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Sand cores are the “hidden tooling” of metal casting. They create internal passages and cavities that cannot be formed by the external mold alone—cooling channels, oil galleries, hollow structures, undercuts, and complex internal geometry. In many foundries, the majority of scrap and rework associated with internal defects can be traced back to core-related variables: core strength, gas management, thermal stability, dimensional repeatability, surface integrity, and collapsibility after pouring.
Technical Feature: How Sand Cores Are Made—and Where Fused Ceramsite Sand Adds Real Process Value
Lost Foam Casting—also called EPC (Evaporative Pattern Casting) or LFC (Lost Foam Casting)—is often described as a “no-parting-line” process. In reality, it’s a process where the foam-to-gas transition happens inside the mold while molten metal is filling. That single fact changes what “good sand” means.
Process Matters: Why Lost Foam Casting (EPC/LFC) Demands a Different “Sand System”
Over the past quarter we audited two resin-coated sand (RCS) plants—one in East China, one in Southeast Asia—tracking material data from incoming base sand to cores, castings and reclamation. Their equipment and resin systems differed, yet the same patterns kept appearing: periodic spikes of gas-related defects, shell-strength variability, and burn-on/penetration clustered around hot spots when reclaimed sand “tail” growth went unchecked.
Resin-Coated Sand (RCS) Plants, Unfiltered: Defect Mechanisms and a Repeatable Process Window
Two molding sands can share the same AFS number yet behave very differently in the mold. The missing piece is the thermal-expansion curve—the way a sand body expands between roughly 600–1000 °C, where most casting shells experience their peak thermo-mechanical stress.
Same AFS, Different Results: How Thermal-Expansion Curves Drive Veining and Dimensional Drift