Жоғары тығыздықтағы талшықты тақта (MDF) туралы ақпарат

Engineered wood product

Medium density fibreboard (MDF) is an engineered wood product made by breaking down hardwood or softwood residuals into wood fibre, often in a defibrator, combining it with wax and a resin binder, and forming it into panels by applying high temperature and pressure. MDF is generally denser than plywood. It is made up of separated fibre but can be used as a building material similar in application to plywood. It is stronger and denser than particle board. The name derives from the distinction in densities of fibreboard. Large scale production of MDF began in the 1980s, in both North America and Europe. Over time, the term "MDF" has become a generic name for any dry process fibreboard.

MDF is typically made up of 82% wood fibre, 9% urea formaldehyde resin glue, 8% water, and 1% paraffin wax. The density is typically between The range of density and classification as light , standard , or high density board is a misnomer and confusing. The density of the board, when evaluated in relation to the density of the fibre that goes into making the panel, is important. A thick MDF panel at a density of may be considered as high density in the case of softwood fibre panels, whereas a panel of the same density made of hardwood fibres is not regarded as so. The evolution of the various types of MDF has been driven by differing need for specific applications.

In Australia and New Zealand, the main species of tree used for MDF is plantation grown radiata pine, but a variety of other products have also been used, including other woods, waste paper, and fibres. Where moisture resistance is desired, a proportion of eucalypt species may be used, making use of the endemic oil content of such trees.

The trees are debarked after being cut. The bark can be sold for use in landscaping or used as biomass fuel in on site furnaces. The debarked logs are sent to the MDF plant, where they go through the chipping process. A typical disk chipper contains four to 16 blades. Any resulting chips that are too large may be rechipped; undersized chips may be used as fuel. The chips are then washed and checked for defects. Chips may be stored in bulk, as a reserve for manufacturing. However, MDF is not entirely isotropic since the fibres are pressed tightly together through the sheet. Typical MDF has a hard, flat, smooth surface that makes it ideal for veneering, as no underlying grain is available to telegraph through the thin veneer as with plywood. A so called "premium" MDF is available that features more uniform density throughout the thickness of the panel. MDF may be glued, doweled, or laminated. Typical fasteners are T nuts and pan head machine screws. Smooth shank nails do not hold well, and neither do fine pitch screws, especially in the edge. Special screws are available with a coarse thread pitch, but sheet metal screws also work well. MDF is not susceptible to splitting when screws are installed in the face of the material, but due to the alignment of the wood fibres, may split when screws are installed in the edge of the board without pilot holes.

MDF is often used in school projects because of its flexibility. Slatwall panels made from MDF are used in the shop fitting industry. MDF is primarily used for indoor applications due to its poor moisture resistance. It is available in raw form, or with a finely sanded surface, or with a decorative overlay. MDF is also usable for furniture such as cabinets, because of its strong surface. MDF's density makes it a useful material for the walls of pipe organ chambers, allowing sound, particularly bass, to be reflected out of the chamber into the hall.

When MDF is cut, a large quantity of dust particulate is released into the air. Formaldehyde resins are commonly used to bind together the fibres in MDF, and testing has consistently revealed that MDF products emit free formaldehyde and other volatile organic compounds that pose health risks at concentrations considered unsafe, for at least several months after manufacture. Urea formaldehyde is always being slowly released from the edges and surface of MDF. When painting, coating all sides of the finished piece is a good practice to seal in the free formaldehyde. Wax and oil finishes may be used as finishes, but they are less effective at sealing in the free formaldehyde. According to International Composite Board Emission Standards, three European formaldehyde classes are used, E0, E1, and E2, based on the measurement of formaldehyde emission levels. For instance, E0 is classified as having less than 3 mg of formaldehyde out of every 100 g of the glue used in particleboard and plywood fabrication. E1 and E2 are classified as having 9 and 30 g of formaldehyde per 100 g of glue, respectively. All around the world, variable certification and labeling schemes are there for such products that can be explicit to formaldehyde release, such as that of Californian Air Resources Board.

Veneered MDF provides many of the advantages of MDF with a decorative wood veneer surface layer. In modern construction, spurred by the high costs of hardwoods, manufacturers have been adopting this approach to achieve a high quality finishing wrap covering over a standard MDF board. One common type uses oak veneer. Making veneered MDF is a complex procedure, which involves taking a slice of hardwood about 1–2 mm thick and then, through high pressure and stretching methods, wrapping them around the profiled MDF boards. This is possible only with simple profiles; otherwise, when the thin wood layer dries, it breaks at bends and angles.