Technical Considerations for Manufacturing Southern Pine Plywood

Technical information obtained from a survey of studies and observations at commercial plants indicated that veneer logs with uniformly slow growth are preferable to fast-grown stock. Compression wood should be avoided for southern pine veneer. Select logs with a well centered pith. Log diameters from 16 to 20 inches are very good for plywood. Some efficient plants can economically go as low as 11 or 12 inches. A proper understanding of softwood veneer grades is essential to get an adequate picture of the grades of logs required for veneer and plywood production. A sheathing grade product should be given major consideration due to problems of face checking, grain raising, and paintability. Heating logs to 150 to 180?F. is necessary for good cutting, and to reduce roughness and deep knife checks. Overheating causes end checks in bolts and curled, stiff, and unmanageable veneer. Recommended veneer thicknesses are 1/10, 1/8, and 3/16 inch with a 5-1/2 inch core diameter. Commercial plywood plants should concentrate on two thicknesses. A moderate drying temperature such as 300?F. is recommended to minimize bucking and splitting. Minimum size plant would produce 30 to 36 million square feet of 3/8 inch plywood per year. It would require 12 to 15 million board feet of logs per year. This estimate is based on an average conversion factor of 2.4, i.e. 1 board foot of log scale will yield 2.4 square feet of 3/8 inch plywood.

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