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Studies on Air Drying Characteristics of Garjan Sleepers

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

M.O. Ali
Seasoning &Timber Physics Division, Bangladesh Forest Research Institute, Chittagong.

Abstract/ Executive Summary:

Air drying characteristics of garjan (Dipterocarpus spp.) railway sleepers were investigated employing 1´5, 2´5, 1´7 and 2´7 piling methods. Although there was no significant difference among the drying periods in different methods, the 2´7 method appeared to be the most efficient one. This method exhibited a relatively shorter drying time irrespective of higher density and higher initial moisture content of sleepers as compared to those in other methods. The faster drying in the 2´7 method was attributed to better air circulation. Sleepers stacked in the month of April, dried down to 28% moisture content in about eight months on the average. It is recommended that garjan sleepers be air dried following the 2´7 method during the active drying season beginning November, instead of April, as was done in the present study, with a view to achieving further reduction in total drying time.The moisture distribution inside the sleepers was highly variable; the moisture gradient was steeper with increasing depth of the zone, but the steepness of the gradient decreased with increasing drying time.

Keywords: Air drying characteristics, Garjan, Moisture content, Sleepers

Location:

Start Date: 00-00-0000

End Date: 00-00-0000

Program Area: Postharvest and Agro-processing

Commodity: Gorjon

Objectives:

To investigate the air drying characteristics of garjan sleepers in order to evolve a proper air drying method for satisfactory preservative treatment.

Methodology:

Five hundred 4.5 inch ´ 8 inch freshly sawn Metre-Gauge garjan sleeper were procured from the commercial stock of Forest Industries Development Corporation at Kalurghat, Chittagong. These were ordered in 12.5 feet lengths, and were processed into standard 6 feet lengths at the Institute. Four pilling methods, 1´5, 2´5, 1´7 and 2´7 were employed for this study. Fifty-six sleepers were randomly selected of which five sleepers were used for each pile as moisture loss samples, and two sleepers were used to determine moisture gradient samples for each pile. The remaining 444 sleepers were sorted into eight lots; 2 lots of 45 each, 2 lots of 52 each, 2 lots of 59 each and 2 lots of 66 each to evaluate, respectively, the 1´5, 2´5, 1´7 and 2´7 piling methods. One complete set of piles in duplicate was stacked in the open air drying yard of the Forest Research Institute, Chittagong in the month of April, 1962. The top of each pile was roofed with rejected sleepers to protect it against direct sun. The sleepers were stacked with the length in the east-west direction. The spacing between lateral and the front alleys were three feet.

Moisture loss samples were placed in tiers 1,2,3,5 and 6 with two moisture gradient samples in tier 4. All samples were end-coated with bitumin paint to inhibit end drying. The initial moisture content of individual sleepers was estimated by cutting one moisture section from each sample at the time of cross-cutting 12.5 feet sleepers into 6 foot lengths. The specific gravity of the sample sleepers was determined from one-inch sections on the basis of green volume and over dry weight.Air drying was started from the beginning of April, 1962 and the observation was continued till the end of January, 1963. Moisture loss samples were weighed at one month intervals using a portable balance to the nearest 0.1 Ib. Moisture gradient specimens were prepared at three month interval. Moisture gradients were studied in four periods, the first period being the initial one prior to drying while the second, third and fourth periods were, respectively, after 3, 6 and 9 months of drying. A one-inch strip was cut six inches apart from one end of each gradient sleeper and seven specimens comprising of four zones were prepared from this strip.Of the four zones the first, second and third zone consisted each of a 0.5-inch thick strip and their distance from the surface was 0.5, 1.0 and 1.5 inches respectively. The fourth zone was the residual one-inch centre portion. The moisture content of each zone was determined by the oven dry method. At the end of drying, two moisture sections were cut from each moisture loss sample and the average moisture contents of individual samples were estimated. Based on these final moisture content values, the individual weights of moisture loss samples were converted to moisture contents.

Source of Information: Bano Biggyan Patrika, January 1977 : 6 (1), 27-32

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Garjan sleepers followed the same general pattern of air drying in all the piling methods.
There was no statistically significant difference among the drying periods in different methods. It took about eight months to dry from green to a 28% moisture content in all the cases.
Among the four methods, the 2´7 method was found to ensure comparative faster drying due to better air circulation. This method is recommended for air drying garjan sleepers during active air drying months.
There was a highly variable moisture distribution inside the sleepers. This variation was significantly affected by the zone and the period.Moisture gradient was found to be steeper with the increasing depth of the zone, but the steepness of the gradient decreased with increasing drying period.

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