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usually takes place for hardwoods in order to decrease the variation in moisture content (Lamb, 1990). This procedure contributes to fewer problems related to wide variations of moisture content. Milota & Smith (1994) mention that hardwoods, due to their higher density and consequently greater shrinkage during drying, are. more susceptible to defects such as collapse, honeycomb and surface checking compared to softwoods. Hardwood operations appeared to be facing more problems with respect to all three defects than softwood producers. Honeycomb was found to be significantly more important in drying hardwoods compared to softwoods (mean value 2.9 versus 1.9). This difference may be partially attributed to the greater difficulty with which water moves inside hardwoods. Honeycomb will be prevented if the board core has a moisture content below the fibre saturation point when the temperature is raised. As a result, pre-drying or seasoning can reduce honeycomb problems (Ward & Simpson, 1997). Surface checking was significantly more important for companies that dried hardwoods (mean value 3.4 compared to 2.5 for softwoods and 2.3 for both softwoods and hardwoods). Since appearance is more important for hardwoods, it makes sense that surface checking should be of more concern. Moreover, hardwood lumber constitutes a higher value material compared to softwood lumber and this can also justify companies' concerns about surface checking. Milota & Smith (1994) state that the main focus in hardwood operations is on product quality, which differs from softwood operations that focus on production volume. They also mention that surface checking is more acceptable in softwoods than in hardwoods. Milota & Smith (1994) remark that a major difference with regards to kiln controls between softwoods and hardwoods is that, in the case of the former, time-based control is used, while for the latter, monitoring of moisture content is commonly practiced. In the case of hardwoods, moisture content needs to be measured continuously, while for softwoods it is sufficient to measure it at the end of the drying 89PDF Image | KILN DRYING PROBLEMS AND ISSUES IN CANADA
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