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Funding Project: National Forestry Science and Technology Achievement Promotion Project of the State Forestry Administration, "Promotion and Application of Solid Timber Layered Compression Technology ([2017] No. 25)".
About the author: Huang Rongfeng (1963-), female, researcher at the Wood Industry Research Institute of the Chinese Academy of Forestry.
Research Background
Wood compression technology first appeared in the United States and Germany in the 1930s. Initially, compressed wood was used to replace metal materials in military aircraft to avoid radar detection. It was not until the 1990s that research on wood compression technology, aimed at improving the performance of softwoods and expanding the application range of plantation timber, received attention from scholars and industries around the world.
After more than 20 years of research, wood compression technology, especially the moist heat softening wood compression technology, has been gradually improved in terms of wood softening, plastic deformation, changes in the properties of compressed wood, compression deformation fixation and its mechanism, compression methods, and compression processes. A comprehensive system of compressed wood processing technologies has been developed, including log shaping and compression after moist heat softening, integral sawn timber compression, veneer compression, surface sawn timber compression, and high-frequency heating softening and deformation fixation, which have been widely applied in the timber industry. However, to date, integral wood compression technology has not yet achieved industrial-scale application.
Note: The darker areas represent the compressed layer. From left to right, the compressed wood and control wood show surface compression of 5 mm, surface compression of 10 mm, middle layer compression of 5 mm, and middle layer compression of 10 mm, respectively.
The main differences between laminated and solid wood compression
Low-density Japanese cedar can have its wood density increased to over 0.80 g/cm³ through bulk compression, significantly improving its mechanical properties. Based on this research, the densities of poplar, cedar, and Japanese cedar, major plantation species in my country, are approximately 0.40, 0.38, and 0.28 g/cm³, respectively. If bulk compression is used to increase hardness to reach the levels of commonly used hardwoods for furniture and flooring, the overall compression rate would need to reach 50%-140%. This not only increases manufacturing costs but also makes it difficult to maintain compression deformation due to high compressive stress. Although saturated steam pressure can permanently fix compression deformation, its high equipment and production costs make industrial application difficult.
Solid wood layered compression is a process that uses water and heat distribution control to compress only the layers or parts that need to be reinforced, while leaving the rest almost uncompressed. This achieves selective and directional compression of the wood, and by controlling the amount of compression, the mechanical properties of the wood are improved.
3. Comparison of the thickness of compressed wood after layered compression with that of wood before compression.
Because the compression amount is small, the required pressure for the layered compression process is only about 50% of the overall compression. After hot steam pressurization heat treatment, the compression deformation rebound rate is reduced to below 1.50%.
Content,
Advantages of solid wood laminated compression
Layered compression of solid wood allows for selective and directional compression densification. While ensuring the material's performance meets product requirements, it minimizes the compression rate, effectively conserving wood and reducing the manufacturing cost of compressed wood. This is manifested in:
1) Layered compression technology can significantly improve the hardness and strength of wood at low compression rates, effectively reducing production costs;
2) Layered compression requires less pressure and has a low springback rate in compression deformation;
3) Laminar compression is achieved through moisture and heat regulation. The processing cost mainly includes heat consumption and labor costs. The production process is simple, low-cost, and environmentally friendly.
4) The product is lightweight, has high surface hardness, and high strength. Solid wood flooring made from surface compressed wood has a high surface density and a low core density, making the flooring more elastic and providing a softer, more comfortable feel underfoot.
5) Wide adaptability of tree species. All coniferous and broad-leaved tree species with a density below 0.7 g/cm³ can be reinforced using layered compression technology.
Note: From left to right: Japanese cedar, Chinese fir, Scots pine, poplar, lacquer, and okoume.
After years of basic research and production experiments, solid wood layered compression technology has formed a series of patented technologies (zl201010522617.1, zl201310044738.3, zl201020580419.6, zl201720651024.2) and products, with a relatively complete intellectual property system. Two companies have successfully completed production trials with an annual output of 100,000 square meters and an annual output of 400,000 square meters, respectively. The technology is highly mature, and sufficient preliminary research and production practice have been carried out for the promotion and application of the technology.
Solid wood lamination compression technology is a wood modification technology that can improve the quality of low-density plantation timber without the addition of any chemical agents, enabling it to meet the requirements of high-quality solid wood boards for furniture, flooring and other wood product processing. It opens up new avenues for the utilization of low-density timber and has broad application prospects in the wood product processing industry.