Equalizing and conditioning spruce-pine-subalpine fir lumber

Problems associated with grade recovery in spruce-pine-subalpine fir (SPF) lumber drying have been largely attributed to the wide variation in final moisture content (MC) distribution and drying stresses. Grade recovery is largely affected during planing and re-manufacturing because of the development of warp that results from drying stresses. Over 10 sawmills in the interior of British Columbia and Alberta were surveyed. The results indicated that the SPF lumber drying problems related to uneven final MC distribution and warp during re-manufacturing still exist and affect grade recovery. Sixteen kiln-drying runs, using Forintek?s experimental 3-foot kiln, were performed using different combinations of 3, 6, 9, and 12 hours of equalizing and conditioning with two types of humidification systems (cold water and low-pressure steam). Initial MC, final MC, and drying stresses were evaluated for drying each run. In general, 9 to 12-hour equalizing/conditioning treatment can significantly reduce the amount of over-dried lumber as well as reduce internal stresses.

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