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Treatment of Green Garjan Sleepers with Oil-borne Preservative.

M. A. Latif
Divisional Officer
Wood Preservation Division, Bangladesh Forest Terearch Institute, Chittagong.

Abstract/ Executive Summary:

Green Garjan, Dipterocarpus spp. sleepers, which are very difficult to treat, were treated successfully with an oil-borne preservative. Bethel full cell process was followed. Before treatment the sleepers were conditioned by alternate steaming and vacuum to facilitate impregnation. Sleepers thus treated had and average penetration of 4.9 cm (1.95 in) which is higher than that required for outdoor use in Bangladesh.The necessity of adjusting the temperature as well as the duration of pretreatment in relation to residual moisture content of green Garjan sleepers has been discussed.

Keywords: Oil borne preservative, Penetration & Retention, Impregnation Phase, Bethel full cell process, Alternate steaming.

Location: Wood Preservation Division, Bangladesh Forest Research Institute, Chittagong.

Start Date: 01-07-1985

End Date: 30-06-1986

Program Area: Postharvest and Agro-processing

Commodity: Wood

Objectives:

To develop a treatment method for green Garjan sleepers effectively with oil-borne preservatives.

Methodology:

The treating process was designed in two phases :

i) Pre impregnation phase (steam drying), and

ii) impregnation phase (pressure treatment with Bethel full-cell process).

The efficiency of this process was demonstrated at the commercial wood treating plant of the Lumber Processing Complex of BFIDC at Kaptai. A charge of 20.95 cu m (740 cu ft) green Garjan sleepers was treated with the above process. The sleepers had an initial moisture content between 60 and 70 percent. Since the moisture content of the sleepers was 30 to 40 percent above the fiber saturation point, the steam drying phase was carried out twice to bring down the moisture content of the outer zone of the sloopers to a level favorable for impregnation of the preservative. Since, railway sleepers in Bangladesh need creosote with a preferable penetration of 3.8 cm (1.5 in), Bethel full cell process was therefore, employed.Immediately after the steam drying phase, a vacuum of 558.8 mm (22 in) of Hg was created in the cylinder and held for 20 minutes before the hot (85⁰C) preservative was sucked in under the existing vacuum to fill up the cylinder. The preservative fluid, a mixture of 5 percent pentachlorophenol in light diesel oil and furnace oil (40:60), was preheated in the Rueping tank to 85⁰C (185⁰F). The treating cylinder was filled up with preservative until a preservative pressure of 7.87 kg/sq cm (112 psi) was reached. This pressure was maintained during the next 2-hour treating period by forcing in compressed air into the treating cylinder. Once the above pressure was reached the temperature of the cylinder was brought to 82.2⁰C (180⁰F) and held there during the entire period of treatment. After the treatment the pressure was released and the preservative was pumped back to Rueping tank and Batching tank. A vacuum of 558.8 mm (22 in) of Hg was then created in the cylinder in 10 minutes and held there for 15 minutes. The vacuum was then broken and the recovered preservative was again pumped back to Batching tank. From the difference of the level of preservative in the Batching tank the net absorption of preservative fluid by the sleepers was determined.

Source of Information: Bano Biggyan Patrika, a Journal of Forest Science, January & July 1979, Vol. 8, No.1 & 2 : 27-33pp.

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Garjan sleeper in green condition can be pressure treated with oil-borne preservatives if it is conditioned with alternate steaming and vacuum treatment immediately preceding the impregnation. A pretreatment phase of two cycles of 2-hours steaming at 110⁰C (230⁰F) and 30 minutes’ vacuum of 558.8 mm (22 in) of Hg alternately can condition green Garjan sleepers to receive preservative up to a depth of 3.81 cm (1.5 in).

Knowledge Management: Journal