Optimisation of hardwood drying schedules allowing for biological variability

The amount of biological variability in timber creates considerable problem s in producing timber of adequate and reproducible quality with a predictab le amount of variability in final moisture contents. The development of opt imised drying schedules for addressing these problems is therefore desirabl e. Previous methods (largely of a stochastic type) are reviewed in this wor k and their limitations assessed. The physical parameters which have the gr eatest impact on the stress levels (and hence quality) of the timber have b een assessed using a diffusion model for the drying of Australian hardwood timber. This deterministic model is then used, together with statistical me thods for quantifying the confidence regions for the variability in the phy sical parameters with the greatest impact, in a systematic technique to dev elop a new optimised schedule for grey ironbark timber (Eucalyptus panicula ta). This new schedule is then compared with a previous optimised schedule, which did not rake this variability into account. The productivity (amount of good quality timber divided by drying time) appears to be maximised whe n the schedule is such that 90% of the timber produced is good quality.