Abstract:
As lumber producers are faced with a diminished and increasingly expensive raw
material, the need to maximize resource recovery will increase. Trim-ends (particularly
from waned boards) often contain some of the highest quality wood in any given log
and lack functionality only in length. This waste, traditionally chipped for pulp, can be
finger-jointed into lumber if the material can be dried properly for gluing. This research
explores how different length submerchantable pieces dry relative to each other and
merchantable lumber when subjected to typical commercial drying schedules as well as
how trim-ends in two different charge configurations perform in a conventional dry kiln.
Sixteen -foot long, Douglas-fir boards in nominal four, six and eight inch widths
were used to produce simulated trim-ends in 0.5-, 1.0-, 1.5-, 2.0-, 2.5- and 3.5-foot
lengths. Eight-foot-long boards were also dried as a comparison to the simulated trimends.
One course of each width was stacked tight while a second was stacked with a
0.375 inch space between the ends of the blocks. Four charges were dried using United
States Department of Agriculture (USDA) recommended schedules for high and low grade Douglas-fir. Eight by four foot, self stickered aluminum racks with slots
corresponding to each of the sampled widths and a wire-mesh box (random piled),
loaded with actual trim-ends and subjected to the USDA low-grade Douglas-fir
schedule, were compared.
Although it was demonstrated that length affects the final moisture content of
pieces with similar anatomy and initial moisture content, it is not a significant factor in
determining the mean final moisture content of the average charge of short blocks.
Using the methods in this experiment, sorting by length would not be necessary.
Current commercial kiln schedules are likely in appropriate for drying short pieces. An
applicable schedule should be developed using real time moisture content monitoring in
the kiln (i.e. load-cells). Providing a space between blocks can significantly accelerate
the drying rate of fresh lumber and may have a greater effect when combined with an
appropriate kiln schedule. The aluminum racks and the wire-mesh box exhibited
comparable final moisture content deviation when used to dry trim-ends. The space
efficiency of the wire-mesh box was it primary disadvantage and was approximately 63
percent that of the aluminum racks.
