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Shrinkage and Swelling Characteristics of Three Selected Timbers of Bangladesh

M. S. Rahman
Associate Professor
Department of Farm Structure, Agricultural University Mymensingh-2202, Bangladesh

M. K. H. Bhuiyan
Associate Professor
Department of Physics, Bangladesh Agricultural University,Mymensingh-2202, Bangladesh

M. H. Begum
Postgraduate students
Department of Farm Structure, Agricultural University Mymensingh-2202, Bangladesh

M. Afrin
Postgraduate students
Department of Farm Structure,Agricultural University Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

The study elucidates an attempt to determine and compare the volumetric swelling and shrinkage .:of Jam (Syzygium spp.), Rain tree (Samanea saman) and Jack-fruit (Artocarpus heterophylus) 'timbers in the longitudinal, tangential and radial directions. The swelling of the wood was caused by the wood being increased in water whilst placed in a swelling container and the shrinkage made in an oven by drying. The dimension of the air-dried timber specimen was selected as 40 x 40 x 20 mm. The experimental results showed that, the differences of swelling and shrinkage rapidly occur in the first 5 hours; swelling and shrinkage are then negligible in all the three directions. The result also showed that, Jam variety exhibit the highest swelling value, medium in Rain tree and jack-fruit shows the lowest swelling value in all direction. In case of the shrinkage of all direction, Rain tree exhibit the highest shrinkage value, medium in Jam and Jack-fruit shows lowest the shrinkage value. Among the selected species, Jack-fruit has been shown to exhibit the best performance in accordance with the swelling and shrinkage properties. Rain tree as a poor quality timber and Jam has been identified as a moderate quality timber in respect of swelling and shrinkage behabiour.

Keywords: Shrinkage of Jam, Rain tree, Jack-fruit timbers

Location: Bangladesh Agricultural University,Mymensingh-2202, Bangladesh

Start Date: 01-01-2009

End Date: 31-12-2009

Program Area: Postharvest and Agro-processing

Commodity: Timber

Objectives:

To determine and compare the volumetric swelling and shrinkage of Jam (Syzygium spp.), Rain tree (Samanea saman) and Jack-fruit (Artocarpus heterophylus) 'timbers in the longitudinal, tangential and radial directions.

Methodology:

There are more than 500 timber species found in Bangladesh but among those very limited numbers of species are well known for their extensive usage across the country. In this study the species of timber were selected on the basis of the availability at local markets and obviously the priority was given to the species which are being used significantly at various level of its practice and got economical importance for commercial purpose. The selected species were; Rain tree (Samanea saman), Jam (Syzygium spp.) and Jack-fruit (Artocarpus heterophylus). The timbers were collected from different saw mills in Mymensingh city. Primarily the samples were taken from three different locations of freshly sawn lumbers for each category of the tests and were brought to the laboratory and stored in a dry place having a sufficient aeration system. After few days they were cut and shaped into the desired sites of samples. The specimens for swelling and shrinkage measurement were 40x40x20 mm (tangential x radial x longitudinal) solid wood block and completely free from any knots, checks, flaws and other defects. The specimen blocks were prepared carefully with the help of a saw and Jack plane to attain perfect dimensional uniformity for each of the species.For the swelling test, a first measurement was made of the dimensional lengths i.e. for redial, tangential and longitudinal lengths of an air-dried block then the block were completely immersed in water, and the readings were taken one every 10 minutes for upto 1 hour and then one every 30 minutes for up to 4 hours. Thereafter, one reading was taken every hour for 5 hours and then one every 5 hours for 20 hours. Measurements were made until a steady weight was recorded. For the shrinkage test, three dimensional measurements in green condition were made for redial, tangential and longitudinal lengths and each experimental block was than weighed before the blocks were placed in an oven. Thereafter, all the blocks were dried in the oven maintained initially at 60°C and then progressively raising the temperature to 100°C to make the blocks shrink. Readings from the oven were made as in the swelling study. Each experimental block was consequent removed from the oven according to the set time and immediately put back in the oven after weighing and dimensional measuring by a digital slide caliper, and this continued until a steady weight was recorded.

Source of Information: Bangladesh Journal of Agricultural Engineering, ISSN 1015-4426, Vol: 21(1&2), pp: 35-41, 2010

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

From the results of this study it could be concluded that, Jam variety exhibit the highest swelling value, Rain tree exhibit the medium value for swelling and jack-fruit shows the lowest swelling value in all direction. In case of the shrinkage of all direction, Rain tree exhibit the highest shrinkage value, Jam exhibit the medium value and Jack-fruit shows the lowest shrinkage value. Among the selected species, Jack-fruit has been shown the best performance in accordance with the swelling and shrinkage properties. Based on the same properties, Rain tree has been identified as a poor quality and Jam as a moderate quality timber. Wood swells and shrinks in response to the level of humidity or continual wetting by rainwater runoff. To reduce the problems of wood swelling it could be suggested that regular covering of the wood in a water resistant material, i.e. paint or varnish. The most important thing to reduce the problems caused by swelling or shrinkage of wood is to match the wood to the conditions it will experience, i.e. do not fit wet wood inside the house or dry wood out side.

Knowledge Management: Journal