Page 129 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

has low tensile strength. Aluminium is very widely used in aircraft industry and fabrication work because of its
lightness. Its application in the electrical industry is also on the increase. It is also very much in use in household
heating appliances.

Physical and mechanical properties of metals
Metal:
Metal is a mineral used in all types of engineering works such as machineries, bridges, aero planes etc., so we
must have basic knowledge about the metals.

Understanding the physical and mechanical properties of metals has become increasingly important for a
machinist since he has to make various components to meet the designed service requirements against factors,
such as the raise of temperature, tensile, compressive and impact loads etc. A knowledge of different properties
of materials will help him to do his job successfully. If proper material/metal is not used it may cause fracture or
other forms of failures, and endanger the life of the component when it is put into function.
Fig 1 shows the way in which the metals get deformed when acted upon by the same load.
Note the difference in the amount of deformation.

Physical properties of metals
– Colour

– Weight/specific gravity
– Structure
– Conductivity
– Magnetic property

– Fusibility
Colour
Different metals have different colours. For example, copper is distinctive red colour. Mild steel is blue/black
sheen.
Weight
Metals may be distinguished, based on their weights for given volume. Metals like aluminium lighter weight
(Specific gravity 2.7) and metals like lead have a higher weight. (Specific gravity 11.34)

Structure (Figs2 and 3)
Generally metals can also be differentiated by their internal structures while seeing the cross-section of the bar
through a microscope. Metals like wrought iron and aluminium have a fibrous structure and metals like cast Iron
and bronze have a granular structure.

116

CITS : WCS - Electrical - Exercise 11