DEVELOPMENT OF DRYING SCHEDULES FOR RUBBER AND PINE TIMBER FOR THE DEHUMIDIFICATION KILN DRYING

Most of the limber in Sri Lanka is used in unseasoned state or seasoned using conventionalkilns which use fuel wood boilers or open fires as a heating source. A study has beenconducted to introduce dehumidification drying kiln. which is easy to fabricate andconsumes less energy hence ideal for small scale timber industries.Experiments were conducted to investigate drying behaviour. to develop kiln schedules andto evaluate the developed kiln schedules for Pine (Pinus caribaea ; and Rubber (11('\'('(/brasiliensis) timber. The dehumidification kiln used in the present study is locallyfabricated and it has 25 cuhic feet capacity. The temperature of the kiln can be increasedto 50flC and relative humidity can he reduced to 16%.Drying rate. percentage shrinkage and drying defects were observed for these two speciesby drying 21.'ix75x300 mm stakes in temperature. humidity and air circulation controlledmini chamber. It was found that Pinus caribaea was relatively fast drying timbercompared with l lcvea brasiliensis. However. II. brasiliensis showed higher percentageshrinkage and defects over P. caribaea during the early stages of drying. This indicatesthat 1/. brasiliensis should be dried slowly at the initial stages of drying.Three k iln schedules with slow. medium and fast drying rates were developed forseasoning 25 nun planks based on the results of drying behaviour. Drying rate. dryingefficiency. drying defects. drying cost and thermal efficiency of these kiln schedules wereevaluated by drying 25x 150x 1O00 mm sample hoards in the dehumidification kiln.Compared with conventional kiln seasoning. dehumidification kiln seasoning gave higherquality dried timber with more than