| Summary: | To minimize resin consumption in the manufacture of oriented strand board, while
maintaining the mechanical properties of the finished product, several factors must be optimized.
The focus of this work is to answer the following questions: what is the optimum droplet
diameter and dot-pitch (distance between droplet centres), and how should the rotary drum
blender be operated to achieve this? This work examines the effect of droplet diameter and dotpitch
on the Mode I fracture toughness of a discontinuous adhesive bond and presents
preliminary results on the blending dynamics of oriented strand board.
The major conclusions from the work are that the fracture toughness appears to increase
linearly with resin droplet diameter and with the square root of bonded area, a finding that is
supported by an analytical model. Furthermore, the study shows that the fracture toughness is
not strongly dependent on the amount of resin applied. Therefore, by modifying the droplet
diameter and dot-pitch it should be possible to maintain the current mechanical properties of the
board with reduced resin consumption. Since the bond fails in the substrate, a similar square root
relationship between the retention of solid wood fracture toughness by the discontinuous bond
and the area of solid wood failure is postulated and confirmed. A minimum ratio of bonded area
to total area of 0.3 is suggested, below which the bond does not form. To determine the above
results a modified flexographic printing technique was used to deposit resin droplets of known
size and spacing. The mass of resin applied was relatively constant, however, the mass applied
is affected by resin viscosity, relative humidity and substrate moisture content.
The preliminary work on blending examines the effect of blender rotation speed and
drum-wall friction on the tumbling behaviour of strands. Increasing the rotation speed causes the
strands to pass through various tumbling regimes, from sliding to centrifuging. Experiments on
drum-wall friction show the necessity of flights. Initial models in the area ignore the effect of
friction, which limits their usefulness. === Applied Science, Faculty of === Materials Engineering, Department of === Graduate
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