Determining the source of changing shrinkage rates during kiln drying

The conclusions drawn by researchers on the source of changing shrinkage ra tes are discussed. The objective of this study was to determine the source of changing shrinkage rates early in drying and whether shrinkage would mak e a useful parameter for an automated kiln control system. In this study, f our loads of red oak and one of maple were kiln dried using established sch edules. Shrinkage of the lumber was continuously recorded, and moisture con tent and released elastic strain were periodically recorded. The moisture c ontent and strain data showed that the changing shrinkage rates early in dr ying boards were caused by reduced internal stress levels, not the occurren ce of fiber saturation point or temperature as reported by some. Results of this study indicate it may be possible to develop an automated kiln system using shrinkage as the controlling parameter. This would reduce the drying time while avoiding additional drying defects.