New Kiln Schedule for Presurfaced Oak Lumber

An accelerated kiln schedule, previously developed (FPL 122) for presurfaced northern red oak (Quercus rubra L.) was found satisfactory for 1-inch (25.4 mm) upland white oak (Q. alba L.) but not for cherrybark oak (Q. falcata var. pagodaefolia Ell.) grown on a bottomland site. Surface checking was minimal, 1.84 in./100 in.2 (7.244 cm per 1000 cm2), in the flat-grain portions of white oak but excessive, 11.23 in./100 in.2 (44.213 cm/1000cm2), in cherrybark oak. Internal checking (honeycombing) was minimal, 0.1 in./width in. (0.1 cm/width cm) in both species. Presurfacing involved removal of all saw marks. The accelerated schedule used 115?F (46?C) initial and 120?F (49?C) and 130?F (54.5?C) early intermediate dry-bulb temperatures. Air velocity through the small-scale experimental loads was 375-400 ft./ min. (1.9-2.0 m/sec.). Wet-bulb depressions were conventional, but changes in depression were made on basis of average moisture content of all specimens (essential for kiln automation) and at somewhat higher moisture levels than customary in presently recommended schedules. A modification of the first part of the new schedule to use low, gradually increasing early dry-bulb temperature, (96? to 110?F (35.5? to 43.5?C), a series of smaller-than-normal wet-bulb depressions, and low air velocity, 200 ft./min. (1.0 m/sec.), satisfactorily dried cherrybark oak, with surface checking 1.46 in./100 in.2 (5.748 cm/1000 cm2), but took longer time. On the basis of the previous experiment with northern red oak and the present white oak drying time (15.8 days from 62 to 5 percent moisture content), it is estimated that presurfacing, accelerated schedule, and higher air velocity can reduce commercial drying time of upland red and white oak 25 percent compared with that for rough green oak dried under conventional schedules and air velocity. Two pilot tests toward commercial application are cited. For cherrybark oak, air drying under shed or pile roofs, followed by kiln drying is suggested. A forced-air drying schedule using 85? to 110?F (29.5? to 43.5?C) and air velocity of 600 ft./min. (3.0 m/ sec.) also was successful for the white oak.

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