Lesson Notes By Weeks and Term - Junior Secondary School 3

TERM: FIRST TERM

SUBJECT: BASIC TECHNOLOGY

CLASS: JSS 3

REF MATERIALS

• EVANS BASIC TECH FOR JSS BOOK 3
• NERDC BASIC TECH FOR JSS BOOK THREE

WEEK ONE AND TWO

TOPIC: PRDUCTION OF MATERIALS: WOOD

CONTENT

• Concept of wood processing:
• Timber growth
• Wood felling
• Wood conversion
• Wood seasoning
• Wood preservation

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:

1. Timber growth 
2. Wood felling
3. Wood conversion
4. Wood seasoning 
5. Wood preservation

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:

1. The Free Area (F. A.): This is owned by individuals, the amount of money paid to the government by the timber contractor for permission to cut down any tree for commercial purpose is called TARRIF.
2. The Forest Reserve Area (F.R.A.): This is owned by the government. The amount of money paid for the timber to be cut in F.R.A. depends on the volume of tree to be cut down. Hence this is termed O.T.V. (Out Turn Volume) 

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.

EVALUATION

1. State the five stages of wood processing
2. What is wood felling?
3. What is limbering?
4. Where can felling takes place?

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.

EVALUATION

1. Define wood conversion
2. Differentiate between plain sawn method and quarter sawn method.

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

1. It makes the wood lighter in weight.
2. It makes the wood more stable
3. It makes the wood to take paints, polishes and preservatives.
4. It makes the wood to be durable i.e. last longer.
5. It reduces the insect and the fungi attack on wood
6. It reduces the moisture content of the 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%

                                                                     Dry weight

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%

                      Dry sample

MC  =80Kg -50KgX`100

50Kg

 =30KgX100%=60%`

50Kg

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?

EVALUATION

1. Define wood seasoning.
2. Mention the two types of wood seasoning we have and differentiate between them.
3. The weight of sample of woodbefore drying was found to be 10Kg. The percentage moisture content was found to be 50%, whatis the weight of the sample of woodafter 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

1. Water soluble preservatives
2. Oil soluble preservatives
3. Solvent soluble preservatives

METHODS OF APPLYING PRESERVATIVES

1. By bushing: This is the process of using brush to apply the preservatives to the wood
2. By spraying method:  This is the method of using spraying gun in applying the preservatives to the wood.
3. By cold immersion method: This is the process of immersing  (dipping) the plank in an unheated solution of preservatives for one or two days
4. By open tank method (hot and cold method): This is the process in which the plank is immersed in a tank containing hot preservatives liquid.This process is normally used for treating poles and fence posts.
5. By pressure treatmentmethod: This is the process in which the plank is placed inside an enclosed metal cylinder. In this process, the preservatives are being forced into the plank under high pressure.

PROPERTIES OF GOOD PRESERVATIVES

1. It must be poisonous to the destructive agent.
2. It must be safe to handle.
3. It must be permanent to the wood on application.
4. It must be easy to apply on the wood
5. It must be chemically stable

EVALUATION

1. What are preservatives?
2. Mention four properties of a good preservative.
3. Mention three methods of applying preservatives.

GENERAL EVALUATION

1. Name three important things to consider before a tree is felled.
2. Mention two methods of wood conversion.
3. What is seasoning? 
4. Why should timber be seasoned?
5. How do you prevent insect and fungi attack on wood?

READING ASSIGNMENT

Read about wood defects and manufactured board.

REF. BOOK:NERDC BASIC TECH FOR JSS BK 3 PG 13-18.

WEEKEND ASSIGNMENT

1. Which of the following is not a stage of woodproduction and processing?(a) wood seasoning (b) wood logging (c) wood conversion (d) wood preservation.
2. Felling of trees is done with aid of ------- (a) Chain saw (b) German knife (c) Israel hoe (d) Oxford scriber.
3. Trees that provide timbers are usually trees with big trunk, which include the following except (a) Mahogany (b) Palm Tree (c) Obeche (d) Teak 
4. The kind of seasoning that involves putting a stacker between logs of wood in a saw-mill is called---------- (a) kiln (b) air (c) plain sawn (d) artificial.
5. What is the weight of wood that weighs 20Kg after seasoning? If the percentage moisture content is 40% (a) 28Kg (b) 140Kg (c) 78Kg  (d) 56Kg.

THEORY

1. What is wood conversion? Mention the two methods of wood conversion.
2. List five reasons for seasoning wood. (b) list five properties of a good preservatives.