A new green veneer moisture measurement method was developed based on the principle of light transmission. Compared to current radio frequency (RF) moisture measurement, the new method shows improved accuracy in green veneer MC detection for regular softwood veneer. As well, an off-line portable veneer testing system was developed based on the light transmission, which was successfully used in the mill trials to evaluate the accuracy of current green veneer moisture sorting. Meanwhile, a laboratory dry veneer moisture measuring system was successfully modified to measure the variation of dry veneer MC. Further a pilot-scale veneer dryer was upgraded to simulate the mill drying conditions. These developments ensure us to promptly transfer the technologies to the industry.
The effect of drying temperature, air flow velocity and air humidity on dry veneer final MC was investigated. It was found that drying at high temperature was faster than at the low temperature. The difference in final MC between low temperature drying and high temperature drying was greater when the initial MC was higher. However, the variation of final MC was smaller with low temperature drying compared to high temperature drying. The effect of air velocity was more apparent when the initial veneer MC was higher. When the initial veneer MC was below 70-80%, the effect of air velocity on veneer drying was very small, which may indicate that for heart veneer drying, the velocity was not a dominant factor whereas for sap and light-sap veneer drying, the air velocity played a significant role. In general, the effect of air humidity on veneer drying was drying temperature dependent. At low drying temperature, low humidity helped veneer drying. In contrast, at a drying temperature higher than 150 °C, the effect of air humidity on veneer drying rate was not significant. However, to improve the veneer drying quality and material recovery, high humidity could be used to reduce veneer brittleness for easy handling.
During stacking period, the moisture spread from the wet area to the dry area. The variation of MC between and within veneer decreased with the stacking time before reaching an equilibrium state. The equilibrium MC depended on the initial MC of veneer and stacking conditions. Compared to lower temperature stacking, the higher temperature stacking accelerated the moisture spread. Therefore, the allowable maximum MC of wet spot on veneer before stacking could be determined based on target dry veneer MC, ambient temperature (season) and stacking time.
A hot stacking model was developed to simulate the change of veneer MC during hot stacking. The prediction results agreed well with the experimental results. This model will be incorporated into the existing VDry models to simulate the effect of post-drying on final veneer MC.
It is recommended that the light green veneer moisture scanner should be further developed for industrial applications. The VDry model is a useful tool which should be applied for mill customization and optimization.