Process for Straightening and Drying Southern Pine 2 By 4’s in 24 Hours

The objective was development of a process for steam straightening and drying (in 24 hours) 8-foot studs cut from small southern pine logs as well as from veneer cores. Drying schedules used were: 1) low-temperature long schedule with studs conventionally stacked, and 2) high-temperature 24-hour schedule with studs restrained against warp. In the 24-hour, high-temperature schedule, green lumber was clamped rigidly in aluminum frames. The studs were then wheeled into the preheated kiln and dried for 21 hours at a dry-bulb temperature of 240?F. and a wet-bulb temperature of 160?F. For the last 3 hours they were steamed at a dry-bulb temperature of 195?F. and a wet-bulb temperature of 185?F. Throughout the 24 hours, air was cross circulated at 1,000 f.p.m.; direction of air flow was reversed every 75 minutes. With the schedule completed, the studs were wheeled from the kiln and cooled 48 hours in an atmosphere that ranged from 70 to 80?F. and 40- to 60-percent relative humidity. Lumber dried at low temperature was not restrained in clamps, but was piled on sticks in the conventional manner. The low-temperature schedule (approximately 110 hours in duration) was patterned after schedule T12-05 from Rasmussen (1961); dry-bulb temperature did not exceed 180?F. Air velocity was 500 f.p.m. with fan reversal every 75 minutes. Both kiln schedules brought the lumber to about 10-percent moisture content. Grade yields were assigned after planing to 1-1/2 by 3-9/16 inches. Eight-foot 2 by 4’s dried at high temperature under total mechanical restraint and then planed had substantially less warp than those stacked conventionally and dried at low temperature. Reductions in MOE, proportional limit, MOR and toughness caused by the high-temperature schedule did not prove statistically significant (0.05 level); however, larger scale tests would probably indicate slight reductions in strength properties of log-run 2 by 4’s compared to schedules that do not exceed 180F. Studs from the veneer cores in this sample were stronger and of higher grade than those cut from small logs. The high-temperature drying schedule consumed less than one-fourth the time and only about one-half the energy required by the low-temperature schedule.

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