Question

How much percentage of sodium silicate (Na2SiO3) is added to the sand mixture in Co2 moulding?

(a) 0 to 2 %

(b) 2 to 6 %

(c) 6 to 10 %

(d) 10 to 14 %

The question was posed to me in an international level competition.

The doubt is from CO2 Process in division Special Casting Techniques of Casting-Forming-Welding I

Answer 1

Correct answer is (b) 2 to 6 %

Best explanation: No other things like clay, water and resins are added to the sand except sodium silicate, which reacts with the sand mix to increase the flow-ability to fill up corners and intricate contours. Then the Co2 is supplied to the mould and reaction takes place as follows:

Na2SiO3 + Co2   —–>                   SiO2 + Na2Co3

Where, SiO2 is having gelling action (Silica gel).