WHY IS WOOD DRYING SO DIFFICULT?
Drying is difficult to manage because the process includes many variables
which are difficult to measure.
The behaviour of wood during drying varies with many fundamental wood properties.
For example, the variation in density and grain angle in stems of plantation
grown softwoods is reflected in moisture content and distortion results
after drying. This is due in part to the difficulty in managing these stem
based variations through a batch process such as kiln drying.
Where operations include more than one species and/or the material being
processed is prone to drying defects, managing the variation imposed by
wood properties is increasingly difficult.
Modern drying processes can assist in controlling the affect of variation
in wood properties. Additional control is attained by pre-sorting of material
prior to kiln drying so that batches are relatively homogenous with respect
to wood properties. While this appears obvious, systems for measuring green
wood properties in the mill and dealing with variation are not well developed.
Consequently, the best drying systems are usually characterised by a homogenous
resource and careful production management.
The hardware that comprises a drying process is complex and expensive.
Drying kilns should provide a consistent drying environment that can be
varied precisely according to a drying schedule. This is difficult as the
drying environment is dynamic, expensive to maintain and varies considerably
with small performance changes in the many 'moving parts'.
Development of softwood drying in the past 20 years has resulted in quantum leaps in productivity. Current research is making drying systems more precise and complex. Access to developing technology is critical to a successful business.
