Prepared by James KATO and Zakaria ZIRABAMUZALE , Kabale University - Uganda.

1. Metal casting
process
DEFINITION: THIS IS A PROCESS BY WHICH METAL IS
MELTED AND THEN POUREDBINTO A PREVIOUSLY
MADE MOULD WHERE IT SOLIDIFIES AS A CASTING
WHOSE SIZE AND SHAPE ARE A REPRODUCTION OF
THE MOULD CAVITY

2. Major key terms in metal
casting
Casting Terms
Flask: A metal or wood frame, without fixed top or bottom, in which the mold is formed. Depending upon the position of the flask in the molding structure, it is referred to by
various names such as drag – lower molding flask, cope – upper molding flask, cheek – intermediate molding flask used in three piece molding.
Pattern: It is the replica of the final object to be made. The mold cavity is made with the help of pattern.
Parting line: This is the dividing line between the two molding flasks that makes up the mold.
Molding sand: Sand, which binds strongly without losing its permeability to air or gases. It is a mixture of silica sand, clay, and moisture in appropriate proportions.
Facing sand: The small amount of carbonaceous material sprinkled on the inner surface of the mold cavity to give a better surface finish to the castings.
Core: A separate part of the mold, made of sand and generally baked, which is used to create openings and various shaped cavities in the castings.
Pouring basin: A small funnel shaped cavity at the top of the mold into which the molten metal is poured.
Sprue: The passage through which the molten metal, from the pouring basin, reaches the mold cavity. In many cases it controls the flow of metal into the mold.
Runner: The channel through which the molten metal is carried from the sprue to the gate.
Gate: A channel through which the molten metal enters the mold cavity.
Chaplets: Chaplets are used to support the cores inside the mold cavity to take care of its own weight and overcome the metallostatic force.
Riser: A column of molten metal placed in the mold to feed the castings as it shrinks and solidifies. Also known as “feed head”.
Vent: Small opening in the mold to facilitate escape of air and gases.

3. Steps in making sand castings
There are six basic steps in making sand castings:
Patternmaking
Core making
Molding
Melting and pouring
Cleaning
These are further explained ….

4. As follows…..
Pattern making
The pattern is a physical model of the casting used to make the
mold. The mold is made by packing some readily formed
aggregate material, such as molding sand, around the pattern.
When the pattern is withdrawn, its imprint provides the mold
cavity, which is ultimately filled with metal to become the
casting. If the casting is to be hollow, as in the case of pipe
fittings, additional patterns, referred to as cores, and are used to
form these cavities.
Core making
Cores are forms, usually made of sand, which are placed into a
mold cavity to form the interior surfaces of castings. Thus the
void space between the core and mold-cavity surface is what
eventually the casting becomes.
Molding
Molding consists of all operations necessary to prepare a mold for
receiving molten metal. Molding usually involves placing a
molding aggregate around a pattern held with a supporting frame,
withdrawing the pattern to leave the mold cavity, setting the cores
in the mold cavity and finishing and closing the mold.
Melting and Pouring
The preparation of molten metal for casting is referred to simply
as melting. Melting is usually done in a specifically designated
area of the foundry, and the molten metal is transferred to the
pouring area where the molds are filled.
Cleaning
Cleaning refers to all operations necessary to the removal of sand,
scale, and excess metal from the casting. Burned-on sand and
scale are removed to improved the surface appearance of the
casting. Excess metal, in the form of fins, wires, parting line fins,
and gates, is removed. Inspection of the casting for defects and
general quality is performed.

5. Classification of moulding sand
Silica sand (up to 2% clay)
Lean/weak sand(2-10% clay)
Moderately strong sand(10-20% clay)
Strong sand(up to 30%clay)
Extra strong sand (up to 50% clay)

6. Types of sands according to
functions
Facing sand: this is used directly next to the surface of the pattern and
comes intact with molden metal when the would is poured
Backing sand: this is used to back up facing sand and to fill the whole
volume of the flask
System sand: it is used in machine mouldings
Core sand: this must be highly refractory and permeable to gasses.it is used
as binding material

7. Properties of moulding sand
Should be gas permeable
Strength to withstand fluid pressure
Plasticity
Collapsibility
Refractiveness( to withstand high temperature)
Moisture content should be optional

8. Procedure for producing a
casting
1. The pattern is placed with its flat face on the moulding board
2. The drag is set over the pattern on the same moulding
3. After powdering the pattern with graphite,facing sand is niddled on the pattern
4. The drag is then filled with layers of backing sand
5. Excess sand is removed by a straight edge
6. Venting then follows
7. The drag is turned upside down so that the parting plane faces up
8. The parting plane is covered with fine parting sand
9. The cope is then fitted on the drag and the pattern is powdered
10. A sprue pin is placed to one side of the pattern
11. The pattern is then ridded with facing sand and the cope is then filled with
backing sand. The sand is compacted by ramming
12. Excess sand is levelled off
13. Vent holes are made
1. The cope is carefully separated from the drag
2. Runners and gates are cut from the pattern to the sprue impression
3. The mould cavity is cleaned and sprayed with graphite
4. The sprue pin is pulled out of the cope and a funnel shaped opening is
scooped out at the top of the sprue impression to form a pouring basin
5. Assembling follows
6. Pouring and subsquent cooling of the metal follows
7. The sand around the pattetn should be moistured to avoid crumbling when the
pattern is extracted using a draw pin
8. The pattern is extracted
9. A heavy weight is placed on the mould
10. Shake out
11. Cleaning casting

9. Gating system
A system of channles including the pouring basins by means of which
molten metal is delivered to moulding cavity.
Functions of the gating system
To provide continuous uniform feed of metal to the mould cavity.
To supply the casting with liquid metal during shrinkage and
solidification.
To prevent slag and non-metallic inclusion from entering the mould.
To prevent the destruction of mould walls by the stream of metal.

10. FOUNDRYA foundry is a factory that produces metal castings.
The most common metals processed are aluminium and cast iron. However, other metals,
such as bronze, brass, steel, magnesium, and zinc, are also used to produce castings in
foundries. In this process, parts of desired shapes and sizes can be formed.
Foundry furnaces include;
Cupola furnaces
Flame furnaces
Crucible or pot
Electric frnaces

11. VIDEO 1

12. VIDEO 2

13. VIDEO 3

14. VIDEO 4

15. General critisms of casting
1. Difficult and sometimes impossibility to produce casting with
desired accuracy of dimensions and surface finish.
2. Non-uniformity of structure and properties of the castig across.
3. Lower level of strength and defecifieces of mechanical properties as
compared to forged components.

16. Casting defects
I. Internal stresses
II. Shrinkage cavity
III. Sagregation and polarity(blow holes)
IV. Non-uniform structures.
V. Moulding material/ pouring metal defects/mould shift.