We expect lumber to perform as specified, but the importance of measurement and management of lumber moisture content is seldom understood outside the lumber industry. Sawmills must integrate strict and continuous assessment of lumber moisture at key phases of the manufacturing process in order to optimize the quality of the lumber. Inadequate management of lumber moisture can cost a sawmill operation many hundreds of thousands of dollars per year.
Incoming: Sorting of “Green” Lumber in the Sawmill
Although not done as routinely as it should be, pre-kiln sorting of lumber by moisture (and sometimes total density) can optimize dry kiln schedules for drying lumber. Green sort lumber systems are designed to assess green lumber moisture and/or total density from which decisions can be made regarding which driability category (fast, medium, slow) each piece of lumber belongs in.
There are three distinct advantages of green sorting. First, green lumber sorting allows for accurate categorizing of lumber for kiln drying, which enables kiln operators to more accurately determine drying times. Second, overall drying times can be reduced when green sorting allows all of the fast-drying lumber pieces to be dried together, rather than being mixed with packs of slow-drying lumber. Third, green sorting also decreases the occurrence of drying-related lumber degrade due to over-drying or under-drying. When lumber mills apply green sorting technology at the start of the process, the positive financial benefits begin to accrue almost immediately.
The Drying Process: In-Kiln Moisture Measurement
Lumber quality control (QC) is especially crucial in kiln drying systems. Advanced technology has existed for a number of years that permits kiln operators to place moisture measurement probes inside lumber packages within the kiln. These moisture-sensing probes send real-time moisture data directly to kiln drying control software running on a personal computer, where kiln operators can monitor moisture content in their kilns in real-time. Operators can develop moisture-based drying schedules to allow better quality and more efficient kiln drying, and to better determine the optimum point at which the drying process should stop. In-kiln moisture measurement systems can also reduce the need for manual “hot checks”. In essence, the moisture content management at this drying stage of the process augments the mill’s profitability with enhanced processing efficiency.
Planer Mill: In-Line Moisture Measurement of the Dried Lumber
In-Line moisture measurement systems in the planer mill are the most important tools for capturing moisture data for every piece of lumber, allowing quality control personnel, especially related to kiln drying, to have the critical data to help improve the kiln drying process. Without these systems, mill personnel are very limited in their ability to accurately analyze their drying process.
If moisture tracking is a science, internal lumber processing moisture systems provide the crucial data from which the art of optimum drying can operate.