Sorting Aspen Bolts and Drying Aspen Flitches for SDR

--Log sorting is necessary when processing aspen saw-dry-rip (SDR) to select optimum log diameter and to minimize number of logs with dark-colored centers. Wetwood, which is difficult to dry, is commonly associated with these dark centers. SDR processing involves drying 7/4to 8/4-thick live-sawn flitches. Drying the flitch and then sawing studs produces straighter studs than sawing first and drying in stud form. High-temperature kiln drying (230oF to 240oF) has given good results with several species (such as, basswood and yellow-poplar). For species likely to contain wetwood (aspen, cottonwood, willow), high-temperature drying is not recommended. A kiln schedule for aspen with maximum temperatures of 190oF to 200oF followed by equalizing at 12 percent EMC is suggested. SORTING ASPEN BOLTS Sorting of logs or bolts is necessary when processing aspen for the saw-dry-rip (SDR) process for two reasons: (1) to select optimum log diameter and (2) to minimize the number of logs with dark-colored centers or hearts. We must sort for size because we have found that logs with diameters from 7 to 14 in. produce the straightest pieces when manufactured by the SDR process. Logs smaller than 7 in. are not usually profitable to saw, and those that are much larger have large knots, more decay, and increased cross grain and thus give poorer results than those in the 7to 14-in. category. Sorting to minimize the number of logs with dark-colored centers is necessary because this dark-colored wood usually is associated with or contains “wetwood” and is difficult to dry. This sorting is related specifically to aspen and not to the SDR process. Aspen has a reputation for being difficult to dry. This is usually due to the presence of wetwood or wet streaks, which in turn are associated with the darker brown or black wood near the center of the log. White bright aspen sapwood or normal heartwood containing no wetwood is datively easy to dry. Several other species, including cottonwood and willow, frequently have streaks or pockets of wetwood that present various drying problems. 1R. Sidney Boone, Research Forest Products Technologist, U.S. Department of Agriculture, Forest Service, Forest Products Laboratoy, Madison, Wisconsin 53705-2398. The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright. In: Adams, Roy D., ed. Proceedings of aspen symposium ’89; 295 1989 July 25-27; Duluth, MN. Gen. Tech. Rep. NC-140. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station; 1990: 295-299.