Theory:
Casting process is based on the
property of a liquid to take up the shape of vessel containing it. Molten metal
poured into a mould flows into the corners and fills all the voids. When metal
solidifies it takes the shape of mould but not exactly the same because solid
being demos there is reduction of volume. A foundry is a collection of the
necessary materials or equipments to produce a casting. Practically all metals
are initially cast. The casting process involves the following basic steps.
1)
Pattern
making
2)
Mould
making
3)
Melting
the metal
4)
Pouring
it into the cavity
5)
Allowing
the molten metal cold and solidify it the mould
6)
Removing
the solidified component, cleaning it and subjecting it for further treatment
if necessary.
One of the most attractive features
of casting is its ability to form any shape in one operation. Casting is one of
the most versatile forms of mechanical process for producing components;
because there is no limit to the size, shape and intricacy of the articles that
can be produced by casting. It offers one of the cheapest methods and gives
high strength and rigidity even to intricate pasts, which are difficult to
produce by other methods of manufacturing.
Types of Casting Methods:
1)
Casting in
metallic moulds
1.
Permanent
mould casting
2.
Stush
casting
3.
Press
casting
4.
Die
casting
2)
Casting in
non-metallic moulds
1. Centrifugal casting
a)
True
centrifugal
b)
Semi
centrifugal
c)
Centrifugal
2. Precision casting
a)
Lost
wax method
b)
Plaster
moulds
c)
Mercast
process
d)
Shell
molding
3. Moulds of wood, rubber paper etc.
3)
Continuous
casting
1.
Reciprocating
moulds
2.
Draw
methods
3.
Stationary
moulds
4.
Direct
sheet casting
Tools
required:
1.
A
pattern
2.
Molding
box
3.
Metal
4.
Furnace
5.
File
A pattern:
A pattern is a model made of suitable
material and is used for making to cavity in molding sand or other suitable
mould materials. A pattern is defined as a model of casting, constructed in
such a way that it can be used for forcing as mould in damp sand. The first
step in making a casting is to prepare a model, known as a pattern, which
differs in a number of respects from the resulting casting. Most patterns are
made of wood because of its cheapness, ease of availibity, lightness, ease of
obtaining smooth surface and preserving surface by applying coating of shellac,
ability to be worked on easily. It has been said that a poor casting may be
produced from a good pattern but a good casting will be made a poor pattern.
The Mould:
A mould is the container that
has the cavity or cavities of the shape to be cast. Good casting cannot be
produced without good mould. Mould may be of two types.
1)
Permanent
type
2)
Temporary
type
According to
the sand there are various types of mould
a)
Green
sand mould
b)
Dry
sand mould
c)
Loam
sand mould
d)
Core
sand mould
e)
Cemented
bounded mould
f)
Resin
bounded sand mould
g)
Skin
dry sand mould etc.
The mould must be strength enough
to hold the weight of the metal and resist corrosive action of the rapidly
flowing metal during pouring. The mould must generate a minimum amount of gas
when filled with molten metal and must be constructed so that any gases formed
can pass through the body of the mould itself. The necessary equipment that a
mould being made are given below-
a)
Molding
board
b)
Shovel
c)
Riddle
d)
Rammer
e)
Bellows
f)
Lifters
g)
SW
h)
Vent
wire
i)
Gate
cutter
