In recent years, China has made great efforts to develop the production of fast-growing industrial materials such as poplar, Chinese fir, Paulownia and Pinus elliottii. As fast-growing forest wood is more suitable for processing blockboard, it provides abundant raw materials for the production of blockboard, and because of the rapid development of furniture and home improvement industry, it provides a broad market for blockboard. Therefore, blockboard has become the current One of the fastest growing plates in China's wood-based panel varieties. Compared with particleboard and medium density fiberboard, the process and equipment of blockboard seems to be relatively simple, but from the analysis of sheet metal structure, the blockboard is not only complicated in level, but also causes unevenness, thickness deviation and warpage of the sheet. More. The flatness, thickness deviation and warpage of the blockboard are much more difficult to achieve the same level as particleboard and medium density fiberboard. In recent years, the production process of medium and high-grade blockboard has been continuously changed to improve product quality. However, due to fierce market competition and other factors, reports on process modification are extremely limited. Based on the practice and research of blockboard production for many years, the author introduces the relevant situation as follows for reference by scientific research, production and application personnel.
1 The main factors affecting the quality of blockboard The quality factors such as the bonding strength of the blockboard, the deviation of the finished board, the moisture content, the nail holding power, and the swelling ratio of the water absorption thickness are roughly the same as those of the particle board and the fiberboard. Needless to say, the surface flatness, warpage and thickness deviation of blockboard are relatively important quality indicators [1], the main influencing factors are as follows.
1.1 Influence of the core strip unit In general, the smaller the basic constituent unit of the artificial board, the more uniform the material. The constituent elements of the fiberboard are fine fibers, the particleboard is shaved and polished, and the plywood is a thin veneer. These units are easily plastically deformed under high temperature and hot pressing, and the residual stress is small. The blockboard is mainly composed of a core assembled by a core strip. The size of the core strip is much larger than that of the fiber and the shavings, and the processing precision and water content are difficult to achieve the same plastic deformation and uniform material properties at the same time.
1.2 Influence of core material of the core material Even if the core of the same core type is used, the hardness, dry shrinkage and swelling of the core strip are still affected by factors such as site conditions, early and late wood, tree age and wood defects. Differences. When the material properties of adjacent core strips are large, it is difficult to manufacture high quality blockboard by ordinary processing techniques. If the core material is sorted according to different materials and processed separately, although the degree of influence can be reduced, it is obviously unrealistic in large-scale production.
1.3 Influence of core board The surface and back board of domestic blockboard manufacturers mainly adopt imported single-board materials. Due to cost factors, they have become thinner and thinner, and the thinnest has been below 0.2mm. With such a thin surface and back sheet, to produce a blockboard with a high surface flatness, the requirements for the core board are obviously higher. At present, most of the core plates are made of domestic fast-growing materials such as poplar, paulownia, etc. Due to poor material, the rotary-cut veneer has many holes, the surface is rough, the burr groove is large, and the thickness deviation is large, which not only has a great influence on the surface flatness. Moreover, in the case of using the core sheet sizing process, subsequent processes such as repairing and drying are difficult to perform. The factory basically adopts the process of cutting and taking a plurality of veneers manually by hand or mechanically assembling. In this way, the difference in the thickness deviation, the moisture content of the veneers in the single core sheets after the flattening, and the difference in the material properties of the heartwood or the early and late materials are reflected on the quality of the core board, thereby affecting the surface of the blockboard. Flatness, dimensional stability and thickness deviation.
1.3 Influence of structure level Common blockboard is generally a five-layer structure, namely panel, core board, core board, core board and back board. The layered structure of different materials and different geometrical dimensions is prone to local stress due to the different species, material properties, geometric dimensions, processing and processing methods of the various layers of materials, thereby causing changes in the size and shape of the panels. In addition, the multilayer structure material is required to maintain dimensional and shape stability, and one of the important conditions is the symmetry of the structure. For blockboards, it is also difficult to make the symmetry of the panel, backboard and two core boards in terms of tree species, material properties, thickness, and moisture content.
