TYPES of moulding processes used in casting-MP2

– Bhautik malaviya [130120119094]
Pavan Narkhede [130120119111]
Darshit Panchal [130120119114]
Topic :- Types of moulding used in casting process
:
Prof. Dixit patel

What is a mould?
A mould is a hollowed-out block that is filled with a liquid
like plastic, glass, metal, or ceramic raw materials .The liquid
hardens or sets inside the mold, adopting its shape. A mold is
the counterpart to a cast.

(A) According to the method used :
1) Floor moulding
2) Bench moulding
3) Pit moulding
4) Machine moulding

This method of moulding is commonly used for preparing the mould
of heavy and large size of jobs.
In floor moulding , the floor itself acts as a drag.
 It is preferred for such rough type of casting where the upper surface
finish has no importance.

 Bench moulding is done on a work bench of a height convenient to
the moulder.
 It is best suited to the mould of small and light items which are to be
casted by non- ferrous metals.

 Large sizes of jobs which cannot be accommodated in moulding
boxes are frequently moulded in pits.
 Here, the pit acts as a drag. Generally, one box, i.e. cope is sufficient
to complete the mould.
 Runner and riser , gates and pouring basin are cut in it.

 Machine moulding method is preferred for mass production of
identical casting as most of the moulding operations such as ramming
of sand, rolling over the mould, and gate cutting etc. are performed by
moulding machine.
 Therefore, this method of moulding is more efficient and economical
in comparison to hand moulding.

1) Green sand moulding
2) Dry sand moulding
3) Loam sand moulding
4) Core sand moulding

 Procedure involved in making green sand moulds
1. Suitable proportions of silica sand (85 - 92 %),
bentonite binder (6-12 %), water (3-5 %) and
additives are mixed together to prepare the green
sand mixture.
2. The pattern is placed on a flat surface with the drag
box enclosing it as shown in figure (a). Parting sand
is sprinkled on the pattern surface to avoid green
sand mixture sticking to the pattern.
3. The drag box is filled with green sand mixture and
rammed manually till its top surface. Refer figure
(b).

4. The drag box is now inverted so that the
pattern faces the top as shown in figure (c).
Parting sand is sprinkled over the mould
surface of the drag box.
5. The cope box is placed on top of the drag box
and the sprue and riser pin are placed in
suitable locations. The green sand mixture is
rammed to the level of cope box as shown in
figure (d).

6. The sprue and the riser are removed from
the mould. The cope box is lifted and placed
aside, and the pattern in the drag box is
withdrawn by knocking it carefully so as to
avoid damage to the mould.
7. Gates are cut using hand tools to provide
passage for the flow of molten metal. Refer
figure (e) and (f).

8. The mould cavity is cleaned and finished.
Cores, if any, are placed in the mould to obtain
a hollow cavity in the casting. Refer figure (g).
9. The cope is now placed on the drag box and
both are aligned with the help of pins. Vent
holes are made to allow the free escape of
gases from the mould during pouring. The
mould is made ready for pouring. Refer figure
(h).

Advantages
Green sand molding is adaptable to machine molding.
No mold baking or drying is required.
There is less mold distortion than in dry sand molding.
Time and cost associated with mold baking or drying is eliminated.
Green sand molding provides good dimensional accuracy across the parting
line.
Disadvantages
Green sand molds possess lower strengths.
They are less permeable.
There are more chances of defects (like blow holes etc.) occurring in castings
made by green sand molding.
Surface finish deteriorates as the weight of the casting increases.
Dimensional accuracy of the castings decreases as their weight increases.
13

 Here, in the preparation of the mixture for dry sand moulding, special binding
material such as resin, molasses, flour, or clay are mixed to give strong bond to
the sand.
 All parts of mould are completely dried before casting.
 Dry sand moulding is widely used for large size of work such as parts of engine,
large size of fly wheel and rolls for rolling mill.
 This process is costlier than green sand moulding but much superior in quality.

 Loam sand moulding are prepared with coarse grained silica sand, clay, coke,
horse manure and water.
 This process of moulding is performed in different way.
 First, a rough structure of desired shape is made by hand by using bricks and
loam sand.
 The surface of structure are blackened and dried before being casted.

