Development of Continuous Press Systems for Compressed Wood

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(1) A roller press machine was newly designed and manufactured on the basis of the results from transverse compression test of wood. The press is equipped with a pair of replaceable metal rollers with a servomotor (4.4kW). The size of rollers are 200, 300, 400 mm (diameter) by 300 mm (width). The roll temperature is controllable up to 220℃ by using cartridge heater (14.4kW). The maximum load, torque and rotation speed are 40kN, 5000 kNm and 15 rpm, respectively. The roller gap is controllable from 0 to 150 mm by shifting the position of upper roller. The load cells (5000 kgf) are set under the axle box of lower roller.(2) We found the several defects of compressed wood. Some of them occurred by roller pressing only. The specific phenomena resulting from roller pressing are alligatoring crack, surface check and shear cracks. Besides, longitudinal split, cup and crook are evident on visual check.(3) These failures correlate to contact angle θ and surface strain ε・θ is calculated by the equation [cos θ = 1-(T-H)/φ] with thickness of wood sample (T), compression rate (T-H)/T, and roll diameter (φ), εby [ε =μθ/180 sin θ-1]. Bending properties of dry and wet Sugi dramatically decreased when contact angle exceeded 8 and 9.5° , respectively.(4) We have proposed the novel liquid impregnation method using roller-compression of green timber in the treatment vessel with solution. In this process, free water inside the green timber is removed from the cell cavities in the treatment vessel and concurrently replaced with treatment solution. This technique seems applicable to chemical treatment of timber without drying before treatment, and resultantly a reliable uniform liquid impregnation and reduction in production costs are achievable.