Kiln Drying of Southern Pine Poles: Results of Laboratory and Field Studies

Accelerated schedules of constant dry-bulb temperatures of 160?F. to 225?F. and constant wet-bulb depressions of 40 to 50 degrees were used to dry southern pine poles in a laboratory kiln. A schedule with a constant dry-bulb temperature of 165?F. and a wet-bulb temperature of 120?F. was used to dry southern pine poles in commercial kilns at cooperating plants. Poles were dried to :a moisture content of 25 to 35 percent in the outer 3-inch zone. Charges dried in the laboratory kiln at dry-bulb temperatures of 225, 212, and 160?F. required 44, 66, and 90 hours, respectively, to reach 30 percent moisture content, compared to 177 hours required by a conventional pole schedule. Modulus of rupture of clear wood samples of poles dried at 225?F. was reduced by 14 percent compared to control samples. Strength of clear wood from poles dried at 212?F. was not significantly affected. Internal temperatures of poles dried at 212? and 225?F. approximately equaled the average of the dry-bulb and wet-bulb temperatures of the drying environment, although they did increase slowly as drying progressed. Poles dried by the accelerated schedules checked in a fashion comparable to poles dried by the conventional schedule. Poles dried by the accelerated schedule received an average retention of about 17 lbs./cu.ft. and above standard penetration when treated with a commercial creosote load designed for 10 lbs./cu.ft. retention. Commercial kiln charges were dried by the accelerated schedule in 44 to 94 hours compared to 168 hours required by conventional schedules. Poles so dried had acceptable checking patterns and were adequately treated with creosote, pentachlorophenol, and CCA type preservatives. Cooperating plants are currently using accelerated schedules.

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