General description
Plywood is a sheet of material made from many layers of natural wood sliced about 1 mm thin. These layers of wood are arranged perpendicularly in the direction of the wood grain of each layer, then pressed together under high temperature and pressure with the participation of adhesives.
Plywood is considered the first type of industrial wood invented. Archaeologists have found the first traces of plywood in Pharaoh's tombs in Egypt around 3500 BC. About a thousand years ago, the Chinese knew how to thin wood and glue them together for interior applications. The British and French were also recorded to have basically applied plywood in the 17th and 18th centuries.
In 1797, Samuel Bentham - a famous English mechanical engineer and shipbuilder - registered a patent for several types of wood thinning machines. In his patent application, he described a concept of gluing thin layers of veneer together to form a thicker panel of wood – this is considered the first description of the concept of laminated wood. we use today.
About 50 years later, Immanuel Nobel - father of famous scientist Alfred Nobel realized that, when thin layers of natural wood are bonded together, it will form a sheet of material with incredible durability.
In 1905, the first plywood was exhibited at the Lewis & Clark Fair in Finland.
In 1928, plywood panels with standard dimensions of 4 feet x 8 feet (1.2m x 2.4m) were first introduced in the United States as a construction material.
The structure of plywood is divided into three components:
Raw materials for plywood production are usually woods such as pine, birch, acacia, eucalyptus, etc.
The average density of plywood is 600 - 700 kg/m3.
Common plywood size: 1220 x 2440 mm; 1160 x 2440 mm; 1000 x 2000 mm.
Common plywood thickness: 3, 4, 5, 6, 8, 10, 12, 15, 18, 20, 25 (mm).
The layers of a plywood board are always odd numbers (3, 5, 7, 9...) so that the board has a core layer in the middle, to create the same grain direction in the two layers outside the core layer. From there, these layers of wood restrain each other from warping or cracking. As a result, the thin layers on both sides of the core layer are held tightly by the core layer and cannot expand freely. Because of this arrangement of wood layers, plywood does not warp and shrink under normal conditions.
The horizontal and vertical grain wood layers are arranged interwoven and pressed under high temperature and pressure with the participation of adhesives.
Plywood production process:
- Round logs are cut to specified sizes and peeled to ensure uniformity and smoothness of the veneer layers.
- The log continues to be peeled into thin layers of wood using a specialized peeling machine.
- These thin layers of veneer are chopped to a size of 8 feet x 2 feet for the whole slab and 4 feet x 2 feet for the core layer. Then, they are sent to a specialized machine to improve elasticity.
- The veneer layers will then pass through a temperature-controlled drying system for drying.
- Next, they are stored for 24 hours to retain moisture from 6 to 8%.
- These laminated wood layers are then transferred to the assembly line and the wood glue spraying line.
- In order for the glue to penetrate better and the board to be stiffer, these laminated wood layers are pre-pressed under a fixed pressure level for a certain period of time.
- These preliminary stacks of plywood are then fed to a hot press line and pressed under controlled temperature and pressure. - The next step is rough cutting. The boards are cut into rectangles.
- After rough cutting, the boards are processed with a scrubber to achieve a smooth and uniform finished surface. - In the next step, the boards are sent to the glue spraying line to glue the surface layer on top.
- To achieve optimal hardness, the board continues to be pressed 4 more times. First, pre-press under controlled pressure.
- Then, the board is pressed using a hot pressing line equipped with an elastic compression system under controlled temperature to maintain appropriate moisture and ensure the flatness of the board surface.
- The board continues to be brought to the final cutting stage.
- Finally, to achieve the best quality, the board is transferred to a scrubbing machine for final quality inspection.
- Due to the arrangement of interwoven wood layers, plywood is very hard and has very high mechanical strength.
- Compared to MDF boards, plywood is less affected by water and the board does not swell easily when soaked in water like MDF boards.
- Plywood has the ability to hold screws and adhere extremely well.
- The board withstands moisture quite well in a well-ventilated environment.
- Compared to MDF or chipboard, the cost of plywood is higher.
- When cutting plywood, the edges of the board are easily chipped.
- If not treated according to standards, the board is susceptible to warping, has a rough surface and is susceptible to delamination in high humidity environments.
- Plywood is widely used in construction such as making concrete molds or coating materials.
- Multi-layer plywood is used for load-bearing products with high dimensional stability such as floors and walls.
- Plywood can continue to be coated on surfaces for interior applications such as tables, cabinets, beds, etc. - In addition, plywood is also used to build boats and boats.
