How Growth Rate Affects Properties of Softwood Veneer

The effects of growth rate on various properties of Douglas-fir and southern pine veneer were evaluated. Shelling occurred most frequently in fast-grown material of both species where springwood was on the surface and summerwood was sloping at about a 7 degree angle, with the rings running out of the surface in the direction of the movement of the block. Very high compression was used to accentuate shelling. In rotary veneer cutting, fast-grown samples of both species with one summer-wood band in the cross section developed deep, S-shaped knife checks in that band. Checks in the slow-grown material were generally limited to the first or second summerwood band. The development of knife checks is apparently related to the compressibility and stiffness across the grain of the veneers. The position and thickness of the summerwood bands in the veneer are critical. Drying specimens were rotary-cut veneer 0.094 inch thick, 1 inch along the grain, and 5 inches wide. They were dried at 80?F. and 30 percent RH. The slow-grown material proved to be less subject to cupping. Standard shear specimens were used to test glue bonds made from exterior phenolic resins. In pine, deep wood failure occurred when springwood was on the surface of the veneer and considerable glue failure when summerwood was on the surface. Specimens containing loosely cut cores resulted in high wood failure for both species. Growth rate was the only factor tested and material used was selected to bring out the extremes. Slow growth is a desirable wood property for softwood veneer logs with a marked contrast between springwood and summerwood.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member