7. METALS:
There are hundreds of metals which are used
in engineering. All the metals are extracted
from quarries in the form of ores. They are
made pure by some special methods in the
industries.
10. (1) Ferrous metals:
All those metals which contain iron
as chief constituent are called ferrous
metals.
Such as:
(1) Pig iron
(2) Wrought iron
(3) Cast iron
11. (2) Non-Ferrous metals:
All those metals which do not contain iron as
principal constituent are called non-ferrous metals.
Such as:
– Zinc
– Lead
– Nickel
– Chromium
– Silver
– Platinum
– Gold and all other metals except steel and iron.
12. DUCTILE MATERIALS:
A material which can undergo considerable
deformation without rupture is called ductile
material. E.g. steel.
(OR)
A material that can be stretched, drawn or
hammered thin without breaking.
BRITTLE MATERIALS:
A material which can not undergo any deformation
is called brittle material. Brittle material has
tendency to break into pieces easily, e.g. concrete
and glass.
13. STEEL:
Steel is an alloy (mixture of two
or more than two metals) of
carbon and iron. It is most
important metal which is widely
used in RCC construction of civil
engineering.
14. Types of Steel:
Steel is classified into three main
types depending upon
carbon content.
15. (1) Low / Mild / Soft /Plain Carbon Steel:
In this type of steel, the carbon content is 0.15% to
0.3%.
Properties:
(1) It is ductile and malleable.
(2) It corrodes quickly.
(3) It can be easily forged, welded and riveted.
(4) It withstands shocks and sudden impacts well.
(5) It is not much affected by saline water.
(6) It is equally strong in tension, compression and
in shear. Continued-------
16. Uses:
Mild steel round bars are extensively used
as reinforcement in R.C.C construction.
It is extensively used in the manufacturing of
various tools and equipments, machine parts,
railway tracks , transmission towers and
industrial buildings.
20. (2) Medium carbon Steel:
In this type of steel, the carbon content is
0.3 to 0.8 %.
Medium steel has characteristics between
those of low –carbon and high carbon
steel.
It is widely used for boilers.
21. (iii) High- Carbon Steel (or) Hard Steel:
In this type of steel, the carbon content is more than
0.8 to 1.5 %. Higher %age of carbon in it renders it
harder and tougher.
Properties:
(1) Its structure is granular.
(2) It is more tough and elastic than mild steel.
(3) It is easier to harden and to temper.
(4) It is more difficult to forge and to weld.
(5) Comparatively it is stronger in compression than
in tension or in shear.
(6) It with stands shocks and vibrations better.
22. Uses of High carbon steel:
(1) It is used in the pre-stressed concrete.
(2) It is used for making tools such as
drills, files, chisels, fine types of cutlery.
(3) It is also used in the manufacturing of
cutters,keys,knives,razers,etc.
(4) It is used in the manufacturing of those
parts of machinery that need a hard, tough,
durable material capable of withstanding
shocks and vibrations.
23. REINFORCED STEEL BARS:
As plain cement concrete (PCC) is strong in compression
but very weak in tension and shear. As mild steel bars are
strong in tension. Therefore, mild steel bars or high carbon
steel bars are embedded as reinforcement in the concrete to
make good that deficiency of the plain concrete. Therefore,
round, flat or square bars too can be used for that purpose.
Welded wire mesh and expanded metal too are used as
reinforcement in cement concrete.
Commonly deformed bars or twisted bars are used in cement
concrete.
Therefore, RCC sections will carry compression as well as
tension safely without failure.
In these sections compression will be taken by concrete and
tension by steel.
25. (1) ALUMINUM:
It is more commonly used non-ferrous metal. It is widely
used in every field of Engineering. Due to improved strength
and durability, aluminum is a versatile material for use by
Engineers.
Properties and Uses:
(1) Its colour is silvery white.
(2) It shows bright luster on a freshly broken surface.
(3) It is ductile material,
(4) It is very light in weight.
(5) It also resists atmospheric corrosion,
(6) It is very good conductor of electricity,
(7) It is used for making door and window frames,
(8) It is also used in roofing, piping, etc,
(9) It is also used in electric wires, cables.
26. (2) COPPER:
It is one of the most widely used non-ferrous
metals. It is not widely used in Engineering due
to its high cost.
