TERM: FIRST TERM
SUBJECT: BASIC TECHNOLOGY
CLASS: JSS 3
WEEK ONE AND TWO
TOPIC: PRDUCTION OF MATERIALS: WOOD
PRDUCTION OF WOOD
Wood gotten from trees must pass through processing stages before it becomes useful for domestic and industrial purposes.
Production of wood involves the following stages:
TIMBER GROWTH: Timber is used for various domestic and industrial woodwork. Timber is obtained from trees especially the trunk and branches. Trees that provide timbers are usually trees with big trunk. These trees are grown in the southern parts of Nigeria in the Rain Forest vegetation. Common examples of such trees areOmo, Iroko, Oak, Obeche, teak etc.
WOOD FELLING: The process of cutting down a tree in the forest is called felling of timber. The felling of tree is done with the aid of chain saws. The wood that is suitable for technology work is called timber. The process of felling of trees for timber use in the forest is called LUMBERING.
The felling of timber for use can be done broadly in two areas:
The log of wood obtained from the forest can be transported to the sawmill where it is converted into planks by road transport, by train and by waterways.
WOOD CONVERSION: this is the process of sawing log of wood into commercial or marketable sizes. The popular methods of wood conversion are plain sawn method and quarter sawn method
PLAIN SAWN METHOD: This is also known as ‘’through and through method’’. Here, the planks are sawn plank after plank without paying attention to the rays. The method is simple, quick and cheap.
QUARTER SAWN METHOD: This method is the method of sawing log of wood into planks by cutting along the rays of the wood. In quarter sawn method planks are cut at right angle to the growth rings.The planks produced by this method have fine figures.
SEASONING OF TIMBER: This is the process of reducing the moisture content or drying the timber. There are two methods of seasoning
THE AIR SEASONING (NATURALSEASONING): This method of seasoning wood involves stacking the wood in the open shed for a long period of time and allows it to dry naturally. The stacked planks (wood) are arranged on top of one another with one piece of wood called STACKER. This method of seasoning is relatively cheap and requires little attention although the rate of drying is slow.
THE KILN SEASONING (ARTIFICIAL SEASONING): This method of seasoning wood involves stacking the timber in a specially heated chamber.The planks are stacked in the same way as in air seasoning. In this process, the planks dry quicker.
REASONS FOR SEASONING WOOD
MOISTURE CONTENT(M.C.)The moisture content is defined as the excess water in the wet wood. The moisture content is expressedas a percentage.Moisture Content of the wood MC
MC = Wet Weight-Dry WeightX 100%
EXAMPLE (1): If a sample of wood weight 80Kg before and 50 Kg after drying. What is the percentage moisture content of the wood sample?
MC=Wet Sample –Dry Sample* 100%
MC =80Kg -50KgX`100
ACTIVITY: the weightof a sample of wood after drying was found to be60Kg. The percentage moisture content was 40%,what is the weight of the wood before drying?
WOOD PRESERVATION: This is the process of applying chemicals on wood to prevent insect and fungi attack. Preservatives help to protect wood against termite, insect and fungi. Examples include coaltar,solignum, creosote, chlorinated phenol and sodium PCP.
TYPES OF WOOD PRESERVATIVES
METHODS OF APPLYING PRESERVATIVES
PROPERTIES OF GOOD PRESERVATIVES
Read about wood defects and manufactured board.
REF. BOOK:NERDC BASIC TECH FOR JSS BK 3 PG 13-18.
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