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Assessment of the Quality of the Solar Dried Timber

M. A. Sattar
Director (Ex.)
Seasoning & Timber Physics Division, Bangladesh Forest Research Institute, Chittagong.

Abstract/ Executive Summary:

Drying defects were quantitatively assessed from the identical timbers of solar, air and steam kiln drying. The stresses in the form of moisture gradients developed in these drying methods were determined. Drying defects were found dependent on the stresses. The quality of the solar dried timber was superior due to reduction of drying stresses because of re humidification inside the solar kiln during the night.

Keywords: Solar, Air, Steam kiln drying, Drying defects, Drying stresses

Location: BFRI, Chittagong.

Start Date: 00-00-0000

End Date: 00-00-0000

Program Area: Postharvest and Agro-processing

Commodity: Tree

Objectives:

To assess the quality aspect in a simple greenhouse type solar kiln developed at the Bangladesh Forest Research Institute (BFRI) Chittagong.

Methodology:

Four important indigenous wood species, viz., chapalish (Artocarpus chaplasha), champa (Michelia champaca), garjan (Dipterocarpus turbinatus) and mango (Mangifera indica) were selected for the study. The fourth species is a common homestead species used for furniture and construction purposes in the villages. Green timber in the log form was procured and converted into planks of 4 cm ´ 20 cm ´ 2 m dimensions. Six representative planks of each species were taken as sample boards for each charge of drying. Four charges were dried covering the four seasons-winters, post winter, monsoon and post monsoon. Air drying was undertaken simultaneously with solar drying in the open yard adjacent to the solar kiln. Another batch of identical timber was dried in a compartment type steam heated kiln of 3 m³ capacity.

A set of trips measuring 2 cm thick was cut 15 cm away from both ends of the samples. The initial moisture gradients from the surface, sub-surface and core layers were measured for all the three drying methods. The sample boards were end-coated with bituminous paint immediately after end stripping to inhibit end drying. Based on the initial moisture content, the daily progress of drying was ascertained. During the middle of drying, two sets of strips were similarly prepared once in the evening and another in the next morning. The moisture gradients from the surface to the core layers were evaluated after a day’s drying and night’s conditioning/cooling. At the conclusion of drying, similar procedures were adopted for determining the moisture gradients. The visual drying stress in the form of stress specimen was found out. The quantitative assessment of drying defects was made from the sample boards.

Source of Information: Bangladesh Journal of Forest Science, Vol : 22 (1 & 2), Jan-July 1993, 6-17

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

No objectionable drying defect was observed in any batch of solar dried timber, whereas defects like end split, surface check and distortion were observed in severe form in many air and steam dried timber. The quality of the solar dried timber was observed to be superior to both conventional air and steam kiln dried timber. The reason seems to be that in solar drying the timber received a mini-conditioning treatment every night due to re humidification. The stresses formed in the timber during the day time were reduced during the night.

Knowledge Management: Journal