Hoeyrn Kaeyttoe Sahatavaran Kuivauksessa (Using Steam in Drying of Sawn Timber).

摘要

In convective air-drying of sawn timber the drying process is not well controlled during the warm-up phase, because the humidity of the air condenses on the cold timber and the kiln walls. As a result of this drying taking place when the wood is still cold, very small initial cracks appear at the wood surface. Later on, these so-called micro-checks open and form the macroscopic checking to be observed at the end of the during process. It has been shown that this phenomenon is the most important single factor causing drying checking, but it can be entirely avoided by humidifying the air effectively during the warm-up phase. The most effective method is using low-pressure steam. With steam drying checking can be reduced by 50% and the time needed for the warm-up phase be diminished by 50-80% increasing the drying capacity by as much as 10%. The power needed in kiln with nominal volume of 100 cu m is about 500 kW. Both the investment and the operation cost of the steam boiler will be compensated for by the lower loss in timber value caused by checking.