Free-close Molding Versus Molding to Stops in Wood-resin Blend Processing
Charles J. Gatchell · Bruce G. Heebink
Jan 1965 · U.S. Department of Agriculture, Forest Service Forest Products Laboratory
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The influence of the manner and degree of compression on some physical and mechanical properties of molded wood-resin blends was studied. Yellow birch (Betula alleghaniensis) and Douglas-fir (Pseudotsuga menziesii var. menziesii) particles, processed from .015-inch by 1-inch flakes, were used. Blends were made with two particle sizes (20-40 and 40-80) and three powdered phenolic resin contents (6, 12, and 18 percent). These blends were compressed with two different procedures: (1) A linear application of pressure to 1,000 pounds per square inch in 2 minutes; (2) A linear deformation of the wood-resin mat to 3/16-inch stops in 2 minutes. The properties evaluated were modulus of rupture, modulus of elasticity, dimensional stability, water absorption, and "flow." Flow was considered to be the ability of a blend to move in directions at right angles to an applied force. A method for evaluating such flow is described that can be used for wood-resin blends that normally exhibit little or no real flow properties. Toward the upper limit of the compressive range, the degree of compression is more important than the manner (rate) of compression. Along with resin content, the degree of compression controls the formation of glue bonds which, in turn, control the properties of the molded product. The primary importance of species and particle size is in the influence of these variables on effective mat compression.
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