2 Core processing technology Blockboard is actually one of the special plywood. The difference from ordinary plywood is that the center layer is a combination of small-sized wood strips, that is, the core. The quality of the core has a great influence on the quality of the blockboard, and it is also extremely sensitive to the cost response of the product. The grade of the blockboard is often distinguished by the quality of the core. Therefore, the core material and processing technology are the key sections for the production of blockboard.
1 The main factors affecting the quality of blockboard The quality factors such as the bonding strength of the blockboard, the deviation of the finished board, the moisture content, the nail holding power, and the swelling ratio of the water absorption thickness are roughly the same as those of the particle board and the fiberboard. Needless to say, the surface flatness, warpage and thickness deviation of blockboard are relatively important quality indicators [1], the main influencing factors are as follows.
1.1 Influence of the core strip unit In general, the smaller the basic constituent unit of the artificial board, the more uniform the material. The constituent elements of the fiberboard are fine fibers, the particleboard is shaved and polished, and the plywood is a thin veneer. These units are easily plastically deformed under high temperature and hot pressing, and the residual stress is small. The blockboard is mainly composed of a core assembled by a core strip. The size of the core strip is much larger than that of the fiber and the shavings, and the processing precision and water content are difficult to achieve the same plastic deformation and uniform material properties at the same time.
1.2 Influence of core material of the core material Even if the core of the same core type is used, the hardness, dry shrinkage and swelling of the core strip are still affected by factors such as site conditions, early and late wood, tree age and wood defects. Differences. When the material properties of adjacent core strips are large, it is difficult to manufacture high quality blockboard by ordinary processing techniques. If the core material is sorted according to different materials and processed separately, although the degree of influence can be reduced, it is obviously unrealistic in large-scale production.
1.3 Influence of core board The surface and back board of domestic blockboard manufacturers mainly adopt imported single-board materials. Due to cost factors, they have become thinner and thinner, and the thinnest has been below 0.2mm. With such a thin surface and back sheet, to produce a blockboard with a high surface flatness, the requirements for the core board are obviously higher. At present, most of the core plates are made of domestic fast-growing materials such as poplar, paulownia, etc. Due to poor material, the rotary-cut veneer has many holes, the surface is rough, the burr groove is large, and the thickness deviation is large, which not only has a great influence on the surface flatness. Moreover, in the case of using the core sheet sizing process, subsequent processes such as repairing and drying are difficult to perform. The factory basically adopts the process of cutting and taking a plurality of veneers manually by hand or mechanically assembling. In this way, the difference in the thickness deviation, the moisture content of the veneers in the single core sheets after the flattening, and the difference in the material properties of the heartwood or the early and late materials are reflected on the quality of the core board, thereby affecting the surface of the blockboard. Flatness, dimensional stability and thickness deviation.
1.3 Influence of structure level Common blockboard is generally a five-layer structure, namely panel, core board, core board, core board and back board. The layered structure of different materials and different geometrical dimensions is prone to local stress due to the different species, material properties, geometric dimensions, processing and processing methods of the various layers of materials, thereby causing changes in the size and shape of the panels. In addition, the multilayer structure material is required to maintain dimensional and shape stability, and one of the important conditions is the symmetry of the structure. For blockboards, it is also difficult to make the symmetry of the panel, backboard and two core boards in terms of tree species, material properties, thickness, and moisture content.
2 Core processing technology Blockboard is actually one of the special plywood. The difference from ordinary plywood is that the center layer is a combination of small-sized wood strips, that is, the core. The quality of the core has a great influence on the quality of the blockboard, and it is also extremely sensitive to the cost response of the product. The grade of the blockboard is often distinguished by the quality of the core. Therefore, the core material and processing technology are the key sections for the production of blockboard.
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