This second report for project entitled “Reduction in Folded strands to Improve OSB Properties” contains studies of flaking yellow birch to reduce strand folding plus additional studies carried out on aspen to further understand the basic mechanisms of strand folding.
In this report, the impacts of wood temperature and counter knife angle were investigated. The effect of flaking parameters on strand tensile strength, flaking energy and strand size distribution was also investigated. Different ways to reduce strand folding were tested, including: flaking birch wood with different knife projections and with different knife clearance angles, drying strands at different temperatures; longitudinal flaking at different rake angles, microbevel angles and different strand lengths. In addition basic flaking studies were carried out to evaluate tangential flaking of aspen wood from different locations with different moisture contents, different counter knife thicknesses and different tilt angles. Strands with different curl indexes were correlated with panel performance in order to study the impact of strand folding on panel properties.
A key finding was that birch strands were more liable to yield folded strands compared to aspen strands. Counter knife angles of 78° and wood temperature of 21°C tended to yield the lowest birch strand folding. Increasing strand thickness and decreasing knife clearance angle decreased the folding of both birch and aspen. Flaking birch strands with a large rake angle and microbevel reduced strand folding.
Strand folding was also dependent on strand drying temperature and strander knife clearance angle. Drying wood at different temperatures resulted in different levels of strand folding. The impact varied among wood species with birch being more prone to folding than aspen.
Longitudinally flaking birch strands shows that an increase of strand length increased strand curl.
Among the following variables, changing wood moisture content, changing the distance between counter knife edge to strand knife edge (edge distance), adjusting strand drying temperature, adjusting knife sharpness angle, and adjusting rake angle, increasing rake angle was the most effective way to reduce strand folding. The effect of wood drying temperature is worthy of further investigation.
Making panels with furnish containing large amounts of folded strands resulted in panel delamination or low IB. Further investigation of the relationships between strand folding and panel properties is needed to develop a more complete understanding of the full impact of strand folding.
These studies indicated that by combining higher wood temperature, larger counter knife angle and larger rake angle with certain microbevel, it will be possible to reduce strand folding, fines and energy consumption.