English
Plywood (Plywood) refers to a three-layer or multi-layer board material that is made of wood segments into veneers or sliced into veneers, and then glued with adhesives, and makes the fiber direction of adjacent layers of veneers. They are glued vertically to each other. The usual length and width specifications are: 1220×2440mm, and the thickness specifications are: 3, 5, 9, 12, 15 and 18mm.
Features and Applications
In order to improve the anisotropic properties of natural wood as much as possible, and make the plywood feature uniform and stable in shape, in addition to requiring the adjacent layers of veneer fibers to be perpendicular to each other, the plywood must also comply with the principle of "symmetry", that is, the symmetrical center plane of the plywood is required. The veneers on both sides should maintain mutual symmetry in terms of wood properties, number of veneer layers, thickness, fiber direction, and moisture content.
For the same sheet of plywood, veneers of a single species and thickness can be used, or veneers of different species and thicknesses can be used. For this reason, the number of layers of plywood is generally three layers, five layers, seven layers and other odd layers. The names of each layer are: the surface veneer is called the surface board, and the inner veneer is called the core board; the front surface board is called the front board, and the back surface board is called the back board; in the core board, the fiber direction is parallel to the surface board. It is called a long core board or a medium board.
Since plywood is a slab made of glued veneers criss-crossed in the direction of the wood grain, and pressed under heating or unheated conditions, it can overcome the defects of wood to a greater extent and improve the utilization rate of wood. Moreover, the physical and mechanical properties of the vertical and horizontal directions are small, which can greatly improve and improve the physical and mechanical properties of the wood, and the dimensional stability is good. In addition, plywood also has many advantages, such as large format, the ability to retain the natural texture and color of wood, and convenient application and construction.
In terms of product use, most of the major industrialized countries use it in the construction industry, followed by shipbuilding, aviation, trucks, military, furniture, packaging and other related industrial sectors; while China's plywood products are mainly used in furniture, decoration, decoration, etc. Packaging, building formwork, trucks, ships, and production maintenance.
Development Path
Plywood is the oldest traditional product in the wood-based panel industry, and its application can be traced back to the seat backs of ancient Egyptian kings 3,500 years ago (Richard F, 1981).
In 1812, the invention patent for the world's first veneer saw was granted in France. In 1819, Professor Feisel of Russia and engineer Feivillier of England invented a rotary cutter for turning wood segments into thin wood chips. After decades of development, Germany began to produce plywood in 1850, using it to make laminate edges for grand pianos, and then successively used in sewing bodies, chair backs, seat seats and furniture panels. But limited by backward equipment and craftsmanship, the quality of plywood products at that time was very poor. At the beginning of the 20th century, Japan, the United States, Finland and other countries began the industrial production of plywood, and the quality of plywood was improved.
In the subsequent development process, the plywood industry broke through several important applicable technical bottlenecks:
The first is the invention of synthetic resin in 1934, which replaced all the original protein glue, so that the production of plywood has entered the production of structural materials from the original indoor product, and even the aircraft wings of World War II also used plywood;
The second is the invention of the double-clip rotary cutter in the 1960s, which solved the difficulty of manufacturing plywood in small-diameter plantations, while the emergence of no-clamp and computer-aided centering in the 1980s made the yield of modern plywood An increase of more than 10 percentage points has greatly promoted the development of the modern plywood industry.
