Schedules for Kiln-Drying White Fir and Hemlock to the Proposed New Standards

Better and more precise kiln schedules are needed for 1-1/2 inch dimension lumber expecially the species Tsuga heterophylla, Abies amabilis, Abies procera, and Abies grandis. These species have a large green moisture content distribution that makes them difficult to kiln dry with little degrade to low moisture contents. Since kiln degrade increases as final moisture content decreases, and since kiln degrade increases with severity of kiln-drying, new ways of drying are needed to lessen degrade. One method is to green chain sort into drying types and another is to use special drying schedules. An equalization period seems to help to achieve more uniform charges, but it takes longer. This is, however, not termed detrimental because a 13 percent increase in kiln space is available due to a decrease in dimension lumber size. Study criteria of new schedules involved kiln residence time, kiln degrade, and moisture uniformity after drying. Moisture uniformity was greatly increased by equalizing, but degrade was not necessarily improved. An intermediate 5-1/2 days drying time with equalizing proved to be the most economical as far as degrade, time, and uniform moisture content were concerned.

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