Characterizing veneer roughness and glue-bond performance in Douglas-fir plywood Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/nc580q36r

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  • A changing raw material supply and smaller, generally lower quality peeler logs, are causing surface characteristics in veneer that can adversely affect glue-bond performance. When lower quality logs are peeled, rougher veneer is usually produced. The typical response by plywood manufacturers is to increase adhesive spread when using rough veneer. The effectiveness of increasing adhesive spread rates has not been quantified. To do so, a method to quantify roughness is needed so that it can be correlated with percent wood failure, the standard for defining glue-bond quality. The objectives of this research were to define the relationships between seven traditional 2- dimensional measures of surface roughness and glue-bond performance in order to determine if a measure or combination of measures could be used to develop a glue-bond performance prediction model. Rotary peeled, 1/8 inch thick Douglas-fir veneer was visually categorized as being smooth, intermediate, or rough. Samples on each sheet were selected at random and their locations tracked throughout the study. The surface roughness of each sample was measured on the tight and loose sides using a modified laser scatter/optical imaging system. The scanning data were used to calculate seven roughness measures. Three-ply plywood panels were manufactured using the measured samples as core material and smooth veneer as face and back plys. Each panel was cut into standard shear specimens according to U. S. Product Standard 1-95. The test area for each shear specimen was the measured sample selected prior to panel assembly. The shear specimens were tested and evaluated for load at failure and percent wood failure. Each of the roughness measures and visual categories were compared to load at failure and percent wood failure data. Each shear specimen was also examined to determine the nature of the failure and with the failure being categorized into one of seven types. Analysis of variance and multiple linear regression tests indicated no statistically significant relationship between any of the seven roughness measures or combination of measures and load at failure or percent wood failure. There was also no significant difference in roughness between the tight and loose side of the veneer, except for the skewness, kurtosis, and 3rd highest peak measures. Analysis of the visual categories showed there was strong evidence that an increase in surface roughness was associated with a decrease in load at failure and percent wood failure. This indicates that a 3- dimensional measure of surface roughness may be more effective for modeling glue-bond performance. Analysis of the nature of failure data indicated that the samples tended to fail on the loose side of the veneer. This trend was noted across all roughness categories. It is believed that this may be associated with lathe check depth and that an interaction between lathe check depth and veneer roughness may determine glue-bond performance.
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