Evaluation of the arrangement of wood strands at the surface of OSB by image analysis

Abstract

The objective of this paper is to evaluate the arrangement of wood strands at the surface of oriented strand board (OSB) by image analysis. Two-dimensional image analysis enables the number of strands and the area of each strand to be computed. In addition, the fiber direction of each strand may be measured manually by recording the acute angle between the fiber direction and the longitudinal axis of the specimen. The image analysis results suggest the following: the average strand area is proportional to the reciprocal of the number of strands. Samples containing many smaller strands exhibit a larger variation in strand size. The average strand area does not correlate with the distribution of the strand area represented by the coefficient of variation. However, there is a reasonable correlation between the number of smaller strands in the range 0 to 1 cm2 and the coefficient of variation of strand area. At low average fiber orientations, i.e. better orientation with the principal panel axis, there is smaller variability in orientation. The upper side and lower side of OSB exhibit a different relationship between average fiber orientation and strand area. The upper side of the specimens contains larger strands and exhibits better fiber orientation than the lower side. This is thought to be a function of the production process. The lower side strands fall on a smooth moving substrate, whereas the upper side strands fall on a stable substrate of strands. The number of strands is lower on the upper side of the OSB panel because small size strands tend to migrate to the lower side of the OSB during production. The small particles tend to be vibrated through the strand mat to the lower face before pressing.