The Value of Presteaming for Drying Some Collapse-Susceptible Eucalypts

The effect of presteaming at 212?F under saturated conditions on drying rate of 1-inch thick stock lumber was examined. The samples used were 6 feet long and 4- to 9-inches wide from head and butt logs of ash-type Eucalypts grown in Australia. Reductions in drying time of from 20 to 35 percent of that required for unsteamed material was obtained by presteaming green material for 2 hours. A total of up to 40 percent reduction in drying time was possible by a combination of presteaming and prestressing. Treatments longer than 6 hours (6, 12, 24, or 48 hours) failed to effect any further improvement in drying rate but tended to accentuate collapse. Presteaming increased total shrinkage during drying, reduced intensity of checking, and caused slight discoloration to the wood. No undesirable color effect should be expected if pretreatment is kept short. Statistical analysis failed to reveal any significant effect on strength for 2-hour presteamed Eucalyptus oblique. Tests conducted were static bending, impact, and compression paralled to the grain. A recommended procedure of 2-hour presteaming (not exceeding 4 hours for heating up and treatment) at 212?F has been formulated for 1- to 2-inch thick green lumber similar to ash-type eucalypts studied. It has been concluded that an estimated saving of $278,000 per year could result by introduction of presteaming in Australia.

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