The document discusses the CO2 casting process. In this process, CO2 gas is used to harden sand molds. When CO2 gas comes into contact with sodium silicate in the sand mixture, it forms a stiff gel that strengthens the mold. The CO2 is forced into the packed mold at pressure. This process produces dimensionally accurate castings with a fine surface finish more quickly than green sand casting. However, it is not as economical. The molds also cannot be easily reclaimed.

2. Introduction
Co2 Casting is a kind of sand casting process. In
this process the sand moulding mixture is hardened
by blowing gas over the mould.
In addition, one can be sure of getting
dimensionally accurate castings with fine surface
finish. But, this process is not economical than
green sand casting process.
The process is basically a hardening process for
moulds and cores.

3. Process
The principle of working of the co2 process is
based on the fact that if co2 gas is passed through a
sand mix containing sodium silicate, the sand
immediately becomes extremely strongly bonded as
the sodium silicate becomes a stiff gel.
This gel is responsible for giving the necessary
strength to the mould.

4. The sand used for the process must be dry and
free from clay. Suitable additives such as coal
powder, wood flour, graphite may be added to
improve certain properties like collapsibility.
The suitable sand mixture can then be packed
around the pattern in the flask or in the core box by
machines or by hand.
When the packing is complete, co2 is forced into
the mould at a pressure of about 1.45 kgf/cm2(142
kn/m2) . The gas is inert upto 15 to 30 seconds.
The volume of co2 required can be calculated if
the quantity of sodium silicate present is known.

5. As a thumb rule, for every 1 kg of sodium silicate,
0.50-0.75 kg of gas is required.
Over gassing is wasteful and results in
deteriorating the sand.
Patterns used in this process may be made of
wood, metal or plastic.
Carbon dioxide casting is favoured both by the
commercial foundry men and hobbyist for a number
of reasons. In commercial operations, foundry men
can assure customers of affordable castings which
require less machining.

6.  The moulding process which can be fully
automated is generally used for casting process
that require speed, high production runs and
flexibility. In home foundries this is one of the
simplest process that improves the casting
quality .

8. Co2 casting process is ideal where speed and
flexibility is the prime requirement.
Molds and cores of a varied sizes and shapes can
be molded by this process.
Applications

9. This process has many advantages in comparison to other
forms of castings some of them are as follows:
Compared to other casting methods cores and moulds are
strong.
Reduces fuel cost since gas is used instead of to other
costly heating generating elements.
Operation is speedy. Moulds and cores can be immediately
after processing.
Great dimensional accuracy can be attained than other
moulding or core making process.
Semi-skilled labour can be used.
This process can be fully automated.
Advantages

10. Difficulty in reclaiming used sand.
Bench life of sand mixtures is much shorter than for most
other mould and core mixes.
Disadvantages