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MATEC Web of Conferences 108, 10001 (2017) ICMAA 2017 Two kekatong logs were sawn into 30 mm x 120 mm and 55 mm x 120 mm according to cutting pattern as shown in Figure 1. Flat sawn boards, or tangential cut, was used because this cutting is easier or cheaper to produce and is susceptible to deformation during drying. Each board then was cut into 990 mm and 1,700 mm long which was the length required for KD and RFV, respectively. Two 25 mm thick strips were cut between samples, 100 mm from both ends, for estimating MC for each sample at time of sawing. Samples measuring 20 mm x 20 mm x 20 mm were obtained from each logs for determination of moisture content and density variations in cross section. Initial weight of each sample was weighed and its oven- dry weight was estimated in accordance with [1]. Samples for KD were end-coated with bituminous paint in order to minimize effect of end drying. DBT = dry bulb temperature RH = relative humidity DOI: 10.1051/matecconf/201710810001 WBT = dry bulb temperature EMC = equilibrium MC Quartersawn (sample) 2.3 Radio frequency-vacuum drying Drying was carried out in an experimental-scale RFV dryer of 0.54 m3 capacity. RF generator operates at a fixed frequency of 6.7 Mhz with maximum output 6kW at a maximum electrode voltage of 7.3 kV. The samples were stacked in the drying chamber without stickers between three 1.5 mm thick aluminium plates. Drying was conducted under continuous mode of heating with input current to the RF generator was set to 0.4 A and voltage of HFV tube set at 5.5 kV. Heating temperature and pressure were set to 40oC and 50 torr, lowering the boiling point of water to approximately 38oC. During drying process, sample boards were weighed every two days until the MC of between 10 to 14 % is reached. 2.4 Drying quality The following drying characteristics were investigated in this study: - Drying time. - Moisture content variation within and between boards. - Shrinkage of boards in width and thickness, determined by measuring its dimension before and after drying. - Cupping, bowing, and spring, measured on each sample before and after drying by measuring deflection from a straight line between two ends. - Twisting, quantified by holding three corners of the lumber against a flat surface and the rise in the fourth corner was measured. - The residual drying stress (casehardening), evaluated by cutting 30 mm thick sections into three equal sized prongs and the central portion were removed as described by [9]. After 24 hours, the severity of casehardening, given by degree of turning in, was evaluated and classified into four classes, namely not casehardened, slightly casehardened, casehardened and reverse casehardened [9]. - Surface checks and end checks were assessed by estimating the percentage of checked area. 3 Results and discussion The physical properties and drying characteristics of 30 mm and 55 thick kekatong boards dried using KD and RFV system are summarized in Table 2 and Table 3, respectively. Table 2. Density and moisture content of kekatong. Flatsawn (sample) Discard for other uses N4 Diagonal/Bastard N.. N3 N2 N1 S1 S2 S3 S4 S.. 120 mm sawn (dummy) S1 Figure 1. Sawing pattern of a log (E=East, N=North, W=West, S=South). 2.2 Kiln drying Drying was conducted in a 0.21 m3 capacity experimental-scale conventional kiln drying. Drying condition was controlled by setting the dry-bulb temperature and the wet-bulb temperature. Humidity was provided by steam and controlled using an automatic damper during drying. Heat was supplied by passing steam through heating coils. Air flow through the stack was provided by the fan located at one side of the kiln with air velocity of 1.5 m/s. The samples were stacked on 25 mm by 25 mm stickers. The stacks were restrained by placing iron block on top of the stack to minimize warping. Drying condition was set according to Table 1. Drying was conducted in different batch for each thickness. High steaming was provided during drying to reduce surface checking, 24 hours in the initial stage of drying and 4 hours for every 2 days. MC (%) Starting Green 60 60 40 35 Table 1. Kiln drying schedule. DBT WBT RH EMC (oC) (oC) (%) 40.5 40.5 40.5 40 40.5 39.5 (%) Green Oven-dry density density (kg/m3) (kg/m3) 1165 970 863 822 1425 1189 Basic MC density (%) (kg/m3) 821 42 708 21 895 59 40.5 39 90 19.8 40.5 38 85 16.9 43.5 40 80 14.9 43.5 39 75 13.3 Mean Min Max SD 117 111 38 11 46 40.5 70 12.2 2 30 or 55 mm W.. W2 W1 E1 E2 E..PDF Image | Characteristics of Timbers Dried Using Kiln Drying
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