The wood-based panel manufacturing process

Cutting

Raw material handling and final product processing all require cutting processes such as veneer peeling, planing, wood chips, wood shavings, fiber grinding and separation, sawing, sanding and the like in the final machining. Cutting wood into differently shaped elements and reassembling them in a variety of ways can improve certain properties of the wood, such as anisotropy, inhomogeneity, swelling and shrinkage. The mechanical strength of the plate composed of large units is higher, and the platelets composed of small units have better homogeneity. Precise control of the thickness of the rotary veneer error can increase the material rate of 2 to 3%. The shape of the shaved chips affects the entire physical and mechanical properties of the particleboard; the fiber morphology is also closely related to the strength of the fiberboard. The final sawing, grinding and other products also affect the quality of the specifications.

dry

Including veneer drying, shaving drying, fiber drying in dry-laid fiberboard processes, and heat treatment of wet-laid fiberboard. Drying process and process control and drying are different. Drying process control is based on the relative humidity of the drying medium shall prevail, we must pay attention to prevent the generation of drying stress; and wood-based panels used in sheet, granular material drying is relatively high temperature, high speed and continuous conditions, heating The end of the stage immediately into the deceleration drying stage. Veneer and shavings and other materials thin, large surface area, the impact of dry stress is very small or does not exist. Coupled with the wood in the cutting process to varying degrees of relaxation, water diffusion resistance is small, the internal law of wood moisture diffusion veneer, wood shavings and other meaningless.

Dry heat, mostly steam or combustion gases. Infrared drying consumes too much energy and requires 5500 ~ 18000 kJ per 1 kg of water evaporated; while steam drying only requires 4200 ~ 5000 kJ. The advantage of high-frequency drying is the drying rate is high when the dry material moisture content, the final moisture content uniform, but the drying cost is too high. If combined with steam to achieve duplex heating is beneficial. Vacuum drying is not only expensive, the production efficiency is low. When using steam as a heat source, 1 kg of water is evaporated per evaporator, 1.75 to 2 kg of steam is required for drying the veneer, about 1.8 kg of steam is required for drying the wood shavings, and 1.6 to 1.8 kg of steam is required for the drying of the soft fiber slab.

Sizing

Including board gluing, wood shavings and fiber sizing. Veneer is still used in Europe, the traditional roller rubber, the United States since the 70s many plywood factory has switched to plastic. Chinese plywood factory also use roller glue. Lining method suitable for the entire plate in the process of automation and blank group. Wood shavings and fiber sizing now mainly using the method of spraying.

In the late 1970s, some countries in Europe and the United States studied the glueless bonding technology. More progress was made in activating lignin molecules and using lignin gluing under certain conditions; or using hemicellulose in wood or other materials to treat it Converted to cementing material for gluing. In the early 1980s, Canada successfully made use of the slag residue made of particleboard. Research institutes and universities in China are also conducting research on glueless bonding technology and have achieved initial results.

Forming and pressing

Plywood blank group, particleboard fiberboard slab forming and pressing are all wood-based panel manufacturing process. Lumber's study of wood construction reveals that wood fibers are arranged in natural wood in a hierarchical and directional manner that can withstand the natural forces imposed on the wood to a limited extent. The evolution of man-made board manufacturing process is undoubtedly affected by this understanding: Particleboard and fiberboard slab are changed from single-layer to three-layer and multi-layer structure; the arrangement of shavings and fibers in the slab also tends from random to directional; The adjacent layers of plywood perpendicular to each other to improve the direction of the fibers formed in the natural growth of anisotropic defects formed to improve the dimensional stability.

Pressure points pre-press and hot pressing. The slab must be pre-pressed when using a plateless system. It keeps the slab from being damaged while advancing the hot press. Hot pressing process is to determine the production capacity of enterprises and key processes, commonly used in the wood-based panel industry, hot pressing equipment is multi-layer hot press, in addition, single-layer large-format hot press and continuous hot press is gradually being adopted. Particleboard factory multi-use single-layer hot press, MDF manufacturing single-layer press can be used in combination of high-frequency and steam heating, help to shorten the pressure cycle and improve product cross-section density uniformity.

Final processing

After unloading plate from the hot press, after cooling and moisture content of the stage, namely sawing, sanding, hardboard by heat treatment and humidity conditioning. In the past, the sawing edges were all cold sawing. Hot sawing is also used now, but the hot sanding method must never be used. Hot sand can damage the finished surface quality. According to the requirements of use, some boards need special treatment such as dipping, painting, double-faced and edge sealing