Properties:
(1) It is crystalline in structure,
(2) Its color is reddish brown,
(3) It is highly ductile,
(4) It is excellent conductor of electricity,
(5) When exposed to sun, its colour turns
greenish,
Continued------
27. (6) It with stands corrosion,
(7) It is soft and highly flexible,
(8) It is light in weight,
(9) Dents in copper can be hammered out
without any damage to it.
Uses:
(1) It is used for winding electric motors,
generators and for transmission of electricity,
(2) Its sheets are used as damp proofing in
buildings.
28. (3) LEAD:
It is widely used in building construction and has draw
back of being poisonous.
Properties:
(1) It is bluish grey metal,
(2) It is soft as it can be cut with a knife,
(3) It is highly ductile,
(4) It is a good conductor of heat and electricity,
(5) It does not corrode,
(6) Its specific gravity is 11.35.
Uses:
(1) It is used as a base in paints,
(2) Lead pipes and lead joints in sanitary fittings are
extensively used.
29. (4) TIN:
It is one of the mostly used protective metals
used in construction activities.
Properties:
(1) It is lustrous silvery white metal,
(2) It is highly ductile,
(3) It is a good conductor of heat and electricity,
(4) It is soft and has good plasticity,
(5) Its specific gravity is 7.3.
Uses:
It is used to give protective coatings to iron and
steel sheets.
30. (5) ZINC:
It is commonly used in building construction either as a
base for paints or as protective coverings for metals.
Properties:
(1) It is bluish white crystalline metal,
(2) It is brittle metal at ordinary temperature,
(3) It becomes ductile between 100-1500
C,
(4) It is a good conductor of heat and electricity,
(5) It resists corrosion.
Uses:
(1) It is used for galvanizing iron sheets and pipes, for
batteries and printing blocks,
(2) It is also used for preparing paints.
32. (1) BRASS:
Brass is an alloy of about 60-70 % copper and
zinc. Hardness of this alloy depends upon the
amount of zinc present in it.
Properties:
(1) It is very strong,
(2) It is ductile alloy,
(3) It resists corrosion,
Uses:
It is widely used for making house hold utensils,
water pumps and other machine parts.
33. (2) BRONZE:
Bronze is an alloy of 90 % copper and 10 % tin. It
can be easily machined and cast.
Properties:
*It resists corrosion.
*It takes a fine polish.
Uses:
(1) It is used for manufacturing of house hold
utensils.
(2) Phosphorous bronze is used for making radio
aerials and certain other instruments.
35. CORROSION:
Conversion of metals into various compounds by
natural means or agencies is described as
corrosion. Corrosion of ferrous metals appears
in the form of rusting.
Corrosion of metals is explained in two ways.
One is by the formation of oxides. As in case of
iron, reaction with oxygen, carbon dioxide and
water results in the formation of bicarbonate,
which in turn alters into carbonate and finally
changes into hydrated oxide. Continued---
36. According to other explanation, the
metal surface processes areas which
act as cathode and anodes. The
presence of water or moisture etc
provides a contact between such
areas which results in corrosion.
37. Protection against Corrosion:
Ferrous metals have tendency for corrosion.
It is maximum for steel and least for cast
iron. Wrought iron has a moderate tendency
to rust. Therefore, all the products require a
protective cover to prevent the possibility of
corrosion and thereby adding to its
durability. Various methods which are in
commonly used include Electroplating,
Galvanizing, Tin plating, Metal spraying,
Painting, etc.
38. (1) Electroplating:
This method involves the use of electric current to
give a coating of chromium or nickel which is
highly resistant to corrosion.
(2) Galvanizing:
In this method zinc is used to give a coating on the
ferrous metal products.
(3)Tin Plating:
This method is similar to the galvanizing process.
The iron products are thoroughly cleaned and
washed. Then these are dipped into the hot molten
tin and it will give protection against corrosion.
39. (4) Metal Spraying:
This method involves the use of a special sprayer
in which fuel gas, oxygen and air are used to
make flame. The wire of metal to be sprayed like
zinc, tin, or aluminium is used in these sprayers.
The wire metals and a thin layer is sprayed over
the ferrous metal items.
(5) Painting:
The iron made goods are often coated with paint.
Care should be taken to first clean the iron surface
thoroughly and then give a good coating of good
quality paint.
