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Civil tech presentation, Term 3 work

A short lesson preparation for grade 10 civil technology learners, term 3. I like this subject already, while on the other side i am still studying to become a teacher on this field. Actually i like technology in broad.

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Civil tech presentation, Term 3 work

  2. 2. LESSON OBJECTIVES • To define wood and timber. • To types of trees and timber (Softwood and Hardwood). • To explain the physical characteristics of softwood and hardwood. • To list the properties of wood. • To explain and define the term “seasoning of timber” • To state advantages of seasoning of timber. • To explain the methods and types of seasoning timber.
  3. 3. DEFINITIONS • WOOD-Is the organic matter obtained from trees • TIMBER-Timber denotes wood which is suitable for building or carpentry and for various engineering and other purposes.
  4. 4. TYPE OF TREES Trees are classified into two groups 1. Endogenous trees The trees which grow inwards in longitudinal fibrous mass 2. Exogenous trees The trees which grow in out wards across horizontal section of stem. These trees are only fit for engineering construction.
  5. 5. Exogenous trees fit for engineering construction( two types) Conifers or Evergreen They give soft wood and they have pointed leaves. Examples: Déodar, Pine, Chir, Kail,etc Deciduous or Broad leaf Trees These have hard wood and they have broad leaves. Examples: Teak, Sal, Shisham, etc
  6. 6. CHARACTERISTICS NO: Item Soft woods Hard woods 1 Annual Distinct Indistinct 2 Colour Light Dark 3 Density Low High 4 Fire resistance Poor More 5 Weight Light Heavy 6 Strength strong for direct pull & weak for equal resisting thrust strong for resisting tension, compression & shear
  7. 7. SESSONING OF TIMBER As fresh timber which is obtained from trees contains about 30 to 40 % sap or moisture. This moisture is very harmful for the life of a timber. Therefore, it is necessary to remove that moisture by applying some special methods. All those methods which are used for removing the moisture from timber are collectively termed as seasoning of timber.
  8. 8. ADVANTAGES OF SEASONED TIMBER 1. It has reduced weight. 2. It is strong and durable. 3. It has resistance to decay or rot. 4. It takes high polish. 5. It is easier to work. 6. Its life is more.
  9. 9. TYPES OF TIMBER SEASONING 1. Natural Seasoning 2. Artificial Seasoning a. Kiln Seasoning-special heating( 3 TO 12 DAYS) b. Chemical Seasoning-carbon dioxide, ammonium carbonate or urea( 30 TO 40 DAYS) c. Electric Seasoning-electric current is passed through the timber logs( 5 TO 8 HOURS) 3. Water Seasoning
  10. 10. METHODS 1. Natural Seasoning-timber is dried by direct action of air, wind and sun. months or a year. 2. Water Seasoning-timber logs are kept immersed whole in the flowing water to wash away the sap present in timber, then taken out of water and exposed to air. 2 to 4 weeks.