Plywood Used in Containers

Most plywood for packaging purposes is procured under some type of specification. The specification may be federal or military in origin, calling either for flat panel or Container Grade plywood. In many instances, however, plywood for packaging is procured under the Commercial Standards for the industry. In general, there is little conflict between government specifications for flat panel plywood and industry practice in as much as the former frequently incorporate the Commercial Standards directly. However, government specifications for Container Grade plywood have frequently been in conflict with the Commercial Standards. Such conflicts arise basically from the desire of the specifier for plywood that will be suitable for containers, and the desire of the plywood manufacturer to utilize his veneer most efficiently, and to avoid all possible confusion in his operation. The important factors relating to plywood manufacture covered by both the Commercial Standards and the container specifications include type of glue bond and grade of veneer. Other miscellaneous manufacturing details are also covered, such as size tolerances and moisture content. A comparison of requirements for the waterproof plywood shows that all the specifications require that shear specimens pass a boil-bake-boil cycle without delamination. The Commercial Standards require in addition a cold soak and. drying cycle without delamination. Because containers may be subjected to conditions conducive to mold growth in the plywood glueline, the container specifications call for addition of 5 percent chlorinated phenols or their sodium salts. Container Grade plywood can be produced by the normal fir plywood mill without altering routine procedure. However, the grade of the veneer requires a classification separate from the ordinary Commercial Standard grade. The increase in permissible knothole size to 2-l/2 inches made under NN-P-515 has removed a primary objection to this specification by the manufacturers of Douglas-fir and western softwood plywood, as this size knothole coincides with the maximum limit set for D grade veneer under CS45 and 122. The other restriction in NN-P-515 regarding size of knots and permissible defects within a 12-inch circle cause little or no difficulty with normal D grade veneer. The same holds true of permissible sizes of work or borer holes, as well as pitch or bark pockets. The requirements for splits, gaps and open joints differ between NN-P-515 and CS45. The former permits gaps up to 3/16 inch in the faces, while those in the inner plies can range up to l/2 inch with limitations on their frequency.

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