Wood processing is processing wood as raw material, mainly by mechanical or chemical methods, and its products still maintain the basic characteristics of wood. In the forest industry, the wood processing industry and the chemical processing of forest products are both the follow-up industries of forest logging and transportation, and they are important sectors for the comprehensive utilization of wood resources.
The discipline to study wood processing technology is wood technology, which is based on wood science and applies theories and methods in the fields of physics, chemistry, biology, mechanical engineering, thermal engineering, etc. It is a comprehensive combination of multiple disciplines.
1.Classification of wood
The wood currently used in design is mainly divided into man-made panels and natural wood. Wood-based panels are commonly used in the design of large core boards, plywood, decorative panels, fiberboard, particleboard, polystyrene board, Huali board, fireproof board (plastic board), paper decorative panels, etc. As natural wood grows, various defects inevitably exist and produce. At the same time, wood processing also produces a large amount of scraps. In order to improve the utilization rate of wood and improve product quality, use wood and other plant scraps and fibers The manufactured man-made panels have been widely promoted and applied. The commonly used natural woods mainly include Fraxinus mandshurica, Northeast elm, Willow eucalyptus, camphor, basswood, birch, color wood, teak, beech, cherry wood, red sandalwood, cypress, yew, red pine, oak wood, yellow pineapple, Walnut, Schima superba, rosewood, redwood, neem, toon, wild jujube, etc.
Wood processing technology mainly includes basic processing technologies such as wood cutting, wood drying, wood-glued wood surface decoration, and functional processing technologies such as wood protection and wood modification. Here we mainly introduce the basic processing technology of several kinds of wood. Wood cutting can be divided into three forms:
- The workpiece is cut off a layer of relatively deformed chips, and the rest is semi-products or products, such as planing, turning, etc.;
- The chips themselves are products, such as veneer peeling. , Planing, etc.;
- The chips and the remaining workpieces are all products, such as milling used in chipping.
In addition to the direct use of logs in the design, the wood is processed into square lumber or other products for use. In order to reduce the deformation and cracking of the wood in use, the board and square lumber must be dried naturally or artificially. Natural drying is the air drying of wood stacks. The manual drying method is mainly dry kiln method, but also simple baking method. The drying kiln is a drying room equipped with circulating air equipment, which can adjust and control the temperature and humidity of the air. The quality of the wood dried by the drying kiln is good, and the moisture content can reach below 10%. Wood that is prone to decay in use should be treated with preservatives in advance. The gluing method can be used to glue the boards into large components, which are used for wooden structures, stakes, etc. Wood can also be processed into plywood, chipboard, fiberboard, etc. Wood is susceptible to swelling and shrinking due to the influence of air humidity, which will make wood products damp, and will soon be corroded and destroyed, so the wood drying technology was born. Wood drying is the process of reducing the moisture content of the wood to a suitable value by heating and using the pressure difference between the internal and external water vapor of the wood. An indispensable production link in the wood industry. The function of wood drying is to reduce weight, save labor and cost of transportation; prevent moth and corrosion, extend service life; prevent deformation and warpage, increase elasticity, and help improve the quality of wood products. Improving the drying speed while ensuring the drying quality is the basic principle of drying. Drying quality requirements: the final moisture content and drying uniformity of the dried wood can meet the requirements of the processing technology. Maintain the integrity of the wood, do not occur defects that are not allowed by the process specifications, and do not change the properties of the wood products.
Wood gluing is the technology of gluing wood and wood or other materials into a whole. It is the development of mortise and nailing methods for wood products. The birth of wood-based panels is based on gluing technology. Gluing can also extend the length of short timber, increase the thickness of thin timber, widen narrow timber, and improve the quality of inferior timber, and improve the utilization effect and level of wood, thus playing an important role in wood processing. According to the purpose of the glued products and the performance of the selected adhesive, there are two types of structural glue and non-structural glue. In order to use the glued product as a building structural material, wood gluing with a glue with high gluing strength and good aging resistance is called structural gluing, and non-structural gluing. The gluing between wood is mainly characteristic gluing (also known as ratio gluing) and mechanical gluing. In addition, chemical bonding also exists, but its effect is small, and it is often omitted when considering bonding strength. Wood gluing mainly undergoes processes such as preparation of the glued wood, gluing (gluing), forming embryos, drying, closing, heating and post-processing. The basis for the development of wood gluing is the development of adhesives, the invention of new processes, the manufacture of new equipment and the development of wood science. Many scholars are studying improved adhesives such as lignin gum, tannin gum, isocyanate gum, etc.; sugar-based non-formaldehyde-based adhesives will sooner or later be used in industrial production. The creation of new technology is mainly manifested in the development of glueless gluing technology. These will bring the future wood gluing technology to a new level.
5.Wood surface processing
The surface processing process of wood and its products according to the final use requirements and visual requirements. Wood products are mostly made after the final product is made, and wood-based panels are made before use or after making wood products. In ancient China, raw lacquer and tung oil have been used to decorate wood products. In addition to painting, Ming Dynasty furniture also had decorative techniques such as carving and inlay. After the 1940s, phenolic resin coatings began to be adopted in some countries, and synthetic resin coatings gradually became dominant. In the 1960s, new and veneer decoration materials appeared one after another, which provided conditions for the further development of wood surface decoration technology.