Processing of Wood Materials – JSS3 Basic Technology Lesson Note (First Term)

TOPIC: PRODUCTION OF MATERIALS: WOOD

CONTENT

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

 PRODUCTION OF WOOD

Wood obtained 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 a big trunk. These trees are grown in the southern parts of Nigeria in the Rain Forest vegetation. Common examples of such trees are Omo, 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 the tree is done with the aid of chainsaws. The wood that is suitable for technology work is called timber. The process of felling trees for timber used 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 purposes 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 trees to be cut down. Hence this is termed O.T.V. (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 take place?

 WOOD CONVERSION: this is the process of sawing logs of wood into commercial or marketable sizes. The popular methods of wood conversion are the plain-sawn method and quarter-sawn method.

PLAIN SAWN METHOD: This is also known as the ‘’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 a log of wood into planks by cutting along the rays of the wood. In the quarter-sawn method, planks are cut at a right angle to the growth rings. The planks produced by this method have fine figures.

 EVALUATION

1.         Define wood conversion
2.   Differentiate between the plain-sawn method and the 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 (NATURAL SEASONING): This method of seasoning wood involves stacking the wood in the open shed for a long period and allowing 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 quickly. 

 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 fungi attack the 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 expressed as a percentage. Moisture Content of the Wood MC

MC       = Wet Weight – Dry Weight X  100%

                                   Dry weight

EXAMPLE (1): If a sample of wood weighs 80 kg 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 -50Kg X`100

50Kg

 =30KgX100%=60%`

50Kg

ACTIVITY: the weight of a sample of wood after drying was found to be 60 kg. 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 the sample of wood before drying was found to be 10 kg. The percentage moisture content was found to be 50%, what is the weight of the sample of wood after drying?

 WOOD PRESERVATION: This is the process of applying chemicals on wood to prevent insect and fungi attacks. Preservatives help to protect wood against termites, insects, and fungi. Examples include coaltar, solignum, creosote, chlorinated phenol, and sodium PCP.

 TYPES OF WOOD PRESERVATIVES

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

METHODS OF APPLYING PRESERVATIVES

1.         By bushing: This is the process of using a brush to apply the preservatives to the wood
2.         By spraying method:  This is the method of using a spraying gun to apply 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 preservative liquid. This process is normally used for treating poles and fence posts.
5.         By pressure treatment method: This is the process in which the plank is placed inside an enclosed metal cylinder. In this process, the preservatives are 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 attacks on wood?

 READING ASSIGNMENT

Read about wood defects and manufactured boards.

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

 WEEKEND ASSIGNMENT

1.         Which of the following is not a stage of wood production and processing? (a) wood seasoning (b) wood logging (c) wood conversion (d) wood preservation.
2.         Felling of trees is done with the aid of ——- (a) Chain saw (b) German knife (c) Israel hoe (d) Oxford scriber.
3.         Trees that provide timbers are usually trees with big trunks, 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 20 kg 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 good preservatives.