In foundry sand technology for moulding, the property responsible for allowing the large quantities of steam and other gases (generated during pouring and solidification) to escape through the mould is called what?

Introduction / Context:

When molten metal enters a sand mould, moisture flashes to steam and binders decompose, releasing gases. If these gases cannot escape, casting defects such as blows, pinholes, and gas porosity arise. The sand property that governs the passage of gases through the body of the mould is a cornerstone of foundry science and quality control.

Given Data / Assumptions:

• Standard green-sand or chemically bonded sand moulds are considered.
• Gas generation is inevitable due to moisture and binder breakdown.
• Core and mould vents supplement inherent sand properties.

Concept / Approach:

Permeability is defined as the ability of the moulding sand to allow gases to pass through it. It depends on grain size/shape, bonding, moisture content, and degree of compaction. High permeability facilitates the escape of steam and decomposition gases, reducing internal pressure and the risk of gas-related defects. Other properties—cohesiveness (bonding strength), adhesiveness (sand-to-flask stick), collapsibility (ability to yield during contraction)—address different performance needs.

Step-by-Step Solution:

Verification / Alternative check:

Permeability is routinely measured using standard permeability meters (air-flow tests) and specified in process sheets for a given casting and sand system.

Why Other Options Are Wrong:

• Cohesiveness: relates to internal bonding strength, not gas passage.
• Adhesiveness: describes the tendency of sand to stick to the flask/pattern.
• Collapsibility: helps avoid hot tears by yielding during contraction, not by venting gases.
• Green strength: overall strength in moist condition; again not gas flow.

Common Pitfalls:

• Misreading ‘‘evolves gases’’ as a property of sand; the key is the escape of gases through sand (permeability), not their generation.
• Over-compacting sand, which reduces permeability despite good strength.

Final Answer:

permeability