 For core sand moulding, mixture is prepared with silica sand, olivine, carbon and
chamotte sands.
 Sand that contains more than 5% clay may not be used as core sand.
 For core making by hand, the core sand is filled and rammed in the core box
properly.
 The Whole operation takes a short time after the core box is withdrawn and the
core removed.

1) Shell moulding
2) Permanent mould casting
3) Carbon dioxide moulding

 Shell moulding is an efficient and economical method for producing
steel castings.
 The process was developed by Herr Croning in Germany during
World war-II and is sometimes referred to as the Croning shell
process.

a. A metallic pattern having the shape of the
desired casting is made in one half from carbon
steel material. Pouring element is provided in
the pattern itself. Refer figure (a).
1. The pattern is inverted and is placed over a box
as shown in figure (1). The box contains a
mixture of dry silica sand or zircon sand and a
resin binder (5% based on sand weight).

2. The box is now inverted so that the resin-sand
mixture falls on the heated face of the metallic
pattern. The resin-sand mixture gets heated up,
softens and sticks to the surface of the pattern.
Refer figure (2).
3. After a few seconds, the box is again inverted to its
initial position so that the lose resin-sand mixture
falls down leaving behind a thin layer of shell on the
pattern face. Refer figure (3).

4. The pattern along with the shell is removed from the
box and placed in an oven for a few minutes which
further hardens the shell and makes it rigid. The shell
is then stripped from the pattern with the help of
ejector pins that are provided on the pattern. Refer
figure (5).
5. Another shell half is prepared in the similar manner
and both the shells are assembled, together with the
help of bolts, clips or glues to form a mould. The
assembled part is then placed in a box with suitable
backing sand to receive the molten metal. Refer
figure (6).

6. After the casting solidifies, it is removed from the
mould, cleaned and finished to obtain the desired
shape as shown in figure (7).
Better surface finish and dimensional tolerances.
Reduced machining.
Requires less foundry space.
Semi-skilled operators can handle the process easily.
Shells can be stored for extended periods of time.
 Initially the metallic pattern has to be cast to the desired shape, size and finish.
 Size and weight range of castings is limited.
 Process generates noxious fumes.

Steps in permanent mold casting: (1) mold is preheated and coated

Steps in permanent mold casting: (2) cores (if used) are inserted and
mold is closed, (3) molten metal is poured into the mold, where it
solidifies.

 Carbon dioxide moulding also known as sodium silicate process is one of the
widely used process for preparing moulds and cores.
In this process, sodium silicate is used as the binder. But sodium silicate activates
or tend to bind the sand particles only in the presence of carbon dioxide gas. For
this reason, the process is commonly known as C02 process.

Suitable proportions of silica sand and sodium silicate binder (3-5% based on
sand weight) are mixed together to prepare the sand mixture.
Additives like aluminum oxide, molasses etc., are added to impart favorable
properties and to improve collapsibility of the sand.
The pattern is placed on a flat surface with the drag box enclosing it. Parting sand
is sprinkled on the pattern surface to avoid sand mixture sticking to the pattern.
The drag box is filled with the sand mixture and rammed manually till its top
surface. Rest of the operations like placing sprue and riser pin and ramming the
cope box are similar to that of green sand moulding process.

Figure (a) shows the assembled cope and
drag box with vent holes. At this stage, the
carbon dioxide gas is passed through the
vent holes for a few seconds. Refer figure
(b).
Sodium silicate reacts with carbon dioxide
gas to form silica gel that binds the sand
particles together. The chemical reaction is
given by:
Na2Si03 + C02 -> Na2C03 + Si02
(Sodium Silicate) (silica gel)
The sprue, riser and the pattern are
withdrawn from the mould, and gates are
cut in the usual manner. The mould cavity
is finished and made ready for pouring.
Refer figure (c).

Instantaneous strength development. The development of strength takes place
immediately after carbon dioxide gassing is completed.
Since the process uses relatively safe carbon dioxide gas, it does not present sand
disposal problems or any odour while mixing and pouring. Hence, the process is
safe to human operators.
Very little gas evolution during pouring of molten metal.
Poor collapsibility of moulds is a major disadvantage of this process.
There is a significant loss in the strength and hardness of moulds which have
been stored for extended periods of time.
Over gassing and under gassing adversely affects the properties of cured sand.

TYPES of moulding processes used in casting-MP2

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