The main five processes for the production of various wood-based panels

The manufacturing process of various wood-based panels includes the following five main processes.

First, cutting   The processing of raw materials and the final processing of the products must be applied to cutting processes, such as rotary cutting and cutting of veneers, cutting of wood chips and shavings, grinding and separation of fibers, and sawing and sanding in final processing. Cutting the wood into units of different shapes and recombining them into various sheets in a certain way can improve certain properties of the wood, such as anisotropy, heterogeneity, swelling and shrinkage. The plate composed of large units has higher mechanical strength, and the plate composed of small units has better homogeneity. Precise control of the thickness error of the rotary cutting veneer can increase the yield of 2 to 3% . The cut wood shavings affect the overall physical and mechanical properties of the particleboard; the fiber morphology is also closely related to the strength of the fiberboard. The final sawing, grinding, etc. of the sheet also affect the quality of the product.

Second, drying includes veneer drying, shaving drying, fiber drying in the dry fiberboard process, and heat treatment of the wet fiberboard. Drying process and process control are different from finished drying. The process control of the drying of the material is based on the relative humidity of the drying medium, and care must be taken to prevent the generation of drying stress. The drying of the sheet-like and granular materials used for the wood-based panel is carried out under relatively high temperature, high speed and continuous conditions. At the end of the phase, it is immediately transferred to the deceleration and drying phase. Veneer and shavings are thin, have a large surface area, and have little or no effect on dry stress. In addition, the wood tissue undergoes different degrees of relaxation during the cutting process, and the water diffusion resistance is small, and the law of moisture diffusion inside the wood loses its meaning on the veneer and the shavings.

Most of the dry heat sources use steam or combustion gases. Infrared drying energy consumption is too large, 5500 ~ 18000 kJ per evaporation of 1 kg of water ; and steam drying only 4200 ~ 5000 kJ. The advantage of high-frequency drying is that the drying rate of the dry material is high and the final moisture content is uniform, but the drying cost is too high. It is advantageous if combined with steam is used to achieve duplex heating. Vacuum drying is not only expensive but also has low production efficiency. When the vapor as a heat source, per 1 kg of water evaporated, veneer drying steam required 1.75 to 2 kg, about 1.8 kg shavings vapor drying need, the soft fibrous web drying steam demand of 1.6 to 1.8 kg.

Third, the sizing includes veneer coating, shavings and fiber sizing. Veneer gluing still uses traditional roller gluing in Europe. Since the 1970s , many plywood factories have switched to laminating. Chinese plywood factories also use roller coating. The leaching method is suitable for the process of sizing the intermediate plate and the automated slab. Shavings and fiber sizing are now mainly used by spray glue.

In the late 1970s, some countries in Europe and the United States studied non-adhesive gluing technology. The more advanced is the activation of lignin molecules, the use of lignin glue under certain conditions; or the use of hemicellulose in wood or other materials. It is converted into a cemented material for gluing. In the early 1980s, Canada successfully used steamed slag to make glueless particleboard. The Chinese Academy of Forestry and the Northeast Forestry University are also conducting research on glueless bonding technology, and preliminary results have been achieved.

4. Molding of formed and pressed plywood, slab forming and pressurization of particleboard fiberboard are all molding processes for the manufacture of wood-based panels. The study of wood structure by wood science reveals that the arrangement of wood fibers in natural wood is hierarchical and directional, and thus can withstand a certain amount of external force exerted by nature on wood. The evolution of the manufacturing process of wood-based panels is undoubtedly affected by this understanding: the slab level of particleboard and fiberboard is changed from a single layer to a three- layer structure and a multi-layer structure; the arrangement of shavings and fibers in the slab also tends to be oriented from a random type; The orientation of the adjacent layers of the plywood fibers perpendicular to each other improves the anisotropy of the wood under natural growth conditions and improves dimensional stability.

Pressurization is divided into pre-pressure and hot pressing. It is necessary to pre-press the slab when using a padless system. It keeps the slab from being damaged when it is pushed into the hot press. The hot pressing process is the key process to determine the production capacity and output of the enterprise. The hot pressing equipment commonly used in the wood-based panel industry is mainly a multi-layer hot press. In addition, single-layer large-format hot presses and continuous hot presses are gradually being adopted. The single-layer hot press is used in the particleboard factory. The single-layer laminator can be used in the manufacture of medium-density fiberboard to achieve the combined heating of high frequency and steam, which is beneficial to shorten the pressurization cycle and improve the uniformity of product section density.

5. After the final processed sheet is discharged from the hot press, it is subjected to the stage of cooling and moisture content balance, that is, sawing and sanding, and the hard fiber board is subjected to heat treatment and humidity control. In the past, the sawing edges of the plates were cold sawing. Now, the hot sawing method is also used, but the hot sanding method must not be used. The hot sand will damage the surface quality of the finished product. According to the requirements of use, some plates need special treatment such as dipping, painting, laminating and edge sealing.

Tags: wood, wood-based panels, top ten brands of Chinese plates , plates

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