Adin Berberovic at OSU completed a thesis last year in which the factors affecting hemlock drying were studied. Mills often presort based on initial MC (or weight) but other work in the past suggests that the wettest heaviest boards going in are not the wettest boards coming out. We were looking for some other measurable wood factor that causes boards to reach the final moisture content at different times. Then, instead of sorting based on weight or initial moisture content, one could sort on expected drying time.
Dr. Berberovic dried matched samples at 220F and 180F. Each board was continuously weighed during drying. Basic density, initial moisture content, percentage of heartwood, position of heartwood within a board, ring count, rings from the pith, growth ring angle, and earlywood and latewood coverage on board faces were measured on each board. At the lower temperature basic density, initial moisture content, heartwood percentage, and growth ring angle affected the drying rate. At high temperature, only the initial moisture content affected the drying rate. Modeling with both the drying rate and initial moisture contents suggests that sorting based on both specific gravity and initial moisture content reduces final moisture content variability better than sorting on any one criterion.
The complete thesis is available at http://ir.library.oregonstate.edu/xmlui/handle/1957/17702
A shorter publication will be out later this year.Linkback: http://www.kilndrying.org/moisture-variability/4/causes-of-variability-in-hemlock/259/