood, plywood for structure, plywood for cement template, fire plywood and special plywood.
The physical and mechanical properties of the plywood are described by the moisture content, density, thermal conductivity, and gluing strength. International Organization for Standardization of ordinary plywood production, from the structure, finished product moisture content, quality 3 to make the provisions: ① structure. The texture of the adjacent veneer should be at right angles; the center layer is symmetrical with respect to the center layer, and the thickness of the layers is the same; ② moisture content. Between 12 and 14% (according to Chinese national standards, Ⅰ, Ⅱ plywood absolute moisture content of not more than 13%; Ⅲ, Ⅳ type plywood moisture content of not more than 15%). ③ quality. Finished products should have rectangular straight edges and obvious edges and corners; the minimum number of layers of each nominal thickness to comply with the relevant provisions.
The density of the plywood is greater than that of the same species. The greater the unit pressure when gluing, the greater the density of the plywood. As the wood at high temperature easy to produce plastic deformation, hot glue gluing than the compression of the compression rate is greater. As the plywood from the criss-cross the preparation of the veneer, the thermal conductivity is lower than the same species of wood.
Plywood bonding strength, according to the Chinese national standards: Ⅰ class plywood for 1.2 to 1.6 MPa, Ⅱ class 1 to 1.4 MPa, Ⅲ class 1 to 1.2 MPa, Ⅳ class 1 MPa.
Plywood quality requirements include appearance level, size, physical and mechanical properties of the three elements. Appearance level, size, physical and mechanical properties of the three tests are qualified to determine the product is a qualified product, or judged to be unqualified. Plywood should be manufactured with the quality inspection department of the production plant product quality certification, specify the type of plywood, specifications, grade, bonding strength and moisture content.
Ordinary plywood size: plywood thickness of 2.7mm, 3.3mm, 4.5mm, 5.5mm, 6mm ... ... since 6mm, according to lmm increments. Thickness from 4mm below is a thin plywood. 3mm, 3.5mm, 4mm thick plywood for common specifications. Other thickness of the plywood should be provided by both sides after the agreement.
Appearance grade: ordinary plywood according to the processing of plywood can be seen on the material defects and defects are divided into four grades: special, first class, second class, third, which, one, two, three for the general grade of the main plywood.
The above four levels of the panel should be sand (scrap) light, special needs may not sand (scrap) light or two sand (scrap) light. Sanding plywood refers to the plywood of the sanding machine (or scraper) sanding (or scraper). It is generally judged by visualizing the allowable defects on the plywood. The grade depends on the permissible material defects, machining defects, and the requirements for splicing.