A Study on the Phases of Consciousness about Wood Drying (1) : On the Structure of Production of Dried Lumber in Saw Mills of Central Kyushu

Recently, the demand for dried lumber has been increasing, as the structure of the housing construction and timber distribution have changed. Saw mill managers are taking more interest in wood drying and some timber districts have begun to dry wood as a regional measure to strengthen their competitive position in timber markets. But the increase in demand and supply of dried lumber is being hindered by confused approach on the part of lumber producers and timber distributors. This confuse can observed in the lack of attention to moisture content and immature approach to reasonable wood drying costs. In this paper, the author analyzes the structure of the production of dried lumber and the approaches to wood drying using a questionnaire given to saw mill managers who have wood drying kilns in central Kyushu. (1) According to research by the Forest Agency 1988, there were 1470 wood drying kilns attached to saw mills throughout Japan. Of these saw mills, steam type kilns were present in 59%, dehumidifier type kilns in 29%, and other types in 12%. Volume of dried wood production was 945 thousands m^3. Of this, domestic timber represented 44% and foreign timber 56%. Structural timber represented only 29%. Dried wood production in Kyushu was 20% of nationwide volume, domestic timber representing 60%, whereas structural timber only 12%. (2) In the central Kyushu (Kumamoto pref. and Oita pref.) there were 51 saw mills with drying kilns. There were in the upper range in terms of their annual sales and their number of employees. 50% of saw mills with drying kilns had a dehumidifier type, 33% had a steam type and 24% had other types. The greatest volume of dried lumber was hinoki(Chamaecyparis obtusa) and next was sugi(Cryptomeria japonica). Few saw mills were drying foreign timber. (3) Classifying saw mills acording to the utilization of dried lumber, there were four types. The 1st was construction lumber type, drying interior member, fancy colum and other construction timber. The 2nd was a laminated lumber type, drying board for flooring or glued -laminated lumber. The 3rd was a furniture lumber type, drying lumber for furniture, sliding doors, paper screens etc., And the 4th were ohter lumber types. The 1st was present in 69% of mills, the 2nd in 33%, the 3rd in 31%, and the 4th in 28% (this total is over 100% because some mills had two or three kiln types). There was a close correlation between utilization and drying method. Most dehumidifier types were of construction lumber type, and most steam kilns were of laminated type. Farmers used small drying types and small annual production volumes, the latter being comparatively larger. (4) 70% of the steam type used air seasoming as a pretreatment in artificial drying, whereas less than half of the dehumidifier type did. The final moisture content of the steam type aimed to concentrated under 20%, but dehumidifier types had no convergent level. Dehumidefier type had not considered final moisture content. (5) The lumber drying cost per m^3 of the steam type was between six and ten thousand-yen. But the drying cost of the dehumidifier type varied widely from four to fifteen thousand-yen, and convergent level of the cost was blurred. In the case of both the standard method of wood drying and most efficient method, drying costs were scatterd, because concept of a reasonable drying cost had 1101 developed. (6) As a means of reducing the cost of wood drying, most saw mills advocate air seasonig of sawn lumber and seasonig of logs in forests. Especially air seasoning of sawn lumber is considered to be important by steam type mills. It is therefore necessary that moisture content should be controlled throughout all processes in lumber production from felling to sawing. (7) In order to increase the demand for dried lumber, it is necessary not to increase the supply of dried by more investment in drying kilns but also to reach a consensus concerning reasonable drying costs between producers, deale