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SO₂ (sulfur dioxide process, also known as ISOSET), is a type of chemically bonded sand core used in metal casting. It is made using the SO₂ process, where sand is bonded using an epoxy acrylic resin and cured by exposure to sulfur dioxide gas.

SO₂ Process:

1. Sand Mixture: A combination of dry sand and a liquid resin binder (epoxy acrylic) is prepared.
2. Core Box Filling: The sand mixture is pneumatically blown or packed into a core box.
3. Curing with Gas Catalyst: Sulfur dioxide (SO₂) gas is introduced into the core box. This gas acts as a catalyst, reacting with the resin to cure the core almost instantly.
4. Core Removal: Once cured, the core is removed from the core box.
5. This process is similar to the Isocure (cold box) process, but instead of an amine catalyst, it uses sulfur dioxide (SO₂) gas to cure the core.

Features of SO₂ Cores:

• Fast Curing Process: The SO₂ gas rapidly cures the resin, allowing for high-speed production.
• Good Strength & Dimensional Accuracy: Produces durable cores with excellent precision and smooth surfaces.
• Minimal Binder Usage: Requires less binder compared to other cold box processes, reducing gas emissions during casting.
• Good Collapsibility: After metal solidification, the core breaks down easily, aiding in core removal from the final casting.