Veneer Mechanical Grading Based on Online Local Wood Fiber Orientation Measurements to Model and Manufacture Stiffness Optimized Structural Beams

Abstract

Grading veneer for plywood manufacturing is often performed on line using visual criteria issued from EN 635-3 standard. For mechanical applications, the only visual criteria can be not sharp enough to accurately grade veneers as it was noted in the literature for sawmill industry. For logs with a high variability and heterogeneity, the transformation in LVL (laminated veneer lumber) product can be a good valorisation if the veneer grading is efficient. This article presents a new methodology to measure in process the local fiber orientation of a peeled veneer using tracheid effect on a specific apparatus. This device called LOOBAR for Local Online Orientation fiBer AnalyseR, is composed of 4 cameras and a beam supporting 50 red-dot lasers disposed above the peeling lath conveyers allowing for grain angle surface scanning on the ribbon or each veneer if located after the clipper. This field data, put together with the veneer global density, allow for modeling accurately the local elastic properties of each veneer produced to sort them and latter on, to optimize the mechanical properties of a composed engineering wood product such as LVL by adapting the local beam stiffness to the desired purpose. This article presents the results of LVL beams manufacturing and characterization using computed local stiffness to sort veneers. Veneer grading using ther local longitudinal modulus of elasticity and EN635-3 method are compared. The pertinence of the local fiber orientation usage to estimate mechanical veneer properties appears clearly. This approach opens important perspectives using local density and grain angle to sort heterogeneous veneers.