Wood Particle Molding

Some 8-1/2 million pounds of resin and ten times this weight of ground wood were used in 1955 to mold products such as toilet seats, croquet balls, shuffle-board discs, women’s shoe heels, buttons, and furniture parts. These figures do not include panel boards. The process of mixing particles of wood with an adhesive (powdered phenol-formaldehyde resin) and pressing the mixture in a heated mold until the adhesive is cured, offers the wood industry a new outlet for wood byproducts. The product must have a shape that is reasonably flat, does not have abrupt changes in cross-section, and does not have large thin areas. Any savings resulting from the molding process, when compared to solid wood, must come from the labor costs required to produce the molded product. A large, continuous volume of identical parts is required to justify the investment in molding equipment, which the author estimates to be $60,000. Power consumption is estimated to be 6 HP (boiler with 120-150 psi steam) and 30 HP electricity. If the operation is large enough, the cost of molding the part will be 1/3 to 2/3 the cost of a solid wood part. The flexural strength of the molded-wood part is about 5 times the strength of cross-grain yellow birch and about 1/3 the strength of birch along the grain. Screw-holding ability of molded wood is equivalent to yellow pine or fir. Its weight is about 50 percent greater than dry maple; water-absorption rate is 10-50 percent that of dry wood. Molded parts should be sanded prior to finishing to improve coating adhesion or a special primer may be used.

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