DETERMINING THE SOURCE OF CHANGING SHRINKAGE RATES DURING KILN DRYING∗

∗Patented 5,873,182

ABSTRACT

The conclusions drawn by researchers on the source of changing shrinkage rates are discussed. The objective of this study was to determine the source of changing shrinkage rates early in drying and whether shrinkage would make a useful parameter for an automated kiln control system. In this study, four loads of red oak and one of maple were kiln dried using established schedules Shrinkage of the lumber was continuously recorded, and moisture content and released elastic strain were periodically recorded. The moisture content and strain data showed that the changing shrinkage rates early in drying boards were caused by reduced internal stress levels, not the occurrence 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.

Keywords and Phrases:

• stress reduction
• stress reversal
• peak stress
• moisture content
• automated dry kiln control
• fiber saturation point
• temperature

Notes

∗Patented 5,873,182