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made by hot forming of wood particles (wood shavings) with a binding agent. Urea-formaldehyde and phenol-formaldehyde resins are used as binding agents. The use of chipboard in various branches of the national economy creates a variety of demands, which accounts for the large number of types available. Chipboard is classified according to the means of forming, the structure, the type of milled wood used, the binding agent, and the facing material.
According to the means of forming, chipboard is classified as flat-formed or extruded. The former type is made with pressure applied at right angles to the plane of the board; the latter is produced by pressure applied parallel to the board. Flat-formed chipboard is produced in one, three, five, and many layers; extruded board is produced in single layers, either of continuous composition or with channels within the board. In single-ply board the size of the wood chips and the amount of binding agent are uniform throughout the entire thickness of the board; in three- and five-ply board, one or both outer layers (from each side) are made of thinner particles and with more of the binding agent than in the inner layers. Such board has a smooth surface and high strength. Chipboard is manufactured unfinished or finished (with one or two layers of shaved or planed veneer, paper impregnated with synthetic resins, or a synthetic emulsion) and in polished or unpolished form.
Chipboard is divided into groups in terms of density (depending on the means of forming and the brand): very low density (350-450 kg/m3), low density (450-650), medium (650-800), and high (700-800). The following basic dimensions (in mm) for chipboard have been established in the USSR (1970): for flat-formed board—length 2,500-3,500, width 1,220-1,750, and thickness 10-25; extruded board-length 2,500, width 1,250, and thickness 15-52.
The physical and mechanical properties of chipboard depend mainly on weight per volume, the shape and size of the wood particles, the amount and quality of the binding agent, and the structure. It is characterized by the following indexes: moisture, 8 percent; water absorption, 12-88 percent; coefficient of thermal conductivity, 0.07-0.25 watts per (m° K), or 0.06-0.22 kcal/nvhr-°C; specific heat capacity, 1.7-1.9 kilojoules per (kg-0 K), or 0.4-0.45 kcal/(kg-° C). swelling (in 24 hours), 5-30 percent in thickness; perpendicular tensile strength, 0.25-0.4 meganewtons per sq m, or 2.5-4 kilograms-force per sq cm. Chipboard is more biologically resistant than natural wood because of the presence of formalin in the binding agents. Chipboard is widely used in the furniture industry, in construction, and in other branches of the economy.
V. S. LEBEDEV