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and MCs that are too high or too low. Knife and machine set-up can contribute. Gluing problems, especially end splits, are a result of incorrect MC of the lumber. Planer splits are usually a result of excessively dry lumber. Avoid 180°F dry-bulbs and 50°F depressions. Saw pinching or warp immediately during manufacturing is a result of inadequate stress removal. Warp that does not occur immediately is related to incorrect MCs. Bad odors in dried wood are usually a result of a bacterial infection that originated in the tree. Quality Control Almost all defects can be prevented by proper operation of the dryer, assuming that the equipment is correctly designed and in acceptable operating condition. The key to controlling defects is a quality control program. A good program will identify the cause of degrade (often before the amount of degrade becomes catastrophic), indicate the cost of fixing what is wrong, and indicate the benefit of fixing it. Following up on the benefit of eliminating degrade, it must be appreciated that there is a difference in benefit (or perspective) if the dried lumber is to be sold under conventional grading rules or if the wood will be used in-house. In general, the grading rules do not appreciate the improvements in quality as much as the user will benefit from the quality improvement. For example, with hardwoods, a 12" long end check in an FAS piece of lumber does not, by itself, eliminate a clear 8" x 12' piece of lumber from the FAS grade. Yet the 12" split can easily reduce the useful area of the lumber for a furniture manufacturer by 1/12 or 8%. One way to look at a QC program is to ask the question "If someone stole 5% of your lumber, would you go after him/her (spending time and money) and try to get it back?" Sure, we all would. It is common that drying losses exceed 7%; yet a good operation can limit losses to under 2%. A QC program will go after that 5% or more that is being stolen. The following techniques or procedures can form the basis for a topnotch QC program. Note that most of these techniques are simple to implement, require minimal labor, and can be done "in-house." They are divided into three categories: analyzing the lumber, analyzing the equipment, and operating techniques. Analyzing the Lumber Drying quality control analyses involve assessing the level of degrade after drying. Although one measure of degrade might be the yields when the lumber is cut up into furniture parts or processed into a finished piece, such studies are quite involved and time consuming. 55PDF Image | Principles and Practices of Drying Lumber
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