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Operating a Lumber Dryer There are many techniques for operating a dryer that must be used to assure high quality and efficient operation. Many of these techniques, such as how to insert and use moisture probes for moisture content measurement, are mentioned in other chapters. This discussion is meant to provide, from a wood standpoint, how to operate a dryer. Log Handling and Storage Logs should be handled correctly if drying degrade is to be controlled. Specifically, logs should be end coated. If not, then end checks will develop in the logs and these checks will develop into serious end splitting degrade as the lumber is dried. Checks do not get better when lumber is dried; they get worse. In studies done by Virginia Tech on red oak, end coating reduced end splits in 5/4 lumber to zero in 75% of the pieces. The lumber was predried and then kiln dried conventionally. Logs that are stored in ponds can also develop degrade, including bacterial infections, which make the lumber much more likely to check and honeycomb. Logs stored in warm weather, even when sprinkled with water, can develop the precursors for chemical stains, making staining of the lumber during drying inevitable. Stacking Lumber must be stacked immediately for drying if the risk of staining is to be minimized. Fungicides will prevent some damage, but chemical stains can still occur. Stickers must be properly aligned, in line with the stickers directly above and below. Bolsters must be in alignment and under every sticker. Foundations must be flat. Preparing and Selecting Samples The key to successful drying is accurately knowing the MC of the lumber in the dryer. The following procedure has been developed after decades of experience. There are no shortcuts. In order to measure the moisture content of lumber during drying, it is impractical to weigh every board in the dryer. Therefore, we use the sample board method to estimate the moisture of the lumber in the kiln. This method uses short, carefully chosen sample boards sawn from larger pieces of lumber. These samples boards are weighed periodically and their moisture contents are calculated. Generally, because the wettest lumber in the kiln has the highest risk of degrade development, most of the sample boards should represent the wettest lumber in the dryer; this means the lumber that is the most recently cut, is the widest and thickest, contains the heartwood, and is quartersawn. To avoid overdrying, a sample or two should also be taken from 34PDF Image | Principles and Practices of Drying Lumber
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