Can Coating Alone Prevent Penetration?

April 5, 2021
Today’s foundry operations insist on high-quality castings that are defect-free as-cast, with little to no rework time, and high dimensional tolerances.

Q: Is it possible to prevent persistent veining and penetration defects using only a premium refractory coating, without the aid of a sand additive?

A: ASK Chemicals has premium refractory coatings that will enhance the iron casting process without the additional expense and production process requirements of sand additives. These coatings have been formulated to provide consistent microstructure and metallurgical properties to gray iron, ductile iron, and compacted graphite iron (CGI) casting.

These coatings also provide an insulating barrier between the molten iron and the sand core or mold, having a direct effect on cooling rates of the metal, promoting good nodularity.

Using these types of premium coatings promotes excellent peel, providing a clean casting with little to no residual sand or coating in the casting.

In order for a coating to provide sufficient protection against veining and penetration defects, the operators must apply an adequate sand coating layer of approximately 10-12 mils, or greater, depending on casting section.

Depending on the casting and dimensional tolerances you may need to make allowances for the heavier coating layer within the tooling.

One such coating is MIRATEC MB 508, specifically designed to penetrate the sand core in order to provide greater protection than just a proud layer of coating can provide.

If extreme veining defects are occurring with the current casting program, and using a premium coating is not possible based on the selected process it may be likely that a sand additive like VEINO ULTRA RS 4 will still be required to provide 100% defect-free castings.

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