What is Shrinkage Porosity?
Shrinkage porosity refers to irregular cavities formed in metal as it shrinks while solidifying, that is a common occurrence in jewelry casting. This shrinkage results from a sudden reduction in volume as metals transform from a liquid to a solid state. In different alloys, this shrinkage can range from 4-6% for metals like gold and silver. If not effectively managed, shrinkage porosity leads to visible defects in cast items, like irregular holes and caves.
Formation and Appearance
During the solidification process, metal dendrites (branch-like crystals) develop, and liquid metal must flow between these branches to compensate for the shrinkage. When this “feeding” process fails, it results in porosity. Certain metals, such as white gold, are more susceptible to shrinkage porosity compared to others like yellow gold or sterling silver. Protech Transfer’s advanced casting machines can help optimize the feeding process to reduce these risks. Special attention should also be paid to the correct location and size of the sprues and feeders.
Prevention Methods
- Effective Feed-Sprue Systems
Designing effective feed-sprue systems is essential. Feed-sprues is a reservoir of liquid metal that fills the voids created by shrinkage. Proper positioning of the sprue is crucial; it should be attached to the heaviest section of the jewelry piece. - Control of Flask and Casting Temperatures
Flask and casting temperatures significantly influence shrinkage. Higher flask temperatures can be beneficial, but they must be carefully managed to avoid introducing other defects, such as gas porosity.
Conclusion
To avoid shrinkage porosity, effective sprue design and temperature control are vital, especially for alloys with lower thermal conductivity, like white gold. Utilizing Protech Transfer’s machinery from Indutherm.de can enhance your casting process, reducing the likelihood of defects and improving the overall quality of your jewelry.
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