Release agents indirectly but significantly influence solidification by affecting heat exchange efficiency between the mold and casting, thereby linking to shrinkage porosity and shrinkage marks.
Thermal Barrier Effect: Release agent films add a micro-thermal resistance layer between the mold and casting. If the film is too thick or has poor thermal conductivity, it impedes heat dissipation from the casting to the mold—acting as "insulation." This delays overall solidification, potentially freezing feed channels prematurely. Thick sections then lack liquid compensation for shrinkage, forming porosity. Uneven cooling also amplifies shrinkage stress, causing surface indentations (shrinkage marks).
Disrupted Directional Solidification: Ideal solidification progresses from gate-distal regions toward the gate, enabling pressure-driven feeding. Non-uniform release agent coatings create uneven mold cooling, disrupting this temperature gradient. Hot spots may solidify isolatedly, inducing porosity.
Minimize and Uniformize Coating Thickness: Prioritize efficient film formation. Use precision spraying to balance demolding performance with thermal conductivity—avoid over-thinning (compromising mold release) or over-thickening (impeding heat transfer). Adjust based on alloy fluidity: thicker films may be needed for low-fluidity alloys to ensure proper filling.
Zoned Spraying Strategy: For hot spots (thick sections), increase spray volume/frequency—coordinated with mold temperature control and cooling—to enhance local cooling. For thin, scratch-prone areas, ensure adequate lubrication. This requires fine-tuned spray programming.
Select Appropriate Release Agents: Tailor choices to process needs. For thick, hot-spot-prone castings, opt for release agents with thermal conductivity fillers to reduce thermal barrier effects.
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