Description:
Eighteen-hundred grand fir (Abies grandis) studs, curve sawn from small-diameter [approximately 4-7 inches (102-178 mm)] sawlogs, were kiln dried to determine effects
of drying schedule and restraint on energy consumption, drying time, and warp (bow,
crook, and twist). The experimental design included 18 kiln charges with three replications
of three kiln schedules. Nine of the kiln charges were restrained and nine were
unrestrained. Kiln schedules were high-temperature [240/ F (116/ C) dry bulb with no
venting or steam spray], elevated [190-220/ F (88-104/ C) dry bulb and 190-165/ F (88-
74/ C) wet bulb], and conventional [180/ F (82/ C) dry bulb and 170-145/ F (77-63/ C) wet
bulb]. Restraint loading was 200 pounds per square foot (psf) (976 kg/m2).
Results showed that the high-temperature schedule consumed approximately one-third
and one-half of the energy of the elevated and conventional schedules, respectively. In
addition, drying time averaged 21.1 hours with the high-temperature schedule, 42.0 hours
with the elevated schedule, and 50.3 hours with the conventional schedule. Although
there were several significant differences in bow, crook, and twist in lumber dried by the
three schedules, no schedule showed significantly lower warp. Results also showed that
restraint reduced warp in lumber in the high-temperature and elevated schedules, and
much of the warp reduction was in lumber within the top six courses of the stack. In
addition, restraint reduced the variance of warp in lumber dried by all three schedules.