Seasoning and preservation techniques fo

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Seasoning and preservation techniques for silver oak N.KANAGARAJ BSF-06-007 BSC[FORESTRY]

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SEASONING Seasoning is the controlled process of reducing the moisture content (MC) of the timber so that it is suitable for the environment and intended use.

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Stacked stable and safely with horizontal spacing of at least 25 mm. Vertical spacing achieved by using timber battens (piling sticks) of the same or neutral species. SEASONING

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Today some timber yards are using plastics.   The sticks should be vertically aligned and spaced close enough to prevent bowing say 600 to 1200 mm.

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Ends of boards sealed by using a suitable sealer or cover to prevent too rapid drying out via the end grain. The stack raised well clear of the ground, vegetation, etc to provide good air circulation and free from rising damp, frost, etc. Over head cover from effects of direct sunlight and driving weather.

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For a one-inch thick board oak will take about 12 months. 25 mm thick, stacked in autumn reduces to about 20 % the following summer. 50 mm thick, stacked in autumn reduces to about 20 % the following autumn.

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PRESERVATION For use in Doors and Windows, timber should be chemically treated under Pressure Impregnation Method. According to this method the timber is stacked inside a circular steel chamber and after closing the door of the chamber, vacuum is created to draw the air from the cylinder.

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After creating vacuum, chemicals are pumped into the cylinder and pressure is applied @ 150 PSI for a duration of 1 1/2 to 2 Hrs. The pressure forces the chemicals into the wood, which has empty pockets inside on account of the vacuum created earlier.

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Boric Acid, Copper Sulphate, and Sodium Dichromate. These are mixed in water @ 5% concentration as per the IS Specifications (IS Code 401). Timber, after such treatment, is protected from attack by termites and biological agents.

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Brushing or Spraying is mostly used The depth of the preservative penetration which is obtained, is only sufficient to give superficial protection to the timber. Hence this method is adopted for its use as packing cases.

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Full Cell Process or Bethell Process For the treatment of silver oak by full cell process the chemical used Is borax at a pressure of 6 MPa

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Air Drying: The process of seasoning the timber in the open air – protecting it from the sun and rain by cover boards or an open sided shed. Air seasoning is required for most species prior to kiln drying. Case Hardening/Honeycombing: Warping as a result of stress, after seasoning, between adjacent layers in the structure of the timber. Caused by too rapid surface drying in the kiln.

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End Racking/Plastic Stickers: Some timbers, such as Sycamore are prone to sticker marks, which occur when the moisture in the board cannot be released from a freshly sawn board because it is trapped under a wooden drying sticker. End racking prevents this by placing the boards vertically for a period of time on the sticker. Modern plastic tickers now have a shape that avoids the problem altogether.

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Equilibrium Moisture Content: The moisture content at which wood is stable and in equilibrium with the humidity of its surroundings. Equalising: The process at the end of a kiln drying run by which the moisture content of the whole kiln change is equalised before cooling down and discharged from the kiln chamber.

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Kiln Drying: The process of drying timber to a moisture content which cannot be achieved by a natural air-drying process. It is carried out in chambers where the temperature and humidity are mechanically and scientifically controlled.

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Kiln Shrinkage: When any timber dries, some shrinkage will occur with the normal loss in volume being around 6% to 8%. In order to allow for this, when sawing a log we saw the thickness of the boards ‘off the saw’, which allows a minimum of 6% over the required thickness after kiln drying.

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Part Seasoned: The term used for Beams and Billets, which have been air drying for a period of 6 months or more. During the first 6 to 12 months of air seasoning, beams will settle down and if movement and face shake are to occur it will be during this initial period of air drying.

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Thank you