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PDF : 02040168.pdf
title(En) :Studies on the Drying of Plywood.
author(En) :Manjiro Fukuyama, Shigeru Kadita
information :Mokuzai Gakkaishi 2(4), 168-173 (1956)
assort :Original Article
summary(En) :   Under the constant drying condition we made experiments on the drying of plywood, especially the drying process, evaporating- and drying velocity, moisture diffusion in plywood and elevating process of surface and inner temperature of plywood. The plywoods used are as follows; 1) veneer: birch wood (thickness 0.5mm) and lauan wood (thickness 1.5 mm), 2) construction: 3-ply and all layers perpendicular with each other, (a) A-plywood: outside layer-birch veneer, center layer-lauan veneer, (b) B-plywood: outside and center layer, birch veneer, 3) adhesive: urea-formaldehyde resin, 4) spreading: 40 g/ft2, 5) pressure: 10kg/cm2, 6) temperature: 100°C, 7) time: 10min, 8) specimen: 25×25cm, thickness: A-plywood 2.7±0.1mm, B-plywood 1.9±0.1mm. The test pieces of about 5×5 cm were coated with urea-formaldehyde resin to prevent the drying from four side faces and then soaked in water until saturated (initial moisture content: A-plywood 92∼120%, B-plywood 66∼98%).
   Results obtained are as follows;
   1) The drying process (moisture content u: drying time z) of A- and B-plywood are shown in Fig. 1 and the relationship between logu and z in Fig. 2. From these we can obviously recognize the three periods of constant rate, first and second stage of falling rate of drying.
   2) The elevating process of surface and inner temperature of plywood during drying are shown in Fig. 3 and 4. We can recognize the three periods concerning elevating process of temperature (i.e. heating, constant and elevating period of temperature by R. KEYLWERTH) .
   3) From Fig. 2, the first formula indicated by R. KELWERTH (du/dz = -K(u - ueq) seems to apply to the results of our experiments (Fig. 5). Coefficient K and its reciprocal 1/K are given in Table 2.
   4) The relationship between the evaporating velocity dw/(A · dt) and average moisture content u are shown in Fig. 6. The surface evaporating coefficient (K) in the constant rate of drying of plywood (A- and B-plywood) was K = 3.7×10-3g/cm2 · h · mmHg (Fig. 7) and relationship between the rate of effective evaporating area A' to total surface area A, A'/A and u (%) are shown in Fig. 8.
   5) The relationship between the vav/v0 (vav = um - ueq, v0 = u0 - ueq, um = average moisture content) and t/(a/2)2 (t = drying time, a = thickness of plywood) of A- and B-plywood are shown in Fig. 9. It seems, consequently, that the general diffusion formula ∂u/∂t = K(∂2u/∂x2) can apply to the drying of these plywoods. Then we find the coefficient K (moisture diffusivity), λ(≈ (K' · r0)/100, diffusion constant) and K0 [K0 = K(a/a0)n-2, n = 1.0 - 1.5, a and a0 = thickness of plywood] of A- and B-plywood which are shown in Table 3.