Controlling microwave heating and its effect on the properties of wood

Sammanfattning: Drying wood with microwave energy is not so common, but could be a complement to conventional air circulation drying due to the possibility of drying wood faster than with conventional drying methods with preserved quality. An industrial-scale, on-line microwave drier for wood components is under development at the Division of Wood Physics. This drier will be mainly used for demonstrations, product testing and for students? laboratory work. The purpose of the present work was to study the drying of wood by microwave heating and to investigate whether the method affects the properties of wood. The aim was also to ascertain how to adjust the design of a microwave construction for industrial use. Testing of the mechanical properties of the wood showed no difference in bending strength in comparison with the conventional air-circulation method. Nor did testing of wood hardness (Janka) show any significant difference between the drying methods and the temperature level during microwave drying. Furthermore, when using the microwave drying method, the infrared (IR) images showed that it is very important to control microwave heating and to move the components during the drying process in order to achieve more uniform heating and avoid thermal runaway at the end of the process. This runaway effect can negatively affect the mechanical properties of the wood.