ESTIMATION OF THE MOISTURE-CONTENT OF LUMBER BY MEASURING DENSITY

A method of measuring the moisture content (MC) of lumber was examined for the purpose of quality control, especially moisture control of the lumber. The method is based on the relationship between the density and MC of wood expressed by Equation (2) and (3). The species used in this study were ezomatsu (Picea jezoensis Carriere) and todomatsu (Abies sachalinensis Masters). The following results were obtained: 1) This method has the potential to be employed for the measurement of MC of lumber because of its several merits. One is that, a simple estimation can be made from the easy measurement of the weight and volume of lumber. Calibration for differences of species, dimensions and temperatures of lumber are not necessary. A simple measuring system can be constructed, and the average MC of the lumber can be obtained. 2) The confidence intervals of MCs estimated from the weights of lumber were +/-32% for boards, +/-30% for planks, and +/-21% for square timbers towards the values estimated from linear regression equations at a 75% confidence coefficient (see Table 1). 3) The confidence intervals of MCs estimated from Equation (2) and (3) in which a representative oven-dry density of the species was substituted was +/-16% for boards, +/-17% for planks and +/-15% for square timbers at a 75% confidence coefficient (see Table 2). The confidence interval of MC of all lumber at a 95% confidence coefficient was +/-28%. 4) The confidence intervals of MCs estimated from Equations (2) and (3) in which the oven-dry density of each type of lumber was substituted was +/-7.5% at a 75% confidence coefficient for the data of all lumber (see Table 3). 5) For the development of measuring accuracy by this method, several techniques must be added. One is a technique of measuring the oven-dry density of lumber and the accurate measurement of the volume of lumber deformed by drying. The development of an equation expressing the relationship between the density and the MC at low MC levels of lumber is also necessary.