Carbon dioxide (CO2) Moulding Process (All you need to know)

Carbon dioxide (CO2) Moulding Process

What is Carbon dioxide moulding process?
Carbon dioxide (CO2) moulding is a molding process in which the carbon dioxide gas is forced to pass over the sand mold containing 3 to 5% sodium silicate, which ultimately produces the hardened mold due to reaction of sodium silicate with CO2.

The mold material is made up of pure dry silica sand (free from clay), 3 % to 5 % sodium silicate and moisture content (less than 3 %).

The entire CO2 moulding process diagram is shown in the above image.

Now, let me tell you the detailed process and a few other important things about Carbon dioxide molding.

15 things to know about Carbon dioxide moulding (CO2 moulding)

  1. Earlier, the CO2 moulding process was widely used in Europe for hardening the green sand molds.
  2. In Carbon dioxide molding, the mold material is made up of pure dry silica sand which is free from clay. It also contains 3 % to 5 % sodium silicate as a binder and it has less than 3 % of moisture content.
  3. Starch may be added in the molding sand to improve its green compression strength.
  4. In order to increase the collapsibility of the molding sand, a little amount of coal dust, dextrin, sea coal, pitch, wood floor, graphite and sugar can be added to it.
  5. Kaolin clay is also added to the molding mixture in order to increase its stability.
  6. The mold cavity is prepared by ramming the sand around the pattern by using the conventional sand molding tools.
  7. Now, the carbon dioxide gas is forced all around the mold surface for approximately 20 to 30 seconds. The CO2 gas is passed at the pressure of about 1.3 to 1.5 kg/cm2 using CO2 head or curtain or probe.
  8. In order to direct the carbon dioxide gas in all directions, a special type of patterns are also used (see diagram).
  9. The carbon dioxide gas plays a major role in baking the cores and mould. The baking of sand mold takes place due to the presence of sodium silicate in the moulding mixture.
  10. The sodium silicate which is present in the sand mould reacts with the CO2 gas and because of this, a hard substance is formed known as silica gel.
  11. The chemical reaction for the carbon dioxide moulding process is mentioned below.

Na2SiO3 + CO2  —–>  Na2CO3 + SiO3.xH2O (Silica gel)

  1. The hard silica gel is like a hardened cement and this helps in binding the sand grains.
  2. The molds made by CO2 moulding process are used for casting the ferrous metals as well as non-ferrous metals.
  3. The CO2 Moulding process is very simple and it can be done by semi skilled workers too.
  4. In the carbon dioxide moulding process, once the sand is used in molding, it can not be reclaimed back for reuse.

Now let me tell you few advantages and disadvantages of CO2 moulding process.

Advantages of CO2 moulding

The advantages of carbon dioxide molding process are mentioned below.

  • The molds and cores produced by the carbon dioxide molding process are strong and hard as compared to other processes.
  • There is no costly heating system used for hardening the sand molds. It’s just Carbon dioxide gas and sodium silicate which hardens the sand molds.
  • The CO2 moulding process is easy and it can be done by semi skilled workers.
  • CO2 Moulding process is speedy and the molds and cores can be produced and used for casting work immediately after they are hardened.
  • The molds prepared by CO2 moulding have good dimensional accuracy.
  • The process can be automated which can increase the production rate with less human interference.
  • This process can be used for casting the ferrous metals as well as non-ferrous metals.

Disadvantages of CO2 moulding

The disadvantages of carbon dioxide moulding are mentioned below.

  • In CO2 moulding process, once the sand is used in molding, it can not be reclaimed back for reuse.
  • The bench life of sand mixtures is comparatively shorter than other mold and core mixes.

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