Research On Flexible Vacuum Drying For Lumber Of Larix Gmelinii And Acacia Mangium

In this study, flexible vacuum drying experiments were conducted on study Larix gmeliniisawn timber and Acacia mangium sawn timber. The effects on drying rate, themoisture content,drying checks and deformation by different drying parameters, such as temperature andvacuum pressure, were analyzed to find optimal drying parameters. These results could providetheoretical basis to standard formulation for flexible vacuum drying process.The results are summarized as follows:1.Under three kinds of different drying temperature and vacuum pressure, dryingtemperature and vacuum pressure plays significant impact on overall average drying rate in theprocess, and temperature plays greater role than the effect of vacuum pressure. Because of theinteraction of temperature and vacuum pressure, in this study, we should take into account thecombined effect of the two parameters when examining the effect of drying conditions on thedrying rate. Under the same temperature, when the vacuum pressure decreased, the drying rateincreased. And in the same conditions of vacuum pressure, when the temperature increased, thedrying rates also increased.2.In the drying process, the fitting curve for drying of this two timber is different. Thefitting curves of Larix gmelinii sawn timber approximate parabola, which showed the binarylinear equation. But the fitting curves of Acacia mangium sawn timber is a line approximatly,namely the drying rate of Acacia mangium sawn timber trends upward to a fixed value.3.After flexible vacuum drying process, the moisture content distribution are broadlysimilar. Closer to the end of the timber along its longitudinal direction, the moisture content islower. There is no apparent rules on moisture distribution in the thickness direction. Theinfluence of vacuum pressure on the moisture content of test piece in the thickness direction isgreater than the effect of temperature. With the lower vacuum pressure or higher temperature,the moisture content deviation value decreases. 4.Under the conditions of this study, cracking did not appear in Plantation Larch sawntimber, while a little crack appeared under60°C and50mmHg in Acacia mangium sawntimber.5.In this study, temperature plays greater impact on width and thickness shrinkage ofLarix gmelinii sawn timber. Vacuum pressure influence the width shrinkage rate of Larixgmelinii sawn timber significantly, and width shrinkage rate is about two times higher thanthickness shrinkage rate. The drying shrinkage of Larix gmelinii changes little under differenttemperatures. With the increase of temperature or the reduction of vacuum pressure, thenumber of test meterial surface check and total check length increases, and the width of thesurface check trends to increase.The cup of Larix gmelinii is significantly influenced by thecharacteristics of the material itself, and the effect of temperature and vacuum pressure on it isnot obvious. Temperature plays greater impact than vacuum pressure on bow, crook,andtwist.6.Bow, crook,andtwist did not happen on Acacia Mangium sawn timber after this dryingprocess. The width of shrinkage and the residual stress increased with the increasingtemperature, and the residual stress also increased with the reduction of pressure.7.Comprehensive consideration suggests that the optimal drying temperature of Larixgmelinii sawn timber is55℃, the pressure is50mmHg, and the average drying rate is0.68%h-1. And the optimal drying temperature of Acacia Mangium sawn timber is60℃, thepressure is75mmHg, and the average drying rate is1.41%h-1.The drying quality could reachfirst order.