Sodium silicate binder for foundry

In the CO₂ process, sodium silicate is mixed through clean silica sand at a few percent by weight. Carbon dioxide gas is then passed through the packed core or mould. The CO₂ reacts with the silicate to form a silica gel, which sets hard in seconds and locks the sand grains together. No heat and no baking oven are needed.

The attraction is that it is clean. Unlike resin binders it produces no smoke, no acrid odour and no organic emissions on pouring, which matters for workshop air and increasingly for compliance. It is also considerably cheaper per tonne of sand.

What we supply for this

Technical guidance

Which ratio to run

Higher ratios gas off faster and give a quicker set; lower ratios give longer bench life and more forgiving working time. Most CO₂ work sits in the 1:2.0 to 1:2.4 band. If your cores are setting before you have finished ramming, move down the ratio, not up.

The shakeout trade-off

This is the real limitation. Silicate-bonded sand is hard to break down after pouring because the silica gel does not burn away like an organic binder. Keep the binder addition as low as will hold the core, and use a breakdown additive if collapsibility is a problem. Over-adding binder is the most common cause of shakeout complaints.

Sand and water quality

Silicate is sensitive to what else is in the mix. Clay-bearing or dirty sand consumes binder; hard water can start the gelling reaction early. Use washed, dried silica sand and consistent water.

Lumps versus liquid

If you are a long haul from us, silicate glass in lump form dissolved on site can land cheaper than shipping liquor, since you are not paying freight on water. Worth comparing at volume.

Common questions

Other applications