Kiln-drying maple structural lumber from log heavy cants

Structural lumber products an traditionally manufactured from softwoods. However, with shrinking supplies of softwood lumber and abundant supplies of hardwood lumber, there is increasing interest in the use of hardwoods for structural applications. One factor that will be important in both the technical and economic feasibility of using hardwoods for structural lumber is drying. This study investigated the feasibility of using accelerated kiln schedules in drying maple lumber for structural uses. Traditionally, kiln schedules for maple lumber intended for appearance products were developed so that surface checking or discoloration would not develop. However, these are not degrading features in structural lumber so it is not necessary to use conservative and slow kiln schedules. In this study, maple lumber was dried in a laboratory-scale kiln in a series of incrementally more severe schedules. The result was that even the most severe, thus the most efficient, schedule caused no more structural grade loss than did the mildest schedule. This will make a positive contribution to the economics of structural applications for hardwood lumber. Using a computer simulation based on the drying time in the laboratory-scale kiln, the drying time of hard maple from 60 to 19 percent moisture content in a commercial-sized kin was estimated to be about 4 days.