Page 142 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

Classification

• Timbers are classified as
a Softwood
b hardwood
Softwood timber
• Usually all trees with needle leaves of softwood and those with broad leaves are of hard-wood.

• The wood contains resins and turpentines.
• The wood has a fragrant smell.
• Fibres are straight.
• Texture is soft and regular.

• Tough for resisting tensile stresses.
• Weak across the fibres.
• Annual rings are distinct, having one side soft, porous and light coloured. The other side is dense and dark.
• The general colour of the wood is pale tinted or light such as pine spruce, fir, ash, kail, deodar etc.
Properties of hardwood
• The wood generally contains a large percentage of acid.

• It is brightly coloured.
• Annual rings are not distinct.
• It is difficult and hard to work with.
• It resists shearing stress.

• Fibre are overlapped.
• The general colour is dark brown such as oak, walnut, teak, mahagony, sishim, babul, sal etc.
Uses
Soft timber
• Because of its cheapness it is used for low grade furniture, doors and windows for cheap type of houses.

• Used as fuel.
• Some timbers are used for baskets and mat making.
• The bark is used as garment is some places.
Hard timber
• Used for high quality furniture such as chairs, tables, sofas, dewans, beds, etc.

• Used for door, window frames for high quality houses as they can take good polish and painting finish.
• Used for manufacturing katha.
Wood as an electrical insulator
Wood is impregnated with oil or other substance, for use as insulator.
Example

It is used in electrical machine windings, as slot wedges.

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CITS : WCS - Electrical - Exercise 11