Porosity and sand holes are common defects in castings, mainly caused by the following reasons:
Molding sand quality issues: Insufficient permeability or excessive moisture content in the molding sand prevents gas from escaping smoothly during pouring, forming porosity.
Improper pouring process: Poor pouring temperature or excessively fast pouring speed can lead to poor molten metal flow, preventing sufficient gas expulsion.
Mold design defects: Poor venting in the mold or an unreasonable gating system design can also cause gas retention.
Insufficient purity of molten metal:** Inclusions or excessive gas content in the molten metal can easily form porosity during solidification.
Improper cooling rate: Excessively rapid cooling can cause stress concentration inside the casting, forming micropores.
Solutions:
Optimize molding sand ratio: Select molding sand materials with good permeability, such as sodium bentonite, and control the moisture content to ≤10%.
Improve pouring process: Adjust the pouring temperature and speed to ensure smooth filling of the mold with molten metal.
Improve mold design: Increase venting channels and optimize the gating system layout.
Purify molten metal: Use filters or degassing agents to reduce inclusions and gases in the molten metal.
Control cooling rate: Adjust cooling time according to the casting thickness to avoid excessively rapid cooling.
Precautions: Molding sand treatment: Regularly test the permeability and moisture content of the molding sand to avoid performance degradation due to reuse.
Process parameter monitoring: Real-time monitoring of pouring temperature and speed is necessary to ensure process stability.
Mold maintenance: Regularly clean the mold vents to prevent blockage.
Of course, professional foundries will strictly avoid these defects. For example, Mulan Manufacturing Group. If you have large-volume custom casting needs, you can entrust Mulan Manufacturing Group with production. Mulan Manufacturing Group has 13 years of experience in casting production and ships to Europe, America, Japan, and South Korea year-round. We have complete certifications and look forward to your cooperation and consultation.
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