Ultrasound evaluation of lathe check depth in birch veneer

Abstract

In this study, the lathe checks in birch veneer were examined with contact ultrasound and a preliminary study for the measurement with air-coupled ultrasound from green birch veneer (moisture content 60–75%) was carried out. The contact measurements were conducted from dry veneer and then from moistened veneer. Several ultrasound parameters measured from dry veneers were related with lathe check depth, e.g. correlation between ultrasound transit time and lathe check depth was 0.63 (p<0.001, N=30) when measuring perpendicular to grain from unchecked face of the veneer. The same correlation for moistened veneers was 0.74 (p <0.01, N=12). Furthermore, air-coupled reflection and through-transmission measurements were carried out with green veneer samples. In air-coupled through-transmission measurements, it seemed that moisture content dominated the measurement when measuring parallel to checks. There was also positive correlation between energy-related parameters in through-transmission and reflection measurement, which could be utilised to measure the properties of veneer with transducers on one side.