Density determination of tropical hardwoods with the Resistograph

Abstract

This research focused on the question whether it is possible to predict the density of tropical hardwoods with acceptable accuracy based on drill resistance measurements. To assess the feasibility, the influence of the characteristics of the drill resistance measurement tool; the Resistograph® and the wood species have been investigated. With respect to the measurement tool, drill sharpness, feed speed and rotation rate were examined. For the wood samples, the influence of extractives, moisture content, drill direction and density were investigated. It was found that the influence of drill sharpness cannot be ignored and a calibration procedure was developed. No significant difference in drill resistance was observed between drilling in radial and tangential directions; however, drilling in the longitudinal direction resulted in a significant higher drill resistance. Moisture content influences the drill resistance; however, the effect is small and not statistically significant, it can usually be ignored. The influence of extractives on the drill resistance most likely depends not only on the mass fraction of extractives but also on the sort and the composition of the cell wall. Meranti has a typical density within the range 350 to 860 kg/m3. With an appropriate calibration procedure, it is possible to predict the density of meranti with 95% confidence to an accuracy of ± 70 kg/m3