Effect of Press Cycles and Moisture Content on Properties of Douglas-Fir Flakeboard

Press cycles, moisture content, and moisture content distribution affect such physical properties of particle boards as layer density, moduli of rupture and elasticity, internal bond strength, and dimensional stability. These three factors also affect the penetration rate of platen heat to the board center, and rate of temperature rise in the center determines resin polymerization time and, therefore, rate of production. The raw material for the study was clear, 1-inch Rocky Mountain Douglas-fir lumber. Flakes 1/2-inch long by 0.008- inch nominal thickness were produced on a 30-inch laboratory disc flakes. Five percent urea-formaldehyde resin adhesive and water were the only additives used. Boards were made in an electrically heated 15- by 15-inch hydraulic hot press at 290?F. The boards were carefully felted by hand in a 13- by 13-inch deckle box. Aluminum caul plates 3/32-inch thick were used to make the board with nominal thickness of 3/4- inch. During hot pressing, the rate of initial heat penetration to the center of the boards increases as the overall moisture content of the board mat increases and as the initial platen pressure increases. Layer density influences the strength properties of particle boards. High surface moisture content significantly improved modulus of rupture strength. High-initial-pressure cycles and high surface moisture contents developed significantly superior modulus of elasticity. Linear expansion stability improved as press-cycle time at maximum pressure increased.

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