Foundry

Different perlite grades support several stages of the casting process through their insulating properties, expansion characteristics and interaction with moulding materials.

In riser sleeves and hot topping compounds, expanded perlite serves as a lightweight insulating component. It helps limit heat loss from the riser, allowing the metal to remain liquid longer and feed the casting as it solidifies. When incorporated into a properly designed feeding system, it can help reduce shrinkage cavities and shrinkage porosity, supporting casting soundness and improved metal yield.

Suitable grades of unexpanded perlite are used as slag coagulants on molten metal. Upon contact with the hot surface, the particles expand and help collect slag into a cohesive mass that can be removed more easily from the furnace or ladle. Effective skimming helps limit the carryover of slag into the mould and reduces the risk of slag inclusions in the casting.

In ladle topping applications, perlite forms an insulating layer over the molten metal, helping reduce heat loss during holding and transfer. Expanded perlite provides this layer directly, while suitable unexpanded grades expand upon contact with the molten metal. Grade selection and application practice depend on the metal, operating temperature and whether insulation, slag removal or both are required.

Perlite can also be incorporated into selected moulding and core sand mixtures. Its cushioning effect helps accommodate the thermal expansion of silica sand, reducing expansion related defects such as veining, buckling and fissuring. In suitable formulations, it can also improve permeability and gas evacuation, helping reduce defects associated with inadequate venting. Performance depends on the sand system, binder, perlite grade and addition rate.

From riser insulation and temperature retention to slag removal and sand performance, perlite offers several functions in foundry operations. The appropriate grade and application rate should be selected according to the metal, operating temperature, moulding system and intended function, with performance confirmed under actual casting conditions.